A New Class of Pseudoelliptic Waveguide Filters Using Dual-Post Resonators

A new class of inline pseudoelliptic waveguide filters is presented in this paper. The proposed structure is based on a novel resonator, namely, the dual-post resonator, consisting of a pair of antipodal partial-height posts. The odd and even symmetry modes of the dual-post resonator are exploited as the resonant mode and nonresonating mode, respectively. The nonresonating mode generates a direct input-to-output coupling, thus providing a transmission zero that can be located either below or above the pole of the resonant mode. The coupling between the resonant mode and the source (or load), as well as the input-to-output coupling, can be controlled by properly selecting the height and position of each post of the dual-post resonator, no additional waveguide discontinuity being needed. N th-order filtering functions with a number of transmission zeros up to the number of poles can be realized by cascading N dual-post resonators. With respect to the conventional inline waveguide filter with inductive obstacles, the dual-post filter is easier to tune, shorter, and more selective, such advantages being paid by a somewhat lower Q factor. The design of fourth- and sixth-order dual-post filters is presented; the experimental results demonstrate the feasibility of the approach proposed.