CAD of T-Septum Waveguide Evanescent-Mode Filters

This paper presents a mode-matching-based design of evanescent-mode waveguide filters with T-septum shaped metal inserts. Owing to the wideband characteristics of the T-septum waveguide, the proposed design constitutes a significant improvement over common evanescent-mode filters with respect to both size reduction and stopband behavior. The theoretical approach is verified at the example of a three-resonator 8.8-GHz filter prototype of less than 3/4 inch length. The second passband is beyond 27 GHz. Since the design procedure takes higherorder mode interactions into account, good agreement between theory and experiment is obtained over the entire measurement range between 8.2 and 40 GHz.