Low frequency, log-periodic acoustic array

A method of determining the sequential dipole spacing of a plurality of hydrophone dipole pairs about an array acoustic axis so as to form a low frequency, log-periodic acoustic line array wherein the acoustic beam pattern formed by each independent dipole pair has a quasi-constant directionality over a frequency band and the assembled array covers at least a decade range of frequencies through juxtaposition of contiguous frequency bands, said method comprising the steps of:

• selecting an operational frequency range;
• determining the spacing (2d.sub.n) of the innermost dipole pair using the following relationship
• 2 d.sub.n =(c/f) (A)
• wherein d.sub.n is the distance of each dipole element from the array acoustic axis, c is the speed of sound in seawater at the operational frequency, temperature and pressure the array will experience and f is the maximum desired operational frequency;
• selecting a minimum null depth commensurate with desired directionality descrimination;
• selecting a (d/.lambda.).sub.max for the ideal null from a graph wherein d equals 2d.sub.n and represents the distance between dipole pairs and .lambda. is the wavelength of the associated acoustic frequency;
• selecting a (d/.lambda.).sub.min from said graph for said minimum null depth;
• solving the following relationship for .tau. ##EQU8## wherein .tau. is an arbitrary constant associated with the log-period;
• solving the following relationship for d.sub.n-1 ##EQU9## using .tau. from (B) supra;
• repeating (C) supra iteratively substituting the previous d.sub.n-1 result for d.sub.n in (C) and solving for new d.sub.n-1's until 2d.sub.n, 2d.sub.n-1, etc. spacing for a frequency decade has been described;
• and
• arranging said hydrophones in accordance with said 2d.sub.n, 2d.sub.n-1, etc. spacing.