Design of Wideband Bandpass Filter Based on Microstrip-Ridge Gap Waveguide

In this paper, a new microstrip-ridge gap bandpass filter based on the odd-even mode analysis is proposed. As a new millimeter-wave waveguide structure, gap waveguide has the characteristics of in-phase reflection and electromagnetic bandgap, which can effectively reduce radiation leakage. In addition, the microstrip-ridge gap waveguide can use air as propagation medium, which can greatly reduce the dielectric loss. A new third-order wideband bandpass filter is the result of combining the characteristics of microstrip transmission line and microstrip-ridge gap waveguide. The center frequency of the third-order filter is 12.5 GHz, while the 3 dB bandwidth is 30%, with a transmission zero on each side of the band, which optimizes the filter selectivity. Both simulated and physical measurements indicate that this return loss is less than 10 dB as well as the insertion loss is about 0.8 dB and 1.5 dB, respectively. The analysis demonstrates that the designed filter is distinguished by the following features: low-insertion loss, wide passband, miniaturization and easy integration. Therefore, the proposed filter has great engineering utility.