If the ohmic resistance of a half-wave dipole is 2 ohms, and the radiation resistance is 72 ohms, what is the antenna efficiency?

Antenna efficiency is calculated by dividing the radiation resistance by the total antenna resistance, then multiplying by 100 to get a percentage. The total resistance is the sum of the radiation resistance and the ohmic (loss) resistance. In this problem, the total resistance is 72 ohms (radiation) + 2 ohms (ohmic) = 74 ohms. The efficiency is therefore 72 divided by 74, which equals 0.9729, or 97.3%. Distractors like 72% or 74% are trap answers derived from incorrectly using just the raw numbers given in the prompt instead of applying the proper ratio formula.