1,052,932. Radar simulation. CURTISS-WRIGHT CORPORATION. July 19, 1963 [July 23, 1962], No. 28689/63. Heading H4D. Means are provided in radar simulation apparatus whereby the variation of the vertical width of the radar beam can be simulated. Said means basically comprises generating means producing signals representing respectively the instantaneous detecting range of a simulated radar beam, the simulated antenna tilt angle, and radar altitude with reference to the simulated portion of terrain under instant observation, further generating means producing gated video signals representing characteristics of said terrain portion, an indication responsive to said gated video signals, function generating means responsive to the range signals and adjustable according to the simulated antenna tilt angle signals for producing function signals representing tangent functions of the tilt angle and simulated maximum vertical beam width, and occasioning and attenuating means responsive to the function signals and adjustable to produce two function signals for representing the variable vertical beam width, said two function signals controlling the gated video signals according to the variable vertical beam width. The arrangement to be simulated is shown in Fig. 3 (not shown), and comprises a radar antenna at a height h above mean sea level, over terrain having height e. The antenna radiates a beam at an angle # below the horizontal, and having an apparent variable width of 2# with a maximum width of 8 (e.g. 5 degrees). In one embodiment, Fig. 1, a range generator produces the sloping waveform signal shown, the instantaneous voltage x thereof representing the radar range after a time t measured from a reference time t 0 . The range generator output is fed to an amplifying arrangement 1 which produces a signal at one output which is proportional to the said generator output, and a signal at a second output which is the inverse of the first. The two signals are respectively represented as + x and - x, and are applied to either end of centre tapped non-linear potentiometer arrangements 4 and 5. The potentiometers have wipers 4<SP>1</SP> and 5<SP>1</SP> ganged together and controlled by a servo motor 6, in accordance with the beam inclination angle #. The zero positions for the wipers of potentiometers 4 and 5 are respectively below and above the centre earth tappings, by amounts respectively representative of + S/2 and - S/2. In this embodiment S is taken as 5 degrees. The non-linearity of the potentiometers is such that the wipers 41 and 5<SP>1</SP> respectively pick off voltages representing x tan (# + 2.5 degrees) and x tan (# - 2.5 degrees) These two voltages are fed, via isolating amplifiers 8 and 7 to either side of linear potentiometers 9 and 10 and respective proportioning resistances 12 and 13. The wipers 91 and 10<SP>1</SP> of the two potentiometers are controlled to move equal amounts in opposite directions by detail servo 11 under the control of the operator of the apparatus. The outputs picked off by the wipers 9<SP>1</SP> and 10<SP>1</SP> thus respectively represent x tan (# - #) and x tan (# + #). It is seen from Fig. 3 that these functions respectively represent the lower and upper limits of the depth below the antenna of objects detectable by the beam, thus at the maximum range or valueof x these limits are respectively represented by points D and C. The depth of the terrain below the antenna is given by (h - e) and a signal representing this quantity is produced, possible by apparatus described in Specification 1,007,966, for comparison with the signal representing x tan (# - #) and the signal representing x tan (# + #), in start comparator 18 and stop comparator 19 respectively, the two signals being fed to the comparators via a D.C. amplifying system include D.C. level restoration means 16 and 17. The comparators produce gating signals which are passed to control a video gate 20 which passes video information signals, produced, for example, by the apparatus described in the said Specification, to an indicator. the control being such that only video information arising from terrain having heights with the range of the beam, are displayed. In a second embodiment, Fig. 2 (not shown), the potentio - meters 4 and 5 are replaced by two electromagnetic tangent function resolvers and again control may be used by the student for controlling the detail servo and video amplifier for obtaining optimum detail and clarity.