GB963590A - Improvements in or relating to transmission lines for electromagnetic wave energy - Google Patents

Abstract

963,590. Non-reciprocal networks. WESTERN ELECTRIC CO. Ltd. Dec. 1, 1960 [Dec. 8, 1959], No. 41335/60. Heading H1W. A non-reciprocal gyromagnetic phase-changer or alternator comprises a two-conductor transmission line arranged to intersect itself in the region of an element of magnetically polarized gyromagnetic material, the intersecting portions of the line being divided by gaps into resonant sections. In the coaxial arrangement of Fig. 1, a central strip-like conductor is arranged as a loop within a correspondingly shaped channel 12 in a conductive block 10. The channel is closed by cover-plate 18. Located between the strip conductors at their point of intersection is a disc 21 of gyromagnetic material polarized by a field Hdc applied at right-angles to the axes of the strips. If the distance around the loop is electrically equal to an odd number of quarter wavelengths at the signal frequency, the magnetic fields produced by the strips at the intersection will be in time and space quadrature and hence will give rise to a magnetic vector rotating in the plane of the disc about an axis lying in the direction of Hdc. It is not necessary that the conductors should cross at right-angles, provided that an appropriate phase delay is chosen. Thus, in general, for an angle of intersection #, a phase delay # is chosen such that # = (2n+1)#+#. The direction n of rotation of the R.F. vector depends upon the direction of propagation, this being the usual condition for non-reciprocal gyromagnetic effects. If the field Hdc is adjusted to the value at which resonance occurs, the apparatus behaves as a non-reciprocal attenuator. For other values of Hdc, non-reciprocal phase delay is obtained. In order to enhance the strength of the R.F. magnetic fields, the conductor is divided by gaps d to provide two open-ended resonant sections 15, 17 which cross in the region of their current maxima. If the sections are one half-wavelength long, the intersection occurs at their centres. The gaps introduce series reactances in the line which load the resonant sections and modify the electrical length of the loop. Thus from the electrical length L between the ends of the resonators 15, 17 it is necessary to subtract a compensatory amount ¢[arc tan 2/X 1 + arc tan 2/X 2 ], where X 1 and X 2 are the reactances of the gaps d. A similar adjustment is made to the length of the resonant sections. It is possible to adjust the values of X 1 and X 2 such that the length L becomes zero and the two gaps between the ends of the resonator 15, 17 merge to form one gap of reactance X 1 X 2 =X<SP>2</SP>. Fig. 7 shows a modification in which such a gap provides the necessary 90 degree phase-delay between the ends of intersecting resonators 70, 71. In this construction, the transmission line is of the strip-line type, the strip conductors 70, 71, 72 being spaced from a ground conductor 73 by a dielectric layer 74. It is stated that twowire transmission lines or balanced strip lines may also be used. The gyromagnetic material is preferably aluminium-substituted yttrium iron oxide.