Patent Publication Number: US-7714789-B2

Title: Antenna having a diversity effect

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority of Taiwanese application no. 097112992, filed on Apr. 10, 2008. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an antenna, more particularly to an antenna that is applicable to worldwide interoperability for microwave access (WiMAX) technology. 
   2. Description of the Related Art 
   Worldwide interoperability for microwave access (WiMAX) technology is undergoing rapid development. However, since WiMAX technology supports a transmission range of up to 50 kilometers, WiMAX technology is susceptible to multipath interference, especially in an urban setting where there is a large number of buildings. 
   Therefore, there exists a need for an antenna that is applicable to WiMAX technology and that minimizes, if not eliminates, the above-described problem. 
   SUMMARY OF THE INVENTION 
   According to the present invention, an antenna comprises a dielectric substrate, a grounding plane, first and second grounding elements, first and second radiating elements, and first and second feeding points. The grounding plane is formed on the dielectric substrate and has a connecting end. The first and second grounding elements extend from the connecting end of the grounding plane away from each other. The first and second radiating elements are spaced apart from each other. The connecting end of the grounding plane is disposed between the first and second radiating elements. The first radiating element is spaced apart from and coupled electromagnetically to the first grounding element, thereby permitting operation of the first grounding element and the first radiating element in a frequency range. The second radiating element is spaced apart from and coupled electromagnetically to the second grounding element, thereby permitting operation of the second grounding element and the second radiating element in the frequency range. Each of the first and second feeding points is formed on the dielectric substrate and is coupled to a respective one of the first and second radiating elements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which: 
       FIG. 1  is a schematic view of the first preferred embodiment of an antenna according to this invention; 
       FIG. 2  is a schematic view illustrating a connecting end of a grounding plane, first and second grounding elements, and first and second radiating elements of the first preferred embodiment; 
       FIG. 3  is a plot illustrating a voltage standing wave ratio (VSWR) of each of first and second antenna units of the first preferred embodiment; 
       FIG. 4  shows a plot illustrating an isolation of the first preferred embodiment; 
       FIG. 5  shows plots of radiation patterns of the first antenna unit of the first preferred embodiment respectively on the x-y, x-z, and y-z planes when operated at 3300 MHz; 
       FIG. 6  shows plots of radiation patterns of the first antenna unit of the first preferred embodiment respectively on the x-y, x-z, and y-z planes when operated at 3500 MHz; 
       FIG. 7  shows plots of radiation patterns of the first antenna unit of the first preferred embodiment respectively on the x-y, x-z, and y-z planes when operated at 3700 MHz; 
       FIG. 8  shows plots of radiation patterns of the second antenna unit of the first preferred embodiment respectively on the x-y, x-z, and y-z planes when operated at 3300 MHz; 
       FIG. 9  shows plots of radiation patterns of the second antenna unit of the first preferred embodiment respectively on the x-y, x-z, and y-z planes when operated at 3500 MHz; 
       FIG. 10  shows plots of radiation patterns of the second antenna unit of the first preferred embodiment respectively on the x-y, x-z, and y-z planes when operated at 3700 MHz; 
       FIG. 11  is a perspective view of the second preferred embodiment of an antenna according to this invention; 
       FIGS. 12 to 16  are schematic views of modified embodiments of the second preferred embodiment according to this invention; 
       FIGS. 17 to 19  are perspective views of modified embodiments of the second preferred embodiment according to this invention; 
       FIG. 20  is a plot illustrating a voltage standing wave ratio (VSWR) of each of first and second antenna units of the second preferred embodiment; 
       FIG. 21  shows plots of radiation patterns of the second preferred embodiment when operated at 2500 MHz; 
       FIG. 22  shows plots of radiation patterns of the second preferred embodiment when operated at 3500 MHz; 
       FIG. 23  shows plots of radiation patterns of the first antenna unit of the second preferred embodiment respectively on the x-y, x-z, and y-z planes when operated at 2500 MHz; 
       FIG. 24  shows plots of radiation patterns of the first antenna unit of the second preferred embodiment respectively on the x-y, x-z, and y-z planes when operated at 3500 MHz; 
       FIG. 25  shows plots of radiation patterns of the second antenna unit of the second preferred embodiment respectively on the x-y, x-z, and y-z planes when operated at 2500 MHz; and 
       FIG. 26  shows plots of radiation patterns of the second antenna unit of the second preferred embodiment respectively on the x-y, x-z, and y-z planes when operated at 3500 MHz. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure. 
   Referring to  FIGS. 1 and 2 , the first preferred embodiment of an antenna according to this invention is shown to include a dielectric substrate  1 , a grounding plane  6 , first and second antenna units  100 ,  200 , and first and second feeding points  7 ,  8 . 
   The antenna of this invention is applicable to a card (not shown), such as an Express Card or a wireless network card, and is operable in a first operating range from 3300 MHz to 3800 MHz. 
   The dielectric substrate  1  is generally rectangular in shape, has a surface  10 , and includes opposite first and second edges  11 ,  12 , and opposite third and fourth edges  13 ,  14  that interconnect the first and second edges  11 ,  12 . In this embodiment, the dielectric substrate  1  has a length of 98 millimeters and a width of 29 millimeters. 
   The grounding plane  6  is formed on the surface  10  of the dielectric substrate  1 , extends from the first edge  11  toward the second edge  12  of the dielectric substrate  1 , and has a connecting end  61  that is distal from the first edge  11  of the dielectric substrate  1 , that is tapered, and that has a tip. 
   The first antenna unit  100  includes a first grounding element  2  and a first radiating element  4 . 
   The second antenna unit  200  includes a second grounding element  3  and a second radiating element  5 . 
   Each of the first and second radiating elements  4 ,  5  is spaced apart from and electromagnetically coupled to a respective one of the first and second grounding elements  2 ,  3 , thereby permitting operation of each of the first and second antenna units  100 ,  200  in the first frequency range, in a manner that will be described hereinafter. 
   The first grounding element  2  is formed on the surface  10  of the dielectric substrate  1 , is generally L-shaped, and includes first and second segments  21 ,  22 . The first segment  21  of the first grounding element  2  extends from the tip of the connecting end  61  of the grounding plane  6  toward the third edge  13  of the dielectric substrate  1  and is substantially parallel to the second edge  12  of the dielectric substrate  1 . The second segment  22  of the first grounding element  2  extends transversely from the first segment  21  of the first grounding element  2  and is substantially parallel to the third edge  13  of the dielectric substrate  1 . In this embodiment, the first grounding element  2  has a length of one-quarter wavelength in the first frequency range. 
   The first radiating element  4  is formed on the surface  10  of the dielectric substrate  1 , is disposed between the connecting end  61  of the grounding plane  6  and the first grounding element  2 , and includes a feeding segment  40 , and first, second, and third segments  41 ,  42 ,  43 . The feeding segment  40  of the first radiating element  4  has opposite first and second ends. The first segment  41  of the first radiating element  4  extends from the feeding segment  40  of the first radiating element  4 , and has a first end connected to the second end of the feeding segment  40  of the first radiating element  4 , and a second end opposite to the first end thereof. The second segment  42  of the first radiating element  4  extends from the first segment  41  of the first radiating element  4 , is disposed adjacent and substantially parallel to the first segment  21  of the first grounding element  2 , and has a first end connected to the second end of the first segment  41  of the first radiating element  4 , and a second end opposite to the first end thereof. The third segment  43  of the first radiating element  4  extends from the second segment  42  of the first radiating element  4  and has an end connected to the second end of the second segment  42  of the first radiating element  4 . In this embodiment, the first, second, and third segments  41 ,  42 ,  43  of the first radiating element  4  cooperatively define an elongated slot  48  thereamong. Moreover, in this embodiment, the first radiating element  4  has a length of one-quarter wavelength in the first frequency range. Further, in this embodiment, the second segment  42  of the first radiating element  4  has a length of less than one-eighth wavelength in the first frequency range. In addition, the third segment  43  of the first radiating element  4  has a generally axe-shaped. 
   The second grounding element  3  is formed on the surface  10  of the dielectric substrate  1 , is generally L-shaped, and includes first and second segments  31 ,  32 . The first segment  31  of the second grounding element  3  extends from the tip of the connecting end  61  of the grounding plane  6  toward the fourth edge  14  of the dielectric substrate  1  and is substantially parallel to the second edge  12  of the dielectric substrate  1 . The second segment  32  of the second grounding element  3  extends transversely from the first segment  31  of the second grounding element  3  and is substantially parallel to the fourth edge  14  of the dielectric substrate  1 . 
   In this embodiment, the first and second grounding elements  2 ,  3  are partially symmetrical with respect to an axis of symmetry (L). In particular, while the first segments  21 ,  31  of the first and second grounding elements  2 ,  3  have shape and size that are identical, the second segment  32  of the second grounding element  3  has a length shorter than that of the second segment  22  of the first grounding element  2 . 
   The second radiating element  5  is formed on the surface  10  of the dielectric substrate  1 , is spaced apart from the first radiating element  4 , and is disposed between the connecting end  61  of the grounding plane  6  and the second grounding element  3 . 
   In this embodiment, the first and second radiating elements  4 ,  5  are partially symmetrical with respect to the axis of symmetry (L). In particular, the second radiating element  5 , like the first radiating element  4 , includes first, second, and third segments that cooperatively define a slot  58  thereamong. The second segment of the second radiating element  5  has a width narrower than that of the second segment  42  of the first radiating element  4 . As such, the slot  58  in the second radiating element  5  is smaller than the slot  48  in the first radiating element  4 . 
   It is noted that since the connecting end  61  of the grounding plane  6  is disposed between the first and second radiating elements  4 ,  5 , the antenna of this invention has a high isolation. Moreover, since the first and second grounding elements  2 ,  3  are partially symmetrical and since the first and second radiating elements  4 ,  5  are partially symmetrical, the first antenna unit  100  resonates at a first resonance frequency, and the second antenna unit  200  resonates at a second resonance frequency different from the first resonance frequency. This results in substantially constant isolation values for the antenna of this invention in the first frequency range, as shown in  FIG. 4 . 
   During impedance matching for the antenna of this embodiment, a desired impedance for the antenna of this invention may be achieved by increasing or decreasing the electromagnetic coupling between the first grounding element  2  and the first radiating element  4 . The electromagnetic coupling between the first grounding element  2  and the first radiating element  4  may be increased or decreased by adjusting the dimensions of the second segment  42  of the first radiating element  4  or the gap  49  between the first segment  21  of the first grounding element  2  and the second segment  42  of the first radiating element  4 . 
   Alternatively, the desired impedance for the antenna of this embodiment may be achieved by increasing or decreasing the electromagnetic coupling between the second grounding element  3  and the second radiating element  5 . The electromagnetic coupling between the second grounding element  3  and the second radiating element  5  may be increased or decreased by adjusting the dimensions of the second radiating element  5  or the gap  59  between the first segment  31  of the second grounding element  3  and second segment of the second radiating element  5 . 
   Moreover, the size of the slot  48 ,  58  in each of the first and second radiating elements  4 ,  5  or the length of each of the first and second grounding elements  2 ,  3  may be adjusted to achieve a desired resonance frequency for the antenna of this invention. 
   Further, when it is desired for the first frequency range to cover frequencies slightly higher than 3800 MHz, the first radiating element  4  may be lengthened such that the length thereof is longer than that of the first grounding element  2 . Similarly, when it is desired for the second operating frequency to cover frequencies slightly lower than 3300 MHz, the first grounding element  2  may be lengthened such that the length thereof is longer than that of the first radiating element  4 . 
   The first feeding point  7  is formed on the surface  10  of the dielectric substrate  1 , is disposed between the first grounding element  2  and the connecting end  61  of the grounding plane  6 , and is connected to the first end of the feeding segment  40  of the first radiating element  4 . 
   The second feeding point  8  is formed on the surface  10  of the dielectric substrate  1 , is disposed between the second grounding element  3  and the connecting end  61  of the grounding plane  6 , and is connected to a feeding segment of the second radiating element  5 . 
   Experimental results, as illustrated in  FIG. 3 , show that each of the first antenna unit  100 , as indicated by line (a), and the second antenna unit  200 , as indicated by line (b), achieve a voltage standing wave ratio (VSWR) of less than 2.0 when operated in the first frequency range. Moreover, when operated in the first frequency range, as shown in Table I, the antenna of this embodiment has a minimum isolation of 18.6 dB, and as shown in Table II, the first antenna unit  100  has a maximum efficiency of −1.8 dB and a maximum peak gain of 5.0 dBi, and the second antenna unit  200  has a maximum efficiency of −1.7 dB and a maximum peak gain of 5.7 dBi. Further, the radiation patterns of the first antenna unit  100 , as illustrated in  FIGS. 5 to 7 , complement the radiation patterns of the second antenna unit  200 , as illustrated in  FIGS. 8 to 10 . It is therefore apparent that the antenna of this embodiment has a diversity effect that significantly reduces the susceptibility thereof to multipath interference, and thus, an increase in the efficiency thereof is achieved. 
   
     
       
         
             
             
           
             
                 
               TABLE I 
             
           
          
             
                 
                 
             
             
                 
               Frequency (MHz) 
             
          
         
         
             
             
             
             
             
             
             
          
             
                 
               3300 
               3400 
               3500 
               3600 
               3700 
               3800 
             
             
                 
                 
             
          
         
         
             
             
             
             
             
             
             
          
             
               Isolation (dB) 
               18.6 
               20.3 
               19.4 
               20.1 
               21.3 
               22.3 
             
             
                 
             
          
         
       
     
   
   
     
       
         
             
             
             
             
             
           
             
                 
               TABLE II 
             
           
          
             
                 
                 
             
             
                 
               first antenna 
                 
               second antenna 
                 
             
             
                 
               unit 100 
                 
               unit 200 
             
          
         
         
             
             
             
             
             
          
             
               Frequency 
               Efficiency 
               Peak gain 
               Efficiency 
               Peak Gain 
             
             
               (MHz) 
               (dB) 
               (dBi) 
               (dB) 
               (dBi) 
             
             
                 
             
             
               3300 
               −1.8 
               3.1 
               −2.1 
               3.8 
             
             
               3400 
               −2.3 
               3.1 
               −2.0 
               3.8 
             
             
               3500 
               −2.6 
               3.2 
               −1.8 
               4.4 
             
             
               3600 
               −2.4 
               4.0 
               −1.7 
               5.1 
             
             
               3700 
               −2.1 
               5.0 
               −1.8 
               5.7 
             
             
               3800 
               −2.1 
               5.0 
               −2.2 
               5.4 
             
             
                 
             
          
         
       
     
   
     FIG. 11  illustrates the second preferred embodiment of an antenna according to this invention. 
   The antenna of this embodiment is applicable to a card (not shown), such as a Personal Computer Memory Card International Association (PCMCIA card) or a wireless network card, and is operable in a second operating range from 2300 MHz to 3800 MHz. 
   Each of the first and second radiating elements  4 ,  5  is spaced apart from and coupled electromagnetically to a respective one of the first and second grounding elements  2 ,  3 , thereby permitting operation of each of the first and second antenna units  100 ,  200  in the second frequency range, in manner that will be described hereinafter. 
   The first segments  21 ,  31  of the first and second grounding elements  2 ,  3  diverge from the connecting end  61  of the grounding plane  6 , and the second segments  22 ,  32  of each of the first and second grounding elements  2 ,  3  has a generally triangular shape. The construction as such increases a bandwidth of the antenna of this embodiment. 
   The dimensions of the second segment  22 ,  32  of each of the first and second grounding elements  2 ,  3  may be adjusted to achieve a desired impedance bandwidth for the antenna of this embodiment. 
   Each of the first and second radiating elements  4 ,  5  is generally T-shape, has a first segment  41 ′,  51 ′ that is generally rectangular in shape and that has opposite ends, and a second segment  42 ′,  52 ′ that is generally rectangular in shape and that is connected to the first segment  41 ′,  51 ′ thereof at a position between the ends of the first segment  41 ′,  51 ′ thereof. 
   In this embodiment, each of the first and second grounding elements  2 ,  3  operates in the 2300 MHz to 2700 MHz range, while each of the first and second radiating elements  4 ,  5  operates in the 3300 MHz to 3800 MHz range. 
   In an alternative embodiment, each of the first and second grounding elements  2 ,  3  operates in the 3300 MHz to 3800 MHz range, while each of the first and second radiating elements  4 ,  5  operates in the 2300 MHz to 2700 MHz range. 
   In this embodiment, each of the first and second grounding elements  2 ,  3  has a length of one-quarter wavelength in the 2300 MHz to 2700 MHz range. Moreover, in this embodiment, each of the first and second radiating elements  4 ,  5  has a length of one-quarter wavelength in the 3300 MHz to 3800 MHz. 
   The second segment  42 ′,  52 ′ of each of the first and second radiating elements  4 ,  5  has a distal end distal from the first segment,  41 ′,  51 ′ of the respective one of the first and second radiating elements  4 ,  5 . 
   Each of the first and second feeding points  7 ,  8  is connected to the distal end of the second segment  42 ′,  52 ′ of a respective one of the first and second radiating elements  4 ,  5 . 
     FIG. 12  illustrates a modified embodiment of the second preferred embodiment according to this invention. In this embodiment, each of the first and second grounding elements  2 ,  3  is formed approximately in the shape of an axe. Moreover, in this embodiment, as illustrated in  FIGS. 13 to 16 , each of the first and second radiating elements  4 ,  5  is an irregular hexagonal shape. 
     FIG. 17  illustrates another modified embodiment of the second preferred embodiment according to this invention. In this embodiment, the second segment  22 ,  32  of each of the first and second grounding elements  2 ,  3  is spaced apart from the dielectric substrate  1 . Moreover, in this embodiment, the first segment  41 ′,  51 ′ of each of the first and second radiating elements  4 ,  5  is spaced apart from the dielectric substrate  1 . 
     FIG. 18  illustrates yet another modified embodiment of the second preferred embodiment according to this invention. In this embodiment, only the second segment  22 ,  32  of each of the first and second grounding elements  2 ,  3  is spaced apart from the dielectric substrate  1 . 
     FIG. 19  illustrates still yet another modified embodiment of the second preferred embodiment according to this invention. In this embodiment, only the first segment  41 ′,  51 ′ of each of the first and second radiating elements  4 ,  5  is spaced apart from the dielectric substrate  1 . 
   Experimental results, as illustrated in  FIG. 20 , show that each of the first antenna unit  100 , as indicated by line (a), and the second antenna unit  200 , as indicated by line (b), achieves a voltage standing wave ratio (VSWR) of less than 2.0 when operated in the second frequency range. Moreover, when operated in the second frequency range, the antenna of this embodiment achieves a minimum isolation of 18.7 dB, as shown in Table III, and a minimum envelop correlation coefficient (ECC) of 0.01, as shown in Table IV. Further, when operated in the second frequency range, the first antenna unit  100  achieves a maximum efficiency of −0.7 dB and a maximum peak gain of 6.5 dBi, as shown in Table V, and the second antenna unit  200  achieves a maximum efficiency of −0.6 dB and a maximum peak gain of 6.7 dBi. In addition, it is evident from  FIGS. 21 and 22  that the relationship between the first and second antenna units  100 ,  200  is small. 
   
     
       
         
             
           
             
               TABLE III 
             
           
          
             
                 
             
             
               Frequency (MHz) 
             
          
         
         
             
             
             
             
             
             
             
          
             
                 
               2300 
               2500 
               2700 
               3300 
               3500 
               3800 
             
             
                 
                 
             
          
         
         
             
             
             
             
             
             
             
          
             
               Isolation (dB) 
               19.8 
               23.2 
               18.7 
               21.6 
               23.6 
               19.6 
             
             
                 
             
          
         
       
     
   
   
     
       
         
             
             
             
           
             
                 
               TABLE IV 
             
           
          
             
                 
                 
             
             
                 
               Frequency (MHz) 
                 
             
          
         
         
             
             
             
             
             
             
             
          
             
                 
               2300 
               2500 
               2700 
               3300 
               3500 
               3800 
             
             
                 
                 
             
          
         
         
             
             
             
             
             
             
             
             
          
             
                 
               ECC 
               0.05 
               0.06 
               0.10 
               0.06 
               0.05 
               0.01 
             
             
                 
                 
             
          
         
       
     
   
   
     
       
         
             
             
             
             
             
           
             
                 
               TABLE V 
             
           
          
             
                 
                 
             
             
                 
               first antenna 
                 
               second antenna 
                 
             
             
                 
               unit 100 
                 
               unit 200 
             
          
         
         
             
             
             
             
             
          
             
               Frequency 
               Efficiency 
               Peak gain 
               Efficiency 
               Peak Gain 
             
             
               (MHz) 
               (dB) 
               (dBi) 
               (dB) 
               (dBi) 
             
             
                 
             
             
               2300 
               −0.7 
               6.5 
               −0.6 
               6.4 
             
             
               2400 
               −0.8 
               6.0 
               −0.8 
               6.1 
             
             
               2500 
               −1.2 
               5.2 
               −1.3 
               5.3 
             
             
               2600 
               −0.8 
               5.5 
               −0.7 
               5.9 
             
             
               2700 
               −1.0 
               5.3 
               −1.0 
               5.4 
             
             
               3300 
               −0.8 
               5.4 
               −0.9 
               5.8 
             
             
               3400 
               −1.2 
               5.0 
               −1.1 
               6.1 
             
             
               3500 
               −1.4 
               5.1 
               −1.1 
               6.1 
             
             
               3600 
               −1.4 
               5.1 
               −1.2 
               6.3 
             
             
               3700 
               −1.1 
               6.0 
               −0.9 
               6.7 
             
             
               3800 
               −1.1 
               6.0 
               −1.0 
               6.3 
             
             
                 
             
          
         
       
     
   
   Furthermore, the radiation patterns of the first antenna unit  100 , as illustrated in  FIGS. 23 and 24 , complement the radiation patterns of the second antenna unit  200 , as illustrated in  FIGS. 25 and 26 . It is therefore apparent that the antenna of this embodiment has a diversity effect that significantly reduces the susceptibility thereof to multipath interference, and thus, an increase in the efficiency thereof is achieved. 
   While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments 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.