Patent Publication Number: US-2003231139-A1

Title: Wide band antenna

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to wide band antennas, and particularly to a dipole microstrip wide band antenna used in an electronic device for wireless transmission.  
       [0003] 2. Related Art  
       [0004] Wireless LAN currently has four standards, which include IEEE802.11, IEEE802b, and Bluetooth in the 2.4 GHz frequency band, and IEEE802.11a in the 5 GHz frequency band. Antennas, which satisfy more than one standard are available for wireless electronic devices working in multiple frequency bands. However, conventional single dipole antennas can only be used in a narrow frequency band, and are usually limited to mono-frequency use so do not satisfy the above mentioned needs.  
       [0005] Such a conventional antenna is disclosed in China Pat. No. 01,224,549. The antenna has a substrate, and an upper metal layer and a lower metal layer printed on two opposite surfaces of the substrate. The upper metal layer forms a signal feed conductive strip, and a quarter wavelength radiation conductive strip extending from the signal feed conductive strip. The lower metal layer includes a grounding conductor and two quarter wavelength radiation conductive strips extending from the grounding conductor. The radiation conductive strip of the upper metal layer and the two radiation conductive strips of the lower metal layer act together as a dipole to achieve antenna radiation. However, this antenna can only be used in a single frequency band, which is 2.4-2.5 GHz in the embodiment described.  
       [0006] Another prior art antenna is disclosed in U.S. Pat. No. 5,598,174, and it can also only be used in a frequency band.  
       [0007] Accordingly, an improved antenna is desired to overcome the above problems.  
       SUMMARY OF THE INVENTION  
       [0008] An object of the present invention is to provide a wide band antenna which can be used in different frequency bands.  
       [0009] To achieve the above object, a wide band antenna in accordance with a preferred embodiment of the present invention includes a printed circuit board, a dipole mounted on the printed circuit board, and a feeder apparatus through which the dipole is fed. The dipole includes a first pole and a second pole spaced apart from the first pole. The first pole forms a middle portion, a first portion, and a second portion, and the first and the second portions respectively extend rearwardly from two opposite ends of the middle portion. A length of the first portion differs from a length of the second portion. The second pole is a bar microstrip adjacent to the middle portion, a gap being maintained therebetween. The first portion and the second portion can each transfer signals, to allow the antenna to operate in two different wide band frequency bands.  
       [0010] These and additional object, features and advantages of the present invention will become apparent after reading the following detailed description of a preferred embodiment of the invention taken in conjunction with the appended drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011]FIG. 1 is a plan view of a wide band antenna according to a preferred embodiment of the present invention;  
     [0012]FIG. 2 is an orientation schematic diagram of the wide band antenna of FIG. 1 in an XYZ coordinate system;  
     [0013]FIG. 3 is a graph of experimental results for VSWR of the wide band antenna of FIG. 1, using coordinate system shown in FIG. 2;  
     [0014]FIG. 4 is a horizontal radiation graph in an XY-plane of the wide band antenna of FIG. 1 located in the coordinate system of FIG. 2 in the 2.4-2.5 GHz frequency band;  
     [0015]FIG. 5 is a vertical radiation graph in the XY-plane of the wide band antenna of FIG. 1 located in the coordinate system of FIG. 2 in the 2.4-2.5 GHz frequency band;  
     [0016]FIG. 6 is a horizontal radiation graph in the XY-plane of the wide band antenna of FIG. 1 located in the coordinate system of FIG. 2 in the 5.15-5.35 GHz frequency band;  
     [0017]FIG. 7 is a vertical radiation graph in the XY-plane of the wide band antenna of FIG. 1 located in the coordinate system of FIG. 2 in the 5.15-5.35 GHz frequency band;  
     [0018]FIG. 8 is a table of describing the gain characteristic of the wide band antenna of FIG. 1, using the coordinate system of FIG. 2;  
     [0019]FIG. 9 is another orientation schematic diagram of the wide band antenna of FIG. 1 in a different XYZ coordination system;  
     [0020]FIG. 10 is similar to FIG. 3, but using the coordinate system of FIG. 9;  
     [0021]FIG. 11 is similar to FIG. 4, but using the coordinate system of FIG. 9;  
     [0022]FIG. 12 is similar to FIG. 5, but using the coordinate system of FIG. 9;  
     [0023]FIG. 13 is similar to FIG. 6, but using the coordinate system of FIG. 9;  
     [0024]FIG. 14 is similar to FIG. 7, but using the coordinate system of FIG. 9; and  
     [0025]FIG. 15 is similar to FIG. 8, but using the coordinate system of FIG. 9. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0026] Referring to FIG. 1, a wide band antenna  1  in accordance with a preferred embodiment of the present invention is a dipole microstrip wide band antenna, and includes a printed circuit board (PCB)  2 , a dipole  6  and a feeder apparatus  5 .  
     [0027] The dipole  6  is formed on a surface of the PCB  2 , and includes a first pole  3  and a second pole  4  opposite to the first pole  3 . The first pole  3  has approximately the shape of the letter n, and forms a middle portion  33 , a first portion  31 , and a second portion  32 , and the first and the second portions  32  extend rearwardly from two opposite ends of the middle portion  33 . The middle portion  33  defines a first feed point  34  in a center thereof. The first portion  31  and the second portion  32  can receive or transmit signals. A length of the first portion  31  is greater than a length of the second portion  32 , so that the first portion  31  allows the antenna  1  to operate in a low frequency band, and the second portion  32  allows the antenna  1  to operate in a high frequency band. The operating frequencies are determined by these lengths of the first portion  31  and the second portion  32 . Breadths of the first portion  31  and the second portion  32  determine bandwidth at the associated frequency. So tuning the lengths and the breadths of the first portion and the second portion of the first pole allows the wide band antenna  1  to operate in different frequencies and frequency bands.  
     [0028] The second pole  4  is an integral bar microstrip which is disposed opposite to the middle portion  33  of the first pole, with a gap therebetween. One end of the second pole  4 , adjacent to the first pole  3 , forms a second feed point  41  thereon.  
     [0029] In this preferred embodiment, the feeder apparatus  5  is a coaxial cable, which includes a central conductor  51  and a braiding layer  53  surrounding the central conductor  51 . The central conductor  51  serves as a signal feed and connects to the first feed point  34 . The braiding layer  53  serves as a grounded shield and connects with the second feed point  41 . The feeder apparatus  5  feeds the dipole  6  through the first feed point  34  and the second feed point  41 .  
     [0030] In this preferred embodiment, the first pole  3  and the second pole  4  are located on the same surface of the PCB  1 , but they can alternatively be located on different surfaces of the PCB  1 . Moreover, the PCB can be a flexible PCB or an inflexible PCB.  
     [0031] The dimensions of the antenna elements are chosen to satisfy different needs. L1, L5 and L6 shown in FIG. 1 respectively designate breadths of the second pole  4  and the first and the second portions  31  and  32  of the first pole  3 . L2, L3 and L4 respectively designate lengths of the second pole  4  and the first and the second portions  31  and  32  of the first pole  3 . A length of the middle portion  33  of the first pole  3  is also L1, and its breadth is equal to or smaller than L5.  
     [0032] The structural dimensions of the preferred embodiment of the invention are as follows: L1=8.00 mm, L2=27.20 mm, L3=25.20 mm, L4=12.15 mm and L5=L6=2.00 mm. These dimensions allow the antenna  1  to operate in two wide band frequency bands, one of which is 2.4-2.5 GHz, and another of which is 5.15-5.35 GHz.  
     [0033] FIGS.  2 - 15  show basic performance measures of the preferred embodiment wide band antenna  1  having the dimensions detailed in the paragraph above. Firstly referring to FIGS.  2 - 8 , FIG. 2 defines an orientation in an XYZ coordinate system of the antenna  1  for measured values graphed and tabled in FIGS.  3 - 8 . FIG. 3 is a graph of measured values showing VSWR of the wide band antenna  1  varying with frequency. The results show that the VSWR are all less than 2.0 in the frequency ranges of 2.4(point  1 )-2.5(point  2 ) GHz and 5.15(point  3 )-5.35(point  5 ) GHz and thus comply with industry-standard antenna design specifications. FIG. 4 and FIG. 5 respectively show a horizontal and a vertical radiation graphs in the XY-plane of the wide band antenna  1  in the frequency band 2.4-2.5 GHz. The values were measured for the three frequencies 2.4 GHz, 2.45 GHz and 2.5 GHz. FIG. 6 and FIG. 7 respectively show a horizontal and a vertical radiation graphs in the XY-plane of the wide band antenna  1  in the frequency band 5.15-5.35 GHz. The values were measured for the three frequencies 5.15 GHz, 5.25 GHz and 5.35 GHz. These graphs show that the wide band antenna  1  has optimum diversity radiation efficiency. FIG. 8 shows measured gain characteristics of the wide band antenna  1 ; the results shown comply with industry-standard antenna design specifications.  
     [0034] Next referring to FIGS.  9 - 15 , FIG. 9 defines another orientation in an XYZ coordinate system of the antenna  1  for measured values graphed and tabled in FIGS.  10 - 15 . FIGS.  10 - 15  respectively correspond to FIGS.  3 - 8 , but under the different reference coordinates. Measured values graphed and tabled in FIGS.  10 - 15  also comply with industry-standard antenna design specifications.  
     [0035] In comparison with the prior art, this present invention can be used in either or both of two different wide band frequency bands, so it can be used in wireless electronic devices operable under either of two frequency band standards.  
     [0036] Although the present invention has been described with reference to a specific embodiment thereof, the description is illustrative and is not to be construed as limiting the invention. Various modifications to the present invention may be made to the preferred embodiment by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.