Electromagnetic scattering by a straight thin wire

The traveling-wave energy, which multiply diffracts on a straight thin wire, is represented as a sum of terms, each with a distinct physical meaning, that can be individually examined in the time domain. Expressions for each scattering mechanism on a straight thin wire are cast in the form of four basic electromagnetic wave concepts: diffraction, attachment, launch, and reflection. Using the basic mechanisms from P.Ya. Ufimtsev (1962), each of the scattering mechanisms is included into the total scattered field for the straight thin wire. Scattering as a function of angle and frequency is then compared to the moment-method solution. These analytic expressions are then extended to a lossy wire with a simple approximate modification using the propagation velocity on the wire as derived from the Sommerfeld wave on a straight lossy wire. Both the perfectly conducting and lossy wire solutions are compared to moment-method results, and excellent agreement is found. As is common with asymptotic solutions, when the electrical length of wire is smaller than 0.2 λ the results lose accuracy. The expressions modified to approximate the scattering for the lossy thin wire yield excellent agreement even for lossy wires where the wire radius is on the order of skin depth     

A reflection ansatz for surfaces with electrically small radii of curvature

Uniform reflection coefficients are developed for two- and three-dimensional, edge-like, perfectly conducting surfaces in the deep lit region. The uniformity is with respect to the electrical size of the radii of curvature at the surface's specular point. This uniformity allows one to physically interpret the reflected field from a smooth surface as one of the radii of curvature approaches zero as a diffracted field. The coefficients are heuristically generated from the exact scattered field for a two dimensional parabolic cylinder with plane wave illumination. The significant variables in this solution are the radii of curvature at the specular point and the distance between the specular point and the incident shadow boundaries in the principal planes. The field prediction accuracy of these reflection coefficients are critically examined through comparisons with reflected fields extracted from scattered fields of canonical surfaces.     

Mixed-field hybrid FEM/BEM formulation for two-dimensional TEradiation and scattering by resistive strips

A new mixed-field, hybrid finite-element method (FEM) (E-field)/BEM (H-field) formulation is presented for modeling the two-dimensional (2-D) radiation and scattering from scatterers comprised with inhomogeneous materials including resistive cards and perfectly electrically conducting (PEC) strips for the TE polarization. Using the usual H-field formulation leads to the requirement for the use of a special gap element. The E-field formulation will result in a much more cumbersome BEM integral. The new mixed-field formulation retains the simplicity of the scalar formulation and is useful for problems which cannot be treated elegantly with the existing approach. The new formulation has been implemented into a 2-D FEM/BEM computer code. Numerical results obtained compare well to previously published results     

Transient scattering analysis for a circular disk

The backscattered fields of a perfectly conducting circular disk are analyzed from a transient signature viewpoint. The significant dominant scattering mechanisms are identified for both principal polarizations at a variety of angles. Particular attention is given to the edge wave. The backscattered field behavior due to an incident plane wave on a perfectly conducting disk is presented. Good agreement was obtained between the eigenfunction and geometric theory of diffraction solutions. The expected mechanisms from first-, second-, and third-order diffractions with an accurate edge wave representation are demonstrated through the use of transient signatures. The most significant error in the geometric theory of diffraction (GTD) solution occurs in time where the nonprincipal plane double diffraction term exists     

RCS measurement of small circular holes

The Rayleigh scattering from small circular holes in a thin screen was studied. The backscattered fields calculated from a dipole expansion were compared those from an exact solution and measurements for a single, electrically small hole. The backscatter from the holes is given by rather simple expansion where the first term is adequate for a good engineering solution. These expressions are within 1 dB of the exact solution for ka⩽0.96 for E-plane scattering and ka⩽0.69 for H-plane scattering when a is the hole's radius and k is the propagation constant     

Electromagnetic scattering by an inhomogeneous penetrable material with an embedded resistive sheet

This paper presents the method of moments (mom) formulation for the electromagnetic scattering by an inhomogeneous penetrable material with an embedded resistive sheet. Triangular surface facets and tetrahedral volume cells are used to discretize the scatterer allowing for greater flexibility in the geometric modeling of the material body. The formulation is very general in that it allows for a variety of material configurations : open or closed conducting surfaces, open or closed resistive (thin dielectric) surfaces, solid dielectric/ferrite material volumes, embedded conducting/resistive surfaces in material volumes, and partially embedded conducting/resistive surfaces (cladded materials). Results for a material coated resistive spherical shell and a material propeller blade are presented.     

Edge wave visualization

Scattering mechanisms that involve edge waves are addressed. The behavior of edge waves and their interaction with flat perfectly conducting plates are depicted in the time domain through a visualization of surface currents that flow on the surface, as an incident Gaussian pulse of energy washes over the surface. Viewing these surface currents allows a very clear physical interpretation and appreciation of the scattering process     

Parameter de-embedding accuracy dependency upon material sampledimensions

The sensitivity of the sample fit in rectangular waveguide fixtures is examined for constitutive parameter de-embedding. The sensitivity is characterized through a percent error figure between the de-embedded and known parameter values when an air gap exists between the sample and the side walls of the fixture. The de-embedding process assumed a completely filled waveguide in which rigorously calculated S parameters for material sample air gaps in either the E- or H-plane walls of the waveguide were used. The presence of an air gap was very noticeable for a E-plane gap. Commonly used gap correction factors provided limited improvement in reducing air gap related errors     

An investigation of new FETD/ABC methods of computation ofscattering from three-dimensional material objects

Finite-element time-domain (FETD) and absorbing boundary condition (ABC) methods for computation of scattering from three-dimensional (3-D) material objects are developed and investigated. The methods involve discrete-time FETD solution of the time-domain Helmholtz equation in a region that comprises the 3-D scatterer and its immediate vicinity. Coupling of the solution to the surrounding infinite space is achieved through the ABC. This FETD/ABC formulation is examined for a number of various geometries: sphere, plate, and ogive     

An additional physical interpretation in the Luneburg-Kline expansion

The Luneburg-Kline (LK) expansion provides an asymptotic representation of the reflected field from a smooth surface in inverse powers of k. The physical interpretation of the first term in the expansion has long been recognized. The physical significance of the second term is suggested here. Through analysis of the expansion for a parabolic, circular, and elliptic cylinders, further geometric information is seen other than the radius of curvature at the specular point. The other geometric information is the distance between the specular point and the incident shadow boundary.