Strip Line Circulator Wherein The Branch Arms Have Portions Extending In A Nonradial Direction

Abstract

Branch lines radially extend from a circular junction of an intermediate conductor on a ferri-magnetic disc and include one portion running circumferentially of the disc. This causes an increase in area with which the disc overlaps the branch lines while the lines are maintained relatively small in radial length resulting in a small-sized circulator low in center frequency.

Description

BACKGROUND OF THE INVENTION

This invention relates to improvements in strip line-type circulators.

The conventional type of stripline-type circulator widely employed has comprised a ground conductor, an internal conductor composed of branch lines and their junction, and a plate of ferri-magnetic material disposed between the ground and internal conductors. The plate of ferri-magnetic material has been applied with a magnetic field of direct current orthogonal to the main faces thereof. In the general configuration of such circulators comprising the circular junction and the branch lines radially extending at substantially equal angular intervals from the junction, the wider an area with which the plate of ferri-magnetic material overlaps the branch lines the lower the center frequency of the circulator will be. If it is desired to provide such a type of circulator having its center frequency as relatively low as in the order of 1 GHz. it has been required to sufficiently increase both the diameter of the ferri-magnetic disc and the length of the branch lines leading to the disadvantage that the resulting circulator has inevitably become large sized. Therefore, for use in apparatus required to be small sized as those equipped on artificial satellites, they have been unsuitable, and not so practical while being expensive.

SUMMARY OF THE INVENTION

Accordingly, it is one object of the invention to provide a new and improved stripline-type circulator small in dimension and cheap in manufacturing while being operated at relatively low frequencies wherein the above-mentioned disadvantages of the conventional circulators are eliminated.

It is another object of the invention to provide a new and improved strip line type circulator which is small sized and operative over a range of relatively low frequencies by increasing the effective magnitude of distributed capacitance presented by branch lines radially extending at substantially equal angular intervals from their junction with no increase in radial length of the branch lines.

The invention accomplishes the above cited objects by the provision of a stripline-type circulator comprising a ground conductor, an internal conductor including a plurality of branch lines and a junction thereof, the branch lines radially extending at substantially equal angular intervals from the junction, a body of ferri-magnetic material greater in area than the junction and disposed between the ground and internal conductors and in overlapping relationship therewith, and magnet means for applying a magnetic field of direct current substantially orthogonal to and across the body of ferri-magnetic material, characterized in that the intermediate portions of the branch lines extend in a direction other than the radial direction in the region of the body of ferri-magnetic material and in the same plane as the junction to increase the effective area with which the body of ferri-magnetic material overlaps the branch lines.

If desired, that portion projecting beyond the junction of the body of ferri-magnetic material may be replaced by a dielectric member in the form of a toroid integral to the body of ferri-magnetic material.

Conveniently, the turned portion of each of the branch lines may vary in length to change the center frequency of the circulator while maintaining a constant area of that portion projecting beyond the junction of the body of ferri-magnetic material.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a fragmental plan view of a wye-branched stripline-type circulator constructed in accordance with the principles of the prior art;

FIG. 2 is a partly exploded perspective view of the conventional type of stripline-type circulator;

FIG. 3 is a fragmental plan view of a wye-branched stripline-type circulator constructed in accordance with the principles of the invention;

FIGS. 4a and 4b are fragmental plan views illustrating the conventional stripline-type circulators equal in center frequency to the circulator of the invention shown in FIG. 3;

FIG. 5 is a Smith chart and illustrating an input admittance as looking from in each branch line of the circulator shown in FIG. 4b ;

FIG. 6 is a chart similar to FIG. 5 but illustrating the circulator shown in FIG. 4a ;

FIG. 7 is a graphic representation of insertion losses of the present device plotted against a magnetic field applied thereto; and

FIG. 8 is a fragmental plan view of a modification of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and FIGS. 1 and 2 in particular, there is illustrated a wye-branched stripline-type circulator constructed in accordance with the principles of the prior art. The arrangement illustrated comprises an internal conductor of any suitable electrically conductive material generally designated by the reference numeral 10 and including a circular central junction portion 12 called hereinafter a junction and a plurality of branch lines 14 in the form of strips radially extending at substantially equal angular intervals from the junction 12, and a disc 16 of any suitable ferri-magnetic material such as garnet, disposed in concentric relationship under the internal conductor 10.

Then the assembly thus formed is concentrically located within a metallic housing 18 of circular cross section and the branch lines 14 are connected at their free ends to respective terminals 20 disposed at substantially equal angular intervals on the periphery of the housing 18 as shown in FIG. 2. Another ferri-magnetic disc 16', as shown on the upper portion of FIG. 2, substantially identical to the ferri-magnetic disc 16 is concentrically disposed upon the internal conductor 10 and a metallic cover (not shown) is used to close the upper end of the housing 18 as well as suitable holding the internal conductor 10 and ferri-magnetic discs 16 and 16' in place within the housing 18. It will be appreciated that the housing 18 and the cover form a conductor which, in turn, serves to sandwich or superimpose the ferri-magnetic discs between the same and the internal conductor.

As shown in FIG. 1, the garnet disc 16 having a diameter D radially projects beyond the junction 12, having a diameter d, by a radial length l . Thus it will be appreciated that with an electric field applied orthogonally to the main faces of the circulator and therefore between the internal conductor 10 and the ground conductor, as shown by the arrow in FIG. 2, the electric field is weakly established on the peripheral portion in the form of an annulus having a radial width of l of the ferri-magnetic disc 16 whereby that portion disposed directly below each of the branch lines 14 of the disc 16 serves only as a matching element.

In FIG. 4b, wherein like reference numerals designate like components corresponding to those illustrated in FIG. 1, is illustrated a circulator similar to that shown in FIG. 1 excepting that the disc 16 of ferri-magnetic material and the junction 12 of the internal conductor 10 have a common diameter d. When a magnetic field of H.sub.1 is applied to the arrangement of FIG. 4b operated at its center frequency of 4.2 GHz., an input admittance as looking from each of the branch lines 14 is inductive with the reference plane located at its position spaced away from the peripheral edge of the disc 16 by a distance of (D-d)/2, and such is illustrated in the chart of FIG. 5 wherein two orthogonal sets of circles represent conductance and susceptance components respectively.

On the other hand, if the ferri-magnetic disc 16 of FIG. 4b having the diameter of d has snugly fitted thereon an annulus of ferri-magnetic material, such as garnet, having an inside diameter of d and an outside diameter D such as shown in FIG. 1, then the resulting circulator exhibits the effect equivalent to the loading of a capacitance and therefore has an input admittance as shown in the chart of FIG. 6 similar to that illustrated in FIG. 5. It has been found that the annulus of ferri-magnetic material may be replaced by an annulus having the same shape and composed of a dielectric material substantially equal in specific dielectric constant to the ferri-magnetic material for the annulus.

From the foregoing it will be understood that the larger the width or l =(D- d)/ 2 (see FIGS. 1 and 4a ) of the above-mentioned annulus formed of the ferri-magnetic or dielectric material the lower the center frequency of the circulator will be.

The invention is based upon the phenomenon just described and contemplates to decrease the center frequency of the circulator by increasing a length of each branch line with which the associated ferri-magnetic disc overlaps the individual branch line for the purpose of decreasing the center frequency of the circulator. That is, the invention contemplates to increase the length l of the branch portion as shown in FIG. 1 without an increase in diameter of the ferri-magnetic disc.

Referring now to FIG. 3 wherein like reference numerals designate like components corresponding to those shown in FIG. 1, there is illustrated a stripline-type circulator constructed in accordance with the principles of the invention as above described. As in the arrangement of FIG. 1, the circular junction portion 12 of the internal conductor 10 is disposed in concentric relationship on the disc 16 of ferri-magnetic material such as garnet. The junction 12 has a diameter d and the disc 16 has a diameter D greater than the diameter of the junction portion 12. The junction 12 has a plurality of branch lines 14 in the form of strips radially extending at substantially equal angular intervals from the junction 12. At the periphery of the disc 16, the branch lines 14 each are turned in one direction, for example in the clockwise direction, as viewed in FIG. 3 of the disc to follow the periphery of the latter by a predetermined circumferentially extending arc length portion l.sub.1 . Then the branch lines 14 are again turned in the radial direction of the disc 16. That is, a branch lines 14 each have the first radial portion having a radial length of l.sub.2 the circumferential portion having an arc length of l.sub.1 , and the second radial portion leading to the associated terminal such as shown at 20 in FIG. 2.

Under these circumstances, it will be appreciated that that portion of each branch line 14 superposing the ferri-magnetic disc 16 increases in length by an amount corresponding to the arc length l.sub.1 as compared with the prior art type devices including the ferri-magnetic disc of the same diameter. This means that the ferri-magnetic disc 16 has effectively increased in radius by an amount corresponding to the l.sub.1 . This provides a stripline-type circulator equivalent to a circulator including a ferri-magnetic disc 16 increased in radius by about the l.sub.1 as shown in FIG. 4a . Therefore the center frequency of the circulator can decrease by a magnitude corresponding to this effective increase in radius of the ferri-magnetic disc, while the overall dimension of the circulator remains unchanged.

A stripline-type circulator such as shown in FIG. 3 had applied perpendicularly thereacross a magnetic field of direct current progressively increased in strength with the center frequency f.sub.o of 2.1 GHz. Then it exhibited its insertion loss as shown in FIG. 7 wherein the ordinate represents the insertion loss in decibels and the abscissa represents a magnetizing direct current in amperes flowing through the associated electromagnet device (not shown). The reference characters L f and Lb designate the forward and reverse insertion losses.

It has been found that if the circumferential portion of each branch line 14 varies in arc length, the resulting center frequency can change over a fairly wide range. For example, a circulator such as shown in FIG. 3 including the circumferential branch portions having a perimetric length equal to one sixth the diameter of the associated ferri-magnetic disc has its center frequency decreased by a factor of 2 as compared with the conventional one including no circumferential branch lines with the discs having the same diameter.

FIG. 8, wherein like reference numerals designate like components similar to those shown in FIG. 3, illustrates a modification of the invention. In FIG. 8, the ferri-magnetic disc 16 is equal in diameter to the junction 12 and is integral with a dielectric member 18. The dielectric member has the configuration of a toroid and the circumferentially extending arc length portion of each branch line 14 is superposed with the outer perimeter of the toroid.

It has been found that the present circulators are particularly effective for operating at frequencies under 1 GHz. This is because the ferri-magnetic disc can overlap the branch lines with an area capable of being selected to be sufficiently large while the radial length of each branch line is maintained relatively small.

While the invention has been illustrated and described in conjunction with a single preferred embodiment thereof it is to be understood that various changes and modifications may be resorted to without departing from the spirit and scope of the invention. For example, as long as those portions connected to the junction and those portions projecting beyond the ferri-magnetic disc of the branch lines are disposed in radially symmetric relationship with one another, those portions superposing the ferri-magnetic disc of the branch lines may assume any desired configuration other than that previously described in conjunction with FIG. 3. Also it is to be understood that the invention is equally applicable to any desired configuration other than the circular one as previously described and with other than three branch lines.

Claims

What we claim is:

1. A stripline-type circulator comprising a ground conductor, an internal conductor including at least three branch lines connected together at a junction portion, said branch lines radially extending at substantially equal angular intervals from said junction portion, a body of ferri-magnetic material greater in area than said junction portion and disposed between said ground and internal conductors and in overlapping relationship therewith, magnet means for applying a magnetic field of direct current substantially orthogonal to and across said body of ferri-magnetic material, and wherein intermediate portions of each of said branch lines extend in a direction other than the radial direction a region overlying said body of ferri-magnetic material and in the same plane as said junction portion to increase the effective area with which said body of ferri-magnetic material overlaps said branch lines.

2. A stripline-type circulator as claimed in claim 1 wherein that portion of said ferri-magnetic material projecting beyond said junction portion is replaced by a dielectric member in the form of a toroid connected integrally to said body of ferri-magnetic material.

3. In a stripline circulator having a planar conductor and a planar body of ferri-magnetic material superimposed on one side of said planar conductor; another planar conductor superimposed on the opposite side of said planar body in overlapping relationship therewith having a central junction portion smaller in area than said planar body and having at least three branch lines connected to and extending radially outwardly from said junction portion in equidistantly circumferentially spaced-apart relationship; each of said branch lines having a first portion extending in a first radial direction radially outwardly from said junction portion a distance no greater than the radial extent of said planar body, a second portion extending in a direction other than a radial direction with respect to said junction portion and overlying said planar body, and a third portion extending radially outwardly from said junction portion in a radial direction different than said first radial direction.

4. A stripline circulator according to claim 3; wherein said first, second and third portions of each branch line have substantially the same cross-sectional configuration.

5. A stripline circulator according to claim 3; wherein said second portion of each branch line extends in the same direction as that of the perimeter of said planar body.

6. A stripline circulator according to claim 3; wherein said first-mentioned planar conductor, said planar body and said another planar conductor are all concentrically disposed in layered relationship.

7. In a stripline circulator having a planar conductor and a planar body of ferri-magnetic material superimposed on one side of said planar conductor; another planar conductor superimposed on the opposite side of said planar body having a central junction portion equal in area to that of said planar body and having at least three branch lines connected to and extending radially outwardly from said junction portion in equidistantly circumferentially spaced-apart relationship; a dielectric member composed of dielectric material surrounding the periphery of said planar body; and wherein each of said branch lines has a first portion extending in a first radial direction radially outwardly from said junction portion a distance no greater than the radial extent of said dielectric member, a second portion extending in a direction other than a radial direction with respect to said junction portion and overlying said dielectric member, and a third portion extending radially outwardly from said junction portion in a radial direction different than said first radial direction.

8. A stripline circulator according to claim 7; wherein said first, second and third portions of each branch line have substantially the same cross-sectional configuration.

9. A stripline circulator according to claim 7; wherein said second portion of each branch line extends in the same direction as that of the perimeter of said dielectric member.

10. A stripcirculator according to claim 7; wherein said first-mentioned planar conductor, said planar body, said dielectric member and said another planar conductor are all concentrically disposed in layered relationship.