Patent GB-1195181-A (GB)
Title: Signal Channel Evaluation Network for Monopulse Radar Receiver.
IPC: G01S13/44
Filed: 1969-01-06
Abstract: 1,195,181. Monopulse radar. COMPAGNIE FRANCAISE THOMSON HOUSTONHOTCHKISS BRANDT. 6 Jan., 1969 [9 Jan, 1968], No. 801/69. Heading H4D. Specification describes a phase comparison monopulse radar, Fig. 1, wherein the sum S and difference De, Da, signals are sequentially applied to a common transmission channel F in periods I, II and III respectively, the phase of the sum signal is recording during period I by means of phase-locking local oscillator circuit H and said recorded phase is used in periods II and III to determine the phase differences #e and #a between the sum signal and the two difference signals. In addition a gain control circuit G operates during period I such that the amplification of the channel during periods II and III is inversely proportional to the amplitude of the sum signal. The integrators 20 and 21 thus produce signals: during periods II and III respectively. The periods I, II and III are defined by gauged switches 10, 11 and 12. In greater detail, Fig. 2, the transmission channel F comprises I.F. components 1, 2 and 3, two variable-gain amplifiers 4 and 6 producing the inverse amplification variation under the control of circuit G, band pass filter 7 and a synchronous demodulator 8, fed with the sum or difference signal and the phase quadratured output F of local oscillator 18. During the sum period I, frequency changer 5 is fed with the output of variable oscillator 17, so adjusted that the sum signal at the demodulator is in phase with the quadratured output R. To so adjust oscillator 17 the limited output of amplifier 6 is compared in frequency with output R in discriminator 15 whereby a large or coarse correction signal is fed to oscillator 17 (to compensate for doppler shifts &c.) and once said coarse correction is achieved (equality of frequency of the two demodulator inputs) a phase comparison is carried out in discriminator 14 to provide a fine correction signal. By means of the open contacts of switch 11 during periods II and III, the sum signal representative phase and frequency of the output of oscillation 17 is retained. The input to the phase discriminator 14 may be taken from the output of band-pass filter 7, Fig. 3 (not shown). During the coarse correcting stage the frequency of oscillator 17 may be swept by means of an applied sawtooth wave, Fig. 4 (not shown). Arrival of the correct frequency causing the removal of the sawtooth output and the application of the output of the phase discriminator. In the arrangement of Fig. 8 two transmission channels F1 and F<SP>11</SP> are provided sequentially sharing the same phase locking circuit H. During a first period the sum signal is applied to channel F<SP>1</SP> with the circuit H operative therewith and the difference signals are applied sequentially to channel F<SP>1</SP>. During the second, equal, period, the sum signal is applied to channel F<SP>11</SP> with H operative therewith and the difference signals are applied to channel F<SP>1</SP>. Switches 100 and 122 operate at twice the rate of switches 101<SP>1</SP> ,  101<SP>11</SP> ,  121<SP>1</SP> ,  121<SP>11</SP> and 120, whereby a continuous output is produced at the input to switch 122.