Antenna Gain
Calculate antenna gain in dBi from aperture size, frequency and efficiency.
About Antenna Gain
Antenna gain measures how effectively an antenna concentrates energy in a direction compared to an isotropic radiator. For aperture antennas (dishes, horns), gain is proportional to the physical aperture area, the square of frequency, and the aperture efficiency factor.
Formula
Parabolic antenna gain
G = efficiency * 4*PI*A / wavelength^2
- eta
- Aperture efficiency (0-1)
- A
- Physical aperture area (m^2)
- lambda
- Wavelength (m)
Worked example
With the default values below, Antenna Gain returns Antenna Gain of 34.66. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Antenna Diameterminimum 0.01 m
- 1.2 m
- Frequencyminimum 0.01 GHz
- 5.8 GHz
- Aperture Efficiencyaccepts 1–100 %
- 55 %
Results
- Antenna Gain
- 34.66 dBi
- Gain (linear ratio)
- 2,925.77
- Wavelength
- 0.051688 m
- Physical Aperture
- 1.1310 m²
Step by step
- 1Wavelength= 0.051688 m
- 2Physical aperture area= 1.131 m^2
- 3Gain (linear)= 2925.77
- 4Gain (dBi)= 34.66 dBi
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or fees or charges into account.
- Figures are rounded for display to 6 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
What is dBi?
dBi is decibels relative to an isotropic antenna — a theoretical point source that radiates equally in all directions. A 30 dBi antenna concentrates energy 1000x more effectively in its main beam direction than an isotropic radiator would.
Why does gain increase with frequency for the same dish size?
Higher frequency means shorter wavelength, so the same physical aperture captures more wavelengths across its diameter, producing a narrower beam and higher gain. This is why large dishes are extremely high-gain at microwave frequencies.