<p>We present a 3D method to numerically design a realizable metasurface, which transforms a given incident field into a radiated field that satisfies mask-type (inequality) constraints. The method is based on an integral equation formulation, and the local impedance boundary condition (IBC) approximation. The procedure yields the spatial distribution of the surface impedance, yet the process involves the synthesis of the equivalent current only. This current is constrained to correspond to a realizable surface impedance, i.e., passive, lossless, and with reactance values bounded by practical realizability limits. The current-based design avoids the solution of the forward problem at each step, and the impedance is obtained from the synthesized current only at the end of the process. This allows handling large metasurfaces, with full spatial variability of the impedance in two dimensions. The method requires no a priori information or heuristic, and is formulated so that all relevant operations in the iterative process can be evaluated with <em>O</em>(<em>N</em> log<em>N</em>) complexity. Application examples concentrate on the case of on-surface excitation and far-field pattern specifications; they show designs of circular metasurface antennas of 10 wavelengths in diameter, with pencil- and shaped-beam patterns, and for both circular and linear polarization.</p>
In this paper, we present a fully automated procedure for the direct design of a novel class of single-feed flat antennas with patterning of a conductive surface. We introduce a convenient surface discretization, based on hexagonal cells, and define an appropriate objective function, including both gain and input matching requirements. The reference geometry is constituted by a very thin, single feed-point square panel. It features a backing metal plate (“ground”) and a top conductive layer, which is automatically patterned to achieve the desired radiation and input matching properties. The process employs an evolutionary algorithm combined with a boundary element electromagnetic solver. By applying this method, we designed an antenna tailored to the 2.4 GHz ISM frequency band, with a size of $$24\,\hbox {cm} \times 24\,\hbox {cm}$$24cm×24cm, i.e., $$2 \times 2$$2×2 wavelengths and an height of 4 mm, or 0.03 wavelengths. Measured data confirmed the expected high gain (13 dBi), with a remarkable aperture efficiency (higher than 50%, including losses), thus validating the proposed approach.
<p>We present a 3D method to numerically design a realizable metasurface, which transforms a given incident field into a radiated field that satisfies mask-type (inequality) constraints. The method is based on an integral equation formulation, and the local impedance boundary condition (IBC) approximation. The procedure yields the spatial distribution of the surface impedance, yet the process involves the synthesis of the equivalent current only. This current is constrained to correspond to a realizable surface impedance, i.e., passive, lossless, and with reactance values bounded by practical realizability limits. The current-based design avoids the solution of the forward problem at each step, and the impedance is obtained from the synthesized current only at the end of the process. This allows handling large metasurfaces, with full spatial variability of the impedance in two dimensions. The method requires no a priori information or heuristic, and is formulated so that all relevant operations in the iterative process can be evaluated with <em>O</em>(<em>N</em> log<em>N</em>) complexity. Application examples concentrate on the case of on-surface excitation and far-field pattern specifications; they show designs of circular metasurface antennas of 10 wavelengths in diameter, with pencil- and shaped-beam patterns, and for both circular and linear polarization.</p>
<p>We present a 3D method to numerically design a realizable metasurface, which transforms a given incident field into a radiated field that satisfies mask-type (inequality) constraints. The method is based on an integral equation formulation, with local impedance boundary condition (IBC) approximation. The procedure yields the spatial distribution of the impedance, yet the process involves the synthesis of the equivalent current only. This current is constrained to correspond to a realizable surface impedance, i.e., passive, lossless, and with reactance values bounded by practical realizability limits. The current-based design avoids any solution of the forward problem, and the impedance is obtained from the synthesized current only at the end of the process. The procedure is gradient-based, with the gradient expressed in closed form. This allows handling large metasurfaces, with full spatial variability of the impedance in two dimensions. The method requires no a priori information, and all relevant operations in the iterative process can be evaluated with <em>O</em>(<em>N</em> log<em>N</em>) complexity. Application examples concentrate on the case of on-surface excitation and far-field pattern specifications; they show designs of circular and rectangular metasurface antennas of 20 wavelengths in size, with pencil- and shaped-beam patterns, and for both circular and linear polarization.</p>
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