Measured performance of an endfire superdirective line array in littoral water

Superdirective line arrays can provide high gains whenever the interelement spacing is much less than half a wavelength. In practice these arrays have fallen short for two reasons: First, performance degrades appreciably in the presence of uncorrelated system noise. Second, the optimum array weights are specific to the form of the noise field and the choice of these weights is often sensitive to deviations from that noise field. Furthermore, since the process involves computing signal differences between hydrophones, the signal to noise ratio (SNR) degrades as the steering angle approaches broadside. In spite of these drawbacks, a superdirective array can provide substantial improvement over a conventional array in specific instances. For example, the present application requires an endfire array of limited extent (1 m in length) and wide bandwidth (1–5 kHz) making a conventional array impractical. Moreover, improvements in array hardware have substantially reduced uncorrelated system noise, and increased computer speed makes it reasonable to process data using several weighting schemes. In this paper, the superdirective array will be described and its measured performance will be compared to theoretical predictions.