Abstract:
The present invention discloses a directional antenna for a multi-in multi-out or antenna beam switchable wireless communication system, including a substrate, at least one directional antenna, formed on the substrate, for generating a radiating pattern of a radiation plane according to a feeding signal, and a reflector, disposed in parallel to the radiation plane of the directional antenna, for reflecting the radiating pattern of the directional antenna, to increase a gain of the directional antenna corresponding to the radiation plane.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a directional antenna and radiating pattern adjustment method, and more particularly, to a directional antenna and radiating pattern adjustment method increasing antenna gain by adding a reflector. 
     2. Description of the Prior Art 
     An electronic product with a wireless communication function, such as a laptop computer, a personal digital assistant (PDA) and soon, transmits or receives radio signals through an antenna to access a wireless network. Therefore, for facilitating the wireless network access, an ideal antenna should have a wide bandwidth and a small size to meet the trends of compact electronic products. 
     A highly directional antenna such as a Yagi-Uda antenna achieves high gain over a rather narrow band. As a result, multiple Yagi-Uda antennas are commonly utilized in a wireless communication system supporting multi-in multi-out (MIMO) technology or a beam switchable antenna system. With a proper arrangement of the multiple Yagi-Uda antennas, the wireless communication system can reach high data throughput and significantly increase transmission distance under limited bandwidth or power expenditure. 
     In order to reach better performance of the Yagi-Uda antenna, a conventional method is to add directors to the Yagi-Uda antenna, which can direct a current route in a radiator of the Yagi-Uda antenna. In such a situation, directivity and antenna gain of the Yagi-Uda antenna increase. However, antenna body and the area of the Yagi-Uda antenna also increase. 
     In order to meet the trends of compact electronic products, there is a need to increase antenna gain and directivity of the Yagi-Uda antenna without increasing antenna area. 
     SUMMARY OF THE INVENTION 
     It is therefore an object to provide a directional antenna and radiating pattern adjustment method for a multi-in multi-out or a beam switchable antenna system. 
     The present invention discloses a directional antenna for a multi-in multi-out or a beam switchable antenna system, including a substrate, at least one directional antenna, formed on the substrate, for generating a radiating pattern of a polarization direction according to a feeding signal, and a reflector, disposed in parallel to the radiation plane of the directional antenna, for reflecting the radiating pattern of the directional antenna, to increase a gain of the directional antenna corresponding to the polarization direction. 
     The present invention further discloses a radiating pattern adjustment method for a directional antenna, including reflecting a radiating pattern of a signal transmitted from the directional antenna by a reflector in parallel to a radiation plane of the directional antenna, to improve a gain of the directional antenna corresponding to the radiation plane. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a directional antenna according to an embodiment of the present invention. 
         FIG. 2A  to  FIG. 2D  are schematic diagrams illustrating feasible shapes of the reflector in  FIG. 1 . 
         FIG. 3  is a schematic diagram of a radiating pattern adjustment process according to an embodiment of the present invention. 
         FIG. 4  is a schematic diagram of a transceiver according to an embodiment of the present invention. 
         FIG. 5  is an antenna gain pattern diagram of the directional antenna shown in  FIG. 4 . 
         FIG. 6A  and  FIG. 6B  are side-view and isometric diagrams of a transceiver according to an embodiment of the present invention. 
         FIG. 7  is an antenna gain pattern diagram of the directional antenna shown in  FIG. 6A . 
         FIG. 8  is a schematic diagram of a transceiver according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 , which illustrates a schematic diagram of a directional antenna  10  according to an embodiment of the present invention. The directional antenna  10  is suitable for a wireless communication system supporting MIMO technology, such as IEEE 802.11n system, but not limited to this. The directional antenna  10  includes a substrate  102 , a directional antenna ANT, and a reflector  104 . The directional antenna ANT is a dual-band horizontally polarized antenna and is arranged on the substrate  102 , for generating radiating patterns RP_H and RP_L according to a radio-frequency (RF) signal RFS, and performing RF signal transmission and reception simultaneously. As shown in  FIG. 1 , the radiating patterns RP_H and RP_L are substantially along a horizontal radiation plane XY. The reflector  104  is disposed in parallel to the radiation plane XY, for reflecting the radiating patterns RP_H and RP_L, so as to increase a gain corresponding to the radiation plane XY of the directional antenna ANT. 
     In addition, the radiating pattern RP_H of the directional antenna ANT is the maximum gain cutting plane for high operating frequency bands, e.g. 5.45 GHz. The radiating pattern RP_L of the directional antenna ANT is the maximum gain cutting plane for low operating frequency bands, e.g. 2.45 GHz. As can be seen from  FIG. 1 , the maximum gain cutting plane of the radiating pattern RP_H is substantially within the radiation plane XY, while the maximum gain cutting plane of the radiating pattern RP_L is a sloping downward plane. In such a situation, a distance D between the directional antenna ANT and the reflector  104  is adjustable to change the radiating patterns RP_H and RP_L, so as to meet system requirements, and thus antenna design is more flexible. 
     More specifically, according to electromagnetic theorem, when a metal sheet is insulated from a radiator with an area which is greater than a half wavelength of an incident radio wave radiated from the radiator, surface electrons of the metal sheet resonant with the incident radio wave, to generate a reflected radio wave with a frequency the same as a frequency of the incident radio wave, and with a reflected angle corresponding to an incident angle of the incident radio wave. In such a situation, the metal sheet appears reflecting the incident radio wave from the incident angle toward the reflected angle. Likewise, when the directional antenna ANT radiates the RF signal RFS to the air, the reflector  104  reflects the radiated RF signal RFS, such that a part of the RF signal RFS is reflected toward the radiation plane XY due to a reflection effect of the reflector  104 , and thus a radiating pattern of the directional antenna ANT is changed. As a result, the gain corresponding to the radiation plane XY of the directional antenna ANT is improved. 
     In other words, the reflector  104  reflects a part of the RF signal RFS radiated from the directional antenna ANT, such that a part of the RF signal RFS is reflected toward the radiation plane XY, which adjusts the radiating patterns RP_H and RP_L, and thus the gain corresponding to the radiation plane XY of the directional antenna ANT is improved. 
     Please note that, the present invention is to increase the gain corresponding to the radiation plane XY of the directional antenna ANT via disposing the reflector  104  in parallel to the radiation plane XY. Type and number of the directional antenna ANT are not limited; for example, the directional antenna ANT can be any kind of directional antenna, such as a Yagi-Uda antenna, and may dispose or print multiple directional antennas on the substrate  102 , as long as the multiple directional antennas have a same polarization direction, e.g. horizontal or vertical polarization direction. Material and shape of the reflector  104  are not limited either. For example, the reflector  104  can be made of iron, copper, or other pure or hybrid metal materials. The shape of the reflector  104  is not limited. For example, please refer to  FIGS. 2A-2D , which are schematic diagrams illustrating feasible shapes of the reflector  104 , i.e. a hexagon, a circle, a square and a triangle. Certainly, other geometric figures or irregular shapes may suitable for the reflector  104 . Those skilled in the art should make modifications or alterations, and not limited to the above description and examples. 
     Operations of adjusting the radiating patterns RP_H and RP_L to increase the gain corresponding to the radiation plane XY of the directional antenna ANT can be summarized into a radiating pattern adjustment process  30  as shown in  FIG. 3 . The radiating pattern adjustment process  30  includes the following steps: 
     Step  300 : Start. 
     Step  302 : Reflect the radiating patterns RP_H and RP_L of the RF signal RFS transmitted from the directional antenna ANT by the reflector  104  in parallel to the radiation plane XY of the directional antenna ANT, to increase the gain of the directional antenna ANT corresponding to the radiation plane XY. 
     Step  304 : End. 
     Details of the radiating pattern adjustment process  30  can be derived by referring to the above description. 
     Please refer to  FIG. 4 , which is a schematic diagram of a transceiver  40  according to an embodiment of the preset invention. The transceiver  40  includes a substrate  402 , directional antennas ANT_ 1 -ANT_ 3  and a reflector  404 . The directional antennas ANT_ 1 -ANT_ 3  are identical printed Yagi-Uda antennas with the horizontal polarization direction, and are arranged on the substrate  402  to equally divide a circle into three 120-degree sectors, for transmitting and receiving RF signals from the horizontal radiation plane. To compare antenna performance before and after adding the reflector  404 , herein taking the directional antenna ANT_ 1  as an example. Please refer to  FIG. 5 , which is a schematic diagram denoting the directional antenna ANT_ 1  with and without the reflector  404  by a solid line and a dotted line, respectively. As can be seen from  FIG. 5 , a peak gain of the directional antenna ANT_ 1  is 4.5 dBi without the reflector  404 , while a peak gain of the directional antenna ANT_ 1  is 6.5 dBi with the reflector  404 . Moreover, an antenna directivity of the directional antenna ANT_ 1  is improved as well. Since the directional antennas ANT_ 1 -ANT_ 3  are identical, antenna peak gains and directivities of the directional antennas ANT_ 2  and ANT_ 3  are also improved via adding the reflector  404 . As a result, by adding the single reflector  404 , the antenna gains and the directivities of the directional antennas ANT_ 1 -ANT_ 3  are improved simultaneously. 
     Furthermore, the transceiver  40  may also combine another transceiver for increasing different directional antennas, so as to increase different polarization direction and enhance radiation coverage of the transceiver  40 . Please refer to  FIG. 6A  and  FIG. 6B , which are side-view and isometric diagrams of a transceiver  60  according to an embodiment of the present invention, respectively. The transceiver  60  includes the transceiver  40 , vertically polarized antennas ANT_ 4 -ANT_ 7  and a system board SBD. The directional antennas ANT_ 4 -ANT_ 7  are identical printed Yagi-Uda antennas with the vertical polarization direction. The directional antennas ANT_ 4  and ANT_ 5  are formed on the substrate  612 , and the directional antennas ANT_ 6  and ANT_ 7  are formed on the substrate  622 , for transmitting and receiving RF signals from the vertical polarization direction. The substrates  612  and  622  are FR4 double-layered fiber glass boards, and include insertion elements ISE_ 1  and ISE_ 2 . The transceiver  40  further includes an insertion element ISE_ 0  and the reflector  404  of the transceiver  40  includes slots SL_ 0 , SL_ 1  and SL_ 2  corresponding to the insertion elements ISE_ 0 , ISE_ 1  and ISE_ 2 , for fixing the reflector  404  and the substrates  402 ,  612  and  622 . Please note that, the method of fixing the reflector  404  is not limited, and the reflector  404  can be fixed by other mechanical parts on a housing of the transceivers  40  and  60  as well. 
     In such an arrangement, the directional antennas ANT_ 4 -ANT_ 7  form a radiating pattern within the radiation plane XY, and the system board SBD is disposed in parallel to a radiation plane XZ. Please note that, the system board SBD is regarded as a reflector performing reflection. As a result, please refer to  FIG. 7 , which is a schematic diagram denoting the antenna gain of the directional antenna ANT_ 4  with and without the system board SBD by a solid line and a dotted line, respectively. As can be seen from  FIG. 7 , a peak gain of the directional antenna ANT_ 4  is 5.6 dBi without the system board SBD, while a peak gain of the directional antenna ANT_ 4  is 7 dBi with the system board SBD. Moreover, an antenna directivity of the directional antenna ANT_ 4  is improved as well. Since the directional antennas ANT_ 4 -ANT_ 7  are identical, antenna peak gains and directivities of the directional antennas ANT_ 5  and ANT_ 7  are also improved via adding the system board SBD. As a result, by adding the single system board SBD, the antenna gains and the directivities of the directional antennas ANT_ 4 -ANT_ 7  are improved simultaneously. 
     The transceiver  60  may further include a directional antenna ANT_ 8  at the other side of the system SBD as shown in  FIG. 8 , so as to cover 360 degree radiation plane XY. The directional antenna ANT_ 8  is a printed dual-band slot antenna, which also has a reflector  604 . Similarly, the reflector  604  reflects a radiating pattern of the directional antenna ANT_ 8 , for increasing an antenna gain and a directivity of the directional antenna ANT_ 8 . 
     To sum up, the present invention adds the reflector insulated from the directional antenna and disposed in parallel to the radiation plane, to reflect the radiating pattern of the directional antenna, which increases antenna gain corresponding to radiated direction of the directional antenna without modifying the directional antenna. In comparison, the traditional method is to add directors to the direction antenna, for directing a current route in the radiator, which changes the radiating body and increase area of the directional antenna. Besides, when there are multiple directional antennas, the traditional method has to add directors on each of the antennas respectively, which significantly increases the total antenna area. However, the present invention adds single reflector in parallel to the radiation plane, such that antenna gains of the multiple directional antennas are increased at one time, which is simpler and easier. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.