Theory of conical equiangular-spiral antennas: Part 2--Current distributions and input impedances

According to the behavior of the current, an equiangular-spiral antenna may be divided into three distinct regions. Since the positions of these regions are frequency independent, it is possible to obtain a complete description of the current distribution on almost all practical equiangular-spiral antennas by a set of carves, which is given in this paper. It is also found that for rapidly expanding antennas there are, in general, two or more active regions that are characterized by differences in rate of attenuation. Such a phenomenon is interpreted in terms of the Brillouin diagram. A variational formulation of the input impedance of the antenna is also presented. The variation method using the approximate current provided by the set of curves gives a quick, direct means of finding the input impedances.