Gene Fuller wrote:
1) Only the total current matters. I have never found a detailed
treatment of antennas that was based on anything other than the total
current (or total current density) at each point on the antenna. Have you?

Check out my tag line, Gene. Balanis says we can use the component
currents If and Ib to analyze a standing-wave antenna. Kraus says
essentially the same thing when he says: "A sinusoidal current
distribution may be regarded as the standing wave produced by two
uniform (unattenuated) traveling waves of equal amplitude moving in
opposite directions along an antenna." This was in regards to the
"Fields of a thin linear antenna with a uniform traveling wave."

Just because there is no "detailed treatment" doesn't mean that it
should be forbidden to discuss. We are out on the edge of what has been
detailed (so far) so don't be afraid to think outside of the box. The
opposite phase shift between If and Ib is the cause of the decrease in
coil current in a typical mobile antenna. It happens even if there is
zero loss in the coil and zero radiation from the coil. It also
happens in a lossless transmission line. There is a decrease in standing
wave current on each side of a current maximum point even when the
transmission line is lossless. The same thing applies to a lossless
coil with dimensions larger than a point.

Current components may be useful for discovering the total current or
for handwaving explanations, but they have no further role in antenna
analysis.

Check my tag line again, Gene. They are absolutely useful for transmission
line analysis and are therefore useful for standing-wave antenna analysis.

2) Where did this 90 degree phase shift requirement come from? There is
virtually no phase shift in the current of a half-wave dipole (or
quarter-wave monopole) from feedpoint to tip.

Yes, you are talking about the standing-wave current which is the
superposition of the forward and reflected currents. A 1/4WL wire
is 90 degrees of a traveling-wave antenna. The forward current rotates
by 90 degrees and the reflected current rotates by 90 degrees.

I am looking at figure 9.6
on page 370 in Kraus "Antennas" (2nd Ed.), and it shows perhaps a few
degrees phase variation over the entire length of the dipole antenna.

Yes, that is true for the superposed forward and reflected currents and
is shown to be true by my phasor diagrams on my web page. The forward
current is a traveling wave. The reflected current is a traveling wave.
I'm sure you are familiar with the change in phase undergone by traveling
waves in perfectly matched systems. Apply that knowledge to the separate
forward and reflected current traveling waves and you will understand
the magnitude variation in If+Ib caused by their respective phase shifts
in the opposite direction even if their magnitudes remain constant.

I suspect you may be confusing the argument (AKA, the phase) of the
cosine function presumed to describe the behavior of the current
amplitude. However, current amplitude and current phase are not at all
the same thing.

Nope, I fully agree that the superposed net current has almost zero
phase shift because it is a *standing wave*. Traveling waves, OTOH,
experience phase shifts when traveling along a wire. The forward
current and reflected current on a standing-wave antenna are
*traveling waves*.

This is an onion-type problem, Gene. Please peal back the net current
layer and look at the component currents underneath even if you feel
presently that it will be a waste of time.

Incidentally, I bounced most of this stuff off of Dr. Balanis when
I was working with him on a joint Intel/ASU project. He agreed so
far (1995) and my extensions since 1995 are logical. If you will
take it step-by-step, I think you will agree. If you find any error
at all on my part, you will, no doubt, call my attention to it and
I will learn something.
--
73, Cecil http://www.qsl.net/w5dxp
"The current and voltage distributions on open-ended wire antennas are
similar to the standing wave patterns on open-ended transmission lines ...
Standing wave antennas, such as the dipole, can be analyzed as traveling
wave antennas with waves propagating in opposite directions (forward and
backward) and represented by traveling wave currents If and Ib ..."
_Antenna_Theory_, Balanis, Second Edition, Chapter 10, page 488 & 489


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