GB812799A - Improvements in or relating to radar apparatus - Google Patents

Abstract

812,799. Pulse radar; aerials. DECCA RECORD CO. Ltd. May 23, 1957 [Feb. 23, 1956], No. 5718/56. Class 40 (7). [Also in Group XL (b)] Radar apparatus includes a waveguide system for providing rectangular section horn aerial with waves of adjustable ellipticity or direction of linear polarization. The embodiment described (see Fig. 1) comprises a pulse radar transmitter 10 feeding through a duplexer 11 waves linearly polarized with the electric vector parallel to the shorter side of rectangular waveguide 12, to a rotating coupling 21 formed by relatively rotatable circular coaxial lines 23, 24. Rectangular waveguide 26 is coupled by transition section 27 to square waveguide 28 which is coupled by further transition section 29 to square waveguide 30 whose walls are at 45 degrees to those of guide 28. Guide 30 (see Fig. 5) incorporates a phase shifter comprising a dielectric sheet 31 adjustable by rods 32 which may be remotely controlled by a power-driven cam. The output wave from the phase-shifting section is in general an elliptically-polarized wave; when it degenerates into a linearlypolarized wave the plane of polarization can be rotated by rotating the assembly lying between couplings 21, 42. The major axis of the ellipse may be rotated likewise. Conversely, received elliptically-polarized signals are converted into linearly-polarized waves at duplexer 11. Waveguide 28 has an internal wire grating 50 (see also Fig. 4), a rectangular slot 51 and a dummy load 53, so that waves of undesired polarization may be absorbed; the load may be replaced by a receiver. The invention may be used to minimize interference from rain or from other transmitters. The horn aerial may illuminate a reflector 14 or a lens, forming part of an aerial system for rotational or oscillatory scanning. Specification 805,977 is referred to.