GB950199A - Improvements in or relating to electromagnetic wave transmission systems - Google Patents

Abstract

950,199. Gyromagnetic waveguide devices. WESTERN ELECTRIC CO. Inc. July 28, 1960 [Aug. 3, 1959], No. 26300/60. Heading H1W. A non-reciprocal gyromagnetic waveguide device comprises two wave-energy paths supporting mutually orthogonal polarizations coupled by a magnetically polarized gyromagnetic element arranged to produce a region of linear polarization inclined at an angle of 45 degrees to the waves in the coupled paths. It is stated that the effect is different from the normal Faraday effect, taking place at lower field strengths and being less dependent upon frequency. The effect depends upon the coupling of orthogonal modes in the loaded coupling section and is analogous to the effect described in Specification 803,621. In the construction shown in Fig. 1, two rectangular waveguides 12, 13 are so dimensioned and orientated that they support mutually orthogonal polarizations, each being beyond cut-off for energy polarized to propagate in the other. They are connected by a guide 11 in the form of a tetrahedron taporod in both crosssectional dimensions. The gyromagnetic element may consist of a suitably polarized rod 14 of ferrite. Alternatively, other materials exhibiting the gyromagnetic effect such as yttrium iron garnet, paramagnetic substances or ionized gases may be used. In the degenerate form of this coupling shown in Fig. 3, the length of the tetrahedral waveguide is reduced to zero and the cross-polarized waveguides 31, 32 are directly abutted and coupled by a polarized ferrite rod 33. The Specification contains a detailed theoretical analysis of the coupled modes existing in those parts of the system loaded by the gyromagnetic material and it is shown that (a) when there is no polarizing field the incident wave is fully reflected; (b) under certain conditions determined by the crosssectional dimensions of the guides, the components of the permeability tensor and the frequency, there is full transmission. The phase of waves propagated in opposite directions differs by 180 degrees, i.e. the device is non-reciprocal. The device may thus be used as a switch or as a reversible gyrator whose direction of rotation is determined by the direction of the polarizing field. In general the polarization in the region of the centre of the ferrite rod is elliptical and both the linear polarizations of the output and input are beyond cut-off in this region. The parameters may be adjusted so that a linear polarization at 45 degrees to the input and output polarizations is obtained in the central region. This linear polarization lies in one of two orthogonal directions depending upon the direction of propagation. Thus guide 13, Fig. 1, may be coupled to an output probe extending through a corner of the guide 11 at a point about half-way along it and lying at 45 degrees to the sides of the guide. Guide 12 may be coupled to a similar probe extending through an adjacent corner of the guide 11 and lying at right-angles to the first probe. The probes may be replaced by waveguide T-junctions. The whole arrangement forms a 4-port circulator. Fig. 7 shows a further form of circulator using two gyrators of the kind shown in Fig. 1 coupled by a coaxial line 73 having terminal probes 74, 75 lying at 45 degrees to the sides of the tetrahedral guides 71, 72. Transmission takes place in the directions a to b, b to c, c to d and d to a. A coaxial line switch or gyrator may be formed by abutting the ends of two coaxial lines 92, 93 and 95, 96, Fig. 10, in such a manner that their cross-sections overlap in two regions A, B, and providing two rods of gyromagnetic materials at points within these regions where the magnetic field distributions (shown by arrows] lie at right-angles to each other. Coupling between fields is only possible when the rods are polarized (in opposite directions) since the junction does not normally support the wave energy propagated in the coaxial lines. The construction of Fig. 1 may also be used as an isolator by providing a resistive card lying in a diagonal plane of the waveguide 11 which includes the longitudinal axis (Fig. 5, not shown). Only energy propagated in one direction will give rise to an electric field lying in the plane of the card. Specification 789,639 also is referred to.