Technical momorandum. Directivities of helical antennas radiating in the axial mode

Based on a theoretical model, assuming the current along the helix to be a single outward travelling wave of constant amplitude, the directivities of helical antennas radiating in the axial mode are computed and compared with the gain measurements of King and Wong and the values predicted by the well known formula suggested by Kraus. Our calculated values are closer to the former than the latter.