US3851279A

US3851279A - Tee junction waveguide circulator having dielectric matching posts at junction

Info

Publication number: US3851279A
Application number: US00407374A
Authority: US
Inventors: C Andrikian
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1973-10-17
Filing date: 1973-10-17
Publication date: 1974-11-26
Anticipated expiration: 1991-11-26

Abstract

A broadband tee junction waveguide circulator of improved design is disclosed. A ferrite element of triangular cross-section is disposed in the region of the junction of the two waveguides. Dielectric matching ''''posts'''' extending between the broad walls of the waveguide junction near each of the apexes of the ferrite element provide improved impedance matching. The matching posts present independently adjustable capacitive susceptances to the propagating wave energy in the three arms of the device for matching purposes and minimize higher order mode conversion. Those higher order modes which are generated are below cut-off and decay rapidly. The advantages of this configuration are its light weight, relatively small size and ease of tuning.

Description

nited States Patent 1191 Andrikian Nov. 26, 1974 1 TEE JUNCTION WAVEGUIDE CIRCULATOR HAVING DIELECTRIC MATCHING POSTS AT JUNCTION [75] Inventor: Charles P. Andrikian, Los Angeles,

Calif. I

[73] Assignee: Hughes Aircraft Company, Culver City, Calif.

[22] Filed: Oct. 17, I973 21 Appl. No.: 407,374

[52] US. Cl.....- 333/l.l, 333/9, 333/98 M [51] Int. Cl. Il0lp 1/32 [58] Field of Search 333/1.l, 9, 98 M [56] References Cited UNITED STATES PATENTS 3.231.835 1/1966 Nielsenvet a1, 333/l.1 3,337,812 8/1967 Webb 333/l.l UX 3,350,664 10/1967 Pistilli et a1. 333/1.1 3,466,571 9/1969' CONDUCTIVE PEDE STAL} Primary li.ramt'ner-Pau1 L. 'Gensler Attorney, Agent, or Firm-W. H. MacAllister, Jr.; D. O. Dennison [57] ABSTRACT A broadband tee junction waveguide circulator of improved design is disclosed. A ferrite element of triangular cross-section is disposed in the region of the junction of the two waveguides. Dielectric matching posts extending between the broad walls of the waveguide junction near each of the apexes of the ferrite element provide improved impedance matching.

The matching posts present independently adjustable capacitive susceptances to the propagating wave en ergy in the three arms of the device for matching purposes and minimize higher order mode conversion. Those higher order modes which are generated are below cut-off and decay rapidly. The advantages of this configuration are its light weight, relatively small size and ease of tuning.

6 Claims, 2 Drawing Figures i DIELECTRIC SLAB GYROMAGNETIC MATERIAL Pmmmv 3.851279 Fig. 1.

CONDUCTIVE H DIELECTRIC PEDESTALN f SLAB DIELECTRIC POST ,w- IO TEE JUNCTION WAVEGUIDE CIRCULATOR HAVING DIELECTRIC MATCHING POSTS AT JUNCTION FIELD OF THE INVENTION This invention relates generally to ferrite devices and more particularly to broadband teejunctionwaveguidecirculators.

DESCRIPTION OF THE PRIOR ART "tors or switching means. In the past, a large number of such means have been proposed and used, some of which have been acceptable for most applications. Probably the mostasuccessful circulators and switches for use in the microwave spectrum employ an element of gyromagnetic material such as a ferrite. Commonly, thismaterial is disposed in the junction of one ormore sections of waveguides through which the microwave energy is propagated. Bycreating a magnetic flux field through this element there will be a gyromagnetic effect which may be effectively utilized to control they microwave energy in the desired manner.

Unfortunately,.the presence of such a gyromagnetic element in a waveguide causes a change in the impedance of the'junction through which the electromagnetic energy ispropagated. The resultant mismatching of impedances, in turn, causes standing waves and other losses to occur in the device. In an effort to overcome this effect many schemes have been proposed to match the impedance of the section of waveguide'containing the ferrite with the surrounding portions of the waveguides. Since the equipment utilizing such devices is required to operate over a relatively wide band of frequencies it is desirable that the devices themselves have broadband frequency response characteristics. In other words, the impedance match of the device must be within acceptable limits over a relatively broad range of frequencies.

space limitations are important it is desirable to use waveguide circulators of other than the Y-junction variety. For example, because of the fact that the arms of the Y-junction circulator are mutually l apart, it is generally necessary to provide additional waveguide bends at at least two of the ports of the junction. Due tothis fact, it is desirable to use circulators of the tee junction variety. When this is done, however, the inherently asymmetrical geometry of the tee junction gives rise to much greater problems of impedance matching, particularly impedance matching over frequency ranges comparable to those obtainable with circulators of the Y-junction variety.

Due to symmetry, Y-junction waveguide circulators generally utilize identical matching obstacles in all three ports. However, because the tee junction is asymetrical matching obstacles of different values are generally required. Theproblem then.is one of obtaining matching obstacles whose values can be adjustedwithout substantial interaction with the other obstacles. The feature of independently adjustable matching obstacles also allows greater design freedom and relaxed manufacturing tolerances.

Accordingly, it is a general object of the present invention to provide an improved waveguide circulator of the tee junction type having broadband characteristics. I It is another object of the present invention to provide a tee junction circulator having independently adjustable matching obstacles.

SUMMARY OF THE INVENTION It is therefore proposed, in accordance with the present invention to provide tee junction waveguide circulators in which the energy may be controlled more uniformly over a considerably greater bandwidth. More particularly, this is accomplished not only by utilizing the proven impedance matching and broadbanding techniques employed with Y-junction circulatorsj but by also including unique dielectric matching structures for the gyromagnetic element, These techniques include the mounting of the gyromagnetic element within the junction formed by the constituent waveguides between metallic pedestals and insulating members and by also including dielectric posts'in the vicinity of the corners of the triangular gyromagnetic element. The use of dielectric posts rather than other impedance matching obstacles minimizes the generation of higher BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals correspond to like structural elements and, wherein:

FIG. 1 is a partially broken-away pictorial view of a preferred embodiment of the present invention; and

FIG. 2 is a cross-sectional plan view of the embodiment of FIG. 1. l

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more specifically to the drawing, FIG. 1 is a partially broken-away pictorial view of a tee junction waveguide circulator according to the present invention. In FIG. 1 three sections of rectangular conductively bounded

waveguide

10, 11 and 12 meet in a common Hplane tee junction. Waveguide sections 11 and 12 are arrangedcoaxially and can comprise, for example, a single rectangular waveguide. Waveguide section 10 abuts waveguide sections 11 and 12 at a right angle to form the junction. Disposed within the junction in a manner to be discussed in greater detail hereinbelow is a triangular slab-like gyromagnetic element 13, together with its triangular matching and supporting structures.

The supporting structure for element 13 comprises an upper conductive pedestal 14, a lower conductive pedestal l5, and upper and lower

dielectric slabs

16 and 17, respectively. Conductive pedestals I4 and 15 are jointed and conductively bonded to the upper and lower broad walls of the junction, respectively. Upper and lower

dielectric members

16 and 17 provide insulating support for element 13 and can be conveniently bonded in place by means of a suitable low-loss adhesive. The composite structure, therefore, resembles a triangular shaped, multi-layer sandwich with gyromagnetic element 13 being sandwiched between

dielectric elements

16 and 17 and this combination, in turn, being sandwiched between conductive pedestals l4 and 15.

In practice,

dielectric members

16 and 17 can be fabricated of dielectric material such as Teflon having a dielectric constant on the order of 2.1. An external magnetic field generated, for example, by a permanent magnet or by a suitably energized electromagnet is directed through the gyromagnetic element in a direction perpendicular to the broad wall of the junction. As shown in FIG. 1, the magnetic field H is directed from above. However, as is well-known in the art, this field can be reversed, thereby reversing the direction of energy circulation.

Although the broadbanding characteristics of the composite pedestal, dielectric member, gyromagnetic element struture of FIG. 1 is well-known, it has been found that in circulators of the tee junction variety, mismatches and narrow band operation can still occur. With the tee junction circulator of FIG. 1, therefore, additional impedance matching obstacles are employed. These obstacles comprise

dielectric posts

18, 19 and 20 which are disposed near the apexes of element l3 and its composite supporting structure.

Dielectric posts

18, 19 and 20, in the shape of right circular cylinders, extend across the interior of the waveguide junction between the broad walls thereof. In general, the dielectric constant of

dielectric posts

18, 19 and 20 should be relatively high, on the order of nine to 15. These limits, however. are not absolute but rather represent a good design compromise.

Dielectric posts

18, 19 and 20 present a capacitive susceptance to the wave energy propagating within the guides. The value of the respective capacitive susceptance is a functiotn of the dielectric constant of the material, the diameter of the posts, and their location within the junction. In general, a higher dielectric constant allows a smaller post diameter. Lower dielectric constant and correspondingly greater post diameter may give rise to undesirable multimode effect. Higher dielectric constants and correspondingly smaller post diameters. on the other hand, may result in posts which are more fragile than desirable. In any event, once located, posts 18, 19 and 20 can be bonded in place by a suitable low loss adhesive such as epoxy resin.

Referring now to the cross-sectional view of FIG. 2, the arrangement of the

dielectric posts

18, 19 and 20 is shown, together with the location of gyromagnetic element 13 within the tee junction. Element 13 is preferably disposed within the junction with one apex thereof coinciding with the axis of waveguide section 10. The opposite side of the gyromagnetic element extends parallel to the axes of waveguide sections 11 and 12 and may be slightly displaced therefrom in the direction of waveguide section 10. Also the planar top and bottom surfaces of element 13 are parallel to the top and bottom broad walls of the junction. The location of element 13 in this manner is to approximate as nearly as possible symmetrical loading to the wave energy in all three of the waveguide sections forming the junction.

Dielectric posts

18, 19 and 20 are individually disposed adjacent each of the apexes of triangular element 13.

The optimum position for each of the dielectric posts l8, l9 and 20 can be conveniently obtained experimentally. In general, for a given post diameter and dielectric constant, the proper phase position of the compensating capacitive susceptance is found by varying the position of the post longitudinally along the direction of its adjacent waveguide axis (e.g., to the right or left for ports 18 and 19). The magnitude of the capacitive susceptance presented by the post is adjusted by varying the post position transversely to the waveguide section. The optimum spacing between the apexes of element 13 and its corresponding post is a very small fraction of a wavelength of the propagating wave energy.

In operation, it is assumed that the tee junction circulator of FIG. 1 is interconnected in a microwave circuit by flange couplers or other means well-known in the art. In a typical application waveguide section 11 may be coupled to a source of electromagnetic wave energy and waveguide section 12 may be coupled to a utilization device. Waveguide section 10 may be coupled to a matching load impedance. Such an arrangement comprises an isolator structure widely used in microwave systems. The wave energy is thus coupled into waveguide section 11 and, depending upon the direction and magnitude of the magnetic biasing field H. out of

waveguide section

12 or 10. If it is assumed that the direction and strength of the magnetic field is such as to cause the energy to be coupled out ofwaveguide section 12, then any energy entering the junction from waveguide section 12 will be coupled out of waveguide section 10 and any energy entering waveguide section 10 will be coupled out through waveguide section 11.

Other elements such as screws, capacitive irises and metallic buttons have been proposed for matching purposes. In general, however, these elements are characterized by conductive discontinuities of the sort which give rise to higher order mode conversion. (i.e., modes other than the dominant TE mode.) In general, higher order modes are to be avoided. Since the dielectric posts present no discontinuities in the vertical or E- field direction mode conversion is minimized. Any .other higher order modes caused by the presence of the dielectric posts l8, l9 and 20 are such that they are above cut-off for the waveguide sections l0, l1 and 12. Thus, they propagate only a short distance in these waveguide sections.

Tee junction circulators of the type shown in FIGS. 1 and 2 have been constructed and operated in the 4 GHz and 6 GHz regions. Such structures have displayed performance characteristics comparable to broadband Y-junction circulators of the type described in US. Pat. No. 3,104,361 cited hereinabove. Such circulators have displayed a bandwidth on the order of 12 percent measured between the 20 db points. In a typical device design for the 4 GHz region the following approximate dimensions and parameters were utilized:

TABLE I Waveguide Sections 11 and 12 Section 10 TABLE I-Continued Gyromagnetic element l3 In all cases it is understood that the above-described embodiment is merely illustrative of but one of a number of the many possible specific embodiments which can represent applications of the principles of the present invention. Numerous and varied other arrangements can be readily devised in accordance with these principles by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

l. A microwave circulator comprising, in combination:

three rectangular conductively bounded waveguide sections joined to form a common tee junction and having a pair of opposite broad walls at said junction;

at least one slab-like element of gyromagnetic material of substantially triangular shape disposed within said junction, one apex of said gyromagnetic element being substantially coincident with the axis of the side arm of said tee junction;

three dielectric elements of substantially solid cylindrical cross-section disposed within said junction, each of said dielectric elements extending between said opposite broad walls with one element being immediately adjacent each of the apexes of said gyromagnetic element; and

means for subjecting said gyromagnetic element to a magnetic field directed normal to said broad walls.

2 The circulator according to claim 1 wherein said element of gyromagnetic material is supported within said junction between a pair of dielectric support members and conductive pedestals.

3. In a microwave circulator structure of the type having three sections of rectangular conductivelybounded waveguide sections abutting to form an H- plane tee junction, at least one triangular shaped element of gyromagnetic material disposed within said junction, means for biasing said element with an external magnetic field, and impedance matching members disposed within said junction; the improvement comprising a completely dielectric post extending across the interior of said junction adjacent each apexof said element of gyromagnetic material.

4. The microwave circulator according to claim 3 wherein said posts have a dielectric constant between nine and 15.

5. A microwave circulator comprising, in combination:

first, second and third sections of rectangular, conductively bounded waveguide, said waveguide sections abutting to form a common H-plane tee junction with said first and second sections extending coaxially and said third section extending at a right angle to said first and second sections;

at least one slab-like element of gyromagnetic material of substantially triangular shape disposed within said junction;

at least three dielectric elements of substantially solid cylindrical cross-section disposed within said junction, one of said dielectric elements being adjacent each of the apexes of said gyromagnetic element, and

means for subjecting said gyromagnetic element to a magnetic field.

6. The circulator according to claim 5 wherein one apex of said gyromagnetic element substantially coincides with the axis of said third waveguide section and the opposite side of said gyromagnetic element substantially coincides with the common axis of said first and second waveguide sections.

Claims

1. A microwave circulator comprising, in combination: three rectangular conductively bounded waveguide sections joined to form a common tee junction and having a pair of opposite broad walls at said junction; at least one slab-like element of gyromagnetic material of substantially triangular shape disposed within said junction, one apex of said gyromagnetic element being substantially coincident with the axis of the side arm of said tee junction; three dielectric elements of substantially solid cylindrical cross-section disposed within said junction, each of said dielectric elements extending between said opposite broad walls with one element being immediately adjacent each of the apexes of said gyromagnetic element; and means for subjecting said gyromagnetic element to a magnetic field directed normal to said broad walls.

2. The circulator according to claim 1 wherein said element of gyromagnetic material is supported within said junction between a pair of dielectric support members and conductive pedestals.

5. A microwave circulator comprising, in combination: first, second and third sections of rectangular, conductively bounded waveguide, said waveguide sections abutting to form a common H-plane tee junction with said first and second sections extending coaxially and said third section extending at a right angle to said first and second sections; at least one slab-like element of gyromagnetic material of substantially triangular shape disposed within said junction; at least three dielectric elements of substantially solid cylindrical cross-section disposed within said junction, one of said dielectric elements being adjacent each of the apexes of said gyromagnetic element, and means for subjecting said gyromagnetic element to a magnetic field.