Patent GB-698412-A (GB)
Title: Improvements in or relating to radar systems
Inventor: RUST NOEL MEYER
IPC: G01S13/34
Filed: 1950-03-16
Abstract: 698,412. Radialocation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Feb. 7, 1951 [March 16, 1950], No. 6651/50. Class 40 (vii). An F.M. radar system of the kind wherein echo signals are mixed with signals corresponding to the transmitted signal to produce a beatfrequency signal which is analysed by a frequency-filter device to enable a determination of range to be made, comprises means for separating out simultaneously the component frequencies of the beat-frequency signal, means for storing the signals thus separated out, and means for utilizing the stored signals in a predetermined sequence to operate a range indicator. As illustrated in Fig. 1, continuous waves having a saw-tooth law of frequency modulation are generated at T and radiated from a directional aerial, having a directivepattern TA, which either rotates continuously or oscillates over a limited arc to provide a sector scan. The amplitude of the modulating saw-tooth wave is varied, either in steps or continuously, so that the range corresponding to a predetermined beat frequency varies correspondingly. Echo signals received at R are mixed with a portion of the transmitted signal applied through attenuator AA and the resulting beat-frequency signal is applied in parallel to the twenty band-pass filters AN, successive ones of which select successive adjoining portions of the frequency band of the beat-frequency signal. The output of each filter is fed through a respective rectifier D to a corresponding resistance-capacity storage network which is connected to a respective contact of a distributer (in practice an electronic device), shown as comprising twenty contacts ANP and a continuously rotating wiper arm ANW. The signal picked off by the wiper is applied to the brightness control electrode BCE of a display cathode-ray tube, the cathode-ray beam of which is deflected radially in synchronism with the rotation of the wiper arm and is deflected circumferentially in accordance with the rotation of the aerial systems. A further component of radial deflection is applied to the cathoderay tube in accordance with the variation in the deviation of the frequency-modulated wave as indicated by the coupling SWB. Thus, considering a continuously rotating aerial system and a continuously varied deviation, the variation in the deviation is so chosen with respect to the overall width of the band selected by the filters AN and the rate of rotation of the aerial system, the radial deflection of the cathode-ray beam being modified correspondingly, that the display on the cathode-ray tube is traced out spirally as indicated, for example, in Fig. 2. In the alternative case where the amplitude of the frequency modulating wave has a number of discrete values, the display comprises a corresponding number of annular sections. A second embodiment, Fig. 3 (not shown), comprises two magnetic storage devices, beat-frequency signals being recorded on and reproduced from each in alternation, so that while signals are being recorded on one device they are being reproduced from the other for subsequent application to a cathode-ray display unit. The beat frequency signal is applied via a switch operated in synchronism with the aerial unit to twenty filter units, the outputs from which produce records on a slowly rotating drum. After one complete rotation of the drum, the switch is operated, thereby causing the slowly rotating drum to rotate rapidly, while the other drum which was previously rotating rapidly is made to rotate slowly and is connected to record the beat-frequency signals. The signals previously recorded on the firstmentioned drum are picked off and applied to a P.P.I. display arrangement, the scanning in which is controlled in synchronism with the rate at which signals are picked-off from the drum. The Specification also states that the rangescanning carried out by the band of ranges corresponding to the pass-bands of the twenty filter units may be varied by a frequencychanging device operating at the receiver to change the frequencies of the beat-frequency signals. In order to provide greater resolution at the closer ranges the elemental widths in range corresponding to the separate pass-bands of the filter units may be appropriately graded. To reduce the appearance of spiral lines on the display when it is of the type employing a gradual change in the band of ranges explored, a radial wobble may be superimposed upon the cathode-ray beam.