天线原理介绍-Antenna-Theory

OneCompany.AWorldofSolutions.1BaseStationAntennasCONFIDENTIAL-ProprietaryInformationAntennaTheoryBasicPrinciplesforDailyApplicationsNovember2004OneCompany.AWorldofSolutions.2F0(MHz)(Meters)(Inches)3010.0393.6803.75147.61601.8773.82801.0742.24600.6525.78000.3814.89600.3112.317000.186.9520000.155.90F0¼¼DipoleOneCompany.AWorldofSolutions.33DViewAntennaPatternSource:COMSEARCHOneCompany.AWorldofSolutions.4UnderstandingtheMysterious“DB”“dBd”–Signalstrengthrelativetoadipoleinemptyspace“dBi”–Signalstrengthrelativetoanisotropicradiator“dB”–Differencebetweentwosignalstrengths“dBm”–Absolutesignalstrengthrelativeto1milliwatt1mWatt=0dBm1Watt=30dBm20Watts=43dBm“dBc”–Signalstrengthrelativetoasignalofknownstrength,inthiscase:thecarriersignalExample:-100dBc=100dBbelowcarriersignalIfcarrieris100Watt=50dBm-100dBc=-50dBmor0.00001mWattNote:TheLogarithmicScale10*log10(PowerRatio)OneCompany.AWorldofSolutions.5EffectofVSWRVSWRReturnLoss(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.OneCompany.AWorldofSolutions.6ShapingAntennaPatternsVerticalarrangementofproperlyphaseddipolesallowscontrolofradiationpatternsatthehorizonaswellasaboveandbelowthehorizon.Themoredipolesarestackedvertically,theflattertheverticalpatternisandthehighertheantennacoverageor“gain”inthegeneraldirectionofthehorizon.OneCompany.AWorldofSolutions.7ShapingAntennaPatterns(cont...)Stacking4dipolesverticallyinlinechangesthepatternshape(squashesthedoughnut)andincreasesthegainoversingledipole.Thepeakofthehorizontalorverticalpatternmeasuresthegain.Thelittlelobes,illustratedinthelowersection,aresecondaryminorlobes.ApertureofDipolesVerticalPatternHorizontalPattern4DipolesVerticallyStackedSingleDipoleGENERALSTACKINGRULE:•Collinearelements(in-linevertically).•Optimumspacing(fornon-electricaltilt)isapproximately0.9λ.•Doublingthenumberofelementsincreasesgainby3dB,andreducesverticalbeamwidthbyhalf.OneCompany.AWorldofSolutions.8GainWhatisit?Antennagainisacomparisonofthepower/fieldcharacteristicsofadeviceundertest(DUT)toaspecifiedgainstandard.Whyisituseful?Gaincanbeassociatedwithcoveragedistanceand/orobstaclepenetration(buildings,foliage,etc).Howisitmeasured?Itismeasuredusingdatacollectedfromantennarangetesting.Thereferencegainstandardmustalwaysbespecified.WhatisAndrewstandard?Andrewconformstotheindustrystandardof+/-1dBaccuracy.OneCompany.AWorldofSolutions.9GainReferences(dBdanddBi)Anisotropicantennaisasinglepointinspaceradiatinginaperfectsphere(notphysicallypossible)Adipoleantennaisoneradiatingelement(physicallypossible)Againantennaistwoormoreradiatingelementsphasedtogether0(dBd)=2.15(dBi)Isotropic(dBi)Dipole(dBd)GainIsotropicPattern3(dBd)=5.15(dBi)DipolePatternOneCompany.AWorldofSolutions.10PrinciplesofAntennaGainDirectionalAntennasTopView0dBd+3dBd+6dBd+9dBd-3dB180°90°-3dB45°-3dBOmniAntennaSideView0dBd+3dBd+6dBd+9dBd60°-3dB-3dB30°-3dB7.5°-3dB15°-3dBOneCompany.AWorldofSolutions.11TheoreticalGainofAntennas(dBd)Couldbehorizontalradiatorpairsfornarrowhorizontalapertures.3dBHorizontalAperture(InfluencedbyGroundedBack“Plate”)TypicalLengthofAntenna(ft.)#ofRadiatorsVerticallySpaced(0.9)800/900DCS1800VerticalMHzPCS1900Beamwidth360°180°120°105°90°60°45°33°1034568910.51'0.5'60°236789111213.62'1'30°34.57.58.59.510.512.513.515.13'1.5'20°469101112141516.64'2'15°67.510.511.512.513.515.516.518.16'3'10°8912131415171819.68'4'7.5°OneCompany.AWorldofSolutions.12Gainvs.Length65°AzBW90°AzBW120°AzBWAntennaLength(wavelengths)Gain(dBi)01234567891011121314150510152025G=log()2.2pLWe2OneCompany.AWorldofSolutions.13Gainvs.Beamwidths65°AzBW90°AzBW120°AzBWElevationHalfPowerBeamwidth(deg)Gain(dBi)246810121416182022242628300510152025G=log()29000AzBWEIBWOneCompany.AWorldofSolutions.14AntennaGainGain(dBi)=Directivity(dBi)–Losses(dB)Losses:ConductorDielectricImpedancePolarizationMeasureUsing‘GainbyComparison’OneCompany.AWorldofSolutions.15FeedNetworksCableMicrostripline,CorporateFeeds–DielectricSubstrate–AirSubstrateT-LineFeedandRadiatorOneCompany.AWorldofSolutions.16DB812OmniAntennaVerticalPatternOneCompany.AWorldofSolutions.17932DG65T2E-MPatternSimulationOneCompany.AWorldofSolutions.18MainLobeWhatisit?Themainlobeistheradiationpatternlobethatcontainsthemajorityportionofradiatedenergy.Whyisituseful?Shapingofthepatternallowsthecontainedcoveragenecessaryforinterference-limitedsystemdesigns.Howisitmeasured?Themainlobeischaracterizedusinganumberofthemeasurementswhichwillfollow.WhatisAndrewstandard?Andrewconformstotheindustrystandard.35°TotalMainLobeOneCompany.AWorldofSolutions.19Half-PowerBeamwidthHorizontalandVerticalWhatisit?Theangularspanbetweenthehalf-power(-3dB)pointsmeasuredonthecutoftheantenna’smainloberadiationpattern.Whyisituseful?Itallowssystemdesignerstochoosetheoptimumcharacteristicsforcoveragevs.interferencerequirements.Howisitmeasured?Itismeasuredusingdatacollectedfromantennarangetesting.WhatisAndrewstandard