Design of Planar and Conformal, Passive, Lossless Metasurfaces That Beamform

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. Metasurface, beamforming, conformal, adjoint variable method. INDEX TERMS

All-Metal Tensor Metamaterials: Characterization and Design

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“…With increasing capacitance, the transverse wavenumbers of supported surface waves become larger. Thus, to limit the minimum transverse wavelength of the supported surface waves to twice the unit cell dimension, the sheet reactances used in the optimization must be less than −j20Ω [28]. For a cell size equal to λ/20, this limited the extent of the evanescent spectrum to surface waves with a transverse wavenumber of 10k 0 .…”

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