Abstract:
The present invention relates to a multimode resonator comprising: a housing provided with a cavity substantially corresponding to one accommodation space; a plurality of resonance arms arranged at preset intervals from each other in the cavity and generating resonance signals by complex mutual coupling; and a plurality of resonance legs for respectively supporting the plurality of resonance arms.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/KR2014/009887 filed on Oct. 21, 2014, the entire content of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a resonator configured to implement a radio frequency (RF) filter, and more particularly, to a multi-mode resonator that outputs resonant frequencies in multiple resonant modes. 
       BACKGROUND ART 
       [0003]    A radio frequency (RF) device such as an RF filter is typically configured using a connection structure of multiple resonators. Such a resonator is a circuit element that resonates at a specific frequency based on a combination of an inductor L and a capacitor C as an equivalent electronic circuit, and each resonator is structured such that a dielectric resonance (DR) element or metallic resonance element is installed inside a cavity such as a metallic cylinder or a rectangular parallelepiped, etc., surrounded by a conductor. Thus, each resonator allows existence of only an electromagnetic field of a unique frequency in a processing frequency band in the cavity, enabling microwave resonance. Generally, the resonator has a multi-stage structure including sequentially connected multiple resonance stages, each of which is formed for multiple cavities. 
         [0004]      FIG. 1  illustrates an example of a conventional 6-pole bandpass filter  10 . Referring to  FIG. 1 , in the conventional example, the bandpass filter  10  includes a housing  110  having, for example, six cavities sectioned by a predetermined interval or space inside hexahedral metal, and in each cavity, eight dielectric or metallic resonance elements  122  having a high quality factor (Q) values are fixed using a support. Input and output connectors  111  and  113  mounted on a side of the housing  110  and a cover  160  for shielding an open surface of the housing  110  are also provided in the bandpass filter  10 . Each cavity of the housing  110  is sectioned by a partition  130  having predetermined-size windows  131  through  135  formed therein to adjust the amount of coupling between resonators, and an inner surface of the housing  110  is silver-plated to stabilize electric performance and to maximize conductivity. A coupling screw  175  that is insertable into the windows  131 - 135  through the cover  160  or the housing  110  is also provided for fine adjustment of the amount of coupling. 
         [0005]    Each resonance element  122  is supported by the support provided erect on a bottom surface, and a tuning screw  170  for tuning a frequency is installed above each resonance element  122  in such a way to be inserted into the cavity through the cover  160  and thus, fine adjustment of a resonant frequency may be possible by frequency tuning with the tuning screw  170 . 
         [0006]    On a side of the housing  110  are provided the input and output connectors  111  and  113  which are connected to input and output feeding lines (not shown), respectively, in which the input feeding line delivers a signal input from the input connector to a resonance element on the first stage and the output feeding line delivers a signal input from a resonance element on the last stage to the output connector. 
         [0007]    An example of an RF filter having the above-described structure is disclosed in a Korean Patent Laid-Open Gazette No. 10-2004-100084 (entitled “Radio Frequency Filter”, published on Dec. 20, 2004, and invented by Jongkyu Park, Sangsik Park, and Seuntaek Chung) filed by the present applicant. 
         [0008]    However, in the conventional bandpass filter (or band rejection filter), to construct a filter having multiple poles, a coupling means for coupling multiple cavities with each resonance element  122  is inevitably needed. That is, in the conventional filter, one resonance element  122  implements only a single resonance mode, and thus to implement a multi-mode filter, a structure in which multiple resonators are connected is required. As a result, a significantly large space is needed for implementation of the multi-mode filter, increasing the size, weight, and manufacturing cost of the filter. 
         [0009]    As such, a filter having a multi-mode resonator structure is one of communication facilities that occupy large spaces, and research has been steadily and actively performed to reduce the size and weight of the filter. Moreover, in line with a recent trend where each base station has evolved into a small (or micro) cell to respond to high processing speed and improved quality in the recent mobile communication market, the small size and light weight of the filter are required more crucially. 
       SUMMARY 
       [0010]    Accordingly, the present disclosure provides a multi-mode resonator capable of interconnecting multiple identical-mode resonant frequencies. 
         [0011]    The present disclosure also provides a small-size multi-mode resonator. 
         [0012]    The present disclosure also provides a light-weight multi-mode resonator. 
         [0013]    The present disclosure also provides a multi-mode resonator contributing to manufacturing cost reduction. 
         [0014]    To achieve the foregoing objects, there is provided a multi-mode resonator including a housing provided with a cavity corresponding to a substantially single accommodation space, a plurality of resonance arms which are arranged with a predetermined interval therebetween in the cavity and generate a resonant signal by multiple coupling therebetween, and a plurality of resonance legs which support the plurality of resonance arms, respectively. 
         [0015]    The multi-mode resonator may further include a resonance rod installed in a center of the cavity. 
         [0016]    The multi-mode resonator may further include a tuning structure installed in a center of an entire arrangement structure of the plurality of resonance arms to electrically float. 
         [0017]    The multi-mode resonator may further include an input probe and an output probe which are connected to the plurality of resonance legs to exchange input and output signals with a pair of resonance arms among the plurality of resonance arms. 
         [0018]    The cavity may have a polyhedral shape. 
         [0019]    The plurality of resonance arms may be arranged with an equal interval therebetween. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The above and other aspects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0021]      FIG. 1  is a partial exploded perspective view of an example of a conventional 6-pole bandpass filter; 
           [0022]      FIG. 2  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a first embodiment of the present disclosure; 
           [0023]      FIGS. 3A through 3E  illustrate multi-mode resonance characteristics of the multi-mode resonator illustrated in  FIG. 2 ; 
           [0024]      FIG. 4  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 2 ; 
           [0025]      FIG. 5  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a second embodiment of the present disclosure; 
           [0026]      FIG. 6  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a third embodiment of the present disclosure; 
           [0027]      FIG. 7  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a fourth embodiment of the present disclosure; 
           [0028]      FIG. 8  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a fifth embodiment of the present disclosure; 
           [0029]      FIG. 9  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a sixth embodiment of the present disclosure; 
           [0030]      FIG. 10  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a seventh embodiment of the present disclosure; 
           [0031]      FIG. 11  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to an eighth embodiment of the present disclosure; 
           [0032]      FIG. 12  illustrates frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 11 ; 
           [0033]      FIG. 13  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a ninth embodiment of the present disclosure; 
           [0034]      FIGS. 14A through 14E  illustrate multi-mode resonance characteristics of the multi-mode resonator illustrated in  FIG. 13 ; 
           [0035]      FIG. 15  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a tenth embodiment of the present disclosure; 
           [0036]      FIGS. 16A through 16D  illustrate multi-mode resonance characteristics of the multi-mode resonator illustrated in  FIG. 15 ; 
           [0037]      FIG. 17  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to an eleventh embodiment of the present disclosure; 
           [0038]      FIGS. 18A through 18D  illustrate multi-mode resonance characteristics of the multi-mode resonator illustrated in  FIG. 17 ; 
           [0039]      FIG. 19  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twelfth embodiment of the present disclosure; 
           [0040]      FIGS. 20A through 20D  illustrate multi-mode resonance characteristics of the multi-mode resonator illustrated in  FIG. 19 ; 
           [0041]      FIG. 21  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a thirteenth embodiment of the present disclosure; 
           [0042]      FIG. 22  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 21 ; 
           [0043]      FIG. 23  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a fourteenth embodiment of the present disclosure; 
           [0044]      FIG. 24  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 23 ; 
           [0045]      FIG. 25  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a fifteenth embodiment of the present disclosure; 
           [0046]      FIG. 26  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 25 ; 
           [0047]      FIG. 27  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a sixteenth embodiment of the present disclosure; 
           [0048]      FIG. 28  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 27 ; 
           [0049]      FIG. 29  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a seventeenth embodiment of the present disclosure; 
           [0050]      FIG. 30  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 29 ; 
           [0051]      FIG. 31  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to an eighteenth embodiment of the present disclosure; 
           [0052]      FIG. 32  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 30 ; 
           [0053]      FIG. 33  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a nineteenth embodiment of the present disclosure; 
           [0054]      FIGS. 34A through 34D  illustrate multi-mode resonance characteristics of the multi-mode resonator illustrated in  FIG. 33 ; 
           [0055]      FIG. 35  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twentieth embodiment of the present disclosure; 
           [0056]      FIG. 36  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 35 ; 
           [0057]      FIG. 37  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twenty-first embodiment of the present disclosure; 
           [0058]      FIG. 38  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 37 ; 
           [0059]      FIG. 39  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twenty-second embodiment of the present disclosure; 
           [0060]      FIG. 40  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 39 ; 
           [0061]      FIG. 41  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twenty-third embodiment of the present disclosure; 
           [0062]      FIG. 42  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 41 ; 
           [0063]      FIG. 43  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twenty-fourth embodiment of the present disclosure; and 
           [0064]      FIG. 44  is a graph showing frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 43 . 
       
    
    
     DETAILED DESCRIPTION 
       [0065]    Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific details such as detailed elements, etc., will be provided, but they are merely provided to help the overall understanding of the present disclosure and it would be obvious to those of ordinary skill in the art that modifications or changes may be made to the specific details within the scope of the present disclosure. 
         [0066]    The present disclosure proposes a multi-resonance-mode filter that provides multiple resonance modes. Conventionally, it is general that to provide, for example, four resonance modes, four cavities and one resonance element in each of the cavities are required. However, the multi-resonance-mode filter according to the present disclosure may provide four resonance modes (quadruple modes) or five resonance modes (quintuple modes) in one cavity. 
         [0067]      FIG. 2  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a first embodiment of the present disclosure, in which (a) of  FIG. 2  shows a top plan structure, (b) of  FIG. 2  shows a side structure, and (c) of  FIG. 2  shows a perspective projection structure. The resonator illustrated in  FIG. 2  may include a cavity  200  having a space formed by a metallic housing (bottom cover) like a typical filter structure, and  FIG. 2  does not illustrate a structure of the metallic housing, input and output connectors formed on an outer portion of the housing, etc., for convenience of a description. 
         [0068]    Referring to  FIG. 2 , the multi-mode resonator according to the first embodiment of the present disclosure may include the cavity  200  in the shape of a rectangular box or in a shape similar thereto, which has a substantially single accommodation space inside a housing (not shown). However, such a structure of the cavity  200  may have various shapes such as a polyprism, a cylinder, and so forth, as well as the rectangular box. 
         [0069]    In the cavity  200  are provided a plurality of resonance arms arranged with a predetermined interval or space therebetween. The plurality of resonance arms may be made of a metallic material, and may be arranged with an equal interval therebetween. In this case, the plurality of resonance arms are arranged in pairs to face each other and the pairs of resonance arms may be arranged to cross each other. More specifically, as in the first embodiment illustrated in  FIG. 2 , in the cavity  200 , for example, resonance arms adjacent to each other are orthogonal to each other, and four resonance arms  211 ,  212 ,  213 , and  214  are individually installed in such a way to be separated from each other. The four resonance arms  211  through  214 , that is, first through fourth resonance arms  211  through  214  are arranged globally (planarly) in the shape of ‘+’, that is, a center of the entire arrangement structure of the four resonance arms  211  through  214  corresponds to a center of the cavity  200 . Each of the four resonance arms  211  through  214  has the shape of a rectangular parallelepiped bar that is longitudinally long. The four resonance arms  211  through  214  are fixedly installed by first through fourth resonance legs  221 ,  222 ,  223 , and  224  which extend from (or are fixedly installed on) a bottom surface of the cavity  200  (a bottom surface of the housing), and are formed of, for example, a metallic material, in a cylindrical shape. 
         [0070]    In the first embodiment illustrated in  FIG. 2 , a resonance rod  215  having a structure similar to a resonance element of a conventional filter structure is further installed in the center of the entire arrangement structure of the four resonance arms  211  through  214 , that is, in the center of the cavity  200 . The four resonance arms  211  through  214  and the resonance rod  215  are installed physically spaced apart from each other with a proper distance therebetween, such that signals therebetween may be complexly coupled with each other. The amount of signal coupling is adjusted based on adjustment of the distance. In such an entire structure of the four resonance arms  211  through  214 , the four resonance arms  211  through  214  are complexly coupled with each other unlike in the structure of the conventional resonator that provides sequential coupling. 
         [0071]    If the arrangement structure of the four resonance arms  211  through  214  and the resonance rod  215  is substituted into three axes, for example, x, y, and z axes, which are orthogonal to each other around the center of the cavity  200 , then the first resonance arm  211  and the third resonance arm  213  may be on the x axis, the second resonance arm  212  and the fourth resonance arm  214  may be on the y axis, and the resonance rod  215  may be on the z axis. 
         [0072]    Meanwhile, an input connector (not shown) and an output connector (not shown) may be formed on one pole of the x axis and one pole of the y axis, respectively, and an input probe  231  for connection with the input connector formed on one pole of the x axis and an output probe  232  for connection with the output connector formed on one pole of the y axis are provided, and the input probe  231  and the output probe  232  exchange input and output signals with one pair of resonance arms among the plurality of resonance arms  211  through  214 . In an example of  FIG. 2 , the input probe  231  and the output probe  232  are directly or indirectly connected with the third resonance leg  223  and the second resonance leg  222 , respectively, to deliver the input and output signals, thus exchanging the input and output signals with the third resonance arm  213  and the second resonance arm  212 . 
         [0073]    Multi-mode resonance characteristics of the resonator structured as described above are shown in  FIGS. 3A through 3E .  FIG. 3A  illustrates a magnetic field (or an electric field) of a first resonance mode formed by a total combination (coupling) of a resonance structure,  FIG. 3B  illustrates a magnetic field (or an electric field) of a second resonance mode where dominant resonance is formed along the y axis, for example, by the second resonance arm  212  and the fourth resonance arm  214 ,  FIG. 3C  illustrates a magnetic field (or an electric field) of a third resonance mode where dominant resonance is formed along the x axis, for example, by the first resonance arm  211  and the third resonance arm  213 ,  FIG. 3D  illustrates a magnetic field (or an electric field) of a fourth resonance mode formed by a total combination of the first through fourth resonance arms  211  through  214 , and  FIG. 3E  illustrates a magnetic field (or an electric field) of a fifth resonance mode where dominant resonance is formed along the z axis, for example, by the resonance rod  215 . In each of  FIGS. 3A through 3E , (a) shows E-field characteristics and (b) shows H-field characteristics. In  FIGS. 3A through 3E , a direction of each arrow indicates a direction of an electric field or a magnetic field in a position in each resonance arm, and a size of each arrow indicates an intensity or strength of the electric field or the magnetic field. 
         [0074]      FIG. 4  is a graph showing an example of frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 2 . Referring to  FIG. 4 , it can be seen that frequency filtering characteristics vary with five multi-mode characteristics shown in  FIGS. 3A through 3E . 
         [0075]    As such, the multi-mode resonator according to the first embodiment of the present disclosure implements the five resonance modes in one cavity  200 , and in this case, the multi-mode resonator structured according to the present disclosure has a quality factor (Q) value improved by about 30%-40% when compared to a general-structure transverse electric and magnetic (TEM) mode resonator having the same size or has a physical size reduced by about 30%-40% when compared to the general structure TEM mode resonator having the same Q value. 
         [0076]    Meanwhile, in the above-described structure according to the first embodiment of the present disclosure, a frequency of each resonance mode may be shifted and a resonance mode of a proper frequency may be set and adjusted by changing a shape, a length, and a width of the first through fourth resonance arms  211  through  214 , a length and a width of the first through fourth resonance legs  221  through  224 , a distance of the first through fourth resonance legs  221  through  224  with respect to the center of the cavity  200 , and a size and a height of the cavity  200 , and so forth. If necessary, only three or four resonance modes may be implemented. 
         [0077]      FIG. 5  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a second embodiment of the present disclosure, in which (a) of  FIG. 5  illustrates a top plan structure, (b) illustrates a side structure, and (c) illustrates a perspective projection structure. The resonator according to the second embodiment illustrated in  FIG. 5 , similarly with the structure according to the first embodiment illustrated in  FIG. 2 , may include a cavity  300  having a rectangular box shape or a shape similar thereto, four resonance ribs  311 ,  312 ,  313 , and  314  arranged to have an overall ‘+’ shape in the cavity  300 , are orthogonal to each other, and are individually installed to be separated from each other, first through fourth resonance legs  321 ,  322 ,  323 , and  324  that support the four resonance ribs  311 ,  312 ,  313 , and  314 , respectively, a resonance rod  315  installed in the center of the entire arrangement structure of the four resonance arms  311  through  314 , and an input robe  331  and an output probe  332  connected to the third resonance leg  323  and the second resonance leg  322 , respectively. 
         [0078]    In the resonator according to the second embodiment structured as described above, unlike the structure according to the first embodiment illustrated in  FIG. 2 , as indicated by A in  FIG. 5 , at least a part of corner portions of each of the four resonance arms  411  through  414  in a rectangular bar shape is cut by processing such as trimming, etc., and with this structure change, characteristics such as coupling intensity, etc., are adjusted. In the example illustrated in  FIG. 5 , four corners of corner portions of the four resonance arms  411  through  414  are cut. In this way, through a change such as a cut structure of a corner of a resonance arm through trimming, etc., the intensity of coupling between the resonance arms, generation of a notch, etc. may be adjusted. 
         [0079]      FIG. 6  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a third embodiment of the present disclosure, in which (a) of  FIG. 6  illustrates a top plan structure, (b) illustrates a side structure, and (c) illustrates a perspective projection structure. The resonator according to the third embodiment of the present disclosure illustrated in  FIG. 6 , like the structure according to the first embodiment illustrated in  FIG. 2 , may include a cavity  400 , four resonance arms  411 ,  412 ,  413 , and  414 , first through fourth resonance legs  421 ,  422 ,  423 , and  424 , and a resonance rod  415 . 
         [0080]    In the third embodiment of the present disclosure, unlike in the structure according to the first embodiment, an input connector (not shown) and an output connector (not shown) may be formed in both poles on the x axis, respectively, and an input probe  531  and an output probe  532  for connection with the input connector and the output connector formed in both poles on the x axis are directly and indirectly connected to the third resonance leg  423  and the first resonance leg  421 , respectively. With the structure according to the third embodiment illustrated in  FIG. 6 , five satisfactory resonance modes are formed. 
         [0081]      FIG. 7  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a fourth embodiment of the present disclosure, in which (a) of  FIG. 7  illustrates a top plan structure, (b) illustrates a side structure, and (c) illustrates a perspective projection structure. The resonator according to the fourth embodiment of the present disclosure illustrated in  FIG. 7 , like the structure according to the first embodiment illustrated in  FIG. 2 , may include a cavity  600 , four resonance arms  611 ,  612 ,  613 , and  614 , first through fourth resonance legs  621 ,  622 ,  623 , and  624 , a resonance rod  615 , and an input probe  631  and an output probe  632 . 
         [0082]    In the fourth embodiment according to the present disclosure, unlike in the structure according to the first embodiment, two corners of corner portions of the four resonance arms  611  through  614  are cut, and the four resonance arms  611  through  614  are arranged in the shape of X in the cavity  600  having a globally rectangular box shape. That is, the four arms may be arranged in positions rotated at 45 degrees when compared to the structure illustrated in  FIG. 2 . Thus, the input probe  631  and the output probe  632  are formed in the corner portions of the cavity  600 . 
         [0083]    Especially, in this case, the input probe  631  and the output probe  632  may directly deliver a signal to the third resonance arm  623  and the second resonance arm  622 , respectively, instead of delivering the signal to the resonance arms through the resonance legs as in the first embodiment illustrated in  FIG. 2 . 
         [0084]      FIG. 8  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a fifth embodiment of the present disclosure, in which (a) of  FIG. 8  illustrates a top plan structure, (b) illustrates a side structure, and (c) illustrates a perspective projection structure. The resonator according to the fifth embodiment of the present disclosure illustrated in  FIG. 8 , like the structure according to the first embodiment illustrated in  FIG. 2 , may include a cavity  700 , four resonance arms  711 ,  712 ,  713 , and  714 , first through fourth resonance legs  721 ,  722 ,  723 , and  724 , and an input probe  731  and an output probe  732 . 
         [0085]    However, the structure according to the fifth embodiment illustrated in  FIG. 8  is such that the resonance rod is removed from (that is, is not included in) the structure according to the first embodiment. This structure is suitable for implementation of four resonance modes. 
         [0086]      FIG. 9  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a sixth embodiment of the present disclosure, in which (a) of  FIG. 9  illustrates a top plan structure, (b) illustrates a side structure, and (c) illustrates a perspective projection structure. The resonator according to the sixth embodiment of the present disclosure illustrated in  FIG. 9 , mostly like the structure according to the fifth embodiment illustrated in  FIG. 8 , may include a cavity  800 , four resonance arms  811 ,  812 ,  813 , and  814 , first through fourth resonance legs  821 ,  822 ,  823 , and  824 , and an input probe  831  and an output probe  832 . 
         [0087]    In the sixth embodiment illustrated in  FIG. 9 , in addition to the structure according to the fifth embodiment illustrated in  FIG. 8 , a metallic tuning structure  841 , for example, in a cylindrical shape, is further installed to electrically float in the center of the entire structure of the four resonance arms  811  through  814  for signal coupling and coupling adjustment between corresponding resonance modes. 
         [0088]    The coupling structure  841  is fixed and supported by a support member (not shown) made of a material such as Al 2 O 3 , Teflon, etc., on an inner surface of the housing or cover or adjacent resonance arms in the cavity. 
         [0089]      FIG. 10  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a seventh embodiment of the present disclosure, in which (a) of  FIG. 10  illustrates a top plan structure, (b) illustrates a side structure, and (c) illustrates a perspective projection structure. The resonator according to the seventh embodiment of the present disclosure illustrated in  FIG. 10 , mostly like the structure according to the sixth embodiment illustrated in  FIG. 9 , may include a cavity  900 , four resonance arms  911 ,  912 ,  913 , and  914 , first through fourth resonance legs  921 ,  922 ,  923 , and  924 , an input probe  932  and an output probe  931 , and a tuning structure  941 . 
         [0090]    In the seventh embodiment illustrated in  FIG. 10 , unlike in the structure according to the sixth embodiment illustrated in  FIG. 9 , the four resonance arms  911 ,  912 ,  913 , and  914  are arranged in the shape of X in the cavity  900  having a globally rectangular box shape. In addition, the four resonance arms  911 ,  912 ,  913 , and  914  have a globally cylindrical shape, rather than the globally rectangular shape. 
         [0091]      FIG. 11  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to an eighth embodiment of the present disclosure, in which (a) of  FIG. 11  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the eighth embodiment of the present disclosure illustrated in  FIG. 11 , like the structure according to the fourth embodiment illustrated in  FIG. 7 , may include a cavity  1000 , four resonance arms  1011 ,  1012 ,  1013 , and  1014 , first through fourth resonance legs  1021 ,  1022 ,  1023 , and  1024 , and an input probe  1031  and an output probe  1032 . 
         [0092]    However, the structure according to the eighth embodiment illustrated in  FIG. 11  is such that the resonance rod is removed from (that is, is not included in) the structure according to the fourth embodiment illustrated in  FIG. 7 . This structure is suitable for implementation of four resonance modes. 
         [0093]      FIG. 12  is a graph showing an example of frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 11 . Referring to  FIG. 12 , it can be seen that frequency filtering characteristics vary with four multi-mode characteristics in the structure illustrated in  FIG. 11 . 
         [0094]      FIG. 13  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a ninth embodiment of the present disclosure, in which (a) of  FIG. 13  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the ninth embodiment of the present disclosure illustrated in  FIG. 13 , like the structure according to the first embodiment illustrated in  FIG. 2 , may include a cavity  1100 , four resonance arms  1111 ,  1112 ,  1113 , and  1114 , first through fourth resonance legs  1121 ,  1122 ,  1123 , and  1124 , and a resonance rod  1115 . 
         [0095]    In the ninth embodiment illustrated in  FIG. 13 , unlike in the structure according to the first embodiment illustrated in  FIG. 2 , the four resonance arms  1111 ,  1112 ,  1113 , and  1114  are arranged in the shape of X in the cavity  1100  having a globally rectangular box shape. That is, the four arms may be arranged in positions rotated at 45 degrees when compared to the structure illustrated in  FIG. 2 . Thus, an input probe and an output probe are formed in corner portions of the cavity  1100 . 
         [0096]    Multi-mode resonance characteristics of the resonator having the structure illustrated in  FIG. 13  are illustrated in  FIGS. 14A through 14E .  FIG. 14A  illustrates a magnetic field (or an electric field) of a first resonance mode formed by a total combination (coupling) of a resonance structure,  FIG. 14B  illustrates a magnetic field (or an electric field) of a second resonance mode formed by, for example, the second resonance arm  1112  and the fourth resonance arm  1114 ,  FIG. 14C  illustrates a magnetic field (or an electric field) of a third resonance mode formed by, for example, the first resonance arm  1111  and the third resonance arm  1113 ,  FIG. 14D  illustrates a magnetic field (or an electric field) of a fourth resonance mode formed by a total combination of the first through fourth resonance arms  1111  through  1114 , and  FIG. 14E  illustrates a magnetic field (or an electric field) of a fifth resonance mode formed by the resonance rod  1115 . In each of  FIGS. 14A through 14E , (a) shows E-field characteristics and (b) shows H-field characteristics. 
         [0097]      FIG. 15  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a tenth embodiment of the present disclosure, in which (a) of  FIG. 15  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the tenth embodiment of the present disclosure illustrated in  FIG. 15 , like the structure according to the ninth embodiment illustrated in  FIG. 13 , may include a cavity  1200 , four resonance arms  1211 ,  1212 ,  1213 , and  1214 , and first through fourth resonance legs  1221 ,  1222 ,  1223 , and  1224 . 
         [0098]    However, the structure according to the tenth embodiment illustrated in  FIG. 15  is such that the resonance rod is removed from (that is, is not included in) the structure according to the ninth embodiment illustrated in  FIG. 15 . This structure is suitable for implementation of four resonance modes. 
         [0099]    Main multi-mode resonance characteristics of the resonator having the structure illustrated in  FIG. 15  are as illustrated in  FIGS. 16A through 16D . In each of  FIGS. 16A through 16D , (a) shows E-field characteristics and (b) shows H-field characteristics. 
         [0100]      FIG. 17  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to an eleventh embodiment of the present disclosure, in which (a) of  FIG. 17  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the eleventh embodiment of the present disclosure illustrated in  FIG. 17 , like the structure according to the tenth embodiment illustrated in  FIG. 15 , may include a cavity  1300 , four resonance arms  1311 ,  1312 ,  1313 , and  1314 , and first through fourth resonance legs  1321 ,  1322 ,  1323 , and  1324 . 
         [0101]    In the structure according to the eleventh embodiment illustrated in  FIG. 17 , when compared to the structure according to the tenth embodiment illustrated in  FIG. 15 , the first through fourth legs  1321  through  1324  are installed to be spaced apart from each other as far as possible. That is, the first through fourth resonance legs  1321  through  1324  are installed in such a way to support the first through fourth resonance arms  1311  through  1314 , respectively, by being coupled with outer portions of the first through fourth resonance arms  1311  through  1314  with respect to the center of the cavity  1300 . 
         [0102]    In this way, when the first through fourth resonance legs  1321  through  1324  are installed spaced further apart from each other, a similar effect to when a diameter of the entire structure of the first through fourth resonance legs  1321  through  1324  increases may be generated, leading to adjustment of a processing frequency band. 
         [0103]    Main multi-mode resonance characteristics of the resonator having the structure illustrated in  FIG. 17  are as illustrated in  FIGS. 18A through 18D . In each of  FIGS. 18A through 18D , (a) shows E-field characteristics and (b) shows H-field characteristics. 
         [0104]      FIG. 19  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twelfth embodiment of the present disclosure, in which (a) of  FIG. 19  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the twelfth embodiment of the present disclosure illustrated in  FIG. 19 , like the structure according to the eleventh embodiment illustrated in  FIG. 17 , may include a cavity  1400 , four resonance arms  1411 ,  1412 ,  1413 , and  1414 , and first through fourth resonance legs  1421 ,  1422 ,  1423 , and  1424 . 
         [0105]    However, in the structure according to the twelfth embodiment illustrated in  FIG. 19 , unlike structures according to other various embodiments as well as the eleventh embodiment illustrated in  FIG. 17 , lengths of the first through fourth  1411  through  1414  are not the same as each other, but for example, a longitudinal length of any one pair of resonance arms among a plurality of resonance arms is set different from that of the other pair of resonance arms. Likewise, designing may be performed such that differences exist in diameters, lengths, and so forth of the resonance legs  1421  through  1424 . That is, for example, as illustrated in  FIG. 19 , the first resonance arm  1411  and the third resonance arm  1413  may be formed to have a relatively short length. The second resonance arm  1412  and the fourth resonance arm  1414  may be formed to have a relatively long length, such that end portions therebetween are closer to each other than in the first resonance arm  1411  and the third resonance arm  1413 . Intervals between facing ends of the first through fourth resonance arms  1411  through  1414  may be equal to each other. 
         [0106]    This structure is intended to change a transmission zero position, and in this case, the intensity and direction of the field coupled, for example, between the second resonance arm  1412  and the fourth resonance arm  1414  are changed, adjusting a notch point. 
         [0107]    Main multi-mode resonance characteristics of the resonator having the structure illustrated in  FIG. 19  are as illustrated in  FIGS. 20A through 20D . In each of  FIGS. 20A through 20D , (a) shows E-field characteristics and (b) shows H-field characteristics. 
         [0108]      FIG. 21  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a thirteenth embodiment of the present disclosure, in which (a) of  FIG. 21  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the thirteenth embodiment of the present disclosure illustrated in  FIG. 21 , like the structure according to the twelfth embodiment illustrated in  FIG. 19 , may include a cavity  1500 , four resonance arms  1511 ,  1512 ,  1513 , and  1514 , and first through fourth resonance legs  1521 ,  1522 ,  1523 , and  1524 . The first and third resonance arms  1511  and  1513  are formed to have a relatively short length, and the second and fourth resonance arms  1512  and  1514  are formed to have a relatively long length. In  FIG. 21 , an input probe  1531  and an output probe  1532  connected to the second resonance leg  1522  and the third resonance leg  1523 , respectively, are illustrated. 
         [0109]    In the thirteenth embodiment illustrated in  FIG. 21 , unlike in the twelfth embodiment illustrated in  FIG. 19 , the second resonance leg  1522  and the third resonance leg  1523  are formed to have a longer length than the first and fourth resonance legs  1521  and  1524 . Such a structure is intended to increase a capacitance component by reducing a distance between the second and third resonance arms  1512  and  1513 , supported by the second and third resonance legs  1522  and  1523 , respectively, and the top surface of the cavity  1500 . Thus, proper capacitor component adjustment is possible in an input side and an output side of the filter, connected to the input probe  1531  and the output probe  1532 . 
         [0110]    In the thirteenth embodiment, in a proper position as well as between the input side and the output side as in a position A or B, a partition or a tuning screw may be further installed. Thus, perturbation may occur between resonance arms, thereby adjusting a transmission zero position, notch generation, and so forth. 
         [0111]      FIG. 22  is a graph showing an example of frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 21 . Referring to  FIG. 22 , frequency filtering characteristics including a formed notch as well as four multi-mode characteristics can be seen. 
         [0112]      FIG. 23  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a fourteenth embodiment of the present disclosure, in which (a) of  FIG. 23  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the fourteenth embodiment of the present disclosure illustrated in  FIG. 23  is structured such that the structure according to the thirteenth embodiment illustrated in  FIG. 21  is formed dually. 
         [0113]    That is, a first resonator  16 - 1  and a second resonator  16 - 2 , each having the same structure as that of the resonator illustrated in  FIG. 23 , are formed, and an output side of the first resonator  16 - 1  and an input side of the second resonator  16 - 2  are coupled to each other by a coupling window  1640 . In the coupling window  1640 , a coupling structure  1642  is further installed in such a way to extend from bottom surfaces of cavities for facilitating coupling. 
         [0114]      FIG. 24  is a graph showing an example of frequency filtering characteristics of the multi-mode resonator illustrated in  FIG. 23 . Referring to  FIG. 24 , frequency filtering characteristics corresponding to an 8-stage filter can be seen. 
         [0115]      FIG. 25  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a fifteenth embodiment of the present disclosure, in which (a) of  FIG. 25  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the fifteenth embodiment of the present disclosure illustrated in  FIG. 25 , like the structure according to the thirteenth embodiment illustrated in  FIG. 21 , may include a cavity  1700 , four resonance arms  1711 ,  1712 ,  1713 , and  1714 , and first through fourth resonance legs  1721 ,  1722 ,  1723 , and  1724 . 
         [0116]    In the fifteenth embodiment, unlike in the thirteenth embodiment illustrated in  FIG. 21 , first through fourth resonance arms  1711  through  1714  are formed to have an equal length, and a metallic tuning structure  1741 , for example, in a cylindrical or disc shape, is further installed to electrically float in the center of the entire structure of the four resonance arms  1711  through  1714  for signal coupling and coupling adjustment between corresponding resonance modes. The coupling structure  1741  facilitates coupling between coupling resonance arms when compared to a case having no coupling structure, broadening the entire bandwidth of the filter. Frequency filtering characteristics of the resonator according to the fifteenth embodiment are as shown in  FIG. 26 . 
         [0117]      FIG. 27  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a sixteenth embodiment of the present disclosure, in which (a) of  FIG. 27  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the sixteenth embodiment of the present disclosure illustrated in  FIG. 27 , like the structure according to the fifteenth embodiment illustrated in  FIG. 25 , may include a cavity  1800 , four resonance arms  1811 ,  1812 ,  1813 , and  1814 , and first through fourth resonance legs  1821 ,  1822 ,  1823 , and  1824 . 
         [0118]    However, in the sixteenth embodiment illustrated in  FIG. 27 , unlike in the fifteenth embodiment illustrated in  FIG. 25 , in the center of the entire structure of the four resonance arms  1811  through  1814  is provided, in place of a tuning structure electrically floating, a tuning screw  1843  which is installed to pass through a cover, etc., from an upper end of a housing (not shown). By using the tuning screw  1843 , signal coupling between the four resonance arms  1711  through  1714 , coupling adjustment between corresponding resonance modes, and resonant frequency tuning may be performed. Frequency filtering characteristics of the resonator according to the sixteenth embodiment are as shown in  FIG. 28 . 
         [0119]      FIG. 29  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a seventeenth embodiment of the present disclosure, in which (a) of  FIG. 29  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the seventeenth embodiment of the present disclosure illustrated in  FIG. 29  is structured such that the structure according to the sixteenth embodiment illustrated in  FIG. 27  is formed dually. 
         [0120]    That is, the resonator according to the seventeenth embodiment illustrated in  FIG. 29  may include a first resonator  19 - 1  and a second resonator  19 - 2 , each having the same structure as that of the resonator illustrated in  FIG. 27 , and an output side of the first resonator  19 - 1  and an input side of the second resonator  19 - 2  are coupled to each other by a coupling window  1940 . In the coupling window  1940 , a coupling structure  1942  is further installed to facilitate coupling. Frequency filtering characteristics of the resonator according to the seventeenth embodiment are as shown in  FIG. 30 . 
         [0121]      FIG. 31  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to an eighteenth embodiment of the present disclosure, in which (a) of  FIG. 29  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the eighteenth embodiment of the present disclosure illustrated in  FIG. 31 , like the resonator according to the seventeenth embodiment illustrated in  FIG. 29 , is structured such that a first resonator  20 - 1  and a second resonator  20 - 2  are coupled to each other. 
         [0122]    However, the first resonator  20 - 1  has the same structure as the structure according to the thirteenth embodiment illustrated in  FIG. 21 , and the second resonator  20 - 2  has the same structure as the structure according to the sixteenth embodiment illustrated in  FIG. 27 . That is, the first resonator  20 - 1  and the second resonator  20 - 2  have different structures. As such, resonators having various structures according to the above-described embodiments, as well as an example of the structure illustrated in the current eighteenth embodiment, may be coupled dually. Frequency filtering characteristics of the resonator according to the eighteenth embodiment are as shown in  FIG. 32 . 
         [0123]      FIG. 33  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a nineteenth embodiment of the present disclosure, in which (a) of  FIG. 33  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the nineteenth embodiment of the present disclosure illustrated in  FIG. 33 , like the structures according to the above-described embodiments, may include a cavity  2100 , four resonance arms  2111 ,  2112 ,  2113 , and  2114 , and first through fourth resonance legs  2121 ,  2122 ,  2123 , and  2124 . 
         [0124]    However, the structure according to the nineteenth embodiment illustrated in  FIG. 33 , unlike in the structures according to the other embodiments, at least a pair of resonance arms have a plate shape. For example, in  FIG. 33 , all of four resonance arms  2111  through  2114  have the shape of a relatively wide plate. In this case, the first through fourth resonance arms  2111  through  2114  have a rectangular plate shape, and in the example of  FIG. 33 , each of the first through fourth resonance arms  2111  through  2114  has a shape in which at least a corner portion is cut as indicated by A. In addition, as indicated by B, a partition may be further installed between resonance arms. 
         [0125]    When the first through fourth resonance arms  2111  through  2114  have a wide plate shape, such a structure is favorable to a filter that has a large size (and also a large cavity) and is applied to a low-frequency band, and increases a capacitance component between the resonance arms and the housing. Also, in this case, to address a difficulty in coupling between resonance arms, the first through fourth resonance arms  2111  through  2114  may have a rectangular plate shape as described above, facilitating coupling therebetween. Moreover, a corner portion of each of the first through fourth resonance arms  2111  through  2114  may be cut, such that the intensity of coupling therebetween, notch generation, etc., may be adjusted. 
         [0126]    Main multi-mode resonance characteristics of the resonator having the structure illustrated in  FIG. 33  are as illustrated in  FIGS. 34A through 34D . In each of  FIGS. 34A through 34D , (a) shows E-field characteristics and (b) shows H-field characteristics. 
         [0127]      FIG. 35  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twentieth embodiment of the present disclosure, in which (a) of  FIG. 35  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the twentieth embodiment of the present disclosure illustrated in  FIG. 35 , like the structure of the resonator according to the nineteenth embodiment illustrated in  FIG. 33 , may include a cavity  2200 , four resonance arms  2211 ,  2212 ,  2213 , and  2214 , and first through fourth resonance legs  2221 ,  2222 ,  2223 , and  2224 . 
         [0128]    However, in the twentieth embodiment illustrated in  FIG. 35 , unlike in the nineteenth embodiment illustrated in  FIG. 33 , in the center of the entire structure of the four resonance arms  2211  through  2214  is provided a tuning screw  2243  which is installed to pass through a cover, etc., from an upper end of a housing (not shown). Frequency filtering characteristics of the resonator according to the twentieth embodiment are as shown in  FIG. 36 . 
         [0129]      FIG. 37  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twenty-first embodiment of the present disclosure, in which (a) of  FIG. 37  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the twenty-first embodiment of the present disclosure illustrated in  FIG. 35 , like the structure of the resonator according to the nineteenth embodiment illustrated in  FIG. 33 , may include a cavity  2300 , four resonance arms  2311 ,  2312 ,  2313 , and  2314 , and first through fourth resonance legs  2321 ,  2322 ,  2323 , and  2324 . 
         [0130]    However, in the twenty-first embodiment illustrated in  FIG. 37 , the shapes of the four resonance arms  2311  through  2314  are different from those in the nineteenth embodiment illustrated in  FIG. 33 . That is, as illustrated in  FIG. 37 , when compared to the nineteenth embodiment illustrated in  FIG. 33 , the first and fourth resonance arms  2311  and  2314  may have a complete rectangular shape without a cut corner portion, and cut portions of the second and third resonance arms  2312  and  2313  are designed differently than in the nineteenth embodiment. Frequency filtering characteristics of the resonator according to the twenty-first embodiment are as shown in  FIG. 37 . 
         [0131]      FIG. 39  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twenty-second embodiment of the present disclosure, in which (a) of  FIG. 37  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the twenty-second embodiment of the present disclosure illustrated in  FIG. 39 , like the structure of the resonator according to the nineteenth embodiment illustrated in  FIG. 33 , may include a cavity  2400 , four resonance arms  2411 ,  2412 ,  2413 , and  2414 , and first through fourth resonance legs  2421 ,  2422 ,  2423 , and  2424 . 
         [0132]    However, in the twenty-second embodiment illustrated in  FIG. 39 , the four resonance arms  2411  through  2414  are different from those in the nineteenth embodiment illustrated in  FIG. 33  in terms of shapes, etc. That is, as illustrated in  FIG. 39 , the first and fourth resonance arms  2411  and  2414  may have cut corner portions that are different from those in the nineteenth embodiment illustrated in  FIG. 33 , and shapes and thicknesses of a plate shape are also set different from in the nineteenth embodiment. Moreover, thicknesses of the four resonance legs  2421  through  2424  may also be set different from in the nineteenth embodiment. Frequency filtering characteristics of the resonator according to the twenty-second embodiment are as shown in  FIG. 40 . 
         [0133]      FIG. 41  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twenty-third embodiment of the present disclosure, in which (a) of  FIG. 41  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the twenty-third embodiment of the present disclosure illustrated in  FIG. 41 , like the structures according to the above-described other embodiments, may include a cavity  2500 , four resonance arms  2511 ,  2512 ,  2513 , and  2514 , and first through fourth resonance legs  2521 ,  2522 ,  2523 , and  2524 . 
         [0134]    In the twenty-third embodiment illustrated in  FIG. 41 , the four resonance arms  2511  through  2514  have a wide plate shape like in the nineteenth embodiment illustrated in  FIG. 33 , and especially, the first through fourth resonance arms  2511  and  2514  may have a disc shape. In this case, to solve a difficulty in coupling between resonance arms, an extending structure (indicated by A in  FIG. 41 ) in a proper shape is formed in each of the first through fourth resonance arms  2511  through  2514  to extend from each disc structure toward the center of the entire structure of the four resonance arms  2511  through  2514 . With such extending structures, the first through fourth resonance arms  2511  through  2514  are electrically close to one another, enabling smooth coupling therebetween. In addition, in the example illustrated in  FIG. 41 , a tuning structure  2541  is further installed to electrically float in the center of the entire structure of the four resonance arms  2511  through  2514 . Frequency filtering characteristics of the resonator according to the twenty-third embodiment are as shown in  FIG. 42 . 
         [0135]      FIG. 43  is a structural diagram of a multi-mode resonator corresponding to a bandpass filter according to a twenty-fourth embodiment of the present disclosure, in which (a) of  FIG. 43  illustrates a perspective projection structure, (b) illustrates a top plan structure, and (c) illustrates a side structure. The resonator according to the twenty-fourth embodiment of the present disclosure illustrated in  FIG. 43  is structured such that a first resonator  26 - 1  having the same structure as the structure of the resonator according to the sixteenth embodiment illustrated in  FIG. 27  and a second resonator  26 - 2  having the same structure as a general structure of a single-mode resonator are coupled to each other. That is, an output side of the first resonator  26 - 1  and an input side of the second resonator  26 - 2  are connected to each other by a coupling window  2640 , and a coupling structure  2642  extending from a bottom surface of a cavity is further installed in the coupling window  2640 . 
         [0136]    As such, the single-mode resonator having the general structure and the resonators according to the embodiments of the present disclosure may be coupled, and it would be understood that in the example illustrated in  FIG. 44 , the resonators having various structures according to the embodiments of the present disclosure may be coupled with the resonator having the general structure. Frequency filtering characteristics of the resonator according to the twenty-fourth embodiment are as shown in  FIG. 44 . 
         [0137]    The multi-mode resonator according to an embodiment of the present disclosure may be structured as described above, and while detailed embodiments have been described in the description of the present disclosure, various modifications may be made without departing from the scope of the present disclosure. 
         [0138]    For example, in the above-described structures, multiple tuning structures may be further installed in multiple positions inside the cavity for resonant frequency tuning and coupling adjustment between resonance modes. Such a tuning structure may have a cylindrical shape and may be fixedly installed by a separate support in the cavity as shown in  FIGS. 9 and 10 , or may have a shape of a tuning screw installed to pass through the housing (or cover) and inserted into the cavity like in a conventional filter structure. 
         [0139]    Although the number of resonance arms is 4 in the foregoing description, a more number of resonance arms may be installed in one cavity. Also in this case, the number of resonance arms may be designed to be a multiple of 2. 
         [0140]    In some of the above-described embodiments, a filter structure is designed such that two or more multi-mode resonators are provided and are dually connected overlappingly, but in other embodiments of the present disclosure, but in other embodiments of the present disclosure, the filter structure may be designed by connecting the structures according to the embodiments in two stages or three or more stages to obtain desired characteristics. 
         [0141]    Also, in the foregoing embodiments, the first through fourth resonance arms are made of a metallic material, but they may also be made of a dielectric material like dielectric resonance elements in other embodiments of the present disclosure. 
         [0142]    As described above, a multi-mode resonator according to the present disclosure may provide resonant frequencies in multiple modes to a single resonator. 
         [0143]    Thus, the size, weight, and manufacturing cost of the filter may be reduced. 
         [0144]    As such, various modifications and changes may be made to the present disclosure, and thus the scope of the present disclosure should be defined by the appended claims and equivalents thereof, rather than by the described embodiments.