Patent GB-1312049-A (GB)
Title: Generation of navigating planes for aircraft landing
IPC: G01S1/14
Filed: 1970-02-23
Abstract: 1312049 Aerials; radio navigation UNIVERSITY OF ADELAIDE and E O WILLOUGHBY 23 Feb 1970 [24 Feb 1969] 8575/70 Headings H4A and H4D An aerial system comprises a symmetrical parabolic cheese aerial fed from two excitation centres symmetrically disposed about the focal line of said cheese in a plane perpendicular to said focal line, said centres producing the equivalent of two identical radiation patterns from the same radiation centre, rotated with respect to each other. The excitations are produced by the sums and differences of carrier and navigation side bands passed through a hybrid network, and are used to define a navigating plane. In a first embodiment, two colinear spaced apart resonant slots, each of which terminates a length of short circuited waveguide, are symmetrically disposed about the focal line of a parabolic cheese reflector, which they excite, their centre lines being in a plane which is perpendicular to said focal line (Figs. 2(a) and 2(b). The waveguide lengths are provided with matching screws behind the slots, and they are fed at points E 1 , E 2 , the system being adapted for setting up a navigational plane derived from overlapping beams. As shown in Fig. 2(c), I.L.S. 330 MHz carrier signals (C) plus sum of 150 and 90 Hz sideband signals (S) are modulated in a modulator to provide higher frequency signals F<SP>1</SP>+S<SP>1</SP> in, for example, the 4 to 5 GHz band. The difference of said sideband signals (D) is modulated in another modulator and is given quadrature phasing to produce higher frequency signals jD<SP>1</SP>. Signals F<SP>1</SP>+S<SP>1</SP>-jD<SP>1</SP> and F<SP>1</SP>+S<SP>1</SP>+jD<SP>1</SP> are derived by means of a hybrid, and are supplied to respective feed points E 1 , E 2 . It is stated that aperture illuminations are simultaneously produced with amplitude variations substantially of the forms: and wherein C and D are constants, 2a is the length of the aperture, and x is the distance from its centre. Aperture blocking may be reduced by providing a secondary aerial unit B at the rear of the exciter unit (Fig. 2(a)) and feeding it with part of the F<SP>1</SP>+S<SP>1</SP> signals (Fig. 2(c)). In another arrangement, outer aerials (2), (3), Fig. 5 (not shown), are mounted on either side of the main aerial. The aperture may be provided with flares, the edges of which may be crenellated to reduce radiation thereover (Figs. 3(a), 3(b), not shown), and in another arrangement beam spread in azimuth is reduced by using the output from the cheese reflector as a focal line source for a parabolic cylinder (Fig. 4, not shown). In a second embodiment two colinear dipoles mounted on a reflecting plate are used instead of two co-linear slots, to excite a parabolic cheese reflector (Figs. 8(a), 8(b), 8(c), not shown). The axes of the dipoles lie in a plane which is perpendicular to the focal line of the reflector and the direction of the electric vector of the radiation is also perpendicular to that line, and not parallel to it, as in the first embodiment. The aerial system can be applied both to localizer and glide slope planes, and suitable receiving arrangements are also discussed (Fig. 6, not shown).