gain of parabolic antenna calculator

What this gain calculator does

A parabolic reflector focuses incoming or outgoing electromagnetic energy into a narrow beam. The tighter that beam, the higher the directivity and gain. This calculator gives a practical estimate of parabolic antenna gain based on three key inputs:

• Dish diameter
• Frequency (or wavelength, derived automatically)
• Efficiency of the dish/feed system

It is useful for satellite links, point-to-point microwave systems, radio astronomy setups, and general RF link budget work.

Core formula used

The calculator uses the standard gain relationship for a circular parabolic dish:

G(linear) = η × (πD / λ)2

Where:

• η = antenna efficiency (0 to 1)
• D = dish diameter in meters
• λ = wavelength in meters

It then converts linear gain to dBi:

G(dBi) = 10 × log10(G(linear))

Wavelength comes from frequency:

λ = c / f, where c = 299,792,458 m/s.

How to use the calculator

1) Enter dish diameter

Add your reflector size and choose the unit. For example, 90 cm, 1.2 m, or 3 ft.

2) Enter operating frequency

Choose the correct unit (GHz/MHz/kHz/Hz). Ku-band, C-band, and X-band values are commonly entered in GHz.

3) Enter efficiency

Use a realistic estimate for total aperture efficiency. If you are unsure, start around 60%.

4) Click calculate

You’ll receive:

• Gain in dBi
• Linear gain ratio
• Wavelength
• Approximate 3 dB beamwidth
• Effective aperture area
• dBd equivalent

Example

If you enter a 0.9 m dish at 10.7 GHz with 60% efficiency, the expected gain is around the high-30s dBi range. That’s why small satellite dishes can still deliver high directional performance at microwave frequencies.

Why efficiency matters so much

Two dishes with identical diameter and frequency can have different gain due to aperture efficiency. Real performance is affected by:

• Surface accuracy and panel alignment
• Feed illumination taper
• Spillover and blockage
• Polarization mismatch
• Manufacturing tolerances
• Installation and pointing errors

Interpreting dBi and dBd

dBi is gain referenced to an isotropic radiator. dBd is referenced to a half-wave dipole. The conversion is:

dBd = dBi - 2.15

Most satellite and microwave equipment specs are listed in dBi, so this calculator reports dBi first.

Practical design tips

Frequency increase boosts gain

For fixed dish size, higher frequency means shorter wavelength, which increases gain.

Larger diameter boosts gain

Gain scales with D². Doubling diameter increases gain by about 6 dB (if efficiency and frequency stay constant).

Narrower beam requires better pointing

As gain rises, beamwidth shrinks. Installation precision becomes more critical for stable links.

Where this calculator fits in a full link budget

Dish gain is one piece of the RF chain. For complete planning you should also include:

• Transmit power and EIRP
• Cable and connector losses
• Free-space path loss
• Atmospheric/rain fade margins
• Receiver noise figure and G/T

Quick FAQ

What is a good default efficiency?

60% is a practical starting point for many systems.

Can I use this for receive and transmit?

Yes. Antenna gain is reciprocal, so the same gain applies in both directions at the same frequency.

Is this exact?

It is an engineering estimate using standard equations. Real measurements vary based on hardware and environment.