An optimised balanced twin arm oblated spherical helical antenna with a high permittivity core

Abstract

This paper considers a twin arm wire spherical helical antenna with a balanced feed. Each arm of the antenna forms a hemispherical helical antenna. The frequency of operation is 2.45 GHz. Under a genetic algorithm the antenna was optimised for axial ratio, gain and half-power beam width using core permittivity, radius, wire thickness and length. In the limit the antenna becomes two flattened spiral arms with a balanced feed. The GA design included the possibility of core material of higher permittivity than free space that could be placed either inside the windings, inside and extended beyond the windings or only outside the windings as a shell. The GA selected structures exhibit broad beam patterns with good gain and useful axial ratio when simulated using the time-domain Transmission-Line Matrix (TLM) method (CST Microwave Studio). Results are presented and compared for optimised versions of the ellipsoidal helical and dual planar spiral antenna with balanced feeds for use on the 2.45 GHz ISM band.