Patent Publication Number: US-7724195-B2

Title: Antenna apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to an antenna apparatus, and more particularly relates to an antenna apparatus which includes a UWB antenna encased in an antenna case and is normally attached to another apparatus when used. 
   2. Description of the Related Art 
   In recent years, wireless communication technologies using UltraWideBand (UWB) have gotten a lot of attention because of UWB&#39;s wide range of applications such as radar positioning and high capacity transmission. In 2002, the Federal Communications Commission (FCC) of the United States approved the use of UWB in the frequency band between 3.1-10.6 GHz. 
   UWB is a transmission system which uses ultrawideband signals for communication. An antenna used for UWB must be capable of sending/receiving ultrawideband signals. 
   An antenna, which is composed of a base board and a power feeder, for use in the frequency band between 3.1-10.6 GHz approved by FCC has been proposed (non-patent document 1). 
   [Non-patent document 1] 2003 IEICE (The Institute of Electronics, Information and Communication Engineers) General Conference, Mar. 22, 2003, Room B201, B-1-133: An Omnidirectional and Low-VSWR Antenna for the FCC-Approved UWB Frequency Band, Takuya Taniguchi and Takehiko Kobayashi (Tokyo Denki University). 
   An antenna as described above has a use for devices such as a personal computer and a mobile communication device, and there has been a demand for a more compact and thinner antenna. 
   In Japanese Patent Application No. 2005-160286 titled “Antenna Apparatus” filed by the same applicant as the present application, a compact and thin antenna for UWB is proposed. 
   To attach such an antenna to a device and to actually use the antenna, an easy-to-use antenna apparatus for adjusting the position of the antenna to achieve good reception is necessary. 
   SUMMARY OF THE INVENTION 
   The present invention provides an antenna apparatus that substantially obviates one or more problems caused by the limitations and disadvantages of the related art. 
   Embodiments of the present invention provide an antenna apparatus which makes it possible to easily adjust the position of an antenna to achieve good reception. 
   According to an embodiment of the present invention, an antenna apparatus includes an antenna case housing an antenna; a connector to be connected to a device which connector is electrically connected to the antenna; and an antenna case supporting mechanism which supports the antenna case and enables changing a position of the antenna case at least to a horizontal position and a vertical position. 
   The antenna case supporting mechanism of the antenna apparatus according to an embodiment of the present invention allows the user to easily adjust the position of the antenna case at least to a horizontal position and a vertical position, thereby making it easier for the user to adjust the antenna to a horizontally polarized wave and a vertically polarized wave. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an antenna apparatus according to an embodiment of the present invention; 
       FIG. 2A  is a front transparent view of the antenna apparatus shown in  FIG. 1 ; 
       FIG. 2B  is a back transparent view of the antenna apparatus shown in  FIG. 1 ; 
       FIG. 3  is a drawing used to describe how an antenna case of an antenna apparatus attached to a device is rotated stepwise in a Y-Z plane; 
       FIG. 4  is a drawing used to describe how an antenna case of an antenna apparatus attached to a device is rotated in an X-Z plane; 
       FIGS. 5A through 5C  are drawings used to describe how the direction of an antenna case of an antenna apparatus attached to a device is changed; 
       FIG. 6A  is a front perspective view of a UWB antenna; 
       FIG. 6B  is a back perspective view of the UWB antenna; 
       FIG. 7  is a graph showing VSWR vs. frequency characteristics of a UWB antenna; 
       FIGS. 8A and 8B  are perspective views of a pair of a coaxial connector and a connecting board seen from the Y 2  direction; 
       FIGS. 9A and 9B  are perspective views of a pair of a coaxial connector and a connecting board seen from the Y 1  direction; 
       FIG. 10  is a cross-sectional view of a coaxial connector to which a connecting board is soldered; 
       FIG. 11A  is an entire perspective view of an antenna case; 
       FIG. 11B  is an enlarged view of an arm of the antenna case; 
       FIG. 11C  is an enlarged view of rods of the antenna case; 
       FIG. 12  is an exploded perspective view of an antenna case; 
       FIG. 13  is an enlarged perspective view of arm parts and rod parts shown in  FIG. 12 ; 
       FIG. 14  is an exploded perspective view of a connector case; 
       FIG. 15  is a drawing used to describe how a connector case is assembled; 
       FIG. 16  is a cross-sectional view of a connector case taken along line XVI-XVI shown in  FIG. 1 ; 
       FIG. 17  is a cross-sectional view of a connector case taken along line XVII-XVII shown in  FIG. 1 ; 
       FIGS. 18A and 18B  are drawings illustrating the angle within which a connector case can be rotated; and 
       FIG. 19  is an exploded perspective view of an antenna case supporting mechanism. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention are described below with reference to the accompanying drawings. 
   [Outline of Antenna Apparatus] 
     FIG. 1  is a perspective view of an antenna apparatus  10  according to an embodiment of the present invention.  FIG. 2A  is a front transparent view of the antenna apparatus  10 ; and  FIG. 2B  is a back transparent view of the antenna apparatus  10 . Arrows X 1 -X 2  show the width directions, Y 1 -Y 2  show the length directions, and Z 1 -Z 2  show the thickness directions. The Y 2  side is the bottom of the antenna apparatus  10  and the Y 1  side is the head of the antenna apparatus  10 . 
     FIG. 3 ,  FIG. 4 , and  FIGS. 5A through 5C  illustrate an antenna case in various positions. 
   The antenna apparatus  10  is used to send/receive UWB signals. As shown in  FIG. 1 , the antenna apparatus  10  has a shape of a long narrow board and includes an antenna case  11 , a connector case  30 , and a coaxial connector  60 . Also, as shown in  FIGS. 2A and 2B , the antenna apparatus  10  includes, in its interior, a UWB antenna  100 , a coaxial cable  110 , and a connecting board  120 . The coaxial connector  60  protrudes from the Y 2  end of the antenna apparatus  10  in the Y 2  direction. The coaxial connector  60  is positioned at the bottom of the antenna apparatus  10  and the UWB antenna  100  is positioned at the head of the antenna apparatus  10 . The UWB antenna  100  is in the antenna case  11 . 
   A part of the coaxial connector  60  is housed in the connector case  30 . A screw connector  64  of the coaxial connector  60  protrudes from the connector case  30  in the Y 2  direction. A second axis  202  of the coaxial connector  60  is parallel to the Y 1 -Y 2  directions. The connecting board  120  is fixed to the Y 1  end of the coaxial connector  60 . The connecting board  120  is housed in a space  45  inside the connector case  30  (see  FIG. 16 ). 
   The coaxial cable  110  extends from the UWB antenna  100  through the antenna case  11  in the Y 2  direction. The coaxial cable  110  runs through an antenna case supporting mechanism  80  described later into the connector case  30 . The Y 2  end of the coaxial cable  110  is connected to the connecting board  120 . In this way, the antenna  100  is electrically connected to the coaxial connector  60  via the coaxial cable  110  and the connecting board  120 . 
   The connector case  30  is joined to the coaxial connector  60  by a connector case supporting mechanism  70 . The connector case  30  is rotatably joined to the coaxial connector  60  (which is non-rotatably fixed to the coaxial connector of a device) by the connector case supporting mechanism  70 . The connector case  30  is rotatable in the directions of arrows  212 C and  212 CC around the second axis  202  in the X-Z plane within an angle β. 
   The antenna case  11  is rotatably joined to the connector case  30  by the antenna case supporting mechanism  80 . The antenna case  11  is rotatable stepwise in the directions of arrows  211 C and  211 CC around a first axis  201  (an X 1 -X 2  axis) of the connector case  30  in the Y-Z plane within an angle α. The antenna case supporting mechanism  80  locks the antenna case  11  at every 30 degrees within the angle α. 
   As shown in  FIG. 1 , the antenna apparatus  10  is attached to a device, for example, a personal computer  300 , by screwing the screw connector  64  of the coaxial connector  60  into a coaxial connector  601  of the personal computer  300 . In  FIG. 1 , the antenna apparatus  10  is in the X-Y plane and the antenna case  11  is positioned at zero degrees (in a horizontal position). 
     FIG. 3  shows the range within which the antenna case  11  joined to the connector case  30  by the antenna case supporting mechanism  80  can be rotated. In  FIG. 3 , rotation angles in the counterclockwise direction or upward direction are indicated by “+”, and rotation angles in the clockwise direction or downward direction are indicated by “−”. The antenna case  11  can be locked at every 30 degrees within the angle α between +120 degrees and −120 degrees. The antenna case  11  can be locked at 0 degrees, +30 degrees, +60 degrees, +90 degrees (upward vertical position), +120 degrees, −30 degrees, −60 degrees, −90 degrees (downward vertical position), and −120 degrees. 
   As described above, the antenna case supporting mechanism  80  makes it possible to easily position the antenna case  11  at 0 degrees, +90 degrees (upward vertical position), and −90 degrees (downward vertical position). In other words, the antenna case supporting mechanism  80  makes it possible to easily adjust the UWB antenna  100  to a horizontally polarized wave and a vertically polarized wave. 
     FIG. 4  is a drawing illustrating the antenna apparatus  10  in  FIG. 1  seen from the Y 2  side and shows the range within which the connector case  30  joined to the coaxial connector  60  by the connector case supporting mechanism  70  can be rotated. The connector case  30  is rotatable around the coaxial connector  60  within the angle β (about 100 degrees) and is kept at a desired angle by friction of rubber as described later. When the connector case  30  is rotated around the coaxial connector  60 , the antenna case  11  is rotated together with the connector case  30 . 
   When the antenna apparatus  10  is attached to the personal computer  300  to send/receive signals, the position of the UWB antenna  100  can be adjusted as shown in  FIGS. 5A ,  5 B, and  5 C to achieve good reception. 
     FIG. 5A  shows the antenna case  11  rotated to a position perpendicular to the connector case  30 . 
   In  FIG. 5B , the connector case  30  is rotated a certain number of degrees around the coaxial connector  60  and, as a result, the antenna case  11  is rotated a certain number of degrees around the second axis  202  into an inclined position. 
   In  FIG. 5C , the antenna case  11  is rotated a certain number of degrees around the first axis  201  of the connector case  30  and the connector case  30  is rotated a certain number of degrees around the coaxial connector  60 . As a result, the antenna case  11  is positioned at a “+” angle and also inclined. The user can rotate the connector case  30  around the coaxial connector  60  by holding and rotating the antenna case  11 . 
   Parts of the antenna apparatus  10  are described in detail below. 
   [UWB Antenna  100 ] 
   As shown in  FIGS. 2A and 2B  and  FIGS. 6A and 6B , the UWB antenna  100  includes a dielectric board  101 . A home-plate-shaped element pattern  102  and a microstrip line  103  are formed on the upper surface of the dielectric board  101 , which microstrip line  103  provides electrical connectivity to the element pattern  102 . On a portion of the back surface of the dielectric board  101  which portion corresponds to the microstrip line, a ground pattern  104  is formed. 
   The characteristics of the antenna apparatus  10  change according to an angle θ between a side of the element pattern  102  and a side of the ground pattern  104 . 
   The UWB antenna  100  has VSWR (voltage standing wave ratio) vs. frequency characteristics as shown in  FIG. 7 . In the frequency band between 3.1-10.6 GHz where the UWB antenna  100  is to be used, the VSWR is equal to or lower than 1.4. 
   The UWB antenna  100  may also include a filter in the middle of the microstrip line  103 . 
   [Coaxial Cable  110 ] 
   The coaxial cable  110  has a structure where an electric wire  111  is covered by a braided wire  112 , and the braided wire  112  is covered by an insulating sheath  113 . The Y 1  end of the electric wire  111  of the coaxial cable  110  is soldered to the Y 2  end of the microstrip line  103  by solder  130 , and an end  112   a  of the braided wire  112  is soldered to the ground pattern  104  by solder  131 . An electrically conductive adhesive or laser welding may be used instead of solder. 
   For the connection between the coaxial cable  110  and the UWB antenna  100 , high frequency connectors may also be used. In this case, a high frequency connector is attached to the Y 1  end of the coaxial cable  110  and another high frequency connector is attached to the Y 2  end of the microstrip line  103  of the UWB antenna  100 , and the two high frequency connectors are joined. 
   [Connecting Board  120 ] 
   As shown in  FIG. 8  and  FIG. 9 , the connecting board  120  is used to make it easier to electrically connect the Y 2  end of the coaxial cable  110  extending from the UWB antenna  100  to the coaxial connector  60 . For example, the connecting board  120  is composed of a polyimide board, a wiring pattern  121  on the front surface of the polyimide board, and a ground pattern  122  on the entire back surface of the polyimide board (see  FIG. 10 ). The connecting board  120  fits in a space in the connector case  30 . 
   [Coaxial Connector  60 ] 
   As shown in  FIGS. 8A ,  8 B,  9 A,  9 B, and  10 , the coaxial connector  60  is composed of a metal connector body  61 , a core wire  62  running through the center of the connector body  61 , an insulator  63  covering the core wire  62 , the screw connector  64  at the Y 2  end, and an O-ring  65  made of rubber and placed around the connector body  61 . The connector body  61  includes a cylinder  61   a , a flange  61   b , and a bracket  61   c . The O-ring  65  is placed around the cylinder  61   a . A mark  66  is formed on the surface of the cylinder  61   a  in a position circumferentially opposite from the bracket  61   c  and close to the Y 2  end. 
   The connecting board  120  is supported by the bracket  61   c  and the Y 2  end of the connecting board  120  is placed between the bracket  61   c  and a protrusion  62   a  of the core wire  62 . The end of the bracket  61   c  and a portion of the ground pattern  122  on the back surface of the connecting board  120  are soldered by solder  132 . The protrusion  62   a  and the Y 2  end of the wiring pattern  121  on the front surface of the connecting board  120  are soldered by solder  133 . As described above, the connecting board  120  is at the Y 1  end of the coaxial connector  60  and is fixed to the coaxial connector  60 . 
   Also, as shown in  FIG. 10 , the Y 2  end of the electric wire  111  of the coaxial cable  110  is soldered to the Y 1  end of the wiring pattern  121  by solder  134 , and the end  112   a  of the braided wire  112  is soldered to the ground pattern  122  by solder  135 . 
   In this way, the antenna  100  is electrically connected to the coaxial connector  60  via the coaxial cable  110  and the connecting board  120 . 
   Instead of soldering, an electrically conductive adhesive or laser welding may be used. 
   For the connection between the coaxial cable  110  and the connecting board  120 , high frequency connectors may also be used. In this case, a high frequency connector is attached to the Y 2  end of the coaxial cable  110  and another high frequency connector is attached to the Y 1  end of the connecting board  120 , and the two high frequency connectors are joined. 
   Also, the Y 2  end of the coaxial cable  110  may be directly connected to the protrusion  62   a.    
   The mark  66  is not a printed mark but formed as a dent, and therefore will not be rubbed off. 
   [Antenna Case  11 ] 
     FIG. 11A  is an entire perspective view of the antenna case  11 ;  FIG. 11B  is an enlarged view of an arm  20  of the antenna case  11 ; and  FIG. 11C  is an enlarged view of a first rod  21  and a second rod  22  of the antenna case  11 .  FIG. 12  is an exploded perspective view of the antenna case  11 .  FIG. 13  is an enlarged perspective view of arm parts and rod parts shown in  FIG. 12 . 
   The antenna case  11  is composed of a case body  12  and a cover  15  which are joined and fastened at five points with screws  16 . The antenna case  11  is subdivided into an antenna case main part  11   a , the arm  20  protruding from the Y 2  end of the antenna case main part  11   a  in the Y 2  direction, the first rod  21  protruding from the arm  20  in the X 1  direction, and the second rod  22  protruding from the arm  20  in the X 2  direction. The first rod  21  and the second rod  22  are aligned along the X 1 -X 2  axis. The second rod  22  has a flange  23  at its end. The UWB antenna  100  is housed in the antenna case  11  near the Y 1  end. 
   As shown in  FIG. 12 , the case body  12  has a shallow recess  12   a  in the Y 2  side and a UWB antenna containing part  12   b  in the Y 1  side. The case body  12  also has five threaded holes  12   c , an arm part  20 - 1  protruding from the Y 2  end of the case body  12 , a first rod part  21 - 1 , a second rod part  22 - 1 , and a flange part  23 - 1 . 
   A groove  20 - 1   a  is formed in the arm part  20 - 1 ; and a groove  21 - 1   a  is formed in the first rod part  21 - 1 . 
   The cover  15  is subdivided into an arm part  20 - 2  protruding from the Y 2  end, a first rod part  21 - 2 , a second rod part  22 - 2 , and a flange part  23 - 2 . A groove (not shown) is formed in the arm part  20 - 2  and a groove  21 - 2   a  is formed in the first rod part  21 - 2 . 
   The arm part  20 - 1 , the first rod part  21 - 1 , the second rod part  22 - 1 , and the flange part  23 - 1 ; and the arm part  20 - 2 , the first rod part  21 - 2 , the second rod part  22 - 2 , and the flange part  23 - 2  are respectively symmetric with respect to the X-Y plane. 
   As shown in  FIG. 12 , the antenna case  11  is assembled as follows. The UWB antenna  100  is placed in the UWB antenna containing part  12   b  of the case body  12 . The coaxial cable  110  is laid loosely through the case body  12 . Then, the coaxial cable  110  is laid along the grooves  20 - 1   a  and  21 - 1   a  to form an L-shape and to protrude from the end of the first rod  21 - 1 . The cover  15  is placed on the case body  12  and fastened to the case body  12  at five points with the screws  16 . 
   The arm part  20 - 1  and the arm part  20 - 2  together form the arm  20 ; the first rod part  21 - 1  and the first rod part  21 - 2  together form the first rod  21 ; the second rod part  22 - 1  and the second rod part  22 - 2  together form the second rod  22 ; and the flange part  23 - 1  and the flange part  23 - 2  together form the flange  23 . The groove  20 - 1   a  and the corresponding groove (not shown) in the arm part  20 - 2  form a tunnel in the arm  20 . The groove  21 - 1   a  and the groove  21 - 1   b  form a tunnel in the first rod  21 . 
   The coaxial cable  110  runs through a flat space between the case body  12  and the cover  15 , goes through the tunnels in the arm  20  and the first rod  21 , and protrudes from the end of the first rod  21 . 
   Three protrusions  24 - 1 ,  24 - 2 , and  24 - 3  are formed on the X 2  side of the flange  23 . 
   The case body  12  and the cover  15  are made of a non-magnetic and non-metal material such as ABS resin. In the case body  12 , no threaded hole  12   c  is provided near the element pattern  102  of the UWB antenna  100 . A distance L between the element pattern  102  and the nearest threaded hole  12   c  is substantially long (see  FIG. 12 ). Therefore, the antenna case  11  does not affect the element pattern  102 . 
   Also, the screws  16  may be made of a synthetic resin so that the screws  16  do not affect the element pattern  102 . 
   [Connector Case  30 ] 
     FIG. 14  is an exploded perspective view of the connector case  30 . The connector case  30  is composed of a lower connector case  31 - 1  and an upper connector case  31 - 2 . The lower connector case  31 - 1  and the upper connector case  31 - 2  are made of a non-magnetic and non-metal material such as ABS resin. Between the lower connector case  31 - 1  and the upper connector case  31 - 2 , the coaxial connector  60 , the connecting board  120 , the first rod  21  and the second rod  22  of the antenna case  11 , and a stopper  90  are sandwiched. 
   As shown in  FIG. 14 , an arm space  41 - 1  for housing the arm  20  is formed in the Y 1  side of the lower connector case  31 - 1 . The lower connector case  31 - 1  has, on the upper side, a rod bearing  32 - 1  for holding the coaxial connector  60 , a recess  33 - 1  to form the space  45  for holding the connecting board  120 , a protrusion  34 - 1  protruding from the bottom of the recess  33 - 1 , a rod bearing  35 - 1  for holding the first rod  21 , a rod bearing  36 - 1  for holding the second rod  22 , a flange hole  37 - 1  for holding the flange  23 , a stopper hole  38 - 1  for holding the stopper  90 , a helical compression spring hole  39 - 1  for holding a helical compression spring  95 , and a groove  40 - 1  for holding the coaxial cable  110 . The rod bearing  32 - 1  has an O-ring groove  42 - 1  for holding the O-ring  65 . 
   The upper connector case  31 - 2  has substantially a similar structure as the lower connector case  31 - 1 . The upper connector case  31 - 2  has a rod bearing  32 - 2 , a recess  33 - 2 , a protrusion  34 - 2 , a rod bearing  35 - 2 , a rod bearing  36 - 2 , a flange hole  37 - 2 , a stopper hole  38 - 2 , a helical compression spring hole  39 - 2 , a groove  40 - 2 , an arm space  41 - 2 , and an O-ring groove  42 - 2 . 
   The connector case  30  is assembled as described below. 
   As shown in  FIG. 15 , the stopper  90  is placed in the stopper hole  38 - 1  of the lower connector case  31 - 1 , the helical compression spring  95  is placed in the helical compression spring hole  39 - 1 , the arm  20  is placed in the arm space  41 - 1 , the first rod  21  is placed in the rod bearing  35 - 1 , the second rod  22  is placed in the rod bearing  36 - 1 , and the flange  23  is placed in the flange hole  37 - 1 . Also, the coaxial connector  60  as shown in  FIG. 10  is placed in the rod bearing  32 - 1 . The coaxial cable  110  is laid along the groove  40 - 1  and laid loosely through the recess  33 - 1 . 
   Then, the upper connector case  31 - 2  is placed on the lower connector case  31 - 1 . The Z 1  side of the coaxial connector  60  is placed in the rod bearing  32 - 2 , the Z 1  side of the first rod  21  is placed in the rod bearing  35 - 2 , the Z 1  side of the second rod  22  is placed in the rod bearing  36 - 2 , the Z 1  side of the flange  23  is placed in the flange hole  37 - 2 , the Z 1  side of the stopper  90  is placed in the stopper hole  38 - 2 , and the Z 1  side of the helical compression spring  95  is placed in the helical compression spring hole  39 - 2 . The recess  33 - 1  and the recess  33 - 2  together form the space  45  (see  FIG. 16 ). 
   Finally, the upper connector case  31 - 2  is fastened to the lower connector case  31 - 1  with screws. 
   As described above, the connector case  30  is assembled by sandwiching a part of the antenna case  11 , a part of the coaxial connector  60 , the stopper  90 , and the helical compression spring  95  between the lower connector case  31 - 1  and the upper connector case  31 - 2 , thereby forming the connector case supporting mechanism  70  and the antenna case supporting mechanism  80 . 
   The tightening strength of the above screws determines how much the O-ring  65  is pressed, and thereby determines the rotational friction of the connector case supporting mechanism  70 . 
   The upper connector case  31 - 2  has a mark  46  (see  FIG. 1 ). 
     FIG. 16  and  FIG. 17  show the inside of the connector case  30 .  FIG. 16  is a cross-sectional view of the connector case  30  taken along line XVI-XVI shown in  FIG. 1 .  FIG. 17  is a cross-sectional view of the connector case  30  taken along line XVII-XVII shown in  FIG. 1 . 
   [Connector Case Supporting Mechanism  70 ] 
   As shown in  FIG. 16 , the connector case supporting mechanism  70  has a structure where the coaxial connector  60  is sandwiched between the rod bearings  32 - 1  and  32 - 2 . The connecting board  120  and the bracket  61   c  are housed in the space  45  in the connector case  30 . 
   The above structure enables rotating the connector case  30  around the connector body  61  of the coaxial connector  60 . 
   As shown in  FIG. 17 , the protrusion  34 - 1  is positioned close to the Z 2  side of the bracket  61   c.    
   When the user holds the connector case  30  and rotates the connector case  30  clockwise around the connector body  61  as indicated by the arrow  212 C in  FIG. 17 , the protrusion  34 - 1  comes into contact with the bracket  61   c  as shown in  FIG. 18A . When the user holds the connector case  30  and rotates the connector case  30  counterclockwise around the connector body  61  as indicated by the arrow  212 CC in  FIG. 17 , the protrusion  34 - 1  comes into contact with the bracket  61   c  as shown in  FIG. 18B . 
   Such a structure limits the rotation of the connector case  30  around the connector body  61  to within the angle β (about 100 degrees) between the positions shown in  FIGS. 18A and 18B . Limiting the rotation of the connector case  30  to within the angle β prevents twisting the coaxial cable  110  too much, and thereby prevents breaking the coaxial cable  110  or disconnecting the coaxial cable  110  from the solder  134  and  135 . 
   The space  45  is large enough so that the connecting board  120  housed in the connector case  30  does not obstruct the rotation of the connector case  30 . Therefore, the connecting board  120  does not rotate together with the connector case  30 . 
   The connector case  30  is kept at a desired angle by the friction between the O-ring  65  and the connector body  61 . The strength of this frictional force is adjustable by tightening/loosening the screws fastening the upper connector case  31 - 2  to the lower connector case  31 - 1 . 
   Also, the movement of the coaxial connector  60  in the Y 1  and Y 2  directions in the connector case  30  is limited by the flange  61   b  and the protrusions  34 - 1  and  34 - 2 . 
   Also, as shown in  FIG. 16 , the mark  66  is provided on the outside of the connector case  30 . Since the Y 2  end of the coaxial connector  60  has an approximately round shape, it is difficult to determine its direction. With the mark  66  and the mark  46  on the connector case  30 , the user can easily determine the angle between the connecting board  120  and the connector case  30 . Since the connector case  30  has an approximately square shape and its direction can be easily determined, the mark  46  on the connector case  30  may be omitted. 
   The groove for the O-ring  65  may be provided on the connector body  61  of the coaxial connector  60 . In this case, the O-ring grooves  42 - 1  and  42 - 2  in the lower connector case  31 - 1  and the upper connector case  31 - 2  are omitted. 
   The connector case supporting mechanism  70  may also be configured so that the protrusion  34 - 1  comes into contact with the connecting board  120  when the connector case  30  is rotated, thereby limiting the rotation of the connector case  30  around the connector body  61 . 
   [Antenna Case Supporting Mechanism  80 ] 
     FIG. 19  is an exploded perspective view of the antenna case supporting mechanism  80  shown in  FIG. 16 . 
   The antenna case supporting mechanism  80  has a structure where the first rod  21  and the second rod  22  are rotatably supported by the rod bearings  35 - 1 ,  36 - 1 ,  35 - 2 , and  36 - 2 . The antenna case supporting mechanism  80  also includes the flange  23 , the stopper  90 , and the helical compression spring  95 . 
   The flange  23  is placed between the flange holes  37 - 1  and  37 - 2  and limits the movement of the first rod  21  and the second rod  22  in the X 1  and X 2  directions. 
   The stopper  90  has a structure where twelve holes  92  are formed at 30 degree intervals along the circumference of a circular part on a square board  91 . 
   The stopper  90  is placed between the stopper holes  38 - 1  and  38 - 2  of the connector case  30  so that the stopper  90  cannot be rotated. The helical compression spring  95  presses the stopper  90  in the X 1  direction. 
   Three protrusions  24 - 1 ,  24 - 2 , and  24 - 3  on the X 2  side of the flange  23  fit into three of the twelve holes  92  on the stopper  90 . 
   When the user holds and rotates the antenna case  11  in the direction indicated by an arrow  211 C or  211 CC, the protrusions  24 - 1 ,  24 - 2 , and  24 - 3  push back the stopper  90  in the X 2  direction against the pressure of the helical compression spring  95  and are released from the three holes  92 . When the user further rotates the antenna case  11 , the protrusions  24 - 1 ,  24 - 2 , and  24 - 3  are placed into the next set of three holes  92 . In this way, the antenna case  11  is rotated stepwise and locked at 30 degree intervals within the angle α between +120 degrees and −120 degrees as shown in  FIG. 3 . The antenna case  11  can be locked at 0 degrees, +30 degrees, +60 degrees, +90 degrees (upward vertical position), +120 degrees, −30 degrees, −60 degrees, −90 degrees (downward vertical position), and −120 degrees. 
   The pressure of holes  92  against the protrusions  24 - 1 ,  24 - 2 , and  24 - 3  is provided constantly by the helical compression spring  95 . 
   As described above, the antenna case  11  is locked by the three protrusions  24 - 1 ,  24 - 2 , and  24 - 3  engaging three of the holes  92 . This locking mechanism provides a locking force three times greater than that provided by a locking mechanism where one protrusion engages one hole, enabling secure locking of the antenna case  11 . 
   Also, such a three-point locking mechanism provides better durability compared with a one-point locking mechanism, since the contact pressure is distributed to the three points (protrusions). 
   The bearings  35 - 1 ,  36 - 1 ,  35 - 2 , and  36 - 2 , the first rod  21 , and the second rod  22  are lubricated. Therefore, the antenna case  11  can be rotated smoothly. 
   The protrusions  24 - 1 ,  24 - 2 , and  24 - 3  may be formed on the stopper  90 ; and the holes  92  may be formed on the flange  23 . 
   A spring made of a synthetic resin may be used instead of the helical compression spring  95 . The locking force of the locking mechanism as described above can be adjusted by changing the strength of the helical compression spring  95  or a synthetic resin spring. Also, the locking force of the locking mechanism can be increased by pressing the helical compression spring  95  further by inserting a spacer in the X 2  end of the helical compression spring hole  39 - 1 . Further, a helical compression spring or a similar spring for pressing the flange  23  in the X 2  direction may be incorporated in the arm  20 . 
   A different type of antenna may be used instead of the UWB antenna. Also, a different type of connector may be used instead of the coaxial connector  60 . 
   The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
   The present application is based on Japanese Priority Application No. 2005-378396 filed on Dec. 28, 2005 with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.