Which factor directly affects antenna gain?

• A. Efficiency
• B. Color
• C. Volume
• D. Temperature

Answer: (A)

A gain value reflects how much power is radiated in a particular direction compared to an isotropic source, and it comes from combining how the radiation is shaped (directivity) with how efficiently the antenna converts input power into radiated power (efficiency). The usual relation is G = ηD, so efficiency directly scales the realized gain. If there are losses in the conductors or dielectrics, less input power is radiated, lowering the gain even if the radiation pattern (directivity) is unchanged. Color has no electrical impact on radiation; volume (size) influences directivity but isn’t the direct factor in determining gain, and temperature can affect losses only indirectly through material properties, not as the primary factor in the gain definition.