Reduced dimensionality optimizer for efficient design of wideband millimeter‐wave 3D metamaterial GRIN lenses

Abstract

AbstractIn this article we present a method for the rapid design of wideband, high efficiency metamaterial GRIN lenses with rotational symmetry. The method achieves rapid optimization by reducing the number of optimized parameters while maintaining wideband impedance matching for high aperture efficiency. For rotationally symmetric lenses with isotropic GRIN media it is sufficient to design a two‐dimensional (2D) cross section. By using intrinsically matched unit‐cells which prescribe a permittivity gradient along the axis of beam propagation the optimizer only needs to define the transverse permittivity gradient along a line, reducing the design domain from three dimensions (3D) to a single dimension (1D). At each step of the optimizer a 2D finite‐difference‐time‐domain code rapidly solves each realization of the GRIN lens cross‐section across a wide bandwidth. We demonstrate the proposed method by optimizing and fabricating a 4‐inch GRIN lens which achieves 60%–65% measured aperture efficiency from 26 to 40 GHz. The prototype lens provides a high‐efficiency aperture for Ka‐band satcom and 5G millimeter‐wave bands and the approach is suitable for higher future millimeter‐wave bands in 6G and beyond networks.