Research On The Method Of SAR Radio Frequency Interference Suppression

Synthetic Aperture Radar(SAR),as an all day,all-weather and high-resolution observation equipment,has achieved great development.It plays a role that is difficult for other observation methods such as visible light and infrared and has been used in many fields such as military and civilian.However,as the electromagnetic environment becomes complex increasely,the radio frequency interference(RFI)in space will pollute the received echo of SAR,which will further affect the imaging quality and image-based applications,and finally reduce the utilization rate of SAR products.Two aspects are mainly concerned in this thesis: RFI detection for SAR in azimuth and RFI suppression algorithm for SAR based on signal processing.Firstly,the sources of RFI are introduced and the basic characteristics of it are analyzed in this thesis.On this basis,the RFI is classified and its mathematical model is established.And to obtain its time,frequency domain and statistical distribution characteristics,an in-depth analysis of the SAR echo affected by RFI is completed by simulation technology.In addition,the influence of RFI is analyzed from the aspects of interference-signal power ratio and imaging.The above content is the basis of follow-up research.Secondly,the general of RFI detection technology: method based on time domain and spectrum characteristics are analyzed in this thesis.In addition,based on the research on the azimuth correlation characteristics of SAR echoes and the correlation coefficient method,the detection process based on paired sample t-test is further proposed.The simulation results prove the effectiveness of the detection method.Thirdly,under the premise of dividing RFI into narrowband interference and wideband interference,and the suppression technology based on single-channel SAR is studied.To make the interference suppression more thorough and ensure that the useful signal is not distorted,the GST time-frequency filtering method and the STFr FT-based filtering method are proposed respectively by studying and judging the classical methods.The proposed methods are still belong to the spectrum processing category,but are more refined than frequency-domain processing methods: they both map signals to their respective 2-D plane,and then perform filtering operation to complete the effective separation of RFI and useful signal.Further,the derivation and analysis of the principle of the methods based on spectrum processing are completed,and then the essence of this type of processing is given.After that,in order to evaluate the interference suppression results effectively,the evaluation index of RFI suppression effect is given.Simulation and index comparison results show that the performances of the proposed methods are better than those of the general methods.Finally,two methods of RFI suppression are analyzed for multi-channel SAR system in this thesis: multi-channel interference cancellation technology and space-time adaptive technology,and their effectiveness is verified by simulation.