Abstract:
A printed antenna includes a dielectric substrate having a pair of printed antenna elements to form a dipole antenna. On an antenna plane, an xy axis system is defined so that an origin is defined at a center of location of the antenna elements, and an x axis is set in a direction that the antenna elements are arranged, a y axis is set in the direction perpendicular to the x axis, and a size of the antenna elements in the direction of the y axis become gradually larger according to the x axis changing in an outer direction. Each of the antenna elements has an impedance matching part at a feeding side of the antenna elements. The printed antenna can be used in an ultra wide-band frequency, and is small profile, is light weight and low in cost.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to Japanese Patent Application No. 2003-317160, filed Sep. 9, 2003 in Japan, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a printed antenna, which has an ultra wide-band (“UWB”) frequency range. The ultra wideband antenna is loaded on UWB wireless devices for its use. Therefore, it is required to be low and small profile, light weight and low cost. Moreover, the characteristics of ultra wideband antenna have to be constant gain and omni-directional patterns.  
         [0004]     2. Description of the Related Art  
         [0005]     Growing use of wireless communication devices has forced the need of large bandwidth, and large bit-rates, such as bit-rates of several hundred Mbps. It requires an antenna having excellent characteristics in the range of ultra wideband frequency. Further the antenna has to be small profile, light weight and low cost.  
         [0006]      FIG. 14A  and  FIG. 14B  show a prior art of an example of wide frequency band patch antenna, that is a bow-tie type patch antenna.  FIG. 14A  shows a cross sectional view of the antenna, and  FIG. 14B  shows a top view of same. In  FIG. 14A  and  FIG. 14B , a substrate  20  is composed of dielectric material such as FR4. A patch  21  has a figure like a bow-tie. The patch  21  is made of metal as copper. A ground plate  22  of copper is provided on the back surface of the substrate. The patch  21  is connected to a line of coaxial cable which penetrates through the substrate  20 . The shield of the coaxial line is connected to the ground plate  22 .  
         [0007]     The prior art of a printed bow-tie type antenna shown in  FIG. 14A  and  FIG. 14B  does not have the wide frequency range such as the ultra wide frequency, thus it is unsuitable to cover the ultra wideband frequency range. Several designs to make the patch antenna wide band have been reported, such as noted below in references 1-6. Their frequency range, however, is not be able to cover the ultra wideband communication frequency range of 3.1-10.6 GHz.  
         [0008]     As mentioned above the prior art printed antenna have not satisfied the practical use of the ultra wideband communication devices so far. Because it is very difficult to make the wideband printed antenna having good frequency characteristics of the ultra wideband communication.  
         [0009]     The following are references to the related art: 
    1. G. Kumar and K. C. Gupta, “Directly coupled multi resonator wide-band microstrip antenna,” IEEE Trans. Antennas Propagation, vol. 33, pp. 588-593, June 1985.     2. K. L. Wong and W. S. Hsu, “Broadband triangular microstrip antenna with U-shaped slot,” Elec. Lett., vol. 33, pp. 2085-2087,1997.     3. F. Yang, X. X. Zhang, X. Ye, Y Rahmat-Samii, “Wide-band E-shaped patch antenna for wireless communication,” IEEE Trans. Antennas Propagation, vol. 49, pp. 1094-1100, July 2001.     4. A. K. Shackelford, K. F. Lee, and K. M. Luk, “Design of small-size wide-bandwidth microstrip-patch antenna,” IEEE Antennas Propagation Magz., vol. 44, pp. 75-83, February 2003.     5. J. Y Chiou, J. Y. Sze, K. L. Wong, “A broad-band CPW-fed strip-loaded square slot antenna,” IEEE Trans. Antennas Propagation, vol. 51, pp. 719-721, April 2003.     6. N. Herscovici, Z. Sipus, and D. Bonefacic, “Circularly polarized single-fed wide-band microstrip patch,” IEEE Trans. Antennas Propagation, vol. 51, pp. 1277-1280, June 2003.    
 
       SUMMARY OF THE INVENTION  
       [0016]     The present invention has as an object to provide an ultra wideband printed antenna, which is small in profile and light weight and has wide potential use for UWB portable wireless devices. The present invention relates to a printed antenna that is a new type of dipole antenna, which has impedance matching portion connected to strip lines and covers the ultra wide frequency band range. The dipole antenna is printed on a dielectric substrate, so that it is small profile, light weight, easy to fabricate and low cost.  
         [0017]     That is, the printed antenna comprises a substrate of dielectric and a pair of antenna elements on the substrate. The antenna elements are set separately and adjacently on the substrate. On the antenna plane, an xy axis system is defined, wherein its origin is defined at a center of location of the antenna elements. The x axis is defined in the direction that the antenna elements are arranged on the x axis, and y axis is perpendicular to the x axis. The size of the antenna elements in the direction of y axis becomes gradually larger toward the outer portion on the x axis. Further, there are impedance matching parts and each impedance matching part is formed to each antenna element with one body at their sides to strip lines.  
         [0018]     The VSWR characteristic of the antenna according to aspects of the present invention is under 3 in a frequency range from 3.1 GHz to 10.6 GHz, and the other frequency characteristic, like gain, etc. is good in the range of a wide frequency of 3.1 GHz to 10.6 GHz, and is an omni-direction pattern in the frequency range. Because of these features, the ultra wideband antenna of the present invention can be used for devices of an ultra wideband communication system from 3.01 GHz to 10.6 GHz. The antenna profile, moreover, is a very small size, such as a length of 16 mm, a width of 40 mm, and a thickness of 0.5 mm, very light weight, easy to fabricate and low-cost. The present invention has as further object to create a fine effect for practical use and its fabrication. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The objects, advantages and features of the present invention will be more clearly understood by referencing the following detailed disclosure and the accompanying drawings.  
         [0020]      FIG. 1A  is an explanation drawing of a plain view of an embodiment of an antenna according to the present invention.  
         [0021]      FIG. 1B  is an explanation drawing of a cross-sectional view of the embodiment of the antenna according to the present invention.  
         [0022]      FIG. 1C  is an explanatory drawing of an xy axis system defined on the antenna plane of the embodiment of an antenna according to the present invention.  
         [0023]      FIG. 2A  is another explanatory drawing of a plain view of the embodiment of an antenna according to the present invention.  
         [0024]      FIG. 2B  is another explanatory drawing of a plain view of the embodiment of an antenna according to the present invention.  
         [0025]      FIG. 3  is a graph of frequency characteristics of return loss of the embodiment of a printed antenna according to the present invention.  
         [0026]      FIG. 4  is a graph of frequency characteristic of VSWR of the embodiment of a printed antenna according to the present invention.  
         [0027]      FIG. 5  is a graph of frequency characteristics of antenna gain of the embodiment of a printed antenna according to the present invention.  
         [0028]      FIG. 6  is a graph of frequency characteristics of characteristic impedance of the embodiment of a printed antenna according to the present invention.  
         [0029]      FIG. 7  is a graph of frequency characteristic of a real part of characteristic impedance of the embodiment of a printed antenna according to the present invention.  
         [0030]      FIG. 8  is a graph of frequency characteristic of an imaginary part of characteristic impedance of the embodiment of a printed antenna according to the present invention.  
         [0031]      FIG. 9  is a graph of frequency characteristic of phase of characteristic impedance of the embodiment of a printed antenna according to the present invention.  
         [0032]      FIG. 10  is a graph of the frequency characteristic in the frequency at 3.1 GHz in Φ=0° of the embodiment of a printed antenna according to the present invention.  
         [0033]      FIG. 10B  is a graph of the frequency characteristic in the frequency at 3.1 GHz in Φ=90° of the embodiment of a printed antenna according to the present invention.  
         [0034]      FIG. 11  is a graph of the frequency characteristic in the frequency at 5.1 GHz in Φ=0° of the embodiment of a printed antenna according to the present invention.  
         [0035]      FIG. 11B  is a graph of the frequency characteristic in the frequency at 5.1 GHz in Φ=90° of the embodiment of a printed antenna according to the present invention.  
         [0036]      FIG. 12A  is a graph of the frequency characteristic in the frequency at 7.1 GHz in Φ=0° of the embodiment of a printed antenna according to the present invention.  
         [0037]      FIG. 12B  is a graph of the frequency characteristic in the frequency at 7.1 GHz in Φ=90° of the embodiment of a printed antenna according to the present invention.  
         [0038]      FIG. 13A  is a graph of the frequency characteristic in the frequency at 9.1 GHz in Φ=0° of the embodiment of a printed antenna according to the present invention.  
         [0039]      FIG. 13B  is a graph of the frequency characteristic in the frequency at 9.1 GHz in Φ=90° of the embodiment of printed antenna according to the present invention.  
         [0040]      FIG. 14A  is a plain view drawing of a prior art bow-tie type patch antenna.  
         [0041]      FIG. 14B  is a cross sectional view of a prior art bow-tie type patch antenna. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]      FIG. 1A  and  FIG. 1B  show an ultra wideband printed antenna according to a preferred embodiment of the present invention. Each of antenna elements  11 ,  12  is the same size, and a pair of the antenna elements makes a bow-tie shape. They are printed on a thin substrate of 0.5 mm made with the relative permittivity of ε r =4.4. The printed antenna according to the preferred embodiment of the present invention is a kind of dipole antenna, which is different from the bow-tie type patch antenna shown in  FIG. 14A  and  FIG. 14B . Moreover impedance matching portions are formed between the antenna elements and strip lines. The printed antenna according to the preferred embodiment of the present invention is fed through a co-planar strip line of 75 Ω for example.  
         [0043]     In the following embodiment, substrate  20  is made of FR4, and the printed pattern comprising antenna elements  11 ,  12  and impedance matching parts  13 ,  14  are made of copper. Insulation materials, such as Silicon (Si) or Teflon, other than FR4, however also can be used for the substrate  20 . Electric conductive metal, such as Al, Ag, Au, other than copper, also can be used for the printed pattern of antenna elements  11 ,  12  and impedance matching parts  13 ,  14 .  
         [0044]      FIG. 1A  is a top view of an antenna according to an embodiment of the present invention and  FIG. 1B  shows a cross-sectional view of the antenna.  FIG. 1C  shows a xy axis system defined on the antenna plane of an antenna according to the embodiment of the invention.  
         [0045]     The antenna pattern in  FIG. 1A  is made, for example, by photo etching a copper plate formed on the substrate. A pair of right and left side patterns of antenna elements  11 ,  12  and impedance matching parts  13 ,  14  make a figure like a bow-tie. The impedance matching portions  13 ,  14  are formed as one body with each antenna element  11 ,  12  at their sides of strip lines  15  and  16 .  
         [0046]     Each antenna element  11 ,  12  shown in  FIG. 1A  comprises small cut portions  111 ,  112 ,  121  and  122 , which are cut in a direction parallel to the x axis at the ends of the sides A and B. Making the cut portions shortens the antenna length along the y axis, and improves a VSWR characteristic of the antenna.  
         [0047]      FIG. 1C  shows the xy axis system defined on the surface of the printed antenna according to the embodiment of the invention. On the antenna plane, the xy axis system is defined as shown in  FIG. 1C . The origin xy axis is set at a center of the gap between the antenna elements  11  and  12 , the x axis is set in the direction along two antenna elements, and the y axis is set perpendicular to the x axis. Each side of the antenna elements is defined to be sides A, B, C, D, E, F, G and H as shown in  FIGS. 1C and 2B .  
         [0048]      FIG. 2A  is an explanatory drawing of a power feeding of the printed antenna according to an embodiment of the present invention. The antenna elements  11 ,  12  are driven by power fed through the impedance matching portion  13 ,  14  from a feeding side as shown.  
         [0049]      FIG. 2B  shows an example of a size of the printed antenna according to an embodiment of the present invention. The antenna width that is the distance between sides A and B is 40 mm, and the antenna length that is the length of side A and B is 16 mm. The sides A and B are parallel to each other. The gap distance between sides C and D is 2 mm, and the sides C and D are parallel to each other. The distance between sides A and side C is 19 mm. Each length of the cut portions of the ends of sides A and B is 1 mm, and parallel to each other. Angle α i.e., the angle of side E from x axis and the angle of side F from x axis, is 23.96° and β that is the angle of side G from x axis and the angle of side H from x axis, is 20.55°. The thickness of the substrate h is 0.5 mm. The impedance matching parts  13  and  14  in  FIGS. 2A and 2B  are narrowed by three steps with the size in  FIG. 2B , and the impedance matching portion is connected to the strip lines  15  and  16 .  
         [0050]     The printed antenna according to an embodiment of the present invention is made using a plate comprising a substrate of FR 4 and a copper plate layered on the substrate. The antenna patterns comprising the antenna elements and the impedance matching portions are made by photo-etching the copper plate, for example, a layer of photo-resist film is formed on the copper plate by painting photo-resist. Next the painted photo-resist layer is exposed to light through a photo-mask, which has the pattern of the antenna elements and the impedance matching portions. The photo-resist film is soaked in solution to dissolve the unlighted portion. The lighted portion of the photo-resist layer is left on the copper plate. The left portion of the exposed photo-resist layer on the copper is used for an etching mask to etch the copper layer. Further the whole plate is soaked in etching liquid and etches the copper plate with the etching musk of photo-resist. Thus the antenna pattern of copper of the antenna elements and the impedance parts are united each as one body and formed on the substrate.  
         [0051]      FIGS. 3-13  show the characteristics of the above mentioned printed antenna according to the embodiment of the invention. The antenna characteristics are analyzed by a simulator of the title “ANSOFT ENSEMBLE”.  
         [0052]      FIG. 3  shows scattering characteristics of an S11 matrix, that is frequency characteristic of return loss, in the frequency rage of 3.1-10.6 GHz.  FIG. 3  shows that the return loss is under −6 dB in a range from 3.1 GHz to 10.6 GHz. It shows that the printed antenna according to the embodiment of the present invention has excellent ultra wide range characteristics.  
         [0053]      FIG. 4  is a graph showing a frequency characteristic of VSWR (Voltage Standing Wave Ratio) of the frequency characteristic of the antenna, that is magnitude of VSWR vs. frequency.  FIG. 4  shows that the VSWR is about 2.5-3 in a range from 3.1 GHz to 10.6 GHz. It shows that the antenna according to the embodiment of the present invention has excellent VSWR characteristic in the frequency range of ultra wide band.  
         [0054]      FIG. 5  is a graph showing a frequency characteristic of antenna gain that is magnitude of gain vs. frequency. The printed antenna according to the embodiment of the present invention has a gain 2.5 dBi in a frequency range of 3.1 GHz-10.6 GHz, and the maximum gain is 4.7 dBi.  
         [0055]      FIG. 6  is a graph showing a frequency characteristic of characteristic impedance at the port (see  FIG. 2A ) in a frequency range from 3.1 GHz to 10.6 GHz, that is magnitude of port characteristic impedance vs. frequency. The characteristic impedance is about from 71 Ω to 73 Ω, that is the fluctuation of 2 Ω.  FIG. 6  shows that the characteristic impedance is kept almost constant in the frequency range.  
         [0056]      FIG. 7  is a graph showing a frequency characteristic of a real part of characteristic impedance at the port in the frequency range of 3.1 GHz to 10.6 GHz. The real part of characteristic impedance is about from 71 Ω to 73 Ω that is the fluctuation of 2 Ω.  FIG. 7  shows that the real part of the characteristic impedance is kept almost constant in the frequency range.  
         [0057]      FIG. 8  is a graph showing a frequency characteristic of an imaginary part of the characteristic impedance at the port in the frequency of 3.1 GHz to 10.6 GHz. The imaginary part is about 0 Ω in the frequency range.  
         [0058]      FIG. 9  is a graph showing a frequency characteristic of phase of characteristic impedance at the port in the frequency range from 3.1 GHz to 10.6 GHz, that is phase (°) of port characteristic impedance vs. frequency.  FIG. 9  shows the phase is constant in the frequency range from 3.1 GHz to 10.6 GHz.  
         [0059]      FIG. 10A  through  FIG. 13B  show radiation patterns at frequency of 3.1 GHz-9.1 GHz to angle θ respectively in Φ=0° and Φ=90°, and in particular,  
         [0060]      FIG. 10A  shows radiation patterns at frequency of 3.1 GHz in Φ=0°;  
         [0061]      FIG. 10B  shows radiation patterns at frequency of 3.1 GHz in Φ=90°;  
         [0062]      FIG. 11A  shows radiation patterns at frequency of 5.1 GHz in Φ=0°;  
         [0063]      FIG. 11B  shows radiation patterns at frequency of 5.1 GHz in Φ=90°;  
         [0064]      FIG. 12A  shows radiation patterns at frequency of 7.1 GHz in Φ=0°;  
         [0065]      FIG. 12B  shows radiation patterns at frequency of 7.1 GHz in Φ=90°;  
         [0066]      FIG. 13A  shows radiation patterns at frequency of 9.1 GHz in Φ=0°; and  
         [0067]      FIG. 13B  shows radiation patterns at frequency of 9.1 GHz in Φ=90°.  
         [0068]     The radiation patterns in  FIGS. 10A through 13B  according to an embodiment of the present invention show characteristics of a dipole antenna. The radiation patterns are almost omni-directional.  
         [0069]     According to preferred embodiments of the present invention, there is achieved a printed antenna having characteristics of small return loss and VSWR in the ultra wide range. Also the gain of the antenna is nearly constant in a wide range. Moreover, the characteristic impedance is almost constant and further the fluctuation is small in the frequency range.  
         [0070]     According to preferred embodiments of the invention, the printed antenna has excellent radiation patterns of characteristic of dipole antenna in the ultra wide rage with an omni-directional patterns.  
         [0071]     According to preferred embodiments of the invention, the printed antenna of the present invention is simple in structure, and further has a small profile, is light weight, easy to fabricate and is low in cost. Because of the excellent performance and attractive features of simplicity and small size, the present invention has great potential of wide use for ultra wide band communication devices.  
         [0072]     The many features and advantages of the present invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modification and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modification and equivalents falling within the scope of the invention may be included in the present invention.