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3 ABSTRACT MOXON BASED RFID TAG READER AND GPS ANTENNA by Haojiog Liu Moder commuicatio applicatios at UHF frequecies require ateas with wide bad, high forward gai, low backward radiatio, high cross-polarizatio, small size ad low maufacture cost. The Moxo atea based o a two elemet Yagi-Uda atea over the groud reflector is oe of the most favorite ateas for HAM operators which ca produce outstadig frot to back ratio of radiated power, good match over the desired bad ad relatively low elevatio height. A sequece of topologies has bee proposed from a sigle vertical elemet to two vertical elemets of the Moxo arms, util the lately pateted Broadbad Circularly Polarized Moxo Based Ateas for UHF satellite commuicatios (SATCOM). The logic was to obtai the best possible performace based o Fao-Chu limits for electrically small atea with maximum radiatig elemets i a give volume. This dissertatio is a extesio of this cofiguratio to cover Radio Frequecy IDetificatio (RFID) (850 MHz-1050 MHz) ad Global Positioig System (GPS) (cetered at 1227 MHz ad 1575 MHz) bads. Prototype ateas are built based o HFSS-11 simulatios ad experimetal measuremets yielded satisfactory results. Various desig parameters of the proposed complex atea are optimized to obtai a sigificat size reductio ad much improved performace tha the commercial couterpart ateas.

4 MOXON BASED RFID TAG READER AND GPS ANTENNA by Haojiog Liu A Thesis Submitted to the Faculty of New Jersey Istitute of Techology i Partial Fulfillmet of the Requiremets for the Degree of Master of Sciece i Electrical Egieerig Departmet of Electrical ad Computer Egieerig May 2012

5

6 APPROVAL PAGE MOXON BASED RFID TAG READER AND GPS ANTENNA Haojiog Liu Dr. Edip Niver, Thesis Advisor Professor of Electrical ad Computer Egieerig, NJIT Date Dr. Gerald Whitma, Committee Member Professor of Electrical ad Computer Egieerig, NJIT Date Dr. Ali N Akasu, Committee Member Professor of Electrical ad Computer Egieerig, NJIT Date

7 BIOGRAPHICAL SKETCH Author: Haojiog Liu Degree: Master of Sciece Date: May 2012 Udergraduate ad Graduate Educatio: Master of Sciece i Electrical Egieerig, New Jersey Istitute of Techology, Newark, NJ, 2012 Bachelor of Sciece i Electrical Egieerig, Uiversity of Electroic Sciece ad Techology of Chia, Chegdu, P. R. Chia, 2010 Major: Electrical Egieerig iv

8 To my beloved family, teachers ad frieds v

9 ACKNOWLEDGMENT I would like to express my deepest appreciatio to Professor Edip Niver. Dr. Niver served as my thesis advisor. He gave me the chace to do work o his recetly developed cocept ad providig valuable isight ad ituitios. He gave me costat support ad ecouragemet throughout the whole year of my study. Researcher Oksaa Mazhura helped me greatly durig my thesis ad her optimistic suggestios always ecouraged me. Special thaks are give to Professor Gerald Whitma ad Professor Ali N. Akasu for participatig i my committee. I also appreciate the support ad help from my girlfried Yuche Guo ad my fried Yuteg Zheg ad Yifei Zhag. Fially, all my special thaks to my beloved family for their edless support, love ad belief i me. vi

10 TABLE OF CONTENTS Chapter Page 1 INTRODUCTION Atea for Radio Frequecy IDetificatio Atea for Global Positioig System. 2 2 MOXON (TWO ELEMENT YAGI-UDA) ANTENNA Itroductio Yagi-Uda Atea: Two Elemets 4 3 ELECTRICALLY SMALL ANTENNA Electrically Small Atea Physical Limitatios of Omidirectioal Atea Field of a Vertically Polarized Omidirectioal Atea Far Field Characteristics Equivalet Circuits for Atea Criterio I: Maximum Gai Criterio II: Miimum Q Criterio III: Maximum G/Q Other Limitatios for Electrically Small Ateas Mai Miiaturizatio Techiques Effect o the Performace SIMULATION, EXPERIMENTAL RESULTS AND DISCUSSION Simulatio Procedures ad Results Simulatio of RFID Atea Simulatio of GPS Atea vii

11 TABLE OF CONTENTS (Cotiued) Chapter Page Optimizatio of Parameters of the RFID Atea Optimizatio of Parameters of the GPS Atea Experimetal Procedure ad Results Compariso with Other Ateas CONCLUSION REFERENCES viii

12 LIST OF TABLES Table Page 4.1 Compariso of RFID tag Reader Ateas Compariso of GPS Ateas 52 ix

13 LIST OF FIGURES Figure Page 2.1 A array of two parallel dipoles, oe drive, oe parasitic Two parallel Dipoles H-Plae Power Patters for Two-Elemet Yagi-Uda Arrays Schematic diagram of a vertically polarized omidirectioal atea Equivalet circuit for a vertically polarized omidirectioal atea Equivalet circuit of Z Q for omidirectioal atea. Criterio: Max Gai with fixed umber of terms. I ormal gai. II twice the ormal gai G/Q of omidirectioal atea. Criterio: Max G/Q Bet dipole atea over a groud plae Two perpedicular bet dipole ateas for circulaly polarzatio radiatio Bet bow tie atea for RFID S 11 of RFID atea Gai of RHCP ad radiatio patter at 950 MHz Radiatio Patter at 950 MHz Bet bow tie atea for GPS S 11 of GPS atea Gai of RHCP ad radiatio patter at 1227 MHz Radiatio Patter at 1227 MHz Gai of RHCP ad radiatio patter at 1575 MHz Radiatio Patter at 1575 MHz x

14 LIST OF FIGURES (Cotiued) Chapter Page 4.13 Atea layout with optimizatio parameter umbered from 1 to Layout of bet bow tie atea for RFID Layout of bet bow tie atea for GPS Retur loss test setup for RIFD atea Retur loss test results for RFID atea Retur loss test results for GPS atea VSWR measuremet for ew bet bow tie RFID atea (gree) ad Poytig Patch A 0025 atea (blue) S 11 measuremet for ew bet bow tie RIFD atea (gree) ad Poytig Patch A 0025 atea (blue) xi

15 CHAPTER 1 INTRODUCTION Atea is commoly described as a trasducer that coverts electric currets/em waves to EM waves/electric currets depedig o beig used i a trasmittig/receivig mode. Moder applicatios of ateas ecompass various fuctios, commuicatio systems, radars, RFID, GPS are just few of the whole array of that is beig used today. Various costraits ad specificatios arise depedig o the eeds of the particular applicatio. Here, we focus o optimizig gai ad badwidth for reduced physical dimesios of the RFID tag reader ad GPS atea utilized i circular polarizatio excitatio. This work is a extesio of the previously developed SATCOM atea [1] based o Moxo atea [2] to RFID ad GPS frequecy bads. 1.1 Atea for Radio Frequecy IDetificatio Radio Frequecy IDetificatio (RFID) is a wireless o-cotact system use of radio frequecy electromagetic fields to probe remote tags to retrieve/chage data for idetificatio ad trackig through a tag reader [3]. A basic RFID system cosists of two elemets, reader ad tags. The reader is a scaer uit ad the tags are sets of remote traspoders which could either be passive or active. Every tag icludes a atea ad a microchip trasmitter with iteral read/write memory. Tags could be classified as passive tags with o iteral battery or as active tags with a battery. RFID techology has several stadardized bads of operatio. Ultra-high frequecy (UHF, MHz) bad allows 1

16 2 loger commuicatio rages ad smaller tags especially i sesor etwork applicatios. RFID ateas are usually desiged based o several factors [4], such as operatig frequecy bad, tag s readig distace from the reader, tag s kow orietatio to the reader, tag s arbitrary orietatio to the reader, polarizatio of the reader atea. Higher gai of the RFID Tag reader atea is critical i icreasig the physical rage betwee the tag reader ad the tag. Circular polarizatio of the tag reader atea improves the overall receptio due to tag ateas which are mostly liearly polarized. 1.2 Atea for Global Positioig System Global Positioig System (GPS) [5] is a space-based satellite avigatio system that ca provide locatio ad time iformatio. GPS system operates i dual frequecy bads at L1 ( MHz) ad L2 ( MHz) bads. L1 bad is used for civilia purposes whereas L2 bad is ecrypted for demadig applicatios that require better accuracy ad altitude iformatio ad primarily used by military. There are may importat parameters such as gai, efficiecy, radiatio patter ad badwidth that should be cosidered carefully for a successful GPS receptio i terms of the sigal to oise ratio performace at the receiver. A radiatio patter with a broad frot lobe is required to obtai uiform coverage of ecessary satellites. The radiatio patter also should have a sharp slope for low elevatio agles to avoid multipath ad tropospheric effects. A high cross-polarizatio will also help to provide discrimiatio betwee the direct ad reflect sigals to elimiate the multipath effects. This thesis is divided ito five chapters. Chapter 1 itroduces the basic idea of atea for RFID ad GPS applicatios. Chapter 2 describes the priciple of the Moxo

17 3 atea (two elemet Yagi-Uda atea). Chapter 3 icludes the defiitio of electrically small atea, the physical limitatios for electrically small atea ad some miiaturizatio techiques. Chapter 4 is the procedure of simulatio ad results for the simulatio ad prototypes that have bee built. It also cotais some compariso betwee the ateas desiged i the thesis ad some other ateas that already i the practice. Chapter 5 summarizes coclusios.

18 CHAPTER 2 MOXON (TWO ELEMENT YAGI-UDA) ANTENNA 2.1 Itroductio Yagi-Uda atea is a kid of directioal atea cosist oe drive elemet (usually a dipole) ad additioal parasitic elemets (reflector ad oe or more directors). The reflector elemet is loger tha the drive dipole ad the director elemets are shorter tha the drive dipole. Directio of radiatio is from the reflector towards the drive elemet ad the director(s). Yagi-Uda atea is popular because of its highly directioal properties ad high gai. However, this high gai ca oly be achieved i a arrow rage of the specified badwidth. 2.2 Yagi-Uda Atea: Two Elemets A two elemet Yagi-Uda atea cosist two parallel dipoles with a distace d apart. Oe coected to the source ad the other shorted. The geometry is show i Figure 2.1. [6] 4

19 5 Figure 2.1 A array of two parallel dipoles, oe drive, ad oe parasitic [6]. The mesh equatios for this array are V I Z I Z I Z I Z (2.1) ad I I Z (2.2) Z Sice the array factor is give by I e jkd I 2 cos ( ) 1 (2.3) 1

20 6 Oe ca obtai that the shape of the patter is domiated by the spacig d / ad by Z 12 / Z 22. It is also kow that if the legths of the two dipoles are ear first resoace, the phase of the mutual impedace as a fuctio of d / ca be igored because it is quite isesitive to the value of 2l 1 / ad 2l 2 /. So that the phase of I 2 / I 1, is cotrolled by the phase of Z 22 as show i (2.2). From the derivatio of two parallel dipoles, the mutual impedace Z 12 ca be obtaied with equatio (2.4) ad (2.5): Figure 2.2 Two parallel Dipoles [6]. si kr si kr kr R ( 2cos kl ) si k( l ) d( ) (2.4) 30 l2 / 1 2 si si kl 2 / 1 si kl l 2 r1 / r2 / r / cos kr cos kr kr X ( 2cos kl ) si k( l ) d( ) (2.5) 30 l2 / 1 2 cos si kl 2 / 1 si kl l 2 r1 / r2 / r /

21 7 Where (0, y, z+ 2 ) is the positio of a poit o the axis of dipole 2 with the cetral poit of dipole 2 at the arbitrary positio (0, y, z) i the YZ-plae, ad dipole 1 is cetered at the origi. (2.7): Z 22 ca also be obtaied usig Kig-Middleto secod-order solutio (2.6) ad 4 4 a m a R( kl, ) am( kl) ( ) (2.6) m a m a X ( kl, ) bm( kl) ( ) (2.7) m0 0 Where a / is the ormalized radius, a m ad b m are expasio coefficiets. Sice the goal is to obtai a ed-fire patter with this two elemet Yagi-Uda atea, if 2l 1 / is give, oe ca seek if there are combiatios of d / ad 2l 2 / which will ehace ed-fire radiatio. As the iput impedace ofte desired to be pure real, it is eeded to adjust the ratio of 2l 1 /. From (2.1), V I Z ZIN Z Z Z (2.8) I I Z The imagiary part of Z 11 ad the imagiary part of - Z 12 / Z 22 has to cacel each other. For a two elemet Yagi-Uda atea, a forward optimum ad a rearward optimum caot be achieved at the same spacig. Examples of forward radiatio ad rearward radiatio are show i Figure 2.3:

22 8 Figure 2.3 (a) H-Plae Power Patters for Two-Elemet Yagi-Uda Arrays (forward) [6]. Figure 2.3 (b) H-Plae Power Patters for Two-Elemet Yagi-Uda Arrays (rearward) [6]. Moxo atea [1] is a extesio of the two elemet Yagi-Uda array where liear dipole is bet over the reflector (groud). Such a combiatio results i higher forward gai, weak back lobe radiatio ad uiform impedace over a sufficiet badwidth.

23 CHAPTER 3 ELECTRICALLY SMALL ANTENNA 3.1 Electrically Small Atea Electrically small atea has bee a attractive feature for umerous applicatios where the largest dimesio of the atea is o more tha oe-teth of the wavelegth [7]. However, this costrait could be relaxed further to maximum physical dimesios of less tha half a wavelegth. It is almost always desirable to have a smaller atea without compromisig the performace. Electrically small atea has various applicatios i HF ad VHF bads for tactical radios for mobile use, SATCOM ateas o broad of vehicles, helicopters ad ships are just few worth to metio. Performace limitatios such as gai ad efficiecy become obvious as atea dimesios get smaller followed by impedace match over the desired frequecy bad. Most applicatios are embedded i the eviromet with a fiite groud plae resultig i back lobe radiatio as well as reduced cross-polarizatio. Cosiderig above parameters Moxo atea [1] has bee very popular amog the HAM operators worldwide. Moxo atea is kow for its compact size ad its directive properties due to the presece of the groud plae. Keepig i mid the physical costraits placed as Fao-Chu limits for electrically small ateas [8]-[9] resultig i electrically small atea with maximum radiatig elemets i a give volume. 9

24 Physical Limitatios of Omidirectioal Atea Electrically small ateas pose a major problem i regard to their electrical performace [10]. The radiatio resistace of these ateas decreases rapidly with decreasig size but have a large reactive compoet, that makes the matchig very difficult ad iefficiet due to the sigificat impedace of large reactive compoet i the system that cotributes to system loss. As a cosequece, the atea performace parameters such as radiatio efficiecy, S/N-ratio, ad badwidth ted to deteriorate to uacceptable levels. The limitatios of omidirectioal ateas are estimated based o the followig three criteria: - Maximum gai (G) for a give complexity of the atea structure, - Miimum Q, - Maximum ratio of G/Q Field of a Vertically Polarized Omidirectioal Atea Cosider the field of a vertically polarized omidirectioal atea lies totally withi a spherical surface of a radius a. Uder the spherical coordiate system ( R, ),, with a arbitrary curret distributio ad atea structure, the three o-vaishig field compoets ca be expressed i terms of a complete set of orthogoal, spherical waves, propagatig radially outward. For a vertically polarized omidirectioal atea, oly TM modes exit. H A P (cos ) h ( kr) 1 h ( kr) ER j A ( 1) P (cos ) kr 1 1 d E j A P (cos ) [ Rh ( kr)] kr dr (3.1)

25 11 where P (cos ) is the Legedre polyomial of order, P 1 (cos ) is the first associated Legedre polyomial, h ( kr ) is the spherical Hakel fuctio of the secod kid, k 2 /, / is the wave impedace of a plae wave i free space ad 1/ is the velocity of a plae wave i free space. A is a complex coefficiets that ca be determied from the boudary coditios if the atea structure is give. I the equatios, the time factor j t e is omitted. Figure 3.1 Schematic diagram of a vertically polarized omidirectioal atea [10].

26 Far Field Characteristics I the far field, the asymptotic field becomes jkr e E A P kr H E ( 1) (cos ) (3.2) by the defiitio of directivity gai, G( ) A( 1) P (cos ) 4 E E sidd A ( 1) 2 1 (3.3) The deomiator is obtaied from the orthogoality of the associated Legedre polyomials: 2 1 [ P (cos )] si 0 ad 2 ( 1) d [ P (cos )] '(cos )si 0 0 P d for ' I the equatorial plae, /2, P 1 (0) 0 for eve ad (0) ( 1) P! 1 2 (!) for odd Thus all the eve terms have o cotributio to the radiatio field alog the equator plae. To obtai a high directivity gai i the equatorial plae, it is ecessary to have A 0 for eve

27 13 While all the A for odd terms have the same phase agle. Cosider all A to be positive real umbers for odd ad zero for eve, the directivity gai o the equatorial plae ca be rewritte as G( ) [ A( 1) P (0)] A 2 ( 1) 2 1 (3.4) Equivalet Circuits for Atea The complete equivalet circuit for the atea is give i Figure 3.2. Figure 3.2 Equivalet circuit for a vertically polarized omidirectioal atea [10].

28 14 The circular box is a couplig etwork that represets the space iside the geometrical sphere is show i Figure 3.1. The iput termial represets the source of the atea. Because of the orthogoal properties of the spherical waves, there will be o couplig betwee ay two of the spherical waves outside the sphere. That meas the total eergy, electric or magetic is equal to the sum of eergies of each spherical wave compoet. I that case, it is possible to replace the space outside the sphere by a umber of idepedet equivalet circuits, each with a pair of termials coected to the box which represets the iside of the sphere. The umber of the termials is N+1 while N is the umber of spherical waves used i describig the field outside the sphere. The curret, voltage, ad impedace of the equivalet circuits are: A 4 ( 1) V 4 j( h)' k 21 A 4 ( 1) I 4 h k 21 Z j( h )'/ h (3.5) where d ka, h h( ), ( h)' h( ). d The impedace Z ca also be writte as a cotiued fractio: Z j 1 (3.6) j j This fuctio represets a cascade circuit of series capacitaces ad shut iductaces termiated with a uit resistace. This circuit is show i Figure 3.3.

29 15 Figure 3.3 Equivalet circuit of Z [10]. The capacitaces ad iductaces are proportioal to the ratio of the radius of the sphere to the speed of light. To approximate the equivalet circuit of Z use simple RLC circuit that has the same frequecy behavior of the operatig frequecy, R, C ad L ca be calculated by (3.7): R C L h 2 2 dx X [ ] 2 d 1 dx [ X ] 2 d 1 (3.7) where 2 X [ j ( j)' ( )'] h, j ad are the spherical Bessel fuctios of the first ad secod kid. The average power dissipatio i ca be obtaied. Zad the average electric eergy stored i Z P 2 ( 1) A ( ) 2 21 k (3.8)

30 16 W A dx X 2(2 1) k d ( 1) 2 2 ( ) [ h ] (3.9) Defie Q as 2W 1 2 dx Q h [ X ] (3.10) P 2 d Assume there is o coductio loss i the atea structure, there will be o electrical eergy stored besides the form of travellig wave ad the average magetic eergy stored beyod the termials is equal to the average electric eergy stored at operatig frequecy. Now, defie a quatity Q at the iput termials: Q 2ω times the mea electric eergy stored beyod the iput termial power dissipated i radiatio I this case, if this Q is low, the iput impedace of the atea varies slowly with frequecy, that meas the atea is potetially widebad. If it is high, the badwidth of the atea is equal to the reciprocal of Q. Now, Q ca be writte as: Q A 2 ( 1) Q( ) ( 1) A 2 1 (3.11) where Q is give i (3.10) Criterio I: Maximum Gai Wheever the atea s structure is give, it is always demaded that the atea ca yield the possible maximum gai. Differetiatig the gai i the equatorial plae, [Eq. (3.4)], with the respect to the coefficiet A ad settig the derivative to zero,

31 17 ( 1) ( 1) (0) 2 1 P 1 ( 1) 2 1 A( 1) P (0) A A Noticed that there are as may equatios of this form as the umber of terms i the A series, therefore, A ca be solved i terms of the first coefficiet A 1 as 1 2(2 1) 2 1 A ( 1) P (0) A1 3 ( 1) (3.12) Remember that A 0 for eve, the correspodig gai ad Q of the atea will lead to N G( ) a (3.13) 2 1 N N Q a Q / a (3.14) 1 1 where N is a odd iteger idicate the order of the series, which represeted the complexity of the source distributio, ad a 2 1 [ P (0)] ( 1) 1 2 (3.15) Except for the first few terms, a 4/ (3.16) Uder this criterio, the gai has o relatioship with the size of the atea. It idicates that a extremely high gai ca be achieved by a ifiite small atea. However, i Equatio (3.14), the deomiator has approximately equal amplitudes while the umerator is a ascedig series of ( N 1) / 2 terms. For ay give value of 2 a /, Q icreases with at a rapid rate. Whe 2 a / greater tha N, Q is of the

32 18 order of uity or less, idicatig that the atea potetially a broadbad system. Whe 2 a / smaller tha N, Q will rises rapidly as 2 a / decreases. The trasitio occurs at correspodig gai is 2 a/ N (3.17) 2 2 a 4a G (3.18) This gai is called the ormal gai for omidirectioal atea, ad it is equal to the gai obtaied from a curret distributio of uiform amplitude ad phase alog a lie of legth 2a. I Figure 3.4, curve I shows the ormal Q for the omidirectioal atea. Curve II shows a gai twice the ormal gai. It is obvious that i order to make it happeed, twice as may as terms are eeded, ad a high Q is required. The slop of curve II idicates the difficulty of gettig additioal gai as the ormal gai icreases.

33 19 Figure 3.4 Q for omidirectioal atea. Criterio: Max Gai with fixed umber of terms. I ormal gai. II twice the ormal gai [10] Criterio II: Miimum Q Differetiatig Q fuctio with respect of ( 1) ( 1) Q A A Q A, Q s will have differet values whe varies 2 a / are give. Hece the equatio above ca be satisfied whe there is oly oe term uder the summatio sig. The Q of atea is equal to the Q of the term used. Sice Q 1 has the smallest amplitude, it ca be

34 20 cocluded that the ifiitesimally small dipole has the potetially broadest badwidth of all ateas. The gai of a ifiite small atea is Criterio III: Maximum G/Q I most cases, it is impossible to give a ifiite large Q i order to obtai a huge gai, ad a gai of 1.5 is also ot acceptable. Hece a compromise betwee maximum gai ad miimum Q is required. So, the maximum ratio of the gai to Q is cosidered. The problem is to fid a proper combiatio of Form Equatios (3.4) ad (3.11) A s for maximum G/Q. 1 2 G [ A( 1) P (0)] Q 2 ( 1) A Q (3.19) With the same method used before, 1 2(2 1) Q 2 A ( 1) P (0) A1 3 ( 1) 1 1 Q (3.20) The correspodig values of G, Q ad the ratio G/Q are: [ a / Q ] G a / Q 2 2 (3.21) a / Q Q a / Q 2 (3.22) G / Q a / Q (3.23) where a 2 1 [ 1 (0)] 2 P. ( 1) I above equatios, cosider Q to be uity wheever its actual value is equal to or less tha uity. Sice the series i (3.21) ad (3.22) coverge rapidly as N icreases, the

35 21 gai approaches asymptotically the value of 4 a / which is the ormal gai prove before. Curves of G/Q are show i Figure 3.5. As i practical, it is always broadbad is always wated, that meas Q is required to be low, so it is this physical limitatio, amog others, which limits the gai of ateas to the approximate value of 4 a /. For horizotally polarized omidirectioal atea, the aalysis follows that of the vertically polarized atea, ad for circularly polarized atea, it is a combiatio of both vertically polarized atea ad horizotally polarized atea. The results for horizotal polarized atea ad circularly polarized atea stay the same with the vertically polarized oe. The coclusio is that i order to obtai a gai higher tha the ormal gai, it is a must to sacrifice the badwidth uder the most favorable coditios.

36 22 Figure 3.5 G/Q of omidirectioal atea. Criterio: Max G/Q [10]. 3.3 Other Limitatios for Electrically Small Ateas There are may other limitatios for the electrically small atea. I practical, the performace of atea desiged o the free space basis always will be affected by the

37 23 objects i the eighborhood. Objects earby will give additioal scattered radiatio because of the iduced curret ad also will distract the origial curret o the atea structure. For badwidth, it was iterpreted freely as the reciprocal of the Q factor. But i real, the badwidth ca be icreased by choosig a proper matchig etwork. 3.4 Mai Miiaturizatio Techiques Effect o the Performace [11] I order to obtai better performace, there are several methods ca be used i the real practice. - Loadig atea with lumped elemets. As we kow that electrically small atea will have a small radiatio resistace ad a strog reactive part of the impedace, it is logical to loadig them reactively. A matchig etwork will usually ecessary to match the radiatio resistace to the trasmissio lie. The effect of loadig atea with lumped elemet will be, if the added elemet has losses, the efficiecy will decreased, ad if the added elemet is lossless, the atea s quality factor will be ehaced which meas the badwidth will be reduced. - Makes some parts of the atea could be treated as virtual groud plae or equivalet short circuits may help to reduce the physical size. - Optimizig the geometry of the atea. This method cotais geometrical loadig with otches, slots bed ad curvature. Due to the curret cocetratio, the efficiecy will decrease ad the badwidth will be decreased due to frequecy sesitivity of the techique.

38 24 Overall coclusio is that if the equivalet volume is filled with maximum umber of radiatig elemets cotaiig currets with uiform distributios, the atea gai will be maximized. This cocept has bee exteded to Moxo ateas for SATCOM applicatio [1].

39 CHAPTER 4 SIMULATION, EXPERIMENTAL RESULTS AND DISCUSSION 4.1 Simulatio Procedures ad Results Moxo atea is kow for its compact size ad its directive properties due to the presece of the groud plae; a sketch of the bet dipole atea is show i Figure 4.1 [1]. The legth of the oe arm of the dipole is L+W, ad the arm is beded towards the groud from L distace away from the ceter of the dipole. The bottom of the dipole is H away from the groud plae. The bet dipole is fed with a iput from the ceter. A circularly polarizatio ca be achieved by placig two bet dipole ateas perpedicular to each other show i Figure 4.2, oe i x-z plae ad the other i y-z plae ad feedig though a hybrid quadrature coupler. Figure 4.1 Moxo atea [1]. 25

40 26 Figure 4.2 Two perpedicular Moxo ateas for circularly polarizatio radiatio [1]. The first topology studied was a sigle vertical elemet Moxo atea, ad the two vertical elemets Moxo atea. After that, wideed strip arm elemets were ivestigated to uderstad its effects o icrease of the badwidth. This idea was based o Fao-Chu limits which idicate that more metallizatio i the radiatig cofiguratio that fill the volume would yield higher gai for electrically small atea. Further, wideig the strips lead to further improvemet i the performace cofirmed by Fao-Chu limits for electrically small atea with maximum radiatig elemets i a give volume. Furthermore, splittig the tapered bow tie elemets [12] icreased the volume filled with radiatig elemets improved overall performace. Fially, beds at the tip of the tapered sectios parallel to the groud pushig to optimized performace. Durig the simulatio, great attetio was paid o fidig the effects o overall performace of each physical parameter of the atea i terms of its dimesios ad shape.

41 Simulatio of RFID Atea The purpose of RFID atea simulatio was to obtai wider badwidth, lower retur loss, higher gai ad better cross-polarizatio. The operatig frequecy was first desiged to be cetered at 950 MHz, ad the, every parameter of the atea was carefully optimized separately to fid its effect o the overall performace i terms of low frequecy resoat poit, high frequecy resoat poit, badwidth, retur loss S 11 ad gai of right had circular polarizatio (RHCP). A summary is give at the ed of this sectio. Ultimately, a optimized bet bow tie Moxo atea for RFID at frequecy rage 850 MHz to 1050 MHz was obtaied. The cofiguratio of the optimized bet bow tie Moxo RFID atea is give i Figure 4.3. Figure 4.3 Bet bow tie atea for RFID.

42 28 The total horizotal legth of the atea is 99.9 mm, the height from the top of the atea to the groud plae is 40.0 mm, the bottom of the atea to the groud plae is 18.0 mm, the cross sectio area (feedig area) is 1 mm 1 mm. The results of retur loss (S 11 ), RHCP gai ad radiatio patter at ceter frequecy 950 MHz is give i Figure Figure 4.4 S 11 of RFID atea.

43 29 Figure 4.5 Gai of RHCP ad radiatio patter at 950 MHz. Figure 4.6 Radiatio Patter at 950 MHz. From Figure 4.4, the optimized RFID atea has a wide badwidth from 850 MHz to 1100 MHz with a low retur loss uder -8 db. From Figure 4.5, the gai for RHCP is about 6.75 db ad the cross polarizatio is about db. The atea has o back scatterig lobe ad it has 80 degrees forward beam width with 3.5 db due to ifiite groud

44 30 plae cosideratio which requires much less computatioal effort compared to fiite groud plae Simulatio of GPS Atea For a GPS atea, oe of the cirtical requiremets is desig it at the proper frequecy bads. GPS atea has a dual bad of operatio; which are cetered at MHz ad MHz. High gai, low retur loss, high cross-ploarizatio are also desired requiremets for the GPS atea. First, the effect of every optimizatio parameter o overall performace was ivestigated as was doe for the simulatio of the RFID atea. Most of the parameters behave same as for RFID atea, but because the dimesio of GPS atea is smaller tha RFID atea, some parameters chaged their behaviors, as show the summary listed at the ed of this sectio. The, lower resoat frequecy was set arroud 1225 MHz while the higher resoat frequecy was set aroud 1570 MHz. The optimized results was very hard to obtai because the size of the GPS atea was too small, eve slight chage of dimesio will cause huge chage i the overall performace. A optimized GPS atea was fially obtaied with two resoace poits at MHz ad MHz, which almost matches the ideal cetral operatio frequecies of L1 ad L2 bads. The cofiguratio of bet bow tie GPS atea is give below:

45 31 Figure 4.7 Bet bow tie atea for GPS. The total horizotal legth of the atea is 72.7 mm, the height from the top of the atea to the groud plae is 30.0 mm, the bottom of the atea to the groud plae is 15.3 mm, the cross sectio area (feedig area) is 1 mm 1 mm. The results of S 11, RHCP gai ad radiatio patter at operatio frequecies 1227 MHz ad 1575 MHz are give i Figure

46 32 Figure 4.8 S 11 of RFID atea. Figure 4.9 Gai of RHCP ad radiatio patter at 1227 MHz.

47 33 Figure 4.10 Radiatio Patter at 1227 MHz. Figure 4.11 Gai of RHCP ad radiatio patter at 1575 MHz.

48 34 Figure 4.12 Radiatio Patter at 1575 MHz. From Figure 4.8, the optimized atea has wide badwidth from MHz to MHz (20.4 MHz) ad from MHz to MHz (79.7 MHz) for the two operatio frequecies with a low retur loss uder -8 db. From Figure 4.9 ad Figure 4.11, the Gai for RHCP is about 6.65 db at 1227 MHz ad 8.26 db at 1575 MHz, the cross polarizatio is about db at 1227 MHz ad 17.0 db ad 1575 MHz, which are satisfactory requiremets for a successful GPS atea. Due to ifiite groud plae cosideratios, the atea has o back scatterig lobe ad it has 80 degrees forward beam width with 3.5 db at 1227 MHz ad 4.4 db at 1575 MHz Optimizatio Parameters of the RFID Atea I order to clearly show the behavior of each optimizatio parameter s effect o the overall performace of the RFID atea ad GPS atea, every parameter was umbered ad show i Figure 4.13

49 35 Figure 4.13 Atea layout with optimizatio parameters umbered from 1 to 15. The optimizatio parameters ad their effect o the performace are outlied below for the RFID tag reader atea:

50 36 No 1: Horizotal wedge positio. Away from the axis: Low resoace poit stays i frequecy but drops dow i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. Closer to the axis: Low resoace poit stays i frequecy but goes up i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. No 2: Horizotal wedge agle. Bigger: Low resoace poit stays i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. Sharpe: Low resoace poit moves higher i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. No 3: Vertical legth (vertical sectio oly). Loger: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves lower i frequecy ad drops dow i S 11. Total badwidth decreases. Shorter: Low resoace poit movers higher i frequecy but drops dow i S 11, high resoace poit moves higher i frequecy ad goes up i S 11. Total badwidth icreases. No 4: Legth of the first bed. Loger: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth icreases.

51 37 Shorter: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth decreases. No 5: Outer agle of the first bed. Bigger: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves lower i frequecy ad drops dow i S 11. Total badwidth decreases, Sharpe: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves higher i frequecy ad goes up i S 11. Total badwidth icreases. No 6: Outer agle of the vertical sectio. (I our case is 90 degrees) It was observed that desig was isesitive to the agular radiatio. No 7: Ier agle of the vertical sectio. Bigger: Low resoace poit moves lower i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad drops dow i S 11. Total badwidth stays. Sharpe: Low resoace poit moves higher i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad goes up i S 11. Total badwidth stays. No 8: Horizotal legth (horizotal sectio oly, o tip). Loger: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves lower i frequecy ad drops dow i S 11. Total badwidth decreases.

52 38 Shorter: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves higher i frequecy ad goes up i S 11. Total badwidth icreases. No 9: Outer agle of the horizotal sectio. Bigger: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. Sharpe: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. No 10: Legth of the bottom bed. Loger: Low resoace poit stays i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. Shorter: Low resoace poit stays i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. No 11: First bed agle (vertical plae bed). Bigger: Low resoace poit moves higher i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad goes up i S 11. Total badwidth decreases. Smaller: Low resoace poit moves lower i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad drops dow i S 11. Total badwidth icreases.

53 39 No 12: Top to groud height. Higher: Low resoace poit moves higher i frequecy but drops dow i S11, high resoace poit moves higher i frequecy ad drops dow i S11. Total badwidth icreases. Lower: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. No 13: Half gap legth. Loger: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. Shorter: Low resoace poit moves lower i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. No 14: Legth of the tip. Loger: Low resoace poit moves lower i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. Shorter: Low resoace poit moves higher i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad goes up i S 11. Total badwidth icreases. No 15: Outer agle of the tip. Bigger: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases.

54 40 Sharpe: Low resoace poit moves lower i frequecy but drops dow i S 11, high resoace poit stays i frequecy ad goes up i S 11. Total badwidth icreases Optimizatio Parameters of the GPS Atea No 1: Horizotal wedge positio. Away from the axis: Low resoace poit moves higher i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. Closer to the axis: Low resoace poit moves lower i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. No 2: Horizotal wedge agle. Bigger: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. Sharpe: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. No 3: Vertical legth (vertical sectio oly). Loger: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves lower i frequecy ad drops dow i S 11. Total badwidth decreases.

55 41 Shorter: Low resoace poit movers higher i frequecy but drops dow i S 11, high resoace poit moves higher i frequecy ad goes up i S 11. Total badwidth icreases. No 4: Legth of the first bed. Loger: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. Shorter: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. No 5: Outer agle of the first bed. Bigger: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad drops dow i S 11. Total badwidth decreases, Sharpe: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad goes up i S 11. Total badwidth icreases. No 6: Outer agle of the vertical sectio. (I our case is 90 degrees) It was observed that desig was isesitive to the agular radiatio. No 7: Ier agle of the vertical sectio. Bigger: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases.

56 42 Sharpe: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. No 8: Horizotal legth (horizotal sectio oly, o tip). Loger: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves lower i frequecy ad drops dow i S 11. Total badwidth decreases. Shorter: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves higher i frequecy ad goes up i S 11. Total badwidth icreases. No 9: Outer agle of the horizotal sectio. Bigger: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. Sharpe: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. No 10: Legth of the bottom bed. Loger: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves lower i frequecy ad drops dow i S 11. Total badwidth icreases.

57 43 Shorter: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves higher i frequecy ad goes up i S 11. Total badwidth decreases. No 11: First bed agle (vertical plae bed). Bigger: Low resoace poit moves higher i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad goes up i S 11. Total badwidth decreases. Smaller: Low resoace poit moves lower i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad drops dow i S 11. Total badwidth icreases. No 12: Top to groud height. Higher: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. Lower: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. No 13: Half gap legth. Loger: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. Shorter: Low resoace poit moves lower i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases.

58 44 No 14: Legth of the tip. Loger: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. Shorter: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad goes dow i S 11. Total badwidth icreases. No 15: Outer agle of the tip. Bigger: Low resoace poit moves higher i frequecy but drops dow i S 11, high resoace poit moves lower i frequecy ad goes up i S 11. Total badwidth decreases. Sharpe: Low resoace poit moves lower i frequecy but goes up i S 11, high resoace poit moves higher i frequecy ad drops dow i S 11. Total badwidth icreases. 4.2 Experimetal Procedure ad Results Prototype ateas were built based o the simulatios. Layout of RFID ad GPS atea are show i Figure 4.14 ad Figure 4.15.

59 Figure 4.14 Layout of bet bow tie atea for RFID. 45

60 46 Figure 4.15 Layout of bet bow tie atea for GPS. Ateas are fed by a hybrid quadrature coupler. Retur loss is tested by vector etwork aalyzer. The prototype atea uder test is show i Figure 4.16.

61 47 Figure 4.16 (a) Retur loss test setup for RIFD atea. Figure 4.16 (b) Retur loss test setup for GPS atea.

62 Figure 4.16 (c) Retur loss test setup for RIFD atea. 48

63 49 Figure 4.16 (d) Retur loss test setup for GPS atea. Figure 4.18 Retur loss test results for RFID ad GPS ateas are show i Figure 4.17 ad

64 50 Figure 4.17 Retur loss test results for RFID atea. Figure 4.18 Retur loss test results for GPS atea.

65 51 I Figure 4.17, the retur loss at the ceter frequecy 950 MHz is about -28 db, ad it shows the retur loss i the whole bad from 850 MHz to 1050 MHz is lower tha -20 db. I Figure 4.18, the retur loss at the ceter frequecy MHz is about -18 db, ad the retur loss over the whole bad is lower tha -15 db. The test results show that the whole desig is very successful. 4.3 Compariso with Other Ateas I order to show that the ew desiged bet bow tie atea for RFID ad GPS applicatios is worthy ad advaced, a compariso betwee the ew desiged RFID ad GPS atea ad the ateas for RFID or GPS applicatio i the market is show i Tables 4.1 ad 4.2. Table 4.1 Compariso of RFID tag Reader Ateas Name New Bet Bow Tie RFID Atea IA33A INTELLITAG AvalLAN wireless 6 dbi idoor atea Laird Tech S8656-X, Special Applicatio Ateas Poytig Patch A 0025 Atea Dimesios (cm) Frequecy rage (MHz) Gai (db) Frot-to- Back ratio (db) Beam width degrees at 3.5 db degrees at 3 db degrees at 3 db

66 52 Additioal compariso of VSWR ad S 11 betwee ew bet bow tie RFID atea ad Poytig Patch A 0025 atea are show i Figure 4.19 ad Figure Table 4.2 Compariso of GPS Ateas Name Dimesios (cm) Frequecy rage (MHz) Gai (db) L1 L2 L1 L2 New Bet Bow Tie GPS Atea ALLICOM SB240 Marie GPS Atea GPS SOURCE L1/L2 DARG ANTENNA GPS SOURCE RUGGEDIZED L1/L2 GPS PASSIVE ANTENNA (20.4) (30) (20.3) (79.7) ± (30) (21) Data from the above Tables 4.1 ad 4.2 suggest that comparable gai performace has reached for almost half size i dimesios for RFID atea, ad for GPS atea, with comparable size, better gai has bee obtaied. Further experimetal characterizatio is still i progress. The proposed atea yields excellet badwidth ad impedace match over that badwidth.

67 53 Figure 4.19 VSWR measuremet for ew bet bow tie RFID atea (gree) ad Poytig Patch A 0025 atea (blue). Figure 4.20 S 11 measuremet for ew bet bow tie RIFD atea (gree) ad Poytig Patch A 0025 atea (blue).

68 CHAPTER 5 CONCLUSIONS Moxo based RFID ad GPS ateas were proposed, Extesive umerical simulatios based o optimizatio of various parameters o the atea structure were carried out to achieve higher gai, wide bad impedace match, high cross-polarizatio ad low profile. Prototype ateas were built ad tested cofirmig good agreemets betwee simulatio ad experimetal results. Furthermore, prototype ateas were compared with commercial couterparts ad were observed that RFID tag reader atea was almost 4 times smaller i physical dimesios for the comparable gais. Also the badwidth of the prototype atea was sigificatly wider. I case of GPS atea the overall gai was observed to icrease for the comparable dimesios. Further ivestigatio of how to improve the performace of the atea ca be doe by addig more vertical arms, makig more beds alog the horizotal part or addig folded elemets [12]. 54

69 REFERENCES [1] I. Teki, O. Mazhura ad E. Niver, Broadbad Circularly Polarized Ateas for UHF SATCOM, IEEE Geeral Assembly ad Scietific Symposium, 2011 XXXth URSI, Aug [2] L. Moxo, HF Ateas for ALL Locatios, 2 d Editio, Radio Society of Great Britai, UK, [3] K. Fikezeller, RFID Hadbook, Joh Wiley, Hoboke NJ, [4] G. Marrocco, The Art of UHF RFID Atea Desig: Impedace-Matchig ad Size-Reductio Techiques, IEEE Ateas ad Propagatio Magazie, vol. 50, No.1, , [5] B.W. Parkiso ad J.J. Spilker Jr., Global Positioig System: Theory ad Applicatios, AIAA, vol.1 &2, Washigto, D.C., [6] R.S. Elliott, Atea Theory ad Desig, Pretice-Hall, Ic., Eglewood Cliffs, New Jersey [7] F. Schwerig, Workshop o Electrically Small Ateas: Backgroud ad Purpose. Proceedigs of the ECOM-ARO Workshop o Electrically Small Ateas, Fort Momouth, NJ May 6-7, [8] L.J. Chu, Physical Limitatios o Omi-Directioal Ateas, J. Appl. Phys., vol. 19, pp , [9] R.M. Fao, Theoretical limitatios o the broadbad matchig of Arbitrary Impedace. J.Frakli Ist, vol.249, pp.58-83, , Ja, Feb, [10] L.J. Chu, Physical Limitatios o Omi-Directioal Ateas, Techical report N0.64, Research Laboratory of Electroics, MIT, May 1, [11] A.K. Skrivervik ad J.F. Zürcher, Electrically Small Atea Desig, Ecole Polytechique Fédérale de Lausae, CH-1015 Lausae, Switzerlad Iteret: [Apr.13, 2012]. [12] M. Nagatoshi, S. Taaka, S. Horiuchi ad H. Morishita, Dowsized Bow-Tie Atea with Folded Elemets, IEICE tras electro, vol. E93-C, o7, July [13] Iteret: [Apr. 13, 2012]. 55