Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2000-08-31
2002-12-31
Lee, Benny T. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S206000
Reexamination Certificate
active
06501347
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric filter having an auxiliary conductor of a predetermined pattern which is provided on an open end surface and is electrically connected to an outer conductor provided on a side surface. The present invention also relates to a method of manufacturing such a dielectric filter.
2. Description of the Related Art
There are known various kinds of dielectric filters in which the inner surfaces of through-holes extending through a dielectric ceramic block are coated with conductive material forming inner conductors so as to produce a plurality of resonators disposed in parallel, and in which the outer surface of the dielectric ceramic block is coated with a conductive material forming an outer conductor, except for an open end surface at which one end of each of the through-holes opens.
Further, a dielectric filter having an improved structure is disclosed in Japanese Utility Model Publication (kokoku) No. 4-8643. As shown in
FIG. 1
which is based on the disclosure of that publication, in the improved dielectric filter, strip-shaped or strip-form auxiliary conductors f, i.e., conductor strips, are formed on the open end surface d such that one auxiliary conductor f is located between resonators a and b, the other auxiliary conductor f is located between resonators b and c, and the auxiliary conductors f are electrically connected to an outer conductor e formed on the outer surface. Due to formation of the strip-form conductors f, the frequency characteristic of the resultant dielectric filter exhibits an attenuation peak on the higher frequency side with respect to the center frequency. Through modification and adjustment of the shape and the width of the auxiliary conductors f, the mutual electromagnetic coupling between the resonators a and b and between the resonators b and c can be adjusted.
In addition, as shown in
FIG. 2
, in the dielectric filter disclosed in Japanese Patent Application Laid-Open (kokai) No. 9-219605, a counterbore h is formed at the end of a through-hole g that opens at the open end surface d, such that the diameter of the counterbore h increases at the open end; and an inner conductor j covering the inner surface of the counterbore h is extended inwardly in the radial direction, to thereby increase the effective resonance length. An advantage of this structure is that the overall length of the dielectric filter is decreased as compared with a conventional dielectric filter having the same resonance length.
It will be appreciated that, depending on the purpose or use to which a dielectric filter is to be put, there is a demand for various different types of dielectric filters having different shapes and characteristics. In this regard, there is a demand for a dielectric filter which exhibits a filter characteristic having an attenuation peak on the higher frequency side thereof and which can be made compact. Such a dielectric filter can be produced by combining the filter structure shown in
FIG. 1
in which the strip-form conductors f are formed such that the filter characteristic has a particular attenuation peak, and the filter structure shown in
FIG. 2
in which the overall length is shortened through formation of the counterbore h. However, in this case, because both the strip-shaped or strip-form conductors f and the counterbore h must be formed on the same open end surface, the simultaneous formation of the strip-shaped conductors f and the counterbore h on this surface is difficult because the surface is limited in area.
Moreover, the basic dielectric filter shown in
FIG. 1
has a particular drawback. Specifically, the auxiliary conductors f and the outer conductor e are formed through a process in which a conductive material in the form of paste is applied, by means of screen printing, to each surface of the dielectric ceramic block in a predetermined pattern, followed by a baking step carried out at a predetermined temperature. In order to provide the required connections between the auxiliary conductors f on the open end surface d and the outer conductor e on the outer surface, the conductive paste material must be applied such that a conductive material layer on the open end surface and the conductive material layer on a selected side surface must overlap each other at an edge portion where the open end surface and the selected side surface intersect each other, so as to ensure that a mutual connection is established between the conductive material layers. However, since each layer of applied conductive material is very thin and becomes thinner at the edge portion due to surface tension of the conductive material, when the baking step is carried out, the thin portion of the conductive material layer located at the edge portion of the block can easily break due to the difference in the thermal expansion coefficients between the dielectric ceramic block and the conductive material, with the result that such electrode breakage can occur at the edge portion.
The above-described drawback of the layer of applied conductive material, i.e., the fact that the layer becomes thinner at the edge portion due to surface tension, can be overcome by manually applying the conductive material to the edge portion after completion of screen printing to thereby increase the thickness of the layer to a desired level. Since a manual operation is difficult and time consuming, and manufacturing efficiency is low, with the result that the abovementioned solution is simply not practical.
Moreover, in the conventional dielectric filter, when the auxiliary conductors f are formed, a conductive material in the form of paste is screen-printed on the flat open end surface. Therefore, the conductive material easily runs and spreads, which makes accurate formation of the auxiliary conductor f impossible as a practical matter.
SUMMARY OF THE INVENTION
In view of the foregoing, a first object of the present invention is to provide a dielectric filter which has a shortened overall length and which can be made to exhibit a peak in the filter characteristic thereof on the higher-frequency side with respect to the center frequency.
Another object of the present invention is to provide a dielectric filter which has a structure that prevents electrode breakage which would otherwise occur at an edge portion, as described above, and which also enables the accurate formation of auxiliary conductors in a desired pattern.
Still another object of the present invention is to provide a method of manufacturing a dielectric filter, which method prevents electrode breakage which would otherwise occur at an edge portion and enables the accurate formation of auxiliary conductors in a desired pattern.
According to a first aspect of the invention, there is provided a dielectric filter including at least three resonators, the filter comprising: a dielectric ceramic block having at least three through-holes formed therein, in parallel, in a group having opposite ends, each of the through-holes including an inner surface, and the at least three through-holes including end through-holes located at opposite ends of the group and at least one intermediate through-hole located between the end through-holes, the dielectric ceramic block including an open end surface at which one end of each of said through-holes opens; an inner conductor covering the inner surface of each of the through-holes to respectively form corresponding end resonators and at least one intermediate resonator; an outer conductor covering a predetermined outer surface of the dielectric ceramic block, excluding said open end surface; and input/output pads formed on one side surface of the dielectric ceramic block such that the pads are located near the open end surface and face the end resonators so as to be capacatively coupled thereto, each of the end through-holes including a counterbore formed at one end of the corresponding end through-hole and opening at the open end surface such that the corresponding end through-hole is of increase
Ito Kenji
Ono Shoji
Wakita Naomasa
Cathey Damian
Larson & Taylor PLC
Lee Benny T.
NGK Spark Plug Co. Ltd.
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