A multi-mode sonar transmitter

Abstract

This project was initiated to evaluate appropriate microprocessor and digital logic techniques that could increase the flexibility and effectiveness of a sonar transmitter. The study led to a multi-channel signal synthesis concept designed to exploit 'phased array' steering techniques. Two versions of the equipment have now been built and evaluated. Mk.I is a relatively low power 15 channel system with 2 kilowatts total electrical power using a 40 kHz 15 λ x 1 line array. This system proved the practicability of the basic concept and its success led to the 16 kilowatt Mk2 high power version which drives a 16λ x 16 λ wideband transducer array. The study included: The design and construction of a multi-channel signal generator. The writing of control and signal synthesis software. The design, evaluation and commissioning of suitable linear power amplifiers . Investigations into suitable transducers and phased array design, leading to the manufacture of suitable matched wide band multi-channel 'staved' transducer arrays. Finally, a series of trials were made in a variety of open water conditions to evaluate the systems performance and investigate the multiple modes of operation that have been developed. The system has successfully demonstrated that transmitter beam steering is both practical and flexible. The techniques implemented permit sector interrogation by 'within-pulse' type sweeps, by 'Ripple-fire' and by transmitting steered 'Pings' sequentially on prededermined bearings. Each mode allows considerable flexibility in the generated waveform shape and frequency. The 'Multi-Mode' capability of this approach was conceived primarily as a research tool but many of the modes can be isolated and exploited in dedicated applications.