Novel Double Rejection Cavity to Improve Selectivity in Inline Rectangular Waveguide Filters

In this paper, we introduce a new cavity structure capable of generating two poles and two transmission zeros (TZs). The novel structure is realized by incorporating a circular waveguide section with two irises mounted on the rooftop of a rectangular waveguide cavity. Starting from a traditional inductive iris filter in a rectangular waveguide, the proposed design does not alter the total length of the filter. Furthermore, the height of the structure added to the cavity rooftop is comparable to that of the rectangular waveguide flange and does not extend beyond it. This configuration enables the creation of an inline filter with two TZs on opposite side of the passband and very close to it. The feasibility of the proposed method has been demonstrated through the design of a seven-pole narrowband filter (with five poles in the passband).