Application of blind signal separation techniques to airborne antenna arrays

Airborne antenna arrays suffer from the problem of multipath, formed due to scattering of the desired signal by the aircraft propellers. The direct path includes the desired signal coming from a sonobuoy floating in the ocean or from other airborne radars, and their reflections from the ocean surface. Numerous techniques have been proposed for multipath mitigation and localization of the desired signal, that assume the propeller scatters to be point sources, which is not true in actual scenarios. Also, the multipath from the ocean that accompanies the direct signal, leads to a complicated spatial signature, making existing techniques unsuitable. In this paper, we propose a new technique which deals with the propeller scatters as spatially extended sources, and also takes into account the signal reflections from the ocean. The problem is presented as that of blind signal separation. The objective is two-fold, localization of the desired signal and extraction of its waveform. The Second order Blind Identification (SOBI) algorithm is applied to obtain the spatial signatures of the desired signal and the multipath, which are then used to obtain both the temporal and spatial characteristics of the signals. An efficient method for recovering the desired waveform is also formulated.