Planar Lens Antennas of Subwavelength Thickness: Collimating Leaky-Waves With Metasurfaces

High-gain lens antennas with a subwavelength thickness that radiate linearly and circularly polarized waves are reported. The lens antennas are fed with a planar, leaky radial waveguide that generates a TM-polarized Bessel beam (Bessel beam launcher). Two different metasurface lenses are placed a subwavelength distance from the Bessel beam launcher to collimate the radiation with minimal reflection loss. The unit cells of the two metasurface lenses are designed to act as inhomogenous wave plates to convert the polarization from radial to linear and circular, respectively. The lens antennas are fabricated using standard printed circuit board processes, and their performance is experimentally characterized. The antennas achieve an order of magnitude thickness reduction over previously reported lens antennas since the metasurface lenses are directly integrated with the antenna feed.