JPH0367361B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a dielectric filter in which a resonant element is a hole formed in a dielectric block.

Prior art and problems In mobile radio devices such as portable or vehicle-mounted devices,
Dielectric filters are often used because they are small and have stable characteristics. Such a dielectric filter, for example,
As shown in the longitudinal cross-sectional view in Figure a and the cross-sectional view in Figure b along line A-A in the same figure, a dielectric block 1 in the shape of a rectangular parallelepiped made of a barium titanate dielectric with low dielectric loss, for example. , a plurality of holes 2-1 to 2-n are formed, and a conductive film using, for example, silver-platinum paste is formed on the lower surface, both side surfaces, and the inner surfaces of the holes 2-1 to 2-n. 3, 4, and 5 are formed, and an excitation body 7 is inserted near both ends of the dielectric block 1. The hole into which the exciter 7 is inserted is not metallized.

The lower surface and both side surfaces of the dielectric block 1 are housed in close contact with a casing 8 made of metal such as aluminum, and are connected to a connector 10 that constitutes an input/output terminal provided on the side surface of the casing 8. A cover plate 9 is connected to the excitation body 7 and is provided on the upper surface of the dielectric block 1 with a predetermined gap. This cover plate 9 has holes 2-1 to 2-n of the dielectric block 1.
Adjustment screws 11-1 to 11-n are provided correspondingly. These adjusting screws 11-1 to 11-n are used to finely adjust the resonant frequency of the resonant element constituted by each hole. Further, the holes 2-1 to 2-n of the dielectric block 1 are short-circuited by the casing 8 through the conductor film 5 on the inner surface thereof via the conductor film 3 on the lower surface. By setting the depth of n to 1/4 wavelength, a 1/4 wavelength filter can be constructed.

Such dielectric filters have good temperature characteristics and are strong against mechanical vibrations, so
Suitable for in-vehicle wireless equipment. However, since the dielectric block 1 is formed by a sintering method, the distance between the hole into which the excitation body 7 is inserted and the hole constituting the resonant element varies. If this distance is not a predetermined value, the capacitance value between them will also not be a predetermined value, resulting in variations in the amount of coupling between input and output. Dispersion in distance can be reduced by machining with a tool such as a diamond after firing, but there is a drawback that the cost increases due to the machining process. Also, due to variations in the diameter of the hole into which the excitation body 7 is inserted and the diameter of the excitation body 7, the excitation body 7
This causes variations in the contact state between the two, which is one of the causes of variations in the amount of bonding. This has been dealt with by adjusting the length of the metal rod constituting the exciter 7 depending on the contact state of the exciter 7, that is, the amount of coupling. In addition, in an antenna duplexer that combines filters through appropriate electrical lengths,
There was a problem in that the phase changed and was synthesized depending on the contact state of the exciter 7.

OBJECTS OF THE INVENTION An object of the present invention is to provide a dielectric filter that can reduce product variations and simplify adjustment. Examples will be described in detail below.

Embodiment of the Invention FIGS. 2a and 2b are a longitudinal cross-sectional view and a cross-sectional view taken along line B-B of an embodiment of the present invention, and the same reference numerals as in FIG. 1 indicate the same parts. Holes 2 at both ends of holes 2-1 to 2-n formed in dielectric block 1
The conductive film 5a on the inner surface of holes 2-1 and 2-n is
2 to 2--(n-1), and the metal rods 13 are inserted into the holes 2-1 and 2-n so as to contact the conductive film 5a. A flat capacitor 12 is placed on the metal rod 13, one electrode of the capacitor 12 is connected to the metal rod 13, and the other electrode is connected to the connector 10.
are connected. Therefore, since the amount of input/output coupling is determined by the capacitor 12 that provides uniform capacitance, there is no variation in the amount of coupling. Further, the conductor film 5 on the inner surface of the holes 2-1 and 2-n constituting the resonant element
If a is the same as the conductive film 5 on the inner surface of the other holes 2-2 to 2-(n-1), the dielectric constant ε of the dielectric block 1 is 40, and in the 900 MHz band λ/4 resonator. ,
When coupled with a 1 pF capacitor 12, the resonant frequency of the resonant element due to the holes 2-1 and 2-n at both ends is approximately
It is 30MHz lower. However, as in the above embodiment, by shortening the conductive film 5a on the inner surface of the holes 2-1 and 2-n at both ends by about 0.5 mm, the other holes 2-2 to 2-(n-1) could be made similar to the resonant frequency of .

FIG. 3 is an enlarged view of a part of FIG. 2a, and the conductor film 5a formed on the inner surface of the hole 2-1 at the end of the dielectric block 1 is shorter than the conductor film 5 on the inner surface of the other holes. , a metal rod 13 is connected to the conductor film 5a.
, place the flat capacitor 12 on the metal rod 13, and connect the connector 10 and capacitor 12.
Connect with. The amount of input/output coupling is determined by the capacitance of the capacitor 12, and since the amount of coupling does not depend on the processing accuracy of the dielectric block 1, variations in the amount of coupling are extremely small. Also, in assembling,
Since it is only necessary to insert the metal rod 13 and perform soldering to connect the capacitor 12, it can be manufactured easily and at low cost.

FIG. 4 shows an enlarged view of main parts of another embodiment of the present invention, and the same reference numerals as in FIGS. 2 and 3 indicate the same parts. In this embodiment, a flat capacitor 12 is placed on the upper surface of the end of the dielectric block 1, and a hole 2-1
This shows a case where the conductor film 5a on the inner surface of the conductor is connected to the conductor film 5a by a ribbon-shaped conductor 14. Instead of this ribbon-shaped conductor 14, it is also possible to form a conductor pattern at the same time when forming the conductor films 5, 5a, and to connect the capacitor 12 and the conductor film 5a by this conductor pattern. .

FIG. 5 shows an enlarged view of the main parts of still another embodiment of the present invention, and the same reference numerals as those in the previous figures indicate the same parts, and the metal rod in the embodiment of FIG. 3 is used. Instead, the capacitor 12 is inserted into the hole 2-1, and the conductor film 5a on the inner surface of the hole 2-1 is connected to one electrode of the capacitor 12.
The other electrode of the connector 10 is connected to the connector 10.

FIG. 6 is an enlarged view of main parts of still another embodiment of the present invention, which is similar to the embodiment shown in FIG. 5 in that the capacitor 12 is inserted into the hole 2-1, but the electrodes of the capacitor 12 are is composed of a center electrode and an outer peripheral electrode, the center electrode is connected to the connector 10, and the outer peripheral electrode is connected to the conductor film 5a on the inner surface of the hole 2-1.

FIG. 7 is an enlarged view of a main part of still another embodiment of the present invention, in which the capacitor 12 to be inserted into the hole 2-1 has a structure with a flange, and an electrode is provided on the outer peripheral surface of the part to be inserted into the hole 2-1. A conductive film 5a is formed on the inner surface of the hole 2-1.
The electrode formed on the upper surface of the capacitor 12 and the connector 10 are connected to each other.

Hole 2 in each embodiment shown in FIGS. 2 to 7
The conductor film 5a on the inner surface of hole 2-1, 2-n is formed shorter than the conductor film 5 on the inner surface of the other holes 2-2 to 2-(n-1), as described above. −
1, 2-n inner conductor film 5a and capacitor 12
The configuration is such that it is connected to the connector 10 via.

Effects of the Invention As explained above, the present invention provides a plurality of holes 2-
In the dielectric filter, conductor films 3, 4, and 5 are formed on the lower surface, both side surfaces, and the inner surface of the holes of a rectangular parallelepiped dielectric block 1 in which the holes 1 to 2-n are arranged in parallel. The conductor film 5a on the inner surface of the holes 2-1, 2-n at both ends is formed shorter than the conductor film 5 on the inner surface of the other holes, and the conductor film 5a on the inner surface of the holes 2-1, 2-n at both ends 5a is connected to the input/output terminal via the capacitor 12, and the amount of coupling is the capacitor 1.
Since the capacitance is determined by the capacitance of 2, it is not affected by dimensional errors due to firing of the dielectric block 1, and a dielectric filter with little variation can be constructed. Also, by making the conductor films 5a on the inner surfaces of the holes 2-1 and 2-n at both ends of the dielectric block 1 shorter than the conductor films 5 on the inner surfaces of the other holes, the reduction in the resonant frequency of the resonant element due to the holes at both ends can be prevented. It is possible to provide a dielectric filter that can be corrected and has stable characteristics.

[Brief explanation of drawings]

1A and 1B are vertical and horizontal cross-sectional views of a conventional dielectric filter, FIGS. 2A and 2B are vertical and horizontal cross-sectional views of an embodiment of the present invention, and FIG. FIGS. 4 to 7 are partially enlarged views of main parts of other embodiments of the present invention. 1 is a dielectric block, 2-1 to 2-n are holes,
3, 4, 5 are conductor films, 8 is a housing, 9 is a cover plate, 10
is a connector, 11-1 to 11-n are adjustment screws, 1
2 is a capacitor, 13 is a metal rod, and 14 is a ribbon-shaped conductor.

Claims (1)

[Claims] 1. In a dielectric filter in which a conductive film is formed on the lower surface, both side surfaces, and the inner surface of the holes of a rectangular parallelepiped dielectric block in which a plurality of holes are arranged in parallel, the inner surface of the hole at both ends of the plurality of holes. A dielectric filter characterized in that the conductor film is formed shorter than the conductor film on the inner surface of the other holes, and the conductor films on the inner surfaces of the holes at both ends are connected to input/output terminals via capacitors.