A Miniaturized Evanescent Mode Waveguide Filter Using RRRs

In this paper, a miniaturized evanescent mode waveguide filter using rectangular ring resonators (RRRs) is presented. The evanescent mode waveguide resonator cell (EWRC), composed of a section of evanescent mode waveguide loaded with a pair of RRRs, is designed and analyzed. Quality factors of the EWRC are simulated and calculated. The resonant mechanism and the values of the equivalent lumped elements of EWRCs are given for further design and application of this kind of filter. A miniaturized waveguide filter is designed and fabricated to operate at Ka-band, using the W -band standard waveguide (WR-10) with a cross-sectional size of 2.54∼\text {mm} \times 1.27 mm. The proposed filter can realize a large size reduction compared with the conventional waveguide filter, especially leading to a cross-sectional size reduction of 87.2%. Despite a slight frequency shift, good agreement has been achieved between the simulation and measurement results. The proposed filter has large out-of-band rejection, wide stopband, and high selectivity. In addition, a compact diplexer with high isolation is presented.