Groove Gap Waveguide Filter Based on Horizontally Polarized Resonators for V-Band Applications

In this article, resonators based on air-filled rectangular cavity consisting of one perfect magnetic conductor (PMC) wall and the rest of walls as the perfect electric conductor (PEC) are proposed. The proposed cavity can be engraved in the top or bottom metal plate of a gap waveguide structure, and the PMC wall is realized by the periodic metallic pins located within the gap waveguide geometry. The resonant frequency and electromagnetic (EM) field distribution of the cavity are investigated, and it is shown that the electric field is horizontally polarized with respect to the wave propagation direction. Two bandpass filters are designed by inserting the proposed cavity in the cutoff region of the gap waveguide, on the top and bottom plates. In the latter case, all pins are the same, and the cavities and coupling structure are easily implemented by engraving the top plate. Therefore, by using this concept, a common pin plate can be used to implement different passive millimeter-wave devices. For instance, three different filters working at 60, 65, and 70 GHz with a common bottom pin plate are designed and fabricated. The measured results show a minimum insertion loss of 1.4, 1.1, and 1.1 dB with 0.83%, 1.4%, and 1.8% fractional bandwidth for the three bandpass filter designs, respectively, with aluminum as metal.