有耗介质覆盖导电圆柱的电磁散射

本文给出了在平面波垂直照射下，均匀覆盖有耗介质后的导电圆柱散场的本征函数级数解。     

A General Spectral-Domain Formulation of the Electromagnetic Scattering by a Perfectly Conducting Circular Cylinder

A full-wave method for the two-dimensional scattering problem by a perfectly conducting circular cylinder is presented, providing an exact solution for the Helmholtz equation in very general cases. The method is based on the Fourier series expression of the boundary conditions (Dirichlet and Neumann) generated by an arbitrary, finite-power, incident beam, and the analysis is performed in the complex plane of the analytic continuation of a space spectral variable. This approach allows us to define an analytic continuation for cylindrical wave expansions, working with lossy propagation media and with a full incident spectrum, including inhomogeneous waves, both in E and in H polarization. Convergence of the modal expansion is investigated, to verify that very weak hypotheses are needed, and no geometrical or paraxial approximation is required. Extact expressions for the expansion coefficients are given, in terms of complex intergrations involving the Fourier spectrum of the incident beam.     

Scattering of an Electromagnetic Pulse by a Moving Wedge

The paper is concerned with the analysis of 2-D scattering of an electromagnetic (EM) pulse by a perfectly conducting wedge moving with a relativistic velocity in a free space. The incident signal is described by a Dirac delta function. Analytical solution to this scattering problem is found, and its physical interpretation is given. The field representation, valid for all scatterer velocities, is then simplified to the case of moderate and low velocities, appropriate for practical applications.     

Electromagnetic Scattering by an Inhomogeneous Impedance Cylinder

In this paper, the electromagnetic scattering problem related to a circular cylinder with inhomogeneous impedance boundary is solved. This kind of problem may have practical applications such as antenna design since one can obtain a certain radiation pattern by choosing thesurface impedance in an appropriate way. The approach presented in this paper is based on the series representations of the scattering and incident fields. The impedance function is also expanded into a Fourier series. By using orthogonality properties of some special functions the problem is reduced to the solution of a system of linear equations. The problem isalso solved through the extended boundary condition method (T-matrix method). Since an extensive treatment of the T-matrix method is available in the open literature the paper is weighted towards the Fourier series method. The results of both methods are compared. Some illustrative examples showing the effects of different parameters on the scattered field are given.     

任意截面导体柱的电磁散射数值解

卡门翼形和任意多边形是两种典型的不规则形体，由于其不规则曲边和尖锐的角点，它们的电磁散射问题给传统的FDTD数值求解造成了一定的困难，这是因为要获得较高的精度，必须细分网格，从而增加内存需求和计算时间，本文利用形体变换结合时域有限差分法的Thompson-FDTD方法对这两种典型的不利形体的散射问题进行了数值模拟，其结果进一步验证了Thompson-FDTD方法对散射体几何形状变化具有较强的适应能力和较高的数值精度。     

An Experimental Investigation of the Distribution of Current And Charge Induced on a Tubular Conducting Cylinder by an Electromagnetic Pulse

The distribution of current and charge induced on a tubular cylinder by an electromagnetic pulse (EMP) is investigated experimentally in the Harvard parallel-plate EMP simulator (HES). The pulse shapes of the current and charge induced on the surface of the cylinder are measured. After Fourier transforms of the observed pulse shapes are taken, the distributions of the several frequency components on the surface are obtained. The measured distribution of each frequency component is then compared with the theoretical distribution calculated using Kao's method.     

Scattering of Electromagnetic Waves by a Coated Nihility Cylinder

An analytical solution for the scattering of electromagnetic plane waves from an infinitely long nihility cylinder, coated with a double positive (DPS), double negative (DNG), epsilon negative (ENG), or mu negative (MNG) layer of uniform thickness is presented. The solution is determined by solving the scalar wave equation in the cylindrical coordinates, for different regions and applying the appropriate boundary conditions at the interfaces. Both TM and TE polarizations as incident plane have been considered in the analysis. Comparison of behaviors of a coated nihility cylinder with a coated PEC cylinder has been made. It is noted that two situations are more closer for DNG coating as compared to DPS coating.     

Scattering by a Conducting Infinite Cylinder Illuminated with a Shaped Beam

An analytic solution to the shaped beam scattering by a conducting infinite cylindrical particle is constructed within the framework of the generalized Lorenz-Mie theory (GLMT). The expansion coefficients of the scattered electromagnetic fields are derived by using the boundary conditions. As an example, for a tightly focused Gaussian beam propagating perpendicular to the cylinder axis, the scattering characteristics that obviously demonstrate the three-dimensional nature, as with the case of a dielectric infinite cylinder, are described in detail, and numerical results of the normalized differential scattering cross section are evaluated.     

Scattering and Pattern Perturbation by a Conducting Tubular Cylinder of Finite Length

This paper uses the plane-wave-spectrum (PWS) scattering technique to determine the scattering and pattern-perturbation effects of a conducting tubular cylinder of a finite length situated in the neighborhood of a 2 x 4 dipole array. Both the axial and the circumferential current distributions induced on the cylinder due to a unit-magnitude incident plane wave have been calculated. Typical patterns for the scattered field and the perturbed radiation field are presented for various cylinder locations.     

Two-Dimensional Scattering by a Conducting Elliptic Cylinder Coated With a Homogeneous Anisotropic Shell

A solution to the two-dimensional scattering properties of a conducting elliptic cylinder coated with a confocal homogeneous anisotropic elliptical shell is obtained. The transmitted field of the anisotropic shell is expressed as an integral equation based on waves with different wave numbers and different directions of propagation. The waves in all directions are represented as the eigenfunction expansion in elliptic coordinates in terms of Mathieu functions. In order to solve the nonorthogonality properties of Mathieu functions, Galerkin's method is applied and a matrix is required for the computation of unknown expansion coefficients of the scattered and transmitted fields. Only the transverse magnetic (TM) polarization is presented, while the transverse electric (TE) polarization can be obtained in the same way. Some numerical results are presented in graphical forms. The result is in agreement with that available as expected when a coated elliptic cylinder degenerates to the coated circular one.      

导体球涂覆各向异性铁氧体介质电磁散射的解析解

该文用球矢量波函数对各向异性铁氧体介质涂覆导体球的电磁散射解析解开展研究。各向异性铁氧体介质中电磁场的球矢量波函数解可表示成第一、二、三、四类球矢量波函数之和。根据球Bessel函数的性质,可以得出导体球涂覆各向异性铁氧体介质的球矢量波函数解析解。应用铁氧体与自由空间分界面上电磁场切向连续和在导体球面上切向电场等于零的边界条件以及球矢量波函数切向正交性质,可分别得出铁氧体介质中电磁场和散射场的展开系数。给出了平面波入射情况下的数值计算结果。该文的结果可应用于有关微波器件、天线以及目标特征的分析和计算。     

时域MEI方法在矩形导体柱散射问题中的应用

本文用时域有限差分法（FDTD）模拟二维矩形导体柱的电磁散射场，采用时域不变性测试方程（MEI）作为吸收边界条件对该散射场进行求解。将所得计算结果与截断边界网格点采用Mur二阶吸收边界条件所得的数值结果相比较，两者吻合很好。结果表明使用时域MEI方法作为吸收边界条件能有效缩短截断边界与物体边界的距离，且能得到足够精确的解。     

Scattering of Electromagnetic Waves by a Cylinder Moving Along its Axis

The scattering of a time-harmonic, linearly polarized plane electromagnetic wave by a cylinder uniformly moving along its axis is discussed. The formalism is relativistically exact, and explicit forms are provided for first-order velocity effects. Consideration is given to both a cylinder moving in free space, using the procedure suggested by Einstein, and two refractive media; it is veritied that the first case is a special case of the second one. Thin scatterers are considered and it is shown that no first-order velocity effects are present. For a moving medium, having in its rest frame the same constitutive parameters as the surrounding medium, it is shown that the velocity-independent part vanishes, but scattered fields of the first order in the velocity are still present. Moreover, these waves appear with the opposite polarization (compared to the incident wave).     

Electromagnetic Scattering by Multiple Perfectly Conducting Arbitrary Polygonal Cylinders

We analyze the scattering by multiple perfectly conducting cylinders with arbitrary polygonal cross-section. The proposed method is very efficient as few expansion functions are needed in a Galerkin scheme. This is achieved by means of the analytical regularization of the problem obtained by factorizing the correct edge singularity of the electromagnetic field. A particular attention has also been paid to the numerical computation of the integrals involved, and formulas for their accurate and quick evaluation are given.     

Electromagnetic-Field Distortion Due to a Conducting Rectangular Cylinder in a Transverse Electromagnetic Cell

This paper deals with the distortion effects in a TEM cell resulting from loading by the object under test. To insure that higher order modes are ruled out as contributing factors, a brief discussion of the cutoff frequencies of these modes is presented. The paper then proceeds to a theoretical and experimental analysis of the loading effects. In the theoretical analysis for the loading effects, i.e., the electromagnetic-field distortion caused by an object under test in a TEM cell, the frequency-domain integral equation for the magnetic field, or equivalently, the current density on the surface of a perfectly conducting cylinder in a parallel-plate waveguide, is solved by the method of moments to predict the degree of magnetic-field distortion. The experimental investigations are performed by mounting a number of electrically small half loops on the surface of the conducting cylinder in a TEM cell. The loading effects in terms of magnetic-field distortion are analyzed as the ratio of one of the object dimensions (height) to the separation distance between the inner conductor and the ground plane of the TEM cell. Also, the response of an electrically small loop to both the magnetic and electric components of the electromagnetic field is used to measure the phase relation between the magnetic and electric fields, which in turn can be used to determine the degree of degradation of the TEM mode due to the presence of the conducting cylinder. These theoretical and experimental results are compared with the available quasi-electrostatic results.     

超宽带电磁脉冲二维金属柱体时域逆散射成像的研究

本文研究了利用超宽带电磁脉冲对二维金属散射体进行成像算法 ,通过参考LSF算法〔5～ 8〕的基本思想 ,基本克服了Born迭代法在处理金属散射体时理论上的缺陷。并通过对求解大型“病态”线性方程组算法的改进 ,提高了二维金属散射体的时域逆散射成像算法的稳定性和二维金属散射体 (尤其是在存在多个散射体的情况下 )的成像质量。最后给出了相应的实验结果     

非同轴多层介质椭圆柱体的电磁散射—任意方向斜入射电磁波

本文基于椭圆柱谐基函数展开，对非同轴任意多层介质椭圆柱体的电磁散射进行了严格地电磁场分析，利用Ｍａｔｈｉｅｕ函数及其加法定理，在各层边界面上进行场的匹配，获得了任意方面斜入射电磁波下电磁散射解析解。     

涂覆型大尺寸有限长圆柱散射特性的混合解法

本文首先从理论上导出了能计算斜入射绕射场的阻抗劈并矢绕射系数,然后利用该绕射系数结合物理光学法对涂覆型大尺寸有限长圆柱的散射特性进行了分析和计算。在绕射区计及了一阶和二阶绕射贡献,在镜反射方向附近作了驻相法近似,由此得到的数值结果与实验结果吻合较好。     

阻抗边界圆柱散射场的UTD解

本文分析了二维阻抗圆柱的电磁散射机理，讨论了金属圆柱、有耗涂层圆柱与阻抗圆柱的等效特性，获得了它们的散射场一致性绕射理论（ＵＴＤ）解。最后，给出了一组计算实例。     

电大导体目标电磁散射特性的投影迭代法分析

将投影迭代法应用于分析任意二维和三维电大导体目标的电磁散射特性。该方法首先剖分传统矩量法得到的矩阵方程,然后通过投影迭代逐步修正未知电流值,进而计算目标的雷达散射截面。数值计算表明：该方法与传统矩量法计算结果相吻合,计算量大大降低。