X-band differential bandpass filter with high common-mode suppression using substrate integrated waveguide cavity

A novel X-band differential bandpass filter based on substrate integrated waveguide is proposed. By making an aperture etched in the middle common ground of the vertically stacked cavities, the common-mode (CM) signals can be highly suppressed. Compared with conventional structures, the proposed design possesses a relatively simple and effective measure for the rejection of the CM signals. Based on simulated and measured results, good differential-mode responses can be observed along with a CM rejection of more than 45 dB in a wide frequency range.