Search

Design, realization, and measurements of an X-band antenna for data downlink (DDL) from low Earth orbit (LEO) satellites are presented. This antenna has an isoflux radiation pattern and operates in dual circular polarization with cross-polar discrimination (XPD) higher than 18 dB on the operational bandwidth. Two solutions are first proposed: one realized by a metasurface with circular strips printed on a dielectric slab and another realized by concentric metallic corrugations. Starting from a basic scattering mechanism of a self-complementary ring-type metasurface excited by a perfectly polarized source, both these antennas are designed by optimizing an equivalent anisotropic impedance surface excited by a short hat feed. The corrugated antenna is realized and measured, confirming that the performances are compliant with the requirements for next-generation DDL antennas. [ABSTRACT FROM AUTHOR]

This article presents an exact solution for a perfect conversion of a TM-polarized surface wave (SW) into a TM-polarized leaky wave (LW) using a reciprocal and lossless penetrable metasurface (MTS) characterized by a scalar sheet impedance, located on a grounded slab. On contrary to the known realizations of LW antennas, the optimal surface reactance modulation which is found here ensures the absence of evanescent higher-order modes of the field Floquet-wave expansion near the radiating surface. Thus, all the energy carried by the SW is used for launching the single inhomogeneous plane wave into space without accumulation of reactive energy in the higher-order modes. It is shown that the resulting penetrable MTS exhibits variation from an inductive to a capacitive reactance passing through a resonance. The present formulation complements a previous article of the authors, in which a perfect conversion from TM-polarized SW to TE-polarized LW was found for impenetrable boundary conditions. Here, the solution takes into account the grounded slab dispersion, and it is convenient for practical implementation. [ABSTRACT FROM AUTHOR]

A Ku -band low cross-polarization conical horn based on thin metasurface (MTS) walls is presented in this article, along with the relevant design method. The necessary boundary conditions are realized by printing a tensor MTS on the internal walls of the horn, which yields a radiation performance similar to a standard corrugated Gaussian horn yet with the benefits of thin walls. The design method is based on the adiabatic approximate solution for the hybrid mode of a conical waveguide with generic balanced impedance walls, which allows the determination of the impedance profile supporting a single balanced mode. The impedance design is based on the usual locally flat approximation of the wall and on the assumption of plane wave incidence. This approach results in an analytic design method that requires no optimization. The design has been first validated by solving the problem with homogenized impedance boundary conditions through a body of revolution (BoR) method of moments. The actual structure, including impedance wall implementation, is then simulated in full detail with a full-wave fast code. Finally, the horn has been realized and experimentally characterized; measurements show excellent agreement both with theory and with simulations, with a cross-polarization level below −20 dB over a 2 GHz bandwidth. [ABSTRACT FROM AUTHOR]

Multibeam and beam-scanning capabilities of metasurface (MTS) antennas using multiple feeds are investigated. The MTS synthesis is performed by direct inversion of an electric field integral equation (EFIE) obtained after expanding the unknown equivalent impedance profile into Fourier-Bessel basis functions. Two approaches are explored. The first one assumes a priori a discrete azimuthal symmetry in the impedance profile, so as to constrain the solution to a subspace which automatically provides multiple beams when illuminated with feeds regularly arranged along azimuth. In the second approach, there are not a priori assumptions on the impedance profile, but the systems of equations corresponding to each beam are stacked and solved simultaneously in the least-squares sense. This second approach can also be used to obtain polarization diversity. More importantly, it also enables continuous beam scanning. The latter functionality is achieved through the generation of two embedded patterns in a common azimuthal window with opposite phase slopes, followed by a continuous phasing of the two feed points. Various designs are presented in this article. All the results are validated with the method of moments (MoM). [ABSTRACT FROM AUTHOR]

A parity time-reversal duality symmetric structure constituted by a perfect electric conductor and perfect magnetic conductor (PMC) parallel plate waveguide is analyzed. This waveguide supports unimodal transverse electromagnetic (TEM) edge mode propagation protected against backscattering from a certain class of deformations and defects. The TEM solution is found in analytical form by using three different methods, namely, conformal mapping, mode-matching, and Fourier-transform methods. It is shown through numerical simulations that the mode propagation is robust with respect to deformations such as 90° bends and discontinuities such as transition to free space. Implementation of the PMC boundary conditions via both a bed of nails and a mushroom structure is also successfully investigated. [ABSTRACT FROM AUTHOR]

This paper presents a simple and effective way to increase the scan range of phased array antennas by using a metasurface (MTS) curved dome. The technique is based on a phase-gradient passive MTS that deflects the incident rays coming from the array aperture, and on a predistortion of amplitude and phase applied to the original phased array. We assume, therefore, to have at disposal an array capable of electronic beam scanning over a limited angular range with control of amplitude and phase. Geometrical optics ray tracing is used for the design of the metadome and physical optics for the analysis. For the sake of simplicity, the idea is illustrated here for a 2-D scan case; however, the extension to full 3-D scanning appears to be straightforward. [ABSTRACT FROM AUTHOR]

The surface wave dispersion of a grounded layer of liquid crystals (LCs) is investigated by taking into account the inherent electrical reconfigurability of such a material. The spectral dyadic impedance Green’s function of the tunable LC grounded slab is calculated and the dispersion curve of the fundamental mode supported by the structure is presented, showing that the orientation of the optical axis of the LCs modifies the surface wave dispersion curve significantly enough to be applied for surface wave propagation control. Furthermore, it is demonstrated that the presence of an inductive metasurface on top of the LC layer impressively reduces the resonance frequency and increases the sensitivity to the continuous voltage biasing. [ABSTRACT FROM AUTHOR]

Different types of efficiencies are introduced for metasurface (MTS) antennas based on single point-source excitation: 1) the feed efficiency \varepsilon \mathrm{ feed} is the power delivered by the feed to surface wave (SW) over the input power; 2) the tapering efficiency \varepsilon \mathrm{ tap} quantifies the deviation with respect to a uniform illumination; 3) the conversion efficiency \varepsilon \mathrm{ conv} defines the capability of the MTS to transform the SW power into leaky-wave power; and 4) the ohmic efficiency \varepsilon \Omega 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 \varepsilon \mathrm{ feed} can reach also 90% by using planar or quasi-planar circularly symmetric sources. It is also proven that the product \varepsilon \mathrm{ conv} \varepsilon \mathrm{ tap} cannot be larger than 58% for a uniform modulation; however, by using a nonuniform modulation, it can be increased to reach \varepsilon \mathrm{ conv} \varepsilon \mathrm{ tap} \approx a / \lambda /(a / \lambda +2) , where $a/\lambda $ 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Metasurfaces are thin metamaterials used for manipulating propagation of plane waves and surface-waves (SWs). They can be characterized by homogenized–boundary 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

A formulation is presented for fast interactions between subdomains in two-dimensional (2-D) scattering problems. The formulation combines inhomogeneous plane waves with cylindrical harmonic decompositions of fields radiated by the subdomains. It is shown that the complexity of interactions naturally decays with the distance between subdomains and that very few elementary operations are involved at the lowest level. An example of iterative solution for scattering by a collection of cylinders validates the proposed approach. [ABSTRACT FROM PUBLISHER]

Metasurfaces are thin metamaterial layers characterized by unusual dispersion properties of surface/guided wave and/or reflection properties of otherwise incident plane waves. At the scales intervening in their design, metasurfaces can be described through a surface impedance boundary condition. The impedance, possibly tensorial, is often “modulated,” i.e., it can vary from place to place on the surface (by design). We investigate on different integral equation formulations of the problem, with special attention to the stability properties of the resulting system matrix. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

Different procedures are presented for the retrieval of effective constitutive parameters of metamaterial structures realized by multilayer lossless periodic structures. These structures are modeled as Floquet-wave based multiport networks connected by pieces of transmission lines. A generalized Bloch method is then adopted to find the dominant modes of the volumetric homogenized metamaterial. Starting from the results of this analysis, the constitutive tensors of an equivalent homogeneous material are defined. Different levels of equivalence are defined, denoted as “external equivalence,” “dispersion equivalence,” “single-mode equivalence,” and “double-mode equivalence.” The corresponding homogenization processes are characterized by an increasing level of completeness (in the description of the metamaterial behavior) and of sophistication (concerning the processing of the full-wave analysis outcomes). The defined homogenization procedure accounts for dispersion in time (frequency) and space (wavenumber), as well as for anisotropy. [ABSTRACT FROM PUBLISHER]

A generalized network formulation using a spherical wave expansion is applied to the analysis of the perturbation induced at the input port of an antenna by nearby scatterers. The antenna is characterized by using the total scattering matrix; the scattering from the obstacles is studied through a physical optics approach, and the interactions are described in terms of radiated spherical waves. The resulting procedure is simple, has a moderate computational cost and can be directly interfaced with measurements. Results show a very good agreement with full-wave simulations. [ABSTRACT FROM PUBLISHER]

A compact broadband Edge-Line Coupler (ELC) based on Parity Time-reversal Duality (PTD) symmetry has been conceived, designed, constructed and measured. The coupler connects four PTD bifilar edge lines (BELs), recently introduced by the authors. The PTD-BELs are constituted by a parallel plate waveguide whose walls are formed by a junction between Perfect Electric Conductor (PEC) and Perfect Magnetic Conductor (PMC) boundary conditions. Reversing the axis orthogonal to the plates interchanges the position of PEC and PMC. Such a waveguide supports unimodal transverse electromagnetic (TEM) propagation, extremely confined along the top and bottom junction edges; its propagation is protected against backscattering from any discontinuity that preserves the PTD symmetry. The ELC presented here is constituted by a 4-port junction in which each port is intrinsically matched due to the PTD symmetry, strongly coupled with a second port, strongly decoupled with a third port, and weakly coupled with a fourth port. The ELC is designed by using a mushroom metasurface for the PMC portion of the device; the connection is based on a switch circuit which imposes open and short conditions on the two opposite sides of the structure. Switching simultaneously the open and short circuits reroutes the signal in a different port, while maintaining the same level of coupling with the other ports. A static prototype has been built and its measurements have confirmed the matching performance and the good directionality of the coupler in a broadband frequency range between 24 and 30 GHz. [ABSTRACT FROM AUTHOR]

This article presents the design and experimental characterization of microwave structures based on parity time-reversal duality symmetric bifilar edge waveguides (PTD-BEWs) realized through a parallel plate waveguide (PPW) loaded by a metasurface. The analyzed structures include transmission lines with bends and multiple line arrangements. Due to their unique symmetry properties, these structures are robust against backscattering, thus resembling the behavior of topological WGs, despite the fact they are reciprocal. This makes it possible to guide the electromagnetic (EM) waves along the edge with low insertion losses and unique matching properties. Measurements, performed in the frequency range between 24 and 32 GHz, have confirmed the feasibility of the theoretical concept. [ABSTRACT FROM AUTHOR]

A simple and effective procedure for the reduction of truncation errors in planar near-field measurements of aperture antennas is presented. The procedure relies on the consideration that, due to the scan plane truncation, the calculated plane wave spectrum of the field radiated by the antenna is reliable only within a certain portion of the visible region. Accordingly, the truncation error is reduced by extrapolating the remaining portion of the visible region by the Gerchberg-Papoulis iterative algorithm, exploiting a condition of spatial concentration of the fields on the antenna aperture plane. The proposed procedure is simple and computationally efficient; it does not require any modification of the measurement procedure and it allows for the usual probe correction. Far-field patterns reconstructed from both simulated and measured truncated near-field data demonstrate its effectiveness and stability against measurement inaccuracies. [ABSTRACT FROM AUTHOR]

A theoretical analysis of the impact of clear-air tropospheric scintillation on a radio occultation link between two low Earth orbit satellites in K- and Ku-bands is presented, with particular reference to differential approaches for the measure of the total content of water vapor. The troposphere is described as a spherically symmetric turbulent medium satisfying Kolmogorov theory. Rytov's first iteration solution for weak fluctuations is used to derive an expression for the variance of amplitude fluctuations of the wave as well as their spectrum and the correlation between fluctuations at different frequencies. The validity of the assumptions made and the influence of atmospheric parameters on the quantities of interest are also investigated and discussed. Finally, numerical results are presented to provide an estimate of the level of scintillation-induced disturbances. [ABSTRACT FROM AUTHOR]

Focuses on line integral representation of physical optics scattering from a perfectly conducting plate illuminated by a Gaussian beam modeled as a complex point source. Assessment of complex point sources under observation; Comparison of the process with that of surface integration; Overview of the feasibility of the proposed approach.

A hybrid finite-element-modal-expansion procedure for the three-dimensional analysis of passive microwave devices exploiting higher order vector basis functions and an innovative class of curved elements is presented. If modal expansions on ports are not analytically known, they can be numerically obtained via a preliminary two-and-one-half-dimensional finite-element analysis; curved triangular and tetrahedrical elements are defined by a rational Bézier mapping, which provides a remarkable increase in accuracy and flexibility over the conventional polynomial mapping without a significant increase in computational burden. Numerical results are provided to illustrate the efficiency and feasibility of the proposed technique. [ABSTRACT FROM AUTHOR]

The robustness of straight and curved tetrahedral elements with higher order basis functions is tested against mesh quality with respect to some test cases. Results show not only an overall and expected better performance of higher order basis functions, but also an increased robustness to element distortion. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 27: 17–20, 2000. [ABSTRACT FROM AUTHOR]

A new approach is presented for synthesizing modulated metasurface (MTS) antennas (MoMetAs) with arbitrary radiation patterns, assumed to be given in amplitude, phase, and polarization. The MTS is defined on a circular domain and is represented as a continuous sheet transition impedance boundary condition (IBC) on the top of a grounded substrate. The proposed method relies on an entire-domain discretization of the electric field integral equation (EFIE). Via the dyadic Green’s function of the grounded substrate, the desired radiation pattern is translated into the visible part of the surface current spectrum, decomposed into entire-domain and orthogonal basis functions, while the invisible part of the spectrum stems from the solution of the unmodulated sheet problem. The EFIE is then inverted to obtain the sheet impedance, which is constrained to be anti-Hermitian, as required for implementation with lossless patches. The efficiency of the method relies on the precomputation of the reaction integrals between three functions: basis functions for currents and impedances and testing functions for fields. The formulation is presented first for the scalar (isotropic) MTS case and then generalized to the tensorial (anisotropic) MTSs. Several radiation patterns are presented and designed successfully. A full-wave method-of-moment code is used to validate the designed MTSs IBC. [ABSTRACT FROM AUTHOR]

The experimental validation of a Ku-band dual-circularly polarized (CP) broadside-beam metasurface (MTS) antenna is presented. A radially modulated anisotropic single-layer MTS has been synthesised employing subwavelength elliptical slotted metallic patches printed on top of a thin Arlon grounded substrate. In the structure, two decoupled phase-matched transverse magnetic and transverse electric surface waves (SWs) are excited, which interact with the modulated surface leading to a CP broadside radiation. Two different orthomode transducers have been designed to excite the SWs with orthogonal polarization and equal amplitude. The first feeding system is composed of a metallic stepped septum inside an air-filled square waveguide. A conical section is included to match the output port of the square waveguide with the terminal, dielectric filled circular waveguide. The second feed is much more compact and efficient, and it is composed of a circular waveguide completely filled by a dielectric. Depending on the input port excited on the feeds, two TE11 modes are excited with ±90° phase shift, which determine the right-hand or left-hand sense of the broadside beam generated by the MTS. Manufacturing details of the MTS and excitations are given, and the measurements are compared with the simulation results. Finally, conclusions are drawn. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper presents the design of a modulated metasurface (MTS) antenna capable to provide both right-hand (RH) and left-hand (LH) circularly polarized (CP) boresight radiation at Ku-band (13.5 GHz). This antenna is based on the interaction of two cylindrical-wavefront surface wave (SW) modes of transverse electric (TE) and transverse magnetic (TM) types with a rotationally symmetric, anisotropic-modulated MTS placed on top of a grounded slab. A properly designed centered circular waveguide feed excites the two orthogonal (decoupled) SW modes and guarantees the balance of the power associated with each of them. By a proper selection of the anisotropy and modulation of the MTS pattern, the phase velocities of the two modes are synchronized, and leakage is generated in broadside direction with two orthogonal linear polarizations. When the circular waveguide is excited with two mutually orthogonal TE11 modes in phase–quadrature, an LHCP or RHCP antenna is obtained. This paper explains the feeding system and the MTS requirements that guarantee the balanced conditions of the TM/TE SWs and consequent generation of dual CP boresight radiation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

The design and experimental validation of a wide scanning dome antenna with reduced profile is presented. The antenna is based on the combination of a planar phased array with limited scanning capabilities and a dielectric lens which allows to broaden the field of view. The angular variation of the scan loss can be almost arbitrarily designed if no constraint is imposed on the size of the dielectric lens. However, the focus of this article is on the size minimization of the dome as required for applications where the form factor is critical. Therefore, a lower boundary of the height of the dome is derived and imposed as a design constraint. The antenna is analyzed using in-house ray tracing and physical optics software tools. It is shown that, when the array is combined with the dielectric dome, a significant directivity enhancement can be achieved for wide scanning. A demonstrator of the lens is designed, manufactured and combined with an available phased array working in $Ku$ -band. The experimental tests confirm the theoretical predictions, validating the analysis tools, and show a scanning range of 70° in all scanning planes over a 15% bandwidth. The directivity is enhanced by approximately 2 dB at the limits of the scanning range compared to the standalone illuminating array. The active element pattern is rotationally symmetric, thus, the radiation performance is almost independent on the scanning plane. Moreover, the dielectric lens allows to preserve the cross-polarization performance of the illuminating array without adding a significant contribution. [ABSTRACT FROM AUTHOR]

Hepatitis E is an emerging disease in industrialized countries. The food-borne transmission of hepatitis E virus (HEV) is associated principally with products derived from the domestic pig, the wild boar, and deer; however, few quantitative data are available on HEV loads in animals used in food production. This study assessed HEV occurrence, viral load and genetic variability in wild boar hunted for domestic consumption in the district of Viterbo (Central Italy) where high anti-HEV IgG seroprevalence values are reported in humans. A total of 332 liver and 69 intestine samples were obtained from wild boar hunted between 2011 and 2014. The liver tissue in 54 of the animals (16.3%) was HEV-positive. Viral loads in quantifiable liver samples (n = 29) ranged between 3.2 × 102 and 3.8 × 105 genome copies (g.c.)/g with a mean value of 1.85 × 104 g.c./g. A statistically significant positive correlation was found between viral concentration in liver and intestinal tissue, though mean viral load in the intestines was lower (3.13 × 103 g.c./g). Twenty-six samples were characterized molecularly as genotype 3 (G3) and four subtypes (a, c, f and l) were detected. Finally, twelve samples with near identical sequences were identified as G3 but could not be assigned to any of the known subtypes, and could therefore represent a potentially new subtype. • HEV RNA prevalence in the livers of 332 wild boar hunted for domestic consumption in Central Italy was 16.3%. • The average viral load in quantifiable samples was 3.8 × 105 HEV g.c./g in liver and 3.13 × 103 g.c./g in intestine. • Four G3 subtypes (a, c, f and the putative subtype l) were detected in the HEV-positive animals. • A G3 sequence that could not be assigned to any known subtype was obtained from several samples. [ABSTRACT FROM AUTHOR]

Risk assessment, environmental monitoring, and the disinfection of water systems are the key elements in preventing legionellosis risk. The Italian Study Group of Hospital Hygiene of the Italian Society of Hygiene, Preventive Medicine, and Public Health and the Italian Multidisciplinary Society for the Prevention of Health Care-Associated Infections carried out a national cross-sectional survey to investigate the measures taken to prevent and control legionellosis in Italian hospitals. A multiple-choice questionnaire was developed, comprising 71 questions regarding hospital location, general characteristics, clinical and environmental surveillance, and control and preventive measures for legionellosis in 2015. Overall, 739 hospitals were enrolled from February to June 2017, and 178 anonymous questionnaires were correctly completed and evaluated (response rate: 24.1%). The survey was conducted using the SurveyMonkey® platform, and the data were analyzed using Stata 12 software. Of the participating hospitals, 63.2% reported at least one case of legionellosis, of which 28.2% were of proven nosocomial origin. The highest case numbers were reported in the Northern Italy, in hospitals with a pavilion structure or cooling towers, and in hospitals with higher numbers of beds, wards and operating theaters. Laboratory diagnosis was performed using urinary antigen testing alone (31.9%), both urinary antigen testing and single antibody titer (17.8%), or with seroconversion also added (21.5%). Culture-based or molecular investigations were performed in 28.8% and 22.1% of the clinical specimens, respectively. The water systems were routinely tested for Legionella in 97.4% of the hospitals, 62% of which detected a positive result (> 1000 cfu/L). Legionella pneumophila serogroup 2–15 was the most frequently isolated species (58.4%). The most common control measures were the disinfection of the water system (73.7%), mostly through thermal shock (37.4%) and chlorine dioxide (34.4%), and the replacement (69.7%) or cleaning (70.4%) of faucets and showerheads. A dedicated multidisciplinary team was present in 52.8% of the hospitals, and 73% of the hospitals performed risk assessment. Targeted training courses were organized in 36.5% of the hospitals, involving nurses (30.7%), physicians (28.8%), biologists (21.5%), technicians (26.4%), and cleaners (11%). Control and prevention measures for legionellosis are present in Italian hospitals, but some critical aspects should be improved. More appropriate risk assessment is necessary, especially in large facilities with a high number of hospitalizations. Moreover, more sensitive diagnostic tests should be used, and dedicated training courses should be implemented. [ABSTRACT FROM AUTHOR]

This paper presents two methods for the efficient evaluation of the power balance in circular metasurface (MTS) antennas implementing arbitrary modulated surface impedances on a grounded dielectric slab. Both methods assume the surface current in the homogenized MTS to be known. The first technique relies on the surface current expansion with Fourier-Bessel basis functions (FBBF) and proceeds by integration of the Poynting vector on a closed surface. The second method is based on the evaluation of the residue of the electric field spectrum at the surface-wave (SW) pole, and is demonstrated by using a current expansion in Gaussian ring basis functions (GRBF). The surface current expansions can be directly obtained either by analyzing the antenna with a Method of Moments (MoM) tool for homogenized MTSs based on FBBF or GRBF, or derived by a projection process. From there, the power contributions, namely the total power delivered by the feed, the radiated power, the SW power, and the Ohmic power losses in the dielectric are computed. Several efficiency metrics are presented and discussed: tapering efficiency, conversion efficiency, loss factor, and diffraction factor. Since the MTS apertures at hand are leaky-wave (LW) antennas, the designer must find a compromise between the aperture efficiency and the conversion efficiency. This requires accurate and fast computational techniques for the efficiency. The present paper demonstrates for the first time that the efficiency of MTS antenna devices can be accurately evaluated in a few minutes. The compromise that should be made during the design process between the tapering efficiency and the conversion efficiency is highlighted. The impact on the efficiency of isotropic versus anisotropic MTS, uniform versus non-uniform modulation index, is analyzed. An excellent agreement is obtained between both approaches, commercial software, and experimental data. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]