The aim of this paper is twofold. On the one hand, to provide a better understanding of a composite right/left-handed (CRLH) waveguide, going into those aspects of interest for an antenna designer. A longitudinal slot as a radiating element has been considered to be studied and compared with its classic counterpart. On the other hand, to present the new design approach that is needed when using the CRLH waveguide technology to built array antennas. To that end, a slot array antenna has been designed, built, and measured. The simulations and measurements are in excellent agreement, confirming not only the backward-to-forward beam steering and broadband far-field performance, but also the validity of the design procedure used.