Abstract:
The present invention relates to a radio frequency filter having a cavity structure, comprising: a container which has a hollow inner portion and a cavity that is cut off from the outside, and a resonance element which is placed in the hollow inner portion of the container, wherein the container has a wrinkled structure for adjusting the intervals between a longitudinal front end surface of the resonance element and the inner surfaces of the container facing the longitudinal front end surface using external pressure. Thus, the invention can be further miniaturized and is lightweight, and the design of the invention enables frequency tuning without employing a coupling structure of a tuning screw and a fastening nut, thereby obtaining a convenient and simplified structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/KR2013/001518 filed on Feb. 26, 2013, which claims priority to Korean Application No. 10-2012-0019722 filed on Feb. 27, 2012 and Korean Application No. 10-2013-0006945 filed on Jan. 22, 2013, which applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a radio signal processing apparatus used in a radio communication system, and more particularly to a radio frequency filter having a cavity structure. 
       BACKGROUND ART 
       [0003]    A radio frequency filter having a cavity structure generally includes a plurality of accommodation spaces having a rectangular parallelepiped shape or the like, that is, a plurality of cavities through a metallic housing, and a dielectric resonance (DR) element or a resonance element having a metallic resonance rod is provided in the cavities to generate resonance of high frequency waves. In the radio frequency filter having the cavity structure, a cover for shielding an opened surface of the cavity structure is provided at an upper portion of the cavity structure, and a plurality of tuning screws and nuts for fixing the tuning screws are installed in the cover as a tuning structure for tuning filtering characteristics of the radio frequency filter. An example of a radio frequency filter having a cavity structure is disclosed in Korean Application Publication No. 10-2004-100084 (entitled “Radio Frequency Filter” and published on Dec. 2, 2004; inventors: Jonggyu Park, Sangsik Park, and Seungtaek Jeong) filed by the present applicant. 
         [0004]    The radio frequency filter having a cavity structure is used for processing of a radio signals transmitted and received in a radio communication system, and it is applied to a base station or a relay in a mobile communication system. 
         [0005]    Meanwhile, in the base station or the relay of the mobile communication system, the base station body apparatuses are installed on the ground, as compared with antenna apparatuses (generally, having a large volume and a heavy weight) installed at a column located at a high place above the ground, and the antenna apparatus and the body apparatuses are currently connected through cables. However, the installation method causes a loss problem due to connections of cables between the antenna apparatus and the body apparatuses and an installation space problem of the body apparatus. Accordingly, as the equipment has been gradually become lightweight and miniaturized recently, the body apparatuses (or at least some modules) are installed in a column for installation of antenna apparatuses to be connected to the antenna apparatus or to be included in the antenna apparatus. 
         [0006]    Thus, when a radio frequency filter is applied to a base station or a relay of a mobile communication system, being small-scale and lightweight are more important considerations. 
         [0007]    However, because a radio frequency filter having a cavity structure includes a resonance element in a housing and basically should have a coupling structure between a cover and a housing, there is a limit how small-scale and lightweight it can be. Further, the coupling structure for a plurality of tuning screws and fixing nuts acts as an important restriction in how lightweight and small-scale of a radio frequency filter is. 
       SUMMARY 
       [0008]    Therefore, the present invention has been made in view of the above-mentioned problems, and an aspect of the present invention is a radio frequency filter having a cavity structure that is both small-scale and a lightweight. 
         [0009]    The present invention also provides a radio frequency filter having a cavity structure which can be easily manufactured and has a simplified structure. 
         [0010]    The present invention also provides a radio frequency filter having a cavity structure by which frequency turning can be allowed without employing a coupling structure for tuning screws and fixing nuts. 
         [0011]    In accordance with an aspect of the present invention, there is provided a radio frequency filter including: a box having a hollow interior and having a cavity blocked from the outside; and a resonance element located in the interior hollow of the box, wherein the box has a wrinkle structure for adjusting the spacing between a lengthwise tip end surface of the resonance element and an inner surface of the box facing the tip end surface of the resonance element. 
         [0012]    The box includes a first case in which the resonance element is located and a second case covering the first case, and the first and second cases are formed through pressing by using one mold each. 
         [0013]    According to the present invention, a radio frequency filter having a cavity structure can be both small-scale and a lightweight, can allow frequency tuning without employing a coupling structure for tuning screws and fixing nuts, and can have a simplified structure. 
         [0014]    Accordingly, costs of the radio frequency filter can be reduced due to a simple manufacturing process thereof, and the radio frequency filter can be easily installed in a station such as a base station due to it being small-scale and lightweight. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is an exploded perspective view of a radio frequency filter having a cavity structure according to a first embodiment of the present invention; 
           [0016]      FIG. 2  is a perspective view showing a coupled state of  FIG. 1 ; 
           [0017]      FIG. 3  is a cutaway perspective view taken along line A-A′ of  FIG. 2 ; 
           [0018]      FIG. 4  is a cutaway sectional view taken along line A-A′ of  FIG. 2 ; 
           [0019]      FIG. 5  is an exploded perspective view of a radio frequency filter having a cavity structure according to a second embodiment of the present invention; 
           [0020]      FIG. 6  is a cutaway perspective view taken along line A-A′ of  FIG. 5 ; 
           [0021]      FIG. 7  is an exploded perspective view of a radio frequency filter having a cavity structure according to a third embodiment of the present invention; 
           [0022]      FIG. 8  is a cutaway perspective view taken along line A-A′ of  FIG. 7 ; 
           [0023]      FIG. 9  is an exploded perspective view of a radio frequency filter having a cavity structure according to a fourth embodiment of the present invention; 
           [0024]      FIG. 10  is a perspective view showing a coupled state of  FIG. 9 ; 
           [0025]      FIG. 11  is a cutaway perspective view taken along line A-A′ of  FIG. 10 ; 
           [0026]      FIGS. 12 to 15  are views showing modifications of the present invention; 
           [0027]      FIG. 16  is a perspective view of an upper case of a radio frequency filter having a cavity structure according to a fifth embodiment of the present invention; 
           [0028]      FIG. 17  is a cutaway sectional view taken along line A-A′ of  FIG. 16 ; 
           [0029]      FIG. 18  is a diagram of a frequency tuning apparatus for the radio frequency filter according to the fifth embodiment of  FIG. 16 ; 
           [0030]      FIG. 19  is a perspective view of an upper case of a radio frequency filter having a cavity structure according to a sixth embodiment of the present invention; 
           [0031]      FIG. 20  is a cutaway sectional view taken along line A-A′ of  FIG. 19 ; 
           [0032]      FIG. 21  is a perspective view of an upper case of a radio frequency filter having a cavity structure according to a seventh embodiment of the present invention; 
           [0033]      FIG. 22  is a cutaway sectional view taken along line A-A′ of  FIG. 21 ; 
           [0034]      FIG. 23  is a perspective view of an upper case of a radio frequency filter having a cavity structure according to an eighth embodiment of the present invention; 
           [0035]      FIG. 24  is a cutaway sectional view taken along line A-A′ of  FIG. 23 ; 
           [0036]      FIG. 25  is a perspective view of an upper case of a radio frequency filter having a cavity structure according to a ninth embodiment of the present invention; and 
           [0037]      FIG. 26  is a cutaway sectional view taken along line A-A′ of  FIG. 25 . 
       
    
    
     DETAILED DESCRIPTION 
       [0038]    Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
         [0039]      FIG. 1  is an exploded perspective view of a radio frequency filter having a cavity structure according to a first embodiment of the present invention.  FIG. 2  is a perspective view showing a coupled state of  FIG. 1 .  FIG. 3  is a cutaway perspective view taken along line A-A′ of  FIG. 2 .  FIG. 4  is a cutaway sectional view taken along line A-A′ of  FIG. 2 . Referring to  FIGS. 1 to 4 , in a fashion similar to the related art, the radio frequency filter having a cavity structure according to the first embodiment of the present invention has a box of which an interior is hollow and having a cavity blocked from the outside, and a resonance element is provided in the hollow of the interior of the box. The box may include a first case, in which the resonance element is located, and a second case covering the first case. That is, an upper case  10  of the box corresponding to an upper side of the box with respect to a preset border surface (that is, a joint surface) of the entire case forming the cavity is the second case, and a lower case  20  corresponding to a lower side of the box with respect to the border surface of the entire case is the second case. The upper and lower cases  10  and  20  are jointed to each other on the border surface through soldering or welding. 
         [0040]    In the example of  FIGS. 1 to 4 , it is shown that the upper case  10  is plate-shaped to form an upper surface of the box when the entire filter structure is considered and functions as a cover, and the lower case  20  forms a lower surface and a side surface in the entire filter structure. Although  FIGS. 1 to 4  show that the planar structure of the cavity is circular as a whole and the planar structures of the upper and lower cases  10  and  20  are circular accordingly, it is apparent that the planar structures of the upper and lower cases  10  and  20  may be formed in various forms such as a tetragonal shape. 
         [0041]    The lower case  20  protrudes upwards toward the interior of the cavity at the center of the lower surface thereof such that an interior of the protrusion is empty and the pocket-shaped protrusion  202  of which an entrance faces the outside of the entire case is integrally formed with the remaining parts seamlessly—that is, with no separated joint surface. The protrusion  202  functions as a resonance element in the radio frequency filter. The lower case  20  having the protrusion  202  may be formed, for example, through pressing by using a plate-shaped mold formed of aluminum or magnesium (including an alloy thereof), and in particular, may be formed by using a deep drawing press to form the protrusion  202  having a relatively large depth. Of course, the size of the protrusion  202  is properly designed in consideration of a frequency such that the protrusion  202  may act as a resonance element. A through-hole (not shown) is further formed at a predetermined portion of the lower case  20  in consideration of the location of the protrusion  202  to connect an input/output terminal to the lower case  20 . 
         [0042]    Like the lower case  20 , the upper case  10  may be formed by pressing by using a plate-shaped mold formed of aluminum or magnesium (including an alloy thereof). During the pressing, a wrinkle structure  102  for adjusting a spacing between a lengthwise tip end surface of the protrusion  202  and an inner surface of the box facing the tip end surface of the protrusion  202  (that is, an inner surface of the upper case) with an external pressure is formed at a portion of the upper case  10  corresponding to the protrusion  202  acting as the resonance element of the lower case  20 . The wrinkle structure  102  is formed such that one or more curved surfaces protruding upwards and downwards are formed along a closed loop (for example, along a circle). As clearly shown in  FIG. 4 , the wrinkle structure  102  is formed such that a cutaway surface of the upper case  10  is zigzagged. 
         [0043]    The wrinkle structure  102  is adapted to replace a coupling structure of a tuning screw and a fixing nut according to the related art, and in the embodiment of the present invention, the wrinkle structure  102  is pressed from the upper side such that the wrinkled portion is spread out, so that a distance between the wrinkle structure band an upper end of the protrusion  202  of the lower case  20  may be narrowed until the filtering characteristics are optimized or the reference value is satisfied while the filtering characteristics are monitored during tuning of the frequency.  FIG. 4A  exemplifies the wrinkle structure  102  in the initial manufacturing process, and  FIG. 4B  exemplifies that the wrinkle structure  102  is spread out through a frequency tuning operation. 
         [0044]    In this way, in the embodiment of the present invention, the frequency tuning structure may be formed by using the wrinkle structure  102 , and the wrinkle structure  102  is set to a material, a thickness, and a size such that it is not restored to an original state after being deformed according to the frequency tuning operation. The thickness of the wrinkle structure  102  may be set to be thinner than the thickness of the upper case  10 . 
         [0045]    In the radio frequency filter having a cavity structure according to the first embodiment of the present invention which is shown in  FIGS. 1 to 4 , because the upper case  10  having the wrinkle structure  102 , that is, a frequency tuning structure may be formed through a single pressing process and the lower case  20  having the protrusion  202  acting as a resonance element may be formed through a single pressing process, the radio frequency filter has a structure simpler than a structure employing a coupling structure of the tuning screw and the fixing nut according to the related art and can be manufactured promptly at low costs, and can be made smaller and lighter. In this case, because a tuning screw is not provided and a separate resonance element is not attached as compared with the related art, Passive Intermodulation Distortion (PIMD) characteristics due to the discontinuity of an inner surface forming the cavity can be improved. 
         [0046]    In particular, the radio frequency filter structure according to the embodiment of the present invention may be used in a small structure with a high output as compared with the tuning screw according to the related art. When the tuning screw is used, a spacing between the tuning screw and the resonance element should be maintained at 5 mm or longer, for example, if it is used for a high output of 50 W. This is because a capacitance is concentrated at an edge portion of the tuning screw, and thus a spark may occur as the spacing between the tuning screw and the resonance element becomes smaller. In contrast, because the present invention does not include such a tuning screw, spacing between an upper end of the resonance element and the upper case can be narrowed, and the radio frequency filter can be operated more stably at a high output as compared with the related art. 
         [0047]      FIG. 5  is an exploded perspective view of a radio frequency filter having a cavity structure, according to a second embodiment of the present invention.  FIG. 6  is a cutaway perspective view taken along line A-A′ of  FIG. 2 . The structure according to the second embodiment of the present invention shows an example in which a plurality of cavities, for example, six cavity structures are connected in multiple stages. The structure shown in  FIGS. 5 and 6  may be regarded as a structure in which three structures according to the first embodiment of the present invention shown in  FIGS. 1 to 4  are located in each of two rows to be sequentially connected to each other. 
         [0048]    Referring to  FIGS. 5 and 6 , in the structure according to the second embodiment of the present invention, a plurality of pocket-shaped protrusions  222  which protrude upwards toward a plurality of cavities at the centers thereof corresponding to the cavities have an empty interior, and having an entrance facing the outside of the entire case are formed in the lower case  22  without a seam with the remaining parts to act as resonance elements. Of course, the lower case  22  having the plurality of protrusions  222  is formed through a single pressing process by using a plate-shaped mold. Then, in the lower case  22 , in order that the cavity structures have a sequential coupling structure, a coupling window  224  which is a connection passage structure is formed between the cavity structures having a sequential connection structure. Referring to  FIGS. 5 and 6 , the coupling window  224  may be formed such that a portion of the coupling window  224  is removed to a preset size at a portion corresponding to the partitions between the cavities. 
         [0049]    A plurality of wrinkle structures  122  in which one or more curved surface protruding upwards and downwards is formed along a closed loop (for example, along a circle) at portions corresponding to the plurality of protrusions  222  of the lower case  22  are formed in the upper case  12  to be used for frequency tuning. Of course, the upper case  12  having the plurality of wrinkle structures  122  are formed through a single pressing process. 
         [0050]    Conductive pin introducing holes  1222  of a fine size are formed at locations of the upper case  12  corresponding to the plurality of protrusions  222  of the lower case  22 , and the conductive pin introducing holes  1222  are used to introduce conductive pins for short-circuiting the upper case  12  and the protrusions  222  of the lower case  22  during a frequency tuning operation. In more detail, the frequency tuning operation may be sequentially individually performed for the resonance elements (that is, protrusions) of the cavity structures according to the frequency tuning method, and in this case, it is necessary to electrically short-circuit the resonance elements in the remaining cavity structures other than the cavity structure on which a tuning operation is currently performed. Accordingly, the resonance element (protrusion) of the cavity structure can be short-circuited by introducing the conductive pins into the plurality of conductive pin introducing holes  1222 . 
         [0051]    Meanwhile, in  FIGS. 5 and 6 , an input terminal  52  and an output terminal  54  of the radio frequency filter are attached through the holes  22  of the lower case  22  to be connected to the cavity structures of an input end and an output end. 
         [0052]      FIG. 7  is an exploded perspective view of a radio frequency filter having a cavity structure according to a third embodiment of the present invention.  FIG. 8  is a cutaway perspective view taken along line A-A′ of  FIG. 7 . Referring to  FIGS. 7  and  8 , although the entire external appearance of the structure according to the third embodiment of the present invention is similar to the structure of the first embodiment shown in  FIGS. 1 to 4 , the upper case  14  includes an upper surface and a side surface to have a pocket shape—taking into consideration the entire filter structure and the lower case  24  form only a surface corresponding to the lower surface of the entire filter structure. Of course, even in the structure according to the fourth embodiment of the present invention, a protrusion  242  is formed in the lower case  24  and a wrinkle structure  142  is formed in the upper case  14 . 
         [0053]    In the structure of the third embodiment shown in  FIGS. 7 and 8 , a border surface (joint surface) between the upper case  14  and the lower case  24  is set differently as compared with the structure of the first embodiment. The border surface may be properly set at any location on a side surface of the entire structure of the radio frequency filter, and accordingly, the upper case  14  and the lower case  24  may be formed. 
         [0054]      FIG. 9  is an exploded perspective view of a radio frequency filter having a cavity structure according to a fourth embodiment of the present invention.  FIG. 10  is a perspective view showing a coupled state of  FIG. 9 .  FIG. 11  is a cutaway perspective view taken along line A-A′ of  FIG. 10 . The structure, according to the fourth embodiment of the present invention, shows an example in which a plurality of cavities, for example, six cavity structures are connected in multiple stages. The structure shown in  FIGS. 9 and 11  may be regarded as a structure in which three structures according to the third embodiment of the present invention shown in  FIGS. 7 to 9  are located in two rows to be sequentially connected to each other. 
         [0055]    Referring to  FIGS. 9 to 11 , in the structure according to the fourth embodiment of the present invention, a plurality of protrusions  262  corresponding to a plurality of cavity structures are formed in the substantially plate-shaped lower case  26 , and wrinkle structures  162  are formed at portions of the upper case  16  corresponding to a plurality of protrusions  262  of the lower case  26  in the upper case  16  in which a plurality of pockets corresponding to the cavity structures are connected. Then, in the upper case  16 , in order that the cavity structures have a sequential coupling structure, a coupling window  264  which is a connection passage structure is formed between the cavity structures having a sequential connection structure. Conductive pin introducing holes  1622  are formed at locations of the upper case  16  corresponding to the plurality of protrusions  262  of the lower case  26 . 
         [0056]    As described above, a radio frequency filter having a cavity structure according to a plurality of embodiments of the present invention may be provided, and various embodiments or modifications may be additionally made. 
         [0057]    For example, although it is shown that the wrinkle structure is formed in the upper case, the wrinkle structure may be omitted when the filter can be manufactured with almost no processing tolerance through a precise process or when the filter does not require precise frequency tuning. 
         [0058]    As in the embodiment shown in  FIG. 5 , although it has been described that conductive pin introducing holes for short-circuiting the upper case and the protrusions of the lower case are formed at locations of the upper case corresponding to the protrusions of the lower case for a frequency tuning operation in the filter structure having a plurality of cavities, a structure in which holes having this purpose are formed at upper ends of the protrusions of the lower case may be further provided. 
         [0059]    As in the embodiment shown in  FIG. 5 , in the filter structure having a plurality of cavities, a wrinkle structure similar to the tuning structure for frequency tuning may be further formed at locations of the upper case corresponding to the coupling window of the lower case to employ a structure for coupling tuning. 
         [0060]    Although it has been described that both the upper case and the lower case are formed of aluminum or magnesium, they may be formed of various materials, and in particular, the upper case and the lower case may be formed of the same material or may be formed of different materials. 
         [0061]    As shown in  FIG. 5 , in particular, when the upper case is formed of a thin plate, the upper case may be formed of plastic. Of course, the upper case or the lower case may be made by plastic in a form other than a thin plate. 
         [0062]    Although it has been described that the wrinkle structure formed in the upper case is formed at a location corresponding to the protrusions of the lower case, for example, is formed at a central planar portion, the wrinkle structure  104  may be formed at a peripheral planar portion as shown in  FIG. 12 . That is, it can be seen that the size of the circular locus appearing due to the wrinkle structure  104  shown in  FIG. 12  is larger than that of the other embodiments. 
         [0063]    Although it has been described that the wrinkle structure is formed in the upper case, it may be formed on a side surface of the protrusion of the lower case acting as a resonance element as shown in  FIG. 13 . As shown in  FIG. 14 , a structure providing a jabara-shaped wrinkle  206  and  106  may be employed at a box surface of the lower case facing a widthwise tip end of the protrusion acting as a resonance element—that is, at a portion corresponding to a side surface of the entire filter structure. 
         [0064]    Although it has been described that both the upper case and the lower case of the present invention are formed through a pressing operation, the lower case may be realized without a wrinkle structure according to the related art and only the upper case having a wrinkle structure according to the present invention may be advantageous to the small-scale and lightweight design of the product. 
         [0065]    Referring to  FIG. 15 , in another embodiment of the present invention, a protruding member  1108  having a proper shape may be further formed at a location of the upper case having a wrinkle structure. The protruding member  1108  may be formed at the same time when the upper case is pressed, or may be separately manufactured and attached later through laser welding. The protruding member  1108  is to be pulled on directly or by connecting a separate ring to a catching structure such as a hole, which may be formed in the protruding member  1108 , and the wrinkle structure pressed and spread out downwards may return to an original stage (to a degree) during frequency tuning to be more useful or be retuned during the frequency tuning operation. 
         [0066]      FIG. 16  is a perspective view of the upper case (that is, the second case) acting as a cover of the radio frequency filter having a cavity structure according to the fifth embodiment of the present invention.  FIG. 17  is a cutaway sectional view taken along line A-A′ of  FIG. 16 . In the fifth embodiment shown in  FIGS. 16 and 17 , the lower case is omitted for convenience of description. As in the second embodiment shown in  FIG. 5 , in the fifth embodiment shown in  FIGS. 16 and 17 , a six-cavity structure, for example, a structure in which two groups of three cavities are sequentially connected in two rows is provided and the upper case  11  has a structure corresponding to the six-cavity structure. The lower case (not shown) may have a structure similar to the structure of the second embodiment shown in  FIG. 5 , and a structure in which a separately manufactured resonance element is installed may be provided as a general structure according to the related art. In this situation, the upper case  11  may be screw-coupled to the lower case, and a plurality of screw holes (not shown) for screw coupling may be formed at locations of the upper case  11 . 
         [0067]    Referring to  FIGS. 16 and 17 , as in the other embodiments of the present invention, where a plurality of wrinkle structures  112  in which one or more curved surfaces protruding upwards and downwards are formed along a closed loop (for example, along a circle) to be used for frequency tuning at portions of the upper case  11  acting as a cover in the radio frequency filter according to the fifth embodiment of the present invention, the portions of the upper case  11  corresponding to a plurality of resonance elements  21  (or protrusions) are formed or installed in the lower case. 
         [0068]    However, unlike the other embodiments in which the side surface shapes of the curved surfaces protruding upwards and downward have a triangular curved shape, the wrinkle structure  112  of the fifth embodiment of the present invention has a rectangular curved structure. As an example, in order to form a rectangular curved structure, a plurality of substantially circular recesses  112   a  and  112   b  are alternately formed on an upper surface and a lower surface of the upper case  11  so as not to meet each other. 
         [0069]    As in the other embodiments, the upper case  11  may be manufactured through a single pressing process at the same time when the wrinkle structure  112  is formed. In addition, it may be more efficient to manufacture the wrinkle structure  112  by forming the recesses  112   a  and  112   b  through cutting after the plate-shaped upper case  11  is manufactured according to the size of the radio frequency filter. 
         [0070]    Referring to  FIGS. 16 and 17 , in the fifth embodiment of the present invention, at least one depression  114  recessed toward the interior hollow may be formed near the wrinkle structure  112  of the upper case  11 . 
         [0071]    The depression  114  is for auxiliary or additional frequency tuning, and a dot peen structure  1142  is formed in the depression  114  through stamping or pressing by a stamping pin  502  of external stamping equipment during an auxiliary frequency tuning operation. As a result, the dot peen structure  1142  performs an auxiliary frequency tuning operation by narrowing a distance between the lower surface of the depression  114  and the resonance element  21  (also, by changing the volume of the interior hollow). 
         [0072]    Referring to  FIG. 18 , in the entire configuration of the frequency tuning apparatus, the radio frequency filter  1  according to the fifth embodiment of the present invention which is an object for frequency tuning is positioned on a shelf of the stamping equipment  5 , which includes a stamping pin  502 . The stamping equipment  5  may include a general dot peen-marking machine. The operation characteristics of the radio frequency filter  1  is measured by measurement equipment  2 , and accordingly, the measurement equipment  2  is connected to the radio frequency filter  1  to provide an input signal of a preset frequency to the radio frequency filter  1  and receive an output of the radio frequency filter  1 . The operation characteristics of the radio frequency filter  1  measured by the measurement equipment  2  are provided to control equipment  3 , which can be recognized by a PC. The control equipment  3  controls an operation of the stamping equipment  5  until the filtering characteristics are optimized or a reference value is satisfied (while monitoring operation characteristics of the radio frequency filter  1 ), and the stamping equipment  5  forms a predetermined number of dot peen structures  1142  having a predetermined shape on the recessed surface of a convexo-concave structure  114  of the radio frequency filter  1 . 
         [0073]    A plurality of dot peen structures  1142  may be formed in the depression  114 . The thickness and width of the depression  114  are properly set so as not to be deformed even by a stress during a frequency tuning operation during which the dot peen structure  1142  is formed. A dot peen structure  1142  representing a different variable amount may be formed even when an operation is performed by the same stamping equipment  5  according to the differences of the widths, thicknesses, or shapes of the depression  114 . The detailed structure of the depression  114  may be properly designed according to the feature or condition required by the radio frequency filter  1 . 
         [0074]      FIG. 19  is a perspective view of an upper case of a radio frequency filter having a cavity structure according to a sixth embodiment of the present invention.  FIG. 20  is a cutaway sectional view taken along line A-A′ of  FIG. 19 . In the sixth embodiment shown in  FIGS. 19 and 20 , the lower case is omitted for convenience of description. The lower case (not shown) may have a structure similar to the structure of the second embodiment shown in  FIG. 5 , and a structure in which a separately manufactured resonance element is installed may be provided as in a general structure according to the related art. 
         [0075]    Referring to  FIGS. 19 and 20 , as in the other embodiments, a wrinkle structure  132  is formed at portions of the upper case  13  acting as a cover in the radio frequency filter according to the sixth embodiment of the present invention, the portions of the upper case  13  corresponding to a plurality of resonance elements  21  (or protrusions) are formed or installed in the lower case, and a plurality of recesses  132   a  and  132   b  are formed on an upper surface of the wrinkle structure  132  in a closed loop form (for example, a circle) while a lower surface of the plate-shaped upper case  13  is not deformed. 
         [0076]    The structure shown in  FIGS. 19 and 20  requires a rather stronger pressing pressure as compared with the other embodiments when the wrinkle structure  132  is pressed during a frequency tuning operation, and one or more additional connection recesses  132   c  connecting the plurality of circular recesses  132   a  and  132   b  may be further formed. 
         [0077]    As in the other embodiments, the upper case  13  may be manufactured through a single pressing operation at the same time when the wrinkle structure  132  is formed, and it may be manufactured by forming the recesses  132   a,    132   b,  and  132   c  through cutting after the upper case  13  is manufactured. 
         [0078]      FIG. 21  is a perspective view of an upper case of a radio frequency filter having a cavity structure according to a seventh embodiment of the present invention.  FIG. 22  is a cutaway sectional view taken along line A-A′ when the pressed portion of  FIG. 21  is pressed in an arrow direction. The lower case is not shown for convenience of description. Referring to  FIGS. 21 and 22 , in the radio frequency filter according to the seventh embodiment of the present invention, the wrinkle structure of the other embodiments is not provided in the upper case  15 , but press portions  152  of a preset shape (for example, a circle) are formed at portions of the upper case corresponding to the plurality of resonance elements  21  (or protrusions) formed or installed in the lower case. 
         [0079]    Almost all the contours of the press portions  152  are formed by one or more slots  152   a  and  152   b  to form an entire shape. One or more connecting points a and b (having no slots) of the contours are connected to other portions of the upper case to support the press portions  152 . That is, the press portions  512  are surrounded by the slots  152   a  and  152   b  and the connecting points a and b. 
         [0080]    Referring to  FIGS. 21 and 22 , the press portions  152  are formed in a circular shape having a dual structure in which three arc-shaped slots, denoted by reference numeral  152   a,  form a circle while the connecting point a is interposed therebetween; and three arc-shaped slots, denoted by reference numeral  152   b,  form a circle while the connecting point b is interposed therebetween. In another embodiment of the present invention, it is apparent that the press portions do not have a dual circular shape but have one circular structure or a triple circular shape. 
         [0081]    In this structure, as shown in  FIG. 22 , if the press portions  152  are pressed during a frequency tuning operation, the press portions  152  are introduced into the resonance element  21  of the lower case by extending or bending the connecting points a and b, and a frequency tuning operation is performed by adjusting the distance between the press portions  152  and the resonance element  21 . 
         [0082]    Although a radio signal may be leaked through the slots when the slots are formed in the upper case of the radio frequency filter, it may be considered that a radio frequency filter is employed in an apparatus which is not sensitive to a leakage of a signal. 
         [0083]      FIG. 23  is a perspective view of an upper case of a radio frequency filter having a cavity structure according to an eighth embodiment of the present invention.  FIG. 24  is a cutaway sectional view taken along line A-A′ when the press portion of  FIG. 23  is pressed in an arrow direction. The lower case is not shown for convenience of description. Referring to  FIGS. 23 and 24 , the radio frequency filter according to the eighth embodiment of the present invention includes a press portion  172  which is realized by a principle similar to the seventh embodiment disclosed in  FIGS. 21 and 22 , and the difference between the eighth embodiment and the seventh embodiment lies in the overall shape of the press portion  172 . 
         [0084]    In more detail, referring to  FIGS. 23 and 24 , as in the seventh embodiment, almost all the contour of the press portion  172  is formed by one or more slots  172   a  and  172   b  to form an entire shape. One or more connecting points a and b of the contour are connected to other portions of the upper case  17  to support the press portions  172 . The press portion  172  may have a substantially long bar shape, and the connecting points a and b may be formed at opposite ends of the bar shape. 
         [0085]    As shown in  FIG. 24 , if the press portion  172  is pressed during the frequency tuning operation in this structure, the connecting points a and b are extended and bent, and a central portion of the press portion  172  in the form of a bar is bent toward the resonance element  21  of the lower case for frequency tuning. 
         [0086]      FIG. 25  is a perspective view of an upper case of a radio frequency filter having a cavity structure according to a ninth embodiment of the present invention.  FIG. 26  is a cutaway sectional view taken along line A-A′ when the pressed portion of  FIG. 25  is pressed. Referring to  FIGS. 25 and 26 , the radio frequency filter according to the ninth embodiment of the present invention includes a press portion  192  which is realized by a principle similar to the seventh and eighth embodiments disclosed in  FIGS. 21 and 24 , and the difference between the ninth embodiment and the other embodiments lies in the overall shape of the press portion  192 . 
         [0087]    As in the seventh and eighth embodiments of the present invention, the contour of the press portion  192  is formed by one or two slots  192   a  to form a substantial U-shape. The press portion  192  is connected to another portion of the upper case  19  through the connecting point a of the contour where a slot  192   a  is not formed. 
         [0088]    As shown in  FIG. 26 , if the press portion  192  is pressed during the frequency tuning operation in this structure, the connecting points a and b are extended and bent, and one end of the press portion  192  in the form of a U shape is pushed and lowered toward the resonance element  21  of the lower case for frequency tuning. 
         [0089]    Although it is shown that one or two resonance elements  21  are formed at a particular location rather deviating from the center of the upper case facing the upper end of the resonance element  21 , the locations and number of the press portions  192  may be properly set according to the characteristics of the filter in  FIGS. 25 and 26 . 
         [0090]      FIGS. 25 and 26  show that the upper case  19  further includes a coupling tuning press portion  194  having a structure similar to that of the press portion  192 , and the coupling tuning press portion  194  is installed at a portion of the lower case which is a passage structure of the cavities. The coupling tuning press portion  194  performs coupling tuning in a way similar to the tuning method for frequency tuning. 
         [0091]    As shown in  FIGS. 16 to 26 , the fifth to ninth embodiments of the present invention may be formed, and at least one configuration of the embodiments may be applied to the other embodiments, including the first to fourth embodiments. For example, the depression shown in  FIG. 16  may be applied to the other embodiments. 
         [0092]    The press structure for coupling tuning shown in  FIG. 25  also may be applied to the other embodiments, and the press structures of the other embodiments also may be applied for coupling tuning. 
         [0093]    In addition, depending on certain situations, the structures according to the embodiments of the present invention may be applied to the radio frequency filter in which the cavity structures are connected by stages.