Realization of Millimeter-wave Dual-mode Filters Using Square High-order Mode Cavi- Ties

Some interesting results are presented in this paper by investigating the characteristics of square high-order mode cavities. Based on the standard printed circuit board (PCB) process and the substrate integrated waveguide (SIW) technology, two different square cavities which exhibit dual-mode filtering response are studied and implemented. Their bandwidths can be controlled by adjusting the eigen-frequencies of the resonating modes and the coupling apertures. The proposed configurations also allow implementing transmission zeros to improve the selectivity in an easy way. A Q-band quasi-elliptic filter using such two cavities in a folded configuration is designed, fabricated and measured. High selectivity and small insertion loss are achieved which are in good agreement with the simulated results.