We consider the estimation of two- dimensional (azimuth and elevation) direction-of-arrival (DOA) using a pair of uniform circular arrays under a coherently distributed source model. Since the coherently distributed source is characterized by four parameters, the nominal azimuth DOA, angular extension of the azimuth DOA, nominal elevation DOA, and angular extension of the elevation DOA, the computational complexity of the parameter estimation is normally highly demanding. We
propose a low-complexity estimation algorithm, called the sequential one-dimensional searching algorithm by concentrating only on the estimation of DOAs. The SOS algorithm has a basis on the eigenstructure between the steering matrixand signal subspace, and utilizes preliminary estimates obtained at a pre-processing stage. The SOS algorithm estimates the DOAs, but not the angular extensions: although the SOS algorithm does not provide estimates of angular extensions, it is useful when the angular extensions are small. Specifically, it is shown from simulation results that the SOS algorithm exhibits as good an estimation performance as the maximum likelihoood method for coherently distributed sources.