大转角条件下二维计算雷达像的改进

为提高转台目标成像时的横向分辨率,需增大转角,而增大转角会引起雷达像模糊。文中在频率空间的直角坐标系中用板块法仿真出大转角转台目标的雷达回波数据,然后用二维快速傅里叶变换对回波数据进行处理,从而获得转台目标的雷达像。经过对仿真数据进行验证,用该方法获得的二维雷达像,其质量高于用极坐标回波数据所成的像     

分析二维导体电磁散射问题的FEM/POPTD方法——TE模(英文)

提出了一种分析计算带有裂缝的二维电大尺寸复杂导体目标电磁散射问题的混合方法—— FEM/ PO-PTD方法。该方法采用基于棱边的有限元法 ( Edge-basedFEM)为低频方法 ,物理光学法与物理绕射理论 ( PO-PTD)为高频方法 ,通过耦合技术将两者结合在一起。本文将该方法应用于带有缝隙的二维导电柱 TE模的电磁散射特性分析 ,计算结果与有关文献的数据一致性很好 ,从而验证了该方法的准确性。文中还给出了另外几种截面的导电柱体雷达截面的计算曲线。理论分析与计算结果表明 ,本文提出的混合方法与其他计算同类问题的方法相比 ,能节省计算机存储单元、提高计算速度     

2μm波段单频拉曼光纤放大器中受激布里渊散射研究

2μm波段高功率单频拉曼光纤放大器(SF-RFA)的性能通常会受到受激布里渊散射(SBS)效应的影响.本文考虑SBS效应下拉曼光纤放大器的速率方程,建立了SBS限制下的SF-RFA理论模型,计算了SF-RFA的能量分布和功率输出.讨论了泵浦功率、光纤长度等因素对光纤放大器中SBS效应和输出功率的影响,总结了如何在提高放大器输出功率的同时有效抑制SBS效应的方法.本文数值模拟结果为实验研究高功率SF-RFA中抑制SBS效应提供一定的指导.     

基于优化加权高分辨距离像的雷达目标识别(英文)

对雷达目标高分辨距离像进行特征加权可以解决高分辨距离像各距离单元因目标姿态变化而导致的稳定性不一致问题。针对已有加权系数求解方法存在的不足,提出一种加权系数优化方法。该方法通过定义目标函数来度量不同雷达目标之间加权高分辨距离像的可分性,并采用梯度下降算法优化加权系数值,从而达到增强高分辨距离像稳定距离单元作用,减小不稳定距离单元影响的目的。基于5种飞机目标模型高分辨距离像的仿真实验表明,该方法可以有效优化加权系数,并提高雷达目标识别率。     

机载箔条弹雷达回波的建模与仿真

飞机目标通常抛撒箔条弹来干扰雷达的工作。针对这一作战场景,首先研究分析了飞机与箔条的运动特性和雷达回波特性,导出了对于地基防御雷达而言,箔条弹在时域上可视为点目标、在多谱勒域上可不考虑其多谱勒展宽效应的结论。在此基础之上,建立了箔条干扰的数学和仿真模型,模拟并分析了飞机加箔条的运动状态和雷达回波特性。研究成果有助于揭示箔条干扰的雷达特性,评估箔条的干扰效果。     

X-Rays From Mars

X-rays from Mars were first detected in July 2001 with the satellite Chandra. The main source of this radiation was fluorescent scattering of solar X-rays in its upper atmosphere. In addition, the presence of an extended X-ray halo was indicated, probably resulting from charge exchange interactions between highly charged heavy ions in the solar wind and neutrals in the Martian exosphere. The statistical significance of the X-ray halo, however, was very low. In November 2003, Mars was observed again in X-rays, this time with the satellite XMM-Newton. This observation, characterized by a considerably higher sensitivity, confirmed the presence of the X-ray halo and proved that charge exchange is indeed the origin of the emission. This was the first definite detection of charge exchange induced X-ray emission from the exosphere of another planet. Previously, this kind of emission had been detected from comets (which are largely exospheres) and from the terrestrial exosphere. Because charge exchange interactions between atmospheric constituents and solar wind ions are considered as an important nonthermal escape mechanism, probably responsible for a significant loss of the Martian atmosphere, X-ray observations may lead to a better understanding of the present state of the Martian atmosphere and its evolution. X-ray images of the Martian exosphere in specific emission lines exhibited a highly anisotropic morphology, varying with individual ions and ionization states. With its capability to trace the X-ray emission out to at least 8 Mars radii, XMM-Newton can explore exospheric regions far beyond those that have been observationally explored to date. Thus, X-ray observations provide a novel method for studying processes in the Martian exosphere on a global scale.     

Planar laser scattering visualization of streamwise vortex pairs in a Mach 6 flow

A series of cross-sectional flow fields of Counterrotating Vortex Pairs(CVPs) generated by a large-scale ramp vortex generator is observed using an ice-cluster-based Planar Laser Scattering(PLS) method in a shock tunnel with a nominal flow Mach number of 6. Combined with a numerical simulation, two streamwise CVPs with opposite rotating directions are identified in the wake flow of the vortex generator with an absence of a boundary layer, namely, a Primary CVP(PCVP) and a Secondary CVP(SCVP). Th...     

一种直升机进气道方案的电磁散射特性

本文对一种与发动机舱融合设计的直升机进气道在不同的极化方式、不同终端、不同攻角和方位角下的电磁散射特性进行了实验研究,分析了各种状态下雷达散射特性。研究表明,该类进气道RCS在垂直极化方式时比水平极化方式小;采用短路终端时的RCS明显要比采用叶片终端时高;近侧飞时(90°～105°)比前飞和近倒飞状况下的雷达散射截面大;在攻角分别为-10°,-5°,0°,5°,10°的实验中,当攻角为10°时的RCS值较小,而当攻角为-5°时的RCS值较大。     

运动等离子柱体的电磁散射

 本文应用Minkowski变换研究了轴向运动非均匀等离子柱体的电磁散射。表明在坐标变换中易于导出相应稳态问题的解。文中详细研究了一半径为1m的等离子柱体的一些散射远场特性,其中包括远场方向图和后向散射横截面积(RCS)。     

复合材料的射线检测技术

简述了复合材料无损检测方面一些通用的射线检测方法，并通过对胶片射线照相技术、射线实时成像技术、计算机断层扫描成像技术、康普顿背散射成像技术等射线检测技术的系统介绍，展望了未来复合材料射线检测技术的发展趋势。