An approach for DOA estimation in the presence of near field scatterers

Direction of arrival (DOA) estimation of radio waves is one of the basic tasks in radio source location systems, where array super-resolution technologies are widely applied. In the ship-borne and airborne applications, there are many near-field scatterers nearby, due to the space limitations. Thus, the received signal includes both the desired components from the far-field sources and the coherent interferences from the near-field scatterers. This paper analyzed the effects of the near-field scattering on the DOA estimation. It is shown that the estimated angular spectrum could be dramatically degraded, even totally ruined by the near-field scattering. The spatial smoothing approach, a popular approach to handle coherent sources, was also shown to be inappropriate to the near-field scattering. This paper proposes a new approach that treats the near-field scatterers as a part of the receive antenna. The simulation results, using the Multiple Signal Classification (MUSIC) as an example algorithm of DOA estimation, illustrated that the new approach works perfectly in the presence of near-field scattering without other extra operations such as spatial smoothing.