BROADBAND MICROWAVE POWER LIMITERS - MACON - DTIC.pdf

7/29/2019 BROADBAND MICROWAVE POWER LIMITERS - MACON - DTIC.pdf

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UNCLASSIFIED A D 45 09 D E F E N S E O C U M E N T A T I O N E N T E R

F O R S C I E N T I F I C N D E C H N I C A LN F O R M A T I O N

C A M E R O NT A T I O N . L E X A N D R I A .IRG IN IA

UNCLASSIFIED


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NOTICE:hen governmentorotherdrawings,speci-ficationsor otherdataareused foranypurposeotherthaninconnectionwithadefinitelyrelatedgovernmentprocurementoperation,theU .S .Governmenttherebyincursnoresponsibility,nor anyobligationwhatsoever;and thefactthattheGovern-mentmayhaveformulated,furnished,orinanywaysuppliedthesaiddrawings,specifications,orotherdatai sno ttoheregarded by implicationorother-wiseasin anymanner licensing theholderoranyotherpersonorcorporation,orconveyingany rightsorpermissiontomanufacture,us eorsellanypatented inventionthatmayinanyway berelatedthereto.


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I O S 1 '':**> :..VIT!1 Hi FIRSTQUARTERLYREPORT2 1June1963to30September1963

BROADBANDMICROWAVEPOWERLIMITERS

ContractNObsr-89462ProjectSerialNo.SR-0080302

Task9637NavyDepartment,BureauofShips

MICROWAVEASSOCIATES,INC.BURLINGTON,MASSACHUSETTS

T

o _ nn^i L * * ^ . - ^

ti DECS i9ojr ;u :Li\z\\''..TISIA B


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IIFIRSTQUARTERLYREPORT

21June1963to30September1963

.

L

BROADBANDMICROWAVEPOWERLIMITERS

ContractNObsr-89462ProjectSerialNo .SR-0080302

Task9637NavyDepartment,BureauofShips

Preparedby:RobertTenenholtz

Approvedby:M .E.Hines

MICROWAVEASSOCIATES,INC.BURLINGTON,MASSACHUSETTS


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TABLEOFCONTENTSPageNo ,

TITLEPAGETABLEOFCONTENTS iABSTRACT iiPART

PURPOSEGENERALFACTUALDATA

1 .heDiodeLimiterConcept2 .emiconductorLimiterDiodes

(2-a)heVaractorDiode(2-b)hePINDiode

3 .iodePackageCharacteristics(3-a)eramicPackageDiodes 0(3-b)ntegratedDiodes 1

4 .heBasicDiodeLimiter 2(4-a)heDiodeLimiterEquivalentircuit2(4-b)iodeLimiterCircuitLossquations 1 4

5 .heBroadbandLimiterConcept 4(5-a)heLo wPassFilterLimiter5(5-b)heBandPassFilterLimiter0

CONCLUSIONS 2PARTI I

PROGRAM FORTHENEXTINTERVAL 3LISTOFILLUSTRATIONS 4


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ABSTRACTThisreportcontainsresultssecuredduringtheinitialstudy

phaseofthiscontract. Sectionsaredevotedtodiscussionoftheb a s i cdio delimiterconcept,limiterdio decharacteri sti csandd iodepackag ingconsiderations.

Alsoincludedisaquant it at ivetreatmentofthe"ideal"diodelimitercircuitanditslimitationsw i t hrespecttothedirectproblemsofconcern.

Concludingthetechnicalstudypresentedinthisreportisadiscussiononbroadbanddio delimiterdesignscapableofachievingmultioctavebandwidthsbelow5Km candoctavebandwidthsbetweentherangeof5Km cto11Kmc.


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PARTIPURPOSE

Thepurposeofthiscontractistodevelopafamilyofbro adbandhighpowerlimiterscoveringtherangeof1Km cto1 1Kmc. Proposeddesigngoalspecificationsfortheselimitersarelistedasfollows:

FrequencyRange,Km cMaximum OperatingPeakPower,KWMaximumAveragePower,WMaximumPulse Width,^secMaximumSpikeLeakage,ErgsMaximumFlatLeakage,WattsMaximumInsertionLoss,DBT ransmi s s ionLineForm

( a ) ( b ) ( c )1-4.5 4-7.5 7-1110 5 110 5 110 1 10.5 0.5 0.30.040 0.040 0.0400.5 1.0 1.0Coax Coax W/G

c


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- 2 -GENERALFACTUALDATA

1 .HEDIODELIMITERCONCEPTTh emicrowavediodelimitercanbebasicallystatedasbeinga

powersensitivepassiveattenuatorbasedonthenonlinearproperties*o fmicrowavePN-junctioniodes.henlo wpowerlevelsareincident

uponthelimiterstructure(lessthan1mW),andwithintheratedoperationalfrequencyrange,negligiblelosswillbeencountered.Therefore,thelimiterwillactasasectionofmatchedtransmissionlinewithsomesmallfiniteloss. Inthecaseofahighpowerlevelincidentuponthelimiterstructure,ahighdegreeoflosstakesplacean dthelimiterwillactasahighlymismatchedsectionoftrans-missionline.it hrespecttothepowerlostinthiscase,itwillbeduetobothreflectionanddissipationwiththeformerbeinggreatlydominantdu etopowercapabilityconsiderations.bviously,thiscon-siderationisofextremeimportancesincet hepowerdissipatedbythelimitingdiodeordiodeswillprimarilydeterminemaximumpowerhand-lingcapabilityoft helimiter.

Inadditiontot hepowersensitivityoperationalcharacteristicso fthelimiter,o neotherimportantcharacteristicisdisplayed.hi sisthefactthatt helimiteriscompletelypassiveinoperationwithrespecttopriorknowledgeofinputsignalcharacteristics.hatis,noinformationneedbesuppliedfromthesystemsthatthelimiteris

Pointcontactdiodeswillno tbeconsideredduetotheirinherentlowpowerhandlingcapability.


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employedinorusedtoprotectagainst.Ingeneral,thePN-junctiondiodelimitercanbeconsideredas

beingasolid-stateequivalentoftheconventionalgaseousTR-tube.However,intheoryitdoesno tsufferfromtheTR-tubedrawbackssuchaslifeandinter-pulseprotection.hileitseemsunlikelythatPN-junctiondiodelimiterswillreplaceTR-tubesonthebasiso fpowerhandlingcapability,it soctavebandwidthcapabilityo foperationoffersafeaturepreviouslyunobtainable.

2.EMICONDUCTORLIMITERDIODESInt heareaofcontrolo fmicrowavepowerthroughuseo fsemi-

conductors,twomainPN-junctiontypediodeshavebecomeprominent.ThesearethevaractorandPINdiode.nFigure(l),generalcharacter-isticso fbothtypesarecomparedonthebasiso fconstruction,equi-valentcircuitandimpedancecharacteristicsatmicrowavefrequencies.Ascanbeseen,thevaractorcanbecharacterizedasavoltagedepend-en tcapacitancewhilethePI Ndiodeexhibitsallessentialpropertieso favoltagedependentresistance.

InadditiontothepropertiesshowninFigure(l),bothdiodetypesexhibitt henormalcurrentvoltagerelationshipo ftheclassicPN-junction.hi stakest heformofasharpcurrentrisewhensub-jectedtoasmallforwardbias(+o nthePside)andanavalanchebreakdownconditionwiththeapplicationo fsomecomparativelylargereversebias.


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-4-Becauseeachdiodecanexhibitaradicalchangeofimpedancestate

atmicrowavefrequencies,theirapplicationtopassivecontrolofmicro-wave powercanatoncebeappreciated.hisiswellillustratedbytheSmithChartimpedanceplotsshowninFigure(l).owever,oneothernecessarypropertymustfirstbeinvestigatedandthisi stheabilityofthediodetointeractdirectlywithanappliedRFwaveformatmicro-wavefrequencies.asically,thisamountstorectificationefficiencyandchargestoragecharacteristicsofthediodeinthefrequencyrangeofconcern.

(2-a)HEVARACTORDIODEInFigure( l ) ,thevaractorconstructionalschematicshows

itt oconsistofaPNNandwicharrangementofsemiconductormater-ial,therebycreatingaPN-junction.tzerobias,iti satequilibriumasaresultofholesandelectronsdistributingthemselvessuchthatthereareessentiallynocarriersi nthevicinityofthejunction.hisregionwhichi sfreeofelectronsandholesi scalledthedepletionlayer,It spresenceenablesthevaractort oexhibittherequiredcharacteristicofaparallelplatecapacitor withthedepletionlayerformingthesepa-rationbetweentwoconductiveregions.nordertocontrolmagnitudeofcapacitance,junctionareacanbevariedinsize.ereagain,theeffectsareidenticalt othatobtainedwithvariationofareai naparallelplatecapacitor.

I fapotentialwereno wappliedacrossthesemiconductorjunction,the depletionlayerwouldchangeinthicknessduetochargemovementandthereforevarycapacitance.fmadesufficientlylargeandpositivein


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polarity,th enoreialforwardconductionprocessofaPN-junctionwouldoccurnregardtovaractora,nodifficultyhasbeenencounteredwithrespecttothisprocessrespondingfaithfullytoanappliedRFvoltageofrelativelylowpowerlevel(0.1-0.5watts).hiscanbeattributed tothefactthathole*andelectronsneedonlymoveasmallportionofthedepletionlayerwidth. Athigherpo werlevels,aconsiderableamountofcarriers,bothholesandelectrons9ereinjectedintotheNregionwithaneffectivedisappear anceofthedepletionlayer. Infact,thisoccurstosuchadegreethatthenegativeRFvoltageexcursionsareunabletosweepcutanappreciableportionofthischarge.hevaractorwillthenappearashavinganinfinitecapacit anceandhenceverylowimpedance

The varactorequivalentcircuit,asshowninFigure(l),containsaaeriesresistance Rnadditiontoitsvolt agedependentcapacitance. Thisprimarilyarisesfromresistanceasso ciatedwiththebaseregionandisconstantuntilappreciableforwardconductiontakesplace.henthisoccurs,theinjectionofcarriersasdescr ibedinthepreviouspara-gr aphcancausealargereductioninseriesresistanceyasmuchas80&.hisprocessIstermedconductivitymodulationandisillustrated inthevaractorimpedanceplotofFigure(l)bydeviationfromthe

Uhlir,A.Jr."ThePotentialofSemiconductor DiodesinHighFrequencyCommunication."roc.IRE,Vol.46pp1099-1115(June1958).Thiseffectisnormallyverypronouncedinsiliconvaractorsandmayormayhotbeevidentinothersemiconductormaterialtypes.


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constantresistancecircle.nthiscast,itI scausedbya DC volt-agebutwillalsooccurunderRFconditionstoalasserdegree.henew valueofresistancewillbereferredt oasRhethercausedbyaDC OrRFvoltageappliedacrossth ePNjunction.

(2-b)HEPI N DIODE2ThePI Ndiode#thoughsimilartothevaractor,contains

oneimportantconstructionaldifference.hi si stheinclusionofarelativelythickintrinsicsemiconductorregion( Iregion)betweenPandKateriallayersecause ofthisthePI Ndiodeexhibitsamuchlargerareaper unitcapacitanceandhigheravalanchebreakdownratingascomparedto varactorshevariableresistanceproperty ofthe PINdiodeiscausedbyinjection ofbothholesand electronsintoth eIregionupontheapplication ofaforwardbias*hi screatesaneffec-tiveelectron-holeplasmain whatwasformerlyadielectricregion,thusconverting itintoaconductingmediumhe overallresulti sthatthe PI Ndiodeischangedfrom a veryhightoaverylowresistanceasillustrated byitstypicalSmithChartimpedanceplotinFigure( 1 ) .Alsoillustratedinthisplotisthe effectof Cnth eregionfromzerotoreversebreakdownhi stendstomaketh ePI N diode appearancedeviate slightlyfromapure variableresistance.

Withrespecttothe PI Ndiodeinteractingdirectlywithanapplied Rf voltageseriousdifficultiescanbeencountered.hi s2Leenov,D .Forster,J .H.,Crann,N ."PINDiodesfo r ProtectivelimiterApplications."olid-StateCircuitsConference Digest,pp .84-85,1961.


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occursbyvirtu ofthtrequirementthatanappreciabledistancemustbetravelledbycarrierinordertocreateaneffectivelo wresistivityelectronholeplasma. FortypicalPINdiodes,thiseffecti squitepro-nouncedatL-band. Itcanbeconsideredaformoftransittimephenomenonsincereductioni nIregionthicknesswillimprovethesituation.ow -everthe ultimateofthisapproachi sdegenerationintothebasicvar-actordesignwithit srelativelyhighcapacitanceperunitareachar-acteristichus,larger powerhandlingcapabilitiesofthePINdiodebyvirtueOfcomparativejunctionsizei slost.

Thereforea scanbeseen,thePINdiodedoesno tdirectlylenditselftohighpowerlimitingapplicationsduetoitsrelativelyslowinteractiontimewithanappliedR waveform. Thisinabilitypre-cludesits useas amicrowavepowerlimiterinthenormalsenseofopera-tionbutha slittleeffectanitsabilitytobeuseda sa moderatelyfastswitchdrivenbyanexternalbiassource.owever,a s waspreviouslystatedfonlypassivedevicesareofconcernheresothatsynchronizeddrivingpulsescannotbesuppliedfromanexternalsource.

By utilizingahybridform ofoperationwhichcombinesaspectsfromboth diodelimitingandswitchingconcepts,atrulypassivePI Nlimitercapableof operating athighermicrowavefrequenciescanbeachievedhe circuitrequiredtoachievethisisshowninfigure(2).Asshown,the PI Ndiodeiplacedinshuntacrossetransmissionlintin asuitable microwaveswitchingcircuitryconfiguration .recedingDetailsofappropriatediodecircuitrywillbedescribedi nsection4ofthisreport.


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thePIN diodeitasignalsamplingdevice(directionalcoupler)ttrmi-natedbyahighburnoutxteldiode.hi sdiodei softhepointcontacttypeand ha sanexceedinglyfastresponsetime.

AsanincidentR?signali sapplied,a portion willbedeliveredt othextaldiode.tsrectified videooutputi*thenfedtothePI Ndiodecausingit t ochanget oaforwardconductionstateandbecomehighlyreflective,hisconstitutesaneffectivelimiteraction whosethreshold oflimitingi scontrolledbythextaldiodedecouplingmagni-tude withrespecttothemaintransmissionline.

Attractiveatthisapproachmayseemitstillha sseverald r a w - *beckshemostImportanti sduet othefactthataleakagespikeintheRFwaveform willbe presentdue totherelativelylongswitchingtimerequiredbythePI Ndiode.oweverthiscanbecompensatedforbyfollowingthePI Nlimiterbyaconventionalvaractortype whichwillineffectgreatlyreduceth espikeamplitude*he otherdrawbackcon-cernsrecoverytime*ereagainslownessofresponseofthe F i t diodeieevidentbecauseafinitetimei srequiredforittochangefromaconductingt onon-conducting state*hi smakesitselfevidenti nth eform o fafiniterecoverytime*oweverhereseveralschemeswhichillbecoveredinlaterreportsexistwhichenablerecoverytimevaluesmuchleesthana s e ctobeobtained.

Theconventional3 DBpointfo rrecoverytimei sassumedherea sinth ecase o fTR-tubes.


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Despitetheabovementioneddisadvantages,thePI Nd i odeinafeedbacklimiterconfigurationcanbeadvantageouslyemployed whereinitialreductionofhighpowerlevelsi6ofconcern.nceaccomp-lishedconventionalvaractorlimiterscanbeusedtocopewiththeremaining powerlevels.herefore,thePI Nfeedbacklimitercanbeconsideredasasolid-stateequivalentofthenormalgaseouspreTR-tube.

3 . DIODEPACKAGECHARACTERISTICSBeforeproceedingintoadiscu ssio nondisjunctiondio delimiter

circuitry*amoredetailedknowledgemustbegainedwithrespecttotheactuald i odeequivalentcircuit.tverylowfrequencies,theequivalentd i odecircuitca nbeconsideredasthatofthePN-junctionalone.owever,inthefrequencyrangeofconcern,1Kmcto11Kmc,theeffectofphysicallypackagingthed i odemustbeconsidered.

Unfortunatelyoncethedio deispackaged,strayreactancesareintroducedthatmustbeaccountedforinthemicrowavecircuitryenvironment.hesetaketheformofinductance,L inserieswiththed i odeJunctionandashuntcapacitance,C ,inparallelw i ththepreviouscombination.hegeneraldio depackageequivalentcircuitisshowninFigure(9).lsoshownisaseriesequivalentrepresenta-tionthatlendsitselfmoreeasilytocircuitperformancecalculations thatwillbediscu sse dlater.henecessarytransformationequationsfortheseriesrepresentationarelistedbelow.

u D li

D


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10-X2B = P iT. 2*(x s*xp> 2

Xn2 ( x X) X Xx=-^_LiB - A J BR2 ( XX )6 S pwhereX= -~P .

s S U ) C

LshearasiticseriesinductanceCshearasiticshuntcapacitanceRsheiodejunctionseriesresistanceCsheiodejunctionseriescapacitances

(i)

( 2 )

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Inthecasewhereeitheraforwardcurrentbiasorhighpoweri semployed,abarnotationwillbeused.hereforeRillbecomeRandXhangestoX sforthelatteritcanbeassumedt obe u o LsunderforwardbiassinceCillapproachinfinityit hrespecttoCndL theyarefixedandthereforeunaffectedbybiasconditionsP s

(3-a)ERAMICPACKAGEDIODESInFigure( 4 )tvarioustypicaldiodepackagetypesare

shownwhichwillbeemployedinfuturecircuitdevelopmentonthiscontract.heyareofceramicpackage construction withtheceramicportionsindicated.hepilltypeshowninFigure(4-a),hasbeenmanufacturedbyMicrowaveAssociatesforth epastseveralyearsand


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resultstodateShoeittobeextremelyruggedinnature.houghhownwithtwoconnecting prongs,threadedstudsca nbosubstitutedifdesired or onestudremovedcompletely.

The is-sUckpackagedesign,showninFigur(4b),i sofarecentdesignandi s stillundergoingdevelopment.owevar,prototypeunitshavebeenfabricatedandteststodateshowalargeimprovement withrespect toparasiticreactancea sshowninthetableoffigure( 4 ) .Thisfeatureisbelieved t obeabsolutelynecessaryinordert oachievehighfrequencybroadband operationuptol lKmcwithpackageddiodes.Asforlowerfrequencyoperationat4. 5Kmc,orbelow,iti sbelievedatthistimethatth epilldiodeoraslightlymodifiedformwillbeadequate

(3-b)NTEGRATEDDIODESInordertoachieveths ultimatewithrespecttopackage

parasiticreduction,anintegratediodei snowunderdevelopmentandpreliminaryresultshaveshownitscapabilityofoperating wellaboveX-bandoweverfa price i spaidforthisinth eformo ffragilecon-struction ethodsOfspringloadingthisformofdiodehavebeendevelopedandare currentlybeingevaluated.scanbeseenthistypeofdiodeconstructionisbyfarthemostdesirableforabsolute minimumparasiticreactancevalues.

Theterm Integrateddiodei susedtodescribeapackagelesstypeconstruction withthaPN-junctionaxposed.


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Thereasonsfo racquisitionoflowparasiticreactanceswillbeexplainedlaterinth esectioncoveringlo wpassfilterlimiterdesigns.tthispointit willsufficetoeaythatthelargerthestrayseriesinductivereactance*thelargertheapparentdiodejunctioncapacitance*hi scanbeseenbyexaminationofthepackageddiodeequivalentcircuitshowninFigure(3)incethe strayinductance,L i sinseries with th e Junctionapacitance*C,itwilltendtocanceloutaportionofthecapacitlvereactanceandcause Coappearlargerthan itactually i s .he expressionforKillustratesthiseffect,

4. THE BASICDIODELIMITERAspreviouslymentioned,PN-Junction diodescanbeemployedto

controlmicrowavepowerintheform oflimitersorswitches.heformerisofconcernherethoughnecessarymicrowave circuitryfo reithercaseisidenticalinmanyrespects.norderto achieve efficientlimitingoperation,thediodemustbeproperlyarrangedina microwavecircuitwhenplacedinshuntacrossatransmissionlineitshouldappearasanopencircuitatlow powerlevelsen deshortcircuitathighlevelstoachievedesiredoperation.heabilityto accomplishthisis adirectresultof thelargeimpedancechangeexhibitedby aPN-junctionwhensubjectedtotheextremesinpowerlevels.

(4-a)HEDIODELIMITE*EQUIVALENT CIRCUITInFigure( 5 ) ,theschematicofenidealdiodelimiterfo r

narrowfrequencyoperationi sshown.houghwidebendoperationi sthe


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primaryconcernofthisprogram,adiscussionofthiscircuitcanbeusedtosecureanunderstanding ofgeneralmicrowavecircuitryproblemsinvolved.lsopresentedinFigure( 5 )are aset ofequationsrelatingt o parameters ofthe packaged diodeandexternaltuningreactancesneces-sarytosecure efficientlimitingoperation.heseequationsreducetheoverallcircuittoasimplenormalizedshuntadmittanceequivalentcir-cuitrepresentation*ncetheseexpressions areknown,g +jbandg+jo,limiter performancecanbecalculatedbyus eofthelossequationstabulatedinFigure(6)*

ReturningtoFigure(9),inspectionshowsthattwoexternalreactancesX-andXreutilised*hesearerequiredtoachievemini-mumlossatlow powerlevelsand highestisolationathighpowerlevels

respectivelyppropriatecircuitrelationshipstosatisfythesecondi-tionsare alsoshowninFigure( 5 ) .tfrequenciesupthroughS-band,thislumpedcircuit approachha sbeenfoundtoyieldexcellentcorrela-tionwithexperimentalresults.nallprobability,thiswilldeparttosomedegree at X-bandbu tthemagnitude ofdiscrepancyha syet tobedetermined*orsimplecoaxtransmissionlinestructures,diodeimped-anceCharacteristicsmaybedeterminedbyplacingadiodeinshuntwiththeline andmeasuring VSWRendinsertionloss.ls ovariationofdiodeThe valueofXss ochosenthati tresonateswith X_asshowninthediodeseriesrepresentationofFigure( 3 )underhigh power.hi sassumes f taschangedtoRnd Xsequalto X . hevalueofX_i scholentoparallelreionatewiththeseriesombinationofX^+X

D


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capacitance*bybiasapplication,can t o usedtodeterminetheexactvalue ofInthiscase,Xnd XreomittedandCsvariedsothatseriesresonanceandthusmaximuminsertionlossi ssecured*romthe knowledgeofCtth e properbiaspointandthefrequencyofopera-tionLanbedetermined.

3

(4-b)IODEUMXTEACIRCUITLOSSEQUATIONSThelossequationstabulatedinFigure( 6 )canbeusedt o

predictlimiterperformanceonceappropriatenormalizedadmittancecomponents are known. Iti s worthytonotethattheseequationsareindependentoftheactualmicrowavecircuitryinvolvedandrequireonlythe normalizedshuntadmittanceexpressionsofthelimitercir-cuit \ g jb andg jb.hereforetheyrepresentanexceedinglyvaluabletoolinproviding acapabilitytoanalyzeperformanceofanylimitercircuitconfiguration.tis ,ofcourse,assumedthatthetransmissionlineitselfexhibitsnegligiblelossatthefrequencyofconcernhi sassumptioncanbeconsideredquitevaliduptothemaxi-mumfrequencyofconcern1 1 Kmc

5 . fHBROADBAND LIMITERCONCEPTInordertoachievebroadbandlimiting,iti sdifficulti fno t

impossibletoemployseriesresonanttuningconfigurationsasshowni nFigure{% ) bytheuseofX.hi sapproachisnarrowbandinnaturewhichisnotcompatiblewith thebroadband performancesoughtafter.Thereforeitappears&or*logicaltosimplyplaceadiodeinshunt

withatransmissionline.owever,thisinitselfi snotsufficient


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- 1 5 -with respecttolowlevellotunlessthevalueofXj9assho wninFigure(3)ismuchgreaterthanthetr ansm issionlinecharacteristic im pedanceZithpresentd aydiodetechnology,thisa pproachseemsimpracticalwhenconcernedwithZ valueintherangeof25to5 0ohmsatafrequencyof1 1 Kmc.herefore,m icro wavestructuresmustbeutilizedwhichwillbebroadbandinnatureandemploythedio deshunt*i ngimpedance,X_,intheirdesign.

(5-a)HELO WPASSFILTERLI1WTERO neformofcircuitwhichlendsitselftous einbroadband

limiterdesignsisthelow pa s sfilter.hiscircuitnormallytakestheformoflumpedshuntca pa citancesa ndseriesinductancesformingacascadedseriesoff t networksasshowninFigure(7).heoryofthis

3typestructureha sbeenadequatelycoveredintheliteraturendonlynecessary pertinentdesigninformationwillbediscussedhere.

AscanbeseeninFigure(7),thecircuitlendsitselftouseasabroadbandlimiterbyvirtue ofitsemploymentofshuntcapa-citors. Thesecouldobviouslybesecuredintheformofzerobiasedv ar actor sorPI Ndiodesprovidedthepropercapacit ance valueswereCbterved.herequiredseriesinductancescanbesecuredthroughuseofshortsectionsofhighimped ancetr ansm issionlinehavingavalueofetleasttw i ceZ

Underlowpowerconditions,amatchedlow passfilter

S .B.Gohn"DirectCoupled ResonatorFilters",Proc.IREVol.43,pp .167196(Feb.1987)

i:


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1 6tttlgnedforasufficientlyhighcutofffrequencyfouldofferlittuattenuationtoth esignal.owever,underhighpowerconditionsRFinteractionwiththePM*junctionmould causethevaractorpackageimpedancetoappearasalowvalueofinduct ivereactance.hiswouldobviouslydestroythem at chedpropertiesofthelowpassfilterstruc-tureandcauseittoprov ideahighdegree ofattenuationtotheincom-ingsignal.hereforelim it ingactionwouldbeobtained.ypicalresponseplotsofthefilterlimiterstructureunderthetwoextremepowerlevelsofconcernarealsoshowninFigure(7).

T herippleexhibitedbythelowlevelresponseisduetothefact

thateTchebyscheffdesigni semployedyuseofthisasoppo sedtoaButterworthor"maximallyflat"responsedesigngreaterlowlossbandwidthi sachievedforequalshuntingcapacit ance values.hepr icepa i disrippleintheoperatingfrequencyrange.owever,atthehigherfrequencies,suchasX-bandthiswillprobablybenecessaryduetothelowant icipatedcapacit ancevaluesrequired

Thoughthegeneralappro achisstr aightfor war dseveralpr act icaldifficultieswillbeencountered.heshuntingcapacitancevaluesrequiredconsistnotonlyoftheverectororPI Njunctioncapacitance,C butparasiticeffects.herefore,actualrequiredvalueswillbemo difiedbythefollowing:

(a )huntpackagepar asit iccapacitance,C asshewninFigure(3).

(b)eriesinductance par asit icL whichwillcauseanapparentincreaseinjunctioncapacitance.


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(c)tructuraldiscontinuitycapacitanceasencounteredatthejunctionofanabruptchangeincoaxlineimpedance.

( d )heinherentfinitecapacitanceperunitlengthofacoaxlineoverthephysicalregionoccupiedbyadiodepackage.

Theoveralleffectofalltheseconsiderations f i l lbetheneedofadiodejunctioncapacitancelowerinvaluethanthatpredictedbytheory.hisat onceillustrateswhy minimumpackageparasiticvalues(CndL)aredesirable.

Returningno wtotheclassiclow passfiltertheory,thevariousLandCvaluescanbecomputatedfromthefollowingexpressions.

LZ9kk uck Z oc

( 3 )

( 4 )where C ,and ,aretherequiredfiltercapacitanceandinductancevalues.

Zstheinputandoutputtransmissionlineimpedance.< Bsequalt o2 r ? ffsthedesigncutofffrequencyofthe

filter.)g ,istheappropriateconstantnecessaryforcalculationof

filtercapacitanceandreactancevalues(SeeTable1 ) .l i t allcasesnwillbeoddi nvalueand1km. Odd valuesofkillb e ? usedfor determinationofcapacitanceandevenvaluesfor

i :


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v 18 -JABL^OFTCHEBYSCHEFFCONSTANTS.gk>FO RLOWPASSFILTERDESIGNS

i

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NO. OFILTER1 ELEMENTS

g, VALUESk i h ^2 *3 94 % g6 s?

M2 S ft J .63 .97 .63 -- i I is : 5 .756 1.31 1.58 1.31 .7561.75 1.39 .797

* V o o 7 .797 1.39 1.75 1.63If ^ 1.-, ........ 1.03 1.1b 1.03 ~ ! -Ht 1.15 1,37 1.98 1.37 1.15 1

> - 0 7 ( ' O C U 1.18 ! 1.42i 2.10 1.57 2.10 1.42 1.18

-o a. 1.23 1.15 1.23 ~

i c a03 .H e, 1 CQ DC 1.34 1.34 2.17 1.34 1.34 1 ! IM U > 10 7

i O C O 1 0.4 1.37 | 1.38

1 2.28 1.50 2.28 1.38 ! 1.37! 1


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requiredinductancecalculations.ne allC value*are determined,parasiticandstraycapacitanceeffectsmustbetakenintoaccountinordertodeterminetheactualjunctioncapacitance,C,required.sforLvalues,theymaybe secured,as previouslymentionedbyuseofshortsectionsofhighimpedancetransmissionline.heactuallengthoflinerequiredmaybesecuredthrough us eofthefollowingexpression.

L=.0852^nH/in.o ( 5 )whereLi stheinductance perunitlength

ZQ sthecharacteristicimpedanceofthehighimpedancelinesection(Z Zo o

Inpractice,thismethodofsecuringaneffectivelumpedinductanceinacoaxiallinestructureisvalidprovidedthelinelengthusedi slessthanone eighthofthefiltercut-offfrequencywavelength.

Asafinalpointinthisinitialdiscussiononlo wpassfilterlimiterdesigntechniquesfabriefdiscussionontheisolationchar-acteristicasdfunctionoffrequencyis worthmentioning.hegeneralisolationvaluetrendasShowninFigure(7)showsadecreasing valueasfrequencyincreases*hisisduetothefactthatthediodepackageequivalentcircuitappears asan inductivereactancewhenth efilterlimiterissubjectedtohighpower '- > *$ecauseofthis,theshortingeffectofthe diode becomeslesseffectiveasfrequencyi sincreasednd hencelowerisolation.er eagain,thedesirabilityoflo wpackageparasiticreactancevaluesbecomesapparent.

Asfrequencyincreases X . increasecausingagreaterdeviationfromashortcircuitasideallfdesired.


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isolat ionunderhighpower,ithattheundesir able propertyofbeingfrequencysensit ivea ndexhibitingapeakedresponse.oagreatdegree,itissim ilarinnaturetothelimitercircuitprev iouslydiscussedandshowninFigure(5).

InFigure(8),thegeneralcir cuitemployingthisformofbro adbandlimiterdesignifsho wnalongwithatypicalresponsethatcanbeexpectedforbothinsert ionlossa ndisolat ioncharacteristics. Thisapproach,ifutilisedwouldbeforthehighestfrequencyrangerequired,7to11KmcoderatecapacitancePN-junctionscouldbeemployedwhich wouldovercometheproblemoflowvaluesneededinthisrangeifal o w / passfilterdesignwereutilizedoweverhere,theproblem ofbandwidthappear stobe themost challenging.

TodateTR-tubesutiliz ingthistechnique havebeendesignedwithbandwidthsupto3 0 f t houghthisdoesnotrepresenttheultimatelimit,a7to11Km cdesigndict atesabandwidthof4 4 . 5 $whichisconsider ablygreater.lso,broadb andPN^unctionlimiterdesignspresentlyav ailableatX-bandereonly1 3 f tinbandwidth.here-fore,animprovementinthisareabyafactorof3. 4isrequired.

Atthisearlypo intinthe progr amitisant icipatedthatthebandpassfiltertechniquewillbeusedfortheX -b andregion.his,ofcourse,doesnotprecludethepo ssibilityofawaveguidelowpassfilterdesigniffutureworkshowsittobepromising.

a


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CONCLUSIONS

Atthispoint,withinitialinvest ig at ioncompleted,nodefiniteconclusionsbasedonexperimentresultscanbemade.owever,thefollo winggeneralstatementsarefelttobereasonablycorrectonthebasisofinformationpresentedinthisreportandpastexperienceobt ainediniimitertechnologyatMicro waveAssociates.

(a )hetwolowerfrequencyranges( l-4. 5and4-7.5Kmc)will,inallprobability,employ* o m eformoflowpa s sfilterIimiterdesign.

(b)hehighestfrequencyrange(7-11Kmc)seemstodictateabandpassfilterIim iterdesignapproach. However,thiswilldependgreatlyonthedevelopmentoflowpar asist icpackageandinte-grateddiodes.hisisthem ainchar acter ist icthatprecludestheemploymentofalowpassfilterdesignforthiscase.

(c )nallcases,theemploymentofaPI Ndio defeedbackIim iterwillbeemployedastheleaddio ded uetoitsinherenthigherpowerhandlingcapability.

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PARTHPROGRAMfORTHENEXTINTERVAL

Duringthenextquarterlyintervalofthisprogram,basicdio dechar acter ist icswillbeinvestigatedw i t hrespecttotheeffectofpackagepar asit ic*onlimitingfrequencyofoperation.hiswilltaketheformofcir cuittestsonexistingtypes(pillpackage)andtestingnewerversionsastheybecomeavailable. Inaddition,filterlimiterdesignswillbedevelopedtocoverthetwolowerfrequencyrangesofinterest.

Asforthe X-bandregion,individuallimiterdesignsw illbedevelopedandtestedinanefforttoextendthepresentcapabilityof13& bandwidth.sapo ssiblealternateappro achforthisregion,theemploymentofalowpassfilterlimiterdesign w illbefurtherinvesti-gatedandprelim inarydesignsdevelopedifwarranted.

Also,theareaofhighpowerd iodecapabilityinvest ig at ionw illbestarted.hisw illpr im ar ilyinvolvepreliminarytestsandanalysisonPI Nfeedbacklimiterdesignsoverthecompletefrequencyrangeofconcern.

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LISTOFILLUSTRATIONS

GeneralChar acter ist icsofVaractorsandPI NDiodesPI NDio deFeedbackLimiterConfigur at ionGeneralDio dePackageEquivalentCir cuitandTr ansform at ionEquationsforaSeriesEquivalentRepresent at ionVariousLimitingDiodePackageConfigur a-tionsandAssociatedApproximatePar asit icChar acter ist icsPN-JunctionDiodeLimiterEquivalentCircuitandAssociatedNorm alizedAdmittanceCom ponentEquationsGener alShuntAdmittanceStructureLossEquationsLo wPassFilterTypeLimiterEquivalentCir cuitandGeneralPerformanceChar acter ist icsBandPassFilterTypeLimiterEquivalentCir cuitand Gener alPerformanceChar acter ist ics

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FIGURE3BANDPASS FILTER TYPE LIMITER EQUIVALENTCIRCUIT ANDGENERALPERFORMANCECHARACTERISTICS

Documents

BROADBAND MICROWAVE POWER LIMITERS - MACON - DTIC.pdf