Owen Duffy wrote:
Further to Roy's notes, keep in mind that for most antennas, you cannot
determine the Effective Aperture Area (or Capture Area) using a ruler.
This effect is demonstrated if you consider that a short low loss dipole
with low loss matching has an Effective Aperture Area nearly as large as
the much larger half wave dipole.

For many purposes, you would determine the Effective Aperture Area by
determining Gain from Directivity and Loss, thence Effective Aperture
Area from Gain and Wavelength.

Owen

Andy writes:
Thanks to all for the discussion....... I have used the results of
these
calculations for many years but wanted to see what explanations I
would
get from others who also have experience in these matters.....

For capture area, I use " Gee lambda squared over four pi ",
which
is the standard definition for a well behaved antenna with a main
lobe, and it has always worked well for me. I don't remember doing
the
derivation for this, but I'm sure I must have done it in the past
(olden times)...

Yet, I was not comfortable with what seemed like a discrepancy
between
"all the extracted power goes to the load" and the proposition that
the
cosmos and antenna acted like a generator and therefore had an
internal
impedance which must be Thevenin matched for max extracted power....
I resolved it, in my mind, by ignoring the latter explanation
(grin)..... and
apparently it was the correct thing to do...

So, thanks again, guys........

Andy W4OAH