Theory of the frequency responses of uniform and quasi-taper helical antennas

The frequency responses of uniform and quasi-taper helical antennas radiating in the axial mode are characterized by expressions for the far zone electric field. These are obtained by summing the current element contributions from one end of the helix to the other, on the basis of a model which assumes a single traveling wave of current. It is found that the Hansen-Woodyard condition results in a monotonic increase of the electric field with frequency over the entire axial mode range, in violation of the experimental results of King and Wong (1979). The Sensiper (1951) phase velocity yields frequency response curves, however, which are consistent with the King and Wong results. Numerical results are given for uniform helices and quasi-taper helices consisting of two uniform sections of different diameters.