This communication describes the use of a 3D microwave active imaging system based on a Frequency-Modulated Continuous-Wave radar for the wireless localization, identification and reading of passive (battery-less) and chipless electromagnetic sensors. The beam scanning of the scene is performed mechanically and allows detecting passive sensors from the visualization of 3D microwave image of a scene. A preliminary imaging system demonstrator operating at 24GHz is briefly described and resulting 3D images are reported for different scenarios. An estimation of the maximal density of detectable passive sensors is given. Keywords— 3D active imaging system; beam steering; FMCW radar; passive electromagnetic sensors