arXiv:2611.06053v1 Announce Type: cross Abstract: This paper presents a novel method for converting the divergent Gaussian intensity distribution of a millimeter-wave source into a uniform (flat-top) distribution using a single curved surface. The proposed method combines the surface profile of a collimator with that of a beam shaper. To validate the method, the profile of a single-sided (plano-convex) lens is derived and placed 52 mm in front of a conical horn antenna operating at 100 GHz. The lens transforms the Gaussian radiation of the horn, with an incident beam radius of 11.9 mm, into a uniform beam with a radius of 400 mm at a distance of 3 m. The lens surface profile is optimized using a full-wave-simulation-based procedure, and the resulting output beam is compared with that of a previously designed double-sided (concave-convex) lens. Simulation results show that, within the desired field of view, the optimized single-sided lens produces a flat-top intensity distribution with satisfactory ripple and roll-off. Finally, the sensitivity of the optimized lens to frequency variation is investigated. The proposed lens is suitable for generating uniform illumination in active stand-off millimeter-wave imaging systems.