Patent GB-1098614-A (GB)
Title: Radar system
IPC: G01S13/42
Filed: 1965-05-17
Abstract: 1,098,614. Radar; aerials. HOLLANDSE SIGNAALAPPARATEN N.V. May 17, 1964 [May 21, 1964], No. 20773/65. Headings H4A and H4D. A pulse radar system for determining the range, azimuth and elevation of targets, comprising a first aerial 5, having a vertical cosecant squared beam and rotating about an axis 7, to produce the range and azimuth of detected targets at output 53 and on PPI display 10, additionally comprises a second aerial 15 rotating about an axis 18 parallel with axis 7 and comprising a line of radiating slots inclined at an angle K to the axis 18 to produce a beam lying in a plane extending through the slots and having an elevation dependent on the frequency of the radiated pulse, pulses only being transmitted by the second aerial when its azimuth coincides with that of a target detected by the first aerial, the frequency variation from pulse to pulse, the angle K, and the rotation rate of the aerial 15 being such that consecutive pulses are all radiated along the vertical azimuth plane of the target to perform a scan in elevation and produce the range and elevation of the target at output 53 and on display 17. The echoes received by aerial 5 are passed via detector 23 to an azimuth counter 24 and a range counter 25. The azimuth counter is fed with pulses from an aerial conversion unit 29, and delivers a count representing the targets azimuth, and the range counter is fed with pulses from terminal 30, starting with each transmitted pulse to deliver a count representing the targets range. These two counts are stored in memory 20 and fed to output 53, whilst the azimuth count only is fed to one input of an azimuth comparison circuit 21. The other input of the comparison circuit is fed with the output of an azimuth counter 37, determining the azimuth of aerial 15. Thus, when the two azimuths are equal the two inputs to the comparison circuit are also equal, and the circuit produces an output pulse which starts a frequency control unit 41. This commences to pass pulses of successively increasing frequency to the transmitter 12 for transmission thereby, through aerial 15. The construction of aerial 15 is such that each pulse, being of higher frequency than the last, is transmitted along a higher elevation beam. The frequency control unit therefore is able to produce count pulses indicating the elevation of the beam, and these are passed to an elevation counter 43, which is used in conjunction with a range counter 49. The determined range and elevation of the target is passed to memory 20 and output 53. The system comprises criteria determining means in automatic detectors 23 and 42 such that only echo pulses having amplitudes above a certain threshold and occurring for a minimum number of successive echo periods, cause corresponding pulses to be passed to the counters. If the pulse repetition rate in relation to the beam width is too low to provide said minimum number of successive echoes, the radiated pulse may comprise two frequencies, such that two adjacent beams are radiated to give two possible echoes. The difference between the two frequencies is constant from pulse to pulse (Fig. 4, not shown). If the angle of tilt K is reversed, the transmitted frequency may be reduced from pulse to pulse, to produce a descending beam. In a second embodiment of the invention, Fig. 5 (not shown), the two aerials may be mounted back-to-back on the same mounting. In this embodiment, the range azimuth and elevation of a target are found as described using double frequency radiated pulses, with constant frequency differences. When all three dimensions have been determined, the three dimensional position of the target is checked by switching the system to a second mode. In this mode, each transmitted pulse still has two frequencies, but the difference between the two frequencies is no longer constant, but is initially large and decreases to zero from pulse to pulse, and the reverses sign to increase again. The result is that one beam #<SP>1</SP>, Fig. 6 (not shown), describes a vertical scan, whilst the second beam P<SP>1</SP> describes a horizontal scan. A computer fed with the determined dimensions of the target, controls the frequencies of the radiated pulses such that the intersection of the paths of the two beams occurs at or near the position of the target D. From the echoes, the computer determines the position errors ##<SP>1</SP> and #P<SP>1</SP> and corrects the corresponding dimensions of the target.