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1、上海交通大学 硕士学位论文 低可截获概率雷达信号波形侦察技术的研究 姓名：毛炜 申请学位级别：硕士 专业：电磁场与微波技术 指导教师：金荣洪 20051201 上海交通大学硕士学位论文 I 低可截获概率雷达信号波形侦察技术的研究 摘 要 雷达隐身目前已成为雷达在现代战争中生存的重要手段之一 低可截获概率LPI技术是雷达抗干扰抗侦察抗摧毁技术与战 术的综合体现LPI技术在雷达和通信领域有着十分广泛的应用 本论文的研究对象为 LPI 雷达波形侦察技术着重探讨高噪声 背景中雷达回波信号的检测参数估计和干扰信号分离论文立足 于 LPI 雷达信号的最新研究前沿以线性调频连续波FMCW作 为雷达信号研究模
2、型对于时频分析法在非平稳信号处理中的应用 引入希尔伯特-黄变换HHT并提出了改进形式从而提高算法的 效率和精度论文通过仿真说明了改进算法的可行性合理性和有 效性论文研究的目的是为 LPI 雷达信号检测特别是为低信噪比 非平稳信号的时频联合分析提供新的研究方法 论文中以 Gabor 变换Cohen 类时频分布和小波分析为例探 讨了传统时频分析法在 FMCW 信号时频分析中的优势和不足在此 基础上简述一种新的时频分析法FrFT 以及 FrFT 的改进形式 分数阶傅立叶变换域频率相差法该方法可以在低信噪比条件 下对 FMCW 回波信号进行检测并对频移与时延参数进行精确估 计 HHT 变换是一种全新的
3、自适应非平稳信号处理方法论文描述 上海交通大学硕士学位论文 II 了非平稳信号的瞬时频率定义及其存在的意义与前提条件说明了 HHT 变换对于非平稳信号分析的必要性然后根据 HHT 方法的已 有原理改进了 EMD 分解过程中的筛选停止准则提高了分解精 度给出了 Hilbert 谱分析的完整过程简述了 HHT 方法求取局部 均值的合理性论文以 FMCW 信号模型作为研究对象结合改进的 EMD 分解和完整的 Hilbert 谱分析通过分析时频分布特征实现高 噪声背景下雷达目标信号的检测以及干扰信号的提取仿真结果表 明了改进后的 HHT 方法对于低信噪比非平稳信号分析的有效性 作为对 HHT 变换的探
4、索性研究论文还将 HHT 变换引入通信 信号平稳信号处理主要是实现 2FSK 系统的解调通过与传 统解调方法的比较论述了 HHT 方法对于 2FSK 信号的解调过程 仿真表明该方法在解调过程中的抗噪声性能介于相干与非相干解调 之间HHT 方法作为 2FSK 系统解调的核心不仅合理可行而且 易于数字实现 论文对于非平稳信号时频分析法的算法改进研究均通过编写 相应的 MATLAB 程序进行建模仿真和实验验证 论文最后在简要小结研究工作的基础上介绍了 LPI 雷达的现 实实现基础并展望了 LPI 雷达的未来发展趋势 关键词 低可截获概率 LPI时频分布希尔伯特- 黄变换 HHT 调频连续波FMCW调
5、制解调 上海交通大学硕士学位论文 III RESEARCH ON SIGNAL WAVEFORM DETECTION TECHNOLOGIES FOR LOW PROBABILITY OF INTERCEPT (LPI) RADAR ABSTRACT Radar concealment has now become one of the most important technologies for its survival in the current modernized warfares. Low Probability Intercept (LPI) technology is the
6、 centralized reflection of the techniques and tactics which provide radar with the capabilities of anti- interference, anti-detection and anti-destruction. LPI technology has a wide range of applications in the field of both radar and communications. This thesis, which focuses on the research of LPI
7、 radar signal waveform detection technology, mainly aims at the target detection and parameter estimation of radar reflected waves, as well as the extraction of interference signals. Based on the new research achievements of LPI radar, the thesis adopts linear frequency-modulated continuous waveform
8、 (FMCW) signals as the radar signal research model, and in addition briefly discusses the basic conception of time-frequency distribution and Hilbert-Huang Transform (HHT) respectively as the new time-frequency analysis methods in the application of non-stationary signal processing, so as to improve
9、 the effectiveness and precision of the corresponding algorithms. The main purpose of this paper is to find a new creative way for LPI radar signal detection, or say, time-frequency analysis of non- 上海交通大学硕士学位论文 IV stationary signals in low signal-noise ratio (SNR). In this thesis, the traditional t
10、ime-frequency analysis methodGaber transform, Cohen time-frequency distribution and wavelet method are respectively analyzed for their advantages and disadvantages in the applications of time-frequency distribution for FMCW signals. A relatively new time-frequency analysis method, FrFT, is introduce
11、d and the characteristics of FMCW signals by FrFT are shown. An improved form of FrFT, called Frequency Differential Method in FrFT Domain, is genenally described. This new method performs well in the detection of FMCW target signals and precise estimation for the associating time delay and frequenc
12、y shift, even if the SNR is very low. HHT is a completely new adaptive method for non-stationary signal processings. In this thesis, the definition and meaning of instantaneous frequency along with its precondition for existence is described, and the necessity and significance of HHT in non-stationa
13、ry signal processings is accordingly explained. Based on the current theory of HHT, the rationality for HHT to obtain the local mean of the signal is briefly described; the sifting stop guide is improved so that the precision and correctness of the EMD is enhanced; The whole process of Hilbert spect
14、rum analysis is also given and is combined with the corresponding modified EMD. Through the time-frequency distribution characteristics, the HHT method is adopted to detect radar target signal still in the form 上海交通大学硕士学位论文 V of FMCW in strong noise background and extract the interference one as imp
15、ortant potential applications. Simulation results clearly suggest the effectiveness of the method in low-SNR non-stationary signal analysis. As a deeper probe, HHT is also applied to communication signal (stationary signal) processings and is adopted to realize the demodulation of 2FSK systems. The
16、whole process of demodulation by means of HHT is dissertated in detail by comparison with traditional methods. The simulation results prove the fine anti-noise capability and demodulation effectiveness of this new method. For all the algorithm improvements of time-frequency analysis, MATLAB codes are made for simulation models and experiment tests. Brief conclusion of the research above is made in the last part of this thesis. And current realization foundation and future development trend for L
