GB679641A - Improvements in or relating to structures for providing refracting media for radio waves - Google Patents

Abstract

679,641. Radio refractors. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Sept. 18, 1950 [Sept. 16, 1949], No. 23904/49. Class 40 (vii). A refracting medium for radio waves of the type having a refractive indexless than unity comprises a plurality of grids arranged transversely to, and spaced along, the intended propagation path through the medium, each grid comprising a plurality of substantially parallel rod or wire conductors, which are also substantially parallel from grid to grid, spaced apart by less than half the freespace wavelength for which the medium is designed, the spacing of the grids along the intended propagation path being also limited similarly. Fig. 3 shows a section through a cylindrical plano-concave positive lens for focusing radio waves polarized in the plane of the section. The lens comprises a plurality of metallic rods 31, 32, &c. supported upon endplates 21, 22. The rods which do not extend all the way between the end plates are supported in dielectric tubes 37, 38, &c. The free ends of these rods may also be bent slightly to the right as shown so that they may be more nearly along the direction of polarization of radiation incident upon the curved surface. Fig. 4 illustrates a section of a cylindrical lens for focusing radio waves polarized perpendicularly to the plane of the section, and comprising a plurality of rods extending perpendicularly to the plane of the section. As shown, the inner contour of the lens is irregular; by suitably varying the spacing between the rods while also controlling the refractive index appropriately, a smooth inner contour may be achieved. Fig. 5 shows a lens comprising a rectangular array of uniformly-spaced rods, the diameters of which are so chosen that the refractive index decreases with increase of distance from the lens axis OE. In order to increase the range over which the refractive index may be varied, the central portion of the lens may include a block of dielectric within which the rods are placed. Presius and spherical lenses, which may be stepped, may also be constructed according to the invention. In the case of stepped lenses some short lengths of rod will require to be supported away from the endplates; these may be supported by dielectric tubes as described with reference to Fig. 3.