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This article presents planar dual-band omni-directional antennas employing a composite right/left-handed (CRLH) metamaterial for UHF applications. The antennas are compact and in a simple double-sided planar configuration without using vias or lumped-elements and have an omni-directional radiation pattern regardless of having a ground plane at the backside. A dual-band antenna operating at a pair of the negative (f-1) and positive (f+1) resonant frequencies is designed at 373/817 MHz and the dual-band operation with omni-directional radiation patterns are demonstrated. The physical size of the presented antenna is lambda-1/13 times lambda-1/18 times lambda-1/1005 at f-1, and lambda+1/8 times lambda+1/6 times lambda+1/459 at f+1, where lambda-1 and lambda+1 are free space wavelengths at f-1 and f+1, respectively. Maximum measured gains at f-1 and f+1 are -13.8 dBi and -0.5 dBi, respectively.