Differential-mode BPF design using folded substrate integrated waveguide cavities

The contribution of this work is to propose a differential-mode bandpass filter design using folded substrate integrated waveguide cavities. The proposed differential mode filter is composed of two folded substrate integrated waveguide cavities in a juxtaposition arrangement. Each folded cavity of the filter formed by bending its square-shaped counterpart is capable of two degenerated modes resonance, TE102 and TE201, for the dual-mode operation. The hybrid microstrip/slot feed is employed to suppress the unwanted common-mode signals in both the in-band and out-band regions. The measured common-mode signal rejection levels are over 40 dB. Experiment is conducted to verify this novel differential BPF design.