On the Interpretation for Radiation from Simple Current Distributions

In this Magazine and at the recent [1997] IEEE Antennas and Propagation Symposium, Ed Miller has raised some interesting questions about the interpretation for the radiation from simple, filamentary current distributions [l, 21. The length of the filament is h, and the current is time-harmonic with frequency w (freespace wave number ko = w/c = 2z/& ). He shows that for an electrically long filament (limit koh + cc)), the total time-averaged power radiated by a sinusoidal or standing-wave distribution is (qad) a ln(koh), whereas for a un2form distribution it is (*ad) a koh . For an electrically short filament (limit k,h -+ 0), both distributions have (qad) cc (koh)*. He asks interesting questions about the physical interpretation of these results, which we will summarize with the single question: Where does the radiation originate for the two distributions? butions, that the total energy radiated, Urad, for pulse excitation depends on the length of the filament, h, in the same way as does (qud) for the time-harmonic case.