Compact Second and Third order Bandpass Filters based on QMSIW with Wide Fractional Bandwidth

This work describes a class of compact bandpass filters (BPF) based on a quarter-mode substrate integrated waveguide (QMSIW) cavity. The benefit of using these filters is that they combine the features of SIW structures with improved size-reduction capabilities. First, a two-pole BPF is proposed featuring a quarter-mode SIW cavity with two orthogonal 50 Ω microstrip feedlines. The designed filter-I has the center frequency at 3.3 GHz with an insertion loss of 1.1 dB and a wide stopband of 2.23f
0
with a minimum of 20 dB rejection level. It has a small footprint of $0.11\lambda _g^2$. Then, a three-pole BPF is achieved from filter-I by coupling it with an L-shaped microstrip line. The filter-II has the center frequency at 3.1 GHz with an insertion loss of 1.82 dB and a wide stopband of 1.9f
0
with a minimum of 20 dB rejection level. The footprint of the filter-II remains almost the same. The proposed QMSIW filters are suitable for WiMAX applications due to their compact size, planar structure, and adequate bandwidth.