By superimposing radiation spherical wave modes of the scalar‐wave equation, a beam is formed. The farfield of the chosen beam is the truncated delta‐function spectrum expanded on the basis of Legendre functions. By introducing an error criterion, the passage from the farfield to the nearfield is investigated. It is found that the nearfield along the direction of the main beam begins approximately at a radial distancernf, given byrnf= 2G/k(G=GAIN,k= 2π/λ, λ is the wavelength) and for other directions, on the average, byr̄nf= 2√G/k. For both radial distancesrnf, andr̄nf, the corresponding errors are bounded between 8% and 15%.