"rickman" wrote in message ...

On 9/12/2015 5:33 PM, Brian Morrison wrote:
On Sat, 12 Sep 2015 22:17:27 +0100
"gareth" wrote:

"rickman" wrote in message
...
Uh, if they are matched, there won't be any reflection energy.

Untrue, because you match the inout impedance but not the radiation
resistance,
which in the case of a dipole are largely the same, so, yes, in a dipole
it
does all get radiated.



If it doesn't get radiated with a matched antenna that has a small
radiation resistance then that remaining energy is converted into heat
in the antenna/matching network, not reflected back to the Tx.

# Picture that with ideal components and then tell me what happens. Or
# better yet, since we are talking about antenna geometry and not feed
# lines and matching networks, imagine *no* feed line, just a signal
# generator with a dipole attached directly to the output. The output
# impedance of the generator exactly matches the input impedance of the
# antenna in each case. The power measured going into the antenna in each
# case is 100 W. Will the emitted field be the same?

I'm with you. For a valid comparison of the radiation of two antennas, they
both have to have the same power radiated to start with.
If one has power reflected/consumed by heat or whatever, then simply crank
up the power for that antenna until they both radiate the same power.

Let's consider an isotropic antenna (that's about the limit of "shortness")
compared with whatever bigger antenna.

At distance D, the isotropic antenna will have all its power spread over a
spherical surface of radius D.

As I understand Gareth's assertion, at every position on the point source
sphere, the field strength would be lower than for a bigger antenna
replacing the point source.
I doubt that is true.