Re: artificial dielectric
They are generally small particles or bits of metals that are suspended in a low dielectric material or even in air if there are rod connectors between them.
They were invented in the 1939-1945 war or at least were perfected then. These materials are then shaped into lenses.
Many decades ago there was a patent issued on a multilayer PC board with different metal square patterns/sizes on each layer. It was only a mm or two thick but acted as a relatively good lens for placement over a horn antenna to improve the radiation pattern. It also sealed the horn so that dry nitrogen could be used to pressurize it so that atmospheric humidity would not get inside.