Direct-Coupled TE–TM Dual-Mode Waveguide Cavities

This paper introduces a novel quadruplet structure in waveguide technology, comprising a TM cavity within two λ/4 TE cavities. This structure demonstrates the capability of generating responses with four poles and two transmission zeros (TZs). Notably compact, it accommodates both wide and narrow band responses effectively. The TZs are obtained by harnessing the non-resonating modes within the TM section. The coupling between the resonant mode of the TE section and both resonating and non-resonating modes is achieved by precise positioning of the TE section relative to the TM section. This inherent flexibility in TZ positioning renders the structure highly adaptable. Moreover, this structure can be exploited as building block for the design of higher order filters. Experimental results validate the viability and effectiveness of the proposed structure.