Abstract: Interrupted sampling repeater jamming(ISRJ) is a very threatening intra-pulse forwarding interference faced by radar systems in recent years. Through interrupted sampling and time-sharing forwarding technology, the jammer repeats the process of "intercept-slice-forward" in the jamming period. The sampling, storage and forwarding of intercepted radar signals can produce multiple false targets in the current repetition period, and the interference amplitude is strong, which seriously affects the radar's detection and tracking level of targets. Therefore, ISRJ suppression technology has become a research hotspot in the field of radar countermeasures.An improved ISRJ suppression algorithm based on time-frequency analysis is proposed for the complex scenario of "multi-interference & strong and weak interference coexistence". Firstly, the time-domain duty cycle of jamming is reduced by dechirp and time-domain alignment; secondly, the impact of noise is further reduced by time-frequency image binarization and thedetection probability of target and jamming is improved; then, target components are eliminated according to the cumulative characteristics of short-time Fourier time-frequency analysis in the time dimension, and the corresponding bandpass filter is designed to remove ISRJ; finally, the target signal is reconstructed by recovering the slope of the dechirped target echo. In addition, a number of simulation experiments are conducted to verify the effectiveness and robustness of the proposed algorithm under different SNR and different intensity combined ISRJ scenarios. Two existing classical algorithms are used as control groups to compare and verify the superior jamming suppression performance of the proposed algorithm.Simulation results show that the proposed algorithm can adapt to different SNR, and the jamming suppression ability is obviously better than the two control algorithms, and both remain at a high level. With the increase of SNR, jamming suppression performance of the proposed algorithm is also gradually improved. The proposed algorithm can adapt to the jamming of different intensity combinations, especially in the scene containing weak jamming, through the analysis and processing of time-frequency domin, the weak jamming components are effectively eliminated, and the improvement factor of the SIR is greatly improved.The proposed algorithm has good practicability for ISRJ suppression, and provides an important reference for the subsequent reconnaissance and jamming system design in the field of wide and narrow band radar countermeasures. It is of great significance for improving radar detection efficiency and grasping information control dominance in complex electromagnetic environment.

Key words: interrupted sampling repeater jamming, jamming suppression, linear frequency modulation, time-frequency analysis, binarization