高频传输线损耗的精确计算

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1、AccountingforHighFrequencyTransmissionLineLossEffectsinHFSSAndrewByersTektronixTransmissionLineRefresherg=a+jb=(R+jwL)*(G+jwC)Zo=Zr+jZi=(R+jwL)/(G+jwC)TransmissionlinecharacteristicsdescribeaparticularmodeNumberofmodes=numberofconductors-1a=attenuationconstant(lossin

2、eithermetalordielectric)b=propagationconstant(dependentoneandm)ooR,L,C,G=frequencydependentequivalentcircuitparametersTransmissionLineRefresherZo[W]Breakfrequency1:log(S21)ZoapproachesasymptotevaluedBSreferencedto50W[dB/m]21areferencedtoZo(f)log(a)dB[dB/m]a=(R/2Z)oBr

3、eakfrequency2:skineffectregionstartslog(freq)“log-log”scalereference:NationalBureauofStandardsTechNote1042Frequency-dependentLossMechanismsinTransmissionLinesDielectricLoss•functionofdielectriclosstangent,tand•dielectriclossdominatesinPCBenvironmentsonFR4-likesubstra

4、tes•lossisdirectlyproportionaltofrequencyandtandFrequency-dependentLossMechanismsinTransmissionLinesConductorLosses•Currentcrowdstosurfaceoftransmissionlineasfrequencyincreases•Resistanceoflineinverselyproportionaltocurrent-carryingcross-section:R=r/A•Asthecurrentapp

5、roachesthe“skindepth”,theresistanceofthelinebeginstoincreasewiththesquarerootoffrequency:d=1spfsmo•Conductorlossdominatesinhigh-performancepackageandchipenvironment(lowdielectriclosssubstratesorverythinmetal)Frequency-dependentLossMechanismsinTransmissionLinesSurface

6、Roughness•Surfaceofconductorscanbe“rough”-sometimesintentionallytoaidinmetaladhesiontosubstratesurface•increaseintotalcurrenttraveldistancewillresultinanincreaseinlosswithfrequencya’=a[1+2/ptan-1{1.4(D/d)2}]*ccsa’=attenuationforroughsurfaceca=attenuationforsmoothsurf

7、acecd=skindepthssurfaceroughnessD=r.m.s.surfaceroughnessheight*Edwards,Terry.FoundationsforMicrostripCircuitDesign.JohnWileyandSons,1992.PCBMicrostripHFSSSimulationsTypicalPCBdimensions:w=8mils,t=1.6mils,h=4mils,er=4lossproperties:tand=0.04s=5.8E7HFSSSimulations:HFSS

8、v9view-lossydielectriconly-lossymetal(solveinside)onlyinspectthe-lossymetal(surface)onlyattenuationconstant,a,toviewloss-bothlossyd