This paper is to investigate the pattern distortion that happens in the extremely low incidence angle for a flat TM-polarized half Luneburg lens antenna (HLLA) by using a purely reactive impedance surface (RIS). For the scenario of a radar mounted on an unmanned aerial vehicle, a curved RIS is further examined to verify that the proposed conformal HLLA would be able to work for a non-flat RIS-coated object. The simulation results of the proposed antenna show that the right-hand 1st sidelobe at the lowest incidence of y = 15 mm is suppressed to -14.9 dB at 10 GHz and the single-side scanning range is broadened to -20 similar to -57 degree, while the antenna gain of similar to 13.5 dBi is as smooth as the original one. Therefore, a miniaturized Luneburg lens antenna with the wide-scanning capability is successfully achieved.