Demonstration of Broadband Reflectarray Using Unit Cells With Spline-Shaped Geometry

In this paper, we propose an accurate and fully automatic method to design a unit cell with optimized shape metal patch. The method determines the outer boundaries of the metal patch based on the spline technique, resulting in a smooth and continuous shape for the patch. In order to find the best position of the points of the element boundaries and achieve the best phase response for the element, we employ a continuous genetic algorithm as an optimization tool. An in-house code is developed to link MATLAB and CST softwares for numerically calculating the phase response of the investigated unit cell in each iteration of the optimization process. As a typical case, we achieve a single-layer wideband unit cell that has a nearly ideal phase response from 8 to 12.5 GHz. In order to verify the validity of the designed unit cell, a 210 mm × 210 mm reflectarray is designed, fabricated, and tested by the proposed unit cell. Experimental results show that the antenna has a 1 dB gain of 37% (8.85-12.8 GHz) and the maximum efficiency of 64.7%, which are regarded as highly acceptable achievements.