Simplified low-profile metamaterial-based spiral antenna without a balun circuit

A spiral antenna excited by a coaxial line without using a balun circuit is designed as a low-profile circularly polarized (CP) radiation element. The antenna is composed of only one arm, which has metamaterial (MTM) properties. Five key frequencies are introduced for the antenna design. It is found that the MTM-based spiral operates as a dual-band anti-CP radiation element.