Jamming Suppression Technology In LFM Radars

The jamming suppression technology of a radar system is one of the most important research areas in radar signal processing.Only the radars which can work well in the complex electromagnetic environment are capable to win the electronic warfare.However,with the rapid development of high-speed digital circuits,the electromagnetic environment is deteriorating.Conventional blanket jamming is still one of the main interference strategies,and meanwhile the deception jamming based on the digital radio frequency memory technique and direct digital synthesis technique brings in huge challenges for the radars.Besides,a plenty of complex new jamming patterns are proposed constantly.Therefore,the anti-jamming capability of a radar system causes widespread exploratory research and attention.In this dissertation,the electronic counter countermeasures for the linear frequency modulated radars against typical active jamming patterns are studied and analyzed.The dissertation focuses mainly on the jamming suppression algorithms for the noise amplitude modulation jamming,dense false targets repeater jamming and convolution smart noise jamming.The principal works and contributions of this dissertation are as follows.1)Noise amplitude modulation jamming suppressionAn adaptive iteration parameters estimation algorithm is proposed based on the maximum likelihood method,and the jamming is suppressed by utilizing the frequency domain cancellation algorithm.According to the model of the noise amplitude modulation signal,the likelihood function is derived and its characteristics are analyzed.A coarse parameters estimation method is proposed by fixing the interpolation of the Fourier coefficients,and the performance of this method is presented and the Cramer-Rao lower bounds of the parameters estimation are also derived.A noise power ratio estimation algorithm is also provided,and then an iterative algorithm for precisely estimating parameters is proposed.Especially,the convergence conditions for different gradient descent iteration methods are obtained by theoretical analysis.Simulation results demonstrate that the mean square errors of the parameters estimation algorithm approach the Cramer-Rao lower bound asymptotically,and the proposed algorithm is also verified having superior performance over other existing algorithms.The suppression performance of the noise amplitude modulation jamming has a great improvement when the proposed algorithm is applied.2)Dense false targets repeater jamming suppressionFor the intact repeater jamming pattern,the characteristics of the jamming in real testing data is analyzed and the signal model of the intact dense false targets repeater jamming is established.A parameters estimation algorithm is proposed based on the multistep interference cancellation method for this temporal overlap multi-components linear frequency modulated signal,and the jamming is suppressed by reconstruction and subtraction.The Cramer-Rao lower bounds of the parameters estimation for the linear frequency modulated signal are derived.The simulation results demonstrate that the mean square errors of the proposed parameters estimation algorithm can approach the Cramer-Rao lower bounds.The verification via utilizing real data indicates the effectiveness of the proposed jamming suppression method and the application conditions of this method are also given.For the partial repeater jamming pattern,the common characteristics of different jamming patterns are summarized and the general signal model is established.Based on the fact that different partial repeater jamming segments will be spliced together,a parameters estimation algorithm is proposed based on the ensemble empirical mode decomposition method,and the jamming is suppressed by reconstruction and subtraction.Simulation results validate that the proposed jamming suppression method has superior performance over other existing algorithms.For the real situations where radars may suffer from the influence of communications,the characteristics of the unintentional communication interferences in real testing data are analyzed,and then the jamming model is also established.A batch processing method is proposed based on the multivariate empirical mode decomposition.The communication interferences will de decomposed into different multivariate intrinsic mode functions and suppressed separately.Simulation results show that the feasibility of the proposed jamming suppression method3)Convolution smart noise jamming suppressionThe differences between target returns and jamming signals are analyzed.After the pulse compression of the convolution smart noise jamming,the relationships of the chirp rates,frequency shift and peak positions are derived.A jamming suppression method based on the smeared spectrum technique is proposed to distinguish the target return from the smart noise jamming.Simulation results verify the feasibility and of the proposed method when the convolution smart noise jamming exhibits different jamming patterns,and the superior performance over other existing algorithms is also demonstrated.For the convolution smart noise jamming,the delayed autocorrelation property of the linear frequency modulated signal is analyzed and a jamming suppression method based on the atomic decomposition is investigated to separate the target return and jamming signals.Simulation results are provided to validate the feasibility and practicability of the proposed method.