Suppressing Interference And Target Detection For Over-the-horizon Radar

Over-the-horizon radar which usually works in high-frequency (HF) band has twomain types: sky-wave over-the-horizon radar (OTHR) detect target at a long distance byrefracting propagation from ionosphere, and surface-wave over-the-horizon radar alsocalled High Frequency surface wave radar (SWHFR), detects target by Hertzian wavesdiffraction in earth surface. Over-the-horizon radar has the feature of long distancedetection, large areas surveillance, anti-stealth, and so on. In military, it is mainly usedto make experimentation detection in atmosphere, detection of smoke pole produced bymissile launch , precaution of ballistic missile, low air bomber, cruise missile and attackfleet at sea. Within HF band, Bragg scattering occurs when Hertzian waves refractocean surface-wave, thus over-the-horizon radar is widely used to remotely sensingocean surface-waves. At present, some problems in the process of over-the-horizon radar signalprocessing are difficult to deal with. Combined with our projects, a series of newmethods are proposed on the paper and applied to practice successfully. In aspect ofsuppressing interference for over-the-horizon radar, some methods of eigen-subspaceprojection, wavelet transformation, time-frequency analysis, digital beamforming etcare used to analyze the behavior of the interference, and restrain them effectively.Evolution Algorithms are applied for super-resolution direction estimation for over-the-horizon radar. Space-time adaptive processing (STAP) technique is also applied for targetdetection for over-the-horizon radar. The main innovative points are as follows: (1) In order to study exterior distribution of interference of over-the-horizon radar in spatial, temporal and frequency domains, some methods of modern signal processing such as FFT, STFT, wavelet transform and digital beamforming, are used to analyze the behavior of those interference. (2) In the system of suppressing interference for over-the-horizon radar, the vital Key Laboratory for Radar Signal ProcessingIV Suppressing Interference and Target Detection for Over-the-horizon Radar importance is selection of the optimal working frequency. An approach of selecting working frequency for over-the-horizon radar based on adaptive beamforming is presented. At first, received data are filtered in space field in order to restrain some interference, and then optimal working frequency is selected after analyzing its spectrum. (3) With the problem of interference of over-the-horizon radar being solved, three kinds of restraining exterior interference of over-the-horizon radar in temporal domain are presented. The first one presented is based on eigen-subspace theory, firstly, sea (ground) clutter is eliminated by MTI filtering and then it is easy to find the position of the transient interference and get rid of those in temporal domain. Lastly, some useful signals, which are loss in period of restraining the interference, are resumed according to interpolation of the model of AR. The second method refers to wavelet transform. Filter is presented with the characters of reconstruction and decomposition of dyadic wavelet, and the interference is detected and eliminated in scale domain,then remaining signals are reconstructed according to wavelet transform. Compared with the first method, the difference of this method is that the work of detecting and eliminating interference and resuming the useful signals is finished in the process of wavelet reconstructing and decompositing, which makes this technique fit for engineering project. The third method of suppressing long interference is based on twice MTI filtering. Interference and target signal are separated from sea (ground)...