The unidirectional equiangular spiral antenna

Circularly polarized unidirectional radiation, over a bandwidth which is at the discretion of the designer, is obtainable with a single antenna. The antenna is constructed by wrapping balanced equiangular spiral arms on a conical surface. The non-planar structure retains the frequency-independent qualifies of the planar models, and, in addition, provides a single lobe radiation pattern off the apex of the cone. Practical antennas have been constructed with radiation patterns and input impedance essentially constant over bandwidths greater than 12 to 1 and there is no reason to assume that these cannot be readily extended to more than 20 or 30 to 1.