A linear array antenna using bifilar helical elements for mobile satellite communications

In mobile satellite communication systems such as the AMSC/TMI system [Lunsford et al., 1992], circularly polarized omni-directional antennas are attractive for vehicle antennas because any satellite tracking mechanism in the azimuth direction is not necessary for these antennas [Ohmori, 1991]. As one type of omni-directional antenna, a bifilar helical antenna has been proposed [Nakano et al., 1991]. This antenna is convenient owing to its thin diameter. However, this antenna. has a disadvantage that the beam direction in an elevation plane moves according to frequency change. In the present paper, the authors propose a linear array antenna using two bifilar helical antenna elements placed along the helix axis. The capability of reduction of beam direction movement is discussed for this array antenna.<>