Study On Radio Frequency Interference Suppression For P Band Spaceborne Synthetic Aperture Radar

Synthetic Aperture Radar(SAR) is imaging radar with the ability of all-day, all-climate and high resolution, which obtains the target information by transmiting the electromagnetic wave. SAR plays an important role in earth remote sensing, especially the P band spaceborne SAR. Because of the long wavelength of P band(30MHz~1GHz), the P band spaceborne SAR can detect the military target buried underground and forest with strong penetrability, which has attracted more attention of the military application. In addition, the P band spaceborne SAR has bright foreground in forest biomass measurement, iceberg surveillance, geography exploration and mapping.Among the P band, there are many broadcast and TV signals, namely Radio frequency interference(RFI). RFI will influence the imaging performance seriously. Acting as one of the key technologies in keeping the high performance of P band spaceborne SAR, RFI suppression has important significance. For the problem of P band spaceborne SAR RFI suppression, this dissertation focus on the RFI source survey, the model of RFI, the analysis of RFI influence, RFI suppression and evaluation. The main content included in this dissertation is organized as follows:Chapter 1 introduces the background and significance of this study, and summarizes the present status of spaceborne SAR RFI suppression. The main work comes in the end.Chapter 2 studies the model and influence of RFI for P band spaceborne SAR. The present status of P band spaceborne SAR is introduced. The model of RFI is built by the interference source survey. Then, the influence of RFI in SAR image is analyzed.Chapter 3 studies RFI suppression approach. Aiming at the complicated electromagnetic environment of P band, three methods are proposed. One of the methods is frequency notch filtering based on max-mean-ratio(MMR) threshold. The threshold is adaptive with the change of interference, which can keep the useful signal while RFI suppression. Another method is eigensubspace decomposition based on wavelet in determining the number of main eigenvalue. This method can determine the number of main eigenvalue correctly to improve the precision of interference subspace construction. At last, a RFI suppression method based on time frequency transform by median gain coefficient is proposed. By the interference detection and suppression for every instantaneous frequency spectrum in time frequency domain, the useful signal can be kept correctly but the RFI will be suppressed extremely.Chapter 4 verifies the performance of the proposed methods by full digital simulation system. Aiming at the point target and scene target, several interference suppression effect evaluation methods are introduced, and the results after RFI suppression are evaluated by these methods. The dependability of evaluation methods is demonstrated.Chapter 5 is the conclusion. The main work in this dissertation is summarized, and the future work is discussed according to the present research work.