Dual-band flexible FSS conformal to elliptic cylindrical surface

Abstract

This paper introduces a conformal frequency selective surface (FSS) with dual passbands from 9 to 9.3 GHz and 13.1–13.7 GHz, as well as one stopband from 10.4 to 10.9 GHz. The frequency response of the curved FSS coincides with the performance of the planar FSS with the same unit cell under normal incidence. The unit cell comprises two compact flower-shaped metallic slots patched on the dielectric substrate. This design has excellent stability of the incident angle up to 70°. The equivalent circuit model considering the mutual coupling between the two slots is illustrated to analyse the resonance mechanism. The whole antenna system enclosed by the conformal FSS is simulated to evaluate the loss in the far-field beam's directivity and aberration. The impact caused by the different curvatures is investigated. The samples in planar and elliptic cylindrical surfaces are fabricated. The insertion losses of both polarisations are less than 1.5 dB, as the angle of incidence varies to 60°. The frequency response of curved FSS is identical to the planar FSS under normal incidence. The maximum attenuations of both polarisations in the passbands are less than 1.38 dB, and the average transmission coefficient in the stopband is −22 dB. The conformal FSS brings slight aberration in the half power beamwidth (HPBW) of the incident beam in the passbands. Furthermore, it suppresses the main beam in the stopband by at least 25 dB.