Metamaterial Spiral Antenna

Conventional spiral antennas radiate either a left-handed circularly polarized (CP) wave or a right-handed CP wave in a specific direction (single CP radiation). This letter presents a novel spiral antenna, designated as the metamaterial spiral, which radiates a dual CP wave. First, the principle for left-handed CP radiation and right-handed CP radiation is explained using “current bands.” Second, based on this principle, a prediction for dual CP radiation is made for a spiral structure. Third, for confirming this prediction, spiral arms are constructed using numerous straight filaments, each having a left-handed property with an inherent right-handed property. Numerical simulation confirms the predicted dual CP radiation. The gain and radiation pattern are discussed.