Patent GB-788345-A (GB)
Title: Improvements in or relating to non-reciprocal circuit components
IPC: H01P1/32
Filed: 1956-01-25
Abstract: 788,345. Non-reciprocal attenuators and phase-changers. WESTERN ELECTRIC CO., Inc. Jan. 25, 1956 [Jan. 31, 1955; Jan. 31, 1955], No. 2469/56. Class 40 (8). A non-reciprocal transmission arrangement for frequencies below the microwave range comprises a number of elongated conductors forming a transmission line capable of supporting a circularly-polarized field within an elongated ferrite element disposed parallel to the conductors. When the element is polarized by an axial magnetic field of strength sufficient to cause gyromagnetic resonance at the signal frequency, radio-frequency energy having a magnetic field component which rotates clockwise when viewed in the positive direction of the polarizing field is absorbed, but energy polarized in the opposite..sense is transmitted with little attenuation. If the polarizing field strength is reduced below the resonance value, waves circularly-polarized in opposite senses will encounter different effective permeabilities in the element and will be delayed by different amounts. Since waves propagated in two opposite directions in the system have opposite senses of polarization with respect to the positive direction of the polarizing field, they will suffer different degrees of attenuation on phase delay in the ferromagnetic element. The propagating system may comprise two conductors 11, 12, Fig. 2, arranged within a conductive tube 13 dimensioned below cut-off and bounded at either end by conductive discs 18, 19. The conductors 11, 12 extend through the discs 18, 19 to form the inner conductors of input and output coaxial loops 20, 21 whose outer conductors are electrically connected to the discs. Input and output T-junctions 24, 26 are so located on the loops 20, 21 that a phasedifference of 90 degrees exists between the equal portions of input or output energy in the parallel limbs of the loop. The ferromagnetic element 27 is located at one of the two positions where the transverse magnetic fields of the conductors 11, 12 are normal to each other. Because of the 90 degrees phase-difference, a circularly-polarized field is produced within the element. A polarizing field suitable to provide either a differential attenuation or phase delay may be provided by a solenoid 28 or by a permanent magnet or by permanent magnetization of the element 27. In the embodiment of Fig. 3, the propagating system comprises conductors 41, 42, 43, 44 symmetrically arranged within a conductive, non-conductive or lossy shield 49 and connected in pairs by bridge-pieces 57, 58, 59, 60 to balance input and output lines. The centrally located ferromagnetic element 51 is similar to the element 27 of Fig. 1. In order to obtain a circularly polarized wave within the element 51 the voltage between the diametrically opposite conductors 41, 44 is delayed by 90 degrees with respect to the voltage between the conductors 42, 43. This is accomplished by means of a dielectric plate 55 which extends between the conductors 41, 44. A similar vane 56 is provided on the opposite side of the element 51 to delay by 90 degrees the voltage between the conductors 42, 43. The phase difference may alternatively be produced by differences in the physical lengths of the conductors. In the embodiment of Fig. 4 the propagation system consists of three conductors 61, 62, 63 which are excited 120 degrees out of phase so as to produce the desired circularly polarized wave within the axial ferromagnetic element 66. The conductors 61, 62, 63 and the element 66 are supported at either end by conically tapered dielectric plugs 64, 65. Embedded within the plugs are conductive helices 69, 76 formed by the ends of the inner conductors of input and output coaxial lines 71, 77. The helices have a circumference of the order of a wavelength and are arranged in front of conductive plates 72 of diameter at least equal to one half wavelength. Both helices have the same sense of rotation and radiate in the axial direction a wave circularly polarized in this sense of rotation. The wave is supported by the intermediate conductors 61, 62, 63. This construction may be modified by arranging for the conductors to be excited by a three-phase transformer or by appropriately spaced tappings on a delay transmission path. A preferred material for the ferromagnetic element in the various constructions is magnesium-manganesealuminium ferrite.