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The simultaneous transmission of a number of specially coded waveforms can provide a number of substantial advantages for active sonar imaging. Two of the possible advantages are increased imaging speed and better sidelobe rejection. In order to maintain the integrity of the individual, but simultaneously transmitted, beams, the signals must possess specific mathematical properties. A narrow autocorrelation function and a small cross-correlation function are desirable in order to insure both accurate range resolution and rejection of neighboring beams. It is demonstrated that this design criterion is identical to that encountered in multiaccess, spread spectrum, communication systems. The time-bandwidth properties of the system therefore limit the simultaneous requirement of decorrelatable beams and good range resolution. As a specific implementation of the technique, a frequency hopping code is presented. The performance of this code is examined and it is demonstrated that this code is nearly optimal with respect to the above criterion. Various configurations of transducers are considered that specifically exploit the properties of spatially variant insonification (SVI). The principles of multibeam sonar imaging systems using spatially variant insonification are illustrated by constructing several examples of active sonar systems whose performances are superior over traditional designs.

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