Effect Evaluation And Suppression Methods On Block Jammings In UWB SAR

Jamming suppression is one of the key techniques of UWB SAR. RFI and noise interferences are the most representative jammings in UWB SAR which receive great considerations in jamming suppression. Based on theoretical deductions and data simulations, this dissertation analyzes properties of echo data in time domain, frequency domain and wavelet packet transform(WPT) domain. We also analysize properties of complex image data in image domain, image frequency domain and image wavelet packet transform domain. Several methods are proposed for jamming suppression in signal domain and image domain respectively.At first, we build models of echo signal and several typical noise interferences and then analyze effects on UWB SAR by interferences with different power, bandwidth and type. So a good beginning for later work is made. Evaluation method is formed, in which jamming effects and performances of suppression methods can be evaluated by gray image, SNR and correlation coefficient.For RFI and narrowband noise interferences, this dissertation studies notch filter and spectrum equilibrium and uses them to suppress narrow jammings in signal domain. By analysises on difference between signal and jamming in wavelet packet transform domain, we study methods of narrowband jamming suppression in signal domain based on WPT. Considering the real time feature, and by further analysises on difference between signal and jamming in image wavelet packet transform domain, we propose a method of Narrowband Jamming Suppression in Image Domain based on WPT(NJSIDWPT). The efficiencies of all methods mentioned are validated by simulation experiments and the evaluation result shows that performances of NJSIDWPT on narrowband noise interferences suppression outperform other methods greatly.For wideband noise interferences, this dissertation studies wavelet packet threshold method and uses it to suppress wideband noise interferences in signal domain and image domain. In order to improve the flexibilities of methods, we propose an approach to Remove Noise from Complex Image based on Wavelet Packet Threholding and Adaptive Windowing(RNCIWPTAW). Evaluating by simulation, we find that wavelet packet theshold method is invalid in signal domain but RNCIWPTAW is valid with fine properties.