Patent GB-664672-A (GB)
Title: Improvements in or relating to devices for changing the phase velocity of electromagnetic waves
IPC: H01Q15/02
Filed: 1947-10-10
Abstract: 664,672. Aerials. WESTERN ELECTRIC CO., Inc. Oct. 10, 1947 [May 16, 1947], No. 27274/47. Class 40 (vii). A device for refracting radio waves is constructed of a dielectric medium comprising a plurality of uniformly - distributed conducting elements, the maximum dimensions of which are small compared with those of the refracting device. The elements, which may be supported in air or vacuum or in a solid dielectric material, act as electric dipoles under the action of an electromagnetic field and modify the polarizability of the surrounding medium, whereby the dielectric constant, and consequently the refractive index, are altered. Alternatively, the action of the elements may be regarded as a " capacity loading " of the medium, whereby the phase-velocity of the radiation transmitted through it is reduced. Substantially non-dispersive media, Fig. 3, illustrates an arrangement comprising a large number of metallic rods mounted in a dielectric medium such as air, polystyrene or hard rubber. The elements are less than a half-wavelength long (e.g. a quarter-wavelength or less) and are spaced apart along the X, Y and Z dimensions by a wavelength or less. The artificial dielectric medium thus produced is non-isotropic and delays only waves polarized along the direction of the rods. In the arrangement shown in Fig. 3, the array is not " staggered," i.e. the rods in any XY plane are immediately behind, in the Z direction, the rods in the preceding XY plane. Fig. 6 shows a side view of a staggered array; this arrangement allows a greater number of conductors per unit volume whereby a greater refractive index may be attained. Fig. 11 illustrates a side view of a prism and Fig. 13 a side view of a lens formed of spherical conductors, the medium in these cases being truly isotropic. The spheres are supported on wooden pillars and are arranged to form a staggered array. The convex surface of the lens is made to conform to a hyperboloidal configuration, whereby radiations from the focus 54, for example by the horn radiator shown, will be converted to a parallel beam. Fig. 15 shows a side view of a lens formed of spherical conductors embedded in polystyrene foam. The lens is constructed of panels 71, 72, 73, which are separated by the spacer sheets 74 and 75. Fig. 16 illustrates a side view and Fig. 18 a back view of an embodiment wherein the conducting elements comprise metallic discs attached to slabs of polystyrene foam which are separated by spacers 108, adjacent slabs being so arranged that the discs form a staggered array. The artificial dielectric in this case, although not truly isotropic, behaves equally to all polarization of radiation, arriving perpendicularly to the discs. Fig. 22 illustrates the elements of a lens comprising a plurality of polystyrene-foam plates of which the conducting elements are attached in the form of patches of conducting paint. The plates are spaced apart by further plates, the centre portions of which are cut away, and are held together by wooden frame members and nut-and-bolt assemblies. In this arrangement the conducting elements are not staggered. Fig. 24 shows a cylindrical lens constructed of polystyrene-foam slabs and dots of conductive paint used in conjunction with a sectoral horn feed producing a narrow beam of radiation in both the horizontal and the vertical planes. A lens may be inserted into the horn mouth to improve further the directivity of the system. Dispersive media. In the previous embodiments the dimensions of the conducting elements have been made considerably less than a half-wavelength, e.g. a quarter-wavelength or less, so that the refractive index of the medium is substantially independent of frequency. When, however, the linear dimensions of the elements approximate to a half wavelength the medium becomes substantially opaque and when the dimensions are increased beyond this value the refractive index becomes less than unity. Fig. 27 shows the front view of an arrangement comprising a plurality of aluminium rods 161, tilted as shown to reduce the coupling to the vertical electric vector, and set in polystyrene-foam panels 167, which are spaced apart by the panels 168. The rods 161 are approximately a half-wavelength long. The medium may be employed for the construction of convergent lenses which will be made convex or concave accordingly as to whether the refractive index is more or less than unity. Such lenses may be used in conjunction with the lens arrangement of Fig. 16, or with the lens arrangements described in Specification 650,767 to provide an " achromatic " combination. Lenses or prisms constructed of the dispersive medium may be used to separate closely-adjacent radio-frequency channels. Specifications 655,936 and 664,673 also are referred to.