The currents on a cylinder illuminated by a generalobliquely-incident plane wave

A relation is presented that determines the total current induced by a general plane wave obliquely incident or a perfectly electrically conducting cylinder of arbitrary cross section from the total current induced by a normally incident plane wave. Remarkably, this same relation ran also be used to determine the physical optics (PO) and nonuniform (NU) currents for oblique incidence directly from the PO and NU currents, respectively, for normal incidence     

Transient currents on a cylinder illuminated by an impulsive plane wave

An analytical and numerical study of the transient current density induced on a perfectly conducting circular cylinder has been carried out. Both TE and TM incident plane waves with impulsive time dependence are considered. Complete closed form expressions for the TE and TM current density at all points on the cylinder and for all time values are obtained by a functional interpolation of both large and small time asymptotic solutions. The complete expressions should he useful in future transient radar scattering problems for approximating the transient current behavior on portions of a complex scatterer. The numerical results are presented in the form of "snapshots" of the current density at specific instants of time. The results are interpreted in terms of specular reflection and creeping waves. The creeping wave pulses are seen to be a continuation of pulses generated on the illuminated surface; their propagation into the shadow region is a highly dispersive phenomenon. The natural mode spectrum is seen to have both discrete and continuous components with the response at very large times determined by the latter.     

Closed-form expressions for uniform currents on a wedge illuminatedby TM plane wave

Closed-form expressions for nonuniform currents on a perfectly conducting, infinite wedge illuminated by a transverse magnetic plane wave are presented. The expressions are derived by requiring that they agree with the current predicted by the eigenfunction solution close to the edge and J.B. Keller's geometrical theory of diffraction (1962) far from the edge. The angle of incidence is arbitrary and the expressions remain uniformly valid even for glancing angles of incidence when the geometrical optics boundaries are in the vicinity of the wedge faces. The formulas presented are simple, involving Fresnel functions with complex arguments. These functions can be expressed in terms of complimentary error functions which may be computed using standard subroutine packages. Exact expressions for nonuniform currents are available for the two special cases of half-planes and infinite planes. Closed-form expressions for the axial electric field, and hence all the field components in the vicinity of the wedge axes, are also obtained. Currents computed using expressions obtained are compared with currents computed from the eigenfunction solution of the wedge, with good agreement throughout     

Surface currents induced on a wedge under plane wave illumination: An approximation

An approximate transform for the surface current induced on an infinite wedge is presented. The transform readily allows the investigation of the pulse response of a large class of cylindrical structures of general polygonal cross section. The results for the polarization of the excitation both parallel and normal to the axis of the infinite wedge are presented.     

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.     

Measurements of surface currents on a finite circular tube illuminated by electromagnetic wave

An experiment is designed to confirm a rigorous theory on the three-dimensional electromagnetic scattering from a circular tube of finite length. Both axial and transverse components of the outside total current for the case ofEpolarization have been measured for two finite tubes withka = 1.895andkh = 0.4827piand0.724pi, both as a function ofzortheta. Special care was taken to preserve the continuity of the transverse current after each change in the position of the probe. The measured results are in good agreement with the theoretically computed data. Theoretical curves for the corresponding infinite cylinder are also included to show the limitations of using them as approximations to the currents on finite cylinders.     

Diffraction coefficients and field patterns of obtuse angledielectric wedge illuminated by E-polarized plane wave

The diffraction problem is treated for the incidence of an E -polarized plane wave on both interfaces of an obtuse dielectric wedge. Based on the dual integral equation, the total field is obtained by the sum of the physical optics solution and the edge-diffracted correction term. Calculated diffraction coefficients and field patterns are plotted in figures for a wedge angle of 120°, incident angles of 60° and 70°, and relative dielectric constants of 2 and 10. It is shown that the Neumann expansion to the nonuniform currents provides a more accurate correction to the physical optics currents than the multiple expansion as the angle of dielectric wedge increases     

GTD analysis of near-field and far-field patterns of a parabolic subreflector illuminated by a plane wave

A geometrical theory of diffraction (GTD) analysis of the principal plane far-field and near-field patterns of a near-field Cassegrainian subreflector is presented. The uniform geometrical theory of diffraction (UGTD) [1] that drastically reduces the computation time has been utilized to analyze the subreflector in the form of a paraboloid illuminated by a plane wave. The numerical computations of the far-field amplitude and phase patterns of a typical paraboloidal subreflector based on the above technique correlate well with the results obtained by physical optics current integration, justifying the validity of the analysis presented. The GTD near-field analysis presented here is an improvement over that published earlier [2] and removes some of its limitations.     

Analytical aspects of plane wave illuminated thin wires and slits

The paper deals with simple elementary approximations for the current and charge response on different straight wire structures, dipoles and short slits in the receiving case. After proof that transmission line equations are also valid for single wires without discontinuities, these equations are formulated including the incoming wave. They turn out have simple particular solutions that could be expected for the case, when the electric field is parallel to the wire, but holds true for the general case too. Satisfying the boundary condition at discontinuities (wire ends, lumped elements) gives rise to additional waves appearing as solutions of the homogeneous wave equation. The formulation of currents along and voltages across a slit, including an illuminating magnetic field at one side of the screen, leads again to transmission-line type equations and, consequently, to the inhomogeneous wave equation. As slits in screens are usually small in terms of wavelength, an approximative solution for the short slit will do. For this case, even closed-form expressions are possible for the magnetic near field     

The problem of scattering of a plane wave by a transparent wedge: A computational approach

A 2D scalar problem on scattering of a plane harmonic wave by a wedge is considered. In the wedge, the wave velocity exceeds the velocity in the ambient space. It is shown that the wave interacting with the wedge vertex produces a wave with a circular front. The wave field is specified in the form of a sum of simple layer potentials. A system of integral equations for the Fourier transforms of the densities of these potentials is solved. The diffraction coefficients of the wave scattered by the wedge vertex are found.     

High-frequency surface currents induced on a perfectly conducting cylindrical sheet by an obliquely incident plane wave

Explicit expressions for the surface currents of different kinds induced on a perfectly conducting cylindrical sheet by an obliquely incident high-frequency plane wave are derived. The results are in such forms that they can both be used directly in numerical applications and permit us to understand the structure of the induced surface current. It is shown that the components due to the surface and edge diffractions propagate along certain geodesic lines on which the transfer coefficients as well as the attenuation constants are dependent only on the curvature radius.     

Diffraction of a normally incident plane wave at a wedge withidentical tensor impedance faces

Diffraction of a normally incident plane wave by a wedge with identical tensor impedance faces is studied and an exact solution is obtained by reducing the original problem to two decoupled and already solved ones. A uniform asymptotic solution then follows from the exact one and agrees excellently with numerical results due to the method of parabolic equation     

Radiation of a radar target illuminated by a spherical wave

Physical optics is used to assess the scattering of plane and spherical electromagnetic wave by a target in free space. In both cases the field radiated by the target is calculated in a 2D space, as a function of the frequency and the angle of observation of the target. The sampling criteria permitting inverse processing methods are complied with. Analysing series of synthesised impulse response (or range response), also called sinograms, allows to extract and compare contributors of the target radar cross-section (rcs) under near-field and far-field conditions.     

Early-time currents induced on a cylinder by a cylindricalelectromagnetic wave

An analytical study of the early-time current response of a perfectly conducting circular cylinder to a cylindrical electromagnetic wave, produced by a parallel filament carrying a unit-step current, is presented. Surface current density expressions for both the shadow and illuminated regions are obtained by applying the Watson transformation to the frequency-domain solution and then evaluating the corresponding integrals separately, in the shadow region by a residue series and in the illuminated region by using the saddle point technique. Analytical results obtained by using a double Laplace transform approach for the shadow region and the Luneberg-Kline expansion approach for the illuminated region are given. Numerical results illustrate the variation of the distribution of current density with time for different locations of the line current with respect to the cylinder, and also allows a comparison of the alternate methods applied by the authors, showing their corresponding range of validity. The response to an impulsive plane wave is derived as a special case     

TE scattering by an inhomogeneously filled aperture in a thickconducting plane

The electromagnetic characterization of the transmission and scattering properties of an aperture in a thick conducting plane filled with an inhomogenous composite material for transverse electric polarization is discussed. Of particular interest in this analysis is the introduction of a new technique that combines the finite element and boundary integral methods. To allow the treatment of large apertures, the conjugate gradient method (CGM) and fast Fourier transform (FFT) are also incorporated for the solution of the resulting system. Numerical examples that demonstrate the validity, versatility, and capability of the technique are presented     

Diffraction coefficient of a conducting wedge loaded with a dielectric slab on the illuminated surface

The asymptotic solution for the diffraction of anE-polarized plane incident electromagnetic wave by a conducting wedge, whose illuminated surface is loaded with a dielectric slab of small thickness and relative permittivity, is employed to derive a ray optical diffraction coefficient for the edge.     

Diffraction by a dielectric wedge with the neumann expansion of correction currents on interfaces

A new representation of fringe currents, which corrects the physical optics approximation for edge diffraction by a dielectric wedge, is obtained. In comparison with the multipole expansion at an edge, the proposed Neumann expansion of correction currents along the dielectric interfaces satisfies the edge condition at the edge and provides fast convergence after finite truncation of expansion coefficients.     

TE scattering by a two-dimensional groove in a ground plane usinghigher order boundary conditions

An application of a third-order generalized boundary condition to scattering by a filled rectangular groove is presented. Deficiencies of such higher-order boundary conditions are addressed, and a correction for the present case is proposed. As part of the process of examining and correcting the accuracy of the proposed generalized boundary conditions, an exact solution is developed and a comparison is provided with a solution based on the standard impedance boundary condition     

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