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This letter presents a compact zeroth-order resonance (ZOR) antenna based on a new type of composite right/left-handed (CRLH) transmission-line unit-cells structure. It has a coplanar waveguide (CPW)-fed input port with modified common ground plane. The unit cell of the proposed antenna consists of a series metal-insulator-metal (MIM) parallel-plate capacitor and a shunt stub inductor shorted by a via-hole. In order to improve its efficiency and to reduce the zeroth-order resonant frequency of the antenna, two straight metal-strip lines and asymmetrical unit cell structures were used for the shunt inductors instead of meander lines. As a result, the total electrical size of the fabricated ZOR antenna employing two unit cells was 0.20 λ0×0.14λ0. The measured gain and efficiency of the fabricated antenna have been improved to 2.3 dBi and 79%, respectively, at the zeroth-order resonant frequency of 2.3 GHz.