Research On Interference Suppression Of Mimo Sky-wave Radar Using Combined Transmit And Receive Beamforming Technique

HF sky-wave radars can achieve the over-the-horizon detection for the targets with very long distance by utilizing the refraction and scattering mechanism of ionosphere. However, affected by the multi-mode propagation of ionosphere, the interested targets are often covered by the expanded clutter spectra. Therefore, they are difficult to be detected. Known as an effective means to solve the multi-mode propagation in ionosphere, MIMO radar system is investigated widely in many countries at present.Starting with the mathematical model of MIMO radar system, this dissertation explains the necessity of introducing the MIMO radar system which can suppress the multi-mode interferences. Moreover, on the basis of the maximum signal to interference plus noise ratio, the formula of the combined transmit and receive adaptive beamformer is obtained.Secondly, according to the type of interference, the combined transmit and receive adaptive beamformer can be classified into the sidelobe i nterference suppression beamformer and the mainlobe interference suppression beamformer. In the sidelobe interference suppression part, referring to the MVDR beamforming algorithm, the optimization algorithm based on SVM, the covariance matrix reconstruction algorithm based on the spatial spectrum estimation and the other improved methods are investigated in this dissertation. In the mainlobe interference suppression part, the block matrix method is introduced and a combined transmit receive adaptive beamformer algorithm based on the spatial spectrum estimation is applied, which can effectively suppress the multi-mode propagation interference by the difference of DOD or DOA between the target and the interference.Finally, an improved MUSIC algorithm in the case of the mutual coupling between the adjacent antenna elements is investigated. For the uniform linear array, the coupling correction algorithm based on the virtual antenna element and the spatial smoothing MUSIC is proposed, which can improve the performance of the direction estimation of targets in the different SNR cases and the estimation of the coherent signals. Moreover, this algorithm can also realize the direction estimation of targets with the single snapshot, which improvs the performance of MUSIC algorithm in the non-ideal conditions.