Double Resonance Waveguide Cavity

This paper presents a new cavity structure for the implementation of pseudo-elliptic filter topologies. The basic structure consists of a TE₂₀₁ mode cavity which is loaded at its center by either a capacitive or inductive post. Thanks to the post, the lower order mode of the cavity (TE₁₀₁) can now resonate at the same operating frequencies of the TE₂₀₁ mode, thus creating a two-resonance structure that we named in this paper as a double resonance cavity. The structure implements a transverse doublet topology which is capable of generating filtering functions with two poles and one or two transmission zeros (TZs). These zeros can be located in the upper or lower stop-band by employing an inductive or capacitive post, respectively, while their distance with respect to the poles can be precisely controlled by adjusting the locations of the input and output waveguides. A simple CAD technique to efficiently perform a full-wave optimization for this rather complex structure is presented, thus dramatically easing the design effort especially as far as higher order filters with multiple cascaded cavities are concerned.