由散射数据计算数值绕射系数

本文研究数值一致性绕射系数的提取方法。在建立散射模型并确认其散射中心后，用ＦＤＴＤ方法计算散射场，并通过电流加窗方法或联立方程组方法以提取所关心散射中心的一致性绕射系数。金属板边缘的例子验证了这一途径的可行性。最后，用这种方法获得了涂层金属板的一致性统射系数，其结果与阻抗劈的ＵＴＤ结果一致。     

表面具有分形结构金属劈边缘绕射系数的提取

本文提出了一种计算数值绕射系数有有效方法，并将之用于提取表面具有分形结构金属劈的绕射系统，利用时域有限差分法提供的散射场，根据几何绕射理论建立含有绕射系数未知量的方程组，通过联立方程组的求解，得到散射体边缘的数值绕射系数。具体计算例子表明，该算法是有效的。     

目标边缘后向绕射场特点分析

本文应用等效电流法和物理绕射理论详细地分析了边缘的几何性质、入 射波方向，极化和波长等因素对边缘绕射场的影响，总结了边缘绕射场的特点。了解边缘后向绕射场的这些特点，这助于正确地分析复杂目标电磁散射特性，特别是对于隐身飞行器的RCS特性分析具有重要的参考价值。     

基于ILDC理论的平面结构电磁散射计算

增量长度绕射系数理论(ILDC)是对电大尺寸复杂目标进行边缘绕射计算的有效方法之一。本文基于散射总场、表面光学场和边缘绕射场三者之间的关系,针对几何建模的特点,从另一个角度推导出了ILDC在平表面结构中的应用形式,并验证了该方法的正确性,为目标电磁特性的研究提供了一种可行的计算方法。     

阻抗劈一致性绕射系数的一种简洁表达式

本文给出了阻抗劈一致性绕射系数的一种简洁易算的表达式，避免了原绕射系数表达式的复杂性和不易实现计算机     

涂层金属平板绕射系数的计算

本文介绍了一种计算目标绕射系数的通用数值方法－－根据时域有限差分（ＦＤＴＤ）方法提供的散射场，通过联立方程组求解绕射系数，所述方法对二维ＴＭ、ＴＥ波均适用，有无涂层情况下金属条板绕射系数的计算例子表明该方法是可行的。     

导体楔加载有损圆柱体的绕射的散射场

利用展开系数法解析了导体楔加载有损圆柱体的绕射和散射场，并且以媒质参数，圆柱体半径，楔的角度为参变量，对绕数射场进行了数值计算，并对数值计算中级数解的收敛性进行了讨论。     

有属性的散射中心理论及应用

讨论了基于物理光学和几何绕射理论的散射中心模型，对有属性的散射中心理论进行了详细的介绍推导，并对散射中心模型的各个参数在图像城进行了估计。结果验证了参数估计方法的有效性和散射中心理论模型的实用性。     

基于ILDC理论的平面结构电磁散射计算

增量长度绕射系数理论(ILDC)是对电大尺寸复杂目标进行边缘绕射计算的有效方法之一。本文基于散射总场、表面光学场和边缘绕射场三者之间的关系，针对几何建模的特点，从另一个角度推导出了ILDC在平表面结构中的应用形式，并验证了该方法的正确性，为目标电磁特性的研究提供了一种可行的计算方法。     

近距离散射跨山通信传播损耗的简便算法

近距离散射跨山通信存在山峰绕射和对流层散射2种电波传播模式,需要按照不同的传播方式计算传播损耗。无论是绕射还是散射,现有的算法都不能快速预计出传播损耗。为了便于在实际应用中对传播损耗做出快速预计,结合实测数据,给出了近距离跨山通信中散射传播损耗的简便工程算法。介绍了山峰绕射传播损耗的计算方法,提出了绕射参数的工程算法,并给出了近距离散射跨山通信站址选择的建议,为选址提供理论参考。     

A spectral domain interpretation of high frequency diffraction phenomena

A spectral domain interpretation of high frequency diffraction phenomena is discussed using the concept of a spectral diffraction coefficient, which resembles Keller's coefficients. The solution of the two-dimensional problems of diffraction of an arbitrary field (with no caustics) by a half-plane is investigated and results are given for any observation angle including, in particular, asymptotic determination of the field at the shadow boundaries. The high frequency scalar diffraction by apertures is formulated in a systematic manner and the formulation, which is valid for any observation angle, is compared with that of other techniques. Results are also given for the diffracted field at the caustics.     

Higher-Order Evaluation of Electromagnetic Diffraction by Circular Disks

The problem of the diffraction of an arbitrary electromagnetic field by a circular perfectly-conducting disk has been solved by using a series representation in powers of k = 2 pi/lambda and the rectangular disk coordinates. The surface current density is given in terms of the field and its derivatives at the center of the disk. General expressions for the electric and magnetic-dipole moments, the farfield and the scattering coefficient for the case of a plane wave at arbitrary incidence are presented. The calculations agree with results published by other authors. A bibliography of the most recent publications on this problem is included.     

Diffraction by lossy dielectric wedges using both heuristic UTDformulations and FDTD

An improvement of the uniform theory of diffraction (UTD) coefficient for the case of a lossy dielectric wedge when a transmitted ray exists is presented. We elaborated two new terms that are added to the classical UTD diffraction coefficient, so that we obtain continuity of the total field. This new UTD formulation is compared to a numerical method based on finite difference time domain (FDTD). We outline the adaptation of the FDTD grid calculation, which was necessary to isolate only one edge diffraction and to treat two-dimensional (2-D) structures with two infinite sides. This comparison allows one to conclude that the new diffraction coefficient is relevant for the case of a lossy dielectric wedge. Then we present a comparison between two different versions of the UTD diffraction coefficient based on single or multiple reflection in the case of a dielectric slab. Thus, we can conclude to the significance of the multipaths for modeling dielectric structures. Finally, we analyze the results obtained with two consecutive wedge vertices in order to show that the slope diffraction related to the doubly diffracted field allows one to predict the field behind the structure when the transmitted field does not exist     

A general, uniform double wedge diffraction coefficient

The uniform theory of diffraction (UTD) is extended to include double diffraction by an arbitrary configuration of two wedges. A scalar double diffraction coefficient is defined which is uniform throughout space while reducing to the product of single diffraction coefficients outside overlapping transition regions. The result is formulated in terms of double Fresnel integrals which can be rapidly evaluated     

A Novel Approach to Over-Rooftop Multiple Diffractions by an Array of Buildings of Arbitrary Height and Spacing for Mobile Radio Wave Propagation

A new approach to obtain field at the receiver due to multiple over-rooftop diffraction by an array of buildings with irregular height and spacing is presented. In the literature, the available approach is based on ray-tracing method that requires higher order diffraction coefficient (slope diffraction). The proposed method is efficient in the sense that it does not require higher order diffraction term to compute field strength. The method is validated by comparing the predicted results with available measurements and earlier results from the literature.     

Reflections, diffractions, and surface waves for an interiorimpedance wedge of arbitrary angle

The asymptotic-impedance wedge solution for plane-wave illumination at normal incidence is examined for interior wedge diffraction. An efficient method for calculating the diffraction coefficient for arbitrary wedge angle is presented, as previous calculations were very difficult except for three specific wedge angles for the uniform geometrical theory of diffraction (UTD) expansion. The asymptotic solution isolates the incident, singly reflected, multiply reflected, diffracted, surface wave, and associated surface wave transition fields. Multiply reflected fields of any order are considered. The multiply reflected fields from the exact solution arise as ratios of auxiliary Maliuzhinets functions; however, by using properties of the Maliuzhinets functions, this representation can be reduced to products of reflection coefficients which are much more efficient for calculation. A surface-wave transition field is added to the surface wave boundaries. Computations are presented for interior wedge diffractions although the formulation is equally valid for both exterior and interior wedges with uniform but different impedances on each face for both soft and hard polarizations. In addition, the accuracy of the high-frequency asymptotic expansion is examined for small diffraction distances by direct comparison of the exact and asymptotic solutions     

A uniform asymptotic theory of electromagnetic diffraction by a curved wedge

Diffraction of an arbitrary electromagnetic optical field by a conducting curved wedge is considered. The diffracted field according to Keller's geometrical theory of diffraction (GTD) can be expressed in a particularly simple form by making use of rotations of the incident and reflected fields about the edge. In this manner only a single scalar diffraction coefficient is involved. Near to shadow boundaries where the GTD solution is not valid, a uniform theory based on the Ansatz of Lewis, Boersma, and Ahluwalia is described. The dominant terms, to the order ofk^{-1/2}included, are used to compute the field exactly on the shadow boundaries. In contrast with the uniform theory of Kouyoumjian and Pathak, some extra terms occur: one depends on the edge curvature and wedge angle; another on the angular rate of change of the incident or reflected field at the point of observation.     

Novel open-resonator for a quasioptical gyrotron

A new kind of open-resonator for a quasioptical gyrotron—an axisymmetrical quasioptical cavity of oblique roiation at arbitrary angle (AQCORAA)—is proposed. Using scalar diffraction theory and an approximate method, the field distributions in the AQCORAA are derived, and the influence of rotating angle on the field distributions is analysed. The stored field energy in the cavity is also obtained.     

液晶空间光调制器与相干光波前实时变换

介绍了一种利用纯相位调制液晶空间光调制器进行波前相位实时变换的方法,可将相干平面波变换成任意期望的波前。该方法采用由伪随机编码产生初始相位矩阵的相位恢复优化算法,从期望的远场衍射图形得到液晶空间光调制器所在衍射面的相位分布,当单色相干平面波通过液晶空间光调制器时,利用液晶空间光调制器纯相位调制特性复现该相位分布,在远场产生期望的衍射图形。实验验证了上述波前实时变换的可行性。