Transitional Combline Evanescent Mode Microwave FiltersWElC-2 TRANSITIONAL COMBLINE/EVANESCENT MODE MICROWAVE FILTERS m Ralph Levyt, Hui-Wen Yaos, and Kawthar A. Zakitt t R. Levy Associates, 1897 Caminito Velasco, La Jolla, CA 92037 tt Electrical Engineering Depa”rtment, University of Maryland , College Park, MD 20742 $ CTA Incorporated, 6116 Executive Blvd., Rockville, MD 20852 ABSTRACT Traditional combline filter theory based on TEM mode coupling results in bandwidths which are too large, the increase being a function of the ground plane spacing t o wavelength ratio b / X . As the b / X ratio increases from 0 to 0.35 the bandwidth ratio BWR, defined as actual bandwidth/TEM bandwidth, increases from unity to over 2:l. This bandwidth increase has now been confirmed by calculation of the coupling coefficient bet,weeri combline resonators ……