GB743521A - Improvements in or relating to radar systems and analogous pressure wave systems - Google Patents

Abstract

743,521. Radar. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 11, 1951 [June 8, 1950], No. 14365/50. Class 40 (7). In a radar system in which a number of continuous waves of different frequencies are transmitted, the range of the moving target is determined by means of the Doppler effect. The phases of the Doppler beat notes produced.in the different frequencies are compared to give the range of either approaching or receding targets and separation of the two types of target is effected. The range indicating devices may be either cathode-ray tubes or phase clocks and cathode-ray radial coder tubes having internal or external electrode contact systems may be used to provide output voltages linearly proportional to the target range. Both two and three transmitted frequencies may be employed and the separation of echo signals from approaching and receding targets is effected by either a filter system or the range indicating device, e.g. a phase clock or a double beam cathode-ray tube. With the cathode-ray type indicators, target selection, in accordance with velocity, may be effected by means of either a number of sequentially selectable narrow-band filters, or by means of spectrum analysing filters. First embodiment. Separation of approaching and receding targets by filter systems. In Fig. 1D, two frequencies are transmitted from O1, O2 and received, after reflection at RA where the separation of the Doppler signals from approaching and receding targets is effected by the filters UF1, UF2 and LF1, LF2. The filter outputs are applied to a phase comparison device calibrated in range. In Fig. 8, the Doppler frequencies from approaching and receding targets are separated by means (not shown) and then applied to a series of selectable narrow band filters which are scanned in unison by the switches SWX, SWY. The filter of the series, appropriate to the Doppler frequency and therefore to the target speed, developes an output signal which, after conversion to a pulse train, is applied to the phase comparison cathode-ray tubes CR1, CR2 which indicate range and velocity. In a modification, Fig. 9 (not shown), the band filters are replaced by spectrum analysing filters and a sweeping oscillator. In a further modification, Fig. 13 (not shown), the output from a series of scanned filters, of the type shown in Fig. 8, is applied to phase comparing circuits so as to produce circular deflection in fine and coarse radial coder tubes. The radial coder tubes consist of cathode-ray switching tubes having contacts arranged such that the beam position is defined by the contacts impacted by the beam. The contacts are connected to a translating device which provides an output voltage linearly proportional to the beam position. Second embodiment. Separation of approaching and receding targets by means of the rangeindicating device. In Fig. 3, three frequencies are transmitted from oscillators O1, O2, O3, the three target echoes are received at RA and the corresponding Doppler frequencies are derived at the mixers MM1, MM2, MM3 and Doppler frequency filters DF1, DF2, DF3 and applied through the phase comparing devices PC13, PC123 to the reversible phase clock DPC. In Fig. 10 (not shown), the Doppler frequencies are derived as in Fig. 3, converted into pulse trains and then applied to double beam C.R.T. which indicates range on fine and coarse scales. In Fig. 11 (not shown), the Doppler frequencies are again derived as in Fig. 3 and are applied to spectrum analysing filters the output from which are phase compared and then applied to two cathode-ray tubes which indicate coarse and fine range measurements and target velocity. In Fig. 12 (not shown), the indicating cathode-ray tubes of Fig. 11 are replaced by storage cathode-ray tubes which may be scanned so as to transfer the signals for display on PPI cathode-ray tubes.