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.