Patent GB-577674-A (GB)
Title: Improvements in radiolocation systems
IPC: H01Q3/22
Filed: 1942-06-06
Abstract: 577,674. Radiolocation. HAZELTINE CORPORATION. June 6, 1942, No. 10654/43. Convention date, May 26, 1941. Divided out of 577,672. [Class 40 (v)] [Also in Group XXXVI] A system for locating objects by the reflection from them of wave signals radiated in a scanned beam comprises a number of signal radiators physically spaced in one dimension by predetermined wavelength values, means for supplying them with signals of cyclicallyvarying frequency through wave-delay means which provide an electrical spacing between adjacent radiators of a higher order of magnitude (say 5 to 50 times) than that of the physical spacing, thereby producing a sharplydirective beam, the direction of which varies cyclically with the wavelength, and means for receiving the reflected energy and using it to determine the direction of the reflector. Fig. 1 shows a transmitter providing a beam with scanning movements in mutually perpendicular planes, comprising four sets each of six dipole aerials arranged in one horizontal plane and adapted, when all are energized in the same phase, collectively to emit a sharplydefined beam in a direction perpendicular to this plane. The geometrical spacing of the dipoles of each set, and the spacing of the sets, are preferably approximately half a wavelength; 'whilst the electrical spacing of the dipoles of a set, introduced by delay networks F between them is an integral number, for example five to ten, of wavelengths. Beneath each dipole'is a reflector 17 to suppress downward radiation. Each set of dipoles is energized from a high-frequency oscillator 11 by way of a corresponding phase shifter 12a to 12d connected by a transformer to the oscillator. The magnitude of the phase shift produced by each phase shifter is controlled by a potential derived from a potential divider 9 across the output of a field-frequency generator 15, which is preferably of a saw-tooth wave-form and is controlled by a timer 14. The phases of the oscillations supplied to the sets of dipoles are thereby varied relatively to one another at a frequency of, for example, 10 to 30 cycles, so as to cause a corresponding variation in the direction of the emitted beam in a plane perpendicular to the lines in which the sets of dipoles extend. To produce a tilting movement of the beam for scanning in a perpendicular plane, a line-frequency generator 13, under control of the timer 14, causes a frequency-variation of the output of the oscillator 11, at a frequency of, for example, 500 to 5000 cycles. This causes the delay-networks F between the dipoles of each set to vary the relative phases of the energy supplied to the dipoles, causing a scanning movement of the beam in a plane parallel to the direction of each set. Fig. 2 shows a radiolocation system including the transmitter of Fig. 1 and embodying a cathode-ray indicator 24, the beam of which is scanned synchronously with the beam radiated from the aerial system by deflecting plates connected respectively to the line and field frequency generators 13, 15. Reception of a reflected wave by a non-directional antenna 22, 23 causes a receiver 21 to overcome the normal cut-off bias on the tube 24, so that a spot appears on the screen at a point indicating the direction of the reflecting object. A distance indicator 36 is operated by means involving a comparison of the frequency of the received signals and those emitted at the same moment from the oscillator 11, the signals being supplied to a modulator 32 and the difference frequency being applied to a network 35 which supplies a current of corresponding amplitude to the distance indicator. To enable a single distance indication corresponding to one of a number of reflecting objects to be obtained, the indicator 36 is rendered inoperative by a cut-off bias until supplied with a signal received by way of a differentiating circuit 44 and amplifier 43 from a photo-electric cell 40 which can be moved so as to be energized by any one of the direction-indicating spots on the screen of the tube 24. To compensate the indications on the screen of tube 24 for the delay between the emission of a signal and its reception after reflection, a signal developed by the frequency detector 35 across a resistance 30 is applied to deflecting plates 26, 27 to correct the linescanning of the tube so that it agrees with that of the generator 13 at the moment of emission of the signal. In a modified circuit, one pair of deflection plates of the tube 24 is coupled to the output of the network 35, while the other pair may be connected by a switch alternatively to the line or field scanning generator, whereby traces are obtained, the horizontal positions of which represent the co-ordinates of the position of the object, whilst the height of the trace indicates its distance. The non-directional receiving antenna may be replaced by a directional system similar to that shown in Fig. 1, the phase-shifters of the transmitting and receiving systems being synchronously controlled. Specification 577,672 is referred to.