Spherical wave expansion of the time domain free-space dyadic Green's function

The importance of expanding Green's functions, particularly free-space Green's functions, in terms of orthogonal wave functions is practically self-evident when frequency domain scattering problems are of interest. With the relatively widespread interest in time domain scattering problems, similar expansions of Green's functions are expected to be useful in the time domain. In this paper, an expression, expanded in terms of orthogonal spherical vector wave functions, for the time domain free-space dyadic Green's function is presented and scattering by a perfectly conducting sphere is studied as an application to check numerically the validity of this expression.