Conical radiation pattern characteristics of a quadrifilar helical antenna

In mobile satellite communication system, circularly polarized omnidirectional antennas are preferable for vehicle antennas because a satellite tracking system in azimuth direction is not necessary. As one type of these antennas, a quadrifilar helical antenna (QHA) has been proposed. A QHA can radiate a circularly polarized conical beam. It is desired that the elevation angle of the beam direction can become variable corresponding to the attitude of the vehicles. The conical radiation pattern characteristics of a QHA are analyzed numerically and the parameters used to change the beam direction are investigated.