Anti-ISRJ Method Based on Intrapulse Frequency-coded Joint Frequency Modulation Slope Agile Radar Waveform

Interrupted Sampling Repeater Jamming (ISRJ) is a type of intrapulse coherent jamming that can form multiple realistic false targets that lead or lag behind the actual target, severely affecting radar detection. It is one of the hotspots of current research on electronic counter-countermeasures. To address this problem, an anti-ISRJ method based on an intrapulse frequency-coded joint Frequency Modulation (FM) slope agile waveform is proposed in this paper. In this method, the radar first transmits an intrapulse frequency-coded joint FM slope agile signal to improve the mutual coverability of subpulses by manipulating subpulse center frequency and FM slope agility. Next, the echo signal is divided into several slices according to the subpulse timing of the transmitted signal. Then, the Fuzzy C-Means (FCM) algorithm is used to classify the echo slices. Finally, the interference is suppressed via fractional-domain joint time domain filtering. Simulation results show that the FCM-based method can identify 100% of the interfered echo slices in a jammer synchronous sampling scenario when the Signal-to-Noise Ratio (SNR) is greater than −2.5 dB, and the Jamming-to-Signal Ratio (JSR) is greater than 5 dB. For high JSRs and low SNRs, the proposed method can effectively reduce the target energy loss and suppress the range sidelobes generated via residual interference. Moreover, the target detection probability after interference suppression exceeds 90% when JSR = 50 dB.