A Bandpass Frequency Selective Surface with a Low Cross-Polarization Based on Cavities with a Hybrid Boundary

A novel low cross-polarization bandpass frequency selective surface (FSS) with low passband ripples and a steep roll-off at both sides of the passband is proposed. Different from available substrate integrated waveguide FSSs in which the boundary of every unit cell is electrically conducting, the proposed FSS unit cell is composed of two specially designed cavities with mixed electrically and magnetically conducting boundaries. These boundaries are formed by an array of shorting vias and complementary slots etched on both the top and bottom metallic patches, respectively. A bandwidth enhancement is achieved by properly merging three individual resonances excited in the two hybrid cavities and the slots within the required frequency range. An FSS centered at 4.58 GHz is fabricated and its near-and far-field performances are measured, with the results in good agreement with the prediction. The characteristics, including a steep roll-off, low passband ripples, a low cross-polarization, and stability at oblique incidence angles, are verified by the measurement.