Manufacture-Friendly Millimeter-Wave Filter Based on Double-Folded SIW Resonators

This letter proposes manufacture-friendly millimeter-wave (mm-Wave) bandpass filter (BPF) based on double-folded substrate integrated waveguide (DFSIW) cavities. Using an incompletely folded structure and parallel rectangular slots as coupling structures, the BPF achieves reduced insertion loss (IL) and enhanced robustness against processing errors. Furthermore, the compact space between adjacent folded slots was transformed into a cross-coupling structure, which significantly improves frequency selectivity without introducing additional radiation loss. In addition, high-quality (Q) factor layer stacking is implemented to further minimize IL. A Ka-band filter prototype based on the multilayer printed circuit board (PCB) is fabricated and measured to confirm the feasibility.