Patent Publication Number: US-9905937-B1

Title: Multi-input multi-output antenna device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The instant invention relates to an antenna device; in particular, to a multi-input multi-output (MIMO) antenna device. 
     2. Description of Related Art 
     The conventional single patch antenna has a maximum gain of 8 dBi, so a plurality of the conventional patch antennas must be combined to form an antenna array achieving a larger gain requirement (e.g., more than 8 dBi). However, the conventional antenna array is formed by collecting the conventional patch antennas, so the size of the conventional antenna array is too large, limiting the applied scope. 
     SUMMARY OF THE INVENTION 
     The instant disclosure provides a MIMO antenna device for effectively solving the problem generated from the conventional antenna array. 
     The instant disclosure provides a multi-input multi-output (MIMO) antenna device, comprising: an antenna array defining a first longitudinal direction and a second longitudinal direction perpendicular to the first longitudinal direction, the antenna array comprising: a buffering sheet having a substantially square shape and arranged at a center of the antenna array; a low-frequency unit having four low-frequency antennas and two first jumpers, wherein the four low-frequency antennas each having a substantially square shape are respectively arranged at four corners of the antenna array, wherein any two adjacent low-frequency antennas arranged in the first longitudinal direction are electrically connected by using one of the first jumpers, and the two first jumpers are arranged to face each other; a high-frequency unit having two first high-frequency antennas and two first extending segments, wherein the two first high-frequency antennas each having a substantially square shape are respectively arranged at two opposite sides of the buffering sheet, and the two first high-frequency antennas and the buffering sheet are arranged in the first longitudinal direction, wherein any two adjacent low-frequency antennas arranged in the second longitudinal direction are arranged with one of the first high-frequency antennas there-between, the buffering sheet and each of the first high-frequency antennas are electrically connected by using one of the first extending segments; wherein the length of an edge of the buffering sheet is different from that of an edge of each of the first high-frequency antennas, and the edge of each of the first high-frequency antennas is shorter than an edge of each of the low-frequency antennas; and a feeding unit having a first feeding segment and a second feeding segment, wherein two of the low-frequency antennas arranged in a diagonal of the antenna array are respectively and electrically connected to the adjacent first high-frequency antennas by using the first feeding segment and the second feeding segment; and a grounding member and a plurality of supporting pillars, wherein an end of each of the supporting pillars is fixed on the antenna array, and the other end of each of the supporting pillars is fixed on the grounding member, so that the antenna array is arranged apart from the grounding member. 
     In summary, when the MIMO antenna device of the instant disclosure receives two high-frequency signals through the first feeding segment and the second feeding segment, the first high-frequency antennas and the buffering sheet are shared to transmit the two high-frequency signals, thereby reducing the size of the MIMO antenna device. 
     Moreover, the length of the side of the buffering sheet is different from the length of the side of each of the first high-frequency antennas, so the resonance frequency of the buffering sheet does not overlap the high-frequency band, thereby improving the isolation between two signals, wherein the two signals are traveling along the two first high-frequency antennas and the buffering sheet in two opposing directions. 
     In order to further appreciate the characteristics and technical contents of the instant invention, references are hereunder made to the detailed descriptions and appended drawings in connection with the instant invention. However, the appended drawings are merely shown for exemplary purposes, rather than being used to restrict the scope of the instant invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a MIMO antenna device according to a first embodiment of the instant disclosure; 
         FIG. 2  is a top view of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of  FIG. 1 ; 
         FIG. 4  is a top view of  FIG. 1  showing part of the antenna array corresponding to a first operating mode; 
         FIG. 5  is a top view of  FIG. 1  showing part of the antenna array corresponding to a second operating mode; 
         FIG. 6  is a simulating diagram showing the isolation of the MIMO antenna device in the first operating mode; and 
         FIG. 7  is a planar view showing the MIMO antenna device according to a second embodiment of the instant disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Please refer to  FIGS. 1 through 3 , which show a MIMO antenna device including an antenna array  100 , a grounding member  200 , and a plurality of supporting pillars  300  (shown in  FIG. 3 ). The grounding member  200  in the instant embodiment is a planar plate and has an area larger than that of the antenna array  100 . An end of each of the supporting pillars  300  is fixed on the antenna array  100 , and the other end of each of the supporting pillars  300  is fixed on the grounding member  200 , so that the antenna array  100  is arranged apart from the grounding member  200 . 
     It should be noted that “a substantially square shape” in the following description can be a square shape or a shape similar to a square shape. The following description discloses the construction of the antenna array  100 , and then discloses the operation of the antenna array  100 . 
     The outer contour of the antenna array  100  has a substantially square shape, and two adjacent edges of the substantially square shape of the antenna array  100  respectively define a first longitudinal direction D 1  and a second longitudinal direction D 2  perpendicular to the first longitudinal direction D 1 . The antenna array  100  includes a buffering sheet  1  having a substantially square shape and arranged at a center thereof, a low-frequency unit  2 , a high-frequency unit  3 , a feeding unit  4 , and a matching unit  5 . In the instant embodiment, the center of the buffering sheet  1  is the center of the antenna array  100 , and the antenna array  100  is a four-folded symmetrical construction with respect to the center of the buffering sheet  1 . The buffering sheet  1  and the high-frequency unit  3  are substantially in a coplanar arrangement, and a height H 1  of the low-frequency unit  2  with respective to the grounding member  200  is more than a height H 2  of the high-frequency unit  3  with respective to the grounding member  200 . 
     The low-frequency unit  2  includes four low-frequency antennas  21  in a substantially coplanar arrangement and each having a substantially square shape, two first jumpers  22 , and two second jumpers  23 . The four low-frequency antennas  21  are respectively arranged at four corners of the antenna array  100 , and each low-frequency antenna  21  does not shield the buffering sheet  1  in the height direction. 
     Any two adjacent low-frequency antennas  21  arranged in the first longitudinal direction D 1  (i.e., the left two low-frequency antennas  21  or the right two low-frequency antennas  21  shown in  FIG. 2 ) are electrically connected by using one of the first jumpers  22 , and the two first jumpers  22  are arranged to face each other in the second longitudinal direction D 2 . Any two adjacent low-frequency antennas  21  arranged in the second longitudinal direction D 2  (i.e., the upper two low-frequency antennas  21  or the lower two low-frequency antennas  21  shown in  FIG. 2 ) are electrically connected by using one of the second jumpers  23 , and the two second jumpers  23  are arranged to face each other in the first longitudinal direction D 1 . 
     Moreover, two adjacent edges of each of the low-frequency antennas  21  (e.g., the right edge and the lower edge of the upper left low-frequency antenna  21  shown in  FIG. 2 ) each has a center, and the centers of the two adjacent edges of each of the low-frequency antennas  21  are respectively connected to the corresponding first jumper  22  and the corresponding second jumper  23 . 
     The high-frequency unit  3  includes two first high-frequency antennas  31  each having a substantially square shape, two second high-frequency antennas  32  each having a substantially square shape, two elongated first extending segments  33 , and two elongated second extending segments  34 . The length of an edge of each of the first high-frequency antennas  31  is equal to that of an edge of each of the second high-frequency antennas  32 . 
     The two first high-frequency antennas  31  are respectively arranged at two opposite sides (i.e., the upper side and the lower side) of the buffering sheet  1 , and the two first high-frequency antennas  31  and the buffering sheet  1  are arranged in the first longitudinal direction D 1 . Any two adjacent low-frequency antennas  21  arranged in the second longitudinal direction D 2  (i.e., the upper two low-frequency antennas  21  or the lower two low-frequency antennas  21  shown in  FIG. 2 ) are arranged with one of the first high-frequency antennas  31  there-between, and the buffering sheet  1  and each of the first high-frequency antennas  31  are electrically connected by using one of the first extending segments  33 . The center of the buffering sheet  1 , the two first extending segments  33 , and a center of each of the two first high-frequency antennas  31  are arranged in the first longitudinal direction D 1 . Specifically, ends of the two first extending segments  33  are respectively connected to the centers of two opposite edges (i.e., the upper side and the lower side) of the buffering sheet  1 , and the other ends of the two first extending segments  33  are respectively connected to the centers of adjacent (and parallel) edges of the two first high-frequency antennas  31 . 
     The two second high-frequency antennas  32  are respectively arranged at two opposite sides (i.e., the left side and the right side) of the buffering sheet  1 , and the two second high-frequency antennas  32  and the buffering sheet  1  are arranged in the second longitudinal direction D 2 . Any two adjacent low-frequency antennas  21  arranged in the first longitudinal direction D 1  (i.e., the left two low-frequency antennas  21  or the right two low-frequency antennas  21  shown in  FIG. 2 ) are arranged with one of the second high-frequency antennas  32  there-between, and the buffering sheet  1  and each of the second high-frequency antennas  32  are electrically connected by using one of the second extending segments  34 . The center of the buffering sheet  1 , the two second extending segments  34 , and a center of each of the two second high-frequency antennas  32  are arranged in the second longitudinal direction D 2 . Specifically, ends of the two second extending segments  34  are respectively connected to the centers of two opposite edges (i.e., the left side and the right side) of the buffering sheet  1 , and the other ends of the two second extending segments  34  are respectively connected to the centers of adjacent (and parallel) edges of the two second high-frequency antennas  32 . 
     Moreover, the length L 3  of an edge of each of the first high-frequency antennas  31  is less than the length L 2  of an edge of each of the low-frequency antennas  21 , and the length L 1  of an edge of the buffering sheet  1  is different from (e.g., more than) the length L 3  of the edge of each of the first high-frequency antennas  31 . Preferably, the length L 1  of the edge of the buffering sheet  1  is less than the length L 2  of the edge of each of the low-frequency antennas  21  and is more than the length L 3  of the edge of each of the first high-frequency antennas  31 . 
     Each of the low-frequency antennas  21  in the instant embodiment is configured to transmit a signal in a low-frequency band of 2300 MHz˜2700 MHz. Each of the first high-frequency antennas  31  or the second high-frequency antennas  32  in the instant embodiment is configured to transmit a signal in a high-frequency band of 3400 MHz˜3800 MHz. 
     When the low-frequency unit  2  and the high-frequency unit  3  are orthogonally projected onto the grounding member  200  (as shown in  FIG. 2 ), the outer edge of any two of the low-frequency antennas  21  arranged in the first longitudinal direction D 1  (e.g., the left edges of the left two low-frequency antennas  21 ) and the outer edge of the adjacent second high-frequency antenna  32  (i.e., the left edge of the left second high-frequency antenna  32 ) are aligned with each other and are arranged in a collinear arrangement, the outer edge of any two of the low-frequency antennas  21  (e.g., the upper edges of the upper two low-frequency antennas  21 ) arranged in the second longitudinal direction D 2  and the outer edge of the adjacent first high-frequency antenna  31  (e.g., the upper edge of the upper first high-frequency antenna  31 ) are aligned with each other and are arranged in a collinear arrangement. 
     Moreover, as shown in  FIG. 2 , a first projecting region (not labeled) defined by orthogonally projecting each of the first jumpers  22  onto the adjacent second high-frequency antenna  32  is arranged apart from the center of the adjacent second high-frequency antenna  32  and is arranged away from the buffering sheet  1 , thus the above arrangement of each first jumper  22  can effectively avoid influencing the adjacent second high-frequency antenna  32 . A second projecting region (not labeled) defined by orthogonally projecting each of the second jumpers  23  onto the adjacent first high-frequency antenna  31  is arranged apart from the center of the adjacent first high-frequency antenna  31  and is arranged away from the buffering sheet  1 , thus the above arrangement of each second jumper  23  can effectively avoid influencing the adjacent first high-frequency antenna  31 . 
     The feeding unit  4  includes four separated segments, which are named as a first feeding segment  41 , a second feeding segment  42 , a third feeding segment  43 , and a fourth feeding segment  44 . Two of the low-frequency antennas  21  arranged in a diagonal of the antenna array  100  (i.e., the upper left low-frequency antenna  21  and the lower right low-frequency antenna  21  shown in  FIG. 2 ) are respectively and electrically connected to the adjacent first high-frequency antennas  31  by using the first feeding segment  41  and the second feeding segment  42 . The other two low-frequency antennas  21  arranged in the other diagonal of the antenna array  100  (i.e., the upper right low-frequency antenna  21  and the lower left low-frequency antenna  21  shown in  FIG. 2 ) are respectively and electrically connected to the adjacent second high-frequency antennas  32  by using the third feeding segment  43  and the fourth feeding segment  44 . 
     Moreover, each of the first feeding segment  41 , the second feeding segment  42 , the third feeding segment  43 , and the fourth feeding segment  44  in the instant embodiment has a substantially U-shape and is partially bent to the grounding member  200  for setting a signal feeding point F 1 , F 2 , F 3 , F 4 . The position of the signal feeding points F 1 , F 2 , F 3 , F 4  can be adjusted according to the designer&#39;s demand. 
     The matching unit  5  in the instant embodiment includes four L-shaped matching segments  51  respectively connected to the first feeding segment  41 , the second feeding segment  42 , the third feeding segment  43 , and the fourth feeding segment  44  for providing a matching adjustment to the feeding unit  4 . In addition, the instant disclosure can provide the matching adjustment by using a circuit board (not shown), changing the distance between the feeding unit  4  and the grounding member  200 , or changing the width of at least one of the first feeding segment  41 , the second feeding segment  42 , the third feeding segment  43 , and the fourth feeding segment  44 . 
     Specifically, the first feeding segment  41 , the second feeding segment  42 , the third feeding segment  43 , and the fourth feeding segment  44  of the antenna array  100  can be operated at the same time for receiving a plurality of signals, so the following description sequentially discloses a first operating mode of the MIMO antenna device and a second operating mode of the MIMO antenna device, thereby clearly explaining the operation of the MIMO antenna device. When in the first operating mode, the necessary elements of the antenna array  100  are shown in  FIG. 4 , and when in the second operating mode, the necessary elements of the antenna array  100  are shown in  FIG. 5 . 
     [First Operating Mode] 
     As shown in  FIG. 4 , a first dual-frequency patch antenna A includes the first feeding segment  41  and the connected matching segment  51 , the left two low-frequency antennas  21  and the connected first jumper  22  arranged in the first longitudinal direction D 1 , the two first high-frequency antennas  31 , the two first extending segments  33 , and the buffering sheet  1 . A second dual-frequency patch antenna B includes the second feeding segment  42  and the connected matching segment  51 , the right two low-frequency antennas  21  and the connected first jumper  22  arranged in the first longitudinal direction D 1 , the two first high-frequency antennas  31 , the two first extending segments  33 , and the buffering sheet  1 . 
     Accordingly, each of the first dual-frequency patch antenna A and the second dual-frequency patch antenna B is operated by using the two first high-frequency antennas  31 , the two first extending segments  33 , and the buffering sheet  1  to transmit a high-frequency signal, so the size of the antenna array  100  can be reduced. Moreover, in order to increase the isolation between the first dual-frequency patch antenna A and the second dual-frequency patch antenna B operated in the high-frequency band, the length L 1  of the side of the buffering sheet  1  is different from the length L 3  of the side of each of the first high-frequency antennas  31 , such that a resonance frequency of the buffering sheet  1  does not overlap the high-frequency band corresponding to each first high-frequency antenna  31 . Thus, two signals, which are respectively feeding from the first feeding segment  41  and the second feeding segment  42  and traveling along the two first high-frequency antennas  31  and the buffering sheet  1  in two opposing directions (i.e., two dashed arrows as shown in  FIG. 4 ), have an isolation smaller than −15 dB (i.e., the isolation of the instant embodiment as shown in  FIG. 6  can be smaller than −18 dB). 
     Similarly, as shown in  FIG. 2 , a third dual-frequency patch antenna C includes the third feeding segment  43  and the connected matching segment  51 , the upper two low-frequency antennas  21  and the connected second jumper  23  arranged in the second longitudinal direction D 2 , the two second high-frequency antennas  32 , the two second extending segments  34 , and the buffering sheet  1 . A fourth dual-frequency patch antenna D includes the fourth feeding segment  44  and the connected matching segment  51 , the lower two low-frequency antennas  21  and the connected second jumper  23  arranged in the second longitudinal direction D 2 , the two second high-frequency antennas  32 , the two second extending segments  34 , and the buffering sheet  1 . 
     Accordingly, each of the third dual-frequency patch antenna C and the fourth dual-frequency patch antenna D is operated by using the two second high-frequency antennas  32 , the two second extending segments  34 , and the buffering sheet  1  to transmit a high-frequency signal, so the size of the antenna array  100  can be reduced. Moreover, in order to increase the isolation between the third dual-frequency patch antenna C and the fourth dual-frequency patch antenna D operated in the high-frequency band, the length L 1  of the side of the buffering sheet  1  is different from the length of the side of each of the second high-frequency antennas  32 , such that the resonance frequency of the buffering sheet  1  does not overlap the high-frequency band corresponding to each second high-frequency antenna  32 . Thus, two signals, which are respectively feeding from the third feeding segment  43  and the fourth feeding segment  44  and traveling along the two second high-frequency antennas  32  and the buffering sheet  1  in two opposing directions, have an isolation smaller than −15 dB (i.e., the isolation of the instant embodiment can be smaller than −18 dB). 
     [Second Operating Mode] 
     Please refer to  FIG. 5 , which shows the first dual-frequency patch antenna and the third dual-frequency patch antenna C. The upper left low-frequency antenna  21  and the buffering sheet  1  are shared for the first dual-frequency patch antenna and the third dual-frequency patch antenna C. The shared low-frequency antenna  21  uses the center of the lower edge and center of the right edge to respectively connect to the corresponding first jumper  22  and the corresponding second jumper  23 , so a cross-section of the shared low-frequency antenna  21  along the center of the lower edge or the center of the right edge has an electric field of zero. Thus, when the first dual-frequency patch antenna A and the third dual-frequency patch antenna C are operated in the low-frequency band, the other two low-frequency antennas  21  of the first dual-frequency patch antenna A and the third dual-frequency patch antenna C do not influence each other by using the shared low-frequency antenna  21 . 
     Moreover, ends of the two first extending segments  33  are respectively connected to the centers of two opposite edges of the buffering sheet  1 , and the other ends of the two first extending segments  33  are respectively connected to the centers of adjacent (and parallel) edges of the two first high-frequency antennas  31 ; ends of the two second extending segments  34  are respectively connected to the centers of the other two opposite edges of the buffering sheet  1 , and the other ends of the two second extending segments  34  are respectively connected to the centers of adjacent (and parallel) edges of the two second high-frequency antennas  32 . Accordingly, a cross-section of the shared buffering sheet  1  along the center of any two opposite edges has an electric field of zero, and the resonance frequency of the buffering sheet  1  does not overlap the high-frequency band, so when the first dual-frequency patch antenna A and the third dual-frequency patch antenna C are operated in the high-frequency band, the first high-frequency antennas  31  and the second high-frequency antennas  32  do not influence each other by using the shared buffering sheet  1 . 
     Similarly, the other operating modes of the first dual-frequency patch antenna A, the second dual-frequency patch antenna B, the third dual-frequency patch antenna C, and the fourth dual-frequency patch antenna D are similar to at least one of the first operating mode and the second operating mode, so the instant embodiment does not describe it further. Moreover, when the MIMO antenna device is operated in the high-frequency band and the low-frequency band, the gains of each of the first dual-frequency patch antenna A, the second dual-frequency patch antenna B, the third dual-frequency patch antenna C, and the fourth dual-frequency patch antenna D are shown in the following chart. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                   
               
               
                 Frequency 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 (MHz) 
                 2300 
                 2350 
                 2400 
                 2450 
                 2500 
                 2550 
                 2600 
                 2650 
                 2700 
               
               
                   
               
             
            
               
                 A(dBi) 
                 10.45 
                 11.21 
                 10.94 
                 10.38 
                 10.05 
                 10.54 
                 10.81 
                 10.12 
                  9.94 
               
               
                 B(dBi) 
                 10.63 
                 11.11 
                 11.03 
                 10.74 
                  9.94 
                 10.59 
                 11.07 
                 10.54 
                  9.89 
               
               
                 C(dBi) 
                 11.15 
                 10.17 
                  9.83 
                 10.78 
                 10.34 
                 10.28 
                 10.28 
                  9.72 
                  9.33 
               
               
                 D(dBi) 
                 10.53 
                 11.13 
                 10.40 
                  9.86 
                  9.88 
                 10.61 
                 11.06 
                 10.77 
                 10.60 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                   
               
               
                 Frequency 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 (MHz) 
                 3400 
                 3450 
                 3500 
                 3550 
                 3600 
                 3650 
                 3700 
                 3750 
                 3800 
               
               
                   
               
             
            
               
                 A(dBi) 
                 8.76 
                  9.62 
                 10.84 
                 10.05 
                 8.80 
                 8.43 
                  9.12 
                  8.97 
                 9.02 
               
               
                 B(dBi) 
                 9.21 
                  9.57 
                 10.87 
                 10.51 
                 8.59 
                 8.22 
                  9.92 
                  9.83 
                 9.52 
               
               
                 C(dBi) 
                 9.65 
                 10.10 
                 10.21 
                  9.16 
                 9.02 
                 9.56 
                 10.26 
                 10.22 
                 8.71 
               
               
                 D(dBi) 
                 9.11 
                 10.29 
                 10.88 
                  9.91 
                 8.89 
                 9.13 
                  9.45 
                  9.68 
                 9.81 
               
               
                   
               
            
           
         
       
     
     In addition, the antenna array  100  in the instant embodiment takes  FIG. 2  for example, but in practical use, the antenna array  100  can be formed as shown in  FIG. 4 . Moreover, please refer to  FIG. 7 , which shows a second embodiment of the instant disclosure. Specifically, the length L 1  of the side of the buffering sheet  1  can be less than the length L 3  of the side of each of the first high-frequency antennas  31 , and the isolation of the antenna array  100  of the second embodiment is still better than the conventional antenna array. 
     The descriptions illustrated supra set forth simply the preferred embodiments of the instant invention; however, the characteristics of the instant invention are by no means restricted thereto. All changes, alterations, or modifications conveniently considered by those skilled in the art are deemed to be encompassed within the scope of the instant invention delineated by the following claims.