GB801885A - Improvements in or relating to directional aerials for the transmission or reception of electromagnetic waves - Google Patents

Abstract

801,885. Aerials. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. Sept. 15, 1955 [Sept. 15, 1954], No. 26508/55. Class 40 (7). A travelling wave aerial consists of an imperforate conductive plate 1 and at least one plate pierced with holes the centres of which form a regular system of quadrilaterals. As shown in Fig. 2, there are two such perforated plates 2a and 2b. They may be provided with sets of circular holes as shown in Fig. 3. All the holes are of the same size and the plates 2a and 2b are parallel to plate 1. The aerial is fed by means of a waveguide 4 and horn 3, the energy being polarized perpendicularly to the planes of the plates. The direction of propagation is OD making an angle # with the perpendicular to the plate 1 at O. The angle # is a function of the wavelength and the dimensions of the aerial construction in particular the distances between consecutive holes in the perforated plates which preferably lie between 0.4# and #. In a modification the diameter of the holes in the perforated plates is varied to produce a law of energy distribution at the surface of the external plate symmetrical in relation to the middle of the aerial. At the same time it is arranged that the field at the free end of the aerial is weak to avoid having a reflector there. In this modification the plates are no longer parallel to each other but diverge slightly. To obtain a symmetrical field pattern two sets of plates meeting at an obtuse angle of F - 2# may be fed at their junction point. As shown in Fig. 6, the feed waveguide 4 is extended by a horn 3 to feed two chambers 5 and 6 partially separated by matching rod 7. The imperforate plates 1 and 1<1> are attached to the rear walls EF and E<1>F<1> of these chambers and perforated plates 2a and 2<1>a to the front walls. Further perforated plates 2b and 2<1>b may also be provided. In a modified form of aerial for use with metric' waves the perforated plates may be in the form of metal grids of side between 0.4A and A.