"bilou" wrote in message ...


"Wayne" wrote in message
...


"John S" wrote in message ...

On 7/16/2015 4:46 AM, bilou wrote:
"John S" wrote in message
...
The other thread is getting too long for my mouse wheel to handle.

Do you have any other questions that we might be able to solve
together?

John N1JLS
Hi. (Sorry I have not seen the other thread)
I have one:
Does a receiving aerial reradiates more or at best the same power
it delivers to the receiver ?
Or on the contrary would a perfectly matched antenna be invisible on
radar ?
My own experience of the second proposition is that it is not at all
the
case.
73's

According to Kraus, a matched antenna absorbs half the incoming power and
re-radiates the other half.

As for best re-radiation, consider the reflector element of a Yagi. It is
shorted (no load in the middle).

It is difficult to make metal invisible. Notice that stealth aircraft have
a special rf absorbing coating and they take care to reflect what they
don't absorb away from the incoming rf.

This sounds interesting, and I'm surprised it didn't get picked up for
general discussion.
I'm late responding to this post because I've been "off the grid" on
vacation for a couple of weeks.

So "bilou"....why not post the question as a new thread?
Hi
Here I am quite late too :-)
Now let us imagine a perfect waveguide with a pair of
coaxial /guide transitions (antennas) at each end.
Luckily we don't have a minimum of 3 dB loss.
For me the most satisfying explanation is that antennas behave quite
differently
depending of what is between them. :-)
What happens if ,by design, we use a frequency very much higher than the
cut off frequency of the guide.
There is also the regularly reapearing projects of transmitting
power from a geostationnary solar panel to ground by microwave.
I have great difficulties to understand how it could be efficient.

I don't have much experience with re-radiation. But, I can understand how
yagis might like the concept