The use of LFM and CW combined signals in sonar

The motion characteristics of targets are an important basis for detecting and distinguishing underwater targets. The movement of the target can cause Doppler frequency shift in the echo. When using linear frequency modulation signals as active detection signals, it can lead to a decrease and broadening of the peak output of the echo signal matching filter, which is not conducive to echo signal detection. At present, the commonly used approach is to use Doppler filter banks for search, and the path with the highest output peak in the filter bank is considered to be closest to the true velocity of the target. However, the motion speed categories of underwater targets are diverse, and maintaining a certain speed resolution increases a lot of search costs, which cannot meet the real-time requirements of signal processing. Therefore, this article proposes a combination of long single frequency and linear frequency modulation signals as the form of active detection signals. The long single frequency signal is used for rough estimation of target velocity and provides an approximate range of target velocity. Further use of small-scale Doppler filter banks to process linear frequency modulation signals can accurately determine the target velocity. Compared to using linear frequency modulation signals alone, it greatly reduces the number of matched filters, lowers computational costs, and is implemented through engineering.