Patent GB-654944-A (GB)
Title: Improvements in or relating to lenses for high frequency radio waves
IPC: H01Q15/06
Filed: 1947-04-03
Abstract: 654,944. Directive radio systems. WESTERN ELECTRIC CO., Inc. April 3, 1947, No. 9077. Convention date, April 8, 1946. [Class 40 (vii)]  A lens for use with radio waves has a varying refractive index across its surface. The invention is particularly applicable to lenses of the type comprising one or more dielectric channels wherein the variation of refractive index may be produced by making each channel of variable width, by making adjacent channels of different widths or by filling the channels with dielectric materials of different dielectric constants. Fig. 1 illustrates a sectoral horn wherein a dielectric channel 8 of varying thickness is fitted into the horn aperture. The direction of the electric field is shown by the arrow 6. The phase-velocity of the waves is increased in the narrower portion of the channel 8 so that the phase over the hornaperture is uniform and a narrow fan-beam radiation pattern is obtained. Fig. 5 shows a lens comprising a plurality of tapered channels, similar to the channel of Fig. 1, but shaped as shown so that they fit together to form a compact unit. Energy is fed from or to a linear array 22, which is backed by a plane reflector 27. In the transmitting case, for example, the array emits a cylindrical wavefront which is converted to a plane wave-front by the lens, so that a narrow-beam radiation pattern is obtained. In Fig. 9 (not shown), is illustrated a lens comprising a plurality of tapered channels, successive channels being of different widths. This lens is for use with a point source and has equal focusing actions in the horizontal and vertical planes. In Fig. 7, the lens comprises a plurality of dielectric channels each of uniform width but with the width varying from channel to channel. The lens has a focusing action in the horizontal plane and co-operates with a vertical array 22 and plane reflector 27, having, a focusing action in the vertical plane. The lens is of the three-zone type ; thus as shown in the plan view of Fig. 8, the lens comprises three zones Ll and R1, L2 and R2, and L3 and R3. The path-lengths from the focus 30 to the far surface of the lens differ by a wavelength between the first and second, and second and third zones so that when energy is radiated from a source at 30, the phase at the far surface of the lens is uniform and a plane wave-front emerges from the lens. In a modification of the embodiment of Fig. 7, the lens may alternatively comprise a plurality of channels of equal width but filled with dielectric materials of differing dielectric constants. Fig. 10 shows an arrangement wherein a lens, similar to that illustrated in Fig. 7 is fitted with the mouth of a sectoral horn. The radiation pattern produced is a fan beam and it is stated that the system has a wide-band characteristic. In Fig. 16 (not shown), a sectoral horn and lens, as shown in Fig. 10, co-operate with a stepped, plano-concave cylindrical lens of the dielectric channel type to produce an overall narrow beam radiation characteristic. Specification 650,767 is referred to.