Abstract:
A multi-band planar antenna includes first and second radiating elements. The first radiating element is operable within a first frequency bandwidth. The second radiating element is operable within a second frequency bandwidth. The first radiating element is formed with a slot that generates resonance within the second frequency bandwidth, thereby lowering the VSWR, widening the bandwidth, and increasing the antenna gain of the planar antenna in the second frequency bandwidth.

Description:
[0001]     CROSS-REFERENCE TO RELATED APPLICATION  
         [0002]     This application claims priority of Taiwanese application no. 094122535, filed on Jul. 4, 2005. 
     
    
       [0003]     BACKGROUND OF THE INVENTION  
         [0004]     1. Field of the Invention  
         [0005]     This invention relates to a multi-band planar antenna, more particularly to a multi-band planar antenna applicable to a mobile phone.  
         [0006]     2. Description of the Related Art  
         [0007]      FIG. 1  illustrates a conventional multi-band planar antenna  1  disposed on a circuit board  100  of a mobile phone (not shown). The planar antenna  1  includes first and second radiating elements  11 ,  12 , a feeding point  14 , a grounding point  10 , first and second meandering feeding strips  15 ,  18 , and first and second meandering grounding strips  16 ,  19 . The first radiating element  11  operates within the GSM 900 MHz bandwidth, is rectangular in shape, and has a pair of opposite first and second shorter sides  111 ,  112 , and a pair of opposite third and fourth longer sides  113 ,  114 . The first radiating element  11  is formed with a notch  130  at a corner thereof. The feeding point  14  is disposed adjacent to the first shorter side  111  of the first radiating element  11 . The grounding point  10  is disposed adjacent to the third longer side  113  of the first radiating element  11 . The first meandering feeding strip  15  has opposite ends connected respectively to the first shorter side  111  of the first radiating element  11  and the feeding point  14 . The first meandering grounding strip  16  has opposite ends connected respectively to the second shorter side  112  of the first radiating element  11  and the grounding point  10 . The second radiating element  12  operates within the DCS 1800 MHz and PCS 1900 MHz bandwidths, is rectangular in shape, and has a pair of opposite first and second shorter sides  121 ,  122 , and a pair of opposite third and fourth longer sides  123 ,  124 . The second radiating element  12  is disposed in the notch  130  in the first radiating element  11 . The second meandering feeding strip  18  has opposite ends connected respectively to the first side  121  of the second radiating element  12  and the feeding point  14 . The second meandering grounding strip  19  has opposite ends connected respectively to the third longer side  123  of the second radiating element  12  and the grounding point  10 .  
         [0008]     The aforementioned conventional planar antenna  1  is disadvantageous in that, based from experimental results, as illustrated in  FIG. 3 , the conventional planar antenna  1  provides a relatively high voltage standing wave ratio (VSWR), i.e., greater than three, within the DCS 1800 and PCS 1900 frequency bandwidths. Moreover, the conventional planar antenna  1  has an unsatisfactory bandwidth within the DCS 1800 and PCS 1900 frequency bandwidths, as indicated by line  20 . Further, as illustrated in  FIG. 4 , the conventional planar antenna  1  has a relatively low antenna gain within the DCS 1800 and PCS 1900 frequency bandwidths, as indicated by the diamond symbols.  
       SUMMARY OF THE INVENTION  
       [0009]     Therefore, the object of the present invention is to provide a multi-band planar antenna that can overcome the aforesaid drawbacks of the prior art.  
         [0010]     According to the present invention, a multi-band planar antenna comprises first and second radiating elements. The first radiating element is operable within a first frequency bandwidth. The second radiating element is operable within a second frequency bandwidth. The first radiating element is formed with a slot that generates resonance within the second frequency bandwidth. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiment with reference to the accompanying drawings, of which:  
         [0012]      FIG. 1  is a schematic view of a conventional multi-band planar antenna mounted on a circuit board;  
         [0013]      FIG. 2  is a schematic view of the preferred embodiment of a multi-band planar antenna according to the present invention;  
         [0014]      FIG. 3  is a plot to illustrate voltage standing wave ratios and bandwidths of the conventional planar antenna and the preferred embodiment; and  
         [0015]      FIG. 4  is a plot to illustrate antenna gains of the conventional planar antenna and the preferred embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]     Referring to  FIG. 2 , the preferred embodiment of a multi-band planar antenna  3  according to this invention is shown to include first and second radiating elements  11 ,  12 , a feeding point  14 , a grounding point  10 , first and second feeding strips  15 ,  18 , and first and second grounding strips  16 ,  19 .  
         [0017]     The multi-band planar antenna  3  of this embodiment is to be disposed on a circuit board  100  of a mobile phone (not shown).  
         [0018]     The first radiating element  11  is operable within a first frequency bandwidth, i.e., within the GSM 900 MHz. In this embodiment, the first radiating element  11  is generally rectangular in shape, and has a pair of first and second sides  111 ,  112  opposite to each other in a first direction, and a pair of third and fourth sides  113 ,  114  opposite to each in a second direction transverse to the first direction. It is noted that the first and second sides  111 ,  112  of the first radiating element  11  are shorter than the third and fourth sides  113 ,  114  of the first radiating element  11 . The first radiating element  11  is formed with a notch  130  at a corner thereof such that the first side  111  of the first radiating element  11  is shorter than the second side  112  of the first radiating element  11 , and such that the third side  113  of the first radiating element  11  is shorter than the fourth side  114  of the first radiating element  11 .  
         [0019]     The feeding point  14  is disposed closer to the notch  130  in the first radiating element  11  than the grounding point  10 . In particular, the feeding point  14  is disposed adjacent to the first side  111  of the first radiating element  11  near the notch  130  in the first radiating element  11 . The grounding point  10  is disposed adjacent to the third side  113  of the first radiating element  11  near a junction of the second and third sides  112 ,  113  of the first radiating element  11 .  
         [0020]     The first feeding strip  15  has opposite ends connected respectively to the first side  111  of the first radiating element  11  and the feeding point  14 .  
         [0021]     The first grounding strip  16  has opposite ends connected respectively to the second side  112  of the first radiating element  11  and the grounding point  10 .  
         [0022]     In this embodiment, the first feeding strip  15  and the first grounding strip  16  are configured with a meandering shape.  
         [0023]     The second radiating element  12  is operable within a second frequency bandwidth, i.e., within the DCS 1800 MHz and the PCS 1900 MHz bandwidths. In this embodiment, the second radiating element  12  is generally rectangular in shape, and has a pair of first and second sides  121 ,  122  opposite to each other in the first direction, and a pair of third and fourth sides  123 ,  124  opposite to each other in the second direction. It is noted that the first and second sides  121 ,  122  of the second radiating element  12  are shorter than the third and fourth sides  123 ,  124  of the second radiating element  12 . The second radiating element  12  has a size that is slightly smaller than the notch  130  in the first radiating element  11 , and is disposed in the notch  130 .  
         [0024]     The second feeding strip  18  has opposite ends connected respectively to the first side  121  of the second radiating element  12  and the feeding point  14 .  
         [0025]     The second grounding strip  19  has opposite ends connected respectively to the third side  123  of the second radiating element  12  and the grounding point  10 .  
         [0026]     In this embodiment, the second feeding strip  18  and the second grounding strip  19 , like the first feeding strip  15  and the first grounding strip  16 , are configured with a meandering shape.  
         [0027]     The first radiating element  11  is formed with a slot  110  that extends from the third side  113  toward the fourth side  114  of the first radiating element  11 . The slot  110  in the first radiating element  11  is dimensioned so as to generate resonance within the second frequency bandwidth.  
         [0028]     Based from experimental results, as illustrated in  FIG. 3 , when the length dimension of the slot  110  in the first radiating element  11  is chosen to be 18.5 and 16 millimeters, the planar antenna  3  of this invention provides voltage standing wave ratios (as indicated by lines  21  and  22 ) of less than two within the second frequency bandwidth. Moreover, the bandwidth of the planar antenna  3  of this invention within the second frequency bandwidth is considerably widened, notably within the PCS 1900 MHz bandwidth. Further, the antenna gain of the planar antenna  3  of this invention within the second frequency bandwidth, as illustrated in  FIG. 4 , is dramatically increased. Indeed, the slot  110  in the first radiating element  11  lowers the VSWR, widens the bandwidth, and increases the antenna gain within the second frequency bandwidth.  
         [0029]     While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this invention is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.