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.