Two-Dimensional Wide-Angle Multibeam Flat GRIN Lens With a High Aperture Efficiency

High aperture efficiency 2-D multibeam flat gradient index (GRIN) lenses are developed in this work. New methods based on bifocal analysis are found to determine the refractive index profile of the lens and feed positions along a circular feed locus to enable independent wide-angle multibeam radiations. Distinct formulas for the GRIN profile are provided for two different purposes: 1) multibeam with good average performance in all azimuthal planes and 2) radiation performance optimized in a specific azimuthal plane. The latter solution requires a GRIN variation in both the azimuthal and radial variables. Subwavelength triple-metal-layer unit cells are designed to emulate the local refractive indices. A 2-D multibeam GRIN lens, fed by 13 modules of 2 $\times $ 2 patch arrays displaced along xoz and yoz focus loci, has been successfully simulated, fabricated, and measured. Wide-angle multibeam radiations have been obtained with a beam coverage of around ±45° in both the xoz and yoz planes. The multibeam radiation patterns are stable in a 22.2% bandwidth from 12 to 15 GHz. The beam-scanning losses in this operating band are 1–2.6 dB and 2.1–3.9 dB in the xoz and yoz planes, respectively. The measured peak realized gain is 22.3 dBi at 13.4 GHz, corresponding to an aperture efficiency of 66.4%.