Patent Publication Number: US-7589680-B2

Title: Antenna unit with a parasitic coupler

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority of Taiwanese application no. 096113455, filed on Apr. 17, 2007. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an antenna unit, more particularly to an antenna unit with a parasitic coupler. 
   2. Description of the Related Art 
     FIG. 1  illustrates a conventional dual-band antenna unit mounted in a notebook computer  1 . The notebook computer  1  includes a lower housing  12 , a keyboard  16  mounted on the lower housing  12 , an upper housing  11  coupled pivotably to the lower housing  12 , a liquid crystal display (LCD)  17  mounted on the upper housing  11 , a grounding plate  18  mounted in the upper housing  11 , an image-capturing device  19  mounted on the upper housing  11  and disposed above the grounding plate  18  between upper left and right corners of the upper housing  11 , and a securing member  15  that secures the grounding plate  18  and the image-capturing device  19  on the upper housing  11 . The conventional antenna unit includes left and right antennas  14 ,  13 , each of which is a planar inverted-F antenna (PIFA) and is connected to the grounding plate  18  via the securing member  15 . The left antenna  14  is operable within the 2.4 GHz bandwidth and is disposed adjacent to the upper left corner of the upper housing  11 , whereas the right antenna  13  is operable within the 5.0 GHz bandwidth and is disposed adjacent to the upper right corner of the upper housing  11 . 
   The aforementioned conventional antenna unit is disadvantageous in that the left and right antennas  14 ,  13  have a relatively large physical size. Moreover, the securing member  15  undesirably affects transmission and reception of signals by the left and right antennas  14 ,  13 , and thereby decreasing efficiencies of the left and right antennas  14 ,  13 . 
   To solve the above problem, as illustrated in  FIG. 2 , it has been proposed to place both the left and right antennas  14 ,  13  in close proximity, remove the securing member  15 , and connect the left and right antennas  14 ,  13  directly to the grounding plate  18 . This configuration, however, can cause other problems. Particularly, interference is generated between the signals associated with the left and right antennas  14 ,  13 . Moreover, since this conventional antenna unit is not secured on the upper housing  11 , the left and right antennas  14 ,  13  are easily deformed during assembly. 
   SUMMARY OF THE INVENTION 
   Therefore, the object of the present invention is to provide an antenna unit that can overcome the aforesaid drawbacks of the prior art. 
   According to the present invention, an antenna unit comprises left and right antennas that are spaced apart from each other and that are operable within a first frequency bandwidth, and a parasitic coupler that is spaced apart from and disposed between the left and right antennas, and that is electromagnetically coupled to the left and right antennas so as to be operable within a second frequency bandwidth different from the first frequency bandwidth. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which: 
       FIG. 1  is a schematic view of a conventional antenna unit; 
       FIG. 2  is a schematic view of another conventional antenna unit; 
       FIG. 3  is a schematic view of the first preferred embodiment of an antenna unit according to this invention; 
       FIG. 4  is a schematic view illustrating the first preferred embodiment mounted in an electronic device; 
       FIGS. 5 and 6  are schematic views illustrating modified embodiments of the first preferred embodiment according to this invention; 
       FIG. 7  is a schematic view of the second preferred embodiment of an antenna unit according to this invention; 
       FIGS. 8 to 15  are schematic views illustrating modified embodiments of the second preferred embodiment according to this invention; 
       FIG. 16  is a plot illustrating a voltage standing wave ratio of the second preferred embodiment; 
       FIG. 17  is a plot illustrating radiation patterns of the left antenna and the parasitic coupler of the second preferred embodiment on the x-y, x-z, and y-z planes when operated at 2.437 GHz; 
       FIG. 18  is a plot illustrating radiation patterns of the left antenna and the parasitic coupler of the second preferred embodiment on the x-y, x-z, and y-z planes when operated at 5.470 GHz; 
       FIG. 19  is a plot illustrating radiation patterns of the right antenna and the parasitic coupler of the second preferred embodiment on the x-y, x-z, and y-z planes when operated at 2.437 GHz; and 
       FIG. 20  is a plot illustrating radiation patterns of the right antenna and the parasitic coupler of the second preferred embodiment on the x-y, x-z, and y-z planes when operated at 5.470 GHz. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure. 
   Referring to  FIG. 3 , the first preferred embodiment of an antenna unit  2  according to this invention is shown to include left and right antennas  22 ,  21  and a parasitic coupler  23 . 
   The antenna unit  2  of this embodiment is a dual-band antenna unit that is suitable for wireless networking applications, such as a wireless local area network (WLAN) or a wireless wide area network (WWAN), and that is operable within a first frequency bandwidth, and within a second frequency bandwidth different from the first frequency bandwidth. In this embodiment, the first frequency bandwidth is the 2.4 GHz bandwidth, and the second frequency bandwidth is the 5.0 GHz bandwidth. In an alternative embodiment, the first frequency bandwidth is the 5.0 GHz bandwidth, and the second frequency bandwidth is the 2.4 GHz bandwidth. 
   With further reference to  FIG. 4 , the antenna unit  2  is mounted in an electronic device  4 , such as a notebook computer. In this embodiment, the electronic device  4  includes a lower housing  42 , a keyboard  43  mounted on the lower housing  42 , an upper housing  41  coupled pivotably to the lower housing  42 , a liquid crystal display (LCD)  45  mounted on the upper housing  41 , a grounding plate  46  that is mounted in the upper housing  41  and that has upper and lower edges  461 ,  462 , an image-capturing device  47  mounted on the upper housing  41  and disposed above the grounding plate  46  between upper left and right corners of the upper housing  41 , and first and second signal sources (not shown) mounted in the upper housing  41 . 
   The antenna unit  2  is disposed between the upper left corner of the upper housing  41  and the image-capturing device  47 . 
   The left antenna  22  is operable within the first frequency bandwidth, i.e., the 2.4 GHz bandwidth, is a planar inverted-F antenna (PIFA), and includes a radiating element  221 , a grounding element  222 , and a feeding element  223 . The radiating element  221  of the left antenna  22  has left and right ends  2211 ,  2212 , and an intermediate portion  2213  that interconnects the left and right ends  2211 ,  2212  thereof. The grounding element  222  of the left antenna  22  has an upper end connected to the left end  2211  of the radiating element  221  of the left antenna  22 , and a lower end connected to an upper edge  461  of the grounding plate  46 . The feeding element  223  of the left antenna  22  has an upper end connected to the intermediate portion  2213  of the radiating element  221  of the left antenna  22 , and a lower end connected to the first signal source. 
   The right antenna  21  is spaced apart from the left antenna  22 , is operable within the first frequency bandwidth, i.e., the 2.4 GHz bandwidth, is a PIFA, and includes a radiating element  211 , a grounding element  212 , and a feeding element  213 . The radiating element  211  of the right antenna  21  has left and right ends  2111 ,  2112 , and an intermediate portion  2113  that interconnects the left and right ends  2111 ,  2112  thereof. The grounding element  212  of the right antenna  21  has an upper end connected to the right end  2112  of the radiating element  211  of the right antenna  21 , and a lower end connected to the upper edge  461  of the grounding plate  46 . The feeding element  213  of the right antenna  21  has an upper end connected to the intermediate portion  2113  of the radiating element  211  of the right antenna  21 , and a lower end connected to the second signal source. 
   The parasitic coupler  23  is spaced apart from and disposed between the left and right antennas  22 ,  21 , and is electromagnetically coupled to the radiating elements  221 ,  211  of the left and right antennas  22 ,  21  so as to be operable within the second frequency bandwidth, i.e., the 5.0 Ghz bandwidth. In particular, the parasitic coupler  23  is generally T-shaped, and includes a coupling element  231  and a grounding element  232 . The coupling element  231  of the parasitic coupler  23  has left and right ends  2311 ,  2312 , and an intermediate portion that interconnects the left and right ends  2311 ,  2312  thereof. The grounding element  232  of the parasitic coupler  23  has an upper end connected to the intermediate portion of the coupling element  231  of the parasitic coupler  23 , and a lower end connected to the upper edge  461  of the grounding plate  46 . The right end  2212  of the radiating element  221  of the left antenna  22  is disposed proximate to and above the left end  2311  of the coupling element  231  of the parasitic coupler  23 , and the left end  2111  of the radiating element  211  of the right antenna  21  is disposed proximate to and above the right end  2312  of the coupling element  231  of the parasitic coupler  23 . In this embodiment, the right end  2212  of the radiating element  221  of the left antenna  22  and the left end  2311  of the coupling element  231  of the parasitic coupler  23  define a first vertical distance (D 1 ) therebetween that ranges from 0.5 millimeters to 3.0 millimeters, and the left end  2111  of the radiating element  211  of the right antenna  21  and the right end  2312  of the coupling element  231  of the parasitic coupler  23  define a second vertical distance (D 2 ) therebetween that ranges from 0.5 millimeters to 3.0 millimeters. 
   It is noted herein that since the left and right antennas  22 ,  21  are operable within the first frequency bandwidth, and since the parasitic coupler  23  is disposed between the left and right antennas  22 ,  21 , and is electromagnetically coupled to the radiating elements  221 ,  211  of the left and right antennas  22 ,  21  so as to be operable within the second frequency bandwidth, the antenna unit  2  of this invention has a relatively small physical size. 
   It is further noted herein that the electromagnetic coupling between the parasitic coupler  23  and the radiating elements  221 ,  211  of the left and right antennas  22 ,  21  may be increased or decreased, for the purpose of impedance matching, by simply adjusting the first and second vertical distances (D 1 , D 2 ). 
     FIG. 5  is a modified embodiment of the first preferred embodiment according to this invention. In this embodiment, the parasitic coupler  23  is electromagnetically coupled to the feeding elements  223 ,  213  of the left and right antennas  22 ,  21  so as to be operable within the second frequency bandwidth. That is, the left end  2311  of the coupling element  231  of the parasitic coupler  23  is disposed proximate to the feeding element  223  of the left antenna  22  such that the left end  2311  of the coupling element  231  of the parasitic coupler  23  and the feeding element  223  of the left antenna  22  define a first horizontal distance (D 3 ) therebetween that ranges from 0.5 millimeters to 3.0 millimeters. Moreover, the right end  2312  of the coupling element  231  of the parasitic coupler  23  is disposed proximate to the feeding element  213  of the right antenna  21  such that the right end  2312  of the coupling element  231  of the parasitic coupler  23  and the feeding element  213  of the right antenna  21  define a second horizontal distance (D 4 ) therebetween that ranges from 0.5 millimeters to 3.0 millimeters. 
     FIG. 6  illustrates another modified embodiment of the first preferred embodiment according to this invention. In this embodiment, the intermediate portion  2213 ,  2113  of the radiating element  221 ,  211  of each of the left and right antennas  22 ,  21  is generally L-shaped. Moreover, the right end  2212  of the radiating element  221  of the left antenna  22  is disposed below the left end  2311  of the coupling element  231  of the parasitic coupler  23 , and the left end  2111  of the radiating element  211  of the right antenna  21  is disposed below the right end  2312  of the coupling element  231  of the parasitic coupler  23 . 
     FIG. 7  illustrates the second preferred embodiment of an antenna unit  2  according to this invention. When compared to the first preferred embodiment, the antenna unit  2  of this embodiment further includes a metallic strip  24  that interconnects the lower ends of the grounding elements  222 ,  212  of the left and right antennas  22 ,  21 , the lower end of the grounding element  232  of the parasitic coupler  23 , and the upper edge  461  of the grounding plate  46 . Moreover, the left and right antennas  22 ,  21  are secured to the upper housing  41  (see  FIG. 4 ) with the use of a pair of screws (not shown). In particular, the grounding element  222 ,  212  of each of the left and right antennas  22 ,  21  is formed with a hole  2220 ,  2120  therethrough. Each of the screws extends through the hole  2220 ,  2120  in the grounding element  222 ,  212  of a respective one of the left and right antennas  22 ,  21  and is fastened to the upper housing  41 . 
     FIGS. 8 to 15  are modified embodiments of the second preferred embodiment according to this invention. 
   
     
       
         
             
             
             
             
           
             
                 
               TABLE I 
             
             
                 
                 
             
             
                 
                 
               Total 
               Radiation 
             
             
                 
               Frequency 
               Radiation 
               Efficiency 
             
             
                 
               (GHz) 
               Power (dB) 
               (%) 
             
             
                 
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
             
          
             
                 
               Radiating 
               2.412 
               −1.8 
               66.1 
             
             
                 
               element 221 of 
               2.437 
               −1.6 
               69.3 
             
             
                 
               left antenna 
               2.462 
               −1.4 
               72.9 
             
             
                 
               22 and 
               5.150 
               −2.7 
               53.7 
             
             
                 
               parasitic 
               5.350 
               −1.5 
               71.4 
             
             
                 
               coupler 23 
               5.470 
               −1.8 
               65.6 
             
             
                 
                 
               5.725 
               −1.3 
               74.4 
             
             
                 
                 
               5.785 
               −2.0 
               62.9 
             
             
                 
               Radiating 
               2.412 
               −2.0 
               63.1 
             
             
                 
               element 212 of 
               2.437 
               −1.6 
               69.1 
             
             
                 
               right antenna 
               2.462 
               −1.4 
               73.2 
             
             
                 
               21 and 
               5.150 
               −2.3 
               59.1 
             
             
                 
               parasitic 
               5.350 
               −1.1 
               78.4 
             
             
                 
               coupler 23 
               5.470 
               −1.4 
               71.7 
             
             
                 
                 
               5.725 
               −1.7 
               67.5 
             
             
                 
                 
               5.785 
               −2.3 
               59.4 
             
             
                 
                 
             
          
         
       
     
   
   Based on experimental results, as illustrated in  FIG. 16 , the antenna unit  2  of this embodiment, when operated within 2.4 GHz and 2.4835 GHz and within 5.15 GHz and 5.85 GHz, achieves a voltage standing wave ratio (VSWR) of less than 2.0. In addition, as shown in Table I, the antenna unit  2  of this embodiment, when operated within 2.412 GHz and 2.462 GHz and within 5.150 GHz and 5.785 GHz, achieves satisfactory total radiation powers and radiation efficiencies. Moreover, as illustrated in  FIGS. 17 and 18 , each of the left antenna  22  and the parasitic coupler  23  of the antenna unit  2  of this embodiment has a substantially omnidirectional radiation pattern when operated within the 2.437 GHz bandwidth and within the 5.470 GHz bandwidth, respectively. Further, as illustrated in  FIGS. 19 and 20 , each of the right antenna  21  and the parasitic coupler  23  of the antenna unit  2  of this invention has a substantially omnidirectional radiation pattern when operated within the 2.437 GHz bandwidth and within the 5.470 GHz bandwidth, respectively. Hence, the antenna unit  2  of this embodiment is indeed suitable for WLAN and WWAN applications. 
   While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.