This paper deals with the problem of high-resolution angle of arrival estimation in the presence of coherent signal sources. The receiving antenna is restricted to uniform linear array of sensors.Special attentions are paid to the estimation of signal subspace by the array measurements. A general procedure is developed that

in the first place

estimate the vector （s）of the signal subspace in N（the number of the array elements）dimensonal vector space C

and secondly

estimate the orthogonal projection matrix of a signal subspace in a lower dimensional space C

where M<N. We have shown that the well known spatial smoothing technique can be considered as a special case of the new approach. Simulation results are presented to show the effectiveness of the new approach.