In this paper, a compact circularly polarized asymmetric dielectric resonator antenna (DRA) excited by a quarter-wave transformer (QWT) feedline is proposed for ultra-wideband (UWB) applications. The DRA consists of two rectangular ceramic blocks with the same permittivity (ε_DR = 9.8) and an F-shaped metallic strip combined with the partial ground. The proposed antenna is supported first and third-order modes as TE_δ11 and TE_δ13 at 9.1 and 11.28 GHz. The proposed antenna covers ultra-wideband (UWB) range from 6.4 to 12.4 GHz (impedance bandwidth of 63.8 %) with a peak gain of 6.01 dBi at 11.5 GHz. The broad AR bandwidth of the proposed antenna is achieved by the asymmetric structure of DR and the modified ground. The simulated AR bandwidth (≤ 3 dB) of the proposed antenna is 63.8% (6.4 to 12.4 GHz), and the measured AR bandwidth is 2.5% (5.8 to 6.1 GHz) and 43.7% (6.9 to 10.9 GHz). The proposed antenna can be used for C, X band applications.