Nov. 6, 1962 L. DAVIS, JR I MICROWAVE STRIP TRANSMISSION LINE CIRCULATOR 3,063,024 s Filed Feb. 29, 1960 44 20 y/4 46 50 //v|/EA/7'0/? LUTHER DAV/.5; JR. BY w 31... TTOR/VEY United States Patent Q??ce 1 3,063,024 MECRDWAVE STRIP TRANSMISSION LINE CIRCULATGRS Lather Davis, Jr” Wayland, Mass., assignor to Raytheon Company, Lexington, Mass, a corporation of Dela ware Filed Feb. 29, 1960, Ser. No. 11,740 5 Claims. (Cl. 333-11) Brim“ Patented Nov. 6, 1962 2 later body includes a pair of parallel ground plane mem bers held in spaced-apart relationship by a peripheral cover member. Three coaxial connectors are disposed about the peripheral cover in symmetrical relationship, with the center conductor of each of the connectors being connected to the outer end of a respective one of the three arms of a conductive spider member which is posi tioned midway between and parallel with the ground members to provide a strip transmission line con This invention pertains generally to microwave circu l0 plane ?guration of three branches. lators, and more particularly to improved ferrimagnetic In order to obtain circulator action, a pair of ferrimag microwave circulators employing strip transmission line netic members are positioned substantially centrally with con?guration. As employed herein, the term “ferrimag in the circulator, one on either side of the central portion netic” is intended to connote materials having negligible electrical conductivity and exhibiting either ferrimagnetic or ferromagnetic effects. Ferrimagnetic materials ?nd wide use in microwave de vices as the art advances. Exemplary of devices employ of the spider member, and a magnetic ?eld of ?xed in 15 tensity is established within the ferrite member in a di~ rection perpendicular to the spider and ground plane members. As will be understood by those skilled in the art, this steady-state magnetic ?eld is of an intensity ing magnetized ferrimagnetic materials are gyrators, iso lators, directional phase shifters and circulators. Circu~ 20 amplitude which is signi?cantly removed from (being either greater or smaller) that connected with ferrimag~ lators are considerably more complicated circuit elements netic resonance at a given microwave frequency and for than, for example, isolators, and the uses proposed for a given geometry. The three coaxial connectors con~ them are typically more sophisticated than those for iso stitute the ports of the circulator, and a signal applied to lators. An important distinction between circulators and a ?rst of these ports effectively appears at only a second isolators is that the former diverts or otherwise makes port, with signals applied to the second port appearing use of input power, rather than destroying it, as does the only at the third, and so on, for a given ?eld polarity of latter. It is a basic characteristic of microwave circu magnetic energization. With the D.-C. magnetic ?eld lators that energy introduced into a ?rst port will be pre .reversed, the sense of the commutation between ports is sented (ignoring losses) as an output solely at a second reversed. port (for a given set of operating parameters), energy at 30 With the above considerations and objects in mind the such second port appears at only a third port, and so on, invention itself will now be described in connection with with substantial isolation being provided between a se lected input port and all other ports except the particular a preferred embodiment thereof given by way of example and not of limitation, and with reference to the accom output port. The term “circulator” thus connotes a com panying drawings, in which: . mutation of power from one transmission terminal to 35 FIG. 1 is a plan view of the microwave circulator of another. It is well known that a magnetized ferrirnagnetic body is an anisotropic medium, and that a microwave device in cluding such a body may be electromagnetically asym— metrical even though it has geometrical symmetry. It is this asymmetry of electromagnetic characteristics that renders ferrimagnetic devices the interesting and useful tools that they are, and different theories (based upon ?eld displacement and perturbation theory, for example) the present invention, with the D.-C. magnetic ?eld means being removed for the sake of clarity. FIG. 2 is a sectional view taken on line 2—2 in FIG. 1. FIG. 3 is a fragmentary elevation view of a modi?ca tion of the device shown in FIGS. 1 and 2. In the exemplary embodiment shown in FIGS. 1 and 2, a pair of circular ground plane members 10 and 12 are shown mounted in parallel spaced-apart relationship by have been advanced as to the basis for such asymmetric means of a peripheral cover member 14, with the plates 10 and 12 and the cylindrical member 14 together form The anisotropic electromagnetic properties of mag netized ferrimagnetic bodies have been utilized by prior ing the body of the circulator. These three members are of electrically conductive material, and may convenient ly be secured together by a plurality of threaded fasteners 16 disposed about the peripheries of the two plates'ltl and characteristics. workers in the art to provide Y-junction and other circu lators of hollow waveguide con?guration, and these prior 50 12. A plurality of coaxial connectors 18, 2t} and 22 are art devices have proven satisfactory for some applica symmetrically disposed about the cover member 14 to tions. However, these prior art circulators have lacked form the ports of the circulator. The center conductors sufficient electrical bandwidth in many applications. In 24, 26 and 28 of the three coaxial connectors are con addition, the size and width of the devices of the prior art are often greater than can be tolerated in many in on Or nected to the ends of respective arms of a conductive spider member 30, such spider member having a central . stances. Further, the adequate dissipation of heat from portion 32 in substantial registry with the central portions the ferrimagnetic members of prior circulators has been of the ground plane members 10 and 12.. dif?cult. As will be evident to those skilled in the art, energy It is accordingly a primary object of the present inven tion to provide a microwave circultaor of relatively 60 in coaxial lines connected to the connectors 18, 2t)‘ and 22 will be propagated into the circulator of the present small and lightweight construction. invention by means of the strip transmission line con?ura An additional object of the present invention is to tion of the components therein, and, similarly, micro provide a microwave circulator being characterized by an wave energy within the circulator will be propagated by increased electrical bandwidth. Another object of the present invention is to provide 65 such strip transmission line con?guration to one or more of the ports formed by the connectors 18, 2t) and 22, for a microwave circulator having improved heat-dissipation transmission through coaxial lines connected thereto. characteristics. In order to render this three port strip transmission In accordance with the present invention, the above line junction a circulator, a pair of ferrimagnetic bodies and other objects are achieved by means of a microwave circulator device employing strip transmission line con 70 34 and 36 are suitably mounted (by means not shown) on opposite sides of the conductive spider member 3%, ?guration, as opposed to hollow waveguide members. and in substantial registry with the central portion 32 In the exemplary embodiment described herein, the circu thereof. The particular composition of the members 34 3,063,024 and 36 is not a necessary element of the present inven tion, and any substantially electrically nonconductive ma terials exhibiting ferrimagnetic or ferromagnetic effects may be employed. Yttrium iron garnet polycrystalline materials are exemplary for this purpose. In the operation of the device depicted in FIGS. 1 and 2, a steady-state or D.-C. magnetic ?eld is applied to the ferrite bodies 34 and 36 in one sense or the other in a 4 shown in FIG. 3 is substantially the same as that de scribed in connection with FIGS. 1 and 2, with the D.-C. magnetic ?eld being applied to ferrimagnetic members 40 and 42 by a suitable magnet the pole pieces 48 and 50 of which are shown in FIG. 3. Where circulator action or commutation is desired in but one direction, the pole pieces 48 and 50 may form a part of a permanent magnet of appropriate polarity. On the other hand, where it is desired to reverse the sense of the circulator operation, direction substantially perpendicular to the plane of the spider member 30, such applied magnetic ?eld being sche 10 it is necessary to reverse the sense of the applied D.-C. matically indicated by the dot-dash lines 38 in FIG. 2, and being of a magnitude which is removed from (being either signi?cantly greater or smaller) that connected with ferrimagnetic resonance at the applied microwave frequency and for the given geometry. With the D.-C. 15 magnetic ?eld passing through ferrimagnetic bodies 34 magnetic ?eld. Suitable means for achieving such ?eld reversal are indicated schematically in FIG. 3 by the solenoid '52 which is energized by a D.-C. source 54 through a reversing switch 56. Upon reversal of switch 56 from one position to another, the magnetic ?eld pass ing through members 40 and 42 is reversed in polarity, and the circulator action is correspondingly reversed. The invention has been described above in some detail, and 36 in a selected direction (e.g., into the drawing page of FIG. 1), microwave energy introduced into the and with particular reference to the application of strip circulator at the port formed by coaxial connector 18 will appear as an output (neglecting losses) at the port 20 transmission line con?guration to a three port Y-junction circulator. However, it will be evident to those skilled formed by connector 20, with no effective output appear in the art that the invention is equally applicable to cir ing at connector 22. With the D.-C. magnetic ?eld main culators having other than three ports therein. In addi tained in this same direction, a singal applied to con tion, the circulator ports may take the form of hollow nector 20 will appear as an output signal at connector 22 with no effective coupling toward connector 18. Simi 25 waveguide connectors with central coupling loops being connected to the outer ends of the arms of the strip trans larly, with the D.-C. magnetic ?eld maintained in this mission line spider member. Further, it will be under ?rst polarity, an input signal at connector 22 will produce stood that the strip transmission line structure of the an output at only connector 18. Thus, a commutation present invention need not necessarily be in the form of of signals in a given direction between the several ports of the circulator is achieved. Where the polarity or 30 a central conductor between two spaced-apart ground sense of the applied D.-C. magnetic ?eld is reversed from planes. Instead, the device of the invention may equally that ?rst assumed herein, the direction of commutation well comprise the spider member disclosed herein and between ports is also reversed, and an input at connector only one ground plane member. In such con?guration, 18 appears as an output at connector 22, et cetera. the spider and the ground plane member would be FIG. 3 shows a modi?cation of the device of FIGS. 1 35 mounted in parallel spaced-apart relationship with a ferri and 2, with corresponding elements bearing like refer magnetic member therebetween, with a source of D.-C. ence numerals. Thus, the ground plane members 10 magnetic ?eld, and a plurality of appropriate connectors and 12 are supported in parallel spaced-apart relation suitably matched to the strip transmission line structure ship by means of the cylindrical cover member 14, the 40 so formed. Thus, the invention is not to be considered latter having a plurality of coaxial connectors (one of as limited to the particular details given, nor to the speci?c which is indicated at 20) mounted thereon. The conduc application to which reference has been made during the tive spider member 30 is mounted within the circulator description of the device, except insofar as may be re' body substantially midway between and parallel with the quired by the scope of the appended claims. ground plane members 10 and 12, with the outer ends of What is claimed is: the spider arms being connected to the center conductors 1. A circulator comprising a plurality of strip transmis— (one of which is indicated at 26 in FIG. 3) of respec sion lines coupled together at a common point, said trans tive ones of the coaxial connectors mounted on cover mission lines being oriented with their axes de?ning equal member 14. angles, each line including a center conductor disposed A pair of ferrimagnetic members 40 and 42 are between two outer conductors, means electrically con mounted on opposite sides of the spider memebr 30, and 50 necting together the center conductors of each of said in substantial registry with the central portion 32 thereof, transmission lines at said common point, at least one body as well as with the central portions of ground plane of ferrite material disposed at said common point be members 10 and 12. In contrast to the ferrimagnetic tween said center conductor and one of said outer con members 34 and 36 shown in the preceding ?gures of ductors, at least one other body of ferrite material dis the drawing, members 40 and 42 are of su?icient thick 55 posed at said common point between said center conduc ness to result in a closely contiguous relationship be tween the upper and lower faces thereof, respectively, and the opposing areas of the inner faces of ground plane tor and said other outer conductor, and means magnetiz ing said ferrite bodies in a direction substantially parallel to the electric ?eld of waves conducted by said lines and members 10 and 12. The intimate contact between the with a strength such that electric waves conducted by upper face of member 40 and the contiguous face of 60 each of said lines couple to only one other of said lines ground plane member 10 results in an ef?cient heat trans and said last-mentioned coupling is nonreciprocal. fer between the ferrite 40 and the member 10. Similarly, 2. A circulator as in claim 1 and in which said outer e?icient heat transfer takes place between the lower face conductors of each of said transmission lines extend sub of member 42 and the upper face of member 12. As is common with microwave devices employing ferrimag 65 stantially beyond ‘the edge of the associated center con ductor. netic members, considerable quantities of heat may be 3. A circulator as in claim 1 and in which each of said generated within the members 49 and 42, and the good strip transmission lines couples to a separate connector at thermal contact between these members and the respec tive ground plane members provides a ready sink for such the same distance from said common point. heat. To improve the efficiency with which such heat 4. A circulator as in claim 1 and in which each of said may be dissipated, cooling chambers 44 and 46 are pro bodies of ferrite material has at least one dimension par vided in intimate contact with the outer faces of mem allel to a common plane which is greater than at least bers 10 and 12, and a suitable coolant is circulated through one dimension of said center conductors parallel to said such chambers by means not shown. It will be understood that the operation of the device 75 common plane. 5 3,063,024 6‘ 5. A circulator as in claim 1 and in which said outer OTHER REFERENCES conductors are common to all said lines and are substan tially ?at parallel plates and the outer peripheries of said outer plates are connected together by electrically conduc tive material. “Electrical Manufacturing,” February 1959, pages Aulbl: “IRE Transactions on Microwave Theory and 5 Techniques,” April 1959, pages 238-246. Swanson et al.: “1958 IRE Wescon Convention Re cord—Part 1,” pages 151-156. UNITED STATES PATENTS Chait et al.: “NRL Progress Report,” March 1958 2,946,966 Crowe _______________ __ July 26, 1960 10 (made available to public through OTS on Apr. 11, 1958), page 50. 2,978,649 Weiss _______________ __ Apr. 4, 1961 References Cited in the ?le of this patent 3,015,787 Allin et a1. ____________ __ Jan. 2, 1962 Seidel: “Journal of Applied Physics,” February 1957, pages 218-226.