Harold E. Johnson wrote:



Hi Tom, we've used plastic lensing since at least the late 60's for focusing
mundane 4-12 GHz radio waves. Dielectric refraction was used back then to
extract additional gain from dish antennas by allowing more even
illumination of the dish without illuminating the area around the dish.
Harris radio had a patent on it.


J.C. Bose used dielectric lenses at 90 GHz back at the end of 19th
century (that is, in the late 1800s) when doing his experiments in Calcutta.

Optical techniques have been used in radio for a very, very long time.