| High Frequency Surface Wave Radar has an operating frequency range of 3-30 MHz.When the electromagnetic wave in this frequency band propagates on the ocean surface,the energy attenuation is small.Using this characteristic,the High Frequency Surface Wave Radar can target sea targets including low-altitude flying objects and ships.To achieve over-horizon detection,at the same time,it provides favorable conditions for the monitoring of marine dynamic parameters and the development of marine resources.Therefore,related scientific research on high frequency ground wave radar has become a research hot topics in more and more countries.However,the operating frequency band of high-frequency radars determines that they will be affected by a variety of interferences during their operation.These interferences may come from short-wave radio stations,or they may come from natural phenomena such as lightning.The existence of these interferences has seriously affected the normal operation of radar equipment and is not conducive to target detection.At present,the biggest factor restricting the performance improvement of High Frequency Surface Wave Radar systems is the propagation medium ionosphere of high frequency electromagnetic waves.The radio interference generated by ionosphere at a long distance has time-varying and unstable characteristics,which brings about great interference suppression.difficult.This paper focuses on the problem of airspace suppression in ionospheric disturbances.The main work is summarized as follows:Firstly,The principle of the non-stationarity of spatial domain caused by the widely used short-wave channel Watterson model is analyzed.Based on this,combined with the scatter propagation process of short-wave interference through the ionosphere,a new ionospheric coherent interference model is established.Aiming at the problems existing in this model,a new coherent interference model different from the Watterson model was established.Comparing the two models with the characteristics of actual interference propagation,the simulation results show that the characteristics of the new ionospheric disturbance model in the non-stationary airspace are more in line with the actual propagation results.Secondly,Aiming at the problems existing in conventional adaptive beamforming algorithms in suppressing non-stationary ionospheric interference,this paper proposes a robust adaptive beamforming algorithm based on compressed sensing and prior information.The algorithm first uses the compressed sensing DOA estimation method,combined with the prior information of the angle region where the desired signal is located,to correct the expected directional directionality of the error.Then continue touse the prior information to reconstruct the sampled covariance matrix to obtain a sampled covariance matrix that contains only expected interference and noise information.The simulation results show that compared with the original robust algorithm,the algorithm has better robustness and higher output signal to interference noise ratio.Finally,Another type of non-stationary interference suppression algorithm: a segmented adaptive beamforming algorithm is studied.The performance of several traditional non-stationary interference suppression algorithms is analyzed and compared.The root cause of Doppler broadening that affects the target detection is studied.A new ionospheric interference based on sea clutter maintain.The simulation results show that this algorithm can suppress the sea clutter broadening while suppressing the non-stationary ionospheric interference,and make up for the problems existing in the traditional methods. |
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