Patent GB-588242-A (GB)
Title: Radio glide path systems for landing aircraft
IPC: G01S19/48
Filed: 1943-10-29
Abstract: 588,242. Directive wireless systems. STANDARD TELEPHONES & CABLES, Ltd. Oct. 29, 1943, No. 17941. Convention date, May 29, 1942. [Class 40 (v)] In an overlapping beam glide path system in which carriers modulated with characteristic signals F1 and F2 are radiated from vertically spaced aerials to produce an equi-signal glide path, the vertical directive patterns are modified, to obtain desired results such as increased sensitivity or freedom from false equi-signal lines, by producing them as the sum or difference of elementary patterns produced by the separate aerials. Aerials,A and B, Fig. 1, have vertical radiation patterns as shown at 7 and 8, Fig. 3, in which radiation signal strength is plotted against angle of elevation. Aerial B is fed with carrier modulated with F2 signal while aerial A is fed with carrier modulated with F1 to produce the pattern 7 and with carrier of lesser amplitude modulated with F2 signal as indicated by curve 9. The two carrier components modulated with F2 signals are in opposite phase so that the resultant radiated pattern of F2 modulated carrier is as shown at 17. Variation in the relative amplitudes of the two F2 modulated components produces variation of the resultant pattern as indicated at 17c and 17D with movement of the equi-signal elevation from 18 and modification of the slopes of the intersecting patterns. The circuit for feeding the aerials is shown in Fig. 4. Carrier from source 20 is fed to one point of a conjugate network 21, of the type described in Specification 491,359, which supplies equal amounts of carrier energy to lines 22, 23 for separate modulation by signals F1 and F2 respectively, the modulation being performed by variably-tuned sections 24, 25. A conjugate network 26 feeds to aerial A, the F1 modulated carrier and also a portion of F2 modulated carrier determined by the amplitude control means 29. F2 modulated carrier is also fed directly to aerial B through an amplitude control 30, but is in phase opposition to the component fed to aerial A due to the transposition 28 in network 26. In a modification to produce a lower glide angle, the half-sine wave radiation pattern 7 of the F.t modulated signals is modified by subtracting from it F1 modulated signals in antiphase radiated by aerial B to produce a pattern such as that at 40 (Fig. 7, not shown) ; curve 41 represents a modified. F2 signal pattern with a slow rise similar to that of curve 17D, Fig. 3. The arrangement for feeding the aerials to produce these two radiation patterns is illustrated in Fig. 8 (not shown), a second conjugate network 44 being employed to feed the two signal components to aerial B. In a modification of the invention, to produce the radiation patterns of Fig. 3 without the power loss in the balancing networks inherent in the use of the conjugate networks feeding the aerials, aerial A is replaced by two elements A and B<1>, Fig. 5 (not shown), which are arranged at substantially the same height, but have no mutual coupling. Aerials A and B<1> are then fed with components of F<1> and F2 signals respectively in appropriate amplitude and phase relationship and act effectively in combination in the same manner as aerial A, Fig. 4. In a further modification of the invention, to prevent secondary or false equi-signal lines being produced, three aerials A, B<1> and B<11> (Fig. 5, not shown), of which B<1> and B" are spaced some distance apart, are arranged to produce an F2 signal pattern with a slow rise as indicated at 50, Fig. 9, and an F1 signal pattern 51 which intersects the F2 pattern only once in a range of elevation of 30 degrees. The F2 signal pattern is produced by signals fed to aerials B and B<11> in phase, producing a fat lobe having a periodicity of about 30 degrees, the steepness of the first rising part of the curve being produced by a third component of F2 signal fed to aerial A in opposed phase. The F1 signal pattern is produced by two components radiated from aerials A and B in aiding phase for the lowest lobe to give a first lobe of substantial magnitude in order to produce good sensitivity at the equi-signal point 52, and to prevent subsequent lobes intersecting curve 50. The three aerials are fed to produce these patterns, as illustrated in Fig. 10 (not shown), aerials A and B<1> being fed with both F1 and F2 signals in appropriate phase and amplitude through conjugate networks while aerial B<11> is fed directly with F2 signal only. In a further modification of the invention, Fig. 12, to avoid the use of conjugate networks and the losses in the associated balancing networks, the two signals Fl and F2 are modulated upon two separate carriers f1 and f2, the frequencies of which are maintained at slightly different values by a control device 76. The carrier f2 modulated with signal F2 is fed through amplitude control means 68, 70 to aerials B<1> and B" and through a phase reversal device 66 to aerial A. The F1 modulated carrier f1 is fed through amplitude control 72 and phase reversal device 73 to aerials A, B<1> respectively. Filters 67, 69, 74 and 75 are connected in the lines from the separate signal sources to the various aerials to prevent interaction between the sources. The patterns of the two signals are shown at 62 and 63, Fig. 11 (not shown), the carrier frequencies being sufficiently close to permit both signals being received simultaneously on a single receiver. Specification 565,379 also is referred to.