Tri-section stepped-impedance bandpass filter with wide stopband performance

介绍SIR

TRI-SECTIONSTEPPED-IMPEDANCEBANDPASSFILTERWITHWIDESTOPBANDPERFORMANCE

YunxiuWang,1,2Bing-ZhongWang,1JianpengWang,1ShanshanGao,1andShaoqiuXiao11

InstituteofAppliedPhysics,UniversityofElectronicScienceandTechnologyofChina,Chengdu610054,People’sRepublicofChina2

SchoolofPhysicsandElectronicInformation,China-WestNormalUniversity,Nanchong637002,People’sRepublicofChinaReceived30August2006

ABSTRACT:Inthispaper,acompactmicrostripbandpass lterwithwidestopbandperformanceispresented.Widestopbandperformanceisachievedbyintroducingbothstepped-impedanceresonatorandover-couplingtechnique.Withthenewstructure,the lterhasnotonlywideupperstopbandperformancewithharmonicfrequencyoutside5f0butalsocompactsize.©2007WileyPeriodicals,Inc.MicrowaveOptTechnolLett49:870–872,2007;PublishedonlineinWileyInter-Science(http://www.mianfeiwendang.com).DOI10.1002/mop.22255Keywords:bandpass lter;tri-sectionstepped-impedanceresonator;harmonicfrequency;over-coupling1.INTRODUCTION

Figure1BasicstructureoftheSIR,tri-sectiontype

highsuppressionperformance,weusethetri-sectionSIR.Figure1showsthebasicstructureoftwocascadedtri-sectionSIRs.Atresonance,eachtri-sectionSIR’selectricallengthis /4.ThecharacteristicimpedancesofthreecascadedsectionsareZ1,Z2,Z3,andthecorrespondingelectricallengthsare 1, 2, 3,respectively.Theadmittance,Y,lookingfromoneendoftheSIRtotheotherisgivenby[7]

Z3Z1 Z2Z1tan 2tan 3 Z2Z3tan 1tan 2 Z32tan 1tan 3

Y

12323133112123

Inmodernwirelessandmobilecommunicationsystems, ltersarealwaysplayingimportantandessentialroles.Planar ltersareparticularlypopularstructuresbecausetheycanbefabricatedusingprintedcircuittechnologyandaresuitableforcommercialapplicationsbecauseoftheircompactsizeandlowintegrationcost.Foraplanar lterdesign,itisnecessarytoselectproperresonatortypesinceresonatorsarethebasiccomponentsofa lter.Toreducetheresonator’ssize,severaltypesofresonatorssuchasthestepped-impedanceresonator(SIR),U-shapedhairpinresona-tor,theopen-loopresonator,andthefoldedopen-lineresonatorhavebeenproposedtodesigndifferentkindsofbandpass lters[1].Amongthesepopularresonators,themostfrequentlyusedistheSIRasitispresentednotonlytoreducethesizeofresonators,butalsocontroltheresonantfrequencybychangingitsstructureparameters[2,3].

Toreduceinterferencebykeepingtheout-bandsignalsfromreachingasensitivereceiver,ahighperformance lterwithwideupperstopbandisalsorequired.However,theplannarbandpass ltersmadeof /2uniform-impedanceresonatorshaveinherentlyspuriouspassbandsatthemultiplesofcenterfrequencyf0.Several lterswiththeSIRsarepresentedtoshiftthespuriouspassbandstohigherfrequenciessoastoextendtheupperrejectionband[2–4].However,thestepped-impedancemethodcanonlypushthespuriouspassbandtothehigherfrequencyinsteadofsuppressingit.Byincorporatingresonatorsthathavesamefundamentalreso-nantfrequencybutwithdifferentspuriousfrequencies,thespuri-ousresponsescanbesuppressedwiththestopbandrejectionmorethan4f0[5].Ontheotherhand,over-couplingtechniqueisalsousedintheparallelcoupling lterdesignasitcansuppressharmonicresponseeffectively[6].

Inthisletter,weproposeanovelbandpass lterstructure.Bycombiningboththetri-sectionSIRandtheover-couplingtech-niquementionedabove,thenew lterhasnotonlycompactsizebutalsowidestopbandperformancewithharmonicfrequencyoutside5f0.

2.CIRCUITDESIGN

(1)

Atresonance,Y 0,whichindicatesthattheconditionforresonanceis

Z2Z2Z3

tan 2tan 3 tan 1tan 2 tan 1tan 3 1Z3Z1Z1

(2)

Forthesimplicityofanalysis,wekeeptheconditionof 1 2,andsetk Z2/Z1,m Z2/Z3thenEq.(2)canberewrittenas

m

k

tan 1tan 3 ktan2 1 1(3)

UsingEq.(3)andsubstituting 3with 1,wehavethetotalnormalizedelectricallengthoftri-sectionSIR

1 ktan2 12 1

total 2 2 1 3 / 2 1 tan

1

(4)

Whenmandkare xed,totalelectricallengthbecomesafunction

of 1anditsminimumvaluecouldbefound.Withk 2(atypicalvaluefortwo-sectionSIR)andasetofm(rangingfrom2to8),thetotalnormalizedelectricallengthoftwo-sectionandtri-sectionSIRsasafunctionof 1areshowninFigure2.Itisobservedthatthetotalnormalizedelectricallengthoftri-sectionissmallerthantwo-section’swith 1atcertainvalues.Fromtheanalysismen-tionedabove,wecanalsoknowthattheharmonicfrequencyoftri-sectionSIRcanbeadjustedbychangingtheimpedanceratiokandm.

Tosuppressthespuriousresponse,weusetheover-couplingtechniquehere.Forthecoupled-linestage,atransmissionzerocanbedeterminedbyfollowingequation[6]

Z0osin 0l 0

Tri-section stepped-impedance bandpass filter with wide stopband performance

Z0esin el

(5)

Theconventionaltwo-sectionSIRhasbeenwidelyusedinband-pass lterdesign.Inthisletter,tofurtherreducethesizeandget

870MICROWAVEANDOPTICALTECHNOLOGYLETTERS/Vol.49,No.4,April2007DOI10.1002/mop

Word文档免费下载Word文档免费下载:Tri-section stepped-impedance bandpass filter with wide stopband performance (共3页,当前第1页)

Tri section stepped impedance bandpass filter with wide stopband performance相关文档

最新文档

返回顶部