Patent GB-1427000-A (GB)
Title: Superdirective system
IPC: H04R1/00
Filed: 1973-06-22
Abstract: 1427000 Aerials; sonar systems; radar RAYTHEON CO 22 June 1973 [3 July 1972] 23644/75 Divided out of 1415440 Headings H4A and H4D A super-directive receiving system comprises an array of radiating elements and a plurality of combining circuits, each of which is coupled to the radiating elements to combine selected signals therefrom additively and the remainder of the signals therefrom subtractively, to provide a further signal. The selections of signals are such that a first further signal represents energy as received on a monopole (omnidirectional) radiation pattern, a second corresponds to a dipole (figure-of-eight) radiation pattern, and a third corresponds to a quadrupole (four-lobed) radiation pattern. The system also comprises means for combining these three further signals to provide an output signal which represents energy as received on a composite radiation pattern. The system is particularly suitable for acoustic arrays, but may also be applied to aerial arrays. As described, an array 202, Fig. 1, of acoustic radiating elements comprises an electrode 206 on the outer surface of a ceramic cylinder 204 and eight segmented electrodes 208A-208H on the inner surface thereof. The array 202 is coupled in the receiving mode to a receiver 210 having eight preamplifiers 212A-212H, one for each inner electrode. The receiver further comprises a first set of seven operational amplifiers 216A- 216G, each receiving an input, either positive or negative, from each of the pre-amplifiers 212A-212H. The outputs of the operational amplifiers 216A-216G are the "further signals" representing either monopole, dipole or quadrupole radiation patterns according to the selection of the polarities of the inputs thereto. Thus, the signal from the operational amplifier 216A, which has all inputs positive, represents a monopole radiation pattern, the signals from the amplifiers 216B-216E represent dipole radiation patterns, with major axes in the NW/ SE, N/S, NE/SW, and E/W directions, respectively, and the signals from the amplifiers 216F, 216G represent quadrupole radiation patterns with major axes in the N/S, E/W and NE/SW, NW/SE directions, respectively. A scaling attenuator 223 is provided in the output line from each operational amplifier 216A-216G and, in addition, phase-shifting filters 220, 222A, 222B are provided in the cases of the amplifiers 216A, 216F, 216G to compensate for the characteristics of the ceramic transducer array 202. A second set of eight operational amplifiers 218A- 218H is provided, each amplifier receiving a positive input signal on the line 224 from the "monopole" amplifier 216A, a positive or negative input signal from one of the "dipole" amplifiers 216B-216E, and a positive or negative input signal from one of the "quadrupole" amplifiers 216F, 216G. The output signals from the amplifiers 218A-218H represent the composite radiation patterns, each of which has a main lobe, the eight main lobes being disposed at 45 degree intervals, starting in a Northerly direction (Fig. 2, not shown). The array 202 may be coupled through multiplexing circuitry 240, Fig. 3, to a signal generator 242 as well as to the receiver 210. In an active sonar mode a timing circuit 248 controls the operation of the signal generator and of a range gating unit 250, which is coupled to "gate" terminals of the preamplifiers 212A-212H (Fig. 1) to inhibit them except during a desired range interval. Logic circuitry 244 determines which of the amplifiers 218A-218H has the greatest output, and a cathode-ray tube display 246 shows the direction of the target. In another embodiment, shown in Fig. 4, a receiver 250 is similar to the receiver 210 of Fig. 1, in that it utilizes the eight preamplifiers 212, five of the operational amplifiers 216, and one of the operational amplifiers 218. The signal from the amplifier 216A represents a monopole radiation pattern. The signals from the amplifiers 216B, 216C represent, respectively, a N/S and an E/W dipole radiation pattern. The amplifiers 216D, 216E of Fig. 4, provide signals representing the same quadrupole radiation patterns as do the amplifiers 216F, 216G of Fig. 1. The signals from the amplifiers 216B, 216C are combined in a coordinate converter 252 to provide a signal representing a dipole radiation pattern with an axis orientated at a desired angle # 1  with the coordinate system of the array 202. Similarly, the signals from the amplifiers 216D, 216E are combined in a co-ordinate converter 256 to provide a quadrupole radiation pattern orientated at a desired angle # 2  with said co-ordinate system. The converter 252 comprises a trigonometric unit 262 which receives a # 1  control signal from a beam former 268 and which provides cos # 1  and sin # 1  input signals to multipliers 260A, 260B, respectively. The multiplier 260A also receives an input from the amplifier 216B, and the multiplier 260B an input from the amplifier 216C. The output signals from the two multipliers are summed together by an amplifier 264A, which has a variable gain G 1  controlled by the beam former 268. The trigonometric unit and the multipliers may be of analogue or digital type. The converter 256 is similar to the converter 252 except that the signals provided by the trigonometric unit to the multipliers are proportional to cos 2# 2  and sin # 2 , and that the gain of its summing amplifier 264B is G 2 . An amplifier 266 of variable G 0  is also provided for the monopole radiation pattern signal, and its output, and those from the amplifiers 264A, 264B are coupled to the operational amplifier 218. A logic circuit 270 at the output of the amplifier 218 operates the beam former 268 and may, for example, provide for tracking a target. Use of the arrangements described in this Specification in conjunction with those described in the parent Specification 1,415,440 is discussed.