Dual- and Triple-Mode Single-Layer Substrate-Integrated Waveguide Filters Based on Higher-Order Modes for Millimeter-Wave Applications

In this brief, new dual- and triple-mode SIW cavities based on the higher-order modes in a single-layer substrate integrated waveguide (SIW) cavity are proposed and analyzed. To realize mm-wave filters with the higher-order modes, two-type two-pole dual-mode SIW filters with a lower and an upper stopband finite-transmission zero (FTZ), respectively, are proposed and analyzed firstly. Then, a quasi-elliptic three-pole triple-mode SIW filter with three FTZs is proposed. To realize higher-order response, a quasi-elliptic four-pole SIW filter based on two different dual-mode building blocks is proposed and analyzed. For the verification, a three- and a four-pole filters with the center frequency of 30 GHz are designed, fabricated, and measured. The proposed filters have the merits of high selectivity, low cost, and lower sensitivity to fabrication errors.