Patent Publication Number: US-10770796-B2

Title: Antenna device and method for manufacturing antenna device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an antenna device and a method for manufacturing the antenna device. 
     2. Description of the Related Art 
     Common automobile antenna devices are amplitude modulation/frequency modulation (AM/FM) radio antenna devices capable of receiving AM broadcasts and FM broadcasts. Although AM/FM radio antenna devices of a rod type have been used, AM/FM antenna devices of a shark fin type have been preferred in recent years because of attractive design. The antenna device of a shark fin type is named after its external shape. 
     Antenna devices of a shark fin have an upper limit of 70 mm in height and an upper limit of about 200 mm in length to comply with legal regulations. 
     Low-profile antenna devices due to the regulation have disadvantages, such as low impedance or radiation resistance and thus low receiving sensitivity. 
     For example, Japanese Patent No. 5237617 discloses an antenna device that solves such disadvantages. 
     The device of Japanese Patent No. 5237617 includes an umbrella antenna component and is called a capacity loaded or top loaded antenna. The feeding point of the antenna component is connected to the input terminal of an amplifier through an antenna coil. 
     The antenna device disclosed in Japanese Patent No. 5237617 includes the amplifier to compensate for the low reception efficiency in the low-profile antenna component. 
     However, the low-profile antenna component has low impedance or radiation resistance of the antenna component, resulting in reception loss due to the impedance mismatch between the antenna component and the amplifier. 
     Although the impedance mismatch can be reduced by providing an additional matching circuit including a resistor, a capacitor, and an inductor on the antenna component, the material and production costs increase. 
     SUMMARY OF THE INVENTION 
     An object of the present invention, which has been made in view of the above-mentioned disadvantages, is to provide an antenna device including a coil on an antenna component, where the mount angle of the coil to the antenna component can be modified to adjust impedances without a matching circuit. 
     According to a first aspect of the present invention, an antenna device mounted to an automobile includes: 
     an antenna component; and 
     an amplifier board provided with an amplifier to amplify signals received by the antenna component, 
     wherein the antenna component includes a metal plate and a resonance point adjusting coil having a first end connected to the metal plate, the resonance point adjusting coil being connected to an input terminal of the amplifier board at the first end via the metal plate. 
     Preferably, the resonance point adjusting coil has a second end that is open. 
     Preferably, the impedance of the antenna component is adjustable by the mount angle of the resonance point adjusting coil to the antenna component. 
     Preferably, a direction from the first end of the resonance point adjusting coil to the second end along a central axis of the resonance point adjusting coil is vertically downward. 
     Preferably, the resonance point adjusting coil is mounted at an angle of 90° where a mount angle of the resonance point adjusting coil is defined as 0° when a direction from the first end of the resonance point adjusting coil to the second end along a central axis of the resonance point adjusting coil is vertically downward. 
     According to a second aspect of the present invention, a method for manufacturing the antenna device includes: 
     adjusting the mount angle of the resonance point adjusting coil to the antenna device; and 
     adjusting a pitch and a number of windings and a length of a wire of the resonance point adjusting coil according to the angle to adjust an impedance of the antenna component to a desired level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention. 
         FIG. 1  is an external perspective view of an antenna device according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of the antenna device according to the embodiment of the invention. 
         FIG. 3  is a perspective view of the antenna device according to the embodiment of the invention and illustrates the antenna device from which an antenna cover is removed. 
         FIG. 4  is a perspective view of the antenna device according to the embodiment of the invention and illustrates the antenna device from a different direction from  FIG. 3  and the antenna cover is removed. 
         FIG. 5  is an exploded perspective view of the antenna device according to the embodiment of the invention. 
         FIG. 6  is a Smith chart of the antenna device in  FIGS. 1 to 4 . 
         FIG. 7A  is a cross-sectional view of a traditional antenna device. 
         FIG. 7B  is a Smith chart of the traditional antenna device in  FIG. 7A . 
         FIG. 8A  is a cross-sectional view of an antenna device according to an embodiment of the invention and illustrates a coil mounted at another angle in the antenna device from which an antenna cover is removed. 
         FIG. 8B  is a Smith chart of the antenna device in  FIG. 8A . 
         FIG. 9A  is a cross-sectional view of an antenna device according to an embodiment of the invention and illustrates a coil mounted at still another angle in the antenna device from which an antenna cover is removed. 
         FIG. 9B  is a Smith chart of the antenna device in  FIG. 9A . 
         FIG. 10A  is a cross-sectional view of an antenna device according to an embodiment of the invention and illustrates a coil mounted at still another angle in the antenna device from which an antenna cover is removed. 
         FIG. 10B  is a Smith chart of the antenna device in  FIG. 10A . 
         FIG. 11A  is a cross-sectional view of an antenna device according to an embodiment of the invention and illustrates a coil mounted at still another angle in the antenna device from which an antenna cover is removed. 
         FIG. 11B  is a Smith chart of the antenna device in  FIG. 11A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a preferred embodiment of the present invention will be described with the drawings. However, the scope of the invention is not limited to the disclosed embodiments. 
     An antenna device  1  according to the present embodiment is an exemplary automobile antenna device that can receive radiowaves at the frequency bands for AM/FM broadcasts and is fixed on a mount face of the roof of an automobile. 
     As illustrated in  FIGS. 1 to 5 , the antenna device  1  includes an antenna component  10 , an amplifier board  20 , an antenna holder  30 , an antenna base  40 , an antenna cover  50 , a gasket  60 , and other components, for example, a hook  71 , a cable holder  72 , and a bolt. In the drawing, the X axis indicates the lateral or right-left direction, the Y axis the longitudinal or front-back direction, and the Z axis the vertical direction. The antenna device  1  protrudes from the mounting face and has a height of 70 mm or less. 
     The antenna component  10  includes a metal plate  11  and a resonance point adjusting coil  12  having a first end connected to the metal plate  11 . 
     The antenna cover  50  has a shape of a shark fin that is raised toward its rear portion. 
     The metal plate  11  has a top face  111 , a left sidewall  112 , a right sidewall  113 , a connecting bar  114 , a coil connecting hole  115 , and a fixing slots  116 ,  116 . 
     The top face  111  extends along the upper edge of the antenna cover  50  in the longitudinal direction. 
     The left sidewall  112  extends obliquely downward from the left edge of the top face  111  along the left face of the antenna cover  50 . 
     The right sidewall  113  extends obliquely downward from the right edge of the top face  111  along the right face of the antenna cover  50 . 
     The connecting bar  114  extends downward from the front edge of the top face  111 . The connecting bar  114  is inserted into a connecting terminal  21  mounted to the amplifier board  20  to connect the antenna component  10  to the amplifier board  20 . In this way, the resonance point adjusting coil  12  is connected to the input terminal of the amplifier board  20  via the metal plate  11 . The connecting terminal  21  is composed of a pair of spring terminals holding and crimping the connecting bar  114  therebetween, and the connecting bar  114  can be readily connected to the connecting terminal  21  only by the insertion. 
     The coil connecting hole  115  is provided at the rear end of the top face  111 . The resonance point adjusting coil  12  is inserted into the coil connecting hole  115  at the first end and is soldered. In this manner, the resonance point adjusting coil  12  has the first end connected to the metal plate  11  and a second end that is free or open. 
     The top face  111  has the pierced fixing slots  116 ,  116 , as described above. 
     The amplifier board  20  is a circuit board provided with an amplifier to amplify AM/FM signals received by the antenna component  10 . The amplifier board  20  is fixed on the top face of the antenna base  40 . In the present embodiment, although the amplifier board  20  is disposed adjacent to the front end, the amplifier board  20  may be disposed in any position, for example, in the longitudinal center or adjacent to the rear end. The free selection of the position can be achieved by the position of the connecting terminal  21  and the bend or extension of the connecting bar  114 . 
     The antenna holder  30  is an insulator holding the antenna component  10  and stands on the antenna base  40 . The antenna holder  30  includes a metal plate holding block  31  on which an internal thread is provided. As illustrated, bolts are inserted into the fixing slots  116 ,  116 , and the metal plate  11  is thereby fixed to the antenna holder  30 . 
     The antenna holder  30  is provided with a coil holding block  32  for the resonance point adjusting coil  12 . The coil holding block  32  extends rearward from the rear end of the metal plate holding block  31 . The coil holding block  32  is disposed according to the position of the resonance point adjusting coil  12 . 
     The mount angle of the resonance point adjusting coil  12  to the antenna component  10  in  FIGS. 1 to 5  is 0°. The mount angle of the resonance point adjusting coil  12  is defined as 0° when the direction from the first end of the coil  12  to the second end along the central axis of the resonance point adjusting coil  12  is vertically downward. 
     The angle from 0° in the rearward position is defined as a positive angle. The mount angle is 270° in  FIG. 8A , 180° in  FIG. 9A , 90° in  FIG. 10A , and 270° in  11 A. The configuration in  FIG. 8A  is different from that in  FIG. 11A  in that the resonance point adjusting coil  12  in  FIG. 8A  is disposed under the metal plate  11  whereas the resonance point adjusting coil  12  in  FIG. 11A  is disposed above the metal plate  11 . Although not illustrated in  FIGS. 8 to 11 , the coil holding block  32  (and the entire antenna holder  30  and the antenna cover  50  if required) is disposed according to the position of the resonance point adjusting coil  12 . 
     It should be noted that the metal plate  11  or the resonance point adjusting coil  12  may be appropriately varied so as to be held under the antenna cover  50 . If both the metal plate  11  and the resonance point adjusting coil  12  are held under the antenna cover  50 , the illustrated antenna holder  30  that is disposed under the antenna cover is not necessary. 
     The antenna base  40  has a hole through which a cable extends to the automobile or a protrusion, and is fixed to the mounting face. The gasket  60  is disposed between the antenna base  40  and the mounting face. The lower portion of the antenna cover  50  is fixed to the outer edge of the antenna base  40 . The antenna base  40  and the antenna cover  50  accommodate, for example, the antenna component  10 , the amplifier board  20 , and the antenna holder  30 . 
       FIG. 7A  illustrates a traditional antenna device including a coil  102  connected to an amplifier board  101  at a first end and connected to a capacity hat  103  at a second end. The traditional antenna device is a comparative model. 
     The models in  FIGS. 1 to 4  according to the present invention, the comparative model in  FIG. 7A , and models in  FIGS. 8A, 9A, 10A , and  11 A according to the present invention are simulated. Smith charts are prepared as illustrated in  FIGS. 6, 7B, 8B, 9B, 10B , and  11 B. 
     As apparent from the comparison of the model in  FIG. 7B  with those in  FIGS. 6, 9B, and 10B , the models according to the present invention can more readily match impedances than the comparative model. 
     As apparent from  FIGS. 6, 8B, 9B, 10B, and 11B  illustrating the models according to the present invention, the antenna device  1  can adjust the impedance of the antenna component  10  by the mount angle of the resonance point adjusting coil  12 . 
     In the comparative model in  FIG. 7A , the impedance of the antenna component depends on the capacity hat  103  along the upper edge rather than the coil  102 . The impedance can be adjusted only by a modification of the mount angle of the capacity hat  103 . Since the capacity hat  103  has a large size, the angle cannot be readily modified. In the antenna device  1  according to the present embodiment, the impedance of the antenna component depends on the resonance point adjusting coil  12  at the upper end rather than the metal plate  11 . The modification of the mount angle of the relatively small resonance point adjusting coil  12  enables the impedance to be adjusted. 
     Without limitation to the illustrations, the mount angle of the resonance point adjusting coil  12  can be selected from the range between 0° and 90°, the range between 90° and 180°, the range between 180° and 270°, and the range between 270° and 360°, and the impedance can be finely adjusted. 
     A method for manufacturing the antenna device  1  includes adjusting the mount angle of the resonance point adjusting coil  12  and adjusting the pitch of the resonance point adjusting coil  12 , the number of windings, and the length of the wire according to the mount angle to adjust the impedance of the antenna component  10  to a desired level. 
     After the determination of the position and specification of the resonance point adjusting coil  12 , the antenna holder  30  and the antenna cover  50  are produced and assembled into the antenna device. 
     In accordance with the antenna device  1  according to the present embodiment, the impedance of the antenna component  10  can be adjusted by the modification of the mount angle of the resonance point adjusting coil  12  of the antenna component  10  without a matching circuit. 
     In a traditional antenna device, the input impedance from an amplifier is adjusted by a matching circuit including a resistor in combination with a capacitor and an inductor and is matched with the impedance of the antenna component. In the antenna device  1  according to the present embodiment, the impedance can be adjusted also by the antenna component  10 , and thus the adjustable range of the impedance is wide. The losses caused by the impedance mismatch between the antenna component and the amplifier can be reduced, and a high receiving sensitivity can be achieved. 
     The antenna device  1  according to the present embodiment does not require a matching circuit including a resistor in combination with a capacitor and an inductor on the amplifier board. Thus, the number of components and the production costs can be reduced. 
     In the antenna device  1  according to the present embodiment, the amplifier board  20 , the metal plate  11 , and the coil  12  are connected in sequence, and the impedance can be thereby enhanced compared to the traditional antenna device illustrated in  FIG. 7A  where an amplifier board, a coil, and a capacity hat are connected in sequence. In the antenna device  1  according to the embodiment, the resonance point adjusting coil  12  is soldered with the metal plate  11  at one end, and the connecting bar  114  of the metal plate  11  can be inserted into the connecting terminal  21 . Thus, the assembly of the antenna device  1  is more ready than that of the traditional antenna device. 
     In the present embodiment, the antenna device for AM/FM broadcasting is exemplified. Alternatively, the size of the metal plate  11  and/or the position of the amplifier board  20  are varied, and thereby a composite antenna device can be achieved that includes, for example, a patch antenna, such as SXM antenna or GNSS antenna, and an on-board antenna or a monopole antenna, such as DAB antenna or telecommunication antenna. 
     The antenna device described in the present embodiment is of a shark fin type mounted on a roof. Alternatively, the antenna device according to the present invention can be mounted on, for example, a spoiler, side mirror, wing mirror, or dash board. 
     It should be noted that the amplifier board  20  can be connected to the metal plate  11  without intervention of the connecting terminal to be directly powered. 
     The resonance point adjusting coil may be of a helical type, a zigzagged type, a meander type, or a looped type.