Enter Beamwidths
Approximation
D ≈ 41,253 / (HPBWaz × HPBWel)
This common beamwidth estimate assumes a reasonably clean main lobe and beamwidths measured in degrees.
Worked Example
With 65° horizontal and 30° vertical beamwidths, estimated directivity is 21.16 linear, or about 13.26 dBi.
Important Approximation Warning
Directivity is properly calculated by integrating the complete three-dimensional radiation pattern. Two beamwidth numbers cannot capture sidelobes, backlobes, nulls, asymmetry, or pattern distortion.
Use this result for early estimates only. Use measured or simulated pattern data for design, compliance, coverage, or link-budget decisions.