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1、论文中北大学分校学位论文英文翻译作者姓名：学科、专业：通信工程学号：指导教师：副教授完成日期：2010-6-10目录PROPERTIESOFANTENNAS22.1ANTENNARADIATION32.2GAIN52.3EFFECTIVEAREA82.4PATHLOSS82.5RADARRANGEEQUATIONANDCROSSSECTION102.6WHYUSEANANTENNA?12天线的功能122.1天线辐射132.2天线增益152.3天线有效面积172.4路径损耗182.5雷达距离方程和截面
2、202.6为什么使用一个天线？21英文原文：PROPERTIESOFANTENNASOneapproachtoanantennabookstartswithadiscussionofhowantennasradiate.BeginningwithMaxwell’sequations,wederiveelectromagneticwaves.Afterthatlengthydiscussion,whichcontainsalotofmathematics,wediscusshowthesewavese
3、xcitecurrentsonconductors.Thesecondhalfofthestoryisthatcurrentsradiateandproduceelectromagneticwaves.Youmayalreadyhavestudiedthatsubject,orifyouwishtofurtheryourbackground,consultbooksonelectromagnetics.Thestudyofelectromagneticsgivesinsightintothemath
4、ematicsdescribingantennaradiationandprovidestherigortopreventmistakes.Weskipthediscussionofthoseequationsandmovedirectlytopracticalaspects.Itisimportanttorealizethatantennasradiatefromcurrents.Designconsistsofcontrollingcurrentstoproducethedesiredradia
5、tiondistribution,calleditspattern.Inmanysituationstheproblemishowtopreventradiationfromcurrents,suchasincircuits.Wheneveracurrentbecomesseparatedindistancefromitsreturncurrent,itradiates.Simplystated,wedesigntokeepthetwocurrentsclosetogether,toreducera
6、diation.Somediscussionswillignorethecurrentdistributionandinstead,considerderivedquantities,suchasfieldsinanapertureormagneticcurrentsinaslotoraroundtheedgesofamicrostrippatch.Youwilldiscoverthatweuseanyconceptthatprovidesinsightorsimplifiesthemathemat
7、ics.Anantennaconvertsboundcircuitfieldsintopropagatingelectromagneticwavesand,byreciprocity,collectspowerfrompassingelectromagneticwaves.Maxwell’sequationspredictthatanytime-varyingelectricormagneticfieldproducestheoppositefieldandformsanelectromagneti
8、cwave.Thewavehasitstwofieldsorientedorthogonally,anditpropagatesinthedirectionnormaltotheplanedefinedbytheperpendicularelectricandmagneticfields.Theelectricfield,themagneticfield,andthedirectionofpropagationformaright-handedcoordinatesy
