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We describe an extension of the linear embedding via Green’s operators (LEGO) method to the solution of finite antenna arrays comprised of disconnected elements in a homogeneous medium. The ultimate goal is the calculation of the admittance matrix and the radiation pattern of the array. As the basic idea is the inclusion of an array element inside a LEGO electromagnetic brick, the first steptowards the solution consists of the definition and numerical calculation of hybrid scattering-admittance operators which extend the notion of scattering operators of equivalent currents introduced in the past. Then again, the combination of many bricks involves the usual transfer operators for the description of the multiple scattering between the bricks. Moreover, to reduce the size of the problem we implement the eigencurrents expansion. With the aid of a numerical example we discuss the validation of the approach and the behaviour of the total CPU time as a function of the elements forming the array.

The Adaptive Cross Approximation (ACA) algorithm has been used to compress the rank- deficient sub-blocks of the matrices that arise in the numerical solution of integral equations (IEs) with the Method of Moments. In the context of the linear embedding via Green's operator (LEGO) method — a domain decomposition technique based on IEs — an electromagnetic problem is modelled by combining "bricks" in turn described by scattering operators which, in many situations, are singular. As a result, macro basis functions defined on the boundary of a brick can be generated by applying the ACA to a scattering operator. Said functions allow compressing the weak form of the LEGO functional equations which then use up less computer memory and are faster to invert.

An enhanced version of the Linear Embedding via Green's Operators (LEGO) method is introduced to analyze complex 3-D metallic structures located inside a single electromagnetic (EM) brick. For the sake of computational efficiency and memory storage requirement the surface of the entire structure is divided into smaller sub-domains and over each pair of neighboring sub-domains is defined set of characteristic basis functions (CBFs). To compress the problem all CBFs which are associated with insignificant singular values are truncated. Various comparisons between the direct solution which solves Electric Field Integral Equation (EFIE) directly over the structure and LEGO approach using CBFs are shown to prove the concept.

Gaseous plasma antennas are devices that exploit partially or fully ionized gas to transmit and receive electro-magnetic waves, in contrast with conventional antennas that are only made by metal and dielectric materials. Since plasma discharge parameters, e.g. plasma density, can be tuned, plasma antenna properties can be changed dynamically; this constitutes a promising alternative to conventional metallic antennas for applications in which reconfigurability is desired. In this work, we report on the first steps toward the realization, and the characterization in terms of radiation pattern, and magnitude of the reflection coefficient of an early prototype of a gaseous plasma antenna in the UHF frequency range. Numerical investigations have supported the design of the setup, and helped in the evaluation of the the role of plasma density profiles in affecting the antenna properties.

Gaseous plasma antennas constitute a promising alternative to conventional metallic antennas for applications in which reconfigurability is desired. By tuning the plasma discharge parameters, e.g., plasma density, antenna properties can be changed dynamically. In this work we report on recent numerical investigations into the characteristics of a plasma antenna as a function of the plasma discharge parameters, viz., plasma density, and magnetostatic field. In addition, the effect of different gasses has been examined. We have used ADAMANT (Advanced coDe for Anisotropic Media and ANTennas) — a full-wave numerical tool based on integral equations — to assess the role played by plasma discharge parameters in shaping the radiation pattern, which is mainly determined by the plasma current distribution. The experimental characterization of the plasma discharge to be used as plasma antenna is briefly presented.

We present a full-wave numerical tool for the simulation of plasma antennas. The tool makes use of a hybrid formulation that allows treating the plasma with a Finite Element discretization, and the metallic parts with the Method of Moments. The finite element discretization is solved using a state-of-the-art sparse solver (MUMPS) in order to reduce the computational time at a minimum. The accuracy of the tool is tested by comparing the results obtained with it against those obtained with a benchmark code. Finally, a novel dual-mode plasma antenna is designed using the aforementioned tool.

We present the numerical parametric study of a reconfigurable plasma antenna array (PAA) composed of a metallic half-wavelength dipole and a set of cylindrical plasma discharges arranged in a planar square lattice. Our results, obtained with the linear embedding via Green’s operators (LEGO) method, indicate that beam-forming and beam-steering functionality can be achieved and controlled by appropriately choosing the number and position of the active plasma discharges around the dipole. Furthermore, we show that an external static magnetic field and the plasma density have a noticeable effect on the radiation pattern of the antenna.

For scattering by perfectly conducting objects in a two-dimensionally periodic setup we employ a surface-integral equation, the Ewald representation of the Green function, and the Method of Moments (MoM). For moderate-size matrices, we observe that the computation time is dominated by the computation of the matrix elements. By employing a multi-level decomposition of the Green function based on Lagrange interpolation on a Chebyshev grid, we demonstrate that the overall computation time can be reduced by 73% compared to the original MoM computation.

In the last years, increasing interest has grown on the synthesis of light-weight, miniaturized surfaces for light manipulation based on metamaterials. These surfaces can be easily integrated in photonic systems and they can be used as high numerical aperture lenses, light-deflection surfaces and polarization-dependent surfaces. All-dielectric nanoresonator metasurfaces are particularly promising to synthesize light manipulating devices. By simply adjusting the geometric parameters (height and diameter) of the dielectric particles, it is possible to tune the spectral positions of the electric and magnetic resonant modes. The overlap of these resonances allows to design metasurfaces exhibiting a transmission coefficient with unit-amplitude and arbitrary, spatially-variant phase distribution. Moreover, resorting to asymmetric cross-section resonators, it is possible to define metasurfaces with high-efficiency of cross-polarization. In this work, we exploit both properties of dielectric nanoresonators to design a high numerical aperture micro-lens and a thin linear-to-circular polarizer, both working in the visible range. Numerical simulations of the performances of the devices are reported.