Dielectric filter, dielectric duplexer and communication device

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dielectric filter, a dielectric duplexer, and a communication device.

2. Description of the Related Art

A known dielectric filter in which a plurality of dielectric resonators are provided in a dielectric block is shown in FIG.

20

. The dielectric filter

200

is formed in a dielectric block

201

having a generally parallelepiped shape. A pair of resonator holes

202

a

and

202

b

are formed in the dielectric block, each hole extending between opposing surfaces

200

a

and

200

b

of the dielectric block. The resonator holes

202

a

and

202

b

have large-diameter hole portions

222

a

and

222

b

, and small-diameter hole portions

223

a

and

223

b

communicating with the large-diameter hole portions

222

a

and

222

b

, respectively.

As best shown in

FIG. 21

, the end walls

224

a

and

224

b

of the large-diameter hole portions

222

a

and

222

b

and end walls

225

a

and

225

b

of the small-diameter hole portions

223

a

and

223

b

are formed in a common plane. The axes of the small diameter hole portions

223

a

and

223

b

are displaced from those of the large diameter hole portions

222

a

and

222

b

with the result that relatively small communication areas b are formed between the respective large and small diameter hole portions.

An outer conductor

204

is formed on five of the six outer surfaces of the dielectric block. The front surface

200

a

is not plated. A pair of input/output electrodes

205

are formed on the outer surface of the dielectric block

201

and are spaced from the outer conductor

204

so as to be electrically isolated therefrom. Inner conductors

203

are formed on the entire inner surface of each of the resonator holes

202

a

and

202

b

. The end of the inner conductors

203

located at the front surface

200

a

of the dielectric block is electrically open (i.e., spaced from, and thereby isolated from, the outer conductor

204

). The end of the inner conductors

203

located at the rear surface

200

b

is short-circuited (physically connected) to the outer conductor

204

.

The outer conductor

204

and inner conductors

203

are typically formed on the dielectric block

201

by wet plating. However, with wet plating, the plating liquid in the vicinity of a surface to be plated must be circulated so that new plating liquid is constantly supplied to the surface. To this end, plating liquid is typically stirred or the workplace is moved in the plating liquid to promote the circulation of the plating liquid.

As best shown in

FIG. 21

, the connection portions b between the large and small diameter portions are narrow. This results in poor penetration of the plating liquid through the resonator holes

202

a

and

202

b

, and thus results in a smaller supply of new plating liquid and insufficient plating. With this arrangement, therefore, it is difficult to provide the desired film thickness for the inner conductor

203

to be formed on the inner surface of the resonator holes

202

a

and

202

b.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a dielectric filter, dielectric duplexer, and communication device, which allow the formation of an inner conductor on the inner surfaces of resonator holes with sufficient thickness and stability.

To this end, according to a first aspect of the present invention, there is provided a dielectric filter includes a dielectric block having a plurality of resonator holes therein, an inner conductor formed on the inner surface of each of the resonator holes, and an outer conductor formed on the outer surface of the dielectric block. At least one of the resonator holes comprises a large-diameter hole portion and a small-diameter hole portion communicating with the large-diameter hole portion. The axis of the large-diameter hole portion and the axis of the small-diameter hole portion are displaced from each other so that the at least one of the resonator holes has a bent shape. The large-diameter hole portion and the small-diameter hole portion overlap each other along their respective axial directions.

With this arrangement, the connection portion of the large-diameter hole portion and the small-diameter hole portion is larger in cross section (as measured along a plane lying perpendicular to the main direction of flow of plating liquid through the connection portion) than the connection portion of the known resonator hole, thereby improving the passage of plating liquid through the resonator hole. As a result, it is easier to ensure that the film thickness of the inner conductor of the large-diameter hole portion and the small-diameter hole portion is at desired levels, thus allowing an increase of the Q-value of the resonator. This makes it possible to broaden the passband of the dielectric filter and to facilitate the achievement of the small-sized dielectric filter having an acute attenuation characteristic and high performance.

Preferably, the dielectric filter includes at least two bent resonator holes located adjacent one another and the interaxial distance between the small-diameter hole portions of two adjacent resonator holes is greater than, equal to, or smaller than the interaxial distance between the large-diameter hole portions thereof.

According to a second aspect of the present invention, there is provided a dielectric duplexer. The dielectric duplexer which includes the dielectric filter according to the first aspect of the present invention.

According to a third aspect of the present invention, there is provided a communication device which includes a dielectric duplexer according to the second aspect of the present invention.

Since the dielectric duplexer and the communication device according to the present invention include the dielectric filter having the above-mentioned features, they can provide improved electric characteristics similar to those of the dielectric filter of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.

FIG. 1

is a perspective view of a dielectric filter according to a first embodiment of the present invention;

FIG. 2

is a front view of the dielectric filter, viewed from the side of an open-circuited end surface, according to the first embodiment;

FIG. 3

is a sectional view of the dielectric filter, taken along line III—III, according to the first embodiment;

FIG. 4

is a schematic vertical sectional view illustrating a method for press molding of the dielectric filter according to the first embodiment;

FIG. 5

is a schematic vertical sectional view illustrating a process subsequent to the process shown in

FIG. 4

;

FIG. 6

is a schematic vertical sectional view illustrating a process subsequent to the process shown in

FIG. 5

;

FIG. 7

is a schematic vertical sectional view illustrating a process subsequent to the process shown in

FIG. 6

;

FIG. 8

is a front view of a dielectric filter, viewed from the side of an open-circuited end surface, according to a second embodiment of the present invention;

FIG. 9

is a sectional view of the dielectric filter, taken along line IX—IX, according to the second embodiment;

FIG. 10

is a front view of a dielectric filter, viewed from the side of an open-circuited end surface, according to a third embodiment of the present invention;

FIG. 11

is a sectional view of the dielectric filter, taken along line XI—XI, according to the third embodiment;

FIG. 12

is a perspective view of a dielectric duplexer according to a fourth embodiment of the present invention;

FIG. 13

is a rear view of the dielectric duplexer, viewed from the side of a short-circuited end surface, according to the fourth embodiment of the present invention;

FIG. 14

is a plan view of the dielectric filter according to the fourth embodiment;

FIG. 15

is a block circuit diagram of a communication device according to a fifth embodiment of the present invention;

FIG. 16

is a front view of a dielectric filter according to another embodiment of the present invention;

FIG. 17

is a horizontal-section view of a dielectric filter according to another embodiment of the present invention;

FIG. 18

is a front view of a dielectric filter according to still another embodiment of the present invention;

FIG. 19

is a perspective view of a dielectric filter according to yet another embodiment of the present invention;

FIG. 20

is a perspective view of a dielectric filter of known art; and

FIG. 21

is a sectional view of the dielectric filter, taken along XXI—XXI, of the known art.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A dielectric filter, a dielectric duplexer, and a communication device according to embodiments of the present invention will be described below with reference to the appended drawings. Throughout the embodiments, like elements and like portions are denoted with the same reference numerals and the description thereof will be omitted for simplicity.

First Embodiment

A first embodiment of the present invention will now be described with reference to

FIGS. 1

to

7

. Referring first to

FIG. 1

, a dielectric filter

1

according to a first embodiment of the present invention has a pair of resonator holes

2

a

and

2

b

each extending between opposing surfaces

1

a

and

1

b

of the dielectric filter

1

. The resonator holes

2

a

and

2

b

include large-diameter hole portions

22

a

and

22

b

, preferably having circular cross-sections, and small-diameter hole portions

23

a

and

23

b

, also preferably having circular cross-sections, and communicating with the large-diameter hole portions

22

a

and

22

b

, respectively. The distance d

1

(

FIG. 2

) between the central axes of the small-diameter hole portions

23

a

and

23

b

is greater than the distance d

2

between the central axes of the large diameter hole portions

22

a

and

22

b

with the result that the axes of the small-diameter hole portions

23

a

and

23

b

are displaced from those of the large-diameter hole portions

22

a

and

22

b

, respectively, by a displacement distance P. The displacement distance P falls within a range R−r<P<R+r, where R is the radii of the large-diameter hole portions

22

a

and

22

b

and r is the radii of the small-diameter hole portions

23

a

and

23

b

. Thus, the resonator holes

2

a

and

2

b

have bent (non-aligned) shapes and will be referred to herein as bent resonator holes.

As shown in

FIG. 1

, an outer conductor

4

and a pair of input/output electrodes

5

are formed on the outer surface of the dielectric filter

1

(on the outer surface of the dielectric block

6

in which the filter is formed). The input/output electrodes

5

are spaced from the outer conductor

4

so as to be electrically isolated therefrom. The outer conductor

4

is located on almost the entire outer surface of the dielectric block

6

, but not in the regions in which the input/output electrodes

5

are formed and not on the open-circuited end surface

1

a

. Inner conductors

3

are formed on the entire inner surfaces of the resonator holes

2

a

and

2

b

. The inner conductors

3

are electrically open (i.e., isolated from the outer conductor

4

) at the open-circuited end surface

1

a

, and are short-circuited (i.e., connected to the outer conductor

4

) at the short-circuited end surface

1

b

. In addition, the axial length L of the resonator holes

2

a

and

2

b

is designed to be about λ/4 (where λ is the center wavelength of the resonators corresponding to the resonator holes

2

a

and

2

b

). External coupling capacitance is provided between respective inner conductors

3

of the resonator holes

2

a

and

2

b

and the input/output electrodes

5

.

Referring now to

FIG. 3

, the large-diameter hole portions

22

a

and

22

b

and the small-diameter hole portions

23

a

and

23

b

overlap each other in the axial directions of the resonator holes

2

a

and

2

b

in the regions indicated by dotted lines E. That is, the combined length of the large-diameter hole portions

22

a

and

22

b

(the axial length L

1

from the surface

1

a

to end walls

24

a

and

24

b

of the large-diameter hole portions

22

a

and

22

b

) and the small-diameter hole portions

23

a

and

23

b

(the axial length L

2

from the surface

1

a

to end walls

25

a

and

25

b

of the small-diameter hole portions

23

a

and

23

b

) is longer than a length L of the resonator holes

2

a

and

2

b

(the length from the surface la to the surface

1

b

) by an overlapping length A. As a result, the length a of the cross-sections of the connection portions as measured along a plane lying perpendicular to the main direction of flow of plating liquid through the connection portion is larger than the length of the corresponding connection portions b of the known dielectric filter (see FIG.

21

). Thus, the resonator holes

2

a

and

2

b

have shapes which facilitate the passage of plating liquid therethrough, and it is possible to form inner conductor

3

with a constant desired thickness. As a result, the dielectric filter

1

can have an improved Q-value compared to the prior art filter.

The interaxial distance d

2

between the axes of the large-diameter hole portions

22

a

and

22

b

of the resonator holes

2

a

and

2

b

is selected by the designer of the filter primarily as a function of the number of resonator holes to be formed in the dielectric block. Thereafter, the designer selects the degree of offset of the small-diameter hole portions to adjust the coupling between adjacent resonators. Because the interaxial distance d

1

between the small-diameter hole portions

23

a

and

23

b

(located at the side of the short-circuited end surface

1

b

) is greater than the interaxial distance d

2

between the large-diameter hole portions

22

a

and

22

b

, the magnetic field energy ratio between the adjacent resonators is decreased and the capacitive coupling between adjacent resonators is increased. Thus, stronger capacitive coupling is provided between two resonators formed with the resonator holes

2

a

and

2

b

. With this arrangement, a dielectric filter

1

having stronger capacitive coupling can be provided without changing the external shape or the dimensions thereof.

Now, an example of a method of forming the dielectric block of the dielectric filter

1

by press molding will be described with reference to

FIGS. 4

to

7

. As shown in

FIG. 4

, the press molding machine has a lower die

76

and an upper die

77

. The lower die

76

is provided with a die

70

, a lower punch

71

, and lower core bars

71

a

and

71

b

which are slidable relative to the lower punch

71

. The die

70

has a cavity

70

a

with a rectangular cross-section, and the lower punch

71

is fitted into the cavity

70

a

. The lower core bars

71

a

and

71

b

have substantially the same shape and size as the large-diameter hole portions

22

a

and

22

b

, respectively, and have cylindrical shapes with radii R. The upper die

77

is provided with an upper punch

72

, and upper core bars

72

a

and

72

b

which are slidable relative to the upper punch

72

. The upper core bars

72

a

and

72

b

have substantially the same shapes and size as the small-diameter hole portions

23

a

and

23

b

, respectively, and have cylindrical shapes with radii r. Inclined portions

73

are formed at the lower ends of the upper core bars

72

a

and

72

b

, and inclined portions

74

are formed on the upper ends of the lower core metals

71

a

and

71

b

, respectively.

The positions of the lower die

71

and the upper die

77

are independently servo-controlled. AC servo motors M

1

, M

2

, M

3

, and M

4

are utilized to actuate (lift and lower) the lower core bars

71

a

and

71

b

, the die

70

, the upper punch

72

, and the upper core bars

72

a

and

72

b

, respectively. With the upper surface of the lower punch

71

being a reference surface, the position of the lower surface of the upper punch

72

, the positions of lower surfaces of the upper core bars

72

a

and

72

b

, the upper surfaces of the lower core bars

71

a

and

71

b

, and the distance of the upper surface of the die

70

from the reference surface are measured on a linear scale (not shown). The AC servo motors M

1

to M

4

are numerically controlled on the basis of each piece of the measured positional information.

In operation, the inclined portions

74

of the lower core bars

71

a

and

71

b

are first lifted to a position higher than a surface f

1

, the cavity

70

a

is filled with a predetermined amount of dielectric powder

80

, and then the upper die

77

is lowered. Once the upper die

77

reaches a position where inclined portions

73

of the upper core bars

72

a

and

72

b

, respectively, come into contact with the inclined portions

74

of the lower core bars

71

a

and

71

b

, the lowering of the upper die

77

stops. In the subsequent process, the contacts between the inclined portions

73

of the upper core bars

72

a

and

72

b

and the inclined portions

74

of the lower core bars

71

a

and

71

b

form the connection portions a, shown in

FIG. 3

, of the resonator holes

2

a

and

2

b

, respectively.

As shown in

FIG. 5

, with the inclined portions

73

of the upper core bars

72

a

and

72

b

being in contact with the inclined portions

74

of the lower core bars

71

a

and

71

b

, the upper core bars

72

a

and

72

b

and the lower core bars

71

a

and

71

b

are slid toward the lower punch

71

so that no pressure is applied to the dielectric powder

80

within the cavity

70

a

. Subsequently, once the upper core bars

72

a

and

72

b

and the lower core bars

71

a

and

71

b

reach a predetermined position within the cavity

70

a

, the lowering of the upper core bars

72

a

and

72

b

and the lower core bars

71

a

and

71

b

stops.

Next, as shown in

FIG. 6

, the die

70

, the upper punch

72

, the lower core bars

71

a

and

71

b

, and the upper core bars

72

a

and

72

b

are moved downward, so that the dielectric powder

80

is compressed under pressure to form the dielectric body

6

. In this case, with the inclined portions

73

of the upper core bars

72

a

and

72

b

being in contact with the inclined portions

74

of the lower core bars

71

a

and

71

b

, respectively, the upper core bars

72

a

and

72

b

and the lower core bars

71

a

and

71

b

are slid downward.

After the compression is completed, as shown in

FIG. 7

, the die

70

and the lower core bars

71

a

and

71

b

are moved downward and the upper punch

72

and the upper core bars

72

a

and

72

b

are moved upward, so that a molded dielectric block is removed from therebetween.

As an alternative method for the formation, after molding a dielectric block by compressing under pressure, the opposing surfaces thereof may be machined with large-and small-diameter end mills to form the resonator holes, respectively.

Second Embodiment

A second embodiment will now be described with reference to

FIGS. 8 and 9

. In a dielectric filter

1

of the second embodiment, as shown in

FIG. 8

, the interaxial distance d

3

between small-diameter hole portions

23

c

and

23

d

is configured to be smaller than the interaxial distance d

4

between large-diameter hole portions

22

c

and

22

d

. In addition, as shown in

FIG. 9

, the large-diameter hole portions

22

c

and

22

d

and the small-diameter hole portions

23

c

and

23

d

overlap each other in regions indicated by dotted lines E, in the axial directions of the resonator holes

2

c

and

2

d

, respectively. As a result, the connection portions a of the large-diameter hole portions

22

c

and

22

d

and the small-diameter hole portions

23

c

and

23

d

are larger in cross section than the connection portions b of the known dielectric filter (see FIG.

21

). Thus, the resonator holes

2

c

and

2

d

have shapes which facilitate the passage of plating liquid therethrough, thereby allowing the formation of the inner conductor

3

on the inner surfaces of the resonator holes

2

c

and

2

d

with sufficient film thickness and stability. As a result, the dielectric filter

1

can improve the Q-value of the resonator.

As shown in

FIG. 8

, this dielectric filter

1

is configured such that the interaxial distance d

3

between the small-diameter hole portions

23

c

and

23

d

at the side of the short-circuited end surface

1

b

(see

FIG. 9

) is smaller than the interaxial distance d

4

between the large-diameter hole portions

22

c

and

22

d

, resulting in an increased electromagnetic field (i.e., magnetic) coupling between the adjacent resonators. With this arrangement, it is possible to provide the dielectric filter

1

having stronger inductive coupling without changing the external shape or the dimensions thereof.

Third Embodiment

A third embodiment of the present invention will now be described with reference to

FIGS. 10 and 11

. In a dielectric filter

1

of the third embodiment, as shown in

FIG. 10

, the interaxial distance d

5

between small-diameter hole portions

23

e

and

23

f

is configured to be equal to the interaxial distance d

6

between large-diameter hole portions

22

e

and

22

f

. In addition, as shown in

FIG. 11

, the large-diameter hole portions

22

e

and

22

f

and the small-diameter hole portions

23

e

and

23

f

overlap each other in regions indicated by dotted lines E, in the axial directions of the resonator holes

2

e

and

2

f

, respectively.

Since the dielectric filter

1

according to the third embodiment has a structure similar to those of the first and second embodiments, it offers advantages similar to the dielectric filters thereof. Moreover, this dielectric filter

1

offers more flexibility in designing the degree of electromagnetic field coupling.

Fourth Embodiment

A fourth embodiment of the present invention will now be described with reference to

FIGS. 12

to

14

. The fourth embodiment is directed to a dielectric duplexer for use in a mobile communication device such as a mobile telephone.

FIG. 12

is a perspective view of a dielectric duplexer

51

, viewed from the side of an open-circuited end surface

51

a

, with the mounting surface (the surface adapted to be surface mounted to a circuit board)

51

c

facing upward.

FIG. 13

is a rear view of the dielectric duplexer

51

, viewed from the side of a short-circuited end surface

51

b

, with the mounting surface

51

c

facing downward.

FIG. 14

is a plan view of the dielectric duplexer

51

.

Referring to

FIG. 12

, the dielectric duplexer

51

has an open-circuited end surface

51

a

and a short-circuited end surface

51

b

which oppose each other and which are generally rectangular. Seven resonator holes

52

a

to

52

g

are also formed in a line so as to extend between the pair of end surfaces

51

a

and

51

b

. An external coupling hole

55

a

and a ground hole

56

a

are formed between the resonator holes

52

a

and

52

b

. Similarly, an external coupling hole

55

b

and a ground hole

56

b

, and an external coupling hole

55

c

and a ground hole

56

c

are formed between the resonator holes

52

c

and

52

d

, and

52

f

and

52

g

, respectively.

Referring to

FIG. 14

, the resonator holes

52

a

to

52

g

include large-diameter hole portions

62

a

to

62

g

having circular cross-sections, and small-diameter hole portions

63

a

to

63

g

having circular cross-sections and communicating with the large-diameter hole portions

62

a

to

62

g

, respectively. The axes of the small-diameter hole portions

63

c

to

63

f

are displaced from the axes of the large-diameter hole portions

62

c

to

62

f

, respectively, such that the displacement distance P therebetween is within a range which satisfies the relationship R−r<P<R+r, where R is the radii of the large-diameter hole portions

62

c

to

62

f

and r is the radii of the small-diameter hole portions

63

c

to

63

f

(i.e., the large and small diameter hole portions overlap one another along their axial directions). Thus, the resonator holes

52

c

to

52

f

have bent shapes.

The interaxial distance d

11

between the small-diameter hole portions

63

b

and

63

c

is configured to be smaller than the interaxial distance d

14

between the large-diameter hole portions

62

b

and

62

c

. The interaxial distance d

12

between the small-diameter hole portions

63

d

and

63

e

is configured to be greater than the interaxial distance d

15

between the large-diameter hole portions

62

d

and

62

e

. The interaxial distance d

13

between the small-diameter hole portions

63

e

and

63

f

is configured to be equal to the interaxial distance d

16

between the large-diameter hole portions

62

e

and

62

f.

Referring back to

FIG. 12

, an outer conductor

54

is formed on almost the entire outer surface of the dielectric block in which the dielectric duplexer

51

is formed. A transmitting electrode Tx and a receiving electrode Rx, which serve as input/output electrodes, and an antenna electrode ANT, are formed on the mounting surface

51

c

and extend onto the short-circuited end surface

51

b

of the dielectric duplexer

51

at a predetermined distance from the outer conductor

54

so as to be electrically isolated therefrom.

Respective inner conductors

53

are formed on almost the entire inner surface of each of the resonator holes

52

a

to

52

g

. However, gaps

58

are provided between the inner conductor

53

and the outer conductor

54

at a location near the openings of the large-diameter hole portions

62

a

and

62

g

to provide an open-circuited end of the resonators. The surface

51

b

, in which the openings of the small-diameter hole portions

63

a

to

63

g

are provided, is the short-circuited end surface. The inner conductor

53

is electrically open, i.e., isolated from the outer conductor

54

, at the open-circuited end surface

51

a

, and is short-circuited, i.e., directly electrically connected to the outer conductor

54

, at the surface

51

b

. In addition, the axial length L of the resonator holes

52

a

to

52

g

is designed to be about λ/4 (λ is the center wavelength of the resonators formed with each of the resonator holes

52

a

to

52

g

).

Respective inner conductors

53

are also formed on the entire inner surface of each of the external coupling holes

55

a

,

55

b

, and

55

c

, and the entire inner surface of each of the ground holes

56

a

,

56

b

, and

56

c

. As shown in

FIG. 13

, the external coupling holes

55

a

,

55

b

, and

55

c

are electrically connected to the transmitting electrode Tx, the antenna electrode ANT, and the receiving electrode Rx, respectively. Thus, the inner conductor

53

of each of the outer coupling holes

55

a

to

55

c

is electrically connected to the outer conductor

54

at the open-circuited end-surface

51

a

, and is electrically isolated from the outer conductor

54

at the short-circuited end surface

51

b.

On the other hand, the ground holes

56

a

to

56

c

extend parallel to and adjacent to the outer coupling holes

55

a

to

55

c

. The inner conductors

53

of these ground holes are directly electrically connected to the outer conductor

54

at both the open-circuited end surface

51

a

and the short-circuited end surface

51

b

. Changing the position, shape, and inner dimension (size) of the ground holes

56

a

to

56

c

can cause an increase or decrease in self-capacitance of the external coupling holes

55

a

to

55

c

, thereby allowing for a change in the external coupling so that more appropriate external coupling can be realized. The self-capacitance of the external coupling holes

55

a

to

55

c

herein refers to the capacitance that is generated between the inner conductor

53

of the outer coupling holes

55

a

to

55

c

and a ground conductor (the outer conductor

54

and the inner conductor

53

of the ground holes

56

a

to

56

c

).

The dielectric duplexer

51

includes: a transmission filter (a band pass filter) consisting of two resonators formed with the resonator holes

52

b

and

52

c

; a receiving filter (a band pass filter) consisting of three resonators formed with the resonator holes

52

d

,

52

e

, and

52

f

; and two traps (band elimination filters) consisting of resonators formed with the resonator holes

52

a

and

52

g

that are located at opposite ends of the dielectric block. The external coupling hole

55

a

and the resonator holes

52

a

and

52

b

adjacent thereto, are electromagnetically coupled, which provides the external coupling. Likewise, the external coupling hole

55

b

and the resonator holes

52

c

and

52

b

adjacent thereto, and also the external coupling hole

55

c

and the resonator holes

52

f

and

52

g

adjacent thereto, are electromagnetically coupled, respectively, which provides the external coupling.

As shown in

FIG. 14

, in the dielectric duplexer

51

configured as described above, the connection portions of the large-diameter hole portions

62

c

to

62

f

and the small-diameter hole portions

63

c

to

63

f

are larger in cross section than the connection portions of the known art. Thus, the resonator holes

52

c

to

52

f

have shapes which facilitate the passage of plating liquid therethrough, thereby allowing the formation of the inner conductor

53

on the inner surfaces of the resonator holes

52

c

to

52

f

with sufficient film thickness and stability. As a result, the dielectric duplexer

51

can improve the Q-value of the resonator.

Referring back to

FIG. 12

, while a transmission signal transmitted from a transmission circuit (not shown) to the transmitting electrode Tx is output from the antenna electrode ANT through the transmission filter consisting of the resonator holes

52

b

and

52

c

, a reception signal input from the antenna electrode ANT is output from the receiving electrode Rx to a receiving circuit (not shown) through the receiving filter consisting of the resonator holes

52

d

,

52

e

, and

52

f

. This arrangement provides a stronger inductive coupling between the two resonators formed with the resonator holes

52

b

and

52

c

, so that the coupling between the two resonators formed with the resonators

52

d

and

52

e

results in a stronger capacitive coupling. With this arrangement, it is therefore possible to provide a dielectric duplexer

51

having greater capacitive coupling and inductive coupling without changing the outer shape or the dimensions of the dielectric duplexer

51

.

As shown in

FIG. 14

, the interaxial distance d

13

between the small-diameter hole portions

63

e

and

63

f

of the resonator holes

52

e

and

52

f

may be configured to equal the interaxial distance d

16

between the large-diameter hole portions

62

e

and

62

f

. In this case, without increasing the outer dimensions of the dielectric duplexer, the degree of electromagnetic field coupling between two resonators formed with the resonator holes

52

e

and

52

f

can be kept constant, thereby allowing for an enhanced versatility of design.

In addition, an attenuation pole formed toward a lower pass band (or higher pass band) can be shifted toward further lower frequency (or higher frequency). This arrangement, therefore, can broaden the pass band of the dielectric duplexer

51

and can facilitate the achievement of the small-sized dielectric duplexer

51

having an acute attenuation characteristic and high performance.

Fifth Embodiment

A communication device according to a fifth embodiment of the present invention will be described below in the context of a portable telephone.

FIG. 15

is a block circuit diagram illustrating an RF portion of a portable telephone

150

. In

FIG. 15

, the reference numeral

152

indicates an antenna element,

153

is a duplexer,

161

is a transmission isolator,

162

is a transmission amplifier,

163

is a transmitting interstage bandpass filter,

164

is a transmitting mixer,

165

is a receiving amplifier,

166

is a receiving interstage bandpass filter,

167

is a receiving mixer,

168

is a voltage controlled oscillator (VCO), and

169

is a local bandpass filter.

In this case, for example, the dielectric duplexer of the fifth embodiment described above can, by way of example, be used as the duplexer

153

. The dielectric filters

1

of the first to third embodiments can also, by way of example, be used as the transmitting interstage bandpass filter

163

, the transmitting interstage bandpass filter

166

, and the local bandpass filter

169

. Thus, the use of the dielectric duplexer

51

or the dielectric filter

1

can achieve a portable telephone having improved electric characteristics.

Other Embodiments

The dielectric filter, dielectric duplexer, and communication device according to the present invention are not limited to the embodiments described above, and can take various forms without departing from the spirit and scope of the present invention.

For example, as shown in

FIG. 16

, four resonator holes

2

a

,

2

b

,

2

c

, and

2

d

may be provided in the dielectric filter

1

. In this case, for the resonator holes

2

a

and

2

c

, the axes of the small-diameter hole portions

23

a

and

23

c

are displaced from the axes of the large-diameter hole portions

22

a

and

22

c

, respectively, such that the displacement distance P is within a range which satisfies the relationship 0<P<R−r, where R is the radii of the large-diameter hole portions

22

a

and

22

c

and r is the radii of the small-diameter hole portions

23

a

and

23

c

. For the resonator holes

2

b

and

2

d

, the axes of the small-diameter hole portions

23

b

and

23

d

are displaced from the axes of the large-diameter hole portions

22

b

and

22

d

, respectively, such that the displacement distance P is within a range which satisfies the relationship R−r<P<R+r, where R is the radii of the large-diameter hole portions

22

b

and

22

d

and r is the radii of the small-diameter hole portions

23

b

and

23

d.

In addition, the large-diameter hole portions

22

b

and

22

d

and the small-diameter hole portions

23

b

and

23

d

overlap each other in the axial directions of the resonator holes

2

b

and

2

d

, respectively. Thus, connection portions of the large-diameter hole portions

22

b

and

22

d

and the small-diameter hole portions

23

b

and

23

d

are larger in cross section than the connection portions of the known dielectric filter. Thus, the resonator holes

2

b

and

2

d

have shapes which facilitate the passage of plating liquid therethrough, thereby allowing the formation of the inner conductor

3

on the inner surfaces of the resonator holes with sufficient film thickness and stability. As a result, this can improve the Q-value of the resonator.

Strong inductive coupling is provided between the two resonators formed with the resonator holes

2

a

and

2

c

, and strong capacitive coupling is provided between two resonators formed with the resonator holes

2

c

and

2

d

. In addition, an even stronger degree of inductive coupling is provided between two resonators formed with the resonator holes

2

b

and

2

d

than that between the resonator holes

2

a

and

2

c

. This can enhance the flexibility in designing electromagnetic coupling of a dielectric filter, thereby facilitating the design of a bandpass filter, duplexer, or the like. Naturally, five or more resonator holes may also be provided.

In addition, as shown in

FIG. 17

, large-diameter hole portions

22

g

and

22

h

and small-diameter hole portions

23

g

and

23

h

of the resonator holes

2

g

and

2

h

may be positioned such that the large-diameter hole portion

22

g

is located at the open-circuited end surface

1

a

, the small-diameter hole portion

23

g

is at the short-circuited end surface

1

b

, the small-diameter hole portion

23

h

is at the open-circuited end surface

1

a

, and the large-diameter hole portion

22

h

is at the short-circuited end surface

1

b.

Optionally, as shown in

FIG. 18

, large-diameter hole portions

22

i

and

22

j

and small-diameter hole portions

23

i

and

23

j

of resonator holes

2

i

and

2

j

may have rectangular cross-sections, in addition to or instead of the circular shapes. More generally, the cross-section of the large and small diameter hole portions can take various shapes (e.g., round, square or oblong).

Alternatively, a dielectric filter shown in

FIG. 19

may be used. In this dielectric filter, the outer conductor

4

is formed on almost the entire outer surface of the dielectric block in which the dielectric filter is formed. The pair of input/output electrodes

5

is formed on the outer surface of the dielectric filter

1

at a predetermined distance from the outer conductor

4

and is electrically isolated therefrom. The inner conductor

3

is formed on almost the entire inner surface of each of resonator holes

2

a

and

2

b

, and the gaps

8

are provided between the inner conductor

3

, and the outer conductor

4

formed at the openings of the large-diameter hole portions

22

a

and

22

b

. In this case, the surface

1

a

, in which the gaps

8

and the openings of the large-diameter hole portions

22

a

and

22

b

are provided, is the open-circuited end surface. The surface

1

b

, in which the openings of the small-diameter hole portions

23

a

and

23

b

are provided, is the short-circuited end surface. The large-diameter hole portions

22

a

and

22

b

and the small-diameter hole portions

23

a

and

23

b

overlap each other in the axial directions of the resonator holes

2

a

and

2

b.

The axial length of the resonator holes is not limited to about λ/4, and may be, for example, about λ/2. In such a case, both of surfaces in which openings of the resonator holes are provided must be set as either short-circuited end surfaces or open-circuited end surfaces.

In the resonator holes

2

a

and

2

b

shown in

FIG. 3

, the positions of the overlapping lengths A of the end walls

24

a

and

24

b

of the large-diameter hole portions

22

a

and

22

b

between the end walls

25

a

and

25

b

of the small-diameter hole portions

23

a

and

23

b

may be displaced from each other in the axial directions of the resonator holes

2

a

and

2

b

, respectively. In other words, the resonator holes (in this case,

2

a

and

2

b

) do not necessarily have to be arranged at the same positions in the axial directions as in the embodiments described above. That is, as long as the large-diameter hole portion

22

a

and the small-diameter hole portion

23

a

overlap each other in the axial directions of the resonator holes

2

a

, the length of the large-diameter hole portion

22

a

(the distance from the open-circuited end surface

1

a

to the end wall

24

b

) and the length of the large-diameter hole portion

22

b

(the distance from the open-circuited end surface

1

a

to the end wall

24

b

) may be different from each other. Likewise, as long as the large-diameter hole portion

22

b

and the small-diameter hole portion

23

b

overlap each other in the axial directions of the resonator holes

2

b

, the length of the small-diameter hole portion

23

a

(the distance from the short-circuited end surface

1

b

to the end wall

25

a

) and the length of the small-diameter hole portion

23

b

(the distance from the short-circuited end surface

1

b

to the end wall

25

b

) may be different from each other.

In addition, the dielectric filter or the dielectric duplexer may have resonator holes having uniform inner diameters but are formed of first and second sections whose central axis are displaced from one another. Furthermore, other electromagnetic field coupling means, such as a coupling groove, may be concurrently provided in the dielectric block to further increase the degree of the coupling between resonator holes.

While the description has been made in each of the first to fourth embodiments in conjunction with the resonator holes with the large-diameter hole portions provided in the open-circuited end surface and the small-diameter hole portions provided in the short-circuited end surface, the present invention is not limited to thereto. Thus, the large-diameter hole portions may be provided in the short-circuited end surface and the interaxial distance between the small-diameter hole portions in the open-circuited end surface may be altered. In this case, the coupling relationship of two adjacent resonator holes will be opposite to that of the embodiment described above. That is, the degree of capacitive coupling is gradually increased as the interaxial distance between the small-diameter hole portions is decreased, while the degree of inductance coupling is increased as the interaxial distance between the small-diameter hole portions is increased.

While a description has been given in each of the first to fourth embodiment described above in conjunction with the dielectric filter or the dielectric duplexer in which the input/output electrodes are formed at a predetermined position on the outer surface of the dielectric block, the present invention is not limited thereto. For example, the input/output electrodes may be replaced with resin pins for providing connection with an external circuitry.

While, in the first to fourth embodiments, a description has been given in conjunction with the case in which the axes of the small-diameter hole portions are displaced from the axes of the large-diameter hole portions that are arranged at a predetermined distance, the present invention is not necessarily limited thereto. Thus, the axes of the large-diameter hole portions may be displaced from the axes of the small-diameter hole portions that are arranged at a predetermined distance.

While, in the first to fourth embodiments, the axes of the large-diameter hole portions and the axes of the small-diameter hole portions are arranged in a line, the axes of the large-diameter hole portions and the axes of the small-diameter hole portions may be arranged, for example, in a vertical zigzag in the dielectric block.

Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.

Number	Name	Date	Kind
5945896	Miyamoto	Aug 1999	A
6433651	Kuroda et al.	Aug 2002	B1
6580339	Kuroda	Jun 2003	B2

Dielectric filter, dielectric duplexer and communication device

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Term Extension

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (3)