The spherical helical antenna

Abstract

The spherical helical antenna is investigated as a new variation of the conventional helical antenna. The spherical helix is a wire antenna in a helix shape that is wound over a spherical surface instead of the standard cylindrical one. Analysis of this structure requires numerical methods and experimental measurements because its complex geometry makes it very difficult to develop analytic expressions for its radiation characteristics.

The wire antenna code ESP, based on the method of moments, is used to calculate both the gain and phase of the electric-field components, E(} and E¢J' in the far field for spherical helices having between 3 and 10 turns. Several of these antennas were also constructed and tested on the Virginia Tech antenna test range. The numerical analysis and experimental measurements were performed over a wide range of frequencies corresponding to spherical circumferences of between 0.7 and 2.8 wavelengths.

A literature survey of the conventional helical antenna is presented so that comparisons can be made with the spherical helix. The numerical and experimental results of the spherical helical antenna indicate that its behavior is markedly different than the cylindrical helix. It is a broad beam elliptically polarized radiator, in general, and operates over a relatively wide bandwidth. Under certain conditions, it is circularly polarized over a major portion of the main beam for a narrow bandwidth, a result which has potential applications. The behavior of the spherical helical antenna is not significantly affected by the number of turns and is discussed in this work for a few representative cases.