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.