In article , Richard Clark
wrote:

Lest there be any confusion: an antenna IS a transmission line.


Hello, and I think one would have to include two antennas and the
intervening medium(s) for the above statement to make sense. In any
event, the behavior of an antenna-medium-antenna as a passive 2-port
device can be considered as a transmission line at a given frequency. The
"loss" associated with this topology can be mitigated by keeping the two
antennas within a near, rather than far, field separation. Over a range
of frequencies the behavior of this 2-port can easily differ from that of
a transmission line, though.

In some electromagnetics textbooks an antenna is developed mathematically
via the gradual unfolding of a twin-lead transmission line. And many hams
know that a quick and dirty dipole can be created by simply folding the
braid back on a length of coax so that the braid and the exposed center
conductor become the radiating elements.

A more correct statement might be that a transmission line can be an antenna.
This can include unintended radiotion (e.g. RF flowing on the outside of
caox due to imbalance and/or stray coupling) or intended such as Andrew's
"Radiax" brand of leaky transmission line for installation in tunnels and
elevator shafts as a convenient means to extend the reach of over-the-air
broadcasts. Sincerely, and 73s from N4GGO,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337