Innovative solutions for compact waveguide filters

Innovative solutions for microwave waveguide filters have recently been developed in order to alleviate the problem of size and weight inherent to waveguide technology. Such solutions yield very compact structures along with highly selective pseudo-elliptic responses. A first class of filters is based on the ridge resonator concept, where a partial-height ridge arbitrarily located and oriented within a waveguide behaves as a quasi-TEM resonator. Depending on the position and shape of the ridge resonator, several single- and dual-mode configurations producing also finite frequency transmission zeros can be obtained. A novel class of dual-mode filters using both resonating and non-resonating modes is then presented in this paper. While a pair of TM resonant modes is exploited to generate two poles, non-resonating modes are exploited to realize an additional input-to-output path, so generating two symmetric transmission zeros. Experimental results on several compact filters demonstrate the feasibility of the new classes of waveguide filters.