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1、Three-wayplanarWilkinsonsUpdatedNovember13,2011Clickhere togotoourmainpageonWilkinsonsplittersClickhere togotoourpageonN-waysplittersClickhere togotoourpageontheKouzoujiansplitter,agreatalternativetotheconventionalN-wayWilkinsonNewforJune2010! Thispagewillprov
2、ideabasicanalysisofplanar,three-wayWilkinsonsplittersin50ohmsystemimpedance.Thisissplitterisimperfect,becauseitismissinganisolationresistorbetweenthetwoouterports,however,thisiswhatmakesiteasytolayout.Wedividedtheanalysisintothree"types"whicharedescribedbelow,
3、andrankedaccordingtobandwidthpotential.Type1splitterTheType1splitteristhesimplestnetworkpossible.Thethreearmseachemployasingle quarter-waveimpedancetransformer. Ifyouweretoimpedancematchport1atcenterfrequency,thetransformerswouldallbe86.6ohms(transformseach50o
4、hmlegto150ohms,andthree150ohmsinparallelis50ohms).Sorryaboutthecrummyschematic,you'dthinkbynowAgilentwouldprovideameansforgraphiccapturebeyondtheusualcopy-and-pastintoPowerpoint,thenshrinkimagewithPaintShop...ThevariablesR1andZ1wereallowedtooptimizetoprovideth
5、emaximum"-15dBbandwidth",inotherwords,itwasrequiredthatreflectioncoefficientsS11,S22andS33andisolationtermsS23andS24werelessthan-15dB.Notethatbysymmetry,itisnotnecessarytooptimize(ormonitor)S44,andS43.Thechoiceof-15dBasthegoalisarbitrary.However,intheplanarthr
6、ee-wayWilkinson,youcan'texpectperfectisolationofthesplitports,andwithoutperfectisolation,youwon'tgetperfectreturnlossesforS22,S33andS44.Thetransmissionlineimpedancevalueswererestrictedtonomorethan100ohms(inallthreetypes),tomakethecircuitrealizableinmicrostrip.
7、Itmightbebettertorestricttoalowervaluedependingonwhatsubstrateischosen,andyieldconsiderations.Thesubjectforanotherday!ForType1,Z1wasfoundtobe91.4ohmsandR1was83.6ohms,resultingin-15dBbandwidthof39%.Belowisthetransmissioncoefficient,showingthenear-idealvalueof4.
8、78dB [-10*log(1/3)].Allthreetransmissioncoefficientsareequalinthissimplifiedanalysis,inpracticetheouterbrancheswillbehaveslightlydifferentlyfromthecenterbranch.Herearethereturnloss
