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Wearable RFID Reader and Compact Fractal Patch Antenna Design

Permanent Link: http://ufdc.ufl.edu/UFE0041761/00001

Material Information

Title: Wearable RFID Reader and Compact Fractal Patch Antenna Design
Physical Description: 1 online resource (72 p.)
Language: english
Creator: Altunbas, Ahmet
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: antenna, fractal, patch, rfid, wearable
Agricultural and Biological Engineering -- Dissertations, Academic -- UF
Genre: Agricultural and Biological Engineering thesis, M.E.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The purpose of this thesis was to develop a compact antenna for Wearable RFID (Radio Frequency Identification) Reader applications with a proof of concept prototype. The intended antenna should provide similar properties, compared to a patch antenna resonating at UHF frequency, with a smaller size. The antenna should be integrated into a prototype Wearable RFID Reader and should be able to read RFID tags attached to a box during package handling process. The process of designing a compact antenna was started with analyzing microstrip patch antennas. A probe feed square patch antenna was designed and tested based on transmission line model. A low cost patch antenna prototype was manufactured using simulation parameters and tested with a Network Analyzer. Software for fractal patch calculations was written and used for generating four iterations of the initiator. Iteration factor values of 0.20 and 0.25 were chosen to be simulated and two substrates, FR4 and AD1000 with 4.6 and 10.2 dielectric constant values, were used. Probe feed simulation results were validated with the measured results of the prototype antenna. Although the probe feed patch antenna provided good performance for most of the RFID applications, it had no use case for Wearable RFID Reader application due to size limitations. It is shown that the fractal patch antenna resonant frequency decreases with an increase on the iteration factor and number. It is also observed that iteration factor has more effect on resonant frequency than iteration number. Antenna size miniaturization was achieved with a maximum value of 58.94% for 4th iteration fractal and 0.25 iteration factor. A prototype Wearable RFID Reader constructed using a fractal patch antenna with an iteration factor of 0.20 and iteration number of 1 was also presented in this thesis work. It is concluded that antenna miniaturization can be achieved by using fractal patch antennas which can be integrated into Wearable RFID Readers.
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 Ahmet Altunbas.
Thesis: Thesis (M.E.)--University of Florida, 2010.
Local: Adviser: Emond, Jean-Pierre.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041761:00001

Permanent Link: http://ufdc.ufl.edu/UFE0041761/00001

Material Information

Title: Wearable RFID Reader and Compact Fractal Patch Antenna Design
Physical Description: 1 online resource (72 p.)
Language: english
Creator: Altunbas, Ahmet
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: antenna, fractal, patch, rfid, wearable
Agricultural and Biological Engineering -- Dissertations, Academic -- UF
Genre: Agricultural and Biological Engineering thesis, M.E.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The purpose of this thesis was to develop a compact antenna for Wearable RFID (Radio Frequency Identification) Reader applications with a proof of concept prototype. The intended antenna should provide similar properties, compared to a patch antenna resonating at UHF frequency, with a smaller size. The antenna should be integrated into a prototype Wearable RFID Reader and should be able to read RFID tags attached to a box during package handling process. The process of designing a compact antenna was started with analyzing microstrip patch antennas. A probe feed square patch antenna was designed and tested based on transmission line model. A low cost patch antenna prototype was manufactured using simulation parameters and tested with a Network Analyzer. Software for fractal patch calculations was written and used for generating four iterations of the initiator. Iteration factor values of 0.20 and 0.25 were chosen to be simulated and two substrates, FR4 and AD1000 with 4.6 and 10.2 dielectric constant values, were used. Probe feed simulation results were validated with the measured results of the prototype antenna. Although the probe feed patch antenna provided good performance for most of the RFID applications, it had no use case for Wearable RFID Reader application due to size limitations. It is shown that the fractal patch antenna resonant frequency decreases with an increase on the iteration factor and number. It is also observed that iteration factor has more effect on resonant frequency than iteration number. Antenna size miniaturization was achieved with a maximum value of 58.94% for 4th iteration fractal and 0.25 iteration factor. A prototype Wearable RFID Reader constructed using a fractal patch antenna with an iteration factor of 0.20 and iteration number of 1 was also presented in this thesis work. It is concluded that antenna miniaturization can be achieved by using fractal patch antennas which can be integrated into Wearable RFID Readers.
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 Ahmet Altunbas.
Thesis: Thesis (M.E.)--University of Florida, 2010.
Local: Adviser: Emond, Jean-Pierre.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041761:00001


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1 WEARABLE RFID READER AND COMPACT FRACTAL PATCH ANTENNA DESIGN By AHMET ERDEM ALTUNBAS A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING UNIVERSITY OF FLORIDA 2010

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2 2010 Ahmet Erdem Altunbas

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3 To my mom, dad, sister, b rother, g randparents and f riends

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4 ACKNOWLEDGMENTS First and foremost I offer my sincerest gratitude to my supervisor, Dr JeanPierre Emond, who has not only guided me throughout my studies but also has supported me with his knowledge and vision. I would like to thank my external committee member, Dr. Gisele Bennett for guiding and helping me with the testing of my antennas at their facilities in Georgia Tech. I would also like to thank Dr. Daniel W. Engels for his help as well as all my other committee members for their support I would like to thank Jeff Wells, Steve Dean and all Franwell family for their support on this thesis work and for sponsoring me. I would like to thank my lifelong friends both in Turkey and Gainesville for sharing their moments with me. Finally, I would like to thank all my family who mean more than everything to me.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 7 LIST OF FIGURES .......................................................................................................... 8 ABSTRACT ................................................................................................................... 10 CHAPTER 1 INTRODUCTION .................................................................................................... 12 Problem Description ............................................................................................... 12 Organization of Thesis ............................................................................................ 13 2 LITERATURE REVIEW .......................................................................................... 14 History of RFID ....................................................................................................... 14 RFID Technology Overview .................................................................................... 15 RFID Frequencies ................................................................................................... 16 Microstrip Patch Antennas ...................................................................................... 17 Fractal Antennas ..................................................................................................... 18 3 MATERIALS AND METHODS ................................................................................ 20 Analysis of Patch Antenna Design .......................................................................... 20 UHF RFID Patch Antenna Design .......................................................................... 22 Simulation ......................................................................................................... 27 Prototype Manufacturing of Designed Patch Antenna ...................................... 27 Fractal Patch Antenna Design for Wearable RFID Readers ................................... 28 Wearable RFID Reader Prototype .......................................................................... 29 4 RESULTS ............................................................................................................... 37 Square Patch Antenna Simulation and Measurement Results ............................... 37 Simulation: ........................................................................................................ 37 Measurement: .................................................................................................. 40 Fractal Patch Antenna Simulation Results .............................................................. 41 Fractal Patch Antenna for Wearable RFID Reader Prototype ................................. 47 Simulation: ........................................................................................................ 47 Measurement: .................................................................................................. 49

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6 5 DISCUSSION ......................................................................................................... 50 Square Patch Antenna ............................................................................................ 50 Simulation ......................................................................................................... 50 Measurements and Comparison with Simulation ............................................. 51 Fractal Patch Antenna ............................................................................................ 52 Effect of Iteration Factor and Iteration Number on Resonant Frequency ......... 52 Antenna Si ze Miniaturization with Fractals ....................................................... 53 Fractal Patch Antenna for Wearable RFID Reader Prototype .......................... 53 6 CONCLUSION ........................................................................................................ 54 APPENDIX A Fractal G eometry Calculator Code ......................................................................... 55 B Wearable RFID reader Prototype Schematic .......................................................... 63 C Wearable RFID reader Prototype Printed Circuit Board .......................................... 64 D Wearable RFID Reader Bill of Materials ................................................................. 65 E Return Loss and Radiation Simulations for Fractals ............................................... 69 LIST OF REFERENCES ............................................................................................... 70 BIOGRAPHICAL SKETCH ............................................................................................ 72

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7 LIST OF TABLES Table page 3 1 Bill of materials for UHF RFID Reader Antenna ................................................. 28 3 2 Patch Antenna Design Parameters .................................................................... 29 3 3 Calculated parameters according to transmission line model ............................. 29 3 4 0th iteration square patch antenna dimensions ................................................... 29 4 1 Square Patch Antenna Design Parameters ........................................................ 37 4 2 Square Patch Antenna Simulation Results ......................................................... 37 4 3 Comparison between Simulated and Measured results ..................................... 40 4 4 Fractal Patch Antenna Simulation Results FR4 substrate IF:0.20 ................ 41 4 5 Fractal Patch Antenna Simulation Results FR4 substrate IF:0.25 ................ 42 4 6 Fractal Patch Antenna Simulation Results AD1000 substrate IF:0.20 .......... 43 4 7 Fractal Patch Antenna Simulation Results AD1000 substrate IF:0.25 .......... 44 4 8 Fractal Patch Antenna Simulation Results FR4 substrate IF:0.20 ................ 45 4 9 Fractal Patch Antenna Simulation Results FR4 substrate IF:0.25 ................ 45 4 10 Fractal Patch Antenna Dimensions FR4 (all sizes are in mm) .......................... 45 4 11 Fractal Patch Antenna Simulation Results AD1000 substrate IF:0.20 .......... 46 4 12 Fractal Patch A ntenna Simulation Results AD1000 substrate IF:0.25 .......... 46 4 13 Fractal Patch Antenna Dimensions AD1000 (all sizes are in mm) ................... 46 4 14 Antenna ID:24 Design Parameters ..................................................................... 47 4 15 Fractal Patch Antenna (ID:24) Simulation Results .............................................. 47 4 16 Comparison between Simulated and Measured results ..................................... 49

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8 LIST OF FIGURES Figure page 3 1 Patch antenna components ................................................................................ 31 3 2 Microstrip Line .................................................................................................... 32 3 3 Electric Field Lines ............................................................................................. 32 3 4 Effective Dielectric Constant ( ) .................................................................. 32 3 5 Rectangular microstrip patch antenna top and side views .................................. 33 3 6 Patch antenna design in FEKO .......................................................................... 33 3 7 Prototype UHF Patch RFID Reader Antenna ..................................................... 34 3 8 Fractal geometry iteration technique .................................................................. 34 3 9 0th iteration fractal patch antenna ...................................................................... 35 3 10 1th iteration fractal patch antenna ...................................................................... 35 3 11 2nd iteration fractal patch antenna ..................................................................... 35 3 12 3rd iteration fractal patch antenna ...................................................................... 36 3 13 4th iteration fractal patch antenna ...................................................................... 36 4 1 Return Loss (S11) simulation result .................................................................... 37 4 2 2D radiation pattern for square patch antenna ................................................... 38 4 3 3D radiation pattern for square patch antenna ................................................... 39 4 4 Measured return loss for the UHF Patch RFID Antenna prototype ..................... 40 4 5 Simulated return loss of 0th, 1st, 2nd, 3rd and 4th iteration fractal antenna FR4 substrate IF:0.20 ....................................................................................... 41 4 6 Simulated return loss of 0th, 1st, 2nd, 3rd and 4th iteration fractal antenna FR4 substrate IF:0.25 ....................................................................................... 42 4 7 Simulated return loss of 0th, 1st, 2nd, 3rd and 4th iteration fractal antenna AD1000 substrate IF:0.20 ................................................................................ 43 4 8 Simulated return loss of 0th, 1st, 2nd, 3rd and 4th iteration fractal antenna AD1000 substrate IF:0.25 ................................................................................ 44

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9 4 9 Return loss (S11) simulation result ..................................................................... 47 4 10 2D radiation pattern for fractal patch antenna .................................................... 48 4 11 3D radiation pattern for fractal patch antenna .................................................... 48 4 12 Measured return loss for the fractal patch antenna used in Wearable RFID Reader prototype ................................................................................................ 49

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10 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Engineering WEARABLE RFID READER AND COMPACT FRACTAL PATCH ANTENNA DESIGN By Ahmet Erdem Altunbas May 2010 Chair: Jean Pierre Emond Major: Agricultural and Biological Engineering The purpose of this thesis was to develop a compact antenna for Wearable RFID (Radio Frequency Identification) Reader applications with a proof of concept prototype. The intended antenna should provide similar properties compared to a patch antenna resonating at UHF frequency with a smaller size. The antenna should be integrated into a prototype Wearable RFID Reader and should be able to read RFID tags attached to a box during package handling process. The process of designing a compact antenna was started with analyzing microstrip patch antennas. A probe feed square patch antenna was designed and tested based on transmission line model A low cost patch antenna prototype was manufactured using simulation parameters and tested with a Network Analyzer. Soft ware for fractal patch calculations was written and used for generating four iterations of the initiator. Iteration factor values of 0.20 and 0.25 were chosen to be simulated and two substrates FR4 and AD1000 with 4.6 and 10.2 dielectric constant values were used. Probe fee d simulation results were validated with the measured results of the prototype antenna. Although the probe feed patch antenna provided good performance for most of the RFID applications, it had no use case for Wearable RFID Reader

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11 application due to size limitations. It i s shown that the fractal patch antenna resonant frequency decreases with an increase on the iteration factor and number It i s also observed that iteration factor has more effect on resonant frequency than iteration number. Antenna size miniaturization was achieved with a maximum value of 58.94% for 4th iteration fractal and 0.25 iteration factor. A prototype Wearable RFID Reader constructed using a fractal patch antenna with an iteration factor of 0.20 and iteration number of 1 was also presented in this thesis work. It is concluded that antenna miniaturization can be achieved by using fractal patch antennas which can be integrated into Wearable RFID Readers.

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12 CHAPTER 1 INTRODUCTION Radio Frequency Identification (RFID) is one of the automatic identification and data capturing technologies which has been widely used in many applications for identifying objects remotely. Based on RF signals, object identification and sensor data can be captured in a variety of ways. This technology is mainly divided into groups based on energy source of the transponder. While in passive systems the transponder harnesses the energy from the interrogator, in active RFID systems transponders use their own energy source. With the improvement of semi conductor technology the manufacturing cost of passive RFID tags has been reduced to an acceptable level for supply chain applications. Especially in the supply chain in which warehouse management is one of the fundamental steps, efficiency can be improved by using RFID systems i nstead of barcode systems which have a line of sight requirement. This research focuses on passive RFID systems for supply chain applications. Problem Description While RFID promises fast, reliable, nonline of sight requirement for case level package handling in a warehouse management system, its still an external device used for reading the ID on a package. Having a handheld RFID device in one hand and carrying a box at the same time would be difficult when its desired to be as fast as possible. To solv e this problem, an RFID reader device has to be designed to allow the package handler to work without interrupting his package handling process. The device that would be used in package handling should be compact and easy to use. The device has to have an integrated battery a RFID reader module, a compact

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13 RFID reader antenna and a communication interface for communicating with the host system which runs the desired application. The main goal of this thesis is to design a compact antenna with a prototype Wearable RFID Reader which can be used in package handling operations. Organization of Thesis In Chapter 2 a general overview of RFID Tech nology, patch antennas, f ractal patch antennas is presented. In Chapter 3, detailed information about patch antenna design and fractal patch antenna design is given and design considerations are presented in detail A p rototype patch antenna and fractal patch antennas are also presented with the Wearable RFID reader concept prototype. In Chapter 4, results are given for antenna simulations and measurements A d iscussion is presented in Chapter 5 followed by the conclusion and future work given in Chapter 6.

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14 CHAPTER 2 LITERATURE REVIEW History of RFID The f undamentals of RFID technology are based on elec tromagnetic energy studies, originating with Michael Faradays explanation of light and radio waves as forms of electromagnetic energy back in 1846. James Clerk Max wells theory of electromagnetism in 1864 was confirmed by Rudolf Hertz in 1887 who is also known as the first to be able to transmit and receive radio waves. In 1896 Guglielmo Marconi is the first scientist to have successful RF transmission over the Atlantic [1] O ne of the primary papers explaining the theory of RFID systems is Communication by Means of Reflected Power which was published by Stockman in 1948 [2] During those years a form of RF identification system which is called IFF (Identification Friend or Foe) was used in World War II. RFIDs first known commercial usage which dates back to the 1960s was called EAS (Electronic Article Surveillance) These systems were use d in applications which require 1 bit information; i.e. the presence or absence of a tag in observed RF field [1] In 1975, the publication of Short range Radio Telemetry for Electronic Identification Using Modulated Backscatter [3] resulted in the beginning of commercialization of passive RFID systems. For the last two decades RFID tags have been used in many applications with CMOS (Complementary metal oxide semiconductor) integrated circuit chips. Improvements in semiconductor technology resulted in increased affordability of the RFID tags, which sped up the industrial applic ations of RFID.

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15 RFID Technology Overview RFID Technology can be divided into subcategories according to the energy source of the tags and operating frequencies. According to source of energy in an RFID system transponders can be categorized as; 1. Passive tags 2. Semipassive tags 3. Active tags Passive Tags: Passive RFID tag s have no inter nal power source. In inductively coupled systems; when the tags are present in the RF field of an RFID interrogator the energy induced on the tag circuitry is used for transmitting back the ID of the tag. In UHF systems, electromagnetic backscatter coupling is used at the tag circuitry for changing the impedance of the tag antenna according to its ID. Semi passive Tags: Semipassive systems have internal batteries and are not beaconing signals in a defined period. In the presence of the RF field of an interrogator the tag wakes up and starts to transmit its ID to the interrogator ; using integrated battery supply. The trade off for energy efficiency is to have reduced response time caused by the time slot needed to wake up the transp onder. As proposed by AutoID labs Class 3 categorization; Semi passive tags use their integrated power source for increased communication range, in contrast to fully passive tags and also perform on tag functionality such as sensor data logging. These tags have been proposed to be able to send their ID even when they are out of internal battery power [6]

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16 Active Tags: Active Tags are beaconing in a defined period of time by using integrated power supplies. These tags are commonly used in RTLS (Real Time Location Systems) in which the tag continuous ly reports its ID to the receiver units and location of the tag is usually calculated by using RSS (Received Signal Strength) informatio n and triangulating between different receivers. RFID Frequencies Low frequency (LF): Common LF systems operate at either 125 kHz or 134 kHz, the power supply to the transponder is generated by inductive coupling. RF signals at lower frequencies can penetr ate through the body better than higher frequencies, that i s one of the main reasons for using LF systems in animal identification applications. ISO 11785 defines the standard for animal tracking applications using LF RFID systems. High frequency (HF): Hig h frequency RFID systems operate at 13.56 MHz frequency. Passive 13.56 MHz systems also operate with the inductive coupling principle, in which magnetic fields are playing the major role for energy transfer. That is why 13.56 MHz performs better in the presence of water and metallic surfaces in short range. ISO 15693 defines the standard for Vicinity Cards in HF systems. Ultra high frequency (UHF): The m ost common passive RFID tags used in su pply chain applications operate at 915 MHz in US and 868 MHz in Europe. The a ccepted standard for passive UHF frequency is ISO 180006C (aka UHF Gen2). Active or semi active RFID systems in UHF frequencies operate at 433 MHz. ISO 180007 is the accepted standard for parameter s of active air interface communications at 433 MHz. Microwave frequency: Typical microwave operating frequency is either at 2.45 GHz or 5.8 GHz in the ISM band [5] Microwave systems can be either passive or semi -

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17 passive and provide the fastest data communication rates compared to the other frequencies. Read range performance for passive systems in the presence of water and metallic surfaces is very poor because of the higher signal attenuation at higher frequency. Microstrip Patch Antennas Patch antennas are widely used in commercial applications mostly because they are simple and inexpensive to fabricate, they can be integrated into printed circuit boards and are conformable to planar surfaces. The resonant frequency, polarization, radiation pattern and impedance properties can be eas ily configured by using a particular patch shape and adding loads between the radiating plate and the ground plane. These low profile antennas consist of mainly two parts : a radiating patch and a ground plane. Patch geometrical shapes can vary but the mos t common forms are square, rectangle, ellipse, circle and rectangle with truncated corners [7, 8] Different substrates can be used in Microstrip antennas with dielectric constant values varying between 2 .2 12 Thick substrates with lower dielectric c onstant values are preferred because of their efficiency and larger bandwidth. Although thin substrates with higher dielectric constants are less efficient and have smaller bandwidths they can be manufactured in smaller element sizes with minimum undesired radiation and coupling [8, 9] The r adiating patch can be fed by using one of the methods below: Microstrip line feed Probe feed Aperturecoupled feed Proximity coupled feed

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18 The m icrostrip line is connected directly to the edge of the microstrip patch, and impedance matching can be done by controlling the inset position. In probe feed patch antennas, coax is attached to the radiation patch and the outer conductor is connected to the ground plane. Controlling the feeding point is used for impedanc e matching. Both microstrip line feed and probe feed methods can be categorized as contacting methods. Aperture coupling and proximity coupling feed techniques can be categorized as noncontacting methods. The major disadvantage of these techniques is that they are not easy to fabricate; while aperture coupled feed requires a proper slot on the radiating patch, proximity coupled feed requires proper alignment between two substrates [10] Fractal Antennas Fractals are complex geometric shapes with space fil ling and self similarity propert ies Space filling contours result in electrically large features which can be efficiently packed into small areas Antenna miniaturization can be achieved by using the space filling properties of fractals that lead to curve s that are electrically very long but fit into a compact physical space [2629] Researchers have been working on developing efficient RFID reader antennas and using different methods to achieve smaller sizes, using a vertical ground is one of the options which can reduce the resonant frequency by about 25% in comparison to no vertical ground [21,22] Others worked on corner truncated square patch antennas for creating circular polarization which is crucial when the orientation of the tag is not known [23,24] Although circular polarization gives orientation independency the trade of f is having a lower gain antenna which will affect the battery life time of the wearable RFID reader. A short pin and a highpermittivity substrate can also be used for miniat urization, but these will lead to a sharp deterioration of the antenna performance

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19 [25] In this thesis, design and simulation of fractal patch antennas was performed for size miniaturization.

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20 CHAPTER 3 MATERIALS AND M ETHODS Analysis of Patch Antenna Design Microstrip patch antennas can be analyzed in various methods; the most common methods are as follows: Transmissionline method Cavity method Full wave method Although the transmission line model has the least accuracy and is the most difficult one to model coupling, it is the easiest method to implement and gives good physical insight [11] The c avity model is more accurate, compared to the transmission line method, but more complex to implement. Full wave method is the most complex, accurate and versatile method but gives less physical insight [7] The t ransmissionline method will be described in detail as it is used in this thesis to design patch antennas for RFID applications. Transmissionline Model According to Balanis [7] microstrip patch antennas can be explained by the transmission line model representing two slots with a width of W and separated by transmission line of length L. As its seen in F igures 32 and 33, most of the field lines are inside the substrate and some of them are extended to outer space Since this is a nonhomogenous line of two dielectrics, an effective dielectric constant () has to be taken into consideration for fringing and the wave propagation in the line. The assum ption of embedding the center conductor of the microstrip line into a dielectric material with a uniform dielectric constant ( ) is shown in F igure 34.

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21 can be calculated from [7]; = + 1 2 + 1 2 1 + 12 1 / 2 (3 .1) Where, > 1 and; : Effective dielectric constant : Dielectric constant of the substrate : Width of the radiating patch : Height of the substrate As shown in Figure 35, fringing field lines extends physical antenna Length L on each end by a distance which is a function of the effective dielectric constant and the width to height ratio ( / ). This is given in [12] as; = 0 .412 + 0 .3 + 0 .264 0 .258 + 0 .8 (3.2) Effective length of the patch turned into; = + 2 (3.3) Effective length of the patch can also be described as [13] ; = 2 (3.4)

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22 Width of the radiating patch can be calculated as follows for a good efficiency [1417] = 2 2 + 1 (3.5) UHF RFID Patch Antenna Design Step 1: Design considerations: RFID antenna design process basically starts with defining the operating frequency, desired bandwidth, materials intended to be used by considering antenna dimensions and manufacturing cost. Other requirements can be summarized as; defining maximum gain, 3dB beam width, polarization and axial ratio. Operating Frequency: Although operating frequencies of RFID systems are all in ISM bands because of local regulations they can slightly change in different regions. Operating frequencies can be summarized as follows; North America: 902 928 MHz Europe: 866 869 MHz South Korea: 908914 MHz Japan: 950 956 MHz In this thesis work, the North America n zone will be covered with an antenna resonating fr equency of 915 MHz. = 915 Dielectric Material: For the purpose of making a low cost and easy to manufacture proof of concept antenna, air gap was used as the dielectric substrate

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23 between the radiating patch and the ground plane which has a dielectric constant of 1.0006. = 1 .0006 Plastic spacers were used between the radiating patch and the ground plane. The most common spacers are half inch nylon spacers which can be easily found in most local hardware stores, so the height of the substrate was chosen to be half inch. = 12.72 Step 2: Calculating width of the radiating patch: As described in the transmission line model section, radiating patch width can be calculated from equation (3.5) as given by; = 2 2 + 1 (3.6) can be calculated as; = (3.7) where, speed of light = 3 108 / and using = 915 ; = 1 .0006 we can calculate = 0 .32 substituting all into equation (3.6) will give; = 163.9

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24 Step 3: Calculating maximum height of the substrate: According to Bancroft [13], if we increase the substrate thickness too much undesired surface waves can be generated. Maximum substrate height can be found using the equation below; 0 .3 2 + 1 (3.8 ) Using the Equation (3.8) leads to 15.64 which means our initial choice of = 12.72 is acceptable. Step 4: Calculating effective dielectric constant ( ) Using equation (3.1) : = + 1 2 + 1 2 1 + 12 1 / 2 (3.9) And substituting = 1 .0006 = 12.72 = 163.9 We get, = 1 .000516 Ste p 5: Calculating length extension of the patch ( ) Using equation (3.2) = 0 .412 + 0 .3 + 0 .264 0 .258 + 0 .8 (3.10) And substituting = 1 .000516 into (3.10), can be calculated as; = 8 .81

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25 Step 6: Calculating effective length of the patch () By using equation (3.4) = 2 (3.11) can be calculated as; = 163.89 Step 7: Calculating physical length of the patch By u sing equation (3.3) = + 2 (3.12) And substituting = 163.89 and = 8 .81 can me calculated as; = 146.25 Step 8: Calculating feed point location: After deciding patch length and width, we needed to determine the best feed point location in order to have a good impedance match between the RFID reader and the antenna. The f eed point can be selected on any location along the patch width [19] it is therefore selected as; = 2 Determining exact feed point locati on requires an iterative approach and Kara [20] suggested a starting point for as follows;

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26 = 2 ( ) (3.13) Where; ( ) = + 1 2 + 1 2 1 + 12 1 / 2 (3.14) Substituting ( ) from (3.14) to (3.13) gives us which is; = 86.17 Step 9: Calculating ground plane size : Infinite ground planes are widely used in antenna simulations due to the fact that finite size ground plane simulations requires more calculation time. Its stated that when the size of the ground plane is /20 bigger on each side of the patch, then it can be assumed to be an infin ite ground plane [19] = /20 (3.14) = + and = + This gives us a minimum ground plane size of ; = 179 and = 196 Step 10: Final antenna design decisions and summary : According to calculations based on transmission line model, below are the minimum requirements for an antenna resonating at 915 MHz with a dielectric constant 1.0006 and height of 12.72mm : 146.25

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27 : 163.91 : 179 : 196 Simulation The software called CAD FEKO (Feko, Hampton, VA, USA) was used for simulating the antenna designs throughout this thesis work. FEKO is an electromagnetic field analysis simulator software based on Method of Moments technique. W e have chosen to simulate and manufacture a square pat ch antenna with the parameters gi ven below According to Kumar [18], the width of the patch can be taken smaller with the tradeoff of having smaller bandwidth and decreased gain. Patch dimensions: : 146.25 : 146.25 Ground plane dimensions: : 250 : 250 Calculated antenna design parameters were integrated into FEKO for optimum feed point location iterations and antenna simulation. Prototype Manufacturing of D esigned Patch A ntenna By using the simulation results, a prototype low cost RFID reader antenna wa s manufactured from materials that can be f ound from local hardware stores:

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28 Table 31 Bill of materials for UHF RFID Reader Antenna 1 Galvanized Steel Sheet 1 x 2 $8.49 2 SMA connector + 1foot coax cable $4.00 3 Nylon spacer 1/2Inch $1.2 Total: $13.69 Fractal Patch Antenna Design for Wearable RFID Readers Koch Island fractals can be constructed by forming polygon with the Koch curves on each side. As shown in Figure 38 each segment of the geometry is replaced with the generator. The i teration factor is defined as the ratio of indentation width to the generator. The i nitiator which is shown in Figure 38, is the 0th iteration fractal antenna where other antennas on are named 1st, 2nd and 3rd iterations respectively. Fractal Geometry C alculator Software: A piece of code was written in C# for calculating the 1st, 2nd, 3rd and 4th iteration geometries with the coordinates of each individual corner. The 0th iteration patch size and the iteration factor value should be given as input s to th e software and four separate text files would be generated in the folder, these text files can be imported to CAD FEKO software to generate the geometry without giving coordinates of each corner of a polygon manually. It would be almost impossible to create 4th iteration geometries by manually enteri ng the coordinates. Software code can be found in Appendix A. Fractal Antenna Designs and Simulations: Transmission line model was used for calculating dimensions of 0th iteration square patch antenna. Two different substrates with different dielectric constant values and heights were chosen for simulations. Antenna simulations were performed in CAD FEKO as stated in previous chapter.

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29 Substrates: FR4 with = 4 .6 and = 1 .57 AD1000 with = 10.2 and = 1 .49 Table 3 2 Patch Antenna Design Parameter s Resonant Frequency ( ) ( ) ( ) mm 915 MHz 4.6 1.57 915 MHz 10.2 1.49 Table 33. Calculated parameters according to transmission line model Substrate FR4 97.97mm 7.3mm 4.45 0.73mm 77.73mm 76.27mm 114.36mm 92.67mm AD1000 69.27mm 4.9mm 9.7 0.64mm 52.63mm 51.35mm 85.67mm 67.74mm Table 34. 0th iteration square patch antenna dimensions Substrate Patch Length ( ) Patch Width ( ) FR4 76.27mm 76.27mm AD1000 51.35mm 51.35mm By using Fractal Geometry Calculator Software 1st, 2nd, 3rd and 4th iterations were generated to be imported into CAD FEKO, as shown in the figures below with Iteration Factor 0.20 and 0.25 respectively. Also, an iterative approach was taken for finding the appropriate patch size to be able to resonate at 915 MHz at different iteration number and factor. Wearable RFID Reader Prototype A wearable RFID reader prototype was build throughout this thesis work with a prototype fractal patch antenna. The m ain purpose of this prototype was to show the concept of a wearable RFID reader with minimum capabilities. Size miniaturization of the antenna with fractal geometry was also implemented in this prototype. Main parts of the reader can be summarized as;

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30 UHF RFID Reader Module Skyetek M9 (Skyetek, Denver, CO,USA) o Operating Frequency: 862955 MHz o Supported Protocols: EPC C1G1/G2, ISO 18000 6C/6B, EM4122,EM4444, IP X o Power consumption 800mA at 27 dBm 500mA at 21 dBm o Supply Voltage: 4.5V 5.5V o Host Communication Interface: UART, SPI, USB 2.0, I2C Bluetooth Module (Roving Network RN 41) (Roving Networks, Las Gatos, CA, USA) o Bluetooth 2.1/2.0/1.2/1.1 module o Bluetooth v2.0+EDR support o Class 1 high power amplifier o Power consumption 30mA when connected 250 uA sleep mode o Supply Voltage: 3.3V o Host Communication Interface: UART, USB Voltage Regulator o 5V Voltage regulator LP3963 o 3.3V Voltage regulator LT1963 Battery ( 3.7V 2000mAh Polymer Lithium Ion )

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31 Full list of Bill of Materials can be found in Appendix D. Printed Circuit Board and Schematic design were done by using free version of Cadsoft EAGLE software (Cadsoft, Pines, FL, USA) Schematic of the board can be found in Appendix B and Printed Circuit Board design can be found in Appendix C. The Fractal patch antenna used in the prototype has the following properties: AD1000 substrate Iteration factor:0.20 Iteration number:1 Figure 31. Patch antenna components Ground Plane Substrate Radiating Patch

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32 Figure 32. Microstrip Line Figure 3 3. Electric Field Lines Figure 34. Effective Dielectric Constant ()

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33 Figure 35. Rectangular microstrip patch antenna top and side views Figure 36. Patch antenna design in FEKO

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34 Figure 37. Prototype UHF Patch RFID Reader Antenna Figure 38. Fractal geometry iteration technique

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35 Figure 39. 0th iteration fractal patch antenna Figure 310. 1th iteration fractal patch antenna Figure 311. 2nd iteration fractal patch antenna

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36 Figure 312. 3rd iteration fractal patch antenna Figure 313. 4th iteration fractal patch antenna

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37 CHAPTER 4 RESULTS Square Patch Antenna Simulation and Measurement Results Simulation: Simulation results for square patch antenna design were given in this section. Table 41 gives a summary of the antenna design parameters calculated in Chapter 3, Table 42 represents simulated results of the patch antenna. Table 4 1. Square Patch Antenna Design Parameters ( ) mm ( ) mm ( ) mm ( ) mm ( ) ( ) mm 146.25 146.25 250 250 1.0001 12.7 Table 4 2 Square Patch Antenna Simulation Results Resonance Frequency Max Gain Return Loss (S11) 10 dB Bandwidth 3dB Beam Width Feed Location ( ) 915.19 MHz 9.05 dB i 32.6 dB 45 MHz 60 5 ( 30,0)mm Figure 4 1 Re t urn Loss (S11) simulation result

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38 As shown in Figure 41, bandwidth for 10 dB return loss value can be calculatedfrom two resonant frequencies at each end, which are 894 MHz and 939 MHz respectively and can be calculated as 45 MHz Radiation pattern simulations are performed by plotting elevation patterns for = 0 and = 90 as a function of Figure 4 2 2D radiation pattern for square patch antenna

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39 The maximum gain of 9.05 dBi was achieved at the broadside of the antenna, the 3dB beam width can be calculated from angles on which the antenna gain decreases 3dB below of its max value, which are 29.9 and 329.4 Therefore 3dB beam width is 60.5 Figure 4 3 3D radiation pattern for square patch antenna

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40 Measurement: Measurements are performed by using Anritsu (Anritsu, Richardson, TX, USA) MS2024A Vector Network Analyzer. Figure 4 4 Measured return loss for the UHF Patch RFID Antenna prototype Table 43 Comparison between Simulated and Measured results Simulated Measured Resonance Frequency 915.19 MHz 918.18 MHz Return Loss (S11) 32.6 dB 34.28 dB 10 dB bandwidth 45 MHz 49 MHz With a commercially available RFID reader at 30dBm output power, we had 11m read range with this prototype antenna.

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41 Fractal Patch Antenna Simulation Results Table 44 Fractal Patch Antenna Simulation Results FR4 substrate IF:0.20 Antenna ID iteration # iteration factor Center frequency (MHz) Max Gain (dBi) Return Loss (RL) (dB) BW(RL> 9.5dB)(MHz) h(mm) = 1 0 0 915 4.71 -45.00 12.00 4.60 1.57 76.27 3 1 0.20 762 1.52 -27 8.00 4.60 1.57 76.27 4 2 0.20 726 -3.7 -49 8.00 4.60 1.57 76.27 5 3 0.20 721 -31.2 6.00 4.60 1.57 76.27 Figure 45. Simulated return loss of 0th, 1st, 2nd, 3rd and 4th iteration fractal antenna FR4 substrate IF:0.20

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42 Table 45 Fractal Patch Antenna Simulation Results FR4 substrate IF:0.25 Antenna ID iteration # iteration factor Center frequency (MHz) Max Gain (dBi) Return Loss (RL) (dB) BW(RL> 9.5dB)(MHz) h(mm) = 1 0 0 915 4.71 -45.00 12.00 4.60 1.57 76.27 6 1 0.25 682 2.85 -9.4 4.60 1.57 76.27 7 2 0.25 635 -9.3 -10.5 4.60 1.57 76.27 8 3 0.25 620 -7.8 4.60 1.57 76.27 9 4 0.25 568 -13 6.00 4.60 1.57 76.27 Figure 46. Simulated return loss of 0th, 1st, 2nd, 3rd and 4th iteration fractal antenna FR4 substrate IF:0.25

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43 Table 46 Fractal Patch Antenna Simulation Results AD1000 substrate IF:0.20 Antenna ID iteration # iteration factor Center frequency (MHz) Max Gain (dBi) Return Loss (RL) (dB) BW(RL> 9.5dB)(MHz) h(mm) = 10 0 0 914 2.2 -37.6 10 10.20 1.49 51.35 11 1 0.20 718 -7.7 -24 9.00 10.20 1.49 51.35 12 2 0.20 695 -20 10 10.20 1.49 51.35 13 3 0.20 687 -17 10.00 10.20 1.49 51.35 Figure 47. Simulated return loss of 0th, 1st, 2nd, 3rd and 4th iteration fractal antenna AD1000 substrate IF:0.20

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44 Table 47 Fractal Patch Antenna Simulation Results AD1000 substrate IF:0.25 Antenna ID iteration # iteration factor Center frequency (MHz) Max Gain (dBi) Return Loss (RL) (dB) BW(RL> 9.5dB)(MHz) h(mm) = 10 0 0 914 2.2 -37.6 10 10.20 1.49 51.35 14 1 0.25 618 -21 -23 8.00 10.20 1.49 51.50 15 2 0.25 580 -17 -15 10.2 1.49 51.35 16 3 0.25 566 -11.50 10.20 1.49 51.35 17 4 0.25 632 -6 10.20 1.49 51.50 Figure 48. Simulated return loss of 0th, 1st, 2nd, 3rd and 4th iteration fractal antenna AD1000 substrate IF:0.25

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45 Size Miniaturization (FR4 Substrate) Table 4 8 Fractal Patch Antenna Simulation Results FR4 substrate IF:0.20 Antenna ID iteration # iteration factor Center frequency (MHz) Max Gain (dBi) Return Loss (RL) (dB) BW(RL> 9.5dB)(MHz) h(mm) = 1 0 0 915 4.71 -45.00 12.00 4.60 1.57 76.27 18 1 0.20 915 1.87 -19 9.00 4.60 1.57 63.00 19 2 0.20 911 3.4 -42 10.00 4.60 1.57 60.60 20 3 0.20 913 3.14 -34.9 10.00 4.60 1.57 60.00 Table 49 Fractal Patch Antenna Simulation Results FR4 substrate IF:0.25 Antenna ID iteration # iteration factor Center frequency (MHz) Max Gain (dBi) Return Loss (RL) (dB) BW(RL> 9.5dB)(MHz) h(mm) = 1 0 0 915 4.71 -45.00 12.00 4.60 1.57 76.27 21 1 0.25 916 4.7 -29.7 10.00 4.60 1.57 57.80 22 2 0.25 921 3.48 -20 9.00 4.60 1.57 51.00 23 3 0.25 924 2.7 -16.8 8.00 4.60 1.57 50.00 Table 410. Fractal Patch Antenna Dimensions FR4 (all sizes are in mm) L x W IF=0.2 area(mm2) size L x W IF=0.25 area(mm2) size Square patch 76x76 5776 100.00 76x76 5776 100.00 Fractal 1st iteration 63x63 3969 68.72 57.8x57.8 3341 57.84 Fractal 2nd iteration 60.6x60.6 3672 63.58 51x51 2601 45.03 Fractal 3rd iteration 60x60 3600 62.33 50x50 2500 43.28

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46 Size Miniaturization (AD1000 Substrate) Table 411. Fractal Patch Antenna Simulation Results AD1000 substrate IF:0.20 Antenna ID iteration # iteration factor Center frequency (MHz) Max Gain (dBi) Return Loss (RL) (dB) BW(RL> 9.5dB)(MHz) h(mm) = 10 0 0 914 2.2 -37.6 10 10.20 1.49 51.35 24 1 0.20 915 0.84 -23 11.00 10.20 1.49 42.50 25 2 0.20 923 -1.4 -24.6 10.2 1.49 40.5 26 3 0.20 937 -0.8 -20.20 9.00 10.20 1.49 39.90 Table 412. Fractal Patch Antenna Simulation Results AD1000 substrate IF:0.25 Antenna ID iteration # iteration factor Center frequency (MHz) Max Gain (dBi) Return Loss (RL) (dB) BW(RL> 9.5dB)(MHz) h(mm) = 10 0 0 914 2.2 -37.6 10 10.20 1.49 51.35 27 1 0.25 916 0.86 -25.7 10 10.2 1.49 37.5 28 2 0.25 915 -2.2 -11.6 10.2 1.49 34 29 3 0.25 921 -4.9 -10 10.2 1.49 33 Table 413. Fractal Patch Antenna Dimension s AD1000 (all sizes are in mm) L x W IF=0.2 area(mm2) size L x W IF=0.25 area(mm2) size Square patch 51.3X51.3 2632 100 51.5x51.5 2652 100.00 Fractal 1st iteration 42.5*42.5 1806 69 37.5x37.5 1406 53.02 Fractal 2nd iteration 40.5x40.5 1640 62 34x34 1156 43.59 Fractal 3rd iteration 39.9x39.9 1592 60 33x33 1089 41.06

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47 Fractal Patch Antenna for Wearable RFID Reader Prototype Simulation: Simulation results for fractal patch antenna, used in Wearable RFID Reader prototype, were given in this section. Antenna with ID number of 24, as shown in Table 411, was used in the Wearable RFID Reader prototype. Design parameters are given in Table 414. Table 4 1 4 Antenna ID:24 Design Parameters ( ) mm ( ) mm ( ) ( ) mm Iteration # Iteration Factor 42.50 42.50 10.2 1.49 1 0.20 Table 41 5 represents simulated results of the fractal antenna used in prototype Table 4 1 5 Fractal Patch Antenna (ID:24) Simulation Results Resonance Frequency Max Gain Return Loss (S11) 10 dB Bandwidth Feed Location ( ) 915 MHz 0.84 23 dB 11 MHz ( 7.6,0)mm Figure 49. Return loss (S11) simulation result

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48 Radiation pattern simulations are performed by plotting elevation patterns for = 0 and = 90 as a function of Figure 410. 2D radiation pattern for fractal patch antenna Figure 411. 3D radiation pattern for fractal patch antenna

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49 Measurement: Figure 412. Measured return loss for the fractal patch antenna used in Wearable RFID Reader prototype Table 416. Comparison between Simulated and Measured results Simulated Measured Resonance Frequency 915.19 MHz 91 7 27 MHz Return Loss (S11) 23 dB 28 dB 10 dB bandwidth 11 MHz 7 MHz

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50 CHAPTER 5 DISCUSSION Square Patch Antenna A square patch antenna with air substrate made of galvanized steel metal sheet was designed and manufactured because of its simplicity and ease of comparison between simulation results and measurement results. Antenna design process relies on the simulation results due to its flexibility to change parameters and evaluate antenna eff iciently. To do so, we decided to manufacture an antenna which will be easy to manufacture and will give us enough information to validate our simulated results. Simulation Simulations performed in CAD FEKO described in the previous chapter shows that our antenna perfectly resonates at the desired frequency which is 915 MHz. Although its easy to manufacture pin feed patch antennas, the best feed point location, which impacts antenna impedance for proper matching, was hard to find by using an iterative appr oach. Multiple simulations had to be run for each antenna design to determine the best location. Antenna gain of 9.05 dBi is generally adequate for most of the RFID applications. Due to the allowed output power regulations in different countries, RFID readers should be configured to output at most 0.5W in US with this simulated antenna. Although, these values are half of the allowed output powers in US, readers cannot exceed more due to the fact that with this high gain antenna, the allowed Equivalent Isot ropic Radiated Power (EIRP) of 4W would be exceeded.

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51 Bandwidth of 45MHz is enough for covering US frequencies of 902 MHz 928 MHz with this antenna. This antenna has to be adjusted to allow use in different regions. For example to be able to use this antenna in EU, the resonant frequency should be lower ed down to 868 MHz which can be done by enlarging the patch length. This linearly polarized patch antenna shows good directivity for RFID applications in which zone differentiation would be crucial. A 3dB beam width of 60.5 should be taken into consideration when installing an RFID system for better performance. As can be seen from Figures 42 and 43 the back lobe of the antenna is fairly small. This is acceptable for RFID applications where it is likely to have another antenna attached to the same reader. Measurements and Comparison with Simulation Results presented in Figure 44 show a good match between simulation and measurement. Although imperfection of hand manufacturing the prototype antenna might have caused the 3 MHz shift in resonance frequency, this should not affect antenna performance. Measured return loss and 10dB return loss bandwidth values are also close enough with simulations M easured 4 MHz wider bandwidth giv es more flexibility to the prototype antenna. Read range measurement at 30dBm shows great performance of this antenna and this antenna can be used where linearly polarized directional antennas are needed. Up to this point our measured results showed good agreement with simulated results, so fractal antenna measurements are decided to be based on simulation s.

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52 Fractal Patch Antenna The antenna is one of the most crucial component s of an RFID system especially in battery powered systems due to the fact that an inefficient antenna requires more output power from the reader which will decrease the battery life. Although the prototype antenna developed in a previous chapter performs wel l enough to be used in most RFID applications, its not realistic to have an antenna with a 146mm radiating patch and 250mm ground plane attached to a human arm for wearable RFID applications. Therefore, a compact fractal antenna was developed for wearable RFID applications Since fractal geometries get smaller when iteration number increases, its very difficult to obtain good results with bench made fractal antennas, so we based our fractal antenna design on simulation results Two different substrates, FR4 and AD1000 with different dielectric constant values and very similar heights were used for fractal designs. The higher dielectric constant substrate AD1000 provided smaller patch sizes as expected. Effect of Iteration Factor and Iteration Number on Resonant Frequency Considering Figures 45 to 48 i ndividually, its seen that as iteration number increases, resonant frequency of the antenna becomes lower than that of the 0th iteration. After the 1st iteration, the resonant frequency change is not significant. Comparing f igures within the same substrat e, its observed that as iteration factor changes from 0.20 to 0.25 resonant fr equency dramatically decreases. Its concluded that iteration factor has more effect on resonant frequency than iteration number while both substrates behaved similarly.

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53 Antenna Size Miniaturization with Fractals Its shown that the square patch dimension reduced 37.67% at IF:0.20 and 56.72% at IF:0.25 for the FR4 substrate. Also for the AD1000 substrate, similar results are observed as follows; 40% at IF:0.20 and 58.94% at IF:0.25. Although similar behaviors are observed between different substrates, its shown that higher iteration factor results in better antenna size miniaturization. Fractal Patch Antenna for Wearable RFID Reader Prototype Prototype fractal patch antenna decision was based on measurement results of manufactured antennas. Bench made manufacturing of small size fractals was resulted with poor measurement results. Potential causes of this problem would be summarized as follows: Press and peel technique used for manufacturing fractals is not as precise as machines Smaller patch size with higher iteration number, factor requires more precision. Probe feed location effects on impedance matching Although most of the antennas showed poor results, the fractal patch antenna (Antenna ID:24) with the iteration factor of 0.20 generated from 1st iteration of a square patch antenna performed well enough for integrating into Wearable RFID Reader prototype. Results presented in Table 416 show a close match between the measurement and the simulation.

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54 CHAPTER 6 CONCLUSIO N The aim of this research is to design a compact RFID antenna with a prototype Wearable RFID Reader. This objective was achieved by designing, simulating and measuring microstrip patch antennas as well as fractal patch antennas for size miniaturization. A prototype Wearable RFID Reader was also presented with an integrated fractal patch antenna. Analysis of the microstrip patch antennas was performed by using t ransmission line model and simulation results were validated with the measurement results. Although designed patch antenna performed well enough for general RFID applications, it was still not small enough for a Wearable RFID Reader application. Further r esearch on fractal patch antennas resulted with a significant size reduction. Maximum size reduction of 58.94% was achieved with a fractal patch antenna at 4th iteration and I teration Factor of 0.25. The prototype Wearable RFID Reader was manufactured with an integrated fractal patch antenna. Fractal patch antenna used in the prototype was generated from the 1st iteration of a square patch antenna resonating at 915MHz with iteration factor of 0.20. Results of this research can be used in developing complex Wearable RFID Readers with integrated compact antennas. Future work can be summarized as; manufacturing and testing fractal antennas by using precise manufacturing techniques and also designing Wearable RFID Readers with integrated microprocessors and sensors for standalone applications. To sum up, this thesis work proves that antenna miniaturization can be achieved by using fractal patch antennas for Wearable RFID Readers.

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55 APPENDIX A FRACTAL GEOMETRY CAL CULATOR C ODE namespace Fractal Calculator { public class SquareCoordinates { public double patch_l = 50; public double patch_w = 50; public double IterationFactor = 0.25; public double a0; public double a11, a13; public double a12; public double b; public int t = 0; public int size; double[] CoordinateX = new double[5]; double[] CoordinateY = new double[5]; double[] iterCoordinateX = new double[5000]; double[] iterCoordinateY = new double[5000]; double[] TobeiterCoordinateX = new double[1000]; double[] TobeiterCoordinateY = new double[1000]; public SquareCoordinates() { CoordinateX[0] = patch_l / 2; CoordinateY[0] = patch_w / 2; CoordinateX[1] = patch_l / 2; CoordinateY[1] = patch_w / 2; CoordinateX[2] = patch_l / 2; CoordinateY[2] = patch_w / 2; CoordinateX[3] = patch_l / 2; CoordinateY[3] = patch_w / 2; } public void FirstIteration() { Array.Copy(CoordinateX, TobeiterCoordinateX, 4); Array.Copy(CoordinateY, TobeiterCoordinateY, 4); a0 = (Math.Abs((TobeiterCoordinateX[1] TobeiterCoordinateX[0]))); a12 = a0 IterationFactor; b = a12; a13 = (a0 a12) / 2;

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56 a11 = a13; t = 0;//1 size = 4; } public void SecondIteration() { Array.Copy(iterCoordinateX, TobeiterCoordinateX, 20); Array.Copy(iterCoordinateY, TobeiterCoordinateY, 20); a0 = (Math.Abs((TobeiterCoordinateX[1] TobeiterCoordinateX[0]))); a12 = a0 IterationFactor; b = a12; a13 = (a0 a12) / 2; a11 = a13; t = 0;//1 size = 20; } public void ThirdIteration() { Array.Copy(iterCoordinateX, TobeiterCoordinateX, 100); Array.Copy(iterCoordinateY, TobeiterCoordinateY, 100); a0 = (Math.Abs((TobeiterCoordinateX[1] TobeiterCoordinateX[0]))); a12 = a0 IterationFactor; b = a12; a13 = (a0 a12) / 2; a11 = a13; t = 0;//1 size = 100; } public void ForthIteration() { Array.Copy(iterCoordinateX, TobeiterCoordinateX, 500); Array.Copy(iterCoordinateY, TobeiterCoordinateY, 500); a0 = (Math.Abs((TobeiterCoordinateX[1] TobeiterCoordinateX[0]))); a12 = a0 IterationFactor; b = a12; a13 = (a0 a12) / 2; a11 = a13; t = 0; //1 size = 500; }

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57 public void Iteration() { for ( int i = 0; i < size; i++) { iterCoordinateX[t] = TobeiterCoordinateX[i]; iterCoordinateY[t] = TobeiterCoordinateY[i]; if ((Math.Abs((TobeiterCoordinateX[i + 1] TobeiterCoordinateX[i]))) > 0) { a0 = (Math.Abs((TobeiterCoordinateX[i + 1] TobeiterCoordinateX[i]))); } else { a0 = (Math.Abs((TobeiterCoordinateY[i + 1] TobeiterCoordinateY[i]))); } a12 = a0 IterationFactor; b = a12; a13 = (a0 a12) / 2; a11 = a13; if (i == (size 1)) { if ((Math.Abs((TobeiterCoordinateX[0] TobeiterCoordinateX[i]))) > 0) { a0 = (Math.Abs((TobeiterCoordinateX[0] TobeiterCoordinateX[i]))); } else { a0 = (Math.Abs((TobeiterCoordinateY[0] TobeiterCoordinateY[i]))); } a12 = a0 IterationFactor; b = a12; a13 = (a0 a12) / 2; a11 = a13; t++;//2 iterCoordinateX[t] = iterCoordinateX[t 1]; iterCoordinateY[t] = iterCoordinateY[t 1] + a11; t++;//3 iterCoordinateX[t] = iterCoordinateX[t 1] b;

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58 iterCoordinateY[t] = iterCoordinateY[t 1]; t++; //4 iterCoordinateX[t] = iterCoordinateX[t 1]; iterCoordinateY[t] = iterCoordinateY[t 1] + a12; t++;//5 iterCoordinateX[t] = iterCoordinateX[t 1] + b; iterCoordinateY[t] = iterCoordinateY[t 1]; //t++;//6 //iterCoordinateX[t] = iterCoordinateX[t 1]; //iterCoordinateY[t] = iterCoordinateY[t 1] + a13; t ++; } else { if (TobeiterCoordinateX[i] > TobeiterCoordinateX[i + 1]) { t++;//2 iterCoordinateX[t] = iterCoordinateX[t 1] a13; iterCoordinateY[t] = iterCoordinateY[t 1]; t++;//3 iterCoordinateX[t] = iterCoordinateX[t 1]; iterCoordinateY[t] = iterCoordinateY[t 1] b; t++;//4 iterCoordinateX[t] = iterCoordinateX[t 1] a12; iterCoordinateY[t] = iterCoordinateY[t 1]; t++;//5 iterCoordinateX[t] = iterCoordinateX[t 1]; iterCoordinateY[t] = iterCoordinateY[t 1] + b; //t++;//6 ////iterCoordinateX[t] = iterCoordinateX[t 1] a11; ////iterCoordinateY[t] = iterCoordinateY[t 1]; t++; } if (TobeiterCoordinateX[i] < TobeiterCoordinateX[i + 1]) { t++;//2 iterCoordinateX[t] = iterCoordinateX[t 1] + a11; iterCoordinateY[t] = iterCoordinateY[t 1]; t++;//3 iterCoordinateX[t] = iterCoordinateX[t 1]; iterCoordinateY[t] = iterCoordinateY[t 1] + b; t++;//4 iterCoordinateX[t] = iterCoordinateX[t 1] + a12; iterCoordinateY[t] = iterCoordinateY[t 1]; t++;//5 iterCoordinateX[t] = iterCoordinateX[t 1]; iterCoordinateY[t] = iterCoordinateY[t 1] b; //t++;//6 //iterCoordinateX[t] = iterCoordinateX[t 1] + a13; //iterCoordinateY[t] = iterCoordinateY[t 1];

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59 t++; } if (TobeiterCoordinateY[i] > TobeiterCoordinateY[i + 1]) { t++;//2 iterCoordinateX[t] = iterCoordinateX[t 1]; iterCoordinateY[t] = iterCoordinateY[t 1] a11; t++;//3 iterCoordinateX[t] = iterCoordinateX[t 1] + b; iterCoordinateY[t] = iterCoordinateY[t 1]; t++;//4 iterCoordinateX[t] = iterCoordinateX[t 1]; iterCoordinateY[t] = iterCoordinateY[t 1] a12; t++;//5 iterCoordinateX[t] = iterCoordinateX[t 1] b; iterCoordinateY[t] = iterCoordinateY[t 1]; //t++;//6 //iterCoordinateX[t] = iterCoordinateX[t 1]; //iterCoordinateY[t] = iterCoordinateY[t 1] a13; t++; } if (TobeiterCoordinateY[i] < TobeiterCoordinateY[i + 1]) { t++;//2 iterCoordinateX[t] = iterCoordinateX[t 1]; iterCoordinateY[t] = iterCoordinateY[t 1] + a11; t++;//3 iterCoordinateX[t] = iterCoordinateX[t 1] b; iterCoordinateY[t] = iterCoordinateY[t 1]; t++;//4 iterCoordinateX[t] = iterCoordinateX[t 1]; iterCoordinateY[t] = iterCoordinateY[t 1] + a12; t++;//5 iterCoordinateX[t] = iterCoordinateX[t 1] + b; iterCoordinateY[t] = iterCoordinateY[t 1]; //t++;//6 //iterCoordinateX[t] = iterCoordinateX[t 1]; //iterCoordinateY[t] = iterCoordinateY[t 1] + a13; t++; } } } } public void ShowPoints() { Console.WriteLine("Coordinates of the square"); for ( int i = 0; i < 4; i++) {

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60 Console.WriteLine("X{0} = {1}", i, CoordinateX[i]); Console.WriteLine("Y{0} = {1}", i, CoordinateY[i]); } } public void ShowPointsIter() { // Specify file, instructions, and privelegdes FileStream file = new FileStream( "iterDataPoints.txt", FileMode.OpenOrCreate, FileAccess.Write); // Create a new stream to write to the file StreamWriter sw = new StreamWriter(file); // Write a string to the file //sw.WriteLine("Iteration coordinates"); Console.WriteLine("Coordinates of the square"); for ( int i = 0; i < size 5; i++) { sw.WriteLine("{0},{1},0", iterCoordinateX[i], iterCoordinateY[i]); Console.WriteLine("X{0} = {1}", i, iterCoordinateX[i]); Console.WriteLine("Y{0} = {1}", i, iterCoordinateY[i]); } // Close StreamWriter sw.Close(); // Close file file.Close(); } public void ShowPointsIter2() { // Specify file, instructions, and privelegdes FileStream file = new FileStream( "iterDataPoints2.txt", FileMode.OpenOrCreate, FileAccess.Write); // Create a new stream to write to the file StreamWriter sw = new StreamWriter(file); // Write a string to the file //sw.WriteLine("Iteration coordinates"); Console.WriteLine("Coordinates of the square"); for ( int i = 0; i < size 5; i++) { sw.WriteLine("{0},{1},0", iterCoordinateX[i], iterCoordinateY[i]);

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61 Console.WriteLine("X{0} = {1}", i, iterCoordinateX[i]); Console.WriteLine("Y{0} = {1}", i, iterCoordinateY[i]); } // Close StreamWriter sw.Close(); // Close file file.Close(); } public void ShowPointsIter3() { // Specify file, instructions, and privelegdes FileStream file = new FileStream( "iterDataPoints3.txt", FileMode.OpenOrCreate, FileAccess.Write); // Create a new stream to write to the file StreamWriter sw = new StreamWriter(file); // Write a string to the file //sw.WriteLine("Iteration coordinates"); Console.WriteLine("Coordinates of the square"); for ( int i = 0; i < size 5; i++) { sw.WriteLine("{0},{1},0", iterCoordinateX[i], iterCoordinateY[i]); Console.WriteLine("X{0} = {1}", i, iterCoordinateX[i]); Console.WriteLine("Y{0} = {1}", i, iterCoordinateY[i]); } // Close StreamWriter sw.Close(); // Close file file.Close(); } public void ShowPointsIter4() { // Specify file, instructions, and privelegdes FileStream file = new FileStream( "iterDataPoints4.txt", FileMode.OpenOrCreate, FileAccess.Write); // Create a new stream to write to the file StreamWriter sw = new StreamWriter(file); // Write a string to the file //sw.WriteLine("Iteration coordinates");

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62 Console.WriteLine("Coordinates of the square"); for ( int i = 0; i < size 5; i++) { sw.WriteLine("{0},{1},0", iterCoordinateX[i], iterCoordinateY[i]); Console.WriteLine("X{0} = {1}", i, iterCoordinateX[i]); Console.WriteLine("Y{0} = {1}", i, iterCoordinateY[i]); } // Close StreamWriter sw.Close(); // Close file file.Close(); } class Program { static void Main(string[] args) { SquareCoordinates Square0 = new SquareCoordinates(); Square0.FirstIteration(); Square0.Iteration(); Square0.ShowPoints(); Square0.ShowPointsIter(); Square0.SecondIteration(); Square0.Iteration(); Square0.ShowPoints(); Square0.ShowPointsIter2(); Square0.ThirdIteration(); Square0.Iteration(); Square0.ShowPoints(); Square0.ShowPointsIter3(); Square0.ForthIteration(); Square0.Iteration(); Square0.ShowPoints(); Square0.ShowPointsIter4(); } } } }

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63 APPENDIX B WEARABLE RFID READER PROTOTYPE SCHEMATIC

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64 APPENDIX C WEARABLE RFID READER PROTOTYPE PRINTED CIRCUIT B OARD

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65 APPENDIX D WEARABLE RFID READER BILL OF MATERIALS Bill of Materials (BOM): Project: Wearable RFID reader v1.0 Date: 04/09/2009 Digikey 1. RFID READER MODULE M9 CF FORMAT Part Number: 753-1014-ND Package: Compact Flash http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=753 -1014-ND Price: $274.00 2. MODULE BLUETOOTH W/ANT CLASS1 Part Number: 740-1007-ND Package: Module http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=740 -1007-ND Price: (Price break: 10) Unit: $26.95 Total: $269.50 3. Push Button On/OFF controller IC Part Number: LTC2950CTS8 -1#TRMPBFCT-ND Package: TSOT23 -8 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LTC2950CTS8 1%23TRMPBFCT -ND Price: $4.17 4. Voltage Regulator 5V output Part Number: LP3963ES -5.0-ND Package: TO263-5 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LP3963ES 5 .0 -ND Price: $3.70 5. Voltage Regulator 3.3V output Part Number: LT1963AEQ 3.3#PBF -ND Package: DPak http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LT1963AEQ-3.3%23PBF -ND Price: $5.50 6. Reset IC Part Number: MCP810T -485I/TTCT-ND Package: SOT -23-3

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66 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MCP810T485I/TTCT-ND Price: 0.48 7. LED a. LED 3.2X1.6MM 570NM GRN CLR SMD -50 Part Number: 754-1152-1 -ND http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=754 -1152-1 -ND Price: $0.30 b. LED 3.2X1.6MM 470NM BLUE CLR SMD 50 Part Number: 754-1155-1 -ND http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=754 -1155-1 -ND Price: $0.56 8. SMD DIP Switch Part Number: CT2192MST ND http://search.digikey.co m/scripts/DkSearch/dksus.dll?Detail&name=CT2192MST-ND Price: $0.49 9. Mini USB Part Number: A31727CT -ND http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&nam e=A31727CT -ND Price: $1.62 10. Capacitor a. C1 -C2 : 18pF Ceramic Package: 0805 SMD Part Number: PCC180CNCT -ND Price: $0.48 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PCC180CNCT -ND b. C3: 68uF Tantalum Capacitor Package: 3216 -10 (EIA) 1206 SMD Part Number: 493-2912-1 -ND Price: (Price break:10) Unit: $0.92 Total: $9.24 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=493 -2912-1 -ND c. C4: 0.033uF Package: 0805 SMD Part Number: PCC1834CT -ND Price: $0.31 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PCC1834CT -ND d. C5: 0.082uF Package: 0805 SMD

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67 Part Number: PCC1811CT -ND Price: $0.40 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PCC1811CT -ND e. C6: 0.01uF Package: 0805 SMD Part Number: PCC103BNCT -ND Price: $0.25 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PCC103BNCT -ND f. C7 -C11-C12C13: 0.1uF Ceramic Decoupling Capacitor Package: 0603 SMD Part Number: 709-1004-1 -ND Price: (Price break:10) Unit: $0.771 Total: $7.71 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=709 -1004-1 -ND Quantity: 80 g. C8: 33uF Tantalum Capacitor Package: 3216 -10 (EIA) 1206 SMD Part Number: 493-2906-1 -ND Price: (Price break:10) Unit: $0.655 Total: $6.55 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=493 -2906-1 -ND h. C9 -C10: 10uF Tantalum Capacitor Package: 3216-10 (EIA) 1206 SMD Part Number: 511-1446-1 -ND Price: $0.33 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=511 -1446-1 -ND 11. Resistor a. R1 -R2: 33ohm Thick Film Chip Resistor Package: 0805 SMD Part Number: P33ACT -ND Price: (Price break:10) Unit: $0.07 Total: $0.77 http://search.digikey.com/scripts/DkSearch/dks us.dll?Detail&name=P33ACT -ND b. R3 -R6 R7: 330 ohm Package: 0805 SMD Part Number: P330ACT -ND Price: (Price break:10) Unit: $0.07 Total: $0.77 http://search.digikey.com/ scripts/DkSearch/dksus.dll?Detail&name=P330ACT -ND

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6 8 c. R4: 10K ohm Package: 0805 SMD Part Number: P100KACT -ND Price: (Price break:10) Unit: $0.07 Total: $0.77 http://se arch.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P100KACTND d. R8 -R9: 1K ohm Package: 0805 SMD Part Number: P1.0KACT -ND Price: (Price break:10) Unit: $0.07 Total: $0.77 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P1.0KACTND 12. Transistor a. T1 Part Number: MMBT2222AFSCT -ND http://search.digikey.com/ scripts/DkSearch/dksus.dll?Detail&name=MMBT2222AFSCT ND Price: $0.09 Heilind Electronics 13. Compact Flash: http://www.hirose.co.jp/cataloge_hp/e64070010.pdf Part Number: MI20 -50PD -SF(71) http://estore.heilind.com/partdetail.asp?pn=MI20 -50PD -SF(71)&dp=HIRMI20 50PD -SF(71)&cp = Price: $4.4 Quantity: 20

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69 APPENDIX E RETURN LOSS AND RADI ATION SIMULATIONS FOR FRAC TALS Antenna ID iteration # iteration factor Center frequency (MHz) Max Gain (dBi) Return Loss (RL) (dB) BW(RL> 9.5dB)(MHz) h(mm) = 1 0 0 915 4.71 -45.00 12.00 4.60 1.57 76.27

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70 LIST OF REFERENCES 1. J. Landt The history of RFID, IEEE Potentials, vol. 24 no. 4 pp. 8 11, October 2005. 2. H. Stockman, Communication by means of reflected power, Proceedings of the IRE, pp 11961204, October 1948. 3. A. Koelle, S. Depp, and R.Freyman, Short range radio telemetry for electronic identification using modulated backscatter, Proceedings of IEEE vol. 63, no. 8 pp. 12601261, August 1975. 4. K. Finkenzeller RFID Handbook West Sussex: John Wiley & Sons Ltd, 2003. 5. S. Lahiri RFID Sourcebook, Indianapolis : Prentice Hall PTR 2005. 6. D. Engles, S.E. Sarma, Standardization Requirements within the RFID Class Structure Framework White Paper Series AUTOIDLABS WP SWNET 011, September 2005. 7. C. Balanis, Ant enna Theory Analysis and Design. New York: John Wiley & Sons Ltd, 1997. 8. D Thiel, .,S. Smith, Switched Parasitic Antennas for Cellular Communications, Norwood : Artech House Inc,. 1997. 9. D.M Pozar Microstrip Antennas, Proceedings of IEEE vol.80, no.1 pp.7981, January 1992. 10. T. Milligan, .. Modern Antenna Design, New Jersey : John Wiley & Sons Inc, 2005. 11. E.H. Van Lil and A.R. Van de Capelle, TransmissionLine Model for Mutual Coupling Between Microstrip Antennas, IEEE Trans. Antenna Propagation, vol. AP32 no.8 pp.816821, August 1984. 12. E.O. Hammerstad, Equations for Microstrip Circuit Design, Proceedings Fifth European Microwave Conference pp. 268272, September 1975. 13. R. Bancroft, Microstrip and Printed Antenna Design, Atlanta: Noble Publishing Corporation, 2004. 14. I.J. Bahl, P. Bhartia, Microstrip Antennas, Dehman, MA : Artech House, I.J.,1980. 15. A. Derneryd, Linearly Polarized Microstrip Antennas, IEEE Trans. Antennas and Propagation, AP 24, pp.846851, 1976. 16. M. Schneider, Microstrip Lines for Microwave Integrated Circuits Bell Syst. Tech. Journal, 48, pp.14211444, 1969.

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71 17. E .Hammerstad, F.A Bekkadal. Microstrip Handbook, ELAB Reportm STF 44 A741169, University of Trondeim, Norway, 1975. 18. G .K umar Ray, K.P. Broadband Microstrip Antennas, Boston: Artech House, 2003. 19. Garg, R., Bhartia, P., Bahl, I., Ittipiboon, A., Microstrip Antenna Design Handbook, Bosto : Artech House, 2001. 20. M Kara,.,Formulas for Computation of the Physical Properties of Rectangular Microstrip Patch Antenna Elements with Various Substrate Thickness Microwave and Optical Conference, Vol.12, pp. 234239, 1996. 21. S. Kim, H. Park, D. Lee, J.Choi., A Novel Design of an UHF RFID Reader Antenna for PDA Proceeding of AsiaPasific Microwave Conference, 2006. 22. F. Chang, K. Wong, T. Chiou, Low cost Broadband Circularly Polarized Patch Antenna, IEEE Trans. on Antennas and Propagation, Vol.51, No.10.pp30063009, October 2003. 23. P.Lin, H. Teng, Y. Huang, Design of Patch Antenna for RFID Reader Applications, International Conf. on ASID, Vol. 20, pp.193196, August 2009. 24. J. Lee, N.Kim, C. Pyo, A Circular Polarized Metallic Patch Antenna for RFID Reader Asia Pacific Conference on Communications, October 2005. 25. Z. Wu, S. Lai, Miniturized Microstrip Array for the UHF Band RFID Reader, Microwave and Optical Technology Letters, Vol.48, pp.12991301, July 2006. 26. I. Kim, T. Yoo, J. Yook, H. Park, The Koch Island Fractal Microstrip Patch Antenna, Antennas and Propagation Society Int. Semp. Vol.2. pp.736739,2001. 27. D. Werner, S. Ganguly, An Overview of Fractal Antenna Engineering Research, IEEE Antennas and Propagation Magazine, Vol.45, Iss.1. pp.3857, February 2003. 28. J. Gianvittorio, Y. Rahmat, Fractal Antennas: A Novel Antenna Miniaturization Technique and Applications IEEE Antennas and Propagation Magazine, Vol.44, Iss.1. pp.2036, 2003. 29. J. Ali, A New Reduced Size Multiband Patch Antenna Structure Based on Minkowski Pre Fractal Geometry, Journal of Eng. And Applied Sciences vol.2. pp.11201124, 2007. 30. L. Ukkonen, L. Sydanheimo, M.Kivikoski, Read Range Performance Comparison of Compact Reader Antennas for a Handheld UHF RFID Reader, IEEE International Conference on RFID, pp.6370, March 2007.

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72 BIOGRAPHICAL SKETCH Ahmet Erdem Al tunbas was born in Trabzon, Turkey in 1982. He received his b achelors degree in Telecommunication Engineering from Istanbul Technical University, Turkey. He has been working on Radio Frequency Identification area since 2004 and involved with numerous projects with RFID technology. His research interest mainly includes RFID, Electronic hardware design, antenna design, microcontrollers and RF propagation. In his spare time he enjoys outdoor activities and spending time with family and friends.