GB1131972A - Ils antenna system - Google Patents

Abstract

1,131,972. Aerials; radio navigation. CSF COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. 14 July, 1966 [28 July, 1965], No. 31771/66. Headings H4A and H4D. An aerial system for an I.L.S. localizer transmitter 101 having a modulated carrier output P and a sidebands output B comprises a parabolic cylinder reflector 1 whose axis points along the runway axis 100 and which has a primary aerial 10 at its focus and two primary aerials 11, 12 in its focal plane, said aerials 11, 12 being symmetrically positioned with respect to the aerial 10. The focal distance of the reflector may be 3# (# = wavelength at the mean frequency of the localizer) and its aperture 12#: if the polarizations of the aerials are not the same in the " forward " and " rearward " directions, the focal distance of the reflector must be a whole multiple of #/2. The aerials may be V-shaped with their open ends directed towards the reflector. The aerial 10 is fed with modulated carrier energy, and the aerials 11, 12 are fed in antiphase with sideband energies from terminals 132, 133 of a bridge having three one quarter-wavelength arms a, b, c and one threequarter-wavelength arm d. Modulated carrier energy which is picked up by the aerials 11, 12 passes via the arms b, c of the bridge and a line 14 to a short-circuit 141, from which it is returned for re-radiation. The length of the line 14 is adjusted so that the re-radiated energy combines favourably with that coming directly from the aerial 10. The radiation pattern (Fig. 2, not shown) features a main axially directed lobe of the modulated carrier wave overlapped with antiphased sideband lobes on each side (corresponding respectively to predominances of 90 c/s. and 150 c/s. tones) and a general lower level non-directional coverage on other bearings.