Patent GB-934349-A (GB)
Title: Improvements in and relating to radar apparatus
IPC: G01S13/933
Filed: 1959-10-07
Abstract: 934,349. Pulse radar. SPERRY RAND CORPORATION. Oct. 7, 1959 [Oct. 7, 1958], No. 33957/59. Class 40 (7). Echo signals from a selected target on a P.P.I. indicator are utilized to control a second indicator, specifically a range-height indicator, on which further information concerning the selected target and other targets within a predetermined azimuth sector on the P.P.I. indicator is displayed with a constant effective azimuthal angle which is independent of the range of the selected target. In the arrangement described in which it is desired to examine more closely the cluster of targets, e.g. A, B, C on the P.P.I. display (portion of which is shown in Fig. 2), the target B is selected by means of a control stick 14 (Fig. 4) which in addition to producing in circuit 15 a ring marker (Fig. 1, not shown) for the P.P.I. display 13, also produces, via adjustable potentiometers 17, voltages proportional to the rectangular co-ordinates X, Y of the target B. These voltages are supplied to a gate generator 16 (described in detail in connection with Fig. 5, not shown) in which they are compared with voltages from resolver 11 proportional to the actual rectangular co-ordinates of the target B, the comparison producing at terminal 30 a succession of (negative) pulses which increase in both amplitude and duration from an initial zero to a maximum and then return to zero as the beam from radiator 2 scans in azimuth through the angular position represented by the X and Y co-ordinate voltages from potentiometers 17. These pulses, termed a target designation gate, are combined in summing circuit 47 with the video signals from the radar trans-ceiver 5 and the combined signals fed to an intensity modulation control of the range-height indicator (R.H.I.) 10 which when gated by a pulse from 66 displays (Fig. 3) the targets A, B and C and the target designation gate (shown as a lightly shaded area) having a range r proportional to the range r shown in Fig. 2. Since the " area " of the target designation gate is fixed the azimuthal angle of the display varies inversely as the range of the selected target. In order, therefore, to arrange that a constant azimuth sector independent of the range of the selected target is produced on R. H. I 10 it is necessary to delay the initiation of the gate pulse from generator 66 (which unblanks R. H. I. 10) as a function of the range setting of the target designation gate. This is effected by generating in 49 a pulse the leading edge of which coincides with the first of the target designation pulses and which is supplied to a delay circuit 65 and a paraphase amplifier 50, the latter producing a pair of output pulses of opposite polarity. Such pulses selectively operate gates 51, 52 to connect the output of cathode-follower 53, derived from the ground range sweep output of resolver 8, to a peak detector 54, the output of which is fed to a comparator 67 together with the output of delay circuit 65. The latter generates an exponentially decreasing voltage having decreasing instantaneous values bearing a predetermined time relationship relative to the leading edge of the (negatively-going) pulses from generator 49. It is stated that the delay which is required in the initiation of generator 66 to cause the intensified sweep portion 46 (Fig. 2) to lie along the same radial line of the P.P.I. indication follows the value of this exponential function which is a plot of target ground range versus delay time. Comparator 64 thus compares the exponential function voltage with the output of detector 54 (proportional to target ground range) and on equality of amplitude produces an output pulse which initiates generator 66.