JPH06334405A - Dielectric filter - Google Patents

Abstract

PURPOSE:To increase the attenuation at a lower frequency region than a center frequency of the dielectric filter. CONSTITUTION:First and second resonance holes 4a, 4b and a coupling hole 5 are provided to a box shaped dielectric block 1. Inner conductors 6a, 6b are provided to the 1st and 2nd resonance holes 4a, 4b. An outer conductor film 8 is provided to four side faces 7a, 7b, 7c, 7d of the dielectric block 1 and a conductor film is provided also to the end faces. A groove is provided to the end face conductor film so as to pass through a coupling hole 5 and a groove 11 is provided also to a conductor film 8 of the side faces 7a, 7b by extending the groove provided to the end face conductor film. Two resonators are capacitance-coupled by the operation of the groove 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric filter for use in tuners of television receivers, mobile phones, cordless phones and the like.

[0002]

2. Description of the Related Art A quarter-wave coaxial type dielectric filter is disclosed in, for example, Japanese Patent Application Laid-Open No. 1-277001 (Japanese Patent Application No. 63-108070).
As disclosed in Japanese Laid-Open Patent Publication No. 2004-163242, a rectangular parallelepiped dielectric block having a plurality of resonance holes (through holes) and a coupling hole between them, an inner conductor film provided in the resonance hole, and a dielectric block. The outer conductor film is provided on the four side surfaces of the body block, and the end face (short circuit) conductor film is provided on one end face of the dielectric block. When connecting this dielectric filter to a signal transmission line as a bandpass filter, connect an input coupling capacitor to the inner conductor film of the resonance hole of the input stage and an output coupling capacitor to the inner conductor film of the resonance hole of the output stage. Connecting.

[0003]

By the way, the frequency characteristic of a bandpass filter using a conventional dielectric filter is as shown by a characteristic line B shown by a dotted line in FIG. As is clear from this frequency characteristic, the attenuation on the low frequency side of the resonance center frequency f0 changes gently, and it could not be used for equipment that requires abruptly changing attenuation.

Therefore, an object of the present invention is to set the center frequency f0.
An object of the present invention is to provide a dielectric filter that can obtain steep attenuation characteristics on the lower frequency side.

[0005]

According to the present invention for achieving the above object, there are provided first and second end faces facing each other and an outer peripheral surface between the first and second end faces. A dielectric block having a plurality of resonance holes extending from the end face toward the second end face and a coupling hole provided between the plurality of resonance holes, and wall surfaces of the plurality of resonance holes, respectively. An inner conductor film provided, an outer conductor film provided on the outer peripheral surface of the dielectric block, and an end face provided on the second end face so as to connect the inner conductor film and the outer conductor film. In a dielectric filter including a conductor film, the end face conductor film is provided so that a strip-shaped dielectric exposed portion that is continuous with the coupling hole of the second end face is formed, and the dielectric of the second end face is formed. A dielectric exposed portion that is continuous with the body exposed portion occurs on the side surface. It is intended according to the dielectric filter, wherein the urchin the outer conductor layer is provided.

[0006]

According to the present invention, strip-shaped dielectric exposed portions (conductor film non-forming regions) provided on the end faces and side faces according to the present invention.
Has a function of converting the mutual coupling of the plurality of resonators based on the plurality of resonance holes into capacitive coupling. That is, in the conventional dielectric filter, the resonators are mainly magnetically coupled (M-coupled), but when the dielectric exposed portion (conductor film non-formed region) is provided continuously to the coupling hole according to the present invention. The magnetic coupling is weakened to become mainly capacitive coupling (C coupling). In the case of the conventional M coupling, the attenuation characteristic on the low frequency side is worse than that on the high frequency side of the resonance center frequency, but when the C coupling is strengthened according to the present invention, the attenuation characteristic on the low frequency side becomes steep.

[0007]

EXAMPLE A 1/4 wavelength coaxial dielectric filter according to an example of the present invention will be described below with reference to FIGS. This dielectric filter includes a rectangular parallelepiped dielectric block 1 made of barium titanate porcelain. The dielectric block 1 is provided with first and second resonance holes 4a and 4b, which are through holes extending from the first end surface 2 to the second end surface 3, and one coupling hole 5. First and second inner conductor films 6a and 6b are provided on the wall surfaces of the resonance holes 4a and 4b, respectively, and the outer peripheral surface between the pair of end surfaces 2 and 3, that is, the four side surfaces 7a and 7b.
An outer conductor film 8 is provided on b, 7c and 7d, and an end face conductor film 9 is provided on the second end face 3 so as to connect the inner conductor films 6a and 6b to the outer conductor film 8. Inner conductor film 6a, 6
b, the outer conductor film 8 and the end face conductor film 9 are made of, for example, a conductor which is coated with silver paste and baked. The first end face 2
Has an open end face and no conductor film is provided.

As shown in FIG. 4, a strip-shaped dielectric exposed portion (conductor film non-formed area) 1 is formed on the end face conductor film 9 of the dielectric filter.
A groove (notch) 10 is provided so as to generate 0a, and the second end face 3 is exposed in a band shape. Moreover, the grooves 11 and 12 are formed so that the strip-shaped dielectric exposed portions 11a and 12a are also formed on the outer conductor film 8 on the two opposing side surfaces 7a and 7b.
Is provided, and the side surfaces 7a and 7b are exposed in a strip shape. The groove 10 of the end face conductor film 9 has the first and second resonance holes 4a, 4 and
b and the connecting holes 5 are arranged so as to extend in a direction orthogonal to the direction in which they are arranged (the direction of the line AA in FIG. 1) and include the open end of the connecting holes 5. Therefore, the end surface conductor film 9
Is divided into left and right by a groove 10. Two sides 7a, 7
The grooves 11 and 12 in b are orthogonal to the line AA of FIG. The dimensions of each part of this embodiment are illustrated below. The dielectric block 1 has a horizontal width of 3 mm, a vertical width of 6 mm, and a height of 8 mm. The diameter of the first and second resonance holes 4a and 4b is 2.8 mm, and the diameter of the coupling hole 5 is 1 mm.
Is. The width of the groove 10 of the end face conductor film 9 is 1 mm, and the outer conductor film 8 is
The grooves 11 and 12 have a width W of 1 mm and a length L of 1 mm. The length L of the grooves 11 and 12 is equal to the height of the dielectric block 1.
It is desirable to make it 1/10 or more.

First and second coupling capacitors 1 arranged so as to be partially inserted into the resonance holes 4a and 4b, respectively.
Reference numerals 3 and 14 are porcelain capacitors in which a pair of electrodes are provided on a tubular capacitor porcelain dielectric. First and second terminals 15, 16 for connecting the dielectric filter to an external circuit
Consists of one of the leads of the first and second coupling capacitors 13, 14. The other leads 17, 18 of the coupling capacitors 13, 14 are connected to the first and second inner conductors 6a, 6b by connecting conductors 19, 20, respectively.

First and second coupling capacitors 13, 14
The shield member 21 and the insulator 21 are made of a common synthetic resin 2
It is integrated by two. This integration is performed before disposing the first and second coupling capacitors 13 and 14 in the resonance holes 4a and 4b. The shield member 21 includes an upper surface portion 23 that covers the upper side of the coupling hole 5, a pair of side surface portions 24 and 25 for connecting to the outer conductor film 8 of the pair of long side surfaces 7 a and 7 b of the dielectric block 1, and an external circuit. It is composed of four protrusions 26 for use in mounting on a substrate (not shown) and connection to a ground, and is formed in a U shape as a whole.

FIG. 6 shows an equivalent circuit of the dielectric filter.
The first resonance circuit composed of the capacitor C1 and the inductance L1 is formed based on the inner conductor film 6a of the first resonance hole 4a, the outer conductor film 8 and the end face conductor film 9 which are grounded, and the capacitor C2 and the inductance L2. And a second resonance circuit composed of the inner conductor film 6b of the second resonance hole 4b, the outer conductor film 8 and the end face conductor film 9 which are grounded, and the two resonance circuits are coupled by the impedance Z. ing. The input and output coupling capacitors Ca and Cb of FIG. 6 correspond to the capacitors 13 and 14 of FIG. 2, and the input and output terminals T1,
T2 corresponds to the terminals 15 and 16 in FIG.

A characteristic line A in FIG. 7 shows the frequency characteristic of the dielectric filter (bandpass filter) of this embodiment. The center frequency of this dielectric filter is 965.25 MHz,
A characteristic line B indicated by a dotted line shows the characteristic of the dielectric filter of the conventional structure in which the grooves 10, 11, and 12 are removed from the dielectric filter of FIGS. As is clear from the comparison of the characteristic lines A and B, this embodiment makes it possible to make the attenuation on the low frequency side steeper than the center frequency f0. This is because the first and second resonators are capacitively coupled (C-coupled) as described above.

The characteristic line C shown by the broken line in FIG. 7 is the side surfaces 7a, 7a.
The characteristics when the width W of the grooves 11 and 12 of the conductor film 8 of b are narrowed a little compared with the case of FIGS. As is clear from this, when the width W of the grooves 11 and 12 is narrowed, the pass band width of the frequency characteristic is narrowed and the low frequency side becomes steeper. In addition,
The size of the width of the groove 10 in the end face conductor film 9 does not significantly affect the frequency characteristic. Also, the groove 1 on the side surfaces 7a, 7b
Even if the length L of 1 and 12 is increased, the frequency characteristic does not change so much.

[0014]

MODIFICATION The present invention is not limited to the above-mentioned embodiments, and the following modifications are possible. (1) As shown in FIG. 8, if necessary, the grooves 11 and 12 of the conductor film 8 on the pair of side surfaces 7a and 7b of the dielectric block 1, that is, the dielectric exposed portions 11a and 12a are formed from the second end surface 3 to the first side.
Can be formed so as to reach the end face 2. (2) As shown in FIGS. 9 to 11, a dielectric block 1 is provided with three resonance holes 4a, 4b, 4c, and coupling holes 5a, 5b are provided between them to form a three-stage dielectric filter. By applying the present invention, the end face conductor film 9 may be provided with the groove 10, that is, the dielectric exposed portion, and the outer conductor film 8 on the side surfaces 7a and 7b may be provided with the grooves 11, 12 that is the dielectric exposed portion. 9 to 10 are the same as those of the embodiment of FIGS. 1 to 5 except that the number of resonance holes is increased, the same parts are designated by the same reference numerals and the description thereof will be omitted. Furthermore, the number of resonance holes can be four or more. The pass band shifts to the lower frequency side as the number of resonance holes is increased. (3) It is possible to adopt a configuration in which one of the grooves 11 and 12 on the two side surfaces 7a and 7b of the dielectric block 1 is not provided. In this case, the C bond is weakened, but some effect can be obtained. (4) The dielectric block 1 can be formed into an elliptic cylinder.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of the dielectric filter taken along the line AA of FIG.

3 is a perspective view showing only a dielectric block having a conductor film by removing the assembly of the input and output coupling capacitors and the shield member from FIG. 1. FIG.

4 is a bottom view of a dielectric block having the conductor film of FIG.

5 is a front view of a dielectric block having the conductor film of FIG.

FIG. 6 is an equivalent circuit diagram of the dielectric filter of FIG.

FIG. 7 is a diagram showing frequency characteristics of the dielectric filter of FIG. 1 and another dielectric filter in which the width of the groove is changed and a conventional dielectric filter.

FIG. 8 is a front view of a modified dielectric filter.

FIG. 9 is a plan view of a dielectric filter of another modification.

10 is a bottom view of the dielectric filter of FIG. 9. FIG.

11 is a front view of the dielectric filter of FIG. 9. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Dielectric block 4a, 4b Resonance hole 5 Coupling hole 8 Outer conductor film 9 End face conductor film 10, 11, 12 Groove

Claims (1)

[Claims] 1. A plurality of first and second end surfaces facing each other and an outer peripheral surface between the first and second end surfaces, and extending from the first end surface toward the second end surface. Dielectric blocks having resonance holes and coupling holes provided between the plurality of resonance holes, inner conductor films respectively provided on wall surfaces of the plurality of resonance holes, and the outer periphery of the dielectric block. A dielectric filter including an outer conductor film provided on a surface, and an end face conductor film provided on the second end face so as to connect the inner conductor film and the outer conductor film, The end surface conductor film is provided so that a strip-shaped dielectric exposed portion continuous with the coupling hole of the end surface is formed, and a dielectric exposed portion continuous with the dielectric exposed portion of the second end surface is formed on the side surface. As described above, the outer conductor film is provided. That dielectric filter.