GB600433A - Improvements in or relating to wireless aerials - Google Patents

Abstract

600,433. Wave-guides ; directive radio systems. BOOKER, H. G. Oct. 31, 1945, No. 28911. [Class 40 (vii)] A device such as a wave - guide horn or mirror has means for controlling the wave energy passing into or out of the device, comprising a plate of conductive material placed normal to the direction of propagation and formed with a plurality of resonant slots. Fig. 1 shows a parabolic reflector 10 fed by a wave-guide horn 15. The aperture is closed by a conducting plate 13 , formed with a plurality of linear slots 14. Slots 14 are one half-wavelength long and the .same distance apart, and thus are transparent to waves of this wavelength having the electric vector at right angles to the slots. The bandwidth of the transmitted energy depends on the width of the slots, while a departure from the resonant length effects a control of the phase of the transmitted energy. The density of the slots per unit area determines the amplitude of the energy in the corresponding part of the beam. By making the above factors different in different parts of the beam, the polar diagram may be modified as desired. Fig. 2 shows a spherically-shaped apertured plate 20 for use with a spherical wave front produced by a wave-guide 16a and a reflector plate 19. A second apertured plate 14a may be used. In Fig. 3, three apertured plates 13b, 13c, 13d are used in a wave-guide horn 21 to improve impedance matching. To alter the density of the apertures per unit area some of the slots may be effectively blocked by shortcircuiting their central region as at 24, Fig. 6. The length of a slot may be altered by means of a rotatable snail cam plate 23. For highpower working the slots may be filled with a suitable dielectric.