Design and Experimental Verification of a Passive Huygens' Metasurface Lens for Gain Enhancement of Frequency-Scanning Slotted-Waveguide Antennas

Huygens' metasurfaces have demonstrated their versatility in numerous applications, such as wide-angle refraction and antenna beamforming. These electrically thin structures allow the enhancement of antenna systems with passive designs. Such enhancements include improving the gain and scanning capability of feed antennas. In this paper, the design, simulation results, and measurements of a metasurface lens for gain enhancement of frequency-scanning slotted-waveguide antennas are shown. Both transverse-electric (TE) and transverse-magnetic (TM) metasurface designs are verified with full-wave simulations, which demonstrate upward of 13 dB of directivity enhancement. Additionally, a fabricated 40\lambda long by 15\lambda wide TM metasurface lens centered at 34.3 GHz was experimentally verified in conjunction with a TM frequency-scanning slotted-waveguide antenna. The waveguide antenna radiates through a 1-D slot array operating between 33.5 and 35.3 GHz and produces a 16 dB fan beam which scans in the H-plane between -26° and broadside within its operational bandwidth. The realized metasurface lens, placed at 3.05\lambda at 34.3 GHz away from the waveguide antenna, was able to increase its realized gain by upward of 10 dB while maintaining its scanning capabilities. With the design verified in both simulation and measurements, the proposed metasurface serves as an easy-to-fabricate, efficient, low-profile, and lightweight alternative to standard microwave lenses.