In this patent documentation, we propose a novel balanced bandpass filter (BPF) using the substrate integrated waveguide (SIW) cavity. Two square-shape SIW cavities are used to compose the proposed balanced bandpass filter with each cavity operated in a dual-mode (or term as degenerate mode) resonance. The filter has a central frequency of 13 GHz with 0.64 GHz bandwidth and the maximum in-band insertion loss of 2.52 dB. In this proposed patent, the balanced BPF has its common-mode signal’s rejection levels greater than 40 dB over a wide frequency range and the differential-mode signal’s insertion losses around 2.5 dB in the passband. The microstrip feed together with the coupling slot enable the SIW cavity balanced BPF to have excellent common-mode signal suppression without affecting the differential-mode passband.

In this patent documentation, the proposed novel balanced bandpass filter (BPF) using the substrate integrated waveguide (SIW) cavity. A dual-mode balanced bandpass filter (BPF) design with an excellent common-mode (CM) rejection performance is presented. The balanced filter is composed of coupled substrate-integrated waveguide (SIW) cavities and a hybrid microstrip/slot feed. The cavities are of a square shape to produce two degenerated resonance modes, for dual-mode operation. The hybrid microstrip/slot feed is developed to suppress the unwanted CM signals in both the inband and out-band regions. The measured CM signal rejection levels are over 50 dB. The filter’s central frequency is 13 GHz with 0.64 GHz BW and the in-band insertion loss of 2.5 dB.

Balanced circuits are essential in wired and wireless microwave systems because of their high immunity to environmental noise and electromagnetic interference. Among the various balanced circuits, the balanced bandpass filter (BPF) plays an important role in ensuring a good performance for these systems under differential operation. It is common knowledge that a well-performed balanced BPF should respond to differential-mode (DM) signals and simultaneously ignore common-mode (CM) ones over a given frequency range. Hence, the quality of a balanced BPF mainly depends on the rejection level of CM signals without affecting those of the DM in the passband.