SIW filter with broadband stopband by suppressing the coupling of higher-order resonant modes

This Letter presents a third-order multilayer substrate integrated waveguide (SIW) filter with broadband stopband. The filter is composed of three vertically stacked square SIW cavities. The input/output feeding structure and the coupling slot in the middle metal layer of two cavities are properly designed to just allow the fundamental resonant mode to a couple while other higher spurious resonant modes are isolated. The fabricated filter is at a centre frequency of 6.96 GHz with a stopband suppression of 24 dB up to 2.77f(0).