DE1217002B - Tunable filter for very short electromagnetic waves, which can be tuned by means of the magnetocrystalline anisotropy properties - Google Patents

Description

Tunable filter for very short electromagnetic waves that The invention can be tuned by means of the magnetocrystalline anisotropy properties relates to a tunable filter for the microwave region in which in the course of a at least one line serving the transmission of electromagnetic energy arranged under the influence of a constant magnetic field standing ferrite single crystal is.

In the micro-wave range, they are. various arrangements of resonance circuits and filters known. These include those in which the properties of ferromagnetic resonance of so-called ferrimagnetic crystals are used. With such. Arrangements, a ferrimagnetic crystal is usually provided, for example in the course of a hollow conductor. In order to work, it is necessary to expose the crystal to a constant magnetic field that is generated by permanent magnets or electr. For generating the magnetic field is an electromagnet is used, this can be varied by changing the coil current. In technical applications, however, a permanent magnet will be preferred because it is smaller and lighter and does not require any electrical power to operate. The field of permanent niagnets can be tuned with the help of additional coils or magnetic shunts. - In addition to the cost of material and weight, in the first case there is also the stabilized electrical power supply, and in the second case the precise displacement of relatively large masses is necessary.

The invention is based on the 'task' of finding an arrangement in which the -preferably narrow-band tuning of microwave resonators takes place without the change in the magnetic field associated with great effort.

The object of a tunable resonator for the microwave area, in which at least one ferrite monocrystal under the influence of a constant magnetic field is arranged in the course of a line serving for the transmission of electromagnetic energy, is achieved according to the invention in that the constant magnetic field penetrating the resonator has a has a constant value and that, to adjust the resonance frequency with the help of the magnetocrystalline anisotropy properties, the crystal is rotatably arranged in the constant field and that a ferrite single crystal made of yttrium iron garnet (hereinafter referred to as YIG) or gallium-substituted yttrium iron garnet, in which the iron component is partially replaced by gallium is provided. The latter has a significantly lower saturation magnetization with a comparable or greater anisotropy constant of the 1st order.

Through the. Magnetocrystalline anisotropy is the resonance frequency of ferrimagnetic single crystals with a fixed external magnetic field, H, - depends on the orientation of the crystal. The relationships in the ferromagnetic resonance in Anisotropeneinkristall 's are other lunter- of C.Kittel, "On the Theory of Ferromagnetic Resongnce sublingually ption" .- Phys. Rev., 73 (1948), p. 155, and J. 0. Artmann, “Mierawave Resonance. Relations in Amsotropy Single Crystal. Ferrites ", Proc. IRE, 44 (1956), p. 1284, has been theoretically investigated.

YIG has one. cubic crystal lattice and a negative anisotropy constant of the 1st order (the anisotropy constant of the 2nd order can be neglected to a good approximation for these considerations.

In cubic crystals with a negative anisotropy constant K1, the crystallographic [1001 direction is a so-called heavy direction. If the external constant magnetic field is applied in this direction, the greatest field strength is required for resonance at a fixed frequency. On the other hand, for a given magnetic field, the resonance occurs at the lowest frequency. The [111] direction is an easy direction and the [011] direction is a moderate direction. The position of these individual axes in the unit cell of the crystal is in the. Fig. 1 shown. The (011) plane also drawn in this figure contains all three directions indicated. The angular relationships in the (011) plane are shown in FIG . 2 shown. The (easy) direction forms an angle of 54144 'with the difficult direction. For applications in which a tuning range of around 400 MHz is sufficient, a filter made from YIG resonators can be tuned by changing the crystallographic orientation with respect to the magnetic field.

According to the invention, the single crystal * is spherical and built into a microwave structure in such a way that it is preferably rotatable about the normal to the (011) crystal plane and that the constant magnetic field is always in the (011) i-crystal plane. The magnetic HF field should be directed perpendicular to H.

If H, lies in the [111] -direction, then the resonance condition exists Here y = 17.6 NIII-1z / Oe is the gyromagnetic ratio, Ki the first order anisotropy constant and M the saturation magnetization.

With H "in the difficult direction we get: for the [0111 direction one obtains: The optimum tuning range of a YIG resonator with a fixed magnetic field can be calculated from the difference between the resonance frequencies in the light and heavy directions. One obtains z. B. a tuning range A 420 Wh.

According to the invention, this physical effect is advantageous in the following tunable filters exploited * A filter is constructed in such a way that two on top of each other vertical rectangular waveguides short-circuited on one side in the two Waveguides common section of the short-circuit wall have a coupling opening, in which the ferrimagnetic crystal is rotatably arranged.

Another filter is designed to be in the line in the direction of propagation of the electromagnetic wave, two spherical ferromagnetic crystals one behind the other are arranged and that both crystals preferably have a common drive are adjustable in synchronism.

In it can at least between the rotatable ferrimagnetic crystals another, fixed ferrimagnetic crystal can be arranged.

Another filter is designed so that in a rectangular waveguide short-circuited at one end, two spherical ferrimagnetic crystals with heavy and light directions offset by 901 are rotatably arranged on a common axis.

Finally, a filter is designed so that in the common metallic Partition of two parallel striplines a coupling slot is provided and that preferably between the inner conductors and the coupling slot spherical ferrimagnetic crystals are rotatably arranged and that further the inner conductors on one side are short-circuited with the outer conductors, while on the other hand, they merge into the inner conductors of coaxial feed lines.

The invention is described in greater detail below with the aid of exemplary embodiments explained.

In FIG. 3 a tunable bandstop filter is shown schematically. A ferrimagnetic ball 2 made of yttrium iron garnet is rotatably mounted in a through waveguide 1. The ball 2 is attached to a shaft 3 made of a dielectric material, for example by gluing. The axis 3 is mounted in a socket 4 and rotatable in the direction of the double arrow 5 via a drive, which is not shown in detail in the drawing for the sake of clarity. The drive can consist, for example, of a micrometer screw, the resonance frequency being set by means of a calibration curve. A scale calibrated directly in terms of frequency can also be provided. The constant magnetic field H indicated by arrow 5 can be generated by a permanent magnet, not shown here, and is to be selected so that ferromagnetic resonance occurs in the frequency range of interest when the intended change in crystal orientation occurs. The waveguide is blocked for the relevant frequency. Due to the spatial orientation of the crystal on the axis 3 in relation to the waveguide, the tuning range can be selected within the desired limits. The ferromagnetic resonance is only excited by the positively circularly polarized part of a wave. Therefore, the sphere is arranged at a location of greatest circular polarization of the magnetic high-frequency field in order to obtain the greatest possible absorption. In addition, one then obtains the property of a directional line. The strength of the absorption depends, within certain limits, on the volume of the crystal. The bandwidth is given by the half-width of the ferromagnetic resonance curve and the degree of coupling between the crystal and the high-frequency field. In the case of a fixed volume, the absorption of a material with a small half-width is greater than that of a material with a broad resonance curve. If the blocking effect of one ball is not sufficient, several crystals can be connected in series. - The structure of a band pass filter is in the F i g. 4 shown schematically. Here, two rectangular waveguides 7 and 8 are connected to one another in such a way that their central axes are at least approximately aligned and that the broad sides of the waveguide are perpendicular to one another. The waveguides 7 and 8 are each short- circuited at one end by means of the walls 9 and 10 . In the section of the short-circuit walls 9 and 10 common to both waveguides, a coupling opening 11 is provided in which a spherical crystal 2 made of yttrium iron garnet is rotatably arranged. The ball 2 is fastened to an axis made of a dielectric material, which is only indicated by the dash-dotted line 12 and which can be rotated in the directions indicated by the double arrow 5.

An electromagnetic wave incident in the direction of the arrow 13 in the waveguide 7 is not coupled into the waveguide 8 without the effect of the crystal ball 2, since the two waveguides are decoupled due to the orthogonality of the magnetic field lines at the location of the coupling opening. Only when the frequency of the wave moving in the waveguide 7 corresponds to the ferromagnetic resonance frequency of the crystal ball 2 is a coupling of the two conductors obtained through the precession movement of the magnetization.

In FIG. 5 is a two-circuit bandstop filter with variable bandwidth is shown schematically. In a through waveguide 1 , two spherical ferromagnetic crystals 2 and 2 'are preferably rotatably arranged at the location of greatest circular polarization of the magnetic high-frequency field. The balls 2 and 2 'are glued to the end faces of rods made of dielectric material, which are only indicated by the lines 14 and 15 drawn in broken lines. On a narrow waveguide side there is mounted a central axis, indicated by the dash-dotted line 16 , on which a drive wheel 17 is attached. By rotating in the direction of the arrow 20, the wheels 18 and 19, which are fastened to the shafts 14 and 15 , are driven in the same direction in the direction of the arrows 21 and 22 by the drive wheel 17. The crystals 2 and 2 'are attached in such a way that their heavy and light directions are offset from one another by an angle of 90 <1. The constant field H generated, for example, by a permanent magnet, is perpendicular to the broad sides of the waveguide in accordance with the direction of arrow 6. If both balls are rotated simultaneously via the drive wheel 117, the resonance frequency of one resonator becomes smaller and that of the other increases. If the position of the crystals is chosen so that the heavy direction of one crystal is parallel to the waveguide broadside and the easy direction of the other is perpendicular to the waveguide broadside, then the difference between the resonance frequencies of the two resonators and thus the bandwidth is greatest. After a rotation of 45 ', the resonance frequency of both crystals is the same and thus the bandwidth is the smallest. In its electrical equivalent circuit diagram, such an arrangement therefore corresponds to a two-circuit bandstop filter, the resonance circuits of which are coupled to one another, the resonance frequencies of the individual circuits being adjustable to change the bandwidth. With other crystals, e.g. B. with a non-tunable third resonator at the center frequency of the filter, three-circuit and multi-circuit filters can be built.

The structure of a two-circuit bandstop filter of the reflection type is shown in FIG. 6 shown. A rectangular waveguide 1 is short-circuited at one end by means of a metallic wall 23. Two spherical ferrimagnetic crystals 2 and 2 # are attached to an axis made of a dielectric material, only indicated by the dash-dotted line 24, in such a way that their heavy and light directions are perpendicular to one another. The axis 24 is rotatably mounted in the direction of the double arrow 5. An electromagnetic wave incident in the waveguide 1 in the direction of the arrow 25 is reflected on the short-circuit wall 23. Only crystal 2 is effective for the incoming wave, and only crystal 2 'is effective for the returning wave. This is achieved in that the crystal 2 for the incoming wave sits at a location with a right circularly polarized field, while only a left circularly polarized wave which does not experience any absorption acts on the crystal 2 '. The reverse applies accordingly to the returning wave. With regard to the change in the bandwidth, because of the perpendicular heavy and light directions of the crystals 2 and 2 ', the same applies analogously as in the exemplary embodiment in FIG. 5 given explanations.

In FIG. 7 and 8 , a two-circuit band filter is shown which is constructed with the aid of band lines. FIG. 7 shows a cross section along the section line AB from FIG . 8, FIG. 8 is a top view with the cover plate open.

In two mutually on one broad side 29 adjacent outer conductors 30 and 32 which are constructed as strip conductor inner conductor are 31 and 31 The inner conductor 31 is connected to the inner conductor 34 of a coaxial terminal line 35 connected to the inner conductor 33 to the inner conductor 36 of a Koaxialanschlußleitung 36, 37. The inner conductor 31 is short-circuited on a short-circuit wall 38 attached to the outer conductor 30 , while the inner conductor 33 is short-circuited on the wall 39 of the outer conductor 32 . In the partition 29 common to both outer conductors 30 and 32 , a narrow slot 40 is provided which runs in the direction of the inner conductor. Zwischen.den, inner conductors 31 and 33 and the partition 29 are secured 'in the height of the slot' 40 on rods 41 and 42 of a dielektrischen'Material the spherical ferrimagnetic crystals 2 and 2. FIG. The rods 41 and 42, which are only indicated by dash-dotted lines, can be either separately or rotated in the direction of the double arrows 45 and 46 in the direction of the double arrows 45 and 46 by a suitable drive in the manner already described. The constant magnetic field H is indicated by the arrow 6 and can be generated, for example, by a permanent magnet.

An electromagnetic wave propagating in the conductor system 30, 31 cannot initially be coupled over to the conductor system 32, 33 , since the magnetic field lines 43 forming around the inner conductor 31 run perpendicular to the slot 40. If the frequency of the - in the pipe system 30, 31 propagating electromagnetic waves, at least approximately coincides with the resonance frequency of the ferrimagnetic crystal 3, creates a pointing in the direction of the slit 40 magnetic field component, so that magnetic field lines pass through the slot 40th If, at the same time, the ferrimagnetic crystal 2 'is at least approximately in resonance, a magnetic field component is created in the conductor system 32, 33 which generates a magnetic field 44 that forms around the inner conductor 33 and thus excites an electromagnetic wave in the conductor system 32, 33, which on the coaxial output 36, 37 can be removed. Such an arrangement corresponds to a two-circuit band filter, the center of which can be tuned over a predetermined frequency range.

The bandwidth can also be determined in a simple manner with such a filter change. For this purpose, spherical crystals 2 and 2 'are adjusted so that their heavy and light direction do not run exactly parallel to each other, but rather are inclined to each other at a certain angle. If you see a change in this the angular position in the way before that, for example, at the Axis 41 attached crystal 2 relative to the crystal attached to axis 42 2 'is rotatable, then besides frequency tuning one can be set within wide limits Set changeable bandwidth.

The invention has been explained on the basis of filters made with the aid of rectangular waveguides and ribbon lines are constructed. Instead, you can in an analogous manner any other for the propagation of electromagnetic energy suitable ladder systems are used.

Claims (2)

Claims: 1. Tunable filter for the microwave region, which can be tuned by means of the magnetocrystalline anisotropy properties and in which at least one ferrite single crystal under the influence of a constant magnetic field is arranged in the course of a line serving for the transmission of electromagnetic energy, characterized in that the The constant magnetic field (6) penetrating the resonator has a constant value and that the crystal (2) is rotatably arranged in the constant field to adjust the resonance frequency with the aid of the magnetocrystalline anisotropy properties. 2. Tunable filter according to claim 1, characterized in that a ferrite single crystal made of yttrium iron garnet (2) is provided. 3. Tunable filter according to claim 1 and 2, characterized in that gallium-substituted yttrium iron garnet (2) is provided. 4. Tunable filter according to one of claims 1 to 3, characterized in that the single crystal (2) is spherical. 5. Tunable filter according to claim 4, characterized in that the single crystal is built into a microwave structure in such a way that it can be rotated about the normal to the [011] crystal plane and that the constant magnetic field is always in the [01T1 crystal plane. 6. The tunable filter according to any would appeal 1 to 5, characterized in that two mutually perpendicular, short-circuited to a side rectangular waveguide (7, 8) common to the two hollow conductors in sections having the short-circuit wall, a coupling aperture (11) in which the ferrimagnetic crystal is rotatably arranged. 7. Tunable filter according to one of claims 1 to 5, characterized in that two spherical ferrimagnetic crystals (2, 2) are arranged one behind the other in the line in the direction of propagation of the electromagnetic wave and that both crystals are preferably adjustable in synchronism via a common drive. 8. A tunable filter according to claim 7, characterized in that at least one further, fixed ferrimagnetic crystal is arranged between the rotatable ferromagnetic crystals. 9. Tunable filter according to one of claims 1 to 5, characterized in that two spherical ferrimagnetic crystals with 90 ' offset heavy and light direction are rotatably arranged on a common axis in a rectangular waveguide short-circuited at one end. 10. A tunable filter according to one of claims 1 to 5, characterized in that a coupling slot is provided in the common metallic partition of two striplines running parallel to one another and that preferably spherical ferrimagnetic crystals are arranged rotatably between the inner conductors and the coupling slot and that furthermore the inner conductors are short-circuited on one side with the outer conductors, while on the other side they merge into the inner conductors of coaxial supply lines. Documents considered. Electro-Technology, September 1963, Vol. 72, No. 3, pp. 78 to 83.