Patent Publication Number: US-2009219115-A1

Title: Resonant Element and Method for Manufacturing the Same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of International Application No. PCT/JP2007/071964, filed Nov. 13, 2007, which claims priority to Japanese Patent Application No. JP2007-023461, filed Feb. 1, 2007, the entire contents of each of these applications being incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a resonant element including quarter-wavelength stripline resonators provided on a dielectric substrate, and to a method for manufacturing the resonant element. 
     BACKGROUND OF THE INVENTION 
     A resonant element, such as a filter or a balun, including stripline resonators provided on a dielectric substrate has been used (e.g., see Patent Document 1). 
     Now, a configuration of a conventional resonant element is described by using a filter as an example.  FIG. 1  is a developed view of a conventional filter. 
     A resonant element  101  is constituted through interdigital coupling of five stages of stripline resonators, each functioning as a quarter-wavelength resonator. A ground electrode  103  and terminal electrodes  104 A and  104 B are provided on a rear principal surface  102 A of a dielectric substrate  102 . Principal-surface electrodes  105 A to  105 E are provided on a front principal surface  102 B. Short-circuit electrodes  106 A to  106 E and lead electrodes  107 A and  107 B are provided on side surfaces  102 C and  102 D. 
     The principal-surface electrodes  105 A to  150 E connect to the ground electrode  103  via the short-circuit electrodes  106 A to  106 E, respectively. The principal-surface electrodes  105 A,  105 C, and  105 E are parallel to each other, extend from an edge side of the side surface  102 C toward the side surface  102 D, and have short-circuit ends at the edges on the side surface  102 C side and open ends at the edges on the side surface  102 D side. The principal-surface electrodes  105 B and  105 D are parallel to each other, extend from an edge side of the side surface  102 D toward the side surface  102 C, and have short-circuit ends at the edges on the side surface  102 D side and open ends at the edges on the side surface  102 C side. 
     Also, the open ends of the principal-surface electrodes  105 A and  105 E constituting the resonators in the first and last stages connect to the terminal electrodes  104 A and  104 B on the rear principal surface  102 A via the lead electrodes  107 A and  107 B on the side surface  102 D. Accordingly, the resonant element  101  obtains very strong external coupling. In addition, a plurality of glass layers (not illustrated) are laminated on the front principal surface  102 B of the dielectric substrate  102 . 
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-358501 
     In the resonant element having the above-described configuration, the positions of the short-circuit ends of the principal-surface electrodes constituting the resonators do not match on the side surfaces facing each other, and the positions of the side-surface electrodes are different on the respective side surfaces. 
     Therefore, when side-surface electrode patterns of a plurality of resonant elements are simultaneously printed during manufacturing of the resonant elements, the respective elements need to be aligned on a pallet with the orientations of the respective surfaces of the elements being the same before printing. This process is sophisticated, e.g., the process is performed with the use of an aligning apparatus to recognize and correct respective orientations of a plurality of elements by using an image recognizing technique, thereby increasing the manufacturing cost. 
     Furthermore, when such a resonant element is mounted on a substrate, the amounts of solder on the respective side surfaces are uneven due to asymmetry of the positions of the side-surface electrodes. Accordingly, the tension applied to the resonant element from molten solder differs on the respective side surfaces, so that a mount position may be displaced from an appropriate mount position. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a method for manufacturing resonant elements in a simplified process of aligning a plurality of resonant elements and to provide resonant elements that can be manufactured by the method and that are capable of reducing displacement at mounting. 
     In respective resonant elements, first and second side-surface electrode patterns have the same form, whereby those side-surface electrode patterns can be formed in similar processes, for example, in a process using the same metal mask or screen mask. Therefore, side-surface electrode patterns of a plurality of resonant elements can be printed at one time even if any of the first and second side surfaces is placed on a printing surface. Accordingly, the manufacturing cost can be suppressed. Also, when the resonant element is mounted on a mounting substrate, asymmetry in amounts of solder welded to the side-surface electrode patterns can be prevented. Thus, this configuration reduces the risk of displacement of a mount position of the resonant element due to a difference in tensions of molten solder in a reflow process or the like, so that connection failure or characteristic failure is less likely to occur. 
     The first and second side-surface electrode patterns of the resonant element may be formed symmetrically in the respective side surfaces. In this configuration, asymmetry in amounts of solder welded to the side-surface electrode patterns can be further prevented when the resonant element is mounted on the mounting substrate. Thus, this configuration further reduces the risk of displacement of a mount position of the resonant element due to a difference in tensions of molten solder in a reflow process or the like, so that connection failure or characteristic failure is less likely to occur. 
     The first and second side-surface electrode patterns may be provided with a plurality of side-surface electrodes that are in conduction with the same principal-surface electrode. In this configuration, it is easy to place the respective side-surface electrode patterns in a point-symmetric manner and to form the side-surface electrode patterns that match each other on the side surfaces facing each other. Also, if there are other adjacent side-surface electrodes on the outer side of the above-described plurality of side-surface electrodes, electromagnetic-field coupling occurs between the plurality of side-surface electrodes and the other side-surface electrodes. Thus, in this configuration, the frequency characteristic can be easily adjusted by causing a significant change in electromagnetic-field coupling, particularly multipath coupling, through adjustment of gaps between those side-surface electrodes. 
     The principal-surface electrode that is in conduction with the plurality of side-surface electrodes may have a wide end portion that is in conduction with the plurality of side-surface electrodes. With this configuration, even if a cut error occurs at cutting of a mother substrate into dielectric substrates, no influence is exerted on a narrow portion of the principal-surface electrode and thus an influence on the resonator length reduces. 
     Dummy electrodes separated from the principal-surface electrode constituting part of the resonators may be provided in the first and second side-surface electrode patterns. In this configuration, the dummy electrodes easily enable formation of point-symmetric side-surface electrode patterns and side-surface electrode patterns that match each other on the side surfaces facing each other. If the position where the dummy electrodes are formed is close to the principal-surface electrode constituting the resonators, end capacitance is added to the principal-surface electrode. Thus, in this configuration, the frequency characteristic can be easily adjusted by causing a significant change in end capacitance through adjustment of gaps between the dummy electrodes and the principal-surface electrode. 
     As the principal-surface electrode pattern, an end capacitance electrode that continues to the dummy electrodes and that causes end capacitance to be generated in the principal-surface electrode constituting the resonators may be provided. In this configuration, the gap between the end capacitance electrode and the principal-surface electrode is constant even if a cut error occurs at cutting of a mother substrate into dielectric substrates. Therefore, variations in end capacitance can be reduced and an influence of the cut error exerted on the resonance characteristic can be reduced. 
     A side-surface electrode pattern that is point-symmetric in the side surface is formed on side surfaces placed on a printing surface of a pallet of dielectric substrates placed in holding holes of the pallet, and a side-surface electrode pattern having the same form is formed on the facing side surface, whereby resonant elements are manufactured. Accordingly, side-surface electrode patterns can be formed on the two side surfaces facing each other by using the same printing pattern, so that the process of aligning the resonant elements can be simplified. 
     According to the present invention, a process of aligning a plurality of resonant elements before forming of side surface electrodes is simplified. Accordingly, the manufacturing cost can be suppressed. Also, the risk of displacement of positions where resonant elements are mounted during a mounting process can be reduced, so that connection failure or characteristic failure can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a conventional configuration of a resonant element. 
         FIGS. 2(A) to 2(D)  are developed views illustrating a configuration example of a resonant element according to the present invention. 
         FIGS. 3(A) and 3(B)  are graphs for comparison of frequency characteristics of the configuration example according to the present invention and the conventional configuration. 
         FIG. 4  is a flowchart illustrating a manufacturing process of the configuration example according to the present invention. 
         FIGS. 5(A) and 5(   b ) are diagrams illustrating printing of the configuration example according to the present invention. 
         FIGS. 6(A) to 6(D)  are developed views illustrating another configuration example of the resonant element according to the present invention. 
         FIGS. 7(A) to 7(G)  are developed views illustrating another configuration example of the resonant element according to the present invention. 
     
    
    
     REFERENCE NUMERALS 
       1 : filter element 
       2 ,  12 , and  22 : dielectric substrate 
       2 A,  2 B,  12 A,  12 B,  22 A, and  22 B: principal surface 
       2 C,  2 D,  2 E,  2 F,  12 C,  12 D,  12 E,  12 F,  22 C,  22 D,  22 E, and 
       22 F: side surface 
       3 ,  13 , and  23 : ground electrode 
       4 ,  14 , and  24 : terminal electrode 
       5 ,  15 , and  25 : principal-surface electrode 
       6 ,  16 , and  26 : short-circuit electrode 
       7 ,  17 , and  27 : lead electrode 
       18  and  28 : dummy electrode 
       19  and  29 : end capacitance electrode 
       32 : glass layer 
       33 : skip coupling electrode 
       50 : pallet 
       51 : holding hole 
       52 : chamfered portion 
       53 : printing surface 
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, the present invention is described on the basis of configuration examples of a resonant element. FIGS.  2 (A)- 2 (D) are partial developed views of a resonant element. This resonant element includes stripline resonators and is used as a filter that is used for UWB (Ultra Wide Band) communication of high frequencies in a wide band. 
     This resonant element includes a dielectric substrate  2  having a compact rectangular parallelepiped shape. The dielectric substrate  2  is made of a ceramic dielectric material, such as titanium oxide. The dielectric substrate  2  has a relative permittivity of about 110, a thickness of 500 μm, a dimension in a lateral direction in the figures of about 3.2 mm, and a dimension in a short-side direction of principal surfaces of about 2.5 mm. 
     The composition and dimensions of the dielectric substrate  2  may be appropriately set in view of a frequency characteristic and so on. 
     A rear principal surface  2 A of the dielectric substrate  2  illustrated in  FIG. 2(A)  is a mount surface of this resonant element and is provided with a ground electrode  3  and terminal electrodes  4 A and  4 B as a rear-principal-surface electrode pattern. The ground electrode  3  serves as a ground electrode of resonators and is provided on almost the entire rear principal surface  2 A of the dielectric substrate  2 . The terminal electrodes  4 A and  4 B are placed near both corners contacting a side surface  2 D, while being separated from the ground electrode  3 . The terminal electrodes  4 A and  4 B are connected to a high-frequency-signal input/output terminal when the filter element is mounted on a mounting substrate. The respective electrodes constituting the rear-principal-surface electrode pattern have a thickness of about 12 μm and are formed by screen printing or metal mask printing with a silver electrode paste. 
     A plurality of principal-surface electrodes  5 A to  5 E are provided as a front-principal-surface electrode pattern on a front principal surface  2 B of the dielectric substrate  2  illustrated in  FIG. 2(B) . Any of the principal-surface electrodes  5 A to  5 E is a substantially I-shaped silver electrode having a thickness of about 5 μm and is formed by a photolithography process with a photosensitive silver paste with improved electrode precision for the UWB. Those principal-surface electrodes  5 A to  5 E are portions constituting resonant lines of stripline resonators. The principal-surface electrodes  5 A to  5 E are parallel to each other. The principal-surface electrodes  5 A,  5 C, and  5 E extend from an edge side as a border of a side surface  2 C toward the side surface  2 D. The principal-surface electrodes  5 B and  5 D extend from an edge side as a border of the side surface  2 D toward the side surface  2 C. On the side of short-circuit ends of the principal-surface electrodes  5 A to  5 E, the position reaching the side surface  2 C or  2 D is different on the respective sides of the side surfaces  2 C and  2 D. 
     The front principal surface  2 B of the dielectric substrate  2  is covered by a glass layer having a thickness of 15 μm or more (not illustrated). This glass layer is formed by printing and firing a glass paste composed of an insulating material, such as crystalline SiO 2  and borosilicate glass, or by a photolithography process and firing using a photosensitive material. The glass layer may be a laminate of a translucent glass layer and a light shielding glass layer. The glass layer mechanically protects the front-principal-surface electrode pattern and increases weather resistance of the filter element. Also, in the case where an electrode is further formed on an upper surface of this glass layer or where an electrode is formed on the front principal surface at printing of side-surface electrodes, short circuit between those electrodes and the front-principal-surface electrode pattern can be prevented. The composition and dimensions of the glass layer may be appropriately set in view of the degree of adhesion between the dielectric substrate  2  and the glass layer, resistance to environment, a frequency characteristic, and so on. 
     Short-circuit electrodes  6 A to  6 E and lead electrodes  7 A and  7 B are provided as a side-surface electrode pattern on the side surfaces  2 C and  2 D illustrated in  FIGS. 2(C) and 2(D) . Those electrodes have a thickness of about 12 μm, thicker than the front-principal-surface electrode pattern, and are formed by screen printing or metal mask printing with a silver electrode paste. 
     Although not illustrated in the figure, no electrode is provided on a right side surface  2 F and a left side surface  2 E of the dielectric substrate. 
     The respective principal-surface electrodes  5 A to  5 E provided on the front principal surface  2 B connect to the ground electrode  3  via the short-circuit electrodes  6 A to  6 E, so as to constitute resonant lines of five stages of quarter-wavelength resonators that couple to each other in an interdigital manner. open ends of the principal-surface electrodes  5 A and  5 E constituting the resonators in the first and last stages connect to the terminal electrodes  4 A and  4 B on the rear principal surface  2 A via the lead electrodes  7 A and  7 B on the side surface  2 D, so that strong external coupling (tap coupling) is obtained. 
     The respective principal-surface electrodes  5 A and  5 E constituting the resonators in the first and fifth stages include a wide portion and a narrow portion. The wide portions connect to the short-circuit electrodes  6 A and  6 F so as to constitute resonant lines, whereas the narrow portions connect to the lead electrodes  7 A and  7 B so as to constitute electrodes for tap coupling. The vicinity of the border between the wide portion and the narrow portion serves as an open end of the resonator. 
     The lead electrodes  7 A and  7 B have the same width, which is almost the same as the width of the narrow portions of the principal-surface electrodes  5 A and  5 E. Likewise, the short-circuit electrodes  6 A and  6 F have the same width, which is almost the same as the width of the narrow portions of the principal-surface electrodes  5 A and  5 E. In this way, the short-circuit electrodes  6 A and  6 F are narrow so that the short-circuit electrodes  6 A and  6 F have the same shape as that of the lead electrodes  7 A and  7 B. The positions where the short-circuit electrodes  6 A and  6 F are placed and the positions where the lead electrodes  7 A and  7 B are placed are point-symmetric in the plane where the respective electrodes are formed. For example, even if the front principal surface  2 B and the rear principal surface  2 A are inverted or if the side surface  2 C and the side surface  2 D are inverted, the electrode patterns match each other. 
     Since the short-circuit electrodes  6 A and  6 F are narrow, the resonator lengths of the resonators extend and the resonance frequency decreases. In that case, the resonance frequency may be appropriately set by adjusting the position of the border between the wide portion and the narrow portion of the principal-surface electrodes. 
     The principal-surface electrodes  5 B and  5 D constituting the resonators in the second and fourth stages have the same width. The short-circuit ends of the principal-surface electrodes  5 B and  5 D connect to the short-circuit electrodes  6 B and  6 E on the side surface  2 D. Here, the short-circuit electrodes  6 B and  6 E have the same width, which is almost the same as the width of the principal-surface electrodes  5 B and  5 D. The positions where the short-circuit electrodes  6 B and  6 E are placed are point-symmetric in the plane where those electrodes are formed. For example, even if the front principal surface  2 B and the rear principal surface  2 A are inverted, the electrode patterns match each other. 
     The principal-surface electrode  5 C constituting the resonator in the third stage has a wide portion near the edge side as the border of the side surface  2 C. The wide portion connects to the short-circuit electrodes  6 C and  6 D on the side surface  2 C. The principal-surface electrode  5 C is short-circuited to the ground electrode  3  via the short-circuit electrodes  6 C and  6 D. The wide portion of the principal-surface electrode  5 C extends from the position where the short-circuit electrode  6 C is formed to the short-circuit electrode  6 D, and those electrodes constitute a resonator. The wide portion is formed to continue to the two short-circuit electrodes  6 C and  6 D. If a cut error occurs at cutting of the dielectric substrate, the cut error exerts an influence on the dimension of the line length (short-side direction) of the wide portion, but the cut error does not exert any influence on the dimension of the line length of the narrow portion of the principal-surface electrode  5 C. The resonator length of the resonator constituted by the principal-surface electrode  5 C is mainly determined by the line length of the narrow portion of the principal-surface electrode  5 C. Thus, the influence of the cut error exerted on the resonator length can be reduced by providing the wide portion. 
     The short-circuit electrodes  6 C and  6 D have the same width. The positions where the short-circuit electrodes  6 C and  6 D are placed are point-symmetric in the plane where those electrodes are formed. For example, even if the front principal surface  2 B and the rear principal surface  2 A are inverted, the electrode patterns match each other. Furthermore, the short-circuit electrodes  6 C and  6 D have the same width as that of the short-circuit electrodes  6 B and  6 E provided on the facing side surface  2 D, and the positions thereof match each other. For example even if the side surface  2 C and the side surface  2 D are inverted, the electrode patterns match each other. 
     A side-surface electrode pattern including the short-circuit electrodes  6 A,  6 C,  6 D, and  6 F provided on the side surface  2 C and a side-surface electrode pattern including the short-circuit electrodes  6 B and  6 E and the lead electrodes  7 A and  7 B provided on the side surface  2 D match each other and are point-symmetric in the planes where the respective patterns are formed. Thus, an electrode formation area on the side surface  2 D is equal to an electrode formation area on the side surface  2 C. Therefore, when the filter element is mounted on the mounting substrate, the amounts of solder used to solder the side-surface electrodes on the side surfaces  2 C and  2 D are substantially equal to each other. In that case, the tensions of molten solder on the side surfaces  2 C and  2 D are equal to each other, so that displacement of the filter element on the mounting substrate during soldering hardly occurs. 
     Depending on setting of the shape of the principal-surface electrode  5 C, the vicinity of the border between the wide portion and the narrow portion operates as a short-circuit end of the resonator. Also, multipath coupling occurs between the short-circuit electrodes  6 C and  6 D and the short-circuit electrodes  6 A and  6 F adjacent thereto. In this way, the multipath coupling is added to the short-circuit ends of the resonators, and thus the strength of inductive coupling between the resonators in the first and third stages and between the resonators in the third and fifth stages increases. Incidentally, the degree of multipath coupling is determined by the gap between the short-circuit electrodes  6 C and  6 A and the gap between the short-circuit electrodes  6 D and  6 F. 
     The side-surface electrode patterns are thicker than the front-principal-surface electrode pattern, and thus the current in the part on the short-circuit end side where current concentration typically occurs is distributed so as to reduce conductor loss. With this configuration, this resonant element has a small insertion loss. 
     Now, a difference in electrical characteristic between the filter element of this configuration and a filter element of a conventional configuration is described.  FIG. 3(A)  illustrates a filter characteristic of the filter element of the conventional configuration illustrated in  FIG. 1 , whereas  FIG. 3(B)  illustrates a filter characteristic of the filter element of the present invention shown in  FIGS. 2(A) to 2(D) . 
     The present invention is different from the conventional configuration in that the resonators in the first and third stages and the resonators in the third and fifth stages couple to each other by skipping a resonator. In this configuration, multipath coupling is allowed to occur, so that an attenuation pole on the wideband side of the filter approaches the band, at about 5.9 GHz, as illustrated in  FIG. 3(B) . Compared to the conventional configuration illustrated in  FIG. 3(A) , in which the attenuation pole is at about 6.1 GHz, an improved filter characteristic is obtained. 
     The filter element having the above-described configuration is manufactured through the process illustrated in  FIG. 4 . 
     (S 1 ) First, a dielectric mother substrate having no electrode on any surface is prepared. 
     (S 2 ) Then, screen printing or metal mask printing is performed with a conductive paste on a rear principal surface of the mother substrate, and a ground electrode and a terminal electrode are formed through firing. 
     (S 3 ) Then, printing is performed with a photosensitive conductive paste on a front principal surface of the mother substrate, and respective principal-surface electrodes are formed through firing after a photolithography process including exposure and development. 
     (S 4 ) Then, printing is performed with a glass paste on the front principal surface of the mother substrate and a transparent glass layer is formed through firing. 
     (S 5 ) Then, printing is performed with a glass paste containing an inorganic pigment on the front principal surface of the mother substrate, and a light-shielding glass layer is formed through firing. 
     (S 6 ) Then, many segments are obtained through dicing or the like from the mother substrate constituted in the above-described manner. After the dicing, preliminary measurement of an electrical characteristic is performed on an upper-surface pattern of part of the segments. 
     (S 7 ) Then, the respective segments are fit into holding holes of a printing pallet such that the side surfaces  2 C or the side surfaces  2 D of the respective segments are placed on a printing surface of the printing pallet. 
     (S 8 ) Printing with a conductive paste is performed on the segments on the printing pallet by using a metal mask or a screen mask having a predetermined pattern so as to form a side-surface electrode pattern, and firing is performed. 
     (S 9 ) Then, the respective elements are inverted while being aligned so as to place the side surfaces  2 D or the side surfaces  2 C of the respective segments on the printing surface of the printing pallet. 
     (S 10 ) Printing with a conductive paste is performed on the segments on the printing pallet by using the above-described metal mask or screen mask so as to form the same side-surface electrode pattern as that described above, and filter elements are manufactured through firing. 
     Now, placement of the segments in the holding holes of the printing pallet is described. 
     In this embodiment, a placing pallet and a printing pallet are used in order to place the side surfaces  2 C or the side surfaces  2 D of the filter elements (segments)  1  having a compact rectangular parallelepiped shape on a printing surface  53  of the printing pallet. An example of a representative form of the pallet is illustrated in  FIG. 5(A) . The pallet is held by a vibrating mechanism (not illustrated) so that the pallet can vibrate. 
     The pallet  50  is a member to align a plurality of filter elements and includes the printing surface  53  provided with a plurality of holding holes  51 . A chamfered portion  52  is provided at the edge of the respective holding holes  51 . Also, pushing holes  54  for pushing out the fit filter element  1  are provided at a bottom surface of the respective holding holes  51 . The opening size on the printing surface  53  of the holding hole  51  is substantially equal to the size of the side surface  2 C and the side surface  2 D in the printing pallet. Also, the opening size is substantially equal to the size of the side surface  2 E and the side surface  2 F in the placing pallet. 
     In the configuration according to this embodiment, the size of the side surface  2 C and the side surface  2 D is larger than the size of the side surface  2 E and the side surface  2 F. Thus, the placing pallet provided with a plurality of holding holes having almost the same dimension as that of the side surface  2 E and the side surface  2 F is prepared, and a plurality of segments are placed on the placing pallet. Under this state, vibration is given to the placing pallet so as to drop the respective segments into the holding holes. Since the size of each holding hole is almost the same as the size of the side surface  2 E and the side surface  2 F and is smaller than the size of the side surface  2 C and the side surface  2 D, the segments dropped into the respective holding holes are reliably placed such that the side surface  2 E or the side surface  2 F is oriented to the upper side of the placing pallet. 
     Therefore, the orientation of the side surfaces  2 C and the side surfaces  2 D can be set to the upper side of the pallet by rotating the respective segments by 90 degrees, with the part between the side surfaces  2 A and  2 B being the rotation plane. Thus, the printing pallet provided with a plurality of holding holes having the same dimension as that of the side surfaces  2 C and  2 D is prepared, and the respective segments of which side surfaces  2 C and  2 D are oriented to the upper side of the pallet by rotation of 90 degrees are placed in the holding holes in the printing pallet. 
     If the size of the side surface  2 C and the side surface  2 D is smaller than the size of the side surface  2 E and the side surface  2 F, the placing pallet is unnecessary. This is because the side surfaces  2 C or the side surfaces  2 D of the respective segments dropped in the holding holes of the printing pallet are reliably oriented to the upper side of the pallet when the size of the holding holes of the printing pallet is substantially equal to the size of the side surface  2 C and the side surface  2 D. 
       FIG. 5(B)  is a cross-sectional view taken along the line B-B illustrating an example of the state where the filter elements have been dropped into the holding holes in the printing pallet and a side-surface electrode pattern has been formed on the side surfaces placed on the printing surface. 
     The filter elements  1  fit in the holding holes  51  on the printing pallet  50  are aligned such that the side surfaces  2 C or the side surfaces  2 D are oriented in the same direction. 
     In this state, printing is performed on the side surfaces of the filter elements  1  placed on the printing surface  53  of the pallet  50 . The electrode patterns provided on the side surfaces  2 C and  2 D of the filter elements  1  match each other and have a point-symmetric form. For this reason, the orientations of the respective surfaces of the plurality of filter elements need not perfectly be matched before printing. 
     When the electrode pattern provided on the side surface  2 C matches the electrode pattern provided on the side surface  2 D, printing can be performed by simultaneously placing the side surfaces  2 C or the side surfaces  2 D of the filter elements  1  on the printing surface  53 . 
     When the electrode pattern provided on the side surface  2 C and the electrode pattern provided on the side surface  2 D are point-symmetric, printing can be performed even if the principal surfaces  2 A or the principal surfaces  2 B of the filter elements  1  are oriented to the upper or lower side in the figure. 
     Next, a configuration example of another resonant element is described on the basis of  FIGS. 6(A) to 6(D) . 
     This resonant element is a filter element provided with a filter including two quarter-wavelength resonators and one half-wavelength resonator coupled to each other. Hereinafter, explanation about the same configuration as that of the above-described embodiment is omitted in some cases. 
     This filter element includes a dielectric substrate  12  having a compact rectangular parallelepiped shape. A front principal surface of the dielectric substrate  12  is covered by a glass layer (not illustrated). 
     A ground electrode  13  and terminal electrodes  14 A and  14 B are provided as a rear-principal-surface electrode pattern on a rear principal surface  12 A of the dielectric substrate  12  illustrates in part (A) of the figure. The ground electrode  13  is provided over almost the entire rear principal surface of the dielectric substrate  12 , whereas the terminal electrodes  14 A and  14 B are placed at the vicinity of both corners contacting a side surface while being separated from the ground electrode  13 . 
     Principal-surface electrodes  15 A to  15 C and end capacitance electrodes  19 A and  19 B constituting stripline resonators are provided as a front-principal-surface electrode pattern on a front principal surface  12 B of the dielectric substrate  12  illustrated in part (B) of the figure. Any of the principal-surface electrodes  15 A to  15 C and end capacitance electrodes l 9 A and  19 B is a silver electrode having a thickness of about 5 μm and is formed by a photolithography method using a photosensitive silver paste with an improved electrode precision for high frequencies in a wide band. 
     Short-circuit electrodes  16 A and  16 B and lead electrodes  17 A and  17 B are provided as a side-surface electrode pattern on a side surface  12 D illustrated in part (D) of the figure. On the other hand, dummy electrodes  18 A to  18 D are provided as a side-surface electrode pattern on a side surface  12 C illustrated in part (C) of the figure. The respective electrodes constituting the respective side-surface electrode patterns have a thickness of about 12 μm, thicker than the front-principal-surface electrode pattern, and are formed by screen printing or metal mask printing with a silver electrode paste. 
     Although not illustrated in the figure, no electrode is provided on a right side surface  12 F and a left side surface  12 E. 
     The respective principal-surface electrodes  15 A and  15 C on the front principal surface  12 B connect to the ground electrode  13  on the rear principal surface  12 A via the short-circuit electrodes  16 A and  16 B on the side surface  12 D, and also connect to the terminal electrodes  14 A and  14 B on the rear principal surface  12 A via the lead electrodes  17 A and  17 B on the side surface  12 D. Also, capacitance is added to the vicinity of the open ends thereof by the end capacitance electrodes  19 A and  19 B on the front principal surface  12 B. The degree of the capacitance is determined by the gap between the end capacitance electrodes  19 A and  19 B and the principal-surface electrodes  15 A and  15 C, and the frequency characteristic can be adjusted also by adjusting the gap. 
     Each of the principal-surface electrodes  15 A and  15 C is a substantially L-shaped electrode including a portion extending along the side surface  12 E or  12 F and a portion extending along the side surface  12 D, and constitutes a one-end-opened and one-end-short-circuited quarter-wavelength resonator together with the ground electrode  13 . 
     The principal-surface electrodes  15 A and  15 C continue to the short-circuit electrodes  16 A and  16 B, respectively, at the vicinity of the center of an edge side as a border of the side surface  12 D, and are in conduction with the ground electrode  13  via the short-circuit electrodes  16 A and  16 B, respectively. Also, in the principal-surface electrode  15 A, the portion extending along the side surface  12 E continues to the lead electrode  17 A at the position contacting the edge side as the boarder of the side surface  12 D and is in conduction with the terminal electrode  14 A via the lead electrode  17 A. Likewise, in the principal-surface electrode  15 C, the portion extending along the side surface  12 F connects to the lead electrode  17 B at the position contacting the edge side as the boarder of the side surface  12 D and is in conduction with the terminal electrode  14 B via the lead electrode  17 B. 
     The portions extending along the side surface  12 D of the principal-surface electrodes  15 A and  15 C are inflected. The inflection increases the line length of the respective principal-surface electrodes  15 A and  15 C. The portions extending along the side surface  12 D of the principal-surface electrodes  15 A and  15 C are not necessarily inflected. If the inflection is not provided in the configuration according to this embodiment, the resonator length of the quarter-wavelength resonator can be decreased to increase the resonance frequency. On the other hand, if the inflection is provided to increase the line length, the resonator length of the quarter-wavelength resonator can be increased to decrease the resonance frequency. 
     Each of the continuous portions between the principal-surface electrodes  15 A and  15 C and the lead electrodes  17 A and  17 B includes a wide portion contacting the edge side and a narrow portion extending from the wide portion toward the side surface  12 C. The wide portion is provided in order to suppress an influence of a cut error caused during cutting of the dielectric substrate exerted on tap coupling. 
     The principal-surface electrode  15 B is a substantially C-shaped electrode having a closed portion on the side of the side surface  12 C and an opened portion on the side of the side surface  12 D. The principal-surface electrode  15 B has a portion extending along the side surface  12 C. Furthermore, the principal-surface electrode  15 B has portions that extend from both ends of the portion and that are parallel to the side surfaces  12 E and  12 F. Furthermore, the principal-surface electrode  15 B has portions that extend from the tops of those portions inwardly and that are parallel to the side surface  12 D. Furthermore, the principal-surface electrode  15 B has portions extending from the tops of those portions toward the side surface  12 C. Accordingly, the principal-surface electrode  15 B constitutes a half-wavelength resonator whose both ends are opened together with the ground electrode  13 . Since the principal-surface electrode  15 B is inflected, the resonator length of the half-wavelength resonator can be increased in the limited substrate area. 
     The line widths of resonant lines constituted by the respective principal-surface electrodes  15 A,  15 B, and  15 C are adjusted to realize a necessary frequency characteristic. 
     The formation of the above-described principal-surface electrodes  15 A to  15 C allows the stripline resonator including the principal-surface electrode  15 A to couple to the terminal electrode  14 A by tap coupling. The two stripline resonators including the principal-surface electrodes  15 A and  15 B couple to each other in an interdigital manner, and the two stripline resonators including the principal-surface electrodes  15 B and  15 C couple to each other in an interdigital manner. The stripline resonator including the principal-surface electrode  15 C couples to the terminal electrode  14 B by tap coupling. Additionally, in the two stripline resonators including the principal-surface electrodes  15 A and  15 C, the short-circuit end sides are close to each other and multipath coupling occurs. 
     The lead electrodes  17 A and  17 B on the side surface  12 D have the same width. Also, the short-circuit electrodes  16 A and  16 B have the same width. Also, the dummy electrodes  18 A and  18 D on the side surface  12 C have the same width, which is the same as the width of the lead electrodes  17 A and  17 B. Also, the dummy electrodes  18 B and  18 C on the side surface  12 C have the same width, which is the same as the width of the short-circuit electrodes  16 A and  16 B. Furthermore, the side-surface electrode pattern including the short-circuit electrodes  16 A and  16 B and the lead electrodes  17 A and  17 B provided on the side surface  12 D and the side-surface electrode pattern including the dummy electrodes  18 A to  18 D provided on the side surface  12 C match each other and are point-symmetric in the planes where the respective patterns are formed. Thus, an electrode formation area on the side surface  12 D is equal to an electrode formation area on the side surface  12 C. 
     The respective dummy electrodes  18 A to  18 D are used only for forming, on the side surface  12 C, an electrode pattern that matches the electrode pattern including the short-circuit electrodes  16 A and  16 B and the lead electrodes  17 A and  17 B. The dummy electrodes  18 A and  18 D continue to the end capacitance electrodes  19 A and  19 B provided on the front principal surface  12 B so as to allow the end capacitance electrodes  19 A and  19 B to be in conduction with the ground electrode  13 . Also, the dummy electrodes  18 B and  18 C are in conduction with the ground electrode  13 . Capacitance is added to the resonators constituted by the respective principal-surface electrodes  15 A to  15 C also by the dummy electrodes  18 A to  18 D. 
     In the above-described configuration, too, the side-surface electrode pattern on the side surface  12 C and the side-surface electrode pattern on the side surface  12 D match each other and are point-symmetric in the planes where the respective patterns are formed, so that the manufacturing thereof is simplified. For example, the manufacturing can be performed by the process and method illustrated in  FIGS. 4 ,  5 (A) and  5 (B). Accordingly, resonant elements can be inexpensively provided by reducing the manufacturing cost. 
     Next, a configuration example of another resonant element is described on the basis of  FIGS. 7(A) to 7(G) . 
     This resonant element is a filter element provided with a filter including four quarter-wavelength resonators coupled by comb-line coupling. This filter realizes a narrower-band frequency characteristic due to comb-line coupling compared to the filters according to the above-described other configuration examples. Hereinafter, explanation about the same configuration as that in the above-described embodiment is omitted in some cases. 
     This filter element includes a dielectric substrate  22  having a compact rectangular parallelepiped shape. The front principal surface side of the dielectric substrate  22  is covered by a glass layer  32 . 
     A ground electrode  23  and terminal electrodes  24 A and  24 B are provided as a rear-principal-surface electrode pattern on a rear principal surface  22 A of the dielectric substrate  22  illustrated in  FIG. 7(A) . The ground electrode  23  is provided on almost the entire rear principal surface of the dielectric substrate  22 , and the terminal electrodes  24 A and  24 B are placed at the vicinity of the centers of edge sides as borders of side surfaces  22 E and  22 F, respectively, while being separated from the ground electrode  23 . 
     A plurality of principal-surface electrodes  25 A to  25 D and end capacitance electrodes  29 A to  29 D constituting stripline capacitors are provided as a front-principal-surface electrode pattern on a front principal surface  22 B of the dielectric substrate  22  illustrated in  FIG. 7(B) . Any of the principal-surface electrodes  25 A to  25 D and the end capacitance electrodes  29 A to  29 D is a silver electrode having a thickness of about 5 μm, and is formed by a photolithography method with a photosensitive silver paste with an improved electrode precision for high frequencies. 
     Short-circuit electrodes  26 A to  26 D are provided as a side-surface electrode pattern on a side surface  22 D illustrated in  FIG. 7(D) . Dummy electrodes  28 A to  28 D are provided as a side-surface electrode pattern on a side surface  22 C illustrated in  FIG. 7(C) . A lead electrode  27 A is provided as a side-surface electrode pattern on a side surface  22 E illustrated in  FIG. 7(E) . A lead electrode  27 B is provided as a side-surface electrode pattern on a side surface  22 F illustrated in  FIG. 7(F) . Each of the electrodes constituting the respective side-surface electrode patterns has a thickness of about 12 μm, thicker than the front-principal-surface electrode pattern, and is formed by screen printing or metal mask printing with a silver electrode paste. 
     Also, the glass layer  32  is illustrated in  FIG. 7(G) . The glass layer  32  is provided with a skip coupling electrode  33  on the front principal surface side. The skip coupling electrode  33  is a silver electrode having a thickness of about 5 μm, and is formed by a photolithography method using a photosensitive silver paste with an improved electrode precision for the UWB. 
     The respective principal-surface electrodes  25 A to  25 D on the front principal surface  22 B connect to the ground electrode  23  on the rear principal surface  22 A via the short-circuit electrodes  26 A to  26 D on the side surface  22 D. Also, the principal-surface electrode  25 A connects to the terminal electrode  24 A on the rear principal surface  22 A via the lead electrode  27 A on the side surface  22 E, whereas the principal-surface electrode  25 D connects to the terminal electrode  24 B on the rear principal surface  22 A via the lead electrode  27 B on the side surface  22 F. Furthermore, capacitance is added to the vicinity of the respective open ends of the principal-surface electrodes  25 A to  25 D by the end capacitance electrodes  29 A to  29 D on the front principal surface  22 B. The degree of the capacitance is determined by the gap between the end capacitance electrodes  29 A to  29 D and the principal-surface electrodes  25 A to  25 D, and the frequency characteristic can be adjusted by adjusting the gap. 
     Each of the principal-surface electrodes  25 A and  25 D is a substantially U-shaped electrode having a portion extending along the side surface  22 E or  22 F and a portion extending in parallel with the portion, and constitutes a one-end-opened and one-end-short-circuited quarter-wavelength resonator together with the ground electrode  23 . Strong external coupling is obtained by leading the portions extending along the side surfaces  22 E and  22 F from a middle of resonators and tapping those portions. 
     The principal-surface electrodes  25 A and  25 D continue to the short-circuit electrodes  26 A and  26 D, respectively, at the edge side as the border of the side surface  22 D, and are in conduction with the ground electrode  23  via the short-circuit electrodes  26 A and  26 D, respectively. Also, in the principal-surface electrode  25 A, the portion extending along the side surface  22 E continues to the lead electrode  27 A at the vicinity of the center of the edge side as the border of the side surface  22 E, and is in conduction with the terminal electrode  24 A via the lead electrode  27 A. Likewise, in the principal-surface electrode  25 D, the portion extending along the side surface  22 F continues to the lead electrode  27 B at the vicinity of the center of the edge side as the border of the side surface  22 F, and is in conduction with the terminal electrode  24 B via the lead electrode  27 B. 
     The continuous portions between the principal-surface electrodes  25 A and  25 D and the short-circuit electrodes  26 A and  26 D have a wide portion contacting the edge side and a narrow portion extending from the wide portion toward the side surface  22 C. The wide portion is provided to suppress an influence of a cut error that occurs when the dielectric substrate is cut. 
     The principal-surface electrodes  25 B and  25 C are I-shaped electrodes extending from the edge side as the border of the side surface  22 D toward the side surface  12 C, continue to the short-circuit electrodes  26 B and  26 C, respectively, and are in conduction with the ground electrode  23  via the short-circuit electrodes  26 B and  26 C, respectively. 
     The line widths of resonant lines constituted by the respective principal-surface electrodes  25 A to  25 D are adjusted to realize a necessary frequency characteristic. 
     Due to the formation of the principal-surface electrodes  25 A to  25 D, the stripline resonator including the principal-surface electrode  25 A couples to the terminal electrode  24 A by tap coupling. The two stripline resonators including the principal-surface electrodes  25 A and  25 B couple to each other by comb-line coupling, the two stripline resonators including the principal-surface electrodes  25 B and  25 C couple to each other by comb-line coupling, and the two stripline resonators including the principal-surface electrodes  25 C and  25 D couple to each other by comb-line coupling. The stripline resonator including the principal-surface electrode  25 D couples to the terminal electrode  24 B by tap coupling. 
     The short-circuit electrodes  26 A and  26 D on the side surface  22 D have the same width. Also, the short-circuit electrodes  26 B and  26 C have the same width. Also, the dummy electrodes  28 A and  28 D on the side surface  22 C have the same width, which is the same as the width of the short-circuit electrodes  26 A and  26 D on the facing side surface  22 D. Also, the dummy electrodes  28 B and  28 C on the side surface  22 C have the same width, which is the same as the width of the short-circuit electrodes  26 B and  26 C on the facing side surface  22 D. Furthermore, the side-surface electrode pattern including the short-circuit electrodes  26 A to  26 D provided on the side surface  22 D and the side-surface electrode pattern including the dummy electrodes  28 A to  28 D provided on the side surface  22 C match each other and are point-symmetric in the planes where the respective patterns are formed. Accordingly, an electrode formation area on the side surface  22 D can be equal to an electrode formation area on the side surface  22 C. 
     The respective dummy electrodes  28 A to  28 D are simply provided for forming, on the side surface  22 C, the electrode pattern that matches the electrode pattern including the short-circuit electrodes  26 A to  26 D. The dummy electrodes  28 A to  28 D cause end capacitance to be added to the open ends of the respective resonators, so that the resonator length reduces and that the filter element can be shortened. 
     The dummy electrodes  28 A to  28 D continue to the end capacitance electrodes  29 A to  29 D provided on the front principal surface  22 B and allow the end capacitance electrodes  29 A to  29 D to be in conduction with the ground electrode  23 . Capacitance is added to the resonators constituted by the principal-surface electrodes  25 A to  25 D also by those dummy electrodes  28 A to  28 D. 
     In the above-described configuration, too, the side-surface electrode pattern on the side surface  22 C and the side-surface electrode pattern on the side surface  22 D match each other and are point-symmetric in the planes where the respective patterns are formed, and manufacturing thereof is simplified. For example, the manufacturing can be performed by the process and method illustrated in  FIGS. 4 ,  5 (A) and  5 (B). Accordingly, resonant elements can be inexpensively provided by reducing the manufacturing cost. 
     In addition, the positions of the principal-surface electrodes and the short-circuit electrodes on the side surfaces according to the above-described embodiments are set in accordance with the specifications of products, and any form may be adopted in accordance with the specification of products. The present invention can be applied to a configuration other than the above-described configurations and can be adopted to various pattern forms of filter elements. Furthermore, another configuration (high-frequency circuit) may be placed in this filter element.