Nan Wang

Sinusoidal reaction formulation for radiation and scattering from conducting surfaces

A piecewise-sinusoidal reaction technique is developed for scattering and radiation from perfectly conducting bodies of arbitrary shape. This paper presents the theory and numerical results for scattering patterns of rectangular plates and radiation patterns of corner-reflector antennas. In all cases, experimental measurements are included for comparison with the calculated data.

Electromagnetic scattering from a dielectric-coated circular cylinder

The normalized backscattering width of an infinitely long, dielectric coated circular cylinder is obtained via a high frequency ray solution. The ray solution provides a physical picture of the scattering process in terms of a geometrical optics ray and two surface waves. It is shown that the surface wave resonance phenomena in the backscattering fields of the coated cylinder can be predicted in terms of the Regge poles of the coated cylinder. The numerical results for the backscattering widths of the cylinder obtained via the high frequency ray solution show excellent agreement with the eigenfunction results. The trajectories of the Regge poles associated with the coated circular cylinder are also presented.

Scattering from three-dimensional cracks

Scattering from three-dimensional cracks is analyzed and measured. The crack geometry is modeled as a rectangular groove in a perfectly conducting surface. The groove forming the crack may be terminated with an open aperture creating a slit in the conducting surface or with an impedance boundary creating a trough. The scattered fields from a crack are analyzed with two types of scattering mechanisms: a component directly related to the scattered fields from a two-dimensional crack, and a traveling-wave component. >

New expressions for mutual impedance of nonplanar-skew sinusoidal monopoles

Previously published expressions for monopole-monopole impedance to two nonplanar-skew sinusoidal current filaments are nonreciprocal. A novel version of the monopole-monopole impedance is obtained. This version is not only reciprocal but also contains fewer exponential integral terms. The new expressions can be used to save computer time in the thin wire program developed by J.H. Richmond (1974). >

Regge poles, natural frequencies, and surface wave resonance of a circular cylinder with a constant surface impedance

The radar cross section (RCS) of an infinitely long circular cylinder with a constant surface impedance is obtained via a high frequency ray solution. The ray solution provides a physical picture of the scattering process in terms of a geometrical optics ray and two surface waves. It is shown that the surface wave resonanee phenomenon in the RCS of the cylinder can be predicted in terms of the Regge poles or the natural frequencies of the cylinder. The numerical results for the RCS of the cylinder obtained via the high frequency ray solution show excellent agreement with the eigenfunction results. The condition for predicting the surface wave resonance is also discussed.

Self-consistent GTD formulation for conducting cylinders with arbitrary convex cross section

A user-oriented computer program has been developed for high frequency radiation and scattering from infinitely-long perfectly. conducting convex cylinders. The analysis is based on the self-consistent geometrical theory of diffraction (GTD). The cylinder is modeled as an N -sided polygon. Two cylindrical waves with unknown amplitudes are assumed to travel in opposite directions on each face of the polygon. The boundary conditions for the corners are applied to set up a matrix equation for 2N unknowns (the amplitudes associated with the traveling cylindrical waves). Crouts method is used to solve the matrix equation. Once the amplitudes for the traveling waves are determined, the radiation or scattered field is readily obtained via the usual GTD techniques. Numerical results are presented for radiation and scattering from rectangular, semi-circular, circular, and elliptic cylinders for both principal polarizations. The results show excellent agreement with GTD, moment, and eigenfunction solutions.

Near axial backscattering from finite cones

The near-axial backscattering from a finite cone is studied using the equivalent current concept based on the uniform geometrical theory of diffraction (UTD). The creeping waves associated with the conical surface are also incorporated into the equivalent current technique. The contributions from the creeping waves are significant for the oblique-incidence case. There is evidence to speculate that the poorer agreement between the previously calculated results and the measured data for the vertically polarized backscattering is probably a result of the omission of the creeping wave contribution. >

A physical basis formulation for the electromagnetic backscattering by a finite-length rectangular trough in a ground plane

The electromagnetic backscattering from a finite-length rectangular trough in an infinite ground plane is examined. A physical basis formulation is used to express the unknown currents in the trough aperture in terms of a forced wave resulting from the incident plane wave, and one or more pairs of oppositely directed traveling waves propagating along the trough. A Galerkin solution is employed to solve a very small system of equations to determine the weights of the postulated aperture currents, and then radiated to compute the radar cross section (RCS). These results are then compared with a measurement of a trough in a finite ground. >

Scattering by thin wire loaded with a ferrite ring

A coupled integral equation formulation and a method of moments (MoM) solution are presented for the problem of scattering by a thin conducting wire of circular cross section with ferrite loading. It is proved that ferrite loading can be used to reduce the radar cross section of long thin objects at their resonant frequency. >

Mixed-field hybrid FEM/BEM formulation for two-dimensional TE radiation 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.