Abstract:
An antenna which can be used in different communication standards with a simple structure is disclosed. The antenna includes an antenna section which receives/transmits radio waves, input/output ports to which a signal to be input to the antenna section is input and from which a signal output from the antenna section is output, and transmission lines each of which connects the antenna section to a corresponding input/output port.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to an antenna which can be used in wide band communications. 
         [0003]    2. Description of the Related Art 
         [0004]    Recently, a radio communication technology utilizing UWB (ultra-wide band) has been used. UWB has a radar function, a positioning function, and a radio communication function; and was approved to use the 3.1 to 10.6 GHz band by the US FCC (Federal Communications Commission) in 2002. 
         [0005]    UMB is a radio communication technology in which pulse signals are used in an ultra wide band. Therefore, an antenna which is used in UWB must have a structure which can transmit/receive signals in the ultra wide band. 
         [0006]    An antenna for use in the 3.1 to 10.6 GHz band approved by the FCC is proposed, which antenna includes a base plate and a power supply body (Non-Patent Document 1). 
         [0007]    [Non-Patent Document 1] An Omnidirectional and Low-VSWR Antenna for the FCC-Approved UWB Frequency Band, written and proposed by Takuya Taniguchi and Takehiko Kobayashi, in The General Conference of The Institute of Electronics, Information and Communication Engineers, in 2003. 
         [0008]    As a radio communication technology, there are a wireless LAN (local area network) and Bluetooth other than UWB. An antenna using UWB can be used in frequency bands of the wireless LAN and Bluetooth. Therefore, the antenna using UWB (UWB antenna) can be common in plural radio communication technologies including the wireless LAN, Bluetooth, and UWB. Consequently, when a common antenna such as the UWB antenna is used, antenna space can be less than that of plural antennas for various technologies. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention may provide an antenna which can be used in common in different radio communication technologies with a simple structure. 
         [0010]    According to one aspect of the present invention, there is provided an antenna. The antenna includes an antenna section which receives/transmits radio waves, input/output ports to which a signal to be input to the antenna section is input and from which a signal output from the antenna section is output, and transmission lines each of which connects the antenna section to a corresponding input/output port. 
         [0011]    According to another aspect of the present invention, the antenna section includes an element pattern and a ground pattern which patterns are conductive patterns formed on a dielectric material board. 
         [0012]    According to another aspect of the present invention, the element pattern, the input/output ports, and the transmission lines are formed on one surface of the dielectric material board; the ground pattern is formed on the other surface of the dielectric material board; and a microstrip transmission line is formed of the transmission lines and the ground pattern. 
         [0013]    According to another aspect of the present invention, the element pattern, the ground pattern, the input/output ports, and the transmission lines are formed on one surface of the dielectric material board; and a co-planar transmission line is formed of the transmission lines and the ground pattern. 
         [0014]    According to another aspect of the present invention, a filter circuit is formed in the transmission line. 
         [0015]    According to another aspect of the present invention, the antenna section is connected to the input/output ports via a coupler instead of the transmission lines. 
         [0016]    According to another aspect of the present invention, the coupler is a 3 dB branch line or a power divider. 
         [0017]    According to another aspect of the present invention, the antenna further includes a switching circuit which connects the antenna section to a suitable one of the transmission lines. 
         [0018]    According to another aspect of the present invention, the antenna section is capable of communicating in at least a UWB frequency band and a wireless LAN frequency band. 
         [0019]    According to an embodiment of the present invention, the antenna includes an antenna section which receives/transmits radio waves, input/output ports to which a signal to be input to the antenna section is input and from which a signal output from the antenna section is output, and transmission lines each of which connects the antenna section to a corresponding input/output port. Therefore, the antenna can be used in different communication standards with a simple structure. 
         [0020]    Features and advantages of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a perspective view of an antenna according to a first embodiment of the present invention; 
           [0022]      FIG. 2  is a plan view of the antenna shown in  FIG. 1 ; 
           [0023]      FIG. 3  is a graph showing a VSWR (voltage standing wave ratio) of the antenna shown in  FIG. 1 ; 
           [0024]      FIG. 4  is a perspective view of an antenna according to a second embodiment of the present invention; 
           [0025]      FIG. 5  is a plan view of the antenna shown in  FIG. 4 ; 
           [0026]      FIG. 6  is a perspective view of an antenna according to a third embodiment of the present invention; 
           [0027]      FIG. 7  is a plan view of the antenna shown in  FIG. 6 ; 
           [0028]      FIG. 8  is a graph showing a frequency characteristic of a filter circuit shown in  FIG. 6 ; 
           [0029]      FIG. 9  is a perspective view of an antenna according to a fourth embodiment of the present invention; 
           [0030]      FIG. 10  is a plan view of the antenna shown in  FIG. 9 ; 
           [0031]      FIG. 11  is a perspective view of an antenna according to a fifth embodiment of the present invention; 
           [0032]      FIG. 12  is a plan view of the antenna shown in  FIG. 11 ; and 
           [0033]      FIG. 13  is a schematic diagram showing a structure of the antenna shown in  FIG. 11 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    Referring to the drawings, embodiments of the present invention are described. 
       First Embodiment 
       [0035]      FIG. 1  is a perspective view of an antenna according to a first embodiment of the present invention.  FIG. 2  is a plan view of the antenna shown in  FIG. 1 . 
         [0036]    Referring to  FIGS. 1 and 2 , the antenna according to the first embodiment of the present invention is described. 
         [0037]    An antenna  100  in the first embodiment of the present invention includes a printed circuit board  111  on which an antenna section  112 , input/output ports  113 , and transmission lines  114  are formed of conductive patterns. 
         [0038]    The base board of the printed circuit board  111  is made of a dielectric material such as FR-4 and ceramics and the conductive patterns are formed on the surface of the base board by a conductive material such as copper and aluminum. 
         [0039]    The antenna section  112  is formed of the conductive patterns formed on the surface of the printed circuit board  111  and includes an element pattern  121  and a ground pattern  122 . 
         [0040]    The element pattern  121  is formed on a first surface of the printed circuit board  111  with a pentagon shape similar to home plate. A power supply point P 0  of the element pattern  121  is formed at the position facing the ground pattern  122 . One side of the element pattern  121  whose end is connected to the power supply point P 0  has an angle θ measured from the center line C of the element pattern  121 . Similar to the one side, the other side has the angle θ. The angle θ is, for example, approximately 63°. 
         [0041]    The ground pattern  122  is formed on a second surface of the printed circuit board  111  covering almost all half of the second surface on whose reverse side (first surface) the element pattern  121  is not formed. One side of the ground pattern  122  which side faces the element pattern  121  is located at a position near the power supply point P 0  without contacting the power supply point P 0 . The element pattern  121  is insulated from the ground pattern  122  by the dielectric board of the printed circuit board  111 . 
         [0042]    The input/output ports  113  and the transmission lines  114  are formed on the first surface of the printed circuit board  111  at the part where the element pattern  121  is not formed. Each of the input/output ports  113  is connected to the power supply point P 0  of the element pattern  121  via the corresponding transmission line  114 . Each of the input/output ports  113  is connected to a high-frequency circuit via a connector or a coaxial cable. 
         [0043]    For example, one of the input/output ports  113  is connected to a high-frequency circuit for UWB and the other of the input/output ports  113  is connected to a high-frequency circuit for a wireless LAN. 
         [0044]    A microstrip transmission line is formed by one of the transmission lines  114  and the ground pattern  122 . With this, the characteristic impedance of the transmission line  114  is determined to be, for example, 50Ω. 
         [0045]    A signal line of the connector or the coaxial cable is connected to the input/output port  113  and a shielding line of the connector or the coaxial cable is connected to the ground pattern  122 . 
         [0046]      FIG. 3  is a graph showing a VSWR (voltage standing wave ratio) of the antenna  100  shown in  FIG. 1 . As shown in  FIG. 3 , the VSWR of the antenna  100  can be a value less than a predetermined value at a gain 3 dB when the frequency is 2 GHz or more. With this, communications can be executed in the frequency band of 2.4 GHz of the wireless LAN and in UWB which includes the frequency band of 3.1 GHz and more. 
         [0047]    In the antenna  100 , when the length L ( FIG. 1 ) of the element pattern  121  or the length (not shown) of the ground pattern  122  in the direction orthogonal to the direction facing the element pattern  121  is made greater, the VSWR in a low frequency band is increased. For example, when the length L of the element pattern  121  is approximately 15 mm, the VSWR is increased when the frequency is approximately 3.0 GHz or less; however, when the length L of the element pattern  121  is approximately 20 to 25 mm, the VSWR is increased when the frequency is approximately 2 GHz or less. That is, when the length L is made greater, the VSWR can be improved. 
         [0048]    Consequently, when the length L of the element pattern  121  is determined to be 20 to 25 mm, the antenna  100  can be applied to a wireless LAN at 2.4 MHz. 
         [0049]    As described above, according to the first embodiment of the present invention, since the antenna section  112  can be common for the plural input/output ports  113 , the antenna  100  can be used in communications of, for example, UWB and a wireless LAN. 
       Second Embodiment 
       [0050]      FIG. 4  is a perspective view of an antenna according to a second embodiment of the present invention.  FIG. 5  is a plan view of the antenna shown in  FIG. 4 . 
         [0051]    Referring to  FIGS. 4 and 5 , the antenna according to the second embodiment of the present invention is described. In  FIGS. 4 and 5 , some elements are the same as those shown in  FIGS. 1 and 2 , and each of the same elements has the same reference number; therefore, the same description is omitted. 
         [0052]    An antenna  200  in the second embodiment of the present invention includes a printed circuit board  211  on which an antenna section  212 , input/output ports  113 , and transmission lines  114  are formed of conductive patterns. 
         [0053]    The base board of the printed circuit board  211  is made of a dielectric material such as FR-4 and ceramics and the conductive patterns are formed on the surface of the base board by a conductive material such as copper and aluminum. 
         [0054]    The antenna section  212  is formed of conductive patterns formed on a first surface of the printed circuit board  211  and includes an element pattern  221  and a ground pattern  222 . 
         [0055]    The element pattern  221  is formed on one part of the first surface of the printed circuit board  211  with a pentagon shape similar to home plate. A power supply point P 0  of the element pattern  221  is formed at the position facing the ground pattern  222  without contacting the ground pattern  222 . One side of the element pattern  221  whose end is connected to the power supply point P 0  has an angle θ measured from the center line C of the element pattern  221 . Similar to the one side, the other side has the angle θ. The angle θ is, for example, approximately 63°. 
         [0056]    The ground pattern  222  is formed on the other part of the first surface of the printed circuit board  211  covering almost all the other part. That is, the element pattern  221 , the ground pattern  222 , the input/output ports  113 , and the transmission lines  114  are formed on the first surface of the printed circuit board  211 . The input/output ports  113  and the transmission lines  114  are insulated from the ground pattern  222  by forming a gap therebetween. Further, the element pattern  221  is insulated from the ground pattern  222  by forming a gap therebetween. 
         [0057]    Each of the input/output ports  113  is connected to the power supply point P 0  of the element pattern  221  via the corresponding transmission line  114 . Each of the input/output port  113 s is connected to a high-frequency circuit via a connector or a coaxial cable. 
         [0058]    For example, one of the input/output ports  113  is connected to a high-frequency circuit for UWB and the other of the input/output ports  113  is connected to a high-frequency circuit for a wireless LAN. 
         [0059]    A co-planar transmission line is formed by the transmission lines  114  and the ground pattern  222 . With this, the characteristic impedance of the transmission line  114  is determined to be, for example, 50Ω. 
         [0060]    A signal line of the connector or the coaxial cable is connected to the input/output port  113  and a shielding line of the connector or the coaxial cable is connected to the ground pattern  222 . 
         [0061]    As described above, according to the second embodiment of the present invention, since the antenna section  212  can be common for the plural input/output ports  113 , the antenna  200  can be used in, for example, UWB and a wireless LAN. 
       Third Embodiment 
       [0062]      FIG. 6  is a perspective view of an antenna according to a third embodiment of the present invention.  FIG. 7  is a plan view of the antenna shown in  FIG. 6 . 
         [0063]    Referring to  FIGS. 6 and 7 , the antenna according to the third embodiment of the present invention is described. In  FIGS. 6 and 7 , some elements are the same as those shown in  FIGS. 4 and 5 , and each of the same elements has the same reference number; therefore the same description is omitted. 
         [0064]    In an antenna  300  of the third embodiment of the present invention, one of the plural transmission lines  114  includes a filter circuit  311 . In the filter circuit  311 , a chip capacitor  321  is inserted into the transmission line  114  and the transmission line  114  is connected to the ground pattern  222  via chip inductors  322 . That is, a band pass filter is formed by the filter circuit  311 . 
         [0065]      FIG. 8  is a graph showing a frequency characteristic of the filter circuit  311  shown in  FIG. 6 . As shown in  FIG. 8 , the filter circuit  311  passes a signal of, for example, 2.4 MHz band of, for example, the wireless LAN or Bluetooth, and attenuates a signal of a lower or higher frequency than that of the 2.4 MHz band. 
         [0066]    When a high-frequency circuit for the wireless LAN is connected to the input/output port  113  connected to the transmission line  114  in which the filter circuit  311  is disposed, and a high-frequency circuit for UWB is connected to the input/output port  113  connected to the other transmission line  114 , a process in the high-frequency circuit for the wireless LAN can be simplified. In addition, wireless LAN communications can be executed without being affected by unnecessary frequency components. 
         [0067]    In addition, the filter circuit  311  can be formed to have a frequency characteristic for a UWB band as shown in a dotted line of  FIG. 8 . 
         [0068]    Further, the filter circuit  311  can be disposed in both the transmission lines  114 . 
       Fourth Embodiment 
       [0069]      FIG. 9  is a perspective view of an antenna according to a fourth embodiment of the present invention.  FIG. 10  is a plan view of the antenna shown in  FIG. 9 . 
         [0070]    Referring to  FIGS. 9 and 10 , the antenna according to the fourth embodiment of the present invention is described. In  FIGS. 9 and 10 , some elements are the same as those shown in  FIGS. 1 and 2 , and each of the same elements has the same reference number; therefore the same description is omitted. 
         [0071]    In an antenna  400  of the fourth embodiment of the present invention, a coupler  411  is formed between the element pattern  121  and the input/output ports  113 . 
         [0072]    The coupler  411  is formed by a hybrid circuit, for example, by a 3 dB branch line having 4 ports. The branch line type hybrid circuit in the fourth embodiment of the present invention provides a first port p 1  through a fourth port p 4 . The power supply point P 0  of the element pattern  121  is connected to the first port p 1 , the second port p 2  is open, the third port p 3  is connected to one of the input/output ports  113 , and the fourth port p 4  is connected to the other of the input/output ports  113 . 
         [0073]    The coupler  411  is not limited to the branch line type hybrid circuit, and can be any one of a power divider, a ¼ wavelength distribution coupling type hybrid circuit, a rat race type hybrid circuit, a phase inversion type hybrid circuit, and a Y-shaped power distributor. 
         [0074]    According to the fourth embodiment of the present invention, since the power supply point P 0  of the element pattern  121  is connected to the input/output ports  113  via some of the plural ports p 1  through p 4 , the characteristic impedance between the element pattern  121  and the input/output ports  113  can be matched. Therefore, communications can be stable. 
       Fifth Embodiment 
       [0075]      FIG. 11  is a perspective view of an antenna according to a fifth embodiment of the present invention.  FIG. 12  is a plan view of the antenna shown in  FIG. 11 .  FIG. 13  is a schematic diagram showing a structure of the antenna shown in  FIG. 11 . 
         [0076]    Referring to  FIGS. 11 through 13 , the antenna according to the fifth embodiment of the present invention is described. In  FIGS. 11 through 13 , some elements are the same as those shown in  FIGS. 1 and 2 , and each of the same elements has the same reference number; therefore, the same description is omitted. 
         [0077]    In an antenna  500  of the fifth embodiment of the present invention, a switching circuit  511  is disposed between the element pattern  121  and the transmission lines  114 . 
         [0078]    The switching circuit  511  is connected to a control port  521  and switches the connection between the element pattern  121  and one of the transmission lines  114  to the connection between the element pattern  121  and the other of the transmission lines  114  based on a switching signal supplied to the control port  521  from an external device (not shown). 
         [0079]    When one of the transmission lines  114  is selected by the switching circuit  511 , communications can be executed without being affected by signals from the other of the transmission lines  114 . 
         [0080]    In addition, similar to the third embodiment, when a band pass filter is formed in each of the transmission lines  114  which filter passes a predetermined frequency, communication can be stable. 
         [0081]    Further, the present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention. 
         [0082]    The present application is based on Japanese Priority Patent Application No. 2006-094428 filed on Mar. 30, 2006, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.