Antenna Gain Calculator
Calculate antenna gain (dBi, dBd), directivity, efficiency, and effective aperture.
dBi from D & η
dBd ↔ dBi
Effective Aperture
Directivity (beamwidths)
Gain (dBi) = 10·log₁₀(D × η)
Antenna Presets (typical gain values)
Gain (dBi)
9.03 dBi
D = 10, η = 0.8
Formula
G = 10·log₁₀(D·η)
Linear Gain
8.0
dBd equivalent
6.88 dBd
Key Antenna Formulas
GdBi = 10·log₁₀(D · η)
GdBd = GdBi – 2.15
Aeff = (λ²/4π) · Glin
D ≈ 41253 / (θ₁·θ₂) (θ in degrees)
D – directivity (linear ratio)
η – efficiency (0…1)
λ – wavelength (m)
θ₁,θ₂ – half-power beamwidths (deg)
η – efficiency (0…1)
λ – wavelength (m)
θ₁,θ₂ – half-power beamwidths (deg)
People Also Ask
📡 What is antenna gain and how is it measured?
📊 Difference between dBi and dBd?
📏 How to estimate directivity from beamwidth?
🔧 What is effective aperture and why is it important?
📈 Typical gain values for common antennas?
⚡ How does efficiency affect gain?
Understanding Antenna Gain
Antenna gain is a measure of how much power is radiated in the direction of peak radiation compared to an isotropic radiator (dBi) or a half-wave dipole (dBd). It combines directivity (focusing ability) and efficiency (losses).
Directivity (D)
The ratio of radiation intensity in a given direction to the average intensity. It depends solely on the antenna pattern.
Efficiency (η)
The ratio of radiated power to input power (includes resistive losses, mismatch, etc.). Typical efficiencies: 50-90% for wire antennas, 40-70% for patches, 50-80% for horns.
Typical Antenna Gains
| Antenna Type | Gain (dBi) | Gain (dBd) |
|---|---|---|
| Isotropic radiator | 0 | -2.15 |
| Half-wave dipole | 2.15 | 0 |
| Quarter-wave monopole (over ground) | ~5 | ~2.85 |
| Patch antenna | 6-9 | 3.85-6.85 |
| Yagi (3-element) | 7-9 | 4.85-6.85 |
| Yagi (6-element) | 12-14 | 9.85-11.85 |
| Parabolic dish (60cm @ 2.4 GHz) | ~24 | ~21.85 |
| Horn antenna | 10-25 | 7.85-22.85 |
Detailed FAQs
What is the relationship between gain and beamwidth?
Generally, higher gain means narrower beamwidth. For a typical antenna, gain (in dBi) ≈ 10·log₁₀(41253/(θ₁·θ₂)), where θ₁ and θ₂ are the half-power beamwidths in degrees. This is an approximation for antennas with a single main lobe.
How do I convert dBi to dBd and vice versa?
dBd = dBi – 2.15. Example: a dipole has 2.15 dBi = 0 dBd. A Yagi with 12 dBi = 9.85 dBd. The 2.15 dB difference comes from the dipole's gain over isotropic.