A. Freni

Fast Analysis of Large Finite Arrays With a Combined Multiresolution—SM/AIM Approach

We present a synthesis of the sparse matrix/adaptive integral method (SM/AIM) and the multiresolution (MR) approach for the analysis of electrically large finite arrays, with planar or 3-D radiating elements; the two methods were separately introduced previously. The use of the MR has the effect of a preconditioner and speeds up the convergence rate of the SM/AIM of almost two orders of magnitude, with a total reduction of the numerical complexity with respect to the standard MoM of almost three orders of magnitude

Fast-Factorization Acceleration of MoM Compressive Domain-Decomposition

Domain-decomposition (DD) for Integral Equation can be achieved by aggregating standard basis functions into specialized basis functions on each sub-domain; this results in a strong compression of the MoM matrix, which allows an iteration-free (e.g., LU decomposition) solution also for electrically large problems. Fast matrix-vector product algorithms can be used in the matrix filling and compression process of the employed aggregate-functions approach: this hybrid approach has received considerable attention in recent literature. In order to quantitatively assess the performance, advantages and limitations of this class of methods, we start by proposing and demonstrating the use of the Adaptive Integral Method (AIM) fast factorization to accelerate the Synthetic Function eXpansion (SFX) DD approach. The method remains iteration free, with a significant boost in memory and time performances, with analytical predictions of complexity scalings confirmed by numerical results. Then, we address the complexity scaling of both stand-alone DD and its combined use with fast MoM; this is done analytically and discussed with respect to known literature accounts of various implementations of the DD paradigm, with nonobvious results that highlight needs and limitations, and yielding practical indications.

An Efficient Technique for the Analysis of Large Multilayered Printed Arrays

In this letter, we present an efficient technique based on the extension of the adaptive integral method (AIM) that allows the full-wave analysis of electrically large multilayered printed arrays that have one or more planar metallizations and vertical conductors. The array patches can be of arbitrary shape and orientation and are modeled with subdomain triangular basis functions. This method makes use of a 2D-FTT/CG scheme, reducing the CPU time per iteration to O(N log2N) and the memory requirement to O(N).

Generalized Wait-Hill formulation analysis of lumped element periodically-loaded orthogonal wire grid generic frequency selective surfaces

By combining the work of J. R. Wait on a periodically loaded vertical wire grid and the work of D. A. Hill and J. R. Wait on a wire mesh, a novel generalized formulation, the Wait-Hill formulation, is obtained for the analysis of lumped-element periodically-loaded orthogonal wire grid generic frequency selective surfaces. The Wait- Hill formulation is simple and not restricted by the miniaturization assumption of current approximate simple methods for the analysis of loaded and unloaded wire grids. The results of the Wait-Hill formulation are shown to agree well with those of a commercial software.

An efficient technique for the analysis of reflectarrays

In this paper, we present an efficient technique based on the extension of the Adaptive Integral Method (AIM) that allows the full-wave analysis of microstrip reflectarrays. The reflectarray patches can have arbitrary shape and orientation and are modelled with subdomain triangular basis functions. The method makes use of a 2D-FTT/CG scheme, reducing the CPU time per iteration to 0(N logN) and the memory requirement to O(N).

Multiscale Analysis of Large Complex Arrays

Array modeling issues are challenging, since they involve large structures (in terms of the wavelength), but also fine details that require much-smaller than wavelength discretizations, and that dominate the frequency response of input parameters.

Comparison between different types of green's function factorization for the BMIA/AIM method

Three different formulations that allow to extend the BMIA/AIM method to the analysis of large dielectric stratified structures are introduced. These techniques lead to an approximate form of the multilayer Greens function, valid in the region where the thickness of the substrate can be considered small compared to its transverse dimension. This approximate form results as the product of three terms: two dependent by the source and observation longitudinal position, the other by its transverse distance. The first technique makes use of a suitable description of the Greens function in terms of discrete complex images. The remaining ones deal with the evaluation of the Greens function along the steepest descent path integration and a least-squares interpolation formulation, respectively.

Application of Wait's Formulation to Connected Array Antennas

Waits formulation on plane-wave scattering from wire grids is adapted, for the first time, to the electromagnetic analysis of lumped-element periodically loaded vertical wire-grid connected array antennas. Starting from this formulation, a novel analytical expression for the scan impedance of the array is derived, assuming an infinitesimal lumped element. We also report that as the period decreases and the wavelength increases, there is a simple relation between the scan impedance of the connected array antenna and the transmission-line equivalent circuit impedance of the lumped-element periodically loaded vertical wire-grid frequency selective surface. Consequently, to reduce the variation of the resonance frequency of the scan impedance with the scan angle, we employ the concept of adding an appropriate lumped element inductance to stabilize the resonance frequency of the frequency selective surface.

Estimation of the Electric Field Generated by Power Lines With the Adaptive Integral Method

The electric field generated by power lines is usually evaluated by a simple 2-D model. Due to the presence of buildings or other objects near the power line, measurements are often in disagreement with the model. In this letter, the adaptive integral method (AIM) is used to analyze a power line in a real environment. The presence of a conducting ground plane, as well as a planar dielectric interface, is also efficiently built into the algorithm.

Design, Optimization and Analysis of Broadband Reflectarray Antennas

This paper addresses the design of a broadband reflectarray which takes advantage of the introduction of a suitable non-conventional shape radiating element to assure a large gain bandwidth. The element shape presents sufficient degrees of freedom to compensate the frequency variation of the differential spatial phase delay even when single-layer printed patches are employed.