Research On Theory And Technology Of Radar Altimeter Dynamic Environment Simulation

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.