Patent GB-801831-A (GB)
Title: Improvements in or relating to wave guide switches
IPC: H01P1/11
Filed: 1956-09-11
Abstract: 801,831. Waveguide switches. WESTERN ELECTRIC CO., Inc. Sept. 11, 1956 [Sept. 16, 1955], No. 27759/56. Class 40 (8). An element of gyromagnetic material, e.g. a slab of ferrite, is used to control the effective width and hence the cut-off frequency of a waveguide in order to provide a switch. In the simplest embodiment (Fig. 1, not shown), a slab of ferrite is situated close and parallel to the narrow wall of a rectangular waveguide in a region where the broad dimension is reduced to below the cut-off value. The dielectric constant and dimensions of the slab are chosen so that the narrow' portion of the guide is loaded sufficiently to place it above cut-off. An electromagnet is so positioned that a transverse field may be applied to the ferrite slab and this field may be adjusted so that the effective permeability of the slab is zero. Under these conditions the propagated waves are confined to that part of the waveguide not occupied by the ferrite slab. Since this portion is beyond cut-off no wave is transmitted. Matching of the ferrite slab may be obtained by extending the end portions into the full-size waveguide. In a modification the size of the ferrite slab is insufficient to place the narrow portion of the guide above cut-off and the switch is normally open. To close the switch the permeability of the ferrite slab is increased to a high value by application of a magnetic field of suitably high intensity. This places the narrow portion of the guide above cut-off. In a further form of switch, Fig. 3, a septum 21 is positioned parallel to the narrow walls of a waveguide to provide two narrow channels S, T, both dimensionally beyond cut-off. Two ferrite slabs 22, 23 and a matched termination 24 are disposed as shown in the channels. Each slab is provided with its own electromagnet (not shown). In the closed state of the switch channel S is closed and channel T open. In the open state channel S is open and channel T closed so that energy propagated from the input is absorbed by the termination 24. As seen from the output end, both channels are beyond cut-off and the whole of the energy from this end is reflected. The parts of the channels not occupied by the slabs 22, 23 and termination 24 may be filled with dielectric members whose tapered ends extend into the main waveguide (Fig. 11, not shown). The two field intensities necessary to produce open and closed conditions of the switches of the invention may be produced by the remanent magnetization of a permanent magnet. The required values of remanent polarization may be obtained by applying current pulses of suitable sign and magnitidue to a winding on the magnet. One of the required values may, of course, be zero. In a modification of the switch of Fig. 3, several parallel septa are used to divide the waveguide up into a number of channels each of which may be associated with a coaxial line coupling. Energy in the guide may be diverted to any one or more of the couplings. In the construction of Fig. 9, a conductive septum 84 divides a T-junction 80 into two parts, each dimensionally beyond cutoff.. Propagation of energy into either branch of the junction is controlled by 'ferrite slabs 85. In the construction of Fig. 10, a cut-off portion of guide 200 is defined by a U-shaped conductive member 203 and two ferrite slabs 201, 202 adjacent the upper and lower faces of the guide. Flow of energy in the cut-off portion is controlled by a further ferrite slab 204 which is arranged to complete a magnetic circuit comprising portions of the slabs 201, 202 and the core 205 of an electromagnet 206. The electromagnet is positioned within the waveguide 200 between the arms of the U- shaped member 203. This type of construction may be applied to the switch diagrammatically shown in Fig. 3 by duplicating the components (Fig. 11, not shown).