螺钉/铆钉目标电磁散射特性的试验研究

通过系列化雷达散射截面（RCS）测试,研究了单列、多列螺钉/铆钉板在单站多方位、双站的散射特性,分析了不同极化方式、不同排列、不同方位角以及不同双站角对螺钉/铆钉散射的影响及关系。试验结果表明,圆头钉板水平极化明显强于垂直极化;沉头钉板水平极化仅略强于垂直极化。列距不同,由于相位叠加的不同,会导致叠加波峰的位置发生偏移,在设计时可平行间距布置,将散射方向集中。对双站散射,较小双站角时曲线与单站时有一定相似性,但波峰幅度和位置均发生较大变化;较大双站角时,电磁散射表现出耦合效应;双站角使测试曲线偏转,幅度为双站角的1/2;RCS均值随双站角增大而减小。     

反射面天线的双站雷达截面

 本文导出了任意旋转反射器天线在任意双站角的散射场和雷达截面(RCS),其中反射场由几何光学法(GO)求得,绕射场则利用基于物理绕射理论(PTD)与等效线电流辐射积分公式导出的等效电磁流法求得。分别计算了轴向入射和偏轴向入射时在任意散射方向上水平极化与垂直极化两种情况下的双站RCS,并给出了这些结果的立体图形式。方法简化为单站情况时的计算结果与实验值大致相符。     

台阶目标电磁散射特性研究

 通过系列雷达散射截面（RCS）测试,研究了单台阶板随台阶高度变化的规律,分析了多台阶板电磁散射与其高度、间距、极化方式之间的变化关系,并将台阶板散射结果与金属平板结果进行比较,定量总结了各参数对台阶板散射的影响。试验结果表明,台阶高度增加导致散射增强;多台阶间距增大引起曲线振荡增强,说明台阶间耦合作用加强,但RCS均值相对于平板均值增幅不变;多台阶散射表现为各台阶在不同相位上相互叠加的结果。     

低RCS飞行器表面弱散射源研究

飞行器表面不同宽度缝隙、不同高度台阶、不同结构形式对缝（主要包括横向对缝、锯齿对缝两种）等弱散射源对前方雷达截面（RCS）有着比较重要的影响,为了说明控制弱散射源的重要性,介绍了常规飞行器表面结构的缝隙、台阶等弱散射源的分布情况及特点,采用理论方法分析了缝隙的雷达后向散射强度,设计了低RCS载体和实验模型,开展了不同宽度缝隙、不同高度台阶、不同结构形式对缝的RCS实验。结果表明：减小缝隙宽度、台阶高度,采用锯齿缝隙代替直缝隙等方法,是控制隐身飞行器表面电磁缺陷的有效技术途径。     

多台阶板电磁耦合散射试验测量与RCS估算

台阶板在斜入射时的散射主要来自平板后向散射和台阶绕射回波的贡献,在一定条件下还有表面波的贡献。试验表明入射角大于5°时台阶的绕射回波是散射回波的主要组成部分。对于3台阶板,当台阶沿入射方向的距离为半波长的整数倍时,其散射回波相位相同,产生相干叠加使雷达散射截面(RCS)较大,在RCS曲线上反映为波峰。这些波峰的特点是台阶间距越大,波峰越多,且较高波峰与较低波峰交替出现。一种根据台阶散射的叠加估算多台阶板RCS的方法是用单台阶板和平板散射的试验结果按相位相减得到纯台阶的散射,再将平板的散射与多条纯台阶的散射按相位叠加。对3台阶板的预估结果与测试结果符合较好,预估结果的平均误差在3dB以内。     

锯齿台阶目标电磁散射特性研究

通过系列雷达散射截面(RCS)测试,研究分析了锯齿台阶电磁散射特性与其锯齿齿数、锯齿角度、相对于电磁波入射方向的俯仰角之间的变化关系,并将锯齿台阶散射结果与单直台阶进行比较,分析了各参数对锯齿台阶散射的影响。实验结果表明:对于相同齿数的锯齿台阶,当锯齿角度为适当钝角时,可得到较好的散射特性;对于同一锯齿台阶,随其相对于电磁波照射方向的俯角增大,在一定角度范围内其RCS呈下降趋势,散射特性得到改善。     

高超声速半球绕流流场电磁散射特性分析

分析再入流场对飞行器再入通信及空间散射特性的影响,研究电磁波与再入等离子体作用机理.采用分段线性电流密度递归卷积时域有限差分方法计算导电金属半球高超声速绕流流场电磁散射特性,分析半球等离子体包覆绕流流场雷达散射截面(RCS)随入射电磁波频率、双站角、飞行马赫数和高度变化特性.计算表明,前向是全方位散射中RCS取得最大值的方向.马赫数Ma≤10时,马赫数及高度变化对半球高超声速绕流流场L,S波段后向RCS和双站RCS影响很小;在L,S波段,绕流流场及半球本体的后向和前向RCS差距较小.马赫数Ma=14,16时,过密等离子体鞘套的形成增大了本体投影面积,在L,S波段,绕流流场前向RCS比本体前向RCS大;绕流流场存在对半球本体双站散射特性影响很大.      

隐身飞机机身侧棱电磁散射特点分析

隐身飞机机身侧棱是侧向重要散射源,研究其电磁散射特点具有重要意义。建立机身侧棱分析模型,采用多层快速多极子算法(MLFMM)进行计算,获得雷达散射截面(RCS)沿水平面方位角的分布数据;构建RCS峰值、波峰宽度、旁瓣均值三维度评价方法,基于该方法分析机身侧棱电磁散射的极化特性和频率特性;针对棱边长度、棱边尖劈角、棱边厚度三项关键几何参数,建立变参数模型并通过仿真研究RCS对几何参数的敏感性。结果表明:RCS峰值对棱边长度及棱边尖劈角比较敏感,波峰宽度对频率比较敏感,旁瓣均值对频率及棱边尖劈角比较敏感。     

中心锥锥角对航空发动机腔体RCS的影响

为研究航空发动机中心锥锥角对发动机腔体电磁散射特性的影响,采用迭代物理光学法和矩量法计算了不同锥角下雷达散射截面(RCS)随探测角度的变化,分析了不同探测角度范围下RCS平均值的变化趋势。结果表明:在-6°～6°探测角下,中心锥半锥角45°为RCS均值峰值点,半锥角40°及60°时出现RCS均值波谷值;40°或60°半锥角可作为航空发动机中心锥设计参考值。     

考虑旋翼调制影响的直升机RCS特性分析及评估

考虑旋翼调制的影响,建立了适合于直升机全机雷达散射截面(RCS)特性计算的“面元-边缘法”.兼顾计算效率和精度,在外形变化剧烈地区域,网格进行加密处理,并保证电磁网格密度和尺度满足雷达波波长大小的比例关系.以桨盘倾倒方式计入桨叶的挥舞和变距运动,采用准静态法模拟旋翼对全机RCS特性的影响.分析了某直升机RCS极化、姿态、频率响应特性,并根据直升机RCS和雷达探测距离关系,提出了4级预警机制和角域范围.研究表明:旋翼转动时全机RCS动态响应具有连续性和对称性,振荡区散射水平强,RCS幅值为-5~12dB ·m2;奇数片桨叶比偶数片桨叶的RCS减缩2~5dB ·m2,且有利于控制直升机RCS包络线和散射峰值的时域响应,增强雷达隐身性能.      

Effects of two-way decorrelation on radar detection inscintillation

A 3 dB gain in average signal-to-noise ratio of a monostatic radar operating in scintillation has recently been established both theoretically and observationally. The statistics of two-way scintillation are derived here for the case where the uplink and downlink both experience Rayleigh fading and where there is arbitrary correlation between the scintillation on the two paths. These statistics are then used to compute radar detection curves. A surprising result is obtained. The probability of detection is only weakly dependent (for P _D in the range 0.1 to 0.9) on the degree of uplink-downlink correlation in the scintillation when the average (nonfading) signal-to-noise ratio is constant and when proper account is taken of the change in mean power between the monostatic and bistatic cases. Much larger differences are seen in the detection curves with scintillation compared with nonfading curves (for P_D equal to 0.7 this scintillation loss is about 7 dB). Thus the difference in detection performance of monostatic and bistatic radars is determined primarily by the difference in the radar cross section (RCS) of the target for the two cases     

Comparison between monostatic and bistatic antenna configurationsfor STAP

The unique characteristics of bistatic radar operation on the performance of airborne/spaceborne moving target indicator (MTI) radars that use space-time adaptive processing (STAP) are discussed. It has been shown that monostatic STAP radar has the following properties. 1) For a horizontal flight path and a planar Earth the curves of constant clutter Doppler (isodops) are hyperbolas. 2) For a sidelooking antenna geometry the clutter Doppler is range independent. 3) Clutter trajectories in the cosφ-F plane (F=normalized Doppler) are in general ellipses (or straight lines for a sidelooking array). We demonstrate that these well-known properties are distorted by the displacement between transmitter and receiver in a bistatic configuration. It is shown that even for the sidelooking array geometry the clutter Doppler is range-dependent which requires adaptation of the STAP processor for each individual range gate. Conclusions for the design of STAP processors are drawn     

双基地及其联网系统的定位方法及精度分析

讨论的双基地系统中,发射站只起照射目标的作用,而接收站测量距离和、方位角及俯仰角。分析了双基地系统的目标定位方法和定位误差。通过分析定位精度在受控区域内的分布,提示了双基地系统的定位性能。文中对组网双基地系统的定位处理方法进行了讨论,其中采用WLS(Weighted Least Square)算法进行数据融合处理,仿真结果表明,联网双基地系统的定位精度大有提高。     

缝隙目标电磁散射特性试验

 通过对目标结构进行合理设计,可以在一定角域内显著减小雷达散射截面(RCS)。对飞行器表面常见锯齿缝隙的散射特性进行了研究。在微波暗室内对锯齿缝隙分别沿俯仰角变化、方位角变化的减缩效果进行测试。俯仰角变化时,锯齿缝隙有较好的减缩作用,以114°锯齿缝隙在试验中减缩效果最好。方位角变化时,对114°锯齿缝隙进行了多频段测试,并与相应直缝隙进行了对比研究,结果表明,通过选取合适的方位角角域,锯齿缝隙的减缩作用会随入射波频率的升高和仰角的增大而显著增强。结论可为高性能隐身飞行器外形隐身设计提供参考。     

Position Accuracy in Netted Monostatic and Bistatic Radar

The combined position-finding accuracies of netted monostatic and netted bistatic radars are calculated. Both are compared by the ratio of the areas of the error ellipses. This is illustrated by two symmetrical examples of configurations, a linear and a triangular one, with an equal tangential-to-radial measurement error ratio. It is shown that the results essentially depend on the range dependence of the measurement errors.     

A Raw Signal Simulator for Bistatic SAR

This article proposes a new efficient raw signal simulator for the bistatic synthetic aperture radar (SAR) based on 2D fast Fourier transform (FFT) to deal with cases of both ideal trajectory and trajectory deviation. It begins with analyzing the geometric configuration and the range history of the bistatic SAR in side-looking and squint modes of ideal trajectory as well as trajectory deviation. Then a detailed and mathematical study is conducted on the equivalence relation of bistatic-to-monostatic applications (BTMA) in the case of ideal trajectory and trajectory deviation. Also a set of formulas are derived for the equivalence relation between bistatic SAR and monostatic SAR on some reasonable assumptions. Therefore, the application of the simulation method based on the 2D FFT for the monostatic SAR can be extended to the case of bistatic SAR. Finally, the simulation results prove the validity of this method. By comparing the efficiency of the proposed method with that of the time domain method, it is shown that the former is a few orders of magnitude higher.     

高超声速锥模型及其尾迹电磁散射实验研究

介绍了利用X、Ka波段雷达系统在中国空气动力研究与发展中心超高速所弹道靶上开展了金属锥模型和开槽锥模型及其尾迹的电磁散射截面积（RCS）实验研究,模型底部直径12mm、半锥角和头部半径分别为12.5°和1.0金属锥模型速度大于6km/s,飞行环境压力为6.8kPa;开槽锥模型速度5.4km/s,飞行环境压力7.5kPa,雷达测量方式为X波段单站,Ka波段单站。实验结果表明：在等离子体绕流场包覆模型时,获得的锥模型单站X波段RCS、单站Ka波段RCS的实验结果与数值计算结果较为吻合;锥模型的单站后向电磁散射主要集中在模型头身部区域,尾迹散射相对较小。     

Polar format algorithm for bistatic SAR

Matched filtering (MF) of phase history data is a mathematically ideal but computationally expensive approach to bistatic synthetic aperture radar (SAR) image formation. Fast backprojection algorithms (BPAs) for image formation have recently been shown to give improved O(N/sup 2/ log/sub 2/N) performance. An O(N/sup 2/ log/sub 2/N) bistatic polar format algorithm (PFA) based on a bistatic far-field assumption is derived. This algorithm is a generalization of the popular PFA for monostatic SAR image formation and is highly amenable to implementation with existing monostatic image formation processors. Limits on the size of an imaged scene, analogous to those in monostatic systems, are derived for the bistatic PFA.     

"狼群"干扰对单、双基地雷达的干扰分析

"狼群"干扰是美国正在研制的一种分布式干扰.文中分析了"狼群"干扰对单、双基地雷达的影响,结果表明,"狼群"干扰对单、双基地雷达构成了严重的威胁.在理论分析计算的基础上,提出了抗"狼群"干扰的可能方法.