Dielectric materials for the microwave antenna lens

Some sixty-six years ago, Sir Oliver Lodge machined a lens from a slab of hardened pitch and demonstrated that it had a beaming effect on the radiation from a spark-gap oscillator. While he was perhaps the first man to show that a lens would function as an aerial, he was by no means the first to propose that it would do so. In 1860 Clerk Maxwell designed a two-dimensional lens in which the refractive index of the lens material varied continuously as a function of position. He proved mathematically that it would scan 180° of arc.