A novel X-band differential bandpass filter based on oversized substrate integrated waveguide cavity

A novel X-band substrate integrated waveguide (SIW) differential bandpass filter (BPF) is proposed in this paper. The major design concept is by making an aperture etched in the middle common ground of vertically stacked cavities so that the common-mode signals can be suppressed. Oversized SIW cavities are implemented to achieve a finite transmission zero by utilizing the interaction between the fundamental TE₁₀₁ mode and higher order mode of TE₃₀₁ to improve the attenuation out of the passband. Based on the simulated results, the insertion losses of our proposed differential BPF is extremely low within the passband under differential-mode signals, as well as the common-mode rejection levels are better than 30dB across a very broad band.