Abstract In order to improve the detection performance of active sonar and make up for the shortcomings of pulsed active sonar (PAS), linear frequency-modulated continuous wave (LFMCW) was applied in continuous active sonar (CAS). The expression of transmitting waveform was presented, and the echo model of underwater moving targets was established. To detect the LFMCW echoes, the received signal was first demodulated by the transmitting signal, resulting in a de-chirped signal. Unlike radar system, the target velocity of active sonar was not negligible, comparing with the sound velocity in water, and the de-chirped signal was also a LFM signal, whose chirp rate and frequency were related with the velocity and distance of the target. Fractional Fourier Transform (FRFT), a time-frequency analysis method which is generally used to detect and estimate LFM signals, was proposed to detect and estimate the de-chirped signal. In multiple targets situation, “CLEAN” algorithm was proposed to solve the problem of the detection interference from strong targets to weak targets. Simulations show that LFMCW active sonar with the de-chirp-FRFT receiver can get much higher processing gain than conventional PAS with a matched filter (MF) receiver. The resolutions of velocity and distance with the de-chirp-FRFT algorithm fully meets the needs of underwater target detection. The simulation result also shows that the proposed CLEAN algorithm can detect LFMCW multi-target echoes effectively.

中文翻译：

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基于分数阶傅立叶变换的线性调频连续波有源声纳的多目标检测

摘要 为了提高主动声纳的探测性能，弥补脉冲主动声纳（PAS）的不足，将线性调频连续波（LFMCW）应用于连续主动声纳（CAS）。给出了发射波形的表达式，建立了水下运动目标的回波模型。为了检测 LFMCW 回波，接收信号首先由发射信号解调，从而产生去啁啾信号。与雷达系统不同，主动声纳的目标速度与水中的声速相比是不可忽略的，去啁啾信号也是LFM信号，啁啾频率和频率与目标的速度和距离有关。分数傅立叶变换 (FRFT)，提出了一种通常用于检测和估计LFM信号的时频分析方法来检测和估计去啁啾信号。在多目标情况下，提出“CLEAN”算法来解决强目标对弱目标的检测干扰问题。仿真表明，与带有匹配滤波器 (MF) 接收器的传统 PAS 相比，带有去啁啾-FRFT 接收器的 LFMCW 有源声纳可以获得更高的处理增益。de-chirp-FRFT算法的速度和距离分辨率完全满足水下目标检测的需要。仿真结果还表明，所提出的CLEAN算法能够有效地检测LFMCW多目标回波。为了解决强目标对弱目标的检测干扰问题，提出了“CLEAN”算法。仿真表明，与带有匹配滤波器 (MF) 接收器的传统 PAS 相比，带有去啁啾-FRFT 接收器的 LFMCW 有源声纳可以获得更高的处理增益。de-chirp-FRFT算法的速度和距离分辨率完全满足水下目标检测的需要。仿真结果还表明，所提出的CLEAN算法能够有效地检测LFMCW多目标回波。为了解决强目标对弱目标的检测干扰问题，提出了“CLEAN”算法。仿真表明，与带有匹配滤波器 (MF) 接收器的传统 PAS 相比，带有去啁啾-FRFT 接收器的 LFMCW 有源声纳可以获得更高的处理增益。de-chirp-FRFT算法的速度和距离分辨率完全满足水下目标检测的需要。仿真结果还表明，所提出的CLEAN算法能够有效地检测LFMCW多目标回波。de-chirp-FRFT算法的速度和距离分辨率完全满足水下目标检测的需要。仿真结果还表明，所提出的CLEAN算法能够有效地检测LFMCW多目标回波。de-chirp-FRFT算法的速度和距离分辨率完全满足水下目标检测的需要。仿真结果还表明，所提出的CLEAN算法能够有效地检测LFMCW多目标回波。