On Radiation from Overhead Transmission Lines

The general problem of radiation from lines is discussed and the theoretical background is sketched. The radiation is calculated by the usual approximate method, i.e. the current distribution of the principal wave in an infinite line is first determined, and the radiation field of a finite line is then calculated on the assumption that the current distribution is the same. The method is applied to lines in free space, to single-wire lines above earth of finite conductivity (earth-return lines), and to multiple lines above earth of finite conductivity. The current distribution and possible wave types in some typical multiple-lines are analysed. It is shown that only the wave in the earth-return line, and the corresponding wave type in the multiple line, will produce appreciable radiation. Formulae for calculation of this radiation field are given, and experimental results are described. Conclusions are drawn regarding interference in carrier-line systems and the use of long-wire transmitting antennae.