Antenna Beamwidth

Formula

Description

The half-power (-3 dB) beamwidth of a circular aperture antenna is approximately 70 times the wavelength divided by the aperture diameter, measured in degrees. This relationship applies to dish antennas, horn antennas, and phased arrays. Larger apertures and shorter wavelengths produce narrower beams with higher gain. The constant 70 is an approximation that varies between 58-75 depending on the illumination taper of the aperture. Narrower beamwidth means higher gain but requires more precise pointing.

Variables

• θ — Half-power beamwidth (degrees)
• λ — Wavelength (m)
• D — Antenna aperture diameter (m)

Practical Notes

A 1-meter dish at 10 GHz (λ=0.03m) has a beamwidth of about 2.1°, requiring precise pointing for satellite or microwave links. Antenna gain is inversely proportional to beam solid angle: G ≈ 27000/(θ_az × θ_el) for a pencil beam. Amateur radio EME (moonbounce) stations typically use dishes or large Yagi arrays with beamwidths of 5-15° at UHF/microwave frequencies.