Abstract:
The present invention relates to a stripline connection apparatus for transmitting signals between at least one pair of striplines. The stripline connection apparatus comprises a coupling member arranged between the pair of striplines so as to transmit signals to each stripline via inductive coupling. The coupling member includes a conductor, both ends of which face the respective striplines, and a gap-maintaining means for maintaining a predetermined gap between the conductor and the striplines.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a structure of a strip-line suitable for use as a transmission line in an antenna for a mobile communication base station, and more particularly, to a connection device between strip-lines. 
       BACKGROUND ART 
       [0002]    In various devices for processing Radio Frequency (RF) signals as well as antennas for mobile communication base stations, schemes using coaxial cables, micro-strip-lines, and strip-lines are generally used to implement RF transmission lines. 
         [0003]    The coaxial cables have been widely used as transmission lines in various technical fields, and are often used as RF transmission lines. Recently, however, due to cost reduction or the like, schemes using strip-lines as RF transmission lines have also come into wide use. 
         [0004]    When a transmission line is implemented using a strip-line, multiple strip-lines are separately designed and are connected to each other for transmission line implementation of a device. To connect the strip-lines, soldering is generally used. 
         [0005]    As such, to connect separate parts of two strip-lines, soldering is generally used, but for soldering, the part of the strip-line should be plated (but the plating is not necessarily performed prior to soldering), or the strip-line should be made of a copper material, which is relatively expensive, increasing cost. 
         [0006]    Laser welding, which does not need plating, may be used, but equipment investment cost and work efficiency are degraded. 
         [0007]    Moreover, Passive Inter-Modulation Distortion (PIMD), which is one of antenna characteristics, is affected by incomplete mechanical connection, such that complete mechanical connection is desirable. However, welding is weak to corrosion and as corrosion progresses, the PIMD characteristic deteriorates. 
       SUMMARY 
       [0008]    Accordingly, the present invention provides a strip-line connection structure which is simple, connects strip-lines at a low cost, and prevents signal characteristic degradation. 
         [0009]    According to an aspect of the present invention, there is provided a strip-line connection device for transmitting signals between at least a pair of strip-lines, the strip-line connection device including a coupling member for transmitting signals to each strip-line in a contact-free coupling manner between the at least a pair of the strip-lines, in which the coupling member includes a conductor, both end portions of which face the strip-lines, respectively, and a space-maintaining means installed to maintain a predetermined space between the conductor and each strip-line. 
         [0010]    The space-maintaining means may be an insulating layer formed to have a predetermined thickness on the conductor. 
         [0011]    The coupling member may be a Printed Circuit Board (PCB), the conductor may be a conductive pattern formed on the PCB, and the space-maintaining means may be an insulating layer formed to have a uniform thickness on the pattern. 
         [0012]    The insulating layer may be made of a polyamide material. 
         [0013]    The conductor may be an anodized conductive metallic plate, and the insulating layer may be an anodized oxide layer of the conductive metallic plate. 
         [0014]    At least one through-holes communicating with each other may be formed in the coupling member and each strip-line, and rivets made of an insulating material may be engaged through the through-holes to fix the coupling member and each strip-line. 
         [0015]    The strip-line connection device may further include at least one fixing clips for fixing the coupling member and each strip-line 
         [0016]    As described above, a strip-line connection structure which is simple, connects strip-lines at a low cost, and prevents signal characteristic degradation. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1  is a perspective view illustrating an example of a strip-line connection portion using a strip-line connection device according to an embodiment of the present invention; 
           [0018]      FIG. 2  is a perspective view illustrating a strip-line connection device according to an embodiment of the present invention; 
           [0019]      FIG. 3  is a side cross-sectional view illustrating a strip-line connection device according to an embodiment of the present invention; 
           [0020]      FIG. 4  is a side cross-sectional view illustrating a structure for fixing a strip-line and a coupling member in a strip-line connection device according to another embodiment of the present invention; and 
           [0021]      FIG. 5  is a side cross-sectional view illustrating a strip-line connection device according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Hereinafter, embodiments of the present invention will be described in detail. In a description of the present invention, well-known functions and structures which may unnecessarily obscure the subject matter of the present invention will not be described. 
         [0023]      FIG. 1  is a perspective view illustrating a strip-line connection portion using a strip-line connection device according to an embodiment of the present invention, in which the present invention is applied to a mobile communication base station antenna. 
         [0024]    Referring to  FIG. 1 , in a strip-line connection device according to the present invention, in mechanically discontinuous sections A and B of two strip-lines  21   a  and  21   b  to be connected, portions of the strip-lines  21   a  and  21   b  to be connected are formed to face each other with an appropriately spaced distance therebetween. 
         [0025]    In a device for implementing a strip-line as a transmission line, it is desirable not to have the aforementioned mechanically discontinuous section in the strip-line if possible. However, in  FIG. 1 , for connection with an accessory device  2  (for example, a phase shifter) in which a transmission line is formed with a strip-line, as indicated by the section A, or for installation of a strip-line on the other surface of an antenna reflecting plate  1 , which serves as a ground plate, through a hole formed in the antenna reflecting plate  1  as indicated by the section B, a mechanically discontinuous section in the strip-line is inevitable. 
         [0026]    In the present invention, in the mechanically discontinuous sections A and B of the two strip-lines to be connected, as illustrated in  FIG. 1 , the portions of the two strip-lines  21   a  and  21   b  to be connected are formed to face each other with an appropriately spaced distance therebetween, and then the portions of the two strip-lines  21   a  and  21   b  formed to face each other with the appropriately spaced distance are connected to each other in a contact-free coupling manner by using a coupling member ( 30  of  FIG. 2 ) formed according to the present invention and thus transmit signals therebetween. 
         [0027]    The spaced distance between end portions of the strip-lines  21   a  and  21   b  to be connected is appropriately set such that the end portions do not contact each other in spite of an external shock or expansion of the strip-lines  21   a  and  21   b  due to temperature. When the spaced distance is set, electric characteristics are not an important consideration. 
         [0028]      FIG. 2  is a perspective view illustrating a strip-line connection device according to an embodiment of the present invention, and  FIG. 3  is a side cross-sectional view illustrating a strip-line connection device according to an embodiment of the present invention. The strip-line connection device illustrated in  FIGS. 2 and 3  may be regarded as being installed on the antenna reflecting plate  1  illustrated in  FIG. 1 . Referring to  FIGS. 2 and 3 , the strip-line connection device according to the present invention includes a coupling member  30  installed between at least a pair of strip-lines  21   a  and  21   b  to be connected for transmitting signals in a contact-free coupling manner. 
         [0029]    More specifically, the coupling member  30  includes a conductor  32 , an end of which transmits a signal to an end portion of one of the two strip-lines  21   a  and  21   b  to be connected, in a contact-free coupling manner, and the other end of which transmits a signal to an end portion of the other of the two strip-lines  21   a  and  21   b  to be connected, in a contact-free coupling manner, and a space-maintaining means  33  installed to maintain a predetermined space between the conductor  32  and the respective strip-lines  21   a  and  21   b . The coupling member  30  may be installed in a form covering both end portions of the two strip-lines  21   a  and  21   b.  The coupling member  30  is fixedly installed in the both end portions of the two strip-lines  21   a  and  21   b,  and to this end, at least one through-holes communicating with each other are formed in the coupling member  30  and the strip-lines  21   a  and  21   b.  Rivets  41  of an insulating material may be engaged through the through-holes. For example, multiple through-holes  311  are formed in place in one end and the other end of the coupling member  30 , and through-holes  211  having sizes corresponding to the through-holes  311  of the coupling member  30  are formed in positions corresponding to the through-holes  311  in the both end portions of the two strip-lines  21   a  and  21   b.  Through the through-holes  311  of the coupling member  30  and the through-holes  211  of the two strip-lines  21   a  and  21   b,  the rivets  41 , which are made of a plastic material and have corresponding sizes, are engaged, such that the coupling member  30  is fixedly installed in the two strip-lines  21   a  and  21   b.    
         [0030]    To describe the structures of the coupling member  30  and the two strip-lines  21   a  and  21   b  in more detail, the strip-lines  21   a  and  21   b  may be implemented with strip plates with a thickness of 1 mm and a width of 8.6 mm, which have an impedance value of 50 Ω in an air space having a height d of 2 mm from the ground plate (that is, for example, the antenna reflecting plate)  1 . A design structure and an impedance as well as a spaced distance (height) between the strip-lines  21   a  and  21   b  and the ground plate  1  are very precisely and carefully considered, and therefore, to maintain the spaced distance (height) between the strip-lines  21   a  and  21   b  and the ground plate  1 , it is desirable to install spacers  111  having a proper structure and a proper material between the strip-lines  21   a  and  21   b  and the ground plate  1 . 
         [0031]    The coupling member  30  may be generally implemented with a Printed Circuit Board (PCB) structure, and as illustrated in  FIG. 3 , the conductor  32  may be a conductive pattern formed on the PCB, and the space-maintaining means  33  may be an insulating layer formed to have a uniform thickness on the conductive pattern (a bottom surface in the drawing). The coupling member  30  also includes a PCB dielectric plate  31  formed on a top surface (in the drawing) of the conductor  32  to maintain the shape of the coupling member  30 . 
         [0032]    As such, it can be seen that the conductor  32  of the coupling member  30  maintains a predetermined space with the strip-lines  21   a  and  21   b  by means of the insulating layer  33 . A general method for insulating a PCB copper plate uses Photo Solder Resist (PSR), but a PSR film has a non-uniform thickness. Thus, to maintain a predetermined insulating space and endure high-temperature heat that may be generated in the strip-line, the insulating layer  33  is formed by compressing a polyamide film at high temperature in the embodiment of the present invention. 
         [0033]    Contact-free coupling between the coupling member  30  and the strip-lines  21   a  and  21   b  is designed considering various factors to generate a minimum loss (VSWR, coupling loss). For example, in the foregoing case, a coupling section may be designed as 20 mm, a dielectric constant of the PCB dielectric plate  31  may be designed as 4.1, a thickness of the PCB dielectric plate  31  may be designed as 0.8 mm, a thickness of the copper conductor  32  may be designed as 0.034 mm, and a thickness of the insulating layer  33 , which is made of a polyamide film, may be designed as 0.028 mm. 
         [0034]    The two strip-lines  21   a  and  21   b  may be connected in a contact-free coupling manner by using the coupling member  30  having the foregoing structure according to an embodiment of the present invention, and meanwhile, end portions of the two strip-lines  21   a  and  21   b  may overlap each other to form an insulating layer in overlapping portions for signal transmission in a contact-free coupling manner. However, in such a structure, a height of at least one of the overlapping strip-lines is changed in an unwanted direction with respect to a ground plate, having a negative influence upon signal transmission. For this reason, this structure is not desirable. 
         [0035]      FIG. 4  is a side cross-sectional view illustrating a structure for fixing the strip-lines  21   a  and  21   b  and the coupling member  30  in the strip-line connection device according to another embodiment of the present invention. Referring to  FIG. 4 , in another embodiment of the present invention, a fixing means  50  for fixing the coupling member  30  and the strip-line  21   a  includes a male-screw structure  51  installed through a hole formed to correspond to the coupling member  30 , the strip-line  21   a,  and the ground plate  1 , a ring structure  53  installed between the ground plate  1  and the strip-line  21   a  in such a way to be inserted into the male-screw structure  51 , thus serving as a spacer, and a female-screw structure  52  coupled to a screw thread of the male-screw structure  51  on a rear surface of the ground plate  1 . 
         [0036]    For fixing the coupling member and the strip-lines, a fixing clip for picking up the coupling member and the corresponding strip-line may be used, or bonding may be used. In this manner, the strip-line connection structure according to an embodiment of the present invention may be implemented, and while a detailed embodiment has been described in the foregoing description of the present invention, various modifications may be carried out without departing from the scope of the present invention. For example, the structure for connecting two strip-lines has been described in the foregoing embodiment, but a structure for connecting three strip-lines may also be implemented by including a T-shaped coupling member, and by using the coupling member according to the embodiment of the present invention, the two strip-lines may also be connected in the form of T. 
         [0037]    Moreover, while the coupling member is implemented with the PCB structure in the foregoing description, in another embodiment of the present invention, a conductor of a coupling member  30 ′ may be implemented with an anodized conductive metallic plate, for example, an aluminum plate  62 , and in this case, an insulating layer may be implemented with an anodizing oxide layer  63  of the aluminum plate. The conductive metallic plate may also be implemented with an aluminum alloy, magnesium, or tin as well as pure aluminum. 
         [0038]    As such, various modifications or changes of the present invention may fall within a scope that does not depart from the subject matter of the present invention.