Dish Antenna Gain Calculator (Parabolic Reflector, dBi)
Gain in dBi, beamwidth and effective aperture of a parabolic dish from its diameter, the frequency and the aperture efficiency.
Results
The dashed line marks the value you entered.
What this tool does
A dish's gain grows with the square of its diameter measured in wavelengths, G = η·(π·D ÷ λ)², so doubling the diameter, or doubling the frequency, adds 6 dB. The efficiency η covers feed spill-over, blockage and surface errors, and is commonly around 55–70 % for a well-built dish. The same physics narrows the beam: the half-power beamwidth is roughly 70·λ ÷ D degrees, which is why a large satellite dish must be aimed to within a fraction of a degree. The 70 is a rule of thumb that varies with the feed illumination.
Formula
G = η × (π D ÷ λ)² · G(dBi) = 10 log₁₀ G · beamwidth ≈ 70 λ ÷ D degrees
Variables
| Symbol | Meaning | Unit |
|---|---|---|
d | Diameter | m |
fg | Frequency | GHz |
ef | Efficiency | % |
GD | Gain | dBi |
GL | Gain as a plain ratio | — |
LM | Wavelength | cm |
BW | Beamwidth between half-power points (approximate) | ° |
AE | Effective aperture area | m² |
Worked example
- Diameter1.2 m
- Frequency12 GHz
- Efficiency60 %
- Gain41.4 dBi
- Gain as a plain ratio13,663
- Wavelength2.50 cm
- Beamwidth between half-power points (approximate)1.46 °
- Effective aperture area0.679 m²
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.