A generalized sinusoidal frequency modulated waveform for active sonar

Abstract

Pulse-Compression or Frequency Modulated (FM) active sonar waveforms provide a significant improvement in range resolution and reverberation suppression over Continuous Wave (CW) waveforms. The Sinusoidal FM (SFM) waveform modulates its instantaneous frequency (IF) by a sinusoid to achieve high Doppler sensitivity while maintaining desirable reverberation suppression. This allows the SFM waveform to resolve target velocities much better than the Doppler tolerant Hyperbolic FM waveform. However, the SFM suffers from poor range resolution as the Auto-Correlation Function (ACF) contains many ambiguous peaks generated by the periodicity of the SFM’s IF. The periodic sidelobes in the ACF for the SFM signal are similar to those exhibited by periodic CW waveforms, which motivated the development of FM waveforms to improve range resolution. This suggests that modifying the SFM waveform to use an aperiodic modulating function should improve range resolution while preserving Doppler sensitivity. This talk presents an active sonar waveform where the IF function is itself an FM chirp waveform, and for which the SFM is a special case. This generalized sinusoidal FM waveform resolves target range and velocity with reverberation suppression comparable to other well-established FM waveforms. [Work supported by ONR and the SMART Program.]