IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 10, OCTOBER 2012 4479

Single Feed Stacked Patch Circular PolarizedAntenna for Triple Band GPS Receivers

Oluyemi P. Falade, Student Member, IEEE, Masood Ur Rehman, Member, IEEE, Yue (Frank) Gao, Member, IEEE,Xiaodong Chen, Senior Member, IEEE, and Clive G. Parini, Member, IEEE

Abstract—A novel design of a circular polarized antenna formultiband GPS receivers is presented. The design employs theconcept of multistacked patches fed through a single coaxial probe.Three patches being stacked together with a slit and symmetryI-slot are used to achieve triple operating frequency bands for GPSincluding L1 (1.575 GHz), L2 (1.227 GHz) and L5 (1.176 GHz).The proposed antenna has achieved a bandwidth of 2.0%, 1.5%,and 1.7% at GPS L1, L2, and L5 bands, respectively. It exhibitsa minimum axial ratio of 0.51 dB with broad beamwidth in theupper hemisphere required for the GPS applications. The designof the proposed antenna is verified in the experiment. In addition,a detailed analysis has been carried out to study the effects of dif-ferent geometrical parameters on the performance of the antenna.

Index Terms—Axial ratio, circular polarized, global positioningsystems, stacked patch.

I. INTRODUCTION

T HE GLOBAL positioning system (GPS) is the mostpopular member of global satellite navigation systems

(GNSS). It makes use of the medium earth orbit (MEO) satelliteconstellation to transmit microwave signals allowing a GPSreceiver to determine the position, velocity, and time of theuser [1]. The integration of L5 (1.176 GHz) frequency bandwith L1 (1.575 GHz) and L2 (1.227 GHz) frequency bandshas introduced the triple band GPS operation that will improvethe robustness of this service and techniques for high accuracypositioning.Availability of limited space onGPS receivers is amajor chal-

lenge for the antenna design.Moreover, embedding multiple an-tennas in a GNSS receiver to cover all three frequency bandsgive rise to the problem of mutual coupling that degrades theoverall system performance. Design of a single antenna that cancover multiple GNSS bands effectively, efficiently, and simul-taneously can ameliorate this problem.Circular polarized (CP) microstrip patch antennas is a pop-

ular choice for the GNSS receivers due to their numerous ad-vantages including light weight, low profile, easy circuit inte-gration, low fabrication cost, and ease of fabrication [2]. CP an-tennas have been achieved using both single and dual feed tech-

Manuscript received January 10, 2012; revised April 23, 2012; accepted May18, 2012. Date of publication July 10, 2012; date of current version October 02,2012.The authors are with the School of Electronic and Computer Science,

Queen Mary University of London, London E1 4NS, U.K. (e-mail: oluyemi.falade@eecs.qmul.ac.uk; masood.rehman@eecs.qmul.ac.uk; yue.gao@eecs.qmul.ac.uk; xiaodong.chen@eecs.qmul.ac.uk; clive.parini@eecs.qmul.ac.uk).Color versions of one or more of the figures in this paper are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TAP.2012.2207354

niques [3]–[6]. Many studies have been reported in the litera-ture that describe different methods of achieving multiband CPantennas [7]–[9]. A stacked patch technique with a high permit-tivity dielectric material is used by Yijun et al. [7] to achieve acompact triple band antenna design. However, a dual orthogonalfeed is required to drive the antenna. Rao et al. [8] has utilized afour elements antenna array using hybrid ring to achieve tripleband CP operation. The complexity and size of this antenna de-sign makes it unsuitable for small GNSS terminals. A stackedpatch with vertical choke ring is used by Lee et al. [9] to reducethe backlobes in the radiation pattern of the antenna. The an-tenna also works in the three frequency bands. This antenna hasa ground plane size of 204 mm with a height of 60 mm. Again,the size makes it too big for the compact mobile terminal.Furthermore, to overcome the challenges of narrow axial ratio

bandwidth (ARBW) and impedance bandwidth (ZBW), Tsenget al. [10] have used a slot in their design while Waterhouse etal. and Lien et al. [11], [12] have made use of different dielectricmaterials in a stacked patch design to get a dual band operation.This paper proposes a novel CP antenna design based on

stacked patches with a single feed for the GPS operation inL1, L2, and L5 band. Novelty of this design is its compact-ness, simplicity, and distinct separation of the three bands withgood impedance bandwidth and axial ratio (AR). The paper isorganized as follows: Section II describes the principle of theantenna design, Section III presents the results and discussion,Section IV gives the parametric study of some key structural pa-rameters, while the paper is concluded in Section V.

II. ANTENNA DESIGN

The geometry of the proposed single feed stacked patch CPantenna is shown in Fig. 1. The antenna is made up of threesquare patches stacked on one another. The stacked patch ap-proach utilizes at least one driven element connected directly tothe feeding network and a number of parasitic elements placedbelow the driven patch [13].The use of stacked patch design has helped to solve the issue

of narrow bandwidth in microstrip patch antennas [14]. Thepatches are etched on three different substrates. The lower sub-strate has a thickness of and permittivity

; the middle and upper substrates are similar with athickness of and permittivity of .The lower, middle, and upper patches are designed to resonateat L5, L2, and L1 frequency bands, respectively. The groundplane size is 80 mm 80 mm; the lower (P3), middle (P2), andupper (P1) patches have a length of 66, 56, and 45 mm, respec-tively. The total height of the antenna from the ground plane is

0018-926X/$31.00 © 2012 IEEE

4480 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 10, OCTOBER 2012

Fig. 1. Geometry of the proposed stacked patch CP antenna showing: (a) sideview; (b) upper patch; (c) middle patch; and (d) lower patch.

Note: ( ,, , ,

, , , ,, , and ).

4.8 mm. The other optimized dimensions for the proposed an-tenna are shown in Fig. 1.A single probe feed of 50 input impedance is connected

to the upper patch through via holes in the middle and lowerpatches while the middle and lower patches are excited throughelectromagnetic coupling. The via has contributed a capacitivecoupling to negate the inductance effect due to the inner con-ductor of the probe. The use of slit on the edge of the lowerpatch introduces the dual orthogonal mode necessary for CP ra-diation pattern. Both the middle and upper patches are perturbedby corner truncation which produces near degenerated resonantmode resulting in circular polarization.Optimization of the feeding probe position has been per-

formed through extensive simulations in order to achieve abetter impedance matching for the three patches. Moreover,the centres of the three patches are not aligned. It is kept soas to achieve the desired impedance matching in the requiredfrequency bands. The slit in the lower patch and the cornertruncation of the middle and upper patches play a key role inachieving an AR below 3 dB. Microstrip CP antennas usuallysuffer from poor AR because the resonance is degraded whensingly fed or dual orthogonally fed with a nonisolated splitter[2]. This problem has been overcome in this proposed antennadesign through the use of symmetry I-slot in the middle patch.

III. RESULTS AND DISCUSSION

The proposed antenna is optimized by using the electro-magnetic simulation package named computer simulationtechnology (CST) microwave studio. The software is based onthe finite integral techniques (FIT) for electromagnetic compu-tations [15]. The slit cut in the lower patch and the I-slots in themiddle patch need to be carefully designed to achieve a goodCP operation for the antenna. The use of different substratedielectric material has improved the CP bandwidth in the GPSL5 band [11]. This has occurred as a result of parasitically cou-pled element drawing power from the middle element which

Fig. 2. Photograph of the triple band stacked patch antenna: (a) top view;(b) back view; and (c) side view.

Fig. 3. Measured and simulated reflection coefficients of the proposed antenna.

has increased the L5 band cross polarization. The prototypeof the antenna is then fabricated in the antenna measurementlaboratory at Queen Mary University of London (QMUL).The top, bottom, and side views of the prototype are shown in

Fig. 2. The measured and simulated reflection coefficient are il-lustrated in Fig. 3. A reasonable agreement is observed betweenthe measured and simulated results across the three frequencybands. The measured value of 10 dB impedance bandwidthfor GPS L1, L2, and L5 frequency bands are 1.160–1.182(2.0%), 1.214–1.232 (1.5%), and 1.568–1.598 GHz (2.0%),respectively. The simulated results appear to be 1.164–1.184(1.7%), 1.219–1.242 (2.0%), and 1.550–1.590 GHz (2.5%),respectively. Small discrepancies between the measured andsimulated results are due to cable effects, SMA connector andfabrication imperfection. The simulated axial ratio at broadsidedirection (shown in Fig. 4) illustrates that the minimum axialratio coincides with the resonant frequencies in the three bands.The 3 dB axial ratio bandwidth is 40 MHz (3.40%) in L5frequency band, 10 MHz (0.81%) in L2 frequency band, and13 MHz (0.83%) in L1 frequency band.

FALADE et al.: SINGLE FEED STACKED PATCH CIRCULAR POLARIZED ANTENNA FOR TRIPLE BAND GPS RECEIVERS 4481

Fig. 4. Simulated axial ratio of the proposed antenna.

Fig. 5. Measured and simulated total radiation (LP) pattern at: (a) 1.176;(b) 1.227; and (c) 1.575 GHz.

The antenna radiation pattern has been measured at the centrefrequencies of 1.176, 1.227, and 1.575 GHz in an anechoicchamber at Queen Mary University of London. A standard lin-early polarized (LP) horn is used to measure the total radiationpatterns in horizontal and vertical planes. The measured andsimulated radiation patterns at 1.176, 1.227, and 1.575 GHzplotted in Fig. 5 show symmetric pattern (equal amplitude)which indicates good circular polarization. The simulatedradiation patterns of the antenna in the x-z and y-z plane forthe three frequency bands are shown in Fig. 6. In both planes,

Fig. 6. Simulated radiation pattern at x-z and y-z plane of the proposed antennaat: (a) 1.176; (b) 1.227; d (c) 1.575 GHz.

Fig. 7. Cartesians plot (AR) of the proposed antenna showing a widerbeamwidth at the upper hemisphere.

the pattern is symmetric and right hand circular polarization(RHCP) is stronger than left hand circular polarization (LHCP)by more than 18 dB in the boresight direction. This gives theantenna an excellent multipath rejection capability. Superiorcross-polarization rejection (20 dB) is achieved in the upperhemisphere. The cross polar discrimination (XPD) in L1, L2,and L5 frequency band is 30.7, 27.7, and 21.2 dB, respectively.Fig. 7 illustrates the cartesian plots for the AR at the three

centre frequencies of 1.176, 1.227, and 1.575 GHz. It can beobserved that the minimum AR at the broadside is 1.54, 0.68,and 0.59 dB for the three bands, respectively. Also the antenna

4482 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 10, OCTOBER 2012

TABLE IPERFORMANCE OF THE PROPOSED ANTENNA USING DIFFERENT LOWER PATCH SLIT BREADTHS (S) FOR L5, L2, AND L1 BANDS

exhibits a wide beamwidth of about 172 , 161 , and 205 inthe upper hemisphere. This has met the wide angle coveragerequirement for many spacecraft communication and navigationsystems [16], [17]. The simulated gain appears to be 5.6, 5.6,and 6.3 dBi for the three bands, respectively.These results also show the superiority of the proposed

feeding structure over the conventional arrangement of thefeeding probe in stacked patch antennas. In the conventionalfeed, the probe is connected to the lower patch while theupper patch is electromagnetically coupled. The two patchesare separated by an air layer [18], [19]. A wide impedancebandwidth with axial ratio below 3 dB can also be achievedusing this conventional feed with slots and/or corner truncation[20]. However, the air layer increases the antenna thicknessand adds to the fabrication complexity. Also, the use of airsubstrate compromises the rigidity of the antenna. Moreover,distinction of the individual frequency bands is not alwaysvisible. The minimum axial ratio and the resonant frequency ofthe impedance bandwidth do not always coincide.

IV. PARAMETRIC STUDIES

This section investigates the effects of some key structuralparameters on the performance of the proposed antenna. Theparameters are varied and simulated results are studied and pre-sented.

A. Breadth of Slit (s)

The effect of the breadth of the slit in the lower patch on thereflection coefficient and axial ratio is investigated first. The slitlengthens the surface current path in the y axis direction withlittle effect on the x axis (parallel to the slit). It therefore, cre-ates two orthogonal near degenerated modes. An increase in thesurface current increases the electrical length of the patch thatlowers the resonant frequency or reduces the physical length ofthe patch. As the slit’s breadth increases, the resonant frequencydecreases in L5 and L2 bands with little effect on L1 band. TheAR of L5 band decreases as the slit’s breadth decreases to 2mm before increasing again. The axial ratio and ZBW of L1band almost remains constant which is due to large separationbetween lower and upper patches. Putting the minimum AR andthe reflection coefficient into consideration for the three bands,the optimum value selected for the slit breadth is 2 mm. Table Isummarizes the results for the three bands while the S11 andAR results are shown in Figs. 8 and 9. The length of the slit haslittle impact on the S11 and the AR of the three bands.

Fig. 8. Simulated reflection coefficient for different values of lower patch slitbreadths.

Fig. 9. Simulated axial ratio for different values of lower patch slit breadths.

B. Position of Symmetry I-slot (r)

The position of the symmetry I-slots on the middle patch inthe Y axis direction is another important parameter that affectsthe antenna performance. It has been a means of centralizing theminimum axial ratio at the centre frequency of the impedancebandwidth within the three frequency bands respectively. As thesymmetry I-slot moves from the edge towards the centre of thepatch, the bandwidth increases, the resonant frequency almostremains constant while the axial ratio increases at L5 band. ForL2 band, the impedance bandwidths decreases while the axialratio decreases before rapidly increasing when .At L1 band, the impedance bandwidth increases as r increases

FALADE et al.: SINGLE FEED STACKED PATCH CIRCULAR POLARIZED ANTENNA FOR TRIPLE BAND GPS RECEIVERS 4483

TABLE IIPERFORMANCE OF THE PROPOSED ANTENNA USING DIFFERENT POSITION OF SYMMETRY I-SLOT FROM THE EDGE OF THE PATCH (R) IN THE Y AXIS DIRECTION

FOR L5, L2, AND L1 BANDS

Fig. 10. Simulated reflection coefficient for different I-slot position from theedge of the middle patch in y axis direction.

until it reaches to 17 mm. When exceeds from 17 mm, theimpedance bandwidth starts decreasing. The axial ratio exhibitsan opposite trend. It decreases as r increases from 15 to 17 mm.As r increases further, the axial ratio starts increasing. It showsthat the I-slot can be used to reduce the electrical length ofthe patch; to improve the axial ratio and impedance matchingof the antenna in the three operating frequency bands. The de-crease in the resonant frequency has resulted in a reduction ofthe electrical thickness of the substrate, thus slightly reducingthe axial ratio bandwidth [21]. Therefore, the optimum value of

is selected for the optimized design. The S11 andAR for the different values of are presented in Figs. 10 and11. Table II gives a summary of the performance of the antennawith varying position of the I-slot in the y axis direction. Theposition of the I-slot in the x axis direction has little impact onthe reflection coefficient and axial ratio of the proposed antennain the three bands, respectively.

V. CONCLUSION

A novel design of compact single feed stacked patch CP an-tenna for the GPS receiver has been proposed. The antenna sup-ports a triple band operation with good performance in GPS L1,L2, and L5 frequency bands. The triband operation has beenobtained by using three patches stacked on top of each other.

Fig. 11. Simulated axial ratio for different I-slot position from the edge of themiddle patch in y axis direction.

Slit cut and I-slot techniques have been implemented to achieveimproved operational bandwidth and minimum axial ratio. Thebroad beamwidth, low cross polarization and high gain of thisantenna makes it suitable for the GPS applications.

REFERENCES[1] B. Eissfeller, G. Ameres, V. Kropp, and D. Sanroma, Performance of

GPS, GLONASS and Galileo 2007.[2] G. Ramesh, P. Bhartia, I. Bahl, and A. Ittipiboon, Microstrip Antenna

Design Handbook. London, U.K.: Artech House, 2001, pp. 493–526.[3] Y. Lin, H. Chen, S. Member, and S. Lin, “A new coupling mechanism

for circularly polarized annular-ring patch antenna,” IEEE Trans. An-tennas Propag., vol. 56, no. 1, pp. 11–16, Jan. 2008.

[4] K. P. Esselle, Nasimuddin, and A. K. Verma, “Wideband circularly po-larized stacked microstrip antennas,” IEEE Antennas Wireless Propag.Lett., vol. 6, no. 1, pp. 21–24, Jan. 2007.

[5] A. Vallecchi and G. B. Gentili, “Design of dual-polarized series-fedmicrostrip arrays with low losses and high polarization purity,” IEEETrans. Antennas Propag., vol. 53, no. 5, pp. 1791–1798, May 2005.

[6] X. L. Bao and M. J. Ammann, “Dual-frequency dual circular-polarizedpatch antenna with wide beamwidth,” IEEE Electron. Lett., vol. 44, no.21, pp. 1233–1234, 2008.

[7] Z. Yijun, C. Chen, and J. L. Volakis, “Proximity-coupled stackedpatch antenna for tri-band GPS applications,” in Proc. IEEE AntennasPropag. Soc. Int. Symp., Albuquerque, NM, 2006, pp. 2683–2686.

[8] B. R. Rao, M. A. Smolinski, C. C. Quach, and E. N. Rosario, “Tripleband GPS trap loaded inverted L antenna array,”Microw. Opt. Technol.Lett., vol. 38, no. 1, pp. 35–37, 2003.

[9] Y. Lee, S. Ganguly, and R. Mittra, “Tri-band (L1, L2, L5) GPS antennawith reduced backlobes,” presented at the 28th General Assembly Int.Union Radio Sci., URSI-GA, New Delhi, India, 2005.

4484 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 10, OCTOBER 2012

[10] C. F. Tseng, S. C. Lu, and Y. C. Hsu, “Design of microstrip antennawith modified annular-ring slot for GPS application,” in Proc. PIERS,Suzhou, China, Sep. 2011, pp. 242–245.

[11] R. B. Waterhouse, “Stacked patches using high and low dielectric con-stant material combinations,” IEEE Trans. Antennas Propag., vol. 47,no. 12, pp. 1767–1771, Dec. 1999.

[12] H. C. Lien and H. C. Tsai, “A wide-band circular polarization stackedpatch antenna for the wireless communication Applications,” PIERS,vol. 4, no. 2, pp. 255–258, 2008.

[13] P. Anguera and S. A. Fractus, “Multifrequency Microstrip Patch An-tenna With Parasitic Coupled Elements,” U.S. Patent 7202818, 2007.

[14] M. Clenet, C. B. Ravipati, and L. Shafai, “Bandwidth enhancement ofu-slot microstrip antenna using a rectangular stacked patch,” Microw.Opt. Technol. Lett., vol. 21, no. 6, pp. 393–395, Jun. 1999.

[15] “CST-Microwave Studio, User’s Manual,” 2011.[16] J.-Y. Deng, Y.-Z. Yin, Y.-H. Huang, J. Ma, and Q.-Z. Liu, “Compact

circularly polarized microstrip antenna with wide beamwidth for com-pass satellite service,” Progress Electromagn. Res. Lett., vol. 11, pp.113–118, 2009.

[17] L. Shi, H. Sun, and X. Lu, “A composite antenna with wide circularlypolarized beamwidth,”Microw. Opt. Technol. Lett., vol. 51, no. 10, pp.2461–2464, Oct. 2009.

[18] Y. S. Boo, Nasimuddin, Z. N. Chen, and A. Alphones, “Broadbandcircular polarized microstrip antenna for RFID reader applications,” inProc. APMC, Singapore, 2009, pp. 625–628.

[19] J. L. Masa-Campos, E. C. Sanz, M. Sierra-Perez, and J. M. Fernandez,“Stacked circular patch antenna with dual right/left hand circular po-larization for wideband applications in X band,”Microw. Opt. Technol.Lett., vol. 51, no. 6, pp. 1419–1424, Jun. 2009.

[20] H. C. Lien and H. C. Tsai, “A wide-band circular polarization stackedpatch antenna for the wireless communication applications,” PIERSOnline, vol. 4, no. 2, pp. 255–258, 2008.

[21] W. S. Chen, C. K. Wu, and K. L. Wong, “Single-feed square-ring mi-crostrip antenna with truncated corners for compact circular polariza-tion operation,” Electron Lett., vol. 34, pp. 1045–1047, May 1998.

Oluyemi Peter Falade (S’08) received the HNDdegree in electronic and telecommunication engi-neering from the Federal Polytechnic Offa, Kwara,Nigeria, in 2001, the PGD degree in electrical andelectronic engineering from the Federal Universityof Technology Akure, Ondo, Nigeria, in 2006, andthe M.Sc. degree in wireless networks from QueenMary University, London, U.K., in 2009, where heis currently working toward the Ph.D. degree.His current research interests include small and

compact multifunction/multiband antennas forGNSS mobile/handheld terminals and small satellites.

Masood Ur Rehman (M’11) received the B.Sc.(Hons.) degree in electronics and communicationengineering from the University of Engineering andTechnology, Lahore, Pakistan, in 2004, the M.Sc.degree in wireless networks, in 2006, and the Ph.D.degree in electronic engineering from Queen MaryUniversity, London, U.K., in 2010.He then joined the School of Electronic En-

gineering and Computer Science at Queen MaryUniversity of London as a Research Assistant. Hismain research interests include electromagnetic

interaction of antennas and human body, multipath environment effects onmobile terminal antennas, and UWB communications.

Yue (Frank) Gao (M’07) received the M.Sc. degreein telecommunication systems and the Ph.D. degreein electronic engineering from Queen Mary Univer-sity of London, U.K., in 2003 and 2007, respectively.He joined the Antenna Group at Queen Mary Uni-

versity of London, in 2002 His research interests in-clude multiple antenna design, cognitive radio, navi-gation, and MIMO. He has completed the multipathmodeling project funded by FP7 Galileo Joint Un-dertaking and the on-body propagation project sup-ported by Sony Ericsson. His recent research is on

the spectrum detection for the cognitive radio system. His group has developeddifferent detection methods including energy detection, wavelet detection, andjoint wideband detection. He developed power-control and adaptive thresholdfor the TVWhite Space spectrum detection. He holds one patent, and publishedmore than 30 journal and conference papers.

Xiaodong Chen (M’96–SM’07) received the B.Sc.degree in electronic engineering from the Universityof Zhejiang, Hangzhou, China, in 1983 and thePh.D. degree in microwave electronics from theUniversity of Electronic Science and Technology ofChina, Chengdu, in 1988.In September 1988, he joined the Department of

Electronic Engineering at King’s College, Universityof London, as a Postdoctoral Visiting Fellow. InSeptember 1990, he was employed by the King’sCollege as a Research Associate and was appointed

to an EEV Lectureship later on. In 1999, he joined the School of ElectronicEngineering and Computer Science at Queen Mary University of London andis currently a Professor at the school. His research interests include in thefields of wireless communications, microwave devices, and antennas. He hasauthored and coauthored over 300 publications (book chapters, journal papers,and refereed conference presentations).Dr. Chen is currently a Member of the UK EPSRC Review College and Tech-

nical Panel of the IET Antennas and Propagation Professional Network.

Clive G. Parini (M’96) received the B.Sc. and Ph.D.degrees from Queen Mary University, London, U.K.,in 1973 and 1976, respectively.He then joined ERA Technology Ltd, U.K.,

working on the design of microwave feeds andoffset reflector antennas. In 1977, he returned toQueen Mary University and is currently a Professorof Antenna Engineering and heads the Antennaand Electromagnetics Research Group. He haspublished over 300 papers on different researchtopics including communications, antenna, and

electromagnetics. He is currently the Director of Research for the School ofElectronic Engineering and Computer Science at Queen Mary University ofLondon.Dr. Parini is a Fellow of the IET, an elected Fellow of the Royal Academy

of Engineering (2009), and a Member and past Chairman of the IET Antennasand Propagation Professional Network Executive Team. He is a Member of theeditorial board and past Honorary Editor for the IET Journal Microwaves, An-tennas, and Propagation.