AnalysisandDesignofANovelSmallMicrostripPatchAntennaABSTRACT:Microstripantennashavebeenwidelyusedincommunicationsystems.DesignandanalysisofawidebandU-shapedparasiticMicrostripPatchAntennawhichiscoupledbythemainpatchandU-shapedparasiticpatchesispresentedinthispaper.Twoparasiticelementsareincorporatedintotheradiatingedgesofarectangularpatchwhoselengthandwidthareg/2andg/4,respectively,inordertoachievewidebandwidthwithrelativelysmallsize.Theproposedantennaisdesignedandfabricatedonasmallsizegroundplane(25mm30mm)forapplicationofcompacttransceivers.Themeasuredbandwidthis1.5GHz(4.78-6.28GHz)withtwoseparateresonantfrequenciesat5.12and6.08GHz.Themeasuredradiationpatternsaresimilartothoseofaconventionalpatchantennawithslightlyhighergainsof6.4dBand5.2dBateachresonantfrequency.KEYWORD:Parasiticpatchantenna,U-shapedparasiticpatches,widebandwidth.1. INTRODUCTIONInhigh-performanceaircraft,spacecraft,satellite,andmissileapplications,wheresize,weight,cost,performance,easeofinstallation,andaerodynamicprofileareconstraints,low-profileantennasmayberequired.Presentlytherearemanyothergovernmentandcommercialapplications,suchasmobileradioandwirelesscommunications,thathavesimilarspecifications.Tomeettheserequirements,microstripantennas1-38canbeused.Theseantennasarelowprofile,conformabletoplanarandnonplanarsurfaces,simpleandinexpensivetomanufactureusingmodernprinted-circuittechnology,mechanicallyrobustwhenmountedonrigidsurfaces,compatiblewithMMICdesigns,andwhentheparticularpatchshapeandmodeareselected,theyareveryversatileintermsofresonantfrequency,polarization,pattern,andimpedance.Inaddition,byaddingloadsbetweenthepatchandthegroundplane,suchaspinsandvaractordiodes,adaptiveelementswithvariableresonantfrequency,impedance,polarization,andpatterncanbedesignate,39-44.Demandforcompactandmultifunctionalwirelesscommunicationsystemshasspurredthedevelopmentofmultibandandwidebandantennaswithsmallsize.Microstrippatchantennasarewidelyusedinthisregardastheyoffercompactness,alowprofile,lightweight,andeconomicalefficiency.However,themicrostrippatchantennaislimitedbyitsnarrowoperatingbandwidth.Therearenumerousandwell-knownmethodstoincreasethebandwidthofantennas,includingincreaseofthesubstratethicknestheuseofalowdielectricsubstrate1,theuseofvariousimpedance-matchingandfeedingtechniquestheuseofmultipleresonators3-7,andtheuseofslotantennageometry8.However,thebandwidthandthesizeofanantennaaregenerallymutuallyconflictingproperties,thatis,improvementofoneofthecharacteristicsnormallyresultsindegradationoftheother.Recently,severaltechniqueshavebeenproposedtoenhancethebandwidth.In9-11,utilizingtheshortingpinsorshortingwallsontheunequalarmsofaU-shapedpatch,U-slotpatch,orL-probefeedpatchantennas,widebandanddual-bandimpedancebandwidthhavebeenachievedwithelectricallysmallsize.Inthiswork,awidebandmicrostrippatchantennaemployingparasiticelementsisinvestigated.TwoU-shapedparasiticelementsareincorporatedalongtheradiatingedgesofaprobefedrectangularpatchantennasoastoobtainwidebandoperatingfrequency.Inaddition,theantennaisrelativelysmallincomparisonwiththeconventionalparasiticpatchantennadescribedin4,5.Performanceoftheproposedantennaiscalculatedandmeasured.ThemethodsofanalysisformicrostripantennasisgiveninSection2.TheproposedantennageometryisdescribedinSection3.ThefabricatedantennaandexperimentalvalidationsarepresentedinSection4.2. METHODSOFANALYSISTherearemanymethodsofanalysisformicrostripantennas.Themostpopularmodelsarethetransmission-line16,35,cavity12,16,18,35,andfullwave(whichincludeprimarilyintegralequations/MomentMethod)22,26,71-74.Thetransmission-linemodelistheeasiestofall,itgivesgoodphysicalinsight,butislessaccurateanditismoredifficulttomodelcoupling75.Comparedtothetransmission-linemodel,thecavitymodelismoreaccuratebutatthesametimemorecomplex.However,italsogivesgoodphysicalinsightandisratherdifficulttomodelcoupling,althoughithasbeenusedsuccessfully8,76,77.Ingeneralwhenappliedproperly,thefull-wavemodelsareveryaccurate,veryversatile,andcantreatsingleelements,finiteandinfinitearrays,stackedelements,arbitraryshapedelements,andcoupling.Howevertheyarethemostcomplexmodelsandusuallygivelessphysicalinsight.Inthischapterwewillcoverthetransmission-lineandcavitymodelsonly.Howeverresultsanddesigncurvesfromfull-wavemodelswillalsobeincluded.Sincetheyarethemostpopularandpractical,inthischaptertheonlytwopatchconfigurationsthatwillbeconsideredaretherectangularandcircular.Representativeradiationcharacteristicsofsomeotherconfigurationswillbeincluded.ANTENNADESIGNFig.1.GeometryoftheproposedmicrostripGnd.patchantennawithU-shapedparasiticelements.Fig.1depictsthetopandsideviewsoftheproposedantenna.Theproposedantennaconsistsofaprobefedhalf-wavelengthrectangularpatchandtwoU-shapedparasiticelementsincorporatedaroundtheradiatingedgesoftherectangularpatch.Ingeneral,thelengthandwidthoftherectangularpatchantennaareclosetohalf-wavelength.However,thelength(LR)andwidth(WR)ofthemainpatchvaryfromthepropo