Signal-interference RF wide-band bandpass filters using half-mode substrate-integrated-waveguide (HM SIW) directional couplers

A new type of mixed-technology RF bandpass filter integrable with broad-band substrate-integrated-waveguide (SIW) antennas is presented. It makes use of a half-mode (HM) SIW 3-dB quadrature coupler in a transversal signal-interference scheme with microstrip loading stubs. This bandpass filter, being the first one of this class that utilizes SIW elements, enables to realize passband-widths limited in practice by the operative bandwidth of the HM SIW 3-dB coupler. Electromagnetic-simulation results of two layout-level-designed 14-GHz filters with fractional bandwidths (FBWs) of 25% and 50%, along with their ideal synthesized equivalent circuits, are shown for verification.