【作者】 张雅斌；

【导师】 张守宏；

【作者基本信息】 西安电子科技大学 ， 信号与信息处理， 2010， 博士

【摘要】 近年来,高频地波雷达在军事和民用领域得到了广泛应用。该体制雷达能弥补常规微波雷达的低空盲区和天波超视距雷达的近距盲区,具有远程预警、反隐身、反超低空突防和反辐射导弹等优点。采用综合脉冲与孔径体制(SIAR)的岸舰双/多基高频地波雷达,接收平台可置于移动舰船上,具有良好的机动作战能力。影响高频地波雷达目标检测的主要因素是干扰和海杂波,前者包括短波通信、广播电台、雷电、流星余迹和电离层干扰等,后者包括接收平台运动或海态自身变化等因素产生的频谱展宽海杂波。本论文针对高频地波(综合脉冲与孔径)雷达工作中的各类干扰和展宽海杂波的抑制处理问题展开研究,主要内容和创新点如下:1.详细分析了射频干扰的相关性与能量分布特征,并对雷电、流星余迹瞬态干扰和电离层干扰特征进行了总结。分析表明,射频干扰的相关和能量分布在时域和距离域上都存在明显特征。如果利用干扰相关特性进行抑制,可从距离域出发只针对若干感兴趣距离单元处理,比时域直接处理运算量小。如果利用干扰能量分布特征进行抑制,可以从快时域出发直接进行剔除,剔除过程将减小目标的能量积累,并对海杂波产生时域加窗效应而在频域产生虚假旁瓣。雷电瞬态干扰在距离单元之间不具有相关性,低通滤波输出端上出现区间随调频周期变化,并会出现在所有的距离—多普勒分辨单元上,因此,可以考虑从时域出发利用干扰与目标杂波信号的差异进行检测与剔除。2.从单路接收信号出发,对已有射频干扰抑制方法进行了分析与改进:针对剔除法,借鉴线性调频体制中的时域剔除思想,提出了适合于脉冲编码体制的频域剔除法;针对特征子空间法,引入负距离单元训练样本,提出了通过相关性大小进行距离加权来估计相关矩阵的加权子空间法;针对相消法,根据射频干扰能量分布和信号本身参数之间的关系,给出了单频干扰特征频率的估计方法,然后从时域上反演构造出与原始干扰回波完全相干的参考信号,以此为基础提出了反演相消法。最后,针对包含单频和窄带成分的混合干扰,结合反演相消法给出了综合法的处理流程。仿真结果表明,与其它方法相比,反演相消综合法能够有效抑制射频干扰,具有较高的目标增益。本章方法和结论即适合于常规地波雷达,也适合于综合脉冲孔径雷达。3.基于雷电和流星余迹干扰信号的差异,改进了瞬态干扰抑制方法。对于雷电,提出了小波分析—矩阵分解抑制法:首先应用小波分析检测确定干扰出现区间,然后选取干扰邻近数据构造采样矩阵并进行奇异值分解,最终实现干扰的剔除和目标分量的有效积累。方法可以减小直接对原始序列等分处理进行矩阵构造与分解的计算量,提高置零区间回波的恢复精度。针对流星余迹,给出了海杂波约束条件下的空域自适应滤波法。方法在次累积时间内构造相关矩阵进行自适应波束形成抑制干扰时,考虑了时间分段处理对海杂波调制所产生的频谱展宽影响,使得回波中一阶海杂波时域相关特性不会发生破坏而在频域上虚假展宽,有利于后续频域处理中对落入Bragg峰附近的舰船目标进行检测。4.结合综合脉冲与孔径雷达信号处理流程,对电离层的干扰信号模型进行了分析。通过阵元和快时域联合采样构造空时快拍,给出了基于海杂波主成分随机约束的空时二维自适应滤波抑制法。其中,针对回波中的海杂波主成分,通过构造Hankel矩阵与SVD分解方法实现其瞬时频率的估计与预处理。仿真与实测数据结果验证了电离层干扰抑制方法的有效性。5.对综合脉冲孔径雷达接收平台运动情况下一阶海杂波频谱特征进行分析后,结合海杂波谱空时分布随距离变化和系统参数的先验信息,提出了直接数据域和时空插值联合的海杂波空时二维自适应处理抑制方法。方法首先对训练单元上的非均匀杂波样本进行空时二维插值,然后使用直接数据域法对得到的独立同分布训练样本矩阵进行目标相消与滑窗处理,以扩大空时二维快拍训练样本个数。通过这些训练样本对检测单元杂波相关矩阵进行估计后,构造空时二维滤波器实现了运动平台下的海杂波自适应抑制。6.在非平稳海杂波频谱变化特征与高分辨谱估计方法基础上,提出了基于AR过程的非平稳海杂波时域参数联合估计方法,对非平稳序列包含的多个AR过程出现区间和对应滤波系数进行最优估计,目的是从时域出发对非平稳参数进行估计以提高频谱分析的精度。期间,引入小波分析中的奇异信号检测缩小了各段AR过程分界点的搜索范围,给出了AR子段出现区间和阶数的快速搜索算法。在非平稳海杂波时域参数分析基础上,结合Wigner-Ville时频分析与Radon变换的机动目标运动参数估计,提出了基于海杂波时域参数估计的机动目标检测方法。仿真实验表明,方法能有效抑制非平稳一阶海杂波的频谱展宽与功率,提高机动目标的检测能力。更多还原

【Abstract】 In recent years, HF Surface Wave Radar (HF-SWR) has been widely used in military and civilian fields. Its detection range is up to 300-400Km which can compensate blind spots of conventional microwave radar at low altitude and that of Sky Wave Over-the-Horizon Radar in near ranges. HF-SWR take the advantages of long distance and early warning surveillance, anti-stealth, anti-altitude penetration and ARM(Anti-Radiation Missiles). As a new kind of HF-SWR, coast-ship bistatic/multistatic Surface Wave Over-The-Horizon Radar can adopt Synthetic Impulse and Aperture Radar(SIAR) mechanism and can be installed receiver on maneuvering boats, so the system has good maneuverability during military operation over ocean. HF interference and sea clutter are two adverse factors during target detection of HF-SWR. The former includes the short-wave radio communications, lightning, meteor trail echoes, ionospheric interference and so on. The latter relate to spectrum broadening of sea clutter caused by factors such as bistatic structure and receiver movement. This dissertation is focused on suppression processing of HF interference and sea clutter in HF-SWR and SIAR. The main contents and innovation are summarized as follows:1. Correlation and energy distribution characteristics of Radio Frequency interference were analyzed. Meanwhile, characteristics of transient interference including thunder lightning and meteor trails and ionospheric interference are briefly summarized. Simulation results show that the correlation and energy distribution properties of Radio Frequency interference have distinct characteristics in time and range domain. When using correlation characteristics, interference suppression can be obtained by a number of training samples from interested ranges, and computing load is smaller than suppression processing from time domain. When using characteristic of interference energy distribution, suppression can be obtained by excising process in fast time domain but which has side effectives such as target energy loss and windowing effects to sea clutter and consequently high side-lobe in frequency domain. Correlation coefficients of lightning interference between ranges are small and appear time of interference changes between frequency-modulation periods in the low-pass filtering output. Lightning energy are distributed in all Range-Doppler cell and can be detected and removed in time domain by its difference from target and clutter echoes. 2. RF interference suppression methods are analyzed and improved based on single channel echo. During excising suppression, excising method in frequency domain is proposed for coding-modulation system which is similar to time domain excising in FMICW system. During eigen-subspace suppression, interference subspace is well estimation by adopting negative range training samples and range weights for correlation matrix calculation. During cancellation suppression, estimation algorithm for characteristic frequency of RF interference is proposed according to signal parameters and power distribution location. Then Construction-Cancellation suppression method is proposed based on Wiener filter where the reference signal coherent to interference is constructed by the carrier frequency estimated. Finally the comprehensive suppression procedure based on Construction-Cancellation suppression is proposed for composite interference comprise of single-frequency and narrowband components. Simulation results show that comprehensive suppression procedure can get effective results than other methods and with higher target gain. Suppression algorithms above are suitable for conventional ground wave radar and SIAR.3. Transient interference suppression algorithms were introduced and improved based on the difference between lightning and Meteor trail echoes. The algorithm combining wavelet analysis and matrix decomposition for lightning suppression is proposed. First, wavelet analysis is applied for interference detection and then the sample matrix is constructed adaptively by training data near interference component. Then SVD is applied to the matrix by process of which interference components are removed and target energy is effectively accumulated using AR extrapolation. This method can reduce computing load and increase recovery accuracy of target component when compared to the process of uniform truncation for training matrix construction and decomposition which is regardless of interference information. In Meteor trail suppression, interference covariance matrix is constructed adaptively in sub-CPI and an improved adaptive beamforming algorithm introducing clutter constraints is presented which do not destroy time coherence of the first-order Sea clutter after interference suppression and benefits target detection in frequency domain subsequently.4. With Synthetic Impulse and Aperture Radar signal processing the ionosphere interference is analyzed. Using space-time snapshots constructed jointly through array elements and fast time samples, interference adaptive suppression algorithm is proposed by the virtue of random constraint to sea clutter in space-time domain. Meanwhile, main component of sea clutter is effectively traced by constructing Hankel matrix and instantaneous frequency is estimated by SVD decomposition. Simulation and experimental results validate the suppression algorithm for ionospheric interference.5. Sea clutter spreading spectrum is analyzed under the condition of receiver moving in Synthetic Impulse and Aperture Radar, and joint space-time adaptive processing for non-stationary clutter between range cells is discussed. Based on two dimensional distribution characteristics of sea clutter spectrum, space-time adaptive processing (STAP) algorithm is applied to suppress spreading sea clutter: space-time interpolation is applied to non-uniform training samples according to relationship between clutter spectrum and system geometry parameters , thenafter, Direct Data Domain method is adopt to get enough training samples for Sea clutter STAP.6. Characteristics of nonstationary sea clutter sequence are analyzed and high resolution spectral estimation methods are introduced. To improve the accuracy of frequency-domain analysis for non-stationary radar echoes, joint estimation of multi-parameter method in time domain is proposed for the number of stable AR processes and corresponding filter coefficients. During optimal estimation of signal parameters for nonstationary sequence, wavelet analysis for singular signal detection has reduced the searching ranges which contain borderlines of AR sections. Thenafter, maneuvering target detection method according to time-domain characteristics of sea clutter is proposed after target motion parameter estimation process by Wigner-Ville time-frequency analysis (TFA) and Radon transform. Simulation shows that time-domain parameter estimation and maneuvering target detection methods for high-frequency ground wave radar echo can effectively reduce the first-order spectrum width and suppress second-order spectrum and then improve the detection capability to maneuvering target.更多还原