Compact folded substrate integrated waveguide filter with non-resonating nodes for high-selectivity bandpass applications

A fifth-order pseudo elliptic substrate integrated waveguide (SIW) filter based on non-resonating nodes is presented for high-selectivity bandpass applications. Three singlets and two fundamental-mode resonators are properly cascaded in a folded, thus compact topology. After optimization of the coupling apertures, the filter produces three transmission zeros for improved selectivity. An SIW filter prototype with a center frequency of 11 GHz and 600 MHz bandwidth is designed using HFSS and fabricated on RT/Duroid 5870 substrate. The measured results are in very good agreement with simulations and show excellent out-of-band rejection performance.