Research Of Active Jamming Technology And ECCM For Wideband LFM Radar

Wideband LFM signal is widely used in SAR and ISAR systems, which play important roles in remote sensing, space surveillance and ballistic missile defense. This dissertation focuses on the research of active jamming to wideband LFM radar, serving for enhancing the ability of radar jammer. The main research efforts include the principle of active jamming to wideband LFM radar, the interference modulation techniques based on digital channelized receiver, new active jamming methods to wideband LFM radar, interference recognition and suppression measures for typical radar jamming methods. The research in this dissertation includes the following aspects:In chapter 1, the background and significance of this dissertation is elaborated, the research status of active jamming methods and system to wideband LFM radar is introduced, and the state of interference recognition and suppression measures to wideband LFM radar is presented. Finally, the main contents of this dissertation are presented.In chapter 2, the principle of active jamming to wideband LFM radar is proposed.First, based on the practice of radar jammer engineering research, the active jamming methods to wideband LFM radar are re-divided into three active jamming patterns according to the way of jamming signal generation. The method of jamming signal generation and the modulated signal for each active jamming pattern are introduced. Then, the relationship between modulated signal and jamming result is deduced. Following, by synthesizing the deduced results, the principle of active jamming to wideband LFM radar is given. At the last, from given principle, the analysis of the characteristic and performance for each active jamming pattern is demonstrated.In chapter 3, the digital channelized jamming modulation technology is presented.For enhancing the performance of the radar jammer, the digital channelized receiver is involved in jammer system. The basic structure and the practical structure of the digital channelized jamming modulation system is introduced after analysing of the performance of the digital channelized receiver. Following, by deducing the work flow, the key issues during the realization of the digital channelized jamming modulation system are donated.By analyzing the effect of subchannel-modulated signals on the output error, the way of calculating the subchannel-modulated signals is established. Also, after researching the impact of system’s filter on the output error, the optimization problem for the filter design is established. And following, we give the method for solving the established optimization problem. At the last, a digital channelized jamming modulation systems is built by using the Matlab’s simulink simulator.In chapter 4, several new active jamming methods to wideband LFM radar are proposed. From the proposed principle of active jamming to wideband LFM radar, we can find that the jamming performance of an active jamming method is tightly determined by the coverage that jamming signal has in the pulse compress result. The less coverage it has, the higher output jamming to signal ratio(JSR) can be got. So, by discretizing the coverage that jamming signal has in the pulse compress result of coherent noise jamming method, a discretized coherent noise jamming method is promoted. Also, in the research of digital channelized jamming modulation techniques, the filter has a great effect on the output error. Then, in the digital channelized jamming modulation system, it can form a series of cycle sidelobe by reducing the cutoff frequency of the filter and attain a series of frequency shift sidelobe by increasing the cutoff frequency of the filter. Therefore, some new active jamming methods to wideband LFM radar are achieved.In chapter 5, we present the jamming signal recognition and suppression measures for some typical radar active methods. Fist, for the non-coherent noise jamming(NCNJ)method and coherent noise jamming(CNJ) method, the pulse compress results of them are also random signals, which is different from that of echo signal of real target or false target. Furthermore, the entropy is used for measuring the global randomicity and local randomicity of the pulse compress results. Then, the NCNJ signal recognition method is proposed by using the global randomicity and local randomicity of the pulse compress results. Meanwhile, the CNJ signal recognition method can be achieved by using the local randomicity of the pulse compress results. Following, from the analysis of the interrupted sampling repeater jamming(ISRJ) signal, it can see that the ISRJ signal is discontinuous during the pulse duration and the location of the sidelobe false target is related to the chirp rate of radar signal. Then, by using this discontinuous characteristic, the ISRJ recognition and suppression methods are presented. Moreover, based on the location of the sidelobe false target is related to the chirp rate of radar signal, an ISRJ suppression methods, which has a better ISRJ suppression performance, is proposed by using two radar signals with different chirp rate.In chapter 6, the main contributions and innovative work of this dissertation is summarized, and the potential problems which need future researching are pointed out.