JPS609363B2 - Microwave cavity resonator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microwave cavity resonator constructed from a novel material.

More specifically, the present invention relates to a cavity resonator that does not cause fluctuations in resonance frequency due to changes in operating temperature, that is, is stable against changes in operating temperature.

A device that installs a cavity in the microwave propagation process and absorbs a specific frequency range of the microwave is well known as a so-called microwave cavity resonator.

This microwave cavity resonator is usually made of a material such as brass or aluminum, and is manufactured by plating the inner surface of the material with a metal having low electrical resistivity such as silver, copper, or gold.

However, these commonly used materials are
Due to the rather large coefficient of thermal expansion, the length of the cavity changes with changes in the operating temperature, resulting in variations in the resonant frequency. In order to suppress such fluctuations in the resonant frequency, it has conventionally been possible to use an alloy with a relatively small coefficient of thermal expansion, such as Ampar, but this is a special alloy and is therefore expensive. The disadvantage is that it is difficult to process. The inventors of the present invention have conducted intensive research to develop a microwave cavity resonator that is easy to obtain, easy to mold, and does not cause fluctuations in resonance frequency due to changes in operating temperature. We discovered that structural materials do not necessarily have to be metal materials, but materials such as ceramics can also be used, and that some ceramics are dense and have a significantly small coefficient of thermal expansion.
Previously, we proposed microwave cavity resonators using spodumene ceramics, aluminum titanate ceramics, and their glass ceramics instead of amber, but as a result of further research, we found that among cordierite ceramics, -180qC to +150oo
We found that materials with a thermal expansion coefficient within ±20xlo-7/deg and a water absorption of essentially 0 are particularly excellent as materials for microwave cavity resonators. The present invention has been accomplished.

That is, the present invention provides a cavity resonator having a structure in which a metal coating layer is provided on the inner surface of a cavity-shaped ceramic, in which, as the ceramic, these three components in a triangular composition diagram with M location, A〆203, and Si02 as vertices, respectively. Coordinates 2, 33, 65, 2, 53, 45, 20, 15, 6
5, 10, 55, 35, 30, 16, 55 and 30,
It has a basic composition in the range surrounded by the six points 35, 35, and further contains small amounts of Fe203, alkali metal oxides and alkali metal oxides, and MnutoAso203 as desired.
and 25% by weight or less of Sn02 based on the total amount of Si02
Cordierite-based ceramics containing
It is characterized in that a material having a water absorption rate of substantially 0 within 0×10-7/deg is used.

An example of the cavity resonator of the present invention will be explained with reference to the accompanying drawings.
The figure is a cross-sectional view of a cavity resonator connected to a waveguide, in which a cavity resonator 2 is attached to a waveguide 1 with a silver plate 7 applied to the inner surface of a yellow cavity 8 through a side tube 3. Indicates the condition. The cavity resonator 2 is composed of a cordierite ceramic layer 6 and a metal layer 7 coated on the inner surface thereof. The shape of this part may be either a straight cylinder or a rectangular cylinder. When the microwave moves from the input port 4 to the output port 5 of the waveguide 1, the frequency of the input wavelength having the relationship of 〆=n^ (n is an integer) with respect to the length of the cavity is absorbed and removed. The remaining part becomes the output. The cordierite ceramic layer in this cavity resonator is usually configured to have a thickness of 1 to 5 mm, and the thickness of the metal layer coated on the inner surface is selected within the range of 1 to 50 mm.

If the thickness of the metal layer is smaller than this, it will not be possible to uniformly coat the inner surface of the resonator and provide sufficient conductivity. On the other hand, if this thickness is made larger than 50A, the influence of the coefficient of thermal expansion of the conductive metal on the inner surface becomes large, and the desired effect cannot be obtained. In the present invention, silver, copper, gold, aluminum, etc. are used as the metal to be coated on the inner surface, but silver is most preferred.

Regarding the basic composition of the ceramics in the present invention, Mg○, Aso203 and Si02,
Coordinates of these three components 2, 33, 65, 2, 53, 45,
20, 15, 66, 10, 55, 35, 30, 15, 5
5 and 30, 35, 35, and a smaller amount, for example, an external amount of less than 1% by weight of Fe2
03, those containing an alkali metal oxide and an alkali metal oxide are used.

Even if this ceramic contains up to 25% by weight of tin oxide in addition to these essential components, the desired function will not be impaired. Ceramics is 1800○
Thermal expansion coefficient between 15,000 and ±20×10-
It is necessary that the water absorption rate be substantially 0 within 1' degree. In addition to having a low coefficient of thermal expansion as described above, the cordierite ceramic used in the present invention must have a water absorption rate of substantially 0.

When a material that does not have such a water absorption rate is used as a microwave cavity resonator, it absorbs and releases water vapor.
Electrical measurements are subject to fluctuations. The present invention also provides an operating temperature of -80oC for a microwave cavity resonator.
It is characterized by the discovery of a composition range of cordierite that exhibits low expansion in the range from 0 to 150 qo and exhibits excellent electrical stability. These ceramics are dense, with a porosity of 0.5
% or less.

The cavity resonator of the present invention has a smaller change in absorption frequency due to temperature than conventional brass plated with silver, so it can be used in areas with frequent temperature changes and in devices where frequency fluctuations due to temperature changes are undesirable. be able to. Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Predetermined ingredients were mixed, formed into the shape shown in the attached drawings, calcined at 1100 to 130,000, and further heated to 1250 to 130,000.
By firing at a predetermined temperature in the range of 1440oo,
Cavity resonators using ceramics of various compositions as structural materials were obtained.

The diameter of this cavity was 1 mm, the length of the cavity was 12.5 mm, and the thickness of the structural material was 2 mm. Furthermore, the inside of the cavity was covered with five Buddha statues using silver plating. Next, using the microwave of frequency 11 today Z *, find the frequency change rate (△f/f)△T with respect to the temperature of the resonator, and calculate the coefficient of thermal expansion of the structural material (△evening/evening)/△T. 1 table is shown. R in the table
O is an oxide of an alkali metal; R'20 is an oxide of an alkali metal.

Table 1 Example 2 Ceramics were produced in the same manner as in Example 1 by adding a predetermined amount of tin oxide when blending the raw materials.

The ceramic characteristics and resonator characteristics of this material are shown in Table 2.
Table 2 Comparative Example As the ceramic in Example 1, water absorption rate 1.5%
A cavity resonator with exactly the same structure was manufactured, except that cordierite ceramics were used.

When this resonator was used under conditions of relative humidity of 10% and 80%, the resonator characteristics were 0.1×10-6/d.
A variation in the range of 0.5×10-6/deg from eg was observed. In this way, even if the inner surface is coated with metal, ceramic parts whose water absorption rate is not essentially 0 will absorb moisture during use, and this moisture will fluctuate depending on the usage conditions, causing frequency deviations and affecting the resonator characteristics. changes.

[Brief explanation of the drawing]

The figure is a longitudinal sectional view showing an example of the resonator of the present invention coupled to a waveguide, in which reference numeral 6 indicates a ceramic layer and 7 indicates a metal layer.

Claims (1)

[Claims] 1. In a cavity resonator having a structure in which a metal coating layer is provided on the inner surface of a cavity body-shaped ceramic, as the ceramic,
The coordinates 2 of these three components in the composition triangular diagram with MgO, Al_2O_3 and SiO_2 as vertices, respectively.
33, 65, 2, 53, 45, 20, 15, 65, 10
,55,35,30,15,55 and 30,35,3
It has a basic composition in the range surrounded by the six points of 5, and further contains small amounts of Fe_2O_3, alkaline earth metal oxides and alkali metal oxides, and MgO and Al_2O_ as desired.
25% by weight or less of Sn based on the total amount of 3 and SiO_2
Cordierite ceramics containing O_2, with a thermal expansion coefficient of ±2 between -80°C and 150°C.
A microwave cavity resonator characterized in that a cavity resonator for microwaves is used that has a water absorption rate of substantially 0 within 0x10^-^7/deg.