SAR Echo Signal Detection And Time-Frequency Filtering Method Based On Fractional Fourier Transform

Synthetic aperture radar (SAR) is an all-weather, all-time new high-resolution microwave remote sensing imaging radar, it has been a widely used both in military and in civilian field. The echo signal received from the moving target of SAR is inevitably affected by noise interference, so we must seek to obtain a real moving target Doppler frequency characteristic in order to get a clear picture of the moving target.The echo signals received from the moving targets of SAR have the characteristic of Linear Frequency Modulation (LFM) signal. The Fractional Fourier Transform (FRFT) as a new non-stationary time-frequency analysis method, which is very suitable for dealing with LFM class signal, and it is a linear time-frequency analysis method, there is no cross-term interference problem. So the FRFT can be applied to moving target detection and SAR signal processing to improve the moving target detection and estimation performance. The main work and achievements of this dissertation are as follows:1. Detecting the single-component and multi-component LFM signals based on FRFT. By using two steps search method to detect single-component LFM signal in order to obtain a clear detection result and reduce the computational cost. Whereas in the multi-component signals detection process, for the different strength of the different components of the signal, strong signal components may overwhelm weak signal components, the dissertation has proposed the idea of successive elimination to detect the multi-component LFM signals and done a simulation analysis.2. According to the situation that SAR echo signal can be approximated as LFM signal, it has analyzed SAR echo signal detection theory and procedures based on the fractional Fourier domain filtering. By means of the different strength of the different components of the signal in multi-component LFM signals, the thesis deals with the SAR echo signal with three LFM signal components of great intensity difference. Simulation analysis shows that in the case of the strong and weak signal strength of 12dB difference, in this correspondence, the weak signal can also be detected.3. Filtering of the SAR echo signal mixed with additive white Gaussian noise in fractional Fourier domain. Firstly, the narrowband-pass filter based on observed signal itself on the fractional Fourier domain is constructed, and then the observation signal mixed with white Gaussian noise of mean 0, variance 1 multiplied by the constructed filter to obtain original useful LFM signal, the simulation has confirmed the effectiveness of the method.