Split-Ring FSS Spiral Phase Plate

This letter gives the first report of a planar phase plate structure based on frequency selective surface (FSS) technology for the generation of helical far-field radiation patterns with circular polarization properties. The unit cell of the structure comprises two orthogonal split-ring resonators designed to ensure 180 phase shift between orthogonal transmission coefficients. This property is exploited to obtain progressive rotational phase shift within the structure and thus synthesize 360 spiral phase profile. Measured far-field radiation patterns demonstrate spiral phase front generation for 10-GHz circularly polarized waves transmitted through the structure.