JP3291498B2 - 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.

[0002]

2. Description of the Related Art Conventionally, as a dielectric filter using a dielectric coaxial resonator, a through hole is provided in a dielectric member, and a conductive member (an outer peripheral surface of the dielectric member and an inner peripheral surface of the through hole are provided on the dielectric member). For example, a single-sided short-circuit type coaxial resonator formed by coating silver) is connected to a dielectric substrate, and each coaxial resonator is capacitively coupled by an electrode formed on the dielectric substrate. ing.

[0003] In recent years, in mobile communication, weight reduction and volume reduction have been progressing, and accordingly, there has been a demand for miniaturization of dielectric filters.

Incidentally, in order to obtain a high Qu (Q value at no load), it is necessary to set the ratio of the inner coaxial diameter to the outer coaxial diameter to 3.6. For this reason, when reducing the size of the dielectric filter, for example, if the outer coaxial diameter is 4 mm or less, the inner coaxial diameter is 1.2 mm or less, and the external connection member passes through the coaxial resonator as described above. It is difficult to connect to an external circuit by inserting it into the hole.

As a dielectric filter which solves this problem, the present applicant has proposed Japanese Patent Application No. 2-196572.

When a filter is constituted by three or more stages of coaxial resonators, the size of the middle stage coaxial resonator is made larger than that of the first and second stage coaxial resonators in order to make the resonance frequency of each resonator different. There is a need to. For this reason, there is a problem that coaxial resonators of various lengths are required.

On the other hand, in a mobile communication device, a duplexer for separating and combining signals of different frequencies in accordance with the frequency is used. Such a duplexer includes a transmitting dielectric filter and a receiving dielectric filter having different center frequencies. With such a dielectric filter, with the increase in the frequency of mobile communication,
The interval between the center frequencies of the reception band and the transmission band has become narrow, making it difficult to obtain the necessary out-of-band attenuation. For this reason, a dielectric filter used for a duplexer is required to have an attenuation pole in its characteristics.

As a method of forming a pole in an attenuation region, for example, in a dielectric filter disclosed in Japanese Patent Application Laid-Open No. 62-77703, at least one resonator is skipped and a direct reactance element is used between the resonators. By connecting, such a pole is formed.

However, this configuration has a problem that the number of parts increases and assembly becomes complicated.

[0010] In order to solve this problem, Japanese Patent Application No. 3-4 / 1993 discloses a method for solving this problem.
No. 6,796, proposes a dielectric filter as shown in FIGS. This dielectric filter will be described with reference to the drawings.
A filter is configured using the coaxial resonators ₁₁ to ₁₅ . A concave portion 2 is provided in each of the resonators ₁₁ to ₁₅ , and a dielectric substrate 3 ′ is attached to the concave portion 2. The resonators ₁₁ to ₁₅ are coupled to each other via a coupling window.

As shown in FIG. 14, the dielectric substrate 3 'has input / output connection electrodes 3a', 3a "and capacitance forming electrodes 3c ', 3c", 3c "" on the upper surface, and the lower surface, as shown in FIG. Are formed with stub electrodes 3d 'and 3d "for external connection, which are extended from the electrodes 3a' and 3a" for input and output, and a ground electrode 3b.

The input / output connection electrodes 3a ', 3
a "and resonator ₁ 1, 1 ₅ terminal capacitance between C1, C1 '
Is formed. Also, the capacitance forming electrodes 3c ', 3c ",
3c '''coaxial resonator 1 _2, 1 _3, 1 ₄ of the conductor 1d _2,
1d _3, the resonator length compensation capacitance C2 between 1d _4, C'2,
C ″ 2 is formed. Further, the input / output side connection electrode 3 is formed.
a ′, 3a ″ and capacitance forming electrodes 3c ′, 3c ″, 3
Jump capacitances C3, C'3, and C "3 are formed between the capacitors C '" and c'".

As shown in FIGS. 15 and 16, in this dielectric filter, a pole P is formed in the attenuation region of the filter characteristic due to the jump capacitors C3, C3 'and C3 ".

[0014]

However, in the above-described dielectric filter, when the grounding of the grounding electrode 3b of the dielectric substrate 3 is incomplete, the grounding electrode 3b is connected between the connecting electrodes 3d 'and 3d ". In particular, in a microwave band of 1 GHz or more, it is difficult to obtain perfect grounding, which causes a serious problem.

That is, it is practically difficult to take a complete ground, and an impedance component is included between the ground and the ground electrode 3b. In this case, of the power coming from the input side, a part of the power not coupled to the resonator side is directly coupled to the output side via the capacitor. At this time, in the frequency characteristics of the filter, the attenuation outside the band is significantly deteriorated.

To prevent this, it is conceivable to remove the grounding electrode 3b from the dielectric substrate 3. However, noise from an external circuit or element adjacent thereto may cause the internal conductor of the resonators ₁₁ to ₁₅ or the dielectric substrate 3 Connection electrodes 3d ', 3
d ", which leads to deterioration of filter characteristics.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a miniaturized dielectric filter in which the anti-resonance capacitance and the coupling between the coaxial resonators for obtaining a filter characteristic having an attenuation pole can be manufactured with good workability. .

Still another object of the present invention is to provide a dielectric filter which prevents direct coupling between input and output via a ground electrode due to incomplete grounding of the ground electrode. It is in.

Further, an object of the present invention is to provide a high-order TEM (Transevers e
An object of the present invention is to provide a dielectric filter capable of eliminating undesired filter characteristics at a resonance frequency of an (electromagnetic) mode.

[0020]

SUMMARY OF THE INVENTION In view of the above, a dielectric filter according to the present invention has a first conductor layer and a second conductor layer by coating a conductive member on an outer peripheral surface and an inner peripheral surface, respectively. Is formed, and at least one of the plurality of coaxial resonators has a different resonator length from another coaxial resonator in the dielectric filter including a plurality of coaxial resonators having one end face short-circuited. It has a resonator length and has the same basic resonance frequency as the other coaxial resonator due to the resonance frequency correction capacitor connected to the second conductor layer.

[0021]

According to the dielectric filter of the present invention, in a plurality of coaxial resonators having the same basic resonance frequency, even if the basic resonance frequency is the same due to the resonance frequency correction capacitance,
Since the resonator lengths are different, the higher-order resonance frequency components are different,
Without complicating the circuit, it is possible to realize a small-sized dielectric filter in which the pass characteristics at the resonance frequency of the higher-order TEM mode are suppressed and the undesired filter characteristics are improved.

[0022]

[Embodiment] By the way, as shown in FIG.
3, C′3, C ″ 3, the dielectric filter in which the pole P is formed in the attenuation region of the filter characteristic, when the grounding of the grounding electrode 3b of the dielectric substrate 3 ′ is incomplete, the connection electrode 3
Capacitive coupling occurs between d ′ and 3d ″ via the grounding electrode 3b, which significantly degrades the filter characteristics.
It is difficult to obtain perfect grounding in the microwave band of Hz or higher, and attenuation outside the band is significantly deteriorated in the frequency characteristics of the filter.

The first to third embodiments of the present invention relate to a dielectric filter used for forming a pole P in an attenuation region of a filter characteristic by jumping coupling, in which the grounding of a grounding electrode is incomplete. This prevents direct coupling between input and output that occurs via the ground electrode due to the above.

FIG. 1 shows a first embodiment of the present invention, in which a first coaxial resonator 50 and a second coaxial resonator 51 constitute a dielectric filter. One coaxial resonator 50 is on the input side, and the second coaxial resonator 51 is on the output side. The coaxial resonators 51 and 52 are made of Ti provided with through holes.
O ₂ -SnO ₂ -ZrO ₂ based dielectric member (relative permittivity 4
This is a single-sided short-circuit type coaxial resonator in which the outer peripheral surface of 0) and the inner peripheral surface of the through hole are coated with a conductive material such as silver. And the first
The coaxial resonator 50 and the second coaxial resonator 51 are formed with concave portions 52 and 52 ′, respectively.
A dielectric substrate 53 made of alumina having an input-side connection electrode 53a and an output-side connection electrode 53a 'shown in FIG. 1D is attached to the connection electrode 52a.
3a 'and inner conductors 50d, 51 of the coaxial resonators 50, 51
The bond with d 'is performed.

The coupling (coupling between stages) between the coaxial resonators 50 and 51 is determined by the outer conductors 50c and 50c of the respective coaxial resonators 50 and 51.
This is achieved by joining together windows (not shown) formed by removing a part of 51c.

As shown in the bottom view of FIG. 1C, first and second grounding electrodes are provided on the back surface of the dielectric substrate 53 corresponding to the input and output connection electrodes 53a and 53a ', respectively. 53b and 53b 'are formed. The distance between the first and second grounding electrodes 53b and 53b 'is a distance that does not cause coupling and prevents the entry of noise, and is, for example, 0.2 mm.

FIG. 2 is a diagram showing an equivalent circuit of the dielectric filter of the first reference example, wherein C1 and C1 'denote the coaxial resonator 50,
A coupling capacitance formed between the inner conductors 50 d and 51 d ′ of 51 and the connection electrodes 53 a and 53 a ′ of the dielectric substrate 53;
C2 and C2 'are capacitances formed between the connection electrodes 53a and 53a' and the first and second ground electrodes 53b and 53b ', C3 is an interstage coupling capacitance, and Z and Z' are ground electrodes. 53
b, 53b 'are impedance components generated when the grounding is incomplete.

FIG. 3 is a diagram showing the frequency characteristics of the dielectric filter of the first reference example, and the broken line is that of the dielectric filter having the structure shown in FIG. As is clear from this characteristic diagram, by dividing the ground electrode formed on the back surface of the dielectric substrate 53, direct coupling between input and output is prevented,
The out-of-band attenuation characteristics of the filter are improved.

FIG. 4 is a view showing a second embodiment of the present invention, in which a filter is constituted by using four coaxial resonators 61 to 64. 4A is a perspective view, and FIG. 4B is a bottom view. Each of the resonators 61 to 64 is provided with a concave portion 65, and a dielectric substrate 70 is attached to the concave portion 65. Each of the resonators 61 to 64 has a coupling window (not shown).
Are connected through.

On the dielectric substrate 70, input / output side connection electrodes 70a, 70a 'and capacitance forming electrodes 70c, 7
0c ', and the input / output side connection electrodes 70a, 7
External connection stub electrodes 70d, 70 extended from 0a '
d ', the connection electrodes 70a, 70a' and the capacitance forming electrodes 70c, 70c '
_{1 ~70b 4} is formed.

The input / output connection electrodes 70a, 70
Input / output coupling capacitors C21 and C21 'are formed between a' and the inner conductors 61d and 64d of the coaxial resonators 61 and 64.
Further, the capacitance forming electrodes 70c and 70c 'and the coaxial resonator 6
Resonator length correcting capacitors C24 and C24 'are formed between the inner conductors 62d and 63d of the second and 63 inner conductors.

FIG. 5 shows an equivalent circuit of the dielectric filter of the second reference example. In the circuit diagram, C23, C23 ', C2
3 ″ is an inter-stage coupling capacitance, and C25 and C25 ′ are capacitances formed between the capacitance forming electrodes 70C and 70C ′ and the grounding electrodes 70b ₂ and 70b ₃ .

In the second embodiment, when a pole P is formed in the attenuation region of the filter characteristic, at least one resonator is skipped and the resonators are connected by a transmission line. For example, the input / output side connection electrode 70a and the capacitance forming electrode 70c '
And input / output side connection electrode 70a 'and capacitance forming electrode 70c
May be connected by a transmission line, or one of them may be jump-connected.

FIG. 6 shows a third embodiment of the present invention.
In the dielectric member 81a ', a plurality of through holes 81b, 81b',
81b '', an example of a dielectric filter including a plurality of coaxial resonators, one end of which is short-circuited, in which an outer conductor 81c and an inner conductor are formed by coating a conductive member on the outer peripheral surface and the inner peripheral surface. Is shown.

In the third reference example, a part of the outer conductor on the open surface side of each coaxial resonator or a part of the outer conductor including the dielectric member is removed to form a recess 82, and the recess 82 is formed in the recess 82. Dielectric substrate 83 having external connection electrodes 83a and 83a 'and grounding electrodes 83b and 83b' formed substantially at the center.
Is attached to form a dielectric filter.

In the third embodiment, similarly to the second embodiment, when the capacitance forming electrode is formed on the dielectric substrate, the ground electrode provided on the back surface is divided accordingly.

In the sixth embodiment, when the pole P is formed in the attenuation region of the filter characteristic, the external connection electrode 8
By connecting 3a and 83a 'with transmission lines, respectively,
One resonator is skipped to connect the resonators.

According to the first to third embodiments, the ground electrode formed on the back surface of the dielectric substrate having at least the external connection electrode attached to the concave portion of the coaxial resonator is replaced with the external connection electrode and the ground electrode. Since a plurality of electrodes are provided separately from each other in correspondence with the capacitance forming electrodes, direct coupling between the input and output is prevented, thereby improving the out-of-band attenuation in the frequency characteristics of the filter without impairing the noise shielding effect. be able to.

By the way, in the above-described dielectric filter using the coaxial resonator, by short-circuiting one side of the resonator, a quarter-wavelength that resonates at a quarter of the wavelength at the resonance frequency is generated. A filter using a cavity resonator is well known.

For example, in the dielectric filter shown in FIG. 1, a TiO ₂ -ZrO ₂ -SnO ₂ ceramic is used as a resonator material, and its relative dielectric constant εr is 40.
The dimensions of the coaxial resonators 50 and 51 are such that one side of the cross section perpendicular to the length direction has a length of 3 mm, the diameter of the through hole is 1 mm,
Assuming that the resonator length is 4.6 mm, the characteristic impedance Z ₀ is 12Ω.

In such a dielectric filter, impedance matching occurs in a specific frequency band when viewed from the input side, and exhibits characteristics of a band-pass filter. The resonance condition of the quarter-wave resonator is given by the following equation (1).

[0042]

## EQU1 ## Z ₀ · tan (β · 1) = ∞ (1) (where β is a propagation constant in the resonator)

The resonator length 1 is given by Expression 2 where c is the speed of light.

[0044]

1 = c / (4f ₀ εr ^1/2 ) (2) From the equation (2),

[0045]

F ₀ = c / (4l ₀ εr ^1/2 ) (3)

Therefore, the resonance frequency of the coaxial resonators 50 and 51 in FIG. 1 is 2.6 GHz.

Incidentally, since the resonator constituting the filter usually has two or more resonance modes, it may exhibit undesirable filter characteristics. For example, in order to minimize the resonator length in a quarter-wavelength resonator, a fundamental TEM mode is usually used, but a higher-order TEM having a resonance frequency which is an odd multiple of the frequency of the fundamental TEM mode is used. Mode exists. In the dielectric filter shown in FIG.
The resonance frequency of the mode is 2.6 GHz,
The resonance frequency of the higher order TEM mode is 7.8, 13.0, 1
It exists around 8.2 GHz. FIG. 7 shows the frequency characteristics of the dielectric filter of FIG. The reason why a large resonance characteristic appears at the resonance frequency of the higher-order TEM mode is that the coaxial resonators 50 and 51 strengthen each other because the resonance frequencies of the higher-order TEM mode are equal.

Thus, an undesired filter characteristic having a center frequency near an odd multiple of the center frequency of the desired filter characteristic appears. Such undesired filter characteristics have various adverse effects on microwave equipment. For example, when the filter on the receiving side has such unnecessary filter characteristics, a microwave in another band enters the circuit. When the filter on the transmission side has such unnecessary filter characteristics, microwaves other than the original transmission frequency are emitted into space.

The first embodiment and the second embodiment of the present invention are small in size, do not complicate the circuit, and have a high order T.
An object of the present invention is to provide a dielectric filter that can eliminate undesired filter characteristics at the resonance frequency of the EM mode.

FIG. 8 is a view showing a dielectric filter according to the first embodiment of the present invention. A single-sided short-circuit type coaxial resonator 90,
In the dielectric member 100, a conductive member such as silver is coated on the outer peripheral surface and the inner peripheral surface of the dielectric member provided with the through holes except for the open surfaces 90a and 100a. The resonator material is TiO ₂ -Zr
O ₂ -SnO a _2-based ceramic, the dielectric constant 4
0.

The coaxial resonator 90 is the same as that shown in FIG. 1, and its resonance frequency is 2.6 GHz.
The coaxial resonator 100 has a capacitance forming portion 1 on the open surface 100a.
01 is attached. FIG. 9A shows a coaxial resonator 100.
9B is an exploded perspective view of the capacitor forming unit 101, and FIG.

The dimensions of the coaxial resonator 90 are such that the length of one side of a cross section perpendicular to the length direction is 3 mm, the diameter of the through hole is 1 mm, and the resonator length is 4.6 mm. The dimensions of the coaxial resonator 100 are such that one side of a cross section perpendicular to the length direction has a length of 3 mm,
The diameter of the through hole is 0.8 mm, and the resonator length is 2.3 mm.

On the open surface 100a of the coaxial resonator 100, a first conductor 100d electrically connected to the outer conductor 100b is provided.
And the second conductor 1 electrically connected to the inner conductor 100c
00e is formed.

The capacitance forming portion 101 is formed of a quadrangular prism-shaped dielectric member 102 having a bottom surface substantially the same as the open surface 100a of the coaxial resonator 100. This dielectric material may be the same as that of the coaxial resonator, or another dielectric material. The dielectric member 102 is provided with a through hole 102a, and a capacitor forming conductor 102b is provided on one surface. The surface of the capacitor forming portion 101 where no conductor is formed is attached to the open surface 102 a of the coaxial resonator 100 with an adhesive or a dielectric paste 96. The capacitor forming conductor 102b of the capacitor forming portion 101 is formed by the first conductor 100d and the second conductor 1 on the open surface 100a of the coaxial resonator 100.
00e, the resonance frequency correction capacitors C31 and C32 are formed.

The coaxial resonator 100 and the capacitance forming section 101
Is set to 2.6 GHz as in the case of the coaxial resonator 90, and the combined capacitance C of the resonance frequency correction capacitors C31 and C32 is set to 5 pF. The combined capacitance C is obtained from Expression 4 indicating the resonance condition of the resonator.

[0056]

## EQU4 ## Z ₀ tan (β1) = 1 / (2πf ₀ C) (4)

Then, the resonance frequency of the higher order TEM mode of this resonator appears around 11.1, 21.0 and 31.2 GHz. On the other hand, since the resonator lengths of the coaxial resonators 90 and 100 are different, the resonance frequencies of the high-order TEM mode of the coaxial resonator 90 are 7.8, 13.0, and 18.2 GHz.
different from z. Therefore, since the respective harmonic components are not added, undesired filter characteristics are suppressed.

The coaxial resonators 90 and 100 are provided with a concave portion 95 in the same manner as the dielectric filter of FIG. 1, and the concave portion 95 has a dielectric substrate 110 on which external connection electrodes 110a and 110b are formed. Installed. The external connection electrodes 110a and 110b are connected to the inner conductors 90C and 100C of the coaxial resonators 90 and 100 by an input / output coupling capacitance C3.
3. Form C34. Also, the coaxial resonators 90 and 100
Are coupled via a coupling window (not shown) formed in the outer conductor.

FIG. 10 is an equivalent circuit of the dielectric filter according to the first embodiment of the present invention shown in FIGS. 8, 9A and 9B. In the figure, L is the resonator 90 and the resonator 100 of FIG.
And the coupling inductance between the two. C31 is shown in FIG.
This is a capacitance between the capacitance forming conductor 102b of (B) and the first conductor 100d of the coaxial resonator 100, and one end is connected to the coaxial resonator 100 via an earth as an equivalent circuit. . C32 is the capacitance forming conductor 102b
And a second conductor 100e of the coaxial resonator 100. One end is connected to the capacitor C31, and the other end is connected to the coaxial resonator 100 (the inner conductor 100c). In addition,
C33 and C34 are input / output coupling capacitances.

FIG. 11 is a diagram showing the frequency characteristics of the dielectric filter of FIG. Compared to the frequency characteristic of FIG.
This characteristic diagram shows that the pass characteristic at the resonance frequency of the EM mode is suppressed.

FIGS. 12A to 12C are cross-sectional views showing the second embodiment, in which the configuration of the capacitance forming portion 101 attached to the coaxial resonator 100 is different. In the resonator shown in FIG. 12A, a first conductor 100e electrically connected to the inner conductor 100c is formed on the open surface 100a of the coaxial resonator 100, and a capacitance for electrically connecting to the outer conductor 100b is formed. The dielectric member 102 on which the conductor 102b is formed is attached to the open surface 100a of the coaxial resonator 100. The first conductor 100e and the outer conductor 100b
Is separated from each other by a gap between the two conductors 100e and 100b (where there is no hatching in the cross section).

The resonator shown in FIG.
A first conductor 100d electrically connected to the outer conductor 100b is formed on the open surface 100a of the first member, and the dielectric member 102 on which the capacitor forming conductor 102b electrically connected to the inner conductor 100c is formed. It is attached to the open surface 100a of the resonance 100. The first conductor 100d and the inner conductor 1
00c is, as shown, both conductors 100d and 100c
Gap (where there is no cross-section hatching)
Are separated by

FIG. 12C shows that a plurality of capacitance forming conductors 102b are alternately arranged facing each other in the capacitance forming portion 101, so that a large capacitance can be formed.

In the above-described embodiment, the resonance main fraction correction capacitance is connected to the inner conductor of only one of the pair of coaxial resonators. May be the same. By doing so, the length of both coaxial resonators can be shortened, so that the filter can be downsized.

As described above, according to the first and second embodiments, the pass characteristic at the resonance frequency of the higher-order TEM mode is suppressed without complicating the circuit, and the undesired filter characteristics are reduced. , A small-sized dielectric filter with improved characteristics can be realized.

[0066]

As described above, according to the dielectric filter of the present invention, in a plurality of coaxial resonators having the same fundamental resonance frequency, even if the fundamental resonance frequency is the same due to the resonance frequency correction capacitance, Since the lengths are different, the high-order resonance frequency components are different, and without complicating the circuit, the pass-through characteristic at the high-order TEM mode resonance frequency is suppressed, and the small-sized dielectric body in which the undesirable filter characteristics are improved. A filter can be realized.

[Brief description of the drawings]

FIG. 1A is an external perspective view of a first embodiment of the present invention, FIG. 1B is a cross-sectional view, FIG. 1C is a bottom view, and FIG. 1D is a dielectric substrate. FIG.

FIG. 2 is an equivalent circuit diagram of a dielectric filter according to a first reference example of the present invention.

FIG. 3 is a frequency characteristic diagram of the dielectric filter according to the first reference example of the present invention.

FIG. 4A is an external perspective view of a second reference example of the present invention, and FIG. 4B is a bottom view.

FIG. 5 is an equivalent circuit diagram of a dielectric filter according to a second reference example of the present invention.

FIG. 6A is an external perspective view of a third embodiment of the present invention, and FIG. 6B is a bottom view.

FIG. 7 is a frequency characteristic diagram of a dielectric filter according to a third reference example of the present invention.

FIG. 8 is an external perspective view showing a dielectric filter according to the first embodiment of the present invention.

FIG. 9A is an exploded perspective view showing a resonator including a coaxial resonator and a capacitor forming unit according to the first embodiment of the present invention, and FIG. 9B is a diagram including a coaxial resonator and a capacitor forming unit. It is a cross-sectional view showing a resonator.

FIG. 10 is a diagram showing an equivalent circuit of the dielectric filter according to the first embodiment of the present invention.

FIG. 11 is a frequency characteristic diagram of the dielectric filter according to the first embodiment of the present invention.

12 (A) to 12 (C) show a second embodiment of the present invention.
It is sectional drawing which shows an Example.

FIG. 13A is an external perspective view of a conventional dielectric filter, and FIG. 13B is a transverse sectional view.

14A is a perspective view of a dielectric substrate in a conventional dielectric filter, FIG. 14B is a bottom view of the dielectric substrate, and FIG. 14C is a cross-sectional view of the dielectric substrate. is there.

FIG. 15 is an equivalent circuit diagram of a conventional dielectric filter.

FIG. 16 is a frequency characteristic diagram of a conventional dielectric filter.

[Explanation of symbols]

50, 51, 61, 62, 63, 64, 90, 100
Coaxial resonators 50c, 51c, 61c, 62c, 63c, 64c, 9
0c, 100c Outer conductors 50d, 51d, 61d, 62d, 63d, 64d, 9
0d, 100d Inner conductor 52, 52 ', 65, 95 Depression 53, 70, 110 Dielectric substrate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-50401 (JP, A) JP-A-61-237501 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01P 1/20-1/219 H01P 7/00-7/10

Claims (2)

(57) [Claims] 1. A plurality of coaxial resonators having a first conductor layer and a second conductor layer formed by coating a conductive member on an outer peripheral surface and an inner peripheral surface, respectively, and having one end surface short-circuited. In the dielectric filter, at least one coaxial resonator among the plurality of coaxial resonators has a resonator length shorter than a resonator length of another coaxial resonator, and is connected to a second conductor layer. A dielectric filter having the same basic resonance frequency as the other coaxial resonator due to a frequency correction capacitor. 2. The resonance frequency correction capacitor is formed by attaching a dielectric member having a conductor for forming a capacitor on an open surface of a coaxial resonator.
3. The dielectric filter according to item 1.