What is radiation resistance and how does it relate to total input resistance of an antenna?

• A. Radiation resistance is the portion of input resistance due to radiation; total equals radiation resistance plus ohmic/loss resistance
• B. Radiation resistance is the loss resistance only; total equals radiation resistance
• C. Radiation resistance is the same as ohmic resistance
• D. Radiation resistance only exists at DC

Answer: (A)

The key idea is that an antenna’s input behavior can be split into two resistive parts plus a reactive part. The radiation resistance is the portion of the input that represents power actually radiated away as electromagnetic waves. The ohmic (loss) resistance accounts for power lost as heat in the conductor and surrounding materials. When the antenna is operated so that the reactive part is minimized (typically at resonance), the total input resistance you see is simply the sum of these real components: R_in = R_rad + R_loss. This is why the statement that radiation resistance is the portion of input resistance due to radiation, and that the total input resistance equals radiation resistance plus loss resistance, is the correct description.

In a lossless antenna, R_loss would be zero and the input resistance would equal the radiation resistance. Radiation resistance is an RF concept tied to how much power is radiated, not a DC property, and it isn’t the same as the ohmic loss resistance.