Antenna Beamwidth Calculator

Half-power and first-null beamwidth from dish size, or estimate beamwidth from gain.

What it does

Beamwidth is how wide the main beam is. HPBW is measured between the half-power (−3 dB) points. The calculator also shows the beam’s footprint at a distance.

Where it's used

Pointing dishes, planning link coverage and checking interference with nearby antennas.

How to use it

Choose to work from dish size or from gain.
Enter diameter and frequency, or gain in dBi.
Enter a distance to see the spot size.

The formula explained

HPBW: ≈ 70 λ / D degrees — half-power beamwidth
FNBW: ≈ 140 λ / D degrees — first-null beamwidth
G ≈ 41253 / (θE·θH): Kraus approximation linking gain and beamwidth

Worked example

A 2.4 m dish at 6 GHz, 10 km away.

Inputs:

Calculate from: Dish diameter & frequency
Dish diameter: 2.4 m
Frequency: 6G Hz
Distance (footprint): 10000 m

The calculator gives:

Half-power beamwidth (−3 dB): 1.457 °
First-null beamwidth: 2.915 °
Wavelength: 49.97 mm

Tips and common mistakes

70λ/D assumes typical dish illumination; real patterns vary a little.
A narrow beam needs a rigid mount — wind can knock it off target.
Side lobes outside the main beam can still cause interference.

Questions people ask

What formula gives the beamwidth of a dish?

HPBW ≈ 70 × λ / D degrees. At 6 GHz the wavelength is about 50 mm, so a 2.4 m dish has a beamwidth of about 1.46°.

How wide is the beam at a distance?

About 2 × distance × tan(beamwidth / 2). The 1.46° beam is roughly 254 m wide 10 km away — useful for checking whether a link clears nearby buildings or other antennas.

How are gain and beamwidth related?

They trade against each other: the narrower the beam, the higher the gain. Halving the beamwidth in both directions concentrates the power into a quarter of the area, adding about 6 dB.

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