The operational concept and results of tests are presented for a prototype W-band passive imaging system based on a planar diffraction antenna. A multi-beam (64 beams) rotating antenna pattern is formed due to the dispersive properties of the antenna and by rotating the antenna around the viewing axis by means of a low power electromechanical drive. The operational frequency bandwidth of 16 GHz is split into 64 sub-bands, one for each ‘beam’. Image formation at short distances, ~ several meters, is possible with the addition of a static lens in front of the rotating antenna unit; far field imaging is also possible without an additional lens. Technical parameters and imaging results from the prototype unit are discussed.