Abstract:
A junction circulator suitable for high power, high-frequency use has a microwave junction zone which is penetrated by a static magnetic field. Disposed in the microwave junction zone is a ferromagnetic resonator composed of different dielectric media, at least one of which has ferromagnetic characteristics. The interfaces between the various dielectric media form three-dimensional bodies which extend over the entire height of the junction zone and which have cross sections that do not change in the direction of the static magnetic field. These interfaces may be provided by parallel ferrite rods, or a ferrite body with parallel bores.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The subject matter of this application is related to that of applicants&#39; copending application entitled &#34;High Power Junction Circulator having Ferrite Suspension at the Junction,&#34; Ser. No. 07/103,751, filed Oct. 2, 1987, the copending application being assigned to the assignee of the present application. The subject matter of the present application is also related to that of another copending application entitled &#34;High Power Junction Circulator for High Frequencies,&#34; Ser. No. 07/103,728, filed Oct. 2, 1987, this co-pending application also being assigned to the assignee of the present application. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a microwave junction circulator including a microwave junction zone which is penetrated by a static magnetic field, with a ferromagnetic resonator composed of different dielectric media being disposed at the microwave junction zone, at least one of the different dielectric media having ferromagnetic characteristics. 
     A microwave circulator is a coupling device having a number of ports for connection to microwave transmission lines, such as waveguides or striplines. Microwave energy entering one port of the circulator is transferred to the next adjacent port in a predetermined direction. A threeport microwave circulator, for example, may be used to transfer energy from a klystron connected to the first port to a particle accelerator connected to the second port. Any microwave energy reflected back to the circulator by the particle accelerator then exits via the third port, so that the reflected energy is diverted from the klystron. 
     Circulators which have ferromagnetic resonators in their microwave junction zones and which were designed specifically for very high power, high-frequency applications are disclosed by Fumiaki Okada et al in the publications, IEEE Transactins on Microwave Theory and Techniques, Vol. MTT-26, No. 5, May, 1978, pages 364-369, and IEEE Transactions on Magnetics, Vol. MAG-17, No. 6, November, 1981, pages 2957-2960. In the circulators described in these publications, the ferrite structure is composed of a plurality of ferrite discs which are separated from one another by air gaps and which are arranged perpendicularly to the static magnetic field on metal carriers through which flows a coolant. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a circulator of the above-mentioned type which is suitable, in particular, for operation at very high power at high-frequencies. 
     This object can be attained, according to the present invention, by employing a ferromagnetic resonator having interfaces between the various dielectric media in the resonator, the interfaces forming three-dimensional bodies which extend over the entire height of the junction zone and which have cross sections that do not change in the direction of the static magnetic field. Parallel ferrite rods may be used, for example, or a ferrite body having parallel bores. 
     In the prior art high power circulators, the layering of ferromagnetic dielectric media in the junction zone perpendicularly to the static magnetic field is a very grave drawback with respect to power compatibility. In the customary H-plane junction circulator, the E field lines of the high frequency field lie parallel to the static magnetic field in the ferromagnetic resonator so that the interfaces of the ferrite layers intersect the E field perpendicularly, which results in very great field strength increases in the air gaps between the ferrite layers. Increasing the air gaps by raising the height of the resonator as a countermeasure against field strength increases is possible only conditionally since then the static magnetic field can no longer be generated with justifiable expenditures. In contrast thereto, the circulator according to the present invention has a resonator in its junction zone. The ferromagnetic dielectric medium of the resonator extends over the entire height of the waveguide junction zone and a non-ferromagnetic dielectric medium, which serves to dissipate heat, also extends over the full height of the junction zone. In this case, the static magnetic field as well as the electrical high frequency field are oriented tangentially to the interfaces between the ferromagnetic and the non-ferromagnetic dielectric media. Thus field strength increases are avoided in the ferromagnetic dielectric medium, so that the breakdown strength of the circulator becomes very high and the circulator is thus suitable for operation at extremely high power. 
     The resonator structure according to the invention additionally permits the dissipation of large quantities of heat, which protects the ferromagnetic dielectric medium against thermal destruction. This applies primarily for a finely structured configuration of the ferromagnetic dielectric medium because then a particularly good heat transfer to the heat dissipating dielectric medium is ensured. With the measures according to the invention it is possible to advantageously realize junction circulators in waveguide technology as well as in TEM waveguide technology (e.g. striplines). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a resonator structure in the junction zone of a waveguide circulator in accordance with an embodiment of the present invention. 
     FIG. 2 is a cross-sectional view of a resonator structure in the junction zone of a circulator designed according to stripline technology in accordance with another embodiment of the invention. 
     FIG. 3 is a cross-sectional view showing a further resonator structure for use in a waveguide circulator. 
     FIG. 4 is a top plan view of a waveguide circulator having the resonator structure of FIG. 1. 
     FIG. 5 is a cross-sectional view showing a modification of the embodiment of FIG. 1. 
     FIG. 6 is a cross-sectional view showing a modification of the embodiment of FIG. 3. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With initial reference to FIG. 4, waveguide circulator 30 has three ports 31, 32, and 33 which are connected to microwave transmission lines such as hollow waveguides 34, 35, and 36. Ports 31-33 communicate with a microwave junction zone within circulator 30, and a resonator structure 37 is disposed in the microwave junction zone. FIG. 1 illustrates a sectional view of the resonator structure 37, together with two opposing waveguide walls 1 and 2 of the microwave junction zone and a magnet system which generates a static magnetic field to penetrate the junction zone. 
     The magnet system in the embodiment shown in FIG. 1 includes two pole pieces 3 and 4 disposed above and below the junction zone, respectively, a permanent magnet 5 and a yoke 6 forming the magnetic return outside the junction zone. One side of this yoke 6 rests on pole piece 3, the other side on permanent magnet 5. 
     The resonator structure 37 includes a ferromagnetic dielectric medium in the form of a plurality of ferrite rods 7 which extend between the two opposing waveguide walls 1 and 2 parallel to the E field of the circulator. In these ferrite rods 7, extending parallel to the E field from the one waveguide wall to the opposite wall without changes in cross section, the E field is just as large as in the non-ferromagnetic dielectric medium surrounding the ferrite rods 7. Thus, in contrast to conventional resonator structures having air gaps extending transversely to the E field, there are no field strength increases anywhere in the ferrite rods 7. 
     The result is that resonator structure 37 has an extremely high breakdown strength, so that circulator 30 is suitable for the transmission of very high power. 
     By subdividing the ferromagnetic dielectric medium into a plurality of individual, spaced rods 7, a large cooling surface is created, thus providing extremely favorable conditions for the dissipation of the heat generated in ferrite rods 7. With the aid of a coolant flowing around the ferrite rods 7, e.g. air or some other suitable gas or dielectric fluid, very large quantities of heat can be dissipated in a simple manner. For this purpose, all ferrite rods 7 are surrounded by a dielectric cylinder 8 which delimits the resonator 37 and which is sealed at the waveguide walls 1 and 2. In this dielectric cylinder 8, a liquid or gaseous coolant is introduced through an influx channel 9 in pole piece 4 and a plurality of holes 10 in waveguide wall 2 and is discharged through holes 11 in the opposite waveguide wall 1 and a discharge channel 12 in the other pole piece 3. On the exterior faces of waveguide walls 1 and 2, the two pole pieces 3 and 4 are sealed against the escape of coolant. 
     Passage holes 10 and 11 in waveguide walls 1 and 2 have such dimensions that they are impermeable to the high frequency field in the circulator. 
     Instead of the cooling device shown in FIG. 1, FIG. 5 illustrates an alternative wherein each individual ferrite rod 7 is accommodated in a small dielectric tube 50 and coolant is conducted through each tube 50 via openings in waveguide walls 1&#39; and 2&#39;. Although not illustrated in FIG. 5, tubes 50 are preferably sealed to waveguide walls 1&#39; and 2&#39; by O-rings. 
     The temperature gradient in the ferrite rods 7 is very small in the longitudinal as well as the transverse direction, so that mechanical destruction of the ferrite rods 7 due to thermal stresses need not be feared. 
     As shown in FIG. 1, ferrite rods 7 are brought through openings 13 and 14 in the two waveguide walls 1 and 2. These openings are impermeable to the high frequency field. This provides, on the one hand, a very simple mount for ferrite rods 7. On the other hand, the fact that ferrite rods 7 are brought through waveguide walls 1 and 2 up to pole pieces 3 and 4 causes the magnetic resistance of the magnetic circuit to be reduced in an advantageous manner. As a result, only a relatively small magnetic field strength needs to be generated, so that a relatively inexpensive magnet system can be used. The reduction of the magnetic resistance between the magnet system and the ferrite rods 7 has the additional advantage that the magnetization of the ferrite rods 7 can be increased to such an extent that the circulator is able to operate in above resonance mode at frequencies higher than about 2.5 GHz, the limit for above resonance operation up to now. In that case hardly any spin wave losses occur in the ferrite rods 7, which could otherwise produce non-linear effects. 
     FIG. 2 is a sectional view of the central portion of a planar junction circulator. This circulator has a symmetrical conductor structure composed of two planar outer conductors 15 and 16 and an inner conductor 17 disposed therebetween. Here again, as in the waveguide circulator (FIG. 1), the resonator structure 38 in the junction zone is composed of a plurality of spaced ferrite rods 7 oriented parallel to the E field in the junction zone. Ferrite rods 7 are brought through bores 18, 19 and 20 in outer conductors 15 and 16 and in inner conductor 17 so that ferrite rods 7 extend to pole pieces 3 and 4 of the magnet system. The magnet system corresponds to the one described above and is therefore marked with the same reference numerals as the system of FIG. 1. 
     In order for a liquid or gaseous coolant to be able to flow through the ferromagnetic resonator 38, openings 21, 22 and 23 are provided in outer conductors 15 and 16 and in inner conductor 17. Dielectric cylinders 8&#39; surround the rods 7 and channel the flow of coolant. 
     Instead of cooling the ferromagnetic resonators in the circulator embodiments shown in FIGS. 1 and 2 by means of a liquid or gaseous dielectric medium, a solid dielectric medium (e.g. beryllium oxide ceramic) having good heat conductivity can be employed in which the ferrite rods 7 are then embedded. 
     Any desired cross-sectional shape (e.g. circular, square, star-shaped, hexagonal, or the like) can be selected for the ferrite rods 7 mentioned in the above-described embodiments. Care must only be taken that the cross section of the rods does not change in the direction of the static magnetic field. 
     Another form of a ferromagnetic resonator structure is shown in FIG. 3. Here, the resonator structure 39 is composed of a ferrite body 24 which extends, for example in a waveguide circulator, from one waveguide wall 25 to the opposite wall 26. In this ferrite body 24, bores 27 extend parallel to the static magnetic field. These bores 27 are filled by a heat-dissipating, non-ferromagnetic gaseous or liquid dielectric medium. Bores 27 in ferrite body 24 communicate with bores 28 and 29 in waveguide walls 25 and 26 so that the gaseous or liquid dielectric medium is able to flow through the resonator structure 39. In the modification shown in FIG. 6, resonator structure 39&#39; is not cooled by a fluid (gas or liquid) dielectric medium. Instead, heat-conducting rods 40 of beryllium oxide ceramic are disposed in the bores in ferrite body 24 and transfer heat to walls 25 and 26 via bores 28 and 29. 
     In the modification shown in FIG. 5 pole pieces 3&#39; and 4&#39; and magnetic yoke 6&#39; are made of a ferrite material and, instead of a magnet 5 as in FIGS. 1 and 2, a coil 41 is wound on core 42. Current surges in the coil 41 then very quickly reorient the magnetic field and thus the direction of rotation of the circulator, which is the result of direct contact of ferrite rods 7 with pole pieces 3&#39; and 4&#39;. If the coil 41 is without current, the residual field strength in yoke 6&#39;, pole pieces 3 and 4, and ferrite rods 7 maintains the static magnetic field in the resonator structure. While the drawings illustrate this technique only for the modification shown in FIG. 5, the technique may also be employed in the embodiments shown in FIGS. 1 and 2. 
     An embodiment shown in FIG. 1 which for example operates at a frequency of 4 GHz is dimensioned as follows: 
     The distance between waveguide walls 1 and 2 in the junction zone is 15-20 mm. About 60 dielectric rods 7 having a square cross section (1 mm×1 mm) are positioned in an approximately circular pattern. And the spacing between neighboring rods is about 1 mm. 
     The embodiment shown in FIG. 3 operating at a frequency of 4 GHz has a distance between waveguide walls 25 and 26 of 15-20 mm as well as the waveguide walls 1 and 2 of the above described embodiment of FIG. 1. The ferromagnetic body 24 has the shape of a cylinder with a diameter of 20 mm and is provided with 60 bores 27. Each bore 27 has a diameter of 1.5 mm and the spacing between neighboring bores is about 2 mm. 
     The present disclosure relates to the subject matter disclosed in Federal Republic of Germany application, Ser. No. P 36 33 908.3, filed Oct. 4, 1986, the entire disclosure of which is incorporated herein by reference. 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.