A.G. Kyurkchan, N.I. Smirnova

The role of singularities of analytical continuation of a wave field is investigated at the solution of diffraction problems by the null-field and Т-matrixes methods. It is shown, that these methods are quite correct only if a surface, on which the relation of a null field is satisfied is envelop a singularities of analytical continuation of a wave field. It is shown also, that a surface, on which the null field condition is satisfied in a corresponding method, it is the most appropriate to form by means of analytical deformation of a scatterer boundary.