WO1999010948A1

WO1999010948A1 - Improved dielectric mounting system

Info

Publication number: WO1999010948A1
Application number: PCT/US1998/017059
Authority: WO
Inventors: Timothy M. Ebling; Thomas W. Godan; Lee A. Prager
Original assignee: Control Devices, Inc.
Priority date: 1997-08-25
Filing date: 1998-08-18
Publication date: 1999-03-04
Also published as: WO1999010948B1; AU8911498A

Abstract

A dielectric resonator system (100) having a dielectric element (102) and an attachment assembly (108) both housed within a casing. The attachment assembly (108) is electrically insulating. The attachment assembly (108) couples the dielectric element (102) to the casing. The dielectric element is internally threaded (133). The attachment assembly (108) includes an electrically insulating support structure (110) coupled to the casing by a nut (112) and bolt (114), both of which may also be electrically insulating. The support structure (110) is externally threaded (128) and is nondestructively removably coupled to the threaded dielectric element (102).

Description

IMPROVED DIELECTRIC MOUNTING SYSTEM

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/056,951, filed August 25, 1997.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to dielectric devices, and more specifically to the mounting of dielectric resonators in resonant cavities.

BACKGROUND OF THE INVENTION

It is well known among electrical engineers that energy losses in dielectric resonator systems occur at contact boundaries, such as those between the dielectric and its support or between the dielectric and the cavity boundary. Energy losses both degrade the efficiency of the resonator by subtracting energy from the system and increase its temperature through resistance heating.

In prior dielectric resonator systems, the resonating dielectric has been secured within its resonant cavity by a variety of mounting media. These include a mounting stem formed as part of the resonating body, adhesives to bond the resonator to a ceramic support and the ceramic support to the casing floor, adhesives to bond the dielectric resonator directly to the casing floor, and insulators to sandwich the dielectric resonator securely within the cavity. Mounting materials used in the prior art include dielectrics, quartz, and plastics. Each of these mounting media has its own inherent disadvantages. Adhesives introduce extrinsic energy loss into the system and thereby lower the Q-factor. Furthermore, adhesives degrade with time, temperature cycling, and thermal and mechanical shock. Moreover, adhesives introduce assembly inefficiencies because they are cumbersome, messy, and difficult to use with reproducible accuracy. Finally, adhesives tend to be poor thermal conductors and hinder the dissipation of heat from the system.

A mounting stem formed as part of the dielectric resonator can distort the electromagnetic field within the cavity. Additional energy loss can be introduced as induced current in the casing. Further, many good dielectric resonators tend to be poor thermal conductors, retarding heat dissipation from the system. Finally, the formation of a one-piece resonator with a stem increases the complexity of the manufacturing process.

Plastic support structures are not suitable for use in high temperature applications, as plastic tends to lose structural integrity with increasing temperature. Additionally, plastics typically are poor thermal conductors. Moreover, high-temperature plastics are generally lower Q materials and contribute to frequency drift with temperature. High Q plastics, such as high density polyethylene and high density polystyrene, quickly lose structural integrity above 100 C.

Finally, the use of sandwiching introduces variables such as stacking tolerances and positioning fluctuations within the cavity with respect to the dielectric element. Hence, there is a need for an improved method of securing the dielectric resonator within the resonant cavity. The securing method must be capable of producing a dielectric resonator system with fewer energy losses and better thermal dissipation, and improved mechanical stability at elevated temperatures. A means for satisfying this need has so far eluded those skilled in the art. SUMMARY OF THE INVENTION

One form of the present invention contemplates a dielectric body threadedly coupled to an insulating support member. The insulating support member is in turn threadedly secured to the floor or wall of the cavity.

Another form of the present invention contemplates a dielectric body mounted directly to the cavity floor by means of ceramic screws coupling with mating threads formed in the dielectric body.

One object of the present invention is to reduce energy loss at the dielectric mount interface by providing an improved means for mounting the dielectric.

Another object of the present invention is to provide a means with improved thermal dissipation characteristics for mounting a dielectric within a cavity.

Related objects and advantages of the present invention will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. la is a partial cross-sectional side view of a dielectric element supported by a first embodiment attachment assembly of the present.

FIG. lb is a cross-sectional view of a dielectric element screwed to the first embodiment attachment assembly of FIG. la.

FIG. 2a is a partial cross-sectional view a of dielectric element supported by a second embodiment attachment assembly of the present invention.

FIG. 2b is a cross-sectional view of a dielectric element secured to the second embodiment attachment assembly of FIG. 2a.

FIG. 2c is a partial cross-sectional view of a third embodiment attachment assembly of the present invention.

FIG. 3a is a partial cross-sectional side view of a dielectric element supported by a fourth embodiment attachment assembly of the present invention.

FIG. 3b is a cross-sectional view of a dielectric element screwed to the fourth embodiment attachment assembly of FIG. 3a.

FIG. 4a is a partial cross-sectional side view of a dielectric element mounted by a fifth embodiment attachment assembly of the present invention. FIG. 4b is a cross-sectional view of a dielectric element mounted by the fifth embodiment attachment assembly of FIG. 4b.

FIG. 5a is a partial cross-sectional side view of a dielectric element supported by a sixth embodiment attachment assembly of the present invention.

FIG. 5b is a cross-sectional view of the dielectric element supported by the sixth embodiment of FIG. 5a.

FIG. 5c. is a cross-sectional view of a dielectric element supported by a seventh embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates .

A dielectric is a material that is not electrically conductive. Dielectric resonators generally comprise a dielectric element with a relatively high dielectric constant (greater than about 5) enclosed within a cavity. The casing defining the cavity is usually metallic to minimize interference from external electromagnetic irradiation. A dielectric element used in a dielectric resonator is usually formed of a ceramic material with a high dielectric constant and a high Q-factor and usually has a symmetrical geometry, such as cylindrical. The dielectric may be doped to fine-tune its dielectric and electronic properties to suit a given application, as is known in the art.

Dielectric resonators operate by the reflection of electromagnetic waves at the interface between two dielectrics with different dielectric constants. A resonator operates to absorb and reradiate energy at its resonant frequency. The resonant frequency is dependent upon the dielectric properties of the resonator, and its size and shape. Dielectric resonators are commonly used in filters and oscillators.

A dielectric resonator with a high dielectric constant can confine a large electromagnetic field mostly within its boundaries. Consequently, the availability of dielectrics with increasingly high dielectric constants has lead to increasingly smaller resonators. While attractive for use in smaller and more convenient devices, miniaturization has lead to the same power being drawn through smaller devices. Without a corresponding increase in efficiency, the miniaturization of the dielectric resonator can lead to the same heat being generated in a smaller volume. This can give rise to higher operating temperatures as well as smaller areas through which to dissipate the generated waste heat. It is increasingly critical to develop devices that either exhibit less power loss, have better thermal dissipation capabilities, or both. Furthermore, as the temperature of a dielectric increases, its dielectric constant shifts. While some materials, such as ceramic perovskites, are more thermally stable with respect to their dielectric properties than others, large increases in operating temperatures will nonetheless cause their dielectric properties, and therefore their resonant frequencies, to shift. Moreover, differential thermal expansion and thermal cycling can result in creep, component misallignment , and debonding. It is therefore important to choose components with similar thermal expansion characteristics as well as to allow for fine tuning of the dielectric resonator.

Traditionally, ceramic bodies have been used as structural bodies in applications requiring high compressive strengths. However, ceramic materials are not known for having high tensile or shear strengths. As a result, the use of ceramics as fasteners has been mostly limited to cements and glues. Ceramic fasteners, such as screws or bolts, have long been considered impractical to produce because of their inherent brittleness and frangibility . The present invention relates generally to an improved system for mounting a dielectric body or element within a resonant cavity. More particularly, the present invention has one form wherein a dielectric element is threadedly coupled to an insulating support member that is in turn threadedly secured to the floor or wall of the cavity. The present invention has another form wherein the dielectric element is mounted directly to the cavity floor by means of ceramic screws with mating threads formed in the dielectric element. Where the operation of the resonator will produce significant amounts of waste heat, the support member and the fasteners should be formed of a material with a relatively high thermal conductivity and/or high temperature stability, such as (for example, and not by way of limitation) alumina, zirconia, silicon nitride, or aluminum nitride.

Referring to FIGs. la and b, a first embodiment dielectric resonator 100 is shown having a dielectric element 102 mounted within a casing 104. The dielectric element 102 is composed of a ceramic or other suitable dielectric material. The casing 104 is typically a metallic enclosure defining a cavity 106 for the dielectric element 102; however, the casing composition may vary. The dielectric element 102 is secured within the casing 104 by an attachment assembly 108. In one preferred embodiment, the attachment assembly is nondestructively removable; in other words, the assembly can alternately be engaged and disengaged. In other embodiments the attachment assembly may be threadlocked or otherwise made permanent. In one preferred embodiment, the attachment assembly 108 is composed entirely of electrical insulators. Electrical insulators have resistivities in excess of about 10 ohm cm. In other embodiments, the attachment assembly may include electrically non-insulating elements, such as metallic fasteners. in one preferred embodiment, the attachment assembly 108 comprises an electrically insulating support structure 110 coupled to the casing 104 by means of an electrically insulating nut 112 and bolt 114. The support structure 110 is hollow and substantially cylindrical with an open top portion 116 and partially closed bottom portion 118 with an aperture 120 formed therein. The aperture 120 is sized to allow passage of the shaft 122 of the bolt 114, but not the head 124 of the bolt 114 or the nut 112. The shaft 122 of the bolt 114 penetrates both the casing 104 and the bottom portion 118 of the support structure 110 and is secured by the nut 112. This is most easily accomplished through the use of pre-formed entry apertures 120, 126 for the fasteners . The top portion 116 of the support structure 110 features external threads 128 while the bottom portion 130 of the dielectric element 102 has an internal recess 132. A set of threads 133 is located in the recess 132. The recess 132 is threaded to mate with the threaded top portion 116 of the support structure 110. The threaded recess 132 threadedly interlocks with the external threads 128 of the top portion 116 of the support structure 110. The dielectric element 102 may be nondestructively removably coupled and decoupled with the support structure 110 by rotatably engaging the mated threads 128. The support structure 110 may be a made of any solid electrical insulator, such as a ceramic, glass, wood, stone, or plastic.

Variations on this embodiment include the use of a bolt with no head but with threads on both ends of the shaft, secured in place by a pair of nuts (not shown) . Alternatively, a bolt or screw could be used with threaded apertures to secure the support structure to the casing without the use of a nut (not shown) . Another variation includes a support structure with an internally threaded portion coupled to an externally threaded dielectric element (not shown) .

FIGs. 2a, b, and c illustrate a second and third embodiment of the invention. A dielectric element 202 is mounted inside a casing 204 by an attachment assembly 208. The attachment assembly 208 in this embodiment is electrically insulating and includes a small nut 212, a bolt 214, a large nut 234, and a substantially cylindrical hollow support structure 210. It is noted that in other embodiments the attachment assembly 208 may be electrically non-insulating. The support structure 210 includes a bottom portion 218 and an open top portion 216. The bottom portion 218 has a greater outer radius than the top portion 216, defining a shoulder 236 at the interface. The top portion 216 of the support structure 210 is at least partially externally threaded 228. The outer radius of the top portion 216 of the support structure 210 is less than the inner radius of the dielectric ring 202, which is in turn less than the outer radius of the bottom portion 218 of the support structure 210. Thus, the dielectric ring 202 encircles the top portion 216 of the support structure 210 and rests on the shoulder 236.

The casing 204 and bottom portion 218 of the support structure have respective apertures 226, 220. The bolt 214 protrudes through the apertures 226, 220 in the casing 204 and the support structure 210. The small nut 212 threadedly couples to the bolt 214, coupling the support structure 210 with the casing 204. The large nut 234 has an inner radius matched to that of the outer radius of the top portion 216 of the support structure 210, and includes a threaded inner surface 229 to engage the threads 228 of the support structure 210, while the dielectric ring 202 rests on the shoulder 236. The large nut 234 engages the support structure 210, thereby locking down the dielectric ring 202 between the large nut 234 and the shoulder 236.

FIG. 2c illustrates a third embodiment wherein the apertures 226, 220 in the casing 204 and the bottom portion 218 of the support structure 210 are threaded and coupled directly by a screw or bolt 214 alone (i.e. without the nut 212) . A variation of the third embodiment includes the use of a bolt with no head but with threads on both ends of the shaft for coupling the support structure to the casing, secured in place by a pair of nuts (not shown).

FIGs. 3a and b illustrate a dielectric resonator element 302 mounted within a casing 304 by a fourth embodiment attachment assembly 308. The attachment assembly 308 is electrically insulating and comprises a hollow, flanged support column 310 bolted to the casing 304. The support column 310 has a bottom flange 340, a central portion 342, and a top portion 316. The support column 310 is bolted to the casing 304 by two or more bolts 314 through the flange 340. The top portion 316 is threaded 328 and has a smaller outer radius than does the central portion 342. The intersection of the top portion 316 and the central portion 342 defines a shoulder 336. The support column 310 has a hollow, axially centered cylindrical core 344 of substantially constant radius.

The dielectric element 302 illustrated in FIGs. 3a and b has the shape of a ring, although it can have any desired shape. The dielectric ring 302 has a top portion 346 and a bottom portion 330. The bottom portion 330 of the dielectric ring 302 features a circular recess

332 adapted to threadedly engage the threaded top portion 328 of the support column 310.

The inner core 348 of the top portion 346 of the dielectric ring 302 has a radius substantially equal to that of the inner core 344 of the support column 310. When the dielectric ring 302 is threadedly engaged with the support column 310 and seated on its shoulder 336, an extended axially centered cylindrical core 350 is defined. A substantially cylindrical dielectric plug 352 adapted to slide within the extended axially centered cylindrical core 350 is used to fine-tune the dielectric resonant frequency of the system. The dielectric plug 352 is mounted on a rod 354 that extends from the plug 352 axially through the cylindrical core 350 and protrudes through an aperture 326 in the casing 304. In one embodiment the protruding end of the rod 354 is attached to a control knob 356.

Variations on the fourth embodiment include the use of a bolt with no head but with threads on both ends of the shaft, secured in place by a pair of nuts (not shown).

Alternatively, a bolt or screw could be used with threaded apertures to secure the support structure to the casing without the use of a nut (not shown) . Another variation of the fourth embodiment includes the use of different geometries for the tuning plug, such as cubic or spherical

(not shown) . Yet another variation of the fourth embodiment of the present invention contemplates the use of various compositions for the tuning plug, such as glass, ceramic, plastic, or composite (not shown). Still another variation contemplates the use of a solenoid, linear actuator, or the like to automatically actuate the tuning plug into position (not shown) .

FIGs. 4a and b show a dielectric resonator element 402 mounted directly to a casing 404 in a fifth embodiment of the present invention. In the illustrated fifth embodiment, a pair of electrically insulating bolts 414 protrude through the casing 404 and threadedly engage the dielectric element 402. The dielectric element 402 has a bottom portion 430 that rests flush against the casing 404. The bottom portion 430 of the dielectric element 402 features cavities 458 threaded to mate with the electrically insulating bolts 414. In the illustrated embodiment, the cavities 458 do not extend completely through the dielectric element 402. Variations on the fifth embodiment include the use of screws, clips, or springs to couple the dielectric and the casing (not shown) . Another variation on this embodiment contemplates the bolts completely penetrating the dielectric element and protruding from the face opposite their entry (not shown) .

FIGs. 5a, and b illustrate a dielectric resonator system 500 mounted to a casing 504 in a sixth embodiment of the present invention. In the sixth embodiment a dielectric ring 502 is fastened to the casing 504 by a threaded dielectric screw 560. The casing 504 defines a cavity 506. The inner wall 562 of the dielectric ring 502 is threadedly adapted to mate with the screw 560. The screw 560 may be rotatably advanced through the dielectric element 502. The casing 504 features an aperture 526 also threaded to mate with the screw 560. An electrically insulating support cylinder 564 extends from the casing 504 to the dielectric ring 502, preventing it from moving. The cylinder 564 may be affixed in place with adhesive. Alternatively, one or more discrete support spacers (not shown) may be used to support the dielectric ring 502.

In a seventh embodiment of the present invention illustrated by FIG. 5c, the above-described dielectric resonator system 500 is further modified by the inclusion of a tuning plug 552. The top portion 546 of the dielectric ring 502 has a cylindrical recess 566 adapted to at least partially receive the tuning plug 552. The tuning plug 552 is mounted to a rod 554 that extends through the cavity 506 and protrudes through an aperture (not shown) in the casing 504. In the embodiment illustrated in FIG. 5c, the rod 554 is preferably made of alumina or other suitable material and is threadedly coupled to the plug 552, but may also be affixed by any known coupling means. The resonance of the dielectric system 500 is fine-tuned as the plug 552 is advanced into the recess 566. The advancement of the plug 552 is halted when the desired resonant frequency is attained.

Claims

What is claimed is:

1. A dielectric resonator system comprising: a casing defining a cavity and having an entry aperture; a dielectric element; and an electrically insulating attachment assembly connecting the dielectric element to the casing.

2. The system of claim 1 wherein the dielectric element comprises an internally threaded ring.

3. The system of claim 2 wherein the attachment assembly comprises: an electrically insulating support structure having an externally threaded top portion and a bottom portion defining a shoulder therebetween; a central aperture penetrating the bottom portion; wherein the dielectric ring is threadedly engaged to the top portion and rests on the shoulder; an electrically insulating bolt wherein the bolt protrudes through the entry aperture and the central aperture; and an electrically insulating nut mated to the bolt.

4. The system of claim 3 wherein the attachment assembly is nondestructively removable.

5. The system of claim 1 wherein the dielectric element is a ring.

6. The system of claim 5 wherein the attachment

Claims

assembly comprises: an electrically insulating support structure having an externally threaded top portion and a bottom portion defining a shoulder therebetween; wherein the dielectric ring rests on the shoulder; an insulating internally threaded dielectric large nut; wherein the large nut is threadedly coupled to the top portion, thereby attaching the dielectric ring to the support structure between the large nut and the shoulder; a central aperture formed in the bottom portion; an electrically insulating bolt protruding through the entry aperture and the central aperture; an electrically insulating small nut mated to the bolt.

7. The system of claim 1 wherein the dielectric element has a threaded internal recess.

8. The system of claim 7 wherein the attachment assembly comprises: an electrically insulating hollow support structure having an externally threaded top portion and a central portion defining a shoulder therebetween; a flanged bottom portion; a fastening aperture formed in the flange; a substantially cylindrical core formed in the hollow support structure; wherein the dielectric element is threadedly coupled to the top portion of the support structure; an electrically insulating bolt protruding through the entry aperture and the fastening aperture; an electrically insulating nut mated to the bolt; and a dielectric tuning plug adapted to slidably move within the inner core and ring.

9. The system of claim 8 further comprising a rod coupled to the dielectric tuning plug and protruding through the casing.

10. The system of claim 1 wherein the dielectric element includes a threaded cylindrical recess.

11. The system of claim 10 wherein the attachment assembly comprises: an electrically insulating bolt protruding through the entry aperture and threadedly engaged with the recess; and wherein the bolt couples the dielectric element to the casing.

12. The system of claim 2 wherein the entry aperture is threaded.

13. The system of claim 12 wherein the attachment assembly comprises: a threaded dielectric tuning screw threadedly coupled to the dielectric ring and the casing; and a support cylinder extending from the casing to the dielectric ring.

14. The system of claim 13 wherein the dielectric ring includes a recess and further comprising: a tuning plug; a rod connected to the tuning plug and extending through the casing; and wherein the tuning plug slidably engages the recess .

15. A dielectric resonator system comprising: a casing; a dielectric element housed within the casing; and an electrically insulating attachment assembly coupled to the casing and the dielectric element.

16. The system of claim 15 wherein the attachment assembly comprises ceramic bolts connecting the dielectric element directly to the casing.

17. The system of claim 15 wherein the dielectric element is threadedly coupled to the attachment assembly.

18. The system of claim 15 wherein the attachment assembly comprises electrically insulating bolts connecting the dielectric element directly to the casing.

19. A dielectric resonator system comprising: a casing having an entry aperture; an electrically insulating support structure having a threaded top portion and a bottom portion; a fastening aperture formed in the bottom portion; a dielectric element having a threaded recess coupled to the support structure; a bolt protruding through both the entry aperture and the fastening aperture; and a nut mated to the bolt.

20. The system of claim 19 wherein the bolt has threads at both ends.

21. The system of claim 19 wherein the support is formed from a plastic.

22. The system of claim 19 wherein the support is formed from a ceramic.

23. The system of claim 19 wherein the support is formed from a dielectric.

24. The system of claim 19 wherein the casing is an electrical conductor defining a cavity.

25. The system of claim 19 wherein the placement of the dielectric element within the cavity tunes the resonant frequency of the system.

26. The system of claim 19 wherein the both the nut and the bolt are electrically insulating.

27. The system of claim 19 wherein both the nut and the bolt are formed from ceramics.

28. A dielectric resonator, comprising: a dielectric ring; a casing having an entry aperture; a threaded electrically insulating bolt protruding through the entry aperture; a support member having a threaded top end and a bottom end defining a shoulder therebetween; wherein the bolt threadedly couples the support structure to the casing; and an electrically insulating nut having a threaded inner radius threadedly coupled to the top end, thereby attaching the dielectric ring to the support structure between the nut and the shoulder.

29. The system of claim 28 wherein the support member is hollow.

30. A dielectric resonator comprising: a casing; a dielectric element having a top portion and an internally threaded recessed bottom portion; wherein the recess is cylindrical; and an attachment assembly connecting the dielectric element to the casing.

31. The resonator of claim 30 wherein the attachment assembly comprises an electrically insulating bolt protruding through the casing to threadedly mate with the recess .

32. A dielectric resonator comprising: a casing having a threaded aperture; a dielectric element having a threaded aperture; support members adapted to extend from the casing to the dielectric element; and a threaded dielectric cylinder coupled to the dielectric and the casing.

33. The dielectric resonator of claim 31 wherein the dielectric element has a top portion and a bottom portion, the top portion having an inner cavity, and further comprising : a substantially cylindrical dielectric tuning plug slidably adapted to enter the cavity; and a support rod affixed to the dielectric tuning plug, the rod protruding through the casing.

34. An attachment assembly for connecting a dielectric element to a casing comprising: an electrically insulating support structure; a first fastener coupling the support structure to the casing; and a second fastener coupling the support structure to the dielectric element wherein the second fastener is electrically insulating .

35. The attachment assembly of claim 34 wherein the first fastener is a ceramic screw.

36. The attachment assembly of claim 34 wherein the first fastener is a mated ceramic nut and bolt.

37. The attachment assembly of claim 34 wherein the second fastener comprises a threaded portion of the support structure and is threadedly coupled to the dielectric element .

38. The attachment assembly of claim 33 wherein the dielectric element is a ring.

39. The attachment assembly of claim 38 wherein the second fastener comprises: a threaded top portion of the support structure; a bottom portion of the support structure; a shoulder for supporting the dielectric element formed at the interface between the top portion and the bottom portion of the support structure; and a nut threadedly coupling the dielectric element to the support structure.

40. The attachment assembly of claim 34 wherein the first fastener is a insulating screw threadedly coupled to both the casing and the dielectric element and the second fastener is a plurality of electrically insulating spacers positioned between the casing and the dielectric element.