Stubbed Waveguide Cavity Filters

A new class of reduced-size waveguide filters implementing pseudoelliptic filtering functions is presented in this article. The basic structure of these filters is the stubbed waveguide cavity (SWC), which is proposed in both single- and double-stub configurations. The SWC consists of a main TE201 mode cavity, which is loaded with one or two E-plane stubs. The stubs behave as embedded half-mode cavities supporting additional resonant modes, and they are properly located so as to realize specific coupling schemes for the generation and control of transmission zeros. Depending on its configuration, a sole SWC can generate up to three poles and three transmission zeros. The design of higher order filters employing a cascade of SWCs, as well as combinations between SWCs and conventional waveguide cavities, are presented. The experimental results of a third-order filter employing one SWC (double-stub configuration) and a fifth-order filter employing two SWCs validate the feasibility of this new class of waveguide filters.