GB697163A - Improvements in or relating to radio antennae - Google Patents

Abstract

697,163. Aerials. MINISTER OF SUPPLY. July 13, 1950 [July 22, 1949; Oct. 20, 1949; June 14, 1950], Nos. 19409/49, 27009/49 and 14905/50. Class 40 (vii). Relates to lenses for focusing radio waves comprising a pair of spaced conductive sheets arranged parallel to the E component of the waves. In such a line the effective refractive index Á of the region bounded by the plates is given by Á=#1 - (#/2a)<SP>2</SP> (equation (1)) where a is the spacing of the plates and according to the present invention the spacing a is non-uniform. In one embodiment shown in plan view and side elevation respectively in Figs. 1 and 2 (19409/49) the lens comprises a pair of metal sheets 1 and 2 spaced apart by members 3-6 the lower sheet 2 being planar and the upper sheet 1 having a circular bulge 11 with its convex side upwards. The Specification shows that horizontally polarized radiation from a vertical line source at 7, e.g. a resonant slot or wave-guide horn, will be focused into a parallel beam in the horizontal plane if the refractive index Á within the region bounded by the bulge is given by Á=Áo#2 - (<SP>r</SP>/R)<SP>2</SP> (equation (3)) where r is the radial distance from the centre of the region, R is the radius of the region and Á o is the refractive index in the region bounded by the lower sheet and the plane portion of the upper sheets, the required shape of the bulge being given by combining equations (1) and (3). The direction of the emergent beam may be varied continuously or in steps by moving the feed element 7 around the edge of the bulge portion 11 between the limits A and B or by providing a plurality of circumferentially spaced fixed feeds which may be energized selectively by a switch. In another embodiment, Fig. 3 (27009/49), the lens comprises a semi-cylindrical region bounded by two semi-circular plates 10 and 11 and curved side plates 12 and 13, the upper plate 10 being profiled so that the refractive index Á r at a radial distance r from the axis of the cylinder is given by where # o is the refractive index at the axis. When waves are launched into the lens region in the H1 mode from the wave-guide 15, the emergent beam from the aperture A, B comprises a vertical sheet which is converted into a vertical fan by a cylindrical parabolic reflector 17 attached to an extension of the lower plate 11. In any of the above embodiments both the upper and lower plates bounding the lens region may be curved. In a further embodiment, Figs. 1 and 2 (14905/50), the lens comprises two rectangular plates A and B spaced apart by conductive or dielectric pillars S, the plates having opposed cylindrical bulges so that the spacing between the plates is symmetrical about the axis of propagation op and is such that the refractive index Á(y) at a distance y from the axis op is given by Á(y) = Á o /cos h #y/2 d where Á o is the refractive index at the axis op and d is the thickness of the lens in the direction of the axis; alternatively only one of the plates may be curved. In such an arrangement a feed element at the point o produces a narrow beam in the plane y, o, p, the shape of the radiation pattern perpendicular to said plane being modified by flaring the emergent boundaries C, C<SP>1</SP> of the plates, Fig. 3 (not shown), of the second Provisional Specification. In any of the above embodiments the spacing a must be greater than #/2 and less than #, the metal plates may be replaced by suitably spaced and shaped insulating blocks sprayed or plated with a conductive coating and the arrangements may be used for reception instead of transmission.