Research On Signal Processing Of Sky-wave Over-The-Horizon Radar

Sky-wave over-the-horizon radar(OTHR) is a long-distance surveillance radar which can see beyond the horizon by backward refraction of the ionosphere. Due to the limited frequency resource of HF band, complex target characteristic and propagation environment, OTHR is quite different from traditional microwave radar. Many effective methods should be used to assure it's advantages of long-distance detection, anti-stealth and early warning ability. The main works of this dissertation are focused on the signal processing of OTHR in the practice project. A probing research on the signal designing and improvement of range resolution and anti-interference ability further improves the performance of OTHR. The main contents of the dissertation are described as follows:Chapter 1 provides the background of this work and characteristic of OTHR. A brief introduction of this dissertation is concerned.Chapter 2 first analyzes the principle of ionosphere sounding devices. Then advantage and disadvantage of different kinds of transmitted signal are compared. The design rule of interference sounding system is presented. At last, the optimal and sub-optimal frequency channel are selected by the combination of HF beacon and responder test, which can eliminate bias error of the coordinate registration process and the distortion of ionosphere.Considering the large number of sensors, limited samples and the mismatch of channels, eigenspace projection algorithm and beam-frequency adaptive algorithm were described. The former can improve the performance of pattern while not degrading output Signal-Interference-Noise Ratio(SINR), the later not only reduces processing dimension and the complexity of computation but also suppresses the spatial interference and relaxes the requirement of the amplitude and phase inconsistancy between channels greatly.Chapter 4 analyzes the different characteristics in spatial, temporal and frequency domain of HF interference. The sidelobe canceling algorithm based on adaptive-adaptive construction can effectively suppress lots of sidelobe interference with a low computation burden and fast convergence. Least square and eigen-subspace canceling algorithm are proposed to suppress mainlobe interference. For the impulse interference such as lightning and meteor trail echoes, Gabor series algorithm based on hypothesis testing theory is described which has been proved effective by the real data. To eliminate the nonstationaryinterference caused by the ionosphere, we proposed a method of eigenspace projection and subsection adaptive DBF. Computer simulation results are provided.For the distortion of ionosphere, the estimate and correction algorithms from the received data are presented in Chapter 5. The frequency shift of Bragg peak can be removed by the dual-filter-smooth methods. In order to correct the phase perturbation and multi path effects of ionosphere, it also describes the spatial and temporal cohering algorithm, the instantaneous frequency and instantaneous phase correction algorithm and the spectral deconvolution mode. The results of real data of China examinational OTHR has proved that they are effective for ionosphere distortion.Chapter 6 analyzes the advantage of multifrequency system for OTHR such as multi channel LFM signal and Costas hop-frequency signal. High bandwidth utilization and better anti-interference ability make them have many merits than existing FMCW system especially for small RCS targets such as cruise missile and concealed targets though increasing the complexity of equipment and signal processing.Chapter7 is the summary of the dissertation and discusses some important research areas of OTHR in the future.