Millimeter-wave Ultra-narrowband Band-pass Filter Based on SIW and Archimedean Spiral Slots

This paper presents bandpass filter (BPF) comprising substrate integrated waveguide (SIW) and Archimedean spiral slots, achieving ultra-narrowband, low insertion loss and high selectivity in the millimeter-wave band. Strong current disturbances can be obtained by etching Archimedean spiral slots on each surface of the SIW cavity, which excite the narrow-band filtering characteristics for the SIW cavity. In addition, rotating the Archimedean spiral slots can optimize the input impedance characteristics to achieve the desired impedance matching. A pair of metallic vias are loaded laterally on the SIW cavity to optimize the impedance characteristics of the BPF. A unit cell (UC) of the proposed BPF is composed of the SIW cavity, lateral loaded metallic vias, and Archimedean spiral slots. Ultimately, the three SIW unit cells are cascaded together to get better out-of-band rejection characteristics and serve as our final design. The simulation results demonstrates that the proposed BPF has a center frequency of 31.25GHz, insertion loss as low as 1.25dB, 3-dB bandwidth as narrow as 1.12%, and a low profile of 1.18λ×0.51λ, which has strong potential for use in millimeter-wave detectors and radar applications.