EZR-MZR Resonators for Compact Low-Profile Omnidirectional Circular-Polarized Antenna Design

New zeroth-order resonator (ZOR): the curved EZR-MZR resonator [epsilon-zero resonance (EZR) and mu-zero resonance (MZR)] was proposed for circular-polarized (CP) antenna design with low-profile and omnidirectional characteristics. The proposed curved EZR-MZR resonator has two orthogonal polarizations with 90° phase difference (PD). By forming four resonators in a circular ring array, the MZR can be characterized as a magnetic dipole. Then, the unidirectional pattern of the horizontal polarization was transformed to be omnidirectional while the EZR with vertical polarization can be characterized as an electric dipole and it radiates omnidirectional pattern. As the PD of the vertical and the horizontal polarizations is inherently 90°, the allying of the two orthogonal polarizations leads to a CP radiation with an omnidirectional pattern. To feed the resonators with uniform amplitude and phase, a feeding network with four equal radial arms is used. The proposed omnidirectional CP antenna has the advantages of low profile from ZOR characteristics and high design efficiency from the inherent 90° PD between the orthogonal polarizations. A prototype with resonant frequency of 1.544 GHz was designed with a diameter of 57 mm (0.29 λ
_r
, λ
_r
is the free space wavelength of the resonant frequency) and a height of 4 mm (0.02 λ
_r
).