Design of circularly polarized flat-top pattern with phase gradient metasurface

This article presents a metasurface (MTS) for designing a circular polarized (CP) flat-top radiation pattern using the phase compensation method. The basic idea is to generate multiple beams pointing in different directions by dividing the entire MTS into sub-regions. The MTS consists of four-layered elliptical patches encircled in a square loop printed on three dielectric substrates. The asymmetric nature of the unitcell produces two orthogonal components with equal magnitude and 90 degrees phase difference to obtain the required linear to circular polarization conversion. The proposed MTS consists of 15 x 15 unitcells, and is fed by a rectangular patch antenna operating at 10 GHz. The flat-top pattern has been observed in the 3-D plane for u,v-polarized wave incidences at 9.9 GHz. For u-polarized incidence wave results in left-hand circular polarized (LHCP) flat-top radiation pattern with a 1 dB beamwidth of 37.5 degrees. The axial ratio is less than 3 dB in all planes within the 1-dB beamwidth at 9.9 GHz. Similarly, for v-polarized incident wave, identical characteristics have been observed for right-hand circular polarization (RHCP), which enables the proposed structure for polarization diversity.