Patent GB-1415440-A (GB)
Title: Superdirective system
IPC: G01S7/523
Filed: 1973-06-22
Abstract: 1415440 Aerials; sonar systems; radar RAYTHEON CO 22 June 1973 [3 July 1972] 29811/73 Headings H4A and H4D A super-directive receiving system comprises an array of three or more radiating elements, means for combining signals from a group of the elements in accordance with operations which perform, or have substantially the effect of performing, the operation of differencing signals from 1st and 2nd elements of the group with a 1st relative delay therebetween to provide a 1st difference signal, differencing signals from the 2nd element and a 3rd element of the group with a 2nd relative delay therebetween to provide a 2nd difference signal, and differencing the 1st and 2nd difference signals with a 3rd relative delay therebetween to provide an output signal representing radiation received from a direction determined by the selected group and by the said delays, and control means operative selectively to control the said direction by varying the said delays. As described, an array 22, Fig. 1, of some radiating transducers 28 is mounted on a baseplate 34. One of said transducers is centrally located, with axis 36, and the other six are arranged in a circle thereabout. Each transducer may comprise an electrostrictive ceramic material, such as barium titanite, and its surface pulsates to provide an axially symmetrical directivity pattern. Individual leads 30 from the transducers 28 are connected to a beam switcher 64, forming part of multiplexing circuitry 26, which is coupled to a transceiver 24. The beam switcher is controlled by a signal on a line 62 from an angle tracker 54 in the transceiver, and comprises switching means for coupling particular transducers to the transceiver, for example, any three transducers arranged along a diameter of the array, whereby angular information about a target may be obtained by the sequential lobing method. The circuitry 26 also comprises a transmit-receive circuit 74 and amplifiers 76, 78 for received and transmitted signals, respectively. The transceiver 24 comprises beam formers 38, 40 for forming the array radiation patterns for reception and transmission, respectively. A signal generator 42 feeds the beam former 40. Output from the beam former 38 is processed in a correlator 50, which also receives input from the signal generator 42. The correlator 50 provides range data to a cathode-ray tube or other display device 70, and has an output to the angle tracker 54, which supplies angle data to the display device 70. The signal generator 42, correlator 50, angle tracker 54, display device 70, and the beam formers 38, 40 are co-ordinated by timing signals from a unit 72. The beam formers may employ either digital or analogue techniques, and a digital type receiving beam former 38 is shown in Fig. 4. Signals from three diametrically located elements of the array are coupled through the multiplexing circuit to respective samplers 98, which are driven by pulses from the unit 72, and which give outputs when their respective incoming signals exceed a preset threshold value. Output from the left-hand sampler is combined with output from the centre sampler in a first arithmetic unit 100, Fig. 6 (not shown), a delay being introduced in the output from the centre sampler by a first delay unit 102, Fig. 5 (not shown). Similarly, output from the centre sampler is combined with output from the righthand sampler in a second arithmetic unit, a delay being introduced in the output from the right-hand sampler by a second delay unit. Finally, outputs from the first and second arithmetic units are combined in a third arithmetic unit, a delay being introduced in the output from the second arithmetic unit by a third delay unit. In this way, complex radiation patterns may be realized, such as that indicated in Fig. 2, and said patterns may be different for transmission and reception. Of particular utility is a notched radiation pattern, the notch being positioned in line with a source of noise, such as a ship's propellor, Fig. 3 (not shown). In a simplified beam former, the output from the centre sampler is inverted and is combined with the outputs from the other samplers in respective tapped resistors. Outputs from the tappings are combined in a summer, a delay being introduced in one, Fig. 10 (not shown). The angle tracker 54, Fig. 1, is further described with reference to Fig. 15 (not shown). The system is also applicable for operation with electromagnetic waves.