US3452298A - Temperature compensated three-port stripline circulator - Google Patents

Description

June 24, 1969 c ANDR|K|AN 3,452,298

TEMPERATURE COMPENSATED THREE-PORT STRIPLINE CIRCULATOR Filed Oct. 17, 1967 GYROMAGNETIC MATERIAL x 26 I6 22 I8 22 \-TEMPERATURE COMPENSATING G'YROMAGNETIC MATERIAL COMPENSATING MATERIAL FIG. 3

. INVENTOR CHARLES F. ANDRIKIAN 0 l l I I l I 6 -80 -40 0 40 80 I20 I60 200 240 BY M M 1, 2 J mu ATTORNEYS United States Patent US. Cl. 333-11 2 Claims ABSTRACT OF THE DISCLOSURE A stripline ferrite microwave circulator is temperature compensated over a limited temperature range by using two gyromagnetic materials in the place of the normally used single materiaLThe second material is used only for temperature compensation and is placed at the RF zero location of the circulator to have minimum effect on the radio energy. The relative magnetic characteristics are such that with an increase in temperature a greater percentage of the total externally applied flux is passed through the main gyromagnetic material.

Background of the invention In ferrite microwave devices, performance characteristics such as isolation. VSWR and insertion loss are affected by temperature conditions. Such changes in performance characteristics are due to the decrease in magnetization of both the magnets and microwave garnets with an increase in temperature. One prior art scheme to minimize temperature effects is to place a shunt compensation element outside of the circulator to then variably shunt the flux from a C magnet. This scheme results in a relatively large and heavy package unsuitable for applications in which minimum weight is of importance, such as spacecraft.

It has been observed that if the externally applied magnetomotive force (H is increased along with the increase in temperature the isolation d.b. will remain substantially constant. This can be accompished without increasing over all device size by placing a magnetic compensating material within the circulator body in shunt with the external magnets. However, it is necessary that the compensating material have minimum microwave disturbance.

Summary of the invention In accordance with the present invention the circulator has its gyromagnetic material divided into two parts, referred to hereinafter as the main or regular gyromagnetic material and the compensating gyromagnetic material. The main gyromagnetic material is selected in accordance with known selection criteria to result in a circulator having the desired microwave characteristics. The compensating gyromagnetic material is selected to have microwave characteristics such as line width (AH), dielectric constant and loss tangent as near as possible to the main gyromagnetic material while at the same time having a greater magnetic saturation over the temperature range of interest and a greater slope of magnetic saturation versus temperature over the temperature range of interest. The compensation material is at the center of the circulator where it will cause the least amount of disturbance to the microwave energy because the RF field at the center is zero. At any given temperature the external flux will be applied in part to the main material and in part to the compensating material. As the temperature goes up, thereby decreasing the M of the compensating material by an amount greater than the decrease in M of the main material, a greater portion of the external flux will pass through the main material thereby offsetting the temperature eifect on the isolation characteristic.

3,452,298 Patented June 24, 1969 ICC FIGURE 3 shows a graph of magnetic saturation (M versus temperature for two materials useful in the present invention.

Although the specific embodiment will be described in connection with one particular geometry of a circulator it will be apparent to anyone having ordinary skill in the art that the invention is not confined to the geometry of the circulator or the specific materials described.

The drawings show a three port stripline ferrite microwave circulator including upper and lower common or ground planes 12 and a cylindrical enclosing wall 14. The circulator is divided into upper and lower portions by a flat conductor 26 shaped as illustrated. Each of the three arms of conductor 26 are connected respectively to one of the three port connectors 10. I

The upper portion of the circulator includes a disc shaped gyromagnetic material 20 surrounded by a ring shaped dielectric material 24. The lower portion, identical to the upper portion, includes a disc shaped gyromagnetic material 18 surrounded by ring shaped dielectric material 22. Disc magnets 16 are placed on the upper and lower ground plates to direct magnetic flux through the circulator.

The theory and operation of the device described thus far is well known and therefore need not be discussed herein. The particular dielectric materials 22 and 24 and gyromagnetic materials 28 and 20 are those which would be encountered in the design of conventional circulators without temperature compensation, and the specific types do not form a part of the present invention.

In accordance with the present invention a shunt compensating gyromagnetic material 30 is placed in a hole drilled in the main gyromagnetic material at the center of the circulator. As the temperature increases the relative magnetic saturations of the compensation material 30 and main material 18, 20 decreases, causing a greater amount of flux from disc magnets 16 to be applied to the main gyromagnetic material 18, 20. As shown in the drawing. the compensating material 30 extends from upper ground plane 12 to lower ground plane 12 through a hole in the fiat conductor 26. It is not necessary that the compensating material pass through the conductor 26 but may be placed on opposite sides of the conductor 26 in the same manner as the main gyromagnetic material 18, 20. Also, the compensating material 30 may extend through holes in the upper and lower plates to come into physical contact with the upper and lower disc magnets.

As stated above, the temperature compensating material is a gyromagnetic material. Many gyromagnetic materials and their characteristics are Well known in the art and the particular one used as the compensating element is a matter of choice based upon the particular main material used and the desired temperature range of operation. There are two determining criteria in selection of the compensating material:

(1) The saturation magnetization (M of the compensating material must be greater than that of the microwave ferromagnetic material over the temperature range of operation; and

(2) The change in saturation magnetization with respect to temperature over the temperature range of operation must be greater for the compensating material than for the microwave ferromagnetic material.

It is well known that the saturation magnetization or saturation moment of a ferrite or garnet can be lowered by aluminum substitution methods, the methods of substitution also being well known. The more the substitution of the aluminum ion in the ferrite or garnet, the lower the resulting saturation magnetization.

As a specific example of materials and saturation magnetizations which are suitable in the present invention, an unmodified yttrium iron garnet having a known saturation magnetization of 1780 gauss may be modified by the substitution of aluminum to form a first modified garnet having saturation magnetization of 680 gauss at room temperature and a second modified garnet having a saturation magnetization of 1000 gauss at room temperature. The method of substitution for lowering the saturation magnetization is Well known in the art. The former may be used as the main gyromagnetic material and the latter may be the compensating gyromagnetic material.

The above mentioned main material may be obtained from Microwave Chemical Labs as their product number MC 1116 PH, and the above mentioned compensating material may be obtained from Trans Tech Corporation as their product number G-1010. The curves of magnetic saturation (in gauss) versus temperature C.) for the two materials of the specific example are shown in FIG. 3.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is: t

1. In a microwave stripline circulator of the type comprising a plurality of strip-line arms radiating from a common junction region and having gyromagnetic material at said junction region adapted to be magnetized by a direct current magnetic field, the improvement comprising: dividing said gyromagnetic material into a main material and a compensating material, said compensating material being located substantially at the center of said junction region and surrounded by said main material, said compensating material having a greater magnetic saturation and a greater slope of magnetic saturation versus temperature than said main material over the tem- 4 perature range of desired operation so as to temperature compensate said circulator.

2. A circulator as claimed in claim 1 wherein said compensating material and said main material are yttrium iron garnets with aluminum substitution.

References Cited UNITED STATES PATENTS 3,174,116 3/1965 5hr 3331.1 3,246,262 4/1966 Wichert 3331.1 3,273,082 9/1966 Chiron 33324.1 X

HERMANN KARL SAALBACH, Primary Examiner. P. L. GENSLER, Assistant Examiner.

U.S. Cl. X.R.

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