In telecommunication, the term beamwidth has the following meanings:
1. In a radio antenna pattern, the half power beam width is the angle between the half-power (-3 dB) points of the main lobe, when referenced to the peak effective radiated power of the main lobe. See beam diameter. Beamwidth is usually but not always expressed in degrees and for the horizontal plane.
2. For the optical regime, see beam divergence.