Patent GB-1484344-A (GB)
Title: Multiplexing apparatus for panoramic sonar systems
IPC: G10K11/34
Filed: 1974-09-16
Abstract: 1484344 Direction finding FRANCE ARMED FORCES - MINISTER OF 16 Sept 1974 [17 Sept 1973] 40277/74 Heading G1G A panoramic sonar apparatus for determining the bearing of a received acoustic signal comprises an antenna having n rows of hydrophones regularly distributed, e.g., circularly, around an axis O, and a panoramic scanning means consisting of at least one delay line and a multi-plexing device interposed between the antenna and delay line, wherein detection is made through cyclically exploring listening channels which are distributed in one or more groups around the antenna such that each group is formed solely of channels whose position in relation to the rows of hydrophones relate to predetermined bearings, and produce corresponding reception signals, which are in at least one group such that in any one group the series of rows contributing to a reception signal for a first bearing considering the rows in an order of sequentially increasing delay of their signals, can be deduced from the series of rows contributing to a reception signal for an adjacent bearing by replacing each member of the latter series by a member following about said axis by a constant pitch r. The multiplexing device 2 has n inputs connected to respective ones of the n rows, and is associated with an address register; a demulti-plexing device 6, with its own address register 7, and having n outputs, has its input connected to the output of multiplexer 2 at 5, where, in the embodiment shown n = 28. A time unit is defined as the interval between trains of r pulses generated in an associated time base, which pulses actuate rotation of the detection bearing, a further series of n pulses being provided within each time unit for activation of the multi-plex units, the trains of r pulses acting along line 8 to advance the address register to effect the change in the hydrophone row series by the predetermined pitch r. In Fig. 1, the detection channels V 1  ... V 56  are divided into two groups - an even numbered group and an odd numbered group. The channel bearings are in pairs between the hydrophone rows Hn and are symmetrical about the bisector e.g. B of the angular sector enclosed by each pair of adjacent hydrophone rows. The mode of connection of the hydrophone rows Hn to the inputs e n  of delay line 1 having output S, is given by the construction of a square matrix having rows and columns in time units corresponding to the partial delays introduced by each section of delay line 1, see Figs. 2, 3A and 3B (not shown). In Fig. 4, these connections are established by the series of OR gates 10, e.g. input e 1  of delay line 9 is connected to outputs 1 or 2 of buffer memory 17, e 2  to outputs 1 or 28, &c. Switching network 11 consists of AND gates 12a and 12b which are alternately excited on the occurrence of an even or odd, respectively, time unit, to effect connection of an even or an odd channel group. The time base pulses 15 are divided by frequency divider 14 to provide the even and odd 'validation' inputs 13a and 13b, and also to provide signal 8 to address register 8 to effect the change in pitch where in this case r = 1. In other embodiments r may take other values, and the grouping of the reception channels may be varied, e.g. such that there are k . n reception signals in k groups, where k > 2 and is an integer, so that the outputs of the demulti-plexer scan the hydrophone rows k times before the order of the outputs is advanced by the predetermined pitch of r units. There may alternatively be n/k channels, k > 1, so that the order of the outputs is advanced every time unit by a pitch progression equal to k.