Quadrifilar Helical Antennas with Parasitic Loops

Yasuhiro KAZAMA  Shinobu TOKUMARU  

IEICE TRANSACTIONS on Communications   Vol.E81-B   No.11   pp.2212-2218
Publication Date: 1998/11/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Antennas and Propagation
backfire quadrifilar helical antenna,  current distribution,  parasitic loop,  wire-grid model,  satellite communication,  

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Backfire quadrifilar helical antennas combined with parasitic loops are investigated in detail, focusing on clarifying the function of parasitic loops. First, the basic property is examined for the case of one parasitic loop, and it is found that the loop behaves as a director when the circumferential length of the loop is nearly 0. 9λ, and a reflector when the circumferential length of the loop is nearly 1. 2λ provided the distance between the parasitic loop and the top plane of helical antennas is approximately 0. 1λ, where λ is the wavelength. Next, the function of the parasitic loop is investigated by comparing the current distributions on the helices and the loop with those on a monofilar helix with a ground plane. It is found that the function of the parasitic loop is quite different from that of the ground plane. Then, the case of two parasitic loops is examined, and it is shown that the use of two parasitic loops is very effective and simple measures to control the radiation pattern and gain of the backfire quadrifilar helical antennas. Finally, for this type of antennas with two parasitic loops, an example of structural parameters suited to the use in satellite communications is presented.