Antenna Gain
Calculate antenna gain in dBi from aperture size, frequency and efficiency.
Inputs
Typical parabolic dish: 50-70%
Antenna Gain
34.66dBi
Gain (linear ratio)
2,925.77
Wavelength
0.051688m
Physical Aperture
1.1310m²
Step by step
Wavelength
c / f = 299792458 / 5800000000
= 0.051688 m
Physical aperture area
PI * (1.2/2)^2
= 1.131 m^2
Gain (linear)
0.55 * 4*PI * 1.131 / 0.051688^2
= 2925.77
Gain (dBi)
10 * log10(2925.77)
= 34.66 dBi
How it works
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)
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.