Patent Publication Number: US-7224315-B2

Title: Electronic device and antenna structure thereof

Description:
BACKGROUND 
   The invention relates to an antenna structure, and more particularly to an antenna structure providing improved radiation pattern. 
     FIGS. 1   a  and  1   b  show an antenna structure  12  disclosed in U.S. Pat. No. 6,339,404, which comprises a substrate  14 , radiation elements  22 , a conductive element  24 , a conductive element  26 , a reflective element  28 , impedance matching elements  46  and cables  44 . The substrate  14  comprises a first surface  16  and a second surface  18 . The reflective element  28  is disposed on the first surface  16 . The radiation elements  22  are disposed on two sides of the reflective element  28 . The cables  44  comprise conductive lines  42  and  48 . The conductive lines  42  are coupled to the reflective element  28 . The conductive element  24 , the conductive element  26  and the impedance matching elements  46  are disposed on the second surface  18 . The conductive element  24  and the conductive element  26  are connected to the impedance matching elements  46 . The conductive lines  48  are coupled to the conductive element  24  and the conductive element  26 . 
   Conventional antenna structure  12 , however, comprises two conductive lines  48 , two independent impedance matching elements  46  and two conductive elements  24  and  26 , the structure thereof is complicated, and the radiation pattern cannot be improved by modifying the conductive line  48 , or the conductive elements  24  and  26 . Additionally, when a plurality of antenna structures  12  are connected in parallel to achieve an improved signal transmission, the size thereof is large. 
   SUMMARY 
   An embodiment of an antenna structure for transmitting a wireless signal comprises a substrate, a reflective element, a first radiation unit, a second radiation unit, a first impedance matching unit, a second impedance matching unit, a feed point, a first conductive line and a second conductive line. The substrate comprises a first surface and a second surface. The reflective element is disposed on the second surface. The first radiation unit is disposed on both sides of the reflective element. The second radiation unit is disposed on both sides of the reflective element. The first impedance matching unit is disposed on the first surface corresponding to the first radiation unit. The second impedance matching unit is disposed on the first surface corresponding to the second radiation unit. The feed point is coupled between the first impedance matching unit and the second impedance matching unit. The first conductive line is coupled to the feed point. The second conductive line is coupled to the reflective element. 
   The antenna structure of the invention can be disposed in a housing of an electronic device. 
   The antenna structure of the invention provides a more symmetrical radiation pattern and improved signal transmission with smaller size. 

   
     DESCRIPTION OF THE DRAWINGS 
     The invention will be more fully understood from the following detailed description and the accompanying drawings, given by the way of illustration only and thus not intended to limit the invention. 
       FIG. 1   a  is a bottom view of a conventional antenna structure; 
       FIG. 1   b  is a top view of the conventional antenna structure; 
       FIG. 2   a  shows an antenna structure of the invention; 
       FIG. 2   b  is a bottom view of the antenna structure of the invention; 
       FIG. 3  is a top view of the antenna structure of the invention; 
       FIG. 4  shows signal transmission of the antenna structure of the invention; 
       FIG. 5  shows a modified example of the antenna structure of the invention; and 
       FIG. 6  shows the antenna structure of the invention disposed in an electronic device. 
   

   DETAILED DESCRIPTION 
     FIGS. 2   a  and  2   b  show an antenna structure  100  of the invention, which comprises a substrate  170 , a reflective element  101 , a first radiation unit  110 , a second radiation unit  120 , a feed point  130 , a first impedance matching unit  150 , a second impedance matching unit  160 , a first conductive element  141  and a second conductive element  142 . The substrate  170  comprises a first surface  171  and a second surface  172  (with reference to  FIG. 2   b ). The reflective element  101 , the first radiation unit  110  and the second radiation unit  120  are disposed on the second surface  172 . The reflective element  101  is longitudinal. The first radiation unit  110  and the second radiation unit  120  are disposed on two sides of the reflective element  101 . The first impedance matching unit  150 , the second impedance matching unit  160 , the first conductive element  141 , the second conductive element  142  and the feed point  130  are disposed on the first surface  171 . The first impedance matching unit  150  is connected to the first conductive element  141 , and the first conductive element  141  is connected to the feed point  130 . The second impedance matching unit  160  is connected to the second conductive element  142 , and the second conductive element  142  is connected to the feed point  130 . The first impedance matching unit  150  is a sleeve-shaped structure corresponding to the first radiation unit  110 , and the second impedance matching unit  160  is a sleeve-shaped structure corresponding to the second radiation unit  120 . 
   With reference to  FIG. 2   b , the antenna structure  100  further comprises a cable  180 . The cable  180  comprises a first conductive line  181  and a second conductive line  182 . The first conductive line  181  is coupled to the feed point  130  and passes through the reflective element  101  and the substrate  170 . The second conductive line  182  is coupled to the reflective element  101 . The first radiation unit  110  comprises two radiation elements  111  and two radiation elements  112  disposed on both sides of the reflective element  101 , wherein each side of the reflective element  101  comprises one radiation element  111  and one radiation element  112  disposed thereon. The radiation elements  111  and the radiation elements  112  are L-shaped, and the ends thereof extend in opposite directions. The second radiation unit  120  comprises two radiation elements  121  and two radiation elements  122  disposed on both sides of the reflective element  101 , wherein each side of the reflective element  101  comprises one radiation element  121  and one radiation element  122  disposed thereon. The radiation elements  121  and the radiation elements  122  are L-shaped, and the ends thereof are extending in opposite directions. 
   With reference to  FIG. 3 , the first conductive element  141  and the second conductive element  142  are aligned on a straight line. The first impedance matching unit  150  comprises a first portion  151  and a second portion  152 . The first portion  151  is corresponding to the first radiation unit  110 , the second portion  152  is connected to the first conductive element  141 , and the first portion  151  is connected to the second portion  152 . 
   The second impedance matching unit  160  comprises a third portion  161  and a fourth portion  162 . The third portion  161  is corresponding to the second radiation unit  120 , the fourth portion  162  is connected to the second conductive element  142 , and the third portion  161  is connected to the fourth portion  162 . 
   The width d 1  of the first conductive element  141  is thinner than the width d 2  of the second portion  152 . The impedance matching of the antenna structure  100  is modified by changing the width d 1  of the first conductive element  141  and the width d 2  of the second portion  152 . The radiation pattern of the antenna structure  100  is modified by changing the length L 1  of the first conductive element  141  and the length L 2  of the second portion  152 . The width d 3  of the second conductive element  142  is thinner than the width d 4  of the fourth portion  162 . The impedance matching of the antenna structure  100  is modified by changing the width d 3  of the second conductive element  142  and the width d 4  of the fourth portion  162 . The radiation pattern of the antenna structure  100  is modified by changing the length L 3  of the second conductive element  142  and the length L 4  of fourth portion  162 . 
   A total length of the first conductive element  141 , the second conductive element  142 , the second portion  152  and the fourth portion  162  is about 0.8λ˜1λ, and λ is a wave length of the wireless signal. The length L 1  of the first conductive element  141 , the length L 2  of the second portion  152 , the length L 3  of the second conductive element  142  and the length L 4  of the fourth portion  162  can be modified to achieve improved signal transmission. 
     FIG. 4  shows the signal transmission of the antenna structure  100  of the invention, wherein the bands thereof (bands are defined as signals having voltage standing wave ratios lower than 2) is between 4.85 GHz˜6 GHz. 
     FIG. 5  shows a modified antenna structure  100 ′ of the invention, which further comprises a third conductive element  191 , an impedance matching element  192 , an impedance matching element  194 , an impedance matching element  195  and a third radiation unit  193 . The impedance matching element  194  is connected to the first impedance matching unit  150 . The third conductive element  191  is connected to the impedance matching element  194 . The impedance matching element  195  is connected to the third conductive element  191 . The impedance matching element  192  is connected to the impedance matching element  195 . The impedance matching element  192  and the impedance matching element  195  compose a third impedance matching unit. The third radiation unit  193  is disposed on two sides of the reflective element  101 . The third conductive element  191 , the impedance matching element  192 , the impedance matching element  194 , the impedance matching element  195  and the third radiation unit  193  symmetrize the radiation pattern of the antenna structure  100 ′. 
   The antenna structure of the invention is utilized in transmitting various wireless signals, particularly signals conformed to IEEE 802.11(a). 
   The antenna structure of the invention provides a more symmetrical radiation pattern and improved signal transmission with smaller size. 
   With reference to  FIG. 6 , the antenna structure  100  of the invention can be disposed in a housing  210  of an electronic device  200 . 
   While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation to encompass all such modifications and similar arrangements.