Patent GB-1390216-A (GB)
Title: Multibeam radars
IPC: G01S7/02
Filed: 1972-11-30
Abstract: 1390216 Radar; aerials THOMSON-CSF 30 Nov 1972 [1 Dec 1971] 55433/72 Headings H4D and H4A In a multibeam radar a plurality of primary radiating sources 200, 201, 202, 203, 204,... Fig. 8, are associated with a reflector 1. Said sources are coupled in a distributer 5 using circulators, for example, and they provide in the reception phase a first group of angularly stepped beams. The angular position of a target may be determined by interpolation of the signals received in respect of two adjacent beams. The invention utilizes received signals which have been changed in polarization on reflection to develop a second group of beams, interspersed with the first group, a second distributer 16 being provided to enable the said signals to be coupled in appropriate sets. As described, the reflector 1 is parabolic, and the primary sources are disposed in its focal plane to provide beams which are stepped in elevation. Each source is connected to a first port of a dual-mode coupler, which has two other ports for propagating waves which are linearly polarized in respective perpendicular directions. When the transmitted and received waves are linearly polarized a mode coupler may comprise a circular-section waveguide 11, Fig. 4, to which are coupled an in-line rectangular-section waveguide 9 and a perpendicularly disposed rectangular-section waveguide 14. Allternatively, the main waveguide may be of square-section (Fig. 5, not shown). When the transmitted and received   waves are elliptically or circularly polarized such a mode coupler having a circular-section main waveguide is additionally provided with a quarter wave polarizing fin (Fig. 6, not shown). The waveguides 9 of the mode couplers are connected to the distributer 5, where they are coupled in sets corresponding to the first group of beams, said sets being connected to duplexers 4. A common transmitter 3 feeds all the duplexers during the transmission phase, and said duplexers provide signals to independent receivers 6 during the reception phase. An interpolator circuit 7, which may comprise logarithmic amplifiers, carries out a comparison between the signals in adjacent beams, and provides one input to a logic circuit 20. The waveguides 14 of the mode couplers are connected to the distributer 16, where they are coupled in sets corresponding to the second group of beams. This also applies to a mode coupler associated with a supplementary source 199, which is provided to enable a beam to be developed below the lowest beam of the first group (Fig. 7, not shown), the waveguide 9 of said coupler being connected to an absorptive load 198. The coupled sets from the distributer 16 are connected through limiters 17 to receivers 18. An interpolator circuit 19 carries out signal comparisons, and provides another input to the logic circuit 20. An extraction and display circuit 21 fed from the logic circuit 20 displays data determined by the processing of the data picked up by the radar. The system is able to select those beams in which signals of maximum strength occur, and the larger number of beams available increases the level at which interpolation is made, so improving side lobe blanking.