Patent Publication Number: US-2007120741-A1

Title: Ultra wide bandwidth planar antenna

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a planar antenna, more particularly to an ultra wide bandwidth planar antenna.  
      2. Description of the Related Art  
      In U.S. Pat. No. 6,914,573, there is disclosed a conventional planar antenna that is operable within the ultra wide bandwidth (UWB). The conventional planar antenna includes a radiating element, a feeding strip that extends from the radiating element, and a grounding element that is disposed around and that is physically disconnected from the radiating element and the feeding strip.  
      The aforementioned conventional planar antenna is disadvantageous in that, based from experimental results, when it is operated within the UWB, it has a voltage standing wave ratio of greater than three at the higher frequencies of the UWB.  
     SUMMARY OF THE INVENTION  
      Therefore, the object of the present invention is to provide a planar antenna that can overcome the aforesaid drawback of the prior art.  
      According to the present invention, a planar antenna, which is operable within the ultra wide bandwidth, comprises a dielectric substrate, first and second radiating elements, a feeding strip, and a grounding unit. The dielectric substrate has a surface. The first radiating element is formed on the surface of the dielectric substrate, and has opposite first and second sides. The second radiating element is formed on the surface of the dielectric substrate, and has opposite first and second sides. The first side of the second radiating element is connected to the second side of the first radiating element. The feeding strip is formed on the surface of the dielectric substrate and extends from the second side of the second radiating element. The grounding unit is formed on the surface of the dielectric substrate, is physically disconnected from the first and second radiating elements and the feeding strip, and includes a pair of grounding elements that are physically disconnected from each other and that are disposed on opposite sides of the feeding strip. 
    
    
     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 a planar antenna according to the present invention;  
       FIG. 2  is a plot illustrating a voltage standing wave ratio of the first preferred embodiment;  
       FIG. 3  is a plot illustrating a radiation pattern of the first preferred embodiment on the H-plane when operated at 5 GHz;  
       FIG. 4  is a plot illustrating a radiation pattern of the first preferred embodiment on the E-plane when operated at 5 GHz;  
       FIG. 5  is a schematic view of the second preferred embodiment of a planar antenna according to the present invention;  
       FIG. 6  is a plot illustrating a voltage standing wave ratio of the second preferred embodiment;  
       FIG. 7  is a schematic view of the third preferred embodiment of a planar antenna according to the present invention;  
       FIG. 8  is a plot illustrating a voltage standing wave ratio of the third preferred embodiment;  
       FIG. 9  is a schematic view of the fourth preferred embodiment of a planar antenna according to the present invention; and  
       FIG. 10  is a plot illustrating a voltage standing wave ratio of the fourth preferred embodiment. 
    
    
     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  FIG. 1 , the first preferred embodiment of a planar antenna  1  according to this invention is shown to include a dielectric substrate  2 , first and second radiating elements  32 ,  31 , a feeding strip  30 , and a grounding unit  40 .  
      The planar antenna  1  of this embodiment is operable within the ultra wide bandwidth, i.e., between 3.1 GHz and 10.6 GHz.  
      In this embodiment, the dielectric substrate  2  is available from Rogers Corp. under model no. RO4003C. In an alternative embodiment, the dielectric substrate  2  is a FR-4 substrate.  
      The first radiating element  32  is formed on a surface  20  of the dielectric substrate  2 . In this embodiment, the first radiating element  32  is generally trapezoidal in shape, and has opposite first and second sides  321 ,  322 . The first side  321  of the first radiating element  32  is parallel to and has a length that is longer than that of the second side  322  of the first radiating element  32 .  
      The second radiating element  31  is formed on the surface  20  of the dielectric substrate  2 . In this embodiment, the second radiating element  31  is generally rectangular in shape, and has opposite first and second sides  311 ,  312 , and opposite third and fourth sides  313 ,  314 . The third and fourth sides  313 ,  314  of the second radiating element  31  have a length that is shorter than that of the first and second sides  311 ,  312  of the second radiating element  31 . The first side  311  of the second radiating element  31  is connected to the second side  322  of the first radiating element  32 .  
      It is noted that the first radiating element  32  has an area that is greater than that of the second radiating element  31 .  
      The feeding strip  30  is formed on the surface  20  of the dielectric substrate  2 , and extends from the second side  312  of the second radiating element  31 . In this embodiment, the feeding strip  30  is generally rectangular in shape.  
      It is noted that the width (W 1 ) of the second radiating element  31  is greater than the width (W 2 ) of the feeding strip  30 .  
      The grounding unit  40  is formed on the surface  20  of the dielectric substrate  2 , and is physically disconnected from the first and second radiating elements  32 ,  31  and the feeding strip  30 . In this embodiment, the grounding unit  40  includes a pair of grounding elements  400  that are physically disconnected from each other, that are generally rectangular in shape, and that are respectively disposed on opposite sides of the feeding strip  30 .  
      Preferably, each of the first and second radiating elements  32 ,  31 , the feeding strip  30 , and the grounding elements  400  is made of copper foil.  
      It is noted that each of the first and second radiating elements  32 ,  31 , the feeding strip  30 , and the grounding elements  400  is formed by providing first a copper foil on the surface  20  of the dielectric substrate  2 , and then by patterning and etching the copper foil. Accordingly, manufacturing costs for the planar antenna  1  of this invention can be reduced.  
      Based on simulated results, as illustrated in  FIG. 2 , the planar antenna of this embodiment achieves a voltage standing wave ratio (VSWR) of less than 2.004 when operated within 3.1 GHz and 10.6 GHz. Moreover, the planar antenna of this invention has a doughnut shaped radiation pattern (not shown) when operated at 5 GHz.  FIGS. 3 and 4  illustrate radiation patterns of the planar antenna of this invention on the H-plane (i.e., xy plane) and the E-plane (i.e., xz plane) when operated at 5 GHz.  
       FIG. 5  illustrates the second preferred embodiment of a planar antenna  1  according to this invention. When compared with the previous embodiment, the first radiating element  32  is formed with a first slot  320  therethrough. The first slot  320  is elongated, and extends along a center line (L 1 ) of the first radiating element  32  between the first and second sides  321 ,  322  of the first radiating element  32 . Moreover, the second radiating element  31  is formed with a second slot  310  therethrough. The second slot  31  is generally rectangular in shape, and extends along a center line (L 2 ) of the second radiating element  31 , which is collinear with the center line (L 1 ) of the first radiating element  32 , from the first side  311  toward the second side  312  of the second radiating element  31 .  
      Based on simulated results, as illustrated in  FIG. 6 , the planar antenna of this embodiment achieves a VSWR of less than 2.009 when operated within 3.0799 GHz and 10.618 GHZ.  
       FIG. 7  illustrates the third preferred embodiment of a planar antenna  1  according to this invention. When compared to the first embodiment, the first radiating element  32  is substantially elliptical in shape.  
      Based on simulated results, as illustrated in  FIG. 8 , the planar antenna of this embodiment achieves a VSWR of less than 1.998 when operated within 3.0799 GHz and 10.618 GHz.  
       FIG. 9  illustrates the fourth preferred embodiment of a planar antenna  1  according to this invention. When compared with the third embodiment, the second radiating element  31  is generally trapezoidal in shape. The first side  311  of the second radiating element  31  is parallel to and has a length that is shorter than that of the second side  312  of the second radiating element  31 .  
      Based on simulated results, as illustrated in  FIG. 10 , the planar antenna of this embodiment achieves a VSWR of less than 1.998 when operated within 3.0799 GHz and 10.661 GHz.  
      While the present invention has been described in connection with what is 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.