Compact Cross-coupled Bandpass Filter Based on ISGW with High Selectivity

This paper presents a compact fourth-order band-pass filter (BPF) based on integrated substrate gap waveguide (ISGW) for the K-band. By introducing two half-mode cavity resonators and two microstrip resonators, a significant reduction in device size is achieved. At the same time, transmission zeros (TZs) are introduced on both sides of the passband through a cross-coupling mechanism, which enhances the out-of-band rejection and improves the filter’s selectivity. The periodic Electromagnetic Bandgap (EBG) structure at the bottom effectively suppresses radiation leakage caused by the etched microstrip resonators. The filter has a center frequency of 20 GHz, a 3dB fractional bandwidth of 16%, a passband insertion loss of only 0.53 dB, and an overall size of 0.61λ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> * 0.61λ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf>.