Patent GB-805293-A (GB)
Title: Improvements in or relating to radar simulation apparatus
Inventor: CUTLER ALBERT ERNEST
IPC: G01S7/40
Filed: 1955-02-18
Abstract: 805,293. Trainers for radar. COMMUNICATIONS PATENTS Ltd. Feb. 10, 1956 [Feb. 18, 1955], No. 4967/55. Class 40 (7). Radar training apparatus includes means for simulating the representation obtained on the radar display when the aerial is directed at various levels of a bank of cloud. In particular it is for training aircrew in the use of cloud and collision warning radar to find a safe passage through cumulo-nimbus clouds. Such clouds frequently have a relatively extensive base surmounted by peaks or " towers " rising to a considerable height and between which there are safe gaps through which an aircraft could pass. In the embodiment described the cloud is represented by a patch of varying opacity on a transparent plate. The shape of the patch is a plan of the base of the cloud and the opacity at any point is proportional to the vertical height of the cloud above the base at that point. The plate, indicated at 19, is supported in an appropriate position by transparent plate 15 under cathode-ray tube 12 on which is generated a scanning raster corresponding to the azimuthal components of the aerial scan. The tube 12 is mounted for movement according to the instantaneous position and heading of the craft in which the radar is mounted. Carried below the plate 15 is a lens 17 and photo-cell 18 given a movement corresponding to the tube positioning and developing signals in correspondence with the parts, if any, of the opaque area scanned. The output from the cell 18 (Fig. 6) is fed through amplifier 36 to bottom-cut limiter 40. The cutting level in the limiter is determined in accordance with information fed in to potentiometers 20, 21, 22 and 23 representing respectively aircraft height, angle of tilt of scanner, range of cloud from craft and height of cloud base. This information together with information about the supposed total height of the cloud formation and the spread of the radar beam added by potentiometers 30 and 31 is used in a self-adjusting system to get an output from potentiometer 38 which varies in accordance with the vertical positioning of the radar beam relative to the cloud as shown on the right-hand side of Fig. 8. Vb and Vd correspond respectively to the values at the top and bottom of the cloud. This output is used in limiter 40 to vary the cutting level so that if the aerial is directed at the lower part of the cloud the whole signal from cell 18 is passed whilst if it is directed at higher parts only the peak signals corresponding to the more opaque parts of the plate 19 are fed to brightening circuit 41 controlling the display on cathode-ray tube 57. Range sweep sawtooth generator 42 controls the beam movement in tubes 12 and 57. Its signal is also squared at 43 and 44 to give an output fed to brightening circuit 41 to simulate the reduction in signal strength according to the fourth power of range which would occur in an actual system. An arrangement similar to that shown in Fig. 4 can also be used to generate signals representing echoes from ground features. These signals may be derived from a second cell 45 and are gated at 49 to remove signals representing echoes from ranges less than those " seen " by the aerial beam. The gating pulses are derived from the range sweep, aircraft height and aerial angle information, fed in at potentiometers 46, 47 and 50. Ground return echoes at the height of the craft due to aerial spill may also be simulated and for this purpose height information derived from potentiometer 50 is compared in amplitude with the range sweep voltage in amplitude comparator 53 to give a trigger pulse applied to flip-flop circuit 55. A smaller voltage tapped off the full height voltage at 51 is applied to a second comparator 54 to generate a pulse switching the circuit 55 off again. Its output during the time it is on is fed to brightening circuit 41. An A.V.C. circuit 56 is included in the feed between the circuit 41 and the display to simulate the effect of A.V.C. in actual practice. Two or more cloud scanning devices may be used together or the cloud and ground scanning apparatus may be combined as described in Specification 805,294. The apparatus may also be set up to simulate the effect of rain clutter or a volume of jamming reflectors (window).