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Antenna Beamwidth Estimate Calculator

Enter the antenna gain in dBi to estimate the half-power beamwidth.

How it is calculated

Enter the antenna gain in dBi (between 0 and 60; values outside that range give no result). Step 1 converts decibels to a plain ratio: G = 10^(gain ÷ 10). Step 2 estimates the half-power beamwidth: HPBW = √(41253 ÷ G) degrees. The number 41253 is roughly the count of square degrees on a full sphere, and the formula treats the main beam as equally wide in both planes, so it suits dishes and similar symmetric antennas, not a sector antenna that is wide in one plane and narrow in the other. It also assumes the gain is concentrated in that beam with no losses. Both the beamwidth and G are shown with two decimals.

Worked example

A dish antenna with 24 dBi gain. Linear gain: 10^(24 ÷ 10) = 10^2.4 = 251.19. Divide: 41253 ÷ 251.19 = 164.23. Square root: √164.23 = 12.82°. So the main beam is about 13 degrees wide between the half-power points. At 30 dBi, G is 1,000 and the beam narrows to 6.42 degrees, showing that every 3 dB more gain makes the beam about 1.4 times narrower. At 0 dBi the formula returns 203.11°, which is more than a half circle and not meaningful.

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Common mistakes

  • Entering gain in dBd or as a plain ratio: the field is dBi, and a dipole's 2.15 dBi is not the same as 0 dBd.
  • Applying the result to a sector or panel antenna with different horizontal and vertical beams: the formula gives one equal-in-both-planes angle.
  • Trusting the result at very low gains: near 0 dBi the angle comes out at 200 degrees or more, which cannot be a real beamwidth.
  • Confusing half-power beamwidth with the full angle of radiation: HPBW is the width between the −3 dB points, and energy still leaves outside it.
  • Treating the estimate as the datasheet value: real antennas have sidelobes, losses and unequal planes, so use it for planning and not for pointing tolerances.

About this calculator

An antenna's half-power beamwidth (HPBW) is the angular width of its main radiation lobe measured between the points where power drops to half (−3 dB) of the peak. There's a direct trade-off between gain and beamwidth: a highly directional, high-gain antenna necessarily has a narrow beam, and vice versa — approximated for a symmetric-beam antenna as HPBW ≈ √(41253 / G_linear), where G_linear is the gain converted out of decibels.

This quick estimate is widely used by RF and wireless engineers during initial antenna selection or link-budget planning — for example, sizing a satellite dish or point-to-point microwave link where the beamwidth determines how precisely the antenna must be aimed and how much coverage area it illuminates.

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Comments (1)

  • Editorial team

    Beamwidth turns directly into an aiming tolerance. A 12 dBi antenna returns 51.02°, 24 dBi gives 12.82° and 30 dBi gives 6.42°, so a high-gain dish has to be pointed with real care. The formula treats the beam as equal in both planes, so it suits dishes but not a sector panel that is wide in one plane and narrow in the other. What type of antenna are you estimating?

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