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Optimization based design of a wideband metasurface for utilization in a terahertz reflectarray antenna with high efficiency

In this manuscript, two wideband single layer reflectarray antennas are designed utilizing an optimization‐based metasurface in terahertz (THz) regime. It is demanded to design a metasurface with wide phase variation range in a broad frequency region of terahertz band. The proposed metasurface is designed based on Random Hill Climbing optimization algorithm whereas a multiobjective fitness function is defined to consider the desired characteristics. A provided link between Matlab and HFSS softwares is utilized to define and simulate various metasurfaces. The finalized cell has considerable wide phase variation ≥600∘ and notable bandwidth of 30.76% (1.1–1.5 THz) whereas the mean value of magnitude variation of reflection coefficient is −0.42 dB. Two square and circular metasurfaces are designed based on the optimized cell and illuminated using a THz feeding horn antenna. The angles of incident and reflected waves are considered equal to zero. The simulation results confirm 3‐dB gain bandwidths of 20.3% and 20.4% for square and circular metasurfaces, respectively. Moreover, the considerable efficiencies of 45.67% and 46.27% are achieved for square and circular arrays, consequently. The maximum gain of square array with 361 elements is 25.9 dB whereas it is equal to 24.9 dB for circular metasurface including 277 unit cells.