Circularly polarized antennas based on metamaterial transmission lines

Two types of circularly polarized (CP) antennas based on metamaterial transmission lines will be presented. First, a dual-band omnidirectional circularly polarized (CP) antenna of epsilon negative (ENG) transmission lines (TLs) is introduced. The antenna is based on a circular mushroom structure with curved branches and designed without additional feeding parts for a 90° phase difference between two orthogonal modes as well as additional radiators for dual-band operations. A left-hand CP (LHCP) and a right-hand CP (RHCP) are obtained at the zeroth and the first order resonance modes, respectively. Second, a circularly polarized (CP) antenna based on mu-negative (MNG) transmission lines (TLs) is presented. The antenna consists of two pairs of resonators for two orthogonal polarizations. The 90° phase difference between them is achieved by detuning the corresponding resonance frequencies. The experimental results agree with the theoretical results.