Wave Up Srl

Firenze, Italy

Wave Up Srl

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. | Freni A.,University of Florence | Cuccoli F.,CNIT | Facheris L.,Wave Up S.r.l.
Journal of Atmospheric and Oceanic Technology | Year: 2017

The knowledge of atmospheric refractive index structure constant (C2 n) profiles is fundamental to determine the intensity of turbulence, and hence the impact of the scintillation impairment on the signals propagating in the troposphere. However, their relation with atmospheric variables is not straightforward, and profiles based on statistical considerations are normally employed. This can be a shortcoming when performing simulations for which scintillation disturbances need to be consistent with the assumed atmospheric conditions. To overcome this limitation, this work describes a procedure to obtain an estimate of the refractive index structure constant profile of clear-air turbulence under given atmospheric conditions. The procedure is based on the application of the vertical gradient approach to high-resolution radiosonde data. Since turbulence is known to be confined to vertically thin layers, a preliminary identification of turbulent layers is required. This is accomplished by analyzing the profiles of the Richardson number. The value of the outer scale length is estimated using the Thorpe length calculated from the potential temperature profile. The procedure is applied to high-resolution radiosonde data that have been acquired from the Stratosphere-Troposphere Processes and their Role in Climate (SPARC) Data Center, and the obtained results are consistent with measured C2 n profiles previously published in the literature. © 2017 American Meteorological Society.


Minatti G.,University of Siena | Minatti G.,Wave Up S.r.l. | Faenzi M.,University of Siena | Sabbadini M.,University of Siena | Maci S.,European Space Agency
IEEE Transactions on Antennas and Propagation | Year: 2017

We present analytical expressions for the frequency bandwidth of gain of broadside-beam metasurface (MTS) antennas. These antennas are based on a transformation between a cylindrical surface-wave (SW) and a leaky-wave through interaction with a periodically modulated MTS. The latter is realized by using subwavelength patches of different dimensions printed on a grounded slab. We demonstrate that, for an appropriate choice of the modulation index, the relative bandwidth is inversely proportional to the antenna radius in terms of a wavelength, by a coefficient which is directly proportional to the group velocity at the central frequency of the SW supported by the average impedance. It is seen, therefore that the product bandwidth-gain is linearly proportional by means of the same coefficients to the antenna radius in wavelengths. The simple formulas introduced in the paper have been thoroughly tested through an accurate analysis. © 2017 IEEE.


Minatti G.,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: 2017

Different types of efficiencies are introduced for metasurface (MTS) antennas based on single point-source excitation: 1) the feed efficiency ϵfeed is the power delivered by the feed to surface wave (SW) over the input power; 2) the tapering efficiency ϵtap quantifies the deviation with respect to a uniform illumination; 3) the conversion efficiency ϵconv defines the capability of the MTS to transform the SW power into leaky-wave power; and 4) the ohmic efficiency Ω accounts for the antenna losses. The product of all of these factors provides the overall efficiency of the antenna. New, quite general analytical formulas are suggested to estimate any individual efficiency. In particular, it is seen that ϵfeed can reach also 90% by using planar or quasi-planar circularly symmetric sources. It is also proven that the product ϵconv ϵtap cannot be larger than 58% for a uniform modulation; however, by using a nonuniform modulation, it can be increased to reach ϵconv ϵtap λ/(a λ +2), where λ is the antenna radius in free-space wavelengths. A new closed-form formula for estimating the losses is given. In accordance with the prescription given here, one can reach 75% of global efficiency, including losses, until a radius of 20 wavelengths with commercially available substrates. © 1963-2012 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.


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.

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