US3212028A

US3212028A - Gyromagnetic isolator with low reluctance material within single ridge and fluid coolant adjacent waveguide

Info

Publication number: US3212028A
Application number: US180676A
Authority: US
Inventors: Wantuch Ernest
Original assignee: Airtron Inc
Current assignee: Airtron Inc
Priority date: 1962-03-19
Filing date: 1962-03-19
Publication date: 1965-10-12
Anticipated expiration: 1982-10-12
Also published as: GB989309A; DE1239747B

Description

1965 E. WANTUCH 3,212,028

GYROMAGNETIC ISOLATOR WITH LOW RELUCTANCE MATERIAL WITHIN SINGLE RIDGE AND FLUID COOLANT ADJACENT WAVEGUIDE Filed March 19, 1962 F .5 Erner/ WWW/1 W fl K [62% ,l/farney United States Patent GYROMAGNETIC ISOLATOR WITH LOW RELUC- TANCE MATERIAL WITHIN SINGLE RIDGE AND FLUID COULAN'I ADJACENT WAVE- GUIDE Ernest Wantuch, Livingston, N..I., assiguor to Airtron, Inc., Morris Plains, NJ. Filed Mar. 19, 1962, Ser. No. 180,676 7 (Ilaims. (Cl. 333-242) This invention relates to microwave isolators, and more particularly to ridge waveguide isolators.

In microwave systems, it is frequently necessary to isolate one component from another. Nonreciprocal de vices using ferrite or other gyromagnetic material have been employed for these purposes. However, in the case of broadband, high power, isolator requirements, no altogether satisfactory solutions are available. Thus, in the case of one system employing three-inch diameter coaxial lines, it had been proposed to employ a reduced height fundamental mode waveguide isolator in combination with a pair of coaxial transitions. However, the fundamental mode waveguide was 21 inches wide, requiring more space than was available in the system in question. It has also previously been proposed to use dual ridge waveguides for low power isolators, in view of their relatively small size. In such arrangements, however, the ferrite is supported by means of dielectric material and thus cannot readily be cooled; this dual ridge structure is therefore not practical for high power requirements.

Accordingly, principal objects of the present invention are to increase the power-handling capabilities and to reduce the size of microwave isolator structures.

A collateral object of the present invention is to provide such an isolator for insertion in a coaxial waveguide system.

In accordance with the present invention, the foregoing objects are achieved through the use of a single ridge Waveguide with ferrite or other gyromagnetic material located on the broad flat sidewall of the ridge waveguide, preferably opposite the edge or edges of the ridge. A magnet may have its two poles in contact with the outer surface of the waveguide on its broad flat sidewall, on either side of the centerline of the waveguide, opposite the ferrite material. To close the magnetic circuit, a polepiece is provided within the waveguide ridge.

The resultant structure is eminently suitable for the intended purpose as the radio frequency signals are circularly polarized in the vicinity of the edges of the single ridge waveguide and the circular polarization is opposite at the two edges. Similarly, the direction of magnetization is opposite in the ferrite material adjacent the two edges of the ridge waveguide, as the magnetic field comes down through one of the ferrites and up through the other element of ferrite.

The cooling problem is also solved, as the ferrites are in heat-conducting contact with the conductive metal wall of the waveguide. In addition to the cooling effect provided by the conductive waveguide wall itself, supplemental cooling structures, such as heat radiating fins or a water-cooling system, may be provided. In these cases, of course, the high conductivity of the waveguide structure permits the rapid transfer of heat from the ferrites to the external cooling arrangements.

For insertion in a coaxial waveguide, the ridge waveguide was dimensioned to present the characteristic impedance of the coaxial line. Under these circumstances, a simple door knob type transition in which the coaxial line was rigidly mounted to the top of the Waveguide ridges, was employed. This transition had a voltage standing wave ratio of less than 1.12 over a 50 megacycle bandwidth in the 400 megacycle frequency range.

3,212,028 Patented Oct. 12, 1965 lCe Advantages of the present unit include its relatively small size and weight, in addition to its high power handling capabilities. One representative unit embodying the principles of the invention was approximately onehalf the size and weight of previous units.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of construction, together with further objects, features and advantages thereof, will be better understood from a consideration of the following description and the accompanying drawings in which illustrative embodiments of the invention are disclosed, by way of example. It is to be expressly understood, however, that the drawings are for the purposes of illustration and description only, and do not constitute a limitation of the invention.

In the drawings:

FIG. 1 is an overall view of an isolator of the present invention;

FIG. 2 is a cross-sectional view taken along lines AA of FIG. 1; and

FIG. 3 is a partial cross-sectional view through one of the coaxial transitions of the isolator of FIG. 1.

Referring to the drawings, FIG. 1 is an assembly view of the ridge waveguide of the present invention. In FIG. 1, the single ridge waveguide 12 has its ridge in its lower surface, which is not visible in this view. The two circular stubs 14 and 16 which extends upward from the ends of the ridge waveguide assembly 12 are connectors for securing the isolator to coaxial lines. The upper surface of the ridge waveguide structure 12 carries a set of three permanent magnets 18, 2t) and 22 for biasing the ferrite strips which perform the isolation function within the ridge waveguide. The ferrite elements are not visible in FIG. 1, as they are mounted inside and against the upper broad sidewall of the single ridge waveguide 12.

The cooling system for dissipating heat absorbed by the ferrite elements includes the two end manifolds 241 and 26 and the four coolant channels 28 which extend between the manifolds 2d and 26. Suitable fittings 3t) and 32 are provided for directing water or other suitable coolant through the coolant system.

The cross-sectional view of FIG. 2 is taken along lines AA of FIG. 1. Clearly visible in the showing of FIG. 2 are the

ferrite elements

42 and 44. They are located adjacent the edges of the waveguide ridge structure 46. The waveguide ridge, like the remainder of the conductively-bounded wave-guide channel 12, may be made of conductive material such as aluminum. Within the ridge structure 46 is a plate 48 of magnetic material. The member 48 closes the magnetic path from one pole of the permanent magnet 13 to the other pole. This magnetic circuit serves to bias the

ferrite elements

42 and 44 with steady magnetic fields which are directed, respectively, upward and downward, as indicated by the arrows.

The general theory of isolator action is well known and is disclosed, for example, in S. E. Miller Patent No. 2,946,025, granted luly 19, 1960. In brief, the theory involves the selective attenuation of electromagnetic field energy which is circularly polarized by gyromagnetic material biased by steady magnetic field which is properly oriented with respect to the circularly polarized radio frequency magnetic field. In the present case, the circularly polarized radio frequency magnetic fields are polarized in predetermined senses for one direction of transmission through the single ridge waveguide 12 and are polarized in the opposite senses for transmission in the opposite direction through the ridge waveguide 12. The electromagnetic waves are therefore coupled to the magnetically

biased ferrite elements

42 and 44 for one direction of transmission but not for the opposite direction of transmission. The coupling of the electromagnetic waves to the ferrite material produces loss and heating of the ferrite. Accordingly, energy is freely transmitted through the ridge waveguide isolator in one direction but little or no energy is transmitted through the isolator structure in the opposite direction.

The heat generated in the ferrite material is conducted by the metal of the broad wall 52 of the waveguide 12 to the coolant channels 28 from which the heat is dissipated. The Walls of the coolant channels 28 should, of course, be made of some relatively high heat conduction material such as aluminum or copper.

FIG. 3 is a partial cross-sectional view taken through the center of the left-hand end of the assembly of FIG. 1. In this figure, the coaxial connection stub 14 is clearly shown and the nature of the simple door knob type of transition is also disclosed. The transition includes an outer center conductor element 54, an enlarged circular element 56, and a tapered conical portion 58 which interconnects

elements

54 and 56. This door knob type transition is secured to the ridge 46 of the single ridge waveguide 12. The showing of FIG. 3 does not include the magnets or cooling structure, for purposes of simplicity. In addition, FIG. 3 terminates with the flange 60 and does not show the second coaxial stub 16 of FIG. 1.

In one particular embodiment of the invention, the single ridge waveguide was designed to cover the frequency range from 400 to 450 megacycles per second. The coaxial lines were 3% inches in diameter. The embodiment of the present invention had a voltage standing wave ratio of less than 1.12 over this frequency band. Nickel aluminate ferrite strips having an overall length of 18 inches provided a minimum of six decibels isolation in the single ridge waveguide arrangement. The permanent magnets bias the ferrite elements to resonance. The isolator has successfully handled three megawatt peak and five kilowatt average powers with a coolant temperature of 50 C. The insertion loss, measured under high power conditions, was 0.3 decibel, yielding a front-toback ratio of 20 to 1. The overall length of the isolator, including both input and output transitions to the coaxial line, is about 42 inches and the device weighs approximately 100 pounds. The unit is made airtight to withstand a pressurization of more than two atmospheres. As noted above, the illustrative embodiment of the invention is approximately one-half the size and Weight of previous designs.

It is to be understood that the above-described arrangements are illustrative of the applications of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention. Thus, by way of example and not of limitation, the ferrite strips may be replaced with other gyromagnetic materials, and the isolator may be used in systems which are not coaxial. Similarly, with regard to cooling arrangements, the waveguide itself provides considerable cooling eifect, and radiating fins may be used instead of liquid cooling when they provide sutficient cooling action. Accordingly, from the foregoing remarks, it is to be understood that the preceding description shall be interpreted as illustrative of the invention, and that the appended claims shall be accorded as broad an interpretation as is consistent with the concepts herein taught.

What is claimed is:

1. A compact high power microwave isolator comprising:

a single ridge waveguide;

first and second strips of gyromagnetic material mounted opposite the edges of the ridge on the broad flat inner wall of the waveguide;

a magnet mounted outside the Waveguide with its first and second poles mounted against the broad fiat wall of the waveguide opposite said first and second gyromagnetic strips;

a polepiece mounted within the ridge of the single ridge waveguide to close the magnetic path through the two gyromagnetic elements; and

means for dissipating heat in contact with the broad wall of said waveguide.

2. A compact high power microwave isolator comprising:

a single ridge waveguide;

first and second gyromagnetic elements mounted opposite the edges of the ridge on the broad flat wall of the waveguide;

a permanent magnet mounted outside the waveguide with its first and second poles mounted against the broad fiat wall of the Waveguide opposite said first and second gyromagnetic elements;

a polepiece mounted within the ridge to close the magnetic path through the two gyromagnetic elements; and

a cooling system in contact with said Waveguide.

3. A compact high power microwave isolator comprising:

a single ridge waveguide;

a magnet mounted outside the waveguide with its first and second poles mounted against the broad fiat wall of the waveguide opposite said first and second gyromagnetic elements; and

a polepiece mounted within the ridge to close the magnetic path through the two gyromagnetic elements.

4. A compact high power microwave isolator comprising:

a single ridge waveguide;

gyromagnetic material mounted in heat transferring contact with the broad fiat wall of the waveguide;

a magnet mounted outside the waveguide with its first and second poles mounted against the broad flat wall of the waveguide opposite said gyromagnetic material; and

a polepiece mounted within the ridge to close the mag netic path through the gyromagnetic material.

5. A high power compact isolator for insertion in a coaxial line, comprising:

coaxial input and output connectors;

a section of single ridge waveguide;

transition elements mounted on the upper surface of both ends of the ridge and connected respectively to the coaxial connectors, said transition elements being enlarged adjacent the ridge, and decreasing in crosssection near said connections;

gyromagnetic material mounted off center on the broad wall within the single ridge waveguide near the edges of the ridge; and

means for applying a steady biasing magnetic field to the gyromagnetic material.

6. A high power compact isolator for insertion in a coaxial line, comprising:

coaxial input and output connectors;

21 section of single ridge waveguide;

gyromagnetic material mounted off center on the broad wall within the single ridge waveguide near the edges of the ridge;

means for applying a steady biasing magnetic field to the gyromagnetic material; and

cooling means in contact with the outer surface of the broad wall of the waveguide.

7. A compact high power microwave isolator for insertion in a coaxial line comprising:

a section of single ridge waveguide;

first and second gyromagnetic strips mounted opposite the edges of the ridge 0n the broad flat inner wall of the waveguide;

a magnet mounted outside the waveguide with its first and second poles mounted against the broad flat wall of the waveguide opposite said first and second gyromagnetic strips;

a polepiece mounted within the ridge of the single ridge waveguide to close the magnetic path through the two gyrornagnetic elements;

means for dissipating heat in contact with the broad wall of said Waveguide;

coaxial input and output connectors; and

transition means mounted on the upper surface of both ends of the ridge and connected respectively to the coaxial connectors.

References tCited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Southworth: Waveguide Transmission, Van Nostrand Co., pages 134136 relied upon, 1950.

ELI LIEBERMAN, Primary Examiner.

15 HERMAN KARL SAALBACH, Examiner.

Claims

1. A COMPACT HIGH POWER MICROWAVE ISOLATOR COMPRISING: A SINGLE RIDGE WAVEGUIDE; FIRST AND SECOND STRIPS OF GYROMAGNETIC MATERIAL MOUNTED OPPOSITE THE EDGES OF THE RIDGE ON THE BOARD FLAT INNER WALL OF THE WAVEGUIDE; A MAGNET MOUNTED OUTSIDE THE WAVEGUIDE WITH ITS FIRST AND SECOND POLES MOUNTED AGAINST THE BROAD FLAT WALL OF THE WAVEGUIDE OPPOSITE SAID FIRST AND SECOND GYROMAGNETIC STRIPS;