Patent GB-1253734-A (GB)
Title: Monopulse radar apparatus
IPC: G01S13/44
Filed: 1969-01-23
Abstract: 1,253,734. Radar. HOLLANDSE SIGNAALAPPARATEN N.V. 23 Jan., 1969 [24 Jan., 1968], No. 4020/69. Addition to 1,156,589. Heading H4D. Specification describes a development of the M.T.I. monopulse tracking radar described in parent Specification. In the main embodiment, Fig. 4 Sum #, Azimuth difference (#B), and Elevation difference (#E) intermediate frequency signals are produced on respective output lines 12, 10 and 11 of receiver 4 and are fed to respective mixers 19, 17, and 18 to produce respective doppler frequency signals. The two difference doppler signals are fed to range gated box car circuits and the outputs thereof fed via doppler filters 23 and 24 and normalizing amplifiers 26 and 27 to phase sensitive detectors 29 and 30. The detection is with reference to a signal derived from the sum signal, to produce, from the detectors, respective azimuth and elevation error signals for controlling respective aerial servos 13 and 14. The sum doppler signal is fed to one of two channels, depending on the mode of switch 50 and its contacts 53 to 60. In the intial or searching mode, the contacts are in the opposite states to those shown. Thus contacts 59 and 60 are closed whereby the sum doppler signal is fed to means 35 via a standard delay line cancelar 37. The variation of the sum signal in successive pulse occurrence periods is shown at Fig. 2a, with the return from a moving target being arrowed and the other responses being due to jitter. The output of the delay line canceller is shown at Fig. 2b and is fed to variable threshold means 41 and 42. The thresholds of means 41 and 42 are lowered by respective early and late broad gates Fig. 2c from gate generator 3. The gated outputs are fed to sum and difference means 45 and 44. The difference means produces a range error signal which is applied to generator 3 to reposition the early and late gates. The moving target pulse in the sum means output causes a blocking oscillator 38 to produce a narrow gating pulse Fig. 2d which is fed via closed contacts 54 and 58 to the box cars 20 and 21 and to the box car 22 in circuit 49. This gates through the sum doppler signal for use, via filter and normalizing amplifier 28, as the reference for phase detectors 29 and 30. The narrow gating pulse Fig. 2d is also time compared by means of AND gate 52 with a second mode narrow gating pulse Fig. 3c for generator 3 coincident with the abutting point of the broad early and late gates, Fig. 2c and Fig. 3b. When the range error signal from difference means 44 has adjusted said abutting point on to the moving target response, the two inputs to gate 52 coincide, and a resultant signal causes switch 50 and its contacts to switch to the tracking mode as shown. Means 35 is now inoperative. Early and late narrow gating pulses, Fig. 3e are respectively fed from 3 to box cars 22 and 22<SP>1</SP> and the box car outputs fed to a sum and difference network 64. The sum signal as before provides the reference for the detectors 29 and 30, whilst the difference signal provides a fire range error signal by means of phase sensitive detector 65 using the sum signal as reference. The second mode gating pulse, Fig. 2d is fed to the box cars 20 and 21.