Scattering by an infinite periodic array of thin conductors on a dielectric sheet

The solution to the problem of scattering of a plane wave by an infinite periodic array of thin conductors on a dielectric slab is formulated in this paper. Numerical results are given as well as a comparison of this theory with experimental data.     

Scattering of a plane electromagnetic wave by a linear array of cylindrical elements

An approximate method for numerically calculating the scattered field of a linear array of center-loaded cylindrical elements illuminated by a plane wave incident in theHplane of the array is described. To illustrate the use of the approximation technique, theH-plane scattered field of an eight-element model array is calculated for various conditions of impedance loading and illumination. From extensive calculations, it is found that theHplane scattered field of the array can be represented approximately by the product of the electric field scattered in the reflected direction and an interference factor. The interference factor is the equivalent of the complex array factor of the model array when excited with uniform amplitude and an element-to-element phase progression proportional to the sine of the angle of incidence of the illumination.     

Diffraction of a plane wave by a multiserial lattice located in a dielectric layer

A modified zero field method is applied to solve the 2D problem of scattering by a multiserial lattice. The lattice consists of perfectly conducting elements and is situated in a homogeneous dielectric layer. The system of integral equations is derived and formulas for calculating the reflection and transmission coefficients are obtained for various geometries of the lattice elements. To increase the efficiency of the algorithm work, both polar and elliptic coordinates are applied to choose the auxiliary contour on which the zero field condition is stipulated.     

Scattering of electromagnetic waves from nonlinear thin dielectric coatings

In this paper the reflection and diffraction properties of nonlinear thin dielectric coatings are investigated. A quite simple geometry consisting of two semi-infinite homogenous linear spaces separated by a non-linear coating is considered. An incident plane wave propagating along the z direction towards the nonlinear thin coating is taken. The nonlinear thin coating is divided into elementary sectors, within each one of which one propagating and one reflected wave exists. The boundary conditions are then applied in order to develop an efficient numerical alogirthm to study the properties of the nonlinear thin coating.     

Scattering from thin dielectric straps surrounding a perfectlyconducting structure

Dielectric straps can support very heavy targets and have low backscattering levels, especially at low frequencies (below 8 GHz); thus, they can be used effectively to support targets during backscattered field measurements. The scattered fields of nonmagnetic dielectric straps surrounding a perfectly conducting structure are presented, and the computed results are compared with experimental data. Empirical formulas for the strap scattered fields are also given. These formulas are good for general convex structures whose radii of curvature are large compared with the wavelength and are expected to give a reasonable estimate of the true backscattered fields from the dielectric straps when used as a target support structure     

Scattering by thin dielectric strips

A plane wave incident on a thin dielectric strip with infinite length is considered, letting the incident electric field vector be parallel with the edges of the strip. The field is expanded in the dielectric region as the sum of three plane waves (the forced wave and two surface waves). Thex-axis andy-axis propagation constants are known for each wave, and Galerkin's method is employed to determine the amplitudes of these waves. Finally, the far-zone scattered field is determined by considering the polarization currents radiating in free space. Numerical data are presented to illustrate the scattering properties of lossless and lossy dielectric strips as a function of the angle of incidence and the width of the strip. The calculations show excellent agreement with an earlier moment method using pulse bases and point matching.     

Scattering of electromagnetic plane waves by a circular cylinder

Numerical investigation of scattering electromagnetic plane waves by a circular conducting cylinder is considered. The results presented are 1) validity of asymptotic far-field expressions when it is applied to calculate near-field around the cylinder and 2) equicontours of amplitude and phase of total field around the cylinder.     

Plane wave diffraction by a thin dielectric half-plane

Expressions that apply for all observation points are derived for the field produced by a plane wave incident on a thin dielectric half-plane when the electric vector of the incident wave is parallel to the edge. Away from shadow boundaries the total field comprises an edge wave and a surface wave in addition to the transmitted and reflected waves of geometrical optics. The nature of the edge wave differs from that of a perfectly conducting half-plane in that both the amplitude and phase vary with the observation angle, for a given angle of incidence.     

Scattering performance of a plane wave by conducting finite helix

The scattering of a plane wave with a linear polarization by a conducting finite helix is presented. The analytical expresses of scattering field are obtained based on the boundary condition of a sheath helix model. Effects of a pitch angle and electrical size of the helix on the resonant behavior are investigated. The analysis shows that resonant behavior of the forward/backward scattering far field is only depended on the pitch electrical size and the radial electrical size, but it is independent of the turn of the helix.     

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     

Diffraction of an electromagnetic wave by a three-dimensional planar lattice

The 3D problem of scattering by a planar lattice of impedance bodies of revolution is solved with the help of the modified discrete source method. A system of integral equations is derived. Numerical results are obtained for the case of perfectly conducting elements of the lattice. The validity of the law of energy conservation is checked.     

Scattering from a turbulent rocket-exhaust jet illuminated by a plane wave

It has been found possible to describe the addition of noise to a microwave carrier by a rocket-exhaust jet in terms of a simple quantitative model of incoherent volume scattering by the turbulent discontinuities in the jet. The power scattered is spread throughout the noise spectrum by the variation with position in the jet of the magnitude of the mean gas-velocity vector. Comparison between computer calculation and experimentally determined amplitude and phase noise data is found to be excellent.     

Diffraction of an electromagnetic plane wave by a thick slit

Diffraction of an electromagnetic plane wave by an infinite slit in a conducting screen of finite thickness is studied theoretically using Weber-Schafheitlin discontinuous integrals. The direction of the incident wave is assumed to be in a plane perpendicular to that of the screen, and both polarizations are treated. The problems are reduced to simulataneous equations with an infinite number of unknowns, which are truncated in actual numerical computation. Numerical results for transmission coefficients are compared with those calculated from the Mathieu function expansion, and fairly good agreement is obtained. Far-field patterns are measured experimentally for theE-Polarization using a parallel-plate waveguide. The measured results confirm the validity of the theoretical prediction.     

Diffraction of an arbitrary plane electromagnetic wave by a half-plane

The asymptotic form of the diffracted field produced by a plane electromagnetic wave of arbitrary polarization incident obliquely on a conducting half-plane is expressed very simply in terms of the incident and reflected wavesF_{1}andF_{2}, respectively, rotated to bring their wave vectorsk_{1}andk_{2}onkin the direction of observation. The diffraction coefficients becomepm(sin psi_{i}/2)^{-1}wherepsi_{i}is the angle betweenk_{i} (i = 1,2)and the direction of observationk.     

Scattering of a plane wave by a cascade of two frequency-selective structures

Propagation of a plane electromagnetic wave through a multilayer frequency-selective dielectric structure with biperiodic metallization of two interfaces is considered. A method is proposed for calculation of the reflection and transmission coefficients of the structure. Computation results are presented for a structure with gratings consisting of metal rings. The effects of longitudinal and transverse shifts of gratings on the electrodynamic characteristics of the frequency-selective structure are studied. The computation results are compared to experimental data obtained in the microwave band.     

Scattering of a plane wave by a circular cylinder with uniformlyincreasing radius

The interest in the problems of diffraction by moving objects has become obvious due to the applications of nonstationary models for the simulation of different processes. Among them are radar control for the industry ejections or military explosions in the atmosphere and scattering by moving fronts of ionization, or by mobile artificial space objects. The detailed analysis of such processes implies the choice of an adequate model that on the one hand can be effectively investigated but on the other hand ensures a reliable approximation for the complex nonstationary processes. From this point of view, the set of canonical problems that can be solved accurately has great practical significance. We study the diffraction of an electromagnetic plane wave by a circular cylinder with a uniformly increasing radius. The formulation and analysis include propagating singularities as well as the continuous component of the solution. An accurate result is developed by means of separation of variables. Some numerical examples are discussed     

Scattering of electromagnetic waves by arrays of conducting and dielectric cylinders

A method is developed that enables the solution of scattering by a finite number of cylinders in a convenient and accurate form. It is based on an analytic formulation using the boundary value problem and an application of a point matching technique. The method is then applied to study the scattering properties of both conducting and dielectric cylinders. It is also used to determine the size and spacing of passive scatterers to improve the directivity of linear antennas. In the latter case, a combination of the present method and a space perturbation technique is utilized to optimize the antenna gain.     

Current induced on single and crossed electrically short and thin tubular cylinders by a normally incident plane electromagnetic wave

The currents induced in electrically thin conducting tubes are evaluated from the general solution of the coupled integral equations derived by C. C. Kao [5] in the form of transverse Fourier components. It is shown that on a single cylinder of length2hand radiusain a normally incidentE-polarized field with wavenumberk, the rotationally symmetric zero-order term dominates forka leq 0.1and increases in magnitude askais reduced, but only whenkh > 1. Under these conditions, supplemented with the inequalitya ll h, thin-cylinder theory is valid. The relatively small first-order term produces small departures from rotational symmetry that increase or decrease the current on the illuminated side depending on the condition of axial resonance and the location of the cross section in the standing-wave pattern. Askhis reduced so thatka < kh ll 1, the rotationaily symmetric part of the axial current decreases and becomes negligible compared to the first-order current which is proportional tocos theta. Thin-cylinder theory is then no longer useful. When two electrically thin tubes intersect, thin-wire theory and junction conditions determine only the rotationally symmetric part of the axial currents in the arms. These dominate only when the arms of the cross are not electrically short. The fast-order nonrotationally symmetric components of the axial current and the transverse currents can be determined from the incident magnetic field. They dominate when the arms of the cross are electrically short. The significance of the surface currents and charges on aircraft illuminated by an electromagnetic wave or pulse at low frequencies is pointed out.     

Scattering by an E plane dielectric sheet in rectangular waveguide

A method for the computation of S-parameters associated with a rectangular waveguide with a rectangular dielectric obstacle is presented. The method uses the Method of Lines and discretization of the dielectric permittivity to treat the dielectric discontinuity along the discretization direction. In this way, the Method of Lines can be applied to analyze waveguide discontinuity with dielectric inhomogenousity along the discretization direction. The numerical results have been verified by both theoretical and experimental results.     

Scattering of the electromagnetic wave by a layer with one-dimensional rectangular irregularities

Multiple scattering of a plane electromagnetic wave by a layer with random one-dimensional rectangular irregularities of the permittivity is studied. The dependence of the mean scattered intensity on the parameters of the irregularities is obtained. It is established that the mean intensity of the field oscillates as a function of the mean width of irregularities. The conditions for a substantial increases or decrease in the mean intensity of the wave in the layer are determined.