HPBW

HPBW, or half-power beamwidth, is a measure used in antenna theory to describe the angular width of the main lobe of an antenna’s radiation pattern. It is defined as the angular separation between the directions in which the radiated power falls to half of its maximum value, i.e., the points where the power is −3 dB relative to the peak.

In practice, the HPBW is specified in the azimuth and elevation planes and reflects how directional an antenna is. It is determined from the far-field radiation pattern P(θ, φ) by finding the two symmetric angles around the main lobe peak where P equals Pmax/2 and calculating their difference.

Measurement and interpretation: HPBW is obtained from measurements or simulations of the antenna’s radiation pattern, typically in an anechoic chamber or an open-field range. The pattern is normalized to its maximum, and the HPBW is the width of the main lobe at the −3 dB level. It is influenced by frequency, aperture size, and illumination of the aperture, and it is usually defined for a specific plane (azimuth or elevation).

Relation to performance: A smaller HPBW indicates a more directive antenna and generally higher gain for a given aperture. The HPBW tends to shrink as the aperture size increases or as the wavelength decreases. A common rough guideline for circular apertures is HPBW ≈ 70 × (λ / D) degrees, where D is the aperture diameter and λ is the wavelength.

Limitations: HPBW describes only the main lobe width and does not capture sidelobe levels, nulls, or overall beam shape. Real patterns may have multiple lobes, so HPBW is only one aspect of an antenna’s performance.