Abstract:
A multi-frequency antenna and an electronic device having the multi-frequency antenna are disclosed. The multi-frequency antenna comprises: a first radiating element including a first end and a second end; a grounding element connected to the first end of the first radiating element; a feeding structure for inputting an electrical signal to the first radiating element; and a second radiating element including a first end and a second end. The first end of the second radiating element includes a transitional portion; and the second radiating element is connected to the second end of the first radiating element by the transitional portion. So that the first radiating element forms a first current path to generate a first resonant mode; and the second radiating element forms a second current path to generate a second resonant mode.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a multi-frequency antenna and an electronic device having the multi-frequency antenna, and, more particularly, to an inductively coupled multi-frequency antenna and an electronic device having the multi-frequency antenna. 
         [0003]    2. Description of the Related Art 
         [0004]    With wireless communication technology development, people have higher and higher demands for wireless communication. There are many electronic devices with wireless communication function such as mobile phones, GPS, PDAs, and notebook computers. Meanwhile, more and more information are transmitted via the wireless network, so the bandwidth is also increased. 
         [0005]    Prior art technology includes many different wireless communication technologies for different operation frequencies, such as UWB, WiMAX, WiFi or 3G wireless communication technology. Therefore, in order to satisfy wireless communication at different frequencies, multi-frequency antennas have become the main trend. 
         [0006]    However, people also prefer smaller and lighter electronic devices, and the wireless communication units need to have smaller size too. 
         [0007]    Prior art technology discloses a planar Inverted-F antenna. Please refer to  FIGS. 1A and 1B .  FIG. 1A  is a schematic drawing of a prior art planar Inverted-F antenna.  FIG. 1B  is a VSWR relationship drawing of the prior art planar Inverted-F antenna. As shown in  FIG. 1A , a prior art antenna  90  has a radiating element  91 , a grounding element  92  and a feeding structure  93 , As shown in  FIG. 1B , the antenna  90  only has one single resonant mode, which cannot provide multi-frequencies. 
         [0008]    Therefore, it is desirable to provide a multi-frequency antenna that can provide broad bandwidth and smaller dimensions to mitigate and/or obviate the aforementioned problems. 
       SUMMARY OF THE INVENTION 
       [0009]    A main objective of the present invention is to provide a multi-frequency antenna and an electronic device having the multi-frequency antenna, which can provide broad bandwidth and smaller dimensions. 
         [0010]    The electronic device of the invention comprises a wireless transmission module and a multi-frequency antenna, the multi-frequency antenna and the wireless transmission module are electrically connected together. The multi-frequency antenna comprises: a first radiating element including a first end and a second end; a grounding element connected to the first end of the first radiating element; a feeding structure for inputting an electrical signal to the first radiating element; and a second radiating element including a first end and a second end. The first end of the second radiating element includes a transitional portion; and the second radiating element is connected to the second end of the first radiating element by the transitional portion. So that the first radiating element forms a first current path to generate a first resonant mode; and the second radiating element forms a second current path to generate a second resonant mode. 
         [0011]    In one embodiment of the invention, the first radiating element and the second radiating element are integrated together; the transitional portion has a substantially 90° angle, the second radiating element is connected to the second end of the first radiating element via the transitional portion and extends toward to the first end of the first radiating element, so the second radiating element is substantially parallel with the first radiating element; and a gap is formed between the first radiating element and the second radiating element. 
         [0012]    In one embodiment of the invention, the multi-frequency antenna further has a top load, and the top load and the second end of the second radiating element are electrically connected together; wherein the top load is an inductive load. The top load is electrically connected to the second radiating element via passive component connection, circuit connection or direct connection; the shape of the top load is a loop shape, which is different from the shape of the second radiating element. 
         [0013]    In one embodiment of the invention, the multi-frequency antenna has a base and a third radiating element. The base has a first surface and a second surface, and the first radiating element, the grounding element, the feeding structure, the second radiating element and the top load being disposed on the first surface. The third radiating element is disposed on the second surface and is electrically connected to the grounding element. The feeding structure feeds back the electrical signal to the third radiating element by capacitive coupling. 
         [0014]    Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1A  is a schematic drawing of a prior art antenna. 
           [0016]      FIG. 1B  is a VSWR relationship drawing of the prior art antenna. 
           [0017]      FIG. 2A  is a schematic drawing of a multi-frequency antenna in a first embodiment according to the invention. 
           [0018]      FIG. 2B  is a VSWR relationship drawing of the multi-frequency antenna in the first embodiment according to the invention. 
           [0019]      FIG. 3A  is a schematic drawing of a multi-frequency antenna in a second embodiment according to the invention. 
           [0020]      FIG. 3B  is a VSWR relationship drawing of the multi-frequency antenna in the second embodiment according to the invention. 
           [0021]      FIG. 4A  is a back view schematic drawing of a multi-frequency antenna in a third embodiment according to the invention. 
           [0022]      FIG. 4B  is a front view schematic drawing of a multi-frequency antenna in the third embodiment according to the invention. 
           [0023]      FIG. 4C  is a VSWR relationship drawing of the multi-frequency antenna in the third embodiment according to the invention. 
           [0024]      FIG. 5  is a functional block drawing of an electronic device according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    Pleases refer to  FIG. 2A  and  FIG.2B .  FIG. 2A  is a schematic drawing of a multi-frequency antenna in a first embodiment according to the invention.  FIG. 2B  is a VSWR relationship drawing of the multi-frequency antenna in the first embodiment according to the invention. 
         [0026]    As shown in  FIG. 2A , a multi-frequency antenna  10  of the first embodiment has a first radiating element  11 , a grounding element  12 , a feeding structure  13  and a second radiating element  14 . The first radiating element  11  has a first end  111  and a second end  112 . The grounding element  12  is connected to the first end  111  of the first radiating element  11 . 
         [0027]    The feeding structure  13  has a feeding point (not shown) being electrically connected to a feeding wire (not shown), which is used for inputting electrical signals to the first radiating element  11 . The feeding wire can be a RF cable or other various cables. 
         [0028]    As shown in  FIG. 2A , the second radiating element  14  has a first end  141  and a second end  142 , and the first end  141  of the second radiating element  14  has a transitional portion, the second radiating element  14  is connected to the second end  112  of the first radiating element  12  via the transitional portion. 
         [0029]    Since the second radiating element  14  is connected to the first radiating element  12  via the transitional portion, when the feeding structure  13  feeds electrical signals to the first radiating element  11 , a first current path is formed on the first radiating element  11  and a second current path is formed on the second radiating element  14 . Therefore, the multi-frequency antenna  10  generates two resonant modes to provide multiple frequencies. The first radiating element  11  generates the first resonant mode, and the second radiating element  14  generates the second resonant mode with a lower operation frequency than the first resonant mode. 
         [0030]    As shown in  FIG. 2A , the first radiating element  11  has a V shape, however, the radiating element with any other shape can still be the first radiating element  11 . The second radiating element  14  has an L shape, but radiating element with any other shape can still be the second radiating element  14 . Furthermore, the first radiating element  11  and the second radiating element  14  are integrated together. However, different shapes and lengths of the first radiating element  11  and the second radiating element  14  can change the characteristics of the antenna, and the antenna designer can change the shapes and lengths of the first radiating element  11  or the second radiating element  14  to have different operation frequencies and bandwidth of the multi-frequency antenna  10 . Similarly, a gap is formed between the first radiating element  11  and the second radiating element  14 , and the size of the gap can change the characteristic of the antenna. 
         [0031]    As shown in  FIG. 2A , the transitional portion of the first end  141  of the second radiating element  14  has a substantially 90° angle, and the second radiating element  14  is connected to the second end  112  of the first radiating element  11  via the transitional portion and extends toward to the first end  111  of the first radiating element  11  so the second radiating element  14  is substantially parallel with the first radiating element  11 . Therefore, the multi-frequency antenna  10  can have a smaller dimension to satisfy modern design requirement. However, the transitional portion of the second radiating element  14  can be not the 90° angle, and the second radiating element  14  can be not parallel with the first radiating element  11 . As long as the first radiating element  11  and the second radiating element  14  can form several current paths and several resonant modes, the multi-frequency antenna  10  is accepted. 
         [0032]      FIG. 2B  shows a VSWR relationship drawing of the multi-frequency antenna  10  at different frequencies. As shown in  FIG. 2B , the multi-frequency antenna  10  at operation frequency between 1.7 GHz to 2.2 GHz generates the first resonant mode and at a lower operation frequency 0.95 GHz generates the second resonant mode. 
         [0033]    Comparing  FIG. 1B  with  FIG. 2B , the prior art antenna  90  can only generate one single resonant mode, and the antenna  10  of the invention can generate two resonant modes and has multi-frequencies. 
         [0034]    Please refer to  FIG. 3A  and  FIG. 3B .  FIG. 3A  is a schematic drawing of a multi-frequency antenna in a second embodiment according to the invention.  FIG. 3B  is a VSWR relationship drawing of the multi-frequency antenna in the second embodiment according to the invention. 
         [0035]    As shown in  FIG. 3A , in a second embodiment, the multi-frequency antenna  20  comprises a first radiating element  21 , a grounding element  22 , a feeding structure  23 , a second radiating element  24  and a top load  25 . 
         [0036]    The difference between the second embodiment and the first embodiment is, in the second embodiment, the multi-frequency antenna  20  comprises the top load  25  electrically connected with the second radiating element  24 . With the electric reactance matching effect of the top load  25 , the second resonant mode generated by the second radiating element  24  at low operation frequency can provide broad bandwidth. 
         [0037]    As shown in  FIG. 3A , the top load  25  has a loop shape, which can shorten the resonant path. However, the top load  25  just needs to have a shape different from the shape of the second radiating element  24 , and the top load  25  is able to form an inductive load to change the bandwidth. Furthermore, as long as the top load  25  and the second radiating element  24  are electrically connected together, the antenna of the invention can provide multi-frequencies. For example, the top load  25  and the second radiating element  24  can be electrically connected via passive component connection, circuit connection or direct connection. 
         [0038]      FIG. 3B  shows a VSWR relationship drawing of the multi-frequency antenna  20  at different frequencies. Comparing  FIG. 2B  with  FIG. 3B , the multi-frequency antenna  20  in the second embodiment depends on the electrical connection of the top load  25  so the second resonant mode at low frequency can provide broad bandwidth. 
         [0039]    Please refer to  FIG. 4A ,  FIG. 4B  and  FIG. 4C .  FIG. 4A  is a back view schematic drawing of a multi-frequency antenna in a third embodiment according to the invention.  FIG. 4B  is a front view schematic drawing of a multi-frequency antenna in the third embodiment according to the invention.  FIG. 4C  is a VSWR relationship drawing of the multi-frequency antenna in the third embodiment according to the invention. 
         [0040]    As shown in  FIG. 4A  and  FIG. 4B , the multi-frequency antenna  30  in the third embodiment comprises a first radiating element  31 , grounding elements  32  and  32 ′, feeding structures  33  and  33 ′, a second radiating element  34 , a top load  35 , a third radiating element  36  and a base  37 . The base  37  has a first surface (the back surface)  371  and a second surface (the front surface)  372 . The first radiating element  31 , the grounding element  32 , the feeding structure  33 , the second radiating element  34  and the top load  35  are disposed on the first surface (the back surface)  371  of the base  37 ; and the third radiating element  36 , the grounding element  32 ′ and the feeding structure  33 ′ are disposed on the second surface (the front surface)  372  of the base  37 . The base  37  can be a FR4 (Flame Retardant 4) standard fiber glass printed circuit board or other various design. 
         [0041]    The difference between the third embodiment and the second embodiment is, in the third embodiment, the multi-frequency antenna  30  further has a third radiating element  36 . The third radiating element  36  is disposed on the second surface (the front surface)  372  of the base  37 . The third radiating element  36  and the grounding element  32  disposed on the first surface (the back surface)  371  of the base  37  are electrically connected together via the grounding element  32 ′; and the third radiating element  36  and the feeding structure  33  disposed on the first surface (the back surface)  371  of the base  37  are electrically connected via the feeding structure  33 ′. Therefore, the multi-frequency antenna  30  feeds electrical signals to the third radiating element  36  via the feeding structures  33  and  33 ′ by capacitive coupling, to adjust the matching of the first resonant mode and the second resonant mode to increase the bandwidth. 
         [0042]    As shown in  FIG. 4B , the third radiating element  36  is an irregular shape, or any various shape. 
         [0043]      FIG. 4C  shows a VSWR relationship drawing of the multi-frequency antenna  30  at different frequencies. Comparing  FIG. 3B  with  FIG. 4C , the multi-frequency antenna  30  in the third embodiment utilizes the third radiating element  36  capacitive coupling effect to increase the bandwidth of the first resonant mode and the second resonant mode. 
         [0044]    Furthermore, the multi-frequency antennas  10 ,  20  and  30  can be planar antennas. 
         [0045]    Please refer to  FIG. 5 , which is a functional block drawing of an electronic device according to the invention. In one embodiment of the invention, the electronic device  50  can be a cell phone, a GPS, a PDA, or a notebook computer or any other portable device. As shown in  FIG. 5 , an electronic device  50  comprises the multi-frequency antenna  30  and a wireless transmission module  51 . The electronic device  50  utilizes RF cable (not shown) to feed into the multi-frequency antenna  30  and being electrically connected to the wireless transmission module  51 , to process signals from the multi-frequency antenna  30  via the wireless transmission module  51 . Afterward, the electronic device  50  utilizes the multi-frequency antenna  30  to receive or transmit wireless signals to other device (not shown). 
         [0046]    Moreover, the electronic device  50  can also have either the multi-frequency antenna  10  or  20  to replace the multi-frequency antenna  30 . 
         [0047]    Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.