Art Unwin wrote:
On Mar 10, 1:56 pm, Roy Lewallen wrote:

You can pretty much sum up the characteristics of small antennas as:

Small - Broadband - Efficient: Pick any two.

Roy Lewallen, W7EL


Who knows what "efficiency" represents in the electrical world?

I think the conventional meaning would be power radiated vs power into
the system.

If you define "power radiated" to mean "power radiated in a particular
direction" then you're adding directivity into the mix.

If you define "power into the system" to be 120V Wall power that's
different than RF power at the feedpoint of the antenna which is
different than RF power out at the output of the transmitter.

So, you have to define the appropriate reference plane. The antenna
literature tends to draw the boundary at the feedpoint of the antenna,
because the rest is "circuit theory".

The ham world tends to draw the boundary at the output of the
transmitter (so we include loss in feedlines and matching networks),
because the FCC power limit is usually measured at that point. (although
nothing in the rules says you can't measure after the matching network)

In the commercial broadcast world, there's a sort of hybrid, because
there's an RF power limit AND a requirement to have a particular field
strength in the far field at a particular distance.



It is the word "small" that confuses everybody when the word
should be" fractional wavelength".


Nope.. small in an absolute sense. An antenna that is 10 times bigger
will have more directivity or other figure of merit. Applies pretty
much whether you're comparing an antenna that is 0.01 wavelength to 0.1
or comparing one that is 10 wavelengths to one that is 100 wavelengths.

What you can't say is that the amount of change from 0.01 to 0.1 is the
same as from 10 to 100.

Small and large are meaningles in the antenna world.

They have meaning as far as relative. large is better than small.
And, "directive" antennas that are small relative to a wavelength tend
to have high Q (in the stored vs radiated energy sense, which may or may
not imply narrow bandwidth)


It's probably worth finding a library that can get you copies of the
papers, rather than relying on interpretations and summaries. The most
common misinterpretation is to conceptually equate antenna Q to antenna
bandwidth.

No I diddn't overlook the sniping.