Imaging concealed objects with millimeter-wave coherent radiation is accompanied with speckle. Like all interference phenomena speckle depends on three light parameters of the mm-wave laser beam: phase, wavelength and angle of incidence and could be reduced by the diversity of these three parameters. Diversity tools have been compared to improve images of concealed objects. We report measurements, simulations and image reconstruction results over the whole W-band (75-110 GHz) and demonstrate where each tool works the best. Multi-phase diversity is successful to reduce speckle contrast; multi-angle - to improve the image quality; multi-spectral - to recognizes small object's features. A simple post-processing eliminates the areas, still covered by interference.