Patent ID: 12218396

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Embodiments of the present invention will now be described in detail with reference to the drawings. First, reference is made toFIG.1to describe a configuration of a filter1according to a first embodiment of the present invention.FIG.1is a circuit diagram showing a circuit configuration of the filter1. The filter1is configured to function as a band-pass filter that selectively allows a signal of a frequency in a predetermined passband to pass.

The filter1according to the present embodiment includes a first resonator10, a second resonator20, and a third resonator30arranged between the first resonator10and the second resonator20in a circuit configuration. In the present application, the expression of “in the (a) circuit configuration” is used not to indicate a layout in physical configuration but to indicate a layout in a circuit diagram.

The first to third resonators10,20, and30are configured so that the first resonator10and the third resonator30are adjacent to each other in the circuit configuration to be electromagnetically coupled to each other, and the second resonator20and the third resonator30are adjacent to each other in the circuit configuration to be electromagnetically coupled to each other. InFIG.1, a curve with a sign K13represents an electric field coupling between the first resonator10and the third resonator30, and a curve with a sign K23represents an electric field coupling between the second resonator20and the third resonator30.

The first resonator10is magnetically coupled to the second resonator20not adjacent to the first resonator10in the circuit configuration. Such electromagnetic-field coupling between two resonators not adjacent to each other in the circuit configuration is referred to as cross coupling. InFIG.1, a curve with a sign K12represents a magnetic field coupling between the first resonator10and the second resonator20.

The first resonator10includes a first conductor part11and a second conductor part12having an impedance smaller than that of the first conductor part11. The first conductor part11and the second conductor part12are electrically connected to each other. The first conductor part11is connected to ground. Each of the first conductor part11and the second conductor part12is a distributed constant line. In particular, in the present embodiment, the first conductor part11is a distributed constant line having a small width, and the second conductor part12is a distributed constant line having a width larger than that of the first conductor part11.

The first resonator10further includes a third conductor part13electrically connecting the first conductor part11and the second conductor part12. The third conductor part13may include a distributed constant line having a width smaller than that of the distributed constant line constituting the second conductor part12. The width of the distributed constant line of the third conductor part13may be the same as or different from the width of the distributed constant line constituting the first conductor part11.

A configuration of the second resonator20is basically the same as the configuration of the first resonator10. Specifically, the second resonator20includes a first conductor part21and a second conductor part22having an impedance smaller than that of the first conductor part21. The first conductor part21and the second conductor part22are electrically connected to each other. The first conductor part21is connected to ground. Each of the first conductor part21and the second conductor part22is a distributed constant line. In particular, in the present embodiment, the first conductor part21is a distributed constant line having a small width, and the second conductor part22is a distributed constant line having a width larger than that of the first conductor part21.

The second resonator20further includes a third conductor part23electrically connecting the first conductor part21and the second conductor part22. The third conductor part23may include a distributed constant line having a width smaller than that of the distributed constant line constituting the second conductor part22. The width of the distributed constant line of the third conductor part23may be the same as or different from the width of the distributed constant line constituting the first conductor part21.

The third resonator30includes a first conductor part31and a second conductor part32having an impedance smaller than that of the first conductor part31. The first conductor part31corresponds to a “third conductor part” of the present invention, and the second conductor part32corresponds to a “fourth conductor part” of the present invention. The first conductor part31and the second conductor part32are electrically connected to each other. The first conductor part31is connected to ground. Each of the first conductor part31and the second conductor part32is a distributed constant line. In particular, in the present embodiment, the first conductor part31is a distributed constant line having a small width, and the second conductor part32is a distributed constant line having a width larger than that of the first conductor part31.

All the first to third resonators10,20, and30are each a stepped-impedance resonator composed of a distributed constant line having a small width and a distributed constant line having a large width. All the first to third resonators10,20, and30are each a quarter-wavelength resonator with one end being short-circuited and the other end being open.

The impedance of each of the first conductor parts11,21, and31is within a range from 150 to 350, for example. The impedance of each of the second conductor parts12,22, and32is within a range from 10 to 50, for example. Here, the ratio of the impedance of the second conductor part to the impedance of the first conductor part in each of the first to third resonators10,20, and30is referred to as an impedance ratio. In each of the first to third resonators10,20, and30, the impedance ratio is smaller than 1.

From an aspect of making the resonators small, the impedance ratio is preferably small. For example, by adjusting the widths of the distributed constant line configuring the first conductor part and the distributed constant line configuring the second conductor part, the impedance ratio can be adjusted. For a smaller impedance ratio, the width of the distributed constant line configuring the first conductor part is relatively small, and the width of the distributed constant line configuring the second conductor part is relatively large.

In particular, in the present embodiment, in each of the first to third resonators10,20, and30, the impedance ratio is 0.3 or smaller. In one example, the impedance of the second conductor part of each of the first and second resonators10and20is 2.870, and the impedance of the first conductor part of each of the first and second resonators10and20is 270. In this case, the impedance ratio in each of the first and second resonators10and20is 0.106. In one example, the impedance of the second conductor part32of the third resonator30is 2.550, and the impedance of the first conductor part31of the third resonator30is 270. In this case, the impedance ratio in the third resonator30is 0.094.

When the impedance ratio is made too small, desired characteristics are not obtained in some cases. For example, when the impedance ratio is made too small in a stepped-impedance resonator (quarter-wavelength resonator) with one end being short-circuited and the other end being open, this resonator serves substantially as a half-wavelength resonator composed only of a second conductor part with both ends being open. Consequently, desired characteristics cannot be obtained. To prevent this, in the present embodiment, the impedance ratio in each of the first to third resonators10,20, and30is 0.06 or greater.

The filter1further includes a first port2, a second port3, and conductor portions4and5. The first to third resonators10,20, and30are arranged between the first port2and the second port3in the circuit configuration.

The conductor portion4electrically connects the first port2and the first resonator10. The conductor portion4is connected, at one end thereof, to the first port2. The conductor portion4is connected, at the other end thereof, to the first resonator10between the first conductor part11and the third conductor part13.

The conductor portion5electrically connects the second port3and the second resonator20. The conductor portion5is connected, at one end thereof, to the second port3. The conductor portion5is connected, at the other end thereof, to the second resonator20between the first conductor part21and the third conductor part23.

The filter1further includes a first stub resonator91electrically connected to the first conductor part11of the first resonator10, and a second stub resonator92electrically connected to the first conductor part21of the second resonator20. Each of the first and second stub resonators91and92is a distributed constant line.

The first stub resonator91is connected in the middle of the first conductor part11. InFIG.1, for the first conductor part11, a portion located between a connecting point with the first stub resonator91and the second conductor part12in a circuit configuration is indicated by a reference numeral11A, and a portion located between the connecting point with the first stub resonator91and the ground in the circuit configuration is indicated by a reference numeral11B.

The second stub resonator92is connected in the middle of the first conductor part21. InFIG.1, for the first conductor part21, a portion located between a connecting point with the second stub resonator92and the second conductor part22in the circuit configuration is indicated by a reference numeral21A, and a portion located between a connecting point with the second stub resonator92and the ground in the circuit configuration is indicated by a reference numeral21B.

As will be described later, the shape of the first stub resonator91and the shape of the second stub resonator92are different from each other. In particular, in the present embodiment, the length of the first stub resonator91and the length of the second stub resonator92are different from each other.

Each of the first and second stub resonators91and92may be an open stub with one end being open or may be a short stub with one end being connected to ground.FIG.1shows an example in which each of the first and second stub resonators91and92is an open stub.

Next, other configurations of the filter1will be described with reference toFIG.2.FIG.2is a perspective view showing an external appearance of the filter1.

The filter1further includes a stack50. The stack50includes a plurality of dielectric layers stacked together and a plurality of conductor layers and a plurality of through holes formed in the plurality of dielectric layers. The first to third resonators10,20, and30and the first and second stub resonators91and92are integrated with the stack50. The first to third resonators10,20, and30and the first and second stub resonators91and92are formed by using the plurality of conductor layers.

The stack50has a first surface50A and a second surface50B located at both ends in a stacking direction T of the plurality of dielectric layers, and four side surfaces50C to50F connecting the first surface50A and the second surface50B. The side surfaces50C and50D are opposite to each other. The side surfaces50E and50F are opposite to each other. The side surfaces50C to50F are perpendicular to the first surface50A and the second surface50B.

Here, X, Y, and Z directions are defined as shown inFIG.2. The X, Y, and Z directions are orthogonal to one another. In the present embodiment, a direction parallel to the stacking direction T will be referred to as the Z direction. The opposite directions to the X, Y, and Z directions are defined as −X, −Y, and −Z directions, respectively.

As shown inFIG.2, the first surface50A is located at the end of the stack50in the −Z direction. The first surface50A is also the bottom surface of the stack50. The second surface50B is located at the end of the stack50in the Z direction. The second surface50B is also the top surface of the stack50. The side surface50C is located at the end of the stack50in the −X direction. The side surface50D is located at the end of the stack50in the X direction. The side surface50E is located at the end of the stack50in the −Y direction. The side surface50F is located at the end of the stack50in the Y direction.

The plane shape of the stack50when seen in the Z direction, i.e., the shape of the first surface50A or the second surface50B, is long in one direction. In particular, in the present embodiment, the plane shape of the stack50when seen in the Z direction is a rectangular shape that is long in a direction parallel to the X direction.

The filter1further includes a plurality of terminals111,112,113,114,115, and116provided on the first surface50A of the stack50. The terminal111extends in the Y direction near the side surface50C. The terminal112extends in the Y direction near the side surface50D. The terminals113to116are arranged between the terminal111and the terminal112. The terminals113and114are arranged in this order near the side surface50E in the X direction. The terminals115and116are arranged in this order near the side surface50F in the X direction.

The terminal111corresponds to the first port2, and the terminal112corresponds to the second port3. Thus, the first and second ports2and3are provided on the first surface50A of the stack50. The terminals113to116are connected to ground. Hereinafter, the terminal111is also referred to as a first terminal111, the terminal112is also referred to as a second terminal112, and the terminals113to116are also referred to as ground terminals113to116.

Next, an example of the plurality of dielectric layers and the plurality of conductor layers constituting the stack50will be described with reference toFIG.3AtoFIG.5C. In this example, the stack50includes nine dielectric layers stacked together. The nine dielectric layers will be referred to as a first to a ninth dielectric layer in the order from bottom to top. The first to ninth dielectric layers are denoted by reference numerals51to59, respectively.

FIG.3Ashows the patterned surface of the first dielectric layer51. The terminals111,112,113,114,115, and116are formed on the patterned surface of the dielectric layer51. Through holes51T1,51T2,51T3,51T4,51T5, and51T6connected respectively to the terminals111,112,113,114,115, and116are formed in the dielectric layer51.

FIG.3Bshows the patterned surface of the second dielectric layer52. A conductor layer521is formed on the patterned surface of the dielectric layer52. Further, through holes52T1,52T2,52T3,52T4,52T5, and52T6are formed in the dielectric layer52. The through holes51T1and51T2formed in the dielectric layer51are connected to the through holes52T1and52T2, respectively. The through holes51T3to51T6formed in the dielectric layer51and the through holes52T3to52T6are connected to the conductor layer521.

FIG.3Cshows the patterned surface of the third dielectric layer53. Conductor layers531,532,533, and534are formed on the patterned surface of the dielectric layer53. The conductor layer532is connected to the conductor layer531. The conductor layer534is connected to the conductor layer533. InFIG.3C, each of the boundary between the conductor layer531and the conductor layer532and the boundary between the conductor layer533and the conductor layer534is indicated by a dotted line.

Through holes53T1,53T2,53T3,53T4,53T5, and53T6are formed in the dielectric layer53. The through hole52T1formed in the dielectric layer52and the through hole53T1are connected to the conductor layer532. The through hole52T2formed in the dielectric layer52and the through hole53T2are connected to the conductor layer534. The through holes52T3to52T6formed in the dielectric layer52are connected to the through holes53T3to53T6, respectively.

FIG.4Ashows the patterned surface of the fourth dielectric layer54. A conductor layer541is formed on the patterned surface of the dielectric layer54. Through holes54T1,54T2,54T3,54T4,54T5,54T6, and54T7are formed in the dielectric layer54. The through holes53T1to53T6formed in the dielectric layer53are connected to the through holes54T1to54T6, respectively. The through hole54T7is connected to the conductor layer541.

FIG.4Bshows the patterned surface of the fifth dielectric layer55. A conductor layer551is formed on the patterned surface of the dielectric layer55. Through holes55T1,55T2,55T7, and55T8are formed in the dielectric layer55. The through holes54T1,54T2, and54T7formed in the dielectric layer54are connected to the through holes55T1,55T2, and55T7, respectively. The through holes54T3to54T6formed in the dielectric layer54and the through hole55T8are connected to the conductor layer551.

FIG.4Cshows the patterned surface of the sixth dielectric layer56. Through holes56T1,56T2,56T7, and56T8are formed in the dielectric layer56. The through holes55T1,55T2,55T7, and55T8formed in the dielectric layer55are connected to the through holes56T1,56T2,56T7, and56T8, respectively.

FIG.5Ashows the patterned surface of the seventh dielectric layer57. Conductor layers571,572,573, and574are formed on the patterned surface of the dielectric layer57. Each of the conductor layers571and572has a first end and a second end opposite to each other. The first end of the conductor layer571and the first end of the conductor layer572are connected to each other. InFIG.5A, the boundary between the conductor layer571and the conductor layer572is indicated by a dotted line. The through hole56T1formed in the dielectric layer56is connected to a portion near the second end of the conductor layer571. The through hole56T2formed in the dielectric layer56is connected to a portion near the second end of the conductor layer572.

The conductor layer573is connected in the middle of the conductor layer571. The conductor layer574is connected in the middle of the conductor layer572. InFIG.5A, each of the boundary between the conductor layer571and the conductor layer573and the boundary between the conductor layer572and the conductor layer574is indicated by a dotted line.

Through holes57T7and57T8are formed in the dielectric layer57. The through hole56T7formed in the dielectric layer56is connected to the through hole57T7. The through hole56T8formed in the dielectric layer56and the through hole57T8are connected to a portion near the first end of the conductor layer571and a portion near the first end of the conductor layer572.

FIG.5Bshows the patterned surface of the eighth dielectric layer58. A conductor layer581is formed on the patterned surface of the dielectric layer58. The conductor layer581has a first end and a second end opposite to each other. The through hole57T7formed in the dielectric layer57is connected to a portion near the first end of the conductor layer581.

A through hole58T8is formed in the dielectric layer58. The through hole57T8formed in the dielectric layer57and the through hole58T8are connected to a portion near the second end of the conductor layer581.

FIG.5Cshows the patterned surface of the ninth dielectric layer59. A conductor layer591is formed on the patterned surface of the dielectric layer59. The through hole58T8formed in the dielectric layer58is connected to the conductor layer591.

The stack50shown inFIG.2is formed by stacking the first to ninth dielectric layers51to59such that the patterned surface of the first dielectric layer51serves as the first surface50A of the stack50and the surface of the ninth dielectric layer59opposite to the patterned surface thereof serves as the second surface50B of the stack50.

FIG.6shows the inside of the stack50formed by stacking the first to ninth dielectric layers51to59. As shown inFIG.6, the plurality of conductor layers and the plurality of through holes shown inFIG.3A to5Care stacked inside the stack50.

Correspondences between the circuit components of the filter1shown inFIG.1and the internal components of the stack50shown inFIG.3AtoFIG.5Cwill now be described. First, the first resonator10will be described. The first conductor part11is formed of the conductor layer571. The second conductor part12is formed of the conductor layer531. The third conductor part13is formed of the conductor layer532.

The conductor layer532(third conductor part13) and the through holes53T1,54T1,55T1, and56T1connect the conductor layer571forming the first conductor part11and the conductor layer531forming the second conductor part12. The conductor layer571forming the first conductor part11is connected to the ground terminals113to116via the through holes51T3to51T6, the conductor layer521, the through holes52T3to52T6and53T3to53T6, the through holes54T3to54T6, the conductor layer551, and the through holes55T8and56T8.

Next, the second resonator20will be described. The first conductor part21is formed of the conductor layer572. The second conductor part22is formed of the conductor layer533. The third conductor part23is formed of the conductor layer534.

The conductor layer534(third conductor part23) and the through holes53T2,54T2,55T2, and56T2connect the conductor layer572forming the first conductor part21and the conductor layer533forming the second conductor part22. The conductor layer572forming the first conductor part21is connected to the ground terminals113to116via the through holes51T3to51T6, the conductor layer521, the through holes52T3to52T6and53T3to53T6, the through holes54T3to54T6, the conductor layer551, and the through holes55T8and56T8.

Next, the third resonator30will be described. The first conductor part31is formed of the conductor layer581. The second conductor part32is formed of the conductor layer541.

The conductor layer581forming the first conductor part31is connected to the ground terminals113to116via the through holes51T3to51T6, the conductor layer521, the through holes52T3to52T6and53T3to53T6, the through holes54T3to54T6, the conductor layer551, and the through holes55T8,56T8, and57T8.

Next, the first and second stub resonators91and92will be described. The first stub resonator91is formed of the conductor layer573. The second stub resonator92is formed of the conductor layer574.

Next, the conductor portions4and5will be described. The conductor portion4is formed of the through holes51T1and52T1. The through hole51T1is connected to the first terminal111. The through hole52T1is connected to the conductor layer532forming the third conductor part13and is also connected to the conductor layer571forming the first conductor part11via the through holes53T1,54T1,55T1, and56T1.

The conductor portion5is formed of the through holes51T2and52T2. The through hole51T2is connected to the second terminal112. The through hole52T2is connected to the conductor layer534forming the third conductor part23and is also connected to the conductor layer572forming the first conductor part21via the through holes53T2,54T2,55T2, and56T2.

Next, the structural features of the filter1according to the present embodiment will be described with reference toFIG.2toFIG.8.FIG.7andFIG.8are each a perspective view showing part of an inside of the stack50.FIG.7mainly shows a plurality of conductor layers and a plurality of through holes constituting the first and second resonators10and20and the first and second stub resonators91and92.FIG.8mainly shows a plurality of conductor layers and a plurality of through holes constituting the third resonator30.

The first resonator10is arranged in an area on the −X direction side in the stack50. In other words, the first resonator10is arranged at a position closer to the side surface50C than the side surface50D. As shown inFIG.7, the first conductor part11(conductor layer571) and the second conductor part12(conductor layer531) of the first resonator10are arranged at positions different from each other in the stacking direction T. The second conductor part12is arranged between the first surface50A, where the plurality of terminals111to116are arranged, and the first conductor part11.

The first conductor part11(conductor layer571) includes a plurality of portions extending in a plurality of directions that are orthogonal to the stacking direction T. In particular, in the present embodiment, the first conductor part11(conductor layer571) includes four portions each extending in a direction parallel to the X direction and three portions each extending in a direction parallel to the Y direction.

The shape of the second conductor part12(conductor layer531) is long in a direction crossing the longitudinal direction of the stack50. In particular, in the present embodiment, the shape of the second conductor part12(conductor layer531) is a rectangular shape that is long in a direction parallel to the Y direction.

The second resonator20is arranged in an area on the X direction side in the stack50. In other words, the second resonator20is arranged at a position closer to the side surface50D than the side surface50C. As shown inFIG.7, the first conductor part21(conductor layer572) and the second conductor part22(conductor layer533) of the second resonator20are arranged at positions different from each other in the stacking direction T. The second conductor part22is arranged between the first surface50A, where the plurality of terminals111to116are arranged, and the first conductor part21.

The first conductor part21(conductor layer572) includes a plurality of portions extending in a plurality of directions that are orthogonal to the stacking direction T. In particular, in the present embodiment, the first conductor part21(conductor layer572) includes four portions each extending in a direction parallel to the X direction and three portions each extending in a direction parallel to the Y direction.

The shape of the second conductor part22(conductor layer533) is long in a direction crossing the longitudinal direction of the stack50. In particular, in the present embodiment, the shape of the second conductor part22(conductor layer533) is a rectangular shape that is long in a direction parallel to the Y direction.

At least part of the third resonator30is arranged between the first resonator10and the second resonator20when seen in the Z direction. In particular, in the present embodiment, part of the third resonator30is arranged between the first resonator10and the second resonator20.

As shown inFIG.8, the first conductor part31(conductor layer581) and the second conductor part32(conductor layer541) of the third resonator30are arranged at positions different from each other in the stacking direction T. The second conductor part32is arranged between the first surface50A, where the plurality of terminals111to116are arranged, and the first conductor part31.

The first conductor part31(conductor layer581) includes a plurality of portions extending in a plurality of directions that are orthogonal to the stacking direction T. In particular, in the present embodiment, the first conductor part31(conductor layer581) includes three portions each extending in a direction parallel to the X direction and four portions each extending in a direction parallel to the Y direction.

The first conductor part31(conductor layer581) has an asymmetrical shape with respect to a given XZ plane crossing the first conductor part31and also has an asymmetrical shape with respect to a given YZ plane crossing the first conductor part31. Hereinafter, the given XZ plane crossing the first conductor part31is referred to as a first virtual plane, and the given YZ plane crossing the first conductor part31is referred to as a second virtual plane. The first virtual plane may cross the center of the stack50in a direction parallel to the Y direction. The second virtual plane may cross the center of the stack50in a direction parallel to the X direction.

The shape of the second conductor part32(conductor layer541) is long in the longitudinal direction of the stack50. In particular, in the present embodiment, the shape of the second conductor part32(conductor layer541) is a rectangular shape that is long in a direction parallel to the X direction.

As shown inFIG.5AandFIG.6, the first conductor part11(conductor layer571) of the first resonator10and the first conductor part21(conductor layer572) of the second resonator20are arranged at the same position in the stacking direction T. As shown inFIG.5A,FIG.5B, andFIG.6, the first conductor part31(conductor layer581) of the third resonator30is arranged at a position different from the positions of the first conductor parts11and21in the stacking direction T. Part of the first conductor part11and part of the first conductor part21overlap the first conductor part31when seen in the Z direction. The shape of the first conductor part31is different from the shape of the first conductor part11and the shape of the first conductor part21.

As shown inFIG.3CandFIG.6, the second conductor part12(conductor layer531) of the first resonator10and the second conductor part22(conductor layer533) of the second resonator20are arranged at the same position in the stacking direction T. As shown inFIG.3C,FIG.4A, andFIG.6, the second conductor part32(conductor layer541) of the third resonator30is arranged at a position different from the positions of the second conductor parts12and22in the stacking direction T. Part of the second conductor part12and part of the second conductor part22overlap the second conductor part32when seen in the Z direction. The shape of the second conductor part32is different from the shape of the second conductor part12and the shape of the second conductor part22.

As shown inFIG.5AtoFIG.5C, the shape of the first stub resonator91(conductor layer573) and the shape of the second stub resonator92(conductor layer574) are different from each other. Specifically, the length of the first stub resonator91and the length of the second stub resonator92are different from each other. In the example shown inFIG.5AtoFIG.5C, the first stub resonator91is longer than the second stub resonator92. The first stub resonator91includes two portions each extending in a direction parallel to the X direction and one portion extending in a direction parallel to the Y direction. The second stub resonator92extends in a direction parallel to the X direction. Note that the width of the first stub resonator91and the width of the second stub resonator92are the same or approximately the same.

The first conductor part11of the first resonator10includes a first connecting part to which the first stub resonator91is connected and a first non-connecting part other than the first connecting part. Specifically, the first connecting part is a portion571aof the conductor layer571shown inFIG.5Anear the boundary with the conductor layer573indicated by a dotted line. InFIG.5A, an approximate position of the portion571ais indicated by an arrow. The first non-connecting part is a portion of the conductor layer571other than the portion571a.

The current density of the first connecting part (portion571a) in the center frequency of the passband of the filter1(band-pass filter) is lower than the current density of the first non-connecting part in the center frequency of the passband of the filter1(band-pass filter). In other words, the first stub resonator91is connected to or near a portion of the first conductor part11with the highest current density.

The first conductor part21of the second resonator20includes a second connecting part to which the second stub resonator92is connected and a second non-connecting part other than the second connecting part. Specifically, the first connecting part is a portion572aof the conductor layer572shown inFIG.5Anear the boundary with the conductor layer574indicated by a dotted line. InFIG.5A, an approximate position of the portion572ais indicated by an arrow. The second non-connecting part is a portion of the conductor layer572other than the portion572a.

The current density of the second connecting part (portion572a) in the center frequency of the passband of the filter1(band-pass filter) is lower than the current density of the second non-connecting part in the center frequency of the passband of the filter1(band-pass filter). In other words, the second stub resonator92is connected to or near a portion of the first conductor part21with the highest current density.

As described above, in the present embodiment, the first conductor part11and the second conductor part12of the first resonator10are arranged at positions different from each other in the stacking direction T. Thus, according to the present embodiment, the first conductor part11and the second conductor part12can be arranged while overlapping each other. Hence, according to the present embodiment, the area for arranging the first resonator10can be made substantially smaller than that for a case where the first conductor part11and the second conductor part12are formed in the same dielectric layer to be arranged in the same position in the stacking direction T.

The description of the first resonator10above is also applicable to the second and third resonators20and30. In view of these, according to the present embodiment, the filter1can be miniaturized.

In the present embodiment, part of the first conductor part11of the first resonator10and part of the first conductor part21of the second resonator20overlap the first conductor part31of the third resonator30when seen in the Z direction, and part of the second conductor part12of the first resonator10and part of the second conductor part22of the second resonator20overlap the second conductor part32of the third resonator30when seen in the Z direction. Also in view of this, according to the present embodiment, the filter1can be miniaturized.

In the present embodiment, each of the first conductor parts11,21, and31includes the plurality of portions extending in the plurality of directions different from each other. Hence, according to the present embodiment, the area for arranging each of the first conductor parts11,21, and31can be made substantially smaller than that for a case where each of the first conductor parts11,21, and31extends in one direction.

In the present embodiment, the conductor layer591is connected to the ground terminals113to116via the through holes51T3to51T6, the conductor layer521, the through holes52T3to52T6and53T3to53T6, the through holes54T3to54T6, the conductor layer551, and the through holes55T8,56T8,57T8, and58T8. The first to third resonators10,20, and30are arranged between the conductor layer521and the conductor layer591. Each of the conductor layers521and591overlap the first to third resonators10,20, and30when seen in the Z direction. The conductor layers521and591function as shields.

In the present embodiment, the impedance of the first conductor part11of the first resonator10is larger than the impedance of the second conductor part12of the first resonator10. The first stub resonator91is electrically connected to the first conductor part11having a large impedance. In particular, in the present embodiment, the first stub resonator91is connected to the portion of the first conductor part11with the highest current density. Thus, according to the present embodiment, it is possible to control spurious while suppressing an influence of the first stub resonator91to the basic resonance of the first resonator10.

The description of the first resonator10and the first stub resonator91above is also applicable to the second resonator20and the second stub resonator92. According to the present embodiment, it is possible to control spurious while suppressing an influence of the second stub resonator92to the basic resonance of the second resonator20.

Next, a description will be given of results of a first simulation indicating that the absolute value of attenuation (hereinafter referred to as pass attenuation) can be increased in a wide frequency band on a high-frequency side of the passband by the first and second stub resonators91and92. First, models of first to third comparative examples and a model of a practical example used in the first simulation will be described. The model of the first comparative example is a model of a filter of the first comparative example.FIG.9is a circuit diagram showing a circuit configuration of the filter of the first comparative example.FIG.10is an explanatory diagram showing a patterned surface of a seventh dielectric layer of a stack of the filter of the first comparative example. A configuration of the filter of the first comparative example is almost the same as the configuration of the filter1according to the present embodiment except that the first and second stub resonators91and92and the conductor layers573and574formed on the dielectric layer57of the stack50are not provided.

The model of the second comparative example is a model of a filter of the second comparative example.FIG.11is an explanatory diagram showing a patterned surface of the seventh dielectric layer57of the stack50of the filter of the second comparative example. In the filter of the second comparative example, a conductor layer575is formed on the dielectric layer57instead of the conductor layer573of the present embodiment. InFIG.11, the boundary between the conductor layer571and the conductor layer575is indicated by a dotted line. In the filter according to the second comparative example, the first stub resonator91is formed of the conductor layer575. Other configurations of the filter of the second comparative example are the same as the configurations of the filter1according to the present embodiment.

In particular, in the model of the second comparative example, the shape of the first stub resonator91(conductor layer575) is the same as the shape of the second stub resonator92(conductor layer574). In other words, the first stub resonator91extends in a direction parallel to the X direction.

The model of the third comparative example is a model of a filter according to the third comparative example.FIG.12is an explanatory diagram showing a patterned surface of the seventh dielectric layer57of the stack50of the filter of the third comparative example. In the filter of the third comparative example, a conductor layer576is formed in the dielectric layer57instead of the conductor layer574of the present embodiment. InFIG.12, the boundary between the conductor layer572and the conductor layer576is indicated by a dotted line. In the filter of the third comparative example, the second stub resonator92is formed of the conductor layer576. Other configurations of the filter of the third comparative example are the same as the configurations of the filter1according to the present embodiment.

In particular, in the model of the third comparative example, the shape of the second stub resonator92(conductor layer576) is the same as the shape of the first stub resonator91(conductor layer573). In other words, the second stub resonator92includes two portions each extending in a direction parallel to the X direction and one portion extending in a direction parallel to the Y direction.

The model of the practical example is a model of the filter1according to the present embodiment. In the simulation, in each of the models of the first to third comparative examples and the model of the practical example, the impedance ratio in each of the first and second resonators10and20was set to 0.106, and the impedance ratio in the third resonator30was set to 0.094.

In the first simulation, each of the models of the first to third comparative examples and the model of the practical example was designed to function as a band-pass filter. Under these conditions, pass attenuation characteristics of each of the models of the comparative examples and the model of the practical example were determined.

FIG.13is a characteristic chart showing pass attenuation characteristics of the model of the first comparative example.FIG.14is a characteristic chart showing pass attenuation characteristics of the model of the second comparative example.FIG.15is a characteristic chart showing pass attenuation characteristics of the model of the third comparative example.FIG.16is a characteristic chart showing pass attenuation characteristics of the model of the practical example. In each ofFIG.13toFIG.16, the horizontal axis represents frequency, and the vertical axis represents attenuation.

As shown inFIG.13toFIG.16, a plurality of spurious components are generated on the high-frequency side of the passband in all the models of the first to third comparative examples and the model of the practical example. The frequencies of the plurality of spurious components are different from each other among the models of the first to third comparative examples and the model of the practical example. As described above, in the model of the first comparative example, the first and second stub resonators91and92are not provided. Among the models of the second and third comparative examples and the model of the practical example, the shapes of the first and second stub resonators91and92are different from each other. The results of the first simulation shown inFIG.13toFIG.16indicate that a plurality of spurious components can be controlled with the first and second stub resonators91and92.

When the model of the first comparative example (FIG.13) and the model of the second comparative example (FIG.14) are compared with each other, the peak where the pass attenuation is relatively low is present in a band having frequencies of 17 GHz to 18 GHz in both the model of the first comparative example and the model of the second comparative example. In the model of the second comparative example, the smallest value of the pass attenuation at the peak is slightly greater than that of the model of the first comparative example.

In the model of the third comparative example (FIG.15), the peak where the pass attenuation is relatively low is present in a band having frequencies of 14 GHz to 18 GHz. In terms of a frequency band at the peak described above and near the peak for each of the models of the first to third comparative examples, the pass attenuation is higher in the model of the third comparative example than those of the models of the first and second comparative examples. In contrast, in terms of the band having frequencies of 24 GHz to 31 GHz for each of the models of the first to third comparative examples, the pass attenuation is lower in the model of the third comparative example than those of the models of the first and second comparative examples.

In the model of the practical example (FIG.16), the peak where the pass attenuation is relatively low is present in a band having frequencies of 14 GHz to 16 GHz. In terms of a frequency band at the peak described above and near the peak for each of the models of the first and second comparative examples and the model of the practical example, the pass attenuation is higher in the model of the practical example than those of the models of the first and second comparative examples. In terms of the band having frequencies of 27 GHz to 31 GHz for each of the model of the third comparative example and the model of the practical example, the pass attenuation is lower in the model of the practical example than that of the model of the third comparative example.

As understood from the results of the first simulation shown inFIG.13toFIG.16, spurious to be generated on the high-frequency side of the passband can be controlled with the first and second stub resonators91and92according to the present embodiment. As understood from the results of the first simulation shown inFIG.14toFIG.16, by the shape of the first stub resonator91and the shape of the second stub resonator92being made different from each other, the pass attenuation can be increased in a wide frequency band on the high-frequency side of the passband according to the present embodiment.

Next, a description will be given of results of a second simulation indicating that the pass attenuation (the absolute value of attenuation) can be increased on the high-frequency side of the passband, based on the shape of the first conductor part31of the third resonator30. First, a model of a fourth comparative example used in the second simulation will be described. The model of the fourth comparative example is a model of a filter of the fourth comparative example.

FIG.17is an explanatory diagram showing a patterned surface of an eighth dielectric layer of a stack of the filter of the fourth comparative example. In the filter of the fourth comparative example, a conductor layer1581is formed in the eighth dielectric layer58instead of the conductor layer581of the present embodiment. In the filter of the fourth comparative example, the first conductor part31of the third resonator30is formed of the conductor layer1581shown inFIG.17. In the filter of the fourth comparative example, the first conductor part31(conductor layer1581) has a shape symmetrical with respect to a YZ plane crossing the center of the stack50in a direction parallel to the X direction. Other configurations of the filter of the fourth comparative example are approximately the same as the configurations of the filter1according to the present embodiment.

FIG.18is a characteristic chart showing pass attenuation characteristics of the model of the fourth comparative example. InFIG.18, the horizontal axis represents frequency, and the vertical axis represents attenuation. In the model of the fourth comparative example, the peak where the pass attenuation is relatively low is present in a band having frequencies of 15 GHz to 18 GHz. In terms of a frequency band at the peak described above and near the peak for each of the model of the fourth comparative example and the model of the practical example (refer toFIG.16), the pass attenuation is lower in the model of the fourth comparative example than that of the practical example.

As described above, in the present embodiment, the first conductor part31(conductor layer581) has an asymmetrical shape. As understood from the results of the second simulation, by the first conductor part31having an asymmetrical shape, the pass attenuation can be increased on the high-frequency side of the passband according to the present embodiment.

Second Embodiment

A description will be made on a second embodiment of the present invention with reference toFIG.19.FIG.19is a circuit diagram showing a circuit configuration of a filter according to the present embodiment.

A filter1according to the present embodiment differs from that of the first embodiment in the following respects. The filter1according to the present embodiment includes a fourth resonator40. The fourth resonator40is arranged between the second resonator20and the third resonator30in the circuit configuration. In the present embodiment, the first to fourth resonators10,20,30, and40are configured so that the first resonator10and the third resonator30are adjacent to each other in the circuit configuration to be electromagnetically coupled to each other, the third resonator30and the fourth resonator40are adjacent to each other in the circuit configuration to be electromagnetically coupled to each other, and the second resonator20and the fourth resonator40are adjacent to each other in the circuit configuration to be electromagnetically coupled to each other. InFIG.19, a curve with a sign K13represents electric field coupling between the first resonator10and the third resonator30, a curve with a sign K34represents magnetic field coupling between the third resonator30and the fourth resonator40, and a curve with a sign K24represents electric field coupling between the second resonator20and the fourth resonator40.

A configuration of the fourth resonator40is basically the same as the configuration of the third resonator30. Specifically, the fourth resonator40includes a first conductor part41and a second conductor part42having an impedance smaller than that of the first conductor part41. The first conductor part41and the second conductor part42are electrically connected to each other. The first conductor part41is connected to ground. Each of the first conductor part41and the second conductor part42is a distributed constant line. In particular, in the present embodiment, the first conductor part41is a distributed constant line having a small width, and the second conductor part42is a distributed constant line having a width larger than that of the first conductor part41.

The fourth resonator40, similarly to the first to third resonators10,20, and30, is a stepped-impedance resonator composed of a distributed constant line having a small width and a distributed constant line having a large width.

Although not shown, the first conductor part41and the second conductor part42of the fourth resonator40, similarly to the first conductor part31and the second conductor part32of the third resonator30, are arranged at positions different from each other in the stacking direction T. The first conductor part31and the first conductor part41may be arranged at the same position in the stacking direction T or may be arranged at positions different from each other in the stacking direction T. Similarly, the second conductor part32and the second conductor part42may be arranged at the same position in the stacking direction T or may be arranged at positions different from each other in the stacking direction T.

In the present embodiment, at least part of the third resonator30and at least part of the fourth resonator40are arranged between the first resonator10and the second resonator20when seen in the Z direction (refer toFIG.2).

In the present embodiment, part of the first conductor part11of the first resonator10may overlap the first conductor part31of the third resonator30when seen in the Z direction. In this case, part of the first conductor part21of the second resonator20may overlap the first conductor part41of the fourth resonator40when seen in the Z direction.

In the present embodiment, part of the second conductor part12of the first resonator10may overlap the second conductor part32of the third resonator30when seen in the Z direction. In this case, part of the second conductor part22of the second resonator20may overlap the second conductor part42of the fourth resonator40when seen in the Z direction.

The filter1according to the present embodiment further includes a third stub resonator93electrically connected to the first conductor part31of the third resonator30, and a fourth stub resonator94electrically connected to the first conductor part41of the fourth resonator40. Each of the third and fourth stub resonators93and94is a distributed constant line.

The third stub resonator93is connected in the middle of the first conductor part31. InFIG.19, for the first conductor part31, a portion located between a connecting point with the third stub resonator93and the second conductor part32in the circuit configuration is indicated by a reference numeral31A, and a portion located between a connecting point with the third stub resonator93and the ground in the circuit configuration is indicated by a reference numeral31B.

The fourth stub resonator94is connected in the middle of the first conductor part41. InFIG.19, for the first conductor part41, a portion located between a connecting point with the fourth stub resonator94and the second conductor part42in the circuit configuration is indicated by a reference numeral41A, and a portion located between a connecting point with the fourth stub resonator94and the ground in the circuit configuration is indicated by a reference numeral41B.

The third and fourth stub resonators93and94are used, for example, to control spurious to be generated in a higher frequency region than a passband. Each of the third and fourth stub resonators93and94may be an open stub with one end being open or may be a short stub with one end being connected to ground.

The configuration, operation, and effects of the present embodiment are otherwise the same as those of the first embodiment.

The present invention is not limited to the foregoing embodiments, and various modifications may be made thereto. For example, the number and configuration of resonators are not limited to those shown in the embodiments, and any number and configuration of resonators may be employed as long as the scope of the claims is satisfied. The number of resonators may be one, two, or five or more.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims and equivalents thereof, the invention may be practiced in other embodiments than the foregoing most preferable embodiments.