  2-D diffraction patterns arising in the far-field region were investigated
theoretically for the case, when the plane wave with non collinear group and
phase velocities is incident on the wide slit in opaque screen with arbitrary
orientation. This investigation was carried out by consideration as an example
of magnetostatic surface wave diffraction in tangentially magnetized ferrite
slab. It was deduced the universal analytical formula, which one can use to
calculate the angular width of diffractive beam in any 2-D anisotropic
geometries for the waves of various nature. It was shown, that in 2-D
anisotropic geometries this width may be not only more or less then the value
L/D (L - wavelength of incident wave, D - length of slit), but it also may be
equal to zero in certain conditions.
