An antenna (100) for emitting radiation from at least one electromagnetic traveling wave which propagates along a guide path is designed to reduce reflection of the traveling wave likely to occur at the end of the guide path. To this purpose, the guide path has at least one portion in the form of a spiral segment (11, 12), which is connected to another portion of the guide path in the form of a loop (13). Gain in the antenna's reflection coefficient can be obtained in this manner, which is effective in particular near a lower frequency limit of a transmission band of the antenna.