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Antenna beamwidth (HPBW)

Short answer

HPBW is angular width between half-power (-3 dB) points of main lobe where field is 0.707 of maximum. FNBW ≈ 2×HPBW. Narrow beamwidth gives high directivity: D ≈ 41253/(θE°×θH°). Examples: short dipole 90°, λ/2 dipole 78°.

Explain the beamwidth (half power beamwidth) of an antenna.

Beamwidth is the angular width of the main lobe of the radiation pattern. The Half Power Beamwidth (HPBW) is the angle between the two directions in the main lobe where the radiated power falls to half (−3 dB) of its maximum, i.e. where the field is 1/√2 = 0.707 of maximum.

        max
       .---.     -3 dB
  0.707/  |  \0.707
      /<-HPBW->\
     /    |     \
  null    |      null
     <---FNBW---->
  • FNBW (first null beamwidth): angle between the first nulls; FNBW ≈ 2 × HPBW.
  • Narrow beamwidth means high directivity: D ≈ 41253/(θE° × θH°).
  • Examples: short dipole 90°, λ/2 dipole 78°.

✓ Answer checked by Claude Opus 5.5 (high effort)

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