【作者】 张张；

【导师】 胡修林；

【作者基本信息】 华中科技大学 ， 通信与信息系统， 2011， 博士

【摘要】 雷达高度表被广泛用于测量地球表面上空飞行器的高度。根据不同应用条件的需求,雷达高度表可以应用于零高度至卫星高度的范围,也形成了不同体制及不同的高度测量方法。本研究适用于地形匹配辅助导航系统中的宽波束脉冲雷达高度表。由于宽波束脉冲雷达高度表的照射面积大,照射区域的地形往往又复杂多变、起伏度大,使得回波波形比一般的点目标回波波形复杂得多,这样的信号是一般的雷达信号模拟器无法产生的。因此目前在雷达高度表的研制和生产过程中,在地面仅仅能进行静态测试,需要通过实地试验,来测试高度表的动态性能,代价非常昂贵,在财力和时间上的耗费非常大。因此,研究如何实现环境仿真,获得空间真实条件下的地面回波信号,使得在实验室内即可完成对雷达高度表动态性能的测试与研究,非常有必要。这样一个雷达高度表回波信号仿真系统,可以为雷达高度表提供反映空间动态特性的射频回波信号,不仅能极大地提高雷达高度表的设计、开发效率,同时将增强雷达表的研制与测试的灵活性。本文对雷达高度表动态环境模拟的理论与技术进行了深入的研究,主要工作有:1.对雷达高度表动态环境仿真的实现技术路径进行了深入探讨,提出了一种新的雷达回波信号模拟系统的设计思想,解决了宽波束雷达高度表面目标回波信号难于模拟的难题。采用两种方法来完成雷达高度表空间回波信号的模拟:一种方法是利用在实地试验中采集的真实回波信号,另一种方法是通过对回波信号生成过程的理论分析,建立回波产生数学模型,基于数字地图,通过计算机仿真获得仿真回波数据。这二种技术路径生成的回波数据通过D/A转换成模拟回波信号,再通过上变频,在严格的同步与功率控制下,最终形成所需的雷达射频回波信号。2.分析了表面分布无约束平均高度测量模型及测高算法。与传统的基于布朗模型的测高算法相比,平均高度测量模型摆脱了地表高度服从高斯分布的约束,极大的提高了测高模型的适用范围和测量精度。论文同时也对OCOG算法进行了研究,该算法对复杂地形回波体现出很好的跟踪与测高性能。测高算法的研究成果为回波仿真提供了有效的理论基础。3.研究了形成雷达回波的地面散射特性,建立了宽波束雷达高度表相干视频回波仿真模型和回波功率仿真模型,为回波仿真提供了理论基础。考虑到仿真波形的逼真度对雷达高度表动态环境的性能影响,本文对影响仿真精度的因素进行了深入分析,并将同一地形下的仿真回波与实际采集回波进行波形比对,验证了回波仿真模型与算法的正确性。4.提出了动态门限检测与采样时间窗两种雷达回波数据采集方法,设计了一种采样预触发电路与二级缓存机制,有效降低了采集数据量和数据传输压力,提高了总线带宽利用效率,解决了高速数据采集与实时存储的难题。在雷达高度表动态环境的实现方面,论文重点解决了如下关键技术:(1)实时仿真技术:在1ms内需要完成大范围雷达照射区域的雷达回波计算和合成,并按照雷达时序实时送给雷达高度表,这是本项目的一个关键点和难点。为此,采用DSP并行处理网代替单DSP,DSP之间采用高速LINK口进行高速通信和互连,实现对地面照射区域的分区并行计算。(2)在回波信号同步控制与系统时延测量方面,提出了一种双时钟沿计数的方法,与单个时钟沿计数的方法相比,可以将时钟频率降低一半。在采用200MHz频率的计数时钟时,即可达到2.5ns的测量精度,有效解决了回波延迟的精确同步控制问题。更多还原

【Abstract】 Radar altimeter is widely used to measure the height of aircraft above the earth’s surface. The height-calculation range of radar altimeter is from zero to the satellite height.There are several kinds of radar altimeters with different measurement methods,according to different application conditions.The stduy in this paper can be applied to the wide-beam pulse radar altimeter in terrain-aided navigation system.When facing a complex terrain area with a large degree of fluctuation, the waveform of radar altimeter echo is significantly different from the condition of point target, especially in the wide-beam condition, which means a larger irradiated area. Therefore, we can hardly get such kind of radar echo by common radar signal simulators. For this reason,currently in the research and production process of radar altimeter,only the static test can be provided on the ground.To test the dynamic performance of altimeter, field test is needed,which will spend a lot of money and time.So, it is necessary to research on the methods of environment simulation ,which can help to complete the research and testing of dynamic performance of radar altimeter in laboratory.The Radar Altimeter Dynamic Environment (RADE) can be used as a signal source,providing the RF echo signal which contains the spatial characteristics.This can greatly improve the design and development efficiency of radar altimeter, and greatly shorten the development cycle.This dissertation discusses the theory and technology of RADE simulation, the main content and creative work in this thesis are as follow:1. Research on the theory of radar altimeter dynamic environment system, a new design and implementation method of radar echo simulation system is proposed, which can solve the problem of simulation of the wide beam radar altimeter echo. It uses two methods to realize the simulation, one is based on the actual field test acquisition echo,and the other one is based on mathematic model.The radar echo data generated by the two methods is converted to analog signal by DAC.After up conversion,and in strict synchronization and power control,the system can output radar RF signal.2. Analysis of a new algorithm named“average-height”algorithm, which can measure the average distance to the illuminated surface accurately. The“average-height”model breaks the restriction that the probability distribution of height of the scattering surface should obey the Gauss distributing, which is quite different from the traditional algorithms based on the BROWN model. Therefore, it is superior to the traditional algorithms in application range and as well as in precision.And the thesis also studies the Offset Centre of Gravity(OCOG) algorithm,which is also a robust echo-tracking and height-calculation algorithm.All these achievements in the research will offer the theoretical foundation for echo simulation.3. Research on the scattering characteristics of ground radar echo. The video echo simulation model and power echo simulation model of wide-beam radar altimter are proposed, the principle and method of two kinds of models are discussed in detail, which offers the theoretical foundation for echo simulation.Taking into account that the fidelity of simulation waveforms has a significant impact on system performance, the thesis analysises the factors affecting the accuracy of simulation.4. The concept of dynamic threshold and sampling time window are proposed, which can effectively reduce the amount of data collection and data transfer pressure. A secondary cache mechanism is designed to improve the efficiency of bus bandwidth utilization. These will help to solve the problem of high-speed acquisition and real time storage of radar echo.In the aspects of system implementation, several key technologies are discussed thoroughly in this dissertation, including:(1)Real-time simulation:one of the key difficulties of this system is to accomplish the computation and synthesis of radar echo in one millisecond.To solve this problem,DSP parallel processing network is adopted,instead of using single DSP.Meanwhile,the algorithms in model computation and parallel processing are optimized.(2)The method of recise control of echo delay (i.e.synchronization control) is studied, a new counting method, called dual-clock couting,is proposed. It counts at both the rising edge and falling edge of the clock signal.In this way, the clock frequency can be reduced to half of its original.With this method, accuracy of 2.5ns can be achieved when counting at frequency of 200MHz.更多还原