The transient radiation of thin circular-loop antenna

In this letter, we postulate that the points on the thin circular-loop antenna are excited by the step current pulse synchronously. So, the loop antenna can be considered as a magnetic dipole disk which is formed by vertical magnetic dipoles. By means of analytic integrals, 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 indicates that the field pulse can be considered as that radiated by the diameter of the circular loop, meanwhile, the pulse width is equal to the difference of the wave arrival time from the two terminal endpoints of the diameter to the observer. From our analysis, we find that if the observer's shadow on the loop plane is inside the loop and its offset distance is less than a cos 2/spl theta//sin /spl theta/, the pulse width will be narrowed by increasing the offset distance of the observer; otherwise, it will be broadened by increasing the offset distance and/or the plunge angle of the observer.