Passband broadening of sub-wavelength resonator-based glide-symmetric SIW filters

Abstract

Here, we discuss the virtues of glide symmetry for designing low-frequency band-pass periodic filters in substrate integrated waveguide (SIW) technology based on complementary split-ring resonators (CSRRs). Conventional (non-glide) versions of these filters have a narrow passband, due to the fact that this band is below the cutoff frequency of the background waveguide. When glide symmetry is added to the filter configuration, the low-frequency passband is significantly widened, as well as the first stopband. The dispersion properties of both conventional and glide-symmetric periodically loaded waveguides are analyzed and compared with commercial software and an equivalent circuit model. Finally, two prototypes of the proposed glide-symmetric structure have been designed and built, illustrating the potential of this technique to widen the passband and reduce insertion losses of conventional sub-wavelength CSRR-loaded SIW filters.