"Owen Duffy" wrote in message
...
"AndyS" wrote in news:1175314795.342922.213610
@o5g2000hsb.googlegroups.com:

Andy asks:
I have a quick question about the number of microwatts that an
antenna will extract from the air and put into a known load.

Assume a 70 ohm perfect antenna used for receiving a signal....

Preceived = Pwr density ( watts/sq mtr) X Capture Area (sq
mtrs)


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

and hence if you start with the capture area by definition all the power is
sent to the matched load. basically you measure the capture area by
measuring the power in the load and dividing by the power density.