GB757925A - Unidirectional wave guide attenuator - Google Patents

Abstract

757,925. Waveguide attenuators. STANDARD TELEPHONES & CABLES, Ltd. Oct. 29, 1954 [Nov. 6, 1953], No. 30795/53. Class 40 (8). A unidirectional waveguide attenuator comprises a circular waveguide containing an axially disposed cylinder B of a ferromagnetic material, e.g. nickel-zinc ferrite, capable of gyromagnetic resonance at the frequency of the wave energy under the influence of an axial magnetic field of the correct magnitude. The circular waveguide is connected at either end to rectangular waveguides 3, 4, the linearly-polarized energy from which is converted to left-handed circularly-polarized energy by either of two #/4 dielectric plates A, C which lie in mutuallyperpendicular planes at 45 degrees to the principal longitudinal planes of the rectangular guides. The ferrite body B is only excited into resonance when the sense of rotation of the circularly-polarized wave is the same as the direction of the current (real or hypothetical) producing the axial magnetic field. Since the effect is independent of the direction of propagation and since energy propagated in either direction has a left-handed sense only energy propagated from right to left will be absorbed by the gyromagnetic resonance effect. Energy propagated from left to right is substantially unattenuated and is converted to a planepolarized mode compatible with the rectangular guide and by the #/4 plate C. In a modification the #/4 plates are arranged in the same plane with the cross-section of one of the terminal rectangular guides twisted through 90 degrees relative to the cross-section of the other. In a further modification one of the #/4 plates is omitted. This apparatus behaves in the same manner as the one shown in the Figure, except that a 3 db. loss is incurred for waves travelling in the " pass " direction. A permanent magnet or a solenoid may be used to produce the static magnetic field.