Research On Signal Processing And System Design Of Spaceborne P-Band SAR

Compared with conventional spaceborne Synthetic Aperture Radar(SAR),P band spaceborne SAR can be able to image targets coverd by the foliage or shallow ground,for its better penetration performance.Therefore,P band spaceborne SAR can realize the specific reconnaissance of concealed objects,and benefit improving the anti-camouflage ability of the satelllite reconnaissance.However,due to the spectrum features of P band electromagnetic wave,the system performance of P band spaceborne SAR is prone to be affected by the Ionosphere and Radio Frequency Interference(RFI),and the system design of that is restricted by more stringent conditions.This dissertation focuses on three key techniques of P band spaceborne SAR signal processing and system design: the ionospheric effect,RFI and load parameter design.The major work and innovations in this dissertation are listed as follows:In Chapter 2,the ionospheric effect of P band spaceborne SAR is studied.Firstly,the ionospheric distribution model is presented from two aspects: the background ionosphere and the ionospheric irregularities,respectively,and then the electromagnetic wave propogation effect in the ionosphere is given.Secondly,the ionospheric effects on P band spaceborne SAR images are analyzed.Lastly,the ionospheric correction methods of P band spaceborne SAR images are studied.Aiming at the issue of image deterioration caused by the dispersion effect of the background ionosphere,a new estimation and correction method of the ionospheric total electron content(TEC)in frequency domain is proposed.Taking advantage of the minimum entropy algorithm,the estimation accuracy of the proposed algorithm is effectively improved.Aiming at the image worsening caused by the scintillation effect of the ionospheric irregularities,the auto-focusing algorithm is utilized to realize re-focusing.The validity of the proposed algorithms are verified by simulations.In Chapter 3,the Radio Frequency Interference(RFI)suppression techniques of P band spaceborne SAR is studied.Firstly,the RFI signal features of P band spaceborne SAR is analyzed.Then,the influence of RFI on P band spaceborne SAR images are analyzed.Following,the notching filter method is introduced.Although the notching filter is effective for RFI,it can also produce adverse effects on the overall SAR system performance because of the spectrum distortion.Lastly,according to the different characteristics of the spectra between the RFI and the SAR signals,a new method using subband spectral cancellation(SSC)based Kurtosis detection algorithm is applied to suppress the narrowband interference.The proposed method combines the detection and the suppression method together to improve the efficiency of the RFI suppression.It doesn't need the manual participation and is easy to put in practice.Simulation results show the validity of the proposed method.In Chapter 4,the system parameter design of P band spaceborne SAR is studied.Firstly,aiming at the mutual restrict issue of system sensitivity,geometry resolution,ambiguity ratio and scene width for P band spaceborne SAR,the discussion of parameter design issues of operating frequency,polarization mode,signal frequency width,antenna size,pulse repetition frequency(PRF),transimition loss,emission power,data rate and the incidence angle of the antenna platform is presented.Then,given that the system resolution is 5 m and the scene width is 50 km,the system beam position,Noise Equivalent Sigma Zero(NESZ)and the ambiguity ratio are calculated and analyzed.Lastly,basd on the existing digital simulation system,the simulation trials of P band spaceborne SAR are conducted.The simulated results show the rationality of the system design and the validity of the ionospheric simulation and correction methods and RFI suppression techniques.The goal of this dissertation is to resolve the key techniques of the signal processing and system design for P band spaeborne SAR.This dissertation has achieved some beneficial research results,which could be able to promote the develepment of P band spaeborne SAR.