A Low-Profile and High-Efficiency GRIN Lens Antenna for Wide-Angle Multibeam Radiation

This article presents a new folded multibeam flat gradient-index (GRIN) lens antenna that achieves a wide angular coverage and high aperture efficiency within a compact physical profile. The proposed antenna integrates a transmissive primary lens for multibeam radiation, a secondary lens featuring anomalous reflections for profile reduction, and multiple feeds positioned between the two lenses. The secondary lens is innovatively synthesized to efficiently redirect waves from a designated feed toward the primary lens while compensating for spatial phase delays for optimal beam generations at 0° and ±45°. Several intermediate feed locations are optimized to produce additional beams across the ±45° angular range. For concept validation, a lens prototype incorporating seven compact feeds is designed, fabricated, and measured. Experimental results demonstrate stable multibeam performance between 8.5 and 11 GHz, producing seven independent beams covering around± 45∘with low scanning losses. A measured peak aperture efficiency of 46% is obtained with a 63% reduction of the lens profile compared to the conventional unfolded configuration.