EP0877433A1

EP0877433A1 - Dielectric filter device

Info

Publication number: EP0877433A1
Application number: EP98303595A
Authority: EP
Inventors: Kenji Ito
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 1997-05-07
Filing date: 1998-05-07
Publication date: 1998-11-11

Abstract

A dielectric filter device is compact, shows an enhanced level of mechanical strength and is adapted to select a circuit constant with ease, wherein it comprises a dielectric filter having a plurality of resonators (3A; 3B; 3C) provided in a dielectric ceramic block (2; 2'), and a laminated circuit arrangement (10a; 10b; 10c; 10d; 10e) of a plurality of dielectric sheets which is fitted to the open-circuit end surface (2a; 2a') of the dielectric ceramic block (2; 2') and includes a coupling circuit (L; B, H) to be coupled to appropriate ones of the resonators (3A; 3B; 3C) to realize a low-pass (band-pass, high-pass) filter. The filter device can be made to have a neat and simple profile and downsized to minimize the space it requires and can be effectively and efficiently manufactured on a mass production basis.

Description

BACKGROUND OF THE INVENTION

This invention relates to a dielectric filter device comprising a plurality of resonators arranged in parallel with respect to each other, which can suitably be used for mobile telecommunications equipment such as an automobile telephone set or a portable telephone set.

PRIOR ART

A variety of dielectric filters of this type have been proposed. FIG. 1 of the accompanying drawings illustrates one typical example of such dielectric filters in which a plurality of resonators B are arranged in parallel along a same direction in a dielectric ceramic block A, each having a longitudinal through hole and an inner conductor coating the peripheral wall of the through hole, the dielectric ceramic block A is coated with a grounding conductor C on the outer surface except an open-circuit end surface for exposing the openings of the through holes, an input terminal pad P1 is coupled to one of the outermost resonators T and isolated from the grounding conductor C on a lateral side of the dielectric ceramic block A and an output terminal pad P2 is coupled to the other outermost resonator T and isolated from the grounding conductor C on the lateral side of the dielectric ceramic block A. Then, an electroconductive layer E is formed on each of the hollows D gouged around the openings on the open side of the dielectric ceramic block by coating the surface of the hollows with a conductor film. Alternatively, such electroconductive layer may be formed around each of the openings by printing a patterned conductor on the open side. Thereafter, the electroconductive layers E are coupled to each other to produce a band-pass filter.

However, when a coupling circuit is formed to couple the resonators by forming hollows or by using a pattern, the circuit constant obtained as a result of forming a dielectric filter is accompanied by limitations that in turn restrict the design of the dielectric filter. The use of inductors and capacitors having a concentrated constant has been proposed to solve this problem.

However, while the use of such devices provides an enhanced level of freedom for designing dielectric filters, it is accompanied by a number of problems including an increased number of assembling steps, a rugged profile of the dielectric filter, increased dimensions, an untidy circuit arrangement, a complicated circuit design and a reduced mechanical strength.

There have also been proposed a variety of dielectric filter devices comprising a dielectric filter in which a plurality of resonators are in parallel arranged along a same direction in a dielectric ceramic block which is coated with a grounded conductor material except an open-circuit end surface for exposing the openings of through holes bored through the dielectric ceramic block, and a substrate for carrying the dielectric filter thereon and provided with a coupling circuit connected appropriately to the resonators, said dielectric ceramic block and said coupling circuit being housed in a metal casing. Such dielectric filter devices include those proposed in Japanese Patent Kokai Nos. 61-208902 and 63-311801.

With any of such dielectric filter devices, circuit members including coupling capacitors are mounted on the substrate and electric paths are formed on the substrate to produce a necessary circuit. These elements are covered by the metal casing that operates as a shield case, and output/input electrodes are arranged on the substrate for connecting the dielectric filter with external electric paths to form a unit, which unit provides an advantage of easy handling.

A dielectric filter device having the above described configuration can enjoy an enhanced level of freedom in terms of designing because coupling capacitors are mounted on the substrate in a separate manufacturing step and hence the circuit constants of the dielectric filter can be selected appropriately depending on the specific circuit configuration of the dielectric filter.

However, with conventional dielectric filter devices of the type under consideration, metal terminals are fitted into the respective resonators of the device and then connected to the corresponding electric paths formed on the substrate of the device.

Thus, they have drawbacks of requiring complicated connections and a separate operation of mounting the coupling capacitors on the substrate to make the circuit arrangement a rather complicated one, which is provided with untidily disposed wires.

It is therefore an object of the present invention to provide a dielectric filter device that is free from the above identified problems.

SUMMARY OF THE INVENTION

According to the invention, there is provided a dielectric filter device comprising a dielectric filter which includes a plurality of resonators arranged in parallel along a same direction, each having a through hole provided in a dielectric ceramic block, and an inner conductor provided on a pheripheral wall of the through hole, the dielectric ceramic block having an outer surface coated with a grounding conductor and an open-circuit end surface which has no grounding conductor, and a coupling circuit means for connecting predetermined ones of the resonators of the dielectric filter, wherein the coupling circuit means comprises a laminated circuit arrangement of a plurality of dielectric sheets arranged on an open-circuit end surface of the dielectric filter and connected to predetermined ones of the resonators.

With the above arrangement, a coupling circuit is formed simply by arranging dielectric sheets on the open-circuit end surface of the dielectric ceramic block to produce a streamlined dielectric filter and a desired circuit constant can be obtained for it by appropriately designing the laminated circuit arrangement.

The plurality of dielectric layers may be sintered to produce a single chip circuit arrangment to be bonded to the open-circuit end surface of the dielectric ceramic block. With the use of a single chip circuit arrangment, a dielectric filter can be prepared simply by bonding the chip to the open-circuit end surface of the dielectric ceramic block.

The coupling circuit of the laminated circuit arrangement may be a low-pass filter coupling circuit, a band-pass filter coupling circuit or a high-pass filter coupling circuit coupled to the resonators.

In the filter device according to the present invention, the dielectric filter and the laminated circuit arrangement are mounted on a substrate which includes input/output pads at the surface thereof. The input/output pads are electrically connected to input/output terminals arranged on the substrate and connected to external electric paths.

Additionally, with the above arrangement, a coupling circuit may be formed simply by arranging dielectric sheets on the open-circuit end surface of the dielectric ceramic block to simplify the entire assembling process and the entire circuit configuration.

The dielectric filter may comprise a plurality of coaxial type resonators, each of which is formed by boring a single through hole through a dielectric ceramic block and coated with an inner conductor on the peripheral wall of the through hole. With such an arrangement, the coaxial type resonators can be regulated individually to provide the dielectric filter with desired characteristics. The coaxial type resonators may be assembled together before or after they are rigidly secured to the substrate.

Alternatively, the dielectric filter may be formed by boring a plurality of through holes through a dielectric ceramic block and coating the peripheral wall of each of the through holes with an inner conductor to produce a plurality of resonators arranged in parallel within the single dielectric ceramic block. With such an arrangement, the entire assembling process can be greatly simplified because the dielectric filter is a single structure.

The plurality of dielectric sheets may be sintered to produce a single chip circuit arrangement to be bonded to the open-circuit end surface of the dielectric ceramic block. With the use of a single chip circuit arrangement, a dielectric filter can be prepared simply by bonding the chip to the open-circuit end surface of the dielectric ceramic block and a dielectric filter device can be produced simply by bonding the dielectric filter to a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing a conventional dielectric filter;

FIG. 2 is an exploded schematic perspective view of a first embodiment of dielectric filter device according to the invention;

FIG. 2A is an enlarged section showing a part of one dielectric sheet in the laminated circuit arrangement of FIG.2;

FIG. 3 is a schematic perspective view showing the dielectric filter device of FIG. 2 after assembling;

FIG. 4 is a schematic longitudinal cross sectional view of the dielectric filter of FIG. 2, showing only a part of it;

FIG. 5 is a circuit diagram of an equivalent circuit of a low-pass filter of the first embodiment;

FIG. 6 is an exploded schematic perspective view of a second embodiment of a dielectric filter device according to the invention;

FIG. 7 is a schematic perspective view of the dielectric filter device of FIG.6 after assembling;

FIG. 8 is a circuit diagram of an equivalent circuit of a band-pass filter of the second embodiment;

FIG. 9 is an exploded schematic perspective view of a third embodiment of a dielectric filter device according to the invention;

FIG. 10 is a schematic perspective view of the dielectric filter device of FIG. 9 after assembling.

FIG. 11 is a circuit diagram of an equivalent circuit of a high-pass filter of the third embodiment;

FIG. 12 is an exploded schematic perspective view showing how the filter device according to the first, second or third embodiment is mounted on a substrate and contained in a metal casing;

FIG. 13 is an exploded schematic perspective view of a fourth embodiment of dielectric filter device according to the invention;

FIG. 14 is an exploded schematic perspective view of a fifth embodiment of dielectric filter device according to the invention;

FIG. 15 is a schematic perspective view of the dielectric filter device of FIG. 14 after assembling.

FIG. 16 is an exploded schematic perspective view showing how the filter device according to the forth or fifth embodiment is mounted on a substrate and contained in a metal casing; and

FIG. 17 is an exploded schematic perspective view of the filter device according to the forth or fifth embodiment, showing the dielectric filter, the laminated circuit arrangement and the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be described by referring to the accompanying drawings that illustrate preferred embodiments of the invention.

FIGS. 2 through 5 schematically illustrate a first embodiment of the invention. The illustrated dielectric filter la comprises a rectangular parallelpiped dielectric ceramic block 2 made of a sintered ceramic dielectric material such as titanium oxide series ceramics and barium oxide series ceramics and three

resonators

3A, 3B and 3C arranged in parallel with respect to each other along a same direction in the dielectric ceramic block 2. This filter la is intended to constitute a low pass filter illustrated in FIG. 5.

As shown in FIG. 4, each of the

resonators

3A, 3B and 3C comprises a through hole 4 provided through the dielectric ceramic block 2 and an inner conductor layer 5 formed on the inner peripheral surface or inner wall of the through hole 4. The outer surfaces of the dielectric ceramic block 2 are coated with a grounding conductor layer 6 except an open-circuit end surface 2a thereof where one of the openings of the respective through hole 4 is exposed.

The

resonators

3A, 3B and 3C have a resonant length substantially equal to a quarter of the resonant frequency λ , or λ/4, and constitutes a resonator circuit X shown in FIG. 5.

On the open-circuit end surface 2a of the dielectric ceramic block 2 is provided a laminated circuit arrangement 10a. This laminated circuit arrangement 10a is bonded to the open-circuit end surface 2a of the dielectric ceramic blocks 2. The laminated circuit arrangement 10a may be typically made of a glass ceramic material, a composite material containing both glass and dielectric ceramic or a low melting point oxide. As illustrated in FIG. 2, the laminated circuit arrangment 10a comprises a plurality of identical rectangularly parallelepipedic dielectric sheets 11 through 16, each having a contour same as that of the open-circuit end surface 2a of the dielectric ceramic block 2, which are stacked sequentially and sintered together to form a single chip. Thus the laminated circuit arrangement 10a of a multilayer structure of the dielectric sheets 11 through 16 operates as a low pass filter coupling circuit L which is cooperated with the

resonator

3A, 3B and 3C. Since the laminated circuit arrangement 10a is realized in the form of a single chip obtained by sintering together the dielectric sheets 11 through 16, the dielectric filter device having a neat rectangularly parallelepipedic profile can be prepared with ease simply by bonding the chip to the open-circuit end surface 2a of the dielectric ceramic body 2 or the dielectric filter 1a.

Each of the dielectric sheets 11-16 is provided with a conductor pattern on the surface thereof and cutting through holes therethrough.

Now, a specific mode of preparing a combination of the dielectric filter and the laminated circuit arrangement will be described below.

On the dielectric sheet 11 three through holes h are provided at positions located vis-a-vis the respective resonators 3A through 3C and filled with respective conducting material m as shown in FIG. 2A, and three

electrode layers

11a, 11b and 11c at positions on the front surface thereof located vis-a-vis the respective resonators 3A through 3C. Therefore, the

electrode layers

11a, 11b and 11c are connected to the inner conductor layers 5 of the

respective resonators

3A, 3B and 3C via the conductors filled in the corresponding holes h of the dielectric sheets 11, respectively.

On the dielectric sheet 12,

electrode layers

12a, 12b and 12c are formed on the front surface thereof at positions located vis-a-vis the resonators 3A through 3C respectively. Thus, capacitors C1, C2 and C3 for the low pass filter circuit L are formed between the electrode layers 11a and 12a, between the electrode layers 11b and 12b and between the electrode layers 11c and 12c, respectively, the capacitances of which capacitors are determined as a function of the thickness of the dielectric sheet 12 and the surface areas of the electrode layers 11a through 11c, respectively.

The dielectric sheet 13 is provided with through holes h which are filled with respective conducting material being connected to the

respective electrode layers

12a, 12b and 12c. Winding electroconductive paths are provided on the front surface of the dielectric sheet 13 between the through holes h correlated with the electrode layers 12a and 12b of the dielectric sheet 12, and between the through holes h correlated with the electrode layers 12b and 12c of the dielectric sheet 12, respectively, in order to form inductors L1 and L2.

The dielectric sheet 14 is provided with three through holes h at positions correlated with the

resonators

3A, 3B and 3C. These through holes are filled with respective conducting material. On the front surface of the dielectric sheet 14 an input/output connecting extension 14a is provided to be extended from the through hole h at position correlated with the resonator 3A to the upper edge of the dielectric sheet 14. This input/output connecting extension 14a is connected to the electrode layer 12a of the dielectric sheet 12 via the conductors filled in the through holes h of the

dielectric sheets

13 and 14 at positions correlated with the resonator 3A. Also, an input/output connecting extension 14b is extended from the through hole h at position correlated with the resonator 3C to the upper edge of the dielectric sheet 14.

The dielectric sheet 15 is provided with through holes h each being filled with conducting material and three

electrode layers

15a, 15b and 15c on the front surface thereof at positions correlated with the

resonators

3A, 3B and 3C, respectively. The electrode layers 15a, 15b and 15c are connected to the

electrode layers

12a, 12b and 12c on the dielectric sheet 12 via the conductors filled in the corresponding holes h of the dielectric sheets 13 14, and 15, respectively.

The dielectric sheet 16 is provided with a grounding conductor layer 17 on the front surface thereof which is cooperated with the

electrode layers

15a, 15b and 15c by way of the dielectric sheet 16 to form capacitors C4, C5 and C6.

After the laminated circuit arrangment 10a is prepared by stacking the dielectric sheets 11 through 16 to each other, input/output terminal pads 18a and 18b, and a grounding conductor 19 are provided on the upper surface of the laminated circuit arrangement 10a as shown in FIG. 3. The input/output terminal pads 18a and 18b are arranged to be connected to the input/output connecting extensions 14a and 14b on the dielectric sheet 14, respectively. The grounding conductor 19 is arranged to connect the grounding conductor layer 17 on the front surface of the dielectric sheet 16 with the grounding conductor layer 6 on the outer surfaces of the dielectric block 2.

Alternatively, the input/output terminal pads 18a and 18b and the grounding conductor 19 may be formed by previously conductor layers on the upper edges or surfaces of the respective dielectric sheets 11 through 16.

Thus, simply by laying the plurality of dielectric sheets 11 through 16 on the open-circuit end surfaces 2a of the dielectric ceramic blocks 2, there is provided the low pass filter coupling circuit L including the capacitors C1 through C6 and the inductors L1 and L2. The low pass filter coupling circuit L is coupled to the

resonators

3A, 3B and 3C of the resonator circuit X so that the low pass filter circuit shown in FIG. 5 is provided.

FIGS. 6, 7 and 8 schematically illustrate a second embodiment of the invention. The illustrated dielectric filter 1b has substantially the same construction as that of the dielectric filter la in the first embodiment. That is the illustrated dielectric filter 1b comprises a rectangular parallelpiped dielectric ceramic block 2 and three

resonators

3A, 3B and 3C arranged in parallel with respect to each other along a same direction in the dielectric ceramic block 2.

A laminated circuit arrangement 10b is intended to be bonded to an open-circuit end surface 2a of the dielectric ceramic block 2 for providing a band pass filter coupling circuit B. The laminated circuit arrangement 10b comprises a plurality of identical rectangularly parallelepipedic dielectric sheets 21 through 25, each having a contour same as that of the open-circuit end surface 2a of the dielectric ceramic block 2, which are stacked sequentially and sintered together to form a single chip.

The dielectric sheet 21 is provided with three through holes h at positions correlated with the

resonators

3A, 3B and 3C, which are filled with with respective conducting material.

The dielectric sheet 22 is provided with three through holes h at positions correlated with the

resonators

3A, 3B and 3C, which are filled with with respective conducting material. Also, between the through holes h correlated with the

resonators

3A and 3B and between the through holes h correlated with the

resonators

3B and 3C two paired U-shape electrodes are interdigitally arranged on the front surface of the dielectric sheet 22 for forming capacitors C12 and C13.

The dielectric sheet 23 is provided with two through holes h at positions correlated with the

resonators

3A and 3C, which are filled with with respective conducting material. Also, on the front surface of the dielectric sheet 23 are arranged two

electrode layers

23a and 23b which are connected to the

resonators

3A and 3B through the conductors filled in the corresponding holes h on the

dielectric sheets

21 and 22.

The dielectric sheet 24 is provided with two

electrode layers

24a and 24b at the positions correlated with the electrode layers 23a and 23b on the dielectric sheet 23. The electrode layers 23a and 24a form a capacitor C11, while the electrode layers 23b and 24b form a capacitor C14. The capacitances of these capacitors are determined by the thickness of the the dielectric sheet 23. An input/output connecting extension 26a is arranged to be extended from the electrode layers 24a to the upper edge of the dielectric sheet 24. Another input/output connecting extension 26b is arranged to be extended from the electrode layers 24b to the upper edge of the dielectric sheet 24.

The dielectric sheet 25 is provided with a grounding conductor 27 on the front surface thereof.

In this way, the laminated circuit arrangment 10b can be prepared by stacking the dielectric sheets 21 through 25 to each other. Then, input/

output terminal pads

28a and 28b and a grounding conductor 29 are provided on the upper surface of the laminated circuit arrangement 10b as shown in FIG. 7. The input/

output terminal pads

28a and 28b are arranged to be connected to the input/

output connecting extensions

26a and 26b on the dielectric sheet 24, respectively. The grounding conductor 29 is arranged to be connected to the grounding conductor layer 27 on the front surface of the dielectric sheet 25 and the grounding conductor layer 6 on the outer surfaces of the dielectric block 2.

Alternatively, the input/

output terminal pads

28a and 28b and the grounding conductor 29 may be formed by previously conductor layers on the upper edges or surfaces of the respective dielectric sheets 21 through 25.

Thus, simply by laying the plurality of dielectric sheets 21 through 25 on the open-circuit end surfaces 2a of the dielectric ceramic blocks 2, there is provided the band pass filter coupling circuit B including the capacitors C11 through C14. The band pass filter coupling circuit B is coupled to the

resonators

3A, 3B and 3C of the resonator circuit X so that the band pass filter circuit shown in FIG. 8 is provided.

FIGS. 9, 10 and 11 schematically illustrate a third embodiment of the invention in which the illustrated dielectric filter lc has substantially the same construction as that of the dielectric filter la in the first embodiment. That is the illustrated dielectric filter 1c comprises a rectangular parallelpiped dielectric ceramic block 2 and three

resonators

A laminated circuit arrangement 10c is intended to be bonded to an open-circuit end surface 2a of the dielectric ceramic block 2 for providing a high pass filter coupling circuit H.

The laminated circuit arrangement 10c comprises a plurality of identical rectangularly parallelepipedic dielectric sheets 31 through 36, each having a contour same as that of the open-circuit end surface 2a of the dielectric ceramic block 2, which are stacked sequentially and sintered together to form a single chip.

The dielectric sheet 31 is provided with three through holes h at positions correlated with the

resonators

3A, 3B and 3C, which are filled with with respective conductors. These filled conductors are connected to the

resonators

3A, 3B and 3C,respectively. Also, on the front surface of the dielectric sheet 31 is provided a grounding conductor layer 31a which is electrically separated from the respective conductors filled in the through holes h by space regions s.

The dielectric sheet 32 includes three

electrode layers

32a, 32b and 32c at positions corresponding to the

resonators

3A, 3B and 3C.

The dielectric sheet 33 includes three

electrode layers

33a, 33b and 33c at positions corresponding to the

resonators

3A, 3B and 3C. The electrode layers 32a and 33a form a capacitor C21, the electrode layers 32b and 33b form a capacitor C22, and the electrode layers 32c and 33c form a capacitor C23. These capacitors C21-C23 have capacitances which are determined as a function of the thickness of the dielectric sheet 32 and the surface areas of the electrode layers. The electrode layers 33a and 33c are arranged to be spaced from the intermediate electrode layer 33b so as to provide interstage couplings between which capacitors C24 and C25 are respectively formed.

The dielectric sheet 34 includes three through holes h arranged at positions correlated with the

resonators

3A, 3B and 3C and filled with respective conducting material by which the respective holes h are connected to the

electrode layers

33a, 33b and 33c. Inductors L21 and L23 of zig-zag electroconductive paths are provided on the front surface of the dielectric sheet 34 and then are electrically connected to the electrode layers 33a and 33c via the conductors filled in the righthand and left-hand through holes h. Each of the inductors L21 and L23 has one end extended to the lower edge and the other end extended to the upper edge of the dielectric sheet 34.

The dielectric sheet 35 includes a through hole h filled with conducting material and inductor L22 of a zig-zag electroconductive path which has one end connected to the electrode layer 33b on the dielectric sheet 33 via the conductors filled in the through holes of the

dielectric sheets

34 and 35 and the other end extended to the lower edge of the dielectric sheet 35.

The dielectric sheet 36 includes a grounding conductor 37 on the front surface thereof.

In this way, the laminated circuit arrangment 10c can be prepared by stacking the dielectric sheets 31 through 36 to each other. Then, input/

output terminal pads

38a and 38b are provided on the upper surface of the laminated circuit arrangement 10c as shown in FIG. 10. The input/output terminal pads 38a is arranged to be connected to the other end of the inductor L21 on the dielectric sheet 34, while input/output terminal pads 38b is arranged to be connected to the other end of the inductor L23 on the dielectric sheet 34. Grounding conductors 39 are provided on a center portion of the upper surface and lower surface of the laminated circuit arrangement 10c and are connected to the grounding conductor 37 on the front surface of the dielectric sheet 36 and the the grounding conductor layer 6 on the outer surfaces of the dielectric block 2. Also, the grounding conductor 39 is connected to the one ends of the inductors L21 and L23.

Alternatively, the input/

output terminal pads

38a and 38b and each the grounding conductor 39 may be formed by previously conductor layers on the upper and lower edges or surfaces of all or prerdetermined ones of the respective dielectric sheets 31 through 36.

Thus, the high pass filter coupling circuit H including the capacitors C21 therough C25 and the inductors L21 through L23 can be provided simply by bonding the laminated circuit arrangement 10c of a plurality of dielectric sheets 31 through 36 on the open-circuit end surfaces 2a of the dielectric ceramic blocks 2. Then, a high pass filter circuit shown in FIG. 11 is provided as the high pass filter coupling circuit H is coupled to the

resonators

3A, 3B and 3C of the resonator circuit X.

FIG. 12 illustrates how the assembly of the dielectric filter and the laminated circuit arrangement in each of the first,second and third embodiments is mounted on a substrate and contained in a metal casing.

In FIG. 12 reference numeral 40 denotes a substrate on which two conductor pads 41 and input/output terminals 42 are provided. Reference numeral 43 denotes a metal casing for covering the assembly of the dielectric filter and the laminated circuit arrangement. The input/output terminals 42 can be connected to external electric paths. The

dielectric filter

1a or 1b or 1c is placed on the substrate 40 with the input/output pads 18a and 18b or (28a and 28b) or (38a and 38b) facing downward, and the input/output pads are electrically connected to the conductor pads 41 formed on the substrate 40 so that the input/output terminals 42 are electrically connected to appropriate ones of the filter circuits of the dielectric filter. It will be appreciated that the input/output terminals 42 are exposed when the metal casing 43 is arranged in place so that they can be connected to external electric paths without difficulty.

In short, after mounting the dielectric filter la or (1b or 1c) on the substrate 40, the metal casing 43 is arranged in place to cover the dielectric filter and laminated circuit arrangement with the input/output electrodes 42 exposed to the outside for easy connection with external electric paths. Thus, the dielectric filter device is produced and may be utilized as a simple resonator unit.

FIG. 13 schematically illustrates a fourth embodiment of dielectric filter device according to the invention that comprises a dielectric filter 1d formed by arranging three coaxial type resonators 3A' through 3C' in parallel with respect to each other and bonding them together, a laminated circuit arrangement 10d adapted to cover the entire open-circuit end surfaces of the coaxial type resonators 3A' through 3C'.

Each of the resonators 3A' through 3C'comprises a through hole provided in respective dielectric ceramic block 2' and an inner conductor layer provided on the inner wall of the through hole. Each dielectric ceramic block 2' has an outer surface coated with a grounding conductor layer 6 and an open-circuit end surface 2a' where such grounding conductor layer is not provided.

The laminated circuit arrangement 10d has substantially the same construction as that of the laminated circuit arrangement 10a in the first embodiment. Thus, the components of the laminated circuit arrangement 10d are denoted respectively by the same reference symbols and will not be described here any further.

Thus, a low-pass filter coupling circuit L including capacitors C1 through C6 and inductors L1 through L2 is produced simply by bonding the laminated circuit arrangement 10d of a plurality of dielectric layers 11 through 16 to the open-circuit end surface 2a' of the dielectric filter 1d. Then, a low-pass filter circuit as shown in FIG. 5 is provided as the low-pass filter coupling circuit L is coupled to appropriate ones of the resonators 3A' through 3C' of the resonator circuit X.

FIGS. 14 and 15 show a fifth embodiment of the invention comprising a dielectric filter 1e and a laminated circuit arrangement 10e bonded to the dielectric filter le as a band-pass filter coupling circuit B. The dielectric filter le has substantially the same construction as that of the dielectric filter 1d in the fourth embodiment. Thus, the components of the filter 1e are denoted respectively by the same reference symbols and will not be described here any further.

Also, the laminated circuit arrangement 10e has a configuration same as that of the laminated circuit arrangement 10b in the second embodiment shown in FIGS. 6, 7 and 8, and thus the components of the laminated circuit arrangement 10e are denoted respectively by the same reference symbols. That is, the laminated circuit arrangement 10e is realized by laying a plurality of dielectric sheet layers 21 through 25 into a sinle chipe and forms a band-pass filter coupling circuit as shown in FIG. 8 when the laminated circuit arrangement 10e is bonded to the assemblied dielectric ceramic block 2' and coupled to appropriate ones of the resonators 3A' through 3C' of the resonator circuit X.

The assembly of the dielectric filter le and the laminated circuit arrangement 10e thus prepared as an integral part is then mounted on the substrate 40 as illustrated in FIGS. 16 and 17. In a manner same as that illustrated in FIG. 12, the input/output terminals 42 can be connected to external electric paths. The dielectric filter 1d or le is placed on the substrate 40 with the input/output pads facing downward, and the input/output pads are electrically connected to the conductor pads 41 formed on the substrate 40 so that the input/output terminals 42 are electrically connected to appropriate ones of the filter circuits of the dielectric filter. It will be appreciated that the input/output terminals 42 are exposed when the metal casing 43 is arranged in place so that they can be connected to external electric paths without difficulty. After mounting the dielectric filter 1d or le on the substrate 40, the metal casing 43 is arranged in place to cover the dielectric filter and laminated circuit arrangement with the input/output electrodes 42 exposed to the outside for easy connection with external electric paths. Thus, the dielectric filter device is produced and may be utilized as a simple resonator unit.

In the embodiments illustrated in FIGS. 13-15, it should be noted that the coaxial type resonators 3A' through 3C' may alternatively be mounted on the substrate 40 side by side without being bonded to each other.

While the dielectric filter comprises a plurality of coaxial type resonators in each of the above described fourth and fifth embodiments, it may alternatively be formed by boring a plurality of through holes through a single dielectric block and coating the inner peripheral surfaces of the through holes with an inner conductor to produce a plurality of resonators arranged side by side in a single dielectric ceramic block as in the first, second and third embodiments.

Thus, according to the present invention, a laminated circuit arrangement of a plurality of dielectric sheets is fitted to the open-circuit end surface of a dielectric filter and its coupling circuit L (B, H) is coupled to appropriate ones of the resonators 3A through 3C to realize a low-pass (band-pass, high-pass) filter. Such a dielectric filter device provides the following advantages.

1) The filter device can be made to have a neat and simple profile and downsized to minimize the space it requires.

2) Since it may comprise only a dielectric ceramic block and a laminate of dielectric sheets, it shows an enhanced mechanical strength.

3) Since the coupling circuit L (B, H) is confined within the laminated circuit arrangement 10a (10b, 10c, 10d, loe), it is isolated from the atmosphere and less subjected to moisture and mechanical impacts to enjoy stabilized operations.

4) Since the coupling circuit is formed by a laminated circuit, a desired circuit constant can be obtained to provide an enhanced level of freedom of designing the filter.

5) When the laminated circuit arrangement is formed by laying a plurality of dielectric sheets and sintering them into a single chip, a dielectric filter can be produced simply by bonding the laminated circuit arrangement to the open-circuit end surface of the dielectric ceramic block and dielectric filter device comprising such a dielectric filter can be effectively and efficiently manufactured on a mass production basis.

6) The entire unit can be made to have a neat and simple profile and the filter circuit can be downsized to reduce the surface area of the dielectric ceramic block and hence the entire dimensions of the unit.

7) Since the coupling circuit is confined within the laminated circuit arrangement, a simple wiring arrangement can be used on the substrate so that such units can be manufactured easily and efficiently.

Claims

A dielectric filter device comprising a dielectric filter (1a; 1b; 1c; 1d; 1e) which includes a plurality of resonators (3A, 3B, 3C; 3A', 3B', 3C') arranged in parallel along a same direction, each having a through hole (4) provided in a dielectric ceramic block (2; 2'), and an inner conductor (5) provided on a pheripheral wall of the through hole (4), the dielectric ceramic block (2; 2') having an outer surface coated with a grounding conductor (6) and an open-circuit end surface (2a; 2a') which has no grounding conductor, and an LC coupling circuit means for connecting predetermined ones of the resonators (3A, 3B, 3C; 3A', 3B', 3C') of the dielectric filter (1a; 1b; 1c; 1d; 1e), characterized in that

said LC coupling circuit means comprises a laminated circuit arrangement (10a; 10b; 10c; 10d; 10e) of a plurality of dielectric sheets (11, 12, 13, 14, 15, 16; 21, 22, 23, 24, 25; 31, 32, 33, 34, 35, 36) arranged on an open-circuit end surface (2a; 2a') of the dielectric filter (1a; 1b; 1c; 1d; 1e) and connected to predetermined ones of the resonators (3A, 3B, 3C; 3A', 3B', 3C').
A dielectric filter device as claimed in claim 1, wherein said dielectric filter (1a; 1b; 1c; 1d; 1e) comprises a single dielectric block (2) in which a plurality of coaxial type resonators (3A, 3B, 3C) are arranged in parallel with the respect to each other.
A dielectric filter device as claimed in claim 1, wherein said dielectric filter (1a; 1b; 1c; 1d; 1e) comprises a plurality of dielectric blocks (2'), each including a coaxial type resonator (3A', 3B', 3C'), and the dielectric blocks (2') are integrally assembled.
A dielectric filter device as claimed in claim 1, wherein the dielectric sheets (11, 12, 13, 14, 15, 16; 21, 22, 23, 24, 25; 31, 32, 33, 34, 35, 36) of said laminated circuit arrangement (10a; 10b; 10c; 10d; 10e) are sintered to form a single ship to be bonded to the open-circuit end surface (2a; 2a') of the dielectric filter (1a; 1b; 1c; 1d; 1e).
A dielectric filter device as claimed in claim 4, wherein said laminated circuit arrangement (10a; 10d) comprises a low-pass filter coupling circuit (L) including inductors and capacitors (L1, L2, C1, C2, C3, C4, C5, C6).
A dielectric filter device as claimed in claim 4, wherein said laminated circuit arrangement (10b; 10e) comprises a band-pass filter coupling circuit (B) including capacitors (C11, C12, C13, C14).
A dielectric filter device as claimed in claim 4, wherein said laminated circuit arrangement (10c) comprises a high-pass filter coupling circuit (H) including inductors and capacitors (L21, L22, L23, C21, C22, C23, C24, C25).
A dielectric filter device as claimed in claim 4, wherein said laminated circuit arrangement (10a; 10b; 10c; 10d; 10e) includes input/output terminal pads (18a, 18b; 28a, 28b; 38a, 38b) and a grounding conductor arranged to be connected to the grounding conductor (6) on the dielectric filter (1a; 1b; 1c; 1d; 1e).
A dielectric filter device as claimed in claim 1, wherein the filter device further comprises a substrate (40) on which said dielectric filter (1a; 1b; 1c; 1d; 1e) and said laminated circuit arrangement (10a; 10b; 10c; 10d; 10e) are mounted.
A dielectric filter device as claimed in claim 9, wherein said substrate (40) includes conductor pads (41) arranged to be connected to input/output terminal pads (18a, 18b; 28a, 28b; 38a, 38b) and input/output terminals (42).
A dielectric filter device as claimed in claim 1, wherein the filter device further comprises a metal casing (43) for containing said dielectric filter (1a; 1b; 1c; 1d; 1e) and said laminated circuit arrangement (10a; 10b; 10c; 10d; 10e).