CAD of T-septum waveguide evanescent-mode filters

A mode-matching-based design for an evanescent-mode waveguide filters with T-septum shaped metal inserts is presented. 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 for the example of a three-resonator 8.8-GHz filter prototype of less than 3/4-in length. The second passband is beyond 27 GHz. Since the design procedure takes higher-order mode interactions into account, good agreement between theory and experiment is obtained over the entire measurement range between 8.2 and 40 GHz.>