Patent GB-881023-A (GB)
Title: Improvements in or relating to radar simulation apparatus
Inventor: CUTLER ALBERT ERNEST
IPC: G01S7/40
Filed: 1957-11-04
Abstract: 881,023. Trainers for radio navigation. COMMUNICATIONS PATENTS Ltd. Nov. 4, 1957, No. 34359/57. Addition to 805,293. Class 40(7). The parent Specification describes a radar training apparatus which, in one embodiment, comprises means for generating synthetic signals in accordance with the degree of transmission or reflection of light from a contour map representing the radar reflecting properties of an arrangement of objects (e.g. clouds), computing means to compute the assumed distance from a datum line of the portions of the objects assumed to be illuminated by the radar beam, means controlled in accordance with the computed distance for selecting from the synthetic signals those signals representative of the illuminated portions, and display means. The computing means produces an electrical quantity representative of the instantaneous height of the axis of the radar beam above the base of the cloud formation and the selecting means is controlled in accordance with this quantity. The means for introducing range data to the selecting means comprises an electro-mechanical device which is inherently slow-speed compared to the rate of range scan available at the display. The present invention overcomes this disadvantage and includes means to counteract the reduction in signal strength of the echo when the beam only partially impinges on an object. Considering the case of an aircraft approaching cumulo-nimbus cloud, Fig. 1, the aircraft P is assumed to be flying at a height Ha and to be directing a radar beam of semi-angle d towards the cloud, the axis of the beam having an instantaneous elevation E above the horizontal. The centre-line AB of one column of the cloud is at range R from the aircraft. There are three conditions of the beam; overlapping the cloud at the top (as shown), not overlapping the cloud, and overlapping the cloud at the base, and in each of these cases the echo intensity will be different and proportional to α, the height of the centre C of the illuminated part of the cloud. There will also be three factors #, the angular difference at P between the centre C and the point D where the beam axis cuts AB. Expressions for α and # in terms of Ha, Hb, Hc, E, d and R are given. Of these six parameters, range is determined with respect to the assumed range at any instant of a radar pulse by using the output of the range sawtooth generator, Fig. 2 (not shown). The remaining parameters are set as angular rotations of potentiometer shafts and the three pairs of expressions for α and # corresponding to the three beam conditions are obtained by means of summing amplifiers. These feed gate circuits controlled by further summing amplifiers, and the arrangement is such that the correct factors α and # for any given elevation and range are obtained. The signal representing α is further combined with other signals to obtain a signal representing the height of the radar beam axis, at the centre line of the cloud column, above the cloud base. This signal is then modified according to the height/density variation in the cloud, Fig. 3 (not shown). The resultant signal in turn modifies the synthetic signals which represent the radar pulses. A brightness amplifier follows, this being biased by a voltage derived from the range sawtooth generator and proportional to the fourth power of the assumed range to simulate the effect of range on echo intensity. Finally the signals are fed to the display.