Abstract:
A dipole antenna is disclosed, and two electrodes thereof are respectively disposed on two surfaces of a substrate, wherein those two surfaces are parallel to each other. Metallic layers allocated in the substrate are used to control impedance match, and to promote the antenna gain and operation bandwidth of the dipole antenna.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a dipole antenna, and more particularly, to the dipole antenna having two electrodes disposed respectively on two essentially parallel surfaces of a substrate. 
   BACKGROUND OF THE INVENTION 
   An antenna in the communication products is an element mainly used for radiating or receiving signals, and generally, the features of antenna are determined by the parameters of operation frequency, radiation patterns, reflected loss, and antenna gain, etc. According to different operation requirements, the functions equipped in the communication products are not all the same, and thus there are many varieties of antenna designs used for radiating or receiving signals, such as a dipole antenna, a rhombic antenna, a turnstile antenna, a triangular microstrip antenna, and an inverted-F antenna, etc. 
   A conventional dipole antenna applied in a wireless transmission device generally is a straight-line-typed dipole antenna. Referring to  FIG. 1 ,  FIG. 1  is a schematic diagram showing a conventional dipole antenna. Such as shown in  FIG. 1 , the conventional dipole antenna is composed of two symmetrical electrodes  20  opposite to each other, wherein those two electrodes  20  are located on the same plane of a substrate  10 , and are electrically connected to feeding points  30 . The aforementioned dipole antenna is commonly designed to obtain the antenna features of low Q value, high gain and broad bandwidth, and the method applied therein is generally directed to making the cross-sections of the twin electrodes  20  as large as possible for the dipole antenna. The dipole antenna having larger cross-sections can be made resonate at a lower frequency, and the length thereof can be shortened. Currently, a central-feeding-typed dipole antenna is a better choice, of which the impedance can be changed by adjusting the location of the feeding points  30 , thereby making the impedance of the dipole antenna perfectly matching the impedances of transmission lines. 
   However, for the aforementioned conventional dipole antenna, the antenna performance can be promoted merely by focusing on the design of the length or thickness of the antenna electrodes, and the aforementioned technology still has quite a bottleneck for performance improvement. Further, with more enhanced circuit integration, the antenna design is also expected to be combined with the back-end circuit design, so as to make full use of an electric circuit board. However, conventionally, when an antenna is directly installed on an electric circuit board, the area surrounding the antenna on the electric circuit board usually has to be designed different from the other areas thereon, such as implementing different metallic layers on the area surrounding the antenna. Therefore, the conventional technology has quite a few design limitations and high difficulty level of process. 
   Hence, there is an urgent need to develop a dipole antenna which can be briefly merged into an integral circuit design, and has excellent antenna features of high gain and broad bandwidth, etc. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a dipole antenna, wherein the dipole antenna can be briefly merged into an entire electric circuit layout. 
   Another object of the present invention is to provide a dipole antenna for achieving the purpose of impedance matching by adjusting the number or positions of the metallic layers located in a substrate. 
   Still another object of the present invention is to provide a dipole antenna for obtaining high antenna gain and broad bandwidth. 
   According to the aforementioned objects, the present invention provides a dipole antenna, in which a first radiator and a second radiator are respectively formed on a first surface and a second surface of a substrate, wherein the first surface and the second surface are essentially parallel to each other, and the area covered by the first radiator is not overlapped with the area of the first surface onto which the second radiator is projected. A first feeding point is installed on one end of the first radiator near the second radiator, and a second feeding point is installed on the area of the first surface on which one end of the second radiator near the first radiator is projected, wherein the second feeding point is electrically connected to the second radiator. Further, first metallic layers and second metallic layers which are separated from each other can be further formed in the substrate, wherein the first metallic layers are corresponding to the first radiator in layout, and the second metallic layers are corresponding to the second radiator in layout, and the first metallic layers may not be connected directly to the first radiator, and the second radiator can be directly connected to the second radiator. 
   Hence, with the use of the present invention, the dipole antenna can be briefly merged into the entire electric circuit layout, and the purpose of impedance matching can be achieved, and the excellent antenna features of high antenna gain and broad bandwidth can be obtained as well. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a schematic diagram showing a conventional dipole antenna; 
       FIG. 2  is a 3-D schematic diagram showing a dipole antenna, according to a preferred embodiment of the present invention; 
       FIG. 3  is a schematic diagram showing the cross-sectional front view of the dipole antenna, according to the preferred embodiment of the present invention; 
       FIG. 4  is a schematic diagram showing the top view of the dipole antenna, according to the preferred embodiment of the present invention; 
       FIG. 5  is a schematic diagram showing the bottom view of the dipole antenna, according to the preferred embodiment of the present invention; 
       FIG. 6  is a schematic diagram showing the cross-sectional front view of a dipole antenna, according to the other preferred embodiment of the present invention; 
       FIG. 7   a  and  FIG. 7   b  are diagrams respectively showing radiation patterns in E-plane and H-pane when the dipole antenna of the present invention is operated at 2.4 GHz; 
       FIG. 8   a  and  FIG. 8   b  are diagrams respectively showing radiation patterns in E-plane and H-pane when the dipole antenna of the present invention is operated at 2.45 GHz; and 
       FIG. 9   a  and  FIG. 9   b  are diagrams respectively showing radiation patterns in E-plane and H-pane when the dipole antenna of the present invention is operated at 2.5 GHz. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
   Referring to  FIG. 2  to  FIG. 5 ,  FIG. 2  to  FIG. 5  illustrate a dipole antenna, according to a preferred embodiment of the present invention, wherein the fundamental radiation structure of an antenna  200  is formed mainly by disposing a first radiator  21   a  and a second radiator  21   b  respectively on a first surface  11   a  and a second surface  11   b  of a substrate  100 , and the first surface  11   a  is essentially parallel to the second surface  11   b.    
   The substrate  100  is made of dielectric material, such as FR4, etc. The first radiator  21   a  and the second radiator  21   b  are formed by disposing electrically-conductive material respectively on the non-overlapped areas of the first surface  11   a  and the second surface  11   b,  such as on the left half portion of the first surface  11   a  and the right half portion of the second surface  11   b.  Further, a first feeding point  22   a  is installed on one end of the first radiator  21   a  near the second radiator  21   b,  and a second feeding point  22   b  is installed on an area of the first surface  11   a  which is not disposed with the first radiator  21   a  and is adjacent to the first feeding point  22   a.  The second feeding point  22   b  is made of electrically-conductive material, and is electrically connected to the second radiator  21   b.    
   The aforementioned second radiator  21   b  can be electrically connected to the second feeding point  22   b  by means of a via  22   c  penetrating through the substrate  100 . However, the method for electrically connecting the second radiator  21   b  to the second feeding point  22   b  is not limited thereto, and other electrical connection methods can also be used. 
   On the other hand, the first radiator  21   a  and the second radiator  22   b  are essentially identical in geometrical shape and size, i.e. the first radiator  21   a  and the second radiator  21   b  are skew-symmetrical to each other in the substrate  100 . Moreover, the shapes of the first radiator  21   a  and the second radiator  21   b  can be such as rectangles, circles, inverted-F shapes or any other shapes that can generate required radiation patterns. 
   Further, the substrate  100  can be made of a printed circuit board, and the first radiator  21   a  and the second radiator  21   b  can be formed on the printed circuit board by etching or transfer printing. 
   Referring to  FIG. 6 ,  FIG. 6  is a schematic diagram showing a dipole antenna, according to the other preferred embodiment of the present invention, wherein the major radiation structure of an antenna  200  is formed mainly by disposing a first radiator  21   a  and a second radiator  21   b  respectively on a first surface  11   a  and a second surface  11   b  of a substrate  100 , and the components identical to those in  FIG. 2  to  FIG. 5  are denoted by the same numbers and will not be explained again herein. 
   In comparison to the aforementioned embodiment, one or more layers of first metallic layers  12   a  and second metallic layers  12   b  respectively corresponding to the first radiator  21   a  and the second radiator  21   b  in layout are formed inside or on the surface of the substrate  100 , i.e. the number of the first metallic layers  12   a  and that of the second metallic layers  12   b  can be determined independently in accordance with actual needs. Preferably, there is no direct connection among the first metallic layers  12   a  and the second metallic layers  12   b,  and also no direct connection between the first metallic layers  12   a  and the first radiator  21   a.  However, the second metallic layers  12   b  and the second radiator  21   b  are electrically connected to a second feeding point  22   b.    
   The aforementioned second radiator  21   b  can be electrically connected to the second metallic layers  12   b  and the second feeding point  22   b  at the same time by means of a via  22   c  penetrating through the substrate  100 . However, the method for electrically connecting the second radiator  21   b  to the second metallic layers  12   b  and the second feeding point  22   b  is not limited thereto, and other electrical connection methods can also be used. 
   Further, the antenna impedance matching can be achieved by adjusting the number, thickness, material of the first metallic layers  12   a  or the spacings between the first metallic layers  12   a,  and the second metallic layers  12   b  are coupled with the second radiator  21   b  as a portion of the antenna radiators. When the substrate  100  is a multi-layered electric circuit board, the number and the structure of the metallic layers existing in the multi-layered electric circuit board can be directly used as the structure as shown by the first metallic layers  12   a  and the second metallic layers  12   b,  whereby the antenna  200  can be briefly integrated into the design of the existing electric circuit board and the layout of the metallic layers adjacent to the antenna in the multi-layered electric circuit board does not need to be modified. 
   Referring  FIG. 7   a  and  FIG. 7   b,    FIG. 7   a  and  FIG. 7   b  are diagrams respectively showing radiation patterns in E-plane and H-pane when the dipole antenna  200  of the present invention is operated at 2.4 GHz. According to the radiation pattern in E-plane, the maximum antenna gain is 0.42 dbi, and the minimum antenna gain is −46.50 dbi, wherein the average antenna gain is −3.88 dbi. According to the radiation pattern in H-plane, the maximum antenna gain is 1.79 dbi, and the minimum antenna gain is −0.59 dbi, wherein the average antenna gain is 0.63 dbi. 
   Referring  FIG. 8   a  and  FIG. 8   b,    FIG. 8   a  and  FIG. 8   b  are diagrams respectively showing radiation patterns in E-plane and H-pane when the dipole antenna  200  of the present invention is operated at 2.45 GHz. According to the radiation pattern in E-plane, the maximum antenna gain is 0.12 dbi, and the minimum antenna gain is −27.67 dbi, wherein the average antenna gain is −3.22 dbi. According to the radiation pattern in H-plane, the maximum antenna gain is 1.39 dbi, and the minimum antenna gain is −1.60 dbi, wherein the average antenna gain is −0.04 dbi. 
   Referring  FIG. 9   a  and  FIG. 9   b,    FIG. 9   a  and  FIG. 9   b  are diagrams respectively showing radiation patterns in E-plane and H-pane when the dipole antenna  200  of the present invention is operated at 2.5 GHz. According to the radiation pattern in E-plane, the maximum antenna gain is 0.42 dbi, and the minimum antenna gain is −23.36 dbi, wherein the average antenna gain is −3.67 dbi. According to the radiation pattern in H-plane, the maximum antenna gain is 1.59 dbi, and the minimum antenna gain is −0.70 dbi, wherein the average antenna gain is 0.28 dbi. Hence, it can be from  FIG. 7  to  FIG. 9  that, while being operated at the frequency from 2.4˜2.5 GHz, the dipole antenna of the present invention can obtain high antenna gain and meanwhile maintain the feature of omni-directional antenna. 
   As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures.