Patent GB-940294-A (GB)
Title: Improvements in or relating to air traffic control systems
Inventor: WIERSMA RUDOLF ARNOLD
IPC: G08G5/00
Filed: 1959-11-26
Abstract: 940,294. Pulse radar; radio signalling. AVEL CORPORATION GENEVA. Feb. 27, 1961 [Nov. 26, 1959], No. 6527/61. Headings H4D and H4L. In an air traffic control system a ground interrogator includes in its receiver means to define airspaces in dependence on the instantaneous azimuth of its transmissions so as to issue a further signal when an aircraft responder height-coded signal falls within one or more of the air spaces in order to warn the aircraft that it is entering a prohibited zone. In the embodiment described a ground station narrow beam scanning aerial 14, Fig. 4, embraces a civil aircraft air lane 100 and a military area 101, the system providing a warning to civil aircraft entering area 101 and to military aircraft entering lane 100; in addition an indicator in a civil aircraft may be provided to show that it is travelling in lane 100, and a terrain clearance warning may be given. Fig. 1 shows the interrogator (ground) apparatus, Fig. 2, shows the responder (aircraft) apparatus and Fig. 3 shows the pulses &c. at designated points therein. Initial pulse B1 radiated on frequency f 1  causes an aircraft on the instantaneous bearing to respond via omni-directional aerial 61 with pulses G1, G2 on frequency f 2 , the pulse spacing t h  representing the aircraft height; these pulses as received at the interrogator, H1, H2, are fed to range gate 18 and height gate 30. Cams 22, 23, driven synchronously with aerial 14, adjust delay units 20, 21 to produce pulses J1, J2 corresponding to range delays t 1 , t 2  defining the air lane; range gate K1 is thus formed. Delay t h  is such that it is always greater than the greatest value of delay t 2  to ensure that pulse H 2  cannot pass through gate 18. If a pulse L1 emerges from the gate (showing that the aircraft is above the defined area), further selection is carried out to determine whether it is also within chosen height limits: pulse L1 is delayed by time t 3  to give pulse M1, t 3  defining the lower height limit of the air lane, and a further delay t 4  is imposed to produce pulse M2. Delay t 3 +t 4  characterizes the upper limit of the height zone, and, if the latter is to vary with azimuth, delays t 3 , t 4  are controlled additionally by synchronous cams 26, 27, see also Fig. 6 (not shown). Height gate 30 then determines whether pulse H2 falls within gate pulse N1 and, if so, a pulse P1 is produced to cause the production of an additional transmitted pulse B2, delayed by time t a  from pulse B1. The output of gate 30 is interrupted by cam-operated switch 31 when the aerial is not directed to the zone defined by sorting device 16. At the aircraft Fig. 2 received pulses C1, C2 are delayed in unit 72 by time t a  and coincidence between pulses C1 and D1 triggers warning device 74. The interrogator may include codes B2, B3... corresponding to as many air lanes &c. as required and the aircraft receiver may include a plurality of units 71 incorporating corresponding values of fixed delays. The interrogator may be on a ship. If two or more responding aircraft are on the same azimuth, arrangements are included whereby interrogation coding is suppressed. Specifications 650,451 and 654,302 are referred to.