Characteristics of 5- to 35- turn uniform helical antennas

The measured VSWR, gain, pattern and axial ratio characteristics of a uniformly wound helical antenna are presented. Experimental parametric studies were made of (1) fixed length helices with variable diameter and pitch angle (8.6 to 10 turns), and (2) variable length helices with constant diameter and pitch angle (5 to 35 turns). Simplified design relations are given for the antenna gain and half-power beamwidth (HPBW) as a function of axial length L/lambda and circumference C/lambda for helices consisting of approximately 10 turns. Parametric curves are presented to show the gain and HPBW of a constant pitch helix as a function of L/lambda and C/lambda. An empirical expression is derived for the antenna gain as a function of frequency and the helix design parameters. In addition, the bandwidth characteristics are analyzed.