US3651430A

US3651430A - Strip-line circulator having movable compensating stub strip overlying central strip-line conductors

Info

Publication number: US3651430A
Application number: US491676A
Authority: US
Inventors: Yukio Ito; Haruo Yokouchi; Kenji Konno
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 1964-10-06
Filing date: 1965-09-30
Publication date: 1972-03-21
Anticipated expiration: 1989-03-21
Also published as: DE1293264B

Abstract

1. In a strip-line microwave circulator comprising at least three central strip conductors disposed between parallel outer conductors and connected at one of their ends at a central point with said strip conductors, being parallel to said outer conductors and extending radially outwardly from said point, including predetermined angles with each other, a pair of concentric gyromagnetic discs disposed at said point each between one side of said strip conductors and the adjacent outer conductors, and means to magnetize said discs in a direction substantially at right angle to said conductors, to create microwave circulators switching action; the improvement consisting in the provision of unitary stub conductors disposed between any two adjacent ones of said strip conductors, each of said stub conductors having one end coupled with the junction between the respective strip conductors and extending outwardly along the symmetry line thereof to a distance being in excess of half the radius and less than the full radius of said discs, said strip conductors being in the form of an integral Y-shaped conducting spider strip with the axes thereof including equal angles of 120* between them, said stubs consisting of a further spider strip concentric with and overlying said first spider strip and movable in a parallel plane relative to the latter so as to compensate for any minor imbalance of admittances at the input terminals of the circulator, said outer conductors comprising a first cover member and a bottom member extending over the respective ferrite discs, a casing ring connecting the first cover member to the bottom member, said means to magnetize said discs consisting of a single permanent magnet extending over said first cover member, a second cover member extending over said permanent magnet, the first and second cover members, a substantial portion of the casing ring and the bottom member being formed of magnetic material to provide a magnetic circuit for said permanent material.

Description

United States Patent [451 Mar. 21, 1972 Ito et al.

[54] STRIP-LINE CIRCULATOR HAVING MOVABLE COMPENSATING' STUB STRIP OVERLYING CENTRAL STRIP- LINE CONDUCTORS [72] Inventors: Yukio Ito; I-Iaruo Yokouchi;'Ke 1ji Konno,

all of Kawasaki-shi, Japan [73] Assignee: Fujitsu Limited, Kawasaki-shi, Kanagawaken, Japan [22] Filed: Sept. 30, 1965 211 Appl. No.2 491,676

[30] Foreign Application Priority Data Oct. 6, 1964 Japan ..39/57000 [52] U.S.Cl ..333/1.l, 333/9 [58] FieldofSearch ..333/l.l,9, 84M

[56] References Cited UNITED STATES PATENTS 3,359,510 12/1967 Geiszler ..333/l.1

3,174,116 3/1965 Sur ..333/1.l

2,903,695 9/1959 Jamieson.. ..333/84 X 3,063,024 11/1962 Davis, Jr ..333/1.l

3,165,711 1/1965 Drumheller et al ....333/l.1

3,185,941 5/1965 Freiberg ..333/1.l

Primary ExaminerHerman Karl Saalbach Assistant Examiner Paul L. Gensler Attorney-Greene & Durr EXEMPLARY CLAIM 1. in a strip-line microwave circulator comprising at least three central strip conductors disposed between parallel outer conductors and connected at one of their ends at a central point with said strip conductors, being parallel to said outer conductors and extending radially outwardly from said point, including predetermined angles with each other, a pair of concentric gyromagnetic discs disposed at said point each between one side of saidstrip conductors and the adjacent outer conductors, and means to magnetize said discs in a direction substantially at right angle to said conductors, to create microwave circulators switching action; the improvement consisting in the provision of unitary stub conductors disposed between any two adjacent ones of said strip conductors, each of said stub conductors having one end coupled with the junction between the respective strip conductors and extending outwardly along the symmetry line thereof to a distance being in excess of half the radius and less than the full radius of said discs, said strip conductors being in the form of an integral Y-shaped conducting spider strip with the axes thereof including equal angles of 120 between them, said stubs consisting of a further spider strip concentric with and overlying said first spider strip and movable in a parallel plane relative to the latter so as to compensate for any minor imbalance of admittances at the input terminals of the circulator, said outer conductors comprising a first cover member and a bottom member extending over the respective ferrite discs, a casing ring connecting the first cover member to the bottom member, said means to magnetize said discs consisting of a single permanent magnet extending over said first cover member, a second cover member extending over said permanent magnet, the first and second cover members, a substantial portion of the casing ring and the bottom member being formed of magnetic material to provide a magnetic circuit for said permanent material.

2 Claims, 13 Drawing Figures QQOMPENSAT- mo STUB PATENTEDMARZI m2 SHEET 1 OF 3 T R A R m R P IHVILM'TOR YUKIQ ITO ET AL KM/ Km PATENTEDMARZI I972 3,651,430

sum 2 OF 3 DECOUPLING AMOUNTS 9 f "'10" I. 1.2 N O FREQUENCY TO MEAN FREQUENCY RATIO OF WORKI [NW-.1 ."mR. YUKIO ITO ET AL W f g PATENTEDMAR 21 I972 SHEET 3 BF 3 PERMANENT MAGNET 1/ 1/ 11/11 IIIIIIIIII v hah T 2 &

INVENTOR. YUKIO ITO ET AL STRIP-LINE CIRCULATOR HAVING MOVABLE COMPENSATING STUB STRIP OVERLYING CENTRAL STRIP-LINE CONDUCTORS This invention relatesto broad band strip-line circulators which are recently employed in the microwave technique, especially three-terminal circulators comprising inner gyromagnetic members.

As well known to those skilled in the art, coaxial transmission lines such as called strip lines" for transmission of high frequency electric waves are provided with branching points, especially in the form of a Y or T, generally called strip circulators, each of which comprises gyromagnetic members and is fitted with one or more magnetic bodies having amagnetic field perpendicular to said members. The width of the working frequency band of this kind of circulator depends substantially upon the sizes and the kind and nature of the gyromagnetic material, and specific dimensions of the transmission line.

Various attempts have been made to broaden the said working frequency band by selecting a proper combination of these parameters. Further attempts have also been made to provide a parallel or series resonance circuit in the extension of the circulator zone of the transmission line so as to suppress to a certain degree the frequency characteristics of overall impedance or admittance as provided by the gyromagnetic members in combination with the line material, thereby to improve input impedance, as well as the frequency characteristic of forward and reverse losses.

In the conventional broad band matching arrangement of the kind above referred to, parallel or series resonance circuit is additionally provided. According to the conventional This three-terminal circulator is provided with a thin metallic sheet conductor 11 having three radially extending arms as shown, each free outward end of which constitutes a terminal to be connected through a conventional connector with a high frequency wave transmission line, not shown.

Ferrite discs

12 and 13 are provided to make physical contact with the respective surfaces of the conductor 11 so as to cover a respective concentric zone with a center which is constituted by a crossing point of the longitudinal axes of the three arms. In the same manner as will be more fully described with reference to FIGS. l'and 11, a permanent magnetic disc is placed upon the upper surface of the upper ferrite disclZ so as to establish a unidirectional magnetic field directing in the vertical direction as hinted by a small arrow attached with BBC shown in FIG. 1. It is well known that such an arrangement acts positively as a circulator relative to high frequency electromagnetic wave energy, connecting imaginatively and circutechnique, the additional matching circuit of parallel resonance type is inserted in the line at a considerably remote position from the gyromagnetic members from constructual reasons, resulting in a larger size of the circuit. On the other hand, when a series resonance circuit of half wave length type is employed for the same matching purpose, the resulting circulator will have a larger overall size as in the case of the parallel resonance circuit.

The conventional matching technique requires always a considerable length of the transmission line to utilize for the provision of the resonance circuit, which prevents a smaller size of the circulator assembly from being realized. In addition, the frequency characteristic of the related line length will generally adversely affect upon the desirous broader matching effect.

The main object of the present invention is to provide a more compact and efficient circulator assembly having builtin matching means.

Another object is to provide a circulator of the above kind which embodies therein unique resonance means.

These and further objects, advantages, special features of the invention will become more clear as the description proceeds with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a comparative conventional circulator, shown in its essential constituents only;

FIGS. 2-9 are similar views to FIG. 1, of several preferred embodiments of the invention;

FIG. 10 is an exploded perspective view of a complete circulator assembly as constructed in accordance with the novel teaching of the present invention;

FIG. 11 is a substantially half of a longitudinal section of the assembly shown in FIG. 0, being taken along a, plane XI-Xl in the same figure;

FIG. 12 is a comparative diagram of frequency-responsible admittance characteristics of specific embodiments according to conventional art and the present invention; and

FIG. 13 is a comparative diagram of operating characteristics of specific embodiments of the both kinds above referred to. I

Now referring to FIG. 1, a preferred comparative conventional circulator assembly will preliminarily described.

larly the extreme terminal ends, as denoted by l, 2 and 3, respectively, of the arms of the conductor, for instance, in the order of 1- 2- 3- I. If assuming the mean or central value of working frequency band of this conventional circulator be denoted by as conventionally, the band width will be f}, :L 10 percent at the highest, under such assumption that the decoupling amounts to higher than 20 db. As will be well understood, the working frequency band of this conventional kind of circulator is considerably narrow.

An example of frequency characteristic of admittance in a neighboring zone of the working mean frequency f, of the above mentioned circulator, taking as the reference plane a certain plane existing in a close proximity of the ferrite is shown by a curve A in a Smith chart illustrated in FIG. 12. From this curve, any person skilled in the art will easily conceive that this circulator is in its equivalency a kind of nonreciprocal resonance circuit. It can be further conceived that in order to realize a still broadened operating frequency band for this circulator it is necessary to provide an additional resonance circuit having a substantially same loaded Q as that of the characteristic curve A and at a predetermined distance measured outwardly of the circulator per se from the reference plane for the curve A" and equal to an odd multiple of quarter wavelength. When adopted such a conventional measure, the circulator will become considerably large in its size and provide nevertheless only a minor improvement in its broad band characteristic, thus representing a substantial drawback in the practical view point.

In a first embodiment of the present invention shown in FIG. 2, an inner conductor 14 of the strip line is formed equally as before in the form of three an-n type, having at their free ends terminals denoted equally with numerals l, 2 and 3.

Ferrite discs

12 and 13 are provided similarly as before. In this embodiment, a round end, radial strip projection 15 is formed at the junction of two neighboring side edges of each two arms of conductor 14 and integral therewith. Vertical permanent magnetic field attached equally as before with reference symbols HDC is impressed upon these projections 15. As ascer tained by experiments, projections 15 in combination with

ferrite discs

12 and 13 forms in effect a resonance circuit, thereby providing by way of example an operating frequency characteristic curve denoted by B in FIG. 12. This characteristic depends naturally upon working frequency, the sizes and configuration of each projection 15, the kind and nature of ferrite employed for the projection, and other parameters as will be described again hereinbelow. As will be clearly understood from characteristic curve B," the frequency characteristic of admittance with use of the present circulator assembly is considerably smaller than that obtainable with use of a comparative conventional arrangement as shown by way of example in FIG. 1, thus providing a strip-line branching circulator having a considerably broader frequency band.

Determination of the sizes and configuration of radial projections l5 relying upon sizes and materials of

ferrite discs

12 and 13, thickness, width and the like dimensional data of inner conductor I4, the mean working frequency and the like parameters may be determined ,by practical experiments assisted by conventional calculating formulae commonly known to those skilled in the art.

FIGS. 37, except FIG. 5, illustrate several further preferred and modified circulator assemblies according to this invention from that shown in FIG. 1. More specifically, the modified arrangement shown in FIG. 3 differs from the foregoing embodiment inthat each of radial projections a has a general form of rectangular with straight line extremity, instead of being formed with rounded end.

In the modification shown in FIG. 4, the extreme end of each radial projections 15b is pointed. In FIG. 5, the arrangement shown in FIG. 2 is illustrated in its top plan view for the purpose of comparison.

In the modified embodiment shown in FIG. 6, each of radial projections 150 is formed into a pointed triangle. Each projection 15d shown in FIG. 7 is shaped into a rounded triangle.

In all of the foregoing embodiments, radial projections are formed integral with the strip conductor. In a still further modified arrangement shown in FIG. 8, three radial projections 18 are united into a second and separate conductor 17. This conductor 17 may be placed on the first conductor fitted with reference numeral 16 in direct physical contact therewith, for allowing DC current to be conductive between the both conductors. Or alternatively, the second conductor is positioned on the first one through the intermediary of a thin insulator strip, although not shown, for the interruption of DC current conduction. In the drawing, the second conductor is arranged symmetrically with the first conductor with one and the same center when seen in the top plan view. When necessary, however, the both conductors may be arranged in a offcenter position with each other. Further, as hinted by doubleheaded small arrows, the second conductor may be slightly rotated from the position shown and relatively to the first conductor. By adopting any one of said measures, or any combination thereof, occasional minor imbalance of admittances at the

terminals

1, 2 and 3 may be compensated. Or conversely, these measures may be utilized for intentionally creating such differences as above mentioned, when occasion desires.

In place of several foregoing Y-circulators shown in FIGS. 2-7, a T-circulator is shown in FIG. 9. In this modified arrangement, three

radial projections

20, 21 and 22 are provided, for inner strip conductor 19 the first one 20 of which is considerably larger in its size or covering area than the second and third one 21 and 22. These projections are made integral with said conductor 19 as before. In this way, a considerably broader frequency band can be realized from the similar reasons as set forth in connectionwith V-circulators.

In the foregoing, inside key constituents of the circulator have been shown and described with reference to several preferred embodiments. These constituents are contained in a casing 23, preferably circular as shown in FIGS. 10 and 11. The outward extremities l, 2 and 3 of the inner conductor is placed along the central axes of corresponding screw sockets 24 which are fixedly mounted on the outer periphery of the casing 23 having a closing bottom wall 230. Said sockets are ready for receiving screw connectors (not shown), respectively, so as to establish each a conductive connection with a related coaxial line for reception and delivery of microwave energy, as conventionally. The casing 23 in combination with inside and outside covers 25 and 26, when assembled together as shown in FIG. 1 1, acts as outer conductor for the strip-line. In order to minimize possible transmission losses, these

members

23, 25 and 26 are coated galvanizingly with a thin silver layer. Bottom wall 23a and substantial part of the circular casing wall 23, with exception of mounts 24a for connector sockets 24, are made from magnetic material such as iron, nickel or the like, so as to form a magnetic circuit for permanent magnet 27 in combination with outer cover 26 which is made also from a magnetic material. The permanent magnet is so energized that its magnetic field within the interior of the circulator is transversal to the propagating plane of microwaves to be transmitted.

Gyromagnetic members shaped preferably into

ferrite discs

12 and 13 are arranged concentrically with the center of the circulator and stuck on to the respective surfaces of the inner conductor. If necessary, however, these discs may be mounted in position through the intermediary of a thin insulating layer made from a high dielectric material with low high frequency loss, such as Teflon (trade-mark for tetrafluoroethylene resin). In addition to one permanent magnet disc as at 27, a similar magnet may be provided on the lower surface of bottom wall 23a, although not shown. Inside cover 25 may preferably made of an efficient conductive material such as copper.

Characteristic curves A" and B shown in FIG. 12 have been obtained from test results with the following dimensional and operating particulars (refer to also FIGS. 2, 5, 10 and l l Corresponding dimensions of the comparative conventional circulator are just same as those of the novel one set forth hereinbelow:

d3 38 mm., h4= 3.4 mm. (FIG. 2);

w2=2 mm.,l4=7 mm. (FIG. 5);

d1 74 mm., d2= 53 mm. (FIG. 10).

As gyromagnetic material, a material called YIG" (yttriumiron-garnet) was employed which has the following charac teristic properties:

magnetization 471-Ms l4; gausses at 20 oersteds of magnetic field strength;

dielectric constant e 14;

dielectric loss tangent tan 8 3x I 0- Curie point Tc= 190C.

Intensity of permanent magnetic field was 600 gausses as employed throughout the experiment.

In FIG. 13, several comparative characteristic curves for decoupling amounts, insertion loss, voltage standing wave ratio, and ratio of working frequency to mean frequency are shown by way of example.

These curves were plotted upon several experiments carried out under the same conditions as those employed hereinbefore. Curves Al, A2 and A3 were obtained with use of the conventional circulator, while those of "81," 82" and B3 were plotted from the results with the novel arrangement.

The novel circulator assembly can be effectively utilized as branching organs as provided along microwave transmission line, for instance, duplexer for microwave transmitter-receiver unit; tunnel diode amplifier, parametric amplifier or the like.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

We claim:

1. In a strip-line microwave circulator comprising at least three central strip conductors disposed between parallel outer conductors and connected at one of their ends at a central point with said strip conductors, being parallel to said outer conductors and extending radially outwardly from said point, including predetermined angles with each other, a pair of concentric gyromagnetic discs disposed at said point each between one side of said strip conductors and the adjacent outer conductors, and means to magnetize said discs in a direction substantially at right angle to said conductors, to create microwave circulators switching action; the improvement consisting in the provision of unitary stub conductors disposed between any two adjacent ones of said strip conductors, each of said stub conductors having one end coupled with the junction between the respective strip conductors and extending outwardly along the symmetry line thereof to a distance being in excess of half the radius and less than the full radius of said discs, said strip conductors being in the form of an integral Y-shaped conducting spider strip with the axes thereof including equal angles of between them, said stubs consisting of a further spider strip concentric with and overlying said first spider strip and movable in aparallel plane relative to the latter so as to compensate for any minor imbalance of admittances at the input terminals of the circulator, said outer conductors comprising a first cover member and a bottom member extending over the respective ferrite discs, a casing ring connecting the first cover member to the bottom member, said means to magnetize said discs consisting of a single permanent magnet extending over said first cover member, a second cover member extending over said per-

Claims

1. In a strip-line microwave circulator comprising at least three central strip conductors disposed between parallel outer conductors and connected at one of their ends at a central point with said strip conductors, being parallel to said outer conductors and extending radially outwardly from said point, including predetermined angles with each other, a pair of concentric gyromagnetic discs disposed at said point each between one side of said strip conductors and the adjacent outer conductors, and means to magnetize said discs in a direction substantially at right angle to said conductors, to create microwave circulators switching action; the improvement consisting in the provision of unitary stub conductors disposed between any two adjacent ones of said strip conductors, each of said stub conductors having one end coupled with the junction between the respective strip conductors and extending outwardly along the symmetry line thereof to a distance being in excess of half the radius and less than the full radius of said discs, said strip conductors being in the form of an integral Y-shaped conducting spider strip with the axes thereof including equal angles of 120* between them, said stubs consisting of a further spider strip concentric with and overlying said first spider strip and movable in a parallel plane relative to the latter so as to compensate for any minor imbalance of admittances at the input terminals of the circulator, said outer conductors comprising a first cover member and a bottom member extending over the respective ferritE discs, a casing ring connecting the first cover member to the bottom member, said means to magnetize said discs consisting of a single permanent magnet extending over said first cover member, a second cover member extending over said permanent magnet, the first and second cover members, a substantial portion of the casing ring and the bottom member being formed of magnetic material to provide a magnetic circuit for said permanent magnet.

2. In a microwave circulator switch as claimed in claim 1, both said spider strips being connected in conductive contact with one another.