Patent Publication Number: US-2022231395-A1

Title: Dielectric resonator, dielectric filter, and multiplexer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2019-216297 filed on Nov. 29, 2019 and is a Continuation Application of PCT Application No. PCT/JP2020/039653 filed on Oct. 22, 2020. The entire contents of each application are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dielectric resonator, a dielectric filter, and a multiplexer including the dielectric filter. 
     2. Description of the Related Art 
     Dielectric resonators have been known. For example, Japanese Unexamined Patent Application Publication No. 5-90811 discloses a coaxial dielectric resonator. In the coaxial dielectric resonator, an outer conductor that is a conductive member is formed on the outer peripheral surface of a dielectric member and an inner conductor is formed with conductive paste filled into a through hole of the coaxial dielectric member. With the inner conductor having high conductivity, calories due to loss generated in the coaxial dielectric resonator can be effectively dissipated to the outside of the coaxial dielectric resonator. With the coaxial dielectric resonator, a reduction in Q factor due to miniaturization can be reduced. 
     The frequency characteristics of a dielectric filter (for example, bandpass characteristics or attenuation characteristics) are often formed by a plurality of dielectric resonators. In such a case, the performance of the dielectric filter depends on the steepness of the dielectric resonators. Thus, to achieve a further reduction in loss of the dielectric filter, it is necessary to further improve the Q factors indicating the steepness of the dielectric resonators. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide improvements in Q factor of dielectric resonators and a reduction in loss of dielectric filters. 
     A dielectric resonator according to a preferred embodiment of the present invention includes a dielectric substrate, a distributed element, and a shield conductor portion. The distributed element extends in a first direction inside the dielectric substrate. The shield conductor portion is on a surface of the dielectric substrate and winds around the distributed element when the distributed element is viewed from the first direction in plan view. One end of the distributed element is not connected to the shield conductor portion. The distributed element includes a plurality of conductors. 
     A dielectric filter according to a preferred embodiment of the present invention includes a dielectric substrate, a plurality of distributed elements, a first terminal, a second terminal, and a shield conductor portion. The plurality of distributed elements extend in a first direction inside the dielectric substrate. The first terminal and the second terminal are electrically connected to the plurality of distributed elements. The shield conductor portion is on a surface of the dielectric substrate and winds around the plurality of distributed elements when the plurality of distributed elements are viewed from the first direction in plan view. One end of each of the plurality of distributed elements is not connected to the shield conductor portion. At least one distributed element of the plurality of distributed elements includes a plurality of conductors. The dielectric substrate includes a plurality of dielectric layers stacked in a second direction orthogonal or substantially orthogonal to the first direction. The plurality of conductors each define a distributed constant line that extends in the first direction and the second direction is a normal thereof. The plurality of conductors are on at least 13 dielectric layers of the plurality of dielectric layers. 
     With the dielectric resonators according to preferred embodiments of the present invention, the distributed element includes the plurality of conductors so that an improvement in Q factor is able to be achieved. 
     With the dielectric filters according to preferred embodiments of the present invention, the distributed element includes the plurality of conductors so that a reduction in loss is able to be achieved. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external perspective view of a dielectric filter  1  according to Preferred Embodiment 1 of the present invention. 
         FIG. 2  is a perspective view of the dielectric filter  1  according to Preferred Embodiment 1 of the present invention. 
         FIG. 3  is a diagram illustrating the bandpass characteristics (solid line) and reflection characteristics (dotted line) of the dielectric filter of  FIG. 1 . 
         FIG. 4  is a perspective view of a dielectric filter according to Comparative Example 1. 
         FIG. 5  is a diagram illustrating the minimum value of the insertion loss of the dielectric filter of  FIG. 1  (solid line) and the minimum value of the insertion loss of the dielectric filter of  FIG. 4  (dotted line). 
         FIG. 6  is a perspective view of a dielectric resonator according to Preferred Embodiment 2 of the present invention. 
         FIG. 7  is a sectional view taken along the line VII-VII of  FIG. 6 . 
         FIG. 8  is a perspective view of a dielectric resonator according to Comparative Example 2. 
         FIG. 9  is a plan view of the distribution of field strengths (kV/m) in a simulation in which a high frequency signal is passed through a distributed element of  FIG. 8  when viewed from the X-axis direction. 
         FIG. 10  is a plan view of the distribution of field strengths in a simulation in which a high frequency signal is passed through a distributed element of  FIG. 6  when viewed from the X-axis direction. 
         FIG. 11  is a sectional view of a dielectric resonator according to Modification 1 of Preferred Embodiment 2 of the present invention. 
         FIG. 12  is a sectional view of a dielectric resonator according to Modification 2 of Preferred Embodiment 2 of the present invention. 
         FIG. 13  is a sectional view of a dielectric resonator according to Modification 3 of Preferred Embodiment 2 of the present invention. 
         FIG. 14  is a sectional view of a dielectric resonator according to Modification 4 of Preferred Embodiment 2 of the present invention. 
         FIG. 15  is a perspective view of a dielectric resonator according to Preferred Embodiment 3 of the present invention. 
         FIG. 16  is a plan view of the dielectric resonator of  FIG. 15  when viewed from the X-axis direction. 
         FIG. 17  is a diagram illustrating a case of the dielectric resonator of  FIG. 16  (solid line) and the dielectric resonator of  FIG. 6  (dotted line) in terms of the relationship between the number of the plurality of stacked conductors and the Q factor of the dielectric resonator. 
         FIG. 18  is a plan view of a dielectric resonator according to a modification of Preferred Embodiment 3 of the present invention when viewed from the X-axis direction. 
         FIG. 19  is a perspective view of a dielectric filter according to Preferred Embodiment 4 of the present invention. 
         FIG. 20  is a perspective view of a dielectric filter according to a modification of Preferred Embodiment 4 of the present invention. 
         FIG. 21  is a perspective view of a dielectric filter according to Comparative Example 3. 
         FIG. 22  is a diagram illustrating the bandpass characteristics of the dielectric filter of  FIG. 20  (solid line) and the bandpass characteristics of the dielectric filter of  FIG. 21  (dotted line). 
         FIG. 23  is a diagram illustrating the bandpass characteristics of the dielectric filter of  FIG. 19  (solid line) and the bandpass characteristics of the dielectric filter of  FIG. 21  (dotted line). 
         FIG. 24  is a perspective view of a dielectric filter according to Preferred Embodiment 5 of the present invention. 
         FIG. 25  is a plan view of the distribution of field strengths in a simulation in which a high frequency signal is passed through distributed elements of  FIG. 24  in an odd mode when viewed from the X-axis direction. 
         FIG. 26  is a plan view of the distribution of field strengths in a simulation in which a high frequency signal is passed through the distributed elements of  FIG. 24  in an even mode when viewed from the X-axis direction. 
         FIG. 27  is a plan view of the distribution of field strengths in a simulation in which a high frequency signal is passed through distributed elements of  FIG. 19  in an odd mode when viewed from the X-axis direction. 
         FIG. 28  is a plan view of the distribution of field strengths in a simulation in which a high frequency signal is passed through the distributed elements of  FIG. 19  in an even mode when viewed from the X-axis direction. 
         FIG. 29  is a perspective view of a dielectric filter according to a modification of Preferred Embodiment 5 of the present invention. 
         FIG. 30  is an equivalent circuit diagram of a duplexer that is an example of a multiplexer according to Preferred Embodiment 6 of the present invention. 
         FIG. 31  is an external perspective view of the duplexer of  FIG. 30 . 
         FIG. 32  is a perspective view of the duplexer of  FIG. 30 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention are described in detail below with reference to the drawings. In the drawings, the same or corresponding portions and elements are denoted by the same reference characters and the repetitive description thereof is generally omitted. 
     Preferred Embodiment 1 
       FIG. 1  and  FIG. 2  are perspective views of a dielectric filter  1  according to Preferred Embodiment 1 of the present invention. In  FIG. 1  and  FIG. 2 , the X axis, the Y axis, and the Z axis are orthogonal or substantially orthogonal to each other. The same is also true for  FIG. 4 ,  FIG. 6  to  FIG. 16 ,  FIG. 18  to  FIG. 21 ,  FIG. 24  to  FIG. 29 ,  FIG. 31 , and  FIG. 32 , which are described later. 
     With reference to  FIG. 1  and  FIG. 2 , the dielectric filter  1  has, for example, a rectangular or substantially rectangular parallelepiped shape. The dielectric filter  1  includes a dielectric substrate  100 , distributed elements  131  to  134 , a shield conductor portion  150 , ground electrodes  121  and  122 , an input/output terminal P 1  (first terminal), and an input/output terminal P 2  (second terminal). In  FIG. 2 , to make the distributed elements  131  to  134  inside the dielectric filter  1  easier to see, the illustration of the dielectric substrate  100  of  FIG. 1  is omitted. The illustration of the dielectric substrate is also omitted in  FIG. 4 ,  FIG. 6 ,  FIG. 8 ,  FIG. 15 ,  FIG. 16 ,  FIG. 18  to  FIG. 21 ,  FIG. 24 ,  FIG. 29 , and  FIG. 32 . 
     The dielectric substrate  100  includes a plurality of dielectric layers stacked in the Z-axis direction (second direction). The distributed elements  131  to  134  each extend in the X-axis direction (first direction) inside the dielectric substrate  100 . The X-axis direction length, Y-axis direction length, and Z-axis direction length of each of the distributed elements  131  to  134  are the same or substantially the same as the X-axis direction lengths, Y-axis direction lengths, and Z-axis direction lengths of the other distributed elements, respectively. The distributed elements  131  to  134  are linearly disposed in this order in the Y-axis direction (third direction) between the ground electrodes  121  and  122 . Note that the distributed elements  131  to  134  are not necessarily linearly disposed and may be disposed in a diamond or staggered (zigzag) shape, for example. 
     The input/output terminals P 1  and P 2  are electrically connected to the distributed elements  131  and  134 , respectively, with via conductors and line conductors interposed therebetween. A signal input to the input/output terminal P 1  is output from the input/output terminal P 2 . A signal input to the input/output terminal P 2  is output from the input/output terminal P 1 . The case where two circuit elements are electrically connected to each other includes a case where the two circuit elements are directly connected to each other and a case where the two circuit elements are coupled to each other through an electric field. 
     The outermost surfaces of the dielectric filter  1  in the Z-axis direction are referred to as upper surface UF and lower surface BF. The upper surface UF and the lower surface BF face each other in the Z-axis direction. The surfaces parallel or substantially parallel to the Z-axis direction and the ZX plane are referred to as side surfaces SF 1  and SF 3 . The surfaces parallel or substantially parallel to the Z-axis direction and the YZ plane are referred to as side surfaces SF 2  and SF 4 . 
     On the lower surface BF, the input/output terminals P 1  and P 2  and a ground terminal  110  are provided. The input/output terminals P 1  and P 2  and the ground terminal  110  are, for example, land grid array (LGA) terminals with plane electrodes regularly provided on the lower surface BF. The lower surface BF is connected to a circuit board, which is not illustrated. 
     On the upper surface UF, a shield electrode  116  is provided. The shield electrode  116  covers the upper surface UF. 
     On the side surface SF 1 , shield electrodes  111  and  112  are provided. The shield electrodes  111  and  112  are spaced away from each other in the X-axis direction. The shield electrodes  111  and  112  are each connected to the ground terminal  110 , the ground electrodes  121  and  122 , and the shield electrode  116 . 
     On the side surface SF 3 , shield electrodes  114  and  115  are provided. The shield electrodes  114  and  115  are spaced away from each other in the X-axis direction. The shield electrodes  114  and  115  are each connected to the ground terminal  110 , the ground electrodes  121  and  122 , and the shield electrode  116 . 
     On the side surface SF 2 , a shield electrode  113  is provided. The shield electrode  113  covers the side surface SF 2 . The shield electrode  113  is connected to the ground terminal  110 , the ground electrodes  121  and  122 , and the shield electrodes  112 ,  114 , and  116 . 
     On the side surface SF 4 , no shield electrode is provided. 
     The ground terminal  110  and the shield electrodes  111  to  116  define the shield conductor portion  150 . When the shield conductor portion  150  is viewed from the X-axis direction in plan view, the shield conductor portion  150  is provided on the surface of the dielectric substrate  100  to wind around the distributed elements  131  to  134 . 
     The end portion on the side surface SF 4  side (one end) of each of the distributed elements  131  to  134  is not connected to the shield conductor portion  150 . That is, one end of each of the distributed elements  131  to  134  is an open end that may have a variable voltage. Meanwhile, the end portion on the side surface SF 2  side (other end) of each of the distributed elements  131  to  134  is connected to the shield electrode  113 . That is, the other end of each of the distributed elements  131  to  134  is a fixed end at a voltage fixed to the reference voltage of the shield conductor portion  150 . 
     The X-axis direction length of each of the distributed elements  131  to  134  is approximately one fourth of the wavelength of a desired signal that can pass through the dielectric filter  1 . That is, the distributed elements  131  to  134  are each a λ/4 resonator. The dielectric filter  1  is a four-stage dielectric filter including the four λ/4 resonators. The number of the stages (the number of the resonators) of the dielectric filter  1  may be two, three, five, or more. 
     The distributed elements  131  to  134  include respective pluralities of conductors  141  to  144 . The plurality of conductors  141  each define a distributed constant line that extends in the X-axis direction and has the Z-axis direction as the normal thereof. The plurality of conductors  141  are each provided on any of the plurality of dielectric layers of the dielectric substrate  100 . That is, the plurality of conductors  141  are stacked in the Z-axis direction with an interval corresponding to the dielectric layer thickness. With regard to the plurality of conductors  141 , the intervals between the conductors adjacent to each other in the Z-axis direction may be different from each other. The pluralities of conductors  142  to  144  are each configured the same as or similar to the plurality of conductors  141 . 
     The distributed elements  131  to  134  include respective via conductors V 11  to V 14 . At the one end of the distributed element  131 , the plurality of conductors  141  are connected to each other by the via conductor V 11  (short circuit conductor portion). At the one end of the distributed element  132 , the plurality of conductors  142  are connected to each other by the via conductor V 12  (short circuit conductor portion). At the one end of the distributed element  133 , the plurality of conductors  143  are connected to each other by the via conductor V 13  (short circuit conductor portion). At the one end of the distributed element  134 , the plurality of conductors  144  are connected to each other by the via conductor V 14  (short circuit conductor portion). 
     At the open end of each of the distributed elements  131  to  134 , the plurality of conductors of the distributed element are connected to each other so that the potentials (polarities) of the plurality of respective conductors are matched with each other. Thus, the resonant modes of currents that flow through the plurality of respective conductors can be matched with each other. As a result, the directions in which currents flow through the plurality of respective conductors can be matched with each other. 
       FIG. 3  is a diagram illustrating the bandpass characteristics (solid line) and reflection characteristics (dotted line) of the dielectric filter  1  of  FIG. 1 . The bandpass characteristics are the frequency characteristics of insertion loss. The reflection characteristics are the frequency characteristics of return loss. As illustrated in  FIG. 3 , for example, the pass band is between about 5.5 GHz and about 6.0 GHz and the attenuation pole is between about 5.0 GHz and about 5.3 GHz. 
       FIG. 4  is a perspective view of a dielectric filter  10  according to Comparative Example 1. The dielectric filter  10  has a configuration in which the distributed elements  131  to  134  of the dielectric filter  1  of  FIG. 1  are replaced by respective distributed elements  11  to  14 . The remaining configuration is the same or substantially the same as in Preferred Embodiment 1 so that the repetitive description thereof is omitted. As illustrated in  FIG. 4 , the distributed elements  11  to  14  each include a single bulk material whose interior is filled. The X-axis direction length, Y-axis direction length, and Z-axis direction length of the bulk member are the same or substantially the same as the X-axis direction length, Y-axis direction length, and Z-axis direction length of each of the distributed elements  131  to  134  of  FIG. 1 , respectively. 
       FIG. 5  is a diagram illustrating the minimum value of the insertion loss of the dielectric filter  1  of  FIG. 1  (solid line) and the minimum value of the insertion loss of the dielectric filter  10  of  FIG. 4  (dotted line). With regard to the minimum value of the insertion loss of the dielectric filter  1  of  FIG. 1 , values are indicated in a case where, with the distributed elements  131  to  134  having a certain Z-axis direction length (height) and the conductors each having a certain Z-axis direction length (thickness), the number of divided segments of the dielectric in which the pluralities of conductors  141  to  144  are each provided (the number of stacked layers) is changed. As the number of stacked layers is increased, the intervals between the conductors adjacent to each other in the Z-axis direction of each of the pluralities of conductors  141  to  144  are narrowed. As illustrated in  FIG. 5 , when the number of stacked layers is 13 or more, for example, the insertion loss of the dielectric filter  1  is smaller than the insertion loss of the dielectric filter  10 . 
     In each of the distributed elements  131  to  134  of  FIG. 1 , the plurality of conductors are disposed with intervals in the Z-axis direction. Thus, the volume of the plurality of conductors of the distributed element is smaller than the volume of each of the distributed elements  11  to  14  of  FIG. 4 . 
     In this respect, it has been known that high frequency signals do not flow through an entire conductor but flow through the surface portion of the conductor (skin effect). In each of the distributed elements  131  to  134  of  FIG. 1 , although no current flows between the conductors adjacent to each other in the Z-axis direction, the skin portion of each conductor through which a current flows is increased. That is, a distributed element provided as a multilayer body including a plurality of conductors can have a larger surface area through which high frequency signals can pass. As a result, the Q factor of a dielectric resonator including the distributed element can be increased so that the insertion loss of a dielectric filter including the dielectric resonator can be reduced. 
     From the viewpoint of the skin effect, to ensure a region through which a current flows, the thickness of the conductor of each of the distributed elements  131  to  134  is preferably larger than a skin depth δ of the conductor. The skin depth δ of the conductor indicates a depth from the surface (skin) of the conductor at which a current drops to the reciprocal of a natural logarithm e (approximately 36.7%) as compared to that on the surface. The skin depth δ is expressed as Expression (1) using a resistivity ρ, a permeability μ r , a vacuum permeability μ 0  (4π×10 −7 ), and an angular frequency ω (2π times as large as a frequency f of a high frequency signal) of the conductor. 
     
       
         
           
             
               
                 
                   δ 
                   = 
                   
                     
                       
                         2 
                         ⁢ 
                         ρ 
                       
                       
                         ω 
                         ⁢ 
                         
                           μ 
                           r 
                         
                         ⁢ 
                         
                           μ 
                           0 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     From the above, with the dielectric filter according to Preferred Embodiment 1, a reduction in loss can be achieved. 
     Preferred Embodiment 2 
     In Preferred Embodiment 1, the dielectric filter in which the plurality of distributed elements each has the multilayer structure including the plurality of conductors is described. In Preferred Embodiment 2 of the present invention, a dielectric resonator including a single distributed element having a multilayer structure including a plurality of conductors is described. 
       FIG. 6  is a perspective view of a dielectric resonator  2  according to Preferred Embodiment 2.  FIG. 7  is a sectional view taken along the line VII-VII of  FIG. 6 . The dielectric resonator  2  has a configuration in which the distributed elements  131  to  134  of the dielectric filter  1  of  FIG. 1  and  FIG. 2  are replaced by a distributed element  231 . The remaining configuration is the same or substantially the same as in Preferred Embodiment 1 so that the repetitive description thereof is omitted. 
     As illustrated in  FIG. 6  and  FIG. 7 , the distributed element  231  includes a plurality of conductors  241  and a via conductor V 21  (short circuit conductor portion). The plurality of conductors  241  each define a distributed constant line that extends in the X-axis direction and has the Z-axis direction as the normal thereof. The plurality of conductors  241  are each provided on any of the plurality of dielectric layers of the dielectric substrate  100 . 
     One end of the distributed element  231  is not connected to the shield conductor portion  150 . That is, the one end of the distributed element  231  is an open end that may have a variable voltage. At the one end of the distributed element  231 , the plurality of conductors  241  are connected to each other by the via conductor V 21 . 
     The other end of the distributed element  231  is connected to the shield electrode  113 . That is, the other end of the distributed element  231  is a fixed end at a voltage fixed to the reference voltage of the shield conductor portion  150 . 
     The X-axis direction length of the distributed element  231  is approximately one fourth of the wavelength of a signal that the dielectric resonator  2  resonates. That is, the dielectric resonator  2  is a λ/4 resonator. 
     With reference to  FIG. 7 , the X-axis direction length of each of the plurality of conductors  241  is equal or substantially equal to the X-axis direction length of the dielectric substrate  100 . In the manufacturing process of the dielectric resonator  2 , a cutting operation to determine the X-axis direction lengths of the plurality of conductors  241  and a cutting operation for determining the X-axis direction length of the dielectric substrate  100  can be performed integrally so that the manufacturing variations of the dielectric substrate  100  can be reduced or prevented. 
       FIG. 8  is a perspective view of a dielectric resonator  20  according to Comparative Example 2. The dielectric resonator  20  has a configuration in which the distributed element  231  of  FIG. 6  is replaced by a distributed element  21 . The remaining configuration is the same or substantially the same as in Preferred Embodiment 2 so that the repetitive description thereof is omitted. 
     As illustrated in  FIG. 8 , the distributed element  21  includes a single bulk material whose interior is filled. The X-axis direction length, Y-axis direction length, and Z-axis direction length of the distributed element  21  are the same or substantially the same as the X-axis direction length, Y-axis direction length, and Z-axis direction length of the distributed element  231  of  FIG. 6 , respectively. 
       FIG. 9  is a plan view of the distribution of field strengths (kV/m) in a simulation in which a high frequency signal is passed through the distributed element  21  of  FIG. 8  when viewed from the X-axis direction.  FIG. 10  is a plan view of the distribution of field strengths in a simulation in which a high frequency signal is passed through the distributed element  231  of  FIG. 6  when viewed from the X-axis direction. In  FIG. 9  and  FIG. 10 , the closer the colors of the regions are from white to black, the stronger the field strengths in the regions. The same is also true for  FIG. 25  to  FIG. 28 . 
     As illustrated in  FIG. 9 , due to the skin effect, the electric field is concentrated on the surface of the distributed element  21  and almost no current flows into the distributed element  21 . Meanwhile, as illustrated in  FIG. 10 , with regard to the distributed element  231 , the electric field is also generated inside the distributed element  231 . The distributed element  231 , in which the plurality of conductors  241  are stacked at intervals, is larger in surface area through which high frequency signals can pass than the distributed element  21 . With the increase in region through which high frequency signals can pass, the Q factor of the dielectric resonator  2  can be improved as compared to the Q factor of the dielectric resonator  20 . 
     With the dielectric resonator  2 , the case where the plurality of conductors  241  are connected to each other by the via conductor V 21  provided inside the dielectric substrate  100  is described. The plurality of conductors  241  may be connected to each other outside the dielectric substrate  100 . 
       FIG. 11  is a sectional view of a dielectric resonator  2 A according to Modification 1 of Preferred Embodiment 2. The dielectric resonator  2 A has a configuration in which the via conductor V 21  of  FIG. 7  is replaced by a connection conductor  217  (short circuit conductor portion). The remaining configuration is the same or substantially the same as in Preferred Embodiment 2 so that the repetitive description thereof is omitted. 
     As illustrated in  FIG. 11 , the connection conductor  217  connects the plurality of conductors  241  to each other outside the dielectric substrate  100 . The connection conductor  217  is provided outside the dielectric substrate  100  so that the process of forming via conductors inside the dielectric substrate  100  is unnecessary. As a result, the manufacturing process of the dielectric resonator  2  can be simplified. 
     With the dielectric resonator  2 , the case where the X-axis direction length of each of the plurality of conductors  241  is equal or substantially equal to the X-axis direction length of the dielectric substrate  100  is described. The two may be different from each other. 
       FIG. 12  is a sectional view of a dielectric resonator  2 B according to Modification 2 of Preferred Embodiment 2. The dielectric resonator  2 B has a configuration in which the plurality of conductors  241  of  FIG. 7  are replaced by a plurality of conductors  241 B. The remaining configuration is the same or substantially the same as in Preferred Embodiment 2 so that the repetitive description thereof is omitted. As illustrated in  FIG. 12 , the X-axis direction length of each of the plurality of conductors  241 B is shorter than the X-axis direction length of the dielectric substrate  100 . 
     With the dielectric resonator  2 , the case where the one end of the distributed element  231  is the open end and the other end is the fixed end is described. The ends of the distributed element  231  may both be open ends. 
       FIG. 13  is a sectional view of a dielectric resonator  2 C according to Modification 3 of Preferred Embodiment 2. The dielectric resonator  2 C has a configuration in which the plurality of conductors  241  of  FIG. 7  are replaced by a plurality of conductors  241 C and the shield electrode  113  is removed. The remaining configuration is the same or substantially the same as Preferred Embodiment 2 so that the repetitive description thereof is omitted. As illustrated in  FIG. 13 , the ends of each of the plurality of conductors  241 C are both not connected to the shield conductor portion  150 . That is, the ends of the distributed element  231  are both open ends. The X-axis direction length of the distributed element  231  is approximately one half of the wavelength of a signal that the dielectric resonator  2 C resonates. That is, the dielectric resonator  2 C is a λ/2 resonator. 
     With the dielectric resonator  2 , the case where the plurality of conductors  241  are connected to each other at the open end of the distributed element  231  is described. The plurality of conductors  241  are not necessarily connected to each other at the open end of the distributed element  231 . 
       FIG. 14  is a sectional view of a dielectric resonator  2 D according to Modification 4 of Preferred Embodiment 2. The dielectric resonator  2 D has a configuration in which the via conductor V 21  of  FIG. 7  is removed. The remaining configuration is the same or substantially the same as Preferred Embodiment 2 so that the repetitive description thereof is omitted. 
     From the above, with the dielectric resonator according to one of Preferred Embodiment 2 and Modifications 1 to 4 of Preferred Embodiment 2, an improvement in Q factor can be achieved. 
     Preferred Embodiment 3 
     In Preferred Embodiment 2, the case where the distributed element includes the stacked plurality of conductors having the same or substantially the same linear shape is described. When the number of the plurality of stacked conductors is increased and the intervals between the conductors are reduced, the volume of a dielectric that can be provided between the conductors is reduced. As a result, the rigidity of the dielectric between the conductors is reduced so that the distributed element is likely to be distorted due to stress generated between the conductors and the dielectric. Thus, in Preferred Embodiment 3 of the present invention, a configuration in which no conductor multilayer structure is provided in the core portion of a distributed element is described. With this configuration, the rigidity of a dielectric provided in the core portion is ensured so that the distortion of the distributed element can be reduced while the Q factor of the dielectric resonator can be maintained. 
       FIG. 15  is a perspective view of a dielectric resonator  3  according to Preferred Embodiment 3. The dielectric resonator  3  has a configuration in which the distributed element  231  of  FIG. 6  is replaced by a distributed element  331 . The remaining configuration is the same or substantially the same as in Preferred Embodiment 2 so that the repetitive description thereof is omitted. 
     As illustrated in  FIG. 15 , the distributed element  331  includes a plurality of conductors  341  and a short circuit conductor portion  360  (short circuit conductor portion). The short circuit conductor portion  360  includes via conductors V 31  and V 32 . The plurality of conductors  341  each define a distributed constant line that extends in the X-axis direction and has the Z-axis direction as the normal thereof. 
     One end of the distributed element  331  is not connected to the shield conductor portion  150 . That is, the one end of the distributed element  331  is an open end that may have a variable voltage. At the one end of the distributed element  331 , the plurality of conductors  341  are connected to each other by each of the via conductors V 31  and V 32 . 
     The other end of the distributed element  331  is connected to the shield electrode  113 . That is, the other end of the distributed element  331  is a fixed end at a voltage fixed to the reference voltage of the shield conductor portion  150 . 
     The X-axis direction length of the distributed element  331  is approximately one fourth of the wavelength of a signal that the dielectric resonator  3  resonates. That is, the dielectric resonator  3  is a λ/4 resonator. 
       FIG. 16  is a plan view of the dielectric resonator  3  of  FIG. 15  when viewed from the X-axis direction. As illustrated in  FIG. 16 , the length of the distributed element  331  in the Y-axis direction (width) is a width w 31  (specific length). 
     The plurality of conductors  341  include a conductor  3411  (first conductor), a conductor  3412  (first conductor), a conductor  3413  (third conductor), a conductor  3414  (fourth conductor), a conductor  3415  (second conductor), and a conductor  3416  (second conductor). Of the conductors of the plurality of conductors  341 , the conductors other than the conductors  3411  and  3416  are stacked between the conductor  3411  and the conductor  3416 . 
     The width of each of the conductors  3411 ,  3412 ,  3415 , and  3416  is the width w 31 . The widths of the conductors stacked between the conductors  3411  and  3412  and the widths of the conductors stacked between the conductors  3415  and  3416  are also the width w 31 . 
     The width of the conductor  3413  is a width w 32  (&lt;w 31 ). The width of the conductor  3414  is a width w 33  (&lt;w 31 ). The widths w 32  and w 33  may be different from each other or equal or substantially equal to each other. The conductors  3413  and  3414  are provided between the conductors  3412  and  3415  in the Z-axis direction. The conductors  3413  and  3414  are separated from each other by a distance d 30  (=w 31 −w 32 −w 33 ) in the Y-axis direction. 
     The widths of the conductors stacked between the conductors  3412  and  3413  and the widths of the conductors stacked between the conductors  3413  and  3415  are each also the width w 32 . The conductor  3411 , the conductors stacked between the conductors  3411  and  3413 , the conductor  3413 , the conductors stacked between the conductor  3413  and the conductor  3416 , and the conductor  3416  are connected to each other by the via conductor V 31 . 
     The widths of the conductors stacked between the conductors  3412  and  3414  and the widths of the conductors stacked between the conductors  3414  and  3415  are each also the width w 33 . The conductor  3411 , the conductors stacked between the conductors  3411  and  3414 , the conductors stacked between the conductor  3414  and the conductor  3416 , and the conductor  3416  are connected to each other by the via conductor V 32 . 
     In a core portion Cd of the distributed element  331  (the portion between the conductors  3412  and  3415  and between the conductors  3413  and  3414 ), no conductor multilayer structure is provided. The rigidity of the dielectric in the core portion Cd can be ensured so that the distortion of the distributed element  331  can be reduced. Further, due to the skin effect of high frequency signals, almost no current flows through the core portion of the distributed element  331 . Thus, even when no conductor multilayer structure is provided in the core portion Cd, the amount of current that flows through the distributed element  331  is hardly reduced. As a result, the Q factor of the dielectric resonator  3  can be maintained. 
       FIG. 17  is a diagram illustrating the case of the dielectric resonator  3  of  FIG. 16  (solid line) and the dielectric resonator  2  of  FIG. 6  (dotted line) in terms of the relationship between the number of the plurality of stacked conductors and the Q factor of the dielectric resonator. As described in  FIG. 17 , the two are almost the same. Thus, in the dielectric resonator  3 , the Q factor of the dielectric resonator  2  is maintained. 
     With the dielectric resonator  3 , the case where the conductors having the same or substantially the same width as the outermost conductors  3411  and  3416  are provided between the core portion Cd and the outermost conductor  3411  or  3416  is described. However, no conductor may be provided between the core portion Cd and the outermost conductor  3411  or  3416 . 
       FIG. 18  is a plan view of a dielectric resonator  3 A according to a modification of Preferred Embodiment 3 when viewed from the X-axis direction. The dielectric resonator  3 A has a configuration in which the plurality of conductors  341  of  FIG. 16  are replaced by a plurality of conductors  341 A. Of the plurality of conductors  341 A, between the outermost conductors  3411  and  3416 , at the respective ends in the Y-axis direction of the core portion Cd, a conductor having the same or substantially the same width as the conductor  3413  and a conductor having the same or substantially the same width as the conductor  3414  are stacked. From the viewpoint of the skin effect, the thickness of each of the conductors  3411  and  3416  is preferably larger than the skin depth of each conductor. 
     From the above, with the dielectric resonator according to Preferred Embodiment 3 or the modification of Preferred Embodiment 3, an improvement in Q factor can be achieved and the distortion of the dielectric resonator can be reduced. 
     Preferred Embodiment 4 
     In Preferred Embodiment 4 of the present invention, a two-stage dielectric filter is described. 
       FIG. 19  is a perspective view of a dielectric filter  4  according to Preferred Embodiment 4. The dielectric filter  4  has a configuration in which the distributed elements  131  to  134  of the dielectric filter  1  of  FIG. 2  are replaced by distributed elements  431  and  432 . The remaining configuration is the same or substantially the same so that the repetitive description thereof is omitted. 
     As illustrated in  FIG. 19 , the distributed element  431  includes a plurality of conductors  441  and a via conductor V 41  (short circuit conductor portion). The plurality of conductors  441  each define a distributed constant line that extends in the X-axis direction and has the Z-axis direction as the normal thereof. 
     One end of the distributed element  431  is not connected to the shield conductor portion  150 . That is, the one end of the distributed element  431  is an open end that may have a variable voltage. At the one end of the distributed element  431 , the plurality of conductors  441  are connected to each other by the via conductor V 41 . 
     The other end of the distributed element  431  is connected to the shield electrode  113 . That is, the other end of the distributed element  431  is a fixed end at a voltage fixed to the reference voltage of the shield conductor portion  150 . 
     The distributed element  432  includes a plurality of conductors  442  and a via conductor V 42  (short circuit conductor portion). The plurality of conductors  442  each define a distributed constant line that extends in the X-axis direction and has the Z-axis direction as the normal thereof. 
     One end of the distributed element  432  is not connected to the shield conductor portion  150 . That is, the one end of the distributed element  432  is an open end that may have a variable voltage. At the one end of the distributed element  432 , the plurality of conductors  442  are connected to each other by the via conductor V 42 . 
     The other end of the distributed element  432  is connected to the shield electrode  113 . That is, the other end of the distributed element  432  is a fixed end at a voltage fixed to the reference voltage of the shield conductor portion  150 . 
     The X-axis direction length of each of the distributed elements  431  and  432  is approximately one fourth of the wavelength of a desired signal that can pass through the dielectric filter  4 . That is, the distributed elements  431  and  432  are each a λ/4 resonator. The dielectric filter  4  is a two-stage dielectric filter including the two λ/4 resonators. 
       FIG. 20  is a perspective view of a dielectric filter  4 A according to a modification of Preferred Embodiment 4. The dielectric filter  4 A has a configuration in which the distributed elements  431  and  432  of  FIG. 19  are replaced by distributed elements  431 A and  432 A, respectively. The distributed elements  431 A and  432 A each have the configuration of the distributed element  431  or  432  of  FIG. 19  from which the via conductor V 41  or V 42  is removed. The remaining configuration is the same or substantially the same as in Preferred Embodiment 4 so that the repetitive description thereof is omitted. 
       FIG. 21  is a perspective view of a dielectric filter  40  according to Comparative Example 3. The dielectric filter  40  has a configuration in which the distributed elements  431  and  432  of  FIG. 19  are replaced by distributed elements  41  and  42 , respectively. The remaining configuration is the same or substantially the same as in Preferred Embodiment 4 so that the repetitive description thereof is omitted. 
     As illustrated in  FIG. 21 , the distributed elements  41  and  42  each include a single bulk material whose interior is filled. The X-axis direction length, Y-axis direction length, and Z-axis direction length of each of the distributed elements  41  and  42  are the same or substantially the same as the X-axis direction length, Y-axis direction length, and Z-axis direction length of each of the distributed elements  431  and  432  of  FIG. 19 , respectively. 
       FIG. 22  is a diagram illustrating the bandpass characteristics of the dielectric filter  4 A of  FIG. 20  (solid line) and the bandpass characteristics of the dielectric filter  40  of  FIG. 21  (dotted line). As illustrated in  FIG. 22 , in the dielectric filter  40 , the insertion loss is minimum at frequencies f 41  and f 42  (&gt;f 41 ). The frequency f 41  is the resonant frequency of the dielectric filter  40  in an odd mode in which currents flow through the respective distributed elements  41  and  42  in the opposite directions. The frequency f 42  is the resonant frequency of the dielectric filter  40  in an even mode in which currents flow through the respective distributed elements  41  and  42  in the same direction. The insertion loss is minimum at the frequencies f 41  and f 42  so that the pass band of the dielectric filter  40  is provided between the frequencies f 41  and f 42 . 
     In the dielectric filter  4 A, the insertion loss is minimum at a frequency f 43  (&gt;f 41 ). In the dielectric filter  4 A, resonance occurs in the even mode in which currents flow through the respective distributed elements  431 A and  432 A in the same direction. However, resonance is difficult to occur in the odd mode in which currents flow through the respective distributed elements  431 A and  432 A in the opposite directions. 
     In the dielectric filter  4 A, the pluralities of conductors  441  and  442  are each not connected to each other at the open end of the distributed element  431 A or  432 A so that currents flow through the plurality of respective conductors in a plurality of resonant modes, and the plurality of resonant modes interfere with each other. In particular, in the odd mode, since currents flow through the respective distributed elements  431 A and  432 A in the opposite directions, the plurality of resonant modes cancel each other out. Thus, it is difficult for the dielectric filter  4 A to resonate in the odd mode. 
       FIG. 23  is a diagram illustrating the bandpass characteristics of the dielectric filter  4  of  FIG. 19  (solid line) and the bandpass characteristics of the dielectric filter  40  of  FIG. 21  (dotted line). As illustrated in  FIG. 23 , the two indicate almost the same characteristics. Also in the dielectric filter  4 , like the dielectric filter  40 , the insertion loss is minimum at the frequencies f 41  and f 42  (&gt;f 41 ). 
     In the dielectric filter  4 , the pluralities of conductors  441  and  442  are each connected to each other at the open end of the distributed element  431  or  432  so that the resonant modes of currents flowing through the plurality of respective conductors are matched with each other. As a result, also in the odd mode in which currents flow through the distributed elements  431  and  432  in the opposite directions, resonance occurs in the dielectric filter  4 . 
     From the above, with the dielectric filter according to Preferred Embodiment 4 or the modification of Preferred Embodiment 4, a reduction in loss can be achieved. Moreover, with the dielectric filter according to Preferred Embodiment 4 or the modification of Preferred Embodiment 4, resonance can occur also in the odd mode so that the pass band can be widened. 
     Preferred Embodiment 5 
     In Preferred Embodiment 4, the case where the widths of the plurality of conductors of the distributed element are the same or substantially the same is described. When the plurality of conductors are viewed from the extending direction of the distributed element in plan view, the plurality of conductors form a rectangle or an approximate rectangle as a whole. When a current flows through a distributed element with sharp corner portions, such as a rectangular or substantially rectangular distributed element, the electric field is likely to be concentrated in the corner portions. The electric field concentration causes conductor loss, thus deteriorating the insertion loss of the dielectric filter. 
     Thus, in Preferred Embodiment 5 of the present invention, with regard to the plurality of conductors of a distributed element, the width of the conductor near the outermost layer is shorter than the width of the conductor near the middle layer. When the plurality of conductors are viewed from the extending direction of the distributed element in plan view, the plurality of conductors form a rectangle or an approximate rectangle with rounded corner portions as a whole. In this shape, since the corner portions are not sharp, the electric field concentration is reduced. With the dielectric filter according to Preferred Embodiment 5, the conductor loss is reduced. As a result, the insertion loss can be further improved. 
       FIG. 24  is a perspective view of a dielectric filter  5  according to Preferred Embodiment 5. The dielectric filter  5  has a configuration in which the distributed elements  431  and  432  of  FIG. 19  are replaced by distributed elements  531  and  532 , respectively. The remaining configuration is the same or substantially the same as in Preferred Embodiment 4 so that the repetitive description thereof is omitted. 
     As illustrated in  FIG. 24 , the distributed element  531  includes a plurality of conductors  541  and a via conductor V 51  (short circuit conductor portion). The plurality of conductors  541  each define a distributed constant line that extends in the X-axis direction and has the Z-axis direction as the normal thereof. 
     One end of the distributed element  531  is not connected to the shield conductor portion  150 . That is, the one end of the distributed element  531  is an open end that may have a variable voltage. At the one end of the distributed element  531 , the plurality of conductors  541  are connected to each other by the via conductor V 51 . 
     The other end of the distributed element  531  is connected to the shield electrode  113 . That is, the other end of the distributed element  531  is a fixed end at a voltage fixed to the reference voltage of the shield conductor portion  150 . 
     The distributed element  532  includes a plurality of conductors  542  and a via conductor V 52  (short circuit conductor portion). The plurality of conductors  542  each define a distributed constant line that extends in the X-axis direction and has the Z-axis direction as the normal thereof. 
     One end of the distributed element  532  is not connected to the shield conductor portion  150 . That is, the one end of the distributed element  532  is an open end that may have a variable voltage. At the one end of the distributed element  532 , the plurality of conductors  542  are connected to each other by the via conductor V 52 . 
     The other end of the distributed element  532  is connected to the shield electrode  113 . That is, the other end of the distributed element  532  is a fixed end at a voltage fixed to the reference voltage of the shield conductor portion  150 . 
     The X-axis direction length of each of the distributed elements  531  and  532  is approximately one fourth of the wavelength of a desired signal that can pass through the dielectric filter  5 . That is, the distributed elements  531  and  532  are each a λ/4 resonator. The dielectric filter  5  is a two-stage dielectric filter including the two λ/4 resonators. 
     The pluralities of conductors  541  and  542  have multilayer structures the same as or similar to each other. In the following, the multilayer structure of the plurality of conductors  541  is described. 
     The plurality of conductors  541  include a conductor  5411  (first conductor), a conductor  5412  (second conductor), a conductor  5413  (third conductor), and a conductor  5414  (third conductor). Of the conductors of the plurality of conductors  541 , the conductors other than the conductors  5411  and  5412  are stacked between the conductor  5411  and the conductor  5412 . 
     The width of the distributed element  531  is a width w 53  (specific length). The widths of the conductors  5413  and  5414  and the conductors stacked between the conductors  5413  and  5414  are each also the width w 53 . 
     The width of the conductor  5411  is a width w 51  (&lt;w 53 ). The width of the conductor  5412  is a width w 52  (&lt;w 53 ). The widths w 51  and w 52  may be different from each other or equal to each other. 
     The widths of the conductors between the conductor  5411  and the conductor  5413  are gradually increased from the conductor  5411  to the conductor  5413 . The widths of the conductors between the conductor  5412  and the conductor  5414  are gradually increased from the conductor  5412  to the conductor  5414 . 
       FIG. 25  is a plan view of the distribution of field strengths in a simulation in which a high frequency signal is passed through the distributed elements  531  and  532  of  FIG. 24  in an odd mode when viewed from the X-axis direction.  FIG. 26  is a plan view of the distribution of field strengths in a simulation in which a high frequency signal is passed through the distributed elements  531  and  532  of  FIG. 24  in an even mode when viewed from the X-axis direction. As illustrated in  FIG. 25  and  FIG. 26 , the plurality of conductors of each of the distributed elements  531  and  532  form a rectangle or an approximate rectangle with rounded corner portions as a whole. 
       FIG. 27  is a plan view of the distribution of field strengths in a simulation in which a high frequency signal is passed through the distributed elements  431  and  432  of  FIG. 19  in an odd mode when viewed from the X-axis direction.  FIG. 28  is a plan view of the distribution of field strengths in a simulation in which a high frequency signal is passed through the distributed elements  431  and  432  of  FIG. 19  in an even mode when viewed from the X-axis direction. As illustrated in  FIG. 27  and  FIG. 28 , the plurality of conductors of each of the distributed elements  431  and  432  form a rectangle or an approximate rectangle with sharp corner portions as a whole. 
       FIG. 25  and  FIG. 27  are compared to each other in terms of the odd mode and  FIG. 26  and  FIG. 28  are compared to each other in terms of the even mode. The electric field that is concentrated at each end of the outermost conductors of each of the distributed elements  431  and  432  in  FIG. 27  and  FIG. 28  is distributed on the outermost conductors of the distributed elements  531  and  532  of  FIG. 25  and  FIG. 26 . With the dielectric filter  5 , the electric field concentration is reduced so that the insertion loss can be improved over the dielectric filter  4 . 
     The shape that the plurality of conductors of the distributed constant line may be, for example, circular or substantially circular as a whole may be a circle. Note that the circular shape is not necessarily a perfect circular shape and includes an elliptical or substantially elliptical shape. 
       FIG. 29  is a perspective view of a dielectric filter  5 A according to a modification of Preferred Embodiment 5. The dielectric filter  5 A has a configuration in which the pluralities of conductors  541  and  542  of  FIG. 24  are replaced by pluralities of conductors  541 A and  542 A. The remaining configuration is the same as or substantially the same as in Preferred Embodiment 5 so that the repetitive description thereof is omitted. 
     As illustrated in  FIG. 29 , when the pluralities of conductors  541 A and  542 A are viewed from the X-axis direction in plan view, the pluralities of conductors  541 A and  542 A each form a circle or an approximate circle as a whole. 
     The plurality of conductors  541 A include a conductor  5431  (first conductor), a conductor  5432  (second conductor), and a conductor  5433  (third conductor). Of the conductors of the plurality of conductors  541 A, the conductors other than the conductors  5431  and  5432  are stacked between the conductor  5431  and the conductor  5432 . 
     The width of the conductor  5433  is a width w 53 . The width of the conductor  5431  is a width w 54  (&lt;w 53 ). The width of the conductor  5432  is a width w 55  (&lt;w 53 ). The widths w 54  and w 55  may be different from each other or equal or substantially equal to each other. 
     The widths of the conductors between the conductor  5431  and the conductor  5433  are gradually increased from the conductor  5431  to the conductor  5433 . The widths of the conductors between the conductor  5432  and the conductor  5433  are gradually increased from the conductor  5432  to the conductor  5433 . 
     Note that a dielectric resonator can be provided using the distributed element  531  of  FIG. 24  and  FIG. 29 . 
     From the above, with the dielectric filter according to Preferred Embodiment 5 or the modification of Preferred Embodiment 5, a further reduction in loss can be achieved. 
     Preferred Embodiment 6 
     In Preferred Embodiment 6 of the present invention, a multiplexer including a dielectric filter according to one of the preferred embodiments or modifications thereof described above is described. 
       FIG. 30  is an equivalent circuit diagram of a duplexer that is an example of a multiplexer according to Preferred Embodiment 6. As illustrated in  FIG. 30 , the duplexer  6  includes dielectric filters  6 A and  6 B and a common terminal Pcom. The dielectric filter  6 A includes an input/output terminal P 61 A (first terminal) and an input/output terminal P 62 A (second terminal). The dielectric filter  6 B includes an input/output terminal P 61 B (first terminal) and an input/output terminal P 62 B (second terminal). The common terminal Pcom is connected to the input/output terminal P 62 A of the dielectric filter  6 A and the input/output terminal P 61 B of the dielectric filter  6 B. The pass band of the dielectric filter  6 A is different from the pass band of the dielectric filter  6 B. 
       FIG. 31  and  FIG. 32  are perspective views of the duplexer of  FIG. 30 . With reference to  FIG. 31  and  FIG. 32 , the multiplexer  6  has, for example, a rectangular or substantially rectangular parallelepiped shape. The multiplexer  6  further includes a dielectric substrate  600 , a ground terminal  610 , shield electrodes  611 ,  612 ,  613 ,  614 ,  615 , and  616 , and ground electrodes  621  and  622 . The dielectric filter  6 A includes distributed elements  631 ,  632 , and  633 . The dielectric filter  6 B includes distributed elements  634 ,  635 , and  636 . 
     The dielectric substrate  600  includes a plurality of dielectric layers stacked in the Z-axis direction. The distributed elements  631  to  636  each extend in the X-axis direction inside the dielectric substrate  600 . The X-axis direction length, Y-axis direction length, and Z-axis direction length of each of the distributed elements  631  to  636  are the same or substantially the same as the X-axis direction lengths, Y-axis direction lengths, and Z-axis direction lengths of the other distributed elements, respectively. The distributed elements  631  to  636  are linearly disposed in this order in the Y-axis direction between the ground electrodes  621  and  622 . Note that the distributed elements  631  to  636  are not necessarily linearly disposed and may be disposed in a diamond or staggered (zigzag) shape, for example. 
     The input/output terminals P 61 A and P 62 B are electrically connected to the distributed elements  631  and  636 , respectively, with via conductors and line conductors interposed therebetween. The input/output terminals P 62 A and P 61 B are electrically connected to the distributed elements  633  and  634 , respectively, and are connected to the common terminal Pcom by a via conductor V 60 . When the dielectric filters  6 A and  6 B are viewed from the Z-axis direction in plan view, the input/output terminals P 62 A and P 61 B are overlapped with the distributed elements  633  and  634 , respectively. Note that the input/output terminals P 62 A and P 61 B may be overlapped with the distributed elements  632  and  635 , respectively. 
     Signals input to the input/output terminals P 61 A and P 62 B are output from the common terminal Pcom. A signal input to the common terminal Pcom is output from the input/output terminal P 61 A or P 62 B at the frequency of the signal. 
     The outermost surfaces of the multiplexer  6  in the Z-axis direction are referred to as upper surface UF 6  and lower surface BF 6 . The upper surface UF 6  and the lower surface BF 6  face each other in the Z-axis direction. The surfaces parallel or substantially parallel to the Z-axis direction and the ZX plane are referred to as side surfaces SF 61  and SF 63 . The surfaces parallel or substantially parallel to the Z-axis direction and the YZ plane are referred to as side surfaces SF 62  and SF 64 . 
     On the lower surface BF 6 , the input/output terminals P 61 A and P 62 B, the common terminal Pcom, and the ground terminal  610  are provided. The input/output terminals P 1  and P 2  and the ground terminal  610  are, for example, land grid array (LGA) terminals with plane electrodes regularly disposed on the lower surface BF 6 . The lower surface BF 6  is connected to a circuit board, which is not illustrated. 
     On the upper surface UF 6 , the shield electrode  616  is provided. The shield electrode  616  covers the upper surface UF 6 . 
     On the side surface SF 61 , the shield electrodes  611  and  612  are provided. The shield electrodes  611  and  612  are spaced away from each other in the X-axis direction. The shield electrodes  611  and  612  are each connected to the ground terminal  610 , the ground electrodes  621  and  622 , and the shield electrode  616 . 
     On the side surface SF 63 , the shield electrodes  614  and  615  are provided. The shield electrodes  614  and  615  are spaced away from each other in the X-axis direction. The shield electrodes  614  and  615  are each connected to the ground terminal  610 , the ground electrodes  621  and  622 , and the shield electrode  616 . 
     On the side surface SF 62 , the shield electrode  613  is provided. The shield electrode  613  covers the side surface SF 62 . The shield electrode  613  is connected to the ground terminal  610 , the ground electrodes  621  and  622 , and the shield electrodes  612 ,  614 , and  616 . 
     On the side surface SF 64 , no shield electrode is provided. 
     The ground terminal  610  and the shield electrodes  611  to  616  define a shield conductor portion  650 . When the shield conductor portion  650  is viewed from the X-axis direction in plan view, the shield conductor portion  650  is provided on the surface of the dielectric substrate  600  to wind around the distributed elements  631  to  636 . 
     The end portion on the side surface SF 64  side (one end) of each of the distributed elements  631  to  636  is not connected to the shield conductor portion  650 . That is, the one end of each of the distributed elements  631  to  634  is an open end that may have a variable voltage. The end portion on the side surface SF 62  side (other end) of each of the distributed elements  631  to  636  is connected to the shield electrode  613 . That is, the other end of each of the distributed elements  631  to  636  is a fixed end at a voltage fixed to the reference voltage of the shield conductor portion  650 . 
     The X-axis direction length of each of the distributed elements  631  to  636  is approximately one fourth of the wavelength of a desired signal that can pass through the multiplexer  6 . That is, the distributed elements  631  to  636  are each a λ/4 resonator. The dielectric filters  6 A and  6 B are each a three-stage dielectric filter including the three λ/4 resonators. 
     The distributed elements  631  to  636  include respective pluralities of conductors  641  to  646 . The plurality of conductors  641  each define a distributed constant line that extends in the X-axis direction and has the Z-axis direction as the normal thereof. The plurality of conductors  641  are each provided on any of the plurality of dielectric layers of the dielectric substrate  600 . That is, the plurality of conductors  641  are stacked in the Z-axis direction with an interval corresponding to the dielectric layer thickness. With regard to the plurality of conductors  641 , the intervals between the conductors adjacent to each other in the Z-axis direction may be different from each other. The pluralities of conductors  642  to  646  are each configured the same or substantially the same as the plurality of conductors  641 . 
     The distributed elements  631  to  636  include respective via conductors V 61  to V 66 . At the one end of the distributed element  631 , the plurality of conductors  641  are connected to each other by the via conductor V 61  (short circuit conductor portion). At the one end of the distributed element  632 , the plurality of conductors  642  are connected to each other by the via conductor V 62  (short circuit conductor portion). At the one end of the distributed element  633 , the plurality of conductors  643  are connected to each other by the via conductor V 63  (short circuit conductor portion). At the one end of the distributed element  634 , the plurality of conductors  644  are connected to each other by the via conductor V 64  (short circuit conductor portion). At the one end of the distributed element  635 , the plurality of conductors  645  are connected to each other by the via conductor V 65  (short circuit conductor portion). At the one end of the distributed element  636 , the plurality of conductors  646  are connected to each other by the via conductor V 66  (short circuit conductor portion). 
     At the open end of each of the distributed elements  631  to  636 , the plurality of conductors of the distributed element are connected to each other so that the potentials (polarities) of the plurality of respective conductors are matched with each other. Thus, the resonant modes of currents that flow through the plurality of respective conductors can be matched with each other. As a result, the directions in which currents flow through the plurality of respective conductors can be matched with each other. 
     The dielectric filters of the multiplexer according to Preferred Embodiment 6 are not limited to the three-stage dielectric filters and may be, for example, two-stage dielectric filters, such as the dielectric filter according to Preferred Embodiment 4 or the modification of Preferred Embodiment 4 and the dielectric filter according to Preferred Embodiment 5 or the modification of Preferred Embodiment 5, or dielectric filters with four or more stages. Further, the number of dielectric filters of the multiplexer according to Preferred Embodiment 6 is not limited to two and may be three or more. That is, the multiplexer according to Preferred Embodiment 6 is not limited to a duplexer and a diplexer, and examples thereof include triplexers, quadplexers, and pentaplexers. 
     From the above, with the multiplexer according to Preferred Embodiment 6, a reduction in loss can be achieved. 
     The dielectric resonators according to the above-described preferred embodiments and modifications thereof can each be provided as a coaxial dielectric resonator including an inner conductor and an outer conductor. In this case, the distributed element and shield conductor portion of the dielectric resonators according to the above-described preferred embodiments and modifications thereof can each correspond to the inner conductor and outer conductor of the coaxial dielectric resonator, respectively. That is, the dielectric resonators according to the above-described preferred embodiments and modifications thereof can each provide a coaxial dielectric resonator including an inner conductor divided into a plurality of conductors. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.