Tapered Double Balun

Abstract

Disclosed is a tapered double balun for use with rotationally-symmetrical, frequency-independent antennas that are fed using spiral-mode number 2. The tapered double balun may be used to provide a four-terminal line, where all terminals carry the same voltage, but adjacent terminals are out of phase and opposite terminals are in phase. The antennas may be spirals, sinuous, or other four-arm antennas. The tapered double balun is a stripline device comprising two outer ground planes and a center conductor that is dielectrically separated from the ground planes. The outer ground planes each taper from a wide dimension at the connector end of the device to a narrow dimension at the antenna end of the device. The narrow opposing strips comprising the ground planes are configured to connect to two opposed arms of the antenna. The center conductor is a single conductor at the connector end of the device that tapers to a larger conductor at the antenna end or may bifurcate to form two laterally separated conductors at the antenna end of the device. The center conductor is configured so that, whether single or bifurcated, it connects to the two remaining opposed arms of the antenna.