  A theory for analyzing the radiative and reactive energies for pulse
radiators in free space is presented. With the proposed definition of reactive
energies and radiative energies, power balance at arbitrarily chosen
observation surfaces are established, which intuitively shows that the Poynting
vector contains not only the power flux density associated with the radiative
energies, but also the influence of the fluctuation of the reactive energies
dragging by the sources. A new vector is defined for the radiative power flux
density. The radiative energies passing through observation surfaces enclosing
the radiator are accurately calculated. Numerical results verifies that the
proposed radiative flux density is more proper for expressing the radiative
power flux density than the Poynting vector.
