This paper describes a metamaterial-based miniaturized circularly polarized (CP) antenna with high radiation efficiency and wide beam-width or coverage for 5G indoor application. A novel meta-resonator is first proposed, which is investigated by transmission line and equivalent circuit models. By exploring a split-ring resonator-like metaresonator structure, a high-Q LC resonator tank is formed. Substantial size reduction and a wide beam-width are achieved. Owing to a uniform field on these multiple capacitive gaps incorporated on this meta-resonator surface, enhanced aperture efficiency and gain are obtained. It is partly inspired by the classical metasurface-based antenna. For validation, a miniaturized CP antenna with a size of 0.29 λ 0 × 0.29 λ 0 × 0.04 λ 0 (where, λ 0 is the free-space wavelength at 3.55 GHz) is fabricated and measured. The fabricated antenna achieves a good bandwidth of 3.30-3.80 GHz that well covers 5G-N78 band, a peak radiation gain of 5.4 dBic, a high radiation efficiency of 90% and a wide half-power beam-width of 91 . It exhibits the merits of compact size, good bandwidth and beam-width, high efficiency, and low-cost, demonstrating good potential in miniaturized 5G indoor systems demanding wide-beam coverage.