US3283268A - Remanently magnetizable ferrite arrangement for providing directional attenuation of microwave transmission lines - Google Patents

Remanently magnetizable ferrite arrangement for providing directional attenuation of microwave transmission lines Download PDF

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US3283268A
US3283268A US295962A US29596263A US3283268A US 3283268 A US3283268 A US 3283268A US 295962 A US295962 A US 295962A US 29596263 A US29596263 A US 29596263A US 3283268 A US3283268 A US 3283268A
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wave
waveguide
attenuation
ferrite
magnetization
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Neckenburger Ernst
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/32—Non-reciprocal transmission devices
    • H01P1/36—Isolators
    • H01P1/365—Resonance absorption isolators

Definitions

  • Microwave transmission line elements by which electromagnetic energy travelling in one direction is transmitted substantially without attenuation and electromagnetic energy travelling in the opposite direction is absorbed substantially without reflection, have important uses in microwave technology as directional lines or directional isolators, for example, to avoid load reactions on microwave generators.
  • the bestknown embodiments comprise a wave-guide of rectangular cross-section and a strip of ferrite disposed therein at a suitable point. This strip is magnetized by a magnetic field at right angles to the direction of propagation of such strength that, in moperation with the microwave radiation in the wave-guide, ferromagnetic resonance is produced.
  • the applied magnetic field which at 10 mc./s.
  • the use of highly remanent soft magnetic materials further enables the direction of magnetization to be reversed within a very short period of time with the aid of comparatively small field strengths, so that with nonreciprocal attenuation the forward direction and the reverse direction of the transmission line element are interchanged.
  • This provides the possiblity of its use as a microwave switch or microwave modulator.
  • the operating frequency of which lies far above the ferromagnetic resonance frequency soft magnetic ferrites of cubic crystal structure and rectangular characteristics can be used to very high frequencies. If, however, ferromagnetic resonance losses are to be utilized to achieve directional attenuation, the operating frequency, which in 3,233,263 Patented Nov. 1, 1966 ice this case coincides with the ferromagnetic resonant frequency, is comparatively low in these materials.
  • the present invention relates to a remanently magnetizable ferrite arrangement for providing directional attenuation of microwave transmission lines, which is characterized by the use of a thin-walled hollow cylinder which is adapted to be remanently magnetized in the circumferential direction and consists of polycrystalline ferrite material of hexagonal crystal structure, the individual crystallites of which have a preferred plane of magnetization and are oriented so that this preferred plane is at right angles to the axis of the hollow body extending in the direction of the microwave lines.
  • the invention utilizes known properties and manufacturing methods of hexagonally crystallized ferrites having a preferred plane of magnetization. This mainly comprises the method of crystal orientation in which the preferred planes of the individual hexagonal crystallites are rendered substantially parallel.
  • the polycrystalline final product as a whole is magnetically anisotropic: in accordance with the degree of orientation it has a more or less marked preferred plane of magnetization.
  • the remanent magnetization in this plane in the optimum case is 96% of the saturation magnetization. This is achieved on the base of the hexagonal crystal symmetry in the basal plane of the hexagonal crystallites, assuming the degree of orientation to be 100% and neglecting the stress anisotropy. With stress-free cubic crystallized ferrites the maximum re-manence to be expected is 87%.
  • the ferromagnetic natural resonance of a thinwalled hollow cylinder in accordance with the invention is when the height (i.e. axial length) of the body is large compared with its wall thickness, for example, when the body is tubular, and
  • H,(oe.) represents the crystal anisotropy field which, when the magnetization vector is deflected from the preferred plane, rotates it back into this plane, and M represents the remanent magnetization.
  • the first two columns of the Table 1 show values of H, and 41rM for a number of hexagonal ferrites having a preferred plane of magnetization.
  • ferrites which are commercially available under the trade name Ferroxplana, for example C0 2, Co Y, Zn Y, Ni Y, Mg Y, where Z is an abbreviation for the formula of the radical Ba Fe O and Y for B21 Fe O are particularly suitable.
  • Larmor component the elliptically polarized component of the alternating field which in the condition of ferromagnetic resonance is in maximum interaction with the precessing spin.
  • This component has the sense of rotation of the spin precession and along the circumference a certain ellipticity.
  • the Larmor components are for the tube and the annulus respectively.
  • the anti-Larmor component has no interaction with the precessing spins. Its sense of rotation is opposite to the precession and its ellipticity is reciprocal to that of the Larmor component.
  • the anti- Larmor components are.
  • the region in which the ratio between reverse attenuation and forward attenuation is a maximum substantially coincides with the region of minimum pass attenuation.
  • this region can be calculated in known manner from the mathematical expressions for the undisturbed magnetic field components of the instantaneous wave-guide wave type by relating the values of the two magnetic field components at right angles to the direction of magnetization with the right-hand of the Equation 4a, b.
  • FIGS. la and 1b each show a cross-sectional view of a circular wave-guide.
  • FIG. 2 is a longitudinal sectional view of a circular wave-guide
  • FIG. 3 is a cross-sectional view of a rectangular waveguide.
  • the pass attenuation can be adjusted to a minimum and the ratio of blocking attenuation can be approximately adjusted to a maximum in accordance with p and R.
  • m and m denote the radii where a thin-walled ferrite tube made of the material Co Y may be located in order to achieve minimum forward attenuation. These regions are drawn approximately to scale in the cross-section of the circular Wave-guide 2, for the TE wave (FIG. la) and for the TE Wave (FIG. lb).
  • the cylinder may be located in either of the regions m or m and it is also possible to locate a cylinder at each region if the cylinders at m and m are oppositely magnetized circumferentially. In this case the cylinder 1 is located at radius m and a cylinder 1 is located at the radius m
  • the ferromagnetic resonance absorption of these arrangements occurs at about 22 10 mc./s.
  • a directional line for the HE Wave of a dielectric wave-guide is obtainable by concentrically surrounding the wave-guide for a certain distance by a metal tube.
  • the diameter of this tube must be chosen so that it can only guide the fundamental wave of the screened dielectric wave-guide.
  • a radius of minimum pass attenuation and hence the radius of the ferrite tube in accordance with the invention can be calculated with the aid of the components of the fundamental wave of the screened dielectric line.
  • the Co Y tube In the case of a helical directional wave-guide the Co Y tube must be arranged in accordance with the above conditions relating to the position of the tube within the turns of the wave-guide in order to obtain the maximum value of the ratio between the reverse attenuation and the forward attenuation.
  • the matching of the non-reciprocal waveguide parts is of particular importance.
  • This matching may be effected with the aid of the usual means, for example, by smooth transitions in which, in addition to the ferrite, low-loss dielectric materials may be used.
  • the directional line for the dielectric waveguide wave may be surrounded by a metal tube the diameter of which progressively increases through a distance equal to several wavelengths to a value exceeding twice the limiting radius of the HE wave of the dielectric waveguide.
  • a dielectric tube along the inner or outer periphery of the ferrite tube may serve to improve the quality of the directional waveguide.
  • tapering dielectric branch tubes may be provided.
  • Matching of the directional lines for the TE wave and the HE wave of the circular wave guide may be effected in a similar manner.
  • the rotational symmetry has to be exactly maintained, since otherwise different wave types are generated, the occurrence of which detracts from the quality of the directional line.
  • the comparatively low coercive force in the preferred plane of hexagonally crystallized ferrites enables the directional magnetization to be reversed by the application of correspondingly small external fields. In this manner the forward direction and the reverse direction are interchanged for the above described directional waveguides.
  • the microwave energy can be switched within a very short time with only a small power.
  • the circumferential magnetic field required for switching may be produced, for example, by a small number of wire turns wound on the cylinder in the axial direction.
  • a current conductor which extends along the axis of the system reduces the inductance and hence the perturbation of the micro-wave field.
  • the ferrite 1 is held within the guide by conventional means, such as by means of suitable supports (not shown) to the waveguide wall. If the current conductor is a very thin 'wire, the radius of minimum forward attenuation may be deduced in the above-described manner from the undisturbed magnetic field components of the TE wave. If the current load requires a thicker wire, under certain circumstances the magnetic field components of the T15 wave of the coaxial line have to be allowed for.
  • the wire 4 which extends along the axis of the system, is bent at a sufficient distance from the ferrite towards the wall of the waveguide and is brought out in an electrically insulated manner through two small apertures 5 provided in this wall.
  • the wire substantially does not reflect the TE wave if it lies in the plane extending at right angles to the electric field vector of the TE wave.
  • the straight lines together are loci of minimum pass attenuation only if ferrite strips 6a and 6b disposed in these regions are magnetized in opposite senses.
  • a closed magnetic circuit may be produced through additional ferrite strips 7a and 7b.
  • This magnetic circuit can be circumferentially magnetized to saturation by the central current conductor 4 and, when the current is switched off, shows a remanence corresponding to the material.
  • the strips 7a and 7b provide a greater contribution to the forward attenuation than the strips 6a and 6b, since in the region of the former strips the Larmorcomponent of the TE wave does not disappear. Accordingly the ratio between reverse attenuation and pass attenuation is slightly reduced.
  • the tube is made of the material Co Y, the ferromagnetic resonance absorption lies at about 20 10 mc./s.
  • the quality of a resonance directional waveguide is determined by the maximum ratio between the reverse attenuation and the forward attenuation and also by the bandwidth of the absorption characteristic curve measured in the reverse direction between the 3 db points on either side of the ferromagnetic resonant frequency. Thus a corresponding quality factor is defined.
  • a non-reciprocal microwave device comprising a hollow longitudinally extending conductive waveguide for propagating microwave energy, a hollow body of a remanently magnetized polycrystalline ferrite material of hexagonal crystal structure positioned with said waveguide, the axis of said body extending parallel to the axis of said waveguide, the individual crystallites of said material having a preferred plane of magnetization and being oriented in said body with their preferred planes normal to the longitudinal axis of said body, said body being remanently magnetized circumferentially.
  • H is the crystal anisotropy field which, when the magnetization vector is deflected from the preferred plane, rotates it back to said plane
  • M is the remanent magnetization
  • H is the crystal anisotropy field which, when the magnetization vector is deflected from the preferred plane, rotates it back to said plane
  • M is the remanent magnetization
  • the device of claim 2 comprising a second hollow body of ferrite material of circular cross section within said waveguide, said second body being of the same mat'erial and crystal orientation as the first mentioned body, and being coaxial with and inside of said first mentioned body, said first mentioned and second bodies being circumferentially remanently magnetized in opposite directions.
  • the device of claim 1 comprising conductor means extending through said body for changing the remanent magnetization of said body.

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US295962A 1962-08-09 1963-07-18 Remanently magnetizable ferrite arrangement for providing directional attenuation of microwave transmission lines Expired - Lifetime US3283268A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3707688A (en) * 1971-03-31 1972-12-26 Sperry Rand Corp High frequency gyromagnetic device employing slot transmission line

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2794172A (en) * 1954-01-29 1957-05-28 Bell Telephone Labor Inc Signal routing apparatus
US2849683A (en) * 1953-07-31 1958-08-26 Bell Telephone Labor Inc Non-reciprocal wave transmission
US2868980A (en) * 1956-12-13 1959-01-13 Bell Telephone Labor Inc Frequency changer and wave amplifier
US3051908A (en) * 1960-02-03 1962-08-28 Bell Telephone Labor Inc Slow-wave broadband nonreciprocal microwave devices
US3095547A (en) * 1959-05-28 1963-06-25 Gen Precision Inc High speed microwave switch utilizing gyromagnetic element
US3100288A (en) * 1961-01-05 1963-08-06 Raytheon Co Ferrite isolator utilizing aligned crystals with a specific anisotropy constant
US3114715A (en) * 1961-06-28 1963-12-17 Philips Corp Method of manufacturing an anisotropic ferromagnetic body

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2849683A (en) * 1953-07-31 1958-08-26 Bell Telephone Labor Inc Non-reciprocal wave transmission
US2794172A (en) * 1954-01-29 1957-05-28 Bell Telephone Labor Inc Signal routing apparatus
US2868980A (en) * 1956-12-13 1959-01-13 Bell Telephone Labor Inc Frequency changer and wave amplifier
US3095547A (en) * 1959-05-28 1963-06-25 Gen Precision Inc High speed microwave switch utilizing gyromagnetic element
US3051908A (en) * 1960-02-03 1962-08-28 Bell Telephone Labor Inc Slow-wave broadband nonreciprocal microwave devices
US3100288A (en) * 1961-01-05 1963-08-06 Raytheon Co Ferrite isolator utilizing aligned crystals with a specific anisotropy constant
US3114715A (en) * 1961-06-28 1963-12-17 Philips Corp Method of manufacturing an anisotropic ferromagnetic body

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3707688A (en) * 1971-03-31 1972-12-26 Sperry Rand Corp High frequency gyromagnetic device employing slot transmission line

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