934,057. Electric analog calculating. GENERAL ELECTRIC CO. Ltd. Sept. 27, 1961 [June 29, 1960], No. 22844/60. Class 37. [Also in Group XL (c)] Relates to an angular position control system for controlling the orientation of a beam reflected by an aerial member of an airborne radar in each of four operational phases during the location and following of a target. These phases are:- (a) A " 180 degree scanning " phase in which the radar beam scans a region 180 degrees wide in azimuth and 8 degrees wide in elevation. The elevation of the scanning pattern may be varied by the operation of manual controls so that a hemisphere may be explored, the orientation of the pattern being maintained independent of pitch and roll (but not heading) of the aircraft. The manual control also positions a marker on a radar, type C, display which shows in elevation and azimuth with respect to the centre of the scanning pattern any target within the region scanned. (b) A " 60 degree scanning " phase in which the beam scans a region 60 degrees wide in azimuth and 8 degrees wide in elevation centred upon a position in space corresponding to that of the marker in (a) above. The orientation of this pattern is maintained independent of roll, pitch, or heading, of the aircraft and the position of a further marker on the display may be controlled in this phase to select any displayed echo as the target. (c) An "intermediate-lock " phase in which the beam is brought into alignment with the direction corresponding to the setting of the marker in (b) above. (d) A " lock-follow " phase in which the beam is automatically maintained directed towards the selected target. General.-The aerial member is a plane reflector 5, Figs. 1 and 2 (of an aerial system of a type disclosed in Specification 884,313) on which a collimated beam is incident in a direction parallel to the longitudinal axis 10 of the aerial system to provide a reflected beam whose direction may be varied by rotation of the reflector about an axis 9, which is itself rotatable about a further axis 8. The collimated beam originates from a horn 3 at the focus of a paraboloidal reflector and the horn may be caused to nutate about the axis 10 to cause a corresponding conical movement of the beam. This nutation is only utilized in phases (c) and (d) above and the axis about which the beam rotates during it is, like the direction of the beam in the absence of nutation, governed by the angular position of the reflector about its axes of rotation 8 and 9 (this direction is hereinafter referred to, irrespective of operational phase, as the beam-direction). The angular displacement of the reflector about the axis 8 (#, say) and about the axis 9 (#, say) is due to two mechanical links actuated by a mechanical control unit 14 of the type disclosed, in Specification 905,440, in response to electric signals supplied to the unit overleads 18 and 19. These signals are supplied from an electrical control unit 17, to which the unit 14 feeds-back information concerning the beam-direction by means of shafts 21 and 22 which are rotated, respectively, through angles of # and 2#. Manual controls in the electrical control unit may be set to control either the direction of the beam scanning pattern or the "intermediate-lock" direction and signals relating to the selected target are 'fed to the unit from the radar receiver. From these signals, together with others representative of the aircraft altitude relative to the ground (supplied, over leads 23 to 25, from a master reference gyro unit) the electrical control unit computes the value of the signals which it supplies to the unit 14. Further feed-back signals for directing purposes during the " lockfollow " phase (as described with reference to Figs. 7 and 8 below) which are representative of the angular velocities of the reflector about the axes 8 and 9, are transmitted to the electrical control unit from two rate-gyros provided on a gyro platform 27 coupled to the unit 14 with the platform maintained perpendicular to the beam-direction. During the scanning phases (a) and (b) a pattern generator within the unit 17 provides cyclic signals to provide the necessary variations of demanded orientation of the beam-direction. Electrical control unit, Figs. 7 and 8.-In the electrical control unit signals are initially computed representative -of the beam-direction relative to axes defined with respect to the aircraft and the final control signals are obtained by resolving these signals with reference to axes at angles thereto in dependence on the directions dictated by scanning pattern requirements, marker settings, variations of roll, pitch, heading, and so on, the computation and resolutions being performed by synchro resolvers whose rotors are rotated through angles appropriate to these directions. Three mutually perpendicular axes pertaining to the aircraft, X 1 Y 1 Z 1 , are defined respectively in directions aft to forward, outwardly along the starboard wing and downwardly from the fuselage. A further set is defined relative to the beamdirection such that when the reflector 5 and horn 3 are in their control positions so that the beam-direction is along the axis 10, the beamdirection axes X 0 Y 0 Z 0 are respectively in the directions of X 1 Y 1 Z 1 . Then, irrespective of the direction of the beam, the beam-direction is always in the direction of the X 0 axis and so has direction cosines of 1, 0, 0, relative to the X 0 Y 0 Z 0 axes. Constant amplitude signals representative of these direction cosines are supplied from an A.C. source 58, Figs. 7 and 8, to the first of a chain of three synchro resolvers 52, 54, 56, the rotors of these being respectively displaced through angles -#, -2#, -# by the shafts 21 and 22 (to account for the beamdirection rotating through twice the angles of rotation of the reflector 5) so that the final synchro resolver 56 produces output signals dependent on the beam-direction relative to the aircraft axes X 1 Y 1 Z 1 , as disclosed in Specification 934,058. Signals over leads 23 and 24 from the master reference gyro unit actuate servos 63 and 64 in accordance with the roll angle R and pitch angle P, respectively, to control the rotors of two further resolver stages 62 and 68 so that the output of the latter stage represents the direction cosines of the X 0 axis relative to a set of axes X 2 Y 2 Z 2 stabilized with respect to roll and pitch variations. In the "180 degree scanning" phase this output is supplied directly to another resolver 82. The rotor of this is made to oscillate at a uniform rate through 180 degrees by a servo 83 energized by cyclic signals from a pattern generator 87. This also supplies a step waveform to another servo 88 at the end of each forward and backward rotation of the rotor of stage 82 to effect incremental rotations of the rotor of a further resolver stage 90. As a result the output of the stage 90 represents the direction cosines of the X 0 axis relative to a set of axes X 6 Y 6 Z 6 in which the X 6 axis is periodically sweeping through the required scanning pattern. The X 6 axis represents the demanded beam-direction during this phase and its elevation may also be varied by a manual control 78 which is coupled to a rotor stage 91 whose output signals in this operational phase are also fed to the servo 88. For the beam to follow the demanded direction X 6 , the direction cosines of the actual beam-direction X 0 relative to the axes X 6 Y 6 Z 6 should be 1, 0, 0 and if the latter two (i.e. the direction cosines relative to Y 6 and Z 6 , respectively) are not zero their values should represent error signals indicative of the departure of the actual beam-direction X 0 from that demanded, X 6 . It is stated, however, that for reasons of servo system stability these error signals cannot be supplied directly to the mechanical control unit 14 over leads 18 and 19 to effect the required rotation of the reflector 5 about its gimbal axes 8 and 9, and further correction is applied due to variations in roll of the aircraft. A source 57 supplies constant amplitude signals representative of the direction cosines 0, 1, 0, of the axis Y 0 relative to the axes X 0 Y 0 Z 0 to a chain of resolver stages 51 to 89, whose rotors are mechanically coupled to those in the X 0 resolving chain 52 to 90. The output of the stage 89 corresponds to the direction cosines of the Y 0 axis relative to the axes X 6 Y 6 Z 6 defined relative to the demanded beam direction, and this output is fed to a further resolver stage 95. This produces a signal representative of the direction cosine of the Y 0 axis relative to a further axis which is angularly displaced by an angle r from the axis Z 6 in the plane of the axes Y 6 and Z 6 . A servo 96 rotates the rotor of a resolver 95 (and that of a further resolver 102) to bring this direction cosine to zero and thence bring this further axis to a position in which it is perpendicular to the axis Y 0 in the plane of the axes Y 0 and Z 0 . This is stated to bring the rotor of the stage 102 to the correct position for the stage to resolve the signals from the resolver 90 into a suitable form for feeding via a servo 105 to the mechanical control-unit. Information from the resolver stage 68 as to the elevation of the X 0 axis (i.e. beam-direction) is fed to the display unit over leads 31. Manual operation of the elevation control 78 to vary the elevation of the scanning pattern also controls a further resolver 76 whose output is supplied to the display unit via leads 32 to form a marker on the display. The azimuth position of this marker may be controlled by varying an azimuth manual control 77 (which controls another resolver 74) and the marker is then positioned to form the axis of the " 60 degree scanning " phase. In the "60 degree" phase these two resolvers 74 and 76 are switched into operation, together with others to utilize head