Metasurface Antennas: Design and Performance

Abstract

This paper gives an overview on the design process of modulated metasurface (MTS) antennas and focus on their performance in terms of efficiency and bandwidth. The basic concept behind MTS antennas is that the MTS imposes the impedance boundary conditions (IBCs) seen by a surface wave (SW) propagating on it. The MTS having a spatially modulated equivalent impedance transforms the SW into a leaky wave with controlled amplitude, phase and polarization. MTS antennas are hence highly customizable in terms of performances by simply changing the IBCs imposed by the MTS, without affecting the overall structure. The MTS can be configured for high gain (high aperture efficiency) with moderate bandwidth, for wide bandwidth with moderate aperture efficiency, or for a trade-off performance for bandwidth and aperture efficiency. The design process herein described relies on a generalized form of the Floquet wave theorem adiabatically applied to curvilinear locally periodic IBCs. Several technological solutions can be adopted to implement the IBCs defined by the synthesis process, from sub-wavelength patches printed on a grounded slab at microwave frequencies, to a bed of nails structure for millimeter waves: in any case, the resulting device has light weight and a low profile.

Metasurface Antennas Embedded in Small Circular Cavities for Telemetry Applications

“…Furthermore, it was demonstrated in [7] that, for small cavities of rectangular shape (edge size of 0.25 λ 0 , where λ 0 is the wavelength in vacuum at the operating frequency), a patch antenna placed at the aperture of the cavity does not offer the best performance in terms of BW: The maximum reachable BW was shown to be achieved by replacing a standard patch at the aperture with a metasurface composed of one or several layers of capacitively coupled strips [8], whose dimensions are typically smaller than one tenth of the wavelength [10]. As introduced in previous works [7][8][9]11], loading the aperture of a metallic cavity antenna with a capacitance-only impedance offers two benefits: Increasing the antenna BW [7], particularly compared to stacked patch antennas embedded in a larger cavity [11]; or reduction of the antenna and cavity size for a given BW [9].…”