Implementation of Radiating Aperture Field Distribution Using Tensorial Metasurfaces

Abstract

Abstract-This paper deals with the design of tensorial modulated metasurfaces able to implement a general radiating aperture field distribution. A new aperture synthesis approach is introduced, based on local holography and variable impedance modulation. In particular, it is shown that tensorial metasurfaces can be used to generate general radiating distribution (phase and amplitude). In addition, a step by step algorithm is presented. In order to validate the method, several solutions are presented at 20 GHz which implement aperture distributions able to radiate different beams with general polarization.Index Terms-Metasurface antenna, leaky-waves, periodic surface, surface-waves. I. INTRODUCTIONn recent years, metamaterials have become an appealing subject of research. They are synthetic materials that have exotic properties that cannot be found in nature: double negative materials, negative index materials, left-handed materials… Metasurfaces are the equivalent of metamaterials in the case of 2D structures. The properties of these surfaces are described in terms of tensorial or scalar surface impedances (analogous to the constitutive parameters for volumetric metamaterials). Metasurfaces [9], orbital angular momentum communication [10] or transformation optics [11]-[12].All these works are based on the propagation properties of waves over a sinusoidally modulated impedance [13]. By choosing an appropriate modulated surface impedance, it is possible to control the propagation of SW along a surface or to obtain the transition from SW to leaky wave (LW) modes in order to realize antennas [16], [17].Surfaces composed of sub-wavelength printed elements over grounded dielectric slabs were largely used in order to obtain modulated scalar impedances by locally changing the dimensions of the elements [1]- [15]. Symmetric elements are used to produce scalar impedances [1] [19]. However, the direction of the radiating aperture field (or the equivalent surface current) is dictated by the source [19]. This latter aspect limits the number of possible aperture field distributions that can be implemented.Recently, tensorial metasurfaces were successfully used in antenna design that can radiate CP waves [1], [20] and isoflux shaped beam antennas for space applications [20], [21].The additional degrees of freedom offered by tensorial metasurfaces could be used to overcome the limits of scalar solution by generalizing the procedure presented in [19].Our objective is to propose a systematic procedure for the design of metasurface antennas capable of implementing a general aperture field distribution (amplitude, phase and direction). The principal novelty of this approach is the independent control of the generated aperture field components. This important aspect (critical for general aperture implementation), is achieved by introducing independent modulations of the impedance tensorial components and a new exact holographic formulation. Moreover, average impedance variation along the propagation direction is introduced in ord...

Near-Field Multibeam Generation by Tensorial Metasurfaces

“…Metasurfaces are here adopted to approximate in the best possible way a continuous aperture. Such a solution also offers the freedom of controlling not only the field orientation and phase over the aperture, but also the amplitude [14], [19].…”

“…The metasurface is designed based on the local holography and variable impedance modulation procedure detailed in [14]. The unit cell consists of a V-shaped cut out of a circular patch depicted in Fig.…”

“…The geometrical parameters θ, g and ψ (corresponding to the angle, width, and orientation of the cut, respectively) control the tensorial surface impedance of the unit cell. A detailed explanation of the complete design process and the unit cell properties have been presented in [14] and will be avoided here for brevity. Fig.…”

“…From an antenna perspective, metasurfaces provide enhanced flexibility in defining innovative radiating devices. This is clearly demonstrated by the plethora of scientific production, ranging from polarization [2], [7] and phase [8] manipulation to radiated shaped beams [9]- [14]. Metasurfaces have attracted grown interest for their capability to generate arbitrary radiation patterns at low cost and with very flat and compact structure.…”

“…The synthesized aperture distribution is then practically implemented by a tensorial metasurface antenna. The latter is designed based on the methodology of [14], where a novel design methodology and class of unit cells were introduced. Thanks to this approach, vectorial aperture field distributions can be implemented using metasurfaces, used here to mold the near field.…”