GB1155434A - Improvements in or relating to Directional Aerial Systems and installations for use in Aircraft Landing Assistance - Google Patents

Abstract

1,155,434. Aerials; radio navigation. CSFCOMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. 31 Aug., 1966 [31 Aug., 1965], No. 38930/66. Headings H4A and H4D. An I.L.S. glide-path aerial system comprises an array made up of radiating elements 11, 12, Fig. 1, mounted on a mast 1 which is inclined away from the vertical by an angle equal to the required angle of descent. The number of elements 11 (as shown, twenty one) is greater than the number of elements 12 (as shown, fourteen) and the two groups are interleaved, with each symmetrically disposed about the centre 0 of the array, the spacing between adjacent elements 11, 11 or 12, 12 being one wavelength at the mean operating frequency. The elements 11 are so fed as to produce a lobe of radiation normal to the array, that is, directed along the glide-path, whilst the elements 12 are so fed as to produce a lobe of radiation directed upwardly from the glide-path, but arranged to have the same intensity along the glide-path as the other lobe. The radiating elements may be horizontal dipoles and a plane or curved reflector 13 may be provided behind them. As described, carrier power is fed from a terminal P, Fig. 2 of a transmitter 20 to a terminal 211 of a bridge 21 having three arms a, b, c, each a quarter-wavelength long and one arm d three quarter-wavelengths long, whilst side-band power is fed from a terminal BL of the transmitter to a terminal 212 of the bridge. The elements 11 are supplied with carrier and sideband power from a terminal 213 of the bridge, via a power control system 215 and power dividers 216, 217, 218, 219. The distribution of amplitude over the elements 11 is symmetrical about the centre 0 of the array, but may not be uniform. The elements 12 are supplied with carrier power in phase with that to the elements 11 and with side-band power in anti-phase with that to the elements 11, from a terminal 214 of the bridge. A power divider 220 feeds a sub-group 121 of the elements 12 which are above the centre 0, through an adjustable phase shifter 221 and a power divider 223, and it feeds a sub-group 122 of the elements 12 which are below the centre 0, through an adjustable phase shifter 222 and a power divider 224. The phase shifters 221, 222 give phase shifts of equal magnitudes but of opposite signs, so enabling the direction of the radiation lobe from the elements 12 to be adjusted in a vertical plane (Fig. 3, not shown). Operation of the power control system 215 enables the magnitude of the radiation lobe from the elements 11 to be adjusted, and hence it may be arranged for the intensities of the side-band energies in the two radiation lobes to cancel out along the glide-path direction (Fig. 4, not shown).