Patent GB-654628-A (GB)
Title: Improvements in or relating to scanning systems utilizing radio energy
IPC: G01S13/42
Filed: 1946-06-06
Abstract: 654,628. Automatic control systems. SPERRY GYROSCOPE CO., Inc. June 6, 1946, No. 17238. Convention date, Jan. 25, 1943. [Class 38 (iv)] [Also in Group XL (c)] A radar system for automatically tracking a moving object throughout a wide angle comprises a radar set connected by a switch to either of two directional combined transmitting and receiving aerials capable of being oriented respectively throughout two slightly overlapping sectors, means being provided responsive to the position of the aerial in use, i.e. the " active " aerial, for positioning the inactive aerial and for controlling the switch so that when the object being tracked moves from one of said sectors to the other the inactive aerial becomes active and vice-versa, the two aerials being maintained in complete alignment when the object is in the overlapping zone of the sectors and in partial alignment for other positions of the object. The invention is described as applied to an airborne pulse radar in which it is required to automatically track a target located in any direction, two scanners being mounted respectively on top of and below the fuselage so that they have unobstructed scans throughout complementary upper and lower hemispheres respectively. A target in the lower hemisphere is tracked automatically by the lower scanner and the inactive upper scanner is automatically maintained in alignment with the active scanner so that as the target moves into the upper hemisphere the upper scanner can take over the tracking without any discontinuity, switching means under the control of the upper scanner being provided for reversing the roles of active and inactive scanner. The angular position of the active scanner is fed to a computer of the type described in Specification 606,957, [Group XXI], for controlling guns mounted on the aircraft. As shown in Fig. 2, the upper and lower scanners 26 and 27 are of the type disclosed in Specification 635,821, [Group XL (c)]. The lower scanner 27 comprises a parabolic reflector 89 with a primary aerial element energized through the relay-controlled switch 29 by the transmitter 28, the aerial system being continuously rotated about a spin axis DD and inclined about a transverse nod axis to produce a conical scan. The spin axis is also orientable in azimuth and elevation under the control of servomotors 99 and 101 operating through trains of gears as described in the Specification referred to and a target in the lower hemisphere is automatically tracked by the scanner 27 as described in Specification 621,485, a modulation produced by the aerial scan being obtained in the receiver 32 and compared with reference voltages of spin frequency in the phase-sensitive demodulators 93 to give azimuth and elevation error voltages which are applied through amplifier 96 and control-box 97 to the servomotors 99 and 101. Selsyn-type generators 131 and 132 are geared to the lower elevation and azimuth drive shafts 114, 105, the Selsyn rotors being energized from the A.C. source 161 through the relay 162 and the stator outputs being applied through switch 81, which is in the top position for automatic tracking, to the servomotors 83, 82 of the computer 33 and to the stators of the corresponding Selsyns 77 and 76 which are geared to the elevation and azimuth drive shafts 58 and 47 of the upper scanner 26. The rotors of the latter Selsyns are connected through relay 163 to the amplifier 164, the outputs from which are applied through amplifier 41 and control box 42 to the elevation and azimuth servomotors 54 and 44 of the upper scanner which is thus maintained in alignment with the lower scanner. Both scanners are orientable through 360 degrees in azimuth but only through a limited angular range of elevation, the two elevational ranges being arranged to overlap slightly so that the upper scanner is only aligned in elevation with the lower scanner when the latter is directed in the overlapping zone. When the target moves into the upper hemisphere, movement of the upper elevation drive-shaft 58 actuates the cam-operated switch 152 which reverses the positions of relays 150, 162 and 163 so that the transmitter 28 is then connected through switch 29 to the upper scanner, the rotors of Selsyns 76 and 77 being connected to the A.C. source 161 and the rotors of Selsyns 131, 132 being connected through amplifier 167 to the lower servomotors 99 and 101 so that the upper scanner actively tracks the target and the lower inactive scanner is aligned with the upper scanner. In a modification, Fig. 3 (not shown), the inactive lower scanner is automatically aligned with the active upper scanner by providing an annular split ring geared to the azimuth drive of the lower scanner. The angular position of a radial contact on the ring is adjusted in accordance with the azimuthal position of the upper scanner by means of Selsyns and a D.C. voltage source is connected to the contact, two spaced contacts engaging the ring being connected to the input of the lower azimuthal servomotor which accordingly orientates the lower scanner until the two segments of the ring are symmetrically disposed with respect to the two spaced contacts in which position the two scanners are aligned; a similar system is provided for elevation alignment. When the target passes to the lower hemisphere, the camoperated switch 152 actuates two relays which disconnect the D.C. voltage source from the radial arms of the rings associated with the lower scanner to connect it to the radial arms of the corresponding pair of rings geared to the elevation and azimuth drives of the upper scanner. Specification 610,704, [Group XL (c)], also is referred to.