Patent GB-753038-A (GB)
Title: Radar apparatus
IPC: H01Q3/08
Filed: 1954-03-01
Abstract: 753,038. Radar. NAAMLOOZE VENNOOTSCHAP HOLLANDSE SIGNAAL-APPARATEN. March 1, 1954 [Feb. 27, 1953], No. 5937/54. Class 40 (7). Radar apparatus includes an aerial system for scanning purposes, the beam of which swings about a first axis through a plurality of beam widths and can also rotate about a second axis, preferably at rightangles to the first, wherein the beam is made to perform an auxiliary scan about the second axis (superposed on the rotary movement) which has a major frequency component twice the fundamental frequency of the scanning motion about the first axis. The amplitude of the auxiliary scan is arranged to be not greater than the angle rotated round the second axis whilst the beam performs one cycle of its scan about the first axis. The purpose of the auxiliary scan is to. enable a field of view to be scanned with a minimum of double coverage and so to increase the searching speed. In the limiting case if the combined movement about the second axis resulted in a sudden movement onwards each time the main scan reached the extremities of its movement double coverage would be completely avoided. This, however, is normally impossible due to the inertia of the aerial system or of the element thereof which has to be moved to effect the auxiliary scan. Therefore use is made of a primary scan which passes beyond the field it is required to view at each end of the scanning movements and the shift to the next adjacent scanning path effected when the beam is directed outside the field of view and the transmission of pulses suspended. Suspension of pulse transmission may enable the speed of the main scan over the effective part of its stroke to be increased without danger to the transmitter so that the inclusion of the movement outside the required field of view does not necessarily increase the time it takes to cover the whole of this field. The search aerial system so far described may include means for stopping the operation of the system to scan a complete field of view and to render it effective instead to give accurate positional information about a given target. For this purpose the rotation about the second axis is stopped and the auxiliary scan replaced by one whose fundamental frequency equals the scanning frequency about the first axis, the construction being such that the up and down scanning movements are then over contiguous slightly overlapping paths. With this arrangement it is possible to determine accurately when the median plane of the up and down scans is accurately aligned with the object. Suitable display systems for this are described in Specification 753,039 which claims apparatus scanning in this manner. In the preferred embodiment a wire mesh reflector capable of giving a beam narrow in the vertical plane and fairly wide in the horizontal may be approximately aligned in elevation about axis 102 which is arranged to rotate about a vertical axis by means not shown. The reflector is fed by a horn 120 carried at the end of a waveguide 118 which leads through rotatable joints 113 and 112 to guide 111 coupled through further joints to the transceiver. To provide the primary vertical scan the horn and guide 118 are oscillated about joint 112 by means of arm 121 hinged at 119 and attached by a ball joint at its lower end to crank 116. This crank is rotated by shaft 117 driven from motor 114 by means of gearing 103, shaft 104 and gearing 109. The auxiliary scan is also performed by movement of the primary element, in this case by oscillating it about the axis of joint 113. This is done by rod 122 hinged at 123 and coupled by a ball joint to crank 105 which is coupled to crank 106 carrying a roller cam-follower 108 held against cam 107 on shaft 104 by means of spring 115. The cam 107 is shaped so as to provide the required auxiliary scan motion. To obtain accurate positional information about a particular target, rotation of the whole scanning system about a vertical axis is stopped with the aerial directed as nearly as possible towards the target and the auxiliary scan changed as described above. One way of changing the auxiliary scan is shown in Fig. 5, wherein the arm 503 corresponds to crank 106, shaft 501 to shaft 104, and cam 502 to cam 107. In this embodiment the cam follower roller 505 is not carried by arm 503 itself but by a three-armed lever 504. Operation is just as in Fig. 2 until handle 507 is moved through an angle α to move roller 505 out of engagement with cam 502 and instead bring roller 506 into engagement with cam 509 mounted on the same shaft 501. Cam 509 is shaped to operate arm 503 in such a way as to provide the auxiliary scan required to obtain accurate bearing positional information. Various other means of obtaining the required scanning and auxiliary scanning motions are briefly described. Specification 753,035 also is referred to.