Patent GB-580975-A (GB)
Title: Apparatus for locating objects by means of radio waves
IPC: G01S13/42
Filed: 1940-11-08
Abstract: 580,975. Directive wireless signalling. SPERRY GYROSCOPE CO., Ltd., and NISBET, R. H. Nov. 8, 1940, No. 16260. [Class 40 (v)] A system for locating distant objects comprises an ultra-short-wave transmitter 1 energizing an antenna 4 placed along the focal line of a parabolic reflector 5 mounted for rotation about an axis 6. A receiving antenna 8, arranged in the focal line of a parabolic reflector 9 rotatable about an axis 10 in a plane at right angles to axis 6, is connected to a receiver 2, 15, 16, 17, the output of which is connected to the control grid 23 of a cathode-ray oscillograph 18. The oscillograph is supplied from a tapping 24 on a potentiometer 19, the tapping being adjusted so that the beam is suppressed in the absence of a signal on grid 23. Vertically deflecting electrodes 25 are supplied from a potentiometer 26 driven in synchronism with reflector 5, while horizontally deflecting electrodes 31 are supplied from a potentiometer 32 driven in synchronism with reflector 9. Thus the existence of an indication on the cathoderay tube depends on the existence of an object reflecting a wave, while the position of the indication depends on the co-ordinates of the reflectors 5, 9 and thus shows the position of the object. In order to give a fine indication, reflector 5 is rotated a large number of times per revolution of reflector 9. To compensate for the fact that the radiation patterns of the antennae have maxima in a direction at right angles to the antannµ, the gain of valves 15, 16 is altered in accordance with the positions of reflectors 9, 5 by means of potentiometers 361, 44 moved in synchronism with the reflectors, so as to render more uniform the signal applied to the oscillograph. During the non-useful parts of the travel of the reflectors 5, 9, the output of amplifier 17 is short-circuited by synchronously rotated arms 29, 35<1>, or valves 15, 16 are blocked by potentiometer arms engaging sectors 36x, 49. To avoid the high rotational speeds of reflector 5 an embodiment is described (Figs. 2-4, not shown) in which six antenna and reflector units are mounted for rotation on a spider, the radiation from the successive antennae being caused to emerge from a single aperture in a surrounding screen. The antennµ are energized in succession through a capacity commutator, or an electronic switch. This construction forms the subject-matter of Specification 580,977. The receiving antenna and reflector unit may be replaced by a horizontal antenna (Fig. 5, not shown) arranged at the focus of a parabolic reflector, together with which it is rotated about a vertical axis through the focus. This facilitates reception of a wave polarized in the same plane as the transmitted wave. In a further modification (Figs. 6-8, not shown), the transmitter comprises a pair of antenna and reflector units set at an angle and rotatable together so as to produce a pair of overlapping beams each having a characteristic modulation; the reflected wave being received by a similar unit. The reflected wave after rectification is passed to two channels which separate the components and to further circuits which finally produce two direct currents which are respectively proportional to the sum and difference of the reflected beams. These are passed to relay circuits which ensure that only when the difference is zero and the sum is substantial is a signal passed to the indicator. Instead of rotating antennµ, successively energized antennae giving rotating beams may be employed. The embodiment of Figs. 6-8 forms the subject-matter of Specification 580;978. Specifications 501,996 and 526,658 also are referred to.