A New Class of Pseudo-Elliptic SIW Filters Using Dual Mushroom-Shaped Resonators

A new class of inline pseudo-elliptic substrate-integrated waveguide (SIW) filters is presented in this article. The proposed structure is based on a novel resonator, consisting of a pair of mushroom-shaped resonators. The odd and even symmetry modes of the dual-post resonator are exploited as resonant and nonresonating modes, respectively. The nonresonating mode generates a direct input-to-output coupling, thus providing a transmission zero (TZ) that can be either located above or below the resonant-mode pole. The coupling between the resonant mode and the source (or load), as well as the input-to-output coupling, can be controlled by selecting the disk size and the metal post position of the mushroom resonators, as well as the rotation angle of the pair of mushrooms. The Nth-order filtering functions with a number of TZs up to the number of poles can be realized by cascading N dual-post resonators. With respect to the conventional in-line waveguide filter with inductive obstacles, the proposed filter is easier to tune and more selective. A fourth-order dual-post filter with four TZs was designed and experimentally demonstrated to show the feasibility of the proposed approach.