A New Resonant Coupling Structure for Inline Waveguide Filters with Transmission Zeros

In this work a novel resonant coupling structure in rectangular waveguide is introduced. The proposed structure allows the introduction of transmission zeros in the response of inline filters. The main advantage with respect to the resonant couplings usually adopted (i.e., resonant posts) is that the new structure allows the placing of transmission zeros very close to the passband. Moreover, it does not require any extra space as instead does the stopband singlet recently introduced for the same purpose. An equivalent circuit of the novel coupling structure is proposed, suitable for the use in the synthesis of filters with frequency-dependent couplings. Dimensioning charts are then introduced, to make it easy the initial assignment of the physical dimensions of the structure so that the extracted equivalent parameters have the assigned values. Finally, an example of use of the novel coupling structure in a 6-2 waveguide filter in Ka band is presented.