1. A direction estimation method for coherent signals in an environment of temporally and spatially uncorrelated white additive noise, where a specified number (=p□M/2) of coherent signals are received by a uniform linear array with multiple (=M) antenna elements, comprising step of: calculating M−1 instantaneous cross-correlations at time n between the signal received at one antenna element and the signals received at the other antenna elements; selecting multiple pairs of these cross-correlations, each of which is consisted of p instantaneous cross-correlations from the calculated M−1 instantaneous correlations to form a Hankel correlation matrix and dividing this Hankel matrix into an upper and lower submatrices; calculating a linear operator at time n from these two upper and lower submatrices by using an adaptive LMS algorithm with a fixed or time-varying step-size parameter; estimating a noise subspace by using this estimated linear operator; and estimating the directions of the coherent signals at time n from the estimated noise subspace by using Newton approximation.