Metasurface-Augmented Gradient-Index Lenses for Millimetre-Wave Applications

Abstract

This research project aims to develop metasurface-augmented gradient index (GRIN) lenses for millimetre-wave (mmWave) applications. It introduces a concept combining GRIN lenses with metasurfaces, enhancing the ability to direct beams of high-gain GRIN lens antennas and control focal positions in GRIN lens beamformers. A novel methodology for designing the metasurface is established by analysing the electric field phases within a GRIN lens along with the phase shift in a single unit cell, using full-wave simulation tools available to researchers. The research investigates two GRIN lenses: the 2D Luneburg lens antenna and the 2D Maxwell fisheye lens (MFL) beamformer in reflective and transmit modes. By integrating a half-circle Luneburg lens antenna with a variable-sized square patch reflectarray, beamsteering with a maximum angle of 75° was achieved across a frequency range of 26 – 28 GHz. The operational bandwidth extended to 24 – 38 GHz with a wideband Phoenix reflectarray. The half-circle Maxwell fisheye lens (HMFL) beamformer maintained its focal axis and achieved a maximum angle of 45° within a frequency range of 26 – 28 GHz. This was extended to 22 – 32 GHz using the Phoenix reflectarray. Both lenses were evaluated at normal incidence (0°) and oblique incidences (-15° and -30°). In transmit mode, the GRIN lenses were modified with an all-dielectric phase correction layer composed of cubic unit cells. This layer, placed vertically between two half-circle lenses, formed a 2D circular transmitarray-augmented Luneburg lens antenna, generating directive beams with a maximum angle of 75° across 24 – 30 GHz. The MFL beamformer, combined with the phase correction layer, focused incident energy, achieving a maximum angle of 45° across 22 – 32 GHz. This research explores 3D printing techniques for fabricating GRIN lenses and transmitting metasurfaces and printed circuit board (PCB) technology for the reflective metasurfaces, enabling cost-effective laboratory prototype production.