Abstract:
The present invention relates to a dual polarization antenna comprising a reflection plate, and a radiating module including first to fourth radiating elements having respective first to fourth radiating arms having respective bent portions. The bent portions of the first to fourth radiation arms are sequentially adjacent to each other, and sequentially form           and           shaped structures. The                     and

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a U.S. national phase application, pursuant to 35 U.S.C. §371, of PCT/KR2012/000712, filed Jan. 31, 2012, designating the United States, which claims priority to Korean Application No. 10-2011-0009834, filed Jan. 31, 2011. The entire contents of the aforementioned patent applications are incorporated herein by this reference. 
     TECHNICAL FIELD 
     The present invention relates to a mobile communication (PCS, cellular, IMT-2000, and the like) base station antenna, and more particularly, to a dual polarization antenna and a multiple band antenna system using the same. 
     BACKGROUND ART 
     Currently, various frequency bands are becoming available to sufficiently compensate for deficient frequency bands as mobile communications become common and wireless broadband data communications become activated. The mainly used frequency bands are low frequency bands (698 to 960 MHz) and high frequency bands (1.71 to 2.17 GHz or 2.3 to 2.7 GHz). Further, the multiple antenna based MIMO (Multiple Input Multiple Output) technology is an essential technology for increasing data transmission speed, and is applied to recent mobile communication network systems such as LTE (Long Term Evolution) and Mobile WiMAX. 
     However, when a plurality of antennas are installed to support the MIMO at various frequency bands, installation costs increase and tower spaces for installing antennas are significantly insufficient in an actual external environment. Further, tower rent costs increase and antenna management efficiency becomes an important problem. 
     Thus, triple band antennas are urgently requested instead of dual band antennas. While a high frequency band is inserted into an installation space for a low frequency band antenna and thus a width of the low frequency band antenna may be maintained according to a dual band antenna, it is difficult to insert a high frequency band antenna without increasing an antenna width when a triple band antenna is realized. 
     Meanwhile, due to a fear of common people that electromagnetic waves radiated from an antenna are harmful to human bodies, mobile communication providers conceal antennas if possible and decorate antennas in an environment-friendly way, making sizes of antennas important. Further, since installation of antennas tends to be prohibited unless local residents agree with the installation, recent mobile communication network antennas can be changed and installed only if the widths of the antennas do not exceed a width (for example, about 300 mm) of a conventionally installed low frequency antenna. Of course, classical problems such as a wind pressure load and a load applied to a tower still exist. 
     Thus, although triple band antennas are urgently requested in recent mobile communication network systems, a conventional wide antenna width cannot be allowed in the market. 
     SUMMARY 
     Therefore, the present invention has been made in view of the above-mentioned problems, and an aspect of the present invention is to provide a dual polarization antenna for a mobile communication base station for optimizing a structural arrangement and antenna size of the dual polarization antenna to facilitate a design of the antenna, and a multiple band antenna system using the same. 
     Another aspect of the present invention is to provide a dual polarization antenna for a mobile communication base station for narrowing a width of the antenna and realizing a triple band antenna in a limited width, and a multiple band antenna system using the same. 
     In accordance with an aspect of the present invention, there is provided a dual polarization antenna comprising: a reflection plate; and a radiation module comprising first to fourth radiation devices comprising first to fourth radiation arms having bending parts, respectively, wherein the bending parts of the first to fourth radiation arms are sequentially adjacent to each other and are symmetrical to each other in four directions to form a             shape when viewed from the top, the first to fourth radiation devices have supports integrally extending toward the reflection plate at the bending parts of the first to fourth radiation arms, and the radiation module comprises a first feeding line installed to transfer signals to the first and third radiation arms and a second feeding line installed to transfer signals to the second and fourth radiation arms.
     In accordance with another aspect of the present invention, there is provided a multiple band antenna system comprising: a reflection plate; a first radiation module comprising first to fourth radiation devices comprising first to fourth radiation arms having bending parts, respectively, wherein the first to fourth radiation arms are disposed on the reflection plate such that the bending parts are sequentially adjacent to each other and form a             shape when viewed from the top; and a second or third radiation module installed on the reflection plate at a least one of upper and lower sides of left and right sides of the installation site of the first radiation module having the           shape.
     As described above, a dual polarization antenna for a mobile communication base station and a multiple band antenna system using the same can optimize a structural arrangement and antenna size of the dual polarization antenna to facilitate design of the antenna and narrow a width of the antenna and realize a triple band antenna in a limited width. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing an example of a conventional dual polarization antenna. 
         FIG. 2  is a plan view showing a virtual structure for realizing a triple band dual polarization antenna using the antenna of  FIG. 1 . 
         FIG. 3  is a perspective view showing a structure of a dual polarization antenna according to an embodiment of the present invention. 
         FIG. 4  is a cutaway sectional view taken along line A-A′ of  FIG. 1 . 
         FIG. 5  is an enlarged perspective view of a central upper end of  FIG. 1 . 
         FIG. 6A  is a perspective view of a first modification structure of  FIG. 1 . 
         FIG. 6B  is a perspective view of a second modification structure of  FIG. 1 . 
         FIG. 7  is a schematic plan view showing a multiple band antenna system using the dual polarization antenna according to the embodiment of the present invention. 
         FIG. 8A  is a plan view showing a modification structure of  FIG. 7 . 
         FIG. 8B  is a perspective view of  FIG. 8B . 
         FIG. 9  is a view showing a dual polarization forming state in a dual polarization antenna according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Meanwhile, a structure of a conventional dual polarization antenna will be described first to help understanding of the present invention. 
       FIG. 1  is a perspective view showing an example of a conventional dual polarization antenna, and shows a structure disclosed in U.S. Pat. No. 6,034,649 of ‘Andrew Corporation’. Referring to  FIG. 1 , in the conventional dual polarization antenna, a radiation module  1  has first and second dipoles  1   a  and  1   b  installed to cross each other, and thus is realized in an ‘X’ form as a whole. The first dipole  1   a  includes two half dipoles  1   a ′ and  1   a ″, which are installed at +45 degrees with respect to a vertical axis or a horizontal axis, and the second dipole  1   b  also includes two half dipoles  1   b ′ and  1   b ″, which are installed at −45 degrees. The half dipoles  1   a ′,  1   a ″,  1   b ′, and  1   b ″ of the first and second dipoles  1   a  and  1   b  are supported on a reflection plate by a balun and a base  2 . 
     Then, signals are transferred in a non-contact coupling method by a plurality of microstrip hooks  3  generally similar to a hook shape between the two half dipoles  1   a ′ and  1   a ″ of the first dipole  1   a  and between the two half dipoles  1   b ′ and  1   b ″ of the second dipole  1   b . A plurality of clips  4  are installed to support the plurality of microstrip hooks  3  and maintain intervals between the microstrip hooks  3  and the dipoles. 
     In this way, ‘X’ shaped dual polarizations are generated by the radiation module  1  realized generally in an ‘X’ form. Current mobile communication base station antennas mainly support dual polarization diversities and the mainly used conventional dipole antennas are in the ‘X’ form. 
     However, considering a case of realizing a triple band antenna in a ‘X’ form antenna structure, as shown in  FIG. 2 , an outer end of a low frequency band dipole located at the center thereof is adjacent to outer ends of high frequency band dipoles located on left and right side surfaces thereof, and radiation characteristics of the antenna are significantly distorted by the generated interference. The problem may be easily solved by enlarging a width of the antenna so as not to exclude influences of the interference, but the measure has a size problem and cannot be accepted by the market. 
     The present invention provides a new form of an antenna structure, escaping from the conventional X form dipole structure, which minimizes a width of the antenna particularly when a triple band antenna is applied. 
       FIG. 3  is a perspective view showing a structure of a dual polarization antenna according to an embodiment of the present invention, in which a feeding structure is schematically shown by dotted lines for convenience&#39; sake.  FIG. 4  is a cutaway sectional view taken along line A-A′ of  FIG. 1 .  FIG. 5  is an enlarged perspective view of a central upper end of  FIG. 1 , in which a cut form including the feeding structure is shown. 
     Referring to  FIGS. 3 to 5 , the dual polarization antenna according to the embodiment of the present invention may be realized by a first radiation module  10  for a first frequency band (for example, a frequency band of about 700 to 1000 MHz). The first radiation module  10  includes bending parts, and for example, includes first to fourth radiation devices including first to fourth radiation arms  11 ,  12 ,  13 , and  14  having a             shape, respectively. Then, the bending parts of the first to fourth radiation arms  11 ,  12 ,  13 , and  14  are sequentially adjacent to each other and are symmetrical to each other in four directions to form a           shape when viewed from the top.
     That is, although disposition directions and locations of the first to fourth radiation arms  11 ,  12 ,  13 , and  14  are different, the first to fourth radiation arms  11 ,  12 ,  13 , and  14  may have the same structure. For example, a bending angle of the bending part of the first radiation device  11  may be, for example, a right angle, and includes first and second conductive radiation arms  11   a  and  11   b  in which ends of the ‘┐’ shape form, for example, 90 degrees and which is designed to have a predetermined length. Then, a support  11   c  integrally extending toward an antenna reflection plate  5  is formed at a connecting part of the first and second radiation arms  11   a  and  11   b , that is, the bending part of the first radiation arm  11 . Then, the support  11   c  may be fixedly attached to the reflection plate  5  through screw coupling or welding. Likewise, the second to fourth radiation arms  12 ,  13 , and  14  includes first radiation arms  12   a ,  13   a , and  14   a , second radiation arms  12   b ,  13   b , and  14   b , and supports  12   c ,  13   c , and  14   c . For example, the first to fourth radiation arms  11 ,  12 ,  13 , and  14  sequentially form             and           shapes in the           shape. That is, the           and           parts are located in a third quarter plane, a fourth quarter plane, a second quarter plane, and a first quarter plane, respectively.
     The first to fourth radiation devices are similar to dipole structures in their external appearances at a glance, but it can be seen that they actually employ a bow-tie structure. That is, as will be described below, the supports  11   c ,  12   c ,  13   c , and  14   c  form parts of the feeding structure and the first radiation arms  11   a ,  12   a ,  13   a , and  14   a  and the second radiation arms  11   b ,  12   b ,  13   b , and  14   b  form suitable radiation surfaces according to a corresponding frequency on opposite sides of the supports  11   c ,  12   c ,  13   c , and  14   c . Then, as shown, the first radiation arms  11   a ,  12   a ,  13   a , and  14   a  and the second radiation arms  11   b ,  12   b ,  13   b , and  14   b  are configured such that a width of a surface (a lateral surface in the drawing) of a radiation device facing another radiation device is larger than a surface (an upper surface of the drawing) of the radiation device from which signals are radiated. This configuration is done to minimize an influence to another radiation module and achieve a smooth radiation through impedance matching (adjustment) with an adjacent radiation arm. 
     Meanwhile, in a description of a feeding structure of the first radiation module  10 , the first feeding line  21  having a strip line structure is installed to transmit a signal through non-contact coupling with the supports  11   c  and  13   c  of the first and third radiation arms  11  and  13 , and the second feeding line  22  is installed to transmit a signal through non-contact coupling with the supports  12   c  and  14   c  of the second and fourth radiation arms  12  and  14 . 
     Then, parallel surfaces for maintaining a preset space distance while facing striplines of the first and second feeding lines  21  and  22  are formed at central longitudinal axes of the supports  11   c ,  12   c ,  13   c , and  14   c  so that signals are transferred therebetween through a non-contact coupling method. Spacers  31 ,  32 ,  33 , and  34  having suitable structures for supporting the feeding lines  21  and  22  and maintaining the spacing between the feeding lines and the supports to be constant may be installed at preset locations between parallel surfaces of the supports  11   c ,  12   c ,  13   c , and  14   c  and the strip lines of the first and second feeding lines  21  and  22  to maintain the spacing distance. The spacers  31 ,  32 ,  33 , and  34  may include, for example, a female screw structure located between the paral surfaces of the supports  11   c ,  12   c ,  13   c , and  14   c  and the strip lines of the first and second feeding lines  21 , and a male screw structure coupled to the female screw structure through holes formed at locations of the first and second feeding lines  21  and  22  and/or the supports  11   c ,  12   c ,  13   c , and  14   c.    
     In a more detailed description of the installation structures of the first and second feeding lines  21  and  22 , the first feeding line  21  extends from a lower side of the support  11   c  of the first radiation arm  11  toward an upper side thereof while partially extending along the reflection plate  5  in a strip line structure, exceeds the bending part of the first radiation arm  11  to extend to the third radiation arm  13  of the third radiation device so as to face a slant line direction, and exceeds the bending part of the third radiation arm  13  to further extend to the support  13   c  of the third radiation arm  13 . Likewise, the second feeding line  22  is formed along the supports  12   c  and  14   c  of the second radiation arm  12  and the fourth radiation arm  14 . According to the structure, the first and second feeding lines  21  and  22  cross each other (to be spaced apart from each other) at a middle part of the first radiation module  10 , and a spacer  41  having a suitable structure may be provided at the crossed part to prevent a contact between the two feeding lines and prevent a mutual influence of transmitted signals. 
     Meanwhile, outer sides of the parallel surfaces of the first and second feeding lines  21  and  22  from central longitudinal axes of the supports  11   c ,  12   c ,  13   c , and  14   c , that is, side surfaces of the supports  11   c ,  12   c ,  13   c , and  14   c  further extend to surround the strip lines of the first and second feeding lines  21  and  22 . Since the supports act as the ground terminals, the structure can show a more improved grounding performance. That is, since the extension structure is inclined toward the strip lines to surround the supports, loss of signals can be reduced. 
     Further, since the supports  11   c ,  12   c ,  13   c , and  14   c  electrically serve as ground terminals to the strip lines, a length of the supports is designed according to λ/4 to achieve an open state (ground state). 
     Due to the feeding structure, as shown in  FIG. 9 , the first radiation arm  11  and the third radiation arm  13  form +45 degree polarizations of the ‘X’ polarizations with respect to a vertical axis and the second and fourth radiation arms  12  and  14  form −45 degree polarizations. 
       FIG. 6A  is a perspective view of a first modification structure of  FIG. 1 .  FIG. 6B  is a perspective view of a second modification structure of  FIG. 1 . The structures shown in  FIGS. 6A and 6B  are characterized, in particular, in the feeding structures as compared with the structure shown in  FIG. 1 . In the structure shown in  FIG. 6A , for example, the first feeding line  21  exceeds the bending part of the first radiation arm  11  to extend to the third radiation arm  13  facing in a slant line direction but does not exceed the bending part of the third radiation arm  13  to extend inward. 
     In the structure shown in  FIG. 6B , for example, the first feeding line  21  exceeds the bending part of the first radiation arm  11  to extend to the third radiation arm  13  facing in a slant line direction, and is directly connected to the bending part of the third radiation arm  13  through welding or soldering. 
     Meanwhile, it can be seen that the feeding structure of the present invention employs a so called over bridge method unlike a side bridge method in which the feeding lines are installed between side surfaces of radiation devices in a dipole structure as shown in  FIG. 1 . 
     Further, since the supports include air strip balun structures serving as ground terminals of the feeding lines having a strip line structure in the feeding structure of the present invention, the feeding structure of the present invention can be realized more simply and efficiently as compared with a method of employing balum structures in the conventional radiation structures having the conventional dipole structure. 
       FIG. 7  is a schematic plan view showing a multiple band antenna system using the dual polarization antenna according to the embodiment of the present invention. Referring to  FIG. 7 , the multiple band multiple antenna system according to the embodiment of the present invention includes, for example, a first radiation module  10  for a first frequency band (for example, a frequency band of about 700 to 1000 MHz), second radiation modules  50 - 1  and  50 - 2  for a second frequency band (for example, a frequency band of 1.7 to 2.2 GHz), and third radiation modules  60 - 1  and  60 - 2  for a third frequency band (for example, a frequency band of 2.3 to 2.7 GHz). 
     The first radiation module  10  may have a dual polarization antenna structure according to the embodiment of the present invention shown in  FIGS. 2 to 4 . 
     Although the second radiation modules  50 - 1  and  50 - 2  and the third radiation modules  60 - 1  and  60 - 2  may have the antenna structure according to the embodiment of the present invention shown in  FIGS. 2 to 4 , they may employ antenna structures of various conventional dipole structures and various forms such as a tetrahedral form, an ‘X’ form, and a lozenge form may be applied to the entire outer forms. 
     Then, the second radiation modules  50 - 1  and  50 - 2  and the third radiation modules  60 - 1  and  60 - 2  are installed at upper and lower sides of left and right sides of the installation site of the first radiation module  10  having a             shape as a whole. That is, assuming that the disposition structure of the antenna system forms a tetrahedral shape, the second radiation modules  50 - 1  and  50 - 2  and the third radiation modules  60 - 1  and  60 - 2  are installed at corners of the tetrahedral shape, respectively and the first radiation module  10  is installed at a center of the tetrahedral shape.
     Then, the first radiation module  10  having a             shape has empty spaces at upper and lower portions of the left and right sides of the installation site, and the second and third radiation modules  50 - 1 ,  50 - 2 ,  60 - 1 , and  60 - 2  are installed such that the installation sites of the second radiation modules  50 - 1  and  50 - 2  and the third radiation modules  60 - 1  and  60 - 2  at least partially overlap the empty spaces of the installation site of the first radiation module  10 .
     Due to the installation structure, an entire size of the antenna system can be reduced and can be optimized when an antenna system of multiple bands, in particular, triple bands is realized. 
     Moreover, strong electric fields are generated at outer ends of the radiation structures in the radiation devices to generate interference of signals with adjacent radiation devices, and in the structure of the antenna system according to the present invention, a sufficient distance can be secured between the second and third radiation modules adjacent to an outer end of the radiation device of the first radiation module  10  with a reduced side. 
     Meanwhile,  FIGS. 8A and 8B  show a plan view and a perspective view of the modified structure of  FIG. 7 , and as shown in  FIGS. 8A and 8B , all of the first to third radiation modules  10  may have the dual polarization antenna structure according to the embodiment of the present invention shown in  FIGS. 2 to 4 . 
     The dual polarization antenna for a mobile communication base station according to the embodiment of the present invention and the multiple band antenna system using the same can be configured as described above. Meanwhile, although the detailed embodiments have been described in the description of the present invention, various modifications can be made without departing from the scope of the present invention.