Antenna Aperture Efficiency Calculator
Effective aperture and aperture efficiency from measured gain and physical size.
What it does
Compares an antenna’s measured gain with its physical size to give the effective aperture and the aperture efficiency.
Where it's used
Checking antenna measurements and comparing dish designs.
How to use it
- Enter the measured gain in dBi and the frequency.
- Give the physical size as a diameter or an area.
- Read the effective aperture and efficiency.
The formula explained
- Ae
- G·λ² / 4π — effective aperture
- η
- Ae / A_physical — aperture efficiency
Worked example
A 1.2 m dish measured at 41 dBi at 11 GHz.
Inputs:
- Measured gain: 41 dBi
- Frequency: 11G Hz
- Physical size given as: Diameter (circular)
- Diameter: 1.2 m
The calculator gives:
- Aperture efficiency: 65.8 %
- Effective aperture Ae: 0.74413 m²
- Physical aperture: 1.13097 m²
Tips and common mistakes
- 55–70 % is typical for a dish.
- Above about 80 % usually means a measurement error.
- Losses come from illumination taper, spill-over, blockage and surface errors.
Questions people ask
How is the effective aperture worked out?
Ae = G × λ² / (4π), with G as a plain ratio. 41 dBi is a ratio of about 12 600; at 11 GHz λ is 27.3 mm, giving Ae ≈ 0.744 m² — 65.8 % of the dish’s 1.131 m².
How do I measure an antenna’s gain?
Usually by comparison: swap it with a reference antenna of known gain and compare the received levels. Alternatively, use two identical antennas and the Friis equation, which gives each one’s gain from the measured path loss.
What efficiency do horn antennas reach?
A pyramidal horn designed for maximum gain reaches about 50 %. Use the rectangular-aperture option with the mouth’s width and height for horns.
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- Antenna Gain Calculator
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- Attenuation & dB Calculator
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Enter your values to get the result with the formula, substituted values and an explanation of each step.