Patent Publication Number: US-7218287-B2

Title: Dipole antenna

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an antenna, and in particular to a dipole antenna employed in a laptop computer, a portable electronic device or other electronic devices. 
   2. Description of the Prior Art or Related Art 
   When wireless communication technologies, such as WLAN standards, are applied in electronic devices such as notebook computers or portable game devices, antennas become indispensable components to these devices for wireless access. As a basic antenna structure, a dipole antenna is a popular choice for the RF engineer because it has features of low cost and is easy to design and test. A traditional dipole antenna usually includes a pair of linear dipole elements extending in opposite directions, which can get polarization in a single direction. But if the traditional dipole antenna is assembled in a Liquid Crystal Display (LCD) of a notebook or other portable devices, the receiving and transmitting capability of the dipole antenna could be better when the LCD is in a predetermined position (such as parallel to the ground), but also could be worse when the LCD is in a different position (such as perpendicular to the ground). So the open angle of the LCD relative to a panel of the notebook computer will affect performance of the dipole antenna or other single-liner polarized antenna assembled in the LCD. 
   U.S. Pat. Publication No. 20040012534 discloses a dual-band printed dipole antenna. The dipole antenna comprises a pair of dipole elements (212, 222) operated in a lower frequency and disposed on a substrate. The dipole antenna is formed into inverted-V shape to for impendence matching purpose. However vertical and horizontal polarization improvements are not considered simultaneously in this design. 
   Hence, an improved dipole antenna is desired to overcome the above-mentioned disadvantages of the prior and related arts. 
   BRIEF SUMMARY OF THE INVENTION 
   A primary object of the present invention is to provide a dipole antenna having balanced polarization in both vertical direction and horizontal directions. 
   A dipole antenna in accordance with the present invention includes a first radiating trace and a first grounding trace respectively extending in substantially opposite directions, a second radiating trace extending from an end of the first radiating trace in a direction which substantially perpendicular to the first radiating trace, and a second grounding trace extending from an end of the first grounding trace in an opposite direction to the second radiating trace. The total length of the first and second radiating traces are ¼ operating wavelength of the dipole antenna. 
   Still another objects, advantages and novel features of the invention will become more apparent from the following detailed description of a preferred embodiment when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top plan view of a dipole antenna in accordance with the present invention, which is disposed on a substrate; 
       FIG. 2  is a test chart recording for the dipole antenna of  FIG. 1 , showing Voltage Standing Wave Ratio (VSWR) as a function of frequency; 
       FIG. 3  is a recording of a horizontally polarized principle plane radiation pattern in X-Y plane of the dipole antenna of  FIG. 1  operating at a frequency of 2.45 GHz; 
       FIG. 4  is a recording of a vertically polarized principle plane radiation pattern in X-Y plane of the dipole antenna of  FIG. 1  operating at a frequency of 2.45 GHz; 
       FIG. 5  is a recording of a horizontally polarized principle plane radiation pattern in X-Z plane of the dipole antenna of  FIG. 1  operating at a frequency of 2.45 GHz; 
       FIG. 6  is a recording of a vertically polarized principle plane radiation pattern in X-Z plane of the dipole antenna of  FIG. 1  operating at a frequency of 2.45 GHz; 
       FIG. 7  is a recording of a horizontally polarized principle plane radiation pattern in Y-Z plane of the dipole antenna of  FIG. 1  operating at a frequency of 2.45 GHz; and 
       FIG. 8  is a recording of a vertically polarized principle plane radiation pattern in Y-Z plane of the dipole antenna of  FIG. 1  operating at a frequency of 2.45 GHz. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to a preferred embodiment of the present invention. 
   Referring to  FIG. 1 , a dipole antenna  1  in accordance with the present invention comprises a substrate  10 , a radiating dipole element  2  and a grounding dipole element  3 , impendence matching member  4  and a coaxial cable  5 . 
   With reference to the definition of directions X, Y, Z in  FIG. 1 , the radiating dipole element  2  is L-shaped and includes a first radiating trace  21  that extends in a vertical direction parallel to direction Z and a second radiating trace  22  perpendicularly extending from an end of the first radiating trace  21  and parallel to direction X. The first and second radiating traces  21 ,  22  are also substantially perpendicular to each other. The grounding dipole element  3  has the same dimension as that of the radiating dipole element  2 . The grounding dipole element  3  includes a first grounding trace  31  and a second grounding trace  32  extending from an end of the first grounding trace  31 . The first and second grounding traces  31 ,  32  are substantially perpendicular to each other. The first grounding trace  31  extends oppositely to the first radiating trace  21  and is aligned in a line with the first radiating trace  21 . The second grounding trace  32  is parallel to the second radiating trace  22  but extends in an opposite direction. 
   The impendence matching member  4  includes a pair of parallel matching traces  41 ,  42  perpendicularly extending form ends of the first radiating trace  21  and the first grounding trace  31 , respectively. The matching traces  41 ,  42  are substantially parallel to each other and have the same dimension. The distance between the matching traces  41 ,  42  and the length of the matching traces  41 ,  42  provide convenient adjustment for the impendence matching between the dipole antenna  1  and the coaxial cable  5 . The coaxial cable  5  includes an inner conductor  51  connecting with an end of one matching trace  41  and an outer conductor  52  connecting with an end of the other matching trace  42 . 
   The first radiating trace  21  and the first grounding trace  31  can be treated as a first pair of dipole branches, which provide horizontal polarization improvement on XY, YZ and XZ planes in  FIG. 1 . The second radiating trace  22  and the second grounding trace  32  can be treated as a second pair of dipole branches, which provide perpendicular polarization improvement on each plane described above. In this embodiment, the length of the first and second radiating traces  21 ,  22  and the first and second grounding trace  31 ,  32  are both selected form a scope of 1/12 to ⅙ of operating wavelength of the dipole antenna. The total length of the first and second radiating traces  22  are ¼ of operating wavelength, so do the first and second grounding traces  32 . In such a condition, a balanced polarization on each plane is achieved, which are directly shown on  FIG. 3  to  FIG. 8  with no obvious radiating blind area. The impendence-matching problem will be solved by adjusting the length of the matching traces  41 ,  42  and the distance therebetween. The dipole elements  2 ,  3  and the matching traces  41 ,  42  are all disposed on the substrate  10 , which achieves an impact design and need not to provide a complex impendence member.  FIG. 2  shows a test chart recording of Voltage Standing Wave Ratio (VSWR) of the dipole antenna  1  as a function of frequency. Note that VSWR drops below the desirable maximum value “2” in the 2.4–2.5 GHz frequency band, indicating acceptably efficient operation in this frequency band, which covers more than the total bandwidth of 802.1 lb standard. 
   Since the dipole antenna  1  has a balanced polarization, when it is assembled in a display of a notebook or other like portable device, the dipole antenna  1  can provide desired transmitting and receiving performance regardless what angle of the display (relative to a panel of the notebook) is. Assembled with such balanced polarization antenna, a user may enjoy good wireless communication and need not to adjust the angle of the antenna, the position of his portable device or open angle of the display. 
   It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.