1,221,682. Radar. COMPAGNIE FRANCAISE THOMSON-HOUSTON-HOTCHKISS BRANDT. 21 Feb., 1968 [22 Feb., 1967], No. 8513/68. Heading H4D. Specification describes a pulsed radar using automatic tracking in range and azimuth after manual aquisition of the target, the tracking in range using digital techniques and the tracking in azimuth using analogue techniques. The antenna system and azimth tracking system is shown in Fig. 1 and comprises a continuously rotating search antenna 1 feeding its echo output to a doppler receiver whereby an M.T.I., P.P.I. display is produced, Fig. 2, showing a target 19. The position of antenna 1 is detected by a synchro transmitter/receiver arrangement, 2, 3 fed with the 400 c/s. reference signal R. The rotor of receiver 3 is coupled to a track antenna 13 such that the position of the null in the output signal S 1 of the rotor indicates the track antenna's position. The shaft 11 coupling the track antenna 13 and synchro receiver rotor, also controls a resolver 14 which thereby produces signals producing an alidade 16 on the P.P.I. indiacting the track antenna direction. Output S 1 is detected at 4 and the envelope S 2 used at 5 to produce a pulse a of width T, indicating the azimuthed area being tracked. Tracking antenna 13 is rotated by hand until alidade 16 intercepts target 19. The echo V from the target, of width t is now within pulse a, whereby an AND gate 6 is enabled and lets through the crossover region envelope S 2 through gate 7. If the alidade is exactly positioned then the gated signal S 3 comprises equal positive and negative parts and an integrating circuit 8 gives a null output, whereby a servomotor 10 fed thereby, does not realign the tracking antenna 13. Lack of exact positioning will however give unequal positive and negative parts, a none zero integration output and a restoring or tracking movement of the antenna 13. Azimuth analogue tracking after manual aquisition is thus obtained. In the range digital tracking system, Fig. 3, an observer seeing that the target 19 is for example in the third range zone (not second as shown), adjusts a switchable variable potential means 36 so that a voltage Va arises from resistor 363 and has a valve Va3 indicative of said third range zone. The doppler radar has n range channels, one for each range zone and producing an echo pulse (when present) on inputs V 1 to Vn. In the present example, an input will appear on input V 3 only at the instant search antenna 1 sweeps through it. Each input except V 1 (the farthest range zone), controls a bistable circuit 232/23n, producing a 1 signal at its X 2 /Xn output when it is sot (S) by a 0 output of a NAND gate 222/22n. The said X output is fed to series of digital/analogue converting weighting resistors d 1 /dn whereby an analogue voltage D, representing the range zone being searched, appears at the output of OR gate 24. This voltage is fed to the P.P.I. display to control bright-up spot 17, to be aligned on target 19 and also to one input of comparator 28, having the voltage Va3 at its other input. Thus if the second range zone is being searched, bi-stable 232 is set and X 2 = 1, such that analogue voltage D 2 is fed to 28. D2 # Va<SP>2</SP> whereby a comparator error signal F = 1 is produced. This is fed to an AND gate 30, together with a signal B = 1 indicating that range aquisition has not been attained, whereby gate 30 is enabled. This causes, via OR gate 32, a pulse generator 29 to issue a series of pulses H which are fed to the inputs of all the NAND gates 222/22n and also to OR gate 36, the output (A + H) of which is also fed to all the inputs of the NAND gates. Since V2 = 0 then the output of invertor 212 is 1, therefore the input to NAND gate 223, viz. X 2 .#V 2 .H.( A + H ) is 1, whereby its output is 0, whereby bi-stable 233 is set, such that X 3 = 1, #X 3 = 0 and bi-stable 232 is reset. The 1 input to resistors d 1 /dn changes from X 2 to X 3 such that a correct output D 3 appears therefrom. Spot 17 covers target 19, error F = 0 and AND gate 253 is enabled to pass the echo at input V 3 (when it appears) to OR gate 26 and output V. F being zero, gate 30 is disabled and pulses H stopped. Range aquisition is now achieved, such that B = 0 and B = 1. The latter state sets bistable 33 via NAND gate 34 whereby pulse generator 29 is restarted. The target is tracked with each H pulse. If the target moves towards the radar, F = 1. AND gate 35 is now however enabled (a.B. = 1) such that A = 1, and the next range zone is enabled and searched such that successive bi-stables 232/23n. are set, until F = 0 once more. When the target has moved up to the radar, all the bi-stables are reset, such that #X 2 , #X 3 . . . #X n = 1 X 1 and the system is prepared for the target to reappear in the furthest range zone, or to recommence the range zone search.