In the road field, the need to get information on the thickness of very thin road layers is not solved by GPR. The reason is that the devices are not able to work over several gigahertz. That is why, a research has focused on the conception of a step frequency radar technique, enable to work with very high central frequency synthetic pulses. In collaboration with the LCPC (Central Laboratory of Bridges and Roads), an ultra wide band antenna has been developed at the LEAT (Electronic, Antennas and Telecommunication Laboratory). The ultra wide band antenna, developed for roads application, forms parts of the family of the Vivaldi antennas. It has been realized in stripline technology and one obtains a bandwidth greater than one decade. In a first step, this antenna has been tested on various bituminous concrete samples, with a network analyzer. Different parameters were studied like the bandwidth, the off-set between antennas, the height, and the shape of the pulse depending to the frequencies. A second step concerns GPR dynamic measurements. An homemade software enables to record data from the network analyzer. As LCPC has large testing facilities in the road field, such as a circular Pavement Fatigue Test Track, composed of different known structures, several radar profiles have been done. Results are compared with classical GPR profiles.