Microstrip-Ridge Gap Waveguide Filter Based on Cavity Resonators With Mushroom Inclusions

In this paper, we propose a novel microstrip-ridge gap waveguide (MS-RGW) filter configuration, which is based on cavity resonators with mushroom inclusions. The resonators are realized as defects in surrounding mushroom-based perfect magnetic conductor (PMC), and thus, the filter configuration does not require additional conductive layers nor rearrangement of the PMC elements. The hosting MS-RGW is fed through transition from SMA to microstrip ridge, enabling simple fabrication and excellent impedance matching in a wide frequency range. To demonstrate the potential of the proposed structure, four narrowband filters have been designed, fabricated, and measured. The filters exhibit excellent in-band characteristics and small dimensions.