Time-domain spherical-multipole analysis of the poynting vector of radiated electromagnetic fields

A time-domain spherical-multipole expansion of an electromagnetic field radiated into the free unbounded space is used to evaluate a modal analysis of the corresponding Poynting vector. This decomposition of the Poynting vector is an excellent basis to systematically and more generally investigate the local power flow of the radiated fields in the near- and in the far-zones of radiating structures. Besides an investigation of special cases such as a canonical non-radiating source, an impulse-radiation efficiency is proposed which could be applied to characterize impulse-radiating and UWB antennas.