High-Numerical-Aperture(NA) Microwave Metasurface Lens(Metalens) and Its Applications in High-Gain Antenna

The NA is a basic parameter of a lens, which can determine its focusing spot size in the far field. High NA(close to 0.9 or above) metalens with a deep sub-wavelength focusing spot is an important metadevice in the modern optics and photonics. In this paper, a four-layer microwave metalens and its applications in the high-gain and low-profile antenna are studied and demonstrated. A high NA=0.88 (FWHM is 0.57λ) metalens based on high transmission phase gradient metasurface is firstly designed and is also verified by experimental result. Besides, a feeding source is placed at the focal spot of the proposed metalens, and a quasi-spherical wave is emitted and then transformed to a plane wave. Thus, a high gain antenna is obtained and the beam-width of the bare antenna is also significantly decreased. The simulated results show that the gain of the high NA metalens is largely enhanced by 10.47dB compared to bare antenna at the frequency of optimized 9GHz. More importantly, the relation between the focusing efficiency of high NA metalens and the enhanced gain of lens antenna is discussed and highlighted. The work opens new avenues to design high-gain lens antenna based on high NA plasmonic metalens in the microwave band.