【作者】 周浩；

【导师】 吴世才； 文必洋；

【作者基本信息】 武汉大学 ， 无线电物理， 2004， 博士

【摘要】 各种不同频率、不同功能的雷达正广泛地应用于人类活动的诸多领域，其中工作在高频段的雷达因具有超视距探测能力而在近几十年来受到了特别的关注。借助于天波或地波传播方式，高频雷达的探测范围突破了地球曲率的限制，因此使远距离空中预警和目标监测成为可能，同时高频雷达所具有的独特和良好的对低可探测性目标的探测能力，使之成为探测隐形飞行器和处于强地杂波和海杂波背景中的小型军用飞机、巡航导弹等贴地、贴海飞行的小目标及洲际导弹进行有效探测的有力装备。高频超视距雷达的造价也大大低于星载雷达系统。正是由于这些优势，高频超视距雷达成为近代各军事大国的重要装备，目前已是预警和远程警戒情报雷达中的主要支柱。除了军事目的，高频超视距雷达在国家经济建设中也有重要作用。高频雷达可用于海洋表面状态参数遥感，能大面积、全天候地实时监测海面风、浪和流场参数，较之传统的波浪仪、浮标等海洋测量工具和海洋遥感卫星，具有成本低、实时性好等不可比拟的优势。高频雷达还成功应用于海上冰山的探测。高频雷达在海洋环境预报、渔业、海洋排污、海上搜救、海运管理及海上桥梁建设等方面都有着重要意义，而高频雷达所能提供的有效的海洋实时监测手段，对临海国家在联合国海洋公约规定的200海里(370公里)专属经济区(EEZ)内更好地维护权利和履行义务，则更具有特别的重要意义。 我国国土辽阔，海域宽广，边界线长，高频超视距雷达特别适宜于那些因地理因素、通信及后勤等原因而无法架设雷达所造成的不可探测区域以及海洋环境和海上目标的实时监测。加紧对高频超视距雷达的研究和开发，将为我国的国家安全和经济建设提供强有力的保障，对国计民生都有着重要意义。 高频超视距雷达基本上存在两条技术路线：一是采用传统的大型相控阵利用窄波束实现高的方位分辨率，二是采用小口径天线阵利用宽波束结合现代空间谱估计算法实现高的方位分辨率。窄波束雷达的目标信号处理是在波束指向的特定方位上进行的，其接收的干扰和杂波信号主要来自该方位上的干扰和杂波源，此时所获得的信噪比较高，目标检测也只在距离—多普勒谱上进行，要求较低。而宽波束雷达则会接收到所有方位上的干扰和杂波，信噪比较低，除了需要在距离—多普勒谱上检测出目标外，还需要分别形成目标的阵列快拍以获取其空间谱估计。因此相比较l(lJ-占，窄波束雷达对接收信号的信号处理要求较低，但是系统成本高、选址困难，11.不便于维护;而宽波束雷达则相反，成本较低、选址相对容易、便于维护、可移性好，但是要求的信号处理的复杂度大大增加。一般来说，宽波束雷达的目标检测要比窄波束雷达困难得多，如在进了J;多普勒域检测时，窄波束雷达对接收信号的空域预滤波可大大降低特定方位上的噪声和干扰，而在宽波束雷达中就连不同方位上的有用目标信号也成为彼此之间的干扰。如何更好地利用宽波束雷达进行日标探测目前仍是·个鱼待研究和解决的重要课题。由于高频雷达工作环境的复杂性，其回波中存在大量的干扰，有川目标信号常常被淹没在这些干扰信号，牛，，因此有效地实现干扰抑制是提高「1标检测性能的关键，而为此则必须充分认识于扰在时域、空域和跄离一多普勒域的形式、相关性及其与有用目标信号的差别。此外，现在的对海探测高频超视距雷达往往同时肩负着海洋环境状态监测和海_!二移动目标监测的双重使命，由于海浪和移动目标回波信号的平稳时间不同，二者要求的相干积累时间也不同，因此如何更为合理地选择系统参数以适应不同的探测要求，也是值得探讨的问题。通常海而舰船目标速度范田较大，而径向速度变化也可能较大，即使是匀速航行而由于航行方向的改变也可能导致其径向速度的较大改变。一旦系统参数如相干积累时介lJ、最大探测速度等确定后，若在相干积累时间内目标的径向速度和方位角变化超出雷达的速度和方位分辨率，「!标}:i}波信号则成为非平稳信号，若目标的速度.氖J几雷达有效探测范围，目标信号潜则发生混叠。如何更好地处理这些由速度变化导致的非平稳日标和速度超出有效探测范围的目标，也仍值得进一步研究以提高高频雷达的目标探测能力。 本文基于由武汉大学研制的高频地波雷达OSMAR2000(Ocean stateMeasuring and Analyzing Radar)这一平台，就应用高频雷达进行海洋环境及海上目标监测时的若干问题进行研究和讨论，旨在进一步提高高频雷达的抗干扰能力及更充分地挖掘雷达回波中的有效目标信息，以改善高频雷达的目标探测性能。这些问题主要包括高频雷达中的射频干扰抑制和基于时频分析的目标参数提取方法。 本文第一章阐述高频雷达进行目标探测的基本原理，这是全文分析和讨论的理论基础。主要阐述了脉冲雷达探测目标的原理、线性调频脉冲压缩原理、利用 两次快速傅立叶变换(FFT)得到距离一多普勒谱的原理以及目标的空间谱估计 理论。指出高频雷达信号处理的主要任务是从雷达回波信号中检测出存在的目标 并提取其距离、速度和方位信息，而如何有效地对目标信号进行检测和估值则构 成高频雷达信号更多还原

【Abstract】 Various radars working at different frequencies have been widely used in many domains of human activities, among which high-frequency (HF) radars have received particular attention in recent years for their unique abilities of over-the-horizon (OTH) detection. By sky or ground wave propagation, the detection range of the HF radars breaks through the limit of the curvature of the earth, which makes it possible for long-range air early-warning and target monitoring. At the same time the unique abilities in detecting low-detectable targets of the HF radars makes them powerful equipments for detection of hermit aircrafts, small airplanes in heavy land and sea clutters, and even intercontinental missiles. The costs of HF OTH radars are much lower than those of planet-borne systems. Just for these advantages, HF OTH radars now have become important military equipments of many powerful countries. Besides military objective, HF radars also play important roles in the national economic construction. HF radars can be used for measurements of ocean state parameters such as ocean surface currents, waves and wind. And comparing with other traditional measuring equipments such as buoys and satellites, they have remarkable advantages in their wide detection ranges and real-time and all-weather operation capabilities. HF radars have also been successfully used in floating iceberg detection. HF radars have great significance for ocean environment forecasting, fishing, seeking and rescuing, traffic management, and bridge construction. Moreover, the real-time monitoring provided by HF radars has particular significance for a near-sea country to maintain its rights and fulfill its obligation in the 200-miles (370-kilometers) exclusive economic zone (EEZ).Our country has so long a coastline that the HF radars are much applicable in the ocean environment and target monitoring. Strengthening of researches and development of HF OTH radars will help provide a powerful safeguard for the national securities and economic construction.There are basically two technology trends for HF OTH radars, one is employingconventional large-scale phased antenna array and forming narrow beams for high azimuth resolution, and the other is employing small-scale array and broad beam while using modern spatial spectral estimation algorithms to achieve the same azimuth resolution. The signal processing of narrow-beam radars are in the given direction to which the beam is pointing, so the received interferences and clutters only come from that direction and thus the signal-to-noise ratio (SNR) is relatively high, and target detection is only need to be performed on the range-Doppler spectra, which has a relatively low demand. However, the broad-beam radars will receive all the interferences and clutters in all directions, so the SNR is relatively low, and besides target detection on the range-Doppler spectra, target snapshots need to be formed for their spatial spectral estimation, respectively. In comparison, the narrow-beam radars ask lowly for the signal processing but the system costs are high and it is difficult for the localization and maintenance, while on the contrary the broad-beam radars cost lowly and are easy to maintain and transport, but the signal processing complexities are greatly increased. Generally speaking, target detection with a broad-beam radar is much more difficult than with a narrow-beam radar. Take detection in Doppler domain for example, spatial domain pre-filtering in narrow-beam radars can greatly lower the noise and interference in a given direction, while in broad-beam radars even the target signals in different directions may interfere with each other. It is still an important task to find out ways for better detection performance with broad-beam radars. Because of the complexity of the operation environment, there is large amount of interference, so effective interference suppression will be the key to improvement of the radar detection performance, and first of all full acknowledgement about the interference forms in tem更多还原