Electrically Small Quasi-Isotropic Antenna Based on Split Ring Resonators

An electrically small antenna (ESA), which is based on split ring resonators (SRRs), with quasi-isotropic coverage is developed and investigated. This quasi-isotropic antenna is comprised of two orthogonally arranged SRRs and a circular holding tray to support the antenna structure. Each SRR possesses a quasi-isotropic radiation characteristic for the whole space with a gain variation about 3 dB. This feature is attributed to the equivalent electric and magnetic dipoles for the SRR. The isotropic radiation pattern is achieved by the combination of them. Through the combination of the two linearly polarized SRR, the final antenna could realize the circularly polarized characteristic in the maximum radiation direction. This proposed antenna exhibits an electrically small size (0.19 × 0.15 × 0.15 λ
³
, ka = 0.89), and a radiation efficiency higher than 90% with a -10 dB impedance bandwidth of 1.6% at the center frequency of 748.5 MHz. Additionally, the simulated realized gain differences of the quasi-isotropic ESA is 2.77 dB, which reveals that the antenna has a consistent quasi-isotropic coverage of the whole space.