Patent GB-805294-A (GB)
Title: Improvements in or relating to radar simulation apparatus
Inventor: CUTLER ALBERT ERNEST
IPC: G01S7/40
Filed: 1955-02-18
Abstract: 805,294. Trainers for radar. COMMUNICATIONS PATENTS Ltd. Feb. 10, 1956 [Feb. 18, 1955], No. 4968/55. Class 40 (7). Radar training apparatus simulating forwardlooking aircraft radar includes superimposed charts at least one of which represents aerial objects such as clouds and at least another of which represents ground features. As shown, the chart 15 carries representations of clouds and the chart 16 representations of ground features. Mounted above the charts is a flying- spot light-scanning cathode-ray tube 8 orientated by motor 14 to represent the aircraft heading. The two charts are positioned by independent orthogonal lead screw drives so as to simulate the relative positions of craft and clouds and craft and ground, the origin of the scans on the tube 8 corresponding to the craft position. The chart 15 is made of red filter material with clear patches representing radar reflecting cloud while the chart 16 is of green filter material with clear patches for features on the ground-reflecting radar signals. As tube 8 is scanned in accordance with the output of time base generating circuits 10 light is directed to the charts and the light energy passing through them is concentrated by lens 28 on half-silvered mirror 29 which divides the energy and directs it into two different paths. The part of the energy reflected by the mirror 29 travels to red filter 33 behind which is photo-cell 34; the part transmitted by the mirror travels to green filter 30 behind which is situated photo-cell 31. Green light passing through all parts of chart 16 and filter 30 is cut off when red filter material of chart 15 is in its path. Thus the output of cell 31 consists of signals corresponding to the cloud indications on chart 15. Similarly the output of cell 33 consists of signals corresponding to the indications on chart 16. The output of cell 31 is fed through amplifier 31 to combining amplifier 43 before its application to the display tube 9. The amplified output of cell 34, is, however, first gated to remove signals from objects not within the supposed field of view of the radar before being applied to unit 43. As shown in Fig. 2, the minimum range from which ground signals should be received is HA cot (# + x), where # is the angle of depression of the radar beam and X is the semi-beam width. In the apparatus the supposed height is set in on potentiometer 37 and the angle (# + x) on suitably contoured potentiometer 38. The output from the latter is compared with the range sweep in comparator circuit 39 to produce a negative gate pulse applied to gate circuit 36 to remove the unwanted signals from cell 34. Time base generator 10 also feeds display tube 9 to produce a scan in synchronism with that on tube 8 and a portion of its output is squared at 45 and again at 46 to provide a control signal for amplifier 44 to simulate the effect of distance on the echo signals. By suitable adjustments to the circuits the features on the charts may be represented in colour on a clear background instead of vice-versa. Areas of graded density can also be used to represent, for example, the varying density of reflecting cloud. Instead of achieving a separation of signals derived from the two charts based on red and green coloured light the separation may be by different planes of polarization, the colour filters being replaced by polarization filters. The charts may be constructed from varying grades of polarizing material to simulate the variation of response between different materials. To simulate radar jamming (window) an additional chart or a modified cloud chart can be provided. Representations of one or more aircraft can also be provided on a further chart. Random noise signals may be added by means of a noise generator.