Patent Publication Number: US-11664778-B2

Title: Band-pass filter

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 17/242,053, filed Apr. 27, 2021, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a balanced band-pass filter that includes an unbalanced port and a pair of balanced ports. 
     2. Description of the Related Art 
     As a kind of electronic components that can be used in transmission and reception circuits of wireless communication devices such as cellular phones or wireless LAN communication devices, there are band-pass filters each including a plurality of resonators. The band-pass filter preferably has an attenuation pole at which insertion loss abruptly varies in each of a first vicinity range and a second vicinity range. The first vicinity range is a frequency range lower than a pass band and in the vicinity of the pass band. The second vicinity range is a frequency range higher than the pass band and in the vicinity of the pass band. 
     As the band-pass filters, balanced band-pass filters each including a pair of balanced ports as output ports are known. The balanced band-pass filter is required to have a good amplitude balance characteristic and a good phase balance characteristic. The good amplitude balance characteristic means that two balanced element signals that constitute a balanced signal outputted from the band-pass filter have an amplitude difference of approximately zero. The good phase balance characteristic means that the two balanced element signals have a phase difference of approximately 180 degrees. 
     JP 2002-374139 A discloses a balanced LC filter including a pair of balanced input terminals and a pair of balanced output terminals. In the balanced LC filter, an attenuation pole is provided on a lower frequency side or a higher frequency side than a center frequency of the balanced LC filter using pole adjustment capacitors. 
     JP 2007-267264 A discloses a lumped constant bandpass filter including a pair of balanced terminals and an unbalanced terminal. JP 2007-267264 A describes that an unbalanced-input-and-balanced-output filter is configured by using the unbalanced terminal as an input terminal and using the pair of balanced terminals as output terminals. 
     Mobile communication systems up to the fourth generation are put to practical use at present. Standardization of fifth-generation mobile communication systems is now underway. In these mobile communication systems, it has been difficult for conventional balanced band-pass filters to form an abrupt attenuation pole in each of the foregoing first and second vicinity ranges while satisfying the balance characteristics. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a balanced band-pass filter, including an unbalanced port and a pair of balanced ports, that can form an abrupt attenuation pole while satisfying a balance characteristic. 
     A band-pass filter according to the present invention includes an unbalanced port, a first balanced port, a second balanced port, and first to third resonators provided between the unbalanced port and the first and second balanced ports in a circuit configuration. The second resonator and the third resonator each are a resonator with both ends open. The second resonator and the third resonator are adjacent to each other in the circuit configuration, and electromagnetically coupled by magnetic coupling as main coupling. The first resonator is provided closer to the second resonator than to the third resonator in the circuit configuration, and jump-coupled to the third resonator. 
     In the band-pass filter according to the present invention, the first resonator may be a resonator with one end shorted, and provided between the unbalanced port and the second resonator in the circuit configuration. 
     In the band-pass filter according to the present invention, a distance between the second resonator and the third resonator may be shorter than a distance between the first resonator and the second resonator. 
     The band-pass filter according to the present invention may further include a fourth resonator provided between the unbalanced port and the first and second balanced ports in the circuit configuration. In this case, the fourth resonator may be provided closer to the third resonator than to the second resonator in the circuit configuration, and jump-coupled to the second resonator. In this case, the first resonator may be a resonator with one end shorted, and provided between the unbalanced port and the second resonator in the circuit configuration. The fourth resonator may be a resonator with both ends open, and provided between the first and second balanced ports and the third resonator in the circuit configuration. 
     If the band-pass filter according to the present invention is provided with the fourth resonator, the distance between the second resonator and the third resonator may be shorter than that between the first resonator and the second resonator, and shorter than that between the third resonator and the fourth resonator. 
     The band-pass filter according to the present invention may further include a stack to integrate at least the second and third resonators. The stack may include a plurality of stacked dielectric layers, a plurality of stacked conductor layers, and a plurality of through holes. In such a case, the plurality of conductor layers may include a plurality of resonator-forming conductor layers. The plurality of through holes may include a plurality of resonator-forming through holes. Each of the second and third resonators may include a first through hole line, a second through hole line, and a conductor layer portion. Each of the first and second through hole lines may be formed of serially connected two or more through holes of the plurality of resonator-forming through holes, and may penetrate two or more dielectric layers of the plurality of dielectric layers. The conductor layer portion may be formed of one or more resonator-forming conductor layers of the plurality of resonator-forming conductor layers, and may connect one end of the first through hole line to one end of the second through hole line. 
     The band-pass filter according to the present invention includes the first to third resonators. The second resonator and the third resonator are adjacent to each other in the circuit configuration, and electromagnetically coupled by magnetic coupling as main coupling. The first resonator is provided closer to the second resonator than to the third resonator in the circuit configuration, and jump-coupled to the third resonator. Therefore, according to the present invention, it is possible to provide the band-pass filter that can form an abrupt attenuation pole while satisfying a balance characteristic. 
     Other and further objects, features and advantages of the present invention will appear more fully from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a circuit diagram showing the circuit configuration of a band-pass filter according to a first embodiment of the invention. 
         FIG.  2    is a perspective view showing the band-pass filter according to the first embodiment of the invention. 
         FIG.  3    is a perspective view showing the band-pass filter according to the first embodiment of the invention. 
         FIG.  4    is a perspective view showing the interior of the band-pass filter shown in  FIG.  2    and  FIG.  3   . 
         FIG.  5 A  and  FIG.  5 B  are explanatory diagrams showing respective patterned surfaces of first and second dielectric layers of the stack of the band-pass filter shown in  FIG.  2    and  FIG.  3   . 
         FIG.  6 A  and  FIG.  6 B  are explanatory diagrams showing respective patterned surfaces of third and fourth dielectric layers of the stack of the band-pass filter shown in  FIG.  2    and  FIG.  3   . 
         FIG.  7 A  and  FIG.  7 B  are explanatory diagrams showing respective patterned surfaces of fifth and sixth dielectric layers of the stack of the band-pass filter shown in  FIG.  2    and  FIG.  3   . 
         FIG.  8 A  and  FIG.  8 B  are explanatory diagrams showing respective patterned surfaces of seventh and eighth dielectric layers of the stack of the band-pass filter shown in  FIG.  2    and  FIG.  3   . 
         FIG.  9 A  is an explanatory diagram showing a patterned surface of each of a ninth to an eighteenth dielectric layer of the stack of the band-pass filter shown in  FIG.  2    and  FIG.  3   . 
         FIG.  9 B  is an explanatory diagram showing a patterned surface of each of a nineteenth and a twentieth dielectric layer of the stack of the band-pass filter shown in  FIG.  2    and  FIG.  3   . 
         FIG.  10 A  is an explanatory diagram showing a patterned surface of each of a twenty-first and a twenty-second dielectric layer of the stack of the band-pass filter shown in  FIG.  2    and  FIG.  3   . 
         FIG.  10 B  is an explanatory diagram showing a patterned surface of a twenty-third dielectric layer of the stack of the band-pass filter shown in  FIG.  2    and  FIG.  3   . 
         FIGS.  11 A and  11 B  are explanatory diagrams showing respective patterned surfaces of twenty-fourth and twenty-fifth dielectric layers of the stack of the hand-pass filter shown in  FIG.  2    and  FIG.  3   . 
         FIG.  12    is a characteristic diagram showing the pass characteristics of a first model of a hand-pass filter. 
         FIG.  13    is a characteristic diagram showing the pass characteristics of a second model of the band-pass filter. 
         FIG.  14    is a characteristic diagram showing the pass characteristics of a third model of the band-pass filter. 
         FIG.  15    is a characteristic diagram showing the pass characteristics of a fourth model of the band-pass filter. 
         FIG.  16    is a characteristic diagram showing the pass characteristics of a fifth model of the band-pass filter. 
         FIG.  17    is a characteristic diagram showing an example of pass characteristic of the band-pass filter according to the first embodiment of the invention. 
         FIG.  18    is a characteristic diagram showing a portion of  FIG.  17    on an enlarged scale. 
         FIG.  19    is a characteristic diagram showing an example of amplitude balance characteristic of the band-pass filter according to the first embodiment of the invention. 
         FIG.  20    is a characteristic diagram showing an example of phase balance characteristic of the band-pass filter according to the first embodiment of the invention. 
         FIG.  21    is a characteristic diagram showing an example of reflection characteristic of the unbalanced port of the band-pass filter according to the first embodiment of the invention. 
         FIG.  22    is a characteristic diagram showing an example of pass characteristic of the first and second balanced ports of the band-pass filter according to the first embodiment of the invention. 
         FIG.  23    is a circuit diagram showing the circuit configuration of a band-pass filter according to a second embodiment of the invention. 
         FIG.  24    is a perspective view showing the interior of the hand-pass filter according to the second embodiment of the invention. 
         FIG.  25 A  and  FIG.  25 B  are explanatory diagrams showing respective patterned surfaces of first and second dielectric layers of the stack of the band-pass filter according to the second embodiment of the invention. 
         FIG.  26 A  and  FIG.  26 B  are explanatory diagrams showing respective patterned surfaces of third and fourth dielectric layers of the stack of the band-pass filter according to the second embodiment of the invention. 
         FIG.  27 A  and  FIG.  27 B  are explanatory diagrams showing respective patterned surfaces of fifth and sixth dielectric layers of the stack of the band-pass filter according to the second embodiment of the invention. 
         FIG.  28 A  is an explanatory diagram showing a patterned surface of each of a seventh and a eighth dielectric layer of the stack of the band-pass filter according to the second embodiment of the invention. 
         FIG.  28 B  is an explanatory diagram showing a patterned surface of a ninth dielectric layer of the stack of the band-pass filter according to the second embodiment of the invention. 
         FIG.  29 A  is an explanatory diagram showing a patterned surface of a tenth dielectric layer of the stack of the band-pass filter according to the second embodiment of the invention. 
         FIG.  29 B  is an explanatory diagram showing a patterned surface of each of a eleventh and a sixteenth dielectric layer of the stack of the band-pass filter according to the second embodiment of the invention. 
         FIG.  30 A  is an explanatory diagram showing a patterned surface of each of a seventeenth and a eighteenth dielectric layer of the stack of the band-pass filter according to the second embodiment of the invention. 
         FIG.  30 B  is an explanatory diagram showing a patterned surface of each of a nineteenth and a twentieth dielectric layer of the stack of the band-pass filter according to the second embodiment of the invention. 
         FIG.  31 A  and  FIG.  31 B  are explanatory diagrams showing respective patterned surfaces of twenty-first and twenty-second dielectric layers of the stack of the band-pass filter according to the second embodiment of the invention. 
         FIG.  32 A  and  FIG.  32 B  are explanatory diagrams showing respective patterned surfaces of twenty-third and twenty-fourth dielectric layers of the stack of the band-pass filter according to the second embodiment of the invention. 
         FIG.  33    is a characteristic diagram showing an example of pass characteristic of the band-pass filter according to the second embodiment of the invention. 
         FIG.  34    is a characteristic diagram showing a portion of  FIG.  33    on an enlarged scale. 
         FIG.  35    is a characteristic diagram showing an example of amplitude balance characteristic of the band-pass filter according to the second embodiment of the invention. 
         FIG.  36    is a characteristic diagram showing an example of phase balance characteristic of the band-pass filter according to the second embodiment of the invention, 
         FIG.  37    is a characteristic diagram showing an example of reflection characteristic of the unbalanced port of the band-pass filter according to the second embodiment of the invention. 
         FIG.  38    is a characteristic diagram showing an example of pass characteristic of the first and second balanced ports of the band-pass filter according to the second embodiment of the invention. 
         FIG.  39    is a circuit diagram showing the circuit configuration of a band-pass filter according to a third 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. First, reference is made to  FIG.  1    to describe the circuit configuration of a band-pass filter according to the first embodiment of the invention.  FIG.  1    shows the circuit configuration of the band-pass filter according to the present embodiment. As shown in  FIG.  1   , a band-pass filter  1  includes an unbalanced port  11 , a first balanced port  12 , a second balanced port  13 , a port  14 , a first resonator  21 , a second resonator  22 , a third resonator  23 , and a fourth resonator  24 . 
     The first to fourth resonators  21  to  24  are provided between the unbalanced port  11  and the first and second balanced ports  12  and  13  in the circuit configuration. The second resonator  22  and the third resonator  23  are adjacent to each other in the circuit configuration. The first resonator  21  is provided closer to the second resonator  22  than to the third resonator  23  in the circuit configuration. The fourth resonator  24  is provided closer to the third resonator  23  than to the second resonator  22  in the circuit configuration. In the present application, the expression of “in the(a) circuit configuration” is used to indicate not layout in physical configuration but layout in the circuit diagram. 
     Specifically in the present embodiment, the first to fourth resonators  21  to  24  are provided in this order from the side of the unbalanced port  11 . That is, the second resonator  22  is provided closer to the unbalanced port  11  than the third resonator  23  in the circuit configuration. The first resonator  21  is provided between the unbalanced port  11  and the second resonator  22  in the circuit configuration. The fourth resonator  24  is provided between the first and second balanced ports  12  and  13  and the third resonator  23  in the circuit configuration. 
     The first resonator  21  is a resonator with one end shorted. The band-pass filter  1  further includes capacitors C 1  and C 11 . The capacitor C 1  connects one end of the first resonator  21  to a ground. The capacitor C 11  connects the one end of the first resonator  21  to the unbalanced port  11 . The other end of the first resonator  21  is connected to the ground. 
     The second to fourth resonators  22  to  24  each are a resonator with both ends open. The band-pass filter  1  further includes capacitors C 2 A, C 2 B, C 3 A, C 3 B, C 4 A, and C 4 B. The capacitor C 2 A connects one end of the second resonator  22  to the ground. The capacitor C 2 B connects the other end of the second resonator  22  to the ground. The capacitor C 3 A connects one end of the third resonator  23  to the ground. The capacitor C 3 B connects the other end of the third resonator  23  to the ground. The capacitor C 4 A connects one end of the fourth resonator  24  to the ground. The capacitor C 4 B connects the other end of the fourth resonator  24  to the ground. 
     The band-pass filter  1  further includes capacitors C 12 , C 23 A, C 23 B, C 34 A, and C 34 B. The capacitor C 12  connects the one end of the first resonator  21  to the one end of the second resonator  22 . The capacitor C 23 A connects the one end of the second resonator  22  to the one end of the third resonator  23 . The capacitor C 23 B connects the other end of the second resonator  22  to the other end of the third resonator  23 . The capacitor C 34 A connects the one end of the third resonator  23  to the one end of the fourth resonator  24 . The capacitor C 34 B connects the other end of the third resonator  23  to the other end of the fourth resonator  24 . 
     The first balanced port  12  is connected to the one end of the fourth resonator  24 . The second balanced port  13  is connected to the other end of the fourth resonator  24 . 
     The second resonator  22  and the third resonator  23  are magnetically coupled, and also capacitively coupled through the capacitors C 23 A and C 23 B. In  FIG.  1   , a curve indicated with a symbol M represents the magnetic coupling between the second resonator  22  and the third resonator  23 . Here, out of magnetic coupling and capacitive coupling that contribute to electromagnetic coupling between two resonators, relatively strong coupling is referred to as main coupling, and the other is referred to as sub coupling. Specifically in the present embodiment, the second resonator  22  and the third resonator  23  are electromagnetically coupled by the magnetic coupling as the main coupling and the capacitive coupling as the sub coupling. 
     The first resonator  21  and the second resonator  22  are magnetically coupled, and also capacitively coupled through the capacitor C 12 . Specifically in the present embodiment, the first resonator  21  and the second resonator  22  are electromagnetically coupled by the capacitive coupling as the main coupling and the magnetic coupling as the sub coupling. 
     The third resonator  23  and the fourth resonator  24  are magnetically coupled, and also capacitively coupled through the capacitors C 34 A and C 34 B. Specifically in the present embodiment, the third resonator  23  and the fourth resonator  24  are electromagnetically coupled by the capacitive coupling as the main coupling and the magnetic coupling as the sub coupling. 
     The first resonator  21  is magnetically coupled to the third resonator  23 , which is not adjacent to the first resonator  21  in the circuit configuration. The fourth resonator  24  is magnetically coupled to the second resonator  22 , which is not adjacent to the fourth resonator  24  in the circuit configuration. Electromagnetic coupling between two resonators that are not adjacent to each other in a circuit configuration is referred to as jump-coupling. In  FIG.  1   , curves indicated with a symbol Mc represent the magnetic coupling between the two resonators that are not adjacent to each other in the circuit configuration. 
     The operation of the band-pass filter  1  will now be described. The band-pass filter  1  is a band-pass filter the pass band of which is predetermined. The band-pass filter  1  is a so-called balanced band-pass filter. The band-pass filter  1  is configured so that an unbalanced signal is received at and outputted from the unbalanced port  11 , a first balanced element signal is received at and outputted from the first balanced port  12 , and a second balanced element signal is received at and outputted from the second balanced port  13 . The first balanced element signal and the second balanced element signal constitute a balanced signal. The band-pass filter  1  converts between balanced and unbalanced signals. 
     Next, a structure of the band-pass filter  1  will be described with reference to  FIGS.  2  to  4   .  FIGS.  2  and  3    are perspective views of the band-pass filter  1 .  FIG.  4    is a perspective view showing the interior of the band-pass filter  1 . The band-pass filter  1  further includes a stack  30  for integrating the ports  11  to  13 , the first to fourth resonators  21  to  24 , and the capacitors C 1 , C 2 A, C 2 B, C 3 A, C 3 B, C 4 A, C 4 B, C 11 , C 12 , C 23 A, C 23 B, C 34 A and C 34 B. Although details will be described later, the stack  30  includes a plurality of stacked dielectric layers, a plurality of stacked conductor layers, and a plurality of through holes. 
     The stack  30  is shaped like a rectangular solid. The stack  30  includes a top surface  30 A, a bottom surface  30 B, and four side surfaces  30 C to  30 F, which constitute the periphery of the stack  30 . The top surface  30 A and the bottom surface  30 B are opposite each other. The side surfaces  30 C and  30 D are opposite each other. The side surfaces  30 E and  30 F are opposite each other. The side surfaces  30 C to  30 F are perpendicular to the top surface  30 A and the bottom surface  30 B. In the stack  30 , the plurality of dielectric layers and the plurality of conductor layers are stacked in the direction perpendicular to the top surface  30 A and the bottom surface  30 B. This direction will be referred to as the stacking direction. The stacking direction is shown by the arrow T in  FIG.  2    to  FIG.  4   . The top surface  30 A and the bottom surface  30 B are located at opposite ends in the stacking direction T. 
     Here, X, Y, and Z directions are defined as shown in  FIGS.  2  to  4   . 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 in  FIGS.  2  and  3   , the top surface  30 A is located at the end of the stack  30  in the −Z direction. The bottom surface  30 B is located at the end of the stack  30  in the direction. The side surface  30 C is located at the end of the stack  30  in the −X direction. The side surface  30 D is located at the end of the stack  30  in the X direction. The side surface  30 E is located at the end of the stack  30  in the −Y direction. The side surface  30 F is located at the end of the stack  30  in the Y direction. 
     The band-pass filter  1  further includes first to eighth terminals  111 ,  112 ,  113 ,  114 ,  115 ,  116 ,  117 , and  118 . The first terminal  111  is located to extend from the top surface  30 A to the bottom surface  30 B via the side surface  30 C. The first terminal  112  is located to extend from the top surface  30 A to the bottom surface  30 B via the side surface  30 D. Each of the third to fifth terminals  113  to  115  is located to extend from the top surface  30 A to the bottom surface  30 B via the side surface  30 E. The third to fifth terminals  113  to  115  are arranged in this order in the X direction. Each of the sixth to eighth terminals  116  to  118  is located to extend from the top surface  30 A to the bottom surface  30 B via the side surface  30 F. The sixth to eighth terminals  116  to  118  are arranged in this order in the X direction. 
     The first terminal  111  corresponds to the unbalanced port  11 . The fifth terminal  115  corresponds to the second balanced port  13 . The eighth terminal  118  corresponds to the first balanced port  12 . The fourth terminal  114  corresponds to the second balanced port  13 . Each of the third, fourth, sixth and seventh terminals  113 ,  114 ,  116  and  117  is connected to the ground. 
     The stack  30  will be described in detail with reference to  FIG.  5 A  to  FIG.  11 B . The multilayer stack  30  includes twenty-six dielectric layers stacked on each other. The twenty-six dielectric layers will be referred to as the first to twenty-sixth dielectric layers in the order from bottom to top. The first to twenty-sixth dielectric layers will be denoted by the reference numerals  31  to  56 . 
       FIG.  5 A  shows the patterned surface of the first dielectric layer  31 .  FIG.  5 A  shows terminal parts  111   a  to  118   a  constituting parts of the terminals  111  to  118 , respectively. 
       FIG.  5 B  shows the patterned surface of the second dielectric layer  32 . A ground conductor layers  321  and  322  are formed on the patterned surface of the dielectric layer  32 . The conductor layer  321  is connected to the fourth and seventh terminals  114  and  117 . The conductor layer  322  is connected to the third and sixth terminals  113  and  116 . 
       FIG.  6 A  shows the patterned surface of the third dielectric layer  33 . A conductor layers  331 ,  332 ,  333  and  334  are formed on the patterned surface of the dielectric layer  33 . The conductor layer  333  is connected to the eighth terminal  118 . The conductor layer  334  is connected to the fifth terminal  115 . 
       FIG.  6 B  shows the patterned surface of the fourth dielectric layer  34 . A conductor layers  341 ,  342 ,  343  and  344  are formed on the patterned surface of the dielectric layer  34 . Further, through holes  34 T 1 ,  34 T 2 ,  34 T 3  and  34 T 4  are formed in the dielectric layer  34 . The through holes  34 T 1 ,  34 T 2 ,  34 T 3  and  34 T 4  are connected to the conductor layers  341 ,  342 ,  343  and  344 , respectively. 
       FIG.  7 A  shows the patterned surface of the fifth dielectric layer  35 . A conductor layer  351  is formed on the patterned surface of the dielectric layer  35 . Further, through holes  35 T 1 ,  35 T 2 ,  35 T 3 ,  35 T 4  and  35 T 5  are formed in the dielectric layer  35 . The through holes  34 T 1 ,  34 T 2 ,  34 T 3  and  34 T 4  formed in the fourth dielectric layer  34  are connected to the through holes  35 T 1 ,  35 T 2 ,  35 T 3  and  35 T 4 , respectively. The through hole  35 T 5  is connected to the conductor layer  351 . 
       FIG.  7 B  shows the patterned surface of the sixth dielectric layer  36 . A conductor layer  361  is formed on the patterned surface of the dielectric layer  36 . Further, through holes  36 T 1 ,  36 T 2 ,  36 T 3 ,  36 T 4 ,  36 T 5  and  36 T 6  are formed in the dielectric layer  36 . The through holes  35 T 1 ,  35 T 2 ,  35 T 3 ,  35 T 4  and  35 T 5  formed in the fifth dielectric layer  35  are connected to the through holes  36 T 1 ,  36 T 2 ,  36 T 3 ,  36 T 4  and  36 T 5 , respectively. The through hole  36 T 6  is connected to the conductor layer  361 . 
       FIG.  8 A  shows the patterned surface of the seventh dielectric layer  37 . A conductor layer  371  is formed on the patterned surface of the dielectric layer  37 . Further, through holes  37 T 1 ,  37 T 2 ,  37 T 3 ,  37 T 4 ,  37 T 5  and  37 T 6  are formed in the dielectric layer  37 . The through holes  36 T 1 ,  36 T 2 ,  36 T 3 ,  36 T 4  and  36 T 6  formed in the sixth dielectric layer  36  are connected to the through holes  37 T 1 ,  37 T 2 ,  37 T 3 ,  37 T 4  and  37 T 6 , respectively. The through hole  37 T 5  and the through hole  36 T 5  formed in the dielectric layer  36  are connected to the conductor layer  371 . 
       FIG.  8 B  shows the patterned surface of the eighth dielectric layer  38 . A conductor layer  381  is formed on the patterned surface of the dielectric layer  38 . The conductor layer  381  is connected to the first terminal  111 . Further, through holes  38 T 1 ,  38 T 2 ,  38 T 3 ,  38 T 4  and  38 T 5  are formed in the dielectric layer  38 . The through holes  37 T 1 ,  37 T 2 ,  37 T 3 ,  37 T 4  and  37 T 5  formed in the seventh dielectric layer  37  are connected to the through holes  38 T 1 ,  38 T 2 ,  38 T 3 ,  38 T 4  and  38 T 5 , respectively. The through hole  37 T 6  formed in the seventh dielectric layer  37  is connected to the conductor layer  381 . 
       FIG.  9 A  shows the patterned surface of each of the ninth to eighteenth dielectric layers  39  to  48 . In each of the dielectric layers  39  to  48 , there are formed through holes  39 T 1 ,  39 T 2 ,  39 T 3 ,  39 T 4  and  39 T 5 . The through holes  38 T 1 ,  38 T 2 ,  38 T 3 ,  38 T 4  and  38 T 5  formed in the eighth dielectric layer  38  are connected to the through holes  39 T 1 ,  39 T 2 ,  39 T 3 ,  39 T 4  and  39 T 5  formed in the ninth dielectric layer  39 , respectively. In the dielectric layers  39  to  48 , every vertically adjacent through holes denoted by the same reference signs are connected to each other. 
       FIG.  9 B  shows the patterned surface of each of the nineteenth and twentieth dielectric layers  49  and  50 . A resonator-forming conductor layer  491  is formed on the patterned surface of each of the dielectric layers  49  and  50 . The resonator-forming conductor layer  491  is connected to the fifth and eighth terminals  115  and  118 . Further, in each of the dielectric layers  49  and  50 , there are formed through holes  49 T 1 ,  49 T 2 ,  49 T 3 ,  49 T 4  and  49 T 5 . The through holes  39 T 1 ,  39 T 2 ,  39 T 3 ,  39 T 4  and  39 T 5  formed in the eighteenth dielectric layer  48  are connected to the through holes  49 T 1 ,  49 T 2 ,  49 T 3 ,  49 T 4  and  49 T 5  formed in the nineteenth dielectric layer  49 , respectively. In the dielectric layers  49  and  50 , every vertically adjacent through holes denoted by the same reference signs are connected to each other. 
       FIG.  10 A  shows the patterned surface of each of the twenty-first and twenty-second dielectric layers  51  and  52 . In each of the dielectric layers  51  and  52 , there are formed through holes  51 T 1 ,  51 T 2 ,  51 T 3 ,  51 T 4  and  51 T 5 . The through holes  49 T 1 ,  49 T 2 ,  49 T 3 ,  49 T 4  and  49 T 5  formed in the twentieth dielectric layer  50  are connected to the through holes  51 T 1 ,  51 T 2 ,  51 T 3 ,  51 T 4  and  51 T 5  formed in the twenty-first dielectric layer  51 , respectively. In the dielectric layers  51  and  52 , every vertically adjacent through holes denoted by the same reference signs are connected to each other. 
       FIG.  10 B  shows the patterned surface of the twenty-third dielectric layer  53 . A resonator-forming conductor layer  531  is formed on the patterned surface of the dielectric layer  53 . The resonator-forming conductor layer  531  is connected to the third and sixth terminals  113  and  116 . Further, through holes  53 T 1 ,  53 T 2 ,  53 T 3 ,  53 T 4  and  53 T 5  are formed in the dielectric layer  53 . The through holes  51 T 1 ,  51 T 2 ,  51 T 3  and  51 T 4  formed in the twenty-second dielectric layer  52  are connected to the through holes  53 T 1 ,  53 T 2 ,  53 T 3  and  53 T 4 , respectively. The through hole  53 T 5  and the through hole  51 T 5  formed in the twenty-second dielectric layer  52  are connected to part of the resonator-forming conductor layer  531 , i.e. a portion including the middle of the resonator-forming conductor layer  531  in a longitudinal direction. 
       FIG.  11 A  shows the patterned surface of the twenty-fourth dielectric layer  54 . Resonator-forming conductor layers  541 ,  542  and  543  are formed on the patterned surface of the dielectric layer  54 . The resonator-forming conductor layer  541  is connected to the third and sixth terminals  113  and  116 . The through hole  53 T 5  formed in the twenty-third dielectric layer  53  is connected to part of the resonator-forming conductor layer  541 , i.e. a portion including the middle of the resonator-forming conductor layer  541  in the longitudinal direction. Each of the resonator-forming conductor layers  542  and  543  has a first end and a second end opposite to each other. 
     Further, through holes  54 T 1 ,  54 T 2 ,  54 T 3  and  54 T 4  are formed in the dielectric layer  54 . The through hole  54 T 1  and the through hole  53 T 1  formed in the dielectric layer  53  are connected to a portion of the resonator-forming conductor layers  542  near the first end thereof. The through hole  54 T 2  and the through hole  53 T 2  formed in the dielectric layer  53  are connected to a portion of the resonator-forming conductor layers  542  near the second end thereof. The through hole  54 T 3  and the through hole  53 T 3  formed in the dielectric layer  53  are connected to a portion of the resonator-forming conductor layers  543  near the first end thereof. The through hole  54 T 4  and the through hole  53 T 4  formed in the dielectric layer  53  are connected to a portion of the resonator-forming conductor layers  543  near the second end thereof. 
       FIG.  11 B  shows the patterned surface of the twenty-fifth dielectric layer  55 . Resonator-forming conductor layer  552  and  553  are formed on the patterned surface of the dielectric layer  55 . Each of the resonator-forming conductor layers  552  and  553  has a first end and a second end opposite to each other. The through hole  54 T 1  formed in the dielectric layer  54  is connected to a portion of the resonator-forming conductor lavers  552  near the first end thereof. The through hole  54 T 2  formed in the dielectric layer  54  is connected to a portion of the resonator-forming conductor layers  552  near the second end thereof. The through hole  54 T 3  formed in the dielectric layer  54  is connected to a portion of the resonator-forming conductor layers  553  near the first end thereof. The through hole  54 T 4  formed in the dielectric layer  54  is connected to a portion of the resonator-forming conductor layers  553  near the second end thereof. 
     Although it is not shown in the drawing, a mark may be formed in the patterned surface of the twenty-sixth dielectric layer  56 . 
     The stack  30  shown in  FIGS.  2  and  3    is formed by stacking the first to twenty-sixth dielectric layers  31  to  56  such that the patterned surface of the first dielectric layer  31  serves as the bottom surface  30 B of the stack  30  and the surface of the twenty-sixth dielectric layer  56  opposite to the patterned surface thereof serves as the top surface  30 A of the stack  30 . The first to eighth terminals  111  to  118  are then formed on the periphery of the stack  30 , whereby the band-pass filter  1  shown in  FIGS.  2  and  3    is completed. 
     A correspondence between the components of the band-pass filter  1  and the components inside the stack  30  shown in  FIGS.  5 A to  11 B  will be described below. The plurality of the dielectric lavers of the stack  30  include the plurality of resonator-forming conductor layers  491 ,  531 ,  541 ,  542 ,  543 ,  552 , and  553  to constitute the first to fourth resonators  21  to  24 . The plurality of through holes of the stack  30  include a plurality of resonator-forming through holes to constitute the first to fourth resonators  21  to  24 . 
     The first resonator  21  is formed of the resonator-forming conductor layers  531  and  541 , the through holes  35 T 5 ,  36 T 5 ,  37 T 5 ,  38 T 5  and  53 T 5 , the through hole  39 T 5  formed in each of the dielectric layer  39  to  48 , the through hole  49 T 5  formed in each of the dielectric layer  49  and  50 , and the through hole  51 T 5  formed in each of the dielectric layers  51  and  52 . 
     The second resonator  22  is formed of the resonator-forming conductor layers  542  and  552 , the through holes  34 T 1 ,  34 T 2 ,  35 T 1 ,  35 T 2 ,  36 T 1 ,  36 T 2 ,  37 T 1 ,  37 T 2 ,  38 T 1 ,  38 T 2 ,  53 T 1  and  53 T 2 , the through holes  39 T 1  and  39 T 2  formed in each of the dielectric layer  39  to  48 , the through holes  49 T 1  and  49 T 2  formed in each of the dielectric layer  49  and  50 , and the through holes  51 T 1  and  51 T 2  formed in each of the dielectric layers  51  and  52 . 
     As shown in  FIG.  4   , the second resonator  22  includes a first through hole line  22 A, a second through hole line  22 B, and a conductor layer portion  22 C. The first through hole line  22 A is formed of the through holes  34 T 1 ,  35 T 1 ,  36 T 1 ,  37 T 1 ,  38 T 1 , and  53 T 1 , the through holes  39 T 1  formed in each of the dielectric layers  39  to  48 , the through holes  49 T 1  formed in each of the dielectric layers  49  and  50 , and the through holes  51 T 1  formed in each of the dielectric layers  51  and  52  connected in series. The first through hole line  22 A penetrates the dielectric layers  34  to  53 . 
     The second through hole line  22 B is formed of the through holes  34 T 2 ,  35 T 2 ,  36 T 2 ,  37 T 2 ,  38 T 2 , and  53 T 2 , the through holes  39 T 2  formed in each of the dielectric layers  39  to  48 , the through holes  49 T 2  formed in each of the dielectric layers  49  and  50 , and the through holes  51 T 2  formed in each of the dielectric layers  51  and  52  connected in series. The second through hole line  22 B penetrates the dielectric layers  34  to  53 . 
     The conductor layer portion  22 C is formed of the resonator-forming conductor layers  542  and  552  that are connected to each other via the through holes  54 T 1  and  54 T 2 . The conductor layer portion  22 C connects one end of the first through hole line  22 A to one end of the second through hole line  22 B. 
     The third resonator  23  is formed of the resonator-forming conductor layers  543  and  553 , the through holes  34 T 3 ,  34 T 4 ,  35 T 3 ,  35 T 4 ,  36 T 3 ,  36 T 4 ,  37 T 3 ,  37 T 4 ,  38 T 3 ,  38 T 4 ,  53 T 3 ,  53 T 4 ,  54 T 3 , and  54 T 4 , the through holes  39 T 3  and  39 T 4  formed in each of the dielectric layer  39  to  48 , the through holes  49 T 3  and  49 T 4  formed in each of the dielectric layer  49  and  50 , and the through holes  51 T 3  and  51 T 4  formed in each of the dielectric layers  51  and  52 . 
     As shown in  FIG.  4   , the third resonator  23  includes a first through hole line  23 A, a second through hole line  23 B, and a conductor layer portion  23 C. The first through hole line  23 A is formed of the through holes  34 T 3 ,  35 T 3 ,  36 T 3 ,  37 T 3 ,  38 T 3 , and  53 T 3 , the through holes  39 T 3  formed in each of the dielectric layers  39  to  48 , the through holes  49 T 3  formed in each of the dielectric layers  49  and  50 , and the through holes  51 T 3  formed in each of the dielectric layers  51  and  52  connected in series. The first through hole line  23 A penetrates the dielectric layers  34  to  53 . 
     The second through hole line  23 B is formed of the through holes  34 T 4 ,  35 T 4 ,  36 T 4 ,  37 T 4 ,  38 T 4 , and  53 T 4 , the through holes  39 T 4  formed in each of the dielectric layers  39  to  48 , the through holes  49 T 4  formed in each of the dielectric layers  49  and  50 , and the through holes  51 T 4  formed in each of the dielectric layers  51  and  52  connected in series. The second through hole line  23 B penetrates the dielectric layers  34  to  53 . 
     The conductor layer portion  23 C is formed of the resonator-forming conductor layers  543  and  553  that are connected to each other via the through holes  54 T 3  and  54 T 4 . The conductor layer portion  22 C connects one end of the first through hole line  23 A to one end of the second through hole line  23 B. 
     The fourth resonator  24  is formed of the resonator-forming conductor layer  491  formed in each of the dielectric layer  49  and  50 . 
     The capacitor C 1  is formed of the conductor layers  322  and  351 , and the dielectric layers  32  to  34  interposed between the conductor layers  322  and  351 . 
     The capacitor C 2 A is formed of the conductor layers  321  and  341 , and the dielectric layers  32  and  33  interposed between the conductor layers  321  and  341 . The capacitor C 2 B is formed of the conductor layers  321  and  342 , and the dielectric layers  32  and  33  interposed between the conductor layers  321  and  342 . 
     The capacitor C 3 A is formed of the conductor layers  321  and  343 , and the dielectric layers  32  and  33  interposed between the conductor layers  321  and  343 . The capacitor C 3 B is formed of the conductor layers  321  and  344 , and the dielectric layers  32  and  33  interposed between the conductor layers  321  and  344 . 
     The capacitor C 4 A is formed of the conductor layers  321  and  333 , and the dielectric layer  32  interposed between the conductor lavers  321  and  333 . The capacitor C 4 B is formed of the conductor layers  321  and  334 , and the dielectric layer  32  interposed between the conductor layers  321  and  334 . 
     The capacitor C 11  is formed of the conductor layers  351 ,  361 ,  371  and  381 , the dielectric layer  35  interposed between the conductor layers  351  and  361 , the dielectric layer  36  interposed between the conductor layers  361  and  371 , and the dielectric layer  37  interposed between the conductor layers  371  and  381 . The capacitor C 12  is formed of the conductor layers  341  and  351 , and the dielectric layer  34  interposed between the conductor layers  341  and  351 . 
     The capacitor C 23 A is formed of the conductor layers  331 ,  341  and  343 , and the dielectric layer  33  interposed between the conductor layer  331  and the conductor layers  341  and  343 . The capacitor C 23 B is formed of the conductor layers  332 ,  342  and  344 , and the dielectric layer  33  interposed between the conductor layer  332  and the conductor layers  342  and  344 . 
     The capacitor C 34 A is formed of the conductor layers  333  and  343 , and the dielectric layer  33  interposed between the conductor layers  333  and  343 . The capacitor C 34 B is formed of the conductor layers  334  and  344 , and the dielectric layer  33  interposed between the conductor layers  334  and  344 . 
     Next, structural features of the band-pass filter  1  will be described. As shown in  FIG.  4   , the distance between the second resonator  22  and the third resonator  23  is shorter than that between the first resonator  21  and the second resonator  22 , and is shorter than that between the third resonator  23  and the fourth resonator  24 . 
     As shown in  FIG.  9 B , the resonator-forming conductor layer  491  formed in the dielectric layer  49  and the resonator-forming conductor layer  491  formed in the dielectric layer  50  are located so as to overlap each other when viewed from the Z direction. As shown in  FIGS.  10 B and  11 A , the resonator-forming conductor layer  531  formed in the dielectric layer  53  and the resonator-forming conductor layer  541  formed in the dielectric layer  54  are located so as to overlap each other when viewed from the Z direction. As shown in  FIGS.  11 A and  11 B , the resonator-forming conductor layer  542  formed in the dielectric layer  54  and the resonator-forming conductor layer  552  formed in the dielectric layer  55  are located so as to overlap each other when viewed from the Z direction. The resonator-forming conductor layer  543  formed in the dielectric layer  54  and the resonator-forming conductor layer  553  formed in the dielectric layer  55  are located so as to overlap each other when viewed from the Z direction. 
     As described above, in the band-pass filter  1  according to the present embodiment, the second resonator  22  and the third resonator  23  are electromagnetically coupled by the magnetic coupling as the main coupling. The first resonator  21  is jump-coupled to the third resonator  23 . The fourth resonator  24  is jump-coupled to the second resonator  22 . According to the present embodiment, these couplings can form an attenuation pole at which insertion loss abruptly varies in each of a first vicinity range that is a frequency range lower than the pass band and in the vicinity of the pass band and a second vicinity range that is a frequency range higher than the pass band and in the vicinity of the pass band. 
     The attenuation pole will be hereinafter described with reference to simulation results. In simulation, first to fifth models of a band-pass filter having the same circuit configuration as that of the band-pass filter  1  of the present embodiment were used. In the simulation, the band-pass filter was designed so as to have a pass band between 3.3 and 3.9 GHz. In the simulation, the pass characteristic of the band-pass filter was represented using a mixed mode S parameter, which represented a response of a difference signal between first and second balanced element signals outputted from the first and second balanced ports  12  and  13  when an unbalanced signal was inputted to the unbalanced port  11 . The S parameter is hereinafter referred to as insertion loss. 
     Here, a symbol k23 represents a magnetic coupling coefficient between the second resonator  22  and the third resonator  23 . A symbol k13 represents a magnetic coupling coefficient of the jump-coupling between the first resonator  21  and the third resonator  23 . A symbol k24 represents a magnetic coupling coefficient of the jump-coupling between the second resonator  22  and the fourth resonator  24 . In the first to fifth models, each of the magnetic coupling coefficients k23, k13, and k24 varied from each other. In the simulation, the pass characteristic of each of the first to fifth models as obtained. 
     First, the pass characteristic of each of the first and second models will be described. In the first model, the magnetic coupling coefficient k23 was set at 0.37, and the magnetic coupling coefficients k13 and k24 of the jump-coupling each were set at 0. In the second model, the magnetic coupling coefficient k23 was set at 0.07, and the magnetic coupling coefficients k13 and k24 of the jump-coupling each were set at 0. 
       FIG.  12    shows the pass characteristic of the first model.  FIG.  13    shows the pass characteristic of the second model. In each of  FIGS.  12  and  13   , the horizontal axis represents frequency, and the vertical axis represents insertion loss. It is found from  FIG.  12    that in a case where the second resonator  22  and the third resonator  23  are electromagnetically coupled by the magnetic coupling as the main coupling with the increased magnetic coupling coefficient k23, an attenuation pole is formed in a frequency range higher than the pass band of the band-pass filter. 
     It is also found from  FIG.  13    that when the second resonator  22  and the third resonator  23  are electromagnetically coupled by the capacitive coupling as the main coupling with the decreased magnetic coupling coefficient k23, an attenuation pole is formed in a frequency range lower than the pass band of the band-pass filter. 
     In general, in a band-pass filter constituted by two resonators, it is known that when a magnetic coupling coefficient between the two resonators relatively increases and a coupling capacitance between the two resonators relatively decreases, an attenuation pole is formed in a frequency range higher than a center frequency of a pass band of the band-pass filter. In the first and second models, the magnetic coupling coefficients k13 and k24 of the jump-coupling are set at 0, in order to clarify a variation of the attenuation pole due to difference in the electromagnetic coupling between the second resonator  22  and the third resonator  23 . However, the foregoing explanation of the variation of the attenuation pole holds true for the magnetic coupling coefficients k13 and k24 having a value other than 0. In the present embodiment, as described above, the electromagnetic coupling between the second resonator  22  and the third resonator  23  by the magnetic coupling as the main coupling allows formation of the attenuation pole in the second vicinity range. 
     Next, the pass characteristic of the third model will be described. In the third model, the magnetic coupling coefficient k23 was set at 0.37. The magnetic coupling coefficient k13 of jump-coupling was 0.032, and the magnetic coupling coefficient k24 of the jump-coupling was set at 0. 
       FIG.  14    shows the pass characteristic of the third model. In  FIG.  14   , the horizontal axis represents frequency, and the vertical axis represents insertion loss. It is found from  FIG.  14    and the pass characteristic of the first model (the magnetic coupling coefficients k13 and k24 of the jump-coupling each are 0) shown in  FIG.  12    that an attenuation pole is formed in a frequency range lower than the pass band of the band-pass filter, due to the jump-coupling between the first resonator  21  and the third resonator  23 . In the present embodiment, as described above, the jump-coupling between the third resonator  23  and the first resonator  21  allows formation of the attenuation pole in the first vicinity range. 
     Next, the pass characteristic of the fourth model will be described. In the fourth model, the magnetic coupling coefficient k23 was set at 0.37. The magnetic coupling coefficient k13 of jump-coupling was 0, and the magnetic coupling coefficient k24 of the jump-coupling was set at 0.02. 
       FIG.  15    shows the pass characteristic of the fourth model. In  FIG.  15   , the horizontal axis represents frequency, and the vertical axis represents insertion loss. It is found from  FIG.  15    and the pass characteristic of the first model (the magnetic coupling coefficients k13 and k24 of the jump-coupling each are 0) shown in  FIG.  12    that an attenuation pole is formed in a frequency range lower than the pass band of the band-pass filter, due to the jump-coupling between the second resonator  22  and the fourth resonator  24 . In the present embodiment, as described above, the jump-coupling between the fourth resonator  24  and the second resonator  22  allows formation of the attenuation pole in the first vicinity range. 
     Next, the pass characteristic of the fifth model will be described. In the fifth model, the magnetic coupling coefficient k23 was set at 0.37. The magnetic coupling coefficient k13 of jump-coupling was 0.032, and the magnetic coupling coefficient k24 of the jump-coupling was set at 0.02. 
       FIG.  16    shows the pass characteristic of the fifth model. In  FIG.  16   , the horizontal axis represents frequency, and the vertical axis represents insertion loss. It is found from  FIG.  16   , the pass characteristic of the third model (the magnetic coupling coefficient k24 is 0) shown in  FIG.  14   , and the pass characteristic of the fourth model (the magnetic coupling coefficient k13 is 0) shown in  FIG.  15   , that attenuation pole formed by the jump-coupling of the two pairs of resonators becomes abrupter than the attenuation pole formed by the jump-coupling of the one pair of resonators shown in  FIGS.  14  and  15   . This is because of synergy between the effect of the jump-coupling of one pair of resonators and the effect of the jump-coupling of the other pair of resonators. In the present embodiment, the jump-coupling of the two pairs of resonators makes the attenuation pole formed in the first vicinity range abrupter. 
     As is understood from the simulation results shown in  FIGS.  12  to  16   , according to the present embodiment, it is possible to form an abrupt attenuation pole in each of the first and second vicinity ranges, with the use of the magnetic coupling between the second resonator  22  and the third resonator  23  as the main coupling and the use of at least one of the jump-coupling between the first resonator  21  and the third resonator  23  and the jump-coupling between the second resonator  22  and the fourth resonator  24 . In the present embodiment, it is possible to form an abrupter attenuation pole in the first vicinity range, with the use of both of the jump-coupling between the first resonator  21  and the third resonator  23  and the jump-coupling between the second resonator  22  and the fourth resonator  24 . 
     In the present embodiment, the distance between the second resonator  22  and the third resonator  23  is made shorter than that between the first resonator  21  and the second resonator  22 , and shorter than that between the third resonator  23  and the fourth resonator  24 . Specifically in the present embodiment, the capacitive coupling between the second resonator  22  and the third resonator  23  is made relatively strong while the magnetic coupling between the second resonator  22  and the third resonator  23  is made relatively strong by making the distance between the second resonator  22  and the third resonator  23  relatively short. Thus, the attenuation pole formed in the second vicinity range has a frequency close to the pass band. Therefore, according to the present embodiment, it is possible to achieve a characteristic for abruptly varying the insertion loss in the vicinity of the pass band. Note that a second embodiment will describe an example in which the distance between the second resonator  22  and the third resonator  23  is made longer than that of the present embodiment. 
     According to the present embodiment, it is possible to form the attenuation pole as described above while satisfying balance characteristics. This effect will be described later with reference to an example of characteristic of the band-pass filter  1 . 
     In the present embodiment, each of the second to fourth resonators  22  to  24  is a resonator with both ends open. The resonator with both ends open is able to have a symmetrical circuit configuration with respect to the center of the resonator. As shown in  FIG.  1   , the present embodiment has a symmetrical circuit configuration in which a group of the capacitors C 2 A, C 3 A, C 4 A, C 23 A, and C 34 A and a group of the capacitors C 2 B, C 3 B, C 4 B, C 23 B, and C 34 B are symmetrical with respect to the second to fourth resonators  22  to  74 . 
     Respective ends of the resonator with both ends open are referred to as a first end and a second end. In the resonator with both ends open, when the balance of an electric field and a magnetic field between the side of the first end and the side of the second end is lost, the balance characteristics deteriorate. In the present embodiment, providing the fourth resonator  24  improves the symmetry of the circuit configuration of the band-pass filter  1 , as compared with the case of having no fourth resonator  24 . Therefore, according to the present embodiment, it is possible to improve the balance characteristics by relieving unbalance of the electric field and the magnetic field. 
     Next, examples of characteristics of the band-pass filter  1  according to the present embodiment will be described with reference to  FIGS.  17  to  22   . Here, the examples of characteristics of the band-pass filter  1  that is designed such that the pass band includes a frequency band of 3.3 GHz to 3.9 GHz will be described. 
       FIG.  17    shows an example of pass characteristic of the band-pass filter  1 .  FIG.  18    shows part of  FIG.  17    on an enlarged scale. Here, the foregoing insertion loss is indicated as the pass characteristic of the band-pass filter  1 . In each of  FIGS.  17  and  18   , the horizontal axis represents frequency, and the vertical axis represents insertion loss. It is found from  FIG.  17    that in the band-pass filter  1 , an attenuation pole at which the insertion loss abruptly varies is formed in each of first and second vicinity ranges. 
     The insertion loss is preferably 2.5 dB or less. As shown in  FIG.  18   , the band-pass filter  1  has the insertion loss of 2.5 dB or less in the foregoing frequency bands. 
       FIG.  19    shows an example of amplitude balance characteristic of the band-pass filter  1 . The amplitude balance characteristic of the band-pass filter  1  is represented here using a difference in amplitude between the first and second balanced element signals outputted from the first and second balanced ports  12  and  13  upon input of an unbalanced signal to the unbalanced port  11 , which will hereinafter be simply referred to as the amplitude difference. The amplitude difference is expressed in positive values when the amplitude of the first balanced element signal is greater than the amplitude of the second balanced element signal, and in negative values when the amplitude of the first balanced element signal is smaller than the amplitude of the second balanced element signal. In  FIG.  19   , the horizontal axis represents frequency, and the vertical axis represents amplitude difference. With the amplitude difference denoted as in (dB), in preferably has a value of −1.5 or more and not more than 1.5, and more preferably −1.0 or more and not more than 1.0. As shown in  FIG.  19   , the band-pass filter  1  has an m value of −1.0 or more and not more than 1.0 in the foregoing frequency band. 
       FIG.  20    shows an example of phase balance characteristic of the band-pass filter  1 . The phase balance characteristic of the band-pass filter  1  is represented here using a difference in phase between the first and second balanced element signals outputted from the first and second balanced ports  12  and  13  upon input of an unbalanced signal to the unbalanced port  11 , which will hereinafter be simply referred to as the phase difference. The phase difference represents the magnitude of advancement of the phase of the first balanced element signal relative to the phase of the second balanced element signal. In  FIG.  20   , the horizontal axis represents frequency, and the vertical axis represents phase difference. With the phase difference denoted as p (deg), p preferably has a value of 165 or more and not more than 196. As shown in  FIG.  20   , the band-pass filter  1  has a p value of 165 or more and not more than 195 in the foregoing frequency band. 
       FIG.  21    shows an example of reflection characteristic of the unbalanced port  11  of the band-pass filter  1 .  FIG.  22    shows an example of reflection characteristic of the first and second balanced ports  12  and  13  of the band-pass filter  1 . In each of  FIGS.  21  and  22   , the horizontal axis represents frequency, and the vertical axis represents return loss. The return loss is preferably 10 dB or more. As shown in  FIGS.  21  and  22   , the band-pass filter  1  has the return loss of 10 dB or more in the foregoing frequency band. 
     As described above, the band-pass filter  1  having the characteristics shown in  FIGS.  17  to  22    is usable in at least the frequency band of 3.3 GHz to 3.9 GHz, and has the favorable balance characteristics in this frequency band. As is understood from  FIGS.  17  to  22   , the band-pass filter  1  can form the abrupt attenuation pole in each of the first and second vicinity ranges while satisfying the balance characteristics. 
     Second Embodiment 
     A second embodiment of the invention will now be described. First, the circuit configuration of a band-pass filter according to the present embodiment will be described in brief with reference to  FIG.  23   .  FIG.  23    shows the circuit configuration of the band-pass filter according to the present embodiment. 
     The circuit configuration of a band-pass filter  101  according to the present embodiment is different from that of the band-pass filter  1  according to the first embodiment in the following respect. In the present embodiment, there is no capacitor C 23 B provided for connecting one end of the second resonator  22  on the side of the capacitor C 2 B to one end of the third resonator  23  on the side of the capacitor C 3 B. The other circuit configuration of the band-pass filter  101  is the same as that of the band-pass filter  1  according to the first embodiment. 
     Next, a structure of the band-pass filter  101  will be described.  FIG.  24    is a perspective view showing the interior of the band-pass filter  101 . Just as with the band-pass filter  1  according to the first embodiment, the band-pass filter  101  includes the stack  30  and the first to eights terminals  111  to  118  (refer to  FIGS.  2  and  3   ). The stack  30  of the present embodiment integrates the ports  11  to  13 , the first to fourth resonators  21  to  24 , and the capacitors C 1 , C 2 A, C 2 B, C 3 A, C 3 B, C 4 A, C 4 B, C 11 , C 12 , C 23 A, C 34 A, and C 34 B. The shape and layout of the first to eighth terminals  111  to  118  are the same as those of the first embodiment. 
     The stack  30  of the present embodiment will be described in detail with reference to  FIG.  25 A  to  FIG.  32 B . In the present embodiment, the stack  30  includes stacked twenty-five dielectric layers instead of the dielectric layers  31  to  56  of the first embodiment. The twenty-five dielectric layers will be referred to as the first to twenty-fifth dielectric layers in the order from bottom to top. The first to twenty-fifth dielectric layers will be denoted by the reference numerals  61  to  85 . 
       FIG.  25 A  shows the patterned surface of the first dielectric layer  61 .  FIG.  25 A  shows terminal parts  111   a  to  118   a  constituting parts of the terminals  111  to  118 , respectively. 
       FIG.  25 B  shows the patterned surface of the second dielectric layer  62 . A ground conductor layer  621  is formed on the patterned surface of the dielectric layer  62 . The conductor layer  621  is connected to the fourth and seventh terminals  114  and  117 . 
       FIG.  26 A  shows the patterned surface of the third dielectric layer  63 . A conductor layer  631  is formed on the patterned surface of the dielectric layer  63 . Further, through hole  63 T 5  is formed in the dielectric layer  63 . The through hole  6315  is connected to the conductor layer  631 . 
       FIG.  26 B  shows the patterned surface of the fourth dielectric layer  64 . A conductor layers  641 ,  642  and  643  are formed on the patterned surface of the dielectric layer  63 . The through hole  63 T 5  formed in the third dielectric layer  63  is connected to the conductor layer  641 . The conductor layer  632  is connected to the eighth terminal  118 . The conductor layer  633  is connected to the fifth terminal  115 . 
       FIG.  27 A  shows the patterned surface of the fifth dielectric layer  65 . A conductor layers  651 ,  652 ,  653  and  654  are formed on the patterned surface of the dielectric layer  65 . Further, through holes  65 T 1 ,  65 T 2 ,  65 T 3  and  65 T 4  are formed in the dielectric layer  65 . The through holes  65 T 1 ,  65 T 2 ,  65 T 3  and  651  are connected to the conductor layers  651 ,  652 ,  653  and  654 , respectively, 
       FIG.  27 B  shows the patterned surface of the sixth dielectric layer  66 . A conductor layer  661  is formed on the patterned surface of the dielectric layer  66 . Further, through holes  66 T 1 ,  66 T 2 ,  66 T 3 ,  66 T 4  and  66 T 5  are formed in the dielectric layer  66 . The through holes  65 T 1 ,  65 T 2 ,  65 T 3  and  65 T 4  formed in the fifth dielectric layer  65  are connected to the through holes  66 T 1 ,  66 T 2 ,  66 T 3  and  66 T 4 , respectively. The through hole  6615  is connected to the conductor layer  661 . 
       FIG.  28 A  shows the patterned surface of each of the seventh and eighth dielectric layers  67  and  68 . In each of the dielectric layers  67  and  68 , there are formed through holes  67 T 1 ,  67 T 2 ,  67 T 3 ,  67 T 4  and  67 T 5 . The through holes  66 T 1 ,  66 T 2 ,  66 T 3 ,  66 T 4  and  66 T 5  formed in the sixth dielectric layer  66  are connected to the through holes  67 T 1 ,  67 T 2 ,  67 T 3 ,  67 T 4  and  67 T 5  formed in the seventh dielectric layer  67 , respectively. In the dielectric layers  67  and  68 , every vertically adjacent through holes denoted by the same reference signs are connected to each other. 
       FIG.  28 B  shows the patterned surface of the ninth dielectric layer  69 . A conductor layer  691  is formed on the patterned surface of the dielectric layer  69 . Further, through holes  69 T 1 ,  69 T 2 ,  69 T 3 ,  69 T 4  and  69 T 5  are formed in the dielectric layer  69 . The through holes  67 T 1 ,  67 T 2 ,  67 T 3 ,  67 T 4  and  67 T 5  formed in the eighth dielectric layer  68  are connected to the through holes  69 T 1 ,  69 T 2 ,  69 T 3 ,  69 T 4  and  69 T 5 , respectively. 
       FIG.  29 A  shows the patterned surface of the tenth dielectric layer  70 . A conductor layer  701  is formed on the patterned surface of the dielectric layer  70 . Further, through holes  70 T 1 ,  70 T 2 ,  70 T 3 ,  70 T 4  and  70 T 5  are formed in the dielectric layer  70 . The through holes  69 T 1 ,  69 T 2 ,  69 T 3  and  69 T 4  formed in the ninth dielectric layer  69  are connected to the through holes  70 T 1 ,  70 T 2 ,  70 T 3  and  70 T 4 , respectively. The through hole  70 T 5  and the through hole  69 T 5  formed in the ninth dielectric layer  69  are connected to the conductor layer  701 . 
       FIG.  29 A  shows the patterned surface of each of the eleventh to sixteenth dielectric layers  71  to  76 . In each of the dielectric layers  71  to  76 , there are formed through holes  71 T 1 ,  71 T 2 ,  71 T 3 ,  71 T 4  and  71 T 5 . The through holes  70 T 1 ,  70 T 2 ,  70 T 3 ,  70 T 4  and  70 T 5  formed in the tenth dielectric layer  70  are connected to the through holes  71 T 1 ,  71 T 2 ,  71 T 3 ,  71 T 4  and  71 T 5  formed in the eleventh dielectric layer  71 , respectively. In the dielectric layers  71  to  76 , every vertically adjacent through holes denoted by the same reference signs are connected to each other. 
       FIG.  30 A  shows the patterned surface of each of the seventeenth and eighteenth dielectric layers  77  and  78 . A resonator-forming conductor layer  771  is formed on the patterned surface of each of the dielectric layers  77  and  78 . The resonator-forming conductor layer  771  is connected to the fifth and eighth terminals  115  and  118 . Further, in each of the dielectric lavers  77  and  78 , there are formed through holes  77 T 1 ,  77 T 2 ,  77 T 3 ,  77 T 4  and  77 T 5 . The through holes  71 T 1 ,  71 T 2 ,  71 T 3 ,  71 T 4  and  7115  formed in the sixteenth dielectric layer  76  are connected to the through holes  77 T 1 ,  77 T 2 ,  77 T 3 ,  77 T 4  and  77 T 5  formed in the seventeenth dielectric layer  77 , respectively. In the dielectric layers  77  and  78 , every vertically adjacent through holes denoted by the same reference signs are connected to each other. 
       FIG.  30 B  shows the patterned surface of each of the nineteenth and twentieth dielectric layers  79  and  80 . In each of the dielectric layers  77  and  87 , there are formed through holes  79 T 1 ,  79 T 2 ,  79 T 3 ,  79 T 4  and  79 T 5 . The through holes  77 T 1 ,  77 T 2 ,  77 T 3 ,  77 T 4  and  77 T 5  formed in the eighteenth dielectric layer  78  are connected to the through holes  79 T 1 ,  79 T 2 ,  79 T 3 ,  79 T 4  and  79 T 5  formed in the nineteenth dielectric layer  79 , respectively. In the dielectric layers  79  and  80 , every vertically adjacent through holes denoted by the same reference signs are connected to each other. 
       FIG.  31 A  shows the patterned surface of the twenty-first dielectric layer  81 . A resonator-forming conductor layer  811  is formed on the patterned surface of the dielectric layer  81 . The resonator-forming conductor layer  811  is connected to the third and sixth terminals  113  and  116 . Further, through holes  81 T 1 ,  81 T 2 ,  81 T 3 ,  81 T 4  and  81 T 5  are formed in the dielectric layer  81 . The through holes  79 T 1 ,  79 T 2 ,  79 T 3  and  79 T 4  formed in the twentieth dielectric layer  70  are connected to the through holes  81 T 1 ,  81 T 2 ,  81 T 3  and  81 T 4 , respectively. 
       FIG.  31 B  shows the patterned surface of the twenty-second dielectric layer  54 . A resonator-forming conductor layer  821  is formed on the patterned surface of the dielectric layer  82 . The resonator-forming conductor layer  821  is connected to the third and sixth terminals  113  and  116 . The through hole  81 T 5  formed in the twenty-first dielectric layer  81  is connected to part of the resonator-forming conductor layer  821 , i.e. a portion including the middle of the resonator-forming conductor layer  821  in a longitudinal direction. Further, through holes  82 T 1 ,  82 T 2 ,  82 T 3 ,  82 T 4  and  82 T 5  are formed in the dielectric layer  82 . The through holes  81 T 1 ,  81 T 2 ,  81 T 3  and  81 T 4  formed in the dielectric layer  81  are connected to the through holes  82 T 1 ,  82 T 2 ,  82 T 3  and  82 T 4 , respectively. 
       FIG.  32 A  shows the patterned surface of the twenty-third dielectric layer  83 . Resonator-forming conductor layers  832  and  833  are formed on the patterned surface of the dielectric layer  83 . Each of the resonator-forming conductor layers  832  and  833  has a first end and a second end opposite to each other. Further, through holes  83 T 1 ,  83 T 2 ,  83 T 3  and  83 T 4  are formed in the dielectric layer  83 . The through hole  83 T 1  and the through hole  82 T 1  formed in the twenty-second dielectric layer  82  are connected to a portion of the resonator-forming conductor layers  832  near the first end thereof. The through hole  83 T 2  and the through hole  82 T 2  formed in the dielectric layer  82  are connected to a portion of the resonator-forming conductor layers  832  near the second end thereof. The through hole  83 T 3  and the through hole  82 T 3  formed in the dielectric layer  82  are connected to a portion of the resonator-forming conductor layers  833  near the first end thereof. The through hole  83 T 4  and the through hole  82 T 4  formed in the dielectric layer  82  are connected to a portion of the resonator-forming conductor layers  833  near the second end thereof. 
       FIG.  32 B  shows the patterned surface of the twenty-fourth dielectric layer  84 . Resonator-forming conductor layer  842  and  843  are formed on the patterned surface of the dielectric layer  84 . Each of the resonator-forming conductor layers  842  and  843  has a first end and a second end opposite to each other. The through hole  83 T 1  formed in the twenty-third dielectric layer  83  is connected to a portion of the resonator-forming conductor layers  842  near the first end thereof. The through hole  83 T 2  formed in the dielectric layer  83  is connected to a portion of the resonator-forming conductor layers  842  near the second end thereof. The through hole  83 T 3  formed in the dielectric layer  83  is connected to a portion of the resonator-forming conductor layers  843  near the first end thereof. The through hole  83 T 4  formed in the dielectric layer  83  is connected to a portion of the resonator-forming conductor layers  843  near the second end thereof. 
     Although it is not shown in the drawing, a mark may be formed in the patterned surface of the twenty-fifth dielectric layer  85 . 
     The stack  30  of the present embodiment is formed by stacking the first to twenty-fifth dielectric layers  61  to  85  such that the patterned surface of the first dielectric layer  61  serves as the bottom surface  30 B of the stack  30  (see  FIGS.  2  and  3   ) and the surface of the twenty-sixth dielectric layer  85  opposite to the patterned surface thereof serves as the top surface  30 A of the stack  30  (see  FIGS.  2  and  3   ). The first to eighth terminals  111  to  118  are then formed on the periphery of the stack  30 , whereby the band-pass filter  101  is completed. 
     A correspondence between the components of the band-pass filter  101  and the components inside the stack  30  shown in  FIGS.  25 A to  32 B  will be described below. 
     The first resonator  21  is formed of the resonator-forming conductor layers  811  and  821 , the through holes  70 T 5  and  81 T 5 , the through hole  71 T 5  formed in each of the dielectric layer  71  to  76 , the through hole  77 T 5  formed in each of the dielectric layer  77  and  78 , and the through hole  79 T 5  formed in each of the dielectric layers  79  and  80 . 
     The second resonator  22  is formed of the resonator-forming conductor layers  832  and  842 , the through holes  65 T 1 ,  65 T 2 ,  66 T 1 ,  66 T 2 ,  69 T 1 ,  69 T 2 ,  70 T 1 ,  70 T 2 ,  81 T 1 ,  81 T 2 ,  82 T 1 ,  82 T 2 ,  83 T 1  and  83 T 2 , the through holes  67 T 1  and  67 T 2  formed in each of the dielectric layer  67  and  68 , the through holes  71 T 1  and  71 T 2  formed in each of the dielectric layer  71  to  76 , the through holes  77 T 1  and  77 T 2  formed in each of the dielectric layer  77  and  78 , and the through holes  79 T 1  and  79 T 2  formed in each of the dielectric lavers  79  and  80 . 
     Like the first embodiment, the second resonator  22  includes a first through hole line  22 A, a second through hole line  22 B, and a conductor layer portion  22 C (see  FIG.  24   ). The first through hole line  22 A is formed of the through holes  65 T 1 ,  66 T 1 ,  69 T 1 ,  70 T 1 ,  81 T 1 , and  82 T 1 , the through holes  67 T 1  formed in each of the dielectric layers  67  and  68 , the through holes  71 T 1  formed in each of the dielectric layers  71  to  76 , the through holes  77 T 1  formed in each of the dielectric layers  77  and  78 , and the through holes  79 T 1  formed in each of the dielectric layers  79  and  80  connected in series. The first through hole line  22 A penetrates the dielectric layers  65  to  82 . 
     The second through hole line  22 B is formed of the through holes  65 T 2 ,  66 T 2 ,  69 T 2 ,  70 T 2 ,  81 T 2 , and  82 T 2 , the through holes  67 T 2  formed in each of the dielectric layers  67  and  68 , the through holes  71 T 2  formed in each of the dielectric layers  71  to  76 , the through holes  77 T 2  formed in each of the dielectric layers  77  and  78 , and the through holes  79 T 2  formed in each of the dielectric layers  79  and  80  connected in series. The first through hole line  22 A penetrates the dielectric layers  65  to  82 . 
     The conductor layer portion  22 C is formed of the resonator-forming conductor layers  832  and  842  that are connected to each other via the through holes  83 T 1  and  83 T 2 . 
     The third resonator  23  is formed of the resonator-forming conductor layers  833  and  843 , the through holes  65 T 3 ,  65 T 4 ,  66 T 3 ,  66 T 4 ,  69 T 3 ,  69 T 4 ,  70 T 3 ,  70 T 4 ,  81 T 3 ,  81 T 4 ,  82 T 3 ,  82 T 4 ,  83 T 3 , and  83 T 4 , the through holes  67 T 3  and  67 T 4  formed in each of the dielectric layer  67  and  68 , the through holes  71 T 3  and  71 T 4  formed in each of the dielectric layer  71  to  76 , the through holes  77 T 3  and  77 T 4  formed in each of the dielectric layer  77  and  78 , and the through holes  79 T 3  and  79 T 4  formed in each of the dielectric layers  79  and  80 . 
     Like the first embodiment, the third resonator  23  includes a first through hole line  23 A, a second through hole line  23 B, and a conductor layer portion  23 C (see  FIG.  24   ). The first through hole line  23 A is formed of the through holes  65 T 3 ,  66 T 3 ,  69 T 3 ,  70 T 3 ,  81 T 3 , and  82 T 3 , the through holes  67 T 3  formed in each of the dielectric layers  67  and  68 , the through holes  71 T 3  formed in each of the dielectric layers  71  to  76 , the through holes  77 T 3  formed in each of the dielectric layers  77  and  78 , and the through holes  79 T 3  formed in each of the dielectric layers  79  and  80  connected in series. The first through hole line  22 A penetrates the dielectric layers  65  to  82 . 
     The second through hole line  23 B is formed of the through holes  65 T 4 ,  66 T 4 ,  69 T 4 ,  70 T 4 ,  81 T 4 , and  82 T 4 , the through holes  67 T 4  formed in each of the dielectric layers  67  and  68 , the through holes  71 T 4  formed in each of the dielectric layers  71  to  76 , the through holes  77 T 4  formed in each of the dielectric layers  77  and  78 , and the through holes  79 T 4  formed in each of the dielectric layers  79  and  80  connected in series. The first through hole line  22 A penetrates the dielectric layers  65  to  82 . 
     The conductor layer portion  23 C is formed of the resonator-forming conductor layers  833  and  843  that are connected to each other via the through holes  83 T 3  and  83 T 4 . 
     The fourth resonator  24  is formed of the resonator-forming conductor layer  771  formed in each of the dielectric layer  77  and  78 . 
     The capacitor C 1  is formed of the conductor layers  621  and  701 , and the dielectric layers  62  to  69  interposed between the conductor layers  621  and  701 . 
     The capacitor C 2 A is formed of the conductor layers  621  and  651 , and the dielectric layers  62  to  64  interposed between the conductor layers  621  and  651 . The capacitor C 2 B is formed of the conductor layers  621  and  651 , and the dielectric layers  62  to  64  interposed between the conductor layers  621  and  651 . 
     The capacitor C 3 A is formed of the conductor layers  621  and  653 , and the dielectric layers  62  to  64  interposed between the conductor layers  621  and  653 . The capacitor C 3 B is formed of the conductor layers  621  and  654 , and the dielectric layers  62  to  64  interposed between the conductor layers  621  and  654 . 
     The capacitor C 4 A is formed of the conductor layers  621  and  642 , and the dielectric layers  62  and  63  interposed between the conductor layers  621  and  642 . The capacitor C 4 B is formed of the conductor layers  621  and  643 , and the dielectric layers  62  and  63  interposed between the conductor layers  621  and  643 . 
     The capacitor C 11  is formed of the conductor layers  691  and  701 , the dielectric layer  69  interposed between the conductor layers  691  and  701 . The capacitor C 12  is formed of the conductor layers  651  and  661 , and the dielectric layer  65  interposed between the conductor layers  651  and  661 . 
     The capacitor C 23 A is formed of the conductor layers  631 ,  641 ,  651  and  653 , and the dielectric layers  63  and  64  interposed between the conductor layers  631  and  651 , and the dielectric layer  64  interposed between the conductor layers  641  and  651 . 
     The capacitor C 34 A is formed of the conductor layers  623  and  653 , and the dielectric layer  64  interposed between the conductor layers  642  and  653 . The capacitor C 34 B is formed of the conductor layers  643  and  654 , and the dielectric layer  64  interposed between the conductor layers  643  and  654 . 
     Next, structural features of the band-pass filter  101  will be described with reference to  FIG.  24   . In the present embodiment, the distance between the second resonator  22  and the third resonator  23  is shorter than that between the first resonator  21  and the second resonator  22 , and is also shorter than that between the third resonator  23  and the fourth resonator  24 . In the present embodiment, the distance between the second resonator  22  and the third resonator  23  is longer than that between the second resonator  22  and the third resonator  23  in the first embodiment (refer to  FIG.  4   ). 
     As shown in  FIG.  30 A , the resonator-forming conductor layer  771  formed in the dielectric layer  77  and the resonator-forming conductor layer  771  formed in the dielectric layer  78  are located so as to overlap each other when viewed from the Z direction. As shown in  FIGS.  31 A and  31 B  the resonator-forming conductor layer  811  formed in the dielectric layer  81  and the resonator-forming conductor layer  821  formed in the dielectric layer  82  are located so as to overlap each other when viewed from the Z direction. As shown in  FIGS.  32 A and  32 B , the resonator-forming conductor layer  832  formed in the dielectric layer  83  and the resonator-forming conductor layer  842  formed in the dielectric layer  84  are located so as to overlap each other when viewed from the Z direction. The resonator-forming conductor layer  833  formed in the dielectric layer  83  and the resonator-forming conductor layer  843  formed in the dielectric layer  84  are located so as to overlap each other when viewed from the Z direction. 
     The operation and effects of the band-pass filter  101  according to the first embodiment will now be described. In the present embodiment, just as with the first embodiment, an attenuation pole at which insertion loss abruptly varies is formed in each of a first vicinity range that is a frequency range lower than a pass band and in the vicinity of the pass band and a second vicinity range that is a frequency range higher than the pass band and in the vicinity of the pass band. 
     Specifically in the present embodiment, since the distance between the second resonator  22  and the third resonator  23  is made longer than that of the first embodiment, the capacitive coupling between the second resonator  22  and the third resonator  23  is weakened as compared to the case of the first embodiment while the magnetic coupling between the second resonator  22  and the third resonator  23  is weakened as compared to the case of the first embodiment. To be more specific, by providing no capacitor C 23 B, the capacitive coupling between the second resonator  22  and the third resonator  23  is weakened. The capacitive coupling between the second resonator  22  and the third resonator  23  is adjusted by the capacitor C 23 A. On the other hand, in the first embodiment, the capacitive coupling between the second resonator  22  and the third resonator  23  is adjusted by the capacitors C 23 A and C 23 B. According to the present embodiment, as compared to the first embodiment, the capacitive coupling between the second resonator  22  and the third resonator  23  is easily adjusted. 
     Next, examples of characteristics of the band-pass filter  101  according to the present embodiment will be described with reference to  FIGS.  33  to  38   . Here, the examples of characteristics of the band-pass filter  101  that is designed such that the pass band includes a frequency band of 4.7 GHz to 5.1 GHz will be described. 
       FIG.  33    shows an example of pass characteristic of the band-pass filter  1 ,  FIG.  34    shows part of  FIG.  33    on an enlarged scale. Here, the insertion loss when an unbalanced signal was inputted to the unbalanced port  11  is indicated as the pass characteristic of the band-pass filter  101 . In each of  FIGS.  33  and  34   , the horizontal axis represents frequency, and the vertical axis represents insertion loss. It is found from  FIG.  33    that in the band-pass filter  101 , an attenuation pole at which the insertion loss abruptly varies is formed in each of first and second vicinity ranges. 
     By comparison between  FIG.  33    and  FIG.  17   , which shows an example of pass characteristic of the band-pass filter  1  according to the first embodiment, the following difference can be seen. In the band-pass filter  101 , the attenuation pole formed in the higher-side frequency range is far from the pass band, as compared to the case of the band-pass filter  1 . This is because of weakening of the capacitive coupling between the second resonator  22  and the third resonator  23  by the capacitors C 23 A and C 23 B as compared to the capacitive coupling of the band-pass filter  1 , with weakening of the magnetic coupling between the second resonator  22  and the third resonator  23  as compared to the magnetic coupling of the band-pass filter  1 , by making the distance between the second resonator  22  and the third resonator  23  longer in the band-pass filter  101  than in the band-pass filter  1 . In other words, as can be seen from  FIGS.  17  and  33   , strengthening of the capacitive coupling between the second resonator  22  and the third resonator  23  with strengthening of the magnetic coupling between the second resonator  22  and the third resonator  23 , by making the distance between the second resonator  22  and the third resonator  23  shorter, allows the frequency of the attenuation pole formed in the second vicinity range to get closer to the pass band. 
     The insertion loss is preferably 3.0 dB or less. As shown in  FIG.  34   , the band-pass filter  101  has the insertion loss of 3.0 dB or less in the foregoing frequency bands. 
       FIG.  35    shows an example of amplitude balance characteristic of the band-pass filter  101 . Here, the amplitude balance characteristic of the band-pass filter  101  is represented by using an amplitude difference, just as with  FIG.  19    of the first embodiment. In  FIG.  35   , the horizontal axis represents frequency, and the vertical axis represents amplitude difference. With the amplitude difference denoted as m (dB), m preferably has a value of −1.5 or more and not more than 1.5, and more preferably −1.0 or more and not more than 1.0. As shown in  FIG.  35   , the band-pass filter  101  has an m value of −1.0 or more and not more than 1.0 in the foregoing frequency band. 
       FIG.  36    shows an example of phase balance characteristic of the band-pass filter  101 . Here, the phase balance characteristic of the band-pass filter  101  is represented by using a phase difference, just as with  FIG.  20    of the first embodiment. In  FIG.  36   , the horizontal axis represents frequency, and the vertical axis represents phase difference. With the phase difference denoted as p (deg), p preferably has a value of 165 or more and not more than 196. As shown in  FIG.  35   , the band-pass filter  101  has a p value of 165 or more and not more than 195 in the foregoing frequency band. 
       FIG.  37    shows an example of reflection characteristic of the unbalanced port  11  of the band-pass filter  101 .  FIG.  38    shows an example of reflection characteristic of the first and second balanced ports  12  and  13  of the band-pass filter  101 . In each of  FIGS.  37  and  38   , the horizontal axis represents frequency, and the vertical axis represents return loss. The return loss is preferably 10 dB or more. As shown in  FIGS.  37  and  38   , the band-pass filter  101  has the return loss of 10 dB or more in the foregoing frequency band. 
     As described above, the band-pass filter  101  having the characteristics shown in  FIGS.  33  to  38    is usable in at least the frequency band of 4.7 GHz to 5.1 GHz, and has the favorable balance characteristics in this frequency band. As is understood from  FIGS.  33  to  38   , the band-pass filter  101  can form the abrupt attenuation pole in each of the first and second vicinity ranges while satisfying the balance characteristics. 
     The configuration, function and effects of the present embodiment are otherwise the same as those of the first embodiment. 
     Third Embodiment 
     A third embodiment of the invention will now be described. First, the circuit configuration of a band-pass filter according to the present embodiment will be described in brief with reference to  FIG.  39   .  FIG.  39    shows the circuit configuration of the band-pass filter according to the present embodiment. 
     The circuit configuration of a band-pass filter  201  according to the present embodiment is different from that of the band-pass filter  101  according to the second embodiment in the following respect. In the present embodiment, there is no capacitor C 23 A provided for connecting one end of the second resonator  22  on the side of the capacitor C 2 A to one end of the third resonator  23  on the side of the capacitor C 3 A. 
     The band-pass filter  201  includes capacitors C 5 A and C 5 B. Each of the capacitors C 5 A and C 5 B has a first end and a second end. The first end of the capacitor C 5 A is connected to the capacitors C 2 A and C 3 A. The second end of the capacitor C 5 A is connected to the ground. 
     The first end of the capacitor C 5 B is connected to the capacitors C 2 B and C 3 B. The second end of the capacitor C 5 B is connected to the ground. 
     The other circuit configuration of the band-pass filter  201  is the same as that of the band-pass filter  101  according to the second embodiment. 
     In the present embodiment, each of a group of the capacitors C 2 A, C 3 A, and CSA and a group of the capacitors C 2 B, C 3 B, and C 5 B are connected in so-called. Y-shaped connection. Therefore, according to the present embodiment, it is possible to reduce the capacitance of each of the capacitors C 2 A, C 2 B, C 3 A, C 5 B, C 5 A, and C 5 B, as compared with a case where these groups are connected in so-called π-shaped connection or Δ-shaped connection. As a result, the present embodiment allows downsizing of the band-pass filter  201 . 
     The configuration, function and effects of the present embodiment are otherwise the same as those of the second embodiment. 
     The present invention is not limited to the foregoing embodiments, and various modifications may be made thereto. For example, the band-pass filter according to the present invention may be integrated with another circuit into a stack electronic component. Examples of the other circuits include a branch circuit, a filter, and a matching circuit. 
     Obviously, many modifications and variations of the present invention a 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.