Abstract:
Provided is a dielectric filter that can be anchored in a stable manner without causing damage even when there is variation in the size of the parts. With this dielectric filter, one surface of washers has a concave part, which is equipped with an edge part formed at the perimeter of the one surface, a floor surface provided at a lower position than the edge part, and a tapered part formed between the edge part and the floor surface. The washers are arranged on the upper surface of and fastened by means of screws to dielectric bodies with the concave parts facing the dielectric bodies, with sheet metal therebetween.

Description:
TECHNICAL FIELD 
     The present invention relates to a TM mode dielectric filter. 
     BACKGROUND ART 
     Base stations and mobile stations in a mobile communication system are each provided with a filter to suppress an unnecessary wave other than a desired wave when transmitting and/or receiving a radio signal. A dielectric filter is often used for this filter. 
     The filter on the base station is required to reduce passband loss. Reducing passband loss requires a dielectric having a high Q value, but a reduction of passband loss using a general TE mode dielectric filter would result in an increase in size. Thus, a TM mode dielectric filter which has a lower Q value than the TE mode but can be downsized has been attracting attention in recent years (e.g., see the Citation List for PTLs 1 to 5 listed below). 
     For the TM mode dielectric filter, upper and lower surfaces of the dielectric need to be shielded based on the principles of the TM mode dielectric filter. For this reason, PTL 1, or the like, discloses a technique for fixing the dielectric in place while shielding the upper and lower surfaces of the dielectric. 
     As shown in  FIG. 1 , PTL 1 discloses a technique for firmly fixing dielectric resonator 2 to metal case 1 in a longitudinal direction and a vertical direction of the resonator using resonator fixing plate 3 and spacer 6. Connectors 30 are mounted on both ends of the metal case 1. It is thereby possible to provide a TM mode dielectric filter that remains stable under vibration or impact. PTL 1 corresponds to U.S. Pat. No. 6,320,484 to Furuya et al. 
     CITATION LIST 
     Patent Literature 
     PTL 1 
     Japanese Patent Application Laid-Open No. 2000-165118 
     PTL 2 
     Japanese Patent Application Laid-Open No. 7-66611 
     PTL 3 
     Japanese Utility Model (Registration) Application Laid-Open No. 6-34307 
     PTL 4 
     Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-529666 
     PTL 5 
     Japanese Patent Application Laid-Open No. 2005-223665 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     However, the TM mode dielectric filter described in PTL 1 has a fixing structure in which a sheet metal is sandwiched between a cover and a dielectric, and the dielectric resonator is fixed in place by the sizes of components such as the cover, dielectric, sheet metal. For this reason, if there is a variation in the sizes of the components, the fixing may become unstable or an excessive pressure may be applied to the dielectric, causing damage or the like to the dielectric. 
     An object of the present invention is to provide a dielectric filter stably fixed without damage even when there is a variation in the size of the components. 
     Solution to the Problem 
     A dielectric filter according to an aspect of the present invention includes at least one resonator using a TM mode, in which the resonator includes at least the following elements (1) to (4): 
     (1) a three-dimensionally shaped dielectric that includes a first surface and a second surface opposite to the first surface; 
     (2) a case that includes a first inner surface and a second inner surface facing the first inner surface and that accommodates the dielectric so that the first surface faces the first inner surface while the second surface faces the second inner surface; 
     (3) an intermediate member that is disposed between the first inner surface and the first surface and that is movable at least in a direction from the first inner surface toward the second inner surface; and 
     (4) a pressing member that is capable of pressing the intermediate member in a direction from the first inner surface toward the second inner surface. 
     Advantageous Effects of the Invention 
     According to an aspect of the present invention, it is possible to provide a dielectric filter stably fixed without damage even when there is a variation in size of components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a configuration of a prior art dielectric filter disclosed in PTL 1; 
         FIG. 2  is a top view illustrating an overall TM mode dielectric filter according to an embodiment of the present invention; 
         FIG. 3  is a cross-sectional view of the overall dielectric filter in  FIG. 2 ; 
         FIG. 4  is an enlarged view of the region enclosed by the ellipse in  FIG. 3 ; 
         FIG. 5A  is a perspective view illustrating a configuration of a washer; 
         FIG. 5B  is a perspective view illustrating a configuration of a washer; 
         FIG. 6  is a cross-sectional view illustrating configuration  1 , which is another configuration of the dielectric filter according to the embodiment of the present invention; 
         FIG. 7  is a cross-sectional view illustrating configuration  2 , which is another configuration of the dielectric filter according to the embodiment of the present invention; 
         FIG. 8  is a cross-sectional view illustrating other configuration  3 , which is another configuration of the dielectric filter according to the embodiment of the present invention; and 
         FIG. 9  is a cross-sectional view illustrating configuration  4 , which is another configuration of the dielectric filter according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, each embodiment of the present invention will be described in detail with reference to the accompanying drawings. Throughout the embodiments, the same components are assigned the same reference numerals and the overlapping description thereof will be omitted, however. 
     Embodiment 
     [Configuration of Dielectric Filter] 
       FIG. 2  is a top view illustrating overall TM mode dielectric filter (hereinafter simply referred to as “dielectric filter”)  100  according to an embodiment of the present invention,  FIG. 3  is a cross-sectional view of overall dielectric filter  100  in  FIG. 2  and  FIG. 4  is an enlarged view of the region enclosed by the ellipse in  FIG. 3 . However,  FIG. 2  shows the dielectric filter without a cover  11 .  FIG. 3  and  FIG. 4  show a situation in which screw  111  is inserted into cover  11 . 
     Dielectric filter  100  is provided with at least one resonator using a TM mode. For example, dielectric filter  100  shown in  FIG. 2  is provided with ten resonators. Each resonator is provided with at least case  101 , dielectric  102 , washer  104  ( FIGS. 3 and 4 ) serving as an intermediate member, screw  111  ( FIGS. 3 and 4 ) serving as a pressing member and frequency adjusting screw  105  ( FIG. 3 ). 
     More specifically, case  101  is formed of side and bottom surfaces and provided with case  10  whose one side (top surface in  FIG. 3 ) is open and cover  11  that covers the open surface of case  10 . 
     Case  101  also includes inner surface  101   a  (first inner surface) and inner surface  101   b  (second inner surface) opposite to inner surface  101   a  as shown in  FIG. 3 . That is, in  FIG. 3 , cover  11  is at least part of case  101  and includes inner surface  101   a . Case  10  includes inner surface  101   b.    
     In  FIG. 3  and  FIG. 4 , case  101  ( FIG. 3 ) includes regulation section  101   c  that regulates the movement of washer  104  along direction d 2  ( FIG. 3 ) which is parallel to inner surface  101   a . For example, regulation section  101   c  is a recessed portion provided in inner surface  101   a  of cover  11  having a size corresponding to an outer shape of washer  104 . 
     Dielectric  102  is a three-dimensionally shaped dielectric that includes surface  102   a  (first surface) and surface  102   b  (second surface) as shown in  FIG. 3  opposite to surface  102   a . For example, dielectric  102  has a columnar shape, and surface  102   a  and surface  102   b  are columnar end faces. 
     As shown in  FIG. 3 , dielectric  102  is accommodated in case  101  with surface  102   a  facing inner surface  101   a , and surface  102   b  facing inner surface  101   b.    
     Washer  104  is disposed between inner surface  101   a  of case  101  and surface  102   a  of dielectric  102  and is movable at least in direction d 1  from inner surface  101   a  toward inner surface  102   b.    
     Screw  111  can press washer  104  in direction d 1  from inner surface  101   a  toward inner surface  101   b . For example, when screw hole  110  is provided in inner surface  101   a  of case  101  and a female thread is formed in screw hole  110  in a direction from inner surface  101   a  toward inner surface  101   b , screw  111  is a male screw that is inserted into the above female thread. 
     Frequency adjusting screw  105  adjusts a resonance frequency. More specifically, as shown in  FIG. 3 , screw hole  109  is provided at a position facing surface  102   b  of dielectric  102  at the bottom of case  10 , and frequency adjusting screw  105  is inserted into screw hole  109  and thereby protrudes in direction d 3  from inner surface  101   b  toward inner surface  101   a  of case  11 . The resonance frequency is adjusted by changing the length of frequency adjusting screw  105  protruding from inner surface  101   b  toward inner surface  101   a  of case  11 . 
     As shown in  FIG. 2 , in dielectric filter  100 , a plurality of columnar dielectrics  102  are arranged vertically at predetermined positions at appropriate intervals inside case  101 . As shown in  FIG. 4 , the open surface of case  101  ( FIG. 3 ) is covered with sheet metal  103 . That is, sheet metal  103  is disposed along inner surface  101   a  inside case  101  and between washer  104  and surface  102   a  of dielectric  102 . Furthermore, as shown in  FIG. 2 , in dielectric filter  100  provided with at least two resonators arranged in parallel, sheet metals  103  ( FIGS. 3 and 4 ) for the at least two resonators are integrated into one piece. Sheet metal  103  serves as the ground for each dielectric  102  and contributes to ground reinforcement. 
     [Structure of Washer  104 ] 
     As shown in  FIG. 4 , washer  104  is disposed above surface  102   a  of dielectric  102  with sheet metal  103  interposed in between. For example, as shown in  FIG. 4 , washer  104  has a planar shape including a facing surface (surface  104   a ) facing surface  102   a  of dielectric  102  and surface  104   b  opposite to surface  104   a  ( FIG. 5A  and  FIG. 5B ). Furthermore, washer  104  has a recessed portion in the facing surface (surface  104   a ). 
     For example, as shown in  FIG. 4 ,  FIG. 5A  and  FIG. 5B , washer  104  ( FIGS. 4 and 5A ) has a recessed portion having a size corresponding to the outer shape of surface  102   a  of dielectric  102  in surface  104   a  and the recessed portion is disposed so as to be fitted to surface  102   a  of dielectric  102 . More specifically, as shown in  FIG. 5A , the recessed portion of surface  104   a  includes bottom surface  107  provided at a position recessed by a predetermined thickness from the circumference of surface  104   a  in the direction of surface  104   b , and tapered portion  108  which is formed in a tapered shape between the circumference of surface  104   a  and bottom surface  107 . Surface  104   a  of washer  104  has edge portion  106  around the circumference of the recessed portion of surface  104   a . That is, in  FIG. 5A , washer  104  is provided with bottom surface  107  provided at a position one step recessed (corresponding to a predetermined thickness) from edge portion  106 , and tapered portion  108  which is formed in a tapered shape between edge portion  106  and bottom surface  107 . Washer  104  shown in  FIG. 5A  and  FIG. 5B  serves as a position regulating member with respect to the d 2  ( FIGS. 3 and 4 ) direction of dielectric  102 . 
     [Operation of Dielectric Filter  100 ] 
     As described above with respect to  FIG. 2 , cover  11  that covers sheet metal  103  and washer  104  is placed over the open surface of case  10 . Cover  11  is provided with screw hole  110  at a position facing washer  104 , and screw  111  is screwed into screw hole  110 . 
     In dielectric filter  100  having such a configuration, when screw  111 , inserted into screw hole  110 , is turned clockwise by a predetermined amount, the distal end of screw  111  comes into contact with surface  104   b  of washer  104 . When screw  111  is turned further, screw  111  presses washer  104  in a direction from inner surface  101   a  toward inner surface  101   b  of case  101 . Dielectric  102  can be fixed with the pressure with which screw  111  presses washer  104 . By so doing, even when there is a variation in size of components of each resonator, it is possible to add a pressure on the same (constant) level to dielectrics  102  of all resonators of dielectric filter  100  equally by appropriately performing torque management (that is, adjustment of the amount of rotation of screw  111 ) using screw  111  provided for each resonator for dielectrics  102  of all the resonators in dielectric filter  100 . It is also possible to prevent more than necessary pressure from being imposed on each dielectric  102  and prevent damage to dielectric  102 . 
     Therefore, according to the present embodiment, even when there is a variation in the size of the components, it is possible to realize a dielectric filter stably fixed without damage. 
     Dielectric filter  100  is provided with screw  111  which is inserted into screw hole  110  provided in inner surface  101   a  of case  101 , and screw  105  which is inserted into screw hole  109  provided in inner surface  101   b  of case  101 . That is, in dielectric filter  100 , it is possible to appropriately fix each dielectric  102  using screw  111  provided separately from frequency adjusting screw  105 . 
     [Operation of Washer  104 ] 
     In  FIG. 4 , edge portion  106  ( FIG. 5A ) of washer  104  presses sheet metal  103 , which applies a pressure to dielectric  102  and causes tapered portion  108  to come into line-contact with the circumference of surface  102   a  of dielectric  102 , making it possible to reduce contact variations and stably fix dielectric  102 . When screw  111  is inserted, performing torque management can prevent more than necessary pressure from being applied to dielectric  102  and prevent damage to dielectric  102 . 
     Thus, dielectric filter  100  according to the present embodiment includes, on one side of washer  104 , recessed portion  105  provided with edge portion  106  formed around the circumference of the one side, bottom surface  107  ( FIG. 5A ) provided at a position one step recessed from edge portion  106 , and tapered portion  108  formed in a tapered shape between edge portion  106  and bottom surface  107 , wherein washer  104  is disposed so that recessed portion  105  is positioned opposite to surface  102   a  of dielectric  102  with sheet metal  103  interposed in between, and washer  104  is screwed by screw  111 . 
     In this way, edge portion  106  of washer  104  presses sheet metal  103 , tapered portion  108  ( FIG. 5A ) comes into line-contact with the circumference of surface  102   a  of dielectric  102 , a pressure is applied to dielectric  102 , and dielectric  102  can be stably fixed. Moreover, threaded engagement of screw  111  under torque management can prevent more than necessary pressure from being applied to dielectric  102  to prevent damage to dielectric  102 . As a result, even when there is a variation in size of components, it is possible to stably fix dielectric  102  without damage. 
     Note that sheet metal  103  is not essential in stably fixing dielectric  102 . 
     Other Embodiments 
     The configuration shown in  FIG. 4  has been described in the present embodiment, but the present invention is not limited to this. Hereinafter, configurations  1  to  4  other than the configuration described above will be described using  FIG. 6  to  FIG. 9 . 
       FIG. 6  is a cross-sectional view illustrating configuration  1 , which is another configuration of the dielectric filter according to the embodiment of the present invention. Sheet metal  201  is provided with recessed portion  202  having a size corresponding to the outer shape of surface  102   a  of dielectric  102  at a position overlapping with surface  102   a  of dielectric  102 . When sheet metal  201  is attached to case  101  and fixed to case  101  (not shown herein), recessed portion  202  provided in sheet metal  201  is fitted to surface  102   a  of dielectric  102 , which causes sheet metal  201  provided with recessed portion  202  to serve as a position regulating member in the d 2  direction of dielectric  102 . Washer  203  (flat washer) is disposed on surface  102   a  of dielectric  102  with sheet metal  201  interposed in between. 
       FIG. 7  is a cross-sectional view illustrating configuration  2 , which is another configuration of the dielectric filter according to the embodiment of the present invention. The length of dielectric  301  used here is greater than the height of the side wall of case  10  (not shown herein) so that, when screw  111  is inserted, a pressure is applied from dielectric  301 . 
       FIG. 8  is a cross-sectional view illustrating configuration  3 , which is another configuration of the dielectric filter according to the embodiment of the present invention. No edge portion is provided in recessed portion  402  of washer  401  and tapered portion  403  is formed on bottom surface  107  from the circumference of washer  401 . Washer  401  having such a shape is disposed on surface  102   a  (not shown herein) of dielectric  102  with sheet metal  401  interposed in between, screw  111 , inserted into screw hole  110 , is turned by a predetermined amount to press washer  401 , tapered portion  403  of washer  401  thereby penetrates sheet metal  103  causing tapered portion  403  to come into line-contact with the circumference of surface  102   a  of dielectric  102 . 
       FIG. 9  is a cross-sectional view illustrating configuration  4 , which is another configuration of the dielectric filter according to the embodiment of the present invention. Washer  501  has a planar shape including surface  501   a  facing surface  102   a  (not shown herein) of dielectric  102  and surface  501   b  opposite to surface  501   a . Surface  501   a  of washer  501  is provided with recessed portion  503  including edge portion  502  that contacts (overlaps with) the circumference of dielectric  102  (surface  102   a ) via sheet metal  103  and bottom surface  503  provided at a position recessed by a predetermined thickness from edge portion  502  (circumference of surface  501   a ) in the direction of surface  501   b . In the resonator, a current flows over the side face of dielectric  102 , so that, when current loss is taken into consideration, the angle formed by the side face of dielectric  102  and surface  501   a  of washer  501  is preferably a right angle. In other words, since no current flows through the inside of dielectric  102 , recessed portion  503  may be formed in the portion of dielectric  102  other than the circumference of dielectric  102 , without surface  501  of washer  501  being brought into contact via sheet metal  103 . 
     A case has been described in the above embodiment where the hollow part penetrates the portion between surface  102   a  and surface  102   b  of dielectric  102  in  FIG. 3 , but the present invention is not limited to this configuration. For example, dielectric  102  may also have a recessed portion open toward inner surface  101   b  of case  10  (not shown). In this case, frequency screw  105  is inserted into screw hole  109  and thereby protrudes from inner surface  101   b  of case  10  toward the recessed portion of dielectric  102 . 
     A case has been described in the above embodiment where a screw is used as the pressing member. However, the pressing member is not limited to a screw, and any member may be used as long as the member can press the intermediate member in a direction from inner surface  101   a  of case  101  toward inner surface  101   b . For example, a spring may be used as the pressing member instead of a screw. 
     The disclosure of Japanese Patent Application No. 2012-179284, filed on Aug. 13, 2012, including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     The dielectric filter according to the present invention is applicable to a base station apparatus and the like in a mobile communication system, for example. 
     REFERENCE SIGNS LIST 
     
         
           100 ,  101  Case 
           102 ,  301  Dielectric 
           103 ,  201  Sheet metal 
           104 ,  203 ,  401 ,  501  Washer (intermediate member) 
           105  Frequency adjusting screw 
           106 ,  502  Edge portion 
           107  Bottom surface 
           108 ,  403  Tapered portion 
           11  Cover 
           109 ,  110  Screw hole 
           111  Screw (pressing member)