The Resonant Input: Pushing The Boundaries Of Coaxial Comb-Line Evanescent Mode Filters

This paper extends the state-of-the-art of the coaxial comb-line evanescent mode technology by introducing a unique filter structure capable of reaching performance previously unattainable. A very wide passband, wide stopband, high-power handling capability, as well as a relatively high frequency of operation, are all concurrently accomplished by this new filter. Specifically, the filter showcases an 8–18 GHz passband (covering both X-band and Ku-band) with an upper stopband up to 40 GHz, while guaranteeing a power handling capability of at least 150 W CW. The key idea underlying such an accomplishment is what we call resonant input, which consists of an additional resonance properly generated within the input connector line so as to serve as the first conceptual resonator of the filter. The resonant input makes it possible to maximize the achievable input coupling, which commonly represents the primary aspect limiting the bandwidth of a filter; at the same time, it also significantly alleviates the second typical limitation concerning the amount of inter-resonator coupling within the first pair of resonators. The experimental results of a filter product prove the proposed innovation.