ELECTROMAGNETIC FIELDS OF A SHORT ELECTRIC DIPOLE IN FREE SPACE – REVISITED

Maxwell's equations specify that electromagnetic radia- tion flelds are generated by accelerating charges. However, the electro- magnetic radiation flelds of an accelerating charge are seldom used to derive the electromagnetic flelds of radiating systems. In this paper, the equations pertinent to the electromagnetic flelds generated by ac- celerating charges are utilized to evaluate the electromagnetic flelds of a current path of length l for the case when a pulse of current propa- gates 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 flelds 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 flelds 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 flelds emanating from the two ends of the dipole give rise to fleld terms varying as 1=r and 1=r 2 , while the time-variant stationary charges at the ends of the dipole contribute to fleld terms varying as 1=r 2 and 1=r 3 .