Patent GB-1398768-A (GB)
Title: Wideband non reciprocal integrated devices
IPC: H01P1/387
Filed: 1972-06-02
Abstract: 1398768 Non-reciprocal gyromagnetic devices LIGNES TELEGRAPHIQUES ET TELEPHONIQUES 2 June 1972 [4 June 1971 27 Aug 1971 28 March 1972] 25923/72 Heading H1W Non-reciprocal effects are obtained in devices supporting a non-TEM surface-wave mode. This mode may be a surface TM, quasi-TM or hybrid HE 11 , these modes being characterized by a component of the magnetic field in the direction of propagation. Hence, the possibility of a circularly or elliptically polarized magnetic field which, in a suitable gyromagnetic medium polarized by a magnetic field normal to the direction of propagation, gives rise to non- reciprocal transmission effects. The devices described operate by virtue of a kind of fielddisplacement effect due to the fact that the concentration of the wave-energy around or within the propagating structure depends upon the magnetic and dielectric properties of the surrounding medium. In general, the devices are physically characterized by a support structure for the surface-wave comprising (at least in part) a gyromagnetic element, a mode transformer for transforming between the surface-wave and the input/output TEM waves, and means for producing a transverse magnetic polarizing field. As shown in Figs. 1, 2, plate 1 supports a surface wave within a gyromagnetic element 2 polarized by the field H. The central conductors of input and output coaxial plugs 6, 7 are connected to a mode transformer 5 in the form of a thin, conductive sheet bisecting the gyromagnetic element 5. Although shown as continuous from input to output, this continuity is not necessary, and each set of terminals may be associated with a separate transformer (see, e.g. Fig. 8, not shown). The sheet may take a large variety of shapes; e.g. it is not necessarily asymmetrical as shown (see, e.g. Fig. la, not shown). Because of the non-reciprocal wave-impedance of the propagation medium, the forward wave is concentracted around the edges 54, 52 of the transformer 5, and the return wave around the opposite edge where it is absorbed in a carbon-loaded element 4. The asymmetry of the sheet 5 increases the bandwidth of the isolator. In order to increase the amount of wave energy radiated into the load 4, the sheet 5 may be provided with radiating slots in the vicinity of the load (Fig. 4, not shown) or slots may be cut in the edge of the gyromagnetic element to provide a discontinuity (Fig. 7, not shown). In other modifications (Figs. 9, 11, not shown), the dissipative element 4 is dispensed with and the reverse wave absorbed by gyromagnetic resonance in a high-loss zone of the magnetic element. The device of Figs. 14, 15 comprises the same elements as those of the Fig. 1 device with the addition of an element 3 of dielectric material having a permittivity equal to that of the ferrite element. The effect of the dielectric element is to enhance the magnetic field in the Z-direction and hence to obtain a better approximation to circular polarization. The forward wave sees a comparatively high value of permeability and propagates within the magnetic element 2 along a path followed by the conductive mode transformer 5. The return wave sees a lower value of permeability and propagates within the dielectric element 3 which allows radiation into the dissipative load 4. In a modification (Fig. 17, not shown), the magnetic parameters are such that the reverse wave surrounds the gyromagnetic element where it is absorbed by a dissipative load element. Various isolators are described which dispense with the plate 1 and use, in effect, an all-dielectric propagation medium. These may have elements of roughly the same configuration as those shown in Figs. 1 and 14 except that the surface wave is launched and received by means of open-ended conductive structures, e.g. as shown at 13 in Fig. 22. The isolator of Figs. 24, 25 uses a propagation structure of circular cylindrical form composed of magnetic and dielectric elements 3, 2 enclosing a mode transformer 22 in the form of a diametral conductive sheet with end tapers. The dissipative load element 4 surrounds part of the magnetic element 3. Since the principle of operation depends upon a difference in apparent permeability for the two directions of operations, the devices described may be adapted for use as non-reciprocal phase shifters by suitably adjusting the polarizing field and dispensing with the dissipative load element 4 (see Fig. 26, not shown). Such phase-shifters may be combined in known fashion to provide 3 or 4- port circulators (Figs. 30, 31, not shown). The three-port circulator of Fig. 32 comprises a conductive plate 1 supporting the surface wave, a gyromagnetic element 3 and a mode transformer 5, the arrangement of these elements being as described for the previous embodiments except that a third input/output V3 terminal is provided at the apex of the approximately triangular mode transformer. In addition, the gyromagnetic element is flanked by dielectric elements 44, 45 chosen to afford the same waveimpedance as the gyromagnetic element when in non-polarized condition. Application of a polarizing field H to the gyromagnetic element causes non-reciprocal transmission as indicated by the arrows. A four-port circulator (Fig. 34, not shown) may be created by duplicating the arrangement of Fig. 32, to form a four-terminal device symmetrical about a line parallel to Z and bisecting the dielectric element 45.