What is the term for the ratio of the radiation resistance of an antenna to the total resistance of the system?

Antenna efficiency is a measure of how effectively an antenna converts the radio-frequency power fed into it into radiated electromagnetic waves. Mathematically, it is defined as the ratio of the antenna's radiation resistance to its total resistance. Radiation resistance represents the useful power radiated into space, while total resistance includes both this radiated power and any power lost as heat (ohmic resistance). The higher the proportion of radiation resistance to total resistance, the more efficient the antenna is. Other options like Effective Radiated Power (ERP) refer to the total power emitted taking antenna gain into account, not the internal electrical efficiency. Beamwidth describes the physical shape of the radiation pattern, which is unrelated to the resistance ratio.