A quadrifilar helical antenna with a parasitic loop

In communication systems using satellites circularly polarized, compact antennas with wide-angle radiation patterns are strongly desired. As antennas for those purposes, conical spiral antennas and backfire quadrifilar helical antennas (BQHA antennas) have been proposed. However, these antennas have some disadvantages. That is, conical spiral antennas have complicated structure and a relatively large size, while BQHA antennas involve many parameters which affect antenna characteristics. In these antennas, therefore, once the parameter values are determined, it is not so easy to readjust those values, e.g., to get better radiation patterns. In the present paper, the authors propose BQHA antennas combined with a parasitic loop which enables one to control radiation patterns of BQHA antennas easily. The idea is based on Kazama (1993) and Kazama et al. (1993). It is clarified that the parasitic loop effectively contributes to control the gain as well as the radiation patterns of BQHA antennas. To analyze the characteristics of the BQHA antennas with a parasitic loop, the method of moments is used.<>