For optimizing the computing expenditures when using STAP filters in real-time systems, the determination of the filter coefficients and the filtering of radar source data of the distance Doppler matrices X.sub.left and X.sub.right of two adjacent reception channels are carried out in the frequency domain. On the basis of X.sub.left and X.sub.right, a distance Doppler matrix Y.sub.clutterfree is created, at which the echoes of fixed targets are suppressed and the echoes of moving targets a coherently intensified.