Dedicated short range communications (DSRC) is a wireless technology developed to enhance the safety and the productivity of the transportation system. This paper presents the conception of an antenna for the mobile unit of a DSRC 5.9GHz system. The main feature of the antenna is the omnidirectional radiation pattern in the horizontal plane with circular polarization that allows correct communications among vehicles. In addition, the antenna holds a broad bandwidth enabling its use in 5.8GHz/5.9GHz DSRC bands.