Power gain of helical antenna

A means of increasing the power gain of an axial mode helical antenna (of unchanging axial length) is explored. A comparison is made between monofilar and bifilar helical antennas, and results indicate that a bifilar antenna excited with anti-phase relation has a higher gain than that of a conventional monofilar antenna. However, the bifilar helix requires a complicated feeding system with a hybrid circuit. To eliminate this complexity and maintain an increased gain, a helical antenna with a parasitic helix is proposed. Through an evaluation of radiation patterns, it is deduced that the parasitic helix should be wound only on the cylinder where the surface wave of the driven helix is established. Of particular concern is the initial winding location; it is found that a helical antenna with a parasitic helix wound from a point diametrically opposite to that of 1.5 driven-helix turns has a gain increase of 1.0dB over a frequency range of 1:1.5.