Patent GB-697631-A (GB)
Title: Indicator arrangement for radar system
IPC: G01S7/14
Filed: 1950-12-21
Abstract: 697,631. Radiolocation; valve gating circuits. BENDIX AVIATION CORPORATION. Dec. 21, 1950 [Jan. 13, 1950], No. 31171/50. Classes 40 (vi) and 40 (vii). In a pulse radar system for the ground-controlled approach of aircraft during landing and comprising two aerial systems which scan in azimuth and elevation and apply received echo signals to corresponding azimuth and elevation cathoderay display units respectively, means are provided for controlling the presentation of range-markers on each cathoderay tube in accordance with the angular position of the aerial system corresponding to the other cathode-ray tube in a direction perpendicular to its scanning motion. Thus in one embodiment the range-markers on the azimuth tube are rendered visible only on that portion of the display covered in azimuth by the elevationscanning aerial system. The range-markers on the elevation tube are similarly controlled in accordance with the elevational position of the beam of the azimuth-scanning aerial. In an alternative arrangement, the range-markers are normally visible and are blanked over that portion of the display corresponding to the angular position of the beam of the aerial corresponding to the other tube. General description of system. The apparatus comprises two separate transmitting and receiving systems controlled from a common synchronizing circuit, the elevation-scanning system being shown on the left-hand side of Fig. 1 and the azimuth-scanning being shown by corresponding apparatus on the right-hand side of the figure. The elevation and azimuth aerial systems 10, 10<SP>1</SP> have horizontal and vertical fan-shaped directivity patterns respectively and each comprises a linear array of dipoles fed from a variable-width wave-guide mounted within a cylindrical parabolic reflector. A common scanning motor 17 varies the widths of the waveguides in a periodic fashion to effect the scanning motions of the two aerial beams. The orientation of the aerial beams in a direction perpendicular to their scanning motions is controlled by drive circuits 59, 59<SP>1</SP> controlling the angular positions of the reflectors associated with aerials 10, 10<SP>1</SP> about vertical and horizontal axes respectively. The drive circuit 591 for the azimuth aerial 10<SP>1</SP> comprises an electric motor which is actuated in one direction or the other by a switch 62<SP>1</SP> operated by pedals 601, 611 associated with the elevation display tube 25. A similar drive motor and associated equipment is provided for the elevation aerial 10. Considering the elevation-scanning system, pulses from a synchronizer 21 are applied to transmitter 19 whence they are radiated from aerial 10. Received signals are applied, via a T.-R. switch, to receiver 20 and thence to video amplifier 23 and the control grid of cathoderay tube 25. Pulses are also applied from synchronizer 21 to a gate-pulse generator 39 which generates gating pulses having sufficient duration to encompass the intervals during which echo signals are displayed upon the cathode-ray tube. Pulses from the gate generator 39 are applied to vertical and horizontal sweep generators 40, 41 which generate sawtooth waveforms for application to the deflection coils of the cathode-ray tube. The amplitude of the saw-tooth waveform from vertical sweep generator 40 is also controlled in accordance with the elevation of the beam of aerial 10 by means of a variable condenser 55 controlled from the scanning motor 17 and arranged in parallel with one component of a capacitative potential divider 51; the potential divider thus supplies a potential corresponding to the elevation of the aerial beam to the generator 40. Additional voltages are applied to the cathode-ray tube to displace the origin of the display from the centre of the screen; the display consequently takes the form shown, range being measured horizontally and elevation angularly about the origin point. A cursor 33 is provided which may be moved to indicate any desired direction on the display. The display in the case of the azimuth tube is similarly produced; however, in this display range is measured vertically, as shown, and azimuth is measured angularly about the origin point 35. Gate pulses from generator 39 are also applied to a range-marker generator 44 which generates pulses for application together with the output of video amplifier 23 to the grid of the cathoderay tube 25. A further circuit 71 to which voltages representative of the positions in elevation of both aerials 10 and 10<SP>1</SP> are applied controls the operation of range-marker generator 44 so that pulses are only delivered thereby when the elevations of the two aerial beams do not differ from one another by more than a predetermined amount. Thus range-markers 70 appear only over that portion of the display corresponding to the elevational coverage of aerial 10. Aerial scanning arrangements.-Fig. 3 shows the variable-width wave guide which comprises two relatively sliding sections which are moved laterally with respect to one another by means of a mechanically-driven push-rod 12. The variable condenser 55, Figs. 1 and 3, comprises two vanes, one of which is fixed and the other of which moves in accordance with the motion of the push-rod 12. Blanking of marker pulses.-The signals applied to the circuit 71, Fig. 1, comprise the output 50, Fig. 5, from the potential divider 51 and the output 75 of gate generator 39 together with a voltage derived from a D.C. energized potentiometer 941 forming part of the azimuthaerial drive circuit 59<SP>1</SP>, this latter voltage being indicative of the elevation of the azimuth aerial 10<SP>1</SP>. The circuit 71 is shown in greater detail in Fig. 4, the previously mentioned signals being applied as shown to the grid of a valve 90 which cuts off at - 4 volts and saturates at 0 volts. Consequently only those pulses 75 occurring between the broken lines indicated in Fig. 6, which shows the composite waveform applied to the grid of the valve 90, are passed by that valve to cut-off the normally conducting valve 91. Cessation of current in the valve 91 causes the potential to rise at the grid of valve 85 which is the final stage of the range-marker pulse generator 44 and consequently allows pulses to be passed by this valve to the control grid of the elevation tube 25. In an alternative arrangement, Fig. 8 (not shown) wherein the range-markers are blanked over the portion of the display corresponding to the elevation of the azimuth beam, the signal at the cathode of valve 90 is applied to valve 91 which is normally cut-off so that the valve 91 is rendered conducting by pulses 75 occurring within the range - 4 to 0 volts, thereby cutting off valve 85 and preventing the application of marker pulses to the cathode-ray tube 25 within this range.