Before revision: At still higher frequencies dielectric waveguide (such as optical fibre) becomes the technology of choice, but there are planar types of dielectric waveguide available.Yeh & Shimabukuro, p. 99
After revision: At still higher frequencies dielectric waveguide (such as optical fibre) becomes the technology of choice, but there are planar types of dielectric waveguide available.Yeh & Shimabukuro, p. 99.