GB655315A - Improvements in or relating to dielectric lenses - Google Patents

Abstract

655,315. Aerials. WESTERN ELECTRIC CO., Inc. Dec. 12, 1947, No. 32806. Convention date, Dec. 19, 1946. [Class 40 (vii)] The invention relates to dielectric lenses for use with radio waves and gives design equations for the surfaces of such lenses, which are preferably of the multiple-zone stepped type. The lens may be constructed of material having a uniform dielectric constant, in which case at least one face is figured to produce the desired focusing action, or it may comprise a parallel-sided slab of material having a spatially-variable dielectric constant. Lenses using materials of uniform dielectric constant. Fig. 2 illustrates a lens designed in accordance with the formulµ derived in connection with Fig. 1 (not shown), and which converts radiation from the wave-guide 20 into a parallel beam. A shield 22 surrounds the radiation path between the lens and wave-guide. The lens is attached to the shield by spinning the forward edge of the shield into a groove cut into the periphery of the lens. Fig. 3. (not shown) illustrates a similar system wherein the lens is mounted in the mouth of a conical horn. Fig. 6 shows a doubleconvex lens which may be regarded as two plano-convex lenses with their plane surfaces in contact. Radiation from one focal point S of one plano-convex lens is brought to a focus at the focal point R of the other. In this arrangement radiation parallel to the axis is incident on or emergent from the hypothetical plane surfaces, whereas in the arrangement of Fig. 2 such radiation is emergent from the convex surface. The lens is accordingly designed in accordance with the formulµ derived in connection with Fig. 5 (not shown). In the arrangement of Fig. 6, however, phase steps of 720 degrees occur between adjacent stepped portions of the lens, whenthe lens stepping is made to occur between adjacent zones of the constituent plano-convex lenses. Accordingly, the steps may be cut such that the phase in each stepped portion of the constituent lens changes by 180 degrees. Fig. 7 (not shown) illustrates a lens having a continuous spherical front surface and a stepped back surface. Such a lens is suitable for mounting on aircraft as the shape offers less' resistance to high winds. Fig. 8 (not shown) illustrates a cylindrical lens mounted in the mouth of a sectoral horn. Figs. 9 and 10 show respectively H-plane and E-plane sections of lens for converting a spheroidal, rather than a spherical, wave-front into a plane wave-front. The lens has different focal lengths in the two planes to compensate for the different apparent distances of the lens from the source in the E-plane and H-plane, as is obtained, for example, in radiation from a wave-guide. Fig. 11 shows a front view of the lens showing the phase-delay steps occurring at a plurality of concentric circles but varying in depth around the circle. The depths of the steps may be kept constant when the outline of each zone viewed from the front will become an ellipse. The forms of the lens surfaces in the previously-described embodiments are determined from formulae; the shape of the surface may alternatively be determined from a plot in the plane of the lens of the phases of the iradiation to be passed through the lens. From the diagram obtained the shape of the lens to produce a desired emergent wave-front may be determined. Phase-delay steps are inserted at appropriate positions. Figs. 13 and 14 (not shown) show such lenses mounted in the mouths of conical horns. Lenses having spatially-variable dielectric constants. Fig. 16 shows a front view of a. parallel-sided lens, the material of which varies in refractive index over the surface, the portions of highest refractive index being shown the most heavily shaded. Fig. 17 is a sectional view of a similar lens comprising a spherical shell of uniform thickness. The material for the lenses is obtained by mixing two ingredients, having respectively high and low dielectric constants, in suitable proportions. The lowdielectric-constant component may be polyethylene, polystyrene, polytetrafluoride or various polyvinyl polymers. In the highdielectric-constant component lead chloride, titanium dioxide (rutile) or certain titanates may be used.