JPH0522002A - Dielectric filter - Google Patents

Abstract

PURPOSE:To reduce the dispersion of filter characteristics and man-hour for adjustment by forming a pattern electrode having satisfactory position accuracy and dimension accuracy with simple work at low cost on the opening plane of a dielectric block. CONSTITUTION:A recessed part 22 almost shallower than 1mm is formed on the opening plane of a lambda/4 type dielectric coaxial resonator 2 equipped with plural resonator holes 12, and a conductor film 24 is stuck to the entire bottom and defined as a pattern electrode 20. This recessed part can be simultaneously formed when a dielectric element is formed. Conductive paste is dropped down to the recessed part, and protruded parts are ground and removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric filter mainly used in the microwave band. More specifically, the present invention relates to a dielectric filter in which a shallow concave portion is provided at a predetermined position on an open surface of a λ / 4 resonance type dielectric coaxial resonator, and a conductor film is attached to the entire bottom surface thereof to form a pattern electrode. This filter is useful in various fields such as mobile communication and satellite communication.

[0002]

2. Description of the Related Art A structure using a λ / 4 resonance type dielectric coaxial resonator having a plurality of resonator holes is known as a dielectric filter. As this type of dielectric filter, for example, a plurality of resonator holes and connector holes are alternately arranged in the longitudinal direction of a rectangular parallelepiped dielectric block at specified dimensional intervals, and the surface where they are opened. One of them is an open surface, and a conductor film is formed on the outer surface excluding the open surface and the inner surface of the resonator hole to form an outer conductor and an inner conductor, respectively.

In such a dielectric filter, the resonance frequency of each resonator is mainly determined by the length of the resonator hole. As a technique for variably adjusting the resonance frequency of each resonator, there is a method in which the length of the resonator hole is changed by forming the dielectric block itself in a stepped structure. In addition, there is also a method of extending the inner conductor (conductor film of the resonator hole) to the vicinity of the open end of the open surface. In the latter case, stray capacitance is generated when the end of the extended pattern electrode approaches the outer conductor on the side surface, and the electric field is concentrated on the open surface of the resonator, so that the length of the resonator hole is substantially reduced. (In other words, the resonance frequency is shifted to the low frequency side).

Further, in order to couple adjacent resonators in place of the coupler holes, a pattern electrode protruding from the side outer conductor is formed on the open surface of the dielectric block, or a pattern electrode for connecting the side outer conductors. There is a structure that forms. Furthermore, in order to perform feedback between specific resonators, in the open surface of the dielectric block, it is possible to reach from one resonator hole to another resonator hole and separate them from the conductor film and outer conductor. There is also a structure in which an elongated pattern electrode is formed.

The pattern electrodes formed on the open surfaces of these dielectric blocks fulfill the functions of varying and adjusting the resonance frequency, adjusting the coupling between the resonators, forming a feedback circuit, etc., as described above. The resonance frequency and the filter characteristics change depending on the precision and the forming position precision. Therefore, conventionally, a screen printing method has been used for forming the pattern electrodes on the open surface. That is, this is a method of screen-printing and printing a conductive paste on the flat open surface of the dielectric block.

[0006]

However, the formation of the pattern electrode by the screen printing method has a drawback that it requires a precise work requiring careful attention in order to prevent the positional displacement, resulting in high cost and poor productivity. If the conductive paste is applied thickly, bleeding will occur due to sagging around the pattern, and the pattern forming accuracy will deteriorate, and if thinly applied, the quality of the pattern electrode will deteriorate due to evaporation during baking, and in any case there will be variations in filter characteristics. . Therefore, fine adjustment is required, which also leads to high cost.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art and to form a pattern electrode having good positional accuracy and dimensional accuracy by a simple operation, which reduces variation in filter characteristics and reduces adjustment man-hours. It is to provide a dielectric filter that can be reduced.

[0008]

DISCLOSURE OF THE INVENTION The present invention is a dielectric filter in which a pattern electrode having a desired shape is formed on the open surface of a λ / 4 resonance type dielectric coaxial resonator having a plurality of resonator holes. The pattern electrode has a structure in which a conductor film is attached to the entire bottom surface of the recess formed on the open surface, and this point is a feature of the present invention. This pattern electrode may be one for adjusting the resonance frequency in which a concave portion is formed around the open end of the resonator hole and the conductor film on the bottom surface is connected to the inner conductor. It may be for a feedback circuit formed in an elongated shape so as to reach the vicinity of the resonator hole. Alternatively, it may be a pattern electrode for adjusting the coupling between the resonators.

In this dielectric filter, a shallow recess having a depth of about 1 mm or less is simultaneously formed by press molding at the time of molding the dielectric element on the surface which is the open surface of the rectangular parallelepiped dielectric element.
It is manufactured by forming a conductor film to be an outer conductor and an inner conductor on the outer surface except the open surface and on the inner surface of the resonator hole, respectively, and depositing a conductive paste on the concave portion and baking it to form a pattern electrode. The conductive paste is attached by dropping or immersing, and by polishing the protruding portion,
It can be easily formed in a desired pattern that matches the shape of the recess.

[0010]

[Function] The pattern electrodes formed on the open surface of the dielectric block have functions such as variable / adjustment of the resonance frequency, coupling adjustment between the resonators, and formation of the feedback circuit as described above, depending on the formation position and the shape thereof. Fulfill The shallow concave portion formed on the open surface limits the electrode formation position and range, and enables precise pattern electrode production without using the screen printing method.

[0011]

1 is a perspective view showing an embodiment of a dielectric filter according to the present invention, and FIG. 2 is a longitudinal sectional view thereof. This is an example in which a pattern electrode for varying the resonance frequency is provided in a three-stage band pass filter. Except for the pattern electrode formed on the open surface, the basic structure of the dielectric filter is almost the same as the conventional technique.

A substantially rectangular parallelepiped dielectric block 10 made of a sintered body of a high dielectric constant material for microwaves is used. Three resonator holes 12 are formed at predetermined intervals in the longitudinal direction of the dielectric block 10, and a connector hole 14 is provided between them. The outer surface of the dielectric block 10 and the inner surface of the resonator hole 12 excluding the open surface are one open surface (the upper surface in FIGS. 1 and 2) and the other is a short-circuit surface. A conductor film is formed on the outer conductor 16 and the inner conductor 18, respectively. In FIG. 1, a shaded portion represents a surface on which a conductor film is provided, and a portion with fine dots represents a surface without a conductor film and a base material of a dielectric is exposed. The conductor film is, for example, a thin conductive material layer formed by baking a silver paste.

A pattern electrode 20 is formed on the open surface of the dielectric block 10. In the present invention, this pattern electrode 2
0 indicates that the conductor film 2 is formed on the entire bottom surface of the recess 22 formed on the open surface.
It has a structure in which 4 is attached. In this embodiment, the periphery is partitioned so as to surround the open end of the central resonator hole, and a shallow recess 22 having a depth of about 1 mm or less (separated from the outer conductor on the side surface) is formed, and the entire bottom surface thereof is formed. On the conductor film 2
4 is attached and the conductor film 24 is connected to the inner conductor 18.

Such a dielectric filter is manufactured as follows. When a rectangular parallelepiped dielectric element having a resonator hole and a coupler hole is press-molded, at the same time, a recess for electrode formation having a depth of about 1 mm or less is also press-molded on one surface where the resonator hole is opened. The molded product is sintered to form a dielectric block. Then, with the surface in which the concave portion is formed as an open surface, a conductor film that becomes an outer conductor and an inner conductor is formed on the outer surface and the resonator hole inner surface excluding the open surface, and a conductive paste is attached to the concave portion and baked. A pattern electrode is formed. To attach the conductive paste to the recesses, the conductive paste may be dropped or the dielectric block may be immersed in the conductive paste and the protruding portion may be removed by polishing. By such a work process, anyone can easily form the pattern electrode with high accuracy.

In the dielectric filter of this embodiment, the resonators at both ends have the conductor film formed only on the inner surface of the ordinary resonator hole, but the resonator at the center does not only open the inner surface of the resonator hole but also opens it. This is a structure in which the conductor film extends to the periphery of the edge. Since a stray capacitance is formed between this pattern electrode and the outer conductor on the side surface, the electric field concentrates on the open surface of the central resonator, and apparently
It looks like the dielectric block is locally elevated (like the resonator hole is longer). That is, the resonance frequency of the central resonator is low.

As one of the input / output coupling circuits of the dielectric filter, there is a system in which a coupling capacitor is mounted on the open ends of the resonator holes at both ends and coupling is performed through the coupling capacitor. When a capacitor is attached, the resonance frequency shifts to the low frequency side due to its capacitance. Therefore, even if the dielectric blocks having the same height over the entire length are used, the resonance frequency of the resonator near the center becomes relatively high. Therefore, by forming the pattern electrode as described above on the central resonator, it is possible to adjust the frequency due to such a cause. Although the length of the resonator hole becomes shorter and the resonance frequency shifts to the high frequency side due to the formation of the recessed portion, the recessed portion may be sufficiently shallow as long as it can control the range in which the conductive paste spreads. The effect more than the compensation is produced, and it can be shifted to the low frequency side as a whole.

In the drawing, the recess is clearly exaggerated for the sake of clarity. However, in practice, as described above, it may have a function of limiting the range of adhesion of the conductive paste. It is a thing. The conductive paste usually adheres not only to the bottom surface of the recess but also to the side wall surface, and when it is very shallow, the conductive paste almost fills the recess.

FIG. 3 shows another embodiment of the present invention.
Since it is basically the same as the above-mentioned embodiment except the shape of the electrode on the open surface, the corresponding parts are designated by the same reference numerals and the description thereof is omitted. In this embodiment, elongated shallow recesses (about 1 mm or less) 32 are provided on both sides from the vicinity of the resonator holes at both ends to the vicinity of the central resonator hole, and the conductor film 34 is attached to the entire bottom surface thereof. Thus, the pattern electrode 30 for forming the feedback circuit is formed. Each recess 24 is separated from the outer conductor on the side surface and is also separated from the inner conductor 18 and the pattern electrode 20. A stray capacitance is formed between each pattern electrode 30 and the inner conductor 18 or the pattern electrode 20, and the pattern electrode 30 forms a feedback circuit between the resonators. As a result, the filter characteristic has a pole in the attenuation region (is polarized). The position of the pole can be adjusted by the shape of the pattern electrode 30.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the configurations shown in the drawings. The number of resonator holes formed (the number of steps) is not limited to three, and can be applied to a filter having an arbitrary number of steps.
It can also be applied to a dielectric filter having no connector hole. The resonator forming the pattern electrode for adjusting the resonance frequency is not limited to that near the center. The shape and the forming position of the pattern electrode for forming the feedback circuit are appropriately changed depending on which resonator is used for feedback. Further, the present invention can be applied to a pattern electrode for adjusting coupling.

[0020]

As described above, the present invention has a structure in which a shallow concave portion is formed on the open surface of the dielectric block and a conductor film is adhered to the shallow concave portion. Since the conductor film can be manufactured with high positional accuracy and dimensional accuracy and the conductive film can be formed by dropping a conductive paste or the like, it is possible to easily form the pattern electrode with high accuracy and less variation. Therefore, variations in the characteristics of the dielectric filter are reduced, and the number of adjustment steps can be reduced. Furthermore, since a precision screen printing process, which requires careful attention, is not required, productivity is high and the cost is low.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a dielectric filter according to the present invention.

FIG. 2 is a vertical sectional view of FIG.

FIG. 3 is a perspective view showing another embodiment of the dielectric filter according to the present invention.

[Explanation of symbols]

10 Dielectric block 12 Resonator hole 14 connector holes 16 Outer conductor 18 Inner conductor 20 pattern electrodes 22 recess 24 Conductor film 30 pattern electrodes 32 recess 34 Conductor film

Claims (4)

[Claims] 1. A dielectric filter in which a pattern electrode is formed on an open surface of a λ / 4 resonance type dielectric coaxial resonator having a plurality of resonator holes, wherein the pattern electrode is the entire bottom surface of a recess formed on the open surface. A dielectric filter having a structure in which a conductor film is attached to the dielectric filter. 2. A recess is formed around the open end of the resonator hole,
The dielectric filter according to claim 1, wherein the conductor film on the bottom surface is connected to the inner conductor. 3. The dielectric filter according to claim 1, wherein the concave portion is formed in an elongated shape so as to extend from the vicinity of the resonator hole to the vicinity of another resonator hole. 4. A depth of 1 mm is provided on one surface of the rectangular parallelepiped dielectric element having a plurality of resonator holes in which the resonator holes are opened.
The following recesses are simultaneously formed by press molding during molding of the dielectric element, and then sintered to form an open surface, and an outer conductor and an inner conductor are formed on the outer surface excluding the open surface and the inner surface of the resonator hole, respectively. While forming a conductor film that becomes, the conductive paste is attached to the entire bottom surface of the recess and baked,
A method of manufacturing a dielectric filter for forming a pattern electrode.