Variable-Focus arrays for a height insensitive side-scan sonar

A simple focused electronic beamforming approach is being developed for a side-scan bottom mapping sonar which will not have to be maintained at a constant height above the bottom is described. The signals from the elements of a flat receiving array are phase and amplitude corrected and summed in various combinations to form two parallel fan-beams with relatively constant arc resolution. They are in focus from 2 to 62 meters in range. Refocusing is accomplished with only four incremental changes of phase and amplitude across the array. Computer analysis was used to determine the number of focusing/weighting increments required and to facilitate trading-off array element spacing requirements with electronic complexity.