Gaussian to flat-top beam shaping in an off-axis reflective scenario by a millimeter-wave metasurface

In this paper, we present a metallic reflectarray for shaping the emitted Gaussian beam of a 100 GHz horn antenna in reflective and off-axis mode. The proposed reflectarray is a compact planar surface consisting of a 2D array of unit cells with a thin Rogers 5880 substrate. This reflectarray offers advantages over other beam shapers in millimeter-wave (MMW) imaging, as it generates a flat-top beam in off-axis reflective mode and is straightforward to fabricate. To conduct a feasibility study, we first introduce the 1D reflectarray. The phase profile of the 1D reflectarray is a linear combination of a beam shaping phase profile based on geometrical optics (GO) and a compensating phase profile. The design of the 1D reflectarray involves tailoring the dimensions of the unit cells in one direction. We calculate the scattered field from the 1D reflectarray using the finite element method (FEM) and then determine the generated beam using the Fresnel diffraction integral. Subsequently, we design the 2D reflectarray following the same approach by using a 2D version of the proposed phase profile. The full-wave simulation is employed to calculate the generated beam at a certain distance from the reflectarray. The results reveal the successful generation of a high-quality flat-top beam, showcasing the proposed reflectarray as an evolutionary solution among beam shapers.