Dual-Band Counter Circularly Polarized Radiation From a Single-Arm Metamaterial-Based Spiral Antenna

A single-arm spiral antenna whose arm is made of a metamaterial (MTM) transmission line having right- and left- handed properties is discussed. This antenna, abbreviated as the 1-MTM-SPA, has an extremely low-profile structure (0.016 wavelength at a balanced frequency of 3 GHz) and does not need a balun circuit. It is predicted that the 1-MTM-SPA will operate as a circularly polarized (CP) antenna, where right-handed CP radiation is obtained within a particular frequency band and left-handed CP radiation is obtained within a different frequency band. Numerical analysis results obtained using two different techniques confirm the prediction for this dual-band counter-CP radiation. The 1-MTM SPA used for the confirmation shows an overlapping gain and axial ratio bandwidth of approximately 7%. The VSWR relative to the Bloch impedance value is less than two within the overlapping bandwidth, as desired. Experimental data are also presented.