Patent GB-852099-A (GB)
Title: Radar apparatus
IPC: G01S7/20
Filed: 1959-01-16
Abstract: 852,099. Pulse radar; deflection wave generator circuits. SPERRY RAND CORPORATION. Jan. 16, 1959 [April 3, 1958], No. 1731/59. Classes 40(6) and 40(7). Relates to means for increasing the intensity of a pulse radar C.R.T. display comprising two single-beam cathode-ray storage tubes alternately operative to record and reproduce the video echo signals, the reproducing scan rate being slower than the recording scan rate. In a first embodiment comprising a single beam aerial and a single receiver in which the maximum echo time T is less than the pulse recurrence period P, the duration of the recording and reproducing scans s and r, Fig. 8, are respectively equal to T and P. During any one recurrence period echoes received during that period are recorded on one storage tube and the echoes recorded on the other storage tube during the previous recurrence period are read out and displayed, the recording-reproducing modes of the tubes being interchanged for the next recurrence period. In a second embodiment the invention is applied to a "stacked-beam" radar producing a plan-range P.P.I. display of targets which may be at different angles of elevation. The system comprises five pencil-beam aerials 13, Fig. 1, having different angles of elevation. During a first storage period comprising five pulse recurrence periods the echoes received by the five aerials are stored sequentially on the same track on the first storage tube and during the next storage period also comprising five pulse recurrence periods the echoes stored on the first storage tube are read-out and displayed and the echoes being received are stored sequentially on the second storage tube. General operation Figs. 1, 2, 3 and 6b. The pulse output from the transmitter 10, Fig. 1, triggered by a 1,000 c/s. sync generator 16 is applied simultaneously to the five pencil-beam aerials 13 having different angles of elevation #1-#5, the aerials being connected to separate receivers 15. During the first pulse recurrence period of the first storage period the echoes received by the aerial having the lowest angle of elevation #1 are stored in the first storage tube 42, Fig. 2, of the storage device 20, Fig. 1, along a track o a b c d e, Fig. 6b, produced by a sawtooth waveform, Fig. 3C, of amplitude proportional to cos #1 from the first of five sweep generators 21, Fig. 1, triggered by the sync generator 16 such that the distance along the record track of a stored echo pulse is proportional to the plan range of the corresponding target. Similarly during the 2nd, 3rd, 4th and 5th pulse recurrence periods the echoes received by the 2nd, 3rd, 4th and 5th aerials are recorded along portions o-d, o-c, o-b and o-a respectively of the record track. During the second storage period the received echoes are stored in a corresponding manner in the second storage tube 41, Fig. 2, and the electron beam of the first storage tube 42 is scanned slowly along the record track o-f, Fig. 6b, by a 200 c/s. sawtooth waveform D, Fig. 3, from a read-out sweep generator 36, Fig. 2, to read out the stored echoes which are applied to intensity modulate a P.P.I. C.R.T. 85 having a 200 c/s. radial sweep produced by applying an output from the read-out sweep generator 36 to the X and Y deflection members through a resolver 87 synchronized with the rotation of the aerial system 13. During the third storage period new echoes are again stored in the first storage tube 42 and the echoes stored in the second storage tube 41 are read out. Timing operations Figs. 1, 2 and 3. As shown in Fig. I the video echo pulses and the recording scan control sawtooth voltages, Fig. 3C, corresponding to the five aerials are produced sequentially by means of gates 19 and 22 controlled by time displaced 200 c/s. pulses from a programmer 17 triggered by the sync generator 16. The alternate operation of the storage tubes 42 and 41 in the recording and read-out modes is controlled by applying a 200 c/s. pulse train from the programmer 17 via a lead c to trigger a bistable multivibrator 21, Fig. 2, producing push-pull 100 c/s. square waves A and B, Fig. 3; the first half cycle of the waveforms shown in Fig. 3 correspond to the first storage period referred to above. Considering the first storage tube 42, the video signals to be applied during the first storage period are selected by applying the outputs from the gates 19, Fig. 1, via a lead a to a gate 44, Fig. 2, controlled by the waveform A. The selected video signals are combined with the waveform B giving a resultant H which is applied to the grid of the storage tube 42. The scan control waveform F for the storage tube 42 is produced by applying the output C from the sweep gates 22 via a lead b to a gate 30, Fig. 2, controlled by the waveform A and combining the output in a mixer 32 with the output from a gate 38 to which are applied the read-out scan control waveform D and the control waveform B. The inputs to the second storage tube 41 are controlled in a similar manner by corresponding gates 31, 37, 43 and mixers 33, 45 and the outputs from the storage tubes 41, 42 are selected during the first and second storage periods respectively by applying the outputs from the read-write switches 50, 51 (see below) to gates 80, 81 controlled respectively by the combinations of waveforms A and J and waveforms B and' J, the waveform J being produced by a monostable generator 35 triggered via a delay multivibrator 34 by 200 c/s. pulses from the programmer 17. The waveform J is also applied (1) to the generator 36 to produce the read-out sweep waveforms D and (2) to the grid of the P.P.I. C.R.T. 85. Producing the circuitous scanning track Figs. 2, 3, 4, 5 and 6b. The scanning beam in each storage tube 41, 42 is controlled by X and Y sweep voltages produced in respective sweep chopper circuits 39, 40 from input waveforms E and F from the mixers 33 and 32. Each of the two sweep chopper circuits 39, 40 is as in Fig. 4 and its operation is illustrated in Fig. 5 in which waveform a represents the high-speed recording sawtooth corresponding to the first (lowest) aerial followed by the slower read-out sawtooth. As shown in Fig. 4, the input a is inverted and bottom clipped to give a waveform b which is inverted and top clipped to give a waveform c, waveforms a, b and c being added to give the Y deflection waveform d and waveform a and c being added to give the X deflection waveform e. Storage tube control circuits: Figs. 3 and 7. Fig. 7 shows the storage tube 42 and its readwrite switch 51 which are the same as storage tube 41 and read-write switch 50. The storage tube comprises a single-beam barrier-grid tube such as the Radechon (see R.C.A. Review Vol. 16 June 1955) comprising a barrier screen grid 77 and a mica storage target 78 capacitatively coupled to an output electrode 76, the electrodes 77, 76 being connected across a resistor 68 in series with a load resistor 69 shunted by a diode 73 in the anode circuit of a triode V1. Waveform A, Fig. 3, is applied to the grid of V1 which is thereby rendered conductive during the first storage period to produce a voltage drop of 50v across the resistor 68 so that the video signals on waveform H, Fig. 3, applied to the grid of the storage tube are stored on the target. Due to the small finite forward resistance of the diode 73, a small signal will be developed across the load resistor 69 and this is balanced out by a corresponding signal from an equivalent circuit comprising a triode V2 in which the capacitance of the storage tube is simulated by a capacitor Cl, the two load resistors 69 and 72 being D.C. coupled to a differential amplifier V3, V4. During the second storage period V1 and V2 are cut off and the read-out sweep discharges the storage surface thereby producing read-out output signals across the load resistor 69 which appear at the output terminals 79 of the differential amplifier V3, V4 since there is no corresponding signal across the load resistor 72 of V2. The first embodiment may employ gating circuits, sweep chopper circuits and read-write circuits similar to those described above.