LTCC带通滤波器外文翻译.docx

LTCC带通滤波器外文翻译.docx

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LTCC带通滤波器外文翻译

来源：

MicrowaveConference,2008.EuMc2008.38thEuropean

BandpassFiltersforKa-BandSatelliteCommunicationApplicationsBasedonLTCC

Abstract----ThedesignoftwocompactbandpassfiltersforKa-bandsatellitecommunicationapplications（downlink17–22GHz）ispresented.Bothfiltersaredesignedwithadditionaltransmission

zerosatfinitefrequenciesinordertoimprovetheout-of-bandselectivity.Thefiltershavebeenrealisedaslow-costLTCCmodulesandthescatteringparametershavebeenmeasuredwithon-waferprobing.

I.INTRODUCTION

Modernmultimediasatellitesaregettingmorecomplexwithtransponderconnectivityrequirements,multiplecoveragebeams,etcetera.Hence,satelliteoperatorsincreasinglydemandflexibilityinfunction,efficientsignalroutingandsignalprocessing.Therefore,futureapplicationsinmultimediasatellitecommunicationsrequireinnovativecomponentswithhighRF-performanceand,atthesametime,withlowweight,smallsize,andhighreliability.

Advancedintegrationandpackagingtechnologies,suchaslowtemperatureco-firedceramics（LTCC）,combinedifferentdesigntechniqueswithlowcostoffabrication,smallsizeandmultiplefunctionality.LTCCtechnologyprovidesmodular,hybrid-integratedsystemswithahighdegreeofminiaturizationofmicrowavepayloadequipmentand,hence,flexibilityforadaptationtovaryingapplications.Itisoneofthereasons,whyLTCCbecameverypopular,notonlyforlowfrequency

designs,butforhighfrequenciesinthemicrowaveandevenmillimeter-waverangesaswell.

ThispaperfocusesonbandpassfiltersforKa-banddownlinkfrequenciesasimportantpartsofmultimediasatellitesignalchains,whicharebasedonLTCCmultilayertechnologyandcanbecombinedwithotherKa-bandmicrowaveLTCCmodulespresentlyunderdevelopment.

Thetwofilterspresentedheredisplayhighstop-bandisolationforanefficientsuppressionoftheKa-banduplinkfrequencies,andlowinsertionloss.Theyaredevelopedforseparatingchannelgroupswithtotalbandwidthsof500MHzupto1GHzinthefrequencyrangeof17–22GHz.Fordemonstrationpurposes,thesefiltershavebeendevelopedforacentrefrequencyoff0=19.5GHz.Additionalefforthasbeenspentininvestigatingtheinfluenceofgroundinganddifferentconductivepastesonthefilterperformance.

II.DESIGNOFLTCCBANDPASSFILTERSWITHTRANSMISSIONZEROSATFINITEFREQUENCIES

Thefollowingspecificationshavebeenchosenforthedesignofthebandpassfilter:

----Passband:

18000–21000MHz;

----Maximumin-bandinsertionloss:

2dB;

----Minimumin-bandreturnloss:

12dB（VSWR<1.7）;

---Steepnessofthefilterslopes:

20dB/GHz.

Besidesmeetingthesespecifications,thefollowingproblemshavetobesolvedwithrespecttothehighfrequenciesofoperation:

（a）feedingofthefilterswithlow-losshalf-wavelengthtransmissionlinestoimprovethematchingattheinputandoutputports;（b）providinghigh-qualitytransitionsfromthestriplinesembeddedintheLTCCmoduletothecoplanarground-signal-groundtestportforon-waferprobing.

Becauseofthestrictin-bandrequirements,thenumberofresonatorsconstitutingthefiltercouldnotbehigherthanfour.Inordertoprovidetherequiredsteepnessofthefilterskirts,twodesignswithtransmissionzerosatfinitefrequencieshavebeenchosen:

acoupled-linefilterdesignandacross-coupledfilterdesign.

A.Coupled-lineFilterDesign

Forthecoupled-linefilter,weappliedtheestablisheddesignofbandpassfiltersbasedonhalf-wavelengthcoupledresonatorswithattenuationzeros[8].Withthismethod,attenuation

polesareobtainedbybothinput/outputandinter-stagecoupling.Tap-coupling,parallel-couplingandanti-parallelcouplingstructureswereinvestigated.Forthetap-couplingstructure,anattenuationpoleisgeneratedatthatfrequencyatwhichtheelectricallengthfromthephasecentreofthetaptotheopenendoftheresonatorbecomes90°.Inordertogenerateanattenuationpoleatp×f0,atap-couplingshouldbedevisedatapositionwheretheelectricallength⎝tapfromtheopenisequivalentto90°/patcentrefrequency。

Fortheparallel-coupledlinesstructure,transmissionbecomeszeroatthefrequencywheretheelectricallengthofthecoupledlinebecomes180°.Therefore,togenerateanattenua-tionpoleatp×f0,theelectricallengthofthecoupledlineatcentrefrequencyθphastobechosen180°/p.Sincetheelectricallengthofahalf-wavelengthresonatoris180°,pwillexceed1.Thisimpliesthatanattenuationpolecanonlybeobtainedatfrequenciesabovethepass-band.

Fortheanti-parallelcoupledstructure,wheretheopenendsoftheparallellinesareplacedsidebyside,apoleisgeneratedatp×f0undertheconditionθap=90°/p,whereθapistheelectricallengthofthecoupledlineatcentrefrequency.Asforthetapcoupling,theattenuationpolecanbeobtainedbothbelowandabovethepass-band.

Twotap-couplingsandoneanti-parallelcouplinghavebeenusedtodesignafour-polebandpassfilterwiththreeattenuationzerosplacedat16.82GHz,22.43GHz,and32.88GHz.ThefilterlayoutisshowninFig.1,panel（a）.Half-wavelengthfeed-lineshavebeenemployedtoreducetheinfluenceofthefeed-lineimpedanceandprovide,therefore,goodimpedancematching.Theinitialsimulationofthefilterstructurewasperformedbya2.5-dimelectromagneticfieldsimulator（AWRMicrowaveOffice）.Verificationwascarriedoutwitha3-dimfullwavesimulator（CSTMicrowaveStudio）.Thesimulatedfrequencyresponseofthefilterispresentedinpanel（b）ofFig.1.Thein-bandinsertionlossislessthan1.2dB.Thereturnlossisnotworsethan14.5dB.Thecharacteristicslopesatthebandedgesamounttoabout20dB/GHz.

图1Four-polecoupled-linesbandpassfilterwiththreeattenuationpoles:

layout（a）andsimulatedfrequencyresponse（b）.

B.Cross-coupledFilterDesign

Thesynthesisofbandpassfilterswithsource-loadcouplingwastheoreticallydescribedandexperimentallyverified,especiallyfortwo-polefilters.Suchacross-couplingallowstoobtainafrequencyresponsewithequalnumbersoftransmissionpolesandzeros.Thesamesource-loadcouplingcanbeappliedtohigher-orderfiltersaswell,allowingforadditionalstop-bandattenuation.

Theschemeofafour-polecross-coupledfilterisdepictedinFig.2,panel（a）.Theresonatorsarerepresentedbynodes,andthecouplingsareindicatedasconnectinglines.Twoadditionalcouplingshavebeenaddedtothefilter.ThecouplingC1isacapacitivecouplingbetweentheinputandtheoutputfeedlinesofthefilter;thecouplingC2isaninductivecrosscouplingbetweenthefirstandthefourthresonator.Adjustingthestrengthofthecross-coupling,thepositionsofthetransmissionzerosandthesteepnessofthefilterslopescouldbetunedtothedesiredvalues.

Thetopologyofthefour-polecross-coupledfilterisshowninpanel（b）ofFig.2.ThefilterwasimplementedusingLTCCmulti-layerceramicsandconsistedoffourC-shapedstriplineresonators,situatedintwoconductivelayers:

thefirstandthefourthresonatorlineswereprintedinthebottomlayer,whilethesecondandthethirdresonatoraswellasthefeed-lineswereplacedonthetopconductivelayer.Theseparationoftheresonatorsintheverticaldirectionenablesthereductionoftheoverallsizeofthefilter,comparedwithanentirelyplanarstructure.Thenumericalsimulationswereperformedintwostepsasdescribedabove.Theexpectedfrequencyresponseofthecross-coupledfilterisshowninFig.2,panel（c）.Twopairsoftransmissionzeros,placedsymmetricallyaroundthepass-band,areclearlyvisibleinbothstop-bandsofthefilter.Thein-bandinsertionlossILwasnotworsethan1.4dB,andthereturnlossRLbetterthan15dB.Theareaoccupiedbythefilterwas5×5mm2.Thesteepnessoftheskirtsamountedto45dB/GHz.Comparingtheresponsesofthetwotypesoffilter（Fig.1andFig.2）revealsthatthecross-coupledfilterprovidesmuchhigherattenuationinthenarrowstop-bandbut,at

frequenciesaround32-35GHz,theperformancesuffersfromaspuriousharmonic,whichwassuppressedbyoneofthetransmissionzerosinthecoupled-linefilterdesign.

图2Four-polecross-coupledfilter:

（a）schematic,（b）multi-layerlayout,（c）simulatedfrequencyresponse.

III.FABRICATIONANDMEASUREMENTSOFTHEFILTERS

BothfilterstructuresweremanufacturedusingtheDuPontGreenTape™951LTCCsystemwithathicknessofthedielectriclayersof205μm（DP-951AX/PX）andanominaldielectricpermittivityεr=7.8aftersinteringThismaterialsystemhasbeenchosenforfabricaton,becauseitincludesavarietyofappropriateinks,photoimageablescreenprinting（Fodel®-technology）[12],andprovidessatisfactoryhermeticityandplanarityofthesinteredmodules.Fig.3showsaphotographofLTCC-integratedKa-bandfilters.

图3LTCCmodulewiththefiltersamplesfabricated.

Twodifferentconductivematerialswereusedforthefabrication:

photodefinedsilverpastewithathicknessof7μmaftersintering,andalaser-cutsilverfoilwithathicknessof25μm.ThebuiltstackofLTCC-layersintegratingthedevelopedfilterswaslaminatedwithapressureof20MPaandatemperatureof70°Cfor10minutes.Theco-firedsinteringwasconductedinamufflefurnaceusingafiringprofilewith875°Cpeaktemperaturefor10minutesandanoveralldurationofabout450minutes.

TheelectricalcharacterisationofthefilterswasconductedusinganAgilentE8367APNAvectornetworkAnalyser（upto67GHz）and200-μm-pitchcoplanarground-signal-groundprobetips（|Z|-probesfromSuessMicroTec）.

Themeasuredperformanceofthetwodifferentcoupled-linefiltersamplesisshowninFig.4.W