天线原理介绍-Antenna-Theoryppt课件.ppt

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1、BaseStationAntennasCONFIDENTIAL-ProprietaryInformationAntennaTheoryBasicPrinciplesforDailyApplicationsNovember20041F0(MHz)(Meters)(Inches)3010.0393.6803.75147.61601.8773.82801.0742.24600.6525.78000.3814.89600.3112.317000.186.9520000.155.90F0¼¼Dipole23DVie

2、wAntennaPatternSource:COMSEARCH3UnderstandingtheMysterious“DB”“dBd”–Signalstrengthrelativetoadipoleinemptyspace“dBi”–Signalstrengthrelativetoanisotropicradiator“dB”–Differencebetweentwosignalstrengths“dBm”–Absolutesignalstrengthrelativeto1milliwatt1mWatt=0dBm

3、1Watt=30dBm20Watts=43dBm“dBc”–Signalstrengthrelativetoasignalofknownstrength,inthiscase:thecarriersignalExample:-100dBc=100dBbelowcarriersignalIfcarrieris100Watt=50dBm-100dBc=-50dBmor0.00001mWattNote:TheLogarithmicScale10*log10(PowerRatio)4EffectofVSWRV

4、SWRReturnLoss(dB)TransmissionLoss(dB)PowerReflected(%)PowerTrans.(%)1.001.101.201.301.401.502.00¥26.420.817.715.614.09.50.000.010.040.080.120.180.510.00.20.81.72.84.011.1100.099.899.298.397.296.088.9GoodVSWRisonlyonecomponentofanefficientantenna.5ShapingAnten

5、naPatternsVerticalarrangementofproperlyphaseddipolesallowscontrolofradiationpatternsatthehorizonaswellasaboveandbelowthehorizon.Themoredipolesarestackedvertically,theflattertheverticalpatternisandthehighertheantennacoverageor“gain”inthegeneraldirectionoftheho

6、rizon.6ShapingAntennaPatterns(cont...)Stacking4dipolesverticallyinlinechangesthepatternshape(squashesthedoughnut)andincreasesthegainoversingledipole.Thepeakofthehorizontalorverticalpatternmeasuresthegain.Thelittlelobes,illustratedinthelowersection,aresecondar

7、yminorlobes.ApertureofDipolesVerticalPatternHorizontalPattern4DipolesVerticallyStackedSingleDipoleGENERALSTACKINGRULE:Collinearelements(in-linevertically).Optimumspacing(fornon-electricaltilt)isapproximately0.9λ.Doublingthenumberofelementsincreasesgainby3dB,

8、andreducesverticalbeamwidthbyhalf.7GainWhatisit?Antennagainisacomparisonofthepower/fieldcharacteristicsofadeviceundertest(DUT)toaspecifiedgainstandard.Whyisituseful?Gaincanbeassociatedwi