Anti-interrupted sampling repeater jamming based on intra-pulse frequency modulation slope agile radar waveform joint FrFT

Interrupted sampling repeater jamming (ISRJ) is coherent with the radar-transmitted signal, which can form multi-false targets at the radar receiver. Therefore, ISRJ suppression is a compelling task in electronic counter-countermeasure. Intra-pulse frequency coded signals are not well energy-concentrated in the time-frequency (TF) domain, resulting in interference and target overlapping in the TF domain when the number of intermittent samplings and the number of forwarding times is large. To solve this problem, an anti-ISRJ method is proposed based on intra-pulse frequency modulation (FM) slope agile radar waveform joint fractional Fourier transform (FrFT). Firstly, the radar transmits the intra-pulse FM slope agile signal, and the adjacent sub-pulses are modulated with positive and negative FM slopes. Next, the echo signals are divided into multiple slices with the same sub-pulse timing as the transmitted signals. Then, utilizing the characteristics of transceiver time-sharing and energy suppression of the ISRJ, the FrFT is performed on each slice of the echo, and the interfered echo slices can be identified by fractional search and fractional order comparison. Finally, the interference in interfered echo slices is suppressed by fractional filtering. Simulation results show that the proposed method can recognize the interfered echo slice 100 % when the jamming-to-noise ratio and jamming-to-signal ratio (JSR) are both greater than 0 dB and do not generate false alarms when the signal-to-noise ratio is greater than 0 dB and JSR is greater than 10 dB. Fractional filtering reduces the loss of target energy in the process of interference suppression. Simulation results also verify the effectiveness of the proposed method against three typical types of synchronous ISRJ and the compound interferences formed by the combination of different types of synchronous ISRJ.