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...

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The generation of several beams with strict radiation requirements in the near field of a radiating aperture is demonstrated here. An optimization scheme is adopted to derive the aperture field distribution generating the required nearfield radiation. The optimization tool is based on a set-theoretic approach and takes into account field constraints on the radiation profile and polarization. The challenging case of generating four independent beams in the near field of a radiating aperture and with different polarizations is then considered. A tensorial metasurface is adopted to synthesize the derived aperture field profile to fully control the amplitude and phase distribution of the radiating aperture. Measurement results at 20 GHz validate the proposed approach.

This paper introduces a rigorous and fast procedure for accurate assessment of the peak averaged specific absorption rate (SAR), quantifying the user exposure to the electromagnetic field radiation from new-radio communication devices. Focus is lent to the specific class of user equipment that exploit multiple-input multiple-output (MIMO) technology and using exclusive simultaneous excitations of the active antenna-array system, such as expected on 5G devices. In contrast with the required N(N-1)+1 measurements on traditional SAR systems that only take measurements of the amplitude of the electric field, it is demonstrated in this paper that only N+1 number of measurements are required to evaluate the true SAR of a Nantenna MIMO thanks to using a vector near-field based SAR measurement system.