Arrays with Constant Beam-Width over a Wide Frequency-Range

Abstract

IN many sound-ranging and listening systems (principally used under water) it is necessary to receive signals over a wide range of frequency, the ratio of upper to lower frequency being of the order of ten or more. Transducers (or hydrophones) with a sufficiently wide frequency response are available, but usually have to be used as omni-directional receivers because otherwise their beam-width would be inversely proportional to frequency. Clearly, the use of directional receivers would be very advantageous in many applications, but an essential condition is that the beam-width must be constant over the appropriate range of frequencies. An approach to the solution of this problem is to connect the outermost units of the transducer to the receiving amplifiers through low-pass filters, so that the transducer is virtually made smaller at the higher frequencies. There are, however, many difficulties and complications in this process, which is, at best, rather crude.