What is aperture efficiency?

Aperture efficiency (η) is the ratio of the effective aperture to the physical aperture. It accounts for losses like non-uniform illumination, spillover, phase error, and surface roughness. Parabolic dishes typically achieve 55–75%, while well-designed horn antennas can reach 80–90%.

What is the difference between dBi and dBd?

dBi is gain relative to a theoretical isotropic antenna that radiates equally in all directions. dBd is gain relative to a half-wave dipole, which itself has 2.15 dBi of gain. Therefore dBd = dBi − 2.15. Datasheets may use either unit; this tool shows both.

Does frequency affect gain for the same dish?

Yes. Because gain is proportional to area divided by λ², a larger frequency (smaller λ) yields higher gain for the same physical aperture. Doubling the frequency quadruples the gain (all else equal).

What is the HPBW estimate based on?

The half-power beamwidth (HPBW) is estimated using the approximation HPBW ≈ 70° × λ / √A for a circular aperture. This is a rule-of-thumb; the exact value depends on aperture shape and illumination taper.

Can I use this for Yagi or patch antennas?

This formula applies to aperture-type antennas (dishes, horns, flat panels). Yagi and patch antennas are better characterized by element count or radiation patterns — their gain is not directly derived from a physical aperture area in the same way.

Antenna Gain Calculator

Name: Antenna Gain Calculator
Availability: InStock
Author: Nham Vu

Calculate antenna gain in dBi and dBd from physical aperture area, aperture efficiency, and operating frequency.

Antenna Parameters

Physical Aperture Area

For a circular dish: A = π × (diameter/2)²

Aperture Efficiency (η)

Typical: parabolic dish 55–75%, horn antenna 70–90%

Operating Frequency

Quick Presets

Antenna Gain Results

Enter aperture area and frequency to see results.

Summary

Calculate antenna gain in dBi and dBd from physical aperture area, aperture efficiency, and operating frequency.

How it works

Enter the physical aperture area of the antenna in square meters.
Enter the aperture efficiency (0–100%). Typical values: parabolic dish 55–75%, horn 50–90%.
Enter the operating frequency in MHz or GHz.
The tool computes wavelength λ = c / f, then gain G = η × 4π × A / λ².
Gain is converted to dBi = 10 × log₁₀(G) and dBd = dBi − 2.15.
The effective aperture and half-power beamwidth (HPBW estimate) are also shown.

Use cases

Sizing parabolic dish antennas for satellite or microwave links.
Verifying datasheet gain figures for horn or aperture antennas.
Budgeting link margins in point-to-point RF design.
Teaching RF and electromagnetics in university labs.
Comparing different aperture sizes at the same frequency.
Estimating beamwidth to plan sectorization in cellular networks.
Validating simulation results from HFSS or CST against analytical formulas.
Quick sanity checks during telecom equipment procurement.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu