Patent GB-1329789-A (GB)
Title: Digital scan converter
IPC: G01S7/298
Filed: 1971-06-30
Abstract: 1329789 Scan converter HUGHES AIRCRAFT CO 30 June 1971 30587/71 Heading H4D A digital scan converter for a pulse radar 10, Fig. 1, producing discrete video signals as a field of view is cyclically scanned in a predetermined pattern of successive lines at one particular rate; comprises a converter 11 converting said video signals into quantized elements of digital data, each element consisting of a binary number of K digits representative of the amplitude of a video signal, a buffer storage circuit 12 receiving said elements and storing in a block therein those elements pertaining to a given line; a bulk storage circuit 13 receiving, from said buffer storage circuit said block of elements and storing it in a memory block preassigned to data pertaining to said given line; a readout circuit 16 reading out data from said bulk storage circuit in a predetermined order bearing some relation to the order in which associated lines of said field are scanned for repeated display on a display unit 14 of all lines of said pattern at a rate which differs from said one particular rate; the data being displayed in a frame with lines of data spacially arranged relative to each other in the same sequence as scanned in said field. Various modes of scan and display can be converted, e.g. sideways looking (a range vers. position of aircraft orthogonal display), Fig. 2a (not shown), a B type scan, Fig. 2b (not shown), a sector PPI scan, Fig. 2c (not shown), or a B type scan over a plurality of parallel planes A, B, C, D, Fig. 2d, this last scan type being referred to as a bar-elevation scan. Using interlacings on a 360 line scan, each range scan having 384 range elements and the response in each range element being amplitude coded in a 4-bit miniword, the storage pattern on a magnetic drum buffer memory may be as in Fig. 3, 16 tracks in region 30 being used to record four miniwords (one bit per track) a track 35 recording the instructions for interlacing, a track 37 recording line retrace sync pulses, a track 36 recording clockpulses and a track 38 recording the instructions as to when the buffer can be read-out. Each recorded line in the region 30 is filled with 96 words of 4 miniwords each (Fig. 4, not shown). 16 levels of brightness are therefore codable for the sideways, B type and PPI scans. With the bar-elevation scan each plane is finally analysed and displayed in terms of 90 lines each although storage of each plane returns can be in terms of 360 lines each. There is thus only for one bit per miniword on the region 30 such that only 2 levels of brightness can be recorded, bits from four successive range increments in plane A being recorded in tracks A 1 , A 2 , A 3 , A 4 , Fig. 5b, and bits from the corresponding range increments in plane B being recorded in tracks B 1 , B 2 , B 3 , B 4 . Such interlacing of bits from successive scans can be used to record and display the latest state of a surveyed space together with for example three part history displays, the intensity of each part history display being successively reduced, so that a moving target shows on the final display as a bright spot indicating the present position followed by gradually fading trail of spots. If more range increments are scanned than can be stored, averages of successive groups of the increment responses are taken and stored (Fig. 12, not shown). In the arrangement, Fig. 6, four successive miniwords in a word are stored in respective shift-registers 43-46 and then simultaneously read into the buffer memory 41. The drum memory 40 indicates that it has a particular line available for recording on by means of a code from register 60, this is compared with the addresses of stored responses in the buffer memory by means of comparator 56 and agreement causes read out of the buffer memory.