In this letter, we present a planar half-Luneburg lens antenna based on a glide-symmetric dielectric structure. The proposed half-Luneburg lens antenna provides a compact alternative to planar beamformers such as conventional Luneburg and Rotman lenses, as well as pillbox antennas. Importantly, we demonstrate that the peak gain of the half-Luneburg lens antenna is less than 1 dB lower than the peak gain of a conventional Luneburg lens antenna, despite being almost half the size. The proposed antenna can steer its beam in a 50 degrees range with scan losses lower than 2 dB and side lobe levels below -10 dB. The proposed design is validated experimentally with a robust and cost-effective implementation using additive manufacturing.