GB809365A - Improvements in or relating to wave guides for the transmission of high-frequency polarised electromagnetic waves - Google Patents

Abstract

809,365. Waveguide accessories. MULLARD RADIO VALVE CO. Ltd. Aug. 8, 1955, No. 22866/55. Class 40 (8). The ellipticity of a wave propagated in a symmetrical waveguide is corrected by reactances arranged in a plane at 45 degrees to the major and minor axes of the ellipse. The electric vector of an elliptically-polarized wave may be resolved into two virtual components D, E selected to have equal amplitudes and arranged in space quadrature at 45 degrees to the axes of the ellipse. The vectors are separated in time by a phase angle Πx related to the ellipticity. One or a pair of reactive phaseshifting elements P, P<SP>1</SP> are arranged to shift the phase of one or both the vectors D, E in the appropriate direction so as to reduce the phase difference x to zero. When x is zero the two vectors represent the virtual components of a plane wave polarized in the direction of the major axis of the ellipse. Positive or negative reactive effects may be achieved by the use of slots, conductive or dielectric septa or by deforming the waveguide walls to an elliptical or oval cross-section. A preferred form of reactance comprises an adjustable conductive rod 18 arranged to extend radially into the circular waveguide 1. A further rod 19 may be provided in a plane at right-angles to the first rod, although only one rod is necessary once the direction of rotation of the vector is known. As shown, the guide 1 forms part of a known type of gyromagnetic circulator having input and output iris transformers 2, 3 connected to rectangular guides whose major axes lie at 45 degrees to each other. Two further terminals 5, 6 in the form of side arms lie each in the plane of the major axis of the adjacent rectangular guide. The gyromagnetic element is in the form of a tapered ferrite rod 18 and is arranged in an axial magnetic field adjusted to give a Faraday effect rotation of 45 degrees. Elliplicity due to differential attenuation in the element of the two circularly-polarized components of a plane wave is corrected by the reactive rods 18 or 19 which may be placed on either side of the gyrator. The ferrite element 8 is supported by two diaphragms 9 of foamed polythene held within a metal tube 10. The tube 10 is axially compressed by turnbuckles 12 between shoulders on the two halves of the circular guide 1. Ports 13, 14, 15 in the guide walls and in the diaphragms 9 are provided for circulation of a coolant, e.g. compressed air, within the portion of the guide bounded by the dielectric discs 11. The invention may also be used in conjunction with non-reciprocal devices using gyromagnetic elements in a transverse field, of both the resonant and non-resonant types.