高频无源分布式雷达阵列信号处理技术研究

发布时间：2018-09-19 08:31

【摘要】：高频无源分布式雷达采用天波反射/地波绕射的混合传播模式,能够探测视距以外的低空飞行目标和海面舰船目标。相对于传统的天波高频雷达和地波高频雷达,高频无源雷达具有更大的灵活性,其可实现岸基接收与舰载接收;作为无源雷达,只“静默”接收回波信号而不发射能量,具备抗辐射打击能力,提高了雷达的生存能力。本文所研究的高频无源雷达是一种新体制雷达,其照射源采用DRM数字广播信号,利用天/地混合传播模式,其回波信号中包含强直达波、多径干扰、电离层扰动等多种干扰信号,因而在信号处理过程中会出现诸多难点。本文将对该体制下雷达信号照射源、系统探测模型、信号处理等部分进行探索,为后续研究工作提供必要的基础。课题首先研究了该高频无源雷达所采用的信号体制,完成了DRM数字广播信号的仿真与波形特性分析。进而研究了该信号的模糊函数以及帧结构对信号波形的影响,以判断其是否具有作为雷达照射源的可行性。仿真结果表明,该体制雷达具有图钉状模糊函数,表明其具有良好的分辨性能。讨论了该体制无源雷达系统信号传输模型,分别给出了参考信道、监测信道的回波信号模型,推导了在天地混合传输模式下的雷达方程与目标定位方程;同时,对回波信号中的直达波功率与海杂波信号频率进行了分析。仿真结果表明,直达波相比目标回波信号,其功率高出70 d B以上,这会对目标检测构成影响;理想的海杂波频谱是两根对称的谱线,该性质在信号处理过程中可作为一种特性加以利用。课题研究了切比雪夫准则下的最佳阵列排布问题,推导了最佳阵列排布方程,得到了无方向性等加权条件下的最佳阵列—指数间隔阵列,并分析了该阵列的近轴旁瓣电平、峰值旁瓣电平。由于该阵列旁瓣电平较高,本文讨论了阵列波束优化方案,仿真结果表明:利用改进的窗函数加权后,所得阵列方向图主波束展宽较严重,而最高旁瓣电平并没有得到抑制,而利用凸优化技术进行加权后,所得方向图主波束并未明显展宽,而最高旁瓣电平得到了较好的抑制,对于指数间隔阵列,其最高旁瓣电平降低了1.2 d B,对于对称指数间隔,其最高旁瓣电平降低了1.6 d B。针对高频无源分布式雷达信号处理技术进行了相关研究。由于无源雷达采用DRM数字广播信号,其信号波形具有不确定性,需要利用参考信道信号与监测信道进行相干处理来实现目标检测,这就要求对参考通道信号进行重构,以便得到纯净的信号。在监测信道回波信号中,由于强直达波、电离层干扰以及多径干扰的存在会对目标检测形成干扰,强直达波会淹没目标信号,而电离层引入的调制信息会引起海杂波的展宽,同样会隐藏海杂波附近的目标。本文研究了两种自适应波束形成算法进行直达波、多径干扰的抑制,利用相位梯度算法进行电离层相位扰动补偿。仿真结果表明:MVDR算法与正交投影算法均可以很好的抑制直达波及多径扰动,所得结果目标检测背景并无明显差距,但是相对于MVDR算法,正交投影算法无需对期望信号导向矢量进行估计,这就避免了由于期望信号导向矢量估计不准而引起的误差。通过对电离层相位扰动的分析,可以知道线性相位扰动可以引起频谱平移而不会造成展宽,而非线性相位污染会导致频谱展宽。利用相位梯度算法可以很好地估计小幅度慢变电离层相位污染,较好的对污染结果进行补偿,而对大幅度、快变电离层相位污染,该算法并不适用。
[Abstract]:HF passive distributed radar uses the mixed propagation mode of sky-wave reflection and ground-wave diffraction, which can detect low-altitude flying targets and sea surface ship targets beyond the range of sight. The high frequency passive radar studied in this paper is a new kind of radar. Its illumination source adopts DRM digital broadcasting signal and uses space/ground hybrid propagation mode. Its echo signal contains strong direct wave and multi-path. In this paper, the radar signal illumination source, system detection model, signal processing and other parts of the system will be explored to provide the necessary basis for the follow-up research. First, the signal used by the high-frequency passive radar is studied. The simulation and waveform characteristic analysis of DRM digital broadcasting signal are completed. Then the influence of ambiguity function and frame structure on the waveform of the signal is studied to judge whether it is feasible to be used as radar illumination source. The performance of the passive radar system is discussed. The echo signal model of the reference channel and the monitoring channel is given. The radar equation and the target location equation in the mixed transmission mode are deduced. At the same time, the direct wave power and the sea clutter signal frequency in the echo signal are analyzed. It is shown that the power of direct wave is more than 70 D B higher than that of target echo signal, which will affect target detection. The ideal spectrum of sea clutter is two symmetrical lines, which can be used as a characteristic in signal processing. The optimal array-exponential spaced array without directional weighting is obtained by arranging the array equations. The paraxial sidelobe level and peak sidelobe level of the array are analyzed. The main beam broadening is serious, but the maximum sidelobe level is not suppressed. After weighted by convex optimization technique, the main beam of the pattern is not significantly broadened, but the maximum sidelobe level is well suppressed. For exponential spaced array, the maximum sidelobe level is reduced by 1.2 D B, and for symmetric exponential spaced array, the maximum sidelobe level is the highest. The sidelobe level is reduced by 1.6 D B. The signal processing technology of high frequency passive distributed radar is studied. Because the signal waveform of passive radar is uncertain due to the DRM digital broadcasting signal, it is necessary to use the reference channel signal and the monitoring channel for coherent processing to achieve target detection, which requires the reference channel signal. In the monitoring channel echo signal, the presence of strong direct wave, ionospheric interference and multipath interference will interfere with the target detection, strong direct wave will submerge the target signal, and the modulation information introduced by the ionosphere will cause the sea clutter to widen and also hide the eyes near the sea clutter. In this paper, two adaptive beamforming algorithms are studied to suppress direct wave and multipath interference, and the phase gradient algorithm is used to compensate the Ionospheric Phase disturbance.The simulation results show that the MVDR algorithm and the orthogonal projection algorithm can suppress the direct wave and multipath disturbance very well, and there is no significant difference between the results of target detection background, but the phase gradient algorithm can compensate for the Ionospheric Phase disturbance. Compared with the MVDR algorithm, the orthogonal projection algorithm does not need to estimate the expected signal steering vector, which avoids the error caused by the inaccurate estimation of the expected signal steering vector. The phase gradient algorithm can estimate the phase contamination of the slow ionosphere in small amplitude and compensate for the contamination. However, it is not suitable for the large and fast Ionospheric Phase contamination.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN957.51

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