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1、ProceedingsofAsia-PacificMicrowaveConference2007HairpinTunableBandpassFilterwithImprovedSelectivityandTunabilitySeung-UnChoi,Moon-SeokChung,andSang-WonYunDepartmentofElectronicEngineeringSogangUniversityShinsu-dong,Seoul,121-742,Koreaulysses83gsogang.ac.krAbstract-Inthispaper,ahairpintunablebandp
2、assfilterwhichcharacteristics,weproposethefourth-ordertunablebandpasshasenhancedselectivityandtunabilityisproposed.Thefilter.varactorsloadedopenstubsbetweenquarter-wavelengthresonatorsareintroducedtoexhibittransmissionzerosneartheGenerally,transmissionzerocanbegeneratedbycross-passbandandthusbett
3、erselectivityinthetuningrange.Incoupling[7].Ontheotherhand,theattenuationpoleisaddition,symmetricalfiltershapecaneasilyobtainedbyeachofintroducedbytheopenstubinourstructure.Hence,thetwoopenstubswhichareusefultocontrolnotchfrequencies.Theenhancedselectivitycanbeeasilyobtainedbyadjustingtheoptimald
4、esignoftwo-stagetunablebandpassfilterofvaractortwovaractorloadedopenstubs.Inaddition,atunabilityisloadedhairpinresonatorwithopenstubwhichworksasK-limitedbythefrequencyrangeoverwhichthefilterelementsinvertermakespossibletomeetthewidebandcouplingmaintaintheirreactancesandcouplingrelationshipsaswell
5、asrelationshipsinoverallfrequencytuningrange.Thethetuningrangeofvaractordiodes.Thevaractordiodeisfixedmeasurementresultsshowtheproposedhairpintunableelementintunablefilterdesign,therefore,thecouplingbandpassfilternotonlyhastheenhancedtuningrangeof23.5%,relationshipsmustbeconsideredtoenhancethetun
6、ability.Forbutalsohasthesymmetricalfiltershapeinoveralltuningrangenarrow-bandwidthapplications,ithasbeenshownthattheincomparisonwithconventionalhairpintunablebandpassfilter.couplingcoefficientbetweenadjacentresonatorsandexternalThehairpintunablebandpassfilterisdesignedandtestedat1.7Qareconvenient
7、parameterstoverifythecouplingGHz.relationship.Forthevalidationofcouplingrelationships,werepresentthesimulatedresultofcouplingcoefficientsandKeywords-Bandpassfilters;hairpinresonators;microstrip;externalQ.Inthispaper,th
