GB751046A - Improvements in or relating to aerials for short electro-magnetic waves - Google Patents

Abstract

751,046. Aerials. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. April 23, 1954 [April 24, 1953], No. 11856/54. Class 40 (7). A directional aerial comprises a radiating assembly and energizing means, the radiating assembly consisting of or being equivalent to a refractive medium the refractive index of which varies along the direction of radiation according to a law which can be represented as a sinuous curve with a number of alterations. It is explained mathematically that such an aerial has a greater directivity than known aerials in which the refractive index follows a decaying law over a fraction of a cycle. The length of one alternation of the curve referred to above is preferably approximately equal to two wavelengths of the working energization in a vacuum. In a simple embodiment (Fig. 1) the energizing means consists of a waveguide horn c1 which is supplied by a waveguide b1 with energy in an axially symmetrical mode, if necessary through a mode transformer. The radiating assembly consists of an axially symmetrical dielectric member consisting of a unit of four sinuous variations of tapering form as shown. It is not essential for the operation of the system that the unit shall taper. In a preferred form the actual dielectric material of Fig. 1 is replaced by an assembly of disc elements arranged to form an artificial dielectric medium; this is shown in Fig. 3. Both the discs and the central support rod T are of metal and the radius and/or spacing of the discs may be varied to give the requisite variation in apparent reflective index. The rod T may conveniently be mounted on a plug closing the end of the feed line and if the latter is a coaxial the primary element shown in Fig. 6b may be used. This element consists of a rod 8 welded on to the central conductor 6, passing centrally through a hole 7 in the outer 5, and carry a metal plate 8a. This plate is disposed perpendicular to the axis of the line and is semi-circular with a radius of the same order of magnitude as that of the line. A similar plate 9a on a rod 9 welded to the outer 5 is disposed on the opposite side of the line. To solve the problem of energization so that the radiation is in phase in the usual direction, where a large number of alternations of refractive index in the radiating assembly are used, a number of primary elements is placed at intervals along the assembly. Fig. 4 shows a portion of such an arrangement having 3 primary elements of the form shown in Fig. 6b, energized from a coaxial line which forms the central rod of an artificial dielectric assembly of discs. The individual disc-like elements of the artificial dielectric medium may be made of wire grid construction.