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 singleand 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.