Patent Publication Number: US-9853354-B2

Title: Sleeve antenna and wireless communication device

Description:
This application is a U.S. National Phase Application of International Application No. PCT/JP2013/001676, filed Mar. 13, 2013, which claims priority to Japanese Patent Application No.: 2012-058330, filed Mar. 15, 2012, the entireties of which are all hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a sleeve antenna and a wireless communication device. 
     BACKGROUND ART 
     As one kind of antenna used for communications using electromagnetic waves at frequencies in or higher than the VHF band, a sleeve antenna has been conventionally known. As the simplest structure of this sleeve antenna, a sleeve antenna  50  shown in  FIG. 9  has been known. 
     For this sleeve antenna  50 , a sleeve antenna has been known in which a radiating portion  14  is formed by leaving only a core conductor  20  including an insulating member  18  as an outer skin at an end portion of a coaxial feed line  12 , which is referred to generally as a coaxial cable, and an outer conductor (braided wire)  30  formed of the braided wire  30  that had covered the radiating portion  14  is folded in a reverse direction (or the outside of the braided wire  30  is covered with a coaxial circular tube) to obtain a sleeve  10 . Each of the length of the radiating portion  14  and the length of the sleeve  10  is generally set to a length of λ/4 where λ is the wavelength of a radio wave desired to be received, but a sleeve antenna including those having a length of λ/2 or λ/8, or another length has also been known. 
     Moreover, as an improvement to the sleeve antenna  50  having the simplest structure described above, a meander line sleeve antenna using a dielectric print and having two antenna elements that are small and provide high gain is disclosed (for example, refer to PTL 1). 
     Moreover, a wide-band and high-gain earphone antenna that reduces an influence on the human body is disclosed, and a portable radio apparatus that ensures stability of reception is also disclosed (for example, refer to PTLs 2 and 3). 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP-A-2002-141732 
     PTL 2: JP-A-2005-348252 
     PTL 3: JP-A-2005-64742 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, although many conventional sleeve antennas  50  are used because the structure is simple and the cost is low, the antenna needs, when accommodated in a device, a constant length in a straight direction, and therefore is unsuitable for a reduction in the size of the device. 
     Solution to Problem 
     The invention has been made to solve at least a part of the problem described above, and can be realized as the following modes or application examples. 
     APPLICATION EXAMPLE 1 
     A sleeve antenna according to this application example includes: a coaxial feed line; a radiating portion that has a predetermined length and results from removing an outer conductor at a tip portion of the coaxial feed line; and a sleeve that has a predetermined length and covers the coaxial feed line from a proximal end of the radiating portion toward a direction opposite to the radiating portion, wherein at least one of the radiating portion and the sleeve has a bent portion in at least a portion thereof. 
     According to the application example, since at least one of the radiating portion and the sleeve of the sleeve antenna has the bent portion in at least a portion thereof, the sleeve antenna can be attached to a chassis while maintaining favorable antenna gain even when using, for example, a small circuit board. Hence, compared to the case where a conventional sleeve antenna that needs a constant length in a straight direction is attached to a chassis, the degree of freedom in design is increased, which reduces an influence on the surrounding structures of the sleeve antenna. Therefore, it is possible to reduce the size of a device that accommodates the sleeve antenna. In the application example, the angle of bend is not particularly limited, and the term bend means a bend with which the sleeve antenna can be attached to, for example, a chassis while maintaining favorable antenna gain. 
     APPLICATION EXAMPLE 2 
     The sleeve antenna according to the application example, wherein the bent portion is composed of a substantially L-shaped or a substantially U-shaped curved portion or folded portion. 
     According to the application example, a bent state of the sleeve antenna can be fit to, for example, the position or shape of a member arranged in the vicinity of the sleeve antenna. 
     APPLICATION EXAMPLE 3 
     A wireless communication device according to this application example includes: the sleeve antenna according to the application example; a chassis; and a circuit board that has a connection terminal and is accommodated in the chassis, wherein the sleeve antenna is connected to the connection terminal of the circuit board, and at least one of the sleeve and the coaxial feed line of the sleeve antenna is held to at least one of the circuit board and the chassis. 
     According to the application example, since at least one of the radiating portion and the sleeve of the sleeve antenna has the bent portion in at least a portion thereof, the sleeve antenna can be attached to the chassis while maintaining favorable antenna gain even when using a small circuit board. Hence, compared to the case where a conventional sleeve antenna that needs a constant length in a straight direction is attached to a chassis, the degree of freedom in design is increased, which reduces an influence on the surrounding structures of the sleeve antenna. Therefore, it is possible to reduce the size of a device that accommodates the sleeve antenna. Moreover, since a bent state of the bent portion of the sleeve antenna can be fit to the position or shape of a member arranged in the vicinity of the sleeve antenna, the influence on the surrounding structures of the sleeve antenna is reduced. 
     APPLICATION EXAMPLE 4 
     The wireless communication device according to the application example, wherein the chassis has a hole, and the sleeve is inserted into the hole by a desired length. 
     According to the application example, a distance from a dielectric such as a chassis material is maintained constant, and antenna performance is stabilized. Moreover, by holding a holding member at a distal end of the sleeve of the sleeve antenna, it is possible to reduce an influence of the dielectric of the holding portion on the sleeve antenna (a current distribution of the antenna is not affected). 
     APPLICATION EXAMPLE 5 
     The wireless communication device according to the application example comprising a holding member that holds the sleeve antenna, wherein the holding member is provided between at least one of the circuit board and the chassis and a distal end of the sleeve. 
     According to the application example, the sleeve antenna is arranged in the chassis by providing the bent portion in a portion of the sleeve antenna, and also a proper holding structure is adopted, whereby a distance from a dielectric such as a chassis material is maintained constant, and antenna performance is stabilized. Moreover, by holding the holding member at the distal end of the sleeve of the sleeve antenna, it is possible to reduce an influence of the dielectric of the holding portion on the sleeve antenna (a current distribution of the antenna is not affected). 
     APPLICATION EXAMPLE 6 
     The wireless communication device according to the application example, wherein the holding member is formed of a low dielectric constant material. 
     According to the application example, by holding the sleeve antenna with a low dielectric constant material that allows a radio wave to pass therethrough, it is possible to reduce an influence of the dielectric of the holding portion on the sleeve antenna (a current distribution of the antenna is not affected). 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates schematic views showing a configuration of a wireless communication device according to a first embodiment.  FIG. 1(A)  is a schematic plan view,  FIG. 1(B)  is a schematic elevation view, and  FIG. 1(C)  is a schematic right side view. 
         FIG. 2  illustrates schematic views showing a configuration of a wireless communication device according to a second embodiment.  FIG. 2(A)  is a schematic plan view,  FIG. 2(B)  is a schematic elevation view, and  FIG. 2(C)  is a schematic right side view. 
         FIG. 3  illustrates a schematic plan view showing a configuration of a bent-type sleeve antenna of Modified Example 1. 
         FIG. 4  illustrates a schematic plan view showing a configuration of a bent-type sleeve antenna of Modified Example 2. 
         FIG. 5  illustrates a schematic plan view showing a configuration of a wireless communication device of Modified Example 3. 
         FIG. 6  illustrates a schematic plan view showing a configuration of a wireless communication device of Modified Example 4. 
         FIG. 7  illustrates a schematic plan view showing a configuration of a wireless communication device of Modified Example 5. 
         FIG. 8  illustrates a schematic plan view showing a configuration of a wireless communication device of Modified Example 6. 
         FIG. 9  illustrates an appearance perspective view showing a configuration of a conventional sleeve antenna. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments in which the invention is embodied will be described in accordance with the drawings. The drawings used are appropriately enlarged or reduced to be represented so that a portion to be described is brought into a recognizable state. 
     (First Embodiment) 
       FIGS. 1  are schematic views showing a configuration of a wireless communication device  2  according to this embodiment.  FIG. 1(A)  is a schematic plan view,  FIG. 1(B)  is a schematic elevation view, and  FIG. 1(C)  is a schematic right side view. Hereinafter, a structure of the wireless communication device  2  will be described with reference to  FIGS. 1 . 
     The wireless communication device  2  according to the embodiment includes a bent-type sleeve antenna (sleeve antenna)  6 , a chassis  24 , and a circuit board  22 . 
     The bent-type sleeve antenna  6  includes a coaxial feed line  12 , a radiating portion  14  that has a predetermined length and results from removing a braided wire  30  at a tip portion of the coaxial feed line  12 , and a sleeve  10  that has a predetermined length and covers the coaxial feed line  12  from a proximal end of the radiating portion  14  toward a direction opposite to the radiating portion  14 . At least one of the radiating portion  14  and the sleeve  10  has a bent portion  36  in at least a portion thereof. The bent portion  36  is composed of a substantially L-shaped or a substantially U-shaped curved portion or folded portion. 
     The shape of the bent-type sleeve antenna  6  is not linear in an antenna length direction thereof. In other words, a plurality of bent portions are formed in the antenna length direction. Here, the term bent means that one line has a bent shape with a measurable angle α. Moreover, the term curved means that one line has a curved shape so as to warp with a measurable curvature radius R. 
     The bent-type sleeve antenna  6  is connected to a connector  16  of the circuit board  22 . The bent-type sleeve antenna  6  is held to at least one of the circuit board  22  and the chassis  24 . 
     The bent-type sleeve antenna  6  is fixed using an elastic holding member  26  for providing a function as a shock-absorbing material of the bent-type sleeve antenna  6 . Moreover, the bent-type sleeve antenna  6  may be fixed using a thermoplastic resin (hot melt), an ultraviolet-curable epoxy, or the like to the chassis  24  made of a plastic. 
     As shown in  FIG. 9 , the coaxial feed line  12  has a coaxial structure in which a core conductor  20  is covered with an outer conductor (braided wire)  30  via an insulating member  18  and covered with a protective coating  32  at the outermost circumference. 
     The sleeve  10  is formed of a cylindrical thin-plate conductor having a length about 0.25 times a wavelength to be used, and an upper end thereof is connected to the braided wire  30  by soldering or the like. The sleeve  10  may be formed of any preferred conductive material (for example, a metal such as stainless steel, aluminum, titanium, or copper). The sleeve  10  may have the bent portion  36  in at least a portion thereof 
     The radiating portion  14  is formed to have a length about 0.25 times a wavelength to be used by removing the braided wire  30  from the tip portion of the coaxial feed line  12  exposed from the sleeve  10 . Then, the insulating member  18  of the coaxial feed line  12  functions as a member of supporting the core conductor  20  at the radiating portion  14 . The insulating member  18  may be removed from the radiating portion  14 , and the core conductor  20  may be supported by another supporting member. The radiating portion  14  may have the bent portion  36  in at least a portion thereof. As shown in  FIGS. 1 , the radiating portion  14  has, at an end on the sleeve  10  side, the bent portion  36  that is bent at about 90 degrees. 
     At the proximal end of the coaxial feed line  12 , a connector (not shown) for connecting with a transmitter or receiver is provided. The connector is composed of a screw portion (not shown) that is electrically conducted to the braided wire  30 , a center terminal (not shown) that is electrically conducted to the core conductor  20 , and an insulating spacer (not shown) present between the screw portion and the center terminal. 
     The chassis  24  is a case that covers the circuit board  22 , and composed of a raw material (plastic or the like) that allows an electromagnetic wave to pass therethrough. 
     The circuit board  22  has the connector (connection terminal)  16 . The circuit board  22  is accommodated in the chassis  24 . The circuit board  22  has a surface on which a circuit for realizing a function of the wireless communication device  2  is formed. An amplifier circuit (not shown) that amplifies the power of an electromagnetic wave to be transmitted from the bent-type sleeve antenna  6  to set transmission power is formed on the circuit board  22 . This amplifier circuit radiates, as an electromagnetic wave, the transmission power required for the wireless communication device  2  from the bent-type sleeve antenna  6 . 
     The wireless communication device  2  includes a holding member  26  that holds the bent-type sleeve antenna  6 , and the holding member  26  is provided between at least one of the circuit board  22  and the chassis  24  and the distal end of the sleeve  10 . According to this, the bent-type sleeve antenna  6  is bent at a portion thereof to provide the bent portion  36  and arranged in the chassis  24 , and a proper holding structure is also adopted, whereby a distance from a dielectric such as a material of the chassis  24  is maintained constant and antenna performance is stabilized. 
     The holding member  26  is a low dielectric constant tube formed of a low dielectric constant material. According to this, by holding the holding member at the distal end of the sleeve  10 , it is possible to reduce an influence of the dielectric of the holding portion on the bent-type sleeve antenna  6  (a current distribution of the bent-type sleeve antenna  6  is not affected). The holding member  26  is formed of a soft material (for example, a silicone rubber, a natural rubber, or a synthetic rubber, or other proper elastic compressible materials). 
     Examples of the low dielectric constant material include, for example, a spin-on glass film containing any one of silica glass, alkylsiloxane polymer, alkylsilsesquioxane polymer, alkylsilsesquioxanehydride polymer, and polyarylether, a diamond film, and a fluorinated amorphous carbon film. 
     Further, for example, aerogel, porous silica, a gel having magnesium fluoride fine particles dispersed therein, fluorinated polymer, porous polymer, and a predetermined material containing fine particles may be used as the low dielectric constant material. 
     According to the embodiment, since at least one of the radiating portion  14  and the sleeve  10  of the bent-type sleeve antenna  6  has the bent portion  36  in at least a portion thereof, the bent-type sleeve antenna  6  can be attached to the chassis  24  while maintaining favorable antenna gain even when the circuit board  22  having a small size is used. Hence, compared to the case of attaching to the chassis  24  with the need of a constant length in the straight direction, the degree of freedom in design is increased, which reduces an influence on the surrounding structures of the sleeve antenna. Therefore, it is possible to reduce the size of a device that accommodates the sleeve antenna. Moreover, since a bent state of the bent-type sleeve antenna  6  can be fit to the position or shape of a member arranged in the vicinity of the bent-type sleeve antenna  6 , an influence on the surrounding structures is reduced. 
     (Second Embodiment) 
       FIGS. 2  are schematic views showing a configuration of a wireless communication device  4  according to this embodiment.  FIG. 2(A)  is a schematic plan view,  FIG. 2(B)  is a schematic elevation view, and  FIG. 2(C)  is a schematic right side view. Hereinafter, a structure of the wireless communication device  4  will be described with reference to  FIGS. 2 . In the drawings, the same constituent portions as those of the first embodiment described above are represented by the same reference numerals and signs, and the description thereof is omitted. Moreover, a difference between a bent-type sleeve antenna  6 B of the second embodiment and the bent-type sleeve antenna  6  of the first embodiment is that in the second embodiment, a sleeve  11  is provided so as to be inserted into a hole  28  of the chassis  24  by a desired length from an end of the sleeve  11  on the side opposite to its proximal end, instead of the low dielectric constant tube  26  in the first embodiment. The length of this sleeve  11  is also set to the same length as that of the first embodiment. 
     In the above first and second embodiments, the length of each of the radiating portion  14  and the sleeves  10  and  11  is set to a length of λ/4 where λ is the wavelength of a radio wave desired to be received, but the length is not limited to this. It is needless to say that the length may be set to λ/2 or λ/8, or other lengths. 
     Embodiments are not limited to those described above, and can be implemented in the following modes. 
     (Modified Example 1) 
       FIG. 3  is a schematic plan view showing a configuration of a bent-type sleeve antenna of this modified example. 
     In the first embodiment described above, the respective shapes of the radiating portion  14  and the sleeve  10  are not limited to that of the radiating portion  14  having the bent portion  36  and that of the sleeve  10  not having a bent portion. Also in the second embodiment described above, the respective shapes of the radiating portion  14  and the sleeve  11  are not limited to that of the radiating portion  14  having the bent portion  36  and that of the sleeve  11  having the bent portion  36 . For example, the shape may be the shape shown in  FIG. 3 . The bent-type sleeve antenna of the modified example includes the radiating portion  14  not having a bent portion that extends along an edge of the circuit board  22 , the sleeve  10  having the bent portion  36  that extends along the edge of the circuit board  22 , and the coaxial feed line  12  that is connected to the connection terminal  16  of the circuit board  22  and held to the circuit board  22  by the holding member  26 . The sleeve  10  has, in the middle, the bent portion  36  that is bent in an arc shape (for example, about ¼ arc). 
     (Modified Example 2) 
       FIG. 4  is a schematic plan view showing a configuration of a bent-type sleeve antenna of this modified example. 
     The bent-type sleeve antenna of the modified example includes the radiating portion  14  not having a bent portion that extends along the edge of the circuit board  22 , the sleeve  10  having the bent portion  36  in an arc shape, and the coaxial feed line  12  that is connected to the connection terminal  16  of the circuit board  22  and held to the circuit board  22  by the holding member  26 . The sleeve  10  has, in the middle, the bent portion  36  that is bent in an arc shape (for example, about ½ arc). 
     (Modified Example 3) 
       FIG. 5  is a schematic plan view showing a configuration of a wireless communication device of this modified example. 
     The wireless communication device according to the modified example has a casing  34  and the connector  16 , and includes the circuit board  22  that is accommodated in the casing  34 , the above-described bent-type sleeve antenna of Modified Example  2  that is held to the casing  34  and connected to the connector  16  of the circuit board  22 , and the holding member  26  that holds the bent-type sleeve antenna  6 . The sleeve  10  has, in the middle of a cylindrical shape, the bent portion  36  that is bent in an arc shape (for example, about ½ arc). The holding member  26  is provided between the casing  34  and the distal end of the sleeve  10  having the bent portion  36 . In the interior of the casing  34 , the circuit board  22  and the bent-type sleeve antenna  6  are arranged and each fixed in the interior of the casing  34 . The casing  34  has a ring shape whose cross section is rectangular, and is obtained by integrally molding a disk portion composed of a non-conductive material such as a plastic with a bottom surface of a peripheral portion composed of a non-conductive material such as a plastic. 
     (Modified Example 4) 
       FIG. 6  is a schematic plan view showing a configuration of a wireless communication device of this modified example. 
     The wireless communication device according to the modified example has the casing  34  and the connector  16 , and includes the circuit board  22  that is accommodated in the casing  34 , the above-described bent-type sleeve antenna of Modified Example  2  that is held to the casing  34  and connected to the connector  16  of the circuit board  22 , and the holding member  26  that holds the bent-type sleeve antenna. The holding member  26  is provided between the casing  34  and the distal end of the sleeve  10  so as to be wrapped around the sleeve. 
     (Modified Example 5) 
       FIG. 7  is a schematic plan view showing a configuration of a wireless communication device of this modified example. 
     The wireless communication device of the modified example includes the radiating portion  14  having the bent portion  36  that extends along the edge of the circuit board  22 , the sleeve  10  not having a bent portion, and the coaxial feed line  12  that is connected to the connector  16  of the circuit board  22  and held to the casing  34  by the holding member  26 . The radiating portion  14  has, at the end on the sleeve  10  side, the bent portion  36  that is bend at about 90 degrees. The holding member  26  is provided in a doughnut shape between the casing  34  and the distal end of the sleeve  10  so as to be wrapped around the cylinder of the sleeve. 
     (Modified Example 6) 
       FIG. 8  is a schematic plan view showing a configuration of a wireless communication device of this modified example. 
     The wireless communication device of the modified example includes the radiating portion  14  having the bent portion  36  that extends along the edge of the circuit board  22 , the sleeve  10  having the bent portion  36 , and the coaxial feed line  12  that is connected to the connection terminal  16  of the circuit board  22  and held to the casing  34  by the holding member  26 . The sleeve  10  has, in the middle portion of a cylindrical shape, the bent portion  36  that is bent in an arc shape (for example, about ½ arc). The radiating portion  14  has, in the middle, the bent portion  36  that is bent at about 90 degrees. The holding member  26  is provided between the casing  34  and the distal end of the sleeve  10  so as to be wrapped around the sleeve. 
     The sleeve  10  portion of the bent-type may be composed of the braided wire  30  of the coaxial feed line  12 . Moreover, the bent-type sleeve antennas  6  and  6 B may be applicable to various frequency bands by changing the dimensions thereof. For example, the 2.4 GHz band (WiFi, Bluetooth (registered trademark), Zigbee (registered trademark), GPS, PHS, and the like) and the like can be mentioned. 
     Moreover, the bent-type sleeve antennas  6  and  6 B have a bent shape, and therefore may be arranged either inside or outside the casing  34 .