Patent GB-591853-A (GB)
Title: Improvements in or relating to radio detecting systems employing a common antenna structure for transmitting and receiving
IPC: H01Q3/24
Filed: 1943-11-16
Abstract: 591,853. Radiolocation. STANDARD TELEPHONES & CABLES, Ltd. Nov. 16, 1943, No. 19141. Convention date, Feb. 14, 1942. [Class, 40 (v)] In a pulse radiolocation system a common aerial array is employed for transmission and reception, and during reception is caused, to receive alternately according to a plurality of differently directed over-lapping radiation patterns, in order to determine the direction of a, target. In the arrangement of Fig. 1, two dipoles 1, 2 are connected in phase by a line 3, the centre point of which is coupled by a line 6 to a transmitter 7, and produce a radiation pattern as shown at 15. The transmitter is modulated by a. pulse generator 18 controlled from a master oscillator 18<11>. The.receiver8is connected to the aerial array over two transmission lines 9, 10 connected to symmetrically spaced points on line 3, and lines 6, 9, 10 are arranged to be conducting or blocked as desired by coupled sections 20, 19 and 21 associated with control circuits 23, 22, 24, which operate in the manner described in Specification 591,353. A generator 18<1> supplies pulses of the same frequency, but of slightly greater duration than the transmitted pulses, to control circuits 23, 22, 24 to block lines 9 and 10 and open line 6 during the transmission of a pulse and to block line 6 and open lines 9, 10 during the reception period. In order to produce the beam switching on reception a device 25 produces square waves of a frequency preferably less than that of the transmitted pulses which are fed to control circuits 22, 24, a phase reverser 26 being included in one connection, to cause lines 9 and 10 to be blocked alternately and produce the alternate receiving radiation diagrams 16, 17 which intersect along a line 37 of equal signal strength. Blocking, amplifiers 38, 38<1> and limiters 27, 28 are included in the control circuits to prevent undesired interaction, of the switching pulses. The output of the receiver is fed through a reversing device 30 operated in synchronism with the beam switching to one pair of deflector plates of the cathode ray tube indicator, 36 so that signals. corresponding to the alternate reception polar diagrams appear as back-to-back' deflections on a time base trace produced by saw-tooth generator 29 which feeds the other deflector plates. Equality of signal amplitude on the two sides of the time base trace indicates that the datum line 37 is directed at the target producing the signals, and the position of the signals along the time base indicates range. The coupled section 20 for controlling transmission along line 6 may be dispensed with if the length of line 6 is so adjusted that it resonates and produces at junction points 4, 5, an impedance substantially equal to the transmitter impedance, which will be high in the intervals between pulses. The arrangement shown in Fig. 2 permits the direction of a target in elevation as well as azimuth to be determined. Four aerial elements such as dipoles 41 ... 44 are connected to the corners of a bridge network 45 comprised of four equal arms each an integral number of wavelengths long. A transmitter 48 modulated by a pulse generator 47 controlled from a master source 46 feeds pulses to the centre or electrically equivalent point 49 of one arm of the bridge through a resonant line so that the four aerials are energized in phase to radiate uniformly in a forward direction, while any received signals are not fed back to the transmitter. In order to obtain the directional effect for azimuth determination the arm 52 of the bridge is effectively opened by a coupled section and control circuit 120 fed with a switching pulse while the azimuth receiver 53 is coupled alternately to symmetrically spaced-points 54, 55 on the bridge network, by lines under the control of sections 56, 57 fed with suitable switching pulses. For elevation determination arm 58 of the bridge is opened by a coupled section and control circuit 59 and the elevation receiver 60 is connected alternately to symmetrically spaced points 61, 62 by lines under the control of sections 63, 64. Generation of switching pulses. A generator 70 feeds through a limiting amplifier 74 and diodes 72 to produce two trains of square waves a and b, Fig. 3, while a generator 71 operating at half the frequency feeds through a limiting amplifier 77 and double triodes 78, 88 to produce trains of square waves c and d. Waves a and b are added to wave c in lines 79, 80 and fed to limiters 83, 85 and through inverters 82, 911 to limiters 82<1> and 91 to produce the pulses indicated by the shaded portions of curves e, f, g, h which are fed to the sections 56, 57, 63 and 64 to cause them to be operative in succession. Waves c and d from the double triode 88 are fed to the coupled sections 58, 120 to cause arms 52 and 58 of the bridge network to be opened alternately at one half the frequency at which the other sections are operated so that the reception polar diagram is displaced first left and right and then up and down. In order to ensure -that all circuits are properly conditioned for transmission or reception, pulses from generator 48<1> which are slightly longer than the transmitted pulses are fed to the coupled sections 59, 120 to make them inoperative during transmission and are also fed through an inverter 92 to grids in the limiters 83, 85, 91, 82<1> to prevent pulses being transmitted to cause unblocking of the lines feeding the receiver. Signal display circuits. The signals from the azimuth and elevation receivers 53 and 60 are fed through reversing devices 67, 69, which are operated in synchronism with the blocking and unblocking of the lines feeding the receivers to the horizontal and vertical deflecting plates of the cathode ray tube. The applied signals produce deflections on the cathode ray tube screen to the left and right of the vertical axis and also above and below the horizontal axis, the magnitude of the deflections being equal when the target lies on the line of symmetry of the reception polar diagrams. In order that only signals shall produce indications on the cathode ray tube, it is normally biassed off, a voltage obtained in unit 103 by the rectification of signals being applied to the grid to brighten the cathode ray tube beam when a signal is being received. Alternative indicating systems such as that described in Specification 574,676 may be employed.