Patent GB-1323051-A (GB)
Title: Target location system utilizing the doppler principle
IPC: G01S13/53
Filed: 1964-02-17
Abstract: 1323051 Radar TELEFUNKEN PATENTVERWERTUNGS GmbH 17 Feb 1964 [25 May 1963] 6445/64 Heading H4D  A method of obtaining target information by means of a position indicator working on the Doppler and echo principle, e.g. by means of a Doppler radar device, is characterized in that information is only evaluated and/or indicated about those targets which are within a distance range allocated to their particular relative velocity radially in relation to the position indicator. The method is described in connection with an anti-aircraft system combating lowflying aircraft and recognizes that there is a minimum reaction time necessary for the system to respond and that there is a maximum range for the system. Thus according to the method faster aircraft are indicated at a greater range than slower aircraft and no indication is given of aircraft which are too close for the anti-aircraft system to respond. Moreover, no indication is given of targets lying outside the maximum range of the anti-aircraft system, and the method may also be adapted so that stationary targets are not indicated. Thus the operator is not confused with irrelevant targets. Fig. 2 shows a CW radar employing the method of the invention and comprising a transmitting aerial 3 and receiving aerial 5 rigidly coupled and scanned by a motor 6, the angle data being supplied by lines 8a, 8b to the target velocity indicator 9<SP>1</SP>. The H.F. oscillator 1 is connected to the receiver 4 through a coherent frequency converter 15 having a constant frequency spacing relatively to the transmitting frequency to permit approaching targets to be distinquished from receding ones. The Doppler frequencies from receiver 4 are applied to filter banks 12, 12<SP>1</SP>, 13, 13<SP>1</SP>, 14 through an amplifier 11. Filter bank 12 is allocated to high speed approaching targets and filter bank 12<SP>1</SP> to high speed receding targets; filter 14 is allocated to fixed and very slow targets and filter banks 13, 13<SP>1</SP> are allocated to targets which reverse their direction to give an extra strong intensity signal and sound an alarm bell as described with reference to Fig. 9 (not shown). For each target velocity v there is a minimum detection distance R depending upon the reaction time of the anti-aircraft system, this distance also being related to the maximum range R 0  of the antiaircraft missle. The values of the individual filters 12a 1  ... 12f 4  corresponding to different target velocities are read-off from a graph (Fig. 3, not shown). In a pulse Doppler radar, Fig. 4, employing the method of the invention, the oscillations of generator 1<SP>1</SP> are keyed in the keying device 16 in synchronism with the output signals of the modulation signal generator 17 and are radiated from an aerial 3 through the transmitter 2. The receiver 4 connected to the receiving aerial 5 has its output connected to distance gate circuits 18a ... 18n selecting target information according to the target distances. The gate circuits are controlled by output signals of the generator 17 to which different time-lags are imparted by delay members 19a ... 19n according to the target distances. The filter banks 20a... 20n connected between the gate circuits 18a ... 18n and the indicator 9<SP>1</SP> contain filters for Doppler frequencies such that only targets at the minimum detection distance R corresponding to their speed v are indicated. In both Figs. 2 and 4 the individual Doppler frequency filters comprising the filter banks have band widths which follow one another in succession and increase substantially as the associated relative radial velocity with respect to the position indicator, decreases (Figs. 3, 5, not shown). On indicator 9<SP>1</SP>, Fig. 6 (not shown), which may be employed in Figs. 2 and 4 and shown in conjunction with Fig. 4, comprises rectifiers 21a ... 21n connected to the filter banks 20a ... 20n and supplying their outputs to the Wehnelt cylinder 23 of a cathode-ray indicator tube 24 when gate circuits 22a ... 22n are opened by control signals from a sawtooth generator 25. The signals from the generator 25 also pass to one of the inputs of multiplication stages 35, 36 to the other inputs of which the sine and cosine components of the angle data from the motor 6 are applied. The outputs from the stages 35, 36 pass to the deflection plates 37, 38 and appear on the screen 39. In the azimuth-velocity display on the screen 39, Fig. 8 (not shown), the centre 40 represents the site of the radar installation and the circle 44 represents the dividing line between approaching and receding targets. A fixed target is represented at 47, receding targets at 45, 46 and approaching targets at 41, 42, 43. Sonar or infra-red equipment may be used in certain applications of the method.