最新无线射频技术基础_1讲课讲稿.ppt

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1、无线基本组件馈线发射器天线接收器所有的无线设备(客户端和接入端)分贝（dB）的定义功率度量PowerdBm—deciBelsreferencedto1mW0dBm=1mWPdBm=10Log10PdBm/1mW)dBW—deciBelsreferencedto1WPdBm=10log10(pW/1W)+30dBm=0dBW-30dBW=0dBmGaindBi—deciBelsreferencedtogainofanisotropicantennadBd—deciBelsreferencedtogainofadipoleantennadB—deciBel,UsedtoExpressthe

2、RatioofTwoValues,UsuallyGainorLossastheRatioBetweenTwoPowers:dB=10Log10P2/P1分贝的值和对应的系数IncreaseFactorDecreaseFactor0dB1x(same)0dB1x(same)1dB1.25x-1dB0.8x3dB2x-3dB0.5x6dB4x-6dB0.25x10dB10x-10dB0.10x12dB16x-12dB0.06x20dB100x-20dB0.01x30dB1000x-30dB0.001x40dB10,000x-40dB0.0001xdBm对应毫瓦dBmmWdBmmW0dBm1m

3、W0dBm1mW1dBm1.25mW-1dBm0.8mW3dBm2mW-3dBm0.5mW6dBm4mW-6dBm0.25mW7dBm5mW-7dBm0.20mW10dBm10mW-10dBm0.10mW12dBm16mW-12dBm0.06mW13dBm20mW-13dBm0.05mW15dBm32mW-15dBm0.03mW17dBm50mW-17dBm0.02mw20dBm100mW-20dBm0.01mW30dBm1000mW(1W)-30dBm0.001mW40dBm10,000mW(10W)-40dBm0.0001mW发射功率Powerthatthetransmitterapp

4、liestothetransmissionlineAlsoknownasoutputpoweronsomedatasheetsTypicallyexpressedinmWfor802.11devicesExample:awirelessbridgehasanoutputpowerof30mW;whatpowerindBmisappliedtothetransmissionline?TxPwr=10Log10(30)=14.8dBm馈线－功率衰减DirectlyproportionaltothesquarerootofthelengthofthecableInverselyproporti

5、onaltothediameterofthecable,assumingsimilarconstructionmaterialsProportionaltofrequency:foragivenlengthofcable,ahigherfrequencysignalwillalwaysexperiencemorelossthanalowerfrequencysignalNotdependuponwhichdirectionthesignaltravelsthroughthecable(transmittedsignalslosethesamepercentageofstrengthasre

6、ceivedsignals)Typicallyassume.25dBoflossperconnectorCableType2.4GHz5.8GHzLoss(dB/100ft.)Loss(dB/100ft.)LMR4006.710.8LMR6004.47.3接收灵敏度Examplefor2.4GHzDirectSequenceIndicationoftheabilityofthereceivertodecodethedesiredsignalTheminimumreceivedsignallevel,intheabsenceofinterference,atwhichthedesired

7、signalcanbedecodedwithaparticularBitErrorRate(BER)TypicallyexpressedindBmThemorenegativethevalue,thebetterFunctionofthedatarate:thehigherthedatarate,thehigherthereceiversensitivityrequiredReceiverNoiseFloor(Wi