Metasurface Antennas: New Models, Applications and Realizations

This paper presents new designs, implementation and experiments of metasurface (MTS) antennas constituted by subwavelength elements printed on a grounded dielectric slab. These antennas exploit the interaction between a cylindrical surface wave (SW) wavefront and an anisotropic impedance boundary condition (BC) to produce an almost arbitrary aperture field. They are extremely thin and excited by a simple in-plane monopole. By tailoring the BC through the shaping of the printed elements, these antennas can be largely customized in terms of beam shape, bandwidth and polarization. In this paper, we describe new designs and their implementation and measurements. It is experimentally shown for the first time that these antennas can have aperture efficiency up to 70%, a bandwidth up to 30%, they can produce two different direction beams of high-gain and similar beams at two different frequencies, showing performances never reached before

Analysis and Design of a Compact Leaky-Wave Antenna for Wide-Band Broadside Radiation

A low-cost compact planar leaky-wave antenna (LWA) is proposed offering directive broadside radiation over a significantly wide bandwidth. The design is based on an annular metallic strip grating (MSG) configuration, placed on top of a dual-layer grounded dielectric substrate. This defines a new two-layer parallel-plate open waveguide, whose operational principles are accurately investigated. To assist in our antenna design, a method-of-moments dispersion analysis has been developed to characterize the relevant TM and TE modes of the perturbed guiding structure. By proper selection of the MSG for a fabricated prototype and its supporting dielectric layers as well as the practical TM antenna feed embedded in the bottom ground plane, far-field pencil-beam patterns are observed at broadside and over a wide frequency range, i.e., from 21.9 GHz to 23.9 GHz, defining a radiating percentage bandwidth of more than 8.5%. This can be explained by a dominantly excited TM mode, with low dispersion, employed to generate a two-sided far-field beam pattern which combines to produce a single beam at broadside over frequency. Some applications of this planar antenna include radar and satellite communications at microwave and millimeter-wave frequencies as well as future 5G communication devices and wireless power transmission systems

Perfect non-specular reflection with polarization control by using a locally passive metasurface sheet on a grounded dielectric slab

This paper investigates the conditions for a perfect anomalous reflection through a modulated metasurface consisting of a metallic cladding printed over a grounded slab. Differently to what has been previously published, the problem is rigorously addressed by modeling the metallic cladding through an equivalent penetrable impedance and accounting for the grounded slab through the problem's Green's function. It is shown that without polarization transformation, the exact solution exists only for the special case of retroreflection, and, in that case, it can be done simultaneously for the two orthogonal polarizations, with an arbitrary phase shift among the two. On the other hand, changing the polarization of the reflected wave allows one to find an exact solution for arbitrary combinations of incidence and reflection angles. The exact solution is found by imposing that the induced currents radiating with the Green's function of the background problem simultaneously create the desired reflected beam and cancel the specular reflection from the grounded slab. This approach leads to the derivation of a closed-form expression for the homogenized penetrable impedance profile providing perfect anomalous reflection, i.e., ensuring the vanishing of all the coefficients of the waves associated with unwanted diffraction orders, including the specular reflected wave and the evanescent waves. This result is of great practical interest, since the derived penetrable impedance profile can be readily implemented through a simple distribution of metallic patches. The feasibility of this approach is verified through full wave simulations of both the ideal impedance and the patch-based structure, which confirm the effectiveness of the proposed solution

Synthesis of passive lossless metasurfaces for perfect anomalous reflection

In this paper, practical implementation of metasurfaces providing perfect anomalous reflection (i.e. reflection to a non specular direction with no higher order modes excited) is discussed with reference to metasurfaces consisting of a metallic cladding over a grounded dielectric slab. The metallic cladding is modeled through a continuous penetrable impedance sheet, while the grounded slab is accounted for through the Green's function. It is shown that an exact solution without polarization transformation only exists for the case of retroreflection, while a solution with polarization conversion can be found for arbitrary incidence and reflection angles. The derived solutions are implemented through a distribution of patches and full wave simulations are performed to confirm their effectiveness

Design Methods for Dual Polarized Metasurface Antennas: Three Simple Approaches

Metasurface (MTS) antennas are based on the transformation of a cylindrical-wavefront surface wave (SW) into a general wavefront leaky wave (LW). The MTS aperture is constituted by a grounded dielectric slab printed with an electrically dense distribution of subwavelength patches realizing space-variable, homogenized tensor impedance boundary conditions (IBCs). One of the challenges in this type of antenna is related to obtaining dual polarization operations by using the same impedance modulation. In this article, we explore and compare three simple approaches to obtain two beams with orthogonal polarizations by feeding two ports. A first known method is based on exciting both a transverse electric (TE) and a transverse magnetic (TM) SW mode on the same modulated impedance. A second method exploits the concept of impedance modulation sharing, according to which two distinct modulations, designed to radiate different polarizations when properly illuminated by distinct offset feeding points, are superimposed on the same aperture. A third method consists in duplexing an outward (radially diverging) and an inward (converging to the center) SW. Simple analytical formulas are presented for the synthesis of the impedance that allows for the control of the inward/outward waves to ensure balanced radiation performances in terms of aperture efficiency for the two polarizations. A comparison in terms of performances between the latter two approaches is presented

New antennas for space applications

Metasurfaces (MTSs) are versatile, technologically advanced new materials, which have proven their capability to be successfully employed for constituting variable impedance plane and enabling precisely controlled radiation from equivalent apertures for antenna applications. Among the several requirements that can be desired in Space Communications environment the possibility of obtaining shaped beams is one of the most demanding features, in this framework MTS antennas assume a key role. In this work two new designs of shaped beam antennas are presented. These implement a low-complexity data-downlink aperture for Ka-band LEO missions and, in the second example, a printed MTS is applied for pattern shaping of a Ku-band horn for global Earth coverage

Dual band isoflux ultraflat meta antennas

This paper presents an approach for the design of a dual-band planar antenna radiating an isoflux-shaped beam suitable for earth observation missions. The antenna is based on a modulated metasurface excited by a central feed. Preliminary numerical results are presented to validate the concept

Metasurface leaky-wave antennas: A comparison between slot and patch implementation

This paper is devoted to the analysis and design of a high-gain circularly polarized antenna with low profile for deep space communications in the X-band. In this context, the low-mass and high efficiency requirements can be addressed at the same time by properly designing a layer of patches (slots) printed (etched) on a grounded dielectric substrate. The interaction between this layer and the surface wave launched by a simple and compact feeder leads to leaky-wave radiation. The overall structure is very light and low profile; in particular, for the slot-based solution the dielectric slab is extremely thin (0.15 mm) and characterized by a low permittivity. The design procedure is summarized, and the patch and slot layouts are shown along with their respective directivity patterns