Luneburg lenses for RF are 100% dielectric. You print your lens with a known dielectric constant uv curable resin and it its good to go! Methods like this are

Luneburg lenses for RF are 100% dielectric. You print your lens with a known dielectric constant uv curable resin and it its good to go! Methods like this are the ones that Lunewave (https://lunewave.com/ https://lunewave.com/) use for developing RF lenses for their ADAS system