【作者】 李明；

【导师】 廖桂生；

【作者基本信息】 西安电子科技大学 ， 信号与信息处理， 2011， 博士

【摘要】 空时自适应处理(STAP)技术可以有效地抑制机载雷达地杂波和有源干扰,改善地面动目标检测(GMTD)性能,其处理性能的优劣与杂波干扰协方差矩阵估计的准确性有直接关系。当接收的雷达回波样本不满足独立同分布(iid)特性时,通过统计方法获得的杂波协方差矩阵存在偏差,导致STAP的杂波抑制性能严重下降。如何使得STAP方法在非均匀杂波环境下取得好的杂波抑制性能是本文开展研究的目的。本文的主要工作包括以下几个方面:1.第二章首先对不同阵面摆放结构下的单基机载雷达杂波进行了建模,分析了与其对应的杂波分布特性,然后对STAP进行杂波抑制的基本原理进行了介绍,最后针对杂波呈现非均匀分布的两种情况进行了说明,一种是由实际环境导致的杂波功率非均匀特性;另一种是由机载雷达天线阵面摆放方式所带来的杂波非均匀特性。2.第三章研究了杂波功率非均匀情况下的直接数据域杂波抑制方法。针对直接数据域(DDD)方法中空时子孔径平滑来获取iid样本存在空时孔径损失的问题,将多级维纳滤波器(MWF)引入到直接数据域方法的求解过程里,提出了一种在直接数据域方法后级联多级维纳滤波器的方法。通过对MCARM数据的处理结果验证了该方法在较小空时孔径损失的条件下能够获得较直接处理好的杂波抑制性能。针对实际中距离脉冲压缩加窗函数处理后会导致目标信息扩展现象,提出了一种联合距离的三维直接数据域方法。该方法将目标周边距离单元的数据联合起来,充分利用目标距离向上的信息,在空域上能够对孤立干扰形成深的凹口,提高了对目标导向矢量幅相误差的稳健性。通过MCARM数据处理验证了该方法的有效性。3.第四章研究了由于天线阵面摆放方式导致的杂波非均匀问题,考虑无距离模糊的情况。针对空间角频移方法将参考距离单元的杂波谱旁瓣谱抬高,导致动目标检测性能下降的缺点,提出了一种改进的空间角频移方法。该方法首先对各个距离单元回波进行多普勒频率补偿,然后再进行空间角频移。仿真实验结果表明该方法在旁瓣区比空间角频移方法有性能改善。另外针对导数更新(DBU)方法计算量大的缺点,提出了一种可以直接对前视阵雷达接收的回波数据协方差矩阵进行修正的降维DBU方法。该方法利用矩阵分块求逆定理求出修正矩阵,然后利用已有的3DT-STAP方法进行杂波抑制,不但减少了计算负担而且降低了对独立同分布(IID)样本数目的要求,并且在性能上接近原来的DBU最优处理方法。通过实验结果表明该方法在回波存在误差条件下仍然能达到与最优处理接近的性能。4.第五章研究了因天线阵面放置导致的杂波非均匀性问题,考虑存在距离模糊情况。针对接收阵列没有俯仰自由度,不能直接对模糊的近程杂波进行抑制的问题,根据机载非正侧视阵雷达的杂波谱分布具有一定的先验信息特性,提出了一种基于空时插值的机载非正侧视阵雷达近程杂波抑制方法。该方法首先利用距离采样估计出近程模糊距离门的俯仰角,然后将模糊的近程杂波向远程模糊距离门进行空时插值,并且增加了对待检测方向地面运动目标的保护约束。通过对仿真雷达回波的处理结果验证了该方法的有效性。特别地对于机载前视阵雷达,由于其杂波多普勒-方位分布在空间上呈现对称性,基于这一现象,提出了一种向待检测距离段中间距离单元空域导向矢量空间投影的近程杂波抑制方法,通过对仿真雷达回波的处理结果验证了该方法的有效性。5.第六章研究存在非理想因素条件下稳健的非均匀杂波抑制问题。针对接收阵列具有俯仰自由度的前提下,提出了一种对雷达载机平台高度误差稳健的俯仰预滤波方法。该方法首先根据不同距离门斜距计算出近程距离门对应的俯仰角,然后增加与其临近的距离门俯仰角来辅助进行近程杂波抑制,当存在载机平台高度估计误差时,该方法能够获得较单点预滤波稳健的杂波抑制性能,仿真实验结果验证了该方法的有效性。6.第七章研究了机载双基雷达STAP方法。建立了各种构型的机载双基雷达信号模型,并对其地杂波分布特性进行了分析。由于实际中两载机通常不再一个平面上,针对当两载机之间存在高度差时,产生的垂直基线对不同构型机载双基雷达的地杂波分布影响进行了分析。针对机载双基雷达回波的距离非均匀特性提出了一种基于导数更新的杂波补偿方法,该方法以接收载机主瓣方向的接收斜距与俯仰角为DBU更新变量,能够有效地实现对杂波距离依赖性的补偿,提高机载双基雷达STAP杂波抑制性能,仿真实验验证了所提出方法的有效性。更多还原

【Abstract】 The space-time adaptive processing (STAP) is an important technique for ground moving target detection (GMTD) against strong clutter and interference in airborne radar system, and the performance of STAP is determined by the clutter plus noise covariance matrix estimation. When the clutter samples occur heterogeneous distribution, then the clutter suppression performance declines greatly due to the covariance matrix estimate inaccuracy. The motive of this thesis is that makes STAP obtain anticipant performance by the clutter within heterogeneity. The main work can be summarized as follows:1. In chapter 2, the clutter of different antenna array configuration for airborne radar is modeling. Then the relationship between the clutter distribution characteristic and the configuration is analysised. The principles of the STAP algorithms are described. The clutter occurs heterogeneous distribution on the two sides; the one is the clutter power heterogeneity, the other is antenna array configuration heterogeneity.2. In chapter 3, the Direct Data Domain (DDD) based methods are studied by the clutter within heavy power heterogeneity. As is known that the DDD method obtains enough samples from one range gate by sub-aperture smoothing operation, however, gets the space-time aperture lost. Due to the Multistage Wiener Filter (MWF) does not need covariance matrix estimation and inverse, a new DDD method that hybrid MWF is proposed. This algorithm can obtain better performance than conventional DDD method within low aperture loss. The results of the experiments on the MCARM data show the validity of the method. Usually, the target information spreads due to the range compression by using the window function. To deal with this problem, a robust DDD method is proposed. The algorithm can make full use of the additional information on range and therefore has a deeper notch against isolated interference. Moreover, it is robust to the steering vector with gain and phase uncertain errors. The experiments carried on the MCARM data shows validity of the algorithm3. In chapter 4, the clutter heterogeneity by the antenna array configuration without range ambiguity is studied. To deal with the problem that the moving target detection performance decreases, due to that the spatial angle frequency shifting algorithm enhances the side lobe of the reference range clutter spectrum. Aiming at this problem, a new spatial angle frequency shifting spectrum compensation for forward looking radar is proposed. The algorithm compensates the clutter Doppler frequency of each range cell before using spatial angle frequency shifting. The results of experiment show that the improved algorithm can obtain better performance than spatial angle frequency shifting, and without performance loss under radar clutter with some uncertain errors. To deal with the disadvantage of heavy computational load for derivative based updating (DBU) method, an approach named reduced dimensional DBU algorithm is proposed. The algorithm using matrix block inverse theorem to get revised matrix, then use the reduced dimensional space time adaptive processing(STAP)method of 3-DT. This method can decrease the computational load, reduce the required number of the independent identically distributed (IID) samples, and reach to the original optimal DBU method performance.The results of experiment show that the proposed method still can obtain good performance near the optimal processing when some uncertain errors exist.4. In chapter 5, the clutter heterogeneity by the antenna array configuration with range ambiguity is studied. Due to the linear array has not elevation degree, the short-range clutter cannot be suppressed directly when the range ambiguity exists. By using the pre-information of the clutter spectrum of the non-SLAR, a short-range clutter suppression method for non-SLAR under uniform linear array is proposed. This method estimates the elevation angles of the ambiguous short range gates, and then eliminates short range clutter by space time interpolation while adding the moving target protection in the method. This method can achieve considerable performance of short range clutter suppression. Simulation results show the validity of the method. Especially, the direction-Doppler curves are symmetry for FLAR. Based on this characteristic, a simple and efficient algorithm to suppress range ambiguous clutter for FLAR is proposed. The method uses the data after Doppler filter project to the space of the spatial steering vector which belongs to the middle of the range number. The method reduces the computation complexity and can obtain better performance. The computer simulation results show the valid of this method.5. In chapter 6, the robust nonhomogeneous clutter suppression by the clutter with uncertain errors is studied. A robust elevation prefiltering method is proposed. This method can suppress the ambiguous short-range clutter by adding multi-elevation angles constraint, which results in a deep and wide beam notch in the elevation angle corresponding to the short range. Moreover, the method offers potential robustness to the platform height errors. The residual range-independent clutter can be suppressed by two-dimensional azimuth-Doppler STAP methods. The simulation results show the validity of the method.6. In chapter 7, the clutter suppression for bistatic airborne radar is studied. In factual environments, the vertical heights of the transmitter aircraft and the receiver aircraft are always different, as a result, the vertical baseline appears between the two platforms. This paper analyses the influence of the vertical baseline on bistatic airborne radar. Due to the clutter has range dependence for bistatic airborne radar, and which causes conventional space time adaptive processing (STAP) methods to get low GMTD performance. To deal with this problem, two new compensating methods based on derivative based updating (DBU) are proposed: using received distance in the direction of the main lobe of beam pattern; using receive elevation angle cosine in the direction of the main lobe of the beam pattern. The results of the bistatic radar data based on computer simulation show the two methods can mitigate the clutter range dependence and improve the clutter suppression performance.更多还原