Optimization based design of a wideband near zero refractive index metasurface for gain improvement of planar antennas in the terahertz band

Abstract

In this paper, a broadband near-zero refractive index metasurface is designed in the terahertz band. The Random Hill Climbing optimization algorithm is utilized to propose the corresponding unit cell. The designed metasurface is employed as the superstrate of two planar microstrip wideband antennas resulting to increase the gains of antennas. The impedance and 3-dB gain bandwidths of loaded patch antenna are 46% and 36%, respectively while these parameters are 17% and 28.5% for printed dipole antenna in the presence of designed metasurface. Moreover, the maximum gain of loaded patch and printed dipole antennas are 9.1 dB and 11.74 dB, consequently. The provided results confirm that the proposed structures achieve higher maximum gain and wide 3-dB gain and impedance bandwidths with respect to similar reported antennas. In addition, at least 3 dB gain improvement is achieved in the presence of designed metasurface on the top of antennas.