Polarization properties of frequency-selective surfaces comprised of spiral resonators

Arrays of spiral resonators are used in the design of frequency-selective surfaces operating in the frequency range 2-18 GHz. The transmission spectrum of linearly polarized radiation incident on each array exhibits a multiplicity of resonance features, the number and frequency of which is a function of the design of the spiral geometry. The transmission spectra are also functions of the slant angle, the array rotation angle, and the polarization of the receiving antenna. From an analysis of the acquired data it is concluded that the spiral resonator arrays act primarily as rotators of the incident radiation and that the angle of rotation and the axial ratio is shown to be a function of the frequency of the resonance feature. These general conclusions have been confirmed by numerical simulations performed by Ansoft's finite-element software package HFSS.