Patent GB-1009875-A (GB)
Title: Improvements in or relating to radar systems
IPC: G01S7/292
Filed: 1962-08-01
Abstract: 1,009,875. Pulse radar. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. Aug. 1, 1962 [Sept. 4, 1961], No. 29633/63. Heading H4D. A radar system having target detecting means and computing means for echo signal information, is provided with means for automatically varying the threshold adjustment of the target detecting means by controlled feedback derived from the computing means, the controlled feed-back being so chosen and arranged to ensure automatically that the number of signals detected by the target detecting means cannot exceed a predetermined value (per unit time) below that at which the computer means can be swamped. In Fig. 1 received signal information resulting from a pulse transmitted by apparatus 1 is split up into equidistant time intervals (e.g. 1000) corresponding to the radial resolution and compared with a predetermined threshold in unit 2; thus unit 2 passes on to unit 3 a sequence of " Ones " (strikes) and " Zeros." The unit 3 is a detector which stores the sequences for each range ring in as many positions as the average number of strikes per target (e.g. 20). After each transmitted pulse the detector samples the count of each range ring, and if the count exceeds a predetermined minimum passes on a pulse to the coding stage 4 which delivers the co-ordinate values (polar or cartesian) of the presumed target location to the digital computer 5. The computer 5 tracks targets, by previously calculated anticipated zones in which future echoes must appear; recognises new targets; recognises false echoes; and confirms absent (missed) echoes during tracking. To prevent overloading the computer with too much information there is a feed-back from the computer to the thresholds of units 2 and 3. A control unit 6 may be provided to deliver threshold adjusting pulses in accordance with a deviation control signal derived from the computer. The functions of unit 6 can be carried out by the computer itself, or alternatively the computer can deliver the thresholdvalve itself (instead of the adjustment deviation) to the digital-analogue converter 7 controlling unit 2 or to the detector 3. In one arrangement, Fig. 2, the computer periodically (e.g. after each aerial revolution), calculates the difference between the actual number of echoes and a standard number of echoes (the desired maximum) as a twelve digit binary number, and passes the eight most significant digits Œ#N to registers 8, 9 and 10. Register 8 receives the sign of the number, and registers 9 and 10 the three least significant and the five most significant digits respectively. Registers 9 and 10 are re-set to zero by timing pulses T from the computer passing through gates 12 and 14 which are closed by units 11 and 13 when the registers are at zero. Thus the numbers of timing pulses passing through gates 12 and 14 correspond to the numbers originally stored in registers 9 and 10 respectively. The output from gate 12 together with the sign from register 8 pass via lines A2 and A3 to detector unit 3 and adjust the number of strikes necessary to cause indication of a target; this number may be adjusted between minimum and maximum values, for example between 5 and 15 if the average number of strikes per target is 20. The output from gate 14 passes through gate 16 or 17, according to the sign stored in unit 8, to increase or decrease the number stored in counter 15. The digital value of counter 15 is fed to the digital-analogue converter 7 and is there converted into an analogue voltage which represents the adjusting value for the threshold or the threshold potential itself, which is used in unit 2 to determine whether or not a given signal is counted as a strike. Specification 1,003,390 is referred to.