Triple-Band Rectangular Cavity Bandpass Filter Based on Multiple Odd Modes

This article proposes a triple-band bandpass filter with two H -shaped short-circuit columns and two $\Pi$-shaped shortcircuit rings loaded in a rectangular resonant cavity. Six odd modes are excited in the resonant cavity, with each two modes forming a passband, resulting in a total of three passbands. The first two resonant modes are slot modes generated by feeding slot resonance, while the remaining four resonant modes are higher-order modes of the rectangular cavity itself. The triple-band filter has three distinct passbands centered at 4.155GHz, 4.600GHz, and 5.005GHz, with absolute bandwidths of 100MHz, 100MHz, and 130MHz, respectively. By changing the parameters of the $\Pi$-shaped short-circuit ring and H -shaped short-circuit column, the positions of the passband and transmission zero can be tuned. The coupling matrix of the filter is synthesized by applying the comprehensive techniques. The theoretical results of coupling matrix synthesis and HFSS full-wave simulation results are compared and found to match well, confirming the rationality of the design.