Highly Selective SIW Trisection Filters With Mode Dependent Coupling

In this paper, two Substrate Integrated Waveguide (SIW) trisection filters with high selectivity are presented. The designed filters offer transmission zeros (TZ) either in lower or in upper stopband. Both the three pole filters have one bypass coupling path and sign of this coupling is altered by changing the mode of one resonator in main coupling path. The Filter-I offers a single TZ at upper stopband whereas Filter-II offers two TZs at lower stopband. The center frequencies of Filter-I and Filter-II are centered at 8.125 GHz and 8.3 GHz respectively. Both the filters are designed for 2% Fractional Bandwidth (FBW) and TZs of each filter are placed at the passband center frequency of others.