Jim Lux wrote:

Scott Stephens wrote:

Is this implied by a swr plot? Can I take 3db points as antenna
bandwidth and assume a radiation-resistance loaded-Q from that?

No (this is a common error when folks first hear about the Chu limit and
read about Antenna Q. They mistakenly equate Antenna Q with "tuned
circuit Q" and then leap to the idea that center frequency/bandwidth =
Q.. nope.. Q, in both cases, is the stored energy divided by the energy
lost per cycle. But the mechanism is different...)

Looking up the "Chu Limit, I found:
(http://ceta.mit.edu/PIER/pier43/11.0....Bellett.L.pdf)

I just skimmed, it seems the mechanism of RLC network is the R, but for
antenna, "Q is formed from the independent contribution of all the modes".

Which, for a UWB or impulse-radar antenna, will be an interesting; a
frequency-dependent resistance to model.

From the paper it seems using a ferrite broadens a loop antenna by
raising radiation resistance across frequencies. Whereas dielectrics
increase energy storage (Q) by confining flux, unlike magnetics.

I've even heard of laser-ionized plasma being used for UWB antenna,
since it will quench to stop it from ringing.

Google for "radiation resistance" and "surrey" to find some pages by Dr.
Jefferies at UofSurrey..

Ok, I'll take a long-look.

http://personal.ee.surrey.ac.uk/Pers...es/radimp.html
http://personal.ee.surrey.ac.uk/Pers.../antennas.html

http://www.ece.rutgers.edu/~orfanidi/ewa/ is an online textbook which
you may find useful

Thanks