GB959217A - Improvements in or relating to secondary radar - Google Patents

Abstract

959,217. Pulse radar. A. C. COSSOR Ltd. Dec. 19, 1962 [Sept. 21, 1961], No. 33922/61. Heading H4D. Relates to a secondary radar system of the kind in which a target station in response to an interrogating signal transmitted thereto in a rotating beam, transmits a reply in the form of a signal having a " start " pulse, followed by a sequence of pulses in a code carrying information such as target station identity, height, heading and speed, and an " end " pulse, the start and end pulses being referred to as " frame pulses " and always having the same time separation T. In general, the number of responses in a given period will be large and thereby necessitate a data transmission link of wide bandwidth, e.g. exceeding 100 kc/s.; to avoid this, the present invention comprises (a) a first limiter 11, fed with the reply signals and giving a first predetermined pulse amplitude; (b) a circulating pulse store 20 to 25, fed from the first limiter, which store affords a circulation delay equal to the repetition period of the interrogating signals, adds each reply signal to those already stored and attenuates circulating pulses by a predetermined factor on each circulation; (c) means 45, 48, responsive to a circulating pulse, the amplitude of which has risen to a second predetermined value, for adding a " labelling " signal (applied to terminal 51), representing the bearing at which the beam begins to sweep over the target, to the resultant recirculating reply signal in the store; (d) means 24, limiting the amplitude of pulses circulating in the store to a third predetermined value; and (e) means 47, responsive to a circulating pulse, the amplitude of which has fallen from the third to a fourth predetermined value, giving a signal representing the bearing at which the beam ended its sweep over the target. Delay line 12 and AND gate 15 pass only frame pulses of correct spacing. A second store 2 is provided for a second target station. Gate 39, delay circuit 40 and multivibrator 41 are included to prevent maloperation if two targets each transmit reply signals so delayed with respect to each other that a frame pulse from one reply signal is delayed with respect to a frame pulse from the other reply signal by the interval T. The bearing " labelling " signal is in binary code form. A special identity pulse may follow the last frame pulse of a reply signal and if such pulse is spaced from a preceding pulse by the interval T the transfer of information to the store is adversely affected; gate 58, delay circuit 60 and a pulse generator 61 are therefore provided. Gates 33, 64 may incorporate a differential amplifier, Fig. 2 (not shown), or may comprise AND and NOT gates, Fig. 3 (not shown).