On radiating-zone boundaries of short, λ/2, and λ dipoles

This article presents a critical analysis of the classical definitions of the radiation regions for the particular case of short, λ/2, or λ dipole antennas, regions which we have revisited. We worked out a definition of radiation zones from consistent criteria directly linked with radiation characteristics: radiated field, wavefront, wave impedance, and radiated power. The "far-field zone" boundary is then defined as the distance beyond which the radiated wave is spherical and the radial component of the fields is negligible compared to the transverse component. Next, we consider the "near-field-reactive or very-near-field zone" to be the region wherein the wave impedance is different from Z₀ =120π, and wherein the reactive power is not negligible when compared to the active power. In this paper, the short dipole case is first studied. Dipoles of length up to λ are also treated, considering diameters from 0 up to λ/20. The results obtained lead us to accurately set the boundaries of the radiation zones of dipoles without the need for the restrictive hypotheses of the classical definitions.