Optimising the Sounding Pulse of the Rotational Directional Transmission Sonar

To increase a sonar's source level, continuous or stepwise rotational directional transmission (RTD) is used. Continuous beam rotation has already been employed in analogue sonars. Because controlled phase shifts could not be adjusted precisely, the result was a sounding pulse which apart from the main maximum also carried a number of additional relatively high level side lobes. Stepwise beam rotation works well in a digital technology, it is not, however, free from drawbacks. Adjacent transmitting beams overlap slightly resulting in the transmission of a number of varying amplitude pulses rather than a single pulse. Modern microprocessor technology combined with weighting windows and a continuous beam rotation yields a single sounding pulse with a negligible level of side lobes. Unfortunately, for short sounding pulses and a quick rotation of the transmitting beam, the shape of the pulses suffers. The authors of the paper introduced an additional frequency and phase adjustments of signal excitation which results in a short, single sounding pulse for the entire sector of the sonar. Proposed methods can by realised by the use of modern DDS (direct digital synthesis) technology.