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1、1W:Well,todaywehaveProfessorchenandprofessorweiinourstudiototalkabouttheRadartechnical,goodafternoon,professors.2IntroductionRadarisavariantofradiotechnologyandhasbeenwidelyutilizedinvariousareas.wewillhelpsyouhavearoughideaofwhattheradartechnologyis,howitcameintobeingandwher
2、eithasbeenapplied.Wemainlytalkabouttheradartechnicalovervie:itsgeneralprinciplesandtheCavityMagnetron,oneofitscriticaldevices,whichcancreatehighpowerhighfrequencyelectromagneticpulses.3W1:CanyoutellustheRadartechnical’sdevolop?In1888HeinrichHertzshowedthattheinvisibleelectrom
3、agneticwavesradiatedbysuitableelectricalcircuitstravelwiththespeedoflight,andthattheyarereflectedinasimilarway.Fromtimetotimeinthesucceedingdecadesitwassuggestedthatthesepropertiesmightbeusedtodetectobstaclestonavigation,butthefirstsuccessfulexperimentsthatmadeuseofthemwerein
4、anentirelydifferentcontext,namely,todeterminetheheightofthereflectinglayersintheupperatmosphere.Oneoftheseexperiments,thatofTuveandBreit,madeuseofshortrepeatedpulsesofradiation,andthistechniquewasemployedinmostofthedevelopmentsofradar.4-(5)-62:Howcanweknowaboutthetargetthanit
5、sdistanceusetheRadartechnical?Electromagneticradiationtravelsinemptyspaceataspeedof2.998x108metrespersecond,andinaironlyslightlylessrapidly;wecanthinkofitsspeedasverynearly300,000kilometerspersecond.Thisspeedisdenotedbytheletterc.Letussupposethataveryshortpulseofradiationisdi
6、rectedtowardsanobjectatadistancer,andthatasmallfractionofthisisreflectedbacktothestartingpoint,sothatithastraversedthedistance2r.Forusefulterrestrialdistancestisverysmall;anobject15kmaway,forexample,willreturnasignalinoneten-thousandthofasecond.7W3:Howcanwegetmoretarget?Thisi
7、sdonebyarranginganantennasystemtoprojectasuitableradiationpatternthatcanberotatedinazimuthorelevation.Asmaybededucedfromwhatfollows,averygreatdealofingenuityandengineeringskillhasbeendevotedtothedesignofradarantennas.Thisistheplacetomentionafundamentalfact,namely,thatthesizeo
8、fantennaneededtoproduceabeamofradiationofagivenangularwidthisdirectl
