The transient radiation of thin circular loop antenna

In this paper, the points on the thin circular loop antenna is excited by the step current pulse synchronously, so that the loop antenna can be considered as a magnetic dipoles disk which is formed by vertical magnetic dipoles. By means of analytic integral, the analytic representations of the vector potentials associated with the thin circular loop antenna are obtained, and then, the relationship between the pulse width of the field and the location of the observer has been analyzed. The analysis indicate that the pulse width of the field is broadened with increasing the plunge angle of the observer, and, when the shadow of the observer is inside the disk, the pulse width of the field is also broadened with increasing the offset distance of the observer and tend to a finite value 2a sin/spl Theta//c . The analytic expression also indicate that the field pulse can be considered as radiated by the points which are on a diameter of the circular loop, meanwhile, the pulse width is equal to the difference of the wave arrival time from the two points which are the farthest and the nearest point from the observer on the diameter to the observer.