Patent GB-1171628-A (GB)
Title: Multibeam Antenna System
IPC: H01Q25/04
Filed: 1966-10-14
Abstract: 1,171,628 Aerials; pulse radar. COMPAGNIE FBANCAISE THOMSON HOUSTON-HOTCHKISS BRANDT. 14 Oct., 1966 [15 Oct., 1965], No. 46178/66. Headings H4A and H4D. Relates to a multi-beam aerial system in which individual primary elements, hereafter termed radiators but including receptors, form a primary array on the focal surface of a focusing device. According to the invention gain and resolving power are maximized by arranging that the total field distribution pattern at the radiant surface of the primary array 2, Fig. 2, takes the form of a pair of continuous sinuous orthogonal (analytically) curves FA, FB mutually displaced by the transverse extent of the radiant aperture of one radiator and each undulation of each curve extending over a transverse extent corresponding to both radiant apertures of two adjacent radiators; and each undulation of each curve approximates to the diffraction pattern, Fig. 4 (not shown), produced from a point-source at infinity through the focusing device 1 (which may be a mirror or a lens). In the embodiments each radiating aperture is a nozzle or flared horn, excited in two waveguide modes by two waveguides coupled to it at its non-radiating aperture for example of kind described in Specification 1,002,140. In the embodiment, Fig. 2, each multi-mode structure, e.g. 21, is coupled to signal lines 30, 31 via hybrid junctions 40, 41; matched loads 401, 442 are added at the ends. One multi-mode structure. Fig. 5, is of E-plane type and is used for generating stacked beams displaced along direction OY; sections A, B are rectangular waveguides of similar dimensions stacked with their broad sides parallel and spaced in direction OY. Main section C has width a equal to that of sections A, B and a height b somewhat greater than that of the combined sections A, B, each of which can propagate the TE 10  mode, whereas section C can propagate also some higher modes including TE 11 , TM 11 . The energy fed to section A is randomly phased compared with that applied to section B. It is argued that the output field patterns, Fig. 8c, when input A or input B is selectively excited are FA(y)α (1+k sin (#y/b)) and F B (Y)α (1 - k sin (#y/b)) where k is proportional to the aperture D of section C. k is preferably #2. Decoupling between modes is added by known means, e.g. strips in sections A, B for even modes and in section C for odd modes. To approximate the diffraction curve, Fig. 4 (not shown), it is shown that b= 4#F/3D, where # is wavelength and F is the focal length of the lens. A condition for length L of section C is stipulated. Scanning in the E-plane can be effected by beam switching. An H-plane multi-mode arrangement, utilizing side-by-side A and B sections, may alternatively be provided, Figs. 9-13 (none shown), or a composite structure utilizing E- and H-plane multi-modes for maximizing gain and resolution in all directions. Experimental curves are given of radiation patterns achieved, Figs. 14, 15, 16 (none shown). Section C of a multi-mode structure may be in two parts, the outer one of which is flared, Figs. 17, 18 (neither shown). Resolution may be increased in a pulse radar, Fig. 21, arrangement in which a magic-T41 affords a sum signal in output leg 413 and a difference signal in output leg 414 and the gain-controlled corresponding signals at I.F. are applied to a product detector 13.