Broadband low-sidelobe beam forming in time domain

In modern active and passive sonar systems, broadband digital beam forming for acoustic arrays is widely used to suppress unwanted interference and detect interested target signals. A broadband low-sidelobe beam forming procedure in time domain is proposed. The first step of this procedure was to delay the output of each element in the acoustic array by digital delay lines to accomplish the integer part of the time delay. Finite impulse response (FIR) digital filters were used to implement the fractional part of the time delay. The weighting matrix for all array elements at different frequencies for low-sidelobe beam was also implemented with the FIR digital filters. The outputs of the digital filters were summed up for yielding the time domain beam output. The improved adaptive approach for the design of FIR digital filters was used, and the design requirements of these filters were specified by the weights which formed the low-sidelobe beams of each subband over the broad frequency band. The lowsidelobe beams of each subband were designed using the optimized beam synthesis approach based on the principle of MVDR beam forming. The results of computer simulation and lake-experiment for a twelve-element arc array show that the beam forming procedure can be used in practical acoustic environment.