Dual-Mode Canonical Waveguide Filters.pdf
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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
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