Abstract :
For many years it has been known that, in principle, optical lenses could have been made from non-homogeneous glass. For example, if a glass sphere of unit radius were made with refractive index varying according to the relation. ¿ = ¿(2¿r2) where ¿ = refractive index and r = radial distance from centre, it would act as a lens with the focus on the surface of the sphere. Such non-homogeneous glass cannot be produced in practice; however, a microwave analogue has been constructed using spaced conducting sheets to produce a region of refractive index varying in accordance with the above relation. This lens, being circularly symmetrical, is free from aberrations as the feed is moved around the circumference, and is therefore suitable for wide-angle scanning. It will operate only when the direction of polarization is such that the magnetic vector is normal to the conducting sheets.
