Multipole Radiation in Lorentz Gauge
  The multipole expansion for electromagnetic radiation, valid for all wave-lengths and all distances from bounded sources, is presented in Lorentz gauge, rather than the usual Coulomb gauge. This gauge is likely to be preferred in applications where one wishes to maintain manifest Lorentz invariance. The presentation also serves as a useful exercise in the use of vector spherical harmonics. 
Howard J. Schnitzer