2005.11----MICROWAVE-AND-WIRELESS-COMPONENTS-LETTE

Copyright©2005IEEEReprintedfromIEEEMicrowaveandWirelessComponentsLetters,Vol.15,No.11,November2005ThismaterialispostedherewithpermissionoftheIEEE.SuchpermissionoftheIEEEdoesnotinanywayimplyIEEEendorsementofanyofUniversitätUlm'sproductsorservices.Internalorpersonaluseofthismaterialispermitted.However,permissiontoreprint/republishthismaterialforadvertisingorpromotionalpurposesorforcreatingnewcollectiveworksforresaleorre[e-mail]ment,youagreetoallprovisionsofthecopyrightlawsprotectingit.796IEEEMICROWAVEANDWIRELESSCOMPONENTSLETTERS,VOL.15,NO.11,NOVEMBER2005Ultra-Wideband(UWB)BandpassFiltersUsingMultiple-ModeResonatorLeiZhu,SeniorMember,IEEE,ShengSun,StudentMember,IEEE,andWolfgangMenzel,Fellow,IEEEAbstract—Anovelmicrostrip-lineultra-wideband(UWB)band-passfilterisproposedandimplementedusingamultiple-moderes-onator(MMR),aimingattransmittingthesignalsinthewholeUWBpassbandof3.1–10.6GHz.Inthedesign,thefirstthreeres-onantfrequenciesofthisMMRareproperlyadjustedtobeplacedquasiequallywithintheUWB.Then,theparallel-coupledlinesatthetwosidesarelongitudinallystretchedsoastoraisethefre-quency-dispersivecouplingdegreewiththecouplingpeaknearthecenteroftheUWB.Afteroptimizationofthisfilter,agoodUWBbandpassbehaviorwithfivetransmissionpolesistheoreticallyre-alizedandexperimentallyconfirmed.WithinthewholeUWBpass-band,thereturnlossisfoundhigherthan10dB,andthegroupdelayvariationislessthan0.23ns.IndexTerms—Multiple-moderesonator(MMR),parallel-cou-pledmicrostriplineandsizecompactness.,ultra-wideband(UWB)bandpassfilter.I.INTRODUCTIONULTRA-WIDEBAND(UWB)technologyhasgreatpoten-tialinthedevelopmentofvariousmoderntransmissionsystems,forinstance,through-wallimaging,medicalimaging,vehicularradar,indoor,andhand-heldUWBsystems,etc[1].InFebruary2002,theU.S.FederalCommunicationsCommis-sion(FCC)authorizedtheunlicenseduseofUWBdevicesforavarietyofapplications[1]–[3].Fortheindoorandhand-heldUWBsystems,theFCCrequiredthattheUWBbandwidthmustbestrictlycontainedbetween3.1and10.6GHz.Tomeettheserequirementsontheemissionlevelasdefinedin[1],specialre-searchinterestsinthemicrowavesocietyhavebeenrecentlyarousedonthedevelopmentofUWBbandpassfilters[4]–[6],coveringthewholeUWBpassbandwiththefractionalband-widthof109.5%atthecenterfrequencyof6.85GHz.Thetraditionalfiltertheorywassystematicallyestablishedundertheassumptionofnarrowpassband,andithasbeenfoundtobeverypowerfulinthedesignoffilterswithvariouspass-bands.In[7],afilterwithtightenedcouplingextentviaathree-linecouplingsectionwasreportedtooriginallyshowitsca-pacityinrealizingawidepassbandof40%to70%.In[8],awidebandpassbandof49.3%wasachievedintermsoftwostopbandsofafilterblockwiththetwotuningstubsonaringManuscriptreceivedMay24,2005;revisedJune13,2005.L.ZhuiswiththeDepartmentofMicrowaveTechniques,UniversityofUlm,UlmD-89069,Germany.HeisalsowiththeSchoolofElectricalandElectronicEngineering,NanyangTechnologicalUniversity,Singapore639798(e-mail:[e-mail]).S.SuniswiththeSchoolofElectricalandElectronicEngineering,NanyangTechnologicalUniversity,Singapore639798.W.MenzeliswiththeDepartmentofMicrowaveTechniques,UniversityofUlm,UlmD-89069,Germany.DigitalObjectIdentifier10.1109/LMWC.2005.859011resonator.However,thisfilterconfigurationwasfoundtheoret-icallydifficulttobedirectlyemployedforthedesignofsuchaUWBfilterwithabandwidthofabout110.0%.Tothebestofourknowledge,onlythesetwotypesoffiltershavebeenreportedtodayin[4]–[6]tohavereasonablyachievedsuchaUWBpassband.In[4]and[5],amicrostripringfilterwiththedualstopbandsbelow3.1GHzandabove10.6GHzwascon-structedtomakeupthemostinitialUWBfilter.However,thisfilterinfacthasmanyproblematicissues,suchasunexpectedpassbandsbelow3.1GHz,narrowlower/upperstopbands,largesize,complexityinconfiguration,andsoon.Lateron,analter-nativeUWBfilterwaspresentedin[6],whichwasconstructedbymountingthemicrostriplineinthelossycompositesubstratesoastoattenuatethesignalsathighfrequencies.Thereportedperformancesin[6]showedthatthisfilterhadaninsertionlosshigherthan6.0dBintheUWBpassbandandthereturnlossashighas4.5dBintheupperstopbandabove10.6GHz.Inthisletter,wepresentanovelcompactUWBbandpassfilterusingamicrostrip-linemultiple-moderesonator(MMR)[9]–[11].Itwasinitiallyexhibitedin[9]thatthefirsttworeso-nantmodesoftheconstitutedMMRcouldbeutilizedtogetherwiththeinput/outputparallel-coupledlinestoachievea70%widepassbandwithfourtransmissionpoles.In[10]and[11],thefirstthreeresonantmodesofanimprovedMMRwerenewlyconstructedtorealizefivetransmissionpoleswithloweredre-turnlossinthewholepassband.Followingtheworksin[10]and[11],theMMRhereistobeproperlymodifiedinconfigu-rationsoastoreallocateitsfirstthreeresonantmodesclosetothelower-end,center,andupper-endofthetargetedUWBpass-band.Also,thecouplingdegreeoftheinput/outputparallel-cou-pledlinesectionsislargelyraised,goodUWBpassbandperfor-mancesarerealizedanddemonstratedintheory.Lateron,allthepredictedparameters,i.e.,insertion/returnlossandgroupdelay,areexperimentallyverifiedinawidefrequencyincludingtheUWBpassband.II.PROPOSEDUWBFILTE