The useful model: Radiation resistance is the equivalent resistance at an antenna feed point that represents power carried away as electromagnetic radiation for a stated current reference.
What controls the result
It is not a physical resistor and does not include loss resistance. Its value depends on geometry, current distribution, frequency, ground, and the chosen feed point.
The misleading shortcut
A high radiation resistance does not automatically mean high efficiency, and a low value can make conductor and ground losses dominate even with a perfect match.
Make the better decision
Separate radiation and loss in the model, reference the same feed-point current, estimate conductor/ground loss, and judge efficiency from their ratio rather than impedance alone.
Evidence boundary
Propagation and antenna metrics are meaningful only with their frequency, path, geometry, reference plane, loss assumptions, and measurement method. Use current observations and the exact installed system.
