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1、射频电路理论与技术主讲人：唐万春教授8/13/2021Impedancemeasuredbysmallsignal1.ImpedancemeasuredbySparametermeasurementTheimpedanceofabasicpart(capacitor,inductor,orresistor)canbemeasuredbyusinganimpedancemeteroranetworkanalyzer.Theimpedanceofablock,asub-system,oranentiresystemcan
2、alsobemeasuredbyusinganimpedancemeteroranetworkanalyzer.Allofthemarebasedontheprincipleofsmallsignalmeasurement.8/13/2021Theoretically,therelationsbetweeninputandoutputvoltagereflectioncoefficients,GinandGout,andinputandoutputSparameters,S11andS22,are(2.1)(2.2)
3、8/13/2021Thecables,port1andport2,arewell-calibratedintheimpedancemeasurementbyanetworkanalyzer.TheDUT(DeviceUnderTest)isinanidealstateofeitherforwardorbackwardisolation.ThenwehaveImpedancemeasurementthereforecanbeconductedbymeansoftheS11orS22testingwithanetwork
4、analyzer.8/13/20212.SmithChart:ImpedanceandAdmittanceCoordinationAsamatteroffact,theSmithChartisarepresentationofthereflectioncoefficientcomplexplane,thatisIntransmissionlinetheory,therelationshipbetweenthereflectioncoefficientandtheimpedanceisknownas8/13/2021E
5、liminatingxEliminatingr8/13/2021SometimesitismoreconvenienttocoordinatetheSmithChartbyadmittance,y,insteadofimpedancez,8/13/2021Infigure2.3,thenumberalongUaxisdenotethevaluesofthenormalizedresistancerforthecircle,andthenumbersalongthebiggestcircledenotethevalue
6、softhenormalizedreactancexarcs.Infigure2.4,thenumberalongUaxisdenotethevaluesofthenormalizedconductancegcircles,andthenumbersalongthebiggestcircledenotethevaluesofthenormalizedsusceptancebarcs.Ifamatchingnetworkconsistsofonlypassivepartseitherinseriesorinparall
7、el,thentheimpedancecoordinationisappliedwhenthepartisaddedinseries,whiletheadmittancecoordinationisappliedwhenthepartisaddedinparallel.8/13/2021Somespecialpoints:ThecenterO,r=1,x=0,orR=Z0,X=0.CharacteristicimpedanceTheleft-mostpointW,r=0,x=0,orz=0.“Short-circui
8、ted”stateTheright-mostpointE,r=∞,x=0,orz=∞.“open-circuited”stateTheupper-mostpointN,r=0,x=1PurelyinductiveThebottom-mostpointS,r=0,x=-1PurelycapacitiveInadditiontobothnormal
