art wrote:

. . .

Except what is the definition of efficiency? Radiation resistance,
effective use of the radiation, cancellation of radiation?????

The definition of efficiency with respect to antennas is very well
defined, understood, and agreed upon in all the amateur and professional
literature. Virtually every text and professional paper uses an
identical definition, and that is: the fraction of the power applied to
an antenna which is radiated. I know that Art often uses the term to
mean several other different things which I don't believe he's ever
clarified (at least not that I could understand), so some caution should
be used in making assumptions about its meaning when used in this newsgroup.

. . .

Roy Lewallen, W7EL