Bandpass Filters Based on Triple-Mode Dielectric Waveguide Resonators

This paper presents a novel approach to designing bandpass filters using a triple-mode dielectric waveguide resonator (DWR). The filter is composed of two triple-mode dielectric waveguide resonators. Each triple-mode resonator consists of a rectangular dielectric waveguide resonator with a square ring removed, where two half-wavelength microstrip resonators are plated. The fundamental TM
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mode of the rectangular DWR and the TEM modes of the two microstrip resonators contribute to the triple-mode DWR. By utilizing triple-mode DWR, the number of resonators can be reduced, and a sixth-order filter can be designed with only two triple-mode DWRs. To activate the TM
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mode along with one of the two TEM modes, a probe is introduced into the dielectric waveguide resonator and linked to the microstrip resonators. The source and the three modes of the triple-mode DWR forms a CQ coupling topology, generating a pair of transmission zeros outside the passband. The two triple-mode dielectric waveguide resonators are coupled magnetically, resulting in a sixth-order filter response and four transmission zeros outside the passband.