US3636479A

US3636479A - Microwave strip transmission line circulator

Info

Publication number: US3636479A
Application number: US65070A
Authority: US
Inventors: Norman Hartz; Bruce K Horne
Original assignee: MICROWAVE ASSOCIATES WEST Inc
Current assignee: MICROWAVE ASSOCIATES WEST Inc
Priority date: 1970-08-19
Filing date: 1970-08-19
Publication date: 1972-01-18
Anticipated expiration: 1989-01-18

Abstract

A microwave strip transmission line circulator is disclosed comprising at least one body of ferrite material, a ground plane member overlaying one surface of the ferrite body, and a conductive disk overlaying another surface of the ferrite body. At least three strip transmission line conductors extend radially from the periphery of the conductive disk with the axes of the transmission line conductors defining equal angles. The conductive disk has at least three sets of indentations with each set comprising two convergent indentations extending from the periphery of the disk to two juxtaposed lines located substantially equidistant from and along opposite sides of one of said axes. Means are also provided for magnetizing the body of ferrite material.

Description

United States Patent Hartz et a].

[151 3,636,479 [451 Jan. 18, 1972 Claude A. S. Hamrick ABSTRACT A microwave strip transmission line circulator is disclosed comprising at least one body of ferrite material, a ground plane member overlaying one surface of the ferrite body, and a conductive disk overlaying another surface of the ferrite body. At least three strip transmission line conductors extend radially from the periphery of the conductive disk with the axes of the transmission line conductors def ning equal angles. The conductive disk has at least three sets of indentations with each set comprising two convergent indentations extending from the periphery of the disk to two juxtaposed lines located substantially equidistant from and along opposite sides of one of said axes. Means are also provided for magnetizing the body of ferrite material.

5 Claims, 2 Drawing Figures PATENTEU JAN 1 8 I972 INVENTORS NORMAN HARTZ BRUCE K. HORNE BY WJJM ATTORNEY MICROWAVE STRIP TRANSMISSION LINE CIRCULATOR BACKGROUND OF THE INVENTION This invention relates generally to fen'ite circulators, and particularly to microwave strip transmission line type ferrite circulators.

Circulators, as used herein, are N port microwave devices where N is greater than 2. It has the property that when the ports are suitably numbered 1 through N an applied input electrical signal at port 1 emerges from port 2 with a minimum of attenuation while negligible power emerges from the other ports. Likewise, a signal applied to port 2 emerges from port 3 and so forth.

Microwave strip transmission line circulators of the prior art, such as those disclosed in US. Pat. Nos. 3,063,024 and 3,359,510, have typically employed a pair of ground plane conductors and a center conductor of the stripline type electrically connected to three ports. Ferrite disks are disposed between the center conductor and the ground plane conductors although in some types only one ferrite disk is disposed between a single ground plane conductor and the center conductor. In many cases dielectric disks are placed about the ferrite disks for impedance matching purposes. In both types, however, means are provided for applying a magnetic field having a strength above or below that which would impart ferrimagnetic resonance at the applied microwave frequency for the given geometry of the ferrite disk.

In such circulators the ferrite disks act as nonreciprocal perturbative elements. The dimensions of the disk or ferritedielectric disk assemblies are such that their radii are approximately equal to an integral number of quarter wavelengths of the operating frequency of the circulator. In addition, the ferrite disks also act as resonant cavities in which electric energy is stored in the capacitance between the stripline center conductor and the ground plane, and magnetic energy is stored in the magnetic fields within the ferrite. A DC magnetic field of fixed intensity is established within the ferrite in a direction perpendicular to the stripline center conductor and to the ground plane members. This perpendicular magnetic field causes the permeability of the ferrite to become anisotropic which in turn causing the electrical coupling between the ports to be nonreciprocal. The dimensions of the ferrite disk or disk assemblies determines the resonant frequency of the cavities which, in turn, determine the operating frequency of the circulator. This results in a dependence between circulator diameter, operating frequency and usable bandwidth.

Today circulators find extensive application in the lower range of microwave frequencies such as 50 to 5,000 MHz. As stated above the operating frequency of the device determines the size of the ferrite disk and, in turn, the size of the circulator itself which, for such frequencies, becomes quite large such as several inches in diameter. A typical microwave strip transmission line circulator designed to operate at 150 MHz., for example, has a diameter of some 8 inches. Such relatively large sizes are costly and present space utilization problems for the user.

In 1966 U.S. Pat. No. 3,286,201 issued which was directed towards solving the aforestated problem through the use of lumped constant elements in the form of mutually coupled coils coupled to the ferrite. Though such lumped constant circulators were highly successful in decreasing the required size of circulators for given operating frequencies they were less successful in reducing their costs. This was occasioned by the relatively high amount of manual labor required in assembling the lumped constant elements as opposed to that required in assembling distributed constant elements into the circulators. In addition to added cost the use of lumped elements introduced new and lower power limitations.

Accordingly, it is a general object of the present invention to provide an improved microwave strip transmission line circulator.

More particularly, it is an object of the present invention to provide a relatively small, microwave strip transmission line circulator for given operating frequencies in the microwave frequency ranges. 7

Another object of the invention is to provide a microwave strip transmission line circulator having both relatively small size for given operating microwave frequencies, and relatively high power handling capabilities.

Yet another object of the invention is to provide an inexpensive microwave strip transmission line circulator having a relative broad bandwidth.

SUMMARY OF THE INVENTION Briefly described, the present invention is a microwave strip transmission line circulator comprising at least one body of ferrite material, a ground plane member overlaying one surface of the ferrite body, and a conductive disk overlaying another surface of the ferrite body. At least three strip trans mission line conductors extend radially from the periphery of the conductive disk with the axes of the transmission lineconductors defining equal angles. The conductive disk has at least. three sets of indentations with each set comprising two convergent indentations extending from the periphery of the disk to two juxtaposed lines located substantially equidistant from and along opposite sides of one of the axes. Means are also provided for magnetizing the body of ferrite material.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan view of one embodiment of a circulator incorporating principles of the present invention, a large section of which is shown broken away to reveal internal elements.

FIG. 2 is a cross-sectional view of the embodiment of FIG. 1 cut along line 2--2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in more detail to the drawing there is shown a microwave strip transmission line circulator comprising an aluminum casing 10 through which three coaxial connecting

ports

11, 12 and 13 extend. Each coaxial connecting port has a center conductor 14 which extends through port flange 15. The ends of center conductors 14 are soldered to stripline tabs 16 which are extensions of strip transmission line conductors 17. The three conductors 17 extend radially from the periphery of conductive disk 20 which is coaxially sandwiched between two ferrite disks 22 of ferrimagnetic oxide having approximately the same diameter as that of disk 20. Conductive disk 20 has three sets of indentations each set of which comprises two V-shaped indentations having two communicating

striplike legs

24 and 25. Legs 24 in each set extend from the periphery 26 of disk 20 to two juxtaposed lines 27. Lines 27 are located substantially equidistant from axes 18 of strip transmission line conductors 17 and at least partially define one boundary of legs 25 which extend substantially parallel to axes 18.

The two fen'ite disks 22 are sandwiched between two steel pole pieces 30 and permanent magnets 31 which are housed centrally within

ground plane members

32 and 33. As pole pieces 30 are electrically as well as magnetically conductive they also function as ground planes in addition to such functioning by

members

32 and 33. Finally, steel shunts 34 envelope the permanent magnets and. ground plane members by lining the inside surfaces of aluminum casing 10.

The ferrite disks may have a diameter either larger or smaller than that of disk 20. However, the diameter of the ferrite disks should be at least sufficiently large to extend to the nearest approach of

legs

24 and 25 to the center of disk 20. Such minimum size of the ferrite disks is delineated by are 35. In addition the disks do not have to be circular structures nor have uniform radius. Those portions of periphery 26 of conductive disk 20 connecting any two legs 24 in any one set of indentations, for example, could differ in radius somewhat from that portion of periphery 26 connecting two adjacent legs of two independent sets of indentations.

A complete understanding of the manner in which the just described circulator functions in achieving the aforestated objects of the invention has not yet been obtained. However, it is believed to be primarily attributable to the presence of the described indentations. These indentations evidently break disk 20 up into spaced elements which extend both laterally from the direction of electron flow in each of the three transmission lines and radially from the center of the disk inbetween such directions of electron flow. These spaced elements in effect act partially as lumped and partially as distributed constant elements in relation to the ground plane members. Their location in terms of input signal wavelength enables them to provide resonant reactances in achieving improved tuning and impedance matching for the size of the circulator as a whole. Four inch diameter circulators can be realized for successful operation at 150 MHz. through the utilization of such indentations.

it should be understood that the described embodiment is merely illustrative of application of the principles of the invention and that many modifications may be made thereto without a departure from the spirit and scope of the invention as set forth in the following claims.

We claim:

1. A microwave strip transmission line circulator comprising at least one body of ferrite material; a ground plane 'member overlaying one surface of said ferrite body; a conductive disk overlaying another surface of said ferrite body; at

least three strip transmission line conductors extending radially from the periphery of said conductive disk with the axes of said transmission line conductors defining equal angles; said conductive disk having at least three sets of indentations with each of said sets comprising two convergent indentations extending from the periphery of said disk to two juxtaposed lines located substantially equidistant from and along opposite sides of one of said axes; and means for magnetizing said body of ferrite material.

2. A microwave strip transmission line circulator in accordance with claim 1 wherein each of said indentations is V- shaped and comprises two communicating legs of unequal length.

3. A microwave strip transmission line circulator in accordance with claim 1 wherein said body of ferrite material is cylindrical and wherein said conductive disk overlays said ferrite body in coaxial relationship thereto.

4. A microwave strip transmission line circulator in accordance with claim 3 wherein theradius of said cylindrical body of ferrite material is at least as large as the radius of the circle defined by the closest points to the center of said disk to which each of said indentations extends.

5. A microwave strip transmission line circulator in accordance with claim 3 wherein the radius of said cylindrical body of ferrite material is as least as large as the radius of said conductive disk.

Claims

1. A microwave strip transmission line circulator comprising at least one body of ferrite material; a ground plane member overlaying one surface of said ferrite body; a conductive disk overlaying another surface of said ferrite body; at least three strip transmission line conductors extending radially from the periphery of said conductive disk with the axes of said transmission line conductors defining equal angles; said conductive disk having at least three sets of indentations with each of said sets comprising two convergent indentations extending from the periphery of said disk to two juxtaposed lines located substantially equidistant from and along opposite sides of one of said axes; and means for magnetizing said body of ferrite material.

2. A microwave strip transmission line circulator in accordance with claim 1 wherein each of said indentations is V-shaped and comprises two communicating legs of unequal length.

4. A microwave strip transmission line circulator in accordance with claim 3 wherein the radius of said cylindrical body of ferrite material is at least as large as the radius of the circlE defined by the closest points to the center of said disk to which each of said indentations extends.