Integration of Interresonator Coupling Structures with Applications to Filter Systems with Signal Route Selectivity

This paper presents a positive-to-zero continuously tunable interresonator coupling structure for postloaded substrate-integrated cavity resonators. Two interresonator coupling structures with the opposite coupling signs were integrated. The continuously tunable negative microstrip line coupling structure can generate large enough coupling to cancel out the positive coupling by the inductive iris and accomplish near-zero coupling. The proposed structure was implemented on designing a tunable Butterworth-response filter of which the center frequency and bandwidth can be continuously adjusted. It was further applied to a six-resonator-array filter structure that essentially requires the zero coupling capability in order to acquire signal route selectivity. The two-, three-, and four-pole responses with different signal paths were measured within a frequency range, and for the two-pole case, two signals were simultaneously measured, while one signal is frequency tuned.