Patent GB-582482-A (GB)
Title: Improvements in or relating to the detection of objects by means of ultra-short electromagnetic waves
IPC: G01S17/89
Filed: 1941-09-11
Abstract: 582,482. Radiolocation. WALTON, G. W. Sept. 11, 1941, No. 11648. [Classes 39 (i) and 40 (v)] A system for the detection of objects and indication of their direction and distance by means of ultra-short electromagnetic waves comprises a transmitter for irradiating the objects and a receiver comprising a focusing system which focuses the received reflected waves in an optical manner to form a real invisible image and one or more devices electrically responsive to waves from at least two distinct portions of the invisible image. In the receiver shown in Fig. 5, a concave reflector 13 has a unit 14 fixed at its focus by arms 15. The reflector 13 is mounted on trunnions 16 turning in bearings in a fork 17, which has a vertical spindle 18 free to turn in a base 19. The unit 14 is shown in Fig. 6 and comprises a plaque having two electromagnetic horns 20, 21, the entrances of which are in the plane 22, in which an invisible image is focused by the reflector 13. Arranged in the outer ends of the horns 20, 21 are dipoles 25, 26 connected through amplifiers and rectifiers to a differential galvanometer 28, which gives zero indication when a detail under observation is on the axis of the reflector 13. Harmonic resonators may be used in each horn of a plaque, or the radiation detector described in Specification 560,982 may be placed in an enlarged end of each horn, providing the equivalent of rectifier and amplifiers. A plaque with four horns may be arranged to give two differential responses on separate galvanometers, one for elevation and one for azimuth. The differential responses may control servo-mechanisms for swinging the receiver in azimuth and elevation. The plaques and horns may be replaced by an array of dipoles. The whole of the invisible image focused on the surface 22 of the plaque 14 may be visibly indicated by the provision of a number of horns as shown in Fig. 10, each having a responsive device connected to an individual lamp 37 in a mosaic lamp screen, The lamps 37 may be neon lamps or incandescent filament lamps or each lamp may be a light control device through which passes light from a common source. Instead of separate lamps, a multiple lamp may be used, for instance a mosaic of cathodes with a common anode in an envelope with a neon filling, or a similar mosaic of fi'aments in one envelope. A receiver to obtain a visible image of higher definition is shown in Fig. 12. Concave mirrors 13, 39 focus radiation to form an invisible image in a plane 41, from which radiation passes through a central hole in the mirror 13 and is reflected by a polygon mirror 42 and focused by a lens 40 to form a second invisible image at the surface 22 of a plaque 14, which consists of a line of horns receiving radiation from contiguous areas of a strip of the invisible image focused on the surface 22. Each horn controls an individual lamp 37 in a line of lamps 38, an image of which is formed by a lens 44 on a screen 45 after reflection by a polygon mirror 46. The polygon mirrors 42, 46 have the same number of faces and are rotated at the same speed by motors 43, 47. A complete visible image of the invisible image at 41 is thus produced on the screen 45. Alternatively, the polygon mirror 42 may serve for forming both the invisible and visible images, the mirror 46 being dispensed with. The surface 22 is concave or slightly tilted so as to reflect the radiation on to another part of the polygon mirror 42 so as to form an invisible image at the surface 50 of a second plaque 49 which controls servomotors for swinging the receiver in elevation and azimuth. In a modification, the invisible image is formed on the surface 22 after double reflection from two polygon mirrors with their axes at right angles and rotating at different speeds. The transmitter may send out pulses for determining distances by the echo method, or the irradiation may be periodically subjected to momentary interruption. The oscillation from the generator is also supplied to a chronometric device which measures the time interval between the change of radiation at the transmitter and reception of that change by the receiver. A suitable chronometric device is the cathode-ray apparatus described in Specification 560,928. An optical chronometric device is shown in Fig. 17. A scale 69 is reflected by a polygon mirror 67 driven by a motor 68 and an image of the scale is focused by a lens 70 in a plane near a microscope 71. A spark-gap 72 is energized by the received impulses and the scale is read stroboscopically. Distance may be determined by means of two receivers mounted at a known distance apart so that they can be swung together in azimuth and elevation, while one or both receivers may be separately swung so as to vary the angle between their axes so that these axes intersect at the distant object. Fig. 19 shows a mounting for the receiver shown in Fig. 12. The concave reflector 13 has fixed to it a cover 88 transparent to the ultra-short waves and carrying the concave reflector 39 and a concave reflector 87 of the beam transmitter for irradiating distant objects, together with a dipole or other radiator. Fixed also to the reflector 13 is a container 89 in which is mounted the remainder of the receiver with the screen 45, Fig. 12, fixed at the end when the visible image part swings with the reflector 13. When this part does not so swing, the container 89 is of metal completely shielding the polygons and plaque and the visible image forming part is connected by a multi-lead cable. The unit shown in Fig. 19 swings on trunnions 16. The combined transmitter and receiver may be mounted to form the nose of an aeroplane. When the received radiation is sufficiently intense, direct transformation from invisible to visible images may be effected by the apparatus shown in Fig. 21. The invisible image is focused on a plaque of horns 96, each horn containing a spherical resonator 98. These resonators are connected by a common lead 99 and form cathodes of a discharge lamp containing neon at reduced pressure, the plaque 96 forming the anode. A, potential just below ignition potential is applied and a glow is produced at any resonator which is subjected to radiation, due to the additional oscillatory potential built up by resonance. In a modification, there is an additional ring anode and a fluorescent screen, the whole being sealed within an envelope containing gas at low pressure. In modifications, the resonators 98 are omitted and a separate plate or thermionic cathode is provided, the radiation acting directly on the electron discharge through the horns. Arrays of resonators may be used in place of plaques of electromagnetic horns, an array of dipole resonators being shown in Fig. 23. The resonators are oriented as shown so as to produce minimum coupling between adjacent resonators. The apparatus may be combined with the aerial torpedo control apparatus described in Specification 539,224, or with the remote control apparatus for the detonation of projectiles according to Specification 573,621. The invention may also be used as a bombsight for bombing through clouds. Instead of a generator and antenna a direct generator of waves may be used such as is described in Specification 560,982.