Multilayer Dual-Mode Balanced SIW Filter Utilizing PEC–PMC Characteristic for Common-Mode Suppression

In this letter, a multilayer balanced substrate-integrated waveguide (SIW) bandpass filter (BPF) using the TE102 and TE201 modes is designed with an aperture etched on the common ground between two stacked SIWs. Under common-mode (CM) operation, the aperture is a perfect magnetic conductor (PMC). When the height is less than λ
_g
/4, the space between the perfect electric conductor (PEC) and the PMC cannot transmit the electromagnetic wave, so the structure can effectively cutoff the CM noise in a wide frequency range. Under differential-mode (DM) operation, the aperture is the PEC and has less effect on the DM frequency responses by properly selecting the location and size. Two transmission zeros near the passband edges can be generated to improve the selectivity. Finally, a compact dual-mode balanced SIW BPF with high selectivity and CM suppression has been designed and fabricated, and the measured results show good agreement with the simulated ones.