Parabolic Dish Gain Calculator
Enter dish diameter, operating frequency, and efficiency to estimate antenna gain (linear and dBi), wavelength, effective aperture, and beamwidth.
What this parabolic antenna gain calculator does
A parabolic dish focuses incoming electromagnetic waves into the feed at its focal point. That concentration of energy is what creates antenna gain. This calculator estimates gain from the classic aperture formula, helping you quickly evaluate dish performance for microwave, satellite, or point-to-point radio links.
The output includes:
- Linear gain (ratio, unitless)
- Gain in dBi (decibels relative to isotropic radiator)
- Wavelength at the selected frequency
- Effective aperture (m²)
- Approximate 3 dB beamwidth (degrees)
Core formula used
Parabolic dish gain equation
The calculator uses:
G = η(πD/λ)²
- G = antenna gain (linear)
- η = aperture efficiency (decimal form, so 60% = 0.60)
- D = dish diameter (meters)
- λ = wavelength (meters), where λ = c / f
- c = speed of light (299,792,458 m/s)
- f = frequency (Hz)
Gain in decibels is then:
G(dBi) = 10 × log10(G)
How to use the calculator correctly
1) Enter dish diameter
Use the physical reflector diameter, then choose the correct unit (m, cm, in, or ft).
2) Enter operating frequency
Select the unit and enter the center frequency of your channel or band.
3) Set aperture efficiency
If you do not have manufacturer data, start with 60%. Precision dishes may be higher; poorly aligned systems may be lower.
4) Click calculate
Review dBi for link-budget work and beamwidth for aiming and interference planning.
Worked example
Suppose your dish is 0.9 m, frequency is 11.7 GHz, and efficiency is 65%. The calculator will show a gain in the high-30s dBi range (exact value depends on rounding), a narrow beamwidth, and an effective aperture consistent with a high-directivity antenna.
What affects real-world gain
- Surface accuracy: reflector shape errors reduce efficiency, especially at higher frequencies.
- Feed illumination: spillover and taper impact usable aperture.
- Pointing accuracy: tiny aiming errors can cause large signal drops on narrow beams.
- Blockage: feed supports and geometry can reduce effective area.
- Losses: radome, cable, connectors, and moisture can degrade performance.
Typical gain ranges by dish size (example at ~12 GHz, 60% efficiency)
| Dish Diameter | Approx. Gain (dBi) | Approx. 3 dB Beamwidth |
|---|---|---|
| 0.45 m | ~33 dBi | ~3.9° |
| 0.60 m | ~35.6 dBi | ~2.9° |
| 0.90 m | ~39.1 dBi | ~2.0° |
| 1.20 m | ~41.6 dBi | ~1.5° |
dBi vs dBd: quick clarification
This tool reports dBi, referenced to an isotropic radiator. Some systems use dBd (relative to half-wave dipole). Conversion:
- dBi = dBd + 2.15
- dBd = dBi − 2.15
Practical deployment tips
- Use manufacturer gain data for final design validation.
- Include polarization mismatch and atmospheric losses in your link budget.
- For high-frequency bands, prioritize rigid mounting and precise alignment tools.
- If you are near rain-fade thresholds, add margin rather than relying on idealized gain numbers.
Final note
This parabolic antenna gain calculator is ideal for planning and quick checks. For mission-critical links, always combine these estimates with measured field data, vendor specifications, and full link-budget analysis.