Patent GB-733486-A (GB)
Title: Elements for rotating the plane of polarization of plane polarized electromagnetic waves
IPC: H03H7/00
Filed: 1952-05-23
Abstract: 733,486. Wave-guides. WESTERN ELECTRIC CO., Inc. May 23, 1952 [May 26, 1951; Oct. 22, 1951], No. 13118/52. Class 40 (8). [Also in Group XL (c)] A device for effecting an anti-reciprocal rotation of the direction of polarization of polarized electromagnetic waves comprises a body of magnetizable material arranged within a waveguide and magnetically polarized in the direction of propagation of the waves. The cylindrical element 1 is of ferro-magnetic material, preferably a mixture of 60 per cent by volume of powdered nickel-zinc ferrite with polystyrene. Tapered transition members 2, 3 made of polystyrene cut down reflection from the faces of the ferrite cylinder. The element is magnetized in a direction parallel to the direction of propagation of the electromagnetic wave by means of a solenoid 7. A plane polarized wave may be considered as split into positive and negative circularly polarized components. These travel with different velocities in the ferromagnetic medium and, upon emergence, unite to form a plane polarized wave whose plane of polarization lies at an angle # to that of the incident wave. The rotation # is large (1.2 radians/cm. for a field of 1000 gauss) and can be shown to be independent of frequency and proportional to the magnetization of the ferromagnetic element. The direction of rotation is independent of the sense of propagation along the axis of the element and hence a wave traversing the element first in one direction and then in the other undergoes a double rotation. If the frequency of the incident wave is close to the ferromagnetic resonance absorption frequency the positive circularly polarized component is absorbed whilst the negative component is transmitted. Hence in the region of the absorption frequency the emergent wave is circularly polarized. The electromagnet may . be replaced by a permanent magnet. Fig. 2 shows the device applied to a variable attenuator or modulator. The rectangular guides 5, 6 are arranged with their corresponding transverse axes at 45 degrees to each other and serve as polarizers in that they will accept only that component of the electric vector consistent with the TE 10  mode. By means of a smooth transition this mode is transformed to the TE 11  mode in a circular guide 4 containing the ferromagnetic element 1. A rotation of 45 degrees is produced by the element 1. A variable current supplied to the solenoid 7 by a potentiometer circuit 9 will cause variable rotation of the plane polarized wave from the input guide 5 and hence variable attenuation in the output guide 6. A rotation of 90 degrees produces a wave polarized at right angles to the preferred direction in the guide 6 and substantially no output is produced. The device may be used in a similar manner in A.V.C. and diplexing systems (see Group XL (c)). In the one-way transmission device of Fig. 8 the input and output guides 5, 6 are of rectangular section and lie with their corresponding transverse axes at 45 degrees to each other. The element 1 is arranged to rotate the plane of polarization of energy from the input 5 by 45 degrees in a clockwise direction so that it is propagated in the rectangular output guide 6. Energy propagated from the guide 6 towards the guide 5 is also rotated by 45 degrees in a clockwise direction but is not propagated in the guide 5 since its plane of polarization is in space quadrature to the minor transverse axis of the guide. In the switching system of Fig. 9 the two rectangular guides 41, 42 have their corresponding transverse axes at 90 degrees to each other and the element 1 is arranged to produce a rotation of 90 degrees. The guides 41, 42 lead to a pair of magic-tees 43, 44 joined by a guide 49. With this arrangement transmission is possible from branch a to branch b, from b to c, from c to d and from d to a. If the magnetizing field of the element 1 is reversed the transmission characteristics of the system are reversed. Specification 643,162 is referred to.