Sub-wavelength frequency selective surface design for improved antenna array out-of-band rejection

In this work, the problem of enhancing the frequency selectivity property of an antenna array has been studied. A solution based on a multi-layer frequency selective surface (FSS), composed of sub wavelength elements is proposed. An equivalent circuit model is used for the design, under the assumption that the inter-layer interaction is dominated by a single Floquet mode. This approximation remains valid by keeping the unit-cell size comparable to the inter-layer distance. Results for generic oblique incidence are presented. Fast roll-off is achieved by using a 3 pole Chebyshev filter design. Moreover, the FSS is used in combination with a connected slot array antenna. The resulting structure allows to scan up to 45° in both principal planes with a relative bandwidth (S
₁₁
<; -10 dB) of 15% around the central frequency f
₀
= 4.8 GHz. Higher order harmonics are rejected up to 18 GHz.