Patent GB-1296164-A (GB)
IPC: H01Q13/02
Filed: 1971-04-14
Abstract: 1296164 Aerials; radio navigation SINGER CO 14 April 1971 9381/71 Headings H4A and H4D An aerial array for generating a specially shaped beam comprises an elongated hollow waveguide with a matched impedance load at one end, and feed means in the other end. A series of radiating slots, which is symmetrically arranged about a centre, extends along one face of the waveguide, and each slot is so coupled to said waveguide as to be fed with energy of the amplitude and relative phase necessary for it to make its appropriate contribution towards the array radiation diagram. In a first embodiment, which is according to one aspect of the invention, a series of longitudinal shunt slots extends along a broad face of a waveguide 35, Fig. 9, and is symmetrical about a central traverse axis 60-60. The slots, which as shown are of dumb-bell shape, are divided into two sets. A first set, consisting of slots 46, 47, 48, is located in the middle of the series, and lies along the centre line 55 of the waveguide face. A second set consists of slots 41, 42, 43, 44, 45 to the left of the first set, and of slots 49, 50, 51, 52, 53 to the right thereof. Power is coupled into the slots of the first set by means of cylindrical conductive posts 81 which pass through the waveguide. Capacitive irises 83 are provided with the posts 81 to compensate for impedance mismatches (Fig. 10, not shown). Power is coupled into the slots of the second set by displacing each slot an appropriate distance from the centre line 55. The distances of the slots from the central axis 60-60 are determined according to the relative phase required at each slot, adjacent slots being fed from opposite sides of the centreline 55. An I.L.S. localizer aerial comprises two such arrays of slots in waveguides 35, 91, Fig. 14, said arrays facing a cylindrical parabolic reflector 93. Radiation absorbing walls 95, 97 extend from the reflector to beyond the waveguides 35, 91, which are fed at their adjacent ends by means of waveguides 99, 101. The loaded ends of the waveguides 35, 91 are adjacent the absorbing walls 95, 97. Overlapping beams are produced by the two arrays, and said arrays may be fed sequentially (Fig. 26, not shown). In a second embodiment, which is according to another aspect of the invention, edge slots 111, Fig. 17, having uniform widths and electrical lengths, are provided in a waveguide 113. The distance of a slot from the centre of the series determines its relative phase, and its angle to a plane perpendicular to the waveguide axis determines the relative amplitude of excitation. An open-ended rectangular waveguide element 115 is associated with each slot which receives radiation polarized perpendicular to the line of the slot and emits radiation polarized in a common direction, e.g. vertically polarized. V-shaped conducting plates 116 attached to the ends of the waveguide elements 115 and extending between adjacent pairs thereof protrude outwardly to reduce mutual coupling. Alternatively, radiation absorbing material may be placed between the waveguide elements 115 to reduce mutual coupling. In application as an I.L.S. glide slope aerial element, an array of this kind is provided with two straight reflectors 141, 143, Fig. 25, which extend out to form an H-plane horn. In a complete system a switch directs a signal having a carrier frequency of 15À5 GHz in sequence to a right localizer array, a left localizer array, an upper glide slope array, and a lower glide slope array (Fig. 26, not shown), the arrays being of the types described above. The signal modulations by which the beams are distinguished are applied to the carrier frequency source in synchronism with the array switching.