Patent GB-755174-A (GB)
Title: Coupling arrangements for electromagnetic wave energy transmission systems
IPC: H01P1/38
Filed: 1954-08-13
Abstract: 755,174. Waveguide coupling circuits. WESTERN ELECTRIC CO., Inc. Aug. 13, 1954 [Aug. 17, 1953; Aug. 17, 1953], No. 23589/54. Class 40 (8). [Also in Group XL (c)] A waveguide coupling arrangement comprises at least one element of magnetically-polarized ferrite (ferromagnetic spinel) material disposed between adjoining portions of a pair of waveguides and serving as a non-reciprocal coupling member. Fig. 1 shows a non-reciprocal fourterminal network or " circulator " comprising two parallel waveguides 10, 11 coupled at the right-hand end by a normal (reciprocal) coupling consisting of apertures 13 and at the left hand end by a non-reciprocal coupling consisting of apertures loaded with plugs or posts 15 of ferrite. The apertures are small compared with the wavelength and, in the case of the loaded coupling, extend several wavelengths along the centre lines of the adjoining waveguides 10, 11. The plugs 15 may be made of nickel-zinc ferrite prepared in the manner described in Specification 733,486. The discs may be permanently magnetized or may be polarized by an electromagnet 16. The peculiar properties of the ferrite coupling material due to impaired electron spins associated with a magnetic moment precessing about the direction of the biasing field F results in the fact that the transverse component HX of the microwave field in guide 10 (the only component which affects the coupling elements) induces in the material a component H<SP>1</SP>Z which is at right-angles to and lags 90 degrees in time behind the inducing component HX. The induced field H'Z is capable of exciting a mode which can be propagated within the guide 11 and it is found that, taking into account phase relationships inherent in the coupling, for one direction of propagation past the coupling the induced wave will have a phase 90 degrees ahead of the inducing wave and 180 degrees different from the phase of the induced wave for the opposite direction of propagation. This relationship is illustrated in Fig. 6. The coupling depends upon the value of the biasing field F and is zero when this field is zero. In the circulator system of Fig. 1 the field F is adjusted to give equal division of power between the induced wave and the inducing wave, the number and sizes of the holes 13 in the (ordinary) reciprocal coupler being chosen also to give an equal division of power. The 90 degree phase delay inherent in the ordinary directional coupler is indicated in Fig. 6. A hybrid junction may be used in place of the multi-aperture coupler 13 shown. If a microwave signal is applied to terminal a one half of it is transferred into guide 11 with a phase 90 degrees in advance of the portion in guide 10. At the right-hand (reciprocal) coupler the portion in the line 10 and that coupled into line 10 from line 11 will be in phase and will combine at the output b. The portion of energy which enters line 11 by the non-reciprocal coupler will be out-of-phase with that which enters by the reciprocal coupler and no energy will appear at d. Thus terminal a is coupled to terminal b. In a similar manner it can be shown that terminal b is coupled to terminal c, c to d and d to a. In the coupler of Fig. 8 the ferrite elements 83 are polarized by a magnetic field F and are displaced from the centre-lines of the contiguous sides of guides 80, 81 by a distance equal to about one-fifth of the wide dimension. Because of this displacement the elements 83 are excited by both the HZ and HX components in guide 81 and these components induce respectively components H<SP>1</SP>X and H<SP>1</SP>Z in the ferrite material. The phase relationships between the various components differ according to the direction of propagation in guide 81 and are illustrated in Figs. 10 and 11. The 90 degree phase delay inherent in the coupler affects all components equally and may be ignored. Only the HZ and H<SP>1</SP>Z components can excite a mode which can be supported in guide 80. If the position of the elements 83 and the strength of the field F are arranged so that these components are equal, then for propagation in the positive direction (a to b) in guide 81 the components cancel out in guide 80 (see Fig. 10) and all the energy appears at terminal b. For propagation in the negative direction (b to a) the components HZ and H<SP>1</SP>Z are in phase in guide 80 and energy will be propagated in this guide. If the geometry of the coupling is as described in Specification 706,234 then a complete transfer of energy from b to c can be achieved. It can be shown similarly that energy applied at c is coupled to terminal d and energy applied at d to terminal a. The threeterminal coupler shown in Fig. 12 has a single element 15 polarized by a magnetic field F and located to one side of the centre line of side 11<SP>1</SP> of guide 10. Energy applied at b is coupled to c<SP>1</SP> and energy applied at c<SP>1</SP> is coupled to a. The function of septum 22 provided in guide 13<SP>1</SP> is to reflect a component of the wave coupled from terminal b into guide 13<SP>1</SP> back into guide 10 in such phase as to cancel the component of energy which would otherwise pass directly from b to a. In a modification of this arrangement (Fig. 15, not shown) the narrow dimension of the guide 13<SP>1</SP> is arranged parallel to the axis of guide 10. Under these circumstances coupling is effected by the HX and H<SP>1</SP>X components of the waves. The order of coupling is again a, b, c<SP>1</SP>. Except for the disposition of the guides 55, 58 the construction of Fig. 16 is similar to that of Fig. 12 and identical coupling relationships are obtained. Piston 57 fulfils a purpose similar to that of septum 22. A modification of Fig. 16 in which coupling is effected by the xdirection components of the fields is obtained by arranging the axes of guides 55, 58 at rightangles.