1,720,998 research outputs found
An Incremental Theory of Diffraction. Electromagnetic formulation
No full textRecently, a scalar formulation of the incremental theory of diffraction (ITD) has been introduced, 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 rag field description. Numerical results are presented and compared with those obtained from different techniques
Diffraction at a plane angular sector
No full textA 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
Incremental diffraction coefficients for source and observation at finite distances from an edge
No full textRecently, 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. © 1996 IEEE
Diffraction coefficients at edges in artificially soft and hard surfaces
No full textIn this Letter, both uniform GTD and incremental diffraction coefficients at edge discontinuities in artificially soft and hard surfaces are obtained from the exact solution of the relevant canonical wedge configuration. Numerical results are presented for a dipole on the axis of an artificially soft disk
An incremental theory of diffraction for objects with local cylindrical shape
No full textIn this paper, a quite general systematic procedure is presented for defining incremental field contributions, that may provide effective tools for describing a wide class of scattering and diffraction phenomena at any aspect, within a unitary, self-consistent framework. This is based on a generalization of the localization process for cylindrical canonical problems with elementary source illumination and arbitrary observation aspects. In particular, it is shown that the spectral integral formulation of the exact solution may also be represented as a spatial integral convolution along the axis of the cylinder. Its integrand is then directly used to define the relevant incremental field contribution. This procedure, that will be referred to as a ITD (Incremental Theory of Diffraction) Fourier transform convolution localization process, is explicitly applied to both wedge and circular cylinder canonical configurations, to define incremental diffraction and scattering contributions, respectively. These formulations are asymptotically approximated to find closed form high-frequency expressions for the incremental field contributions. This generalization of the ITD localization process may provide a quite general, systematic procedure to find incremental field contributions that explicitly satisfy reciprocity and naturally lead to the UTD ray field representation, when it is applicable
Analysis of electromagnetic scattering by artificially soft discs
No full textAn analysis of the electromagnetic behaviour of corrugated artificially soft discs, illuminated by a vertical dipole, was carried out by using both numerical and asymptotic methods. The finite-difference time-domain method was used to find near-field distributions. This allows the consistency of the artificially soft model to be tested; furthermore, the near-field data are used to find the radiation pattern by using near-to-far-field transformations. The direct scattering in the far zone was also obtained by using edge integration of incremental diffraction coefficients; these are derived by applying the localisation process of the incremental theory of diffraction to a wedge with perfectly soft boundary conditions on one face and perfectly electric boundary conditions on the other. The effect of the corrugations is analysed in the far-field limit by comparison with a perfectly conducting disc
An incremental theory of double edge diffraction
No full textA novel general procedure for defining incremental field contributions for double diffraction at a pair of perfectly conducting (PEC) wedges in an arbitrary configuration is presented. The new formulation provides an accurate first-order asymptotic description of the interaction between two edges, which is valid both for skewed separate wedges and for edges joined by a common PEC face. It also includes a double incremental slope diffraction augmentation, which provides the correct dominant high-frequency incremental contribution at grazing aspect of incidence and observation. This new formulation is obtained by applying to both edges, the wedge-shaped incremental dyadic diffraction coefficients for single edge diffraction. The total doubly diffracted field is obtained from a double spatial integration along each of the two edges on which consecutive diffractions occur. It is found that this distributed field representation precisely recovers the doubly diffracted field predicted by the uniform theory of diffraction (UTD) and that may be applied to complement ray field methods close to and at caustics. It can be applied as well in all those situations in which a stationary phase condition is not yet well established. Numerical examples are presented and compared with those calculated from both Method of Moment solution and second-order UTD ray techniques. Excellent agreement was found in all cases examined
Recent advances in the Incremental Theory of Diffraction for Complex Source Point illumination
No full textThe accurate prediction of the far field radiated or scattered by large structures, such as large reflector antennas, requires efficient techniques for representing the illuminating field. Complex Source Points (CSP) inherently contain information about the source directivity, hence they can be used as the basis function to expand a given, but arbitrary, radiating wave field [1-3], such as the field incident on an antenna or a more general complex structure. As a consequence, a CSP field representation, when combined with the analytic continuation in complex space of typical ray-techniques such as the Geometrical and the Uniform Geometrical Theory of Diffraction (GTD/UTD), may provide a very efficient tool to estimate the fields radiated by large objects [4]. In this framework, an extension of the Incremental Theory of Diffraction (ITD) formulation for the scattering by wedges illuminated by CSP has been introduced [5], which essentially overcomes the typical impairments of the GTD/UTD ray techniques associated with possible ray caustics and with the difficulties of ray tracing in complex space. On the other hand, when dealing with the description of the field radiated by large structures, many of the existing electromagnetic codes resort to a Physical Optics (PO) representation also with an arbitrary incident field. It is however well known that the PO approach does not always produce accurate field predictions [6]. A significative augmentation of the PO field estimate can be achieved by including along the structure's edges a line integration of an incremental fringe field, that acts as a correction term for the field estimate. Several techniques have been published to derive these elementary contributions, leading to Physical Theory of Diffraction (PTD), Elementary Edge Waves/Incremental Length Diffraction Coefficient (EEW/ILDC), and ITD. In this work we discuss some recent advances in the incremental formulation for the field diffracted by edges in perfect electric conductor (PEC) objects when illuminated by a CSP beam expansion, with application to the analysis of large reflector antennas. A fringe formulation of the field diffracted by wedges with PEC faces when illuminated by a single CSP has been recently presented [7]. At each point on the edge the incremental fringe correction term is deduced from tangential canonical problems as the difference between the local ITD diffracted field [5] and an appropriate incremental end-point PO field (IEPO) scattered by the half-lit plane tangent to the edge [8]. The total spurious effects due to the presence of the edge are corrected by adiabatically distributing and integrating the local incremental fringe field coefficients along the line of the edges. This formulation yields more accurate predictions of the radiated field. For configurations in which several metallic edges are present and for grazing aspects of incidence and observation, the correct interactions between the edges in the problem need to be properly accounted for. Hence we introduce correct incremental double-diffraction coefficients for CSP illumination in the first-order fringe formulation [9]. These incremental coefficients have been derived by a proper analytical continuation of their real counterparts [10]. The formulation provides an accurate first-order asymptotic description of the interaction between two edges, which is valid both for skewed separate wedges and for edges joined by a common PEC face. It also includes a double incremental slope diffraction augmentation, which provides the correct dominant high-frequency incremental contribution at grazing aspects of incidence and observation. The total doubly-diffracted field is obtained from a double spatial integration along each of the two edges on which consecutive diffractions occur. In the application to the analysis of large reflector antennas the first-order fringe correction to the PO scattered fields tends to fail in those directions parallel to the aperture plane. Here, the addition of the incremental double diffracted field provides the correct estimation of the radiated field
Analysis and Optimization of Reconfigurable Intelligent Surfaces Based on S-Parameters Multiport Network Theory
No full textIn this paper, we consider a reconfigurable intel-ligent surface (RIS) and model it by using multiport network theory. We first compare the representation of RIS by using the impedance and scattering parameters, by proving their equivalence and discussing their distinct features. Then, we develop an algorithm for optimizing the RIS configuration in the presence of electromagnetic mutual coupling. We show that the proposed algorithm based on optimizing the scattering parame-ters results in better performance than existing algorithms based on optimizing the impedance parameters. This is attributed to the fact that small perturbations of the step size of the proposed algorithm result in larger variations of the scattering parameters, hence increasing the convergence speed of the algorithm
Design and analysis of a compact antenna for UWB RFID applications
No full textWe present an Ultra Wideband (UWB) antenna for RFID applications. The antenna is designed to comply with the European bandwidth requirements and to be integrated directly on the same board which is used by the UWB pulse generator. The proposed antenna has dipole-like characteristics concerning its radiation properties. Numerical results have shown good impedance matching without the need for any additional impedance matching sections, as well as good radiation properties which are suitable for UWB-RFID applications
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