With the increasing demand for high throughput wireless communications, carrier frequencies have been ever pushed toward higher wavebands, e.g., millimeter wave (mmWave) from 30 to 300 GHz. However, the limited emitting power and high free-space path losses together restrict the coverage range of the mmWave wireless network. One solution for this challenge is to implement highly directive antennas, which concentrate the radiating power in a certain direction to increase the link budget and thus, the coverage of distance. Furthermore, directional beams are expected to be steerable for covering a certain angular range for multi-users and on-the-move communications. Therefore, beam-steering antennas are of vital importance for mmWave applications, which is the main motivation of this work.

At such high frequencies, there are limited solutions to realize beam-steering in both mechanical and electronical manners. Rotating the antenna dishes by motors requires a bulky and power-consuming mechanical system. Microelectromechanical systems suffer from a high fabrication cost and low reliability. On-chip designs occupy a large fabrication area, which is costly using standard semiconductor processes. The discretely packaged semiconductor components are no longer preferred considering the difficulty of soldering and spurious radiation of the connection pins or pads. Compared with the above-mentioned methods, the liquid crystal (LC)-based beam-steering antenna is a promising solution as it features a low fabrication cost and high reliability. Moreover, LC-based devices are voltage driven, which consumes negligible power during operation.

This work focuses on developing an electronical beam-steering antenna in mmWave band using liquid crystal as the tuning mechanism. A waveguide-fed leaky-wave structure is designed to reduce the antenna profile and for ease of integration with monolithic microwave integrated circuits (MMICs). Different from conventional leaky-wave antennas that steer beams by adjusting the phase constant of the guided wave, this work adjusts the period of the aperture-field to achieve a large beam-steering range despite a limited tunability in LC’s permittivity. An LC-filled metamaterial unit cell is specially designed as the building block of the antenna. The radiation mechanism of sidelobes and grating lobes in this type of antenna is thoroughly investigated by space harmonic analysis of the aperture-field. Methods for suppressing sidelobes and grating lobes are proposed and proved to be effective. In order to expand the single leaky-wave antenna into a 2D array, several corporate feeding networks with different fabrication technologies are analyzed and discussed.