A Compact Quasi-Isotropic Antenna Based on Folded Split-Ring Resonators

In this letter, an electrically small quasi-isotropic antenna using folded split-ring resonators is investigated. The antenna is based on split-ring resonators (SRRs) to achieve a quasi-isotropic radiation pattern using the electric and magnetic dipole current of the SRR. Interdigital capacitors are used to make the size more compact, and magnetic coupling of a folded structure is applied to improve the radiation characteristics of the SRR antenna. The electrical size of the antenna has ka = 0.41 at 888 MHz and 1.8% of fractional bandwidth. The measured gain deviation $(\Delta)$ is 5.2 dB and the measured radiation efficiency is higher than 81% in the bandwidth.