Millimeter-Wave Dual-Mode Filters Realized in Microstrip-Ridge Gap Waveguide Technology

In this paper, we propose novel microstrip-ridge gap waveguide (MS-RGW) millimeter-wave bandpass filters based on a dual-mode resonator. The resonator represents a rectangular patch grounded by a set of vias, whose pair of fundamental degenerate modes are separated in the spectrum using the via position perturbation. MS-RGW feeding lines are realized as periodically grounded microstrip lines inserted into a perfect magnetic conductor (PMC) structure, which are fed via the 2.92-mm connector through the specifically designed transition. A detailed analysis of the filters is provided together with the analysis of their building blocks—mushroom-based PMC surface, MS-RGW with periodically grounded microstrip line, and dual-mode resonator. The proposed filters are fabricated using standard PCB technology and the measured results show that the filters exhibit low losses, good in-band and out-of-band characteristics, and good selectivity. As such, the proposed filters represent excellent candidates for millimeter-wave filtering applications since they reconcile the requirements for high performance, low loss, and low cost.