Patent GB-581734-A (GB)
Title: Improvements in or relating to instrument landing systems for aircraft
IPC: H01P1/12
Filed: 1942-08-26
Abstract: 581,734. Wireless blind-landing systems for aircraft. SPERRY GYROSCOPE CO., Inc. Aug. 26, 1942, No. 12058. Convention date, April 4, 1941. [Classes 40 (iii) and 40 (v)] Means for producing overlapping beams of electromagnetic radiation for defining a glide path for aircraft comprise, in one form, two mutually-spaced and alternately-energized antennµ projecting into a directional radiator. In other forms, a separate directional radiator is employed for each beam, each with a wave guide to which the energy is supplied, or there being a wave guide which connects the two radiators, gas discharge tubes being provided in the wave guides for alternately cutting off the energy from each radiator. In a further form, an ultra-high-frequency generator is connected to a pair of radiators, and hollow resonators normally tuned to the generator frequency are included in the connections and are provided with de-tuning means by the operation of which the energy 'is passed alternately to the two radiators. Fig. 1B shows a system in which a Klystron oscillator 22, of the type described in Specification 523,712, supplies energy via antennµ 39, 39<1> to wave guides 24, 24<1> leading to horn radiators 25, 251 which emit the overlapping beams. Each of the wave guides, which are tuneable by plungers 40, 40<1>, contains a gas discharge tube structure 29, 29<1> arranged between the antenna and the horn and consisting for example of a number of separate tubes or a single tube bent to a sinuous form to fit the wave guide. The tube structures are alternately rendered conductive by pulses derived via rectifier valves 31, 31<1> from the split secondary of a transformer 27 fed from the supply main, and as each becomes conductive it acts as a shield preventing passage of energy between the corresponding aerial and horn radiator. An oscillator shown in Fig. 1A supplies to the grid 21 of the Klystron 22 two different modulating frequencies in alternation synchronizing with the operation of the gas discharge tubes, so that the beams emitted by the radiators are differently modulated. The two modulating frequencies are generated by pairs of valves 7, 9 and 7<1>, 9<1> respectively. The feed-back circuit of the oscillator 7, 9 to the tuned input circuit 8 occurs through a condenser 10, leads 5 and a grid-controlled valve 6. This valve is conductive only when positive pulses are applied to it from a transformer 2 by way of a rectifier valve 3, so that the amplifier 7, 9 oscillates only at these times. The amplifier 7<1>, 91 is caused to oscillate alternately with the amplifier 7, 9 by a similar circuit and since the transformers 2 and 27 are supplied from the same mains the modulations of each frequency will be passed only to the corresponding radiator 25 or 25<1>. In a modification, the portion of the concentric line 23 connecting the wave guides 24, 24<1> is replaced by a wave guide fed from an antenna projecting into it at its centre. The gas discharge tubes are arranged in this wave guide, one on each side of the antenna, so that the energy cut off from either radiator is reflected back towards the other. Fig. 5 shows a further modification, in which antennµ 45, 451 projecting into a wave guide 44 attached to a single horn radiator are alternately energized to produce the overlapping beams. They are supplied by concentric lines extending from a wave guide 47 energized from an antenna 48 and containing the gas discharge tubes 50, 50<1>. Instead of employing gas discharge tubes for keying the radiation, tuned resonators may be arranged in the leads from the Klystron oscillator which are detuned from the oscillation frequency during the periods when the energy supply is to be cut off. The de-tuning may be effected by rendering a gas-discharge tube in the resonator conductive, by deforming a flexible end of the resonator by an electromagnet, or by a conducting member rotated within the resonator by a motor.