Coupler

Workingprinciple

Principleanalogy:

LaoZhang’scabbagefieldsonthenorthandsouthsidesaredividedinto3partseach.Thesharelandobtainsasmallpartofthewaterflowfromthemainwaterway,andthewaterflowspeedisassameastheotherland,asshowninFigure1.Inthisway,LaoZhangcanrestintheshadeofthetreesforaperiodoftime,withoutmakinganychangestothewatercourse,andallthegroundispouredatthesametime.

Thecouplerisaradiofrequencydevicethatextractsasmallpartofthesignalfromthewirelesssignalbackbonechannel.AsshowninFigure2,itisapowerdistributiondevicelikethepowersplitter.ThedifferenceisthatthecouplerisnotEqualpowerdistributiondevice.Thecouplerandthepowersplitterareusedtogethertoachieveagoal—tomakethetransmissionpowerofthesignalsourcebeevenlydistributedtotheantennaportsoftheindoordistributionsystemasmuchaspossible,sothatthetransmissionpowerofeachantennaportisbasicallythesame.

Theinputportpowerofanidealcouplerisequaltothesumofthecouplingportpowerandtheoutputportpower,inwatts(W),asshowninFigure3.

Theimportantindexofcoupleriscouplingdegreeandinsertionloss.Thedegreeofcouplingistheratioofthepowerofthecoupledporttotheinputport,expressedindB,generallyanegativevalue.Thegreatertheabsolutevalueofthecouplingdegree,thelessitisequivalenttotakeaway,andthesmallerthelossofthenaturalcoupler.Insertionlossistheratioofthepoweroftheoutputporttotheinputport.Thegreatertheabsolutevalueofthecouplingdegree,thesmallertheabsolutevalueoftheinsertionloss.

ExpressedindB,therearethefollowingrelationships:

Then,therelationshipbetweentheinsertionloss(dB)ofthecouplerandthedegreeofcoupling(dB)canbeexpressedas:

Example:

Acouplerwithacouplingdegreeof−10dBhasaninsertionlossof−0.5dB.Taketheabsolutevalue,andconsiderthedielectricloss.Generally,theinsertionlosswillbelarger,whichisdifferentfordifferentmanufacturers.Generally,theinsertionlosscanbeabout0.7dB.

Iftheinputportpoweris15dBm,thenthepowerofthecouplingportofthiscoupleris15dBm-10dB=5dBm,andthepoweroftheoutputportis15dBm-0.7dB=14.3dBm.

Manypeopleherewillasksuchaquestion:5dBm+14.3dBm>15dBm,energyisnotconserved,why?Thereasonissimple,thenumbersindBmcannotbeadded.

Applyanelectricalsignaltotheinputofthephotocouplertomakethelight-emittingsourceemitlight.Theintensityofthelightdependsonthesizeoftheexcitationcurrent.Afterthislightisirradiatedonthepackagedlightreceiver,itproducesThephotocurrentisdrawnfromtheoutputterminalofthelightreceiver,thusrealizingtheconversionofelectricitytolighttoelectricity.

⒈Workingcharacteristics(takethephotosensitivetransistorasanexample)

Theinternalcommonmoderejectionratiooftheoptocouplerisveryhigh.Becausethecouplingcapacitancebetweentheluminoustubeandthelightreceiverisverysmall(within2pF),thecommon-modeinputvoltagehaslittleeffectontheoutputcurrentthroughtheinter-electrodecouplingcapacitance,sothecommon-moderejectionratioisveryhigh.

⒉Outputcharacteristics

TheoutputcharacteristicsofthephotocouplerrefertotherelationshipbetweenthebiasvoltageVCEappliedtothephotosensitivetubeandtheoutputcurrentICunderacertainluminouscurrentIF.WhenIF=0,thelight-emittingdiodedoesnotemitlight.Atthistime,theoutputcurrentofthephototransistorcollectoriscalleddarkcurrent,whichisgenerallyverysmall.WhenIF>0,undertheactionofacertainIF,thecorrespondingICbasicallyhasnothingtodowithVCE.ThechangebetweenICandIFbecomesalinearrelationship,andtheoutputcharacteristicsofthephotoelectriccouplermeasuredbythesemiconductortubecharacteristicdiagraminstrumentaresimilartotheoutputcharacteristicsofordinarytransistors.

⒊Thephotocouplercanbeusedasalinearcoupler

Provideabiascurrentonthelight-emittingdiode,andthencouplethesignalvoltagetothelight-emittingdiodethrougharesistor,sothatthephototransistorreceivesWhatisobtainedisanopticalsignalthatincreasesordecreasesonthebiascurrent,anditsoutputcurrentwillvarylinearlywiththeinputsignalvoltage.Thephotocouplercanalsoworkintheon-offstatetotransmitpulsesignals.Whentransmittingpulsesignals,thereisacertaindelaytimebetweentheinputsignalandtheoutputsignal,andtheinputandoutputdelaytimesofphotocouplersofdifferentstructuresareverydifferent.

Photoelectrictest

⒈Useamultimetertojudgewhetheritisgoodorbad,asshowninFigure3.Disconnecttheinputpower,useR×1ktomeasuretheresistanceofpins1,2andwhatistheforwardresistanceOnehundredohms,reverseresistancetensofkiloohms,theresistancebetweenpins3and4shouldbeinfinite.Anysetbetweenpins1,2andpins3and4hasaninfiniteresistancevalue.Aftertheinputterminalispoweredon,theresistanceofpins3and4isverysmall.AdjustingRP,theresistancebetweenpins3and4changes,indicatingthatthedeviceisgood.Note:TheR×10kgearcannotbeused,otherwiseitwillcausethelaunchtubetobreakdown.

⒉Simpletestcircuit,whenthepoweristurnedon,theLEDwillnotemitlight,pressSB,theLEDwillemitlight,andtheluminousintensityoftheRPandLEDwillchange,indicatingthatthetestedphotocouplerisgood.

Application

⒈Constituteaswitchcircuit

Whentheinputsignaluiislow,thetransistorV1isintheoffstate,andthecurrentofthelight-emittingdiodeinthephotocouplerB1Approximatelyzero,theresistancebetweentheoutputterminalsQ11andQ12isverylarge,whichisequivalenttotheswitch"off";whenuiishigh,v1isturnedon,thelight-emittingdiodeinB1emitslight,andtheresistancebetweenQ11andQ12becomessmaller,whichisequivalentToswitch"on".Thecircuitisinahigh-levelconductionstatebecausetheswitchisnotturnedonwhenUiislowlevel.Inthesameway,whenthereisnosignal(Uiislowlevel),theswitchisturnedon,soitisinthelow-levelconductionstate.

2.Compositionlogiccircuit

Thecircuitisan"ANDgate"logiccircuit.ItslogicalexpressionisP=A.B.Inthefigure,twophotosensitivetubesareconnectedinseries,onlywhentheinputlogiclevelA=1andB=1,theoutputP=1.Inthesameway,logiccircuitssuchas"ORgate","NANDgate"and"NORgate"canalsobeformed.

3.Toformanisolationcouplingcircuit

ThecircuitisshowninFigure4.ThisisatypicalACcouplingamplifiercircuit.Appropriateselectionofthecurrent-limitingresistorR1ofthelight-emittingcircuittomakethecurrenttransferratioofB4aconstantcanensurethelinearamplificationofthecircuit.

4.Toformahigh-voltagevoltagestabilizingcircuit

Thedrivingtubeneedstouseatransistorwithahighervoltageresistance(thedrivingtubeis3DG27inthefigure).Whentheoutputvoltageincreases,thebiasvoltageofV55increases,theforwardcurrentofthelight-emittingdiodeinB5increases,whichreducesthevoltagebetweenthephotosensitivetubes,andthebiasvoltageoftheregulatortubedecreasesandtheinternalresistanceincreases,sothattheoutputvoltagedecreases.,Whilemaintainingthestabilityoftheoutputvoltage.

⒌Constitutetheautomaticcontrolcircuitofthehalllighting

Aisfourgroupsofanalogelectronicswitches(S1~S4):S1,S2,S3areconnectedinparallel(canincreasethedrivingpowerandanti-interferenceability)Usedinthedelaycircuit,whenitisconnectedtothepowersupply,thebidirectionalthyristorVTisdrivenbyR4andB6,andtheVTdirectlycontrolsthehalllightingH;S4andtheexternalphotoresistorRlformanambientlightdetectioncircuit.Whenthedoorisclosed,thenormallyclosedreedswitchKDinstalledonthedoorframeisactedonbythemagnetonthedoor,anditscontactsaredisconnected,andS1,S2,andS3areinthedataopenstate.Atnight,theownerwenthomeandopenedthedoor,themagnetwasfarawayfromKD,andtheKDcontactwasclosed.Atthistime,the9VpowersupplyisrectifiedandchargedtoC1viaR1.ThevoltageacrossC1quicklyrisesto9V.Therectifiedvoltagemakesthelight-emittingtubeinB6glowthroughS1,S2,S3andR4totriggerthebidirectionalthyristortoconduct,andVTalsoconductsOn,Hlightsuptorealizeautomaticlightingcontrol.Afterthedoorisclosed,themagnetcontrolsKD,thecontactisdisconnected,the9VpowersupplystopschargingC1,andthecircuitentersadelaystate.C1beginstodischargeR3.Afteraperiodofdelay,thevoltageacrossC1graduallydropsbelowtheturn-onvoltage(1.5v)ofS1,S2,andS3,andS1,S2,andS3returntotheoffstate,causingB6toendandVTalsoends.,Hturnsofftorealizethedelayedturn-offfunction.

Distinguishthetypes

Directionaltypes

Thedirectionalcouplerisafour-portelementwithdirectionaltransmissioncharacteristics.Itisatwo-portelementconnectedbyacouplingdevice.Constitutedtothetransmissionsystem.Firstintroducetheperformanceindexofthedirectionalcoupler,andthenintroducethewaveguidedouble-holedirectionalcoupler,double-branchdirectionalcouplerandparallelcouplingmicrostripdirectionalcoupler.

1)Performanceindicatorsofthedirectionalcoupler

Thedirectionalcouplerisafour-portnetwork,theport"①"istheinputterminal,theport"②"isthedirectoutputterminal,andtheport"③""Isthecouplingoutputterminal,theport"④"istheisolationterminal,andthescatteringmatrixis​​setto[S].Theperformanceindicatorsdescribingthedirectionalcouplerare:couplingdegree,isolationdegree,directionaldegree,inputstandingwaveratioandworkingbandwidth.Theyareintroducedseparatelybelow.

2)Isolation

TheratiooftheinputpowerP1oftheinputterminal"①"andtheoutputpowerP4oftheisolationterminal"④"isdefinedastheisolation,denotedasI.

Directiondegree

TheratiooftheoutputpowerP3ofthecouplingterminal"③"totheoutputpowerP4oftheisolationterminal"④"isdefinedasthedirectionality,denotedasD.

⑷Inputstandingwaveratio

Whentheports“②,③,④”areallconnectedtothematchedload,theVSWRoftheinputport“①”isdefinedastheinputstandingwaveratio.Makeρ.

⑸Workingbandwidth

Workingbandwidthistheworkingfrequencyrangewhentheabove-mentionedC,I,D,ρandotherparametersofthespecifiedcouplermeettherequirements.

Waveguidetypes

Thewaveguidedouble-holedirectionalcoupleristhesimplestwaveguidedirectionalcoupler.Themainandauxiliarywaveguidespassthroughtwocommonnarrowwalls.

Thesmallholeswithadistanceofd=(2n+1)λg0/4realizecoupling.Amongthem,λg0isthewaveguidewavelengthcorrespondingtothecenterfrequency,andnisapositiveinteger,generallyn=0.Thecouplingholeisgenerallycircular,butothershapesarealsopossible.Whenworkingatthecenterfrequency,βd=π/2,atthistimeD→∞;whendeviatingfromthecenterfrequency,secβdhasacertainvalue,andDisnolongerinfiniteatthistime.Infact,evenatthecenterfrequencyofthetwo-holecoupler,itsdirectivityisnotinfinite,butcanonlybearound30dB.

Inshort,thewaveguidedual-holedirectionalcouplerreliesonthemutualinterferenceofwavestoachievethedirectionaloutputofthemainwaveguide,superimposesinphaseonthecouplingport,andcancelsoutinantiphaseontheisolationport.Inordertoincreasethecouplingdegreeofthedirectionalcouplerandbroadentheworkingfrequencyband,themulti-holedirectionalcouplercanbeused.Thebranchlinecomposition,wherethelengthandspacingofthebranchline

are1/4ofthecenterwavelength,asshowninFigure5-15.Supposethecharacteristicimpedanceofthemainlineentranceline"①"is,thecharacteristicimpedanceofthemainlineexitline"②"is(kistheimpedanceconversionratio),andthecharacteristicimpedanceofthesecondarylineisolationend"④"isthatofthesecondarylinecouplingend"③"Thecharacteristicimpedanceis,thecharacteristicimpedanceoftheparallelconnectionlineisZ0p,andthecharacteristicimpedanceofthetwobranchlinesisthesum.

Paralleltype

Parallelcouplingmicrostripdirectionalcouplerisareversedirectionalcoupler,thecouplingoutputendandthemaininputendareonthesameside,asshownintherightpicture,Portinisaninputport,portoutisastraight-throughport,portocupisacouplingport,andport"④"isanisolatedport.

Couplertechnicalspecifications(indoordistribution)

Table2Couplertechnicalspecifications

Isolator

Theisolatorisalsocalledareverser.Thereisalmostnoattenuationwhentheelectromagneticwavepassesthroughitintheforwarddirection,andtheattenuationisgreatwhenitpassesinthereversedirection.Commonlyusedisolatorsareharmonic

vibrationtypeandfieldshifttype.

Resonantisolator

Becauseoftheanisotropyofferrite,undertheactionofaconstantmagneticfieldHi,theleftandrightcircularpolesinaleftandrightspiralrelationshipwiththeHidirectionTherotatingmagneticfieldhasdifferentpermeability(settoμ-andμ+respectively).Setatacertainpointonthemicrowavetransmissionlinecontainingferritematerial,theleft-handedmagneticfieldistransmittedinthe+zdirection,andtheright-handedmagneticfieldistransmittedinthe-zdirection.Thetwotransmitthesamedistance,butthecorrespondingmagneticpermeabilityisdifferent,sotheleft-rightmagneticfieldThephasespeedisdifferent,theresultingphaseshiftisalsodifferent,thisistheirreversibilityofferritephaseshift.Ontheotherhand,ferritehasaferromagneticresonanceeffectandaresonanceabsorptioneffectofacircularlypolarizedmagneticfield.

Theso-calledferrite'sferromagneticresonanceeffectmeansthatwhentheworkingfrequencyωofthemagneticfieldisequaltotheresonantangularfrequencyω0oftheferrite,theabsorptionofmicrowaveenergybytheferritereachesthemaximum.Forthecircularlypolarizedmagneticfield,theleftandright-handedpolarizedmagneticfieldshavedifferentmagneticpermeability,sothetwoalsohavedifferentabsorptioncharacteristics.

Fortheright-handedpolarizedmagneticfieldtransmittedinthereversedirection,themagneticpermeabilityisμ+,whichhasaferromagneticresonanceeffect,whilefortheleft-handpolarizedmagneticfieldtransmittedintheforwarddirection,themagneticpermeabilityisμ-,Itdoesnothaveferromagneticresonancecharacteristics,whichistheresonanceeffectofacircularlypolarizedmagneticfield.Theferriteresonantisolatorismadebyusingthischaracteristicofferrite.

Field-shiftingisolator

Thefield-shiftingisolatorismadeaccordingtothedifferentfield-shiftingeffectsofferriteonthewavespropagatingintwodirections.

Itaddsanattenuatoronthesideoftheferritesheet.Duetothedifferenceofthefieldgeneratedbythetransmissioninthetwodirections,theelectricfieldofthewavetransmittedintheforwarddirection(-zdirection)isbiasedtotheonewithoutattenuationsheet.Theelectricfieldofthewavepropagatinginthereversedirection(+zdirection)isbiasedtoonesideoftheattenuator,thusrealizingtheisolationfunctionofsmallforwardattenuationandlargereverseattenuation,asshowninFigure5-32.

Becausethefield-shiftingisolatorhasthecharacteristicsofsmallsize,lightweight,simplestructureandwideworkingfrequencyband,ithasbeenwidelyusedinlow-powerapplications.

Professionaltermsrelatedtocouplers: