The End-tapered wire helix with parasitic element is a modification of the Axial-mode helical antenna with linear end-taper - a moderately wide-band, circularly polarized antenna, which is popular in UHF and microwave frequency applications due to its small cross section. The addition of a parasitic helix - as illustrated in the above image - increases the gain of the driven helix without an increase in axial length or diameter.Comparison between the End-tapered helix with and without the parasitic element. [Both antennas designed for 16 dBi gain at 1 GHz center frequency].
To illustrate the effect of the parasitic element, the dimensions and radiation performance of the two helices (both designed for 16 dBi gain at 1 GHz for a wire diameter of 2 mm) is shown in the previous image. The design which includes the parasitic element requires up to 20% less helical turns and is up to 20% shorter when compared to the standard single wire End-tapered helix. The radiation performance of both helices is very similar....Comparative radiation pattern cuts for an End-tapered helix with and without the parasitic element. [Both antennas designed for 16 dBi gain at 1 GHz center frequency]. Radiation pattern of an End-tapered helix with parasitic element, designed in Antenna Magus for 16 dBi gain at 1 GHz center frequency