Patent GB-1340582-A (GB)
Title: Airport surveillance radars
IPC: G01S13/44
Filed: 1971-09-08
Abstract: 1340582 Pulse radar INTERNATIONAL STANDARD ELECTRIC CORP 8 Sept 1971 [10 Sept 1970] 41834/71 Heading H4D An area surveillance system, e.g. for a runway (Fig. 1, not shown) comprises a monopulse radar surveying regions D0, D1 &c. to D<SP>1</SP>0 (Fig. 1) and providing alarm signals for numerous high accident risk situations. A monopulse radar transmitter and receiver, Fig. 2, provides difference and sum signals, D, S<SP>1</SP>, from a target, at the outputs of respective phase discriminators 16, 19, which are applied to the processor of Fig. 3. The signals are passed to filters F1 and F2. For each surveyed region there are two range selectors processing difference and sum signals, e.g. DS1, SS1 for region D1 (Fig. 1). A range gate generator 22 provides various signals (Fig. 7, not shown) and activates each selector pair in sequence. The outputs from the selectors of each particular pair are passed to a corresponding quotient computer, e.g. Q1 where the ratio D/S<SP>1</SP> is obtained. The resulting signals, representing the deviation of the target from the aerial axis, are then passed to circuit 23. Each region has a particular threshold circuit which decides whether the deviation represents a target within the surveyed area. If so, a corresponding signal OD1 to OD11 is generated together with the corresponding sum signal, now indicated as OS1 to OS11. The sum signal S is also passed to filter F3 and range selector pairs PSA1, PSR1 and PSA2, PSR2. The selectors of a particular pair select adjacent range intervals and are controlled by corresponding range tracking circuit P1 or P2. The quotient of the outputs from a particular pair is obtained in a quotient computer PQ1 or PQ2 and the resulting signal OP1 or OP2 passed to P1 or P2. The quotient represents the position of the echo signal with respect to the centre of the total range interval of the selectors. The corresponding range tracking circuit provides a feedback signal so that the range selectors follow the tracked target, keeping the echo signal S<SP>1</SP> at the middle of the total selected range interval. The processor of Fig. 3 is thus capable of tracking two independent targets. A timing circuit E is fed with signals from P1, P2 and determine if the tracked targets are too close. If so, a signal E m  is generated. P1, P2 also feed computers C1, C2 which determine if the targets are decelerating, accelerating, stopped, taking off or landing. The corresponding signals are a1-, a2-, a1+, a2+, U1, U2, S1, S2 and S1 S2. The various signals are fed, along with the signals from E22, and E23 into alarm circuit 24. A signal S is also supplied, the signal indicating the direction of utilization of the runway. Logic circuits (Figs. 5, 6, not shown) determine when the tracking circuits begin and terminate the tracking process. For example, when a target is detected in regions D1 or D3, the range selectors PSA1, PRS1 are moved to the corresponding range. If detected in D9 or D11 then the selectors are moved after a time interval R to allow the selectors PSA2, PSR2 to lock on first. The tracking loop is only closed on to the target when further conditions are met, e.g. only if there is no signal E m . The loop is opened when the target is at rest, signal V1, or if the tracked target goes beyond the surveyed area, in the case of the first tracking loop, indicated by the coincidence of signals DFP1 or DFP2 from generator 22 and tracking signal DP1. The alarm circuit 24 performs numerous logic operations on the signals and light red lamps corresponding to various undesirable occurrences, examples of which are given in a Table 1 in the description. One of several green lamps is lit when a target is indicated in the corresponding region. If there are no moving targets in the surveyed area then none of the lamps are lit. An arrow, controlled by signal S, is lit on the display panel, and indicates the runway utilization direction. The signals provided by 24 may also be used to control signals on a P.P.I.