Receiving Calibration And Beam Pattern Measurements Of A Large Sonar Array With A Parametric Transmitting Array

A classical problem encountered in the receiving calibration and beam pattern measurement of a large, conventional sonar array is the difficulty involved in producing a plane wavefront at the face of the large array when reflecting boundaries are present. In this paper, an attempt will be made to show that the parametric transmitting array can be used to minimize this problem. Two experimental beam patterns are presented for the case of an 8-ft aperture array receiving at 5 kHz. One beam pattern was taken by using an omnidirectional 5-kHz source. The other was taken by using a parametric array sound source having primary frequencies of 70 and 75 kHz—thus, a difference frequency of 5 kHz. Theoretical results are presented for the parametric array which demonstrate the uniformity of phase and amplitude across the 8-ft aperture. The feasibility of absolute receiving calibration with the parametric array is discussed.