Patent GB-1196556-A (GB)
Title: Improvements in Monopulse Radar Systems
IPC: G01S13/44
Filed: 1961-07-26
Abstract: 1,196,556. Aerials; radar. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. 26 July, 1961 [17 Aug., 1960], No. 27172/61. Headings H4A and H4D. A monopulse radar for automatically tracking a moving target comprises two aerials each comprising a plurality of parallel equispaced and rectilinear radiating lines having equispaced radiating discontinuities and a waveguide containing a ferrite for feeding the lines; and means for producing magnetic fields in the ferrites, the two fields being related to each other and adjusted so that the respective electric lengths of notional transmission lines, formed by the discontinuities nearest to the axis, differ by a constant. There are two aerials each comprising parallel micro strip lines having radiating discontinuities which are built up by line lengths where at least one edge of the line is shifted laterally with respect to the general direction of the line, each radiating discontinuity being shifted lengthwise of the line with respect to the corresponding discontinuity of the adjacent line in such a manner that the phase velocity of the wave in the guide is greater than the velocity of light. In each aerial the lines are connected to a common waveguide in the axis of which is placed a ferrite element surrounded by a coil which produces a magnetic field controlling the ferrite. The coils of the two aerials are connected in series and energized through a control valve, Fig. 5 (not shown), and in addition one of the ferrite elements is surrounded by a further coil connected to an adjustable source of current which is adjusted so that k 1  1-k 2 1 equals a constant which is preferably 2#, 1 being the length of the aerials and k 1  and k 2  the respective wave numbers of the aerials corresponding to the apparent energy propagation along an apparent transmission line including respective discontinuities having the same relative position with respect to the axis of the aerial. Under these conditions it is shown that the radiating patterns of the two aerials are identical in azimuth, and in elevation the maximum radiating direction of aerial 1 is a zero radiating direction of aerial 2 and vice-versa. It is also shown that the vector difference between the signals from the two aerials is a function only of the elevation angle of the target, and that the azimuth error depends only on the phase difference between the two signals. In Fig. 8 the two signals from aerials A 1 , A 2  are fed to a magic T which produces a sum output S and a difference output D which are fed to mixers M 1 , M 2  which are also supplied with a local oscillation from unit OL. A phase comparator C 1  and detector D 1  provide an error signal which is a measure of azimuth error and may be used to alter the direction of the moving body. The signal D from M 1  passes through a #/2 phase shifter to a comparator C 2  and detector D 2  to provide an error signal in elevation equal to the component of D in quadrature with S. This signal may be applied to the ferrite elements to give automatic tracking in elevation. In a modified aerial arrangement, Fig. 6 (not shown), the strips of one of the aerials have their discontinuities inclined to the axis so that the condition k 1 1-k 2 1 equals a constant is fulfilled with equal magnetic fields surrounding the ferrites.