GB1025182A - Improvements relating to radio lenses - Google Patents

Abstract

1,025,182. Aerials. R. L. TANNER. Jan. 30, 1963 [Feb. 23, 1962 (2)], No. 3785/63, Heading H4A. A radio lens comprises a single pair of overlying spaced surfaces at least one being a wire mesh, the mesh size being smaller than the shortest operating wavelength. The lens is stated to be effective over a wide frequency band (e.g. 1 to 1000 Mc/s.) and to afford low side-lobe levels. The mesh may be square, triangular or hexagonal and each wire may have two or more strands. In one embodiment, Figs. 1, 2, portion 24 is the lens, producing azimuthal beam shaping and a peripheral portion 25 forms a horn radiating structure for elevational beam shaping and for matching the lens impedance to that of free space. Mesh 30 is secured to an aluminium ring 31 supported by non-conductive poles 32; the inner edge of the upper horn wire mesh is joined to ring 31 and the outer edge thereof is supported by non-conductive poles 23. The mesh of the horn may be of different form to that of the lens, Fig. 5, or the horn may be of conductive sheet. Meshes 30, 34 are substantially identical to one another and are oriented with respect to one another such that corresponding sides of opposite wire meshes lie in a plane normal to both meshes, at least in those lens portions in which the separation between the meshes is not greater than mesh size. It is stated that when the separation s between the meshes is less than one-tenth the mesh size the velocity of propagation V is 1/#2 that of light V c ; and when s is not less than four times the mesh size, V=V c . To afford a narrow azimuthal beam, the diameter of lens 24 is made several times larger than the longest operating wavelength, e.g. if three times, the half-power beam width at that wavelength is some 20 degrees. A desired frequency range may be 4 to 30 Mc/s. and dimensions therefor are given. Another embodiment is a Luneburg lens, Fig. 3, for converting a peripheral point source 37 into a cophasal wave front 38; design details are given. In a further embodiment one mesh structure is planar, Figs. 4, 5. The qualitative manner in which the lens operates is discussed, Figs. 6, 7. In another embodiment, Fig. 9, capacitors 93 are added across the meshes; or the meshes may be loaded inductively 103, Fig. 10. Wave velocity is thereby reduced. In another method of reducing wave velocity a zig-zag portion is included in the side of a mesh, Fig. 11. A feed horn may be mounted for rotation along the peripheral portion of the structure; or fixed feed horns facing different desired azimuthal directions may be employed. To reduce the variation of distances of separation between the opposite meshes which would otherwise be undesirably large, each conductor of a mesh is made of two strands 132, 133 and 134, 135, Fig. 12. Further details are described with reference to Figs. 14 to 18. Each conductor may have three strands, Figs. 19a, 19b or more than three strands, Figs. 20 to 22.