Patent GB-1267093-A (GB)
IPC: G01S13/937
Filed: 1969-05-28
Abstract: 1,267,093. Ariticollision radar. COMPAGNIE D'ETUDES ET DE REALISATIONS DE CYBERNETIQUE INDUSTRIELLE. 28 May, 1969 [18 April, 1968; 30 May, 1968], No. 27080/69. Heading H4D. Anticollision warning system for a ship comprises a radar T x 1 and R x 2 connected to antenna 3 (Fig. 1); received data being displayed on CRO 5 of indicator 4; a synchronizer 6 controlling the transmission and the display scan. A five-way bearing and distance tracking facility 7 receives signals from the R x , the synchronizer, and antenna position repeater 8, selects echoes, and superimposes specific signals thereof on the totality of the received echoes. A computer 9 receiving bearing and distance signals separately calculates the shortest distance of approach of the fitted ship to each target designated by a selected echo, and the instants of time at which this occurs, the results being displayed through selector 11 on digital tubes 10; an audible and visual warning 12, 13 being given for dangerous approach to one or more targets. The tracking system 7 (Fig. 2) comprises a common section 15 and five identical sections 16 each accommodating a selected target response echo; the receiver signals traversing a clutter filter 20 to section 15 and indicator 4 and also over line 22 to the sections 16. The antenna operates digital bearing encoder 8 connected to computer 9 and to the sections 16. Section 15 receives synchronizer signals at the input of distance finder 25 and maximum distance comparator 26 limiting the maximum distance at which echoes are processed, and the synchronizer signals are also supplied to sections 16 with outputs of distance finder 25. Each section comprises a bearing comparator 30 energized from a bearing register 31 and the antenna digital encoder 8. The comparators respectively energize a bearing selector bi-stable 32, set from comparator 30 to signal AND gate 36, while a range comparator 33 energized from a range register 34 and the range finder 25 operates a distance selector monostable 35 of adjustable duration set from comparator 33 to signal AND gate 36; which also receives ouput from receiver 2. Its output operates totalizing counter 70 synchronized from 6. Digital computer 9 is connected to bearing register 31, distance register 38, registers 62, 66, counter 61 and totalizing counter 70 while receiving clock signals from 40, and supplies digital registers 42-45 and D/A converters 46-49 connected in indicator 4 to energize scanning windings of CRO 5. Registers 50, 51 of indicator 4 derive from ship's log 60 and its compass the cartesian co-ordinates of the speed of the fitted ship for insertion into the computer, and registers 52, 53 similarly derive the instantaneous co-ordinates of the position of the fitted ship for supply to the computer. Sliders of potentiometers 56, 57 are simultaneously operated by manual control 55 to derive analogue voltages of cartesian coordinates of a specific position on the display, which are converted at 58, 59 to digital signals for the computer. In operation, for one antenna rotation the polar co-ordinates # 0 , p of a selected echo are stored in the computer, and for the next rotation the tracking facility for a selected echo responds only to echoes of range zone p + #p and minimum bearing # 0  - ##; #p and ## being selected in dependence on the speed of the fitted ship and expected speeds of other ships, so that a selected echo is included in the distance and bearing sector 2#p and # 0  - ## during succeeding antenna revolutions. Values p - #p and # 0  - ## are calculated by the computer and fed to registers 31, 34. During each rotation, comparator 30 detects coincidence between antenna bearing 0 from encoder 8 and bearing # 0  - # 0  in register 31 to indicate alignment on the echo, selected for tracking. Comparator 30 then sets bi-stable 32 to enable AND gate 36 to allow the selected echo to pass to counters 61, 65. Comparator 33 detects coincidence between distance p from counter 25 and value p - #p in register 34, and sets monostable 35 to enable the AND gate for the time of scanning of distance 2#p, so that a selected echo filtered from clutter at 20 may operate AND gate 36, and the first response operates counter 61 and register 62 to pass a signal S# 0  to computer 9; marking the initial bearing value # 0 . Subsequent echoes operate counter 61 so long as they appear in the range selector, and when there is no further echo response, the count is fed into the computer 64, and counter 65 registers the number of interrogations without response. At a count of 3 register 66 resets the bearing selector bi-stable 32 and marks # F  + # into the computer; # F  being the true bearing of the end of the echo and # the angle of antenna rotation during 3 consecutive sweeps without response. Then the computer determines the mean bearing # 0  + # F /2; # 0  being retained to open the bearing window at # 0  - ## during the next antenna revolution. Simultaneously, when gate 36 is enabled to pass a signal pulse, counter 70 started by the preceding signal is arrested, and at each radial sweep it registers the echo distance and totals the successive valves to #<SP>n</SP>p, for introduction to the computer when no further echo is received after n interrogations. The mean distance of the target is computed as p m  = # 1 <SP>n</SP>p/n, and is applied to set the distance selector at p m  = #p, where #p is a preset distance subtracted from the last measured distances. The computer receives continuous course and speed data of the fitted ship, and consecutive co-ordinates of the selected target echoes. It is programmed to calculate therefrom the shortest distance of approach of the fitted ship to the target, and the time instant of its occurrence for display on digital tubes 10; the display being chosen from any of the five selected and tracked echoes. Values below a preset safety limit trigger alarms 12, 13. The programme also enables computation of cartesian positional coordinates signals of each target or of the fitted ship, which are displayed either as vectors originating at the target or at the fitted ship; such vectors being of fixed length and orientation for marking, or of length and orientation representing calculated target speed.  Registers 42 to 45 receive X, Y cartesian coordinates of the origin and vectorial increments #X, #Y from the computer, which are converted at 46 to 49 into analogue data energizing screen scan windings of the CRO. A mark representing the positional setting of potentiometers 56, 57 is also displayed, and initial echo selection is by operation of control 55 to set the mark into coincidence with the required echo; after which its co-ordinates X 0 , Y 0  are fed into the computer for conversion to bearing and range co-ordinates # 0 , p 0  and storage in section 16 as the initial value. The ship's log data entered into registers 50, 51 may be modified therein by values set up manually by contactors 60 denoting a new course and hypothetical speed. The display may show true speed vectors for the fitted ship and for the surrounding targets, with time marks superimposed on the vectors (Figs. 3, 4, not shown) or relative speed vectors of the targets referred to the fitted ship, assumed to be stationary (Figs. 5, 6, not shown). In a modification, counter 70 determines (but does not totalize) for each response within the scope of the distance selector a distance p, which is introduced to the computer to cause it to mark the associated value #; a sequence of these associated values enabling the future course of a target to be predicted. Bearing and distance may be processed in analogue form and and the speed vectors of targets may be displayed in succession, and that of the most dangerous target may be selected for display.