Generation of a circularly polarised conical beam from backfire helical antennas

In satellite communication, use of circular polarisation eliminates the need for control of the antenna orientation about the bore-sight. In addition, for land mobile antennas, a circularly polarised conical beam is preferable since no satellite tracking system is required. The authors demonstrate the formation of a conical beam in the -Z hemisphere using a backfire helical antenna (BHA) operating in the second mode. The radiation characteristics of the BHA are evaluated on the basis of the current distribution determined by the moment method. Firstly the authors consider the possibility of generating a conical beam by a monofilar BHA. Next, they improve the symmetry of the radiation pattern by using a quadrifilar BHA. Finally, a symmetrical radiation pattern and a simple feeding system are realised by adopting a bifilar BHA