Representation of the near-field, middle-field, and far-field electromagnetic Green's functions in reciprocal space

The electromagnetic field, generated by a source, has four typical components: the far field, the middle field, the near field, and the self-field. This decomposition is studied with the help of the dyadic Green's function for the electric field and its representation in reciprocal (k) space. The representations in k space involve three universal functions, which we call the T(q) functions. Various representations of these functions are presented, and an interesting sum rule is derived. It is shown that the magnetic field can be split in a similar way, leading to a middle field and a far field only. (C) 2001 Optical Society of America.