Patent GB-691968-A (GB)
Title: Improvements in or relating to object locating systems
IPC: G01S1/02
Filed: 1949-11-11
Abstract: 691,968. Radiolocation. PHILCO COR. PORATION. Nov. 11, 1949 [Nov. 12, 1948], No. 28938/49. Class 40 (vii). Relates to pulse radar systems having a single directive aerial for transmission and reception which is rotated mechanically in azimuth. In such systems if the directive axis 6 of the aerial beam 1, Fig. 1, is directed towards a distant target T<SP>2</SP> during transmission then the beam will have moved through an angle # 1  after a time t to a position 4 when the echo is received and the aerial gain is reduced. The present invention comprises means for obviating this effect and in one embodiment, Figs. 4 and 4A, the normal pencil-beam pattern 11, Fig. 3, of the aerial is changed to a broader pattern 12 during transmission, the two patterns being displaced by the angle # 1 ; in another embodiment, Figs. 7 and 8, the transmission and reception patterns are of similar shape but the reception pattern is rotated relative to the transmission pattern at the same angular speed as, but in the opposite direction to, the aerial rotation during the time t and consequently the reception pattern remains fixed in space during the period t coincident with the direction of transmission, i.e. the resultant motion of the reception pattern comprises an intermittent rotation in discrete angular jumps. In both of the embodiments as described, the switching or relative movement of the directive patterns is effected by spark gaps operated by the transmitted energy but it is stated that mechanical means may be employed. In the first embodiment, Fig. 4, the transmission and reception patterns 12 and 11, Fig. 3, are produced sequentially by an aerial system comprising a dipole 53, director 55 and spark gap 54, all embedded in a cylindrical block of dielectric 52 backed by a paraboloidal reflector 51. During reception the spark gap is inactive and a pencil beam 11 results, but on transmission the spark gap ionizes and functions as a reflector which changes the shape of the beam to 12. In order to effect the reverse change rapidly, the spark gap should have a short deionization time, e.g. 1-5 Á sees., and the gas filling may comprise a mixture of hydrogen and water vapour. In the second embodiment, Figs. 7 and 8, the transmitter 96 and receiver 97 are coupled by a T.-R. switch 93 to a wave-guide 90 having two branches 99 and 100 terminating in superimposed horns 101, 103, Fig. 8, co-operating with a tilted paraboloidal reflector 81 the apertures of the horns being relatively displaced so that their respective directive patterns 4 and 1, Fig. 1, are relatively displaced by the angle # 1 . T.-R. and anti-T.-R. spark gap switches 104 and 102 are coupled to wave-guide branches 100 and 99, respectively, and the switches have a long deionization time so that on transmission horn 101 only is energized producing a transmission pattern 4 but immediately following the transmission, horn 101 will function as a receiver with progressively less efficiency and horn 103 will function as a receiver with progressively increasing efficiency in accordance with pattern 1, Fig. 1, so that the resultant reception pattern shifts from position 4 to 1 during the deionization time. The angular width of the reception pattern is preferably equal to the angular shift # 1 . Mechanical rotation of the aerial structure is effected by the turntable 85 driven by motor 89 via gearing 88. The Specification as open to inspection under Sect. 91 also describes a system in which transmission and reception patterns 12 and 11, Fig. 3, are produced by a single paraboloidal reflector fed by differently-shaped transmitting and receiving horns separately connected to the transmitter and receiver respectively. This subject-matter does not appear in the Specification as accepted.