GB1410699A - Dielectric lens antennas - Google Patents

Abstract

1410699 Aerials POST OFFICE 6 Dec 1973 [15 Dec 1972] 56635/73 Heading H4A A dielectric lens for a radio wave aerial is formed of a solid dielectric material having a zone cut-out therefrom and filled with an artificial dielectric, that is, an arrangement simulating the properties of a diele tric material by reason of its comprising a three dimensional array of metallic conductors. As described, a planar-hyperboloidal dielectric lens 34, Fig. 3, converts spherical wave-fronts from a radio source 32 into plane wave-fronts 36. A cylindrically shaped zone 44 of depth T is cut from the planar face of the lens 34, and is filled with an artificial dielectric material of, for example, the egg-crate type. To maintain the plane wavefronts 36, it is necessary that the difference between the number of wavelengths over the depth T when containing the original dielectric material, and when containing the artificial dielectric material, is a whole number N. That is : T/(#d/n0)-T/(#d/na)=N or T=N#d/(n0-na), where, #d is the free space wavelength at a design frequency fd; n0 is the index of refraction of the original dielectric material; na is the index of refraction of the artificial dielectric material. With a parallel-slat type of artificial dielectric material construction, the apparent index of refraction n<1>a at any frequency f is given by n<1>a=[1-(#/#c)<2>]<¢> where X is the free space wavelength at the frequency f, and #c is twice the slat-to-slat spacing in the artificial dielectric material. It is shown mathematically in the Specification that the construction with use of an artificial dielectric material improves the operating bandwidth; and it is stated that optimally the product of n0 and na should be unity. A series of stepped zones, instead of a single zone, may be used. Quarter-wave matching sections may be provided on the faces of the lens, and also-at the interface between the normal dielectric material (the latter can be a simple air gap). In another embodiment, a planar-hyperbolic cylindrical lens 60, Fig. 6, has a plate 62 of artificial dielectric material let into its planar face.