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1、摘要AbstractOwingtotheexponentialgrowthintheapplicationsofradiofrequencyidentification(RFID)，thedesignofRFIDantennawithperfectcharacteristicispresentlyoneofthemostchallengingtopics．TheuseofcommercialRFIDsysteminpracticalenvironmentusuallyrequirescircularlypolar
2、ized(CP)readerantennafororientationdiversity．Atpresent，commerciallyavailableRFIDtagsarecommonlydesignedasdipoleormicrostrip—typewitlllinearpolarization(LP)，thus，thepolarizationmismatchbetweenthereaderandtagwillresultsinonlyhalfofthetransmittedpowerreceivedbyt
3、heLPtag．Theoretically,themaximumreadingrangeofaCPtagCanbeimprovedgreatlywhenthereaderisalsoaCPtype(exhibitingthesamerotation)．ThedesignforcircularpolarizationRFIDantennahasagreatsignificance．Basedonantennaandmicrowavecircuittheories，circularlypolarizedRFIDant
4、ennasarestudiedinthisdissertation．Themainacademiccontributionsaresummarizedasfollows．1)Basedontheradiationcharacteristicsofdipoleantenna,acircularpolarizedRFIDtagantennaisproposed．Byusinggroovingtechnology,twodipoleantennasCanachievesamelengthsandunequalembed
5、slots．Oneofdipoleshasequalrealandimaginarypartsofimpedance，whileanotherdipolehasthecomplex-conjugatedimpedance．Thusthedifferenceimpedanceangleofthedipolesis90。．Then，thecircularlypolarizedradiationisattained．Amodifiedinductivelycoupledloopisappliedfortheimpeda
6、ncematchbetweentheantennaandtag．Theequivlentcircuitsofinductivelyandcapacitivelycoupledfedareproposed．ThiscouplingfeedCanisolatetherealpartandimaginarypartoftheimpedance，whichmadetheantennadesignsimpler．Finally,thecircularpolarizedradiationandimpedancematchin
7、ghavebeenwellexplainedandthedesignprocedureoftheantennashasbeensummarized．2)Basedonmicrostripantenna,acompactcircularlypolarizedtagantennainUHFbandformetallicobjectapplicationisproposed．Theprocessfortheformationofcircularlypolarizedwaveandimpedancematchingise
8、xplainedindetail．ThecompactCPoperationisachievedbyonlyadjustingtwopairsofunequalcrossd-slitlengths．Thecompleximpedancematchingoftheproposedtagantennacanbeeasilyobtainedbyselectingtheprope
