Anti-Jamming Waveform Analysis And Performance Research Of Cognitive Radar

As an important equipment for transmitting electromagnetic waves to obtain information,radar has been fully and widely used in military and civil fields.With the rapid increase of the number of electronic equipment,the electromagnetic environment has become more complex,and new types of active jamming against radar are emerging one after another.Classical radar anti-jamming technology uses the difference between target echo and jamming signal in time domain,frequency domain,airspace and polarization domain to suppress it by means of pulse compression and sidelobe cancellation.With the rapid development of digital RF storage technology,new jamming with the characteristics of suppression and deception has become a new problem of radar anti-jamming,especially the new jamming with self-defense near the target,Based on the cognition of these new smart jamming,it has become a research hotspot of radar anti-jamming technology to adjust and apply common methods to combat new jamming.Starting from the anti-jamming waveform,this paper studies how the traditional waveform can change and deal with these new types of jamming,especially for the self-defense intra pulse intermittent sampling and forwarding jamming from the main lobe.Based on the combination and innovation of the traditional waveform,a set of effective anti-jamming transmission waveform strategy of cognitive radar is formed by using the jamming parameter information of cognitive radar.The main work contents are summarized as follows.Firstly,a set of cognitive anti-jamming system structure and cognitive radar structure model are constructed.Taking the commonly used LFM signal as an example,this paper summarizes the characteristics of three types of typical active interference-suppression interference,deception interference and smart interference from the generation principle and effect,and summarizes the interference effect from the time-frequency diagram of each smart interference by using STFT time-frequency domain analysis method,so as to pave the way for the design of anti-interference waveform.Secondly,in order to improve the anti-interference ability of LFM signal,this paper starts from two directions: phase coding and frequency coding.Firstly,the chaotic phase code is generated by chaotic sequence,and the chaotic two-phase code is combined with LFM signal.The anti-interference performance of chaotic pm-lfm combined signal against intermittent sampling and forwarding interference and spectrum dispersion interference is verified by simulation;For the random characteristics of chaotic sequences,this paper also puts forward the optimization method of chaotic phase coding.By using threshold rapid screening or offline large-scale comparison,the chaotic phase coding signal group with better correlation performance is selected and combined with LFM signal.Second,generate Costas coding sequence through Welch method,and apply this coding sequence to intra pulse frequency agility,and generate alternating Costas sequence by alternately combining a group of Costas sequences,so as to generate intra pulse alternating Costas LFM signal with alternating shielding characteristics.Simulation experiments show the anti-interference effect of intra pulse alternating Costas LFM signal from intra pulse segmented pulse compression,The correctness and effectiveness of the anti-interference method flow of intra pulse alternating Costas LFM signal are verified.Finally,a set of parameter level cognitive anti-jamming transmitting waveform strategy is designed.Firstly,the influence of interference on echo signal is explored from three angles:interference intensity,sampling period and pulse width.Starting with interference sampling period and pulse width,the two interference parameters are input as cognitive system parameters to generate corresponding waveform parameters.For the main lobe self-defense intermittent sampling and forwarding interference,the two signals designed in this paper are used to verify the anti-interference effectiveness of the waveform strategy,and compared with the fixed parameter in pulse frequency agility signal and in pulse phase coding signal.The result of using the transmission waveform strategy can suppress the interference of intermittent sampling and forwarding,and the effect is better than the fixed parameter transmission waveform.