Optically Transparent Holographic Display Antenna: High Gain, Beam Steering, and Lossless Bonding for 5G Millimeter-Wave n261 Band

This paper presents a novel high-gain beam-forming holographic display antenna (HDA) concept that utilizes surface waves on the wide display area of 5G millimeter-wave (mmWave) devices. The HDA consists of two components: a 1×4 surface wave launcher array (SWLA) that excites phased surface waves on the display cover glass, and an optically transparent holographic metasurface that transforms surface waves into radiating waves. Therefore, the proposed HDA is free from the radiation pattern distortion issues reported for conventional display antennas. The surface-wave-based HDA can sustain efficient radiation performance even when the metal pattern area within each unit cell of the holographic metasurface is significantly reduced—unlike conventional transmission-line-based display antennas, whose performance degrades as the metal area is minimized to improve optical transparency. A single-ring-type optically transparent holographic metasurface unit cell was found to exhibit a wide surface reactance range despite having a super-thin linewidth and thickness. Furthermore, the proposed SWLA has a compact form factor to be embedded within a thin display bezel area. It is designed with a unique component-separated structure that eliminates the detrimental bonding loss that occurs in conventional display antennas. Finally, its unique array spacing condition for higher taper efficiency is determined. Measured results show that the HDA exhibits a high gain of 14.2 dBi and a –3 dB beam scan range of 68∘ (–34∘-34∘). The proposed HDA covers the n261 band (27.5–28.35 GHz), while the –3 dB gain bandwidth also covers the n257 band (26.5-29.5 GHz).