Dielectric Laminated Filter

1. Field of the Invention

The present invention relates to a small dielectric laminated filter mainly used for a high frequency radio apparatus such as a portable telephone and a communication apparatus.

2. Related Art of the Invention

In recent years, many dielectric laminated filters have been used as high frequency filters for portable telephones. There is, however, a demand for further reduction of the size and thickness of such filters and attention is being paid to planar dielectric laminated filters that can be made thinner than a coaxial type.

An example of the above conventional dielectric laminated filter is described with reference to the drawings.

FIG. 13 shows an exploded perspective view of a conventional dielectric laminated filter. FIG. 14 shows a laminated body constituted by laminating the layers shown in FIG. 13 which are dissembled, as seen from the direction shown by arrow A. FIG. 15 is a cutaway cross sectional view in which the filter is cut along line D-D' shown in FIG. 13.

In FIGS. 13, 14, and 15, reference numerals 101, 102, 103, 104, 105, 106, and 107 designate dielectric sheets. Reference numerals 108a and 108b designate strip line electrodes formed on a dielectric sheet 105. Reference numerals 109a and 109b denote I/O line electrodes, 110a and 110b are notch capacity electrodes, 111 is a coupling line electrode, and these inner electrodes are formed on the dielectric sheets 106, 104, and 102, respectively.

These dielectric sheets are laminated to form a dielectric laminated block on which shield electrodes 115 and 116 are formed on its top and bottom surfaces, respectively. I/O electrodes 117a and 117b and a ground electrode 118 are formed on the outer circumferential side of the dielectric laminated block.

The effects of the dielectric laminated filter configured as described above are described.

In the dielectric laminated filter shown in FIG. 13, the shield electrodes 115 and 116 are grounded via the ground electrode 118. In addition, one end of each of the strip line electrodes 108a and 108b is grounded via the ground electrode 118 to constitute quarter-wavelength strip line resonators. The coupling line electrode 111 and the I/O line electrodes 109a and 109b act as a distributed constant line. A notch capacity is provided between the notch capacity electrode 110a or 110b and the strip line electrode 108a or 108b. The notch capacity electrodes 110a and 110b are connected together via the coupling line electrode 111 to connect the two strip line resonators in parallel via the notch capacity, and one end of the I/O line electrodes 109a and 109b are connected to the notch capacity electrodes 110a and 110b with the other ends connected to the I/O electrodes 117a and 117b in order to constitute a band elimination filter.

To prevent the electromagnetic coupling between the respective electrodes, for example, between the strip line electrodes 108a and 108b, earth electrodes 112, 113, and 114 are formed between the strip line electrodes 108a and 108b, between the I/O line electrodes 109a and 109b, and between the notch capacity electrodes 110a and 110b, respectively.

To prevent the electromagnetic coupling between the strip line electrodes 108a and 108b and the coupling line electrode 111, a shield electrode 120 is formed on the dielectric sheet 103.

A dielectric laminated filter of this configuration is shown in, for example, Japanese Patent Application Laid-Open No. 6-268410.

This design, however, is complicated in this configuration because the electromagnetic coupling between the I/O line 109a or 109b and the strip line 108a or 108b cannot be prevented.

In addition, if dielectric sheets with a large dielectric constant to reduce the size of the filter are used, the electromagnetic coupling between the I/O and the coupling lines and the strip lines is further increased, thereby preventing a good band elimination filter characteristic from being obtained.

Furthermore, the conventional prevention of the electromagnetic coupling between the strip lines 108a and 108b using the earth electrode 112, the electromagnetic coupling between the notch capacity electrodes 110a and 110b using the earth electrode 113, and the electromagnetic coupling between the I/O lines 109a and 109b using the earth electrode 114 is all imperfect and inductance is in fact provided in the earth electrodes 112, 113, and 114. Thus, unwanted electromagnetic coupling occurs between the strip line electrodes 108a and 108b and the earth electrode 112, between the I/O line electrodes 109a and 109b and the earth electrode 113, and between the notch capacity electrodes 110a and 110b and the earth electrode 114.

Furthermore, the earth electrodes 112, 113, and 114 disturb the distribution of electromagnetic fields from the strip line electrodes 108a and 108b, the I/O line electrodes 109a and 109b, and the notch capacity electrodes 110a and 110b to degrade the unloaded Q. As a result, a good band elimination filter characteristic cannot be achieved easily.

In view of these problems of the conventional dielectric laminated filters, it is an object of this invention to provide a dielectric laminated filter and a communication apparatus that can achieve a much better band elimination filter characteristic compared to the prior art.

To attain the object, a dielectric laminated filter of the first invention comprises a first dielectric laminated block in which a plurality of dielectric sheets are laminated; a plurality of first resonance electrodes formed on an inner layer of said first dielectric laminated block; a second dielectric laminated block in which a plurality of dielectric sheets are laminated; a plurality of second resonance electrodes formed on an inner layer of said second dielectric laminated block; a coupling element formed on an inner layer of said second dielectric laminated block to connect said plurality of second resonance electrodes in parallel; a first shield electrode formed between said first dielectric laminated block and said second dielectric laminated block; a plurality of third resonance electrodes formed on an outer side to connect one end of each of said first resonance electrodes to one end of each of said second resonance electrodes; a second shield electrode formed opposite to one surface of said first shield electrode; a third shield electrode formed opposite to the other surface of said first shield electrode; and a connection electrode formed on an outer side to connect said first, second, and third electrodes together.

According to this dielectric laminated filter, for example, a first and a second dielectric laminated blocks can be laminated via the shield electrodes to eliminate the unwanted electromagnetic coupling between strip line resonators and a coupling element, thereby enabling easy design. This filter can also provide a good band elimination filter characteristic to increase the degree of freedom for design and can be made smaller by increasing the dielectric constant of dielectric sheets.

In addition, by, for example, connecting first, second, and third resonance electrodes together to form resonators, the wavelength can be increased without increasing the size of the laminated body, so the size of the resonators and thus the filter can be reduced.

Furthermore, by, for example, forming the third resonance electrodes of outer electrodes, the filter characteristics can be adjusted.

A dielectric laminated filter of the second invention according to said first invention has said connection electrode which has a plurality of electrodes that are each formed on either of a pair of opposite surfaces among the outer surfaces and wherein said electrode is formed in an area other than the center of the surface.

The dielectric laminated filter can, for example, provide the same potential between shield electrodes and maintain a constant potential distribution within each shield electrode, thereby providing stable filter characteristics with excellent shielding.

A dielectric laminated filter of the third invention according to said first invention has a shield electrode which is formed all over all the outer sides of said first dielectric laminated block other than the one on which said third resonance electrode is formed.

The dielectric laminated filter can, for example, improve the shielding of the first resonance electrodes with a large magnetic density to reduce radiation losses.

A dielectric laminated filter of the fourth invention according to said first invention includes an outer dielectric sheet laminated on an outer surface of said second shield electrode, wherein one end of said third resonance electrode which extends up to the top surface of said outer dielectric sheet.

The dielectric laminated filter can, for example, form ground capacities between the third resonance electrodes and the second shield electrodes to reduce the wavelength of the resonators.

In addition, by, for example, trimming the third resonance electrodes formed on the upper surface of the laminated body, the ground capacity can be varied to adjust the resonance frequency of the resonators. That is, this filter can absorb the dispersion of dielectric sheets and electrode patterns.

A dielectric laminated filter of the fifth invention according to said first invention has said second resonance electrode which has a larger width than said first resonance electrode.

A dielectric laminated filter of the sixth invention according to said first invention has said first and second dielectric blocks which have different thicknesses.

The dielectric laminated filter can, for example, abruptly vary like a step the impedance of the resonators, that is, can constitute SIR resonators to reduce the resonance frequency and thus the length of the resonators.

A dielectric laminated filter of the seventh invention according to said first invention has said first and second dielectric blocks which are formed of said dielectric sheets of different dielectric constants.

According to this dielectric laminated filter, for example, a first dielectric laminated block can comprise a material with a low dielectric constant while a second dielectric laminated block can comprise a material with a high dielectric constant in order to further reduce the unwanted coupling between the resonators and the coupling element without increasing their sizes.

In addition, this filter enables dielectric sheets with different materials to be laminated via the shield electrodes to reduce changes in material due to the chemical coupling between the different materials. Thus, it enables different materials to be laminated easily, compared to the prior art.

A dielectric laminated filter of the eighth invention according to said first invention includes open stubs connected to said coupling element in parallel to attenuate high-order harmonic bands.

The dielectric laminated filter can have built-in LPF (Low Pass Filter) functions to reduce the size of the multi-functional filter and to reduce losses.

A dielectric laminated filter of the ninth invention comprises a dielectric laminated block in which a plurality of dielectric sheets are laminated; a plurality of resonance electrodes formed on an inner layer of said dielectric laminated block; a coupling line formed on an inner layer of said dielectric laminated block to connect each of said plurality of resonance electrodes in parallel; an I/O line formed on an inner layer of said dielectric laminated block; and a shield electrode that separates said plurality of resonance electrodes from said I/O line.

By separating resonance electrodes from I/O lines using the shield electrodes, the dielectric laminated filter can prevent the electromagnetic coupling between the resonance electrodes and the I/O lines, thereby enabling easy design. This filter can also provide a good band elimination filter characteristic to increase the degree of freedom for design and can be made smaller by increasing the dielectric constant of the dielectric sheets.

A dielectric laminated filter of the tenth invention comprises a dielectric laminated block in which a plurality of dielectric sheets are laminated; a plurality of resonance electrodes formed on an inner layer of said dielectric laminated block and electromagnetically coupled together; and a coupling line formed on an inner layer of said dielectric laminated block to connect each of said plurality of resonance electrodes in parallel, wherein the dielectric laminated filter uses electromagnetic coupling occurring between said plurality of resonance electrodes instead of providing an electromagnetic coupling prevention member for substantially preventing said electromagnetic coupling.

The dielectric laminated filter can, for example, appropriately combine the electromagnetic coupling between the resonators with the coupling line electrode to achieve elliptic function characteristics in order to make the attenuation curve steeper compared to Chebyshev's characteristics that do not use the electromagnetic coupling between the resonators. Although insertion losses in the specific attenuation band would be decreased, insertion losses in the pass band could be further improved. Thus, the attenuation band can be increased without providing a multi-stage filter, thereby reducing the size of the filter and thus losses (improving the performance).

A communication apparatus of the present invention comprises a signal processing means using the dielectric laminated filter according to any of the present inventions; and an output means for outputting said processed signal.

FIG. 1 is an exploded perspective view of a dielectric laminated filter according to a first and a second embodiments of this invention.

FIG. 2 is a perspective view of the dielectric laminated filter according to the first and the second embodiments of this invention.

FIG. 3 is an equivalent circuit diagram of the dielectric laminated filter according to the first and the second embodiments of this invention.

FIG. 4 is an exploded perspective view of a dielectric laminated filter according to a third embodiment of this invention.

FIG. 5 is a perspective view of the dielectric laminated filter according to the third embodiment of this invention.

FIG. 6 is an equivalent circuit diagram of the dielectric laminated filter according to the third embodiment of this invention.

FIG. 7 is an exploded perspective view of a dielectric laminated filter according to a fourth embodiment of this invention.

FIG. 8 is a perspective view of the dielectric laminated filter according to the fourth embodiment of this invention.

FIG. 9 is an equivalent circuit diagram of the dielectric laminated filter according to the fourth embodiment of this invention.

FIG. 10 is an exploded perspective view of a dielectric laminated filter according to a fifth embodiment of this invention.

FIG. 11 is a perspective view of the dielectric laminated filter according to the fifth embodiment of this invention.

FIG. 12 is an equivalent circuit diagram of the dielectric laminated filter according to the fifth embodiment of this invention.

FIG. 13 is an exploded perspective view of a conventional dielectric laminated film.

FIG. 14 is an explanatory drawing showing the conventional dielectric laminated filter as seen from the direction shown by arrow A.

FIG. 15 is a cutaway cross sectional view in which the conventional dielectric laminated filter is cut along line D-D'.

FIG. 16 is a graph showing the frequency characteristic of a dielectric laminated filter experimentally manufactured in the third embodiment.

FIG. 17 is an exploded perspective view of a dielectric laminated filter according to a sixth embodiment of this invention.

FIG. 18 is a perspective view of the dielectric laminated filter according to the sixth embodiment of this invention.

FIG. 19 is an equivalent circuit diagram of the dielectric laminated filter according to the sixth embodiment of this invention.

FIG. 20 is an exploded perspective view of a dielectric laminated filter according to a seventh embodiment of this invention.

FIG. 21 is a perspective view of the dielectric laminated filter according to the seventh embodiment of this invention.

FIG. 22 is an equivalent circuit diagram of the dielectric laminated filter according to the seventh embodiment of this invention.

FIG. 23 is a graph comparing an elliptic function characteristic and a Chebyshev's characteristic in a band elimination filter.

FIG. 24 is a graph (narrow span) showing the frequency characteristic of a dielectric laminated filter experimentally manufactured in the seventh embodiment.

FIG. 25 is a graph (wide span) showing the frequency characteristic of the dielectric laminated filter experimentally manufactured in the seventh embodiment.

FIG. 26 is an exploded perspective view of a dielectric filter as a variation of the first embodiment of this invention.

FIGS. 27A to 27F are graphs describing the elliptic function characteristic in this invention.

The dielectric laminated filters according to the embodiments of this invention are described below with reference to the drawings.

(Embodiment 1)

FIG. 1 is an exploded perspective view of a dielectric laminated filter according to one embodiment of this invention. FIG. 2 is a perspective view of the dielectric laminated filter according to this embodiment (simply referred to as a "laminated body"). FIG. 3 shows an equivalent circuit of the dielectric laminated filter according to this embodiment.

In FIGS. 1 and 2, reference numerals 1, 2, 3, 4, and 5 designate dielectric sheets. These dielectric sheets comprise dielectric ceramic of the same material that has been formed into a green sheet and that can be sintered at a low temperature (.epsilon.r=7 to 100. .epsilon.r is a dielectric constant).

Reference numerals 6a and 6b indicate first strip line electrodes corresponding to first resonance electrodes according to this invention. The first strip line electrodes 6a and 6b are formed on the top surface of the dielectric sheet 2, extend from one side to the other, and are disposed in parallel to each other. Reference numerals 7a and 7b indicate second strip line electrodes corresponding to second resonance electrodes according to this invention, are formed on the top surface of the dielectric sheet 4, and extend over a portion to the other of the dielectric sheet 4. Reference numerals 8a and 8b denote notch capacity electrodes, 9a and 9b are I/O line electrodes, and 10 is a coupling line electrode. All these electrodes are formed on the top surface of the dielectric sheet 5. The notch capacity electrodes 8a and 8b are formed opposite to the second strip line electrodes 7a and 7b. The I/O line electrodes 9a and 9b and the coupling line electrode 10 are formed in positions such that they are not opposed to the second strip line electrodes 7a and 7b. One end of the I/O line electrode 9a and one end of the coupling line electrode 10 are connected to the notch capacity electrode 8a, and one end of the I/O line electrode 9b and the other end of the coupling line electrode 10 are connected to the notch capacity electrode 8b. Reference numeral 11 denotes a first shield electrode formed on the top surface of the dielectric sheet 3.

In this manner, these inner electrodes formed in the internal layers of the laminated body have electrode patterns printed thereon using metallic paste such as silver, copper, or gold having a high conductivity.

Furthermore, 12 is the laminated body formed by laminating the dielectric sheets 5, 4, 3, 2, and 1 in this order, pressing them, and simultaneously sintering each dielectric sheet and each inner electrode.

Of course, a plurality of dielectric laminated filters may be simultaneously manufactured from the same laminated body. In this case, a cutting process for cutting the laminated body into a plurality of laminated body pieces is required between the pressing process and the sintering process. These cut laminated body pieces correspond to the dielectric laminated filter.

In addition, 13 is a second shield electrode, 14 is a third shield electrode, and these electrodes are formed almost all over the top and the bottom surfaces of the laminated body 12, respectively. Reference numerals 15a and 15b are third strip line electrodes corresponding to third resonance electrodes according to this invention. The third strip line electrodes 15a and 15b are formed on one of the outer circumferential sides of the laminated body 12. The third strip line electrode 15a is connected to one end of the first strip line electrode 6a and one end of the second strip line electrode 7a. The third strip line electrode 15b is connected to one end of the first strip line electrode 6b and one end of the second strip line electrode 7b. Reference numerals 16a and 16b are connection electrodes formed on the two opposite outer circumferential sides of the laminated body 12 and connected to each of the shield electrodes 11, 13, and 14. Reference numerals 17a and 17b are I/O electrodes formed on the two outer circumferential sides of the laminated body 12. The I/O electrode 17a is connected to the other end of the I/O line electrode 9a and the I/O electrode 17b is connected to the other end of the I/O line electrode 9b. Reference numeral 18 is a ground terminal formed on one of the outer circumferential sides of the laminated body 12 and connected to the other end of each of the shield electrodes 11, 13, and 14 and the other ends of the first strip line electrodes 6a and 6b. In this manner, the outer electrodes formed on the external surfaces of the laminated body are formed by printing or plating electrode patterns using metallic paste such as silver, copper, or gold having a high conductivity. The first dielectric laminated block according to this invention corresponds to a block including the dielectric sheets 1 and 2. The second dielectric laminated block according to this invention corresponds to a block including the dielectric sheets 3, 4, and 5.

The dielectric laminated filter of this configuration is further described with reference to FIGS. 1, 2, and 3.

The other end of the first strip line electrodes 6a and 6b are grounded via the ground electrode 18 to constitute tip shorting strip line resonators 21a and 21b that use the other ends of the second strip line electrodes 7a and 7b as open ends. In addition, the notch capacity electrodes 8a and 8b are formed opposite to the second strip line electrodes 7a and 7b to constitute the notch capacity elements 12a and 12b. Furthermore, the I/O line electrodes 9a and 9b and the coupling line electrode 10 act as coupling elements for distributed constant lines. Thus, by connecting the I/O line electrodes 9a and 9b and the coupling line electrode 10 to the notch capacity electrodes 8a and 8b as described above, the tip shorting strip line resonators 21a and 21b are connected in parallel via the notch capacity elements 20a and 20b as shown in the equivalent circuit diagram in FIG. 3. This allows a band elimination filter using the I/O electrodes 17a and 17b as I/O terminals to be provided.

As described above, this embodiment can laminate via the first shield electrode 11, the first dielectric laminated block including the first strip line electrodes 6a and 6b and the second dielectric laminated block including the second strip line electrodes 7a and 7b and coupling elements in order to prevent the unwanted electromagnetic coupling between the first strip line electrodes 6a and 6b and the I/O line electrodes 9a and 9b acting as the coupling elements and between the first strip line electrodes 6a and 6b and the coupling line electrode 10.

The important point of this embodiment is the use of the structure in which the tip shorting strip line resonators 21a and 21b use the other ends of the second strip line electrodes 7a and 7b as open ends. This structure causes a field distribution to dominate in the second strip line electrodes, thereby allowing the magnetic coupling within the second dielectric laminated block to be neglected. In other words, the field coupling between the second strip line electrodes 7a and 7b and the notch capacity electrodes 8a and 8b is used to form the notch capacity elements 20a and 20b (see FIG. 3).

Furthermore, by disposing the I/O line electrodes 9a and 9b and the coupling line electrode 10 in such a way that they are not opposed to the second strip line electrodes 7a and 7b, the unwanted field coupling with the second strip line electrodes 7a and 7b can be reduced to a negligible magnitude.

As described above, the unwanted field coupling between the resonators (that is, the tip shorting strip line resonators 21a and 21b) and the I/O lines (that is, the I/O line electrodes 9a and 9b) and between the resonators and the coupling element (that is, the coupling line electrode 10) can be reduced to a negligible magnitude, thereby enabling easy design and providing a good band elimination filter characteristic.

In addition, by appropriately combining the electromagnetic coupling between the resonators with the coupling line electrode 10 to achieve an elliptic function characteristic, a steep attenuation characteristic curve can be obtained compared to a Chebychev's characteristic 404 that does not use the electromagnetic coupling M between the resonators, as shown in FIG. 23.

For example, FIGS. 27A to 27F show the transmission characteristic of a band elimination filter in which two strip line resonators are connected in parallel using a coupling line.

FIG. 27A is a graph showing a transmission characteristic obtained when the coupling line has an impedance of 50 .OMEGA. and a line length of a quarter wavelength at 1.5 GHz if there is no electromagnetic coupling between the resonators.

FIG. 27B is a graph that is the same as FIG. 27A except that the resonance frequency is offset.

FIG. 27C is a graph that is the same as FIG. 27B except that the coupling line length is a one-eighth wavelength at 1.5 GHz.

FIG. 27D is a graph that is the same as FIG. 27A except that there is electromagnetic coupling between the resonators.

FIG. 27E is a graph that is the same as FIG. 27D except that the coupling line length is a one-eighth wavelength at 1.5 GHz.

FIG. 27F is a graph that is the same as FIG. 27E except that the gap between the resonators is expanded to reduce the electromagnetic coupling.

As described above, changes in characteristic occurring when the coupling line is changed depend on whether or not there is electromagnetic coupling between the resonators (see FIGS. 27C and 27E). Consequently, to realize a steep elliptic function characteristic in the band elimination filter according to this embodiment, the behavior of the characteristic must be comprehensively considered in design.

Referring again to FIG. 23, insertion losses can be reduced in a pass band 402 used to obtain a desired attenuation band 401 and attenuation amount. Thus, the attenuation band 401 can be expanded without providing a multi-stage filter, thereby reducing the size of the filter and losses (increasing the performance).

If, for example, the line length of the coupling line cannot be configured to be a one-eighth wavelength or more due to a geometrical constraint, the electromagnetic coupling between the resonators can be combined together as shown in FIG. 27F to achieve an elliptic function characteristic with a steep attenuation characteristic curve.

That is, by appropriately combining the electromagnetic coupling M between the resonators with the coupling line electrode 10, coupling elements can be provided which have an impedance and a wavelength that cannot be configured only by the coupling line electrode 10 due to a geometrical constraint.

Thus, by eliminating unwanted electromagnetic coupling and using the electromagnetic coupling between the resonators, the degree of freedom can be increased and the dielectric constant of the dielectric sheets can be increased, thereby reducing the size of the resonators and improving the performance. Due to the active use of the electromagnetic coupling between the resonators, as described above, this embodiment has between the strip line electrodes 6a and 6b no earth electrode such as that described in the conventional dielectric laminated filter. An electromagnetic coupling prevention member according to this invention corresponds to the earth electrode.

Similar effects can be obtained by a structure comprising a dielectric laminated block formed by laminating a plurality of dielectric sheets 1, 2, 3, and 5; a plurality of strip lines 6a and 6b formed on an inner layer of the dielectric laminated block; a plurality of I/O lines 9a and 9b formed on an inner layer of the dielectric laminated block; and a coupling line 10 formed on an inner layer of the dielectric laminated block and connecting the plurality of strip lines in parallel, wherein a shield electrode 11 separates the plurality of strip lines 6a and 6b from the I/O lines 9a and 9b and the coupling line 10, as shown in FIG. 26.

In addition, the thickness of the dielectric sheet 4 can be reduced to reduce the area of the second strip line electrodes 7a and 7b and notch capacity electrodes 8a and 8b used to constitute the desired notch capacity elements 20a and 20b in order to increase the area used to form the coupling element without disposing it opposite to the second strip line electrodes 7a and 7b, thereby further increasing the degree of freedom in design.

Furthermore, by folding and connecting the first, the second, and the third strip line electrodes together to form the tip shorting strip line resonators 21a and 21b, the wavelength of the resonators can be increased without increasing the size of the laminated body, thereby reducing the size of the tip shorting strip line resonators 21a and 21b.

In addition, filter characteristics can be adjusted by forming the third strip line electrodes 15a and 15b of outer electrodes. That is, a trimming grinder or the like can be used to trim the third strip line electrodes 15a and 15b to adjust the interval between the electrodes in order to vary the electromagnetic coupling between the third strip line electrodes 15a and 15b, thereby allowing the attenuation band width within the band elimination filter characteristics to be adjusted.

By forming the connection electrodes 16a and 16b at the respective ends of the two opposite outer circumferential sides of the laminated body 12 and connecting the connection electrodes to each of the shield electrodes 11, 13, and 14, the same potential can be provided between the shield electrodes with a constant potential distribution maintained within each shield electrode, thereby providing stable filter characteristics with excellent shielding. These effects are significant at a frequency of more than 1 GHz.

Therefore, a small adjustable dielectric laminated filter that can be designed easily can be realized.

(Embodiment 2)

A dielectric laminated filter according to this embodiment is described below with reference to the drawings.

The structure of the dielectric laminated filter according to this embodiment is almost the same as that in the first embodiment except that the first and the second dielectric laminated blocks are formed of dielectric sheets of different dielectric constants.

That is, the dielectric constant of the dielectric sheets 1 and 2 differs from that of the dielectric sheets 3, 4, and 5.

As described above, this embodiment not only has the same effects as the first embodiment but, compared to the first embodiment, can also reduce the unwanted electromagnetic coupling between the resonators and the I/O lines and between the resonators and the coupling element without increasing the size of the dielectric laminated filter by making the dielectric sheets 1 and 2 of a material of a low dielectric constant and making the dielectric sheets 3, 4, and 5 of a material of a high dielectric constant.

In addition, the dielectric sheets 2 and 3 of different materials can be laminated via the first shield electrode to reduce changes in material caused by the chemical binding between different materials, thereby enabling different materials to be laminated easily, compared to the prior art.

(Embodiment 3)

A third embodiment of this invention is described below with reference to the drawings.

FIG. 4 is an exploded perspective view of a dielectric laminated filter according to this embodiment of the invention. FIG. 5 is a perspective view of a dielectric body according to this embodiment. FIG. 6 shows an equivalent circuit of the dielectric laminated filter according to this embodiment.

As shown in FIGS. 4 and 5, the structure of this dielectric laminated filter is the same as that in the first embodiment except for the following points.

The second and the third shield electrodes 13 and 14 are formed as inner electrode and dielectric sheets 41 and 42 are laminated on the top and the bottom surfaces to form a laminated body 45. The third strip line electrodes 15a and 15b are formed to extend up to the top surface of the dielectric sheet 41.

As describe above, this embodiment not only has the same effects as the first embodiment but can also reduce the resonance frequency of the tip shorting strip line resonators 21a and 21b (see FIG. 6) by extending the third strip line electrodes 15a and 15b up to the top surface of the dielectric sheet 41 to form ground capacity elements 44a and 44b between the third strip line electrodes 15a and 15b and the second shield electrode 13. Consequently, the length of the tip shorting strip line resonators 21a and 21b, that is, the wavelength can be reduced.

In addition, by trimming partial line electrodes 43a and 43b that are formed on the top surface of the dielectric sheet 41 and that are part of the third strip line electrodes 15a and 15b, the capacity (capacitance) of the ground capacity elements 44a and 44b can be varied to adjust the resonance frequency of the tip shorting strip line resonators 21a and 21b. This adjustment can be normally provided in the middle of a manufacturing process to absorb the dispersion of dielectric sheets and electrode patterns, thereby improving the yield.

Furthermore, if the connection electrodes 16a and 16b, the I/O electrodes 17a and 17b, and the ground electrode 18 are extended up to the top surface of the dielectric sheet 41 and the bottom surface of the dielectric sheet 42 and if the laminated body is mounted on a substrate by reflow soldering, the solder can be more effectively attached to each electrode surface and firmly mounted, thereby improving the reliability of mounting.

Therefore, a small dielectric laminated filter that has higher designability and adjustability than the first embodiment can be realized.

FIG. 16 is a graph showing the frequency characteristic of a dielectric laminated filter experimentally manufactured according to this embodiment. Dielectric sheets with a dielectric constant of .epsilon.r=58 were used and the laminated body 45 had a size of 4.5.times.3.2.times.2.0 mm. The electromagnetic coupling between the resonators and the coupling line electrode 10 were, as described above, appropriately combined together to achieve an elliptic function characteristic 403 such as that shown in FIG. 23.

(Embodiment 4)

A fourth embodiment of this invention is described below with reference to the drawings.

FIG. 7 is an exploded perspective view of a dielectric laminated filter according to this embodiment of the invention. FIG. 8 is a perspective view of a dielectric body according to this embodiment. FIG. 9 shows an equivalent circuit of the dielectric laminated filter according to this embodiment.

As shown in FIGS. 7 and 8, the structure of this dielectric laminated filter is the same as that in the first embodiment except for the following points.

The second shield electrode 13 is formed all over the surface of the laminated body 12. The ground electrode 18 is formed all over one of the outer circumferential sides of the laminated body 12. A fourth shield electrode 71 is formed all over two opposite sides of the dielectric sheets 1 and 2 to connect the connection electrodes 16a and 16b to the fourth shield electrode 71. In addition, the line width of the second strip line electrodes 7a and 7b is formed to be larger than that of the first strip line electrodes 6a and 6b.

As described above, this embodiment not only has the same effects as the first embodiment but also improves the shielding capability of the first strip line electrodes 6a and 6b with a large magnetic density to reduce radiation losses because the shield electrode is formed all over the top surface and all the outer circumferential sides of the first dielectric laminated block other than the one on which the third strip line electrodes 15a and 15b are formed, the first dielectric laminated block including the dielectric sheets 1 and 2 and the first strip line electrodes 6a and 6b. As a result, the unloaded Q of the tip shorting strip line resonators 21a and 21b (see FIG. 9) can be improved to realize a high performance dielectric laminated filter.

The line width of the second strip line electrodes 7a and 7b is formed to be larger than that of the first strip line electrodes 6a and 6b in order to cause the impedance of the tip shorting strip line resonators 21a and 21b to be abruptly varied like a step. This provides SIR resonators to enable the resonance frequency and the length of the resonators to be reduced in order to realize a small dielectric laminated filter.

(Embodiment 5)

A fifth embodiment of this invention is described below with reference to the drawings.

FIG. 10 is an exploded perspective view of a dielectric laminated filter according to this embodiment of the invention. FIG. 11 is a perspective view of a dielectric body according to this embodiment. FIG. 12 shows an equivalent circuit of the dielectric laminated filter according to this embodiment.

The structure in FIGS. 10 and 11 is the same as that in the first embodiment except for the following points. First, open stubs 31a and 31b are formed on the top surface of the dielectric sheet 5 to connect the I/O line electrodes 9a and 9b in parallel. Second, the second dielectric block has a smaller thickness than the first dielectric block.

As described above, this embodiment not only has the same effects as the first embodiment but can also size the open stubs 31a and 31b so as to have a length equal to a quarter wavelength at frequencies double and triple the fundamental pass band to form an attenuating pole at these frequencies. This attenuating pole is effective in attenuating a second and a third harmonic bands and enables an attenuating pole to be formed without affecting the characteristics of the fundamental frequency band.

In addition, the thickness of the second dielectric block (corresponding to the laminated portion including the dielectric sheets 3, 4, and 5) can be reduced below that of the first dielectric block (corresponding to the laminated portion including the dielectric sheets 1 and 2) to reduce the impedance of the second strip line electrodes 7a and 7b below that of the first strip line electrodes 6a and 6b, thereby enabling the impedance of the tip shorting strip line resonators 21a and 21b to be abruptly varied like a step. That is, SIR resonators can be provided to reduce the resonance frequency and thus the length of the resonators.

Consequently, this embodiment can attenuate high-order harmonic bands without the need to add an LPF, thereby reducing the size and losses of the multi-functional filter. Due to its ability to reduce the length of the resonators, this embodiment can realize a much smaller dielectric laminated filter.

(Embodiment 6)

FIG. 17 is an exploded perspective view of a dielectric laminated filter according to this embodiment of the invention. FIG. 18 is a perspective view of a dielectric body according to this embodiment. FIG. 19 shows an equivalent circuit of the dielectric laminated filter according to this embodiment.

In FIGS. 17 and 18, 201, 202, 203, 204, 205, and 206 are dielectric sheets. These dielectric sheets comprise dielectric ceramic of the same material that have been formed into green sheets and that are sintered at low temperatures (.epsilon.r=7 to 100).

Reference numerals 207a and 207b denote the first strip line electrodes formed on the top surface of the dielectric sheet 203 in parallel. Reference numerals 208a and 208b indicate second strip line electrodes formed so as to be narrower than the first strip lines 207a and 207b. The second strip line electrodes are each formed on the top surface of the dielectric sheet 203 to connect one ends of the first strip lines 207a and 207b (corresponding to a plurality of resonance electrodes according to this invention) to one ends of the second strip lines 208a and 208b (corresponding to a plurality of line electrodes according to claim 15 of this invention), respectively. Reference numeral 221 is a ground pattern electrode one end of which is connected to the other ends of the first strip lines 207a and 207b. The first strip line electrodes 207a and 207b correspond to a plurality of resonance electrodes that are electromagnetically coupled together according to this invention.

Furthermore, 209a and 209b are notch capacity electrodes, 210a and 210b are I/O line electrodes, 211 is a coupling line electrode, and 212a and 212b are open stub electrodes. In addition, 1217a and 1217b are ground capacity electrodes formed on the top surface of the dielectric sheet 204.

The notch capacity electrodes 209a and 209b are formed opposite to the first strip line electrodes 207a and 207b. The ground capacity electrodes 1217a and 1217b are formed opposite to the second strip line electrodes 208a and 208b. The I/O line electrodes 210a and 210b, the open stub electrodes 212a and 212b, and the coupling line electrode 211 are formed so as not to be opposed to the first or the second strip line electrodes 207a and 207b or 208a and 208b. One end of the I/O line electrode 210a and one end of the coupling line electrode 211 are connected to the notch capacity electrode 209a, while one end of the I/O line electrode 210b and the other end of the coupling line electrode 211 are connected to the notch capacity electrode 209b. In addition, the open stub electrodes 212a and 212b are each connected to the I/O line electrodes 210a and 210b in parallel, respectively. The capacity electrodes opposed to the open ends of the strip lines via the dielectric sheet according to this invention correspond to the notch capacity electrodes 209a and 209b.

Reference numerals 213a and 213b are matching capacity electrodes formed on the top surface of the dielectric sheet 205. Reference numerals 214 and 215 are shield electrodes formed on the top surface of the dielectric sheets 202 and 206, respectively.

These inner electrodes have their electrode patterns printed using metallic paste such as silver, copper, or gold having a high conductivity.

Reference numeral 216 designates a laminated body formed by laminating the dielectric sheets 206, 205, 204, 203, 202, and 201 in this order, pressing them, and simultaneously sintering the dielectric sheets and the inner electrodes at 960.degree. C., which is the melting point of silver, or lower.

The formation of the outer electrodes is described below.

Reference numeral 222 denotes a ground electrode formed all over one of the outer circumferential sides of the laminated body 216 and connected to the shield electrodes 214 and 215 and frequency adjustment electrodes 217a and 217b. Reference numeral 218 indicates a side shield electrode formed at both ends of two opposite outer circumferential sides of the laminated body 216 and connected to the shield electrodes 214 and 215. Reference numerals 219a and 219b indicate I/O electrodes formed on the two opposite outer circumferential sides of the laminated body 216. The I/O electrode 219a is connected to the other end of the I/O line electrode 210a and a matching capacity electrode 213a, while the I/O electrode 219b is connected to the other end of the I/O line electrode 210b and a matching capacity electrode 213b. Reference numeral 220 designates a ground electrode formed on one outer circumferential side of the laminated body 216, connected to the shield electrodes 214 and 215, and also connected to the other ends of the first strip line electrodes 207a and 207b via the ground pattern electrode 221.

These outer electrodes are formed by printing or plating electrode patterns using metallic paste such as silver, copper, or gold having a high conductivity, which is different from the inner electrode.

The dielectric laminated filter of this configuration is further described with reference to FIGS. 17, 18, and 19.

The other ends of the first strip line electrodes 207a and 207b are grounded via the ground pattern electrode 221 and the ground electrode 220 to constitute tip shorting strip line resonators 230a and 230b that use one ends of the first strip line electrodes 207a and 207b as open ends, thereby causing the electromagnetic coupling M to be generated between the tip shorting strip line resonators 230a and 230b and to act as a coupling element. In addition, the notch capacity electrodes 209a and 209b are formed opposite to the first strip line electrodes 207a and 207b to constitute notch capacity elements 231a and 231b. The I/O line electrodes 210a and 210b and the coupling line electrode 211 act as coupling elements for distributed constant lines. Thus, by connecting the I/O line electrodes 210a and 210b and the coupling line electrode 211 to the notch capacity electrodes 209a and 209b as described above, the tip shorting strip line resonators 230a and 230b are connected in parallel via the notch capacity elements 231a and 231b to constitute a band elimination filter with the I/O electrodes 219a and 219b as I/O terminals.

In addition, matching capacity elements 232a and 232b are provided between the matching capacity electrodes 213a and 213b and the shield electrode 215 via the dielectric sheet 205 to match the impedance of the I/O terminals (see FIG. 19).

Furthermore, ground capacity elements 1233a and 1233b are provided between the ground capacity electrodes 1217a and 1217b and the second strip line electrodes 208a and 208b, respectively.

The ground capacity elements 1233a and 1233b are connected to one ends of the first strip line electrodes 207a and 207b via the second strip line electrodes 208a and 208b, respectively, to allow the resonance frequency to be adjusted. The open stub electrodes 212a and 212b are connected to the I/O line electrodes 210a and 210b, respectively, in parallel to reduce the wavelength of the open stubs to one-fourth in order to form attenuation poles for high-order harmonic frequencies.

As described above, since this embodiment can reduce the unwanted electromagnetic coupling between the first strip line electrodes 207a and 207b and the I/O line electrodes 210a and 210b and between the first strip line electrodes 207a and 207b and the coupling line electrode 211 by forming the I/O line electrodes 210a and 210b, the open stub electrodes 212a and 212b, and the coupling line electrode 211 in positions such that they are not opposed to the first and the second strip line electrodes 207a and 207b, and 208a and 208b.

The dielectric laminated filter according to this embodiment can further reduce the electromagnetic coupling between the strip lines and the coupling element line (meaning the coupling line electrode and the I/O line electrodes) while maintaining a required unloaded Q for the filter characteristics.

The reason is described below. It is known that the electromagnetic coupling can be maximized by reducing the line width of the strip line electrodes 207a and 207b to reduce the area of each strip line electrode. The unloaded Q is degraded as the line width of the strip line electrodes becomes smaller. On the contrary, it is known that the unloaded Q is improved as the laminated portion sandwiched by the shield electrodes becomes thicker.

Thus, in the above structure, even if the line width of the strip line electrodes 207a and 207b is reduced, the total thickness of the laminated portions 202 to 205 sandwiched by the two shield electrodes 214 and 215 is large enough to minimize the unwanted electromagnetic coupling without significantly reducing the unloaded Q, that is, while maintaining a required unloaded Q for the filter characteristics.

In addition, the electromagnetic coupling between the resonators and the coupling line electrode 211 can be appropriately combined to achieve an elliptic function characteristic as described above in order to obtain a steeper attenuation characteristic curve compared to a conventional Chebychev's characteristic 404 that does not uses the electromagnetic coupling M between the resonators, as shown in the graph of the FIG. 23. That is, insertion losses can be reduced in a desired attenuation band 401 and a pass band 402 used to obtain an amount of attenuation. Consequently, the attenuation band 401 can be expanded without providing a multi-stage filter, thereby reducing the size of the filter and losses (increasing the performance).

Furthermore, the electromagnetic coupling M between the resonators and the coupling line electrode 211 can be appropriately combined as described above to provide a coupling element with an impedance and a wavelength that cannot be achieved only by the coupling line electrode 211 due to a geometrical constraint.

In addition, the matching capacity elements 232a and 232b can be provided to match the impedance of the I/O terminals of even an I/O line the length of which has been reduced by reducing the area in which the strip lines are not opposed to the coupling element line.

Since one ends (open ends) of the first strip line electrodes 207a and 207b, and the second strip line electrode 208a and 208b constituting the ground capacity elements 1233a and 1233b, respectively, are connected to the open ends of the tip shorting strip line resonators 230a and 230b, respectively, a field distribution dominates both electrodes. Furthermore, the width of the second strip line electrodes 208a and 208b can be reduced below that of the first strip line electrodes 207a and 207b to reduce the field strength. The interval between the second strip line electrodes 208a and 208b can also be increased to reduce the field coupling between these electrodes 208a and 208b down to a negligible magnitude.

Thus, a frequency adjustment mechanism (a loading capacity) can be configured easily without complicating the design, thereby providing a good band elimination filter characteristic.

As a result, by eliminating the unwanted electromagnetic coupling and using the electromagnetic coupling between the resonators, the degree of freedom in design can be increased to increase the dielectric constant of the dielectric sheets in order to reduce the size of the resonators and the coupling line, thereby reducing the size of the dielectric laminated filter and improving the performance.

In addition, the open stub electrodes 212a and 212b can be connected to the I/O line electrodes 210a and 210b, respectively, in parallel to reduce the wavelength of the open stubs to one-fourth in order to form attenuation poles for high-order harmonic frequencies, as described in the fifth embodiment. These attenuation poles are effective in attenuating high-order harmonic bands and can be formed without affecting the characteristics of the fundamental pass band or the attenuation band.

Thus, since high-order harmonic bands can be attenuated without adding an LPF, the size and losses of this multi-functional filter can be reduced.

In addition, the reliability and performance can be improved by making the outer and the inner electrodes of different electrode materials. For example, assume that silver paste is used as a material of the inner and the outer electrodes. Since the inner electrodes are configured to be sandwiched between dielectric pastes, silver paste with a low adhesion strength and a high conductivity and without glass frits can be used for these electrodes to improve the unloaded Q of the resonators and thus the performance. Silver paste with a low conductivity, a high adhesion strength, and glass frits can be used for the outer electrodes to improve the reliability of the I/O terminals.

(Embodiment 7)

A seventh embodiment of this invention is described below with reference to the drawings.

FIG. 20 is an exploded perspective view of a dielectric laminated filter according to this embodiment of the invention. FIG. 21 is a perspective view of a laminated body according to this embodiment. FIG. 22 shows an equivalent circuit of the dielectric laminated filter according to this embodiment.

As shown in FIGS. 20 and 21, the structure of this dielectric laminated filter is the same as that shown in the sixth embodiment except for the following points.

The other ends of the second strip lines 208a and 208b (corresponding to a plurality of line electrodes according to claim 14 of this invention) are each formed to extend up to one side of the dielectric sheet 203, the frequency adjustment electrodes 217a and 217b are formed as the outer electrodes on an outer circumferential side of the laminated body 216 and connected to the other ends of the second strip line electrodes 208a and 208b, respectively.

Furthermore, frequency adjustment capacity elements 233a and 233b are provided between the frequency adjustment electrodes 217a and 217b and the ground electrode 222, respectively.

The ground capacity electrodes 1217a and 1217b described in the sixth embodiment and the frequency adjustment electrodes 217a and 217b according to this embodiment have the same functions in that all of them can adjust the resonance frequency of the tip shorting strip line resonators 230a and 230b. The electrodes 217a and 217b, however, can adjust the resonance frequency after the lamination of each dielectric laminated sheet, whereas the electrodes 1217a and 1217b can perform the same operation only prior to lamination.

As described above, this embodiment not only has the same operation and features as the sixth embodiment but can also trim the frequency adjustment electrodes 217a and 217b configured as the outer electrodes in order to reduce the frequency adjustment capacity elements 233a and 233b, thereby enabling only the resonance frequency of the tip shorting strip line resonators 230a and 230b to be adjusted.

Since the dispersion of dielectric sheets and electrode patterns can be absorbed and the resonance frequency can be adjusted without affecting a coupling element such as the electromagnetic coupling M between the resonators, the attenuation characteristic of the band elimination filter can be adjusted simply and independently.

This embodiment can thus realize a dielectric laminated filter with a better yield than the sixth embodiment.

FIGS. 24 (narrow span) and 25 (wide span) are graphs showing the frequency characteristic of a dielectric laminated filter experimentally manufactured according to this embodiment. Dielectric sheets with a dielectric constant .epsilon.r=58 and the laminated body 216 had a size of 4.5.times.3.2.times.2.0 mm. The electromagnetic coupling between the resonators and the coupling line electrode 211 were appropriately combined as described above to achieve an elliptic function characteristic 500 shown in FIG. 23. The open stub electrodes 212a and 212b were constructed to provide an attenuation pole 501 for a second-order harmonic band and an attenuation pole 502 for a third-order harmonic band.

The above dielectric laminated filter can be applied to a communication apparatus to reduce its size and to improve its performance.

The dielectric laminated filter according to this embodiment, for example, allows the height of parts to be reduced compared to a coaxial resonator type, thereby enabling the three-dimensional space of the communication apparatus to reduce its size. In addition, by providing a band elimination filter to attenuate only undesired bands, losses in pass bands can be reduced compared to a band pass filter to reduce the power consumption of an amplifier, thereby increasing the lifetime expectancy of batteries or reducing their capacity, that is, their size.

The communication apparatus comprises, for example, a receipt means for receiving a radio signal from a source; a signal processing means comprising the dielectric laminated filter described in any of the above embodiments to extract a predetermined portion from the received signal and processing it; an output means for outputting the processed signal to a speaker, and a signalling means for issuing a signal to the source. Of course, the signalling means can be emitted from the communication apparatus.

The above embodiments can provide a small high-performance dielectric laminated filter that can be designed easily and that enables the resonance frequency of the filter and the electromagnetic coupling between resonators to be adjusted during a manufacturing process.

Although the above embodiments have been described in conjunction with the two strip lines formed on the same dielectric sheet, this invention is not limited to this aspect and three strip lines may be formed thereon. In this case, two coupling line electrodes are required and connected in series.

Although the embodiments 6 and 7 have been described in conjunction with the strip line electrodes formed on the same plane, that is, on the same layer, this invention is not limited to this aspect and the first strip line electrodes 207a and 207b maybe formed on different layers. For example, the second strip line electrodes 208a and 208b can also be formed on different layers.