JP3343527B2 - Dielectric filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric filter formed by cascading a plurality of coaxial dielectric resonator blocks.

[0002]

2. Description of the Related Art A dielectric filter in which a dielectric material is filled between an inner conductor and an outer conductor in a coaxial dielectric resonator block to reduce its size has been conventionally known. Ceramics are generally used as a dielectric in the dielectric filter, and the dielectric filter using the ceramic can reduce the occupied volume, and has a small loss and excellent stability. have.

[0003] Such a dielectric filter is configured by cascade-connecting a plurality of dielectric resonator blocks, and a schematic configuration of the dielectric resonator block is shown in FIG. The dielectric resonator block 100 shown in FIG. 8 has a cylindrical outer conductor 101 having a diameter φ and a height 1 arranged inside a cylindrical outer conductor 101 so that the inner conductor 102 is coaxial with the outer conductor 101. A dielectric 104 is filled between the first and second electrodes 102. One surface of the dielectric resonator block 100 is a short-circuit surface 10 that short-circuits the outer conductor 101 and the inner conductor 102.
It is set to 3. The axial height l of the dielectric resonator block 100 is about λ / 4 when the resonance wavelength is λ.

When the dielectric 104 is made of ceramic, it is made of, for example, a cylindrical ceramic having a through hole therein, and the conductive film is entirely formed on the remaining surface except for only the upper surface thereof. Thus, the inner conductor 102 is formed by the conductive film formed in the through hole, the outer conductor 101 is formed by the conductive film formed on the outer peripheral surface, and the short-circuit surface 103 is formed by the conductive film formed on the lower surface. Thus, the dielectric resonator block 100 can be manufactured. Since the internal wavelength in the dielectric is an internal wavelength that is inversely proportional to the square root of the relative permittivity εr, the size can be reduced as the relative permittivity εr increases. For this reason, a dielectric filter using a plurality of the dielectric resonator blocks 100 described above is used as a filter for various wireless devices and the like that require miniaturization, such as an automobile telephone, a mobile telephone, and a PHS telephone.

[0005]

In such a dielectric resonator block 100, the internal conductor 1 is connected via a capacitor C100 for light coupling from the input terminal 105.
FIG. 9 shows an example of measured resonance characteristics by inputting a signal to the output terminal 02 and extracting an output signal from the output terminal 106 via the capacitor C101 which is lightly coupled to the internal conductor 102.
Shown in However, in FIG. 9, the diameter φ of the dielectric resonator block 100 is 16 mm, the relative permittivity εr of the dielectric 104 is 37, and the height l in the axial direction is 30 mm. Referring to this figure, several resonance frequencies are shown, of which the basic (λ / 4) resonance frequency A is about 0.4 GHz, and the three times (3λ / 4) resonance frequency B is The frequency is about 1.2 GHz, and the five-fold (5λ / 4) resonance frequency C is about 2 GHz. In addition, 7
A double (7λ / 4) resonance frequency D and a nine-fold (9λ / 4) resonance frequency E are shown. In addition to the resonance frequency of the coaxial mode, the resonance frequency of the waveguide mode,
It is shown. The resonance frequency of the waveguide mode is mainly determined by the coaxial outer dimension and the relative permittivity of the filled dielectric 104, and the resonance frequency is about 1.7 GHz.
The resonance frequency is about 2.7 GHz, and the resonance frequency is about 3.4 GHz.

When a plurality of dielectric resonator blocks 100 exhibiting such resonance characteristics are cascaded to form a dielectric filter having a pass band near 0.4 GHz, the dielectric filter is three times (3λ / coaxial mode). 4) A cascade connection of a low-pass filter for attenuating the resonance frequency or higher is performed, but the filter is tripled (3
λ / 4) It is sufficient to attenuate the resonance frequency or higher, so that a sufficient amount of attenuation can be obtained with a low-pass filter having a simple configuration. FIG. 10 shows the resonance characteristics of the dielectric resonator block 100 when the required pass band is set to a higher frequency. The dielectric resonator block 100 shown in FIG. 10 has a diameter φ of 16 mm so as to resonate near 0.6 GHz,
This is a case where the relative permittivity εr of the dielectric 104 is 37 and the height l in the axial direction is 20 mm.

Referring to FIG. 1, several resonance frequencies are shown. Among them, a fundamental (λ / 4) resonance frequency A is set to about 0.6 GHz, and a triple (3λ / 4) resonance frequency is set. Frequency B is about 1.8 GHz, 5 times (5λ / 4)
The resonance frequency C is about 3 GHz. The resonance frequency of the waveguide mode is shown in addition to the resonance frequency of the coaxial mode. The resonance frequency of the waveguide mode is about 1.8 GHz, and the resonance frequency is about 2.6 GHz.
Hz. That is, the resonance frequency of the coaxial mode shifts from 0.4 GHz and its integral multiple to 0.6 GHz and its integral multiple, but the resonant frequency of the waveguide mode hardly changes.

When a dielectric filter having a pass band near 0.6 GHz is constructed by cascade-connecting a plurality of dielectric resonator blocks 100 exhibiting such resonance characteristics, the resonance frequency of the waveguide mode is reduced. Since the resonance frequency is almost the same as the triple (3λ / 4) resonance frequency, it is three times (3λ / 3) of the coaxial mode.
4) a low-pass filter that attenuates the resonance frequency or higher
What is necessary is just to cascade connection. Also in this case, a sufficient amount of attenuation can be obtained with a low-pass filter having a simple configuration. FIG. 11 shows the resonance characteristics of the dielectric resonator block 100 when the required pass band is set to a higher frequency. In the dielectric resonator block 100 shown in FIG. 11, the diameter φ of the dielectric resonator block 100 is 16 mm, the relative permittivity εr of the dielectric 104 is 37, and the height l in the axial direction is such that resonance occurs near 0.8 GHz. Is 15
mm.

Referring to FIG. 1, several resonance frequencies are shown, of which the fundamental (λ / 4) resonance frequency A is about 0.8 GHz, and three times (3λ / 4) the resonance frequency The frequency B is set to about 2.4 GHz. The resonance frequency of the waveguide mode is shown in addition to the resonance frequency of the coaxial mode. The resonance frequency of the waveguide mode is about 2.0 GHz, which is three times as large as the coaxial mode (3λ /
4) The frequency becomes lower than the resonance frequency. That is, the resonance frequency of the coaxial mode shifts greatly from 0.6 GHz and its integral multiple to 0.8 GHz and its integral multiple, but the resonance frequency of the waveguide mode hardly changes.

When a plurality of dielectric resonator blocks 100 exhibiting such resonance characteristics are cascaded to form a dielectric filter having a pass band near 0.8 GHz, the resonance frequency of the waveguide mode is reduced. Since the frequency is lower than the triple (3λ / 4) resonance frequency, it is necessary to cascade connect a low-pass filter that attenuates the resonance frequency of the waveguide mode or higher. However, since the resonance frequency of the waveguide mode is lower than three times (3λ / 4) the resonance frequency of the coaxial mode, in order to obtain a sufficient attenuation, a low-pass filter having a large number of multi-stage elements is required. Required. By the way, it is known that the resonance frequency of the waveguide mode can be made higher than the resonance frequency three times (3λ / 4) of the coaxial mode by decreasing the diameter φ as the height l becomes shorter. ing. However, when the diameter φ is increased with respect to the height l, the no-load Q can be increased,
When a high unloaded Q is required, the diameter φ for the height 1 cannot be reduced. Therefore, when a high no-load Q is required, there is a problem that a multi-stage low-pass filter having a large number of elements is required. Then, since the multi-stage low-pass filter has a large insertion loss, there is also a problem that the low-pass filter insertion loss cancels out the small insertion loss in the dielectric filter obtained by the high no-load Q.

FIG. 11 shows the resonance characteristics of the dielectric resonator block 100 when the required pass band is set to a higher frequency. In the dielectric resonator block 100 shown in FIG. 11, the diameter φ of the dielectric resonator block 100 is 16 mm, the relative permittivity εr of the dielectric 104 is 37, and the height l in the axial direction is such that resonance occurs near 1.0 GHz. Is 12
mm. Referring to this figure, it can be seen that the above-mentioned problem is more remarkably exhibited.

That is, the fundamental (λ / 4) resonance frequency A is set to about 1.0 GHz, and the triple (3λ / 4) resonance frequency B is set to about 3.0 GHz. Is about 2.2 GHz, which is closer to the fundamental (λ / 4) resonance frequency of the coaxial mode. Therefore, when configuring a dielectric filter having a pass band around 1.0 GHz, it is necessary to obtain a sufficient amount of attenuation by using a low-pass filter configured in more stages. The use of a low-pass filter with a configuration increases the insertion loss, so that a small insertion loss in the dielectric filter obtained by a high unloaded Q is
There is a problem that the insertion loss of the low-pass filter cancels out.

Therefore, the present invention is applicable to a case where the diameter is increased with respect to the height to obtain a dielectric filter having a high unloaded Q.
An object of the present invention is to provide a dielectric filter which does not require a multi-stage lossy low-pass filter.

[0014]

In order to solve the above-mentioned problem, a dielectric filter according to the present invention is a dielectric filter comprising a plurality of cascade-connected coaxial dielectric resonator blocks. The resonance frequencies of the coaxial modes of the individual cascade-connected dielectric resonator blocks are substantially equal, and at least one of the plurality of cascade-connected dielectric resonator blocks has the same resonance frequency.
The resonance frequencies of the waveguide modes in the two dielectric resonator blocks are different.

Further, in the dielectric filter of the present invention, the relative permittivity of the dielectric in the dielectric resonator block having the different resonance frequency of the waveguide mode is set to be smaller than the relative permittivity of the dielectric in the other dielectric resonator block. You may make it different from a dielectric constant. Further, in the dielectric filter of the present invention, the diameter of a dielectric resonator block having a different resonance frequency in the waveguide mode may be different from the diameter of another dielectric resonator block. Still further, in the dielectric filter of the present invention, the relative permittivity and the diameter of the dielectric in the dielectric resonator block having a different resonance frequency of the waveguide mode are different from those of the dielectric in the other dielectric resonator block. The relative permittivity and the diameter may be different from each other.

According to such a dielectric filter of the present invention, a plurality of cascade-connected individual dielectric resonator blocks have substantially the same coaxial mode resonance frequency, and at least one cascade-connected dielectric resonator block has at least one cascaded resonance frequency. The resonance frequency of the waveguide mode in the dielectric resonator block is made different. As a result, even when the diameter is increased with respect to the height to obtain a dielectric filter having a high no-load Q, the attenuation at the resonance frequency of the waveguide mode can be increased without connecting a low-pass filter. it can. Therefore, even if the diameter is increased with respect to the height to obtain a high no-load Q, it is not necessary to secure the attenuation at the resonance frequency of the waveguide mode by the low-pass filter. As described above, since the low-pass filter only needs to attenuate a frequency equal to or higher than the resonance frequency three times (3λ / 4) of the coaxial mode, the configuration can be simplified. Therefore,
The loss caused by the low-pass filter is also reduced, and a dielectric filter having stable attenuation characteristics can be realized without substantially impairing the low loss characteristics obtained by the dielectric filter having a high no-load Q.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view showing a configuration example of an embodiment of a dielectric filter according to the present invention. However, FIG. 1 shows a six-stage configuration, and the low-pass filter is not shown. In FIG. 1, a dielectric filter 1 according to the present invention comprises:
Six-stage dielectric resonator blocks 11, 12, 13, 14,
15 and 16 are connected in cascade.
The input terminal 2 is connected to the internal conductor 11b of the first dielectric resonator block 11 via the first coil L1, and the output terminal 3 is connected to the inside of the sixth dielectric resonator block 16 via the seventh coil L7. It is connected to the conductor 16b. The first dielectric resonator block 11 to the sixth dielectric resonator block 16 have the same configuration, and the configuration will be described below by taking the first dielectric resonator block 11 as an example.
The first dielectric resonator block 11 is formed entirely on the remaining surface except for the upper surface of a dielectric 11d made of, for example, a cylindrical ceramic having a through hole. Thereby, the internal conductor 11b is formed by the conductive film formed in the through hole.
Are formed, the outer conductor 11a is formed by the conductive film formed on the outer peripheral surface, and the short-circuit surface 11c is formed by the conductive film formed on the lower surface, so that the first dielectric resonator block 11 is formed.
Has been created.

The second to sixth dielectric resonator blocks 12 to 16 have the same configuration, and the first to sixth dielectric resonator blocks 11 to 1 are used.
The sixth stage is connected by the second coil L2 to the sixth coil L6. These six-stage dielectric resonator blocks 11,
The resonance characteristics of 12, 13, 14, 15, and 16 are not all the same, but dielectric resonator blocks showing two types of pass characteristics are prepared. For example, the first dielectric resonator block 11, the third dielectric resonator block 13,
The fourth dielectric resonator block 14 and the sixth dielectric resonator block 16 are the dielectric resonator blocks A having the same first pass characteristic shown in FIG. 2, and the remaining second dielectric resonator blocks 12 and The fifth dielectric resonator block 15 is a dielectric resonator block B exhibiting the second pass characteristic shown in FIG.

The dielectric resonator block A which has the first pass characteristic shown in FIG. 2 has a pass frequency (basic (λ / 4) resonance frequency) of 0.825 GHz, a diameter φ of 17 mm,
The relative permittivity εr of the dielectric is 44. FIG.
Dielectric resonator block B having the second pass characteristic shown in FIG.
Has a pass frequency (basic (λ / 4) resonance frequency) of 0.825 GHz, a diameter φ of 16 mm, and a relative permittivity εr of 37 for the dielectric. As described above, the relative permittivity εr of the dielectric resonator block B from which the second pass characteristic is obtained is smaller than the relative permittivity εr of the dielectric resonator block A from which the first pass characteristic is obtained. , Its height l is slightly lengthened. Further, the diameter φ of the dielectric resonator block A from which the first pass characteristic can be obtained.
Is 15 mm, whereas the diameter φ of the dielectric resonator block B from which the second pass characteristic is obtained is slightly increased to 16 mm.

As described above, when the heights of the dielectric resonator blocks having different dielectric constants are set so that the resonance frequencies of the coaxial modes become similar, the waveguides are not guided in the first pass characteristic shown in FIG. Tube mode pass frequency is about 1.9G
In contrast, in the second pass characteristic shown in FIG. 3, the pass frequency ′ of the waveguide mode is different from about 2 GHz. Since the pass frequency band of the waveguide mode is extremely sharp as shown in the figure, the dielectric filter 1 having the configuration shown in FIG. 1 in which the dielectric resonator blocks having the first pass characteristic and the second pass characteristic are mixed is shown. As shown in Fig. 4, the attenuation at the pass frequency "in the waveguide mode" cancels out each other, resulting in a large attenuation of about 65 dB. / 4) A basic (λ / 4) resonance frequency of 0.825 GH is provided by preceding or following a simple low-pass filter that attenuates the resonance frequency or higher.
The dielectric filter can pass only a predetermined frequency band in the z band. The number and arrangement of the dielectric resonator block A having the first pass characteristic and the dielectric resonator block B having the second pass characteristic are not limited to the example shown in FIG. The dielectric filter 1 may be configured by using at least one dielectric resonator block having each pass characteristic. Also, the number of stages is not limited to six, but can be a desired number.

In the above-mentioned example, the resonance frequency of the waveguide mode is made different by changing the diameter φ and the relative permittivity εr of the dielectric, but only the relative permittivity εr is changed while the diameter φ is kept constant. Even in this case, the resonance frequency of the waveguide mode can be made different. For example, FIG.
The resonance characteristic of the dielectric resonator block shown in FIG.
Although the relative dielectric constant εr is 6 mm, the height l is 15 mm, and the diameter φ of the dielectric resonator block is 16
FIG. 5 shows resonance characteristics when the basic (λ / 4) resonance frequency of the coaxial mode is also about 0.8 GHz, with mm, the relative dielectric constant εr being 44, the height l being 13.8 mm. FIG.
5 and FIG. 5, while the resonance frequency of the waveguide mode in FIG. 11 is about 2.0 GHz, the resonance frequency ′ of the waveguide mode shown in FIG.
It is different from 8 GHz. Therefore, by mixing the dielectric resonator block having the resonance characteristics shown in FIG. 11 and the dielectric resonator block having the resonance characteristics shown in FIG. 5, the attenuation at the resonance frequency of the waveguide mode can be obtained without using a low-pass filter. Can be formed.

Furthermore, the resonance frequency of the waveguide mode can be varied by changing only the diameter φ while keeping the relative permittivity εr of the dielectric resonator block constant. For example, the resonance characteristics of the dielectric resonator block shown in FIG. 6 are such that the diameter φ is 16 mm, the relative permittivity εr is 44, the height is 15 mm, and the fundamental (λ / 4) resonance frequency of the coaxial mode is about 0. 0.7 GHz, but the diameter φ of the dielectric resonator block is 12 mm, the relative permittivity εr is 44, and the height is 15
FIG. 7 shows resonance characteristics when the basic (λ / 4) resonance frequency of the coaxial mode is set to about 0.7 GHz. 6 and 7, while the resonance frequency of the waveguide mode in FIG. 6 is about 1.7 GHz, the resonance frequency ′ of the waveguide mode shown in FIG. 7 is about 2.0 GHz. Is different. Accordingly, by mixing the dielectric resonator block having the resonance characteristic shown in FIG. 6 and the dielectric resonator block having the resonance characteristic shown in FIG. 7, the attenuation at the resonance frequency of the waveguide mode can be obtained without using a low-pass filter. Can be formed.

As described above, the resonance frequency of the waveguide mode can be varied by changing the diameter φ and the relative permittivity εr of the dielectric resonator block. It is possible to make the diameter φ larger than the height 1 like a body resonator block. Therefore, even if the no-load Q of the dielectric resonator block is increased, a low-pass filter having a simple configuration may be connected.
The loss of a dielectric filter in which a plurality of such dielectric resonator blocks are connected in cascade can be reduced, and the no-load Q can be greatly improved compared to the related art. In the above description, the dielectric resonator blocks are L-coupled using a coil in the present invention, but may be C-coupled using a capacitor instead.
Further, an L bond and a C bond may be mixed.

[0024]

Since the present invention is configured as described above, the resonance frequencies of the plurality of cascade-connected individual dielectric resonator blocks in the coaxial mode are made substantially equal, and at least the plurality of cascade-connected dielectric resonator blocks are connected. The resonance frequency of the waveguide mode in one dielectric resonator block is made different. As a result, even when the diameter is increased with respect to the height to obtain a dielectric filter having a high no-load Q, the attenuation at the resonance frequency of the waveguide mode can be increased without connecting a low-pass filter. it can. Therefore, even if the diameter is increased with respect to the height to obtain a high no-load Q, it is not necessary to secure the attenuation at the resonance frequency of the waveguide mode by the low-pass filter. As described above, since the low-pass filter only needs to attenuate a frequency equal to or higher than the resonance frequency three times (3λ / 4) of the coaxial mode, the configuration can be simplified. Therefore,
The loss caused by the low-pass filter is also reduced, and a dielectric filter having stable attenuation characteristics can be realized without substantially impairing the low loss characteristics obtained by the dielectric filter having a high no-load Q.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration example of a dielectric filter according to an embodiment of the present invention.

FIG. 2 is a diagram showing a first pass characteristic of a dielectric resonator block constituting the dielectric filter of the present invention.

FIG. 3 is a diagram showing a second pass characteristic of a dielectric resonator block constituting the dielectric filter of the present invention.

FIG. 4 is a diagram showing the pass characteristics of the dielectric filter of the present invention.

FIG. 5 is a diagram showing another resonance characteristic of the dielectric resonator block constituting the dielectric filter of the present invention.

FIG. 6 is a diagram showing still another resonance characteristic of the dielectric resonator block constituting the dielectric filter of the present invention.

FIG. 7 is a diagram showing still another resonance characteristic of the dielectric resonator block constituting the dielectric filter of the present invention.

FIG. 8 is a diagram showing a configuration of a dielectric resonator block in a conventional dielectric filter.

FIG. 9 is a diagram illustrating an example of a resonance characteristic of a dielectric resonator block in a conventional dielectric filter.

FIG. 10 is a diagram illustrating an example of a resonance characteristic when a resonance frequency is increased in a dielectric resonator block.

FIG. 11 is a diagram illustrating an example of resonance characteristics when the resonance frequency is further increased in the dielectric resonator block.

FIG. 12 is a diagram illustrating an example of resonance characteristics when the resonance frequency is further increased in the dielectric resonator block.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Dielectric filter 2,105 Input terminal 3,106 Output terminal 11,12,13,14,15,16,100 Dielectric resonator block 11a, 101 Outer conductor 11b, 16b, 102 Inner conductor 11c, 103 Short-circuit surface 11d , 104 Dielectric C100, C101 Capacitor L1-L7 Coil

──────────────────────────────────────────────────の Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01P 1/205 H01P 1/212 JICST file (JOIS)

Claims (4)

(57) [Claims] 1. A dielectric filter comprising a plurality of cascade-connected dielectric resonator blocks, wherein the plurality of cascade-connected dielectric resonator blocks have substantially the same coaxial mode resonance frequency. And a resonance frequency of a waveguide mode in at least one of the plurality of cascaded dielectric resonator blocks is different from each other. 2. The relative permittivity of a dielectric in a dielectric resonator block having a different resonance frequency of the waveguide mode is made different from the relative permittivity of a dielectric in another dielectric resonator block. The dielectric filter according to claim 1, wherein: 3. The dielectric resonator block according to claim 1, wherein a diameter of the dielectric resonator block having a different resonance frequency in the waveguide mode is different from a diameter of another dielectric resonator block. Dielectric filter. 4. The relative permittivity and diameter of a dielectric in a dielectric resonator block having a different resonance frequency of the waveguide mode are respectively set to the relative permittivity and diameter of a dielectric in another dielectric resonator block. 2. The dielectric filter according to claim 1, wherein the dielectric filters are different.