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A Beam Steering, Broadband Microstrip Antenna for Non-Contact Vital Sign Radar Detection

Permanent Link: http://ufdc.ufl.edu/UFE0042746/00001

Material Information

Title: A Beam Steering, Broadband Microstrip Antenna for Non-Contact Vital Sign Radar Detection
Physical Description: 1 online resource (139 p.)
Language: english
Creator: PARK,ZIVIN
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: ANTENNA -- BEAM -- BROADBAND -- PATCH -- STEERING
Electrical and Computer Engineering -- Dissertations, Academic -- UF
Genre: Electrical and Computer Engineering thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The non-contact vital sign radar detection system requires a development of the high gain, broadband, and beam steering patch antenna. The proposed design approach combines the advantages of the wideband antenna, the advantage of the parasitic patch, and the advantage of beam steering antennas within a single microstrip patch antenna. As a result, a 2.8?4.8 GHz beam steering broadband microstrip antenna was designed, fabricated, and measured. The proposed antenna can steer beam in broadband range (sampled at 3, 3.5, 4, and 4.5 GHz) by switching PIN diodes that connect stubs and a partial ground plane. Its broadband beam steering is suitable for a vital sign radar. The proposed antenna requires no array for beam steering but requires only two additional diodes. The wide frequency tuning range allows the radar system to be tuned for an optimum transmission frequency. In addition, effects of modifying the proposed antenna on the antenna characteristics such as reflection coefficient, radiation pattern, gain, or beam steering capability are investigated.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by ZIVIN PARK.
Thesis: Thesis (Ph.D.)--University of Florida, 2011.
Local: Adviser: Lin, Jenshan.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0042746:00001

Permanent Link: http://ufdc.ufl.edu/UFE0042746/00001

Material Information

Title: A Beam Steering, Broadband Microstrip Antenna for Non-Contact Vital Sign Radar Detection
Physical Description: 1 online resource (139 p.)
Language: english
Creator: PARK,ZIVIN
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: ANTENNA -- BEAM -- BROADBAND -- PATCH -- STEERING
Electrical and Computer Engineering -- Dissertations, Academic -- UF
Genre: Electrical and Computer Engineering thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The non-contact vital sign radar detection system requires a development of the high gain, broadband, and beam steering patch antenna. The proposed design approach combines the advantages of the wideband antenna, the advantage of the parasitic patch, and the advantage of beam steering antennas within a single microstrip patch antenna. As a result, a 2.8?4.8 GHz beam steering broadband microstrip antenna was designed, fabricated, and measured. The proposed antenna can steer beam in broadband range (sampled at 3, 3.5, 4, and 4.5 GHz) by switching PIN diodes that connect stubs and a partial ground plane. Its broadband beam steering is suitable for a vital sign radar. The proposed antenna requires no array for beam steering but requires only two additional diodes. The wide frequency tuning range allows the radar system to be tuned for an optimum transmission frequency. In addition, effects of modifying the proposed antenna on the antenna characteristics such as reflection coefficient, radiation pattern, gain, or beam steering capability are investigated.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by ZIVIN PARK.
Thesis: Thesis (Ph.D.)--University of Florida, 2011.
Local: Adviser: Lin, Jenshan.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0042746:00001


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1 A BEAM STEERING, BROADBAND MICROSTRIP ANTENNA FOR NON CONTACT VITAL SIGN RADAR DETECTION By ZIVIN PARK A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2011

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2 201 1 Zivin Park

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3 To my f ather, m other, and g randmother, for their support and encouragement

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4 ACKNOWLEDGMENTS I would like to express my sincere gratitude to my advisor Dr. Jenshan Lin for his advice, encouragement, and mentoring throughout my PhD study. I would also like to thank Dr. Sheng Li, Dr. Huikai Xie, Dr. Changzhi Li, and Dr. Paul Holloway for their time and for being on my committee. I am also thankful to Dr. La nce Covert for his unconditional help when I first started antenna research and for his sincere friendship. Also, I am thankful to Dr. Changzhi Li, who is now one of my committee members, for showing me the epitome of being excellent in research, diligence, and his sincere friendship. I am also thankful to Dongha Shim for the technical advices, equipment, and his sincere friendship. I am thankful to all of the RFSOC group members for their technical support, guidance, and friendship. The antenna measurement s performed by Yazid Yusuf under Dr. Xun Gongs research group at the University of Central Florida are greatly appreciated. I would like to thank my parents for their encouragement and unconditional support

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF FIGURES .......................................................................................................... 8 ABSTRACT ................................................................................................................... 13 CHAPTER 1 MOTIVATION AND BACKGROUND INFORMATION ............................................ 14 1.1 Motivation ......................................................................................................... 14 1.2 Requirements ................................................................................................... 15 1.3 Background Information .................................................................................... 15 1.3.1 Yagi Dipole Antenna ................................................................................ 15 1.3.2 Coupling Mechanism of Patch Antenna ................................................... 16 1.4 Summary .......................................................................................................... 19 2 PROPOSED APPROACHES vs. EXISTING APPROACHES ................................. 20 2 .1 Wideband Microstrip Antennas with a Partial Ground Plane ............................. 20 2.2 Microstrip Antennas using Parasitic Patches .................................................... 22 2.3 Beam Steer ing Patch Antennas ........................................................................ 24 2.4 Patch Antennas using Diodes ........................................................................... 28 2.5 Proposed Design Approaches .......................................................................... 30 2.6 Summary .......................................................................................................... 37 3 BROADBAND DIRECTIONA L MICROSTRIP ANTENNA ....................................... 39 3.1 Fabricated Broadband Directional Mic rostrip Antenna ...................................... 39 3.2 Input Reflection Coefficient (S11) ..................................................................... 39 3.3 Far Field Radiation Patterns ............................................................................. 41 3.4 Isolation ............................................................................................................ 48 3.5 Vital Sign Detection Performance ..................................................................... 48 3.6 Summary .......................................................................................................... 51 4 PRELIMINARY RESULT O F BEAM STEERING BROADBAND M ICROSTRIP ANTENNA ............................................................................................................... 52 4.1 Director and Reflector ....................................................................................... 52 4.2 Influence of Gap Value between Patches on Beam Pattern ............................. 54 4.3 Influence of Shape or Location of Parasitic Patch on Beam Pattern ................. 56 4.4 Influence of A Stub Added to Ground Plane on Beam Pattern ......................... 56 4 5 Simulated L ayout of V arious S tubs, I ts B eam P attern, and I ts S 11 .................. 67

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6 4 6 Simulated L ayout of V arious P arasitic P atches, I ts B eam P attern, and I ts S 11 ...................................................................................................................... 82 4 7 Intermediate Fabrication and M easurement R esults: Regular D iode and RF D iod e ................................................................................................................... 89 4 8 Rough R adiation P attern M easurement M ethod ............................................... 96 4 9 Intermediate Fabrication and M easurement R esults: Alternate A pproaches .. 102 4 10 Summary ...................................................................................................... 113 5 A BEAM STEERING BROADBAND SINGLE MICROST RIP ANTENNA USING DIODES ................................................................................................................ 115 5 .1 Horizontal Beam S teering ............................................................................... 115 5 .2 Vertical Beam S teering ................................................................................... 117 5 3 Fabricated Proposed Antenna ........................................................................ 122 5 .4 Input Reflection Coefficient (S11) ................................................................... 123 5 .5 Far Field Radiation Patterns ........................................................................... 124 5 .6 Limitation of the P roposed A ntenna ................................................................ 128 5 .7 Summary ........................................................................................................ 128 6 SUMMARY ........................................................................................................... 133 LIST OF REFERENCES ............................................................................................. 136 BIOGRAPHICAL SKETCH .......................................................................................... 139

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7 LIST OF TABLES Table page 4 1 Trend of Gain vs. gap between main and parasitic patch .................................. 56 4 2 Trends of E field distribution and gain as the stub changes .............................. 64 5 1 Beam Steering Comparison of ON OFF vs. OFFON at each frequency ........ 127

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8 LIST OF FIGURES Figure page 1 1 Geometry of the Yagi Uda dipole array antenna [Pozar1] ................................ 16 1 2 Mutual conductance between two parasitic patches [Derneryd] ........................ 17 1 3 Mutual coupling between two coax fed microstrip antennas .............................. 18 2 1 An example of a wideband microstrip antenna with a partial ground plane ....... 21 2 2 Another example of a wideband microstrip antenna .......................................... 21 2 3 Yet another example of wideband microstrip antenna ....................................... 22 2 4 Geomet ry of the microstrip Yagi array antenna [Huang1] .................................. 23 2 5 Microstrip Yagi array concept for MSAT application [Huang2] .......................... 25 2 6 I mproved bandwidth using parasitic patches [Kumar] ....................................... 25 2 7 Threeelement array for beam steering [Yusuf1] ............................................... 27 2 8 Reconfigurabl e antenna for dual frequency operation [Lee] .............................. 29 2 9 Reconfigurable antenna for dual frequency operation [Caverly] ........................ 29 2 10 HF SS layout of antenna; Left: bottom layer with diodes .................................... 30 2 11 Layouts of conventional broadband antenna as a reference antenna ............... 31 2 12 The examples of layouts of the arrays of the reference antennas ..................... 32 2 13 Examples of the reference antenna adopting microstrip Yagi array .................. 34 2 14 Layouts of broadband directional microstrip antenna ........................................ 35 2 15 A layout of the proposed antenna ...................................................................... 37 3 1 Layouts of fabricated broadband directional microstrip antenna ....................... 39 3 2 Agilent Vector Network Analyzer (Courtesy of Agilent Technologies, Inc.) ........ 40 3 3 Input reflection coefficients of the reference antenna ........................................ 41 3 4 Inside of an anechoic chamber for the radiation pattern measurement ............. 42 3 5 One of the configurations of mounted AUT ....................................................... 42

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9 3 6 Radiation pattern measurement shown on a computer screen ......................... 43 3 7 Comparison of simulated/measured radiation patterns ..................................... 44 3 8 Antenna gain comparison .................................................................................. 47 3 9 Antennas implemented in the radar ................................................................... 47 3 10 Illustration of the antenna and the radar installation .......................................... 48 3 11 Measured isolation ............................................................................................ 49 4 1 Modifications to the broadband directional microstrip antenna .......................... 53 4 2 A gap between parasitic patch and radiating edge of the wideband antenna .... 54 4 3 The relationship between gap value and the 3D radiation pattern .................... 55 4 4 The relationship bet ween parasitic patch shape and the 3D radiation pattern 57 4 5 A parasitic patch placed in Z direction separated from main patch ................. 58 4 6 An example of an added stub and its 3D radiation pattern ............................... 59 4 7 Another example of an added stub and its 3D radiation pattern ....................... 61 4 8 Yet another example of an added stub and its 3D radiation pattern ................. 62 4 9 Yet another example of an added stub and its 3D radiation pattern ................. 63 4 10 Reflection coefficient of the antenna shown in Figure 48 ................................. 64 4 11 Reflection coefficient of an antenna with shortened stub ................................... 65 4 12 Broadband microstrip antenna with added stub ................................................. 66 4 13 Design 1: Stub shape variation ........................................................................... 67 4 14 Design 2: Stub location and gap ......................................................................... 68 4 15 Design 3: Stub location and gap ......................................................................... 69 4 16 Surface current densit y of Design 3 .................................................................... 70 4 17 Design 4: Stub shape variation ........................................................................... 71 4 18 Surface current density of Design 4 .................................................................... 72 4 19 Design 5: Stub shape variation ........................................................................... 73

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10 4 20 Design 6: Stub shape variation ........................................................................... 74 4 21 Design 7: Stub shape variation ........................................................................... 75 4 22 Design 8: Stub shape variation ........................................................................... 76 4 23 Design 8: Stub shape variation ........................................................................... 77 4 24 Beam patterns of design 8 at different frequencies ............................................ 77 4 25 Design 9: Stub shape variation ........................................................................... 78 4 26 Surface current density of Design 9 .................................................................... 79 4 27 Design 10: Stub shape variation ......................................................................... 79 4 28 Surface current de nsity of Design 10 .................................................................. 81 4 29 Design 11: Stub shape variation ......................................................................... 81 4 30 Design 12: Parasitic patch variation ................................................................... 83 4 31 Design 13: Parasitic patch variation ................................................................... 84 4 32 Design 14: Parasitic patch variation ................................................................... 85 4 33 Design 15: Parasitic patch variation ................................................................... 86 4 34 Design 16: Parasitic patch variation ................................................................... 87 4 35 Design 17: Combinatio n of Parasitic patch and stub .......................................... 88 4 36 Antenna with diodes ........................................................................................... 90 4 37 Antenna with circuit ............................................................................................ 90 4 38 Forward current characteristic of 1N914 ............................................................. 91 4 39 S11 of the antenna shown in Figure 436 ........................................................... 92 4 40 Antenna with fixed ON/OFF status using wire .................................................... 92 4 41 S11 of the antenna shown in Figure 440 ........................................................... 93 4 42 LED as switching devic e for the antenna ............................................................ 93 4 43 Forward current characteristic of AVAGO 50823039 RF diode ......................... 94 4 44 Capacitance vs. reverse voltage o f AVAGO 5082 3039 RF diode ..................... 94

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11 4 45 Antenna with RF diode and variable resistor ...................................................... 95 4 46 Measured s11 of antenna with RF diode, ON/OFF status .................................. 95 4 47 Rough radiation pattern measurement method diagram .................................... 97 4 48 HP E8254A Signal Generator ............................................................................. 97 4 49 HP E4448A Spectrum Analyzer .......................................................................... 98 4 50 HyperLOG 60100 Yagi antenna ......................................................................... 98 4 51 Gain of the Yagi antenna .................................................................................... 98 4 52 Rough radiation pattern measurement method picture ....................................... 99 4 53 Rough radiation pattern measurement method: Antenna rotation .................... 100 4 54 Rough radiation pattern sketch ......................................................................... 101 4 55 Antenna with circuit for rough radiation patt ern measurement ......................... 101 4 56 Beam steering using parasitic patch ................................................................. 102 4 57 MEMS switching example ................................................................................. 103 4 58 Mechanical switch: Slide switch (Radioshack 2750004) ................................. 104 4 59 Mechanical switch:Tact switch (Radioshack 2750006) ................................... 104 4 60 Antenna with handmade slide switch ................................................................ 105 4 61 Relay (Radioshack 275005) ............................................................................ 105 4 62 Antenna with relay in a platform ....................................................................... 106 4 63 S11 comparison of simulation and antenna/relay measurement ...................... 106 4 64 Schematics and switch ..................................................................................... 107 4 65 Pad configuration .............................................................................................. 107 4 66 Isolation between RF1 pin and RF2 pin ............................................................ 108 4 67 Pin connection between the stub and the partial ground plane ........................ 108 4 68 Wiring of RF switch ........................................................................................... 109 4 69 A ntenna with one of the stub connected in RF switch configuration ................. 109

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12 4 70 S11 of antenna shown in Figure 469 ............................................................... 110 4 71 Radiation pa ttern of antenna shown in Figure 469 .......................................... 110 4 72 Antenna with pattern for RF switch and the antenna with RF switch ................ 111 4 73 Microscopic view of the RF switch on the antenna ........................................... 111 4 74 Forward resistance as a function of forward current ......................................... 112 5 1 A layout of the electronic beam steering broadband single microstrip ............. 115 5 2 Reflection coefficient of the antenna shown in Figure 51(B) .......................... 116 5 3 Radiation patterns of the antenna shown in Figure 51(B) .............................. 117 5 4 A layout of the vertical electronic beam steering broadband single microstrip 118 5 5 A layout of the vertical electronic beam steering broadband single microstrip 119 5 6 A layout for simulating the vertical electronic beam steering br oadband ......... 119 5 7 A comparison of the surface currents and radiation patterns .......................... 120 5 8 Reflection coefficients of the layouts o f (A) Figure 5 4 and (B) Figure 56 ...... 121 5 9 Proposed antenna; (A) bottom layer; (B) top layer .......................................... 123 5 10 Reference antenna; (A ) bottom layer; (B) top layer ......................................... 124 5 11 Reflection coefficient; Dashed: measured proposed antenna ......................... 125 5 12 Inside of an anechoic chamber for the radiation pattern measurement ........... 129 5 13 One of the ways of how the AUT was mounted. .............................................. 129 5 14 Comparison o f measured radiation patterns of the proposed antenna ............ 130

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13 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of D octor of Philosophy A BEAM STEERING, BROADBAND MICROSTRIP ANTENNA FOR NON CONTACT VITAL SIGN RADAR DETECTION By Zivin Park Ma y 2011 Chair: Jenshan Lin Major: Electrical and Computer Engineering The non contact vital sign radar detection system requires a development of the high gain, broadband, and beam steering patch antenna. The proposed design approach combines the advantages of the wideband antenna, the advantage of the parasitic patch, and the advantage of beam steering antennas within a single mic rostrip patch antenna. As a result, a 2.8 4.8 GHz beam steering broadband microstrip antenna was designed, fabricated, and measured. The proposed antenna can steer beam in broadband range (sampled at 3, 3.5, 4, and 4.5 GHz) by switching PIN diodes that con nect stubs and a partial ground plane. Its broadband beam steering is suitable for a vital sign radar. The proposed antenna requires no array for beam steering but requires only two additional diodes. The wide frequency tuning range allows the radar system to be tuned for an optimum transmission frequency. In addition, effects of modifying the proposed antenna on the antenna characteristics such as reflection coefficient, radiation pattern, gain, or beam steering capability are investigated.

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14 CHAPTER 1 M OTIVATION AND BACKGR OUND INFORMATION 1.1 Motivation Microwave Doppler radar has been used for detecting physiological movements. The radar transmits a radio frequency (RF), singletone continuous wave (CW) signal, which is reflected off a target and then demodulated in the receiver. This technique enables noncontact detection of vital signs of humans or animals from a distance away, without any sensor attached to the body [Li1]. A non contact solution is desired for several reasons. First, unlike methods using electrodes, it does not cause discomfort in the subjects. Second, the reliability can be increased since the subject is unaware of the measurement. Last, the detector can be ideal for long term, continuous monitoring applications. Compared to either infrared or visible light, microwave has a greater penetration capability through the building materials [Li1]. Therefore, an antenna transmitting an RF signal can be used with the Microwave Doppler radar. In particular, a microstrip patch antenna is desir ed because of its easy integration with the sensor, i.e., integration on a same substrate. Microstrip patch antennas are low profile, conformable to planar and nonplanar surfaces, simple, and inexpensive to manufacture using modern printedcircuit technology. It is mechanically robust when mounted on rigid surfaces, compatible with Monolithic Microwave Integrated Circuits (MMIC) designs, and when the particular patch shape and mode are selected, they are very versatile in terms of resonant frequency, polarization, pattern, and impedance. In addition, by adding loads between the patch and the ground plane, such as pins and varactor diodes, impedance, polarization, and pattern can be designed [Balanis].

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15 For the specific application such as the aforementioned noncontact detection of vital signs, a microstrip patch antenna to be integrated with the sensor needs to have a high gain, broad bandwidth and a size within a limited area. 1.2 Requirements The main criteria of the antenna design for this vital sign detector application can be summarized as follows. First, the patch antenna should cover the frequency range of 4.4 6.7 GHz, which is the full operating range of the portable radar designed [Li2]. The optimal carrier frequency could be as high as in the low er region of Kaband (26.540 GHz) for people with weak physiological movement. However, the operating frequency can be limited by the radar, which uses low cost components. Also, lower broadband range can be desired because of larger penetration depth, better vital sign detection when the subject has large physiological movement, and a smaller FR 4 loss. Second the patch antenna must have a high directivity. Third, the isolation between the transmitting and receiving antennas should be good. Fourth, the patch antenna should fit within an area of 3 inch by 3 inch. Last, broadband beam steering is desired because of its use for radar application. 1.3 Background Information 1.3.1 Yagi Dipole Antenna Figure 1 1 shows a layout of a Yagi dipole antenna. The basi c Yagi Uda array consists of a parallel set of linear dipole radiators. The left most element is typically slightly larger than resonant length and is called a reflector. The next element is a dipole element with a feed line. The right most elements are ty pically slightly less than resonant length and are called directors. Spacing between elements is typically 0.2 0.3 In this way, it is rather easy to achieve gains ranging 10 20 dB. This is in contrast to

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16 a single dipole element, having a gain of 2.2 dB. The gain of the array increases with the number of directors that are used. Adding more reflector elements to the left of the feed has little effect on the array, since radiation is predominantly along the director elements [Pozar1]. Figure 11. Geometr y of the Yagi Uda dipole array antenna [Pozar1] An increase in the number of directors increases the directivity of the array, although this increase reaches the point of diminishing returns after about 10 15 director elements. 1.3.2 Coupling Mechanism of Patch Antenna Mutual coupling is primarily attributed to the fields that exist along the air dielectric interface. The fields can be expressed as Equation 11: Fields = Space waves (~ 1/r) + Higher order waves (~ 1/(r2 Surface wave (~ 1/( )) + r )) + Leaky waves (~ exp ( r) / ( r )) (1 1)

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17 Space waves and higher order waves are dominant for small spacing and surface wave is dominant for large spacing [Balanis]. In addition, a theoretical investigation of the r ectangular microstrip antenna element regarding mutual conductance between two microstrip patches was reported. The mutual conductance between two patches can be expressed as Equation 12 [Derneryd]: G12 = d L J L J J e sin 2 sin 2 sin 2 2 sin cos cos sin 10 0 0 3 0 2 2 (1 2) The represents a center to center separation between patches and J is Bessel function. This equation is shown as graph in Figure 1 2. Figure 12. Mutual conductance between two parasitic patches [Derneryd]

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18 As shown in Figure 1 2, the mutual conductance between the patches decreases as the spacing between the patches increases. The mutual conductance between elements can be seen as composed of conductances between the ends of one element and both ends of the other element. Calculations showed that the mutual conductance is higher along the E plane than along the H plane as shown in Figure 1 3 [Pozar2]. Figure 13. Mutual coupling between two coax fed microstrip antennas, for both E plane and H plane coupling [Pozar2] In addition, for the coupling to occur, the dielectric constant of the substrate material can neither be too low nor too high. The width and length of a rectangular patch is inversely proportional to a square root of a dielectric constant of a substrate [Covert]. If the relative dielectric constant is very low (less than 1.5), the patch size becomes larger than 0.35 freespace wavelength and consequently the separation distance that is required can no longer be held. On the other hand, if the relative dielectric constant is

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19 too high (m ore than 5), the patches will be very small and the gaps between patches become large in order to hold the required element separation [Huang2]. 1.4 Summary Motivations and requirements for the proposed antenna are discussed. As background information, Yagi dipole antenna and coupling mechanisms of microstrip patches are discussed.

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20 CHAPTER 2 PROPOSED APPROACHES VS. EXISTING APPROAC HES 2.1 Wideband Microstrip Antennas with a Partial Ground Plane There have been many design approaches for wideband antennas using partial ground planes. A wideband patch antenna consisting of a rectangular patch with two steps, a single slot on the patch, and a partial ground plane was reported [Choi1]. A further modification of partial ground plane patch antenna was introduced by adding a bent stub on the radiating patch and stepping the ground plane. By inserting an invertedU shaped slot on the circular patch, the antenna showed a bandrejection characteristic [Choi2]. The effects of ground plane dimensions on antenna perform ance such as gain, bandwidth and radiation pattern were investigated [Curto]. These wideband patch antennas operated approximately from 3 GHz to 12 GHz. In detail, Figure 2 1 shows a layout of the wideband antenna example using a partial ground plane. This antenna shows a 3.2 12 GHz frequency range for VSWR < 2 with a maximum gain value of about 5dB [Choi1]. Figure 2 2 shows another example of wideband antenna using a partial ground plane [Choi2]. As seen in Figure 2 2, a bent slot and a bent stub are adde d to the radiating patch, and the ground plane is modified to have a stepped shape. These modifications gave additional characteristics to the basic wideband characteristics. This antenna shows a bandwidth ranging from 2.9 to 12.1 GHz for a VSWR < 2 with a maximum gain less than 4 dB [Choi2]. As a last example of the wideband antennas using a partial ground plane, Figure 2 3 is shown. In this example, by removing the substrate surrounding the radiating patch, impedance bandwidth was increased at the higher end to be 3.1 ~ 11.2

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21 GHz. It was discovered that this antennas bandwidth is dependent on the ground plane size. A B Figure 21. An example of a wideband microstrip antenna with a partial ground pla ne: ( A ) front view (B ) back view [Choi1] Figure 22. Another example of a wideband microstrip antenna with a partial ground plane [Choi2]

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22 Figure 23. Yet another example of wideband microstrip antenna with a partial ground plane [Curto] In particular, wide bandwidth is lost for a very narrow ground plane. In this case, the maximum gain remains below 5dB [Curto]. One common characteristic in all of these wideband antenna examples showed above is that they all demonstrate wideband characteristics by us ing the partial ground plane. Another characteristic common to all of these wideband patch antennas is that there is still room for improvement in directivity or gain value. 2.2 Microstrip Antennas using Parasitic Patches There have been design approaches using parasitic patches to control the peak directivity or improve the bandwidth of microstrip antennas. The Yagi antenna [Pozar1] concept was introduced to control the peak directivity. With parasitic director and reflector patches located on the same pl ane of the driven element, the peak directivity,

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23 by the effect of mutual coupling, was tilted toward the end fire direction with peak gain of 8 dB [Huang1]. The antenna was later used in an array for mobile satellite applications [Huang2]. Figure 2 4 shows a microstrip antenna, which adopted the Yagi concept [Huang1]. Figure 24. Geometry of the microstrip Yagi array antenna [Huang1] It was shown that parasitic patches could be placed around a driven element to increase the gain of this single, driven element by several dBs. The configuration of the planar, microstrip, Yagi array was similar to that of a conventional dipole Yagi array. The dimensions and spacings between the microstrip driven element and reflectors were all designed based on the Yagi dipole array's design. Depending on the substrate thickness and dielectric constant, the dimension ratio of the reflector to the driven element was found experimentally to be between 1.1 and 1.3. The dimension ratio between the director and the driven element should be from 0.8 to 0.9. The distance between the centers of the reflector and the driven element is about 0.35 wavelengths, and the separation should be approximately 0.3 wavelengths between the director and

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24 driven element. The driven element was coax fed. Three Yagi arrays having different dielectric constant and dimensions were experimented for operation at 6.9 GHz and 1.58 GHz. As a result, the peak directivity of the Yagi array was directed at 40 degrees from the broadside direction, and about 2.5 d B of higher peak directivity was achieved by the Yagi than the single patch [Huang1]. Four rows of the same microstrip Yagi antenna were used to achieve the MSAT (mobile satellite) required gain of 10 dB within the angular region between 20 and 60 elev ations, as configured in Figure 2 5 [Huang2]. Antenna gain was measured at various elevation angles at 1552 MHz and 1654 MHz. The rows of Yagi antennas were however, mechanically steered. One common characteristic found in the patch antennas with parasitic patches mentioned above is that all of the antennas show increased gain with tilted directivity using the parasitic patches. Another common characteristic is that both of the antennas operate over a very narrow band. Parasitic patches were not only used f or increasing gain, but also were used for increasing bandwidth. To improve the bandwidth, parasitic patches on all four edges including nonradiating edges were used to increase the impedancematching bandwidth to 815 MHz [Kumar]. Figure 2 6 shows the improvement in bandwidth using multiple, gap coupled patches. However, the maximum bandwidth still remained less than 1 GHz. 2.3 Beam Steering Patch Antennas Beam steerable antennas are widely used in areas such as radar and satellite communications. The beam steering can be performed by mechanical means or

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25 Figure 25. Microstrip Yagi array concept for MSAT application [Huang2] Figure 26. Improved bandwidth using parasitic patches [Kumar] electronic means. As an example of the mechanical beam steering ant enna, four Yagi patch arrays were placed on a mechanically rotating platform which accomplishes

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26 the functions of azimuth rotation by a thin pancake motor whose motion is controlled by a monopulse signal [Huang2]. The rotating platform was required to track a satellite. As another example of the mechanical beam steering antenna, a mechanical reflect array, which uses rotating circular disks immersed in a circularly polarized field was reported [Fusco]. However, in general, the electronic beam steering is pre ferred over the mechanical beam steering because the mechanical beam steering has disadvantages such as a complex and large mechanical structure, high power requirements, and slow orientation speed. One of many examples of the patch antennas with electroni c beam steering capability is microstrip patch array with varactor diodebased phase shifters between the elements [Andersson]. The phase shifters were adopted to give a fast response time. As another example of the patch antenna with electronic beam steer ing capability, Ka band microstrip patch antenna arrays with twelve elements were designed and feeding structures were used to radiate dual beams [Rodenbeck]. For the electronic beam steering, phased array has been the primary type. However, the phased arr ay requires many elements such as additional circuit components including power dividers and phase shifters. Consequently, there have been approaches to minimize the complexity required for electronic beam steering. Recently, a concept termed electronicall y steerable passive array radiator (ESPAR) has been reported for achieving beam steering without the need of phase shifters. In ESPAR, passive radiators can be excited by a driven antenna through a mutual coupling between the passive radiators and the driv en antenna. As an example, an antenna array, which uses one driven element surrounded by a number of parasitic

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27 elements operating near resonance was reported [Preston]. Threeelement phased array, where the center (driven) antenna is fed by an RF source and the two neighboring (passive) antennas are excited through the mutual coupling from the center antenna is reported [Yusuf1]. By adjusting the capacitors value, the beam was tilted from 20 degree to +20 degree. However, this antenna requires array of antennas for steering beam and operates at narrow band (at 3 GHz). Figure 27. Threeelement array for beam steering [Yusuf1] The patch antenna phased array was demonstrated with analog beam steering without using phase shift ers, therefore reducing the cost of a phasedarray system. Another example of the ESPAR antenna array used parasitically coupled and reactively loaded patch antenna array to achieve beam steering in an analog manner [Yusuf2]. The parasitic coupling between closely spaced patch antennas was used to form a phased array with a single driven element. The phase shift between the array elements was adjustable by changing the reactive loading on the parasitic patch antenna. However, most of the examples of the ant ennas require an array of antennas for

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28 electronically steering the beam instead of a single antenna. Therefore there is a room for further simplification because not all applications require the complexity of phase array, and for some applications, an alternative, simpler system is desired. 2.4 Patch Antennas using Diodes Many patch antennas that use diodes have been reported. One example is a reconfigurable, dual frequency, slot loaded patch antenna controlled by PIN diodes. A PIN diode was placed at the extended slot arm to change the electrical length of the slot and thus shifted the two resonant frequencies considerably in different states of the diode. For example, when the diode is switched off, the currents have to flow through a capacitor, with an i ncreased current path, resulting in the shifting of resonant frequencies [Shynu]. Another example is a reconfigurable groundslotted patch antenna using PIN diode switching. A dual frequency operation was achieved by controlling PIN diode conduction [Byun]. A patch antenna consisting of a square radiating patch, a parasitic patch, and PIN diodes, which connect the radiating patch and the parasitic patch was reported. By controlling the DC bias voltage applied to the diodes, surface current distributions ch anged, thus, dual frequency operation was achieved [Lee]. As shown in Figure 2 8, when diodes are turned on, the current flows to the parasitic patch and the antenna operates at WCDMA (2110 ~ 2170 MHz). When the diodes are turned off the current does not f low to the parasitic patch and the antenna operates at DMB (2630 ~ 2655 MHz). As another example, an annular slot antenna using two PIN diodes that are placed on front and back were reported. This antenna was reconfigurable in both frequency and radiation pattern [Nikolaou]. As yet another example, a reconfigurable, spiral antenna array was designed for pattern diversity.

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29 Figure 28. Reconfigurable antenna for dual frequency operation [Lee] It utilizes the fact that the singlearm, Archimedean spiral can produce tilted beams by changing its arm length. The arm length was reconfigured in length using PIN diode switches [Mookiah]. As the last example, a reconfigurable Hilbert antenna using highspeed PIN diodes was reported [Caverly]. The PIN diodes were use d to reconfigure the fractal pattern and the antenna exhibited two resonant frequency bands. Figure 2 9 shows the antenna. By changing the ON/OFF status of the two diodes, the antenna operated at dual frequency. Figure 29. Reconfigurable antenna for dual frequency operation [Caverly]

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30 2.5 Proposed Design Approaches Figure 2 10 shows a layout of the proposed antenna with two diodes connecting the gap between the stubs and the partial ground plane. Figure 210. HFSS layout of antenna; Left: botto m layer with diodes; Middle: bottom layer for simulating one of the diodes being turned on; Right: top layer Design procedures that lead into the above proposed antenna are described as follows. In the beginning of the design procedure, in order to meet th e requirements stated in 1.2, a reference broadband antenna with a partial ground plane was designed. Ansoft HFSS was used for the design and optimization. The dimensions of the reference broadband antenna are shown in Figure 2 11. The FR4 lamination with a thickness of 1.6 mm and a dielectric constant of 4.4 was used as the substrate. The front trace layer consists of a square patch with dimensions of 15 mm 15 mm and a feed line with dimensions of 8 mm 4 mm. The partial ground with a dimension of 7.5 m m 30 mm was placed underneath the substrate (30 mm (W) 35 mm (L)). After achieving its bandwidth requirement (4.46.7 GHz) in the first design stage through the reference antenna, meeting the second criterion, (i.e., increasing gain) was necessary because it was found that

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31 Figure 211. Layouts of conventional broadband antenna as a reference antenna; Left: Top layer, Right: Bottom layer this reference antenna or traditional single patch partial ground plane broadband antenna does not work well with the broadband transceiver because of insufficient gain and directivity, as well as poor isolation between the transm itting and receiving antennas. To meet the second criterion, numerous design approaches were performed. Using an array of antennas is one o f the most common methods to increase gain. Therefore, at first, arrays of antennas were simulated. For example, two, three, or four element arrays of the reference antennas were simulated to improve gain towards the broadside direction of the antennas. Fi gure 2 12 shows the layouts of the examples of the arrays. As seen in the Figure 2 12, each of the array antennas consists of a different number of reference antennas with varying shape of the partial ground plane, and all of them use coax feed. However, i n most of the cases, the reflection coefficient or the first criterion of the requirements, was destroyed by failing to maintain its original broadband characteristics.

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32 Figure 212. The examples of layouts of the arrays of the reference antennas; (Top) Two antenna array (Middle) Threeantenna array (Bottom) Four antenna array Thus, the array approach for boosting gain was discarded from design consideration. After further research of previous work, instead of using an array, it was found out that a mi crostrip Yagi array antenna having a reflector, driven element, directors as seen in Figure 2 4 could be a better approach to increase gain. Figure 2 13

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33 shows some of the early examples adopting the microstrip yagi concept to the reference antenna. In Figu re 2 13, it is shown that the reference antennas use coax feed and have the ground plane with different dimensions. For the antenna ( A ), which has a short partial ground plane, the reflector has a dimension of 17mm X 17mm, or 1.13 times the length of the s ide of the driven element. For the antenna ( B ), which has a long partial ground plane, the reflector has a dimension of 24mm X 24mm or 1.2 times the length of the side of the driven element. In this approach, the reflection coefficient was substantially m aintained. However, the size became quite large, and this time reducing the size became a concern, i.e., meeting the third criterion of the requirements. Thus, additional modifications were performed. After several design considerations, an edge feed was selected and the reflector was eliminated. Removing the reflector and using the edge feed are beneficial in antenna size reduction and fabrication. In addition, simulations showed that having both the reflector and the partial ground plane was not necessar y because the partial ground plane alone can function as the reflector, which will be discussed further in the following chapter. Removing the redundant reflector does not have a negative effect on S11, radiation pattern, or gain. Therefore, a successful design which meets all of the requirements, i.e., bandwidth, gain, and size is created. The layout is shown in Figure 2 14 [Park]. The ratio of directors/driven element size was 0.9. In detail, the two parasitic patches with dimensions of 13 mm X 13 mm are placed on top with 0.8mm gap from the

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34 f ront trace layer and from each other. As seen in Figure 2 14, in addition to the microstrip Yagi array antenna having a reflector, driven element, directors on front A B Figure 213. Examples of the reference anten na adopting microstrip Yagi array ( A ) short partial ground plane ( B ) long partial ground plane layer as seen in Figure 2 14, additional two directors were placed on bottom of the substrate to maximize the improvement of gain. It is known that electromagnet ic energy is coupled from the driven patch to the parasitic patches through both space waves and

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35 surface waves [Huang2]. By placing additional parasitic patches on the bottom of substrate, more energy can be coupled through surface waves in the substrate. Figure 214. Layouts of broadband directional microstrip antenna; Left: Top layer, Right: B ottom layer [Park] Simulation showed that the antenna with both top and bottom patches can increase gain about 0.3 dB at 4.5 GHz and 0.2 dB at 6.5 GHz when comp ared to an antenna with only top patches. Note that the driven element and the ground plane of the broadband directional microstrip antenna have the same dimension as those of the reference antenna. The partial ground plane improves broadband characteristi cs and the parasitic patches improve the gain. Also, note that a simple form of main trace layer that is same as the reference antenna is used, instead of the highly modified trace layer designs as shown in [Choi2] f or simplicity Through this design approach, many variations of the broadband directional microstrip antenna were simulated, such as broadband directional microstrip antenna with a short partial ground plane or a long partial ground plane, broadband directional microstrip antenna with one director or three directors, broadband directional microstrip

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36 antenna having different spacing between elements. Among the variations, the broadband directional microstrip antenna having a long partial ground plane did not show a gain that is as high as the br oadband directional microstrip antenna with short ground plane as shown in Figure 2 14, thus the broadband directional microstrip antenna having a long partial ground plane was discarded from design consideration. The difference between Figure 2 11 and Fi gure 2 14 is basically the additional parasitic patches. It may seem simple to design the broadband directional microstrip antenna from the reference antenna. However, as described above, adopting the Yagi concept to the reference antenna and meeting the r equirements required many simulations and optimization. In the noncontact vital sign radar detection application, broadband beam steering is desired because of its use for radar application. Unlike the patch antennas that use array for beam steering, the proposed antenna requires no array for beam steering but has single antenna and a pair of diodes attached to the single antenna. The diodes can be switched on and off to modify the electrical length of stubs of the single antenna. Numerous simulations t o optimize the stub shape attached to the ground plane and the locations of the stub have been performed for realizing electronic beam steering while maintaining broadband characteristic. The result of optimized layout is shown again in Figure 2 15. In det ail, Figure 2 15 shows two stubs added on the bottom of the substrate to the partial ground plane. The stubs are the only change made to the broadband directional microstrip antenna Thus, the driven element and the ground plane of the proposed antenna hav e the same dimension as those of the broadband directional microstrip

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37 antenna T here are lots of possible design combinations such as changing gap distances between elements and size and/or shape of each element. Figure 21 5. A layout of the proposed antenna or electronic beam steering broadband single microstrip antenna However, due to a limited time for design optimization, not all of the possible combinations were simulated. Some of the design considerations will be discussed in the following chapters. Among the many design considerations, discovering that the partial ground plane can function as a reflector is one of the most important facts found, which will be discussed in the following chapters. 2.6 Summary Examples o f microstip antennas using a partial ground plane to give wideband characteristics are shown; however, there is still a room for improvement in gain and directivity. In addition, microstip antennas using parasitic patches to give increased gain are shown; however, all of these kinds of antennas operate over a very narrow band. Neither case of the antenna is ideal for the specific application of the noncontact

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38 detection of vital signs, where a microstrip patch antenna needs to have a high gain and broad bandwidth at the same time. In addition, examples of antennas for beam steering and patch antenna examples using diodes are shown; however, those antennas operate at narrow band. Proposed design approach combines the advantages of the cited references of each category. In detail, the proposed antenna combines the advantage of the wideband antenna, the advantage of the parasitic patch, and the advantage of beam steering antennas. The proposed antenna requires no array for beam steering but requires only two additional diodes.

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39 CHAPTER 3 BROADBAND DIRECTIONA L MICROSTRIP ANTENNA 3.1 Fabricated Broadband Directional Microstrip Antenna After performing simulations in Ansoft HFSS, the broadband directional microstrip antenna was fabricated on a low cost FR4 substr ate, which was presensitized with photoresist. This allows for simple pattern application via photolithography and subsequent copper etching with ferric chloride. Figure 3 1 shows the fabricated broadband directional microstrip antenna. Also shown in Fig ure 3 1 is the edgemounted, standardpolarity SMA connector. Figure 31. Layouts of fabricated broadband directional microstrip antenna; Left: front layer. Right: bottom layer 3.2 Input Reflection Coefficient (S11) The one port scattering parameters (input reflection coefficients) of the reference antenna and the broadband directional microstrip antenna were measured using an

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40 Agilent E8361A 10 MHz to 67 GHz PNA series network analyzer as shown in Figure 3 2. To accompany the measurements, each antenna was simulated using HFSS. Figure 32. Agilent Vector Network Analyzer (Courtesy of Agilent Technologies, Inc.) The reflection coefficient (S11) of the broadband directional microstrip antenna was compared with the reference broadband antenna as shown i n Figure 3 3. The measurement results show that parasitic patches affected the broadband characteristics of the partial ground plane antenna in the lower frequency. In particular, the measured first resonant frequency of the broadband directional microstri p antenna shifted about 400 MHz up from that of the reference broadband antenna simulation. The discrepancy can be caused by one or more of the following reasons. First, the fabricated antenna may have different line width and different patch size than the values used in simulation model because of the around 0.3 mm resolution of lithography. Second, the actual dielectric constant of FR4 substrate at frequencies above 6 GHz might be different and the actual dielectric constant might vary from board to board Further modifications such as modifying ground plane and patch shape may improve the broadband characteristics [Choi1]. Nevertheless, the measurement result confirms that the broadband directional microstrip antenna has met the design requirement of impedance matching bandwidth.

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41 3.3 Far Field Radiation Patterns The radiation patterns were measured in an anechoic chamber at the Electromagnetic Wave Measurement Center in Seoul, South Korea. For this broadband antenna, it would be ideal to measure the radiation patterns at frequencies with small interval between them, but instead, the radiation patterns were measured at 4.5, 5, 5.5, 6, and 6.5 GHz due to practical reasons. Figure 33. Input reflection coefficients of the reference antenna and broadband dir ectional microstrip antenna At each of the frequencies, E plane and H plane cuts were measured. For the E plane measurement, an E plane that is vertical to the substrate (E1) and another E plane that is horizontal to the substrate (E2) were measured. Also, at each of the frequency, copolarization and cross polarization of the E planes and H plane were measured as well. Figure 3 4 shows inside of the anechoic chamber. The Standard Gain Antenna is shown on the left, and the a ntenna u nder t est (AUT) mounted i s shown on the right. Figure 3 5 shows one of the ways of how the AUT was mounted. After the AUT is securely mounted, it is rotated for the radiation pattern measurement. The

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42 measured data are shown on a computer screen, which is located outside of the ch amber as in Figure 3 6. Also, the radiation patterns were simulated using HFSS. Figure 34. Inside of an anechoic chamber for the radiation pattern measurement Figure 35. One of the c onfigurations of mounted AUT These radiation patterns of the reference antenna and the broadband directional microstrip antenna are reported in Figure 3 7. In particular, E plane copolarization and

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43 crosspolarization radiation patterns measured at frequencies of 4.5 GHz, 5.5 GHz, and 6.5 GHz are compared with simulations. Figure 36. Radiation pattern measurement shown on a computer screen outside of the chamber

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44 A B Figure 37. Comparison of simulated/measured radiation patterns of the broadband directional microstrip antenna and the reference antenna (Solid black: Reference, Dashed blue: broadband directional microstrip antenna simulated, ++ red: broadband directional microstrip antenna measured, x black: broadband directional microstrip antenna measured c ross polarization) along Phi =0 GHz (A), 5.5 GHz (B), and 6.5 GHz (C) are plotted. Antenna configuration with axes is shown in (D).

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45 C D Figure 37. Continued It can be seen in Figure 3 7 that the measured and simulated radiation patterns for the broadband directional microstrip antenna are in good agreement with each other. In addition, it can be seen that the actual measured side lobes of the broadband directional microstrip antenna are smaller than th at of the simulated pattern. Figure 3 7 ( D ) shows the antenna configuration used in HFSS simulation.

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46 Also shown in Figure 3 7 is that the peak directivity was tilted by about 35 from the broadside toward the end fire direction, which is caused by the eff ect of mutual coupling. A 35 of peak directivity angle is chosen because it is an appropriate angle for installation on the ceiling at a corner location. If the angle is tilted too close to endfire direction, the beam will be almost parallel to the ceili ng. If the angle is close to 0, i.e., broadside direction, the radar detection will be limited to a spot just below where the antenna is installed. Neither case is desired for the intended application. The designed radiation pattern of the antenna makes it possible to be mounted on the ceiling at the corner of a room or a hallway for human vita sign detection. The maximum gains of these two antennas are compared in Figure 3 8. In addition, half power beam width (HPBW) is found to be about 43. Simulation shows that adding more than two directors does not change the angle of main beam. It is because the amount of energy that couples into the second director is significantly reduced after most of the energy coupled into the first director has been radiated [Hu ang2]. Specifically, when only a single director is used, the peak directivity angle is tilted only 14 from broadside. However, the angle remains at 35 even after the third director is added. The tilted angle is also known to be a function of dielectric constant, substrate thickness, patch separation, and sizes of the parasitic patches [Huang2]. Therefore, the tilted angle can be modified by varying the above parameters and the number of patches. Figure 3 9 shows two of the broadband directional microstri p antennas mounted on the broadband Doppler radar for noncontact vital sign detection and Figure 3 10 shows the installation diagram.

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47 Figure 38. Antenna gain comparison between the broadband directional microstrip antenna and the reference antenna Fi gure 39. Antennas implemented in the radar

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48 Figure 310. Illustration of the antenna and the radar installation 3.4 Isolation Figure 3 11 shows measured isolations or S12 between the transmitting and receiving antennas mounted on the radar for both the broadband directional microstrip antenna and the reference antenna. The distance between the two antennas feeds were 60mm because it is the actual distance between the feeds of the transmitting and receiving antennas when install ed in radar. It shows the broadband directional microstrip antenna have better isolation than the reference antennas in most of the frequency band. Therefore, in addition to meeting the bandwidth and gain requirements, the broadband directional microstrip antenna shows also good isolation between the transmitting and receiving antennas. 3.5 Vital Sign Detection Performance The broadband directional microstrip antenna and the reference antenna were tested in the system using the same vital sign radar transc eiver and the measurement results were compared.

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49 A B Figure 311. Measured isolation between a pair of the broadband directional microstrip antennas and a pair of reference antenna ( A ) measurement configuration ( B ) result The pair of broadband directi onal microstrip antenna and the pair of reference antenna were mounted in the same configuration as in Figure 3 9. The baseband outputs measured with the two types of antennas are plotted in Figure 3 12. It is clearly shown in the m easurement results that t he broadband directional microstrip antenna

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50 produced much larger signal amplitude with clearer peaks and periodic pattern because of the improved gain. As the frequency increases, increase in signal amplitude becomes less significant due to less improvemen t in gain at high frequency end of the band as shown in Figure 3 8. Overall, the vital sign detection performance is improved by the broadband directional microstrip antenna. Figure 312. Comparison of the I (dashed blue) and Q (solid black) channel signals received by the two types of antennas at the frequencies of: 4.58 GHz (top figures), 5.15 GHz (middle figures), and 5.57 GHz (bottom figures)

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51 3.6 Summary A new design combining the partial ground plane and parasitic patches is presented. The part ial ground plane improves broadband characteristics and the parasitic patches improve the gain. As a result, a 4.3 7 GHz broadband antenna with improved gain was designed and fabricated. Compared to a partial groundplane, single patch, reference antenna, this broadband directional microstrip antenna shows desired directivity and improved gain performance. Its radiation pattern was designed for a vital sign radar detector mounted on the ceiling at corner locations. The radiation pattern also provides a bett er isolation between the transmitting and receiving antennas for this application. The design approach ensures that broadband performance can be achieved while improving the gain of the antenna.

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52 CHAPTER 4 PRELIMINARY RESULT O F BEAM STEERING BROADBAND M IC ROSTRIP ANTENNA 4.1 Director and Reflector The advantages of wideband antenna and the advantages of parasitic patch antenna are combined and validated by fabrication and measurement. In this chapter, the effects of modifying the broadband directional micr ostrip antenna on the antenna characteristics such as reflection coefficient, radiation pattern, gain, or beam steering capability are discussed. The modification can include varying the width and/or length of the partial ground plane, adding stub(s) on th e partial ground plane, varying the width, length, and/or location of the added stub, or varying the number, shape, gap, or location of the directors. These modifications will significantly change the performance of the antenna, however, it is important to evaluate the effects of the modification on the antenna characteristics, since these effects may be exploited to improve the antenna performance. Specifically, the modification on the broadband directional microstrip antenna can give a beam steering capability to the broadband directional microstrip antenna In the previous chapter, the reflector in conventional Yagi patch antenna has been eliminated. In this section, roles of directors and ground plane have been investigated. In particular, the fact that the remaining partial ground plane can actually work as a reflector is illustrated. In addition, the directors role is illustrated. Simulations show that changing the shape or location of ground plane or director can tailor beam shape. For example, a gr ound plane with a stub moves the beam away from the added stub. In other words, beam is reflected to the opposite direction from where the stub is added ( Figure 4 1 B ). As opposed to the ground plane, when directors

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53 are placed on the side of original loc ation, beam is formed in that direction of the directors. In other words, beam is steered towards the direction of the directors ( Figure 4 1 C ). Thus, it can be seen that the ground plane is working as a reflector and the parasitic patchs are working as di rectors. A B C Figure 41. Modifications to the broadband directional microstrip antenna and their 3D radiation patterns: ( A ) Original layout ( B ) Layout with a stub added to the ground plane ( C ) Layout with two directors shifted to the le ft from the original layout

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54 4.2 Influence of Gap Value between Patches on Beam Pattern In this section, influence of different gap values between patches on beam pattern is investigated. An antenna as shown in Figure 4 2 was set up for this simulation. Figure 42. A gap between parasitic patch and radiating edge of the wideband antenna As seen in Figure 4 2, only one parasitic patch is used for simplicity. Figure 4 3 shows the relationship between the gap value and the 3D radiation pattern. It is well k nown that a microstrip patch antenna without a parasitic patch radiates mainly in its broadside direction and radiates very little along the direction of the ground plane. This is the reason that a microstrip patch generally couples very little energy to i ts nearby patches, when the patches' separation becomes large. Consequently, in order for the microstrip patches to function similarly to the Yagi dipoles, the adjacent patches need to be placed very closely to each other so that a significant amount of co upling can be obtained through surface waves in the substrate [Huang2].

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55 A B C Figure 43. The relationship between gap value and the 3D radiation pattern

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56 It was also found experimentally that the gap distance between two patch edges should be equal to or less than the dielectric substrate thickness [Huang1]. From Figure 4 3, it can be seen that as the gap becomes smaller (within a certain limit), the gain becomes higher. It is due to the concentration of the beam towards the parasitic patch due to c oupling effect. Table 41 summarizes the trend. Table 41 Trend of Gain vs. gap between main and parasitic patch Gap Gain 2 mm 5.1 dB 8 mm 4.6 dB 16 mm 3.8 dB 4.3 Influence of Shape or Location of Parasitic Patch on Beam Pattern B eam pattern gets a ffected as parasitic patch shape changes. Figure 4 4 shows the examples. As seen in Figure 4 4, it is shown that the beam shape can be complementary to the shape of parasitic patch. In other words, the beams are filling the space where the patch is not occ upying. Thus, beam can be directed towards specific direction using this effect. In addition, the coupling effect still exists between the trace layers even when parasitic patches are separated from the main antenna. In other words, beam shape can be tilt ed not only in the XY direction but also in Z direction as shown in Figure 4 5. Thus, by replacing only the parasitic patch part from one to another mechanically, different beam shape can be formed while using the same main patch part. 4.4 Influence of A S tub Added to Ground Plane on Beam Pattern The simulation shown in Figure 4 1 showed that the ground plane is functioning as a reflector because beam is steered away from an added stub to the ground plane. In this section, the stub and its influence on bea m pattern is further investigated in depth.

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57 A B C Figure 44. The relationship between parasitic patch shape and the 3D radiation pattern

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58 A B C Figure 45. A parasitic patch placed in Z direction separated from main patch ( A ); a view from +Y direction ( B ); and its 3D radiation pattern ( C )

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59 Figure 46. An example of an added stub and its 3D radiation pattern and the magnitude of the E field at 4.5 GHz

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60 Specifically, the effect of variation of width or length of stub attached to the ground plane to beam pattern is investigated. As shown in Figure 4 6, a stub that has a length shorter than the main patch and a width that is fully occupying the space between the main patch and the substrate boundary is added to the ground plane. The stub has a width of 7.5 mm and length of 10 mm. Its 3D radiation pattern shows a gain value of 5.65 dB and E field magnitude that is concentrated in the main patch. To show the E field magnitude, a plane is placed 25mm from the center of feed in Y direction. Both of the 3D radiation pattern and E field magnitude are plotted at 4.5 GHz. Figure 4 7 shows another example of an added stub. In this case, only the length of the stub is increased to 30 mm from the Figure 4 6. Through the modification of the stub length, the gain has increased to 5.93dB and the E field magnitude is concentrated more to the parasitic patch. Figure 4 8 shows yet another example of an added stub and its 3D radiation pattern and the magnitude of the E field at 4.5 GHz. In th is case, only the stub width is reduced to 2.5mm from the Figure 4 6 and located at the substrate boundary. This time, the gain value is reduced to 5.4 dB. Figure 4 9 shows yet another example of an added stub and its 3D radiation pattern and the magnitude of the E field at 4.5 GHz. In this case, the stub width and length are unchanged from Figure 4 8. Instead, the location of the stub is moved 2.5 mm in the Y direction. This time, the gain value is 5.55 dB. Through these simulations shown in Figure 4 6 ~ Figure 4 9, trends were found and the trends are summarized in Table 42 Based on the trends, beam pattern and gain can be modified and increased by modifying the stub location and dimension.

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61 Figure 47. Another example of an added stub and its 3D radiation pattern and the magnitude of the E field at 4.5 GHz

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62 Figure 48. Yet another example of an added stub and its 3D radiation pattern and the magnitude of the E field at 4.5 GHz

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63 Figure 49. Yet another example of an added stub and its 3D radiation pattern and the magnitude of the E field at 4.5 GHz

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64 Table 42 Trends of E field distribution and gain as the stub changes Stub E field distribution Gai n Increase in length More concentrated on parasitic patch side Increases Decrease in width More concentrated on parasitic patch side Decreases Moved towards driven element More concentrated on driven element Increases However, the broadband character istics or the reflection coefficient has not been considered among the effects of stub because the beam pattern was the main concern of the investigation. Figure 4 10 shows a change in reflection coefficient when the stub was added. As shown in Figure 4 10, the stub compromises the reflection coefficient of the original antenna shown in Figure 3 3 in other words, the broadband is split into two bands Figure 410. Reflection coefficient of the antenna shown in Figure 4 8 After all, it is shown that if the stub shape can be modified in real time, a beam steering can be realized. Especially, if electrical length of the stub can be modified, the beam can be steered electronically. A diode has been used to modify the antennas electrical length.

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65 Figure 411. Reflection coefficient of an antenna with shortened stub Figure 4 11 shows a layout of an antenna with a shortened stub compared to the stub shown in Figure 4 10. This stub has a siz e of 3 mm X 3mm. The short stub recovers the original broadband characteristic (4.3 7 GHz), however, as seen in the 3D radiation pattern of Figure 4 11, the beam steering became compromised i.e.,

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66 weakly tilted beam. As shown in the Figure 4 10 and Figure 4 11, as the stub changes, not only the beam pattern changes, but also the reflection coefficient changes. Again, it can be seen that these antenna parameters are in a tradeoff relationship. It requires numerous simulations to optimize the stub shape tha t affects the beam pattern while maintaining the broadband bandwidth. Figure 4 12 summarizes the relationship between stub, s11, and radiation pattern in a concise manner. Figure 412. Broadband microstrip antenna with added stub; (a) Stub dimension, Example A: W=2.5 mm, L= 10 mm, Pos=12.5mm (from center), Example B: W=3 mm, L= 3 mm, Pos=12 mm; (b) Reflection coefficient; (c) Radiation pattern (a) Stub Dimension Example A Example B (b) (c)

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67 4 5 Simulat ed L ayout of V arious S tubs, I ts B eam P attern, and I ts S 11 I n 4.4, the layout that has only one stub on one side of the antenna has been simulated. In this section, simulation layouts that include stubs on both sides to perform horizontal beam steering in both directions are shown in detail Also, in 4.4, the s11 was not considered, but for optimized layout, the s11 needs to be considered every time a modification is made. Thus, t he following simulations include layout its radiation patterns and its reflection coefficient Description of the design 1: Stub shape is modified to investigate t he influence of stub shape on the beam pattern. The stub is formed by uniting two rectangles of trace layers with finite conductivity. The dimensions of the two rectangles are 2.5 mm X 3.5 mm and 2.5 mm X 7 mm. The beam pattern shown is sampled at 3.5 GHz and has a gain value of 4dB. The shape change does not significantly change the beam pattern from the optimized layout. Figure 41 3 Design 1: Stub shape variation

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68 Figure 41 3 Continued Figure 414. Design 2: Stub location and gap

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69 Figu re 4 14. Continued Description of the design 2: The stub dimension i s 2.5 mm X 10 mm as in the optimized layout, but for the OFF status stub, the gap between the stub and partial ground plane is 5mm, not 1 mm as in the optimized layout. A strong beam steer ing is observed with a gain value of 5.6 dB. However, the s11 is negatively affected as shown. Fig ure 4 15. Design 3 : Stub location and gap

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70 Fig ure 4 15. Continued Description of the design 3 : The stub dimension is 2.5 mm X 10 mm. For the OFF statu s stub, the gap between the stub and partial ground plane is 3 mm. The location of the stub is 4 mm away from the side. A strong beam steering of 5. 7 dB is observed at a sampled frequency of 4.5 GHz. However, the s11 is negatively affected as shown. Fig ur e 4 16. Surface current density of Design 3

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7 1 Fig ure 4 16 shows an additional simulation result or a surface current density of the design 3. In this figure, it is clearly shown that the ON status stub has higher surface current density than the OFF status s tub thus, it results in beam steering. Fig ure 417. Design 4 : Stub shape variation

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72 Description of the design 4 : Its another stub shape variation. The stub is mitered. The mitered angle is 45 and width of the stub is 2.5 mm. The part of the stub after mitered is 5mm long and 2.5 mm away from the main patch. The OFF status stub is 2.5 mm away from the partial ground plane. A strong beam steering is observed at 4.5 GHz with a gain value of 5. 66 dB. However, the s11 is negatively affected as shown. Fig ure 4 18. Surface current density of Design 4 Fig ure 418 shows an additional simulation result or a surface current density of the design 4. In this figure, it is clearly shown that the ON status stub has higher surface current density than the OFF status stub. However, there is still weak current on the OFF status stub due to coupling between the OFF status stub and the main patch and the partial ground plane. Description of the design 5 : It i s a slight change from design 4. In detail, the stub is mitered at two points and the distance between the main patch and the mitered stub is 1 mm. The other dimensions of the stub remain same as design 4. Still a strong beam

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73 steering is observed at 4.5 GHz with a gain value of 5. 62 dB. However, the s11 is negatively affected as shown. Fig ure 4 19. Design 5 : Stub shape variation

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74 Fig ure 4 20. Design 6 : Stub shape variation Description of the design 6 : Its another stub shape variation. In particular, its yet another slight change from design 4, i.e., the distance between the main patch and the mitered stub is now 0 mm. The other dimensions of the stub remain same as design 4. Still a beam steering is observed at 4 GHz with a gain value of 5. 1 dB. However, the s11 is negatively affected as shown.

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75 Fig ure 4 21. Design 7 : Stub shape variation Description of the design 7 : Here, the stub is bent but not mitered. The width of the stub is 2.5 mm and the tip of the stub is 10 mm away from partial gr ound plane and the bent part of stub is 2.5 mm away from partial ground plane and the gap between the stub and the main patch is 0 mm. A beam steering is observed at a sampled 4.5 GHz with a gain value of 5. 3 dB. However, the s11 is negatively affected as shown.

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76 Fig ure 4 22. Design 8 : Stub shape variation Description of the design 8 : The stub width is reduced to 1.5 mm and mitered. The distance between the main patch and the stub is 1mm. The OFF status stub i s 1mm away from the partial ground plane. A beam steering is observed at a sampled

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77 fr equency of 4.5 GHz with a gain value of 5. 13 dB. However, the s11 is negatively affected as shown. Fig ure 4 23. Design 8 : Stub shape variation Fig ure 4 23 shows a zoomed in view of the surface current of the des ign 8. Even if there is current in the OFF status stub, a beam steering occurs because it s less than the current on ON status stub. Fig ure 424. Beam patterns of design 8 at different frequencies Fig ure 424 shows beam patterns of design 8 at different frequencies. In particular, from left to right, 4.5dB at 3.8GHz, 4.8dB at 4GHz, and 4.9dB at 4.3GHz. It can be seen that the gain increases as the s11 decreases.

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78 Fig ure 4 25. Design 9: Stub shape variation Description of the design 9: The difference between the design 8 and design 9 is that in design 9, the connection between the stub and the partial ground plane has reduced width. In design 8, the ON state connection dimension was 1 mm X 1 mm. In design 9, it is 1 mm X 0.5 mm. Even with the narrow ed connection to the ON status

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79 stub, beam steering is observed. A gain value of 4.85 dB is shown at a sampled frequency of 4 GHz Fig ure 4 26. Surface current density of Design 9 Fig ure 4 26 shows the surface current of the design 9 Even if the ON sta tus connection is reduced, a higher current is flowing through that connection than the OFF stub, where current exists through coupling. Thus, beam steering occurs. Fig ure 4 27. Design 10: Stub shape variation

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80 Fig ure 4 27. Continued Description of the design 10: The stub is modified and bent at four points. This layout was tried to position the ON/OFF switching to the side. It was to see if this approach can minimize the current flowing to the OFF status stub. Very interesting results are shown. In detail when the stubs are modified greatly, i.e., bent at four points, the beam steering become inconsistent, i.e., the beam is steered towards the connected ON status stub at a certain frequency and the beam is steered towards the OFF status stub at other frequency. A very strong beam steering is observed at 5 GHz with a gain value of 6.23 dB(left), while a weak beam steering is observed at 4GHz with a gain value of 4dB(right). A lso, the broadband (3.8GHz ~6.7GHz) is observed as shown. Fig ure 4 28 shows the surface current of the design 10 at 4.5 GHz Substantial amount of current is flowing to the OFF status stub through coupling and it is the possible reason for the inconsistent beam steering at different frequencies.

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81 Fig ure 4 28. Surface current density of Design 10 Fig ure 4 29. Design 11: Stub shape variation

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82 Fig ure 4 29. Continued Description of the design 11: The stub width is 1.5 mm and mitered at two points to position t he switching location at sides of the antenna. A beam steering is o bserved at a sampled frequency of 4.5 GHz with a gain value of 4.9 dB. However, the s11 became narrow. 4 6 Simulat ed L ayout of V arious P arasitic P atches, I ts B eam P attern, and I ts S 11 Stub that is connected to the partial ground plane can steer beam hor izontally as shown in 4 5 In addition, parasitic patches can be also used to steer beam horizontally. The advantage of the beam steering using the parasitic patch, instead of stub, is that the parasitic patch does not affect the s11 significantly as stubs do. The disadvantage of beam steering using parasitic patch is that the beam steering is relatively weaker than the beam steering using stubs and the switching might be difficult to implement in fabrication.

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83 Fig ure 4 30. Design 12: Parasitic patch variation Description of the design 12: The parasitic patch is modified to show beam steering. The ON status side of the parasitic patch is connected to the middle piece of the parasitic patch. The connection is 1 mm X 1 mm. The middle piece is 3 mm X 13 mm. The horizontal beam steering shown is sampled at 4.5 GHz and show 4.9 dB of

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84 gain S11 remains almost unchanged from the broadband directional microstrip antenna Description of the design 13: The parasitic patch is modified to show horizontal beam steering. The ON status side of the parasitic patch is connected to the middle Fig ure 431. Design 13: Parasitic patch variation

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85 piece of the parasitic patch. The connection is 1 mm X 1 mm. The middle piece is 9 mm X 13 mm. The beam steering shown is s ampled at 5 GHz and show 4. 8 dB of gain S11 remains almost unchanged from the broadband directional microstrip antenna Fig ure 432. Design 14: Parasitic patch variation

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86 Description of the design 14: The parasitic patch is modified to show horizont al beam steering. The layout is same as design 13 except there is no bottom parasitic patch. C ompared to design 13, which has both top and bottom parasitic patches, the design 14 shows gain value of 4.6dB at 5GHz. Thus, it can be determined that the bottom parasitic patch s contribution to the gain is 0.2 dB. S11 remains almost unchanged from the broadband directional microstrip antenna. Fig ure 4 33. Design 15: Parasitic patch variation

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87 Description of the design 15: The parasitic patch is modified to show horizontal beam steering. The layout has two switching positions, which are shown as two of the 1 mm X 1mm squares. This layout was simulated to see if this can increase gain further. However, the gain was only 4.6 dB at a sample frequency of 4.5 GHz S11 remains almost unchanged from the broadband directional microstrip antenna. Figure 434. Design 16: Parasitic patch variation

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88 Description of the design 16: The parasitic patch is modified to show beam steering. The layout has two pieces of pat ches on both sides of middle piece of patch. The two pieces of patches on each side are 3 mm X 13 mm and the middle piece is 5mm X 13mm. The connection to the middle patch is 9.5mm X 1mm. A weak beam steering is observed. The gain was 4 dB at a sample freq uency of 4.5 GHz. S11 remains almost unchanged from the broadband directional microstrip antenna. Fig ure 4 35. Design 1 7 : Combination of Parasitic patch and stub

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89 Description of the design 17 : Finally, t he parasitic patch modification and stub is com bined to see if it results in higher gain and stronger beam steering. However, the gain sampled at 4GHz is only 5.2 dB. S11 is shifted to lower frequency due to the added stub and the parasitic patch does not affect the lowered s11. 4 7 Intermediate Fabrication and M easurement R esults: Regular D iode and RF D iode In addition to the intermediate simulation results detail of the intermediate fabrication and measurement results is described. Specifically, in HFSS, switching is not simulated in detail because O FF status stub is simulated as a disconnected trace layer and ON status stub is simulated as a connected trace layer. Even if the parasitic capacitance is taken into account by setting the trace layer property of the gap, there is still unknown factors in real implementation In particular wires soldering, battery and resistors that are located close to the antenna are difficult to be considered in simulation. Also, switching devices such as d iode cannot be simulated in HFSS Thus, the actual performance is heavily dependent on the switching device. The key to the beam steering in actual measurement is to find a switching device that has the least amount of OFF current at OFF status. The optimized layout that was found out through simulations was fabricated using the typical lithography and etching process on FR4. The layout used was OFF OFF state because the switching devices will be connecting the gap between the stub and the partial ground plane. A very inexpensive diode was t este d first as the switching device. Specifically, Jameco 1N914 (C = 4pF, Rs = less than 100 ure 4 36 shows the picture of antenna with the diodes on both side

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90 Fig ure 4 36. Antenna with diodes Fig ure 4 37 shows the antenna with diodes and c ircuit for switching the diodes. On the left, two 1.5 V mercury batteries are used on each side of antenna and LED was also used for an easy indication of the ON side. Resistors are used to prevent diode damage. On the right, the two batteries are replaced with one 3V mercury battery for its easy connection. The value of resistor was calculated based on the data sheet of diode as shown in Fig ure 43 8 In other words, the resistor was chosen to flow a forward current of 300mA. Fig ure 4 37. Antenna with c ircuit The measured s11 is shown in Fig ure 4 39. The s11 is ON/OFF status of the antenna. However, it is quite different from the simulated s11 of ON/OFF status shown

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91 Fig ure 4 38. Forward current characteristic of 1N914 in Fig ure 5 2 Please note t he nois e is from the cable that connects the antenna and the network analyzer. To troubleshoot, instead of actual switching devices, a wire was soldered between the partial ground plane and the stub to represent ON status as shown in Fig ure 4 40. Its s11 was measured and shown in Fig ure 4 41. It shows very similar s11 as in simulation of ON/OFF status shown in Figure 5 2 Thus, the problem is narrowed down to the switching device performance. In order to switch properly, the switching device should show a good OF F status at high frequency. Thus, the switching device needs to have a lowest possible parasitic capacitance value. Just out of curiosity, LED was tested as a switching device as shown in Fig ure 442 and the measured ON/OFF s11 showed 2.6~3.2 GHz, which is quite different from the simulated ON/OFF s11. A search for a diode that is suitable for RF application has begun and it appeared the AVAGO 5082 3039 RF diode is a suitable candidate. It has a capacitance value of

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92 Fig ure 4 39. S11 of the antenna shown in Fig ure 436 Fig ure 440. Antenna with fixed ON/OFF status using wire

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93 Fig ure 4 41. S11 of the antenna shown in Fig ure 440 Fig ure 4 42. LED as switching device for the antenna 0.25 pF, i.e., sixteen times smaller the 1N914 and a series resistance value of 1.25 about eighty times smaller than the 1N914. The forward current characteristic of this diode is shown in Fig ure 4 43. It was used to calculate the necessary resistor value of th e circuit to prevent the diode from being damaged Fig ure 4 44 was used to see the capacitance value of the diode when the reverse voltage was applied. Fig ure 4 45 shows the antenna with the RF diode. From this point, also a variable resistor was used because of its easy adjustment of current value. Increasing the

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94 Fig ure 443. Forward current characteristic of AVAGO 5082 3039 RF diode Fig ure 4 44. Capacitance v s. r everse voltage of AVAGO 5082 3039 RF diode

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95 current value that is higher than the forward current did not affect the s11. Fig ure 4 46 shows the measured s11 of antenna with RF diode, an ON/OFF status. It shows a bit of similarity with simulated s11 but the 3~4.2 GHz is above 10 dB. Thus, it needs to be improved. It is because even with the relatively low capacitance value, the diode is not completely OFF at high frequency. Fig ure 4 45. Antenna with RF diode and variable resistor Fig ure 4 46. Measured s11 of antenna with RF diode, ON/OFF status

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96 From numerous measurements, the following facts are found. First, soldering affects11 substantially. Different soldering locations were tried to see if the s11 can be improved. This repeated heat from soldering could have damaged diode performance. Second, even if this diode is RF diode, it is a nonsurface mount type diode, thus, the connection between the stub and the partial ground plane is more like 3 dimensional, rather than 2 dimensional. Third, the soldering amount can be different from left side stub and right side stub. This results in a non symmetrical s11. In other words, the ON / OFF and OFF/ ON s11 are different from each other. Thus, the soldering amount needs to be minimized for symmetrical s11 for each status. Fourth, the diode polarity is critical. The cathode should be connected to the partial ground plane and the anode to the stub. Otherwise, the s11 deviates from the simulated value substantially. Last, the current needs to be checked each time of measurement. It is because the battery can be heated easily and that can cause the voltag e drop and subsequent current drop, which means the current flowing to the ON status diode can be below the minimum forward current. It was found out that the mercury battery overheats quickly. Thus, it was replaced with two of the AA size battery. 4 8 R ough R adiation P attern M easurement M ethod Even though the s11 shown in Fig ure 4 46 still needs to be improved, the radiation pattern needs to be measured concurrently with s11, because the beam steering is the most important characteristic of this antenna. Once the s11 was measured, the rough radiation pattern was measured at randomly sampled frequencies where the s11 is below 10dB.

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97 The description of the rough radiation pattern method is as follows. The rough radiation pattern measurement method can give you a quick look at the radiation pattern roughly. Fig ure 4 47 shows the diagram of rough radiation pattern measurement method. It is easy to set up and can give a quick beam pattern by rotating the antenna under test (AUT) in a plane of interest, i.e., ei ther azimuthal plane (the horizontal plane) for azimuth (horizontal) antenna gain pattern or vertical plane for elevation antenna gain pattern. It does not give the accurate gain value but can give you gain value at each position that is relative to each other. Fig ure 4 47. Rough radiation pattern measurement method diagram Fig ure 4 48. HP E8254A Signal Generator

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98 Fig ure 4 49. HP E4448A Spectrum Analyzer Fig ure 4 50. HyperLOG 60100 Yagi antenna Fig ure 4 51. Gain of the Yagi antenna As shown in Fi g ure 4 47 the AUT is connected to the signal generator and the standard gain antenna is connected to the spectrum analyzer. The Yagi antenna which is equivalent to standard gain antenna(SGA) in anechoic chamber shows a relatively constant gain of 5dB from 680MHz 10GHz as shown in Fig ure 4 51 thus, it is suitable as a SGA. Fig ure 4 52 shows the actual picture of the measurement set up.

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99 Fig ure 4 52. Rough radiation pattern measurement method picture The distance between the SGA and AUT needs to have a minimum far field distance and it can be calculated using the following Friis equation 4 1. ( 4 1 ) Pr : P ower received by the receiving antenna Pt : P ower input to the transmitting antenna Gt: G ain of the transmitting antenna Gr : Gain of the receiv i ng antenna R : D istance between antennas

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100 Also, when is smaller than the largest dimension of antenna (D), the following equation can be used. The calculated minimum distance is about 60 cm. ( 4 2) R : M inimum far field distance (in meters) D = L argest dimension of antenna (in meters) Fig u re 4 53. Rough radiation pattern measurement method: Antenna rotation As shown in Fig ure 4 53 the a ntenna is horizontally rotated for detecting relative change in gain value. At first, the antenna was rotated at a certain state, i.e., ON/OFF or OFF/ON. Ho wever, this method caused too much variation in gain value because the circuits have to rotate along with antenna and it is physically not easy to rotate the antenna at one spot. Thus, later, the antenna was fixed at a position and the switching was perfor med to see a difference in gain value between switching. It is much easier to see the difference in gain by this method.

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101 Fig ure 4 54. Rough radiation pattern sketch Fig ure 4 54 shows the rough radiation pattern diagram On the left, the values are the v alues of gain shown on the spectrum analyzer at the corresponding antenna position. T he short bar inside the rectangle denotes the ON state diode and the beam is steered away from the bar as expected. Fig ure 4 55. Antenna with circuit for rough radiation pattern measurement

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102 As shown in Fig ure 4 55 Multi meter is always needed to check the appropriate amount of current. The forward current value was kept at about 1 20 mA Varing the forward current amount using variable resistor did not affect much on rough radiation pattern as it didn't in s11 measurement. Also, as shown in the figure, alligator clips are used for easy switching and replacement of circuit. In addition, as shown in Fig ure 4 55, r everse voltage is applied to the OFF status diode to maximize i ts off status. According to Fig ure 4 44 9 V would reduce the OFF status diode's capacitance value from 0.5 pF to 0.2pF This can contribute to the OFF status. 4 9 Intermediate Fabrication and M easurement R esults: Alternate A pproaches While working on the configuration of diode connecting the stub and partial ground plane, alternative approach to beam steering were investigated concurrently because the diode showed a different s11 from simulation even if it showed a beam steering from rough radiation pattern. Fig ure 4 56. Beam steering using parasitic patch As described previously the horizontal beam steering was shown in simulation using the parasitic patch modification. The advantage of this approach is that unlike stub, the parasitic modification does not change s11. However, this frequency range is

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103 unchanged from the broadband directional microstrip antenna (4.3GHz ~7GHz) thus, the FR 4 loss is bigger than the beam steering using stub which lowers the frequency range. Thus, it is not preferred Other alternative method would be steering beam in just one direction by switching only one diode connected to only one side of stub because diode on each side can cause two not fully OFF status (or pseudo ON) and the difference in current between pseudo ON on one side and ON on the other side can be smaller than the difference in current between a complete OFF on one side and ON or pseudo ON on the other side. Also, increasing gap from 1 mm might be an option. Another alternative approach is using mechanical switches. As opposed to diode, mechanical switch can be opened up and can be modified to serve the purpose. One of the mechanical switches that were considered was m icroelectromechanical systems (MEMS). Fig ure 4 57 shows an example of switch using MEMS. H owever, after further consideration, MEMS approach was discarded bec ause first, it is for more small application (~ m) .S econd, it's used in application where a high speed switching is required. L ast, the cost will be increased. In other words, MEMS is too 'fancy' for this application. Other easily available small mechanical switches were t este d as shown in Figure 458. Fig ure 4 57. MEMS switching example

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104 Fig ure 4 58. Mechanical switch: Slide switch ( Radioshack 2750004 ) Fig ure 4 59. Mechanical switch : Tact switch (Radioshack 2750006) Neither of the switches worked very well. The slide switch works when only one side is used but when both sides are connected, results we re not good. The tact switch didn't work at all because it was ON even if it s not pressed. Handmade slide switch shown in Fig ure 4 60 worked quite well. Two metal pieces can slide towards the stub direction alternately. A motor can be used to provide this kind of motion. Another mechanical switch that was tested is relay. Commer cially available relays such as Radioshack 275232, 275005, 275240 were tested and 275 005 wa s

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105 chosen for its physical dimension. As shown in Fig ure 4 61 and Fig ure 4 62, the relay was opened and metal arm was attached to the moving parts of the relay. A s shown in Fig ure 4 63, the s11 shows very good agreement with HFSS simulation. Proximity of the metal piece of the off status relay doesnt affect the s11. Also, the rough radiation pattern showed good agreement with simulation. Fig ure 4 60. Antenna w ith handmade slide switch Fig ure 4 61. Relay ( Radioshack 275005) In particular, the c hange of peak value shown on spectrum analyzer closely matches the simulation at each of the frequencies i.e., relative gain difference between the beam directions. A lso, the magnetic field did not affect the antenna performance in either s11 or rough radiation pattern. However, the biggest disadvantage of using relay as a switch in antenna application is that relay requires too high voltage (9V) and

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106 Fig ure 4 62. A ntenna with relay in a platform Fig ure 4 63. S11 comparison of simulation and antenna/relay measurement current. Thus, it s not realistic in actual application. Another approach is using RF switch. Minicircuit CSWA2 63DR+ was tested. It is a single pol e, double throw ( SPDT ) type switch. It was chosen mainly because of its high isolation (36dB~50dB between2 ~6GHz) and its dimension (L= 4 mm X W= 4 mm X H= 1.25mm ). Fig ure 4 64 shows its schematics and the switch. Fig ure 4 65 shows the pad configuration. Fig ure 4 66 shows the isolation between RF1 pin and RF2pin.Fig ure 4 67 shows how the switch pins would fit between the stub and the partial ground plane.

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107 Fig ure 464. Schematics and switch Fig ure 4 65. Pad configuration

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108 Fig ure 4 66. Isolation betw een RF1 pin and RF2 pin Fig ure 4 67. Pin connection between the stub and the partial ground plane Fig ure 4 68 shows the initial wiring of the RF switch. However, it was determined patterning trace layer is an appropriate method. Also, from this point, e poxy was used instead of lead for soldering. Fig ure 4 69 shows the simulation of the antenna with one of the stub connected in RF switch configuration. In particular, it shows the surface current density. Fig ure 4 70 shows it s s11 and Fig ure 4 71 shows its radiation pattern sampled at 4.5GHz with gain value of 5.5dB. Fig ure 4 72 shows the antenna with pattern for RF switch and the antenna with RF switch installed.

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109 Fig ure 4 68. Wiring of RF switch Fig ure 4 69. A ntenna with one of the stub connected in RF switch configuration

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110 Fig ure 4 70. S11 of antenna shown in Fig ure 4 69 Fig ure 471. Radiation pattern of antenna shown in Fig ure 4 69

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111 Fig ure 4 72. Antenna with pattern for RF switch and the antenna with RF switch Fig ure 4 73 shows the microscop ic view of the RF switch on the antenna. In the picture, 47pF capacitor is shown as it was required i n the schematic shown in Fig ure 4 64. Fig ure 4 73. Microscopic view of the RF switch on the antenna The s11 and rough radiation pattern of the antenna w ith RF switch were measured repeatedly. However, the measurement of the s11 and rough radiation pattern showed quite different result from the simulation. Thus, it was determined that the RF switch is

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112 not suitable for this application. However, from the RF switch approach, useful techniques were acquired. First, trace layer pattern is used instead of wires to connect the device to antenna and to circuit. S econd, epoxy soldering is used rather than the lead soldering. Last, surface mount type RF diode is sought after, instead of using nonsurface mount type RF diode. Surface mount type RF diode was searched and it was determined that BAP64 02 i s suitable for this application because of its small capacitance and series resistance value(C=0.5pF and Rd=1.4 1.25mm X 0.85mm) Fig ure 4 74 shows the data of the BAP64 02. Fig ure 4 74. Forward resistance as a function of forward current and d iode capacitance as a function of reverse voltage When the surface mount type RF diode is used with patterned trace layer along with the applied reverse voltage to the OFF status diode, measurement data that resembles the simulation data are obtained. The detail is shown in 5 .4. Thus, it turned out the previous wire s affect ed s11 substantially.

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113 4 10 Summary Effects of modifying the broadband directional microstrip antenna on the antenna characteristics such as reflection coefficient, radiation pattern, gain, or beam steering capability are investigated. The modification can include varying the width and/or length of the partial ground plane, adding stub(s) on the partial ground plane, varying the width, length, and/or location of the added stub, or varying the number, shape, gap, or location of the directors. It is important to evaluate the effects of the modification on the antenna characteristics, since these effects may be exploited to improve the antenna performance. Also, whenever the antenna modification is performed to improve one particular antenna parameter, it is required to check if that modification affects other antenna characteristics negatively. Stub shape can affect s11 substantially and most of time negatively affect s the broadband characteristics. Beam pattern does not change substantially even though the stub shap e is changed substantially. Most of the OFF/ON combination of the both stubs show beam steering, that is, the beam is steered away from the ON status stub. Even the ON stub connection is reduced, the current flowing through that connection is still stronger than the current flowing to OFF status stub through coupling. W hen the stub is modified greatly, the beam steering pattern can be inconsistent. In addition to horizontal beam steering using stubs, parasitic patches can be also used to steer beam horizont ally. The advantage of the beam steering using the parasitic patch, instead of stub is that the parasitic patch does not affect the s11 significantly as stubs do. The disadvantage of beam steering using parasitic patch is that the beam steering is relativ ely weaker than the beam steering using stubs and the switching might be difficult to implement.

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114 In addition to the simulation, different approaches were made for switching the antenna in fabrication and measurement Non RF diode, nonsurface mount type RF diode were tested on the fabricated antenna. Rough radiation pattern measurement was performed for a quick radiation pattern measurement after each s11 measurement before actual radiation pattern measurement in anechoic chamber. Mechanical switches such a s relay w ere tested and the result was satisfactory but it is not suitable for this application. RF switch was tested but it didn't y ie ld satisfactory result s. Finally, w hen the surface mount type RF diode is used with patterned trace layer along with the applied reverse voltage to the OFF status diode, measurement data that resembles the simulation data are obtained.

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115 CHAPTER 5 A BEAM STEERING BROADBAND SINGLE MICROST RIP ANTENNA USING DI ODES 5 .1 Horizontal Beam S teering Fig ure 5 1 ( A ) shows the proposed antenna. By switching the two diodes, electronic beam steering can be realized horizontally. Fig ure 51 ( B ) shows a state where one of the stubs is electronically connected to the partial ground plane. Fig ure 5 2 and Fig ure 5 3 show simulation results of th e Fig ure 5 1 (B). A B Figure 5 1. A layout of the electronic beam steering broadband single microstrip antenna ( A ) proposed antenna ( B ) simulating one of the diodes of the proposed antenna being turned on As shown in Fig ure 5 2, this antenna operates from 3.08 GHz to 5.44 GHz. The broadband directional microstrip antenna showed broadband characteristics from 4.3 GHz (Fig ure 3 3). The additional stubs have lowered the operating frequency about 1.2 GHz from the original layout, which can be beneficial for vital sign detection. Lower operating frequency can be beneficial for at least the following reasons. First, a larger penetration depth is possible and one good application will be a seethru

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116 Figure 5 2. Reflection coefficient of the antenn a shown in Fig ure 5 1( B ) wall radar application. Second, better vital sign detection is possible when the subject has large physiological movement Last at lower frequency, FR 4 loss tangent is smaller. Also, as shown in Fig ure 5 3, the intended beam steering is shown over the operating band (sampled at 3.5, 4, 4.5, and 5 GHz). The radiation patterns are horizontal radiation patterns on XY plane to show that the added stub can steer the beam horizontally. It can be seen that the tilted angles are almost 30 degree from the XZ plane and are consistent in all of the frequencies. By the combination of turning the diodes on and off as shown in Fig ure 5 1, the beam can be steered horizontally 30 degree in both +Y and Y direction. Broadband beam steering is desir ed because of its use for radar application and tracking moving objects. In addition to the hallway application shown in Fig ure 3 10, a possible application will be searchand rescue for victims, border patrols, entrance

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117 A B C D Figure 5 3. Radiation patterns of the antenna shown in Fig ure 5 1( B ); (A ) At 3.5 GHz, 3.75dB ( B ) A t 4 GHz, 4.96dB ( C ) At 4.5 GHz, 5.54dB ( D ) At 5 GHz, 5dB security, and so on. In this chapter, t his design and simulation are validation by fabricating the antenna layout of Fig ure 5 1 measuring its reflection coefficient and radiation patterns. 5 .2 Vert ical Beam S teering In addition to the horizontal electronic beam steering, vertical mechanical beam steering is possible once the substrate including the parasitic patch part is separated form the main patch. However, this requires a mechanical movement of the parasitic

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118 patch parts, thus, it is not preferred method. In this section, a vertical electronic beam steering is simulated. This vertical beam steering can be useful as well as the horizontal beam steering because of its use for radar application. Fi g ure 5 4 shows the layout of the antenna for vertical beam steering. It shows still the same number of directors or two parasitic patches but the size of one of the parasitic patches, which is adjacent to the main patch is reduced to create a vertical beam steering effect. Fig ure 5 5 shows a layout of the antenna shown in Fig ure 5 4 with a diode connecting the two parasitic patches. The distance for the diode to connect is 4mm. By turning on and off the diode, the coupling between the patches can change, wh ich in turn, cause the surface current on the parasitic patches to change, which leads to change of vertical beam pattern. Fig ure 5 6 shows a layout of the antenna where the diode of the Fig ure 5 5 is turned on. Figure 5 4. A layout of the vertical elec tronic beam steering broadband single microstrip antenna

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119 Figure 5 5. A layout of the vertical electronic beam steering broadband single microstrip antenna with a diode Figure 5 6. A layout for simulating the vertical electronic beam steering broadban d single microstrip antenna with a turned on diode Fig ure 5 7 shows the comparison of the surface currents between the antennas depending on the on/off states of the diode. S hown at the bottom of the Fig ure 5 7 are radiation patterns corresponding to each of the top layout. This time, the radiation patterns on XZ plane or vertical radiation patterns are shown to show the vertical beam

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120 steering. The simulation shows that the beam is tilted vertically when there is surface current on the parasitic patch that is located further away from the main patch (Fig ure 5 7 A ). When there is no or weak surface current on the parasitic patch that is located further away from the main patch, beam stays in the broadside direction (Fig ure 5 7 B ). Although its not shown her e, when surface current animation function is used to see different phases of the surface currents on the parasitic patches, Fig ure 5 7 ( B ) shows weak currents on the parasitic patch. However the currents are very weak compared to the currents on patches o f Fig ure 5 7 ( A ) and its influence on beam pattern is negligible. The radiation patterns show the tilted beam has a gain that is 1 dB higher than the nontilted beam. The tilted angle is about 25 degree. A B Figure 5 7. A comparison of the surface currents and radiation patterns of the antennas of (A) Fig ure 5 4 (At 5 GHz, 5 dB) and (B) Fig ure 5 6 (At 5 GHz, 4 dB)

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121 A B Figure 5 7 Continued A B Figure 5 8. Reflection coefficients of the layouts of ( A ) Fig ure 5 4 and ( B ) Fig ur e 5 6

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122 In addition to the beam patterns, reflection coefficients are shown in Fig ure 5 8. The reflection coefficients show that the modification of the directors also reduces the lower end of the bandwidth to 3.7GHz from the original 4.3 GHz. as it happened in the modification of the partial back plane for horizontal beam steering. The radiation patterns showed the tilted beam has a 1 dB stronger gain than the nontilted beam because the vertical steering is based on weakening the coupling between main patch and parasitic patches. Thus, when the beam is not tilted, the gain of the beam will not be as strong as the gain of the tilted beam. As opposed to the vertical beam steering, it should be noted that in the horizontal beam steering, same value of gain was exhibited due to its symmetry. 5 3 Fabricated Proposed Antenna After performing simulations in Ansoft HFSS, the proposed antenna shown in the Fig ure 5 1 ( A ) was fabricated. The FR4 lamination with a dielectric constant of 4.4 was used as the substrate. Si mple pattern application via photolithography and subsequent copper etching with ferric chloride were performed. Fig ure 5 9 shows the fabricated proposed antenna. Please note that the dimensions of the broadband antenna are same as the broadband directio nal microstrip antenna except the additional stubs on the partial ground plane [Park]. The stub is located 7.5 mm from the center and is adjacent to the side of the top driven element. The dimension of the stub is 2.5mm X 10mm for ON state and 2.5mm X 9 mm for OFF state or 1 mm gap between the stub and partial ground plane. The diode is BAP64 02 surface mount RF PIN diode. A DC bias voltage is applied to control ON and OFF status of the diode. The PIN diode exhibits a resistance of 1.4 and capacitance of 0.5 pF with the applied forward bias. For the ON status diode, a 3V DC was applied with a variable resistor (0~25 ). The

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123 current to the diode was kept at 110mA. For the OFF status diode, 1.5V DC reverse bias was applied. In addition to the proposed antenna, a reference antenna having the identical layout of the simulation was fabricated for comparison. Fig ure 5 10 shows the picture of the reference antenna. 5 .4 Input Reflection Coefficient (S11) The input reflection coefficients of the reference antenna and the proposed antenna were simulated using HFSS and measured using an Agilent E8361A 10 MHz to A B Figure 5 9. Proposed antenna; ( A ) bottom layer; ( B ) top layer 67 GHz PNA series network analyzer as shown in Fig ure 5 11. When the pair of d iodes are either ON and OFF or OFF and ON, the antenna operates from 2.8 ~ 4.8 GHz, where beam steering occurs by the peak gain appearing in the opposite direction of the ON state diode (Fig ure 5 14). When both diodes are OFF, the antenna operates from 3.7 ~4.4 GHz and no beam steering occurs. Simulated S11 shows good agreement with the measured s11 of the proposed antenna.

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124 A B Figure 5 10. Reference antenna; ( A ) bottom layer; ( B ) top layer Compared to the previous antenna without stub [Park ], the broadband frequency range has been lowered from 4.3~7GHz to 2.8 4.8 GHz by the added stubs. Lower operating frequency can be beneficial for the reasons stated previously. 5 .5 Far Field Radiation Patterns The radiation patterns were measured in an a nechoic chamber at the Antenna, RF and Microwave Integrated (ARMI) Systems Laboratory at University of Central Florida. For this broadband antenna, it would be ideal to measure the radiation patterns at frequencies with small interval between them, but ins tead, the radiation patterns were measured at 3, 3.5, 4, 4.5 GHz due to practical reasons. At each of the frequencies, E plane that is horizontal to the substrate was measured and copolarization and cross polarization of the E planes were measured. Fig ure 5 12 shows inside of the anechoic chamber.

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125 Figure 5 11. Reflection coefficient; Dashed: measured proposed antenna (ON OFF or OFFON); Solid: measured proposed antenna (OFF OFF); o: simulated proposed antenna (ON OFF or OFFON); + : simulated proposed ant enna (OFF OFF) The Standard Gain Antenna is shown. Fig ure 5 13 shows how the antenna under test (AUT) was mounted for radiation pattern measurement. In the figure, the reference antenna is shown. Fig ure 5 14 shows the radiation patterns. The radiation patt erns for both ON OFF and OFF ON are simulated and measured at 3, 3.5, 4, and 4.5 GHz. The simulated radiation patterns and the measured radiation patterns of reference antenna show good agreement with each other overall However, there are discrepancies between the simulated and measured radiation patterns of proposed antenna which includes nulls in

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126 the measured patterns. It might be contributed by the parasitic capacitance of the diode when it is switched off. This additional parasitic capacitance of about 0.25pF is not considered in HFSS simulation and might cause the change in radiation patterns. In addition, the DC bias wires of the circuit that are connected to the antenna can affect the radiation pattern. Still t he measured radiation patterns of the pr oposed antenna with PIN diodes show clear beam steering patterns, i.e., at each measured frequency, the peak gain appears on the opposite side of the ON state diode as expected from the simulation. The diode performance is critical in beam steering because the imperfect isolation between the ON and OFF modes of the diode can damage the beam steering. The differences in measured peak gains in dB between the reference antenna and the proposed antenna are 0.4, 0.9, 1, and 1.1 (Reference Proposed) at 3, 3.5, 4, and 4.5GHz respectively. Average values of the two peak gains of ON OFF and OFFON configurations are used. The proposed antenna shows less gain than the reference antenna except at 3 GHz. The lower gain is due to loss introduced by the diodes. Also, t he loss due to diode increases slightly as the frequency increases. In addition, compared to the broadband directional microstrip antenna [Park], an increase in gain is observed from the beam steering. Due to the different s11 ranges between the broadband directional microstrip antenna and the proposed antenna, gain only at 4.5GHz can be compared and the beam steering increased the peak gain from 4.5dB to 5.63 dB. Table 5 1 compares the beam steering patterns shown in Fig ure 5 14 q uantitatively. First, peak gain difference between the two regions is observed in an expected manner (i.e., higher peak gain is in 90 180 region at ON OFF mode and in

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127 Table 5 1 Beam Steering Comparison of ON OFF v s. OFF ON at each frequency Freq (GHz) / Mode Peak gain of 90 180 region v s. 180 270 region (Location, HPBW) Average gain of 90 180 region v s. 180 270 region 3 / ON OFF 3.38dB(at 100 70 ) v s. 0.47dB(at 184 26 ) 1.5dB vs. 7.66dB 3 / OFFON 0.37dB(at 148 30 ) v s. 4 28 dB(at 238 30 ) 4.75dB v s. 0. 49dB 3.5 / ON OFF 4.65dB(at 92 50 ) vs. 1.56dB(at 204 32 ) 1.47dB vs. 10dB 3.5 / OFFON 1.11dB(at 172 40 ) vs. 4.48dB(at 256 56 ) 8.9dB vs. 0.93dB 4 / ON OFF 5.69dB(at 112 44 ) vs. 3.31dB(at 192, 22 ) 0.09dB vs. 2.81dB 4 / OFFON 4dB(at 1 60 16 ) vs. 5.25dB(at 226 20 ) 9.29dB vs. 0.81dB 4.5 / ON OFF 5.63dB(at 162 60 ) vs. 4.18dB(at 208 20 ) 3.05dB vs. 3.87dB 4.5 / OFFON 3.18dB(at 142 50 ) vs. 5.99 dB(at 238 40 ) 0.34dB vs. 0.62dB 180 270 region at OFF ON mode) at all of the measured frequencies. Second, peak gain location is not as symmetrical as the simulation but remains within the expected region. Third, HPBW of the steered beams with higher peak gains tends to be larger than the beams with lower peak gains as shown in t he simulation. Last, the

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128 average gains of the two regions are compared. Average gain was calculated by averaging all 45 points in each region. The region where the beam with higher peak gain is located shows higher average gain than the other region, as ex pected. Thus, more energy is directed towards the region where the beam with higher peak gain is located for each status. 5 .6 L imitation of the P roposed A ntenna Although the beam steering is clearly shown as in Fig ure 5 14 and Table 5 1, there are some limitations with the proposed antenna. First, a simple beam steering or binary beam steering is possible with the current design. Second, there are nulls in the measured radiation pattern and discrepancies with the simulated radiation pattern. The nulls an d the discrepancy are considered to be from wires that are connected to the antenna and poor diode performance, i.e., the OFF status of the diode is not completely OFF. Last, thus the antenna beam steering performance is dependent on the diode performance. These limitations need to be further investigated in both simulation and measurement. 5 7 Summary A beam steering, broadband, single patch antenna is simulated, fabricated and measured. The proposed antenna requires no array for beam steering but requir es only two additional diodes. This antenna operates from 2.8 4.8 GHz and shows electronic beam steering over that broadband range (sampled at 3, 3.5, 4, and 4.5 GHz) In addition to the horizontal beam steering, vertical beam steering is simulated. The wi de frequency tuning range allows the radar system to be tuned for an optimum transmission frequency.

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129 Figure 5 12. Inside of an anechoic chamber for the radiation pattern measurement shows standard g ain a ntenna Figure 5 13. One of the ways of how the AUT was mounted.

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130 A B Figure 5 14. Comparison of measured radiation patterns of the proposed antenna, and reference antenna, and simulated radiation patterns of the proposed antenna (Solid black: measured proposed; Dashed blue: measured re ference; ++ red: simulated reference) along Theta = 90 degree plane (X Y plane). Radiation patterns at frequencies of (A) 3 GHz, (B) 3.5 GHz (C) 4 GHz, and (D) 4.5GHz are plotted. Left column is when the pair of diodes is in OFF ON state. Right column is w hen the pair of diodes is in ON OFF state. Antenna configuration with XYZ axes is shown in (E).

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131 C D Figure 5 14. Continued

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132 E Figure 5 14. Continued

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133 CHAPTER 6 SUMMARY The non contact vital sign radar detection system necessitated the d evelopment of the broadband, high gain antenna. The proposed design approach combines the advantage of the wideband antenna, the advantage of the parasitic patch for high gain, and the advantage of beam steering antennas within a single microstrip patch an tenna. The proposed antenna requires no array for beam steering but requires only two additional diodes. The broadband directional microstrip antenna was simulated, fabricated and measured. The partial ground plane improves broadband characteristics and th e parasitic patches improve the gain. As a result, a 4.3 7 GHz broadband antenna with improved gain was designed and fabricated. Compared to a partial groundplane, single patch, reference antenna, this broadband directional microstrip antenna shows desired directivity and improved gain performance. Its radiation pattern was designed for a vital sign radar detector mounted on the ceiling at corner locations. The radiation pattern also provides a better isolation between the transmitting and receiving antenn as for this application. The design approach ensures that broadband performance can be achieved while improving the gain of the antenna. In addition, effects of modifying the broadband directional microstrip antenna on the antenna characteristics such as r eflection coefficient, radiation pattern, gain, or beam steering capability are investigated. The modification can include varying the width and/or length of the partial ground plane, adding stub(s) on the partial ground plane, varying the width, length, a nd/or location of the added stub, or varying the number, shape, gap, or location of the directors. It is important to evaluate the effects of

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134 the modification on the antenna characteristics, since these effects may be exploited to improve the antenna performance. Stub shape can affect s11 substantially, most of time it negatively affect s the broadband characteristics. Beam pattern does not change substantially even though the stub shape is changed substantially. Most of the OFF/ON combination of the both s tubs show beam steering, that is, the beam is away from the ON status stub. Even the ON stub connection is reduced, the current flowing through that connection is still stronger than the current flowing to OFF status stub through coupling. When the stub is modified greatly, the beam steering pattern can be inconsistent. In addition to horizontal beam steering using stubs, parasitic patches can be also used to steer beam horizontally. The advantage of the beam steering using the parasitic patch, instead of s tub is that the parasitic patch does not affect the s11 significantly as stubs do. The disadvantage of beam steering using parasitic patch is that the beam steering is relatively weaker than the beam steering using stubs and the switching might be difficult to implement. Different approaches were made for switching the antenna. NonRF diode, nonsurface mount type RF diode were tested on the fabricated antenna. Rough radiation pattern measurement was performed for a quick radiation pattern measurement after each s11 measurement before actual radiation pattern measurement in anechoic chamber. Mechanical switches such as relay were tested and the result was satisfactory but it is not suitable for this application. RF switch was tested but it didn't yield sati sfactory results. Finally, when the surface mount type RF diode is used with patterned trace layer along with the applied reverse voltage to the OFF status diode, measurement data that resembles the simulation data are obtained.

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135 Finally, a beam steering ov er broadband range is achieved with a single microstrip antenna. Specifically, a 2.8 4.8 GHz beam steering broadband microstrip antenna was designed, fabricated, and measured. Compared to the broadband directional microstrip antenna without stubs, the prop osed broadband antenna shows lower broadband operating frequency, beam steering, and improved gain through the beam steering. The proposed antenna can steer beam in broadband range (sampled at 3, 3.5, 4, and 4.5 GHz) by switching PIN diodes that connect st ubs and a partial ground plane. Its broadband beam steering is suitable for a vital sign radar application and applications where simple beam steering patterns are desired. The wide frequency tuning range allows the radar system to be tuned for an optimum transmission frequency. This antenna can be implemented in a radar sensor, which can be used for noncontact vital sign detection for security or healthcare applications.

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136 LIST OF REFERENCES [Li1 ] C. Li, Doppler Phase Modulation Effect For NonContact Acc urate Measurement Of Vital Signs And Other Periodic Movements, Oral Proposal, 2008 [Balanis ] C.A. Balanis, Antenna Theory: Analysis and Design, John Wiley & Sons, Inc., 1997, 2nd Edition, pp. 811812 [Choi1 ] S. H. Choi, J. K. Park, S. K. Kim, and J. Y. Park, A new ultra wideband antenna for UWB applications, Microwave and Optical Technology Letters, vol. 40, issue 5, pp. 399401, Mar. 2004 [Choi2 ] J. Choi, K. Chung, and Y. Roh, Parametric analysis of a bandrejection antenna for UWB application, Microwave and Optical Technology Letters, vol. 47, issue 3, pp. 287290, Nov. 2005 [Curto ] S. Curto, M John, and M. Ammann, Groundplane Dependent Performance of Printed Antenna for MB OFDM UWB, Vehicular Technology Conference, pp. 352356, April 2007 [Pozar1] Pozar, D.M, Beam Transmission Of Ultra Short Waves: An Introduction To The Classic Paper By H. Yagi, Proceedings of the IEEE, Volume 85, Issue 11, pp. 18571863, Nov. 1997 [Huang1] J. Huang, Planar microstrip Yagi array antenna, 1989 IEEE Ant ennas and Propagation Society International Symposium Digest, vol. 2, pp. 894897, June 1989 [Huang2] J. Huang and A.C. Densmore, Microstrip Yagi array antenna for mobile satellite vehicle application, IEEE Transactions on Antennas and Propagation, vol. 39, issue 7, pp. 1024 1030, July 1991 [Kumar ] G. Kumar, and K. C. Gupta, Nonradiating edges and four edges gapcoupled multiple resonator broadband microstrip antennas, IEEE Transactions on Antennas and Propagation, vol. 33, issue 2, pp. 173 178, Feb. 1985 [Li2 ] C. Li and J. Lin, "Complex Signal Demodulation and Random Body Movement Cancellation Techniques for Noncontact Vital Sign Detection," IEEE MTT S International Microwave Symposium Digest, pp. 567570, Atlanta, June 2008 [Fusco ] Fusco, V.F, Mechanical beam scanning reflectarray, IEEE Transactions on Antennas and Propagation, vol. 53, issue 11, pp. 3842 3844, Nov. 2005 [Andersson] Andersson, M, Goransson, B, Skarin, I, From, K., Cheng, S, Ojefors, E,Hallbjorner, P, Manholm, L,Rydberg, A, Antennas with Fast Beam Steering for High Spectral Efficiency in Broadband Cellular Systems, The 9th European Conference on Wireless Technology, pp. 1215, Sep. 2006

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137 [Rodenbeck ] M. Li, Rodenbeck, C.T, Kai Chang, Millimeter wave dual beam scanning micros trip patch antenna arrays fed by dielectric image lines, IEEE Antennas and Propagation Society International Symposium, vol. 2, pp. 196 199, June 2002 [Preston ] Preston, S.L, Thiel, D.V, Lu, J.W, O'Keefe, S.G, Bird, T.S, Electronic beam steering using switched parasitic patch elements, Electronics Letters, vol. 33, issue 1, pp. 78, Jan. 1997 [Yusuf1 ] Yusuf, Y, Xun Gong, A Low Cost Patch Antenna Phased Array With Analog Beam Steering Using Mutual Coupling and Reactive Loading, Antennas and Wireles s Propagation Letters, IEEE, vol. 7, pp. 81 84, 2008 [Yusuf2 ] Yusuf, Y, Xun Gong, Beam steerable patch antenna array using parasitic coupling and reactive loading, Antennas and Propagation International Symposium, IEEE, pp. 46934696, June 2007 [Shyn u ] Shynu S. V, Gijo Augustin, C. K. Aanandan, P. Mohanan, K. Vasudevan, A reconfigurable dual frequency slot loaded microstrip antenna controlled by pin diodes, Microwave and Optical Technology Letters, vol. 44, issue 4, pp. 374376, Feb. 2005 [Byun] S B. Byun, J. A. Lee, J. H. Lim, T. Y. Yun, Reconfigurable GroundSlotted Patch Antenna Using PIN Diode Switching, ETRI Journal, vol. 29, no. 6, pp. 832834, Dec. 2007 [Lee ] J. A. Lee, S. B. Byun, J. H. Lim, T. Y. Yun, Reconfigurable antenna for wideband code division multiple access and Korean satellite digital multimedia broadcasting controlled by pindiodes, Microwave and Optical Technology Letters, vol. 49, issue 6, pp. 13341337, June 2007 [Nikolaou ] Symeon Nikolaou, Bairavasubramanian, R, Lugo, C., Jr, Carrasquillo, I, Thompson, D.C, Ponchak, G.E, Papapolymerou, J, Tentzeris, M.M, Pattern and frequency reconfigurable annular slot antenna using PIN diodes, IEEE Transactions on Antennas and Propagation, vol. 54, issue 2, Part 1, pp. 439448, Feb. 2006 [Mookiah] Mookiah, P, Piazza, D, Dandekar, K.R, Reconfigurable spiral antenna array for pattern diversity in wideband MIMO communication systems, Antennas and Propagation Society International Symposium, AP S 2008. IEEE, pp. 14, July 2008 [Cave rly ] Caverly, R.H, Hoorfar, A, Reconfigurable Hilbert antennas using high speed pin codes, Radio and Wireless Symposium, 2009. pp. 151 154, Jan. 2009

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138 [Derneryd] Derneryd, A, A theoretical investigation of the rectangular microstrip antenna element, IEEE Transactions on Antennas and Propagation, vol. 26, issue 4, pp. 532 535, July 1978 [Pozar2] Pozar, D, Input impedance and mutual coupling of rectangular micr ostrip antennas, IEEE Transactions on Antennas and Propagation, vol. 30, issue 6, pp. 1191 1196, Nov. 1982 [Covert ] Covert, L.; Lin, J, Simulation and measurement of a heatsink antenna: a dual function structure, IEEE Transactions on Antennas and Pr opagation, vol. 54, issue 4, pp. 1342 1349, Apr. 2006 [Park] Zivin Park, Changzhi Li, Jenshan Lin, A Broadband Microstrip Antenna with Improved Gain for NonContact Vital Sign Radar Detection, IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS Volume 8, pp. 939 942, 2009

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139 BIOGRAPHICAL SKETCH Zivin Park received his B.S. degree in e lectrical e ngineering from Seoul National University, Seoul, South Korea, in 1998. After graduation, he worked as a senior software engineer at Trigemm Infocomm in Seoul unt il 2001, developing voice response system for major telecommunication companies, b anks, g overnm ent in South Korea using Unix C Programming. He received his M.S. degree in e lectrical and computer e ngineering from University of Florida, Gainesville, FL, in 2003. His research topic was Fabrication and Characterization of Transparent ZnO Thin Film Transistor. He also researched on Deep Level Transient Spectroscopy (DLTS) on CIGS Solar Cell. He passed U.S. Patent Bar Exam in Dec. 2006 (Reg. N o. 62851) and worked as a registered U.S. patent agent for a Intellectual Property law firm from 2006 to 2009, handling patent prosecutions in Electronics area. He received his Ph.D. degree in e lectrical and computer e ngineering from University of Florida, Gainesville, FL, in 201 1 His doctorate research topic was designing patch antenna for noncontact Vital Sign Radar Detection, especially a Beam Steering Broadband Microstrip Antenna. His ZnO TFT research is published on Applied Physics Letter as a second author and his ante nna research is published on IEEE Antennas and Wireless Propagation Letters as a first author twice.