"art" wrote
The most efficient radiator is one wave length long where
it is considered to be in equilibrium with a parallel electrical
cuircuit.

For most efficient radiation both the capacitance and the
inductance must act as a energy storage such that when
the terminals are shorted the energy is released in a burst
such that radiation can begin. ... In the case of a fractional
wave length radiator the pendulum type radiation is not
available for radiation
___________

Note (for one example of many) that in an antenna system consisting of a
1/2-wave, center-fed dipole driven by a matched, balanced transmission line,
the dipole itself radiates virtually all of the r-f energy present at the
antenna feedpoint.

The radiation efficiency of a system as in the above example, but using a
full wave dipole is no better than the 1/2-wave version, other things equal.
The full wave version just has a different radiation pattern.

RF