Substrate Integrated Waveguide Wide-Band Notch Filter Based on Second-Order Mode Cancellation

The paper presents a promising filtering method for the cancellation and suppression of dominant mode propagation in Substrate Integrated waveguide structures through the out-of-phase cancellation of the first and second resonance modes. This method achieves a high selectivity by using only two-step coupled resonating cavities, which enhance both stop-band (79–81 GHz) and pass-band (76–77 GHz) bandwidth and selectivity by employing cavities of different internal sizes. Additionally, positioning a row of inductive vias between the two cavities brings the second resonance closer to the first resonance in the stop-band region by modifying the transmission zeroes, resulting in a significant increase in the stop-band bandwidth. The proposed filter demonstrates an insertion loss of less than 0.7 dB, a return loss exceeding 20 dB, and a 6 GHz bandwidth for both pass and stop-bands.