资源描述：
《UWB 天线的基本限制理论》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、Fundamental-LimitPerspectivesonUltra-WidebandAntennasAbstract:Thefundamental-limittheoryforantennasizeprovidesatheoreticallimittoassistintheevaluationofantennaperformanceintermsofantennasizeandfractionalimpedancebandwidth,aswellasavoidsearchingforanantenn
2、awithunrealisticperformancespecifications.Previousresearchonthelimittheoryfocusedonelectrically-small,resonantantennas.Inthispaper,wediscusshowtheclassicalfundamental-limittheorycanbeinterpretedforultra-widebandantennas.ThefrequencyresponseofChu’sequivale
3、ntcircuitmodelforsphericalTMmodessuggeststheconceptofanidealantenna.Theidealantennahasultra-widebandantennacharacteristics.Theimpulseresponseandcut-offfrequencyversusantennasizeforvarioussphericalTMmodesarealsopresented.INTRODUCTIONSinceWheeler[1]firstint
4、roducedtheconceptoffundamental-limittheoryin1947,manypeoplehaveinvestigatedthetheoreticallimitationofantennaperformanceversussize[2—6].Inessence,thefundamental-limittheoryforantennasshowsthatsize,efficiency,andbandwidtharetrade-offsinthedesignprocess.Thep
5、reviousresearcheffortsonthelimittheoryfocusedonelectrically-small,resonantantennas,eventhoughthetheoryisnotnecessarilylimitedtoelectrically-small,resonantantennas.Inaddition,previousresearchemphasizedradiation-Qastheperformanceevaluationfactor.Inthispaper
6、,weinvestigatehowtheclassicfundamental-limittheorycanbeinterpretedforultra-widebandantennas.CONCEPTOFIDEALANTENNATheradialwaveimpedanceofsphericalmodes(normalizedbytheintrinsicwaveimpedance)canbewrittenasthefollowing[2]:(1)WherethesphericalHankelfunctiono
7、fthesecondkindandkisisthewavenumber.Chu’sequivalentcircuit[2]forthesesphericalmodescanbefoundfromthenormalized,radialwaveimpedance.Inthesamemanner,theequivalentcircuitmodelforTEcasescanalsobeobtained.Ifweconsiderhowmuchpowerisdeliveredtospace(radiation),t
8、heChu’sladdercircuitcanbeturnedintoatwo-portproblemasshowninFig.1b.Inthiscase,theport1isantennaspherecircumscribingtheantennastructure(seeFig.la).Theradiusoftheantennasphereisdenotedbya.Port2isaconsideredtorepresent
