Patent GB-896374-A (GB)
Title: Improvements in or relating to radar apparatus
IPC: G01S13/42
Filed: 1958-05-23
Abstract: 896,374. Pulse radar. CONTRAVES A.G. May 23, 1958 [May 24, 1957], No. 16642/58. Class 40(7). Relates to a pulse radar with a conical scan aerial whose axis is automatically directed at a target by means of azimuth and elevation servos controlled by misalignment error signals produced by comparing a scanfrequency reference voltage with the scanfrequency amplitude modulation component of the target echoes as selected by an automatic range gate. According to the present invention the angular position relative to the aerial axis of a second object, e.g. a missile being directed at the target, is determined by selecting the echo pulses from the second object by a second automatic range gate and deriving from said selected pulses a second set of misalignment signals. The first and second sets of misalignment signals are then combined to produce further signals representing the deviation of the missile from the target direction, said further signals being used for automatic control of the missile. As shown in Fig. 1 the azimuth α and elevation # of the directional axis RA of the aerial system RR is controlled by servomotors SÁ and S#. The conical scan is produced by the 100 c/s. eccentric rotation of a dipole which is coupled via a duplexer DU to the pulsed transmitter MG and to a frequency changer M1 whose IF output is applied in parallel to IF amplifiers V1, V2, V3 coupled respectively to gates G1, G2 and G3. The gate G1 is opened to pass the target echoes by a gating pulse i # , Fig. 2c, produced in a circuit D2 which is triggered by a pulse i v , Fig. 2b, produced by applying an output i s , Fig. 2a, from the transmitter trigger pulse generator PG to a variable delay network Dl controlled by a servomotor Sr1. The gating pulse i f  is initially made coincident with the differentiated target echo pulse output i e <SP>1</SP> Fig. 2e, from the gate Gl by applying to the servomotor Sr1 a voltage #u<SP>1</SP> from a manual control unit DW. The coincidence is then maintained automatically by applying the differentiated echo pulse i e <SP>1</SP> to an amplitude comparator D4 together with a waveform i m , Fig. 2d, derived  in a generator D3 from the gating pulse i f  and the transmitter pulse is to give a DC error signal #u1 dependent in magnitude and polarity on any deviation of the echo pulse i e <SP>1</SP> from the mid point of the sloping portion of the waveform i m , said error voltage being applied to the servomotor Sr1 when the switch Sl is in the position shown. A further output i e <SP>1</SP> from the gate G1 is applied 1) to a detector DT giving a 100 c/s. scan modulation component Y1, Fig. 3b (not shown), if the aerial axis RA is not aligned with the target direction ZA, said modulation component being applied in phase quadrature to two phase discriminators PDx, PD#, and a 100 c/s. scan reference voltage Y2, Fig. 3c (not shown), from a generator so synchronized with the conical scan being applied in parallel to the discriminators PDα, PD# to give azimuth and elevation DC error voltages #α1 and ##1  which are converted to corresponding 400 c/s. error voltages #x1, ##1 in modulators MDx and MD# and applied to the azimuth and elevation servomotors Sα, S# to eliminate the misalignment errors. In accordance with the present invention the missile echo is selected by the gate G2 which is controlled in the same manner as the gate G1 by corresponding components D1<SP>1</SP>. .D4<SP>1</SP>, Sr2, the output i e <SP>2</SP> from the gate G2 being applied to corresponding phase discriminators PDα<SP>1</SP>, PD#<SP>1</SP> to produce DC and AC misalignment voltages ##α2, ###2 and #α2, ##2. The azimuthal and elevational deviations of the missile from the aerial axis RA are indicated on a cathode-ray tube SB of the corresponding horizontal and vertical displacement of the spot produced by applying the DC misalignment voltages ##α2 ###2 to the X and Y plates of the tube and AC signals ##α and ### proportional to the azimuthal and elevational deviations of the missile from the target direction ZA are produced by combining the target and missile AC misalignment signals. A further output II from the IF amplifier V1  is applied to a type A cathode-ray tube SA to display the ranges of all objects and a mechanical cursor C is automatically set to indicate the target or missile echo by means of a servomotor Sr controlled selectively by means of a switch Su by the input to the target or missile range servomotors Srl, Sr2. Voltages r1, r2 proportional to the target and missile ranges are produced by generators X controlled by the servomotors Sr1, Sr2. The third gate G3 may be used in a similar manner to determine the position of a second missile. Missile control. Fig. 4 shows the combination of a Fig. 1 type of radar VR with a beam riding missile control system LS of the type disclosed in Specifications 724,031 and 796,875 to effect a closed-loop control of the missile. As shown the missile control system LS comprises a pulsed conical scan guide beam produced in a similar manner to the radar beam, the direction LA of the guide beam being controlled by main and auxiliary azimuth servomotors Sα<SP>1</SP>, Sα<SP>11</SP> and elevation servomotors S#<SP>1</SP>, S#<SP>11</SP>, each pair of motors being connected to its respective drive shaft through a differential gear. The target misalignment signals #α1, ##1 are applied to the main servomotors Sα<SP>1</SP>, S#<SP>1</SP> to maintain the axis LA of the guide beam substantially parallel to the axis RA of the radar beam and the missiletarget misalignment signals ##α, ### are applied to the auxiliary servomotors Sα<SP>11</SP>, S#<SP>11</SP> so that the direction LA of the guide beam is varied automatically until the missile is in line with the target; this latter control is independent of errors in 1) the beam-riding control system and 2) the main servo control of the guide beam direction. Alternatively the missile-target misalignment signals may be transmitted directly to control the missile in a "command" type of guidance system; in this case a detonating signal is transmitted automatically when the difference between the target and missile ranges rl and r2 reduces to zero.