Novel Filter Design Methodusing TimeDomainTransforms ms

Theauthor presents a novelwayatap- proaching coupled-resonator filter design byutilizing thetimedomain response ofthefilter toestablish reso- nator frequency anddetermine coupling factors. This methodcanalsobeusedwithcoupled cavity filters, comb-line filters, discrete LCfilters, amongothers. I.INTRODUCTION: A significant difficulty inthedesign ofcoupled reso- nator filters isdetermining theproper frequencies forthe resonators, andindetermining theproper coupling be- tweentheresonators. There arenumerous sources for obtaining ideal design factors suchascoupling factors asa function offilter typeorpassband ripple (1).Buttrans- lating these values into physical reality inacoupled reso- nator filter canbeextremely difficult. Also, manysources donotaccount forloss, orother non-ideal effects. This novel design method makesuseofthetimedomain trans- formofthereflection coefficient, which isastandard op- tion onsomevector network analyzers (VNA).Inthis paper, theHP 8753Ewithoption 010isutilized. This transform canbeinterpreted todetermine thevalues ofthe individual resonator frequencies, andthevalues ofthe coupling factors inthefilter. This points thewaytoana- lyzing physical filter structures andassociating their re- sponse totheideal filter factors. Thismethod alsoprovides ameansfordetermining changes inresonator frequency andcoupling factors, due toenvironmental changes forexample, thusassociating a filter's change infrequency response totheindividual component that haschanged. This issolves andexceed- ingly difficult problem facing thedesigners offilters used inspace applications, whereenvironmental effects onthe filter frequency response areofparamount importance. Itcanbeshownthat themagnitude ofthetimedomain response ofabandpass passfilter asmeasured inBAND- PASSmodeonaVNAisidentically equal tothetime re- sponse ofthelowpassprototype filter usedtocreate the band-pass filter. From-this equality, itcanbedemon- strated that forallpole filters, nulls inthetimeresponse areassociated with thefilter resonators, andpeaks inthe response with thefilter coupling. Fromthis relationship, a method for -evaluation thecorrespondence between physi- calfilters andsimulation models canbeobtained.