Patent GB-1199008-A (GB)
Title: Improvements in or relating to Navigational Systems
IPC: G08G5/00
Filed: 1967-08-15
Abstract: 1,199,008. Secondary radar. HONEYWELL Inc. 15 Aug., 1967 [22 Aug., 1966], No. 37406/67. Heading H4D. Introduction. The Specification describes traffic supervisory systems, wherein means are provided for supervising the movement of one or more moving vehicles with respect to one or more fixed destinations by making available in each vehicle, azimuth, elevation, range and range rate information relating the vehicle to a particular destination as selected by the vehicle operator. Brief description. The system comprises a plurality of movable stations 21, Fig. 1, one in each vehicle using the system, and a plurality of fixed stations 20, one located at each destination. Each fixed station 20 comprises a directional transmitting antenna array 33, 34, 35, 36, means normally transmitting azimuth and elevation guidance signals from the directional array, an omnidirectional receiving antenna 45, an omnidirectional transmitting antenna 32, and transponder means for transmitting range signal from the latter antenna in response to a suitable interrogation signal received by the former. Esch movable station 21 includes an omnidirectional receiving and transmitting antenna 72, means for receiving the guidance transmissions and presenting them as cross-pointer indications 90, means for transmitting interrogation signals, and means for receiving transponder signals and presenting them as range 80 and range rate 81 indications. Each station includes an adjustable encoder/ decoder. A code identity is assigned to each fixed station, to which its encoder/decoder is adjusted, and any vehicle wishing to approach a particular fixed station must adjust its encoder/ decoder to the known code of the fixed station being sought. The fixed station is normally radiating guidance information carrying its own code, which information is ineffective in any movable station except those having their encoder/decoder adjusted to the code of the particular fixed station, and the interrogation signals received at the fixed stations are ineffective to elicit range responses unless they are properly coded. If desired, each fixed station may be made "secure" or normally silent (switches 91, 92). If this is done, no signal, either guidance or range, is transmitted from the secure station until it receives reliable interrogation from a movable station in its proper code. The movable station includes means for timing the interval between its transmission of an interrogation signal and its reception of the corresponding response signal, said interval representing the distance between the movable and fixed stations. The timing means comprises a long gate circuit and a short gate circuit, means for simultaneously opening both gate circuits after each transmission of an interrogation signal with a delay that increases at a predetermined rate, means for detecting when a response signal is acquired by the longer gate and thereupon decreasing said rate until said response signal is acquired by the shorter gate. Guidance signal transmission from fixed stations, Figs. 2, 7, 8.-A 280 p.p.s. pulse generator, controlled-on/off-by "securing" switch 91 feeds its output to pulse shaping trigger circuits 102, 107, 117, 121 to produce a train of pulses (a). Fig. 8, at the input of variable delay 141 and AND gate 124. AND gate 124 is enabled by a 35 Ás. pulse from trigger circuit 107 and a pulse in train (a) passes via gate 127, enabled together with gates 160, 175 and 220, 30 Ás. after the transmitter power has been switched on, to a modulator 26 whereby a 5 1 Mc/s. transmitter is modulated by said pulse, to produce the first of the group of four position coded transmitted guidance signal pulses (j). The second and third guidance signal pulses are produced by delaying the pulse train (a) by successive known amounts in variable delay means 141, 166. The delays imparted thereby having been set by controls 93, 94 in accordance with the desired coding of the station. The outputs of the two delay means are passed via AND gates, to respective inputs of modulator 26. The position of the fourth pulse varies depending on which of the four antennas 33/36 the pulse group is being radiated from. The third pulse output (c) of delay 166 is therefore fed to a delay 183 having four outputs, respectively giving pulses spaced 2À5 Ás., 3À5 Ás., 4À5 Ás. and 5À5 Ás. from the third pulse (see (d), Fig. 8). The four antenna radiate the pulse group in turn sequentially under the control of switching pulses (e), (f), (g), (h). These switching pulses also gate through the respective output of delay 183 to the modulator 26. The guidance signal transmittion (j) therefore comprises four pulses, the first three being position coded in dependence on the station's identity and the fourth being position coded in dependence on which of the four antennas (Up, Down Right or Left) is radiating. The four antennas produce overlapping beams having the elliptical crosssections shown in Fig. 7. Comparison of the amplitudes of the received fourth pulses at the mobile station gives its azimuth and elevation. Reception of guidance signal at mobile station, Fig. 3.-The pulse group is received at the mobile station and appears as (k), Fig. 8, at the output video amplifier 247. Variable delays 425 and 436 are respectively set the same as fixed station delays 141 and 166 such that when the pulse group is applied to delay 425, AND gate 427, receiving the output of the delay and the pulse group direct, gives one output (m), and when said output is applied to delay 436, AND gate 432, receiving the output of the delay and the pulse group direct, gives an output (O). Output (O) is fed to a delay 376 similar to delay 183, Fig. 2, and produces progressively delayed pulses (p), (q), (r), (s) at its four outputs U, R, D, L, respectively. A gate signal generator 353 synchronized with the pulse group repetition frequency and with the antenna switching by means to be related, produces U, R, D, L gating pulses (t), (u), (v) (w). The gating pulses act on a series of gates 371 receiving the outputs (p), (q), (r), (s), such that, at the output of OR gate 380 pulses (x) synchronous with the fourth pulses of the pulses groups appear. These pulses gate the fourth pulses through AND gate 385 to a 30 ns. gate 445. The thus narrowed pulses trigger a generator 446 to produce two pulses (a), (b), Fig. 13, of opposite polarity and 100 Ás. width. These pulses are fed to an early/late comparator 457. The output of a 280 p.p.s. generator 52, which is to be synchronized with generator 22 in the fixed station, feeds its output to the comparator and causes the output of the comparator to be as shown at (d), the pulse from the generator 52 causing the switch in the output from input pulse (b) to input pulse (a) If the generator 52 is synchronized the switch is midway and the output (e) of integrator 475 is unchanged at the end its integration of output (d). The change in the output of the integrator is used to adjust the generator 52. The dotted lines in (c), (d), (e), show a non-synchronism example. The output of generator 52 controls gate signal generator 353. The gated fourth pulses from gate 452 are fed via 502, 504 to gates 510, 511, 512, 513 which are gated by the outputs (t), (u), (v), (w) of generator 353 such that the fourth pulses from the Left and Right beams are fed to an azimuth substracting circuit and those from the Up and Down beams are fed to an elevation subtracting circuit. Each circuit comprises centre-tapped resistances and a respective pointer of a cross-pointer indicator 90, indicating the position of the mobile station relative to the axis of the four beams. Range measurement. (a) Mobile station, Figs. 4A, 4B, 17.-Variable delays 425, 436, used to decode the received guidance signal are also used to position the three pulses in the interrogation signal, the fourth pulse not being used. After recognition of the interrogation code at the fixed station, a single pulse response signal is transmitted thereby and received by the mobile station. A pulse appears at the output of the modulator 64 on line 23, synchronous with the transmission of the third pulse and this triggers a bi-stable circuit 764. A signal on line 767 resets circuit 764. The output of circuit 764 is integrated in ramp generator 761 to produce the short sawtooth voltages DMN, FOP, HQR... Fig. 17. The free-running output of the bi-stable circuit and ramp generator would be as shown by DEF .... The sawtooth voltages are applied to one input of a voltage comparator 756. An integrator 701 produces slow ramp voltages A, B, B1, C, which resets to zero when a reset circuit 751 detects a rise to 50 v., and which is applied to the second input of comparator 756. Equality of the two input ramp voltages causes the comparator to produce a signal which resets circuit 764 and is used as a "walking strobe" pulse. The walking strobe pulse on line 444 produces a narrow 30 ns. gate pulse from generator 445 and in turn this produces a wide 500 Ás. gate pulse from generator 773. The two gate pulses have simultaneous leading edges. The response pulse and the wide gate are applied to AND gate 781 and when the response is acquired by the wide gate, a positive polarity 100 Ás. pulse is produced by generator 784 and applied to one input of summer 797. Box car 504 is triggered by the output of generator 784 and produces a negative 100 Ás. pulse of amplitude determined by the signal on 503 which is applied to the second input of summer 797. The response pulse and the narrow gate are applied to an AND gate 452 and the output of the gate forms the control input to the box car on line 503. Thus with the response signal acquired only by the wide gate the amplitude of the box car output is zero, and the output of the summer 797 is maximum. Integrator 701 normally integrates a signal from negative source 274 via HI/LO circuit 704. The signal from generator 7