The power gain of an antenna is the ratio of its radiated power to the power radiated by which radiator?

• A. Reference dipole
• B. Isotropic radiator
• C. Dipole
• D. Monopole

Answer: (A)

Power gain measures how much the antenna concentrates radiated power in a given direction compared with a standard radiator. In this context, the standard radiator used for the baseline is a reference dipole. So the antenna’s radiated power in that direction is divided by the power that a reference dipole would radiate with the same input power. This gives a gain value (often expressed as dBd when using a dipole as the reference). Using a reference dipole provides a consistent benchmark for directional performance.

If you were instead comparing to an isotropic radiator, you’d get the gain in dBi, which is a different reference and would yield different numeric values. The other radiators—such as a basic dipole or a monopole—aren’t the standard baseline here, even though they are real radiators with known patterns.