Design of Circularly Polarized and Highly Depointing Reflectarrays with high polarization purity

This work aims to investigate the limitations and possible solutions in designing highly tilted radiation pattern reflectarrays working in double circular polarization and fed by an onset single primary source. To this extent, three single-layer monolithic reflectarrays, producing a pencil beam at increasing radiation angles with high X-polarization discrimination (XPD) have been designed and analyzed. A direct optimization technique shows that an XPD=20 dB can be attained for radiation patterns pointing at sixty degrees, at the cost of co-polarised directivity degradation. An analysis of the target aperture fields, obtained through backscattering techniques, shows that an amplitude modulation on the aperture field components is necessary to obtain highly tilted radiation patterns with high XPD. Since reflectarray cells are not able to produce such amplitude components unbalance, an elliptically polarized source is considered, producing an incident field components amplitude unbalance that results in a radical reduction of the X-polarization levels.