Art Unwin wrote:
On Mar 7, 11:46 am, Jim Lux wrote:

wrote:

I have searched quite a bit for evidence that states that performance
of antennas can be rated by it's size. Formulas do not refere to
radiator size or volume
and aparture is referenced to gain. I understand that sort of thinking
based on Yagi design
but the idea that all small radiators are inefficient is rather
ludicrouse. My work, based on
the sciences of the masters, show that a efficient radiator can be any
size,shape and
configuration as long as it
is in equilibrium . Period
No where can I find reference to "size" in what the masters state
Regards
Art

The work by Chu (Journal of Applied Physics, p1163, v19, Dec 1948) and
subsequently by Harrington (IEEE Trans Ant & Prop, V18#6, Nov 1965,
p896) , Thiele (IEEE Trans on Ant and Prop, v51, #6, June 2003, p1263)
and later others, discusses fundamental limits on performance. Watch
out, though, for the assumptions in the constraints (e.g. whether the
device attached to the feedpoint is reciprocal), and, of course, where
the boundary of the system is.

Watch out also for the definition of "Q", which in this context is the
ratio of stored to disspated/radiated energy, not the ratio of center
frequency/bandwidth.

In short, there is a tradeoff between Q, directivity, and size. And,
because high Q implies high stored energy, for physically realizable
antennas with loss, efficiency is in the mix too.

Googling "chu harrington limit" often turns up useful stuff.


Googled Chu harrington and find that his work is basically empirical
around known arrangements.
When he brought the question of Q into the picture he made the
statement that small antennas
are usually of a low impedance which is correct empirically with
respect to existing designs but it is not exclusive

To summate, my antenna design is considered small yet complies with
Maxwells laws and yet does not have a narrow bandwidth or low
impedance thus Chu's comments cannot be inclusive of all radiators.
Best regards
Art

which is why I mentioned:
"Watch out, though, for the assumptions in the constraints"

However, I believe it is incorrect to characterize his analysis as
empiricism (i.e. getting experimental data and fitting curves). His
analysis (and that of Harrington and Thiele) is entirely theoretical,
and actually doesn't deal with loss in the antenna, per se. Indeed,
Chu's analysis is based on a simple case (a dipole), but that's more
because it's a good first example (and he could use the previous work of
Schelkunoff as a starting point). I believe the analysis is generally
valid, regardless of what the actual antenna is.