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.