An experimental design study of some S- and X-band helical aerial systems

The general characteristics of helical aerials are summarized and the results of polar-diagram measurements in the S- and X-bands are given for single and multiple helices. Reference is made to methods of widening both the beam width and the bandwidth obtained with a helical aerial by means such as end loading and tapering. The possibility of adapting helical aerials to give wide-band linearly polarized arrays is explored experimentally with a considerable measure of success. Tests show that acceptable characteristics may be obtained with helices of `unorthodox¿ form or with dimensions outside the limits suggested by Kraus. Encapsulation of helical aerials in foamed dielectric material in order to improve their rigidity is found to be a satisfactory and practical proposition provided that the materials are selected with some care, particularly in the X-band.