Compact Dual-Band Balanced SIW Bandpass Filter With Improved Common-Mode Suppression

The contribution of this letter is to propose a novel substrate integrated waveguide (SIW) dual-band balanced bandpass filter (BPF), which exhibits characteristics of compact size and improved common-mode (CM) suppression. Two diagonal resonant modes TE102 and TE302 in a square SIW resonator with symmetric field distributions provide the possibility to realize balanced inputs/outputs, dual-passband responses and the vertically stacked structure for compact size. Without affecting the differential-mode (DM) responses, a novel method of using slotlines etched on one broadside of either SIW resonators to shift the resonant frequency of CM away from the DM passband is also proposed, to realize a higher CM rejection for this BPF. Meanwhile, perturbation vias have been utilized to adjust the center frequency of the lower passband, while the higher passband can remain almost unchanged. A second-order prototype is designed for the demonstration. Good agreement between simulation and measurement has been observed in the measurement.