Beamwidth is the angle across which an antenna sends and receives at least half its peak power. Beamwidth is quoted in degrees and measured between the two points either side of the main beam where power has fallen by 3 dB, which is why it is also called half-power beamwidth or 3 dB beamwidth.

Antenna datasheets give beamwidth in two planes. Horizontal beamwidth, also called azimuth beamwidth, is the width of the beam seen from above. Vertical beamwidth, also called elevation beamwidth, is the height of the beam seen from the side. An omnidirectional antenna has a horizontal beamwidth of 360 degrees, so only its vertical beamwidth differs between models.

Beamwidth and antenna gain trade against each other. Putting the same energy into a narrower beam raises the gain, and widening the beam lowers it. A high-gain directional antenna therefore has a narrow beam that needs careful aiming, while a lower-gain panel with a wide beam is more forgiving and can reach masts spread across a wider angle.

Beamwidth decides how precisely an antenna must be installed. A narrow beam aimed accurately at one mast picks up less interference from other masts, which helps SINR, but it loses signal quickly if it is aimed a few degrees off or moves in the wind, so the mounting must be rigid. On many antenna designs the beam also narrows as frequency rises, so a wideband antenna can have a tighter beam on 5G mid-band frequencies than on 700 MHz.