Patent Publication Number: US-8120446-B2

Title: Electronic component

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic component including a plurality of resonators provided within a layered substrate. 
     2. Description of the Related Art 
     There are strong demands for reductions in size and thickness of communication apparatuses for short-range wireless communications, such as communication apparatuses conforming to the Bluetooth standard and communication apparatuses for use on a wireless local area network (LAN). Accordingly, reductions in size and thickness are also demanded of electronic components incorporated in such communication apparatuses. A bandpass filter that filters reception signals is one of electronic components incorporated in the communication apparatuses mentioned above. Reductions in size and thickness are also demanded of the bandpass filter. To meet the demands, a layered filter including a plurality of resonators each formed using at least one conductor layer of a layered substrate has been proposed as a bandpass filter that is operable in the frequency bands used for the above-mentioned communication apparatuses and capable of achieving reductions in size and thickness. Such a layered filter is disclosed in, for example, JP-A-9-148802, JP-A-2001-119209, JP-A-2005-012258 and JP-A-2005-159512. Hereinafter, a conductor layer used for forming a resonator is referred to as a resonator-forming conductor layer. 
     JP-A-9-148802 discloses a layered bandpass filter including at least two resonators. In this bandpass filter, each of the resonators incorporates two types of internal electrodes that are alternately arranged in the stacking direction and that each have a short-circuited end and an open-circuited end whose relative positions are reversed between the two types. 
     JP-A-2001-119209 discloses a layered filter module including a plurality of filters, each of the filters including a plurality of inductor-forming conductors. Each of the filters of this module incorporates three resonators formed using the inductor-forming conductors. In this module, the inductor-forming conductors in every adjacent filters do not include portions extending in parallel with each other along the entire length. 
     FIG. 7 of JP-A-2005-012258 shows a bandpass filter including four resonators. In this bandpass filter, each of the resonators incorporates two types of capacitance-forming electrodes that are alternately arranged in the stacking direction and that each have a short-circuited end and an open-circuited end whose relative positions are reversed between the two types.  FIG. 1  of this publication shows a bandpass filter including three resonators Q 1 , Q 2  and Q 3 . In this bandpass filter, the resonators Q 1 , Q 2  and Q 3  incorporate their respective strip lines for inductors. The strip lines of the resonators Q 1  and Q 2  are combline-coupled to each other, while the strip lines of the resonators Q 2  and Q 3  are interdigital-coupled to each other. 
     JP-A-2005-159512 discloses a layered bandpass filter including three resonator electrodes arranged side by side on one dielectric layer. The three resonator electrodes of this bandpass filter are disposed in a combline form or an interdigital form. 
     Typically, a bandpass filter including a plurality of resonators exhibits a broader passband width and a steeper attenuation pole as the number of the resonators increases. 
     For a conventional layered bandpass filter including a plurality of resonators, it is required to reduce the distance between every adjacent resonators in order to achieve reductions in size and thickness. If this is done, however, the inductive coupling between every adjacent resonators becomes too strong, so that it becomes difficult to attain desired filter characteristics. Specifically, the passband width of the filter becomes too broad if the inductive coupling between adjacent resonators becomes too strong. 
     For reducing the inductive coupling between every adjacent resonators in a layered bandpass filter without interfering with reductions in filter size and thickness, a possible approach is to reduce the width of each resonator-forming conductor layer to thereby increase the distance between every adjacent resonators. However, this reduces the Qs of all of the resonators. 
     To increase the resonator Q, it is effective to increase the surface area of the resonator-forming conductor layer. In view of this, each resonator can be formed using a plurality of resonator-forming conductor layers so as to increase the distance between every adjacent resonators to some extent without reducing the resonator Q. In this case, each resonator can be formed of two types of resonator-forming conductor layers that are alternately arranged in the stacking direction and that each have a short-circuited end and an open-circuited end whose relative positions are reversed between the two types, as proposed in JP-A-9-148802 or JP-A-2005-012258. In this case, the two types of resonator-forming conductor layers alternately arranged in the stacking direction are interdigital-coupled to each other, thereby constituting a resonator including an inductor and a capacitor. 
     However, if all resonators are each formed of the two types of resonator-forming conductor layers that are interdigital-coupled to each other as described above, the inductive coupling between every adjacent resonators becomes too strong, so that it becomes difficult to attain desired bandpass filter characteristics. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electronic component including a plurality of resonators provided within a layered substrate, the electronic component being capable of preventing the inductive coupling between every adjacent resonators from becoming too strong with miniaturization, while preventing reductions in Qs of all the resonators. 
     An electronic component of the present invention includes: a layered substrate including a plurality of dielectric layers stacked; and a plurality of resonators provided within the layered substrate such that every adjacent two of the resonators are inductively coupled to each other. In this electronic component, at least one, but not all, of the plurality of resonators includes a resonator-forming conductor layer of a first type and a resonator-forming conductor layer of a second type that each have a short-circuited end and an open-circuited end, relative positions of the short-circuited end and the open-circuited end being reversed between the first and second types. The resonator-forming conductor layers of the first type and the second type are arranged to be adjacent to each other in a direction in which the plurality of dielectric layers are stacked. 
     According to the electronic component of the present invention, at least one, but not all, of the plurality of resonators includes the resonator-forming conductor layers of the first type and the second type. Consequently, the electronic component of the present invention inevitably includes a portion in which the at least one resonator that includes the resonator-forming conductor layers of the first type and the second type is adjacent to another one that does not include the resonator-forming conductor layers of the first type and the second type. 
     In the electronic component of the present invention, the plurality of resonators may include a first resonator, a second resonator and a third resonator, and the second resonator may be adjacent to and inductively coupled to each of the first resonator and the third resonator. In this case, of the first, second and third resonators, only the second resonator may include the resonator-forming conductor layers of the first type and the second type, or only the first and third resonators may each include the resonator-forming conductor layers of the first type and the second type. 
     In the electronic component of the present invention, at least one of the plurality of resonators, other than the at least one that includes the resonator-forming conductor layers of the first type and the second type, may include a through-hole type inductor formed using at least one through hole provided within the layered substrate. 
     In the electronic component of the present invention, each of the plurality of resonators may be a quarter-wave resonator having a short-circuited end and an open-circuited end. 
     The electronic component of the present invention may further include an input terminal and an output terminal disposed on a periphery of the layered substrate. The plurality of resonators may be located between the input terminal and the output terminal in terms of circuit configuration, and may implement the function of a bandpass filter. It should be noted that the phrase “in terms of circuit configuration” used herein is intended to mean positioning in a schematic circuit diagram, not in the physical configuration. 
     According to the electronic component of the present invention, at least one, but not all, of the plurality of resonators includes the resonator-forming conductor layers of the first type and the second type. Consequently, according to the present invention, there inevitably exists a portion in which the at least one resonator that includes the resonator-forming conductor layers of the first type and the second type is adjacent to another one that does not include the resonator-forming conductor layers of the first type and the second type. In this portion, it is possible to make the inductive coupling between the resonators weaker than in a case where two resonators that each include the resonator-forming conductor layers of the first type and the second type are adjacent to each other. Consequently, the present invention makes it possible to prevent the inductive coupling between every adjacent resonators from becoming too strong with miniaturization of the electronic component, while preventing reductions in Qs of all the resonators. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a main part of an electronic component of a first embodiment of the invention. 
         FIG. 2  is a perspective view showing the outer appearance of the electronic component of the first embodiment of the invention. 
         FIG. 3  is an illustrative view showing the main part of the electronic component as viewed from direction A of  FIG. 1 . 
         FIG. 4  is a schematic diagram showing the circuit configuration of the electronic component of the first embodiment of the invention. 
         FIG. 5A  to  FIG. 5C  are illustrative views respectively showing the top surfaces of first to third dielectric layers of a layered substrate of the first embodiment of the invention. 
         FIG. 6A  to  FIG. 6C  are illustrative views respectively showing the top surfaces of fourth to sixth dielectric layers of the layered substrate of the first embodiment of the invention. 
         FIG. 7A  to  FIG. 7C  are illustrative views respectively showing the top surfaces of seventh to ninth dielectric layers of the layered substrate of the first embodiment of the invention. 
         FIG. 8  is a plot showing the pass attenuation characteristic of the electronic component of the first embodiment of the invention and that of an electronic component of a comparative example. 
         FIG. 9  is a plot showing an enlarged view of a portion of  FIG. 8 . 
         FIG. 10  is a perspective view showing a main part of an electronic component of a second embodiment of the invention. 
         FIG. 11  is a perspective view showing the outer appearance of the electronic component of the second embodiment of the invention. 
         FIG. 12  is an illustrative view showing the main part of the electronic component as viewed from direction B of  FIG. 10 . 
         FIG. 13A  to  FIG. 13C  are illustrative views respectively showing the top surfaces of first to third dielectric layers of a layered substrate of the second embodiment of the invention. 
         FIG. 14A  to  FIG. 14C  are illustrative views respectively showing the top surfaces of fourth to sixth dielectric layers of the layered substrate of the second embodiment of the invention. 
         FIG. 15A  to  FIG. 15C  are illustrative views respectively showing the top surfaces of seventh to ninth dielectric layers of the layered substrate of the second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Preferred embodiments of the present invention will now be described in detail with reference to the drawings. Reference is first made to  FIG. 4  to describe the circuit configuration of an electronic component of a first embodiment of the invention. The electronic component  1  of the first embodiment has the function of a bandpass filter. As shown in  FIG. 4 , the electronic component  1  includes an input terminal  2 , an output terminal  3 , three resonators  4 ,  5  and  6 , and capacitors  17  to  19 . 
     The resonator  4  includes an inductor  11  and a capacitor  14 . The resonator  5  includes an inductor  12  and a capacitor  15 . The resonator  6  includes an inductor  13  and a capacitor  16 . In terms of circuit configuration, the resonator  5  is located between the resonator  4  and the resonator  6 . The resonator  5  is adjacent to and inductively coupled to each of the resonators  4  and  6 . The inductor  12  is inductively coupled to each of the inductors  11  and  13 . In  FIG. 4  the inductive coupling between the inductors  11  and  12  and the inductive coupling between the inductors  12  and  13  are shown with curves M. 
     One end of the inductor  11  and one end of each of the capacitors  14 ,  17  and  19  are connected to the input terminal  2 . The other end of the inductor  11  and the other end of the capacitor  14  are connected to the ground. One end of the inductor  12  and one end of each of the capacitors  15  and  18  are connected to the other end of the capacitor  17 . The other end of the inductor  12  and the other end of the capacitor  15  are connected to the ground. One end of the inductor  13 , one end of the capacitor  16 , the other end of the capacitor  19  and the output terminal  3  are connected to the other end of the capacitor  18 . The other end of the inductor  13  and the other end of the capacitor  16  are connected to the ground. The resonator  5  is inductively coupled to the resonator  4  as mentioned above, and is also capacitively coupled to the resonator  4  through the capacitor  17 . The resonator  5  is inductively coupled to the resonator  6  as mentioned above, and is also capacitively coupled to the resonator  6  through the capacitor  18 . 
     The resonators  4 ,  5  and  6  are located between the input terminal  2  and the output terminal  3  in terms of circuit configuration, and implement the function of a bandpass filter. Each of the resonators  4 ,  5  and  6  is a quarter-wave resonator having a short-circuited end and an open-circuited end. The resonators  4 ,  5  and  6  correspond to the first resonator, the second resonator and the third resonator, respectively, of the present invention. 
     When signals are received at the input terminal  2  of the electronic component  1 , among the signals, those of frequencies within a certain frequency band selectively pass through the bandpass filter formed using the resonators  4 ,  5  and  6 , and are outputted from the output terminal  3 . 
     Reference is now made to  FIG. 1  to  FIG. 3  to outline the structure of the electronic component  1 .  FIG. 1  is a perspective view showing a main part of the electronic component  1 .  FIG. 2  is a perspective view showing the outer appearance of the electronic component  1 .  FIG. 3  is an illustrative view showing the main part of the electronic component  1  as viewed from direction A of  FIG. 1 . 
     The electronic component  1  includes a layered substrate  20  for integrating the components of the electronic component  1 . As will be described in detail later, the layered substrate  20  includes a plurality of dielectric layers and a plurality of conductor layers that are stacked. Each of the inductors  11  and  13  is a through-hole type inductor formed using one or more through holes provided in the layered substrate  20 . The inductor  12  is formed using two or more of the conductor layers located within the layered substrate  20 . Each of the capacitors  14  to  19  is formed using two or more of the conductor layers and one or more of the dielectric layers located within the layered substrate  20 . 
     As shown in  FIG. 2 , the layered substrate  20  is rectangular-solid-shaped and has a top surface  20 A, a bottom surface  20 B and four side surfaces  20 C to  20 F, as the periphery. The top surface  20 A and the bottom surface  20 B are parallel to each other, the side surfaces  20 C and  20 D are parallel to each other, and the side surfaces  20 E and  20 F are parallel to each other. The side surfaces  20 C to  20 F are each perpendicular to the top surface  20 A and the bottom surface  20 B. On the layered substrate  20 , an input terminal  22  is provided to extend from the bottom surface  20 B to the end of the side surface  20 E, and an output terminal  23  is provided to extend from the bottom surface  20 B to the end of the side surface  20 F. Grounding terminals  24  and  25  are provided on the bottom surface  20 B and the top surface  20 A, respectively. The input terminal  22  corresponds to the input terminal  2  of  FIG. 4 , and the output terminal  23  corresponds to the output terminal  3  of  FIG. 4 . The grounding terminals  24  and  25  are connected to the ground. 
     For the layered substrate  20 , the direction perpendicular to the side surfaces  20 C and  20 D is the direction in which the plurality of dielectric layers are stacked. In  FIG. 1  to  FIG. 3  the arrow T indicates the direction in which the plurality of dielectric layers are stacked. 
     Reference is now made to  FIG. 5A  to  FIG. 7C  to describe the dielectric layers and the conductor layers of the layered substrate  20  in detail.  FIG. 5A  to  FIG. 5C  respectively show the top surfaces of the first to third dielectric layers from the top.  FIG. 6A  to  FIG. 6C  respectively show the top surfaces of the fourth to sixth dielectric layers from the top.  FIG. 7A  to  FIG. 7C  respectively show the top surfaces of the seventh to ninth dielectric layers from the top. 
     A grounding conductor layer  311  is formed on the top surface of the first dielectric layer  31  of  FIG. 5A . The conductor layer  311  is connected to the grounding terminal  24 . The dielectric layer  31  has two through holes  314  and  316  connected to the conductor layer  311 . 
     A grounding conductor layer  321  is formed on the top surface of the second dielectric layer  32  of  FIG. 5B . The conductor layer  321  is connected to the grounding terminals  24  and  25 . The dielectric layer  32  has through holes  324  and  326  that are respectively connected to the through holes  314  and  316 . 
     A capacitor-forming conductor layer  331  is formed on the top surface of the third dielectric layer  33  of  FIG. 5C . The conductor layer  331  is connected to the grounding terminal  24 . The dielectric layer  33  has through holes  334  and  336  that are respectively connected to the through holes  324  and  326 . 
     Capacitor-forming conductor layers  341  and  342  are formed on the top surface of the fourth dielectric layer  34  of  FIG. 6A . The conductor layer  341  is connected to the input terminal  22 , and the conductor layer  342  is connected to the output terminal  23 . The through hole  334  is connected to the conductor layer  341 , and the through hole  336  is connected to the conductor layer  342 . 
     A capacitor-forming conductor layer  351  is formed on the top surface of the fifth dielectric layer  35  of  FIG. 6B . 
     A resonator-forming conductor layer  361  is formed on the top surface of the sixth dielectric layer  36  of  FIG. 6C . The conductor layer  361  has a short-circuited end  361   a , and an open-circuited end  361   b  opposite thereto. The short-circuited end  361   a  is connected to the grounding terminal  25 . 
     A resonator-forming conductor layer  371  is formed on the top surface of the seventh dielectric layer  37  of  FIG. 7A . The conductor layer  371  has a short-circuited end  371   a , and an open-circuited end  371   b  opposite thereto. The short-circuited end  371   a  is connected to the grounding terminal  24 . 
     A resonator-forming conductor layer  381  is formed on the top surface of the eighth dielectric layer  38  of  FIG. 7B . The conductor layer  381  has a short-circuited end  381   a , and an open-circuited end  381   b  opposite thereto. The short-circuited end  381   a  is connected to the grounding terminal  25 . 
     A resonator-forming conductor layer  391  is formed on the top surface of the ninth dielectric layer  39  of  FIG. 7C . The conductor layer  391  has a short-circuited end  391   a , and an open-circuited end  391   b  opposite thereto. The short-circuited end  391   a  is connected to the grounding terminal  24 . No conductor layer is formed on the bottom surface of the dielectric layer  39 . 
     The through holes  314 ,  324  and  334  are connected in series to each other to form a through hole line  110  shown in  FIG. 1  and  FIG. 3 . Similarly, the through holes  316 ,  326  and  336  are connected in series to each other to form a through hole line  130  shown in  FIG. 1  and  FIG. 3 . The through hole line  110  constitutes the inductor  11  of the resonator  4 , and the through hole line  130  constitutes the inductor  13  of the resonator  6 . 
     The conductor layers  361 ,  371 ,  381  and  391  each have the short-circuited end and the open-circuited end, and are arranged in the direction in which the plurality of dielectric layers are stacked, such that the relative positions of the short-circuited end and the open-circuited end are alternately reversed. The conductor layers  361  and  381  are the same in relative positions of the short-circuited end and the open-circuited end. Each of the conductor layers  361  and  381  will be hereinafter called a resonator-forming conductor layer of a first type. The conductor layers  371  and  391  are the same in relative positions of the short-circuited end and the open-circuited end. Each of the conductor layers  371  and  391  will be hereinafter called a resonator-forming conductor layer of a second type. The relative positions of the short-circuited end and the open-circuited end are reversed between the resonator-forming conductor layers of the first type  361 ,  381  and the second type  371 ,  391 . Thus, the resonator-forming conductor layers of the first type and the second type, being reversed in relative positions of the short-circuited end and the open-circuited end, are alternately arranged to be adjacent to each other in the direction in which the plurality of dielectric layers are stacked. 
     The resonator-forming conductor layers of the first type  361 ,  381  and the second type  371 ,  391  are interdigital-coupled to each other to thereby constitute the inductor  12  of the resonator  5 . According to the present embodiment, of the three resonators  4 ,  5  and  6 , only the resonator  5  includes the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other. 
     The conductor layers  331  and  341  and the dielectric layer  33  constitute the capacitor  14  of the resonator  4 . The conductor layers  331  and  342  and the dielectric layer  33  constitute the capacitor  16  of the resonator  6 . The conductor layers  361 ,  371 ,  381  and  391  and the dielectric layers  36 ,  37  and  38  constitute the capacitor  15  of the resonator  5 . 
     The conductor layers  341  and  361  and the dielectric layers  34  and  35  constitute the capacitor  17  of  FIG. 4 . The conductor layers  342  and  361  and the dielectric layers  34  and  35  constitute the capacitor  18  of  FIG. 4 . The conductor layers  341 ,  342  and  351  and the dielectric layer  34  constitute the capacitor  19  of  FIG. 4 . 
     The first to ninth dielectric layers  31  to  39  and the conductor layers described above are stacked to form the layered substrate  20  shown in  FIG. 1  to  FIG. 3 . The terminals  22  to  25  shown in  FIG. 2  are formed on the periphery of the layered substrate  20 . 
     In the present embodiment, a variety of types of substrates are employable as the layered substrate  20 , such as one in which the dielectric layers are formed of a resin, ceramic, or a resin-ceramic composite material. However, a low-temperature co-fired ceramic multilayer substrate, which is excellent in high frequency response, is particularly preferable as the layered substrate  20 . 
     In the present embodiment, only the resonator  5  of the three resonators  4 ,  5  and  6  includes the inductor  12  formed of the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other. According to the present embodiment, it is possible to increase the Q of the inductor  12  and consequently increase the Q of the resonator  5 , compared with a case in which the inductor of the resonator  5  is formed only of a single resonator-forming conductor layer. 
     Typically, in an electronic component that includes three resonators and performs the function of a bandpass filter, the resonator located in the middle tends to be lower in Q than the other two resonators. This is because the middle resonator tends to cause an electric field loss between itself and a conductor layer connected to the ground, compared with the other two resonators. According to the present embodiment, of the three resonators  4 ,  5  and  6 , the resonator  5  located in the middle includes the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other. This serves to prevent the resonator  5 , which particularly tends to suffer a reduction in Q, from suffering the reduction in Q. 
     In the present embodiment, the resonators  4  and  6 , which are other than the resonator  5  that includes the resonator-forming conductor layers of the first type and the second type as described above, respectively include the through-hole type inductors  11  and  13  formed using the through holes provided within the layered substrate  20 . Compared with an inductor formed only of a single resonator-forming conductor layer, the through-hole type inductor has a larger surface area and consequently has a higher Q. Accordingly, the present embodiment provides higher Qs for the inductors  11  and  13 , and consequently provides higher Qs for the resonators  4  and  6 , compared with a case in which the inductors of the resonators  4  and  6  are each formed only of a single resonator-forming conductor layer. 
     If all of the resonators  4 ,  5  and  6  each include the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other, the inductive coupling between the resonators  4  and  5  and the inductive coupling between the resonators  5  and  6  become too strong. In contrast, according to the present embodiment, only the resonator  5  of the three resonators  4 ,  5  and  6  includes the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other, and the other two resonators  4  and  6 , which are inductively coupled to the resonator  5 , do not. Consequently, according to the present embodiment, the inductive coupling between the resonators  4  and  5  and the inductive coupling between the resonators  5  and  6  are each weaker than in the case where all of the resonators  4 ,  5  and  6  each include the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other. 
     According to the present embodiment, in particular, the direction of travel of electromagnetic waves in the inductors  11  and  13  of the resonators  4  and  6  and the direction of travel of electromagnetic waves in the inductor  12  of the resonator  5  are orthogonal to each other. This serves to further weaken the inductive coupling between the resonators  4  and  5  and the inductive coupling between the resonators  5  and  6 . 
     Consequently, the present embodiment makes it possible to prevent the inductive coupling between every adjacent resonators from becoming too strong with miniaturization of the electronic component, while preventing reductions in Qs of all the resonators. Furthermore, the present embodiment facilitates reductions in size and thickness of the electronic component  1 , because the embodiment allows a reduction in magnitude of the inductive coupling between every adjacent resonators even in the case where the distance between every adjacent resonators must be reduced with reductions in size and thickness of the electronic component  1 . 
     The electronic component  1  of the present embodiment is designed to function as a bandpass filter having a passband of, for example, approximately 2.4 to 2.5 GHz. The 2.4 to 2.5 GHz band corresponds to the passband of a bandpass filter for use in a communication apparatus conforming to the Bluetooth standard and a communication apparatus for use on a wireless LAN. 
     Reference is now made to  FIG. 8  and  FIG. 9  to describe an example of pass attenuation characteristics determined by simulation on the electronic component  1  of the present embodiment and an electronic component of a comparative example. For this simulation, the electronic component  1  of the present embodiment and the electronic component of the comparative example are each designed to function as a bandpass filter having a passband of approximately 2.4 to 2.5 GHz. The electronic component of the comparative example has the same circuit configuration as that of the electronic component  1  of the present embodiment. In the electronic component of the comparative example, the inductor of each resonator includes three resonator-forming conductor layers stacked. The three resonator-forming conductor layers are connected to each other at portions near their respective one ends. The other end of each of the three layers is connected to the ground. 
       FIG. 8  shows the pass attenuation characteristic of the electronic component  1  of the present embodiment and that of the electronic component of the comparative example.  FIG. 9  shows an enlarged view of a portion of  FIG. 8 . In each of  FIG. 8  and  FIG. 9  the solid curve shows the characteristic of the electronic component  1  of the present embodiment while the dotted curve shows the characteristic of the electronic component of the comparative example. As can be seen from  FIG. 9 , the electronic component  1  of the present embodiment has a smaller attenuation in the passband (2.4 to 2.5 GHz) than that of the electronic component of the comparative example. This is presumably because the inductors  11 ,  12  and  13  of the resonators  4 ,  5  and  6  of the present embodiment have higher Qs. 
     Second Embodiment 
     An electronic component of a second embodiment of the invention will now be described. The electronic component  1  of the second embodiment has the same circuit configuration as that of the first embodiment shown in  FIG. 4 . 
       FIG. 10  is a perspective view showing a main part of the electronic component  1  of the second embodiment.  FIG. 11  is a perspective view showing the outer appearance of the electronic component  1  of the second embodiment.  FIG. 12  is an illustrative view showing the main part of the electronic component  1  as viewed from direction B of  FIG. 10 . 
     The electronic component  1  includes a layered substrate  20  for integrating the components of the electronic component  1 . As will be described in detail later, the layered substrate  20  includes a plurality of dielectric layers and a plurality of conductor layers that are stacked. Each of the inductors  11  and  13  is formed using two or more of the conductor layers located within the layered substrate  20 . The inductor  12  is a through-hole type inductor formed using one or more through holes provided in the layered substrate  20 . Each of the capacitors  14  to  19  is formed using two or more of the conductor layers and one or more of the dielectric layers located within the layered substrate  20 . 
     As shown in  FIG. 11 , the layered substrate  20  is rectangular-solid-shaped and has a top surface  20 A, a bottom surface  20 B and four side surfaces  20 C to  20 F, as the periphery. The top surface  20 A and the bottom surface  20 B are parallel to each other, the side surfaces  20 C and  20 D are parallel to each other, and the side surfaces  20 E and  20 F are parallel to each other. The side surfaces  20 C to  20 F are each perpendicular to the top surface  20 A and the bottom surface  20 B. An input terminal  22 , an output terminal  23  and a grounding terminal  26  are provided on the bottom surface  20 B of the layered substrate  20 . On the bottom surface  20 B the input terminal  22  is located closer to the side surface  20 E, the output terminal  23  is located closer to the side surface  20 F, and the grounding terminal  26  is located between the input terminal  22  and the output terminal  23 . Grounding terminals  27  and  28  are provided on the top surface  20 A. The input terminal  22  corresponds to the input terminal  2  of  FIG. 4 , and the output terminal  23  corresponds to the output terminal  3  of  FIG. 4 . The grounding terminals  26 ,  27  and  28  are connected to the ground. 
     For the layered substrate  20 , the direction perpendicular to the side surfaces  20 C and  20 D is the direction in which the plurality of dielectric layers are stacked. In  FIG. 10  to  FIG. 12  the arrow T indicates the direction in which the plurality of dielectric layers are stacked. 
     Reference is now made to  FIG. 13A  to  FIG. 15C  to describe the dielectric layers and the conductor layers of the layered substrate  20  in detail.  FIG. 13A  to  FIG. 13C  respectively show the top surfaces of the first to third dielectric layers from the top.  FIG. 14A  to  FIG. 14C  respectively show the top surfaces of the fourth to sixth dielectric layers from the top.  FIG. 15A  to  FIG. 15C  respectively show the top surfaces of the seventh to ninth dielectric layers from the top. 
     A grounding conductor layer  411  is formed on the top surface of the first dielectric layer  41  of  FIG. 13A . The conductor layer  411  is connected to the grounding terminals  26 ,  27  and  28 . 
     A grounding conductor layer  421  is formed on the top surface of the second dielectric layer  42  of  FIG. 13B . The conductor layer  421  is connected to the grounding terminal  26 . The dielectric layer  42  has a through hole  422  connected to the conductor layer  421 . 
     A capacitor-forming conductor layer  431  is formed on the top surface of the third dielectric layer  43  of  FIG. 13C . The dielectric layer  43  has a through hole  432  connected to the through hole  422 . 
     A capacitor-forming conductor layer  441  is formed on the top surface of the fourth dielectric layer  44  of  FIG. 14A . The conductor layer  441  is connected to the grounding terminal  26 . The dielectric layer  44  has a through hole  442  connected to the through hole  432 . 
     A capacitor-forming conductor layer  451  is formed on the top surface of the fifth dielectric layer  45  of  FIG. 14B . The through hole  442  is connected to the conductor layer  451 . 
     Resonator-forming conductor layers  461  and  462  are formed on the top surface of the sixth dielectric layer  46  of  FIG. 14C . The conductor layer  461  has a short-circuited end  461   a , and an open-circuited end  461   b  opposite thereto. The short-circuited end  461   a  is connected to the grounding terminal  26 . The conductor layer  462  has a short-circuited end  462   a , and an open-circuited end  462   b  opposite thereto. The short-circuited end  462   a  is connected to the grounding terminal  26 . 
     Resonator-forming conductor layers  471  and  472  are formed on the top surface of the seventh dielectric layer  47  of  FIG. 15A . The conductor layer  471  includes a main body portion  471   c  and a connecting portion  471   d . The boundary between the main body portion  471   c  and the connecting portion  471   d  is shown with a dotted line in  FIG. 15A . The main body portion  471   c  includes a short-circuited end  471   a , and an open-circuited end  471   b  opposite thereto. The short-circuited end  471   a  is connected to the grounding terminal  27 . One end of the connecting portion  471   d  is connected to a portion of the main body portion  471   c  near the open-circuited end  471   b . The other end of the connecting portion  471   d  is connected to the input terminal  22 . 
     The conductor layer  472  includes a main body portion  472   c  and a connecting portion  472   d . The boundary between the main body portion  472   c  and the connecting portion  472   d  is shown with a dotted line in  FIG. 15A . The main body portion  472   c  includes a short-circuited end  472   a , and an open-circuited end  472   b  opposite thereto. The short-circuited end  472   a  is connected to the grounding terminal  28 . One end of the connecting portion  472   d  is connected to a portion of the main body portion  472   c  near the open-circuited end  472   b . The other end of the connecting portion  472   d  is connected to the output terminal  23 . 
     Resonator-forming conductor layers  481  and  482  are formed on the top surface of the eighth dielectric layer  48  of  FIG. 15B . The conductor layer  481  has a short-circuited end  481   a , and an open-circuited end  481   b  opposite thereto. The short-circuited end  481   a  is connected to the grounding terminal  26 . The conductor layer  482  has a short-circuited end  482   a , and an open-circuited end  482   b  opposite thereto. The short-circuited end  482   a  is connected to the grounding terminal  26 . 
     A capacitor-forming conductor layer  491  is formed on the top surface of the ninth dielectric layer  49  of  FIG. 15C . 
     The through holes  422 ,  432  and  442  are connected in series to each other to form a through hole line  120  shown in  FIG. 10  and  FIG. 12 . The through hole line  120  constitutes the inductor  12  of the resonator  5 . 
     The conductor layers  461 ,  471  and  481  each have the short-circuited end and the open-circuited end, and are arranged in the direction in which the plurality of dielectric layers are stacked, such that the relative positions of the short-circuited end and the open-circuited end are alternately reversed. The conductor layers  461  and  481  are the same in relative positions of the short-circuited end and the open-circuited end. Each of these conductor layers  461  and  481  will be hereinafter called a resonator-forming conductor layer of a first type. The conductor layer  471  will be hereinafter called a resonator-forming conductor layer of a second type. The relative positions of the short-circuited end and the open-circuited end are reversed between the resonator-forming conductor layers of the first type  461 ,  481  and the second type  471 . Thus, the resonator-forming conductor layers of the first type and the second type, being reversed in relative positions of the short-circuited end and the open-circuited end, are alternately arranged to be adjacent to each other in the direction in which the plurality of dielectric layers are stacked. The resonator-forming conductor layers of the first type  461 ,  481  and the second type  471  are interdigital-coupled to each other to thereby constitute the inductor  11  of the resonator  4 . 
     The conductor layers  462 ,  472  and  482  each have the short-circuited end and the open-circuited end, and are arranged in the direction in which the plurality of dielectric layers are stacked, such that the relative positions of the short-circuited end and the open-circuited end are alternately reversed. The conductor layers  462  and  482  are the same in relative positions of the short-circuited end and the open-circuited end. Each of these conductor layers  462  and  482  will be hereinafter called a resonator-forming conductor layer of a first type. The conductor layer  472  will be hereinafter called a resonator-forming conductor layer of a second type. The relative positions of the short-circuited end and the open-circuited end are reversed between the resonator-forming conductor layers of the first type  462 ,  482  and the second type  472 . Thus, the resonator-forming conductor layers of the first type and the second type, being reversed in relative positions of the short-circuited end and the open-circuited end, are alternately arranged to be adjacent to each other in the direction in which the plurality of dielectric layers are stacked. The resonator-forming conductor layers of the first type  462 ,  482  and the second type  472  are interdigital-coupled to each other to thereby constitute the inductor  13  of the resonator  6 . 
     According to the second embodiment, of the three resonators  4 ,  5  and  6 , only the resonators  4  and  6  each include the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other. 
     The conductor layers  461 ,  471  and  481  and the dielectric layers  46  and  47  constitute the capacitor  14  of the resonator  4 . The conductor layers  462 ,  472  and  482  and the dielectric layers  46  and  47  constitute the capacitor  16  of the resonator  6 . The conductor layers  431 ,  441  and  451  and the dielectric layers  43  and  44  constitute the capacitor  15  of the resonator  5 . 
     The conductor layers  451  and  461  and the dielectric layer  46  constitute the capacitor  17  of  FIG. 4 . The conductor layers  451  and  462  and the dielectric layer  46  constitute the capacitor  18  of  FIG. 4 . The conductor layers  481 ,  482  and  491  and the dielectric layer  48  constitute the capacitor  19  of  FIG. 4 . 
     The first to ninth dielectric layers  41  to  49  and the conductor layers described above are stacked to form the layered substrate  20  shown in  FIG. 10  to  FIG. 12 . The terminals  22 ,  23  and  26  to  28  shown in  FIG. 11  are formed on the periphery of the layered substrate  20 . 
     In the second embodiment, as in the first embodiment, a variety of types of substrates are employable as the layered substrate  20 , such as one in which the dielectric layers are formed of a resin, ceramic, or a resin-ceramic composite material. However, a low-temperature co-fired ceramic multilayer substrate, which is excellent in high frequency response, is particularly preferable as the layered substrate  20 . 
     In the second embodiment, only the resonators  4  and  6  of the three resonators  4 ,  5  and  6  include the inductors  11  and  13  each formed of the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other. According to the second embodiment, it is possible to increase the Qs of the inductors  11  and  13  and consequently increase the Qs of the resonators  4  and  6 , compared with a case in which the inductors of the resonators  4  and  6  are each formed only of a single resonator-forming conductor layer. 
     In the second embodiment, the resonator  5 , which is other than the resonators  4  and  6  that include the resonator-forming conductor layers of the first type and the second type as described above, includes the through-hole type inductor  12  formed using the through holes provided within the layered substrate  20 . Compared with an inductor formed only of a single resonator-forming conductor layer, the through-hole type inductor has a larger surface area and consequently has a higher Q. Accordingly, the second embodiment provides a higher Q for the inductor  12 , and consequently provides a higher Q for the resonator  5 , compared with a case in which the inductor of the resonator  5  is formed only of a single resonator-forming conductor layer. 
     If all of the resonators  4 ,  5  and  6  each include the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other, the inductive coupling between the resonators  4  and  5  and the inductive coupling between the resonators  5  and  6  become too strong. In contrast, according to the second embodiment, only the resonators  4  and  6  of the three resonators  4 ,  5  and  6  each include the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other, and the other resonator  5 , which is inductively coupled to the resonators  4  and  6 , does not. Consequently, according to the second embodiment, the inductive coupling between the resonators  4  and  5  and the inductive coupling between the resonators  5  and  6  are each weaker than in the case where all of the resonators  4 ,  5  and  6  each include the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other. 
     According to the second embodiment, in particular, the direction of travel of electromagnetic waves in the inductors  11  and  13  of the resonators  4  and  6  and the direction of travel of electromagnetic waves in the inductor  12  of the resonator  5  are orthogonal to each other. This serves to further weaken the inductive coupling between the resonators  4  and  5  and the inductive coupling between the resonators  5  and  6 . 
     Consequently, the second embodiment makes it possible to prevent the inductive coupling between every adjacent resonators from becoming too strong with miniaturization of the electronic component, while preventing reductions in Qs of all the resonators. Furthermore, the second embodiment facilitates reductions in size and thickness of the electronic component  1 , because the embodiment allows a reduction in magnitude of the inductive coupling between every adjacent resonators even in the case where the distance between every adjacent resonators must be reduced with reductions in size and thickness of the electronic component  1 . 
     In the second embodiment, as in the first embodiment, the electronic component  1  is designed to function as a bandpass filter having a passband of, for example, approximately 2.4 to 2.5 GHz. The remainder of configuration, function and effects of the second embodiment are similar to those of the first embodiment. 
     The present invention is not limited to the foregoing embodiments but can be carried out in various modifications. For example, in the case where the electronic component  1  includes three resonators  4 ,  5  and  6  as in the foregoing embodiments, any one of the three resonators, such as the resonator  4  or the resonator  6 , or any two of the three resonators, such as the resonators  4  and  5  or the resonators  5  and  6 , can include the resonator-forming conductor layers of the first type and the second type that are interdigital-coupled to each other. The electronic component of the present invention can include any plural number of resonators, such as two, or four or more. According to the present invention, at least one, but not all, of the plurality of resonators includes the resonator-forming conductor layers of the first type and the second type. Consequently, there inevitably exists a portion in which the at least one resonator that includes the resonator-forming conductor layers of the first type and the second type is adjacent to another one that does not include such two types of resonator-forming conductor layers. In this portion, it is possible to make the inductive coupling between the resonators weaker than in the case where two resonators that each include the resonator-forming conductor layers of the first type and the second type are adjacent to each other. 
     In the present invention, the number of the resonator-forming conductor layers of the first type and the second type may be one each, or two or more each. 
     In the present invention, at least one of the resonators, other than the at least one that includes the resonator-forming conductor layers of the first type and the second type, may include an inductor formed of a resonator-forming conductor layer of one of the two types, instead of the through-hole type inductor. 
     The electronic component of the present invention is applicable not only to a bandpass filter but also to any electronic component including a plurality of resonators. 
     The electronic component of the present invention is useful as a filter, or a bandpass filter, in particular, for use in a communication apparatus conforming to the Bluetooth standard or a communication apparatus for use on a wireless LAN. 
     It is apparent that the present invention can be carried out in various forms and modifications in the light of the foregoing descriptions. Accordingly, within the scope of the following claims and equivalents thereof, the present invention can be carried out in forms other than the foregoing most preferred embodiments.