Compact Square/Triangle Mixed-Shape Quarter-Mode Substrate Integrated Waveguide Bandpass Filter with Wide Stopband

In this paper, a new square/triangle mixed-shape quarter-mode substrate integrated waveguide (SIW) bandpass filter (BPF) is presented. Two transmission poles in the passband and two transmission zeros (TZs) in the stopband can be obtained by using a mixed quarter-mode cavity sharp. For an experimental validation, two-stage with square/triangle mixed-shape quarter-mode SIW BPF is designed at the center frequency (f(0)) of 8 GHz. From measurements, the insertion loss (S-21) and return loss (S-11) of 1.1 dB and 15.1 dB are obtained at f(0), respectively. The passband insertion loss is better than 1.3 dB in the bandwidth of 0.87 GHz (7.55 similar to 8.42 GHz). The return losses better than 15.1 dB for the same bandwidth is measured. The two TZs in stopband make the attenuation characteristics better than 39.6 dB and 33 dB at 11.44 GHz and 15.67 GHz, respectively. And the proposed SIW BPF is compact due to mixed-shape quarter-mode shape.