K7ITM wrote:
I expect the same to be true
on a resonant antenna; the reflected wave is NOT the same amplitude as
the forward, but is similar, so you'll find places where the phase
change is quick but continuous as you move along the wire--this
assumes that the antenna is long enough that you can find such places.

On a 1/2WL standing wave antenna, the reflected current is
within about 10% of the forward current. I think you will
find that under those conditions, the phase change is NOT
continuous.

The total antenna current reported by EZNEC is the sum of
the forward current and reflected current all up and down
a 1/2WL dipole. With the feedpoint as the 0 deg reference,
EZNEC reports only ~3 degree change between the feedpoint
and the end segment of the dipole. The phase change is
NOT quick and never exceeds ~3 degrees.

A typical forward current at the feedpoint might be
1A @ 0 deg while the reflected current might be
0.9A @ 0 deg. That phase angle is obviously zero.

45 degrees out from the feedpoint, the forward current
might be 0.975A @ -45 deg. The reflected current might
be 0.925A @ 45 deg. Adding those two phasors gives a
phase angle very close to zero. The phase angle does
NOT change quickly - it changes hardly at all.

Kraus agrees. On page 464 of "Antennas for all Applications",
3rd edition, Figure 14-2, he graphs the amplitude and phase
of the current in a 1/2WL dipole. The current phase never
exceeds ~3 degrees over the entire length of the dipole.
The phase change is NOT quick. It is exceedingly slow.

This has to do with how the forward current phasor and the
reflected current phasor adding together to obtain a *constant*
zero degrees of phase in a thin-wire dipole. Kraus shows
both a thin-wire dipole and a dipole where the length to
diameter ratio is 75. The length to diameter ratio of a
75m dipole is in the many thousands, closer to a thin
wire than to 75.
--
73, Cecil http://www.w5dxp.com