JPH0336083Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to a dielectric resonator that can provide excellent electrical characteristics at low cost.

(Prior art) Conventionally, as a processing method to obtain the electrical characteristics of a dielectric resonator, a paste such as silver is baked onto the surface of the dielectric material, or electroplating is performed after imparting conductivity by electroless plating. There is.
Furthermore, in the conventional type, all corners were made at right angles because it is easier for the dielectric to have a simple shape in terms of theoretical calculations of the equivalent dielectric constant, resonance frequency, etc. of the dielectric resonator. For example, when the corners are right angles, the resonant frequency f ₀ of a 1/4 wavelength coaxial resonator can be easily determined using the following equation.

f ₀ =C/4 where C is the speed of light, and is the central conductor axis length, that is, the height of the dielectric.

However, this shape had drawbacks such as low resonance sharpness (Qu) or large variations even if a dielectric was formed by applying and baking silver paste, for example.

Furthermore, there was no reproducibility with respect to the firing conditions, and it was difficult to set the conditions. These drawbacks can be overcome to some extent by layering the silver paste and increasing the film thickness, although this will increase the cost.Also, due to the surface tension of the silver paste, the film thickness at the corners is extremely thick compared to other flat parts. The present invention was inspired by the fact that the thickness of the material is becoming thinner.

The sharpness (Qu) of a resonator is a very important characteristic factor that affects the insertion loss and other performance of the filter when it is used to make a high frequency filter or the like. Therefore, a material with such low sharpness (Qu) and large variations cannot be used in products that require high performance and high reliability.

In addition, in the case of electroplating, the current concentrates on the corners of the dielectric surface, causing so-called burrs, which can easily cause dimensional interference or damage when the dielectric resonator is housed in a case, etc. There were flaws.

Figures 1a and 1b show the general shape of a dielectric resonator, where 1 is a dielectric and 2 is a cylindrical hollow part. FIG. 2 shows a cross-sectional view thereof, in which numeral 3 indicates a metal film formed directly on the dielectric 1, and numeral 4 indicates a corner portion. When a high frequency dielectric filter or the like is constructed using this dielectric resonator, current flows through the metal film 3 on the surface. Particularly in the case of high frequency, it flows to the surface of the metal film in contact with the dielectric 1.

Here, in order not to deteriorate the electrical characteristics,
It has been experimentally determined that a film thickness several times the skin depth δ is required as expressed by the following equation.

δ=√2/ωμ ₀ σ (1) However, in formula (1), ω is the angular frequency used, μ ₀ is the vacuum permeability, and σ is the electrical conductivity of the metal film.

Figures 3a and 3b are enlarged views of a corner 4 of a cross section of a dielectric material on which a conventional metal film has been formed.
This shows the case where electroplating is applied.
In the case of the paste shown in Figure 3a, even if the film thickness is 20 μm on the flat part after 3 coats, 1 coat is applied on the corner part 4.
An extremely thin metal film of ~2 μm is formed.
This is due to the surface tension of the paste and cannot be avoided if there are sharp corners. As a result, the conductor cross-sectional area of the corner portion 4 becomes smaller, the resistance increases, and the resonance sharpness (Qu) deteriorates. Furthermore, in order to obtain a predetermined film thickness even at the corner portions 4, it is necessary to further coat the layer, which increases the number of man-hours and has the drawback that the layer becomes unnecessarily thick on the flat portions.
In the case of electroplating shown in FIG. 3b, on the other hand, the current concentrates on the corners 4, resulting in thickening and formation of burrs. The film thickness is 20μm on the flat part, and 100μm on the corner part 4.
There are more than that. This gives rise to drawbacks such as when this dielectric resonator is housed in a metal case and an attempt is made to construct a filter or the like, dimensional interference occurs and the dielectric resonator cannot fit into the metal case or is easily damaged.

(Purpose of the invention) The present invention was made to eliminate these drawbacks, and an object of the invention is to provide a dielectric resonator that can stably obtain excellent electrical characteristics.

(Structure of the device) The present invention provides a dielectric resonator in which a highly conductive metal film is directly formed on the surface of a dielectric material having a hollow portion, and the corner portions of the dielectric material that exist within the area where the metal film is formed are , R or C chamfering is provided.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIGS. 4a and 4b show the first embodiment of the present invention, and are enlarged views of the portion where the corner of the dielectric 1 has been rounded 5 and then the metal film 3 has been formed. 4A shows the case where a paste of silver or the like is baked onto the dielectric 1, and FIG. 4B shows the case where electroplating is applied.

Since the R chamfer 5 can be easily realized using a mold in dielectric molding, the number of man-hours does not increase.

In the case of the paste shown in FIG. 4a, when the film thickness on the flat part is 20 .mu.m by two coats, a film thickness of 10 to 15 .mu.m can be obtained even on the corners where the rounded chamfer 5 has been applied. Therefore, the number of applications of expensive paste such as silver can be reduced. The conventional model had an average resonance sharpness (Qu) of 1000 after 3 coats, with large variations, but with this invention, the average sharpness (Qu) reached 1200 after 2 coats.
The variation is also less than 1/3 compared to the conventional type.
For example, when making a high-frequency dielectric filter using such a dielectric resonator, if the resonance sharpness (Qu) increases by 200, the insertion loss of the filter increases.
It has been experimentally confirmed that the filter performance is reduced by 0.5 dB, which means that the filter performance is dramatically improved. Further, even in the case of electroplating shown in FIG. 4b, the film thickness at the flat part is 20 μm, whereas at the corner part where the rounded chamfer 5 has been applied, the film thickness is 25 to 30 μm, so the film thickness does not increase much.

5a and 5b are enlarged views of the second embodiment of the present invention, in which the corners of the dielectric 1 are chamfered 6 instead of chamfered R, and then the metal film 3 is formed. The corners are obtuse angles.

FIG. 5a shows the case where electroplating is applied. The effects of this second embodiment are similar to those of the first embodiment described above, and in this case, there is an advantage that processing of the mold during dielectric molding is easier than rounding the corners of the dielectric. be.

(Effects of the invention) As explained above, the present invention solves all the drawbacks of the conventional technology, and makes it possible to obtain a dielectric resonator that is inexpensive, has stable and excellent electrical characteristics, and uses this resonator. This is effective when configuring a high frequency dielectric filter or the like.

[Brief explanation of the drawing]

Figures 1a and 1b are outline drawings of a typical dielectric resonator, Figure 2 is a sectional view of Figures 1a and b, and Figure 3 is an enlarged view of the corner of Figure 2. Figures 4a and 4b are enlarged views of the corners of the dielectric resonator according to the first embodiment of the present invention, and Figures 5a and 5b are the second embodiment of the present invention. An enlarged view of a corner of a dielectric resonator. 1...Dielectric material, 2...Cylindrical hollow part, 3...Metal coating, 4...Corner part, 5...R chamfering, 6...C
chamfer.

Claims (1)

[Claims for Utility Model Registration] In a dielectric resonator formed by forming a highly conductive metal film directly on the surface of a dielectric body having a cylindrical hollow part, the dielectric body existing within the area where the metal film is formed; A dielectric resonator characterized in that the corners of the dielectric resonator are chamfered with R or C to make the thickness of the metal film substantially uniform.