If the aperture efficiency η increases for a fixed dish diameter and frequency, what happens to the antenna gain?

• A. Gain decreases.
• B. Gain increases.
• C. Gain remains the same.
• D. Gain becomes unpredictable.

Answer: (B)

Antenna gain increases when the effective aperture increases. The effective aperture A_e equals the physical aperture area A times the aperture efficiency η, so A_e = ηA. For a dish, A = πD^2/4, and the gain is G = (4π/λ^2)A_e = η(πD^2/λ^2). With the dish diameter D and the wavelength λ fixed, boosting η directly boosts G. In plain terms, higher efficiency means more of the collected power is radiated into the main beam (less is lost to spillover, diffraction, or phase errors), so the gain goes up.