Optimization-based design of a single-layer wideband reflectarray antenna in the terahertz regime

An optimization-based metasurface is proposed and employed to design a wideband single-layer reflectarray antenna for use in the terahertz (THz) regime. The random hill-climbing optimization method is utilized to obtain a wideband unit cell. A multiobjective fitness function is defined to consider three required design aims, whereas an established link between MATLAB and HFSS software is employed to simulate the required periodic metasurface. The final created unit cell has a remarkable bandwidth of 44.89% together with −0.44 dB average variation of the magnitude of the reflection coefficient. Moreover, the phase variation versus various scales of the metallic surface of the cell is more than 300° at all of the desired frequencies between 0.95 THz and 1.5 THz. Two different reflectarray antennas are proposed based on the optimized cell, and two excitation scenarios are implemented to investigate the performance of the designed reflectarray antennas. In the first scenario, the metasurface is designed to deflect a plane wave with angle of incidence of 30∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$30^{^\circ }$$\end{document} to the normal direction. In the second one, a THz feeding horn illuminates a metasurface reflector including 201 elements. According to the simulation results, 3-dB and 1-dB gain bandwidths of 39.67% (0.99–1.48 THz) and 20.51% (1.05–1.29 THz), respectively, are achieved, whereas the maximum gain is 19.8 dBi at 1.2 THz.