Art,

I want to know about this concept. Can you tell me how to build one?
By what means might it change the very simple calculation of efficiency
given in the long and rambling thread which I am trying to avoid.

Take an antenna, any antenna you can dream up, measure the power
radiated in each direction. Add it all up. Compare that to the power
fed to the antenna.

A 100% efficient antenna radiates all the power it's fed.

A 50% efficent antenna radiates half the power it's fed.

A 150% efficent antenna radiates half again as much power as it's fed.

Why is an inherently directional "dipole" different from a yagi in this
respect?

Dan