GB814921A - Microwave antenna system - Google Patents

Abstract

814,921. Aerials. BENDIX AVIATION CORPORATION. May 24, 1957 [June 5, 1956], No. 16578/57. Class 40 (7). [Also in Group XL (b)] A directive antenna system having two alternative beam patterns comprises a main reflector 1, an auxiliary reflector 2 of spaced parallel wires in front of part of the main reflector, a co-operating primary radiator arranged substantially at the main reflector focus and energy feeding means provided with a non-mechanical changeover arrangement so that the plane of polarization of energy directed to the reflectors can be changed between two mutually perpendicular directions in one of which the auxiliary reflector is operative and in the other of which it is substantially inoperative. As described, the main reflector may, by itself, provide a pencil beam and, when modified by the auxiliary reflector, a cosecant squared fan beam. This arrangement is intended for aircraft radar providing a weather service with the pencil beam and ground mapping service with the fan beam. The whole aerial system may be mounted for rotation about a pivot 7 as shown in Fig. 1. The feed arrangement (Fig. 2) comprises a rectangular guide 22 coupled by a quarter-wave transformer 23 to a circular section waveguide 12. At the end of guide 12 a taper transition is made from air to the solid dielectric 18 of conical shaped guide 17 which leads to circularly symmetrical dielectric lens radiator 19 backed by reflector 21. The radiator 19 acts as a point source for illuminatirig the reflector and functions equally well whatever the polarization of the wave energy. The means for controlling the energy polarization comprises a ferrite rod 14 mounted centrally in the guide 12 by means of conicallyshaped washers 15 of low loss dielectric abutting against shoulders thereon. A magnetic field parallel to the axis of the guide may be created by energization of the coil 16 mounted round it. Application of this field is arranged to cause the required 90 degrees shift in the plane of polarization between one state in which auxiliary reflector 2 is inoperative and the other in which it is effective. ______