A new type of compact evanescent-mode waveguide bandpass filter using planar dual-behavior resonators

This paper proposes a new type of compact evanescent-mode waveguide filter composed of planar dual-behavior resonators, which can produce multiple transmission zeros without any cross-coupling structures. The introduction of the planar resonators working in the evanescent-mode waveguide makes the length of the interval between the resonators much shorter than one-quarter guided wavelength, thereby resulting in drastic reduction of filter volume. The controllability of the resonant and antiresonant frequencies of the proposed resonator is first investigated by numerical simulations, and the design method for the evanescent-mode waveguide resonator and filter is described. As a design example, a three-order bandpass filter with multiple transmission zeros is demonstrated at X band. The effectiveness of the proposed resonator and filter is validated through the filter design.