GB655936A - Improvements in or relating to transmission systems for radio waves - Google Patents

Abstract

655,936. Wave-guides, directive radio systems. WESTERN ELECTRIC CO., Inc. Jan. 2, 1947, No. 160. Convention date, Jan. 22, 1946. [Class 40 (vii)] [Also in Group XL (b)] A device for refracting or for modifying the polarization of guided or unguided electromagnetic waves comprises a plurality of parallel conductive plates spaced apart by at least a half-wavelength at the frequency for which the device is designed. A device, Fig. 1, for converting plane-polarized waves into circularly polarized waves, comprises a plurality of plates 3 which are spaced apart a distance a and have a depth d such that the phase velocity of waves polarized parallel to the plates is so increased that the relative phase of such waves is altered by 90 degrees, or an odd multiple thereof, with respect to the waves polarized perpendicularly to the direction of the plates. The plane-polarized incident wave is arranged with its plane of polarization at 45 degrees to the direction of the plates and the components perpendicular and parallel to the plates emerge from the device with a phase difference of 90 degrees so that a circularlypolarized wave results. A device for altering the plane of polarization of plane-polarized waves is similar to that shown in Fig. 1, but with the dimension d twice as large. The phase difference between the emergent components is consequently 180 degrees, and with components of equal amplitude the plane of polarization is turned through 90 degrees. Fig. 6 shows a refracting prism which, since it has a refractive index of less than unity, refracts waves towards its apex. The prism illustrated is not isotropic since it does not refract waves of all polarizations ; it may, however, be made isotropic by introducing plates perpendicular to those shown, thereby resulting in a prism of cellular construction. Construction. The devices shown in Figs. 1 and 6 comprise dielectric channels open on two sides and mounted in a wooden insulating frame. They may alternatively be mounted in a metal frame which results in all sides of each channel being closed. In an alternative arrangement the plates are supported in a solid dielectric, such as polystyrene foam having a dielectric constant close to unity. Minimizing reflection from surfaces. The edges of the plates used in Figs. 1 and 6 may be castellated as shown in Fig. 8 to prevent reflection both of incident and emergent waves. In an alternative construction, Fig. 10 (not shown), V-shaped recesses, half a wavelength deep and half a wavelength wide are formed in the edges of the plates. In Fig. 11 (not shown), alternate plates stand out a quarter wavelength from the plates adjacent thereto and in Fig. 12 (not shown), to each plate, which is made of a thick material, there is attached a thin strip a quarter wavelength wide.