Numerical evaluation of dyadic diffraction coefficients andbistatic radar cross sections for a perfectly conducting semi-infiniteelliptic cone

In this paper, the scattering of electromagnetic waves by a perfectly conducting semi-infinite elliptic cone is treated. The exact solution of this boundary value problem in problem-adapted spheroconal coordinates in the form of a spherical multipole expansion is of poor convergence if both the source point and the field point are far away from the cone's tip. Therefore, an appropriate sequence transformation of these series expansions (we apply the Shanks transformation) is necessary to numerically determine the dyadic diffraction coefficients and bistatic radar cross sections (RCS) for an arbitrary elliptic cone. Our far-field data for an elliptic cone, a circular cone, and a plane angular sector are compared with some other results obtained with the aid of quite different methods     

Electromagnetic scattering by a multilayer elliptic cylinder undertransverse-magnetic illumination: series solution in terms of Mathieufunctions

An exact solution to the electromagnetic scattering by a dielectric multilayer infinite cylinder of elliptic cross section is proposed. The interfaces between different media, which are assumed to be lossless and nonmagnetic, are confocal elliptic cylinders. Starting from the series expansions in terms of Mathieu functions, an efficient recursive procedure for the computation of fields and radar cross sections per unit length under a transverse-magnetic illumination is developed. The mathematical formulation is detailed and some numerical results are provided     

双锥天线的普遍模型

椭圆双锥天线是具有普遍性的物理模型。应用坐标变换和共形变换研究椭圆双锥天线,在传输纯TEM波的假设下,把无限长椭圆双锥结构变换为二维平面结构,从而得到椭圆双锥天线输入阻抗闭合解,其典型结果与文献一致。所给出的椭圆双锥天线有关公式可以用来分析许多类型的锥天线,包括非对称锥天线。     

The RCS of a rectangular microstrip patch in asubstrate-superstrate geometry

A general scattering formula is derived for an arbitrary resonant conductive body within a layered medium, which shows that the body radar cross section (RCS) is directly related to the radiation efficiency of the body. The radar cross section of a rectangular microstrip patch antenna in a lossy substrate-superstrate configuration is then investigated as a specific case. Results are presented to show the effects of loss in the substrate, a lossless superstrate, and a lossy superstrate     

近场条件下散射计的绝对定标

在推导散射计定标公式的基础上,本文分析了远区条件对于雷达散射计绝对定标的意义,通过引入有效雷达散射截面的概念,将入射波前球面弯曲和波束限制引超照射不均匀以及接收天线增益的变化等效为目标雷达散射截面的变化。     

Field singularities at the tip of a metallic cone of arbitrary cross section

The "spherical-harmonics" problem is investigated for a cone of arbitrary cross section. The analysis shows that two basic singularities must be considered: 1) the electric singularity, in whichbar{e}becomes infinite likeR^{nu-1}near the tip of the cone, 2) the magnetic singularity, in whichbar{h}becomes infinite likeR^{tau-1}. Numerical results, in particular concerningnuandtau, are given for: 1) the elliptic cone and its limiting case the sector, 2) the pyramidal corner.     

Biconical antenna and V-conical antenna with elliptic cross section

The methods of coodinates transfomation and conformal maping are applied to the problem of ra diation from a biconical antenna and V-conical an tenna with elliptic cross section. The infinite el liptic cone geometry can be transformed into two dimentions plane under the assumption of pure TEM spherical wave. The Closed-form solutions for the fields, currents, and characteristic parameters are obtained.     

Electric singularity near the tip of a sharp cone

The singularity of the electric fields, proportional to the radial coordinate value R^ν-1, is investigated for a very sharp, perfectly conducting cone of arbitrary cross section. It is shown that, in the limit of a very small cone, the exponent ν tends to zero in proportion with the inverse of the logarithm of the maximum opening angle. Results are shown for the circular and elliptic cone, with the flat sector as a special case, and for the pyramid with n equal faces. An expression, valid for arbitrary opening angles, is presented in the case of a flat sector     

低频太赫兹准目标雷达散射截面的实验研究

以研究太赫兹雷达散射截面的特性为目的,选用所搭建低频太赫兹雷达测试系统,并借助于标准目标法开展了有关太赫兹雷达粗糙铝盘散射截面的实验研究工作.实验结果表明:在小角度散射中太赫兹雷达散射截面随散射角的增大变化比较明显,在散射角超过5后太赫兹雷达散射截面随散射角的变化趋向缓慢,但当散射角超过12后探测信号的强度已衰减到无法测量,在太赫兹雷达散射截面的测试中没有出现微波雷达散射截面的大小随散射角的变化而剧烈振荡的现象;将测试结果与同尺寸微波、激光雷达散射截面的结果进行了对比,得到结论:在0附近太赫兹雷达散射截面的数值比同尺寸微波雷达散射截面的数值要小两个数量级,但比同尺寸激光雷达散射截面的数值要高一个数量级.     

激光雷达截面在系统设计评价中的应用分析

讨论分析了激光雷达截面在激光测量系统设计评价中的应用.分析了激光雷达截面的物理意义,给出了目标激光雷达截面的计算、测量原理与方法,从激光雷达截面的理论定义出发,推导出普遍适用于各类激光测量系统和各种散射特性目标的基本测量方程,该方程利用激光雷达截面表征目标的激光散射特性.通过典型实例说明了该方程在激光测量系统设计评价中的应用.与其他用于表征目标激光散射特性的指标相比,激光雷达截面更容易通过计算或测量得到,且更适用于复杂散射特性目标,因此,在激光测量系统的设计评价中应采用由目标激光雷达截面表述的激光测量方程.     

Radar cross section measurements

The progress in radar cross section measurements is strongly related to the progress in radar technology. The recent acceleration in radar technology and processing techniques has generated a corresponding acceleration in interest for radar cross section measurements. Historically, early radar cross section measurements were performed to determine the detection range of radar systems, a fundamental objective that still exists. Later measurements, coupled with analytic techniques and computer codes, were performed to extend our understanding of the radar scattering process. At the present time, the availability of broad-band electronics, signal processing techniques, and digital technology results in radar cross section measurement programs which are directed toward exploring the performance of operational waveforms and processing, target discrimination, target detectability in clutter, and radar scattering control. The fundamentals of radar cross section measurements are reviewed. Measurement facilities, including the present research activities on compact range techniques, are then described. Instrumentation radars have benefited from both wide-bandwidth electronics and digital processing capabilities; Fourier transform techniques, in particular, provide both additional information on target scattering, and increase measurement accuracy by isolating the target from radar returns from the measurement facility. The frequency coverage has also extended to include millimeter-wave frequencies. Achievable accuracy is important in any measurement program, and those factors that limit the accuracy of radar cross section measurements are discussed.     

Extinction cross section of a dielectric strip

The problem of scattering of a plane electromagnetic wave by a dielectric strip is formulated in terms of an uncoupled system of three-part Wiener-Hopf equations by using a set of approximate boundary conditions. The resulting Wiener-Hopf problems are solved approximately for sufficiently large values of the width of the strip by using D.S. Jones' method (1964). An analytical formula is derived for the excitation cross section of the strip under consideration from which numerical values are obtained in specific situations and the results are presented graphically. The radar cross section of the strip is also computed for several special circumstances, and these are presented separately     

Electromagnetic scattering from finite circular and elliptic cones

A formulation based on the physical theory of diffraction (PTD) is presented for finite conical surfaces with circular and elliptic cross sections. The base-rim discontinuity is represented by equivalent currents, including second-order terms extended for elliptic boundaries. Tip-rim interactions are examined as a function of the tip-rim distance, cone angle, and illumination angle for circular cones; and their implication for elliptic cones is noted. The diffraction contribution from tip-rim interactions is shown to be dependent on the cone angle and the illumination angle but to be relatively insensitive to the tip-rim distance. The Fock Ansatz is used to enlarge the validity of the PTD formulation to cases where nonspecular effects arising from surface curvature and shadow boundaries are significant. The formulation is applied to cones with varying ellipticity for axial and oblique illumination. Correlation is made with published results for circular cones and with experimental data for an elliptic cone.     

Rapid hydrometeor bistatic scatter calculations using non‐orthogonal function expansion of reflectivity profiles

A non‐orthogonal Gaussian function expansion of vertical reflectivity profiles is proposed. In conjunction with a generalization of a previously published formula this allows bistatic radar cross‐sections to be calculated rapidly for hydrometeor scatter problems involving arbitrary reflectivity profiles. In particular, it allows scattering from melting band and ice regions to be included in the cross‐section calculation. Copyright © 2000 John Wiley & Sons, Ltd.     

On the radar cross section of a dipole

Literature references dealing with the radar cross section of a dipole target contain a possible source of confusion in that two definitions of cross section have been used. To clarify this situation, the radar cross section of a randomly oriented half-wave dipole is considered using both definitions.     

椭圆形波导管中对空间立体角积分的计算方法

利用任意闭合曲面对曲面外任一点所张立体角为零的特点将椭圆形波导管中对波导管侧面的积分转变为对椭圆形波导管横截面的积分 ,在轴向采用线性插值函数的条件下对椭圆形波导管横截面的积分简化为一维积分。     

Analytical evaluation of the asymptotic impedance matrix of agrounded dielectric slab with roof-top functions

An analytical technique is derived to solve the asymptotic part of impedance matrix elements for printed circuit structures using roof-top subdomain expansions. The key to this problem is the analytical transformation from an infinite double integral to a suitable finite one-dimensional (1-D) integral. The newly developed formula is applied to the monostatic radar cross section (RCS) of a microstrip patch. Comparisons are made with measurements and conventional method of moments predictions     

Radar scattering from blunted cone tips

The radar cross section is calculated for semi-infinite perfectly conducting cones with tips which are blunted in one of several ways. Calculations have been performed for nose-on incidence using exact theory, and for nose-on and near nose-on incidence using the physical optics approximation. The calculations have been restricted to narrow-angle cones and, in most cases, to tip dimensions small compared with a wavelength. For the rounded tip (spherical tip attached smoothly to the cone), the calculations agree very well with the physical optics approximation. Thus, the use of physical optics for nonzero aspect angles seems justified.     

An application of the WKBJ technique to the on-surface radiationcondition

The on-surface radiation condition method and the WKBJ method for approximating solutions to differential equations are used to derive an analytic formula for the surface currents on a two-dimensional perfectly conducting convex target. The currents are induced by an incident TE-polarized plane wave. The case of a circular cylinder is used to demonstrate the usefulness of the combined methods. It is shown that a two-term expansion yields good results for the surface currents and excellent results for the ensuing bistatic radar cross section     

The Contribution of Wedge Scattering to the Radar Cross Section of the Ocean Surface

This letter considers the contribution to the radar cross section of the ocean surface due to scattering from edges for which the local radius of curvature is small compared with the radar wavelength. An analytic expression based on the method of equivalent currents is given for such scattering and is evaluated for several assumed sets of parameters. This contribution is shown to augment the Bragg scattering cross section in regions where the latter underestimates the measured radar cross section, while remaining smaller than the Bragg component elsewhere.