Metallic Delay Lenses

T HE metal lens antennas described by the writer elsewhere 1 comprised rows of conducting plates which acted as wave guides; a focussing effect was achieved by virtue of the higher phase velocity of electromagnetic waves passing between the plates. Higher phase velocity connotes an effective index of refraction less than unity, and a converging lens therefore assumes a concave shape. The relation between the index of refraction n, the plate spacing, a, and the wavelength X n = Vl - (X/2o) 2 , (1)