ON THE APPLICABILITY OF FAST DIGITAL BEAM FORMING METHOD FOR SONAR SYSTEMS WITH COMPLEX SIGNALS

Abstract

This work belongs to the field of hydroacoustics, namely to the problem of digital beamforming based on spatial fast Fourier transform (FFT) in a multibeam echo sounder (MLS) with baseband digital signal processing. The applicability of FFT-based beamforming when using relatively broadband signals is considered. The main attention is paid to the MLS with a static beam pattern, at the same time, obtained results are also applicable to ranging systems that provide dynamic beam control. The aim of the study is to establish the relatio nship between the relative width of the signal spectrum and signal level in the spatial channel of the MLS with a given maximum beam steering. A qualitative condition for the applicability of FFT-based spatial beamforming for a probing signal with a given relative bandwidth is determined. An analytical expression linking the signal attenuation coefficient in the spatial channel with the following signal and receiver characteristics was obtained: the number of elements of the linear equidistant antenna array, the distance between array elements, beam steering, the correlation function of the complex envelope of the signal, the window function for weighting the matched filter response in spectral domain. Presented results can be useful in designing multibeam echo sounders, providing high resolution both in range and in angular coordinates.