91 research outputs found
A uniform geometrical theory of diffraction for vertices formed by truncated curved wedges
No full textA uniform geometrical theory of diffraction (UTD) ray analysis is developed for analyzing the problem of electromagnetic (EM) scattering by vertices at the tip of a pyramid formed by curved surfaces with curvilinear edges when illuminated by an arbitrarily polarized astigmatic wavefront. The UTD vertex diffraction coefficient involves various geometrical parameters such as the local radii of curvature of the faces of the pyramid, of its edges, and of the incident ray wavefront, and it is able to compensate for those discontinuities of the field predicted by the UTD for edges (i.e., geometrical optics (GO) combined with the UTD edge diffracted rays) occurring when an edge diffraction point lies at the tip or vertex. This provides an effective engineering tool able to describe the field scattered by truncated edges in curved surfaces within a UTD framework, as required in modern ray-based codes. Some numerical examples highlight the accuracy and the effectiveness of the proposed UTD ray solution for vertex diffraction
Uniform Ray Description for the PO Scattering by Vertices in Curved Surface With Curvilinear Edges and Relatively General Boundary Conditions
No full textA new high-frequency analysis is presented for the scattering by vertices in a curved surface with curvilinear edges and relatively general boundary conditions, under the physical optics (PO) approximation. Both, impenetrable (e. g., impedance surface, coated conductor) as well as transparent thin sheet materials (e. g., thin dielectric, or frequency selective surface) are treated, via their Fresnel reflection and transmission coefficients. The PO scattered field is cast in a uniform theory of diffraction (UTD) ray format and comprises geometrical optics, edge and vertex diffracted rays. The contribution of this paper is twofold. First, we derive PO-based edge and vertex diffraction coefficients for sufficiently thin but relatively arbitrary materials, while in the literature most of the results (especially for vertex diffraction) are valid only for perfectly conducting objects. Second, the shadow boundary transitional behavior of edge and vertex diffracted fields is rigorously derived for the curved geometry case, as a function of various geometrical parameters such as the local radii of curvature of the surface, of its edges and of the incident ray wavefront. For edge diffracted rays, such a transitional behavior is found to be the same as that obtained heuristically in the original UTD. For vertex diffracted rays, the PO-based transitional behavior is a novel result providing offers clues to generalize a recent UTD solution for a planar vertex to treat the present curved vertex problem. Some numerical examples highlight the accuracy and the effectiveness of the proposed ray description
The Uniform Geometrical Theory of Diffraction and Some of Its Applications
No full textKeller introduced his Geometrical Theory of Diffraction (GTD) in the 1950s. The Geometrical Theory of Diffraction development was revolutionary, in that it explained the phenomena of wave diffraction entirely in terms of rays for the first time, via a systematic generalization of Fermat's principle. In its original form, the Geometrical Theory of Diffraction exhibited singularities at and near ray-shadow boundaries and caustics. For practical applications, it is necessary to patch up the Geometrical Theory of Diffraction in such regions. Uniform asymptotic high-frequency methods overcome the failure of the Geometrical Theory of Diffraction inside those regions, and outside those regions they generally reduce to the Geometrical Theory of Diffraction. One such highly developed approach happens to be the Uniform Geometrical Theory of Diffraction (UTD). The present article focuses on some key Uniform Geometrical Theory of Diffraction developments in a semi-historical fashion, with a few typical applications to illustrate the power and utility of the Geometrical Theory of Diffraction/Uniform Geometrical Theory of Diffraction concept to solve practical problems
A collective UTD ray analysis for the radiation from conformal linear phased array antennas on large cylindrical surfaces
No full textOrigins of RFID concepts in early wireless-based scale model airborne antenna pattern measurements
No full textA uniform geometrical theory of diffraction for radiation by antennas on a smooth convex impedance surface
No full textModeling small antennas on large convex metallic surfaces with a very thin uniform material coating
No full textA collective UTD ray solution for the radiation from conformal linear antenna arrays on a large cylinder
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