Directional interference suppression is based on a recursive estimation procedure of the state of a filter forming the directional interference spectrum. For the stationary filter, this leads to an iterative solution of the Wiener-Hopf matrix equation. It can be shown that the number of samples required for convergence is related to the number of degrees of freedom of the filter. The nonstationary case of a changing interference environment is treated by an appropriate deterministic dynamic process model. Tracking performance and problems of digital implementation are studied by computer simulation.