US3174116A - Trough line microstrip circulator with spaced ferrite surrounding transverse conductive rod - Google Patents

Description

March 16, 1965 su TROUGH LINE MICROSTRIP CIRCULATQR WITH SPACED FERRITE SURROUNDING TRANSVERSE CONDUCTIVE ROD Filed May 15, 1953 m R U0 m T new A hV Om I BIG Fig. 3. 37 39 United States Patent C TROUGH LINE MICRDSTRE CIRCULATOR WITH SlACED FERRKTE SURRGUNDING TRANSVERSE CONDUCTIVE R01) John Sur, Honolulu, Hawaii, assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed May 15, 1963, Ser. No. 280,625 4 Claims. (Cl. 3333-11) This invention relates to a circulator and more particularly to a trough line circulator capable of handling high average power electromagnetic energy.

As is well known in the microwave component art, circulators are nonreciprocal junctions that have three or more ports and are used extensively in radar duplexer, single cavity parametric amplifier, and switching applications. The nonreciprocal property of these devices is a function of a nonreciprocal element disposed symmetrically at the junction. Generally, the nonreciprocal element comprises a ferrimagnetic material such as ferrite or garnet. The basic operational principles of circulators utilizing nonreciprocal elements will not be presented here, but may be found in various texts on the subject, such as Microwave Ferrites and Ferrimagnetics by B. Lax and K. 3'. Button, McGraw-Hill, 1962, pp. 517-539, 609-630.

The relatively large physical dimensions and weight of microwave components has long been a problem sought to be overcome. A particularly compact and light weight circulator has recently been constructed in the form of a strip-line junction and is described in detail in an article entitled A Strip-Line L-Band Circulator in the Proceedings of the I.R.E., vol. 48, p. 115, 1960, by L. Davis, in, U. Milano, and J. Saunders.

Strip-line circulators have been utilized successfully throughout the very high frequency to microwave frequency range with characteristics suitable for most low and medium power radio frequency (RF) applications. However, where high RF power handling capability is required (over 500 watts average), the problem of heat is presented.

The input energy is transformed into heat in ferrimagnetic elements by the presence of inherent losses in the ferrimagnetic material. The heat in turn affects the nonreciprocal magnetic properties of the element until a term perature is reached where no circulator action takes place. This is known as the Curie temperature of the material. Furthermore, some ferrimagnetic materials exhibit an increase in losses as temperature is increased and thus leads to a runaway condition.

In the past, the only areas of the nonrecipcroal elements which had low resistance heat conduction paths to an outer radiant surface in a strip-line circulator were the outer surfaces of the elements adjacent to the two ground planes. The areas of the elements adjacent the center conductor junction, and the center conductor junction itself, had no such means to dissipate unwanted heat. Accordingly, these devices were limited in the amount of power they could handle unless some external means of carrying off the heat was utilized. The most successful solution to this problem has been to provide forced air cooling. However, this involves the use of heavy, bulky and expensive cooling systems which defeat the principal advantages of compactness and lightness of weight which are derived from a strip-line type circulator.

From the above, it can be seen that a circulator which provides a low heat resistance path to dissipate unwanted heat in the area of a center conductor junction without degrading circulator performance would be a substantial advance in the art.

It is therefore an object of the present invention to provide a compact, light weight circulator which will 0,,-

erate at high average power levels Without the necessity of forced air cooling.

This and other objectives are achieved according to this invention in a trough line circulator comprising at least three fiat strip center conductors centrally disposed between, parallel to and spaced from a pair of flat outer conductors. The three center conductors extend from a common junction in a symmetrical relationship and in a common plane. A transverse conductive rod is disposed at the center of the common junction and conductively connects the common junction with the flat outer conductors. Two nonreciprocal elements, each having a centrally located aperture, are disposed on opposite sides of the common junction with their apertures about the transverse rod. Also, a magnetic biasing field means is magnetically coupled to the nonreciprocal elements for providing therein a predetermined magnetic flux parallel to the transverse rod.

Briefly, it may be stated that the transverse conductive rod in conjunction with an appropriate strip-line type of center conductor junction can be thought of as transforming a strip-line circulator mode of operation into a waveguide circulator mode or, more specifically, what is commonly called a trough line mode of operation. In addition to providing a low resistance thermo-conducting path from the center conductor junction to the flat outer conductors or ground planes, the conductive rod may also provide mechanical support for the ground planes when four such circulators are used under common ground planes to reduce any undesirable eifects due to shock or vibration. A further advantage in the use of the transverse conductive rod is that the physical symmetry of the nonreciprocal elements can be accurately obtained.

The invention and specific embodiments thereof will be described hereinafter by way of example and with reference to the accompanying drawing, in which:

FIG. 1 is a plan view of a preferred embodiment of a circulator provided in accordance with the present invention, the circulator having a top ground plane partially removed;

Fit}. 2 is a cross-sectional view of the circulator of FIG. 1 taken along the line 22;

FIG. 3 is a cross-sectional view of the circulator of FIG. 1 taken along the line 33; and

FIG. 4 is a plan view of a center conductor structure according to another embodiment of the invention.

Referring now to the drawing and more particularly to FIGS. 1, 2 and 3, the present invention may be embodied in any desirable microwave system or device incorporating coaxial or strip-line waveguiding means for propagating electromagnetic energy. In the present instance, the invention is embodied in a circulator 11 adapted to be interconnected with the abovementioned waveguiding means by a first connector 13, a second connector 15 and a third connector 17.

Circulator 11 includes a first flat center conductor connected to the first connector 13, a second fiat center conductor 27 connected to the second connector 15 and a third fiat center conductor 2.9 connected to the third connector 17. The three center conductors 25, 27, 29 are all similarly disposed between, parallel to and spaced from a pair of fiat outer conductors or ground planes such as a first common ground plane 31 and a second common ground plane 33. These center conductors 25, 27, 29 also extend from a common junction 35 in a symmetrical relationship and in a common plane to form a general strip-line circula-tor configuration. Although any desired number of symmetrically positioned center conductors may be employed, the circulator 11, for illustrative purposes, has three such conductors equally spaced apart) to form a so-called Y circulator.

A transverse conductive rod 37 which may be of brass or other conductive material is disposed at the center of the junction 35 and is conductively connected by any suitable means such as solder, for example, to junction 35 as well as to both the first ground plane 31 and the second ground plane 33. For ease of assembly, central-ly disposed holes 39, 41 have been provided in the two ground planes 31, 33, respectively, for accepting the conductive rod 37.

In order to provide circulator action in the circulator 11, a steady state magnetic biasing field (from a source not shown) having a direction indicated by an arrow B is magnetically coupled to two nonreciprocal elements such as a first ferrite element 43 and a second ferrite element 45, each of which has a centrally located aperture for mounting about the transverse rod 3'7 in positions on opposite sides of the junction 35. The diameter of the ferrite elements 43, 45 are shown to be larger than the diameter of the common junction 35 merely for simplicity and may have a different relationship depending upon the frequency of the input energy to the circulator. As can be seen from the arrow B, the direction of the biasing field is parallel to the transverse rod 37.

The strength of the biasing field to be used for circulator action will, as is well known, depend upon whether the device is to function in an above or at below gyromagnetic resonance mode of operation. The advantages and disadvantages of operation in each of these modes and the biasing field strength necessary to obtain them is discussed in the above cited reference by B. Lax and K. J. Button.

The circulator 11 is enclosed by a cylindrical wall 47. It should be noted that the geometric configuration of the wall 47 will have little effect, if any, on the performance of the circulator 11. In fact, the circulator 11 may be operated without the wall 47 with only a small loss of energy due to radiation. However, structure should then be provided to support connectors 12, 15 and 17.

It can readily be seen from FIGS. 2 and 3 that heat generated in the two ferrite elements 41, 45 has a very low resistance path to the outer surfaces of the two ground planes 31 and 33 provided by the transverse rod 37.

As stated previously, the transverse rod 37 in effect transforms a strip-line circulator junction into a trough line circulator junction. The well known cross-sectional outline of a trough waveguide may be seen most clearly in FIG. 3 by observing, for example, the section 31a of the ground plane 31, section 35a of junction 35, seck tion 33a of ground plane 33, and the transverse rod 37.

For one practical embodiment of the invention as shown in FIGS. 13 operating in the S-band frequency region (around 3 kmc.), the following dimensions have been used:

Inches Inner diameter of the cylindrical wall 47 3.00 Width of the flat center conductors 25, 27, 29 0.425 Diameter of the common junction 35 1.075 Diameter of the conductive rod 37 0.125 Diameter of the ferrite elements 43, 45 1.075 Thickness of the ferrite elements 43, 45 H 0.130 Length between the inner surfaces of ground planes For operation of other frequencies, reference may be made to articles in the Transactions of the IRE. on the subject of trough waveguides such as, for example, The Cut-Off Wavelength of Trough Waveguides by K. S. Packard in PGMTT, vol. 6, No. 4, pp. 455 and 456, October 1958, and Asymmetrical Trough Waveguide Antenna .by W. Rotman and A.A. Oliner in PGAP, vol. 7, No. 2, pp. 153-162, April 1959.

FIG. 4 illustrates a modification of the center condoctor structure of FIG. 1. Here, parts corresponding to those of the arrangement of FIG. I bear like reference characters. 'In the interest of simplicity, the center conductor structure is illustrated by itself. Its application in the circulator will be evident from FIG. 1.

As shown, the center conductor structure is again generally of Y-shaped configuration having a flat circular center section 35. In this case, however, the periphery of the circular center section intermediate the conductors 25, 27 and 29 is notched or slotted radiaily as shown by reference character 40, providing a notch-type slow wave structure. This provides a circulator requiring less ferrite material than the devices shown in FIG. 1 because of the reduced wave propagation provided by the slow Wave structure.

As can be seen from the flat center conductor structure shown in FIGS. 1 and 4, tapering may be utilized at the extremities of the center conductors 25, 27, 29 coupled, by conventional means such as solder, to the connectors 13, 15, 17 for impedance matching purposes.

From the foregoing, it will be evident that there is achieved a compact, light weight circulator capable of operating in high RF power applications.

Although only the 3-port Y configuration has been illustrated, it should be appreciated that more than 3 ports may be provided, and other organizations of the specific arrangements shown may be made within the spirit and scope of the invention.

Accordingly, it is intended that the foregoing disclosure and the showings made in the drawings shall be considered only as illustrations of the principles of this invention and are not to be construed in a limiting sense.

What is claimed is:

1. A trough line circulator comprising: at least three flat strip center conductors centrally disposed between, parallel to and spaced from a pair of flat outer conductors, said center conductors extending from a common junction in a symmetrical relationship in a common plane; a transverse conductive rod disposed at the center of said common junction and conductively connecting said common junction with said pair of flat outer conductors; two nonreciprocal elements each having a centrally located aperture and disposed on opposite sides of said common junction and with their apertures about said transverse rod; and magnetic biasing field means magnetically coupled to said nonreciprocal elements for providing therein a predetermined magnetic flux parallel to said transverse rod.

2. A trough line circulator comprising: at least three fiat strip center conductors centrally disposed between, parallel to and spaced from a pair of fiat outer condoctors, said center conductors extending from an essentially circular common junction in a symmetrical relationship in a common plane; a transverse conductive rod disposed at the center of said common junction and conductively connecting said common junction with the flat outer conductors; two circular ferrite elements each having an axial aperture and disposed on opposite sides of said common junction and with their apertures about said transverse rod; and magnetic biasing field means magnetically coupled to said ferrite elements for providing therein a predetermined magnetic flux parallel to said transverse rod.

3. A trough line circulator comprising: at least three stripline flat strip center conductors centrally disposed between, parallel to and spaced from a pair of flat outer conductors, said center conductors extending from an essentially circular common junction in a symmetrical relationship and in a common plane; a transverse conductive rod disposed at the center of said common junction and conductivcly connecting said common junction with said pair. of outer conductors to form a trough line waveguiding structure at said common junction; two circular ferrite elements each having an axial aperture and disposed on opposite sides of said common conductor junction and with their apertures about said transverse dm gnetic biasing field means magnetically. Coupied to said ferrite elements for providing therein a predetermined magnetic flux parallel to said transverse rod.

4. A trough line circulator comprising: at least three fiat strip center conductors centrally disposed between, parallel to and spaced from a pair of flat outer conductors, said center conductors extending from an essentially circular common junction in a symmetrical relationship and in a common plane; a transverse bnass rod disposed at the center of said common junction and conductiveiy connecting said circular common junction with said flat cuter conductors to form a trough line Waveguiding structure at said common junction, said circular common junction being radially notched on its outer periphery intermediate said center conductors to provide a slow Wave trough line structure at said common junction; two circular ferrite elements each having an axial aperture and disposed on opposite sides of said common junction and with their apertures about said transverse rod; and magnetic biasing field means magnetically coupled to said ferrite elements for providing therein a predetermined magnetic flux magnitude parallel to said transverse rod.

References tilted by the Examiner UNITED STATES PATENTS OTHER REFERENCES Chait et al.: Electronics, Dec. 18, 1959, New Micro- Wave Circulators, pages 81-83 relied upon.

Milano et al.: Y-Junction Circulator, IRE Transactions on Microwave Theory and Techniques, May 1960, pages 345-350 relied upon.

Auld: Synthesis of Circulators, IRE Transactions on Microwave Theory and Techniques, April 1959, pages 238-246 relied upon.

Bland: Ferrite Y Circulator, IBM Technical Disclosure Bulletin, vol. 4, No. 10, March 1962, pages 45 and 46.

HERMAN KARL SAALBACH, Primary Examiner.

0 ELI LIEBERMAN, Examiner.

Claims (1)

1. A TROUGH LINE CIRCULATOR COMPRISING: AT LEAST THREE FLAP STRIP CENTER CONDUCTORS CENTRALLY DISPOSED BETWEEN, PARALLEL TO AND SPACED FROM A PAIR OF FLAT OUTER CONDUCTORS, SAID CENTER CONDUCTORS EXTENDING FROM A COMMON JUNCTION IN A SYMMETRICAL RELATIONSHIP IN A COMMON PLANE; A TRANSVERSE CONDUCTIVE ROD DISPOSED AT THE CENTER OF SAID COMMON JUNCTION AND CONDUCTIVELY CONNECTING SAID COMMON JUNCTION WITH SAID PAIR OF FLAT OUTER CONDUCTORS; TWO NONRECIPROCAL ELEMENTS EACH HAVING A CENTRALLY LOCATED APERTURE AND DISPOSED ON OPPOSITE SIDES OF SAID COMMON JUNCTION AND WITH THEIR APERTURES ABOUT SAID TRANSVERSE ROD; AND MAGNETIC BIASING FIELD MEANS MAGNETICALLY COUPLED TO SAID NONRECIPROCAL ELEMENTS FOR PROVIDING THEREIN A PREDETERMINED MAGNETIC FLUX PARALLEL TO SAID TRANSVERSE ROD.

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