Phase center of helical beam antennas

When a helical beam antenna is used as a primary source of circularly polarized waves to illuminate a reflector, it is necessary to know the location of its phase center. The first part of this paper formulates an analytical method of determining the phase-center location of helical beam antennas based upon the expressions of the far-zone diffraction fields. Computations have been carried out for typical cases for both and components in the principal planes. The second part presents the experimental results. Dependence of the location of the phase center on the number of turns, the pitch angle and the size of the ground plane is discussed.