Explanation & Formulas

Parabolic Antenna Gain (dBi):

where:

• η = aperture efficiency
• D = dish diameter (meters)
• λ = wavelength

This is the theoretical maximum gain for a given physical aperture and efficiency. Real-world gain can be lower due to surface roughness, feed spillover, blockage, etc.

Typical Efficiencies

• 35% – Poor feed / electrically small dishes
• 50% – Average amateur tropo setup
• 60% – Reasonably well-illuminated dish (common reference)
• 70–75% – High-performance optimized systems (EME, radio astronomy)

Note: Gain increases with frequency (smaller λ) and with diameter. Efficiency has a strong impact — going from 50% to 70% gives almost +1.5 dB extra gain.