Patent GB-1151343-A (GB)
Title: Radio Landing Device for Aircraft
IPC: G01S1/02
Filed: 1966-06-24
Abstract: 1,151,343. Radio navigation. CROUZET. 24 June, 1966 [24 June, 1965], No. 28391/66. Heading H4D. The invention relates to the provision of a glide path Z<SP>1</SP> Z, Fig. 2, at the intersection of a vertical plane V and a sloping plane P, plane V being defined by means of two transmitting ground stations A and B placed equally on either side of plane V, and transmitting frequency modulated signals in synchronism, such that a zero beat frequency is obtained in plane V, and plane P is defined by means of two transmitting stations A<SP>1</SP> and B<SP>1</SP>, B<SP>1</SP> being on the ground, and A<SP>1</SP> above, such that the line A<SP>1</SP>-B<SP>1</SP> is parallel to plane V and perpendicular to plane P, these stations also transmitting frequency modulated signals in synchronism and plane P being defined by resulting zero beat frequency. The frequency variation of the two signals from A and B is shown at Fig. 3, and if the modulation period 1/# is chosen such that AB<C/2# then the beat frequency f will be always increasing (i.e. no ambiguities) and proportional to γ the difference of transmission times from the two stations. A catching angle 2α is defined by the asymtopes to the hyperbolas h b  and h a  along which the difference frequency is f 1 . A value of f does not give the sign of the aircraft's angular displacement from Y<SP>1</SP> Y (i.e. to the left on to the right of Y<SP>1</SP> Y) and to remove this ambiguity the transmission from station B is intermittently, for short intervals, transmitted in advance of that from station A. This results in the hyperbolas h a  and hb moving anticlockwise, such that hb moves to h c  and the beat frequency on an aircraft will undergo a change different for the five regions M 1 -M 5  marked. At the receiver, Fig. 10, the beat frequency f is produced by a high frequency stage 1 and is fed to two channels, one comprising a L.P.F. 10, having a band width extending from zero to f 1 , and the other comprising a H.P.F. 13 having a band width starting from f 1 . The output of the L.P.F. for regions M 1 /M 5 , M 2 , M 3 , M 4  is shown in the lower halves of respective Figs. 5, 6, 7 and 8, and the corresponding H.P.F. output is shown in the upper halves thereof. After integration the H.P.F. output is fed to a relay 20 having a threshold such that it is only actuated in regions M 1 , M 4  and M 5 . When this happens, as shown, relay 18 is not connected and indicator 21 is actuated to give a warning light. When the aircraft comes within regions M 2  or M 3 , relay 20 is released and relay 18 is connected to the intergrated H.P.F. output. Having no threshold relay 18 is actuated in region M 2  but not in region M 3 . This causes the switch-over of the input to a centre zero galvanometer, fed by the L.P.F. output such that it reads in the correct direction. When all four transmitters A, B, A<SP>1</SP> and B<SP>1</SP> are being used, two galvanometers can be combined in a crossed pointer galvanometer (Figs. 11, 12) or an oscilloscope (Fig. 13) can be used having orthogonal deflection plates. The two receivers used with said four transmitters can share a common part 2 on a time division multiplex basis (Figs. 14, 15). If the centre line Z<SP>1</SP> Z passes dangerously near an obstacle, the aircraft can track a more distant hyperbola, either by gradual adjustment of the indicator, or by a fixed phase displacement between the transmissions from A<SP>1</SP> and B<SP>1</SP> (Figs. 16, 17).