Edge diffraction by right-angled dielectric wedge

Rigorous asymptotic diffracted fields from a right-angled dielectric wedge are obtained for plane wave incidence. A correction field to the physical optics approximation is derived from a dual series equation amenable to simple numerical calculation. The edge-diffracted cylindrical wave pattern is calculated and shown.     

Beam scattering by a right-angled impedance wedge

Following earlier developments, a uniform asymptotic solution for two-dimensional high frequency scattering by a right-angled impedance wedge is presented. The wedge supports surface waves on both faces and numerical examples show the relative significance of these surface waves for different surface parameters, source directivities and positions of source and receiver. Surface parameters extracted from experimental data for buildings are used to show that for near grazing incidence surface waves can have a very significant effect along the direction of specular reflection even in the far field. These results should be important in urban propagation modeling.     

Scattering by right angle dielectric wedge

An asymptotic solution of electromagnetic waves scattered by a right-angled dielectric wedge for plane wave incidence is obtained. Scattered far fields are constructed by waves reflected and refracted from dielectric interfaces (geometric-optical fields) and a cylindrical wave diffracted from the edge. The asymptotic edge diffracted field is obtained by adding a correction to the edge diffraction of physical optics approximation, where the correction field in the far-field zone is calculated by solving a dual series equation amenable to simple numerical calculation. The validity of this result is assured by two limits of relative dielectric constantvarepsilonof the wedge. The total asymptotic field calculated agrees with Rawlins' Neumann series solution for smallvarepsilon, and the edge diffraction pattern is shown to approach that of a perfectly conducting wedge for largevarepsilon. Calculated far-field patterns are presented and the accuracy of physical optics approximation is discussed.     

Electromagnetic diffraction of an obliquely incident plane wave bya right-angled anisotropic impedance wedge with a perfectly conductingface

The diffraction of an arbitrarily polarized electromagnetic plane wave obliquely incident on the edge of a right-angled anisotropic impedance wedge with a perfectly conducting face is analyzed. The impedance tensor on the loaded face has its principal anisotropy axes along directions parallel and perpendicular to the edge, exhibiting arbitrary surface impedance values in these directions. The proposed solution procedure applies both to the exterior and the interior right-angled wedges. The rigorous spectral solution for the field components parallel to the edge is determined through the application of the Sommerfeld-Maliuzhinets technique. A uniform asymptotic solution is provided in the framework of the uniform geometrical theory of diffraction (UTD). The diffracted field is expressed in a simple closed form involving ratios of trigonometric functions and the UTD transition function. Samples of numerical results are presented to demonstrate the effectiveness of the asymptotic expressions proposed and to show that they contain as limit cases all previous three-dimensional (3-D) solutions for the right-angled impedance wedge with a perfectly conducting face     

Scattering by an infinite wedge with tensor impedance boundaryconditions-a moment method/physical optics solution for thecurrents

Plane wave scattering by an infinite, two-dimensional wedge whose faces are characterized by impedance tensors is discussed. A combination of the moment method (MM) and physical optics (PO) is used to obtain a solution for the equivalent electric currents. The currents near the edge on each face are expanded with a set of basis functions consisting of pulse functions, defined on a meshed region, plus a function spanning the whole face. The currents outside the meshed region are taken to be the sum of physical optics currents, taken to be known, plus the whole-face basis function current. Expressing the equivalent magnetic currents in terms of the electric currents through the impedance tensors, the expansion coefficients for the electric current expansion are determined through an MM solution of the magnetic field integral equation. Sample results for wedges with isotropic and anisotropic face impedances are presented     

Scattering from finite by infinite arrays of slots in a thinconducting wedge

The radar scattering from a finite by infinite array of slots cut into a thin conducting wedge is considered. The wedge is formed by taking a thin ground plane and applying a bend to create a sharp edge which is parallel to the columns of slots in the infinite axis. Results are derived for thin linear slots whose major axes are either parallel or perpendicular to the edge. A hybrid moment method and geometrical theory of diffraction approach is used, with magnetic current expansion functions defined using Floquet's theorem on single columns of slots. Predictions generally agree with scattering measurements of finite by finite array physical models with monostatic patterns taken in a plane orthogonal to the sharp edge     

Scattering of electromagnetic pulse waves by conducting wedge in uniaxially anisotropic plasma

Asymptotic expansion for the transient response of radiation fields due to electric dipole located above the conducting wedge with an arbitrary angle embedded in a simple plasma is derived by using the saddle point method of integration. The transient time, which is defined as the time required to reach steady state, is discussed for various kinds of wedge angles and plasma frequencies.     

Representation of imperfect dielectric materials by an equivalent circuit

A simple equivalent two-terminal electrical network that represents, over a wide frequency range and with sufficient accuracy, the dielectric properties of imperfect dielectric materials is given. The use of this network is illustrated with one of its applications in the mining industry, namely the determination of the concentration of metal in metallic ores.     

High-frequency scattering by an isorefractive wedge with theparabolic equation method

The parabolic equation (PE) method is applied to the problem of the high-frequency scattering from a diaphanous wedge, that is, a wedge made of a material which is isorefractive with respect to the surrounding medium, illuminated by a plane wave or by a line current parallel to the edge. The proposed approach is able to handle any wedge aperture and incidence angle and presents some novelties that allows overcoming the problems arising in the numerical solution of the parabolic equation applied to penetrable wedges     

Scattering by an Arbitrary Array of Parallel Wires

Equations are developed for the scattering pattern of an arbitrary array of parallel wires. The wires are assumed to be infinitely long, perfectly conducting, and very small in diameter in comparison with the wavelength. The incident wave is assumed to be TM with respect to the wire axis, but it may have normal or oblique incidence on the wires. The solution includes the interaction effects among all the wires. The far-field scattering patterns are presented graphically for plane arrays, circular arrays, semicircular arrays, square arrays, and other configurations. If a sufficiently great number of wires is present, it is shown that the scattering pattern approaches that of a solid conducting cylinder of the same cross-section shape as the wire-grid array.     

Loaded horizontal antenna over an imperfect ground

The Fresnel reflection coefficient technique is employed to establish anE-field integral equation for the antenna current. A resistive loading of the formLambda(x) = Lambda_{0}/(1 - |x|/L)is used to load the antenna. An optimization technique is discussed for determining the value of critical loadingLambda_{0}^{c}, which enforces a traveling wave current on the antenna. Results are given for the critical loading parameters, antenna currents, input impedances and radiation patterns versus different antenna dimensions and ground permittivities and conductivities. Some representative time-domain results for such loaded antennas are also included.     

Diffraction by an arbitrary-angled dielectric wedge. I. Physicaloptics approximation

A complete form is presented of the physical optics solution to diffraction by an arbitrary dielectric wedge angle with any relative dielectric constant in cases of both E- and H-polarized plane waves incident on one side of two dielectric interfaces. The solution, which is obtained by performing the physical optics (PO) approximation to the dual integral equation formulated in the spatial frequency domain, is constructed by the geometrical optics terms, including multiple reflection inside the wedge and the edge diffracted field. The diffraction coefficients of the edge diffracted field are represented in a simple form as two finite series of cotangent functions weighted by the Fresnel reflection coefficients. Far-field patterns of the PO solutions for a wedge angle of 45°, relative dielectric constants 2, 10, and 100, and an E-polarized incident angle of 150° are plotted in figures, revealing abrupt discontinuities at dielectric interfaces     

Scattering of an Electromagnetic Pulse by a Moving Wedge

The paper is concerned with the analysis of 2-D scattering of an electromagnetic (EM) pulse by a perfectly conducting wedge moving with a relativistic velocity in a free space. The incident signal is described by a Dirac delta function. Analytical solution to this scattering problem is found, and its physical interpretation is given. The field representation, valid for all scatterer velocities, is then simplified to the case of moderate and low velocities, appropriate for practical applications.     

Scattering by an infinite array of multiple parallel strips

The transverse electric (TE) and transverse magnetic (TM) electromagnetic scattering solutions for an infinite array of multiple parallel strips are considered. The solution is found using the perturbational form of the modified residue calculus technique (MRCT). In particular, the solution is found from the canonical problem of an infinite periodic array of semi-infinite parallel plates. Numerical results are presented and discussed. In addition, numerical results are given for a polarizer application.     

Scattering by an infinite periodic array of microstrip elements

An analysis of the scattering by an infinite periodic array of microstrip disks is made using a Galerkin solution of a vector integral equation. The solution is examined for convergence and compared with theory and experiment. The solution is used to minimize the loss and maximize the bandwidth of the element in a reflectarray configuration.     

Scattering by a rectangularly corrugated surface: an approximatetheory

We address the problem of the scattering of a plane, TM-polarized electromagnetic wave by a two-dimensional rectangularly corrugated surface. The height of the corrugation is measured by a characteristic length D and its period by Λ. We take the ordering of these scales to be D~Λ~λ where λ is the wavelength of the incident wave. We apply a radiation condition (strictly valid only in the far-field) in the aperture above a rectangular notch. This approximation allows the determination of an explicit representation of the reflection coefficients, the scattered field, and the field within a corrugation. Numerical results are presented which are in excellent agreement with a published finite difference approximation for diffraction gratings     

Scattering of plane waves by an anisotropic dielectric half-plane

Scattering of plane waves by a semi-infinite anisotropic thin dielectric layer is investigated, which can be considered as an example for electromagnetic energy absorbing materials. A pair of second-order boundary conditions is used to simulate an anisotropic thin dielectric layer as an infinitesimally thin sheet. Formulation is based on the Fourier integral transform technique, which reduces the scattering problem to two decoupled scalar Wiener-Hopf equations. Diffracted, reflected, and transmitted field terms are evaluated by using the Wiener-Hopf solutions that is obtained by the standard method. The uniqueness of the solution is satisfied by imposing an edge constraint in addition to the classical edge condition     

Scattering by an indentation satisfying a dyadic impedance boundarycondition

We derive a pair of boundary integral equations for the problem of scattering of an electromagnetic wave by an indentation in a perfectly conducting screen. The wall of the indentation obeys a dyadic impedance boundary condition. The unknowns are the electric current density on the wall of the indentation and the total tangential magnetic field in the opening of the indentation. We also derive integral representations for the fields everywhere in free space, including the far-field region. In all cases, the integrals involved extend over finite surfaces only