Patent Publication Number: US-8982006-B2

Title: Dipole antenna and radio-frequency device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dipole antenna and radio-frequency device, and more particularly, to a dipole antenna and radio-frequency device having a balun to balance a feed-in impedance. 
     2. Description of the Prior Art 
     An antenna is used for transmitting or receiving radio waves, to communicate or exchange wireless signals. An electronic product with a wireless communication function, such as a tablet computer, a laptop or a personal digital assistant (PDA), usually accesses a wireless network through a built-in antenna. 
     Please refer to  FIG. 1 , which is a schematic diagram of an RF (Radio-Frequency) device  10 . The RF device  10  has a function of wireless communication; take a note book computer for example. The RF device  10  includes an antenna  11 , an RF signal process unit  12  and a housing  13 . In general, to prevent the antenna  11  from being disposed within a metallic environment, such as a central area disposed with metal parts, a hard disk, input-output ports or a mother board (not shown in  FIG. 1 ), the antenna  11  is normally disposed on a border of the housing  13 . Thus, it is usual to use a metal wire, e.g. a co-axial cable  14 , to transmit an RF signal received and radiated by the antenna  11  to the RF signal process unit  12  for further signal process. 
     However, the above mentioned design principle may cause the co-axial cable  14  for transmitting the RF signal to become a part of a radiator of the antenna  11 . If the co-axial cable  14  is interfered by noises, the RF signal will be interfered by noises as well, and a signal quality of the RF signal may be decreased accordingly. 
     On the other hand, the co-axial cable  14  may have different levels of influence on antenna performances according to different antenna types. For example, a gain of a dipole antenna is theoretically higher than a gain of a monopole antenna and also higher than a gain of a PIFA (Planar Inverted-F Antenna), but the co-axial cable  14  may unbalance a feed-in impedance of the dipole antenna. As a result, the antenna performance of the dipole antenna may be changed once the co-axial cable  14  is changed, e.g. impedance changes by cable routes, which may decrease stability and reliability of the dipole antenna  11  during manufacture. 
     Therefore, how to design the dipole antenna having a stable performance and a balanced feed-in impedance to improve the stability and the reliability during manufacture has become a topic in the industry. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a dipole antenna and radio-frequency device to improve an antenna performance and balance a feed-in impedance. 
     The present invention discloses a dipole antenna, comprising a feed-in terminal for feeding in an radio-frequency signal, a balun electrically connected to the feed-in terminal for driving out a return current of the dipole antenna to balance a feed-in impedance of the dipole antenna, a first radiator electrically connected to the feed-in terminal and the balun for radiating the radio-frequency signal in a first frequency band, the first radiator comprising a first arm having one end electrically connected to the feed-in terminal and the balun, the first arm having another end opened, and a second arm having one end electrically connected to the balun, the second arm having another end opened, and a second radiator electrically connected to the first radiator, the feed-in terminal and the balun for radiating the radio-frequency signal in a second frequency band, the second radiator comprising a third arm having one end electrically connected to the feed-in terminal, the first arm and the balun, the third arm having another end opened, and a fourth arm electrically connected to the balun and the second arm, the fourth arm having another end opened. 
     The present invention further discloses a radio-frequency device, comprising a radio-frequency signal process unit for generating a radio-frequency signal, and a dipole antenna comprising a feed-in terminal for feeding in the radio-frequency signal, a balun electrically connected to the feed-in terminal for driving out a return current of the dipole antenna to balance a feed-in impedance of the dipole antenna, a first radiator electrically connected to the feed-in terminal and the balun for radiating the radio-frequency signal in a first frequency band, the first radiator comprising a first arm having one end electrically connected to the feed-in terminal and the balun, the first arm having another end opened, and a second arm having one end electrically connected to the balun, the second arm having another end opened, and a second radiator electrically connected to the first radiator, the feed-in terminal and the balun for radiating the radio-frequency signal in a second frequency band, the second radiator comprising a third arm having one end electrically connected to the feed-in terminal, the first arm and the balun, the third arm having another end opened, and a fourth arm electrically connected to the balun and the second arm, the fourth arm having another end opened. 
     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 radio-frequency device. 
         FIG. 2  is a schematic diagram of a dipole antenna. 
         FIG. 3  is a schematic diagram of a dipole antenna according to an embodiment of the present invention. 
         FIG. 4  is a schematic diagram illustrating a voltage standing wave ratio of the dipole antenna shown in  FIG. 2  compared with a voltage standing wave ratio of the dipole antenna shown in  FIG. 3 . 
         FIG. 5  is a schematic diagram of a dipole antenna according to another embodiment of the present invention. 
         FIG. 6  is a schematic diagram of a dipole antenna according to another embodiment of the present invention. 
         FIG. 7  is a schematic diagram of a dipole antenna according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 2 , which is a schematic diagram of a dipole antenna  20 . The dipole antenna  20  maybe substituted for the antenna  11  shown in  FIG. 1 , and used for transmitting and receiving an RF (Radio-Frequency) signal, and the RF signal may be transmitted to the RF signal process unit  12  (not shown in  FIG. 2 ) by the co-axial cable  14 . The dipole antenna  20  includes a feed-in terminal  23 , a first radiator  21  and a second radiator  22 . The feed-in terminal  23  is used for feeding in the RF signal. The first radiator  21  is electrically connected to the feed-in terminal  23  for radiating the RF signal in a high frequency band. The second radiator  22  is electrically connected to the first radiator  21  and the feed-in terminal  23  for radiating the RF signal in a low frequency band. 
     In detail, the first radiator  21  includes a first arm  211  and a second arm  212 , wherein the first arm  211  is electrically connected to the feed-in terminal  23 , the second arm  212  is electrically connected to the woven shield  24  of the co-axial cable  14 . In such a structure, the first radiator  21  maybe regarded as a dipole antenna whose RF current (i.e. the RF signal) may flow on the first arm  211  and a return current may flow from the second arm  212  and following the woven shield  24  of the co-axial cable  14  to the RF signal process unit  12 . Similarly, the second radiator  22  includes a third arm  223  and a fourth arm  224 , wherein the third arm  223  is electrically connected to the feed-in terminal  23 , the fourth arm  224  is electrically connected to the woven shield  24  of the co-axial cable  14 . Hence, the second radiator  22  maybe regarded as a dipole antenna as well, whose RF current (i.e. the RF signal) may flow on the third arm  223 , and a return current may flow from the fourth arm  224  and following the woven shield  24  of the co-axial cable  14  to the RF signal process unit  12 . Lengths of current routes of the first arm  211  and the second arm  212  are different from lengths of current routes of the third arm  223  and the fourth arm  224 , which may induce different resonate modes such that the dipole antenna  20  may operate indifferent frequency bands simultaneously. 
     In short, the dipole antenna  20  electrically connects the first radiator  21  with the second radiator  22 , which may viewed as combining two dipole antennas into one antenna to reach dual operating bands . 
     However, since the return current of the dipole antenna  20  directly flows to the woven shield  24  of the co-axial cable  14 , a matching impedance or a feed-in impedance between the co-axial cable  14  and the dipole antenna  20  may be changed due to an impedance change of the co-axial cable  14  caused by a cable routing change. As a result, the antenna performance of the dipole antenna  20  may be unstable during manufacture. 
     Therefore, to improve the stability of the dipole antenna  20  during manufacture, please refer to  FIG. 3 , which is a schematic diagram of a dipole antenna  30  according to an embodiment of the present invention. The dipole antenna  30  may take the place of the dipole antenna  20  shown in  FIG. 2  to realize the antenna  11  shown in  FIG. 1 . The dipole antenna  30  includes a feed-in terminal  33 , a balun  35 , a first radiator  31  and a second radiator  32 . The balun  35  is electrically connected to the feed-in terminal  33  for driving out a return current of the dipole antenna  30  to balance a feed-in impedance of the dipole antenna  30 . The first radiator  31  and the second radiator  32  are electrically connected to the feed-in terminal  33  and the balun  35 , and are respectively used for radiating the RF signal in high and low frequency bands. The first radiator  31  includes a first arm  311  and a second arm  312 , wherein the first arm  311  has one end electrically connected to the feed-in terminal  33  and balun  35 , and the first arm  311  has another end opened. The second arm  312  has one end electrically connected to balun  35 , and the second arm  312  has another end opened. The second radiator  32  includes a third arm  323  and a fourth arm  324 . The third arm  323  has one end electrically connected to the feed-in terminal  33 , the first arm  311  and the balun  35 , and the third arm  323  has another end opened. The fourth arm  324  has one end electrically connected to the second arm  312  and the balun  35 , and the fourth arm  324  has another end opened. 
     The balun  35  includes a first grounded arm  351 , a second grounded arm  352  and a ground unit  36 . The ground unit  36  is used for providing grounding. The first grounded arm  351  has one end electrically connected to the first arm  311 , the third arm  323  and the feed-in terminal  33 , and the first grounded arm  351  has another end electrically connected to the ground unit  36 . The second grounded arm  352  has one end electrically connected to second arm  312  and fourth arm  324 , and the second grounded arm  352  has another end electrically connected to ground unit  36 . In such a structure, the return current may flow from the first grounded arm  351 , the second grounded arm  352  and return to the ground unit  36  when the RF signal is fed in the dipole antenna  30 , which may reduce an amount of the return current flowing on the woven shield  24  of the co-axial cable  14 , and prevent the noise carried by the return current from flowing into the RF signal process unit  12  through the woven shield  24 . 
     Simply speaking, compared with the dipole antenna  20 , the dipole antenna  30  further includes the balun  35  to convert the feed-in impedance of the antenna  30  from unbalanced into balanced, which may reduce an electromagnetic interference effect caused by the return current and improve the stability of the dipole antenna  30 . 
     Please refer to  FIG. 4 , which is a schematic diagram illustrating a VSWR (Voltage Standing Wave Ratio) of the dipole antenna  20  compared with a VSWR of the dipole antenna  30 . The VSWR of the dipole antenna  20  is denoted with a dashed line, the VSWR of the dipole antenna  30  is denoted with a solid line. As shown in  FIG. 4 , within a low operating frequency band 2.4-2.5 GHz and a high frequency band 5.15-5.85 GHz for a WLAN (Wireless Local Area Network), the VSWR of the dipole antenna  30  is less than two, the VSWR of the dipole antenna  20  is partially greater than two. 
     As can be seen from  FIG. 4 , the dipole antenna  30  having the balun  35  may reach a better antenna performance than the dipole antenna  20 . Besides, the balun  35  may convert the feed-in impedance of the dipole antenna  30  from unbalanced due to the co-axial cable  14  into balanced, which may reach a better stability and an immunity against the noise. 
     Please note that the dipole antenna  30  of the present invention is to utilize the balun  35  to balance the feed-in impedance to improve the antenna performance and stability of the dipole antenna  30 . Those skilled in the art may make modifications or alterations accordingly. For example, a shape of the balun  35  is changeable and a structure of connecting the balun  35  with the first radiator  31  and the second radiator  32  is adjustable to adjust the matching impedance of the dipole antenna  30 . Lengths of arms and shapes of the first radiator  31  and second radiator  32  are adjustable, and a relative location between the first radiator  31  and second radiator  32  is also adjustable to adjust the match impedance of the dipole antenna  30  according to practical requirements. 
     As shown in  FIG. 3 , the second grounded arm  352  of the balun  35  and the ground unit  36  may form a closed loop area A 3 , an area of the closed loop area A 3  may be adjustable to adjust the matching impedance of the dipole antenna  30 . There is a gap B 3  between the first arm  311  and the second arm  312  of the first radiator  31 . The gap B 3  may induce a coupling effect to adjust the match impedance of the dipole antenna  30 . There is a gap C 3  between the first arm  311  of the first radiator  31  and the third arm  323  of the second radiator  32 . The gap C 3  may adjustable to adjust the match impedance of the dipole antenna  3 . The first arm  311  and the second arm  312  of the first radiator  31  respectively have a bend such that the ends opened of the first arm  311  and the second arm  312  may lie on a same extended line. Or, the third arm  323  and the fourth arm  324  of the second radiator  32  may respectively have a bend such that the ends opened of the third arm  323  and the fourth arm  324  may lie on a same extended line. In such a structure, there are a gap D 3  between the end opened of the first arm  311  and the end opened of the third arm  323 , and a gap E 3  between the end opened of the second arm  323  and the end opened of the fourth arm  324 . The gaps D 3  and E 3  may be adjustable to adjust the matching impedance of the dipole antenna  30 . As a result, an antenna designer may adjust multiple parameters, such as the area of the closed loop area A 3  and the gap B 3 , C 3 , D 3  and E 3 , to increase a design flexibility of the dipole antenna  30 . 
     Please refer to  FIG. 5 , which is a schematic diagram of a dipole antenna  50  according to an embodiment of the present invention. Comparing the dipole antenna  50  with the dipole antenna  30 , areas and lengths of a first arm  511  and a second arm  512  of a first radiator  51  are equal such that the first arm  511  and the second arm  512  are symmetric, while the first arm  311  has a greater area than the second arm  312  such that the first arm  311  is asymmetric to the second arm  312 . A gap C 5  of the dipole antenna  50  is less or narrower than the gap C 3  of the dipole antenna  30 , which may increase an effective capacitance between the first arm  511  and a third arm  523 , and increase an effective capacitance between the second arm  512  and a fourth arm  524 . 
     Please refer to  FIG. 6 , which is a schematic diagram of a dipole antenna  60  according to an embodiment of the present invention. Comparing the dipole antenna  60  with the dipole antennas  30  and  50 , two ends of a ground unit  66  are respectively electrically connected to a third grounded arm  661  and a fourth grounded arm  662 . The third grounded arm  661  and the fourth grounded arm  662  are both perpendicular to the ground unit  66 , such that the ground unit  66  has a U shape. In the dipole antenna  30 , a flat coverage of the first radiator  31  and the second radiator  32  is relatively greater than a flat coverage of the ground unit  36 . In comparison, in the dipole antenna  60 , a flat coverage of a first radiator  61  and a second radiator  62  is relatively less than a flat coverage of the ground unit  66 . Thus, most of a return current of the dipole antenna  60  may flow on the ground unit  66 , such that the dipole antenna  60  may reach a better stability and an immunity against the noise. Besides, a length of a current route of the first radiator  61  is relatively less than a length of a current route of a second radiator  62 . Specifically, part of the RF signal may flow the shorter current route that from a feed-in terminal  63 , the first arm  611  and the second arm  612  to the ground unit  66 . On the other hand, part of the RF signal may flow the longer route that is from the feed-in terminal  63 , a third arm  623  and a fourth arm  624  and return to the ground unit  66 . Thus, the first radiator  61  may be used for radiating the RF signal in the high frequency band, while the second radiator  62  may be used for radiating the RF signal in the low frequency band. 
     Please refer to  FIG. 7 , which is a schematic diagram of a dipole antenna  70  according to an embodiment of the present invention. A difference between the dipole antenna  70  and the dipole antenna  60  is that a first radiator  71  of the dipole antenna  70  is used for radiating the RF signal in a low frequency band, and a second radiator  72  is used for radiating the RF signal in a high frequency band. Specifically, part of the RF signal may flow a longer route that is from a feed-in terminal  73 , a first arm  711  and a second arm  712  and return to a ground unit  76 . On the other hand, part of the RF signal may flow a longer route that is from the feed-in terminal  73 , a third arm  723  and a fourth arm  724  and return to the ground unit  76  . Therefore, the first radiator  71  may be used for radiating the RF signal in the low frequency band, and the second radiator  72  may be used for radiating the RF signal in the high frequency band. In short, relative locations of the radiators respectively used for radiating the RF signal in the low or high frequency band may be switched according practical requirements. 
     To sum up, the gain of the dipole antenna is theoretically higher than the gain of the monopole antenna and also higher than the gain of the PIFA, however, the co-axial cable  14  may unbalance the feed-in impedance of the dipole antenna. Therefore, the dipole antennas  30 ,  50 ,  60  and  70  of the present invention include the balun to convert the feed-in impedance of the antenna  30  from unbalanced into balanced, which may reduce the electromagnetic interference effect caused by the return current and improve the stability of the dipole antennas  30 ,  50 ,  60  and  70 . 
     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. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.