Novel X-band dual-mode bandpass filter based on the substrate integrated waveguide

This paper presents a novel dual-mode filter with symmetric transmission zeros based on the substrate integrated waveguide (SIW). This filter contains two dual-mode SIW rectangular cavities. By making use of the inductive discontinuities in an SIW cavity, two coupling degenerate modes can be excited. Due to the phase difference between the two modes in each cavity, two transmission zeros on each side of the passband are created, so the out-of-band rejection of the filter is significantly increased. An SIW dual-mode filter with a center frequency of 12 GHz has been fabricated and measured using the proposed method. Experimental results agree well with the simulation results.