There's no direct way to measure the total power being radiated other
than sampling the field at many points in all directions and
integrating. "Reflected" power is not power that isn't transmitted. You
can find the power being applied to the antenna by subtracting the
"reverse" or "reflected" power from the "forward" power, but that tells
you nothing about what fraction is radiated and what fraction lost as heat.

Roy Lewallen, W7EL

Wayne wrote:
When the subject of antenna efficiency comes up, it often involves a
discussion of ground losses on verticals. What about, for example, a
dipole? Could one calculate "power out/power in" by measuring the VSWR and
declaring that everything not reflected was transmitted? It would seem more
accurate to actually measure power out and power in, but that introduces
inaccuracies by having to calibrate the setup. Thoughts?