Patent GB-654221-A (GB)
Title: Improvements relating to the determination of positions, distances and velocities byradio means and to apparatus therefor
IPC: G01S1/02
Filed: 1941-09-10
Abstract: 654,221. Radiolocation. STEVENS, A. H. (Leland Stanford Junior University, Board of Trustees of). Sept. 10, 1941, No. 11596. [A Specification was laid open to inspection under Sect. 91, July 23, 1946.] Classes 40 (v) and 40 (vii)] Also in Group XL (a)] A radiolocation system comprises a transmitter and a directional receiver for the waves reflected by an object, the receiver comprising two wave-translating devices mounted in a common reflector, said devices having similar directional but angularly-spaced reception characteristics, with means for comparing their outputs and hence the sense in which the object is displaced from the zero line or plane of the receiving system, which system is angularly adjustable to cause the zero line or plane to intersect the object. The apparatus described also gives indications of the distance of the reflecting object and of its velocity relative to the observer. In the apparatus shown in Fig. 1 a projector 1 comprising an antenna with an elongated parabolic reflector and radiating a transversely narrow fan-shaped "Searching" beam is adjustable on trunnions 6 in elevation. The waves reflected from the object are detected by a receiver 3 having a similar fan-shaped reception pattern. After an object has been detected by the fan-shaped beam, its direction is determined by a "Spotting" projector 2 and receiver 4, which have parallel-sided radiation and reception zones, and are adjustable on trunnions 8 to search the space included in the fan-shaped beam. The receiver 4 may be dispensed with, the transmitter 2 being adjusted for maximum reception by the receiver 3, or one projector and one receiver having mutually perpendicular fan-shaped field patterns may be used. Fig. 4 shows diagrammatically a "Spotting" transmitter and receiver arranged as a single unit, the transmitter 14 being surrounded by a shield 15 and set at the focus of a parabolic reflector 12, coaxial with and in front of the reflector 11 of the receiver. Above and below the focus of the reflector 11 are receivers 16, 17 for directing the assembly in altitude, and on each side of it are receivers (not shown) for adjusting it in azimuth. For the system shown in Fig. 1, the apparatus of Fig. 4 is duplicated, each employing only two receivers, and one operating with a fan-shaped field. The oscillator 25 delivers energy at a frequency, for example, of 3 X 10<SP>10</SP> to the transmitter 14 and receivers 16, 17. An oscillator 27 causes alternate interruption of the transmitter and the receivers at a frequency of the order of 10<SP>7</SP>. To avoid non-detection of an object at such a distance that the reflected waves arrive at the receiver during its non-operative periods, the interruption frequency is varied through a range of about 1 per cent of the mean, and at a frequency of between forty and several hundred cycles, by an oscillator 28 which modulates the frequency of the oscillator 27. For distance determination a variable-frequency oscillator 29 interrupts or modulates the transmitter and receivers at a frequency below that of the oscillator 27, dividing the series of pulses into trains of 100 to 1000 or more. On reducing the frequency of the oscillator 29 the strength of reception varies cyclically between a maximum and zero, the lowest frequency giving a maximum being that for which the distance of the reflecting object is one-quarter of the wavelength corresponding to the frequency. To secure a sharp reading the frequency is then increased until the first minimum before this maximum is reached. A klystron oscillator of the kind described in Specification 523,712 for energizing the transmitter with oscillations of from 1.0 to 20 centimetre wavelength is described, the outputs from the oscillators 27, 29 being applied to a modulating grid or to a tubular electrode between the two resonators, or to both. Fig. 6 shows a klystron used as a receiver, comprising a cathode 71, collimating grid 72, resonators 73, 79, having grids 74, 75 and 77, 78, and a detector electrode 80. The incoming signal and a heterodyne frequency are delivered by coupling loops 94, 95, respectively. An adjustable coupling loop, as described in Specification 531,251, provides regeneration. Grids 97, 98 serve for interrupting or modulating the output. The resonators are tuned as described in Specification 523,712 by compressing them by members 83, 84 operated by rods passing through flexible ends 86, 87 of the evacuated container, and adjustable individually or conjointly. A tube 76 between the resonators is axially adjustable by means of a pin-and-slot connection to a lever 91 operated by a member 93. The potential of the detector electrode is adjusted so that under " no signal" conditions either substantially all, or substantially no, electrons reach it. A signal produces respectively in the two cases a decrease and an increase in the current from the electrode 80. A circuit diagram (Fig. 9, not shown), is given showing two of these detectors employed in connection with a pair of receivers such as 16, 17. The outputs from the electrodes 80 of the two detectors are applied respectively to the ends of a potentiometer, from which the grids of two amplifying valves are controlled. By means of a transformer with a centre-tapped primary a voltage representing the difference in the output voltages of these valves is applied to one grid of a mixer-amplifier valve, the sum of these voltages being applied to the other grid. The output of the mixer-amplifier valve, which is thus a measure of the difference in the squares of the signals in the two receivers, operates a centre-zero indicator, giving a reading to one side or the other according to the sense in which the object is displaced from the zero line and a null reading when the receivers are correctly directed towards the object An amplifier connected to one end of the transformer primary delivers signals proportional to the output from one detector to a voltage-operated indicator which is used in distance determinations for observing the maxima and minima of reception produced by adjustment of the oscillator 29. The same amplifier supplies signals to a frequency meter which allows the velocity of the moving object in relation to the observer to be determined by the frequency difference between the transmitted and received signals. Other features of the system described form the subject-matter of Specifications 654,222, 654,223 and 654,226. Specification 585,986 also is referred to. The Specification as open to inspection under Sect. 91 states that instead of antennae with reflectors, resonant chamber projectors and receivers of the type described in Specification 517,264 may be used and describes two constructions thereof now forming the subjectmatter of Specification 654,224. This subjectmatter does not appear in the Specification as accepted.