We report the design of a microstrip leaky-wave antenna for impulse RADAR applications using Ultra Wide Band (UWB) signals in the 6.5 GHz to 8 GHz band. Thanks to its frequency-beam scanning response, this antenna can be used for low-cost angle-of-arrival and range estimation by simply using three different frequency channels available in the UWB standard. The importance of the selection of the dielectric substrate to optimize the angular scanning range using this 1.5 GHz bandwidth, is studied in detail. Finally, using = 2.2, it is reported an angular scanning range of 120 degrees, with a simulated peak gain varying from 9.5 dBi at broadside direction to 7.7 dBi when scanning at ±60º. The antenna shows high radiation efficiency above 50%, and good input matching in the whole scanning bandwidth. Also, the unwanted effects of the beam-squinting in the 500 MHz instantaneous bandwidth of an UWB channel, are analyzed.