复杂涂敷目标的RCS计算

提出了一种计算复杂涂敷目标散射场的一般方法。将带有尾翼的弹体目标分成几个散射中心 ,在每个散射中心上 ,运用物理光学积分和几何绕射理论对其RCS进行分析和计算 ,并将计算结果与无涂敷金属表面目标的RCS进行对比分析 ,结果与预期估计情况吻合较好 ,表明该方法不仅计算简单 ,而且结果也较为精确     

Improvement of the PO-MoM hybrid method by accounting for effectsof perfectly conducting wedges

A correction of the conventional physical optics (PO) current close-to-perfectly conducting wedges based on an application of the uniform geometrical theory of diffraction (UTD) is presented. This improved PO current is used in a hybrid formulation in combination with the method of moments (MoM) to deal with three-dimensional scattering bodies of arbitrary shape. The accuracy of this hybrid method is demonstrated by some examples. As opposed to an application of the physical theory of diffraction (PTD), only surface current densities and no fictitious electric and magnetic line currents along the edges are involved which allows a uniform treatment of the MoM and the PO region by expressing the surface current density as a superposition of basis functions defined over triangular patches     

GRECO中棱边检测方法及其绕射场计算的改进

图形电磁计算(GRECO)方法是计算复杂目标高频区雷达散射截面(RCS)的有效方法之一.本文分析了原始GRECO方法在判定目标图象棱边象素的不足之处,给出了相应的改进措施.改进后的软件能够更准确、充分地判定目标的棱边象素及获得棱边参数.在边缘绕射场的计算方面,本文指出了相关文献中存在的错误^[1],给出了基于等效电磁流法(MEC)和物理绕射理论(PTD)的边缘绕射场计算式,及与物理光学(PO)场叠加求取RCS的完整表达式.计算实例表明,新的方法具有更高的准确度,与实验测量值吻合.     

逆向转动螺旋桨的散射特性分析

在已有研究成果的基础上，计算并分析了一类特殊螺旋桨结构(双层逆转结构)的雷达回波特性。文中用物理光学法结合等效电磁流法分析了该类结构的散射特性，并与其他的螺旋桨散射特性进行了比较。文中未考虑两个螺旋桨的遮挡效应对散射的影响。     

Computation of PO Integral on Parametric Surfaces

The paper presents a general method for computing the physical optics (PO) integral on the most of curved parametric surfaces. Today, most of radar cross section (RCS) codes use the parametric geometry code for modeling complex object geometry. The PO integral formulation is presented that fully utilize the geometry information available in parametric geometry codes. The formulation presented can be used with any of these geometry codes independent of the difference between versions. The PO integral is evaluated over the parametric space of the parametric surfaces using splitting extrapolation method. Therefore, the method is very general, allowing its use for the PO integral on the most of parametric surfaces. Moreover, it is efficient and accurate. The method is applied to calculate the RCS values of several objects modeled with non-uniformed rational B-spline (NURBS) surfaces at a millimeter-wave frequency, the results agree with geometric optics (GO) predictions.     

Comparison of different order GTD solutions of double-edgediffraction problem

A second order diffraction coefficient for the uniform geometrical theory of diffraction (GTD) is obtained explicitly for two knife edges in terms of the usual complex transition function (a modified Fresnel integral). The results from conventional GTD (zero order), slope diffraction GTD (first order), and second order GTD are compared with those obtained from physical optics (PO), which uses the complex Fresnel double integral. The results from second order GTD are close to those from PO in most of the cases studied     

部分涂敷目标的RCS仿真计算

涂敷雷达吸波材料(RAM)是目前最为常用的一种减缩雷达散射截面(RCS)的方法,可以在全角度下减小雷达目标的RCS值.采用非均匀有理B样条(NURBS)参数曲面模拟目标外形,运用物理光学法计算电大尺寸部分涂敷目标的RCS.结果显示,在目标一定的部位上而不是在所有部件上涂敷吸波材料,在一定的观察点上仍然能起到减小RCS的作用,既满足了角度范围的需要又节省了RAM的使用费用.     

Improved PO-MM hybrid formulation for scattering fromthree-dimensional perfectly conducting bodies of arbitrary shape

The method of moments (MM) represents a suitable procedure for dealing with electromagnetic scattering problems of arbitrary geometrical shape in the lower frequency range. However, with increasing frequency both computation time and memory requirement often exceed available computer capacities. Therefore a current based hybrid method combining the MM with the physical optics (PO) approximation suitable for three-dimensional perfectly conducting bodies is proposed in this paper. The hybrid formulation allows a substantial reduction of computation time and memory requirement, while the results are in reasonable agreement with those based on an application of the MM alone. Further improvement can be achieved for flat polygonal parts of the scattering body by a heuristic modification of the PO current density taking into account the effects of edges. As opposed to the physical theory of diffraction (PTD), no additional electric and magnetic line currents along the edges are necessary     

A UGO/EUTD solution for the scattering and diffraction from cubicpolynomial strips

A combined uniform geometrical optics (UGO) and extended uniform geometrical theory of diffraction (EUTD) solution is developed for scattering and diffraction by perfectly conducting cubic polynomial strips. The new solution overcomes the difficulties of the classic GO/UTD solution near caustics and composite shadow boundaries. The approach for constructing the UGO/EUTD solution is based on a spatial domain physical optics (PO) radiation integral representation for the scattered field, which is then reduced using a uniform asymptotic procedure. New uniform reflection, zero-curvature diffraction, and edge diffraction coefficients are derived and involve the ordinary and incomplete Airy integrals as canonical functions. The UGO/EUTD solution is very efficient and provides useful physical insight into the various scattering and diffraction processes. It is also universal in nature and can be used to effectively describe the scattered fields from flat, strictly concave or convex, and concave-convex boundaries containing edges. Its accuracy is confirmed via comparison with some reference moment method (MM) results     

A physical optics version of the geometrical theory of diffraction

The authors derive a diffraction coefficient which is suitable for calculating the filed diffracted by the vertices of perfectly conducting objects. This diffraction coefficient is used to calculate the field scattered by the corner of a metallic sheet. Two diffraction coefficients, one for edges and one for vertices, are derived by solving the appropriate canonical problems using the physical optics (PO) approximation. The diffraction coefficients are calculated by first using the PO approximation which consists of calculating the total field on the surface of an object from the incident field according to the laws of geometrical optics, and then calculating the scattered field by employing this total surface field in a vector diffraction integral. The validity of the diffraction coefficients has been investigated by comparing their predictions with experimental measurements of the scattered field from a single corner of a rectangular metal sheet, and good agreement was found     

Computation of RCS of targets modelled with trimmed NURBS surfaces

A novel technique for the monostatic radar cross-section (RCS) computation of complex targets modelled with trimmed nonuniform rational B-spline (NURBS) surfaces is proposed using physical optics (PO). The stationary phase method (SPM) is demonstrated to be invalid in evaluation of the PO integral over trimmed surfaces. Thus a new method, which combines SPM with the Gordon method (namely SPM-Gordon) is presented as a substitute and good candidate. Examples show that excellent accuracy is obtained.     

基于时域物理光学法的涂覆目标瞬态散射分析

为了对涂覆雷达吸波材料(RAM)的电大尺寸目标的时域瞬态散射特性和宽带RCS进行快速计算,以满足工程上对目标电磁散射特性的计算向宽频带、向时域靠拢的需求。通过引入阻抗边界条件(IBC),计算了涂覆RAM 目标表面的等效反射系数,将等效反射系数代入频域物理光学法(PO)的表达式,并进行逆傅里叶变换(IFT),推导出了适用于涂覆RAM的目标的时域物理光学法(TDPO)积分表达式。使用OpenGL 控制图形处理器(GPU)来对目标的面元模型进行消隐处理,提高了运算速度。最后通过两个仿真算例,对TDPO与频域PO计算所得的时域瞬态响应和宽带RCS 进行对比,验证了TDPO计算结果与频域PO计算结果具有同等精度。     

Application of physical optics to the RCS computation of bodiesmodeled with NURBS surfaces

The paper presents a method for the computation of the monostatic radar cross section (RCS) of electrically large conducting objects modeled by nonuniform rational B-spline (NURBS) surfaces using the physical optic (PO) technique. The NURBS surfaces are expanded in terms of rational Bezier patches by applying the Cox-De Boor transform algorithm. This transformation is justified because Bezier patches are numerically more stable than NURBS surfaces. The PO integral is evaluated over the parametric space of the Bezier surfaces using asymptotic integration. The scattering field contribution of each Bezier patch is expressed in terms of its geometric parameters. Excellent agreement with PO predictions is obtained. The method is quite efficient because it makes use of a small number of patches to model complex bodies, so it requires very little memory and computing time     

High frequency approximations to the physical optics scatteringintegral

Discusses two high frequency (HF) approximations to the physical optics (PO) scattering integral for the far field radar backscatter from a general curved edged reflecting surface viewed at arbitary aspect. The PO scattering integral is first approximated as the sum of a specular effect and an edge effect, where the latter is represented explicitly as a certain line integral evaluated over the boundary edge of the reflector. A closed form result is then obtained by applying the method of stationary phase to the line integral. With the exception of singularities that can occur at caustics, or when the specular point falls on the boundary edge, these HF approximations are found to work reasonably well for smooth surfaces whose Gaussian curvatures have constant sign (positive or negative, but never zero)     

High-frequency RCS of complex radar targets in real-time

This paper presents a new and original approach for computing the high-frequency radar cross section (RCS) of complex radar targets in real time with a 3-D graphics workstation. The aircraft is modeled with I-DEAS solid modeling software using a parametric surface approach. High-frequency RCS is obtained through physical optics (PO), method of equivalent currents (MEC), physical theory of diffraction (PTD), and impedance boundary condition (IBC). This method is based on a new and original implementation of high-frequency techniques which the authors have called graphical electromagnetic computing (GRECO). A graphical processing approach of an image of the target at the workstation screen is used to identify the surfaces of the target visible from the radar viewpoint and obtain the unit normal at each point. High-frequency approximations to RCS prediction are then easily computed from the knowledge of the unit normal at the illuminated surfaces of the target. The image of the target at the workstation screen (to be processed by GRECO) can be potentially obtained in real time from the I-DEAS geometric model using the 3-D graphics hardware accelerator of the workstation. Therefore, CPU time for RCS prediction is spent only on the electromagnetic part of the computation, while the more time-consuming geometric model manipulations are left to the graphics hardware. This hybrid graphic-electromagnetic computing (GRECO) results in real-time RCS prediction for complex radar targets     

Special problems in applying the physical optics method forbackscatter computations of complicated objects

The backscatter computation of complicated objects is carried by the physical optics (PO) method, known as the vector Kirchoff approximation. The object is described by a geometrical model using flat plates (panels). These panels can be nonperfectly conducting and multilayered. The PO solution for the scattering matrix of a single multilayered panel is evaluated in detail using the Fresnel reflection coefficients. An example of the computed reflection coefficient of a two-layered medium is presented. The phase integral of the PO method is solved analytically. The hidden-surface problem is discussed, and the procedure for the treatment of doubly reflecting panels is described. For an ideal conducting cube with additional surfaces that generate shadow and double-reflection effects, the computed radar cross section (RCS) is compared with measurements. Computational results of the RCS for nonperfectly conducting panels are given     

涂层目标散射的双站物理光学公式及其散射矩阵

本文从物理光学基本假设与阻抗边界条件出发，建立了涂覆雷达吸波材料（ＲＡＭ）的任意三维光滑凸型导电物体散射的基本双站公式。公式是从Ｆｒｅｓｎｅｌ反射系统及阻抗边界条件推导的。本文同时得到了涂层物体表面入射场及其同几何结构导体表面入射场之间的关系与电、磁流比系数关系。文末给出了用基本双站公式计算电大物体双站散射矩阵与双站散射截面的计算方法与计算实例。     

优化算法在手征媒质中的应用研究

由于手征媒质的手征参数可调性,使它成为一种新型的吸波材料,在减缩目标雷达散射截面方面有巨大的应用前景.文中运用传输线法分析了金属衬底上涂敷手征媒质的反射特性,计算了手征参数对手征媒质反射特性的影响;然后基于非均匀有理B样条建模,采用物理光学法比较了目标涂敷常规吸波材料与手征媒质时的雷达散射截面,结果说明了手征媒质减小反射电磁波的效果更好;最后运用粒子群算法和模拟退火算法在给定的范围内优化手征参数,并计算了在此参数下目标的散射截面.