A new evanescent-mode filter for densely packaged waveguide applications

A novel evanescent-mode filter structure based on T-septum waveguide technology is presented for applications in extremely compact designs. The excellent characteristics of the T-septum waveguide are utilized to significantly reduce the resonator cutoff frequency compared with standard ridge waveguide designs. This allows the evanescent-mode guide to have a smaller cross-section, hence considerably reducing the overall length of the filter. The computer-aided design uses a full-wave mode-matching technique which takes into account higher-order mode coupling at all discontinuities involved. Design data are given for X- and Ka-bands. The method was verified by measurements. The manufactured 10-GHz prototype measured only 18.4 mm in length.<>