Patent Publication Number: US-10777869-B2

Title: Cavity type wireless frequency filter having cross-coupling notch structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of International Application No. PCT/KR2016/012754, filed on Nov. 7, 2016, which claims the benefit of and priority to Korean Patent Application No. 10-2015-0168430, filed on Nov. 30, 2015, the content of which are herein incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a wireless frequency filter used in a wireless communication system, and more particularly, to a cavity type wireless frequency filter having a cross-coupling notch structure. 
     BACKGROUND ART 
     Generally, a cavity type wireless frequency filter (hereinafter abbreviated as a “filter”) has an accommodation space of a rectangular parallelepiped shape or the like through a metal housing, that is, a plurality of cavities, and for example, a dielectric resonant (DR) element or a resonant element made of a metal resonant rod is provided inside each of the plurality of cavities and thus a high-frequency resonance is generated. In some cases, a structure for generating a resonance with a shape of a cavity without having a DR element may be employed. Further, such a cavity type wireless frequency filter generally includes a cover for blocking an open surface of a corresponding cavity provided at an upper portion of a cavity structure, and as a tuning structure for tuning a filtering characteristic of the corresponding wireless frequency filter, a plurality of tuning screws and nuts for fixing the tuning screws may be installed at the cover. An example of a cavity type wireless frequency filter is disclosed in Korean Patent Laid-Open Application No. 10-2004-100084 (entitled “Radio Frequency Filter,” filed on Dec. 2, 2004, and Inventors: Park Jong-Kyu and two others) filed by the present Applicant. 
     Such a cavity type wireless frequency filter is used to process a transmission and reception radio signal in a wireless communication system, and specifically, the cavity type wireless frequency filter is typically applied to a base station or a repeater in a mobile communication system. 
     Recently, as a required data processing capacity increases in a mobile communication system, a proposal for installing a large number of small (or micro) base stations has been suggested so as to resolve a rapid increase of wireless data traffic. Further, technological development for weight reduction and miniaturization of equipment for processing wireless signals and installed in a base station is continuously underway. Particularly, since the cavity type filter requires a relatively large size due to a characteristic of a structure having a cavity, reduction in size and weight of such a cavity type filter has become a major consideration. 
     Meanwhile, important characteristics of the wireless frequency filter are an insertion loss and a skirt characteristic. The insertion loss refers to power which is lost while a signal passes through a filter, and the skirt characteristic refers to steepness of a pass band and a stop band of the filter. The insertion loss and the skirt characteristics have a tradeoff relationship with each other according to the number of stages (orders) of the filter. As the number of stages of the filter is increased, the skirt characteristic becomes better but the insertion loss becomes lower. 
     A method of forming a notch (an attenuation pole) is mainly used to improve a skirt characteristic of a filter without increasing the number of stages of the filter. A most common method for forming a notch is a cross-coupling method. 
     Generally, a notch structure of the cross-coupling method is mainly configured with a metal workpiece such as a metal rod which forms a capacitance coupling between resonant elements of two cavities which are not continuous in a circuit. The metal rod is installed to pass through an inner wall for separating the two cavities. At this point, in order to electrically isolate the metal rod from the inner wall, an outer portion of the metal rod is surrounded a support of a dielectric material (not shown) such as Teflon, and then is coupled to the inner wall. At this point, a portion at which the metal rod is installed at the inner wall may be formed with a through-hole structure. However, since a process for forming a through-hole at the inner wall is not easy, a portion of an upper end of the inner wall is generally cut and then a metal rod surrounded with the support is installed at the corresponding cut portion. The support serves as insulation of the metal rod as well as has a shape engaged with a shape of the cut portion of the inner wall and is fixed to a portion at which the metal rod is installed, such that the metal rod is fixedly supported. 
     U.S. Pat. No. 6,342,825 of K &amp; L Microwave Co., (entitled “Bandpass Filter Having Tri-section,” Inventor: Rafi Hershtig, and Patented Date: Jan. 29, 2002), or U.S. Pat. No. 6,836,198 of RADIO FREQUENCY SYSTEMS (entitled “Adjustable Capacitive Coupling Structure,” Inventor: Bill Engst, and Patented date: Dec. 28, 2004) discloses an example of a technique for forming a notch using a cross-coupling method. 
     A notch structure using such a cross-coupling method may be almost indispensably applied to implementing a small or micro cavity type filter applied to a small or micro base station. At this point, due to space and size limitations resulting from a characteristic of the small filter, a distance between resonant elements and a metal rod should be designed to be very close so as to obtain a desired coupling amount in the notch structure using the cross-coupling method. However, it is very difficult to precisely implement a distance between the resonant elements and the metal rod to correspond to a required coupling amount with a tolerance in the range of, i.e., about ±0.03 to 0.05 mm, which is commonly used in metal processing, and thus deviation in cross-coupling amount between products becomes larger. 
     Accordingly, in the cross-coupling type notch structure applied to a small or micro filter, when implementing a designed structure as an actual product, it is required a very high processing accuracy when a cross-coupling type metal rod (and resonant elements) are manufactured and installed. For example, a machining tolerance of about 0.01 mm or less may be required in a gap between a metal rod and resonant elements. However, when a very precise machining tolerance is required, difficulty in machining operation is increased and a machining time is increased, and thus machining costs are increased and a production yield is lowered, such that there is a difficulty in mass production. 
     DISCLOSURE 
     Technical Problem 
     Accordingly, it is an objective of some embodiments of the present invention to provide a cavity type wireless frequency filter having a cross-coupling notch structure capable of being reduced in size and weight. 
     Another objective according to some embodiments of the present invention is to provide a cavity type wireless frequency filter having a cross-coupling notch structure capable of providing a stable notch characteristic since it has a simpler structure, is easier to manufacture, and has a stable structure. 
     Technical Solution 
     According to one aspect of the present invention, there is provided a cavity type wireless frequency filter having a cross-coupling notch structure, the filter including a housing having a hollow therein to provide a plurality of cavities and an open surface at one side of the housing, a cover for blocking the open surface of the housing, a plurality of resonant elements disposed in the hollow of the housing, and a notch substrate installed for cross-coupling between at least two resonant elements among the plurality of resonant elements, wherein the notch substrate includes a main substrate made of a non-conductive material and having a first coupling structure and a second coupling structure which are mechanically coupled to the at least two resonant elements, and a conductive line implemented with a conductor pattern formed on the main substrate and transmitting a signal of a first resonant element among the at least two resonant elements to a second resonant element thereamong through a non-contact coupling method. 
     The conductive line may include a first sub conductor pattern electrically connected to a support of the first resonant element in the first coupling structure of the main substrate, and a second sub conductor pattern electrically connected to a support of the second resonant element in the second coupling structure of the main substrate. 
     The first coupling structure and the second coupling structure may form through-holes which are fitted into and mechanically coupled to the supports of the at least two resonant elements. 
     A notch tuning pin for tuning a notch characteristic may be coupled to a portion of the cover corresponding to the notch substrate through a notch tuning through-hole, and a notch tuning hole structure for forming a through-hole having a size corresponding to a lower end portion of the notch tuning pin may be formed at a portion of the main substrate of the notch substrate, which corresponds to the notch tuning pin. 
     A conductive metal film may be formed on an inner surface of each of the through-holes of the first and second coupling structures of the main substrate. 
     The first sub conductor pattern and the second sub conductor pattern may be formed on different surfaces of the main substrate, a first end of the first sub conductor pattern may be configured to be connected to the inner surface of the through-hole of the first coupling structure, and a first end of the second sub conductor pattern may be configured to be connected to the inner surface of the through-hole of the second coupling structure. 
     The first sub conductor pattern and/or the first end of the second sub conductor pattern may be formed to surround at least a portion of a region forming the through-hole of the first coupling structure and to maintain a separation distance from the through-hole of the first coupling structure. 
     The second end of the first sub conductor pattern and the second end of the second sub conductor pattern may be configured to mutually transmit signals through a non-contact coupling method or may be configured to be directly connected to each other. 
     The notch substrate may have a structure for cross-coupling with a third resonant element, a first resonant element, and a second resonant element among the plurality of resonant elements, the main substrate of the notch substrate may have a third coupling structure which is fitted into and mechanically coupled to a third resonant element among the plurality of resonant elements, and the conductive line may include a conductive line for transmitting a signal of the first resonant element or the second resonant element to the third resonant element through a non-contact coupling method. 
     Advantageous Effects 
     As described above, the cavity type wireless frequency filter having a notch structure according to the embodiments of the present invention provides a notch structure capable of being further reduced in size and weight, and particularly, the notch structure can have a simpler structure, can be easier to manufacture, and can have a stable structure, thereby providing a stable notch characteristic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially separated perspective view of a cavity type wireless frequency filter having a cross-coupling notch structure according to a first embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of Part A of the wireless frequency filter  FIG. 1 . 
         FIGS. 3A and 3B  are cross-sectional views taken along the line A-A′ of  FIG. 2 . 
         FIGS. 4A and 4B  are detailed perspective views of a notch substrate of  FIG. 1 . 
         FIGS. 5A and 5B  are perspective views of some modifications of the notch substrate of  FIG. 1 . 
         FIG. 6  is a perspective view of a notch substrate which is applicable to a cavity type wireless frequency filter having a cross-coupling notch structure according to a second embodiment of the present invention. 
         FIGS. 7A and 7B  are configurational diagrams of a notch substrate which is applicable to a cavity type wireless frequency filter having a cross-coupling notch structure according to a third embodiment of the present invention. 
         FIG. 8  is a perspective view of a notch substrate which is applicable to a cavity type wireless frequency filter having a cross-coupling notch structure according to a fourth embodiment of the present invention. 
         FIG. 9  is a perspective view of a notch substrate which is applicable to a cavity type wireless frequency filter having a cross-coupling notch structure according to a fifth embodiment of the present invention. 
         FIG. 10  is a partially separated perspective view of a cavity type wireless frequency filter having a cross-coupling notch structure according to a sixth embodiment of the present invention. 
         FIG. 11  is a detailed perspective view of a notch substrate of  FIG. 10 . 
     
    
    
     BEST MODE 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a partially separated perspective view of a cavity type wireless frequency filter having a cross-coupling notch structure according to a first embodiment of the present invention. Referring to  FIG. 1 , the cavity type wireless frequency filter having the notch structure according to the first embodiment of the present invention includes an enclosure having a plurality of cavities (seven cavities in examples of  FIGS. 1 and 5 ), each of which includes a hollow therein and is blocked from the outside. The enclosure forms seven cavities and is formed to include a housing  20  having one open surface (e.g., an upper surface) and a cover  10  for blocking the open surface of the housing  20 . The cover  10  and the housing  20  may have a structure which is coupled by laser welding or soldering, and in addition to laser welding or soldering, the cover  10  and the housing  20  may be coupled by a screw connection method through a fixing screw (not shown). 
     The housing  20  and the cover  10  may be made of a material such as aluminum (alloy) or the like and may be plated with a silver or copper material on at least a surface forming the cavity to improve electrical characteristics. Resonant elements may also be made of a material such as aluminum (alloy) or iron (alloy) and may be plated with a silver or copper material. 
     For example,  FIG. 1  illustrates an example in which seven cavity structures are connected in multiple stages within the housing  20 . That is, it can be seen that the seven cavity structures are sequentially connected. Each cavity of the housing  20  has a resonant element  31 ,  32 ,  33 ,  34 ,  35 ,  36 , or  37  at a central position of each cavity. Further, a coupling window having a connecting path structure is formed between the cavity structures, which are sequentially connected to each other, so as to allow each cavity structure in the housing  20  to have a sequential coupling structure. The coupling window may be formed at a portion corresponding to each of partition walls  201 ,  202 ,  203 ,  204 , and  205  between the cavity structures in a shape in which a predetermined portion is removed in a predetermined size. 
     In the structure shown in  FIG. 1 , at least some of the resonant elements  31 ,  32 ,  33 ,  34 ,  34 ,  35 ,  36 , and  37  may have the same structure, and for convenience of description, all the resonant elements are shown to have the same structure in the example of  FIG. 1 . For example, each of the first to seventh resonant elements  31  to  37  may be configured with a flat plate portion having a circular flat plate shape and a support for fixing and supporting the flat plate portion, and the support is fixedly installed at an inner bottom surface of a corresponding cavity, that is, the housing  20 . More detailed structures of the flat plate portion and the support in each of the resonant elements  31  to  37  may have various structures according to a design condition of a corresponding filter, and resonant elements of different detailed structures may be mixed to constitute a filter. 
     First to seventh recessed structures  101 ,  102 ,  103 ,  104 ,  105 ,  106 , and  107  for frequency tuning may be formed at the cover  10  by corresponding to the resonant elements  31  to  37  of the cavity structures. Further, a plurality of coupling tuning screw holes  111  may be formed at portions of the cover  10  corresponding to the coupling windows, which are the connecting path structures of the cavity structures in the housing  20 . A coupling tuning screw  41  for coupling tuning may be inserted into each of the plurality of coupling tuning screw holes  111  with a proper depth to perform a coupling tuning operation. At this point, the coupling tuning screw  41  may be additionally fixed using a separate adhesive such as an epoxy resin or the like. 
     Further, an input terminal  21  and an output terminal  22  of a corresponding wireless frequency filter may be installed through a through-hole or the like which may be formed at one side of the housing  20 .  FIG. 1  illustrates an example of a state in which the input terminal  21  and the first resonant element  31  are coupled, and the output terminal  22  is connected to the seventh resonant element  37 . For example, an extension line (not shown) of the input terminal  21  and the support of the first resonant element  31  may be directly coupled or may be connected through a non-contact coupling method. 
     In the described above, the structure of the cover  10  may have a structure similar to that applied to a wireless frequency filter having a conventional cavity structure, and for example, the structure of the cover  10  may have a structure similar to that disclosed in Korean Patent Laid-Open Application No. 10-2014-0026235 (entitled “Wireless Frequency Filter having Cavity Structure,” Published Date: Mar. 5, 2014, and Inventors: Park, Nam Shin and two others). Korean Patent Laid-Open Application No. 10-2014-0026235 proposes a simplified filter structure capable of performing frequency tuning without employing a tuning screw and an engagement structure of a fixing nut, which are a more general structure. As disclosed in Korean Patent Laid-Open Application No. 10-2014-0026235, the cover  10  according to the embodiments of the present invention may include one or more recessed structures  101  to  107  are formed at positions corresponding to the resonant elements  31  to  37 . A plurality of dot peen structures are formed at the recessed structures  101  to  107  by marking or pressing using an embossed pin of external marking equipment, thereby enabling frequency tuning. 
     Meanwhile, in some other embodiments of the present invention, a more generalized frequency tuning method may be applied to the cover  10 , and thus a frequency tuning screw and a fixing nut may be provided without forming recessed structures  101  to  107 . However, the structure including the frequency tuning screw and the fixing nut may have a more complicated structure and may be difficult to be miniaturized. 
     Looking at the above-described structures, the cavity structures formed at the housing  20  and the cover  10  in the wireless frequency filter according to the first embodiment of the present invention and the structures of the resonant elements  31  to  37  inside the cavities are similar to a conventional structure except that the structures according to the present invention may be implemented in a size that is smaller than the conventional structure. However, a notch structure and an installation structure thereof according to the embodiments of the present invention have improved structures compared with a conventional notch structure and a conventional installation structure thereof. 
       FIG. 1  illustrates a notch structure according to the first embodiment of the present invention and an example in which a notch substrate  51  is installed for a cross-coupling between the fourth resonant element  34  and the sixth resonant element  36 . At this point, a window having a shape from which an appropriate portion is removed to allow a notch substrate  51  to be installed is formed at the partition wall  204  for separating the cavity of the fourth resonant element  34  from that of the sixth resonant element  36 . Further, a notch tuning through-hole  121  coupled to a notch tuning pin  61  is formed at the cover  10  to tune a notch characteristic of a portion corresponding to the notch substrate  51 . The notch tuning pin  61  which is set to an appropriate length for notch tuning may be inserted into the notch tuning through-hole  121  and be interlocked with the notch substrate  51  to perform a tuning operation of the notch characteristic. At this point, the notch tuning pin  61  may be generally formed in a screw shape and may have a structure which is coupled to the notch tuning through-hole  121  through a screw coupling. The notch tuning pin  61  may be made of a conductive metal material such as aluminum (alloy) or brass (alloy), and silver may be plated on the notch tuning pin  61 . 
       FIG. 2  is a cross-sectional view of Part A of the wireless frequency filter  FIG. 1 , which is indicated by a dotted-line rectangular box and includes the notch substrate  51  and illustrates relating portions such as the fourth resonant element  34 , the sixth resonant element  36 , and the notch tuning pin  61  in detail.  FIGS. 3A and 3B  are partially cross-sectional views taken along the line A-A′ of  FIG. 2 ,  FIG. 3A  illustrates a structure including the notch tuning pin  61 , and  FIG. 3B  illustrates a structure not including the notch tuning pin  61 .  FIGS. 4A and 4B  are detailed perspective views of the notch substrate  51  of  FIG. 1 ,  FIG. 4A  is a perspective view of the notch substrate  51  when viewed from a first side (e.g., an upper side), and  FIG. 4B  is a perspective view of the notch substrate  51  when viewed from a second side (e.g., a lower side). 
     Describing a configuration of the notch substrate  51  according to the first embodiment of the present invention in detail with reference to  FIGS. 2 to 4B , the notch substrate  51  may generally have a printed circuit board (PCB) structure, and according to some embodiments of the present invention, the notch substrate  51  may include a main substrate  513  made of a non-conductive material such as Teflon or the like, and conductive lines  511  and  512  formed at a first surface (e.g., an upper surface) and/or a second surface (e.g., a lower surface) of the main substrate  513 , which is formed using, e.g., a conductive pattern forming process during a PCB substrate manufacturing process. Similar to a general PCB substrate, the main substrate  513  may be implemented with a single-layer or multilayered substrate of a frame retardant (FR) line or a composite epoxy material (CEM) line. 
     The main substrate  513  has at least two resonant elements, and in the example of  FIGS. 2 to 4B , a coupling structure mechanically coupled to the fourth resonant element  34  and the sixth resonant element  36  and fixedly supporting the main substrate  513 , that is, a first coupling structure  51   a  and a second coupling structure  51   c  in the form of, e.g., a ring are provided to form through-holes. A support  342  of the fourth resonant element  34  is fitted into and coupled to the through-hole of the first coupling structure  51   a , and a support  362  of the sixth resonant element  36  is fitted into and coupled to the through-hole of the second coupling structure  51   c.    
     In the example of  FIGS. 2 to 4B , the conductive lines  511  and  512  are electrically connected to at least two resonant elements, that is, the fourth resonant element  34  and the sixth resonant element  36 , and the conductive lines  511  and  512  are implemented as conductor patterns formed on the upper surface and/or the lower surface of the main substrate  513  so as to transmit a signal of at least one resonant element to another resonant element using a non-contact coupling method. For example, the conductive lines  511  and  512  may be configured with a first sub conductor pattern  511  formed on the upper surface of the main substrate  513  and electrically connected to the support  342  of the fourth resonant element  34 , and a second sub conductor pattern  512  formed on the lower surface of the main substrate  513  and electrically connected to the support  362  of the sixth resonant element  36 , and the first sub conductor pattern  511  and the second sub conductor pattern  512  are configured to transmit signals through a non-contact coupling method. 
     Describing the foregoing in more detail, similar to a structure of a via hole generally formed on a PCB substrate, an inner surface of the through-hole of the first coupling structure  51   a  of the main substrate  513  may be configured to allow a conductive metal film to be formed thereon, and one end (a first end) of the first sub conductor pattern  511  may be configured in the form of being connected to the inner surface of the through-hole of the first coupling structure  51   a . Similarly, a conductive metal film may also be formed on an inner surface of the through-hole of the second coupling structure  51   c , and one end (a first end) of the second sub conductor pattern  512  may be configured in the form of being connected to the inner surface of the through-hole of the second coupling structure  51   c . For example, mutually facing portions between the other end (a second end) of the first sub conductor pattern  511  and the other end (a second end) of the second sub conductor pattern  512  is formed at a central position of the main substrate  513  with a predetermined length by interposing the main substrate  513  to transmit a signal in a non-contact coupling method. 
     A tuning hole structure  51   b  may further be provided at the main substrate  513  to form a through-hole having a size corresponding to a lower end portion of the notch tuning pin  61  so as to allow the lower end portion of the notch tuning pin  61  to be installed in an insertable form at a portion corresponding to a lower end portion of a body of the notch tuning pin  61 . The tuning hole structure  51   b  of the main substrate  513  may be formed at a central position of the main substrate  513 . At this point, the mutually facing portions between the first sub conductor pattern  511  and the second sub conductor pattern  512  may be appropriately formed on the upper and lower surfaces of the main substrate  513  in a peripheral region of the tuning hole structure  51   b . This structure is a structure in which the notch tuning pin  61  for notch tuning is installed at a position at which the first sub conductor pattern  511  and the second sub conductor pattern  512  are non-contact coupled to each other, so that tuning for the notch characteristic may be more effectively performed at a corresponding position. 
     In the notch substrate  51  having the above-described structure, the supports  342  and  362  of the fourth resonant element  34  and the sixth resonant element  36  are respectively inserted into the through-holes formed at the first coupling structure  51   a  and the second coupling structure  51   c  of the main substrate  513  and are respectively coupled to the first coupling structure  51   a  and the second coupling structure  51   c  thereof, and then soldering may further be performed at the corresponding coupling portions. Consequently, the corresponding coupling portions are mechanically and electrically coupled with more stability such that the notch substrate  51  is fixedly installed. After the notch substrate  51  is fixedly installed, the notch tuning pin  61  is coupled to the notch tuning through-hole  121  of the cover  10  as shown in  FIG. 1 , and thus the lower end portion of the notch tuning pin  61  is installed to be insertable into the tuning hole structure  51   b  formed at the notch substrate  51 . 
     A degree of coupling between the notch tuning pin  61  and a portion of a signal transmitted through the notch substrate  51  may be controlled by adjusting a degree of proximity between the lower end portion of the notch tuning pin  61  and the notch substrate  51  and a degree of insertion of the notch tuning pin  61  into the tuning hole structure  51   b , and thus a notch characteristic generated by the notch substrate  51  may be appropriately adjusted. At this point, when the notch tuning pin  61  is formed in a screw structure and is screw-coupled to the notch tuning through-hole  121  of the cover  10 , a screw coupling of the notch tuning pin  61  may be tightened or released to adjust a distance between the notch tuning pin  61  and the notch substrate  51 . Alternatively, the distance between the notch tuning pin  61  and the notch substrate  51  may be adjusted by replacing and installing a notch tuning pin  61  designed to have an appropriate different length or by appropriately cutting a length of the lower end portion of the notch tuning pin  61  and reinstalling the notch tuning pin  61  having the cut length. 
     As shown in  FIGS. 1 to 4A , the notch substrate  51  applied to the wireless frequency filter according to the first embodiment of the present invention may be configured and installed, and the notch substrate  51  basically has a structure in which a conductor pattern for signal transmission is formed on a substrate similar to a PCB substrate, so that a manufacturing process may be simplified and the notch substrate  51  may be accurately implemented compared with a conventional notch structure using a metal bar or the like. Particularly, the notch substrate  51  may be simply installed by fitting two resonant elements which will be cross-coupled, e.g., the supports  342  and  362  of the fourth and sixth resonant elements  34  and  36 , into the first and second coupling structures  51   a  and  51   c  forming the through-holes of the notch substrate  51 , such that the notch substrate  51  may be easily installed while problems due to a conventional machining tolerance and a conventional assembly tolerance may be resolved. 
     Meanwhile, the notch substrate  51  according to the first embodiment of the present invention shown in  FIGS. 1 to 4A  (and notch substrates according to other embodiments of the present invention, which will be described below) may be variously modified or altered in detailed features in form and size of the main substrate  513  or the conductive lines  511  and  512 . For example, in one modification of the notch substrate  51  as shown in  FIG. 5A , a solder injection recess  51   d  is additionally formed at an appropriate portion of the first coupling structure  51   a  forming the through-hole. The solder injection recess  51   d  facilitates solder injection and application during soldering of the first coupling structure  51   a  with a support of a resonant element coupled thereto. Alternatively, such a solder injection recess  51   d  may also be formed at the second coupling structure  51   c  of the notch substrate  51 . 
     In another modification of the notch substrate  51  shown in  FIG. 5B , an incised portion  51   e  is formed such that a portion of the first coupling structure  51   a  forming the through-hole is incised. As described above, the first coupling structure  51   a  and/or the second coupling structure  51   c  of the notch substrate  51  may be formed in a complete ring shape without having a discontinuous portion but may also be formed in a ring shape of which a portion is partially incised. 
       FIG. 6  is a perspective view of a notch substrate  52  which is applicable to a cavity type wireless frequency filter having a cross-coupling notch structure according to a second embodiment of the present invention. Referring to  FIG. 6 , similar to the structure of the first embodiment shown in FIGS.  2  to  4 B, the notch substrate  52  according to the second embodiment of the present invention includes the main substrate  523  having a first coupling structure  52   a  and a second coupling structure  52   a , which form through-holes, and conductive lines  521  and  522  formed on the main substrate  523 . 
     Unlike the first embodiment, in the notch substrate  52  shown in  FIG. 6 , the conductive lines  521  and  522  are formed on the same surface of the main substrate  523 . For example, the conductive lines  521  and  522  includes a first sub conductor pattern  521  formed such that one end (a first end) thereof is in electrical contact with a metal film formed in a region of a through-hole of the first coupling structure  52   a  of the main substrate  523 , and a second sub conductor pattern  522  formed such that one end (a first end) thereof is in electrical contact with a metal film formed in a region of a through-hole of the second coupling structure  52   c  of the main substrate  523 , and the first and second sub conductor patterns  521  and  522  may be formed on an upper surface of the main substrate  523 . Further, mutually facing portions between the other end (a second end) of the first sub conductor pattern  521  and the other end (a second end) of the second sub conductor pattern  522  is formed at a central position of the main substrate  513  with a predetermined length to transmit a signal through a non-contact coupling method. 
     As in the structure of the first embodiment, a tuning hole structure  52   b  may be formed at a central position of the main substrate  523 , and a portion of the other end (the second end) of the first sub conductor pattern  521  and a portion of the other end (the second end) of the second sub conductor pattern  522  may be formed to surround the tuning hole structure  52   b.    
       FIGS. 7A and 7B  are configurational diagrams of a notch substrate  53  which is applicable to a cavity type wireless frequency filter having a cross-coupling notch structure according to a third embodiment of the present invention,  FIG. 7A  is a perspective view of the notch substrate  53 , and  FIG. 7B  illustrates a portion of a side structure showing an installation state of the notch substrate  53 . First, referring to  FIG. 7A , similar to the structure of the second embodiment shown in  FIG. 6 , the notch substrate  53  according to the third embodiment of the present invention includes a main substrate  533  having a first coupling structure  53   a  and a second coupling structure  53   c , which form through-holes, and conductive lines  531  and  532  formed on the main substrate  533 . Further, a first sub conductor pattern  531  and a second sub conductor pattern  532 , which constitute the conductive lines  531  and  532 , are formed on the same surface of the main substrate  533 . 
     However, in the notch substrate  53  shown in  FIG. 7A , the first coupling structure  53   a  and the second coupling structure  53   c  of the main substrate  533  form through-holes for coupling to supports of resonant elements, but unlike the second embodiment shown in  FIG. 6 , a metal film is not formed. At this point, one end (a first end) of the first sub conductor pattern  531  is formed to surround at least a portion of a region forming the through-hole of the first coupling structure  53   a  (an entire region in the example of  FIG. 7A ) on an upper surface of the main substrate  533 . In this case, the portion surrounding the corresponding through-hole in the first sub conductor pattern  531  is formed to be in indirect contact with a support of a resonant element coupled to the corresponding through-hole and to maintain a separation distance from the corresponding through-hole so as to receive a signal through a non-contact coupling method. Similarly, one end (a first end) of the second sub conductor pattern  532  is formed to surround at least a portion of a region forming the through-hole of the second coupling structure  53   c  and to maintain a separation distance from the corresponding through-hole on the upper surface of the main substrate  533 . 
     Further, the first sub conductor pattern  531  and the second sub conductor pattern  532  are directly connected and integrally formed instead of being configured to mutually transmit signals through a non-contact coupling method. For example, the other end (a second end) of the first sub-conductor pattern  531  and the other end (a second end) of the second sub-conductor pattern  532  may be formed to surround a tuning hole structure  53   b  formed at a central position of the main substrate  533 , and mutually facing portions may be configured to be directly connected to each other. 
     In the notch substrate  53  according to the third embodiment as shown in  FIG. 7A , the supports of the resonant elements are fitted into and coupled to the through-holes formed at the first coupling structure  53   a  and the second coupling structure  53   c , but the corresponding coupling portions are not soldered. That is, each of the supports of the resonant elements is configured to transmit a signal to the first and second sub conductor patterns  531  and  532  of the notch substrate  53  through the non-contact coupling method. At this point, as shown in  FIG. 7B , a hook protrusion  341   a  having an appropriate shape may be formed at the support of the resonant element  34  so as to more stably support the coupled notch substrate  53 . 
       FIG. 8  is a perspective view of a notch substrate  54  which is applicable to a cavity type wireless frequency filter having a cross-coupling notch structure according to a fourth embodiment of the present invention. Referring to  FIG. 8 , largely similar to the structure of the third embodiment shown in  FIG. 7 , the notch substrate  54  according to the fourth embodiment of the present invention includes a main substrate  543  having a first coupling structure  54   a  and a second coupling structure  54   c , which form through-holes, and conductive lines  541  and  542  formed on the main substrate  543 . Further, a first sub conductor pattern  541  and a second sub conductor pattern  542 , which constitute the conductive lines  541  and  542 , are formed on the same surface of the main substrate  543 . At this point, the first sub conductor pattern  541  and the second sub conductor pattern  542  may be formed to surround a tuning hole structure  54   b  formed at a central position of the main substrate  543 , and mutually facing portions may be configured to be directly connected to each other. 
     As in the structure shown in  FIG. 7A , in the notch substrate  54  shown in  FIG. 8 , the first coupling structure  54   a  and a portion relating thereto in the first sub conductor pattern  541  are configured to be in indirect contact with a coupled support of a resonant element and to receive a signal through a non-contact coupling method, but similar to the embodiments shown in  FIGS. 2 to 6 , the second coupling structure  54   c  and a portion relating thereto in the second sub-conductor pattern  542  are configured to be indirect contact with a coupled support of a resonant element and to receive a signal. 
     As shown in  FIGS. 2 to 8 , in the notch substrate of the present invention, the first and second coupling structures and the coupling structure of the first and second sub conductor patterns may be selectively configured by appropriately mixing with the structures of the various embodiments according to a design condition for a cross-coupling amount or an installation condition. Further, in another embodiment of the present invention, the first and second sub conductor patterns in the structures shown in  FIGS. 7A and 8  may be configured to transmit signals through a non-contact coupling method without being directly connected to each other. In this case, the first and second sub conductor patterns may be formed on different surfaces of the main substrate. 
       FIG. 9  is a perspective view of a notch substrate  55  which is applicable to a cavity type wireless frequency filter having a cross-coupling notch structure according to a fifth embodiment of the present invention. Referring to  FIG. 9 , similar to the structure of the first embodiment shown in  FIGS. 2 to 4B , the notch substrate  55  according to the fifth embodiment of the present invention includes a main substrate  523  having a first coupling structure  55   a  and a second coupling structure  55   c , which form through-holes, and a tuning hole structure  55   b . Further, the notch substrate  55  includes conductive lines  551  and  552  configured with a first sub conductor pattern  551  and a second sub conductor pattern  552 , which are formed on different surfaces of the main substrate  553  and mutually transmit signals through a non-contact coupling method. 
     Although the notch substrate  51  of the first embodiment shown in  FIGS. 2 to 4B  has been entirely formed in a “-” shape, at least a portion of the notch substrate  55  according to the fifth embodiment shown in  FIG. 9  is formed to be bent, e.g., to entirely have an “L” shape. 
     As described above, the notch substrate according to some embodiments of the present invention may be formed in various shapes such as an arc shape, a shape having multiple bent portions according to a design of a corresponding filter. Further, since the notch substrate of the present invention is implemented with a PCB structure even though being manufactured in various shapes described above, the notch substrate may be easily manufactured without requiring an additional processor additional precision work. 
       FIG. 10  is a partially separated perspective view of a cavity type wireless frequency filter having a cross-coupling notch structure according to a sixth embodiment of the present invention. Referring to  FIG. 10 , the wireless frequency filter according to the sixth embodiment of the present invention is substantially the same as the structure shown in  FIG. 1  except that, as a notch structure according to the sixth embodiment of the present invention, a notch substrate  56  is also installed for cross-coupling between the second resonant element  32  and the fourth resonant element  3  in addition to between the fourth resonant element  34  and the sixth resonant element  36 . At this point, a window having a shape from which an appropriate portion is removed to allow a corresponding notch substrate  56  to be installed is formed at the partition wall  204  between the fourth resonant element  34  and the sixth resonant element  36  and at the partition wall  202  between the second resonant element  32  and the fourth resonant element  34 . 
     Further, a first notch tuning through-hole  121  to which a first notch tuning pin  61  is coupled is formed at a portion of the cover  10 , which corresponds to the notch substrate  56 , so as to tune a notch characteristic between the fourth resonant element  34  and the sixth resonant element  36 , and a second notch tuning through hole  122  to which a second notch tuning pin  62  is coupled is formed at a portion of the cover  10 , which corresponds to the notch substrate  56 , so as to tune a notch characteristic between the second resonant element  32  and the fourth resonant element  34 . 
       FIG. 11  is a detailed perspective view of the notch substrate  56  of  FIG. 10 . Referring to  FIG. 11 , the notch substrate  56  according to the sixth embodiment of the present invention includes a main substrate  565 , and conductive lines  561 ,  562 ,  563 , and  564  formed on a first surface (e.g., an upper surface) and/or a second surface (e.g., a lower surface) of the main substrate  565 . 
     The main substrate  565  is mechanically coupled to at least three resonant elements, i.e., in an example of  FIG. 11 , to the support  342  of the fourth resonant element  34 , the support  362  of the sixth resonant element  36 , and a support  322  of the second resonant element  32 , and thus a first coupling structure  56   a , a second coupling structure  56   c , and a third coupling structure  56   d  are formed to fixedly support the main substrate  565 . 
     For example, the conductive lines  561 ,  562 ,  563 , and  564  includes a first sub conductor pattern  561  formed on an upper surface of the main substrate  565  and electrically connected to the support  342  of the fourth resonant element  34 , and a second sub conductor pattern  562  formed on a lower surface of the main substrate  565  and electrically connected to the support  362  of the sixth resonant element  36 , and the first and second sub conductor patterns  561  and  562  are configured to mutually transmit signals in a non-contact coupling method by interposing the main substrate  565  at a portion of a first tuning hole structure  56   b  formed at the main substrate  565 . Further, the conductive lines  561 ,  562 ,  563 , and  564  includes a third sub conductor pattern  563  formed on the upper surface of the main substrate  565  and electrically connected to the support  322  of the second resonant element  32 , and a fourth sub conductor pattern  564  formed on the lower surface of the main substrate  565  and electrically connected to the support  342  of the fourth resonant element  34 , and the third and fourth sub conductor patterns  563  and  564  are configured to mutually transmit signals in a non-contact coupling method at a portion of a second tuning hole structure  56   e  formed at the main substrate  565 . In  FIG. 11 , the second sub conductor pattern  562  and the fourth sub conductor pattern  564 , which are formed on the lower surface of the main substrate  565 , are omitted. 
     Looking at the structures shown in  FIGS. 10 and 11 , it can be seen that the structure of the notch substrate  56  according to the sixth embodiment of the present invention is a structure in which the structure of the notch substrate  51  according to the first embodiment shown in  FIGS. 1 to 4B  is dually formed. 
     As described above, it can be seen that the notch substrate according to some embodiments of the present invention may be formed by integrating a plurality of notch structures according to a design of a corresponding filter. At this point, even when a plurality of notch structures are integrally manufactured, it can be seen that an additional process or additional precision work may not be required. In this case, when a plurality of notch structures are integrally formed using a single notch substrate, a plurality of coupling structures and a structure of a plurality of conductor patterns of the main substrate may be selectively configured by appropriately mixing the structures of the various embodiments according to a cross-coupling amount, an installation condition, or the like. 
     As described above, a cavity type wireless frequency filter having a notch structure according to the embodiments of the present invention can be configured. In addition to the foregoing, various embodiments and modifications may be made within the scope of the present invention, and therefore, the scope of the present invention should be defined by the appended claims and equivalents thereof instead of the above-described embodiments.