Properties of 2-arm conical equiangular spiral antenna over extended bandwidth

A frequency-independent type of antenna, the 2-arm conical equiangular spiral, has been studied for applications which require hemispherical coverage over a wide bandwidth. At low frequencies the antenna properties are modified by both truncation of the active region and end-reflected currents. These currents have been reduced by the addition of resistive loading and the performance of the antenna then falls of more gradually as the frequency is reduced. Theoretical and experimental results are presented for current distribution, input impedance and radiation patterns, for both the loaded and unloaded cases.