Ultra-compact highly-selective dual-mode pseudoelliptic filters

An innovative ultra-compact dual-mode waveguide filter is presented. The basic idea consists of using a pair of TM_mn0 degenerate cavity modes, while non-resonant modes provide a direct input-to-output coupling. In this manner, the single cavity provides two reflection and two transmission zeros, and is at the same time very compact in the longitudinal direction. Theoretical and experimental results of a two-cavity filter with four transmission zeros demonstrate the feasibility of the approach.