A compact microstrip antenna for GPS and DCS application

Communications______________________________________________________________________A Compact Microstrip Antenna for GPS and DCSApplicationShun-Yun Lin and Kuang-Chih Huang Abstract—This communication presents a novel design of a compact mi-crostrip antenna practical for both the global positioning system(GPS)and dig ital communication system(DCS).The proposed antenna consists of two parts:a fundamental mode truncated square patch antenna and a higher-order mode annular ring patch antenna.The truncated square patch oper-ated in right-hand circular polarization at1575MHz with8-MHz CP band-width,making the desig n suitable for the GPS.Further,four slots were em-bedded into a ground plane to meander the current path of the annular ring patch at the TM mode,which considerably lowered the resonant fre-quency and effectively increased the impedance bandwidth.These features reduce the antenna size and make the desig n appropriate for DCS.Both radiators are placed in a common space but operate independently.The experimental results show that this design is ideally suited for GPS/DCS dual-band mobile communications.Index Terms—Conical radiation pattern,high-order mode antenna,mo-bile communication,satellite communication,slotted ground plane.I.I NTRODUCTIONMobile communications have been indispensable in modern life. There are various communication systems,such as the global posi-tioning system(GPS)and digital communication system(DCS),im-plemented to meet various needs.The GPS offers global positioning function via satellites[1],[2],and the DCS provides personal mobile communication services[3],[4].Because of different radiation perfor-mances of the GPS and DCS,conventional dual-band antennas with single radiation characteristics are not practical for the GPS/DCS ap-plications.The TM21mode annular ring patch antenna could be a promising so-lution with its omnidirectional radiation pattern on the azimuthal plane [4],[5].However,it is impractical for the DCS with its large patch size and narrow impedance bandwidth.Some methods have been devel-oped to reduce the antenna size[6].These techniques mainly centered around two issues:meandering current path and increasing substrate’s permittivity.However,these methods achieved compact design at the expenses of impedance bandwidth and antenna gain.This communication presents a compact dual-band antenna for the GPS and DCS.The design consisted of an annular ring patch and a trun-cated square patch.The truncated square patch was equipped within the annular ring patch,and excited two degenerated modes to obtain cir-cular polarization.A substrate with high permittivity was adopted to make the square patch more compact tofit in with the inner radius of the annular ring.To improve performance,the design integrated an in-novation[5],in which four radial slots were embeded into the square ground plane at diagonal direction to meander the current path of the annular ring patch antenna at the TM21mode.The experimental re-sults show that the resonant frequency is significantly lowered,which brings more compact size;and the impedance bandwidth is enhanced, which yields high performance.Manuscriptreceived February16,2003;revised February23,2004.The authors are with the Department of Electronics Engineering,Cheng Shiu University,Kaohsiung,Taiwan833,R.O.C.(e-mail:yun@.tw). Digital Object Identifier10.1109/TAP.2004.842597Fig.1.Configuration of the compact antenna for GPS and DCS application.II.A NTENNA D ESIGNThe proposed antenna mainly consisted of two radiators:a truncatedsquare patch,which offered a right-hand circular polarization radiationfor communication via the GPS;and a TM21mode annular ring patch,which featured an omnidirectional radiation pattern for the DCS.Bothpatches were centered above a slotted ground plane.The dimension ofthe internal radius of the annular-ring patch was set to be large enoughto contain the concentric configuration.The annular ring radiation patch with outer radius R1and inner ra-dius R2operated at the TM21mode and its resonant frequency can becalculated according to the following[7]:wR=0:4(1)k2R=2(2) where k is2 = 0,w is(R10R2)=2;and R is(R1+R2)=2.To achieve compact size of the annular ring patch,four radial slotswere embedded on the square ground plane.The embedded slots wereoriented at45 to the x-or y-axis(see Fig.1)such that the narrow slotswere in perpendicular to the excited surface currents on the groundplane for the antenna operated at the TM21mode[5].To avoid af-fecting the performance of the GPS antenna,the slots had a distance ofR2(identical to the patch’s inner radius)from the ground-plane center.The width of the slots was set to be2mm for adequate current me-andering,but without sacrificing the antenna gain and F=B ratio.The 0018-926X/$20.00©2005IEEETABLE IP ERFORMANCES OF THE TM M ODE A NNULAR -R ING P ATCH A NTENNA W ITH S LOTTED G ROUND P LANE .T HE O UTER R ADIUS ,I NNER R ADIUS ,H EIGHT OF A IR S UBSTRATE AND W IDTH OF THE S LOTS ARE S ET TO BE 47,19.5,3,AND 2MM ,R ESPECTIVELY .T HEfIS C ALCULATED BY (3),ANDfIS M EASURED BY N ETWORK ANALYZER Fig.2.(a)Measured input impedance on a Smith chart for the GPS antenna.(b)Measured input impedance on a Smith chart for DCS antenna.The geometric dimensions are L =21:4,1L =2:2,R =52:5,R =22,h =6,S =12,L =60,d =38,and d =3:38mm ;and ground plane =1802180mm .resonantfrequency of TM 21mode is about linearly decreased with the increasing slot length,and the following derived linear function can be used to estimate the resonant frequency:f c =f 0019:42L s :(3)where f c is the resonant frequency of the annular ring patch with a slotted ground plane and f 0is the resonant frequency of a regular ground plane.Table I lists the performances of the annular ring patch antenna with embeded slots on the ground plane,indicating that(3)Fig.3.Measured isolation between the feeding points of GPS and DCSantennas studied in Fig.2.Fig.4.Measured radiation pattern of the proposed antenna studied in Fig.2.(a)1575MHz for GPS.(b)1800MHz for DCS.can well describe the resonant frequency of an actual antenna.Different from conventional dual-band designs,this antenna has considerably re-duced size and increased impedance bandwidth.Furthermore,the measured results show that the antenna gain and F =B ratio were lowered with the increasing slot length.The detrimental effects of the proposed are mainly caused by the power leakage through the embedded slots of the ground plane.For applications that a large F =B ratio is preferred,a conducting plate can be added behind the antenna’s ground plane to reflect or block the backward radiation [5].Also,due to the reflection of the backward radiation,the antenna gain can be enhanced simultaneously by the adding of the conducting plate.III.E XPERIMENTAL R ESULTS AND D ISCUSSIONThe prototype of the proposed antenna for the GPS/DCS applica-tions is shown in Fig.1.The geometric parameters were chosen to make the antenna performance meet the requirements of the GPS and DCS.Fig.2(a)shows that the impendance bandwidth for VSWR 2.0was 24MHz (1568–1592MHz)for the GPS antenna.Next,the measured radiation performance indicates that the CP bandwidth was about 8MHz.In addition,Fig.2(b)indicates that the impedance bandwidth was 175MHz for DCS (1705–1880MHz,9.8%).The large enhancement may be caused by the embedded radial slots,which lowered the quality factor of the proposed DCS antenna.Fig.3demonstrates the measuredisolation between the two feeding ports.There is a peak around the res-onant frequency of the truncated square patch.It possibly caused by the inherent drawback of poor radiation efficiency for the substrate with high permittivity,and therefore the resonance of the GPS antenna is easily interfered with other intensed radiation.The isolation was about 020dB in the GPS band,and less than040dB for another band, showing that each antenna operated correctly without significant per-turbation from another band.The radiation patterns were also investigated.Fig.4(a)depicts the patterns of the GPS antenna,indicating that the truncated square patch antenna with high permittivity operated with RHCP pattern at1575 MHz,which meets the requirement of the GPS.Fig.4(b)illustrates the radiation pattern of the DCS antenna.The conical patterns on the x-z and y-z planes indicate that an omnidirectional radiation occured on the azimuthal plane.This monopolarized feature makes the high-order patch antenna suitable for mobile communication.IV.C ONCLUSIONThis communication presents a compact antenna design with high performances for the applications of the GPS and DCS,by using high permittivity substrates and a slotted ground plane.Here,a truncated square patch was adopted for circular polarization,which operated at 1575MHz and with8MHz bandwidth,suitable for the GPS.On the other hand,the antenna is also practical for the DCS with the high performance of the TM21mode and9.8%impedance bandwidth.The experimental results show that this design is ideally practical for dual-band GPS/DCS applications.R EFERENCES[1]H.Ohmine,Y.Sunara,and M.Matsunaga,“An annular-ring microstripantenna fed by a co-planar feed circuit for mobile satellite communica-tion use,”IEEE Trans.Antennas Propag.,vol.45,no.6,pp.1001–1008, Jun.1997.[2]N.Padros,J.I.Ortigosa,J.Baker,M.F.Iskander,and B.Thornberg,“Comparative study of high-performance GPS receiving antenna de-sign,”IEEE Trans.Antennas Propag.,vol.45,no.4,pp.698–706,Apr.1997.[3]J.Ollikainen,M.Fischer,and P.Vainikainen,“Thin dual-resonantstacked short patch antenna for mobile communication,”Electron.Lett., vol.35,pp.437–438,Mar.1999.[4]J.C.Batchelor and ngley,“Microstrip annular ring slot antennasfor mobile applications,”Electron.Lett.,vol.32,pp.1635–1636,1996.[5]S.Y.Lin and K.L.Wong,“Enhanced performances of a compactcon-ical-pattern annular-ring patch antenna using a slotted ground plane,”in Proc.2001Asia-Pacific Microwave Conf.,pp.1036–1039.[6]K.Fujimoto,A.Henderson,K.Hirasawa,and J.R.James,Small An-tennas.New York:Wiley,1987.[7]Y.S.Wu and F..Rosenbaum,“Mode chartfor microwave ring res-onators,”IEEE Trans.Microw.Theory Tech.,vol.21,pp.487–489,1973.Frequency Tuning of the Dielectric Resonator AntennaUsing a Loading CapH.K.Ng and K.W.LeungAbstract—A rigorous analysis of the slot-coupled hemispherical dielec-tric resonator top-loaded by a conducting cap is presented.The resonant frequency of the antenna can be tuned by changing the size of the loading cap.Measurements were carried out to verify the calculations,and reason-able agreement between theory and experiment is obtained.Index Terms—Dielectric resonator antenna(DRA),frequency tuning, parasitic patch.I.I NTRODUCTIONIn the last two decades,the dielectric resonator antenna(DRA)[1] has been studied extensively for a number of advantages,such as its small size,low loss,low cost and ease of excitation.The resonant fre-quency of a DRA depends on its operating mode,dielectric constant and physical shape.Although the source-free resonant frequencies of bare DRAs can be calculated by solving secular equations[2],[3],the method does not take any excitation effects into account and,conse-quently,the results normally deviate from the actual values.Even if a rigorous theory that considers the excitation source is used,the mea-sured and calculated resonant frequencies are usually different from each other because of fabrication tolerances.In recent years,attention has been paid on developing postmanufacturing frequency-tuning tech-niques for DRAs[4]–[6].However,all of them are purely experimental. Lately,an approach for frequency tunable designs using a parasitic slot has been studied theoretically and experimentally[7],but it is used for the design stage rather than for postmanufacturing tuning.In this com-munication,a rigorous theory for postmanufacturing frequency tuning of the hemispherical DRA is presented,with the DRA excited in its fundamental broadside TE111mode by a coupling aperture.The aper-ture-coupled source is commonly used for DRAs because it has sev-eral merits such as the feasibility of integration with monolithic mi-crowave integrated circuits(MMICs)and the avoidance of large probe reactance.In the analysis,use is made of the spectral-domain method to for-mulate the microstrip feedline part[8],whereas exact modal Green’s functions are employed for the DRA part.Integral equations for the cap currentand slotcurrentare formulat ed,which are solved using the method of moments(MoM).By changing the radius of the loading cap,the resonant frequency of the antenna can be tuned easily.Mea-surements were done to verify the calculations and good agreement between them is obtained.II.T HEORYFig.1(a)and(b)shows the side and top views of the DRA config-uration,respectively.The coupling slot of length L s and width W s couples the energy from the microstrip feedline to the hemispherical DRA of radius a=12:5mm and dielectric constant"ra=9:5. The grounded dielectric slab has dielectric constant"rs=2:33andheight d=1:57mm,and the50- microstrip feedline of width W f=Manuscript received July16,2004.This work was supported by the Research Grant Council of the Hong Kong SAR under Project CityU1284/03E.The authors are with the Wireless Communications Research Centre and De-partment of Electronic Engineering,City University of Hong Kong,Kowloon, Hong Kong.Digital Object Identifier10.1109/TAP.2004.8425830018-926X/$20.00©2005IEEE。