Study on the impact of multi-path channel to the horizontal uniform linear array beamforming

The horizontal uniform linear array beamforming technology can be used for measuring the direction of arrival (DOA) of target of interest. In the free field space, it has good performance. However, in the ocean due to the interference´s impact, the underwater acoustic channel has multi-path characterization, which may have some influence on the DOA estimation. When the target is far from the array, the multi-path azimuths are all approaching to the true target azimuth. Here the multi-path impact can be ignored. But when the target is in a short range to the array, the multi-path impact has distinct influence on DOA estimation and can´t be omitted. In this paper the multi-path impact was analyzed theoretically based on the ray propagation model. And the theoretic results were validated through numerical simulation and lake experiment, in which the pulse signal form was used for convenient analysis. Theoretical analysis indicated that the multi-path impact is related to the target range, DOA, the vertical distance from the array reference point to the equiphase plane. In detail, the closer target range, the more deviation from the broadside of the array and the longer the vertical distance from the array reference point to the equiphase plane, the worse influence subjected to DOA estimation. The simulation and experiment results all validated the theoretical analysis.