Abstract:
Disclosed herein is an antenna that can be manufactured in a smaller size and can achieve good wideband characteristics. The antenna includes a substantially semicircular antenna component installed in a monopole or dipole structure. Power is supplied to an end of the diameter of the antenna component.

Description:
PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. § 119 to an application entitled “Antenna” filed in the Japanese Property Office on Dec. 25, 2003 and assigned Serial No. 2003-428649, and an application entitled “Antenna” filed in the Korean Intellectual Property Office on Oct. 5, 2004 and assigned Serial No. 2004-79080, the contents of both of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an antenna for a portable communication device.  
         [0004]     2. Description of the Related Art  
         [0005]     It is known that a circular disc monopole antenna using a circular antenna component obtains wideband characteristics. A circular disc monopole antenna having a circular antenna component modified for miniaturization is disclosed in Japan Patent Laid-Open Publication No. 2002-164731, which discloses the circular antenna component bent perpendicularly with respect to its diameter.  
         [0006]     In conventional portable communication devices, however, the antenna component occupies a large area and the antenna needs to be further scaled down. For example, there is very limited room for securing an antenna in small communication devices. Thus, small-size antennas are required.  
         [0007]     Moreover, the use of a conventional modified circular antenna component causes an anti-resonant point in a desired frequency band, thereby deteriorating Voltage Standing Wave Ratio (VSWR) characteristics and making it difficult to maintain constant wideband characteristics.  
       SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide an antenna which obtains good wideband characteristics and can be scaled down to a smaller size.  
         [0009]     The above object is achieved by providing an antenna that can be made in a smaller size and can achieve good wideband characteristics. The antenna includes a substantially semicircular antenna component in a monopole or dipole structure. Power is supplied to an end of the diameter of the antenna component. Preferably, the semicircular antenna component has a diameter of a quarter of resonant wavelength λ. Further, the semicircular antenna component is preferably provided with a slit for adjusting an impedance bandwidth of the antenna.  
         [0010]     In another aspect of the present invention, an antenna of the present invention includes a dielectric plate and a semicircular conductive component fixedly mounted on the dielectric plate. The dielectric plate is preferably made of ceramic. Further, the semicircular conductive component preferably has a diameter of a quarter of a resonant wavelength λ.  
         [0011]     Preferably, the dielectric plate has a rectangular shape, with one side adjacent to a straight side of the semicircular conductive component.  
         [0012]     Preferably, the antenna further includes a ground plate fixedly connected to the dielectric plate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0014]      FIG. 1  is a side view of an antenna according to a first embodiment of the present invention;  
         [0015]      FIGS. 2A and 2B  are exemplary layouts of antenna components according to the first embodiment of the present invention;  
         [0016]      FIG. 3  is a side view of an antenna according to a second embodiment of the present invention;  
         [0017]      FIG. 4  illustrates an exemplary layout of antenna components according to the second embodiment of the present invention;  
         [0018]      FIG. 5  is a graph illustrating the improvement of VSWR characteristics in the antenna according to the present invention;  
         [0019]      FIGS. 6A  to  6 C illustrate antenna configurations corresponding to curves A, B and C illustrated in  FIG. 5 , wherein  FIG. 6B  is a conventional antenna configuration that corresponds to curve B of  FIG. 5 ; and  
         [0020]      FIGS. 7A and 7B  are side views illustrating a dipole antenna according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the invention with unnecessary detail.  
         [0022]      FIG. 1  is a side view illustrating the configuration of an antenna according to a first embodiment of the present invention. A substantially semicircular antenna component  1  is assembled in a monopole structure.  
         [0023]     Referring to  FIG. 1 , the antenna component  1  is a semicircular conductive disc. Its diameter is preferably about a quarter of the resonant wavelength λ of the antenna. As illustrated in  FIG. 2A , the antenna component  1  can be installed with its diameter perpendicular to a ground plane  3 . Alternatively, the antenna component  1  can be installed in parallel with the ground plane  3 , as illustrated in  FIG. 2B . A substantially semicircular shape suffices for the conductive disc of the antenna component  1 . For example, the antenna component  1  can be semi-oval. A stub member (not shown) can be added around the outer circumference of the antenna component  1 .  
         [0024]     As shown in  FIG. 2B , the ground plate  3  preferably is rectangular in shape, and has one side adjacent to a straight, tangential line of a side of the semicircular antenna  1 .  
         [0025]     A power supply  2  supplies power to the antenna component. The power supply  2  is connected between an end of the diameter of the antenna component  1  and the ground plane  3 .  
         [0026]     In the above configuration, since the antenna component  1  is substantially semicircular, it occupies a smaller area. Also, forming the antenna component  1  as a substantially semicircular conductive disc prevents generation of an anti-resonant point in a desired frequency band, thereby resulting in good wideband characteristics.  
         [0027]     An antenna according to another embodiment of the present invention will be described below.  
         [0028]      FIG. 3  is a side view illustrating an antenna according to a second embodiment of the present invention. Referring to  FIG. 3 , the substantially semicircular antenna component  1  is formed on a dielectric plate  10 . The dielectric plate  10  is, for example, a ceramic, and enables miniaturization of the antenna. As illustrated in  FIG. 4 , the antenna component  1  can be installed with an offset distance “d” with respect to the ground plane  3 . The semicircular antenna component is preferably provided with a slit for adjusting an impedance bandwidth of the antenna.  
         [0029]      FIG. 5  is a graph illustrating the improvement of VSWR characteristics of the antenna according to the present invention.  
         [0030]     Referring to  FIG. 5 , curve “A” denotes a simulation result of an antenna illustrated in  FIG. 6A , which has the semicircular antenna component  1  formed on the dielectric plate  10 . Curve “B” denotes a simulation result of a conventional circular disc monopole antenna illustrated in  FIG. 6B . The conventional antenna has a circular antenna component  100  formed on the dielectric plate  10 .  
         [0031]     Curve “C” denotes a simulation result of a semicircular monopole antenna illustrated in  FIG. 6C . This antenna is produced by bending a circular disc to a semicircular shape. Thus, the antenna has the semicircular antenna component  100  preferably shaped into a sideward “U” shape (i.e. “         ”), formed on the dielectric plate  10 .  
         [0032]     Curve “C” indicates an anti-resonant point generated in the vicinity of 5.1 GHz. Therefore, good VSWR characteristics cannot be expected from the bent semicircular monopole antenna. Also, the antenna component  100  is bent so as to be of the same shape on its front and rear surfaces, such as illustrated in  FIG. 6A . Hence, current flows with opposite phases through the front and rear surfaces of the antenna component  100 . As a result, a frequency band is created whose loss increases due to factors including the material of the dielectric plate  10 , thereby reducing radiation efficiency.  
         [0033]     Meanwhile, the inventive antenna denoted by curve “A” does not have, on the average, as good VSWR characteristics as the conventional circular disc monopole antenna denoted by curve “B”. However, the inventive antenna does not create an anti-resonant point. Considering the tradeoff relation between the area of the antenna and its performance, the inventive antenna can be said to have satisfactory VSWR characteristics.  
         [0034]     While the invention has been shown and described with reference to certain preferred embodiments thereof, they are merely exemplary applications. For example, the present invention is also applicable to a dipole antenna. The term “dipole” will also be recognized to cover “cross dipole” antennas.  FIGS. 7A and 7B  are side views of a dipole antenna according to the present invention.  
         [0035]     Referring to  FIGS. 7A and 7B , two semicircular antenna components  1  are assembled in a dipole structure. The antenna components  1  face in the same direction in  FIG. 7A , and face in different directions in  FIG. 7B .  
         [0036]     In accordance with the present invention as described above, the area that an antenna component occupies can be reduced by shaping the antenna component to be substantially semicircular. Furthermore, this arrangement avoids an anti-resonant point in a desired frequency band, thereby achieving good wideband characteristics.  
         [0037]     Thus, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.