Research On Radio Interference And Sea Clutter Suppression Algorithms For Sky-Wave Radar

By utilizing the reflective nature of the high-frequency electromagnetic waves through the ionosphere,sky wave over-the-horizon radar(OTHR)can ignore the influence of the curvature of the earth and perform a wide-area target surveillance at long range.Thanks to the unique working mechanism,OTHR has played important roles in target detection,radar warning,sea condition monitoring and so on.However,the fact that OTHR works at the high-frequency band(3MHz~30MHz)makes it easy to be affected by various jams,such as the high-power radio frequency interference(RFI)and complex sea clutter.This paper makes an in-depth study of time-frequency characteristics and suppression algorithms about the RFI and sea clutter in OTHR,and the major works are as follows:1.The RFI suppression based on the design of optimal matched filter.This paper firstly analyses the sources and harm of RFI,and discusses its characteristics in Range-Doppler map.Then,a RFI suppression algorithm based on the similar waveform constraint is introduced.But the algorithm might result in a large sidelobe of the receive filter and have a large computational complexity,so a novel RFI suppression algorithm based on extended Kalman(EKF)matched filter is proposed.And the simulation results demonstrate that the proposed method can suppress RFI efficiently and protect the potential targets and sea clutter very well.2.The sea clutter suppression based on the dimensionality reduction algorithm.In this paper,the formation,characteristics in time-frequency domain and the harms to target detection of sea clutter are described.Then,a traditional sea clutter suppression algorithm,named joint domain localised(JDL)algorithm,is introduced.However,JDL algorithm has some artificiality in the design of the dimension reduction matrix and the selection of the reduced dimension is very strict and harsh.For solving the problems,this paper proposes a novel sea clutter suppression algorithm based on joint iterative optimization of filter,named as Joint-RLS algorithm.Through the joint iterative processing,the proposed algorithm can solve the optimal dimension reduction matrix and the optimal filter vector,which lead to the effective suppression of the sea clutter and maximization of the output target power.Simulation results demonstrate that the proposed algorithm has the similar suppression effect of the sea clutter with JDL algorithm.3.The sea clutter suppression based on the sparse filtering algorithm.Taking into account the low rank of the sea clutter in the radar echo,in a generalized sidelobe canceler(GSC)architecture,a small number of the sample at the output of the blocking process are zero and not needed for the sidelobe canceling.Based on this fact,this paper adds a sparse constraint into the optimal filter design,and ultimately proposes a novel rarefaction algorithm to suppress sea clutter.The proposed algorithm can not only suppress sea clutter effectively,but also make the filter vector to be sparse and improve the output signal-to-clutter-plus-noise ratio(SCNR).Simulation results demonstrate that the proposed algorithm has a better clutter suppression compared with the JDL algorithm.