Ed Cregger wrote:

You are the acknowledged expert here (we're not worthy!!!).

What is the flaw in the proposed thinking? You have to admit that lots
of the commercial antenna companies and ham publications either do, or
used to, emphasize the point that "most of the radiation of a 1/4 wave
ground plane antenna (half of a half wave) occurs near the feed point".

Instead of just saying, no, this thinking is incorrect, how about
teaching your students (includes me) precisely what is wrong with this
line of thinking. Not at the engineering level necessarily (oodles of
formulas), but in the analog/real world level.

Please?

Be merciful, oh great one. I'm on enough prescription drugs to put half
a football team to sleep, so, occasionally, I get quite tangential to
the topic at hand. I hope this isn't one of those times. G

Thank you, oh merciful one.

C'mon, now, I'm not the Great Guru. I'm just somebody who's interested
in antennas and has spent a lot of time thinking and learning about
them. As I said when I was in the service (as an enlisted man), "Don't
call me 'sir'! My parents were married."

The question of where radiation "comes from" is really a complicated
one. Not long ago I came across a recent paper in the IEEE Transactions
on Antennas and Propagation which addresses the issue, and it's one of
many. One of the conclusions of the paper is that it's really not
possible to assign any part or parts of an antenna as being responsible
for a particular share of the radiation.

A lot of people confuse the field generated by a current-carrying
conductor with far field radiation. It's very well known and established
that a field is created which is proportional to the current flowing on
a conductor -- antenna analysis programs use this principle to produce
very accurate results. This is certainly the source of claims that the
middle of a half wave dipole or the bottom of a quarter wave monopole
does most of the "radiating", because those points are where the current
is highest and therefore the field most intense.

However, the fields all parts of the antenna add together to become the
radiation which "escapes" beyond the region close to the antenna. You
can, for example, have two different parts of an antenna which each
produce intense fields, but out of phase in some directions so they
cancel completely or partially out of phase in such a way that they
nearly cancel in all directions. If you could somehow make the field
from one of those parts disappear without affecting the other, the
contribution to the overall radiation from the other would increase.
(However, the law of conservation of energy requires that radiation from
somewhere else would have to decrease to keep the total the same.) So
the radiation is the result of contributions from all parts of the
antenna, but in a way that's not easy to apportion to individual parts.
In the example, the two parts of the antenna, in combination, contribute
little to the radiated field. But each one, by itself, would contribute
quite a bit if it weren't for the other. An antenna has an infinite
number of radiating parts which all sum together to produce the radiated
field, so you can hopefully see the problem here.

That being said, some professional papers do establish some sort of
criteria for apportioning it. In ones I've seen, the radiation from half
a dipole as a function of position looks sort of tub-shaped, with
considerable radiation arising from all parts of the antenna, but having
a somewhat larger amount coming from the center and ends. As far as I
can tell, though, this depends on exactly how you define in what way a
particular part of the antenna is responsible for each fraction of the
total radiated power.

The bottom line is that any simplified assignment of radiation as coming
from one part of the antenna or another is too much of a simplification
and will lead to erroneous conclusions.

All I can say about what antenna publications and commercial antenna
manufacturers say is that a very large fraction of it is just plain
wrong. Consequently, they're very poor sources of information. Good
information can be found in textbooks and professional publications, and
very few other places. One exception (that is, one good source not in
these categories) is the _ARRL Antenna Book_, since when Jerry Hall
overhauled it (15th Edition if I recall correctly). The current editor,
Dean Straw, is knowledgeable about antennas and very conscientious about
correcting errors and misinformation. So it's become the only reference
I know of which is fundamentally accurate while keeping explanations at
a level which is easily understood by non-professionals.

Hope this helped.

Roy Lewallen, W7EL