Truncation of infinite sheath spiral antennas

The effect of truncation of the infinite sheath spiral antenna is analyzed by superimposing two known solutions of the structure. The two solutions, one for excitation at the center (CE) and one for excitation with a ring source (RE) at the radius of the truncated antenna (rho-O), are superimposed to achieve a cancellation of the current distribution for radii greater than rho-O. It is shown numerically that by choosing the relative amplitudes of the two sources such that the surface wave part of the two solutions would cancel, the reminder of the current for radii greater than rho-O is about 20 dB below that for radii less than rho-O. Other features of the RE solution and the superimposed solution are explored. In particular the RE solution, which was not explored completely before, is analyzed in full, and certain ambiguities are removed.