Abstract:
The invention relates to a wide-band planar antenna. The wide-band planar antenna includes a substrate, a first radiator, a second radiator, a third radiator, a ground, and a signal source. The first radiator, the second radiator, and the third radiator are designed in a manner that the antenna of the invention can be applied to WiMAX communication devices. Besides, the wide-band planar antenna of the invention is more efficient than a general wide-band antenna and saves a significant amount of electrical power, and therefore, the antenna is particularly suitable for portable communicational devices.

Description:
[0001]    This application claims the priority based on a Taiwanese patent application No. 097141365, filed on Oct. 28, 2008, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a wide-band antenna; more particularly, the present invention relates to a wide-band planar antenna for wireless network communications. 
         [0004]    2. Description of the Prior Art 
         [0005]    As the physical Internet becomes more and more popular, people pay much attention to a wireless, long-distance, and wide-band network in place of the physical Internet to increase the popularity in wideband communications. Thus, more advanced wireless communication network technologies and standards continuously emerge. For example, Wi-Fi wireless network standard is previously defined in IEEE 802.11 by Institute of Electrical and Electronics Engineers (IEEE); Worldwide Interoperability for Microwave Access (WiMAX) is recently defined in IEEE 802.16. Especially for WiMAX, the transmission distance has been increased from meters to kilometers, and the bandwidth becomes wider over the prior art. 
         [0006]    In order to comply with the progress of wireless communication network technology, the antenna needs to be enhanced for receiving/transmitting wireless signals accordingly.  FIG. 1  shows a traditional dual-band antenna disclosed in the U.S. Pat. No. 6,861,986. The dual-band antenna includes a first radiator  31  and a second radiator  32 , both connected to a ground  4 . Signals are fed through a feed-in point  61  directly to excite the first radiator  31  to generate a high frequency band mode, whose central operating frequency is about 5.25 GHz. The direct fed-in signal can also excite the second radiator  32  to generate a low frequency band mode, whose central operating frequency is about 2.45 GHz. Furthermore, the length of the second radiator  32  is about one quarter (¼) of the wavelength at its operating frequency. 
         [0007]    Because the antenna is fed with signals in a direct-feed-in manner, the bandwidth of the low frequency band mode is about 200 MHz, which cannot satisfy WiMAX requirement. Furthermore, in order to meet the operating frequency of the low frequency band mode, the length of the second radiator  32  cannot be further reduced resulting in the restriction of miniaturization of the electronic devices. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the present invention to provide a wide-band planar antenna to reduce required materials for same functional design and to significantly reduce the production cost. 
         [0009]    It is another object of the present invention to provide a wide-band planar antenna having three different frequency bands through direct feed-in and coupling feed-in methods to accommodate the needs of different frequencies. 
         [0010]    It is a further object of the present invention to provide a wide-band antenna, which prevents reflective waves in a specific bandwidth so as to enhance the power of electromagnetic waves and to save more electrical power compared with a general antenna. 
         [0011]    The wide-band planar antenna of the invention includes a substrate, a first radiator, a second radiator, a third radiator, a ground, and a signal source. The substrate includes a first surface and a second surface corresponding to the first surface. In other words, the first surface and the second surface are two opposite surfaces of the substrate. The first radiator is disposed on the first surface. The second radiator connects to the first radiator at a connection part. The second radiator is disposed on either the first surface or the second surface. In other words, the second radiator and the first radiator can be disposed on a same surface or different surfaces of the substrate. 
         [0012]    The third radiator is disposed on either the first surface or the second surface. In other words, the third radiator can be disposed on the first surface or the second surface in accordance with different designs or field patterns. The ground connects to the third radiator and includes a first ground part and a second ground part. The third radiator includes a shorter side and a longer side connected to the shorter side. The shorter side connects to the ground. A lengthwise direction of the shorter side is perpendicular to a lengthwise direction of the longer side. The longer side extends toward the first radiator. The second radiator is disposed between the third radiator and the ground. 
         [0013]    The signal source feeds a high frequency signal including a positive signal and a negative signal. The positive signal is directly fed through the connection part to excite the first radiator and the second radiator to generate a first frequency band mode and a second frequency band mode respectively. The negative signal couples with the ground to be fed into and excite the third radiator to generate a third frequency band mode by a coupling effect. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  shows a schematic view of a traditional dual-band antenna. 
           [0015]      FIG. 2A  shows a schematic view of a first surface of an antenna in accordance with an embodiment of the invention. 
           [0016]      FIG. 2B  shows a schematic view of a second surface of  FIG. 2A . 
           [0017]      FIG. 3A  shows a schematic view of a voltage standing wave ratio (VSWR) diagram of the embodiment illustrated in  FIG. 2A . 
           [0018]      FIG. 3B  shows a schematic view of a field pattern of  FIG. 2A . 
           [0019]      FIG. 4A  shows a schematic view of a first surface of an antenna in accordance with an embodiment of the invention. 
           [0020]      FIG. 4B  shows a schematic view of a second surface of  FIG. 4A . 
           [0021]      FIG. 5A  shows a schematic view of a first surface of an antenna in accordance with an embodiment of the invention. 
           [0022]      FIG. 5B  shows a schematic view of a second surface of  FIG. 5A . 
           [0023]      FIG. 6A  shows a schematic view of a VSWR diagram of the embodiment illustrated in  FIG. 5A . 
           [0024]      FIG. 6B  shows a schematic view of a field pattern of  FIG. 5A . 
           [0025]      FIG. 7A  shows a schematic view of a first surface of an antenna in accordance with an embodiment of the invention. 
           [0026]      FIG. 7B  shows a schematic view of a second surface of  FIG. 7A . 
           [0027]      FIG. 8A  shows a schematic view of a first surface of an antenna in accordance with an embodiment of the invention. 
           [0028]      FIG. 8B  shows a schematic view of a second surface of  FIG. 8A . 
           [0029]      FIG. 9A  shows a schematic view of a first surface of an antenna in accordance with an embodiment of the invention. 
           [0030]      FIG. 9B  shows a schematic view of a second surface of  FIG. 9A . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0031]    It is an object of the invention to provide a wide-band planar antenna and a manufacture process thereof. By a smaller and thinner design, the production cost can be drastically decreased. By designing the radiator for a specific bandwidth, reflective waves can be reduced to increase the power of electromagnetic waves so as to save more electrical power. In an embodiment, a wide-band planar antenna has a wireless communication function applicable to various electronic devices. The electronic devices preferably include laptops, desktop computers, motherboards, mobile phones, personal digital assistants, global positioning systems, electronic game devices, and so on. The wireless signal transmitted/received by the wide-band planar antenna can be applied to wireless local area network (WLAN), WiMAX, and other wireless communication protocols or standards. 
         [0032]      FIG. 2A  and  FIG. 2B  show schematic views of the wide-band antenna of the invention. With reference to  FIG. 2A  and  FIG. 2B , the wideband planar antenna  100  includes a substrate  200 , a first radiator  300 , a second radiator  400 , a third radiator  500 , a ground  600 , and a signal source  700 . The substrate  200  is preferably made of polyethylene terephthalate (PET) or other dielectric materials. For example, a printed circuit board (PCB) or a flexible printed circuit board (FPCB) can be used as the substrate  200 . In the embodiment, the thickness of the substrate  200  is less than, but not limited to, 1 mm. The substrate  200  includes a first surface  210  and a second surface  220  corresponding to the first surface  210 .  FIG. 2A  shows a schematic view of the first surface  210  of the antenna.  FIG. 2B  shows a schematic view of the second surface  220  of the antenna. 
         [0033]    With reference to  FIG. 2A , the first radiator  300  is disposed on the first surface  210  of the substrate  200 . In the embodiment, the first radiator  300  is disposed on the first surface  210  as a metal strip or a metal microstrip in other geometric shapes. The first radiator  300  is preferably printed on the first surface  210 ; however, in other embodiments, the first radiator  300  can be disposed by other processes. Furthermore, the area and the shape of the first radiator  300  can be adjusted according to the impedance matching design. 
         [0034]    The second radiator  400  connects to the first radiator  300  at a connection part  800 . The second radiator  400  is preferably disposed on the first surface  210 ; however, in another embodiment, the second radiator  400  can be disposed on the second surface  220 . In other words, the first radiator  300  and the second radiator  400  can be disposed on different surfaces. In such a case, the connection part  800  can penetrate the substrate  200  to connect to the first radiator  300  on the first surface  210  and to the second radiator  400  on the second surface  220 . The second radiator  400  is preferably printed as a metal strip or a metal microstrip in other geometric shapes. In the embodiment shown in  FIG. 4A  and  FIG. 4B , the area and the shape of the second radiator  400  can be adjusted according to the impedance matching design. 
         [0035]    In the embodiment shown in  FIG. 2A  and  FIG. 2B , the second radiator  400  and the first radiator  300  are disposed on a same surface, i.e., the first surface  210 . For example, the first radiator  300  and the second radiator  400  are two opposite ends of a same metal microstrip. However, in another embodiment, the first radiator  300  and the second radiator  400  are disposed on different surfaces, for example, the first surface  210  and the second surface  220  respectively. In such a case, the first radiator  300  and the second radiator  400  are distanced by the thickness of the substrate  200 . In the embodiment, when the second radiator  400  is disposed on the second surface  220 , the projection area of the second radiator  400  does not overlap with the first radiator  300 . In the embodiment shown in  FIG. 2A  and  FIG. 2B , the second radiator  400  extends away from the first radiator  300 . However, in another embodiment shown in  FIG. 7A  and  FIG. 7B , the second radiator  400  and the first radiator  300  can extend toward the same direction. 
         [0036]    The third radiator  500  can be disposed on the first surface  210  or the second surface  220  of the substrate  200 . The third radiator  500  is preferably printed as a metal strip or a metal microstrip. The area and the shape of the third radiator  500  can be adjusted according to the impedance matching design. In the embodiment shown in  FIG. 2A  and  FIG. 2B , the third radiator  500  is disposed on the second surface  220  and extends toward the first radiator  300 . The third radiator  500  is disposed on the surface where the first radiator  300  and the second radiator  400  are not disposed. In the embodiment shown in  FIG. 2A  and  FIG. 2B , the third radiator  500  includes a longer side  510  and a shorter side  530 . A lengthwise direction of the shorter side  530  is perpendicular to a lengthwise direction of the longer side  510 . In other words, a right angle is formed between the shorter side  530  and the longer side  510 . The third radiator  500  connects the ground  600  through the shorter side  530 . The connecting method includes coupling, welding, and metal printing. The third radiator  500  preferably extends in a direction away from the ground  600 . In the embodiment, the shorter side  530  of the third radiator  500  is distributed on the substrate  200  in a zigzag manner, such as the shorter side  530  shown in  FIG. 9A  and  FIG. 9B . In such an arrangement, it is possible to increase a path length of the third radiator  500  so as to increase or change the bandwidth of the third frequency band mode without requiring additional space. Therefore, the bandwidth of a larger antenna can be achieved by a smaller antenna resulting in the size reduction of the antenna. 
         [0037]    The ground  600  includes a first ground part  610  and a second ground part  630 . In the embodiment shown in  FIG. 2A  and  FIG. 2B , the third radiator  500  connects to the second ground part  630 . The second ground part  630  and the third radiator  500  are disposed on the second surface  220 . Because the shorter side  530  connects to the second ground part  630  and intersects with the longer side  510 , the longer side  510  extends toward the first radiator  300 . In the embodiment, the first ground part  610  and the second ground part  630  are disposed on the first surface  210  and the second surface  220 , respectively. The first ground part  610  and the second ground part  630  are two metal pieces connected to form the ground  600 . However, in other embodiments, the first ground part  610  and the second ground part  630  can be disposed independently as two grounding points. For example, the first ground part  610  can indirectly connect to the second ground part  630  when the two ground parts are disposed on two different surfaces. Furthermore, the antenna can achieve a better performance when the second ground part  630  and the first ground part  610  are disposed on different surfaces of the substrate  200  and indirectly connected to each other. 
         [0038]    In the embodiment shown in  FIG. 2A  and  FIG. 2B , the projection areas of the third radiator  500  and the first ground part  610  on the first surface  210  encircles a semi-open region  900 . The second radiator  400  partially extends into the semi-open region  900 . In other words, the second radiator  400  is disposed between the third radiator  500  and the ground  600 . The semi-open region  900  of the embodiment is a region in a long strip shape. The second radiator  400  extends along the long strip region. Moreover, the first radiator  300  extends from the connection part  800  and opposite to the semi-open region  900 . In other words, the second radiator  400  extends away from the first radiator  300 . For space utilization, one end of the first radiator  300  extending outside the semi-open region  900  forms a bending part  310 . The bending part  310  is bent and then extends toward the first ground part  610 . In other words, the first radiator  300  extends from the connection part  800  in a direction away from the second radiator  400  and includes the bending part  310  extending toward the ground  600 . However, in another embodiment, the first radiator  300  can directly extend without bending. Furthermore, in other embodiment, an extending end of the bending part  310  in the first radiator  300  can be bent to face the longer side  510  (not shown). 
         [0039]    In the embodiment shown in  FIG. 2A  and  FIG. 2B , the semi-open region  900  is defined by the ground  600 , the shorter side  530 , and the longer side  510 . The shorter side  530  and the longer side  510  form a reversed L shape to connect to the ground  600 . Because of the reversed L shape design, the size of the wideband antenna can be reduced to save the required space. However, in other embodiments, the third radiator  500  can be a reversed F shape, an S shape, or other geometric shapes. 
         [0040]    The signal source  700  feeds signals into the wideband planar antenna  100  to excite the first radiator  300  and the second radiator  400  for generating wireless frequency band modes. With reference to  FIG. 2A  and  FIG. 2B , the signal feed-in method of the wideband planar antenna of the invention are a direct feed-in method and a coupling method. The signal source  700  feeds a high frequency signal including a positive signal and a negative signal. The positive signal is directly fed through the connection part  800  to excite the first radiator  300  and the second radiator  400  to generate a first frequency band mode  730  and a second frequency band mode  750 , respectively. The negative signal couples with the ground  600  to excite the third radiator  500  to generate a third frequency band mode  770  by coupling effect. Particularly, the feed-in location of the positive signal of the signal source  700  connects to the connection part  800 , while the negative signal feed-in location couples with the first ground part  610 . The second ground part  630  indirectly connects to the first ground part  610 . The second radiator  400  is disposed within the semi-open region  900  encircled by the longer side  510 , the shorter side  530 , and the first ground part  610  of the ground  600 . The positive signal feed-in location of the signal source  700  (i.e. the connection part  800 ) is disposed outside the semi-open region  900 . However, in other embodiments, the arrangement of the metal strip can be adjusted in accordance with different designs and field patterns. 
         [0041]      FIG. 3A  shows a schematic view of a voltage standing wave ratio (VSWR) diagram of the invention. In the embodiment, with the reference to  FIG. 3A , the first frequency band mode  730  is a second high frequency band mode. The first frequency band mode preferably has a frequency band between 3.3 GHz and 3.8 GHz. The second frequency band mode  750  is a first high frequency band mode and preferably has a frequency band between 5.15 GHz and 5.85 GHz. In the embodiment, the VSWR of the first frequency band mode  730  and the second frequency band mode  750  can be controlled fewer than 2. In the embodiment shown in  FIG. 3A , the third frequency band mode  770  is a low frequency band mode and preferably has a frequency band between 2.3 GHz and 2.7 GHz. In the embodiment, the VSWR of the third frequency band mode  770  can be controlled fewer than 2. The above-identified frequency band is an exemplary portion of the actual frequency band in the third frequency band mode  770 . With reference to  FIG. 3A , because the third frequency band mode  770  is generated by a coupling-feed-in manner, the actual frequency band thereof exceeds the above-identified range. Consequently, the first frequency band mode  730  partially overlaps with the third frequency band mode  770 , but the first frequency band mode  730  does not overlap with the second frequency band mode  750 . Besides, in the embodiment, the first frequency band mode  730  overlaps with the third frequency band mode  770  to form a broader frequency band. In other words, with reference to  FIG. 3A , because the first frequency band mode  730  partially overlaps with the third frequency band mode  770 , possible wave peaks generated in these modes may be eliminated and the VSWR may be controlled under 2, and therefore, the overall frequency band may be considered as the combination of the frequency bands of the first frequency band mode  730  and the third frequency band mode  770 . 
         [0042]    In the embodiment shown in  FIG. 3A , the first frequency band mode  730  has a frequency band between 3.3 GHz and 3.8 GHz, and the field pattern of the first frequency band mode  730  is illustrated in  FIG. 3B . The second frequency band mode  750  has a frequency band between 5.15 GHz and 5.85 GHz, and the field pattern of the second frequency band mode  750  is illustrated in  FIG. 3B . The third frequency band mode  770  has a frequency band between 2.3 GHz and 2.7 GHz, and the field pattern of the third frequency band mode  770  is illustrated in  FIG. 3B . The above-mentioned field patterns are characterized in that there is no free field effect (where a recess is formed in the field pattern and the radiation power is extremely low) in East, South, West, and, North directions. 
         [0043]    In the embodiment shown in  FIG. 5A  and  FIG. 5B , the extending end  515  of the longer side  510  of the third radiator  500  is bent toward the shorter side  530 . In the embodiment, the first radiator  300 , the second radiator  400 , the third radiator  500 , and the ground  600  are disposed on the first surface  210 . In other words, the second surface  220  does not have any metal strip or metal microstrip. Because of the bend of the extending end  515  and the arrangement of the radiators on the same surface, it is allowed to maintain 50% power and not to create any free field effect. In the embodiment, the shorter side  530  of the third radiator  500  connects to the second ground part  630 . The second ground part  630  and the first ground part  610  are formed as a metal piece disposed on the first surface  210  so that the second ground part  630  and the first ground part  610  are combined as an integrated ground  600 . In the embodiment, the second radiator  400  extends into the semi-open region  900  in a direction away from the first radiator  300 . In other words, the free ends of the first radiator  300  and the second radiator  400  extend away from each other. Besides, the second radiator  400  is disposed within the semi-open region  900  encircled by the longer side  510 , the short side  530 , and the ground  600 . However, in another embodiment, the free ends of first radiator  300  and the second radiator  400  can extend toward the same direction, as shown in  FIG. 8A  and  FIG. 8B . In the embodiment shown in  FIG. 5A  and  FIG. 5B , the first radiator  300 , the second radiator  400 , and the third radiator  500  are preferably printed as metal strips or metal microstrips. The area or the shape of the first radiator  300 , the second radiator  400 , and the third radiator  500  can be adjusted in accordance with the impedance matching design. In the embodiment, the shorter side  530  of the third radiator  500  can be distributed on the substrate  200  in a zigzag manner, such as the shorter side  530  shown in  FIG. 9A  and  FIG. 9B . 
         [0044]      FIG. 6A  shows a schematic view of a VSWR diagram of the embodiment illustrated in  FIG. 5A  and  FIG. 5B . As shown in  FIG. 6A , the third frequency band mode  770  is a low frequency band mode having a frequency band between 2.3 GHz and 2.7 GHz. In the embodiment, the VSWR of the third frequency band mode  770  can be controlled fewer than 2. The above-identified frequency band is an exemplary portion of the actual frequency band in the third frequency band mode  770 . In other words, with reference to  FIG. 6A , because the third frequency band mode  770  is generated in a coupling-feed-in manner, the actual frequency band may exceed the above-identified range. Consequently, because the first frequency band mode  730  partially overlaps with the third frequency band mode  770 , possible wave peaks generated in these modes may be eliminated and the VSWR may be controlled fewer than 2. Therefore, the overall frequency band may be considered as the combination of the frequency bands of the first frequency band mode  730  and the third frequency band mode  770 . 
         [0045]    In the embodiment shown in  FIG. 6A  and  FIG. 6B , the first frequency band mode  730  has a frequency band between 3.3 GHz and 3.8 GHz, and the field pattern of the first frequency band mode  730  is illustrated in  FIG. 6B . The second frequency band mode  750  has a frequency band between 5.15 GHz and 5.85 GHz, and the field pattern of the second frequency band mode  750  is illustrated in  FIG. 6B . The third frequency band mode  770  has a frequency band between 2.3 GHz and 2.7 GHz, and the field pattern of the third frequency band mode  770  is illustrated in  FIG. 6B . The above-mentioned field patterns are characterized in that there is no free field effect (where a recess is formed in the field pattern and the radiation power is extremely low) in East, South, West, and, North directions. 
         [0046]    Although the embodiments of the invention have been described herein, the above description is merely illustrative. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.