Bandpass filters based on periodic structures in SIW technology

In this work, the study of two different topologies of S-band band-pass filters based on periodic structures in substrate integrated waveguide (SIW) technology is theoretical and experimentally addressed. The first topology consists of periodic rectangular perforations of the SIW substrate. In this filter topology, the lower cutoff frequency is determined by the cutoff frequency of the first Floquet mode of the periodic structure, while the upper cutoff frequency and the rejection band are conditioned by its first band-gap. The second topology consists of a periodic array of square complementary split-ring resonators (CSRRs) etched on the waveguide surface. In this case, the use of subwavelength resonators with evanescent-wave transmission leads to a much smaller filter, given that the pass-band is below the cutoff frequency of the waveguide. The effect of the different dimensions of the unit cell in the filters characteristics (lower cutoff frequency, pass-band, and rejection-band associated to the first band-gap of the periodic structure) is analyzed through the dispersion diagram of the periodic cell. Finally, two band-pass filters based on each topology have been designed and built, showing in both cases good matching and low insertion loss in the pass-band, and a deep rejection band.This work was supported by the Agencia Estatal de Investigaci´on (AEI) and by the Uni´on Europea through the Fondo Europeo de Desarrollo Regional - Una manera de hacer Europa (AEI/FEDER, UE), under the research project TEC2016-75934-C4-2-R