eng
main beam
main lobe
major part of the radiated field where maximum radiated energy exists (region around the direction of maximum radiation)
Note 1 to entry: The main beam is also defined as 2.5 times 3 dB beamwidth for mathematical computation of antenna main beam efficiency.
Note 2 to entry: The width of main beam (which is commonly called "null to null beamwidth") is defined as the angular span between the first pattern nulls (the magnitude of the radiation pattern decreases to zero, negative infinity dB) adjacent to the main lobes.
[SOURCE: ISO/TS 19159-4:2022, 3.29]