GB2293455A

GB2293455A - Device for measuring temperature coefficient of a dielectric resonator

Info

Publication number: GB2293455A
Application number: GB9514497A
Authority: GB
Inventors: Toshihiko Ogura; Yukio Higuchi; Hirotsugu Abe
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 1994-09-26
Filing date: 1995-07-14
Publication date: 1996-03-27
Anticipated expiration: 2015-07-14
Also published as: GB2293455B; JPH0894688A; KR960011435A; GB9514497D0; DE19527033A1; JP3085102B2; DE19527033C2

Description

i 2293455 1 DEVICE FOR MEASURING TEMPERATURE COEFFICIENT OF A DIELECTRIC

RESONATOR

Background of the Invent on

This invention relates to a device for measuring temperature coefficient of a dielectric resonator of the kind used in a f ilter or a signal emitter.

It has been known to measure temperature coefficient of a dielectric resonator by sandwiching the resonator from both ends between a pair of parallel conductor plates and measuring the TEO,, mode. By this method, however, the accuracy of measurement is only about 0.5ppm/OC because the unload Q-value is lowered due to the conductor loss by the conductor plates and the error in parallel positioning of the plates. A method of setting the resonator on a table placed inside a metallic structure having a cavity and measuring the TEO16 mode has also been known but, since the coefficients of thermal expansion are not the same between the dielectric resonator and the metallic cavity - providing structure, what was measured was not exactly the temperature coefficient of the resonator itself because of the effects of this difference. In view of the above, there has been proposed a method of measuring the temperature coefficient purely of a dielectric resonator itself by using a cavity -providing structure and a supporting table having the same coefficient of thermal expansion as the dielectric resonator, and measuring the TEOjb mode. As shown in Fig. 2, a device which is 2 adapted to be used for measurements by this method may comprise a cylindrical metallic case 1 having a bottom plate and containing therein a cylindrical cavityproviding structure 2 made of a ceramic material with a conductor (Ag) formed on its surface. The ceramic material for this cavity-providing structure 2 has the same coefficient of thermal expansion as the dielectric resonator 20. A cylindrical supporting table 3, made of a dielectric material having the same coefficient of thermal expansion as the dielectric resonator 20 and a low dielectric constant, is fastened to the base plate of the cavity-providing structure 2 at its center by means of an adhesive. A pair of throughholes is formed at mutually opposite positions on the side walls of the metallic case 1 and the cavity-providing structure 2. Connectors 4a, each connected to a coaxial cable 4 having an input-output probe at one end, are attached to these throughholes. The dielectric resonator 20, which is the object of measurement, is affixed to the support- ing table 3 by means of an organic adhesive, and a metallic cover 5 is fastened to the metallic case 1 by means of screws 11 so as to cover the upper opening of the cavity-providing structure 2.

with a prior art device thus structured, the accuracy of measurement is indeed not adversely affected by the difference in coefficient of thermal expansion between the dielectric resonator and the cavity-providing structure or the supporting table. Because an adhesive is used for affixing the dielectric resonator onto the supporting table, however, the dielectric resonator may become displaced due to the thermal expansion of the adhesive, and this adversely affects the accuracy of the measurement.

Because an adhesive is used, furthermore, extra process steps are required for the measurement such as 3 the steps of applying and drying the adhesive. This makes the time longer for the setting of the dielectric resonator on the device. When another sample is to be set for measurement, there is another work requirement for peeling off the adhesive.

Summary of the invention

It is therefore an object of this invention to provide an improved device for measuring temperature coefficient of a dielectric resonator, which does not require the use of any adhesive to affix the resonator and is capable of highly accurate measurements.

A device embodying the present invention for measuring temperature coefficient of a dielectric resonator, with which the above and other objects can be accomplished, may be characterized as comprising a cavity-providing structure, to which input-output probes for transmitting signals to and from the resonator are attached and a table made of a dielectric material is affixed, and a supporting bar provided thereabove such that the force of a coil spring will cause the dielectric resonator to be held securely between the supporting bar and the table. The cavityproviding structure, the table and the supporting bar are each made of a material having approximately the same coefficient of thermal expansion as the dielectric resonator. The cavity-providing structure may be made of a ceramic material and provided with a metallic cover over the cavity. According to an embodiment of the invention, the supporting bar has its upper end attached to a holder bar, which has the coil spring wound around it and is supported by a tubular member attached to the metallic cover.

With a device thus structured, not only do the cavity-providing structure, the table and the supporting 1 4 bar each have a coefficient of thermal expansion approximately equal to that of the dielectric resonator, but also the dielectric resonator is mechanically supported between the table and the supporting bar by the elastic force of a coil spring. Thus, the effects of differences in thermal expansion can be reduced significantly, and temperature coefficient of a dielectric resonator can be measured with higher accuracy. With a device thus structured, furthermore, the process of setting the dielectric resonator to the device can be simplified since no adhesive is required.

Brief Description of the Drawings

The accompanying drawings, which are incorporated in and form a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:

Fig. 1 is a sectional schematic view of a device embodying this invention for measuring temperature coefficient of a dielectric resonator; and Fig. 2 is a sectional schematic view of a prior art device for measuring temperature coefficient of a dielectric resonator.

Detailed Description of the Invention

Fig. 1 shows a device according to this invention for measuring temperature coefficient of a dielectric resonator. Since some of its components are substantially identical or at least similar to those described above with reference to Fig. 2, such components are indicated by the same numerals as in Fig. 2 for convenience.

1 AS shown in Fig. 1, a cylindrical cavity-providing structure 2, made of a ceramic material and having a conductor (not shown) with high conductivity such as Ag formed on its surface, is contained inside a cylindrical metallic case 1, engaging with its inner wall surface.

The ceramic material of the cavity -providing structure 2 has the same coefficient of thermal expansion as the dielectric resonator 20. A cylindrical supporting table 3, made of a dielectric material having the same coefficient of thermal expansion as the dielectric resonator 20 and a low dielectric constant (say, 2-7), is fastened to the base of the cavity-providing struc ture 2 at its center by means of a resin or glass material. A pair of throughholes is formed at mutually opposite positions on the side walls of the metallic case 1 and the cavity-providing structure 2. Connectors 4a, each connected to a coaxial cable 4 having at one end an input-output probe for transmitting signals to and/or from the resonator, are attached to these throughholes. The opening at the top of the cavity providing structure 2 is covered by a metallic cover 5.

A throughhole is formed at the center of this metallic cover 5 for allowing a supporting bar 9 to penetrate therethrough. A metallic tubular member 6 having an upper portion of its inner surface threaded to form a female screw is attached (say, by soldering) to the upper surface of the metallic cover 5 around the throughhole. A metallic holding bar 7, having a coil spring 8 wound around its outer peripheral surface and the supporting bar 9 attached to its lower end surface, is contained inside the tubular member 6. A holder screw 10, having a threaded outer surface to serve as a male screw, engages with the female screw of the tubular member 6. The holder screw 10 has a throughhole at the center for the holder bar 7 to pass therethrough and i 6 serves to hold the upper end of the coil spring 8. The lower end portion of the holding bar 7 has a larger diameter than its upper portions, engaging slidably with a lower smooth portion of the inner surface of the tubular member 6, and a groove is formed for accepting therein the lower end of the coil spring 8. The supporting bar 9, attached to the holding bar 7, is also made of a dielectric material with a low dielectric constant (say, 2-7) and having the same coefficient of thermal expansion as the dielectric resonator 20.

The supporting table 3, the dielectric resonator 20, the supporting bar 9, the tubular member 6 and the holding bar 7 are arranged so as to be in a coaxial relationship.

After the dielectric resonator 20 is thus placed on the supporting table 3, the metallic cover 5 is fastened to the metallic case 1 with the screws 11 so as to cover the upper opening of the cavity-providing structure 2. The holder screw 10 is then rotated, engaged with the tubular member 6, such that the lower end surface of the supporting bar 9 secures the dielectric resonator 20 firmly by pressing it, while the force of the coil spring 8 is controlled. The resonance frequency of the dielectric resonator 20 is thus measured at different temperatures, and the temperature coefficient of the dielectric resonator 20 is calculated as follows from the results of such measurements.

The temperature coefficient T, for the frequency of a dielectric resonator is defined as:

Tt = -TJ2 - a where T, is the temperature coefficient of the dielec tric constant and U indicates the coefficient of linear expansion of the dielectric resonator. After the dielectric resonator is set as described above and shown in Fig. 1, the device is placed inside a high-tempera- 7 ture chamber and the connectors 4 for the input-output proves are connected to semi-rigid cables, the other ends of the cables being connected to a network analyzer. If the resonant frequency is f, and f2 respec- tively at a standard temperature T, (say, in the range of 20C 250C) and at an arbitrary temperature T2, Tf in the unit of (1/OC) is obtained as follows:

2 If (f2 - fl)/{fl(T - TJ}.

In summary, the device described above with 10 reference to Fig. 1 is characterized not only wherein its c avi ty -providing structure, supporting table and supporting bar all have the same coefficient of thermal expansion as the dielectric resonator but also wherein the dielectric resonator is supported mechanically between the supporting table and the supporting bar without the use of any adhesive but by the pressure of the coil spring. Thus, the dielectric resonator can be supported stably at a constant pressure even if there is a temperature change. In other words, the accuracy in the measurement of temperature coefficient is not adversely affected either by the difference in coefficient of thermal expansion with the cavity-providing structure and the supporting table over a wide range of temperature or by the displacement of the dielectric resonator due to the thermal expansion of an adhesive.

Experiments have shown that the accuracy of measurement by a prior art device as shown in Fig. 2 was 0.05 - 0.15ppm/OC but that measurements with accuracy less than about 0.04ppm/OC are possible with a device according to this invention.

Another advantage of the device according to this invention is that it takes much less time to set the dielectric resonator for the measurement because no 1 8 adhesive is used and hence the time for applying and drying the adhesive can be dispensed with. While it used to take about 30 minutes to set a dielectric resonator by using an adhesive, it takes only about one minute with a device according to this invention.

1 9

Claims

I A device for measuring temperature coefficient of a dielectric resonator, said device comprising: a structure having a cavity, said structure being made of a material having approximately the same coefficient of thermal expansion assaid dielectric resonator; input-output means attached to said structure for transmitting signals to and from said dielectric resonator; a table attached to said structure, said table being made of a dielectric material having approximately the same coefficient of thermal expansion as said dielectric resonator; a supporting bar made of a material having approximately the same coefficient of thermal expansion as said dielectric resonator and disposed at an elevated position inside said cavity; and pressure-applying means for applying a force on said supporting bar and thereby securing said dielectric resonator between said supporting bar and said table.

is
2. The device of claim 1 wherein said pressureapplying means comprises a coil spring.
3. The device of claim 1 wherein said structure is made of a ceramic material.
4. The device of claim 1 wherein said table is made of a dielectric material with dielectric constant 2-7.
5. The device of claim 1 wherein said supporting bar is made of a material with dielectric constant 2-7.
6. A device for measuring temperature coefficient of a dielectric resonator, said device comprising: a structure with a base plate and side walls forming a cavity with an upper opening, said structure being made of a ceramic material having approximately the same coefficient of thermal expansion as said dielectric resonator; a metallic case which contains said structure therein; a pair of input-output means attached to said side walls of said structure for transmitting signals to and from said dielectric resonator; a table fastened to a center portion of said base plate of said structure, said table being made of a dielectric material having dielectric constant 2-7 and approximately the same coefficient of thermal expansion as said dielectric resonator; a metallic cover having an upper surface and covering said upper opening of said cavity; 20 a tubular member with a threaded inner surface portion and a smooth inner surface portion, said tubular member being attached to said upper surface of said metallic cover; a holder screw engaging with said tubular member; 25 a holder bar with an upper portion engaging with said threaded surface of said tubular member and a lower portion slidably engaging with said smooth inner surface portion of said tubular member; a supporting bar made of a material having dielec- tric constant 2-7 and approximately the same coefficient of thermal expansion as said dielectric resonator and disposed at an elevated position inside said cavity, said supporting bar being attached to said lower portion of said holder bar; and 1 11 a coil spring wound around said holder bar and adapted to apply a force on said holder bar and to thereby secure said dielectric resonator between said supporting bar and said table.
7. A device for measuring temperature coefficient of a dielectric resonator substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

7. A device for measuring temperature coefficient of a dielectric resonator substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

t 1% A.

Amendments to the claims have been filed as follows 1. A device for measuring temperature coefficient of dielectric resonator, said device comprising:

- a structure having a cavity, said structure being made of a material having approximately the same coefficient of thermal expansion as said dielectric resonator; input- output means attached to said structure for transmitting signals to and from said dielectric resonator; a table attached to said structure, said table being made of a dielectric material having approximately the same coefficient of thermal expansion as said dielectric resonator; a supporting bar made of a material having approximately the same coefficient of thermal expansion as said dielectric resonator and movable within said cavity; and pressure applying means for applying a force on said supporting bar so as to secure a dielectric resonator between the supporting bar and said table.

2. A device as claimed in claim 1, wherein the pressure applying means comprises a coil spring.

3. A device as claimed in claim 1 or 2, wherein said structure is made of a ceramic material.

4. A device as claimed in claim 1, 2 or 3, wherein said table is made of a dielectric material having a dielectric constant of 2 to 7.

5. A device as claimed in any on of claims 1 to 4, wherein said supporting bar is made of a material with dielectric constant of 2 to 7 Ib I.) 6. A device for measuring temperature coefficient of a dielectric resonator, said device comprising:

a structure with a base plate and side walls f orming a cavity with an upper opening, said structure being made of a ceramic material having approximately the- same coefficient of thermal expansion as said dielectric resonator; a metallic case which contains said structure therein; a pair of input-output means attached to said side walls of said structure for transmitting signals to and from said dielectric resonator; a table fastened to a center portion of said base plate of said structure, said table being made of a dielectric material having dielectric constant 2-7 and approximately the same coefficient of thermal expansion as said dielectric resonator; a metallic cover having an upper surface and covering said upper opening of said cavity; 20 a tubular member with a threaded inner surf ace portion and a smooth inner surface portion, said tubular member being attached to said upper surface of said metallic cover; holder screw engaging with said tubular member; holder bar with an upper portion engaging with said threaded surface of said tubular member and a lower portion slidably engaging with said smooth inner surface portion of said tubular member; a supporting bar made of a material having dielec- tric constant 2-7 and approximately the same coefficient of thermal expansion as said dielectric resonator and disposed so as to be mova-ble within said cavity, said supporting bar being attached to said lower portion of said holder bar; and 1 U a coil spring wound around said holder bar and adapted to apply a force on said holder bar so as to secure a dielectric resonator between Said supporting bar and said table.