Patent GB-671737-A (GB)
Title: Improvements in or relating to radar systems
Inventor: EASTWOOD ERIC
IPC: G01S13/02
Filed: 1950-03-10
Abstract: 671,737. Radiolocation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Nov. 29, 1950 [March 10, 1950], No. 6128/50. Class 40 (vii). A radio position determining system comprises two or more spaced radar installations whose aerial arrangements have little or no directivity and means for producing from the echo signals obtained by each installation a display in which the distance of a target from each installation is indicated by a curve whose radius is a function of the distance and whose centre can be adjusted to a position corresponding to the geographical position of the appropriate radar installation so that the point of intersection of the curves indicates the position of the target. The invention may include either continuous-wave or pulse radar apparatus and the wavelengths used may be comparatively long, e.g. 1 to 10 metres, such waves producing better echoes from fast cylindrical objects such as rockets. In a two-station pulse system the radar systems may be electrically separate and the indications displayed on separate cathoderay tube indicators jointly viewed through a half-silvered mirror, Figs. 2 and 3 (not shown). The returned signal is used to intensity-modulate the appropriate tube which is spirally scanned by triggering a saw-tooth generator with the transmitted pulse and using the sawtooth waveform to control the amplitude of the output from a sinusoidal generator whose signals are applied directly to the Y-plates and through a 90-degree phase shifter to the X-plates. The position of the centre of the spiral is controlled by adding bias voltages to the signals fed to the plates. A radar pulse length of 8 Á. sec. and a frequency of 125 kc/sec. for the sinusoidal generator are suggested as this produces a brightening of one complete turn of the spiral trace by the echo signal. If desired, the amplitude of the scanning voltages may be automatically maintained constant during the duration of the echo signal so that a circular trace is developed. In a further embodiment, also using two pulse radar stations, the pulses are generated by a single master pulse generator 13 and fed alternately over lines LR1 and LR2 to one and then the other of the transmitters. The echo signals are received from the stations over lines PR1 and PR2 which are gated at 14 by pulses from generator 13 and fed through an amplifier and limiter to intensity-modulate a common cathode-ray tube. The scanning voltages of this tube are generated by triggering saw-tooth generator 5 directly and through delay circuit 15 alternately. Circuit 15 is inserted to compensate for the difference in travel time to the two radar stations. The saw-tooth waveform controls the amplitude of the waveform from oscillator 7 which feeds the Y-plates through amplitude adjuster 10 and the X-plates through phase-shifter 8 and amplitude adjuster 9. The bias voltages determining the position of the centre of the spiral are changed after each cycle, the values in alternate cycles being the same, this is done by feeding pulses over lines 18 and 19 to operate change-over trigger circuit 17 controlling the bias values.