The need for a corner diffraction coefficient in a UTD scheme arises when the leading edge diffracted field experiences a discontinuity as it occurs when the diffraction point disappears from an edge or changes abruptly its location from one edge to the other. The solution proposed will be used to weigh the plane wave spectrum located at a finite distance from the vertex. Also obtained is the asymptotic evaluation of the spectral integrals and for simplicity, the scalar case is treated in this paper and the formulation for hard boundary conditions given explicitly.

Two leading high frequency theories have provided very effective tools for engineering purposes namely the geometrical theory of diffraction (GTD) especially in its uniform extension (UTD) and the physical theory of diffraction (PTD). An incremental theory of diffraction has been developed which provides a unified framework for describing high frequency phenomena. The electromagnetic scattering from planar structures is investigated in order to demonstrate the validity of the incremental theory of diffraction (ITD).

A high-frequency description of the scattering from complex structures that exhibits surface discontinuities such as edges and vertices, is of importance in a wide variety of practical applications. In this paper, a first order, high-frequency solution for the scattering by a corner is presented. The author's formulation is based on the Incremental Theory of Diffraction (ITD), which has been recently developed.

The shielding effectiveness of a corrugated thick screen is theoretically and experimentally investigated. This screen consists of a half-plane of finite thickness in which corrugations are etched on the smaller side. This structure provides a significant attenuation in the shadow region for both polarizations of the incident field; thus, it can be effectively used for protecting apparatuses from radiating interference as well as for decoupling nearby operating antennas. The shielding properties of the screen are described by a high-frequency formulation that involves dosed-form expressions. An experimental setup at X band has been arranged to test the effectiveness of a corrugated screen; the field in the shadow region is compared with that of a screen without corrugations. The experimental results compare very well with those obtained by the high-frequency expressions.

A closed form, high-frequency solution for describing double diffraction mechanism at a pair of parallel wedges, when they are illuminated by a spherical wave is obtained using a spherical waves spectral representation of the first order diffracted field from each wave. In this solution, the case of two wedges sharing a common face is explicitly considered. Numerical calculations show that the present high frequency formulation fails so gracefully that it gradually blends into the solution of a single wedge when the distance between the two edges vanishes. This property is very significant in the analysis of the shadowing effects of thick screen.

A high-frequency solution is presented for the scattering in the near zone by a pair of coplanar skew edges when they are illuminated by a source at a finite distance. The solution is obtained by using a spherical-wave spectral representation of the first-order diffracted field from each edge. The final closedform asymptotic solution includes terms up to the second order. It is shown that this second-order contribution is of the same order as the first one in overlapping transition regions. Moreover, the solution is cast in a convenient form, which is also directly applicable to treat the case when the two edges share a common face for both soft and hard boundary conditions. By choosing appropriate reference systems, the formulation for the scalar case is directly used to construct the solution of the more general electromagnetic problem for an arbitrarily polarized incident field. Numerical results are presented and discussed. © 1997 IEEE.

Incremental diffraction coefficients at the edge of a circular horn (CH) are derived on the basis of the Incremental Theory of Diffraction (ITD). The resulting distributed diffracted field contributions are used to predict mode radiation in the near zone, as well as to the reciprocal problem of EM coupling of a spherical wave into the CH. Second order, incremental diffraction contributions are also included to preserve accuracy at aspects below the aperture plane. For simplicity purposes, the analysis is restricted to the scalar case, with hard boundary conditions on the walls. Thus, guidelines are provided for the more general EM case.

Asymptotic, closed form expressions of the fringe currents of the plane angular sector of a plane wave far-field regime are derived using the Incremental Theory of Diffraction (ITD). Numerical results show that ITD is more accurate than the Uniform Theory of Diffraction. A double diffracted field is found to occur at a shadow boundary line equal to 52°.

A problem of a semi-infinite array of line sources located on a perfectly conducting half-plane has been studied by using a Floquet modes approach. This approach overcomes the slow convergence of the direct summation of the space fields radiated by each element of the array. The formulation presented can be extended to the 3D case.

A closed form, high-frequency solution is presented for the scattering in the near zone by a semi-infinite thick screen, when it is illuminated by a line source at finite distance. This solution is derived for a thick screen with perfectly conducting side walls, and either perfectly conducting or artificially soft boundary condition on the top face joining the two wedges. This last condition is practically obtained by etching on this face a quarter of wavelength deep corrugations with a small periodicity with respect to the wavelength. Owing to the particular properties of the artificially soft surface, a strong decoupling effect in the shadow region is achieved for both polarizations; thus, an effective shielding from undesired interferences is obtained.