Spiral antennas radiating a circularly polarized conical beam

Three types of spiral antennas (SAs) are analyzed using the method of moments. They are a two-wire SA with one feed (2SA-1F), a four-wire SA with four feeds (4SA-4F), and a four-wire SA with one feed (4SA-1F). Each SA is located above a ground plane. The spiral center is connected to a vertical feed wire, whose lower end is excited by a coaxial line. Attention is paid to radiation from the vertical feed wire. We reduce this feed-wire radiation by adding parasitic elements around the vertical feed wire for the 2SA-1F. After comparing its radiation characteristics with those for the 4SA-4F, we propose a novel spiral antenna, the 4SA-1F. Parasitic elements are again added around the vertical feed wire. It is found that, with the help of the parasitic elements, the feed-wire radiation contributes to the circularly polarized (CP) radiation. The proposed four-wire spiral antenna is a radiator of a CP conical beam.