Study On Jamming And Anti-jamming Techniques For Spaceborne Synthetic Aperture Radar

Without any military violations of national territoriality and airspace, spaceborne Synthetic Aperture Radar(SAR) can work all weather and all time for obtaining a high-resolution image of the illuminating scene. It has become an important mean of battlefield reconnaissance and also attracts the electronic attack from the enemy. For this reason, active jamming and anti-jamming technologies for spaceborne SAR have been hot research areas. However, there still exist some shortcomings and challenges in SAR jamming methods and the anti-jamming capability should be further improved. On this background, this dissertation mainly researchs a series of key techniques of SAR electronic warfare in detail. The major contents of this dissertaion are introduced as following three parts:In the first part, some working parameter estimation methods for SAR are addressed. Firstly, the radar equation of the jammer is analyzed when it locates in the sidelobe region. Based on this equation, a optimization model to estimate the parameters which decribe the SAR antenna radiation pattern is established. Utilizing the prior information, the possible intervals of the SAR antenna sizes and the elevation angle are induced, and the optimization model is solved with Particle swarm optimization(PSO) algorithm. Secondly, for the traditional parameter estimation methods of Linear Frequency Modulation(LFM) signal, the computation load is large and the performance is deteriorated when the signal to noise ration(SNR) becomes low. In order to overcome these shortcomings, a new parameter esitmation algorithm which utilizes the correlation dechirp method and fractional fourier transform is proposed. This algorithm can work without parameter searching, even in a low SNR. Thirdly, for the traditional time delay esitmation method called “cyclic cross-correlation”(CCC), its estimation accuracy is limited to SNR. In order to avoid this limition, a novel method called “Radon- Cyclic Cross Correlation” is presented. It combines the CCC values under different delay time into a image. Through the radon transformation, the delay time estimation is converted to the line parameter estimation. This method can obtain a better performance than the traditional one.In the second part, to form a large deceptive scene in SAR, some fast generation methods of SAR jamming signal are investigated. Firstly, based on the principle of Range-Doppler algorithm, a jamming signal generation method called “inverse Range-Doppler” is proposed. According to the different requirements of the generating time, some approximations of the range cell migration of the false target are made. Brought about these approximations, the influence on the jamming effect is analyzed. In addition, the caculation amount is analyzed. Secondly, a method called “inverse Range Migration algorithm” is put forward similarly. The implementation steps are listed and the computation complexity is analyzed. This method generates jamming signal in a high precision and is suitable for counter high-resolution or high-squint SAR. Thirdly, in order to protect the ground moving targets, a method used to generate uniformly-moving scene jamming signals in real time is proposed. The formula which decribes the relationship between stationary target echo and moving target echo is derived. Based on this formula, the implementation steps which transform the stationary scene jamming signals to moving scene jamming signals are given. Fourthly, the jamming effects caused by the measurement error of carrier frequency, flight speed, distance and pulse repetition interval are analyzed. Some useful formulas are presented to help us develop or use the jammer better.In the third part, the jamming suppression methods based on dual-channel SAR and polarization SAR are proposed. Firstly, with a novel data acquisition mode, a new method based on dual-channel SAR is applied to suppress the interference. Using the received dual-channel data, the two-dimensional location of the interference source can be estimated and then the interference can be removed via a Two-Channel-Cancelation method. By establishing a linear model of the interference-removed signal, the SAR image is reconstructed based on compressed sensing(CS) theory. Our method requires only a minor change to the traditional SAR system hardware while obtains a higher resolution. Secondly, after range compression, the barrage jamming has a noise-like characteristic while the real echo and deceptive jamming are focused. According to this, the barrage jamming is removed via a minimum entropy algorithm. Based on the different polarization characteristics between deceptive jamming and the real echo, the deceptive jamming can be suppressed by phase compensation in doppler domain. Combining the above two method, it is able to suppress both the barrage jamming and deceptive jamming in the same time. However, these methods will lose some polarization information of the real targets.