Patent GB-745571-A (GB)
Title: Improvements in and relating to radar indicating arrangements
IPC: G01S7/20
Filed: 1953-08-21
Abstract: 745,571. Pulse radar. WILLIAMS, B. C. FLEMING-. Aug. 9, 1954 [Aug. 21, 1953], No. 23062/63. Class 40 (7). In a pulse radar with a P.P.I. indicator, echoes from targets at different heights or angles of elevation are displayed on the indicator in different colours. In one embodiment, Figs. 1 and 2, the aerial system comprises a paraboloidal reflector 14 and two vertically displaced wave-guide horn feeds 19 and 20 mounted on a rotatable platform 15. The two horns 19, 20 have resultant directivity patterns 12 and 11, Fig. 1, respectively and are coupled to a hybrid junction 21 which is coupled to a pulse transmitter 29 and separate mixers 33, 34 by wave-guides 22, 23, a double rotating joint 24 and waveguides 27, 28 such that energy from the transmitter 29 is radiated equally by both horns 19 and 20 but the sum of the signals received by horns 19 and 20 is applied to mixer 33 and the difference of the signals received by horns 19 and 20 is applied to mixer 34. A single local oscillator 35 is coupled to both mixers 33, 34 and the sum and difference I.F. signals are applied through amplifiers 36 and 37 to a phase-sensitive detector such that the polarity of its D.C. output voltage depends on the relative amplitude of the signals received by horns 19 and 20. The output from detector 38 is applied in parallel to amplifiers 40 and 42 which are responsive only to signals of positive and negative polarity respectively and the outputs from amplifiers 40 and 42 are applied to intensity modulate cathode-ray tubes 41 and 43 having screens which fluoresce in different colours, e.g. red and green, and which are viewed in superposition through a half silvered mirror 44 so that echoes received in the upper lobe 11 appear red, those received in the lower lobe appear green and those received in the overlapping region 13 appear near-white. Alternatively coloured filters may be used in conjunction with white or coloured fluorescing screens and the horns may be coupled individually to the tubes 41 and 43. Fig. 3 (not shown) illustrates means for adjusting the timebases and rotating scanning coils for the two tubes. When the aerial directivity pattern comprises more than two lobes, Fig. 4, a corresponding number of differently coloured tubes are employed. Fig. 5 shows a multi-lobe arrangement in which echoes from targets above and below a predetermined height h, 73, Fig. 4, are displayed in different colours. As shown, a reflector 62 is associated with a plurality of horn feeds 63, 63<SP>1</SP>, &c., each coupled to a separate receiver 64, 64<SP>1</SP>, &c. which is coupled to the interconnected suppressor grids of an associated # long tail pair " of valves 65, 65<SP>1</SP>; 66, 66<SP>1</SP>, &c., the anodes of valves 65, 66, &c. being connected to the green cathode-ray tube 43 and the anodes of valves 65<SP>1</SP>, 661, &c. being connected to the red cathode-ray tube 41. A saw-tooth voltage 70 from the timebase generator is applied in parallel to the grids of valves 65, 66, &c. which are also connected via diodes 69, 68 to tappings on a potentiometer 67 and the grids of valves 65<SP>1</SP>, 66<SP>1</SP>, &c. are connected directly to tappings on the potentiometer 67 so that during an initial period of the timebase sweep valves 651, 66<SP>1</SP>, &c. are conductive and the signals from all the receivers 64, 641, &c. are applied to the red tube 41. At a time t 1  proportional to h/sin #1, where #1 is the angle of elevation of the top lobe, valve 65 becomes conductive and valve 651 cuts off so that the signal received by the corresponding receiver 64 is transferred to the green tube 43 and the signals received by the other receivers are transferred in a similar manner at times t 2 , t 3 , &c. proportional to h/sin 62 &c. so that echoes from targets above and below the line 73, Fig. 4, are displayed on the green and red tubes 43 and 41 respectively. If a distinction is required between three height levels, each pair of yalves is replaced by three valves with their anodes connected respectively to the control grids of three differently coloured tubes. In any of the embodiments the plurality of colour tubes may be replaced by a single multicolour tube of the type used in colour television. Figs. 6-8 (not shown), illustrate the use of such a tube with a fluorescent screen comprising a repeated sequence of differently coloured strips, the output from the phasesensitive detector 38, Fig. 2, being applied to an internal grid of wires located adjacent and parallel to the strips; alternatively as described in the Provisional Specification the hue is controlled by the difference of the two signals received by horns 19 and 20 and the brightness is controlled by the sum of said two signals. Figs. 9 and 10 (not shown), illustrate the gun of a multi-gun shadow-mask tube with a fluorescent screen comprising a plurality of groups of differentily coloured dots and an internal mask with a corresponding number of apertures, the outputs from the switching valves in Fig. 5 being applied to the corresponding guns. Specification 609,703 is referred to.