Two resistors loaded ultra-wideband spiral array antennas

In this paper, we propose a new type of a small spiral antenna that has a pair of resistors and verify its ultra- wideband characteristics. Spiral antennas have ultra-wideband characteristics such as a nearly constant input impedance, antenna gain, and low axial ratio. However, when reflectors such as conducting planes or cavities are used, their performances are degraded due to reflections from the end of these spiral arms. In particular, this effect is remarkable at low frequencies where these antennas become small in comparison to their wavelengths. Therefore, new termination technique for small spiral antennas backed by a cavity, their array antenna performances were examined and showed high gain and low axial ratio characteristics.