Jeff Liebermann wrote:
. . .
Incidentally, since the top 1/4 wave element represents something
close to perhaps 50 ohms, it would be interesting to measure the
amount of RF that isn't radiated and actually gets to the top section
of the antenna. If my analysis of the antenna is correct, the first
section (near the coax connector) radiates 1/2 the power. The next
section 1/4th. After that 1/8th, etc. By the time it gets to the top
of the antenna, there won't be much left. However, that's theory,
which often fails to resemble reality. It would interesting if you
stuck a coax connector on the top, and measured what comes out.

I'm intrigued by this, and would like to know what "theory" it's based on.

The field radiated from a conductor is proportional to the current on
it. You'll see from either modeling or measurement that the currents on
all sections of a collinear array, or a long wire antenna for that
matter, are nearly the same. So in those directions in which the fields
reinforce, each section is contributing about the same amount to the
total field as any other.

Although the logic is sound for this particular situation, it can't be
used in general to assign particular amounts of radiated power to
particular parts of an antenna. The fields from two parts of the antenna
might partially or fully cancel in some directions, even though both are
producing large fields. Any part of the antenna which is carrying
current is involved in the radiation process, and the total field is the
vector, not algebraic, sum of those fields.

So if you have a valid method of determining how much of the total
radiated power comes from each part of an antenna, I'd be very
interested in learning more about it. References would be welcome.

Roy Lewallen, W7EL