GB569406A - Improvements relating to radio beacons for defining landing-paths for aircraft - Google Patents

Abstract

569,406. Wireless beacons. STANDARD TELEPHONES & CABLES, Ltd. Feb. 27, 1942, No. 2591. Convention date, March 6, 1941. [Class 40 (v)] An antenna system for defining a constantintensity glide-path for aircraft, which is substantially straight at high altitudes and decreases in slope near the point of landing, comprises 'a central radiator 10 and one or more auxiliary radiators 17, 18 symmetrically arranged in alignment on each side of it, the array A being located at a height above ground not exceeding two wave-lengths, at one side of, and with its alignment axis inclined to, the vertical plane containing the glide path 200, and behind the landing point 206, the auxiliary radiators being energized at the same frequency but at a lower power level than the central radiator and the factors determining the shape of the horizontal radiation pattern being so adjusted as to produce two lobes which merge into one another along the antenna axis, as shown at 207. The field strength f at. any point at a height Y above ground and a distance R from the beacon is given by #=KF(#)Y/R<2>, where K is a constant and F(#) is the field strength in a horizontal plane at antenna level and is a function of the angle 0 between the antenna alignment and the vertical plane passing through the point and the centre of the antenna array A. This enables, assuming values for the offset 0 and backset D of the aerial A, the form F(#) of the horizontal radiation pattern for a desired shape of glide path to be calculated. This form of pattern is obtained by suitable choice of the factors affecting it, which are the distance S between the auxiliary and central antennµ, and the relative power levels and phases of the energy supplied to them. Diagrams are given showing the effects of offset O and backset D on the form of radiation pattern desired, and the effects of the spacing S and the relative power levels and phasing of the energy supplied to the antennµ on the form of radiation pattern obtained. As shown in Fig. 1, a transmitter 13 supplies energy to the central antenna 10 directly and to the auxiliary antennµ 17, 18 through a phasing unit, the amounts being determined by tuning the transmission elements 11, 20, 21. The spacing S may vary between one and ten wave-lengths. Two radiators may be used in place of each of the antennµ 20, 21, allowing further control of the radiation pattern by variation of the relative powers fed to the two members of each pair.