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时间:2020-09-20
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1、BasicAntennaTheoryandConceptsICS620CommunicationTechnologiesClass#11IntroductionAnantennaisanelectricalconductororsystemofconductorsTransmission-radiateselectromagneticenergyintospaceReception-collectselectromagneticenergyfromspaceIntwo-waycommunication,thesameantennacanbeusedfortransmissionan
2、dreceptionAntennaDefinitionAnantennaisacircuitelementthatprovidesatransitionformaguidedwaveonatransmissionlinetoafreespacewaveanditprovidesforthecollectionofelectromagneticenergy.AntennaresearchfromMiller&Beasley,2002AntennaDefinition-cont’dIntransmitsystemstheRFsignalisgenerated,amplified,mod
3、ulatedandappliedtotheantennaInreceivesystemstheantennacollectselectromagneticwavesthatare“cutting”throughtheantennaandinducealternatingcurrentsthatareusedbythereceiverReciprocityAnantennaabilitytotransferenergyformtheatmospheretoitsreceiverwiththesameefficiencywithwhichittransfersenergyfromthe
4、transmitterintotheatmosphereAntennacharacteristicsareessentiallythesameregardlessofwhetheranantennaissendingorreceivingelectromagneticenergyPolarizationPolarizationisthedirectionoftheelectricfieldandisthesameasthephysicalattitudeoftheantennaAverticalantennawilltransmitaverticallypolarizedwaveT
5、hereceiveandtransmitantennasneedtopossessthesamepolarizationTypesofAntennasIsotropicantenna(idealized)RadiatespowerequallyinalldirectionsDipoleantennasHalf-wavedipoleantenna(orHertzantenna)Quarter-waveverticalantenna(orMarconiantenna)ParabolicReflectiveAntennabeamwidthantenna•APower3dBdownfrom
6、maximumpointAMaxpower2dipoleDirectionalAntennaRadiatedenergyisfocusedinaspecificdirectionBeamwidthBeamwidthistheangularseparationofthehalf-powerpointsoftheradiatedpatternHalf-waveDipole(Hertz)AntennaAnantennahavingaphysicallengththatisone-halfwavelengthoftheappliedfrequencyiscalledaHertzante
7、nnaorahalf-wavedipoleantenna.Hertzantennasarenotfoundatfrequenciesbelow2MHzbecauseofthephysicalsizeneededoftheantennatorepresentahalf-waveVertical(Marconi)AntennaVerticalAntennasareusedforfrequenciesunder2MHz.Itusesaconductingpathtogrou
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