Design of Planar and Conformal, Passive, Loss-less Metasurfaces that Beamform

TL;DR

This paper presents a comprehensive synthesis method for designing planar and conformal passive, lossless beamforming metasurfaces using full-wave modeling, optimization, and patterning techniques, verified through multiple examples.

Contribution

It introduces a novel three-phase synthesis approach that ensures passivity and realizability of beamforming metasurfaces with high efficiency.

Findings

Achieved near-perfect aperture efficiency in a low-profile metasurface antenna.

Demonstrated controlled sidelobe levels in a scanned-beam reflectarray.

Validated the performance and bandwidth of the designed metasurfaces.

Abstract

A general technique for synthesizing both planar and conformal beamforming metasurfaces is presented that utilizes full-wave modeling techniques and rapid optimization methods. The synthesized metasurfaces consist of a patterned metallic cladding supported by a finite-size grounded dielectric substrate. The metasurfaces are modeled using integral equations which accurately account for mutual coupling and the metasurface's finite dimensions. The synthesis technique consists of three phases: a direct solve phase to obtain an initial metasurface design with complex-valued impedances satisfying the desired far-field beam specifications, a subsequent optimization phase that converts the complex-valued impedances to purely reactive ones, and a final patterning phase to realize the purely reactive impedances as a patterned metallic cladding. The optimization phase introduces surface waves which facilitate passivity. The metasurface is optimized using gradient descent with a semi-analytic gradient obtained using the adjoint variable method. Three examples are presented: a low-profile directly-fed metasurface antenna with near perfect aperture efficiency, a scanned-beam reflectarray design with controlled sidelobes, and a conformal metasurface reflectarray. The far-field and near-field performance of the metasurfaces are verified and the bandwidth and loss tolerance of the metasurfaces are investigated.