Electromagnetic fields of a short electric dipole in free space - Revisited

Abstract

Maxwell's equations specify that electromagnetic radiation fields are generated by accelerating charges. However, the electromagnetic radiation fields of an accelerating charge are seldom used to derive the electromagnetic fields of radiating systems. In this paper, the equations pertinent to the electromagnetic fields generated by accelerating charges are utilized to evaluate the electromagnetic fields of a current path of length l for the case when a pulse of current propagates with constant velocity. According to these equations, radiation is generated only at the end points of the channel where charges are being accelerated or decelerated. The electromagnetic fields of a short dipole are extracted from these equations when r ≫ l, where r is the distance to the point of observation. The speed of propagation of the pulse enters into the electromagnetic fields only in the terms that are second order in l and they can be neglected in the dipole approximation. The results illustrate how the radiation fields emanating from the two ends of the dipole give rise to field terms varying as 1/r and 1/r2, while the time-variant stationary charges at the ends of the dipole contribute to field terms varying as 1/r2 and 1/r3.