Alberto Toccafondi

Tomographic Reconstruction of Rainfall Fields through Microwave Attenuation Measurements

Abstract A new method is presented for estimating the space-time rainfall intensity distribution at ground level over a limited area. This is based on a tomographic technique that exploits the relationship between microwave attenuation and rainfall intensity. At each time step, the spatial distribution of rainfall intensity is calculated from a set of path-integrated microwave attenuation measurements, performed over the monitored area. A set of bilinear basis functions is used to reconstruct the rainfall space distribution from discrete samples. A recursive optimization technique is applied to solve the ill-conditioned system of linear algebraic equations providing the searched solution at each time stop, thus, obtaining an estimate of space-time distribution of rainfall intensity. This method is analyzed using computer simulated data, and various results are shown that validate the proposed tomographic technique. In particular a rainfall event is simulated over a 20 × 20 km2 plane area, assuming that pr...

An incremental theory of diffraction: electromagnetic formulation

A scalar formulation of the incremental theory of diffraction (ITD) has been introduced by Tiberio and Maci (see ibid., vol.42, no.5, 1994), which provides a self-consistent, high-frequency description of a wide class of scattering phenomena, within a unified framework. In this paper, this method is extended to electromagnetic problems. The total field is represented as the sum of a generalized geometrical optics field plus incremental diffracted field contributions. Explicit dyadic expressions of incremental diffraction coefficients are derived for wedge-shaped configurations. The formulation of the field is uniformly valid at any incidence and observation aspects, including caustics and shadow boundaries of the corresponding ray field description. Numerical results are presented and compared with those obtained from different techniques. >

Incremental theory of diffraction: a new-improved formulation

In this paper, a general systematic procedure is presented for defining incremental field contributions. They may provide effective tools to describe a wide class of scattering and diffraction phenomena at any aspect, within a unitary, self-consistent framework. This procedure is based on a generalization of the incremental theory of diffraction (ITD) localization process for uniform cylindrical, local canonical problems with elementary source illumination and arbitrary observation aspects. In particular, it is shown that the spectral integral formulation of the exact solution for the local canonical problem may also be represented as a spatial integral convolution along the longitudinal coordinates of the cylindrical configuration. Its integrand is then directly used to define the relevant incremental field contribution. For the sake of convenience, but without loss of generality, this procedure is illustrated for the case of local wedge configurations. Also, a specific suitable asymptotic analysis is developed to derive new closed form high-frequency expressions from the spectral integral formulation. These expressions for the incremental field contributions explicitly satisfy reciprocity and are applicable at any incidence and observation aspect. This generalization of the ITD localization process together with its more accurate asymptotic analysis provides a definite improvement of the method.

High-frequency Green's function for a semi-infinite array of electric dipoles on a grounded slab .I. formulation

A uniform, high-frequency solution is presented for the electromagnetic field radiated at finite distance by a semi-infinite array of elementary electric dipoles placed on an infinite grounded dielectric slab. This solution is useful for the efficient analysis of printed arrays. The field is represented in terms of a series encompassing propagating and evanescent truncated Floquet waves together with their corresponding diffracted rays, which arise from the edge of the array. The high-frequency formulation also includes surface and leaky wave contributions excited at the array edge. The diffracted waves contain discontinuities which compensate the disappearance of surface, leaky and truncated Floquet waves at their pertinent shadow boundaries.

Mutual coupling between slots printed at the back of elliptical dielectric lenses

This paper presents calculations of the mutual admittance between two slots on a ground plane that are the primary feed of an elliptical dielectric lens antenna. This admittance may also be regarded as the basic constituent of a Galerkin method of moments formulation for the analysis of more complex feeding arrangements of slot antennas and coplanar waveguide circuits, it is found that the contribution of the reflection mechanisms inside the lens significantly affects the mutual admittance especially for H-plane coupling.

Diffraction at a plane angular sector

A closed form solution is presented for the scattering in the far zone by a vertex at the interconnection between the two edges of a plane angular sector, when it is illuminated by a plane wave. The solution is obtained as a superposition of simple interaction mechanisms between the two adjacent edges. The spectral representation of the field diffracted by the first edge is used to illuminate the second edge. The response of the latter is evaluated by applying the induction principle at the plane angular sector. In spite of the simplicity of this basic assumption, the resulting expressions recover in the pertinent directions the dominant edge ray field contributions, including second order diffraction mechanisms. The solution is cast in a very simple, compact matrix form, which explicitly satisfies reciprocity.

Efficient Algorithm for the Evaluation of the Physical Optics Scattering by NURBS Surfaces With Relatively General Boundary Condition

An adaptive integration algorithm is presented for the computation of the Physical Optics (PO) electric and magnetic field scattered by electrically large objects modeled by Non-Uniform Rational B-Splines (NURBS). The algorithm is the customization of a more general-purpose result that has been recently published. By using a unique formulation both impenetrable (e.g., impedance surfaces, coated conductors) as well as transparent thin sheet materials (e.g., thin dielectric panels, or frequency selective surfaces) are treated, via their Fresnel reflection and transmission coefficients. The PO radiation integral is evaluated over the NURBS parametric domain. Since most of the computer-aided geometric design (CAGD) tools are based on NURBS, the proposed algorithm allows a straightforward electromagnetic analysis of the structures by exploiting the standard available geometrical description, with no need of generating new geometrical models. Furthermore, the proposed adaptive sampling requires a number of integration points that is found to be drastically smaller than that resulting from standard Nyquist-based sampling integration algorithms. Such reduction of the sampling points is achieved by resorting to high-frequency technique concepts and allows a significant reduction of the CPU computational burden. Therefore the algorithm is efficient and particulary suitable for the electromagnetic characterization of real-life electrically large objects.

Compact meander line antenna for HF-UHF tag integration

In this paper a compact UHF meander line printed antenna, suitable for integration with HF-RFID transponder is presented. Simulated radiation pattern are in a good agreement with that of a typical planar dipole antenna. The results of the tests conducted on the final prototype obtained using both a UHF and a HF readers, were shown during the oral presentation.

Incremental diffraction coefficients for source and observation at finite distances from an edge

Recently, an incremental theory of diffraction (ITD) has been introduced which provides a self-consistent, highfrequency description of a wide class of scattering phenomena within a unified framework. Explicit expressions of the incremental diffracted field contributions have been obtained for a plane-wave illumination of wedge-shaped configurations and observation points at a finite distance from the incremental point. In this paper, this method is extended to treat the case when both the source and the observation point are at finite distance from the local incremental point along the edge. To this end, a spectral-domain approach is used to derive a spectral-integral representation for the incremental field contribution. The latter is asymptotically evaluated to find high-frequency closed-form expressions which are uniformly valid at any incidence and observation aspects, including caustics and shadow boundaries of the corresponding ray-field description. The expressions of the incremental diffraction coefficients explicitly satisfy reciprocity. Numerical results are presented and compared with those obtained from different techniques.

Compact load-bars meander line antenna for UHF RFID transponder

This paper presents a load-bars meander line dipole RFID tag antenna operating at European UHF Band. The meandered line dipole has been natural choice in order to provides small size, proper bandwidth and omnidirectional pattern in a plane perpendicular to the antenna plane. In order to allows a better control of the input impedance of the antenna, three inductively coupled loading bars have been introduced. It is found that the key parameters of the antenna such as loading bars spacing and width and meander step geometrical dimensions can be easily adjusted to obtain a very good match between antenna and IC.