GB1352249A - Combined antenna system - Google Patents

Abstract

1352249 Aerials THOMSON-CSF 26 May 1971 [3 June 1970] 17349/71 Heading H4A An aerial system, which is described as applied to a combined radar-IFF (identification friend-or-foe) installation in the nose A, Fig. 1, of an aircraft comprises a Cassegrain type aerial operating at the higher radar frequency and, in front, an axially disposed aerial arrangement 1 operating at the lower IFF frequency. The Cassegrain aerial comprises a forward-facing radiator 2, which emits, for example, horizontally polarized waves, a sub-reflector 3 built up by horizontally disposed wires or strips, and a main reflector 4 which changes the polarization of waves at the radar frequency from horizontal to vertical, and which is tiltable for scanning the radar beam R. The IFF aerial arrangement comprises a first vertically disposed dipole radiator, a reflector element in front of said dipole, and director elements behind said dipole. This part of the aerial arrangement produces a narrow interrogation beam I 0 which, since it is vertically polarized, passes through the subreflector 3 to the main reflector 4, and is scanned, with the radar beam, as the beam I 1 . In front of the reflector element is a second dipole radiator which is energized alternately with the first dipole radiator, and which provides a broad control beam C for side lobe blanking. The twistreflector 4 comprises a metal panel 51, Fig. 5, in front of which is a network of parallel wires 53. The wires are at 45 degrees to the horizontal, are spaced # r /10 apart, and are # r /4 from the surface of the metal panel (# r = wavelength at the radar frequency). The spacing between wires may be increased to about # r /4, and their distance from the panel to about # r /3, so as to obtain a wider pass-band. In order to overcome any residual effect of the twist-reflector upon the IFF signals, a second network of parallel wires 54 is provided adjacent the wires 53 and at 90 degrees thereto. The spacing between the wires 54 is # i /10 (# i = the wavelength at the IFF frequency).