RESEARCH ON ELECTROMAGNETIC SCATTERING FROM PARTIALLY COATED CONDUCTING CYLINDERS

In this paper,moment methods are applied to solving the electromagnetic scatteringproblems(for both E-and H-polarizations)involving partially coated conducting cylinders.Thecomputer programs have been compiled for general use.They can be used to solve the electro-magnetic scattering from uncoated,partially coated or entirely coated cylinders of arbitrary crosssectional shape.Numerical examples are also presented to show the validity and versatility of themethod.     

Transient scattering from two-dimensional dielectric cylinders ofarbitrary shape

The problem of transient scattering by arbitrarily shaped two-dimensional dielectric cylinders is solved using the marching-on-in-time technique. The dielectric problem is approached via the surface equivalence principle. Two coupled integral equations are derived by enforcing the continuity of the electric and magnetic fields which are solved by using the method of moments. Numerical results are presented for two cross sections, viz. a circle and a square, and compared with inverse discrete Fourier transform (IDFT) techniques. In each case, good agreement is obtained with the IDFT solution     

Transient scattering by resistive cylinders

The two-dimensional scattering of an electromagnetic pulse normally incident on a collection of infinitely long cylinders of arbitrary shape is considered. ForE-polarization an electric field integral equation is derived that is applicable to solid cylinders and/or thin sheets, resistive and/or perfectly conducting. The contribution of the self-cell at later times is carefully analyzed. The expression obtained represents a generalization of previously known results. For an incident Gaussian pulse, numerical results are presented for surface currents and far-fields, for perfectly conducting and resistive circular cylinders and strips. A fast Fourier transform (FFT) algorithm is implemented to obtain the backscattering radar cross section, which is in good agreement with results obtained from either exact continuous wave (CW) solutions or the method of moments.     

Multiple scattering by two conducting circular cylinders

Multiple scattering by two conducting circular cylinders is studied by applying three different methods: the method of Zitron and Karp (ZK), the method of Karp and Russek, and an iterative method which gives the exact solution. It is found from the numerical results for the total scattering cross section that the ZK method gives very precise results even for rather largekaand smallkd, whereaanddare the radius of the cylinder and the separation between the cylinders, respectively.     

Transient scattering by conducting cylinders-TE case

Transient scattering (transverse electric case) by two-dimensional cylinders, both open and closed, is investigated using the marching-on-in-time technique. A simple averaging scheme is also presented to control the late-time oscillations. Numerical results are presented for certain representative geometries and compared with inverse Fourier transform techniques. Good agreement is noted in each case     

Experimental determination of resonant frequencies by transient scattering from conducting spheres and cylinders

A new experimental technique to measure resonant frequencies of a target is presented. A Tektronix WP 1310 waveform processing system has been employed, which features signal processing software with extensive control over instruments, waveform manipulations, and graphic display. Numerous transient waveforms scattered from spheres and cylinders of various sizes have been recorded. A recently developed data-processing technique has been described and applied to these transient waveforms to extract their resonant frequencies. With the use of a new window designed to have a low near-sidelobe level, the modified fast Fourier transform (FFT) is shown to be able to improve the measurement capability of the system.     

Transient scattering by conducting surfaces of arbitrary shape

The time-domain electric field integral equation (EFIE) is used along with the method of moments to develop a simple and efficient numerical procedure for treating problems of transient scattering by arbitrary shaped conducting objects. The conducting surface is modeled by planar triangular patches for numerical purposes. Because the EFIE is used in the solution procedure, the method is applicable to both open and closed bodies. the EFIE approach is applied to the scattering problems of Gaussian plane wave illumination of a flat square plate and sphere. Comparisons of surface current densities and far-scattered fields are made with previous computations and good agreement is obtained in each case     

Electromagnetic scattering from conducting circular cylinders inthe presence of a stratified anisotropic medium-TM case

Scattering by a conducting circular cylinder in the presence of a stratified ferrite medium is investigated analytically using a combined Green's function (G-function) and integral equation approach. The incident plane wave is polarized along the axis of the cylinder. The bias DC magnetic field is in the same direction. The G-function of the structure is developed by well-known techniques of matrix analysis, and the appropriate integral equation for the electric field is derived on the basis of the modified reciprocity theorem. Its solution is followed by numerical results presented in graphical form for both the current density induced on the scatterer's surface and the scattered far field. The possibility of controlling the scattering properties of the structure by varying the degree of anisotropy is also investigated. The main conclusion is that anisotropic materials can be used to control antenna radiation characteristics     

Analysis of the electromagnetic scattering by perfectly conducting convex polygonal cylinders

An effective method for the analysis of the scattering by a perfectly conducting convex polygonal cross-section cylinder is presented. The effectiveness stems from the generalization of the Neumann series, factorising the right edge behavior of the electromagnetic field, thus leading to a quickly convergent method. The induced currents, the radar cross section (RCS) and the induced field ratio have been evaluated.     

Resonant solutions involved in the integral equation approach to scattering from conducting and dielectric cylinders

Resonant solutions involved in the integral equation formulation for analyzing the scattering problems and the elimination of these erroneous solutions are investigated. The parameter ranges where the resonant solutions are mixed into the correct ones and the degree of errors caused by the resonant solutions are checked on through numerical computation of matrix condition numbers and scattering cross sections for dielectric cylinders of square cross section with side width/wavelength ratio being less than about 1.27. As a method of removing the resonant solutions, the method taking some lower order equations of the so-called "extended boundary condition (EBC) method" into consideration is proposed.     

Electromagnetic scattering by rough conducting circular cylinders.II. Axial corrugation

For pt.I see ibid., vol.36, no.5, p.651 (1988). The coherent and incoherent responses of conducting axially corrugated surfaces (which are on the average circular cylinders) are calculated. The calculation encompasses second-order perturbation. The general approach used is to apply the extinction theorem to write an integral equation for the surface current density, and then to use the perturbation theory to solve it. The results are recast by using Pade approximants to achieve a significant extension of the domain of validity of the original formulation     

Combined field solution for TM scattering from multiple conducting and dielectric cylinders of arbitrary cross section

A simple moment solution is given for the problem of electromagnetic scattering from multiple conducting and dielectric cylinders of arbitrary cross section. The system of conducting and dielectric cylinders is excited by a plane-wave polarized transverse magnetic to the axis of the cylinders. The equivalence principle is used to obtain three coupled integral equations for the induced electric current on the conducting cylinders and the equivalent electric and magnetic currents on the surface of dielectric cylinders. The combined field integral equation (CFIE) formulation is used. Sample numerical results are presented. The agreement with available published data is excellent.     

Electromagnetic scattering from longitudinally corrugated cylinders

The scattering of plane electromagnetic waves from circular cross-section cylinders, longitudinally corrugated to realize anisotropic structures, is analyzed. The solution is devised at oblique incidence and for an arbitrary polarization of the incident wave using a rigorous Floquet modal expansion of the field. The implementation of the procedure is discussed with emphasis to its numerical efficiency     

Electromagnetic scattering from two adjacent cylinders

The problem of electromagnetic scattering from two adjacent cylinders is considered. The approximate analytical scattering solutions up to second order are derived for two adjacent, long finite length cylinders. The method used can avoid the complex evaluation of scattering field under nonplane wave illustrated when calculating the secondary scattering fields. The bistatic specular scattering is discussed, and the results are compared with numerical computations based on the method of moments     

Scattering from conducting finite cylinders with thin coatings

The surface equivalence principle is used to develop an integral equation formulation for electromagnetic scattering from open circular cylinders with thin material coatings. The method of moments with entire domain functions leads to an algebraic system of equations which is solved numerically. Results of calculations for various cylinder aspect ratios, layer thicknesses, and material constitutive properties are presented.     

High frequency scattering from corrugated stratified cylinders

Interest in applying radar remote sensing for the study of forested areas led to the development of a model for scattering from corrugated stratified dielectric cylinders. The model is used to investigate the effect of bark and its roughness on scattering from tree trunks and branches. The outer layer of the cylinder (bark) is assumed to be a low-loss dielectric material and to have a regular (periodic) corrugation pattern. The inner layers are treated as lossy dielectrics with smooth boundaries. A hybrid solution based on the moment method and the physical optics approximation is obtained. New expressions for the equivalent physical-optics currents are used which are more convenient than the standard ones. It is shown that the bark layer and its roughness both reduce the radar cross-section. It is also demonstrated that the corrugations can be replaced by an equivalent anisotropic layer     

二维多导体柱电磁散射特性的特征基函数法分析

特征基函数法是近两年提出来的一种求解电磁散射问题的有效方法,该方法使用的特征基函数不受传统矩量法离散尺寸的限制,因而可以大大减小要求解的矩阵方程。应用特征基函数法分析了二维多导体柱的电磁散射特性,计算了多个无限长导电椭圆柱和方柱的雷达散射截面,结果表明特征基函数法的计算结果与传统矩量法的计算结果吻合良好,而计算量却大为减少。     

High frequency scattering from polygonal impedance cylinders andstrips

An analysis is presented for the high-frequency diffraction by convex polygonal cylinders with arbitrary side impedances. The authors extend their solution for the multiply diffracted fields associated with a double wedge (see ibid., vol.36, no.5, p.664-678, 1988). The analysis thus utilizes the extended spectral ray method (ESRM) that is applicable to nonray optical regions. Diffraction coefficients yielding a uniform total field are given for up to and including all fourth-order mechanisms. An important aspect of this analysis is the rigorous and uniform incorporation of the surface-wave effects in the resulting diffraction coefficients. A general polygon computer code was written that includes up to a third-order mechanisms. Based on this code, backscatter and bistatic patterns are given for impedance cylinders with triangular and square cross sections. The results are found to be in remarkable agreement with corresponding moment method data. As a matter of completeness, uniform diffraction coefficients are presented for a strip (which is a special case of a cylinder) that can have unequal face impedances