Phase Gradient Metasurface for Arbitrary Three-Dimensional Shaped Near-Field

This manuscript introduces a technique for creating custom three-dimensional (3D) near-field patterns using a phase gradient metasurface (PGMS). This approach leverages phase conjugation (PC) backtracking and the deployment of diffraction-free Bessel beam arrays. The PGMS is engineered by integrating Matlab with electromagnetic (EM) simulation tools, specifically CST software. According to the authors, this marks the inaugural instance where a 3D near-field has been successfully generated without escalating costs, structural intricacy, or computational demands. Additionally, a novel methodology has been established for the generation of arbitrary diffraction-free beam arrays, entirely developed within Matlab. To substantiate the efficacy of this method, a planar PGMS has been crafted to accommodate dual x-polarized 3D near-field configurations: <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$q q$</tex> image in direction (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\theta_{1}=5^{\circ}, \varphi_{1}= 0$</tex> °) and a flower image in direction (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\theta_{2}=10^{\circ}, \varphi_{2}=180^{\circ}$</tex>). The advantages of the 3D-shaped near-fields are as follows: high conversion efficiency 30.5 % (measured), wideband 60.5 % and low sidelobe -15 dB. The proposed technique is confirmed by the calculated, simulated and measured results.