Analysis of Eighth-Mode Substrate-Integrated Waveguide Cavity and Flexible Filter Design

In this paper, a systematic research campaign on eighth-mode substrate integrated waveguide (EMSIW) filters is reported. The sizes of these EMSIW resonant cavities are only one-eighth or one-sixteenth of a conventional SIW resonant cavity. Two different coupling topologies, i.e., electric coupling and magnetic coupling, are employed between two EMSIW resonant cavities, which are analyzed theoretically via the response of the structure and the relationship between the cavities. Both coupling topologies enable structural variations that possess advantages and flexibility of the second-order EMSIW bandpass filters (BPFs) designing. By utilizing these basic coupling mechanisms, multilayer board technology, and other practical techniques, a class of triple-order SIW BPFs with the merits of compact size and high selectivity are demonstrated. Specifically, several triple-order EMSIW BPFs composed of pure EMSIW cavities or comprised by combining EMSIW and quarter-mode SIW cavities are simulated, fabricated, and measured for verification.