大时带积非线性调频脉压信号及其性能分析

采用多种频域窗函数综合出了一组大时带积非线性调频脉冲压缩信号,其中一些窗函数的应用尚未见类似的研究报道.本文模拟分析了这类信号的分辨力和多普勒响应性能,并与实验结果进行分析比较,总结了设计大时带积非线性调频脉压信号窗函数的选择原则.该组信号应用于远程警戒雷达可收到增加检测目标动态范围而不降低作用距离的实效.     

椭圆轨道全零多普勒导引律研究

星载合成孔径雷达(SAR)数据处理中,多普勒特性对于方位向性能以及成像精度都有直接的影响。基于轨道动力学理论,在椭圆轨道情况下,该文导出了同时考虑偏航控制和俯仰控制的多普勒中心频率解析表达式,分别分析了偏航控制和俯仰控制对多普勒中心的影响,提出一种基于椭圆轨道的全零多普勒方法,并用TerraSAR-X轨道参数进行了数值仿真,仿真结果表明,使用该方法后,多普勒中心频率被减小到不超过5 Hz,比传统的偏航导引方法缩小了约一百倍,比基于瞬时圆轨道的全零多普勒方法缩小了5倍,表明了该方法的有效性。     

地空导弹系统受噪声干扰时雷达参数测量影响分析

现代战争中导弹和导弹系统在战场中都将受到各种电子干扰 ,导弹系统中的雷达在受噪声等干扰后 ,可能导致各种参数测量误差的增大、发现概率的降低等。研究地空导弹系统中的雷达在受噪声干扰情况下 ,其发现概率、测角精度、测距精度等所受的影响     

SAR图像去噪的分数阶多尺度变分PDE模型及自适应算法

在合成孔径雷达(SAR)图像相干斑噪声抑制中,保持图像的边缘和纹理是非常重要的。该文首先利用分数阶导数和负指数Sobolev空间对图像进行建模,建立了分数阶多尺度变分偏微分方程(PDE)模型,然后给出了模型参数自适应选择方法,并在此基础上提出了区域、尺度自适应的去噪算法。数值实验表明,新方法能在去除噪声,抑制图像的 阶梯效应,保持图像的边缘、纹理细节几个方面取得较好的效果。     

双腔双波长交叉锁模钛宝石飞秒激光器的研究

本文建立了一台双光束泵浦的双腔双波长交叉锁模Ti:Sapphire激光器,实现了中心波长为755nm和845nm的双波长同步锁模输出,得到了脉宽分别为28fs和34fs的锁模脉冲.     

The effects of different dispersion compensation ratios on nonlinear single channel and WDM systems

The effects of the compensation ratio with dispersion post-compensation on nonlinear single channel and WDM systems with 10 Gb/s per channel are numerically investigated. When the transmission signal per channel is 10 Gb/s RZ pulse and the amplifier span is 50 km, proper undercompensation can enhance the performance of the nonlinear single channel system and the nonlinear WDM system. But the enhanced distance of the nonlinear WDM system is not as obvious as that of the single channel system, because the cross-phase-modulation effect plays an important role in the nonlinear WDM system.     

长拖尾K分布杂波下雷达目标散射中心参数的稳健估计

实际条件下,在对基于衰减指数(DE)和模型的雷达目标散射中心参数估计和特征提取时,其噪声背景往往是非高斯的,分布密度函数表现出长拖尾性质。利用基于高斯假设条件下的估计方法进行参数估计时,往往不能得到较好的结果。针对这种情况,该文利用M估计方法来实现对长拖尾杂波下DE模型参数的稳健估计。首先分析了基于PRONY模型的M估计实现方法存在的不足,其次提出了两种较为有效的DE模型散射中心参数M估计的实现方法,并对这两种方法进行了分析和比较。仿真实验结果表明,在一类长拖尾K分布杂波条件下,与ESPRIT方法以及扩展PRONY估计方法相比,该文所提的两种方法均能得到较好的估计结果。     

Impact of wide-band I/Q modulation errors in SAR imaging analysis and compensation method resaerch

Direct quadrature modulation technology is suitable for wide-band radar signal generation. However, this method has rigorous requirements on amplitude and phase balance of the orthogonal input signals. If the requirements are not satisfied, there would be modulation errors such as image frequency and oscillator leakage that cannot be filtered. The modulation errors will therefore raise the noise floor of the range profile and reduce the dynamic range of the Synthetic Aperture Radar (SAR) image as a whole. In this paper, the wide-band In-phase/Quadrature-phase (I/Q) modulation errors are modeling analyzed, and the influence of wide-band I/Q modulation errors on SAR imaging is discussed. Furthermore, a compensation method of modulation errors is proposed, and the circuit implementation of the radar signal generation and pre-distortion is presented. The experimental results illustrate that the curves of the I/Q amplitude and phase imbalance errors are successfully extracted and the rejection of image frequency improved significantly, thus meets the requirements of the SAR imaging.     

Simple algorithm for soil moisture retrieval with co-polarized SAR data

In this paper, an empirical methodology to retrieve bare soil moisture by Synthetic Aperture Radar (SAR) is developed. The model is based on Advanced Integral Equation Model (AIEM). Since AIEM cannot express cross-polarized backscattering coefficients accurately, we propose an empirical model to retrieve soil moisture for bare farmland only with co-polarized SAR data. The soil moisture can be obtained by solving an equation of HH and VV polarized data without any field measurements. Both simulated and real SAR data are used to validate the accuracy of the model. This method is especially effective in a large area where the surface roughness is difficult to be completely measured.     

基于二维ISAR图像序列的雷达目标三维重建方法

该文基于刚体目标3维运动过程中的几何不变性,将因子分解法引入ISAR图像处理领域,成功实现了雷达目标从2维到3维的重建。文中基于卡尔曼滤波和最邻近数据关联准则完成不同姿态下2维散射中心的关联,应用因子分解法进行目标结构的分层重建,最后给出评判准则检验重建性能。仿真实验证明,该文方法简单易行,能够有效实现单天线ISAR 3维成像。