In this paper, a compact coplanar epsilon.negative(ENG) antenna is proposed with ultra.wide operation band and small size of 18×11.5 mm2. The proposed antenna is designed based on a coplanar.waveguide(CPW) feeding antenna, and thus the via.free structure is employed to realize the ENG unit cell, which is convenient to tune the frequency of zeroth.order resonance(ZOR) and extends the ZOR bandwidth. The high.order resonant frequencies are achieved and mainly determined by the separate slots that are located between the radiating patch and the ground plane. Adding the left.handed inductance between the radiating patch and ground has slight impact on the high.order resonant frequencies, and then the ultra.wide band is achieved by merging the ZOR bandwidth with the high.order resonant bandwidths. The ground plane primarily works as a matching network for the proposed antenna. Although it generates a low.frequency resonance, the performance is undesirable due to the impedance mismatching. The measured results show that the reflection coefficient, |S11| <.10 d B, is in a wide frequency range from 5.25 to 13 GHz, which covers the upper operation band of UWB communication. Also, the antenna contains relatively stable gains and omni.directional radiation patterns. In this paper, a compact coplanar epsilon. Negative (ENG) antenna is proposed with ultra.wide operation band and small size of 18 × 11.5 mm2. The proposed antenna is designed based on a coplanar. Waveguide (CPW) feeding antenna, and thus the via.free structure is employed to realize the ENG unit cell, which is convenient to tune the frequency of zeroth.order resonance (ZOR) and extends the ZOR bandwidth. The high. that are located between the radiating patch and the ground plane. Adding the left. worn electrical between the radiating patch and ground has slight impact on the high .order resonant frequencies, and then the ultra .wide band is achieved by merging the ZOR bandwidth with the high.order resonant bandwidths. The ground plane works as a matching network for the proposed antenna. Although it generates a low.frequency resonance, the performance is not due due to the impedance mismatching. T The measured results show that the reflection coefficient, | S11 | <.10 d B, is in a wide frequency range from 5.25 to 13 GHz, which covers the upper operation band of UWB communication. Also, the antenna contains relatively stable gains and omni .directional radiation patterns.