Design of a 900 1800 MHz Dual-Band LTCC Chip Anten

Anotherchipantenna,usingmeanderlinesmountedonLTCCchip,hasawideband-width(19.1percentatVSWR2)at1800MHz.3BecausetheseplanarmeanderlinesaredepositedonthesurfaceoftheLTCCchip,theirsizeislargerthanthatwithembed-dedmeanderlines.Inthisarticle,LTCCtech-nologyisusedtodevelopa900/1800MHzCHI-CHANGLIN,YU-JUICHANGANDHUEY-RUCHUANGNationalChengKungUniversityTainan,Taiwan,ROCRecently,multi-layerLTCCtechnologyhasbeenusedextensivelyfortheminiaturizationofRFpassivecompo-nentsandantennas.Inadditiontothehighin-tegrationbyembeddingcomponentsandin-terconnects,highQpassiveelementshavebeendemonstratedwithLTCCtechnology.1Itissuitabletointegrateantennasandotherpas-sivecomponents,evenwithactivedevices.Higherintegrationandmorecompactstruc-turesmakeLTCCtechnologypopularinRFapplications.AchipantennausingLTCCtechnologyfor2.45GHzapplicationshasbeenreported.2DESIGNOFA900/1800MHZDUAL-BANDLTCCCHIPANTENNAFORMOBILECOMMUNICATIONSAPPLICATIONSThisarticlepresentsthedesignsimulation,implementationandmeasurementofaminiaturized900/1800MHzdual-bandlowtemperatureco-firedceramic(LTCC)chipantennaformobilecommunicationapplications.Theuseofahelix-monopoletypedual-bandantennaisrealizedinamulti-layerprintedLTCCstructure.TheAnsoftHFSS3-DEMsimulator,basedonthefinite-elementmethod(FEM),isemployedfordesignsimulation.Inthesimulatedstructure,thePCBboardoftheRFcircuit,connectedtothechipantenna,isalsoincluded.Ahelix/three-monopolestructurechipantennaisdesignedtoachieveenoughbandwidthatthe900and1800MHzbands.Althoughthemeasuredantennaperformanceisshiftedtoahigherfrequencyforboththe900and1800MHzbands,theantennapatternsoftherealizedchipantennaareveryclosetotheomnidirectionalpatternofadipoleantennaat900and1800MHz.ReprintedwithpermissionofMICROWAVEJOURNAL®fromtheJanuary2004issue.©2004HorizonHousePublications,Inc.dual-bandchipantenna.Themulti-layerprintedhelical-monopoleanten-nastructureisdesignedtoobtainthedual-bandfunction.TheHFSS3-DEMsimulator,basedonthefinite-el-ementmethod,isemployedforde-signsimulation.Simulationresultsarecomparedwiththemeasuredper-formanceanddiscussed.DUAL-BANDANTENNADESIGNAhelical-monopolecombinationstructureforGSM900/1800MHzhasbeenproposedfordual-bandantennadesigns.4Figure1showsadual-bandhelical-monopolecombinationanten-na,amulti-layerprintedhelical-mono-poleLTCCchipantennaandthegeometryofaLTCCchipantennamountedonaFR-4substrateboard.Acrosssectionoftheprintedhelicalstructure,realizedbyusingviaholestoconnectupper-andlower-layermetals,isshowninFigure2.Theprintedmonopoleislocatedonthemiddlelay-er.Thedielectricconstantandlosstan-gentoftheLTCCceramicare7.8and0.0047,respectively.The3.6milthicktop-layerceramicisplacedabovetheupper-layermetal.Thethicknessesoftheotherlayersarealsoshown.Thedi-mensionsoftheLTCCchipandeachlayerareconvertedfromthefree-spacehelical-monopoleantennatothemulti-layerceramicbasedonitsdielec-tricconstant.Thefirstmonopoleantenna,asshowninAppendixA,contributestothehigherfrequency(1800MHz)band.Thehelicalantennaistunedtothelow-erfrequency(900MHz)band.Intheinitialdesign,theinputimpedanceoftheLTCCchipantennaiscapacitive,henceseveralcloserturnsofhelicallinesareusedasaninductorforinputimped-ancematching.Inordertoincreasethebandwidth,threeprintedmonopoleswithdifferentlengthsareused,integrat-edwiththehelix.Figure3illustratesthetripleresonantfrequenciesusedtoachieveawiderbandwidth.ThedimensionsoftheLTCCchipantennaare210×515×44.8mil(5.4×13.1×1.14mm).Thewidthsoftheem-beddedmeanderlinesandprintedmonopoleantennasinsidetheLTCCchipareall10mil.ThedimensionsoftheFR-4circuitboardare1.400×2.265×0.039in.(35.6×57.5×1mm)andthesizeofthegroundplaneis1.400×1.760in.(35.6×44.7mm).Additionaldimen-sionsarelistedinTable1.SIMULATIONANDMEASUREDRESULTSFigure4showsthesimulatedcur-rentdistributionsofthedual-bandLTCCchipantennaat900MHzwithdifferentphaseat0°,45°,90°and135°.ThecurrentflowingalongthemetalstripsinsidetheLTCCpackagecanbeobserved.Figure5showsthephoto-graphofafabricateddual-bandLTCCchipantennaonaFR-4PCBboardandthesimulatedandmeasuredreturnlosses.Itisobservedthatthemeasuredresonantfrequenciesareshiftedfromthesimulated900and1800MHztoTECHNICALFEATURE3.6MIL3.6MIL25.2MIL26.8MIL3.6MIL8LAYERS8.0MIL2LAYERS3.6MIL2LAYERS▲Fig.2CrosssectionoftheLTCCchipantenna.BWFREQUENCYS11f1f3f2▲Fig.3Tripleresonancesfromthemonopoles.DLmLhLS(a)(b)(c)FR-4CIRCUITBOARDLTCCNOGROUNDBELOWLTCCMICROSTRIPGROUNDPLANELENGTHGROUNDPLANEWIDTHS▲Fig.1Adual-bandhelical-monopoleantenna;(a)schematic,(b)LTCCchipand(c)chipantennamountedonaFR-4board.TABLEIPARAMETERSOFADUAL-BANDLTCCCHIPANTENNALengthoffirstmonopole(mil)280(7mm)Lengthofsecondmonopole(mil)170Lengthofthirdmonopole(mil)110Lengthofhelicalantennas(L1)(mil)140Widthofhelicalantennas(W1)(mil)40Widthofmeanderlines(W2)(mil)10Lengthofhelicalinductors(mil)140Widthofhelicalinductors(mil)20LTCCpackage(mil)210×515(5.4mm×13.1mm)FR4substrate(mil)1400×2265(35.6mm×57.5mm)Groundplane(mil)1400×1760(35.6mm×44.7mm)higherfrequencies,1040and1900MHz.Themeasuredreturnloss,S11,is–21.8and–20.9dBat1040and1900MHz,respectively.ThesimulatedandmeasuredreturnlossesarealsolistedinTa