Patent Publication Number: US-9431718-B2

Title: Antenna device including triplate line including central conductor and ground plates

Description:
The present application is based on Japanese patent application No. 2013-179481 filed on Aug. 30, 2013, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an antenna device. 
     2. Description of the Related Art 
     As an antenna device for suppressing a loss in a feed line and simplifying an antenna structure, e.g., an antenna device using a triplate line has been developed. The triplate line includes a central conductor plate and one pair of ground plates sandwiching the central conductor plate as a feed line. 
     Refer to e.g JP-A 63-88902. 
     SUMMARY OF THE INVENTION 
     However, in the conventional antenna device using the triplate line as the feed line, there is a disadvantage in that, e.g., for the case of a frequency sharing antenna device, the central conductor plate cannot be made in one piece but should be divided into plural blocks, so that the number of parts or components will be increased and assembling work of the antenna device will become troublesome. 
     Accordingly, it is an object of the present invention to provide an antenna device which can be easily assembled. 
     According to a feature of the invention, an antenna device, comprises: 
     a feed line comprising a triplate line, each triplate line comprising a central conductor and two ground plates sandwiching the central conductor via an air layer; 
     wherein at least a part of the triplate line is configured such that the two ground plates sandwich a center substrate comprising a wiring pattern as the central conductor provided on a dielectric substrate via the air layer. 
     In the above embodiment of the invention, the following modifications and changes can be made. 
     (i) The dielectric substrate is located at a position where a first distance from one surface provided with the central conductor to one of the two ground plates facing to the one surface is greater than a second distance from the other surface opposed to the one surface to the other of the two ground plates facing to the other surface. 
     (ii) The dielectric substrate is located equidistantly from both of the two ground plates. 
     (iii) The triplate line comprises a first triplate line and a second triplate line connected to be intersected with the first triplate line, 
     wherein a feed signal fed from outside is transmitted from the second triplate line to an antenna element via the first triplate line, 
     wherein at least a part of the first triplate lines is configured such that the two ground plates sandwich the center substrate via the air layer. 
     (iv) The second triplate line is installed on a side of one of the two ground plates of the first triplate line and the antenna element is installed on a side of the other of the two ground plates of the first triplate line, 
     wherein the center substrate comprises the central conductor on the dielectric substrate on a side of the antenna element. 
     (vi) The center substrate is supported by the two ground plates via a spacer provided at a region of the center substrate, and the region is not provided with the spacer. 
     Points of the Invention 
     According to the present invention, it is possible to provide an antenna device which can be easily assembled. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The preferred embodiments according to the invention will be explained below referring to the drawings, wherein: 
         FIGS. 1A and 1B  show a configuration example of an antenna device in the present embodiment, wherein  FIG. 1A  is a schematically cross-sectional view showing the interconnection of triplate lines in the antenna device in the present embodiment, and  FIG. 1B  is a schematically cross-sectional view showing a structure of a first triplate line; 
         FIG. 2A  is a perspective view showing an appearance of the antenna device in  FIGS. 1A and 1B ; 
         FIG. 2B  is a perspective view showing an internal configuration of a radome, in which the plurality of triplate lines and the antenna elements are partially not shown; 
         FIGS. 3A and 3B  show a configuration example of a second triplate line in the antenna device in  FIGS. 1A and 1B , wherein  FIG. 3A  is a perspective view thereof in which one of ground plates is not shown, and  FIG. 3B  is a schematically cross-sectional view of the second triplate line; 
         FIG. 4  is a perspective view showing a configuration of an antenna element in the antenna device in  FIG. 1 , and 
         FIG. 5  is a perspective view of the first triplate line in the antenna device in  FIG. 1  in which one of ground plates is not shown. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Next, an antenna device according to the present invention will be explained below with reference to appended drawings. 
       FIGS. 1A and 1B  show a configuration example of an antenna device in the present embodiment, wherein  FIG. 1A  is a schematically cross-sectional view showing the interconnection of triplate lines in the antenna device in the present embodiment, and  FIG. 1B  is a schematically cross-sectional view showing a structure of a first triplate line. 
       FIG. 2A  is a perspective view showing an appearance of the antenna device in  FIGS. 1A and 1B .  FIG. 2B  is a perspective view showing an internal configuration of a radome, in which the plurality of triplate lines and the antenna elements are partially not shown. 
     As shown in  FIGS. 1A, 1B, 2A and 2B , an antenna device  1  is provided with one or more triplate line  4  as a feed line, each of which comprises a central conductor  2  and two ground plates  3  sandwiching the central conductor  2  via an air layer  9 . The antenna device  1  is used as e.g. a mobile communication base station antenna. 
     The antenna device  1  comprises a radome  21  having a cylindrical shape. The radome  21  accommodates the triplate lines  4 , and is closed by antenna caps (not shown) at both ends thereof. The radome  21  is provided with mounting brackets  22  for mounting the radome  21  on an antenna tower, etc. The antenna device  1  is mounted on the antenna tower, etc. with the mounting brackets  22  such that an axial direction (longitudinal direction) of the radome  21  is a vertical direction. 
     In the present embodiment, the antenna device  1 , which is configured as a frequency sharing antenna for transmitting/receiving signals in two frequency bands, will be explained. When the antenna device  1  is used as the frequency sharing antenna for two frequency bands and both a vertical polarized wave and a horizontal polarized wave are used in each of the two frequency bands, four system feed lines would be required. If all the four system feed lines are incorporated in one triplate line  4 , a space required for the triplate line  4  would be significantly increased and the size of an entire antenna device will be increased. Therefore, in the present embodiment, the triplate line  4  is divided into plural triplate lines and divided triplate lines are connected to be intersected with each other. 
     More specifically, the triplate line  4  comprises a first triplate line (lateral triplate line)  4   a , and one or more second triplate line (vertical triplate line)  4   b  connected to be intersected with the first triplate line  4   a . Here, one second triplate line  4   b  is provided for each of the four system feed lines. Namely, the total number of the second triplate lines  4   b  is four. These second triplate lines  4   b  (four in number) are connected to the first triplate line  4   a  such that the second triplate lines  4   b  are orthogonally intersected with the first triplate line  4   a . In other words, the second triplate lines  4   b  are provided along a direction perpendicular to the first triplate line  4   a  and they are intersected with each other. 
     In the antenna device  1 , a feed signal fed from outside the antenna device  1  is transmitted from the second triplate lines  4   b  to an antenna element portion  5  via the first triplate line  4   a . In the present embodiment, the plurality of second triplate lines  4   b  (four in number) are arranged in parallel to be distant from each other. Two of the second triplate lines  4   b  for respective vertical and horizontal polarized waves in a low frequency band (e.g. 700 to 800 MHz) are located at both outer sides, while the other two of the second triplate lines  4   b  for respective vertical and horizontal polarized waves in a high frequency band (e.g. 1.5 to 2 GHz) are located at an inner side. The number of frequency bands to be shared is not limited to two. Further, the number and arrangement of the second triplate lines  4   b  are not limited to those shown in the attached drawings. 
     As shown in  FIGS. 1A to 3B , each of the second triplate lines  4   b  comprises a central conductor plate  2   b  made of a metal plate as a central conductor  2 , and two ground plates  3   b  for sandwiching the central conductor plate  2   b  via an air layer  9 . The two ground plates  3   b  are opposite each other to be parallel with each other. The central conductor plate  2   b  is located in an equidistant position (i.e. equidistantly) from both of the two ground plates  3   b , i.e., at a middle position between the two ground plates  3   b . As the ground plate  3   b , a plate made of aluminum which is light in weight, low in cost and excellent in weather resistance may be used. 
     In each of the second triplate lines  4   b , the central conductor plate  2   b  is provided with a dielectric insertion type phase shifter  31  which is configured to distribute the feed signals input from the outside and adjust the phase of the feed signals for outputting the phase-adjusted signals to the first triplate line  4   a . The dielectric insertion type phase shifter  31  is connected to a linear motor unit  32  for moving its dielectric plate along the central conductor plate  2   b.    
     One end portion of the ground plate  3   b  of the second triplate line  4   b  is formed to have a flange shape. The flange portion is fixed to the ground plate  3   a  of the first triplate line  4   a  with bolts so that the second triplate line  4   b  is fixed to the first triplate line  4   a  as well as the ground plates  3   a ,  3   b  are electrically connected with each other. 
     The central conductor  2   b  of the second triplate line  4   b  includes a portion extended from the one end portion of the ground plate  3   b , and the extended portion is inserted into a through-hole  41  formed at the ground plate  3   a  of the first triplate  4   a , so that the central conductor plate  2   b  of the second triplate line  4   b  is electrically connected to a central conductor  2  (wiring pattern  2   a ) of the first triplate line  4   a.    
     As shown in  FIG. 4 , an antenna element  51  is provided at the first triplate line  4   a  on the side opposite to the side provided with the second triplate lines  4   b . Namely, in the antenna device  1 , the second triplate lines  4   b  are provided at one ground plate  3   a  side of the first triplate line  4   a  and the antenna element  51  is provided at the other ground plate  3   a  side of the first triplate line  4   a.    
     The antenna element  51  comprises a wiring pattern formed on a plate-like substrate comprising an electrically insulating material such as resin, and the antenna element  51  is installed in a standing manner on the one ground plate  3   a  of the first triplate line  4   a.    
     The antenna element  51  has two antenna element pairs  52 ,  53  corresponding to the two frequency bands. A first antenna element pair  52  for a high frequency band has a first horizontal polarized antenna element  52   a , and a first vertical polarized antenna element  52   b . A second antenna element pair  53  for a low frequency band has a second horizontal polarized antenna element  53   a , and a second vertical polarized antenna element  53   b . It should be noted that the configuration and arrangement of the antenna element  51  are not limited to those shown in  FIGS. 1A to 3B . The antenna element  51  is electrically connected with the central conductor  2  (wiring pattern  2   a ) of the first triplate line  4   a  through a through-hole  42  formed at the ground plate  3   a  of the first triplate line  4   a  (cf.  FIG. 1A ). 
     Referring to  FIGS. 1B and 5 , in the antenna device  1  according to the present embodiment, at least a part of the triplate lines  4  is configured such that the two ground plates  3  sandwich a center substrate  7  comprising the wiring pattern  2   a  as the central conductor  2  provided on a dielectric substrate  6  via an air layer  9 , In the present embodiment, at least a part of the first triplate line  4   a  is configured such that the two ground plates  3   a  sandwich the center substrate  7  via the air layer  9 . The dielectric substrate  6  may be e.g. FR4 (Flame Retardant Type 4) substrate. As the ground plate  3   a , a plate made of aluminum which is light in weight, low in cost and excellent in weather resistance may be used. 
     Since the wiring pattern  2   a  provided on the center substrate  7  is used as the central conductor  2  of each of the triplate lines  4 , even though the central conductor  2  is divided into a plurality of blocks, these parts or components can be handled as an integral part and the assembling thereof will be carried out easily. 
     In the antenna device  1  according to the present embodiment, the feed signals distributed by the second triplate lines  4   b  are further distributed to the respective antenna elements  51  through the first triplate line  4   a . Therefore, the central conductor  2  of the first triplate line  4   a  is necessarily divided into plural (a lot of) blocks as shown in  FIG. 5 . Thus, the assembling of the antenna device  1  can be facilitated remarkably by providing the first triplate line  4   a  including the central conductor  2  to be divided into plural blocks with a triplate structure using the center substrate  7  (hereinafter referred to as “substrate triplate structure”). 
     It should be noted that, in the present embodiment, only the first triplate line  4   a  is explained as the substrate triplate structure, however, the present invention is not limited thereto. The second triplate line  4   b  may have the substrate triplate structure. It should be noted that when the substrate triplate structure is applied to the second triplate lines  4   b , the assembling of the antenna device  1  will be facilitated but the dielectric loss may be increased, because the second triplate line  4   b  includes the central conductor  2  having a relatively long line length for distributing the feed signal. 
     Thus, it is preferable to apply the substrate triplate structure to only a portion in which a line length of the central conductor  2  is short and divided into plural portions, like the first triplate line  4   a  in the present embodiment, in order to suppress the dielectric loss at a low level. 
     As shown in  FIG. 1B , the dielectric substrate  6  is located at the position where a distance “a” from one surface provided with the wiring pattern  2   a  as the central conductor  2  to the ground plate  3   a  facing to the one surface is greater than a distance “b” from the other surface opposed to the one surface to the ground plate  3   a  facing to the other surface. 
     It is necessary to locate the wiring pattern  2   a  as the central conductor  2  and the ground plate  3   a  to be close to each other to some extent, so as to secure isolation between the lines. At this time, the central conductor plate  2   b  of each of the second triplate lines  4   b  is soldered to the wiring pattern  2   a . Therefore, when the wiring pattern  2   a  is too close to the ground plate  3   b , a solder  8  for soldering the central conductor plate  2   b  may contact with the ground plate  3   a . Thus, in the present embodiment, the dielectric substrate  6  is placed at a position closer to the other side opposite to the side formed with the wiring pattern  2   a  than a middle position between the two ground plates  3   a ,  3   a , such that the isolation will be secured while the contact of the solder  8  to the ground plates  3   a  can be suppressed. Herein, the dielectric substrate  6  is located such that the two ground plates  3   a  are arranged equidistantly from the wiring pattern  2   a.    
     Also, in the present embodiment, the center substrate  7  is configured such that the wiring pattern  2   a  is formed on an antenna element  51  side surface of the dielectric substrate  6 . If the wiring pattern  2   a  is formed on a second triplate line  4   b  side surface, such a configuration may reduce a work space for soldering the wiring pattern  2   a  and the central conductor plate  2   b  after fixing the second triplate lines  4   b , thereby the work of the soldering may become difficult. 
     The center substrate  7  is supported by the ground plate  3   a  via a spacer (not shown). The spacer is preferably provided at a region with no wiring pattern  2   a  of the center substrate  7 . If the spacers are provided at a region with the wiring pattern  2   a , the impedance will be varied so that it will be necessary to perform adjustment, e.g., to lengthen the line length. Namely, it is necessary to provide the spacer directly on the central conductor plate  2   b  in the triplate line  4  using the metal plate (central conductor plate  2   b ) for the central conductor  2 , so that it will be necessary to perform adjustment, e.g., to lengthen the line length for impedance matching. Meanwhile, according to the substrate triplate structure, such an adjustment will become needless as well as the line length will be shortened and the center substrate  7  will be downsized. As a result, the installation work of the center substrate  7  will be carried out easily. 
     As described above, in the antenna device  1  according to the present embodiment, at least a part of the triplate line  4  is configured such that the two ground plates  3  sandwich the center substrate  7  comprising the wiring pattern  2   a  as the central conductor  2  provided on the dielectric substrate  6  via the air layer  9 . 
     When a metal plate (central conductor plate) is used for the central conductor  2 , the central conductor  2  is divided for respective frequencies and further for respective polarized waves in order to provide the frequency sharing, which would make the assembling work troublesome. According to the present embodiment, the center substrate  7  comprising the wiring pattern  2   a  as the central conductor  2  provided on the dielectric substrate  6  is used, so that the central conductors  2  for respective frequencies and for respective polarized waves can be integrated and the assembling work can be facilitated. 
     Also, according to the substrate triplate structure, it is not necessary to provide the spacer directly on the central conductor  2 . Further, the wavelength shortening effect can be achieved by the presence of the dielectric substrate  6 . In comparison with the case that the metal plate (central conductor plate) is used for the central conductor  2 , the line length of the central conductor  2  can be shortened and the center substrate  7  will be downsized. As a result, the installation work of the center substrate  7  will be carried out more easily. 
     The present invention is not limited to the above embodiment, and modification or variation may be made without going beyond the scope of the present invention. 
     For example, the shape of the ground plate  3  or the central conductor  2  (including the center substrate  7 ) is not limited to a planar shape or plate-like shape and may be a curved shape. 
     Although the invention has been described with respect to the specific embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.