On the interpretation for radiation from simple current distributions

We have considered the radiation from two simple filamentary current distributions: traveling-wave and uniform. For an excitation that is a Gaussian pulse of characteristic time /spl tau/, the total energy radiated by the distributions, U/sub rad/, was shown to behave as ln(/spl tau//sub a///spl tau/) for the traveling-wave distribution, and as /spl tau//sub a///spl tau/ for the uniform distribution, where /spl tau//sub a/=h/c is the time for light to travel the length of the filament. An examination of numerical results shows that two physical interpretations can be used for the radiation. Radiation can be considered to arise at the two ends of the filament in the form of spherical wavefronts centered at the ends. The overlap of these wavefronts, which changes with the ratio /spl tau//sub a///spl tau/, is the cause of the observed dependencies for U/sub rad/. An alternative explanation is that radiation occurs along the entire length of the filament. Destructive interference of the radiation from different points on the filament then causes the radiation to be insignificant except at the times corresponding to radiation from the ends of the filament.