Patent GB-1463413-A (GB)
Title: Method of identifying the patterns of radar signals
IPC: G01S7/22
Filed: 1974-06-12
Abstract: 1463413 Radar MITSUI SHIPBUILDING & ENG CO Ltd and KYORITSU DEMPA CO Ltd 12 June 1974 [15 Aug 1973] 25954/74 Heading H4D A P.P.I. pulse radar, particularly suitable for use at sea, along coasts &c. analyses the video signals by means of a sliding range window, a constant range increment in depth, e.g. 660 m., but having an azimuth increment extent which decreases with increasing range such that the physical size of the window remains approximately constant for all ranges. To accomplish this, only every Nth video signal is sampled in the analysis, with N being large for small ranges-e.g. every 8th for 0À5 to 1 mile and becoming smaller for larger ranges, e.g. every 4th for 1 to 2 miles, every 3rd for 2 to 4 miles, every 2nd for 4 to 8 miles, and every signal for 8 to 16 miles. The video signals so sampled are stored in an 11 by 11 range R-azimuth # matrix 13 Fig. 3 and Fig. 9a and the binary bit states analysed 14, 16, 17 to indicate whether a large, e.g. coast target or a small, e.g. ship target, has been scanned. In the latter case, tracking can then commence. In practive five sets of items 11, 12, 13, 14, 16, 17, 18 as shown in Fig. 3 operate in parallel, one for each range range - 5 to 1 mile, &c. controlled by a common clock pulse generator 15 (Fig. 5, not shown). In the sliding window memory 11, Fig. 4, data selector 12 and No. 1 matrix 13 for the range 0À5 to 1 mile (every 8th video signal sampled during the time 6À4 Á sec. to 12À8 Á sec. after the transmitter sync. pulse), 81 successive video signals arriving from 81 scans extending over 81 Î 0À3 degrees = 24À3 degrees are available for scanning and every 8th, e.g. the 1st, 9th ... 73rd, 81st, are passed through 11 respective 512 bit shift registers 21-1 ... 21-81 shifted at CL by the range increment period of 0À4 Á sec. The running outputs of the registers are gated through respective AND gates 22 of the data selector 12 by a range gate signal (RGS-2) formed by the coincidence at AND gate 55, Fig. 5, of the clock pulse generator 15 of the output of a counter 57 extending from the 16th range bit (0À5 miles) to the 32nd range bit (1À0 mile) for every video signal period, and that from a counter 54 extending over 3À3/2 m. sec. (#0À3 degrees/2) and occurring every 8th scan. The register outputs pass through the gates 22 and shift through the 11 rows of the matrix 13. The continual shifting of the registers 21-1 ... 21-81 causes the matrix content to "slide" or "walk" through the considered range (0À5 to 1À0 mile). When the 121 bits of the No. 1 matrix Fig. 9a have been occupied and the centre bit C is a 1, a compression or "perturbation" of the data is carried out, i.e. the three middle columns and the three middle rows are inwardly compressed to a single column and row respectively and the same procedure is used for the two sets of diagonal rows S, P. This first stage results in data stored in the 41 bit No. 2 matrix Fig. 9b. If all the bits in the No. 2 matrix are ls, a "land" identification is indicated and the search is continued. If not, the bits of No. 1 matrix are further shifted or compressed as shown in Fig. 2 to give a single azimuth column and a single range row. Analysis of the bit values of column and row determines the co-ordinates of the target and enables its tracking.