Compact Hybrid Filter Based on HMSIFW and SICL Technology with Wide-Stopband Suppression

A bandpass filter (BPF) based on the hybrid substrate integrated coaxial line (SICL) and half mode substrate integrated folded waveguide (HMSIFW) is proposed in this paper. Two SICL resonators are etched between the two HMSIFW cavities. Four transmission poles are generated in the passband. To achieve better frequency selectivity, cross-coupling is introduced between two HMSIFW cavities, which generates two transmission zeros close to the passband. Meanwhile, the coupling between SICL and HMSIFW cavities is designed to constitute a coupling-null structure, which can achieve the suppression of higher mode transmission. Based on the application of SCIL and HMSIFW, a bandpass filter operated at 4 GHz with low loss, high-quality factor, and compact size is designed, simulated, fabricated, and measured for verification.