A double-layer frequency selective surface (FSS) with dual rings is used as a reflector in the design of an Archimedean spiral antenna (ASA) with low radar cross section (RCS) and uni-directional characteristics. The proposed FSS presents a stopband in the range of 2 GHz to 4.7 GHz, which is applied to ASA to form a unidirectional radiation pattern with front to back ratio (FBR) values larger than 10 dB in the stopband, and the maximum FBR value is up to 25.26 dB. Compared with the reference antenna with the same-size metallic ground, the proposed FSS reduces the RCS about 2.5-38 dB in the frequency ranges of 4.8-30 GHz. And the FSS antenna also exhibits better axial ratio characteristics in the frequency range of 2.8-8.1 GHz. The composite structure is compact, with a total height of 0.18 wavelength at the lowest analysis frequency of 2 GHz. Measured results indicate that the proposed antenna reproduces the inherent wideband of the original ASA from 1.6 GHz to 8.1 GHz. Meanwhile, the gain of the ASA is increased by 3 dBi. Full-wave simulations and measurements prove that the novel FSS reflector can be employed to replace a metallic ground which realises a uni-directional ASA with broadband low RCS, high gain and good circular polarization (CP) performance.
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