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1、IEEE TRANSACTIONSONMICROWAVETHEORYANDTECHNIQIJES,VOL.MTT-25,NO.12,DECEMBER1977 1021 REFERENCES 1G. FCravenand C. K, Mok,“Thedesignof evanescentmodewave- guidebandpassfiltersfora prescribedinsertionloss characteristic; IEEETrans.MzcrowaueTheoryTech.,vol.MTT-19, pp. 295-308, Mar.1971. 2R.Levy,“Theoryo
2、fdirect-coupledcawtyfilters,”IEEETrans. MicrowaveTheoryTech.,vol.MTT-15,June1967. 3L, Lewin,AduancedTheoryof Wauegaides.NewYork:Illife,1951, pp. 88-1oo. 4Theoryof Waueguides.HalstedPress,1975, sec. 5.13. 5R. Syderand D. Bozarth,“Sourceand loadimpedancefor simultan- eousconjugatematchof linear2 port,
3、”ElectronwConrnruntcator, Nov./Dee.1967. 6G. F. Cravenand L, Lewin,“Designof microwavefilterswithquarter wavecouphngs,”Proc.Inst.Elec.Eng,PartB, vol.103, no.8, pp. 173-177,Mar.1956. 7R.Ghose,Mwrowa.eCircuitTheoryandAnalysis.NewYork: McGraw-Hill,1963, pp.168-171. 8C. K. Mok,“Designof evanescent-modew
4、aveguidediplexersIEEE Trans.MicrowaueTheoryTech.,vol.MTT-21,pp. 43-48,Jan. 1973. 9W.Edson.“Microwavefiltersusingghost-moderesonance,”pre- sentedat ElectronicComponentsConference,San Francisco,May 2-4,1961. 10B.F.Nicholson,“Practicaldesignofmterdigitalandcombfine filters,”Radioand ElectronteEngineer,
5、pp. 44-45,July1967, 11P. Somlo,“Computationof coaxialhnestepcapacitances;IEEE Trans.MicrowaveTheoryTech.,vol.MTT-15, Jan.1967. Dual-ModeCanonicalWaveguideFilters ALBERTE. WILLIAMS,MEMBER, IEEE, ANDALIE. ATIA,MEMBER, IEEE AbstractThispaperintroducesanewformofdual-mode narrow-bandpasswaveguidecavityfi
6、lter.The filters,whichcan he constructedfromeitherdualmodecircularor squarewavegnide cavities,can realizethe optimumtransferfunctions(includingthe exactellipticfunctionresponse).One of the unique featuresof these filtersis thatall the intercavitycouplingirises may take the formof circularholesrather
7、thanlongnarrowslots.Severalalternative inpututputconfigurationsare described.Experimentalresultson severalfiltersindicateexcellentagreementwiththec)ry. INTRODUCTION T HEDEVELOPMENTof high-capacitycommunica- tionssatellitetranspondershas madeit necessaryto channelizethefrequencyspectrumtoefficientlyu
8、se the availablespacecrafttransmitpower.Toaccomplishthis objective,filterguardbandsmustbe minimizedand hence sharpfrequencyselectivityis required.Further,the filters musthaveflatin-bandgainslopeandsmallgroup-delay variationto minimizecommunicationscross talkanddis- tortion.Therefore,theneedforhigh-p
9、erformancemicro- wave channelizingfilterswhichpossess optimumresponses consistentwithminimumweightandvolumeis apparent. Startingwiththe cascadedwaveguidecavity(Chebyshev or Butterworthdesign1),the developmentof the linear phase filter2, the dual-mode(TE )longitudinalcircular cavityfilter3,andthe sin
10、gle-moderectangular(TE 10J anddual-modesquare(TEIO ) foldedgeometries4are evidenceof the improvementwhichhas occurredin recent years. The key to the developmentsis the recognitionthat simplecascadedwaveguidecavityfilterscannothave finite transmissionzeros. On the otherhand,the optimumfilter Manuscri
11、ptreceivedMay11, 1977;revisedAugust8, 1977. Thispaper was supportedby the InternationalTelecommunicationsSatelhteOrgani- zation(INTELSAT). Theauthorsare withCOMSATLaboratories,Clarksburg,MD20734. must have the maximumpossiblenumberof finitetransmiss- ionzeros, placedat predetermined(arbitrary)locati
12、onsin thecomplexfrequencyplane,as maybe dictatedby the solutionof the approximationproblem. A possibleconfigurationforobtainingthe mostgeneral responsefroma set of n-multiple-coupledsynchronously tunedcavitiesis the canonicalform5.Inthisform,the cavitiesare numbered1to n, with the inputand outputpor
13、ts locatedin cavities1 and n, respectively.Cascade(or series) couplingsofthesamesignmustbeprovidedbetween consecutivelynumberedcavities,i.e., 1 to 2,2 to 3, ,n 1 ton(as in the Chebyshevfilter).In addition,shunt(or cross) couplingsofarbitrarysignsmustbeprovidedbetween cavities1 andn, 2 and n 1, .”,et
14、c. As in the canonical form,themoregeneralresponseswhichcan be obtained frommultiplecouplingsallowa given filterspecificationto be metby fewerelectricalcavities,whichin turnleads to minimumweightand volume. Thecanonicalcouplingset maybe realizedwiththe single-modeor dual-modefoldedgeometries,but its
15、 realiza- tioninthesimplerlongitudinaldual-modecircular(or square)cavitygeometryhas notbeen described.Therefore, the advantagesof the longitudinaldual-modefilter,such as minimumweightand volumeand ease of fabrication,do not coincidewiththe optimumfilterresponse. Thispaperpresentsa newdualTEI modecir
16、cular waveguidecavitystructure,the dualmodecanonicalfilter, whichrealizesthe optimumelectricalresponse,and retains all the mechanicaladvantagesof the longitudinaldual-mode filter.Thisfilteris describedwithreferenceto its equivalent circuit.Its designis outlined,withspecificemphasison the designof it
17、s inputand outputports.Detailedexperimental results for four-poleellipticfiltersindicatethe validityof the design philosophy.Finally,experimentalresults for six- and 1022IEEE TRANSACTIONSONMICROWAVETHEORYANDTECHNIQUES,VOL.MTT-25,NO,12,DECEMBER1977 WWw MI,nM12, .“ M3,.-3 / / D IH R In IF I / Q IH n1
18、IF / / / a- lH in2 lF / -. -. Mn,;“-IMn-I,.2M“, (a) / “m IF aml lH + -l+w- 1 Mm_I,m+2 M m, fn+l / / -D IH Im+z IF / / n3 Mm+2,m+I EB_B_B_- M1223MNM45 .!3 . 1. R Mn_l,. (b) Fig.L(a)Canonicalequivalentcircuit.(b)Longitudinaldual-modeequwalentcircmt. eight-pole,4-GHz,bandpass,canonicaldual-modefilters
19、are presented. THEORY AND DESCRIPTION OF THE NEW REALIZATION Fig.l(a)is the equivalentcircuitof an n-cavitycanonical filter,wheren (=2n3) is an even number.Thecavitiesare identicaland tunedto the same resonantfrequency,whichis thecenterfrequencyofthefilter.Couplingsamongthe cavitiesare assumedto be
20、frequencyinvariant.It has been shown5that,togeneratethegeneralclass of transfer functions,the cascade(or series) cavitycouplings(i, i +1), wherei=l,2,”.”, n 1, must have the same sign, whilethe cross (or shunt ) cavitycouplings(i, n i + 1), wherei =1, 2,”,n/2, musthave arbitrarysigns. The equivalent
21、circuit of this couplingset is shownin Fig. 1(a). This set of couplings can be realizedby the foldedrectangularwaveguidecavity structuredescribedin 4, and shown in Fig2. However,this structureis expensiveand difficultto fabricate,and does not possess thesimplicityandcompactnessof the dual-mode cavit
22、ystructure. On the otherhand,the longitudinaldual-modefilter3, withinputand outputportssituatedon oppositeends of the structure,cannotsatisfythe canonicalcouplingset except for n = 4. The equivalentcircuitof this filteris shownin Fig. l(b).Itisapparentthat,whilecouplingsbetweennon- adjacentcavitiesc
23、an be provided,the two cavitiescannotbe separatedby morethantwocascadedcavities.Thisrestric- tionresultsin the reductionof the numberof finitezeros of tm ELECTRICCOUPLINGHOLE NEGATIVESIGN 1 Y MAGNETICCOUPLINGSLOTS POSITIVESIGN ,/ ( x- _- E t, d ,. t In Fig.2.Single-modewaveguidecanonicalfilter. tran
24、smissionthatcanbe generatedin the filterstransfer function. The significanceof this effect in terms of filterperformance is shownin Fig.3 6, whichcomparesthe responsesof a seriesofeight-cavityequiripplefilters(FZ= 8). Thesere- sponsesare labeled8-O8-3, whereO denotesa Chebyshev responseand1, 2,and3
25、thenumberofrealzerosof transmission.Thelongitudinaldual-modeformshownin WILLIAMSANDATIA: CANONICALWAVEGUIDEFILTER1023 130 t 120 110 ICYI 90 t 80 /” / 8.2/ 70 / 8.! 60/ % 40 COUPLING SLOTS .“ “%“ *I % /“ COUPIINGsCREWS l,?;,/ . .zn 1 , ,f, “P f“ (.)0.,cam., Fig.5.Canonicalfilterinput-outputconfigurat
26、ions. fora TE dual-modecircularcavity,withthe inputand outputelectricalcavitiestakenfromthesamephysical cavity.The mechanicaladvantagesof the dual-modelongi- tudinalstructure,such as ease of fabricationand minimum weightand volume,can now be combinedwiththe optimum electricalresponse.It is also inte
27、restingto note that, since in mostpracticalcases thefiltersare symmetrical,thenew canonicaldual-moderealizationwillhave asymmetricalset ofcouplings,i.e.,M12= M*,H _ 1, M23= M.-l,v-z,etc.; therefore,the intercavitycouplingslots can be made circular couplingholes. Thisfurtherminimizesthe filterfabrica
28、tion timeand expense. A possiblelimitationof the canonicaldual-modefilteris the potentialforspuriouscouplingbetweenthe inputand the outputports, causingdegradationof the filtersresponse. Such coupling,when present,must dependon the particular portconfiguration.Severalpossibleinput-outputport configu
29、rationshavebeenconstructedandexperimentally testedinfour-pole,40-MHzbandwidth,ellipticfunction filterscenteredat4.138GHz.Theseinput-output configurations,shownin Fig.5, includethe following: a) Coaxialcoaxial:Twocoaxialprobesareusedto coupleto the maximumradialelectricfield(E,) positionsin the input
30、-outputcavity,as shownin Fig.5(a). b)Coaxial-endwaueguide:Oneportis formedbya coaxialprobethatcouplesto the radialelectricfield(E,), whiletheotherportisformedbycouplingtheradial magneticfield(H,)at the end of the cavitythrougha long narrowslot,as shownin Fig.5(b). c) End-wallsidewall:One portis form
31、edby couplingthe 1024IEEE TRANSACTIONSONMICROWAVETHEORYANDTECHNIQUES,VOL.NrTT-25, NO. 12, DECEMBER 1977 o IIIIfIIIIIIIIIIIII 10 - 20 - 30 40 - 50 z r. z q 8 0 z E G J IIIIIII11IIIII1I11I 40404rm040s0 41004120 414011604380 422042204240 FREQUENCY(MHZI (a) FREQUENCY04+.) (b) Fig.6.(a) In-bandand return
32、loss responsesof four-polefilters,(b) Out- of-bandresponsesof inputoutputconfigurations. axialmagneticfield(Hz)atthesidewallofthecavity througha slot, whilethe otherportis formedby an end slot, as in (b). Thisconfigurationis shownin Fig.5(c). d)Sidewall-sidewall;Thetwoportsare formedby cou- plingthe
33、 axial magneticfields (Hz) throughsidewallslots, as shownin Fig.5(d). e) Orthomodejunction:An externalorthomodejunction is used to separatethe two orthogonallypolarizedfields, as shownin Fig.5(e), Experimentallymeasuredresponsesofthese configurationsare shownin Fig.6. Thenarrow-bandre- sponses of al
34、l the configurations(withthe exceptionof that shownin Fig.5(d)are virtuallyidenticalto the theoretical response(see Fig.6(a).Significantasymmetryhasbeen observedin the configurationof Fig. 5(d). This asymmetryis probablyattributabletothegenerationofhigher-order modes due to the relativelylarge sidew
35、allslots in the cavity. Themeasuredwide-bandsweptfrequencyinsertionloss (from3.1 to 5.1 GHz)of the configurationsof Fig. 5 is shown in Fig. 6(b). In the case of the coaxialcoaxialstructure(Fig. 5(a), the spuriouscouplinglimitsthe out-of-bandrejection of thisfour-polefilterto about30 dB.Thecoaxial-wa
36、ve- guideandend-wall-sidewallconfigurations(Fig.5(b)and (c) have very similarcharacteristics,and offer an adequate out-of-bandrejection.Theout-of-bandresponseofthe structureusing the orthomodejunctionreflects the isolation characteristicsofthatjunction,whichexhibitsseveral narrow-bandresonances,as s
37、hownin Fig. 6(b). It shouldbe notedthatthe geometriesof Fig. 5(b) and (c)areparticularly suitablefor use in waveguidemanifoldmultiplexerapplica- tionsrequiringat least one waveguidecoupling. FILTERDESIGN Theelectricaldesignof the filterdescribedhereinbegins withthechoiceof thecenterfrequency,bandwid
38、th,and out-of-bandrejectiontomeeta givenspecification.The generationof a generalcouplingmatrixfromthe given filter transferfunctionis describedin 3, and the reductionof this generalcouplingmatrixtothecanonicalcouplingset is describedin 5. Similarto the proceduredescribedin 7, the mechanical filterde
39、sign,whichinvolvesthe determinationof the inter- cavitycouplingslotdimensionsandthecavitylengths, followsfromthe electricaldesign.As mentionedpreviously, one advantageof this type of filteris that,since the couplings Mlz= M.,._ , M23= M._:_,etc.,circulardiameter holes can be used for intercawtycoupl
40、ing.Thiscouplingis computedby usingthe proceduredescribedin 7. TheintercavitycouplingA4ij betweencavitiesconnected by a circularholeis relatedto the free-spacewavelength1, thecavityguidewavelengthAg, andcavityradiusR as follows: 8(PL)22 1- Mj =3A;R2 where PM is the equivalentcorrectedmagneticpolariz
41、ability of a circularholeand is givenby M=1 -(2c,Jy10%3*/lcl-(Ac,A)211/2 FREQUENCY (MHz -J FREQUENCY (MHz) (b) Fig.7.(a)In-bandresponseof six-polebandpassfilter.(b) Out-of-band responseof six-poleband pass filter. where t P;IEEETrans.MicrowaveTheoryTech.,vol.MTT-22,pp. 425-432,Apr.1974. A. E. Atia,A
42、. E. Williams,and R. W. Newcomb,“Narrow-bandmulti- ple coupledcavitysynthesis;IEEETrans.CircuitsSyst., vol. CAS-21, pp. M9-655,Sept.1974. R. Levy,“Filterswithsingletransmissionzerosat realor imaginary frequencies;IEEETrans.MicrowaveTheoryTech., vol.MTT-24,pp. 172-181,Apr.1976. G.L.Matthaei,L.Young,a
43、ndE. M.T.Jones,A4icrowaueFilters, ImpedanceMatchingNetworksand CouplingStructures.NewYork: McGraw-Hill,ch. 5. Componentsfor MicrowaveIntegratedCircuits withEvanescent-ModeResonators KLAUSSCHUNEMANN,MEMBER,IEEE,REINHARDKNOCHEL,ANDGUNTHERBEGEMANN A bstractTheelectricalperformanceof activemicrowavecom-
44、 ponentsforradiolinksystems,whichhave heen realizedutilizing evanescent-moderesonators,is described.Thiswaveguide-below- cutofftechniqueis showntohe an alternativetothetechniques establishedbeforenow. I.INTRODUCTION A FEWYEARSAGO,Craven1 presenteda new type ofpassiveintegratedcircuitryutilizingevart
45、escent- moderesonators.Inthistechnique,inductanceis repre- ManuscriptreceivedMay11, 1977; revisedAugust10, 1977. Thiswork was supportedby the DeutscheForschungsgemeinschaft. Theauthorsare withthe InstitutfiirHochfrequenztechnik,Technische UniversitatBraunschweig,D-3300Braunschweig,FederalRepublicof
46、Germany. sentedbyshortsectionsof rectangularwaveguidebelow cutoff,capacitanceby obstaclesin the waveguide,such as a capacitivescrew or a thinsheet of dielectric.Thus resonators of highunloadedQ-factor(calledevanescentmoderesona- tors)can be formedwhichresemblea reentrantcavity(see, e.g., 2 ) in that
47、the electricstoredenergyis confinedto a smallvolumeof a gap regionsurroundedby a largervolume, whichcontainsthe magneticstoredenergy.In bothcases resonantconditionsare establishedonlyafterinsertionof a post.Onecanthenregardthereentrantcavityas the forerunnerof the waveguide-below-cutofftechnique. Whiletheoryandrealizationof passivecomponentsin waveguide-below-cutofftechniqueare in an advancedstate 2-10,onlylittleworkhas been doneconcerningactive components1115.A varactordiodeupconverterand