Patent GB-862451-A (GB)
Title: Improvements in or relating to resonance isolators
Inventor: SIDWELL JOHN MEARS
IPC: H01P1/365
Filed: 1958-11-20
Abstract: 862,451. Non-reciprocal attenuators. GENERAL ELECTRIC CO. Ltd. Nov. 11, 1959 [Nov. 20, 1958], No. 37384/58. Class 40(8) A non-reciprocal attenuator of the resonance-isolator type comprises an element of ferrite inserted between two parallel or series sections of a transmission-line conductor, the sections being arranged to cross at rightangles and to be in phase-quadrature in the vicinity of the ferrite element so that a circularly-polarized r.f. field is set up within the element. As shown in Figs. 2 and 3, the inner conductors 26, 27 of input and output coaxial terminals 1, 2 are joined by two electrically-parallel conductors 3, 4 in the form of conductive strips disposed on opposite sides of a polytetrafluoroethylene card 12. A conductive casing 9, 10 forms a common outer conductor. The conductors 3, 4 cross one another in the vicinity of a bevelled ferrite disc 7 which is held within an aperture in the card 12 by wire loops 5, 6 forming part of the conductors. The electrical distances from the input 1 to the cross-over point along conductors 3 and 4 are arranged to differ by an odd number of quarter-wavelengths, i.e. by (2n + 1)#/4, so as to set up within the ferrite element two equal-amplitude fields in phase quadrature. An equal but opposite path difference between the crossover point and the output terminal 2 ensures that the total lengths of the two conductors are equal. In order to adjust the lengths of the paths for different frequencies of operation, the capacitance between the conductors and the casing may be varied by means of conductive discs 32, 33 carried on threaded rods 34, 35. The steady magnetic field necessary for operation of the isolator is provided by a pair of parallel magnets 42 (one only visible as shown) having mild steel pole pieces 44, 45. The strength of the magnetic field may be adjusted by plugs 48, 49 of mild steel tapped into the pole pieces. In the modification of Fig. 5 the crossed-over portions of the transmission-line conductor are in series, being formed by the continuous inner conductor 63 of a coaxial line. Portions 66, 68 of conductors 63 lie parallel to one another at the cross-over point whilst portion 67 lies at right-angles to both. The end B of portion 66 is joined to one end of portion 67 by a loop of length (2n + 1) #/4 and the other end of portion 67 is joined to the end 6 of portion 68 by a loop which is longer than the first loop by an odd number of halfwavelengths. The loops (not shown) are in the form of coaxial lines. In the vicinity of the cross-over, the common outer conductor is formed by three suitably shaped brass blocks 74, 75, 76 which also serve to hold in position two ferrite discs 64, 65. The steady magnetic field is provided by a permanent magnet (not shown) whose pole pieces rest on the faces 79, 80 of the blocks 74, 75. In a modification, the terminals are at A and C, and two loops of equal length (2n + 1) #/4 join B and D respectively to the ends of the portion 67. In a further modification, A and C are joined by a loop of length (2m + 1) #/2 and D is joined to one end of the portion 67 by a loop of length (2n +1) #/4 (n and m are either zero or whole numbers). The remaining ends form the terminals.