Patent GB-657303-A (GB)
Title: Improvements in or relating to radar system
IPC: G01S17/933
Filed: 1948-02-27
Abstract: 657,303. Radiolocation; valve circuits. DEPARTMENT OF COMMERCE, DIRECTOR OF THE OFFICE OF TECHNICAL SERVICES OF. Feb. 27, 1948, No. 5937. Convention date, Aug. 11, 1944. [Classes 40 (vi) and 40 (vii)] [Also in Group XL (b)] A pulse radar system for the ground-controlled approach of aircraft, landing under conditions of poor visibility, comprises two aerial systems alternately connected to the radar receiver, one having a fan-shaped beam narrow in azimuth and scanning in azimuth and the other having a fan-shaped beam narrow in elevation and scanning in elevation, the receiver output being applied alternately and in synchronism with the aerial switching to the appropriate one of two cathode-ray-tube displays, from which the deviation of a guided craft from a desired landing path may be determined, whereby information regarding the corrections to be made to the course of the craft may be derived and transmitted either orally or in the form of automatically coded signals to the aircraft. In addition to the main or control radar system, the system comprises a long-range search radar system operating on a different frequency for the selection and identification of echo signals due to aircraft approaching the system before handing them over to the control system. Search radar. A synchronizing pulse from unit 50, Fig. 1, is applied to modulator 15 which controls the transmitters 12 and 62 of both systems. Exploring pulses are radiated from and echo signals are received by the continuously-rotating vertical-fan-beam aerial 10 which is coupled to the sine - potentiometer 34. Voltages from the potentiometer 34 are applied to unit 26 wherein are developed sweep voltages which are applied to cathode-ray tube 20 to provide a P.P.I. display. Echo signals from the receiver 13 are applied to the control grid and a brightening pulse is applied to the anode for the duration of each sweep. Fixed rangemarker pulses are also applied to the anode. An adjustable range-marker signal, which may comprise a pair of pulses adapted to straddle a selected echo signal, is applied to the cathode of tube 20. Control radar. Pulses from the modulator 15 are applied to transmitter 62 whence they are applied via T-junction 65 and wave-guide sections 66, 67 to the aerials 51 and 52. In order that aerials 51 and 52 shall radiate alternately, metallic plates 76 and 77 are mounted on a common shaft which is rotated by motor 78 and alternately pass through gaps in the feeders to the aerials thereby alternately blocking transmission from each. Echo signals are applied to receiver 80 whence they are applied via line 81 to unit 50 and thence via line 83 to the control grids of cathode-ray tubes 92, 93, 99 and 100. Cathode-ray tubes 92 and 93 display the elevation signals and tubes 99 and 100 display the azimuth signals, the electron beams of the tubes being suppressed alternately in synchronism with the aerial switching. Shutters 114 and 115 are rotated by motor 78 and alternately block the illumination of photo-electric cells 112, 113 by light source 111. The photo-cell outputs are applied to unit 50 whence a gain-control voltage is applied by line 105 to receiver 80 and electronbeam suppression voltages are applied via lines 140 ... 143 to the cathodes of cathode-ray tubes 93, 92, 99, 100. As shown, the azimuth aerial 52 is operative and illumination of azimuth photo-cell 113 is blocked. Unit 50 consequently delivers a positive blanking voltage to tubes 92 and 93 and a gain-control voltage which is dependent upon the potentiometer-controlled voltage on line 123 to receiver 80. When aerial 51 is operative the gaincontrol voltage is dependent upon the potentiometer-controlled voltage on line 122. Display arrangements.-The azimuth and elevation display arrangements each comprise two cathode-ray tubes, one providing a shortrange (2 miles) and the other a long-range (10 miles) display. Sweep and beam-intensifying voltages for the elevation and azimuth tubes are generated in units 170 and 171 respectively, which are triggered by pulses from unit 50 over line 36. Voltages on lines 156, 157 which vary in accordance with the angular positions of aerials 51 and 52 respectively, are applied to unit 50 and also to units 170, 171. The aerials beams are oscillated to-and-fro by means which is driven by motor 78 and is coupled to respective variable condensers which each form a part of a potentiometer network to which a constant amplitude oscillatory voltage is applied. The rectified outputs from the variable condensers are applied to lines 156, 157. In units 170 and 171 these outputs are used to control the deflections transverse to the range deflections, which are horizontal on the elevation displays and vertical on the azimuth displays. Rangemarker signals generated in unit 50 are applied to the cathode-ray tubes. Also, under the control of the voltages on lines 156 and 157 elevation and azimuth marker signals are developed in unit 50 and applied to the appro.- priate cathode-ray tubes. The elevation marker indicates the ground direction and the azimuth marker indicates a predetermined direction, such as a line parallel to the runway. The variable range-marker applied to the P.P.I. tube 20 is also injected into unit 50 and is from there applied to the cathodes of the tubes 92, 93, 99 and 100. Operation of system. Pedal controls 270, 275 are so set that elevation aerial 51 and azimuth aerial 52 are correctly positioned in azimuth and elevation, respectively, pedals 270 being connected to aerial 51 and pedals 275 being connected to aerial 52. Correct setting of the aerials is indicated by the coincidence of the cursors 271, 272 and 276, 277 with the selected echo indications. In guiding in azimuth, hand wheel 280 is rotated to align cursors 281, 282 with the selected echo, thereby also adjusting potentiometer 283 which consequently delivers a voltage indicative of deviation from the desired course. This voltage is applied to meter 350 and also to unit 285 which develops a distinctive signal indicative of the degree and sense of the deviation. This signal is applied to unit 318 whence it is transmitted to the aircraft. There it may be received by the pilot to whom it indicates the correction required or it may be used to control an auto-pilot. Cursors 321 and 322 are correspondingly set by hand wheel 320 for elevational guidance and the output from potentiometer 323 varied accordingly. This output is applied to meter 351 and also to unit 285, wherein means are provided so that, should the elevation become less than a predetermined safe minimum, warning lamp 333 glows. If automatic control of the craft is to be effected, controlling signals for elevation are also transmitted from unit 318. Communication may also be effected with the pilot by radio telephone, in which case the unit 285 may be dispensed with and instructions given orally, the necessary directions being determined from the readings of meters 350 and 351. Aerial systems. The azimuth and elevation aerial systems each comprise a wave-guide-fed dipole array, the dipoles being coupled directly into a long guide 200, Fig 5. The array is backed by a reflector 240 and an additional reflecting element 205 is attached to the guide as shown to concentrate the radiated energy to fall on the reflector 240. A member 210, Fig. 9, is mounted within the guide 200 and is so shaped that, together with a suitable shaped portion of the casing of the guide, it forms the wave-guide proper into which probes from the dipoles 206 project. Slots 213 are formed in the outer casing and in element 210, to act as halfwave chokes preventing the leakage of energy from the gaps in the guide. The element 210 is oscillated to-and-fro transversely so as to periodically vary the larger width-dimension of the guide and thus vary the phase-velocity of the waves transmitted therein. This movement is effected by an oscillatory movement of a draw-bar 222, Fig. 8, which is driven by motor 78, Fig. 1. The variable-width guide is coupled to a fixed guide 257 at the input to the aerial system by means of an element 250 pivoted about a point 251 and which is coupled by a lever 255 to the element 210. The element 250 is shaped similarly to element 210 so that the upper width-dimension (as shown in the Figure) of the guide formed thereby follows that of the variable-width guide while the lower dimension remains substantially constant. The dipoles, Fig. 7, are mounted approximately one half guide-wavelength apart and are coupled into the guide in alternately opposite phases. The dipoles each comprise a cylindrical body which has two slots 230 cut therein to dissociate electrically the two halves thereof. One element of the dipole is attached to one half of the cylinder while the other element is attached to the other half and also passes therethrough and coaxially down the cylinder to extend as a probe into the guide. In this aerial system, the dipoles may be replaced by wave-guide apertures. Also several parallel series of dipoles may be used. Valve circuits, Fig. 10. The unit 285, Fig. 1, is shown in greater detail in Fig. 10. The potential from the potentiometer 283 which indicates the deviation of the craft in azimuth from a desired course is applied in parallel to the grids of valves 289, 290. Valve 290 is D.C.-coupled to valve 302, whose cathode is directly connected to that of valve 289. The cathode potential of the valve pair accordingly rises whenever the potential from potentiometer 283 rises or falls above or below a mean level. This cathode potential is used to control the frequency of relaxation oscillator 306 of the gas-filled-valve type so that the frequency of the output thereof increases with deviation of the craft, in either direction, from the prescribed path. In order to determine the sense of the deviation, the output of potentiometer 283 is also applied to a switch valve 311 so that when the o