Tunable Frequency Selective Surface With Angular Stability

In this letter, a paradigm for designing tunable frequency selective surfaces (FSSs) with angular stability is presented. The tunable FSS is implemented by nonresonant subwavelength unit cells loaded with varactor diodes, which can be applied in a dynamic and efficient compensation mechanism. The red shifts introduced by varactor diodes are used to compensate the deviation under oblique incident angles. The proposed tunable FSS is a two-layer structure composed of an array of wire grid and an array of split square ring loaded two varactor diodes. The periodicity of one split square ring is same with that of 2 × 2 wire grids. The equivalent circuit based synthesis method is analyzed to investigate the underlying principle of the proposed FSS. The experimental measurement is carried out in C-band frequency, which demonstrates the feasibility of this method. The measured results are in good agreement with the simulations, manifesting the angular stability at 4.25 GHz.