JPS62183603A - Dielectric filter - Google Patents

Abstract

PURPOSE:To facilitate the manufacture and to reduce number of components by opposing a conductor film and an inner conductor formed at an outer face of one opening of a dielectric block with each other via the dielectric block. CONSTITUTION:Three throughholes 2 are pierced to a dielectric block 1 made of a material such as titanate ceramic at a proper interval. Two holes 2a, 2b in each throughhole 2 are formed stepwise, and the hole area of an opening 2A of the upper hole 2a is made smaller than that of an opening 2B of the lower hole 2b. The inner conductor 4 made of a conductive film is formed onto the inner face of the hole 2b and part 4b of the inner conductor 4 is formed to the inner upper face of the hole 2b. On the other hand, no inner conductor is formed on the inner face of the hole 2a. An outer conductor 3 made of a metallic conductive film is formed to the entire outer face (including an end face 1a at which the hole 2a is formed) of the dielectric block 1. Since the conductive film 8 and the part 4b of the inner conductor 4 are opposed via the dielectric block 1, a static capacitance required for coupling resonance units is constituted between the opposed portions.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dielectric filter used as a distributed constant resonator, for example.

Traditionally, as a filter for a frequency band of several 100 MHz, an outer conductor formed on at least four sides of a dielectric block and a plurality of through holes formed on the inner surface of the dielectric block are used. A dielectric filter is used that electromagnetically couples a plurality of resonant units formed by an inner conductor and a dielectric block existing between both conductors.

An equivalent circuit of such a dielectric filter is shown in FIG.

In this equivalent circuit, for example, three dielectric coaxial resonant units X1 to X3 are coupled by a coupling element K, and a capacitance C is interposed between each resonant unit and the ground. A conventional example of a dielectric filter that realizes an equivalent circuit is shown in FIG. 4 or 5.

The dielectric filter shown in FIG.
Through-holes 102 are provided, and a conductive film (hereinafter referred to as "inner conductor") is formed on the entire inner surface of the through-holes 102. A conductive film (hereinafter referred to as "outer conductor") 103 is also formed on the outer surface of the dielectric block 101,
These inner and outer conductors and dielectric blocks constitute resonance units X1 to X3. In this conventional example, a conductor 3108 is also formed on the upper end surface 101a of the dielectric block. This conductive film 108 is not formed within a certain distance from the periphery of the opening of the through hole 102. In other words,
The open end peripheral portion 105 is a ring-shaped portion where no conductive film is present. In such a configuration, a capacitor is formed between the inner conductor of the through hole 102 and the conductive film 108, and this capacitor equivalently constitutes a filter as shown in FIG. 3. By changing the distance, the capacitance of the capacitor changes, and the degree of electromagnetic coupling between the resonant units changes, resulting in a change in filter characteristics.

Further, the dielectric filter shown in FIG. 5 has an open end surface 101a as an upper end surface, and a shield plate 106 provided above the open end surface 101a.
Three movable metal pieces 107 are screwed together,
The end face of each metal piece 107 and the opening of each through hole 102 are configured to face each other. In such a dielectric filter, a capacitor is formed between the metal piece 107 and the inner conductor 104, and this capacitor equivalently constitutes the filter shown in FIG. 3. By changing the position of the metal piece 107, the capacitance of the capacitor changes, and as a result, the degree of electromagnetic coupling between the resonant units changes.
Filter characteristics also change.

-0(YO'口t') In such a dielectric filter, the filter characteristics change greatly depending on the capacitance value of the capacitor mentioned in 11, so the capacitance of the capacitor must be kept constant. However, in the dielectric filter having the configuration shown in FIG. 4, there is a problem in that it is difficult to configure the conductive film 101a having a ring-shaped opening at a predetermined distance from the through hole 102. The dielectric filter shown in FIG. 5 requires a metal piece 107 and the like, which increases the number of parts and has the problem that it is impossible to reduce costs.

The present invention has been made in view of the problems of conventional dielectric filters, and aims to provide a dielectric filter that is easy to manufacture and has a small number of parts.

. In order to achieve the above object, the present invention comprises an outer conductor formed on at least four sides of a dielectric block, an inner conductor formed on the inner surface of a plurality of through holes bored in the dielectric block,
In a dielectric filter in which a plurality of resonant units constituted by dielectric blocks existing between both conductors are electromagnetically coupled, one opening of the through hole is narrowed, and an inner conductor does not exist in the opening on the narrow side. is formed, and a conductive film is formed over almost the entire surface of the end face of the dielectric block facing the narrow opening, and between the conductive film and the inner conductor, the electrostatic charge necessary for coupling between the resonant units is generated. According to the above structure, the conductive film formed on the outer surface of one opening side of the dielectric block and the inner conductor face each other with the dielectric block interposed therebetween. Therefore, a capacitance is formed between the conductive film and the inner conductor, and as a result, a dielectric filter having an equivalent circuit as illustrated in FIG. 3 is obtained.

Fig. 1 is a sectional view of a combline filter as an embodiment of the dielectric filter according to the present invention, and 1 is a dielectric block made of, for example, titanium oxide ceramic;
Three through holes 2 are bored at appropriate intervals. The through hole 2 is formed in a step-like shape in which two hole portions 2ax2b are stacked, and the opening area of the opening 2A of the upper hole portion 2a is smaller than that of the opening 2B of the lower hole i%2b. There is.

An inner conductor 4 made of a conductive film is formed on the inner surface of the hole 2b, and a portion 4b of the inner conductor 4 is also formed on the inner upper surface of the hole 2b. On the other hand, no inner conductor is formed on the inner surface of the hole 2a.

An outer conductor 3 made of a metal conductive film is formed on the entire outer surface of the dielectric block 1 (including the end surface 1a where the hole 2a opens). Note that the conductive film formed on the end surface 1a is indicated by reference numeral 8.

In this embodiment with such a configuration, the conductive film 8 and the portion 4b of the inner conductor 4 face each other with the dielectric block 1 interposed therebetween, so that static electricity necessary for coupling between the resonant units and the resonant units is created between them. The capacitance is configured, and the equivalent circuit of this embodiment is as shown in FIG.

Such a dielectric filter is manufactured by forming a conductive film on the entire surface of a dielectric block 1 having a predetermined shape (including the inner surfaces 2a and 2b of the through hole 2) by electroless plating, and then scraping off the conductive film on the inner surface 2a (trimming). ) can be manufactured simply by doing the following.

Further, as shown in FIG. 2, the conductive film 8 is extended to the upper part of the inner surface of the hole 2a to form a conductive film part 8', and a part of the inner conductor 4 is extended to the lower part of the inner surface of the hole 2a. Even if the structure is such that the portion 4a is formed by stretching and a portion where no conductive film is present having a predetermined width is formed between the two, the required electrostatic charge can be maintained between the conductive film portion 8' and the portion 4a of the inner conductor 4. A similar dielectric filter can be obtained since the capacitance is configured.

In addition, the coupling between resonance units in a dielectric filter is
It can be changed by controlling not only the above-mentioned capacitance but also the characteristic impedance of each resonance unit, and it is usually best to change it by controlling both the capacitance and characteristic impedance in a complementary manner.

As a characteristic impedance control means, the width of the dielectric block 11 is narrowed down between the through holes 12 (see FIG. 6), and each through hole 14a to 14c formed in the dielectric block 13 is used. There are means such as changing the dimensions of the inner conductor by changing the dimensions of the inner conductor (see FIG. 7), and changing the pitch of the through holes.

Further, as means for controlling the capacitance, there are the above-mentioned adjustment of the amount of trimming, insertion of a dielectric material or metal into the through hole, and the like. An example of inserting metal into this through hole is
As shown in FIG. 8, the through hole 18 is covered by a metal cap 17 fixed to the upper end surface of the dielectric block 15 with solder 16, and a metal rod 19 screwed into the hole in the center of the metal camp 17 is passed through. An example of such a structure is that it is inserted into the hole 18.

In the above description, a combline filter was used as the dielectric filter, but it goes without saying that the dielectric filter of the present invention can also be applied to an interdigital type.

As is clear from the above explanation, in the dielectric filter of the present invention, the conductive film formed on the outer surface of one opening side of the dielectric block and the inner conductor face each other with the dielectric block interposed therebetween. As a result, a predetermined capacitance can be stably constructed between the conductive film and the inner conductor, making it easier to create a filter with predetermined characteristics compared to the conventional filter shown in FIG. Furthermore, compared to the conventional filter shown in FIG. 5, the filter has fewer parts and can be manufactured at a lower cost.

[Brief explanation of drawings]

FIG. 1 is a sectional view of one embodiment of the dielectric filter of the present invention, FIG. 2 is an enlarged sectional view of the main part of another embodiment, FIG. 3 is a diagram showing an equivalent circuit of an example of the dielectric filter, and FIG. FIG. 5 is a perspective view of a conventional example, FIG. 5 is a sectional view of another conventional example, and FIGS. 6 to 8 are explanatory views of other embodiments of the present invention. 1... Dielectric block, 2... Through hole, 2a...
Upper hole, 2b...lower hole, 2A...hole 2
a opening, 2B...opening of hole 2b, 3...outer conductor, 8...conductive film, 8"...conductive film portion, 4...inner conductor, 4at 4b...inside Conductor part. Patent applicant: Murata Manufacturing Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] A plurality of dielectric blocks consisting of an outer conductor formed on at least four sides of a dielectric block, an inner conductor formed on the inner surface of a plurality of through holes bored in the dielectric block, and a dielectric block existing between both conductors. In a dielectric filter in which a resonant unit is electromagnetically coupled, one opening of the through hole is narrowed, a part where no inner conductor is present is formed in the opening on the narrow side, and the opening on the narrow side faces. A dielectric filter characterized in that a conductive film is formed over substantially the entire end face of the dielectric block, and a capacitance required for coupling between resonance units is formed between the conductive film and the inner conductor.