Firenze, Italy
Firenze, Italy

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Caminita F.,Wave Up Srl | Martini E.,Wave Up Srl | Pavone S.C.,University of Siena | Albani M.,University of Siena | Maci S.,University of Siena
IEEE International Symposium on Phased Array Systems and Technology | Year: 2017

This contribution addresses the use of reconfigurable modulated metasurfaces (MTSs) for the realization of electronically scanning antennas without the use of phase shifters. Different approaches can be used to electronically control the average equivalent impedance or the modulation period of the modulated MTS. © 2016 IEEE.

Martini E.,University of Siena | Martini E.,Wave Up S.r.l. | Mencagli M.,University of Siena | Gonzalez-Ovejero D.,University of Siena | And 2 more authors.
IEEE Transactions on Antennas and Propagation | Year: 2016

The name flat optics (FO) has been introduced in a recent paper by Capasso's group for denoting light-wave manipulations through a general type of penetrable or impenetrable metasurfaces (MTSs). There, the attention was focused on plane waves, whereas here we treat surface waves (SWs) excited on impenetrable impedance surfaces. Space variability of the boundary conditions imposes a deformation of the SW wavefront, which addresses the local wavector along not-rectilinear paths. The ray paths are subjected to an eikonal equation analogous to the one for geometrical optics (GO) rays in graded index materials. The basic relations among ray paths, ray velocity, and transport of energy for both isotropic and anisotropic boundary conditions are presented for the first time. This leads to an elegant formulation which allows for closed form analysis of flat operational devices (lenses or beam formers), giving a new guise to old concepts. It is shown that when an appropriate transformation is found, the ray paths can be conveniently controlled without the use of ray tracing, thus simplifying the problem and leading to a flat version of transformation optics, which is framed here in the general FO theory. © 2015 IEEE.

Gonzalez-Ovejero D.,University of Siena | Martini E.,Wave Up S.r.l. | MacI S.,University of Siena
IEEE Transactions on Antennas and Propagation | Year: 2015

This paper investigates the fundamental dispersion properties of surface waves (SWs) supported by a class of metasurfaces (MTSs) that consists of a planar layer made of metal patches and apertures with self-complementary geometries. When the MTS is suspended in free space, the supported SW is TM or TE depending on whether the vertexes of the metallic parts are interconnected or not, whereas the phase velocity is equal in the two cases. A simple analytical model, that depends only on the geometry, is derived to predict the dispersion curves for a quite general class of geometries. The proposed model is also extended to cases in which the MTSs are printed on a grounded or ungrounded dielectric slab, by using an equivalent dielectric constant. Comparisons with dispersion curves obtained through full-wave simulations confirm the accuracy of the model all over the Brillouin region. Finally, it is shown that connecting or disconnecting the metal patches along a given path allows for a confinement of the SWs on such a path. An experimental validation of this concept is also presented. This feature provides the possibility of controlling the wave's direction of propagation by changing the vertexes status by means of miniaturized switches or optical control. © 2015 IEEE.

Mencagli M.,University of Siena | Martini E.,University of Siena | Martini E.,Wave Up Srl | Maci S.,University of Siena
IEEE Transactions on Antennas and Propagation | Year: 2015

This paper presents an effective approach for the derivation of the two-dimensional (2-D) frequency-wavenumber dispersion surface of anisotropic metasurfaces (MTSs) consisting of elliptical patches printed over a grounded slab. These MTSs are important in the design of leaky-wave antennas and transformation optics (TO) surface-wave based devices. The formulation resorts to an analytical expression of the currents excited on the element of the periodic texture to define a reduced spectral method of moments (MoM) procedure with only three basis functions. An exact compact formula, which links the MoM matrix to the homogenized equivalent anisotropic impedance of the MTS, is derived. The formulation presented here has been found accurate and useful for designing MTS antennas and TO devices. © 2015 IEEE.

Mencagli M.,University of Siena | Martini E.,University of Siena | Martini E.,Wave Up S.r.l. | Gonzalez-Ovejero D.,University of Siena | Maci S.,University of Siena
IEEE Antennas and Wireless Propagation Letters | Year: 2014

Transformation electromagnetics has been extended to design modulated anisotropic metasurfaces (MTSs) able to control the propagation path of surface waves (SWs). The proposed methodology consists in simple formulas that link the parameters of the transformation to the local SW wave-vector. The space-dependent wave-vector distribution is eventually implemented by subwavelength patches printed on a grounded slab. New MTS devices are presented based on these formulas. © 2014 IEEE.

Minatti G.,European Space Agency | Faenzi M.,University of Siena | Martini E.,University of Siena | Martini E.,Wave Up S.r.l. | And 6 more authors.
IEEE Transactions on Antennas and Propagation | Year: 2015

This paper presents design and analysis methods for planar antennas based on modulated metasurfaces (MTSs). These antennas operate on an interaction between a cylindrical surface-wave (SW) excited by an isotropic TM radiator, and an MTS having a spatially modulated equivalent impedance. The MTS is realized by using sub-wavelength patches printed on a grounded slab, thus resulting in a structure with light weight and compact volume. Both features are appealing characteristics for space applications. This paper introduces for the first time an impedance-based amplitude synthesis of the aperture field distribution and shows several new examples of antennas for space applications obtained in recent research projects financed by the European Space Agency. © 1963-2012 IEEE.

Minatti G.,University of Siena | Caminita F.,University of Siena | Caminita F.,Wave Up S.r.l. | Martini E.,University of Siena | And 2 more authors.
IEEE Transactions on Antennas and Propagation | Year: 2016

This paper presents a new theory for analyzing the leaky-wave (LW) mechanism supported by planar metasurfaces (MTSs) described by continuous, anisotropic, nonuniform, locally periodic boundary conditions (BCs), and excited by a vertical dipole at the interface. These BCs well represent a dense distribution of subwavelength metal patches of infinitesimal thickness, printed on a grounded slab. We denote succinctly this theoretical formulation as flat optics for LWs. This formulation is based on an adiabatic, asymptotic form of the Floquet theorem, introduced here for the first time. The adiabatic Floquet-wave analysis allows for: 1) describing the mechanism of global interaction between the cylindrical surface wave (SW) launched by the dipole and the modulated MTS; 2) introducing a generalized curvilinear-wavefront LW field that can be used for controlling the radiation-pattern shaping; 3) describing the local and global transfer of energy from SW to LW; 4) establishing an analytical relationship between the aperture field polarization and the anisotropic parameters of the MTS and 5) between the leakage parameter $\alpha$ and the MTS modulation index. Concerning the latter point, a closed-form formula for $\alpha$ is introduced, which allows for unprecedented control of the aperture field amplitude. The theoretical results are successfully validated by comparison with a full-wave analysis, showing impressive accuracy. In a companion paper published in this Journal issue, the present theory is used for the synthesis of a large class of planar aperture antennas. © 1963-2012 IEEE.

Minatti G.,University of Siena | Caminita F.,University of Siena | Caminita F.,Wave Up S.r.l. | Martini E.,University of Siena | And 3 more authors.
IEEE Transactions on Antennas and Propagation | Year: 2016

An effective synthesis procedure for planar antennas realized with nonuniform metasurfaces (MTSs) excited by a point source is presented. This synthesis potentiates previous formulations by introducing a control of the amplitude of the aperture field while improving the polarization and phase performances. The class of MTS antennas we are dealing with is realized by using subwavelength patches of different dimensions printed on a grounded slab, illuminated by a transverse magnetic point source. These antennas are based on the interaction between a cylindrical surface-wave and the periodic modulation of the MTS, which leads to radiation through a leaky-wave (LW) effect. This new design method permits a systematic and simple synthesis of amplitude, phase, and polarization of the aperture field by designing the boundary conditions imposed by the MTS. The polarization control is based on the local value of the MTS anisotropy, the phase is controlled by the shape and periodicity of the modulation, and the amplitude is controlled by the local leakage attenuation parameter of the LW. The synthesis is based on analytical formulas derived by an adiabatic Floquet-wave expansion of currents and fields over the surface, which are simultaneously published in this journal issue. The effectiveness of the procedure is tested through several numerical examples involving realistic structures. © 1963-2012 IEEE.

Mencagli M.,University of Siena | Martini E.,University of Siena | Martini E.,Wave Up S.r.l. | Maci S.,University of Siena
IEEE Transactions on Antennas and Propagation | Year: 2016

Metasurfaces are thin metamaterials used for manipulating propagation of plane waves and surface-waves (SWs). They can be characterized by homogenized- oundary conditions, which, in absence of losses, can be represented through an equivalent reactance. In this paper, we introduce a general representation of isotropic frequency-dependent reactance which is valid along the dispersion curve of the relevant TM SW. This representation is written in terms of a transition function derived from a manipulation of the Cardano's formula for third-degree algebraic equations. Throughout a large portion of the dispersion curve, this transition function depends on one parameter only, which is an equivalent quasi-static capacitance. Approaching the Floquet-Bloch region, where many higher order Floquet modes are excited, two additional parameters should be extracted from the full-wave data to complete the transitional representation of the reactance until the upper boundary of the Brillouin region. The final formula is valid for a generic isotropic reactance and for an anisotropic reactance when the direction of propagation is along a symmetry axis of the unit cell element. © 2015 IEEE.

Gonzalez-Ovejero D.,University of Siena | Martini E.,University of Siena | Martini E.,Wave Up S.r.l. | Vardaxoglou J.,Loughborough University | Maci S.,University of Siena
2015 9th European Conference on Antennas and Propagation, EuCAP 2015 | Year: 2015

This paper investigates the properties of frequency selective metasurfaces (MTSs) made of a layer of conducting elements and a layer of the complementary (aperture) geometry, etched on either side of a dielectric substrate. The elements needed to synthesize such structures are small in terms of the wavelengths comprised within the operating bandwidth. Thus, one obtains improved frequency bandwidth stability and angular response. An interpretation in terms of the MTS's equivalent circuit is provided, along with design guidelines for the proposed structure. © 2015 EurAAP.