beamwidths

Beamwidth is the angular extent of an antenna's radiation pattern, indicating how widely the energy is distributed in space. It is most commonly defined as the half-power beamwidth (HPBW), the angle over which the radiated power falls to half of its maximum. Another common definition is the first-null beamwidth (FNBW), which is the angle between the first nulls of the main lobe. In many cases, beamwidths are specified separately for azimuth (horizontal) and elevation (vertical) planes, reflecting the three-dimensional nature of real patterns.

The beamwidth of an antenna depends on the size and shape of its radiating aperture relative to the wavelength. Larger apertures or higher frequencies (smaller wavelengths) produce narrower beamwidths and higher directivity. For a circular aperture, approximate relationships tie HPBW to the ratio of wavelength to aperture diameter, such that increasing the aperture or operating at a higher frequency reduces the beamwidth.

Beamwidth has direct implications for gain, coverage, and spatial reuse. Narrow beams concentrate energy, increasing gain and reducing interference, but they cover smaller areas and can be more sensitive to pointing errors and misalignment. Antenna arrays can tailor beamwidth by adjusting element amplitudes and phases, and electronically scanned arrays can dynamically change beamwidth while steering the beam, within limits set by spacing and wavelength to avoid grating lobes.

Measurement of beamwidths is typically performed in an anechoic chamber or open-range test range by recording the radiation pattern and identifying the -3 dB points or the first nulls. Beamwidths are fundamental in the design of communication links, radar, and satellite reception systems.