Some remarks on green's dyadic for infinite space

The validity of the often used dyadic
-(\jmath + \frac{1}{k^{2}}\nabla \nabla )\frac{e^{-jkR}{4\piR}
to compute the electric field inside a current-carrying region is investigated. It is found that care must be exercised in the definition of the integrals, which should be taken as principal values around the field point.