Research On LFM Radar Countering The Frequency Shitfing Jamming Signal

Linear frequency modulation pulse compression radar (LFM radar)is a kind of typicalradars. Because it have large time-bandwidth product and invariance under the Dopplerfrequency shift, the LFM radar have been widely applied in some fields. With the technique ofthe pulse compression developing rapidly, it is proved that the radar can normally keepworking in the condition of low SNR and effectively detect the target.However, high coupling of the distance and velocity in the signal of the LFM radarprovide possibility for the wireless jammer to produce a deception LFM jamming. Makinguse of digital radio frequency memory(DRFM), the jammer take the radar signals andtransmit them after modulating some parameters, forming frequency shifting interference. Theradar’s receiver will deal with the echo signals and there will be deceptive signals appearingafter the pulse compression results, which will disturb the judgment on the real signal and itslocation.In order to hide the shifting-frequency parameter, three improved shifting-frequencyjamming are applied to produce more sophisticated signals. Actually, most of smart jammingwhich have brought more threats on LFM radar system are combine with the three jamming.The time frequency analysis is a kind of effective measures to analyze the LFM signal,which belongs to nonstationary signals. WVD, WHT, STFT and FRFT as prime methods forsignal detection could be used to find the LFM radar signal and estimate the relevantparameters. But there are some disadvantages on them such as large cross term, differentsignals’ shadow, seriously influence of noise. Based on the problems above, an algorithmbased on complex FastICA and time frequency analysis to detect the LFM radar signal isproposed which is discussed inside the LFM pulse.The method divides the echo signals intoseveral channels in the time domain first, then ensure the noise channel and deal with signalswith the time-frequency analysis in order to achieve the important parameters.After the pulsecompression, the algorithm called distance compensation can be employed to identify the realecho signal, keep the radar system away from the frequency shifting jamming signal’s impact.According to the following simulation, this conclusion can be made easily that, with the blindseparation combined the time-frequency analysis and distance compensation, the LFM radarsystem can identify the jamming signals and real signal, and achieve the goal ofanti-jamming. Different from deal with the signal inside the pulse,the algorithm of temporal pulsediversity as an important method of the pulse-pulse operations makes use of the correlationbetween several pulses to remove the deceptive jamming. it is possible to eliminate thejamming signals exsiting in the term of pulses. However, confronting with the randomshifting-frequency jamming, the method fails in protecting the real target. In the case, twomeasures are introduced to take the information of the target from the echoes, one is addingthe operation in the pulse to the temporal pulse diversity, the other is coherent accumulation inthe temporal pulse diversity.