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.

中文翻译：

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基于脉冲内调频斜率捷变雷达波形联合FrFT的抗中断采样中继干扰

间断采样中继干扰（ISRJ）与雷达发射的信号相干，可以在雷达接收机处形成多个虚假目标。因此，抑制ISRJ是电子对抗中一项紧迫的任务。脉冲内频率编码信号在时频域能量集中度不高，当间歇采样次数和转发次数较多时，会导致TF域出现干扰和目标重叠。针对这一问题，提出一种基于脉冲内调频（FM）斜率捷变雷达波形联合分数阶傅立叶变换（FrFT）的抗ISRJ方法。首先，雷达发射脉冲内调频斜率捷变信号，并用正负调频斜率调制相邻子脉冲。接下来，回波信号被分成具有与发射信号相同的子脉冲定时的多个片段。然后，利用ISRJ的收发分时和能量抑制的特性，对每个回波切片进行FrFT，通过分数搜索和分数阶比较来识别受干扰的回波切片。最后，通过分数滤波抑制受干扰回波切片中的干扰。仿真结果表明，当干扰噪声比和干扰信号比(JSR)均大于0 dB时，该方法能够100%识别出受干扰回波切片，并且当信噪比大于0 dB时，该方法不会产生误报。 -噪声比大于0 dB，JSR大于10 dB。分数阶滤波减少了干扰抑制过程中目标能量的损失。仿真结果还验证了该方法对抗三种典型同步ISRJ类型以及不同类型同步ISRJ组合形成的复合干扰的有效性。