What is antenna gain?

• A. The size of the antenna aperture.
• B. The efficiency of the antenna material.
• C. Relative signal strength compared to an isotropic antenna.
• D. The directional bandwidth of the antenna.

Answer: (C)

Antenna gain is the measure of how well an antenna concentrates energy in a particular direction compared to an isotropic radiator that would spread energy equally in all directions. It combines directivity—the focusing of radiation in a preferred direction—with efficiency, which accounts for losses in the antenna. We usually express gain with a reference such as dBi, meaning decibels over an isotropic source. A higher gain in the target direction means more signal power arrives there for the same input power, while less power goes in other directions. The size of the aperture or the material efficiency alone doesn’t define gain; they influence it, but gain ultimately describes how effectively the antenna directs energy. Bandwidth, on the other hand, refers to the frequency range over which the antenna operates well, not how much energy is directed in a given direction.