Self-Packaged, Low-Loss, Planar Bandpass Filters for Millimeter-Wave Application Based on Printed Gap Waveguide Technology

A new concept of printed planar technology is introduced for the realization of low-loss bandpass filters in millimeter band. The new technology is self-packaged, and the insertion loss shows meaningful improvement compared to microstrip (MS) filters. The designs are based on the ridge gap waveguide (RGW), which is composed of printed parallel-plate waveguide surrounded by beds of mushrooms that suppress the signal around the waveguide. Several examples are designed, optimized, and measured. All-pole bandpass filters and filters with finite transmission zeros are proposed and studied. The performance of the proposed designs is compared to MS filters with different packaging options. In addition, an efficient transition from MS to printed RGW is designed and used in the circuits. The proposed circuits are low-cost and realizable using conventional printed circuit board technology. Measured results show good agreement with the analyses.