Patent Document

CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on and claims the benefit of priority of Japanese Patent Application No. 2006-38500 filed on Feb. 15, 2006, the disclosure of which is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to an antenna holder for mounting an antenna on a circuit board. 
   BACKGROUND INFORMATION 
   Radio equipment (e.g., keyless receivers) used in, for example, vehicles and dwellings uses radio waves in ranges, such as UHF and VHF bands, of relatively long wavelengths (several tens of centimeters to several meters). In the construction of such radio equipment, the physical size of the radio equipment is governed by the size of an antenna. To reduce the size of radio equipment, therefore, reduction in the size of antennas is unavoidable. 
   As a construction for reducing the size of an antenna, for example, Japanese patent document JP-A-2003-152427 has been disclosed. The antenna disclosed in this patent document includes an internal conductor linearly extended and an external coiled conductor closely wound at a distance from the internal conductor with the internal conductor at the center of winding. The antenna is so constructed that it resonates at a specific frequency. Thus, the antenna is provided with a relatively high gain and further small and simple construction. 
   In case of this construction, the internal conductor is linearly extended, which limits antenna size reduction. The following case will be taken as an example. To reduce the size of radio equipment, the outer size of an antenna is reduced in the direction orthogonal to the direction of extension of the internal conductor. In this case, it is required to lengthen at least either of the internal conductor and the external coiled conductor to ensure an electrical length for resonance. Since the internal conductor is linear, however, the height of the antenna is significantly increased. 
   Meanwhile, the present applicants filed an application for Japanese patent regarding a following antenna structure under application No. JP-2005-188513 (Corresponding US publication No. US2006290590). In the disclosure of the application No. JP-2005-188513, the antenna is so constructed that using two elements, one as a signal wire and the other as a ground wire, an internal element is disposed inside a spirally extended external element at a distance between them. The internal element is in such a shape that it is spirally extended in the direction of the axis of the external element. By forming the internal element in a spiral shape as mentioned above, the band can be narrowed and the gain of the antenna can be enhanced. With substantially the same antenna gain, therefore, the antenna can be reduced in physical size more than antennas having a linear internal element can. 
   The above-mentioned antenna is so constructed that the following is implemented: an internal element is disposed inside a spirally extended external element with a predetermined distance between them; either of the two elements is used as a signal wire and the other is used as a ground wire. This type of antennas is antennas of so-called dipole structure, and the positional relationship between the two elements is important to the performance (resonance characteristic) of the dipole antennas. For example, when the distance is varied, the resonance frequency is varied and this has influence on the radiation characteristic. Further, a component in the direction perpendicular to the circuit board also has influence to the radiation characteristic. Therefore, when the inclination of an element to the circuit board is varied, the radiation characteristic is influenced. 
   However, in cases where two elements are separately mounted on a circuit board so that one end of each element is electrically connected with the wiring provided on the circuit board, problems arise. It takes much time and trouble to mount them, and further it is difficult to bring the two elements into desired positional relationship when they are mounted. Even if desired positional relationship can be obtained, it is difficult to hold the antenna in the desired positional relationship because of vibration produced in a use environment (e.g., in a vehicle-mounted environment). 
   SUMMARY OF THE INVENTION 
   In view of the above-described and other problems, the present disclosure provides an antenna holder that makes it possible to maintain the performance of an antenna and enhance the easiness of mounting it on a circuit board with respect to antennas of such construction that an internal element is disposed inside a spirally extended external element at a distance between them. 
   In an aspect of the present disclosure, the antenna holder includes a spacer for maintaining the predetermined distance between the external element and the internal element and an external tilt suppressor for suppressing a tilt of the external element from a direction being orthogonal to the circuit board. The antenna holder of interest in the present disclosure holds, for example, an antenna that includes signal wiring and ground wiring being disposed on a single circuit board as either one of an external element and an internal element respectively with one end electrically coupled with a circuit on the single circuit board for serving as the external element in a spiral shape and the internal element inside of the external element at a predetermined distance. In this manner, the antenna holder can hold the antenna with the distance between the two elements kept at a predetermined length when it holds the antenna in the course of installation on the circuit board and thereafter. Further, the antenna holder can maintain the distance at the predetermined length and can prevent the antenna to be out of a predetermined position even when the antenna is exposed to disturbance such as vibration or the like. Therefore, the performance of the antenna can be appropriately maintained. 
   In addition, a spacer and an external inclination suppressor are integrally formed with the antenna holder, thereby enabling an improved workability in terms of installation of the antenna on the circuit board. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which: 
       FIGS. 1A and 1B  show illustrations of an antenna to be held by an antenna holder described in the present disclosure; 
       FIG. 2  shows a perspective view of the antenna holder in a first embodiment of the present disclosure; 
       FIGS. 3A and 3B  show illustrations of the antenna holder that holds the antenna in an installation state on an antenna circuit board; and 
       FIGS. 4A and 4B  show illustrations of the antenna holder that holds the antenna in an installation state on an antenna circuit board in a second embodiment of the present disclosure. 
   

   DETAILED DESCRIPTION 
   Hereafter, description will be given to embodiments of the invention with reference to the drawings. In the following description of embodiments, the following cases will be taken as an example: cases where of two elements that construct an antenna, the internal element disposed inside the spirally extended external element at a distance between them is in such a shape that it is spirally extended in the direction of the axis of the external element. 
   First Embodiment 
     FIGS. 1A and 1B  are drawings illustrating a schematic configuration of an antenna held by an antenna holder in this embodiment.  FIG. 1A  is a perspective view, and  FIG. 1B  is a side view.  FIGS. 1A and 1B  show the antenna as is not held by an antenna holder in the present embodiment and is mounted on a circuit board. 
   With such a construction that radio waves in ranges, such as UHF and VHF bands, of relatively long wavelengths (several tens of centimeters to several meters) are used as in radio equipment (e.g. keyless receivers) used in vehicles, dwelling, or the like, the physical size of the radio equipment is governed by the size of antennas. An antenna  100  shown in  FIGS. 1A and 1B  is so constructed that using two elements, one as a signal wire and the other as a ground wire, an internal element  120  is disposed inside the spirally extended external element  110  at a distance between them. The internal element  120  is formed in such a shape that it is spirally extended in the direction of the axis of an external element  110 . By forming the internal element  120  in a spiral shape as mentioned above, the band can be narrowed and the gain of the antenna can be enhanced. With substantially the same antenna gain, therefore, the antenna can be reduced in physical size more than the antenna  100  having a liner internal element  120 . In this manner, the physical size of radio equipment can be reduced. Refer to Japanese patent application No. JP-2005-188513 for technical detail of the size reduction. 
   In an antenna  100  of so-called dipole structure in which an internal element  120  is disposed inside a spirally extended external element  110  at a distance between them as illustrated in  FIGS. 1A and 1B , the positional relation between the two elements  110 ,  120  is indispensable to the performance (resonance characteristic) of the antenna  100 . For example, when a distance D 3  between the opposite areas of the two elements  110 ,  120  is varied, the capacitance of a capacitor formed between the opposite areas of the two elements  110 ,  120  is varied. Therefore, the resonance frequency is varied, and the radiation characteristic is influenced. Further, a component in the direction perpendicular to a circuit board  10  contributes to the radiation characteristic. Therefore, when the inclination of an element  110 ,  120  in the direction perpendicular to the circuit board  10  is varied, the distance between the opposite areas of the elements  110 ,  120  (in the direction of height) is varied. (That is, when heights L 1 , L 2  of an element  110 ,  120  from the board surface is varied, the distance between the opposite areas of the elements  110 ,  120  (in the direction of height) is varied.) As a result, the radiation characteristic is influenced. 
   In cases where an antenna  100  is directly mounted on the circuit board  10  provided with an amplifier circuit or the like, the measures illustrated in  FIGS. 1A and 1B , for example, are taken. That is, ends of the two elements  110 ,  120  on one side are inserted into through holes formed in the circuit board  10 , and electrically connected with wirings (lands), not shown, provided on the back surface opposite the surface of the circuit board  10  where the antenna is disposed through solder. Therefore, the two elements  110 ,  120  must be individually mounted on the circuit board  10 , and it is difficult to bring the two elements  110 ,  120  into desired positional relation when they are mounted. (That is, it is difficult to set the distance D 3  to a predetermined value and to ensure the perpendicularity of (the central axis of) each of the elements  110 ,  120  to the circuit board  10 .) Especially, since the two elements  110 ,  120  are both spiral, it is difficult to bring them into desired positional relation. In  FIG. 1B , numeral  130  denotes a feeding point, or contact with wiring, at an end of the internal element  120 , and numeral  131  denotes a ground point, or contact with wiring, at an end of the external element  110 . Actually, the feeding point  130  and the ground point  131  are periodically switched by a high-frequency current passed through both the elements  110 ,  120 . The drawings show the numerals as are fixed for the sake of convenience. 
   Each element  110 ,  120  is fixed on the circuit board  10  only at one end thereof (feeding point  130 , ground point  131 ). Therefore, even if desired positional relation is obtained when they are mounted, the elements  110 ,  120  are prone to have runout because of vibration produced in a use environment (e.g. in a vehicle-mounted environment). That is, it is difficult to hold the two elements  110 ,  120  in desired positional relation in a use environment. 
   Since the two elements  110 ,  120  must be individually mounted on the circuit board  10 , a number of man-hours required for mounting is increased. 
   Meanwhile, an antenna holder in this embodiment brings the following advantage when an antenna  100  so constructed that an internal element  120  is disposed inside a spirally extended external element  110  at a distance between them is mounted on a circuit board  10 : the performance of the antenna  100  is maintained, and the easiness of mounting it on the circuit board  10  is enhanced.  FIG. 2  is a perspective view illustrating the schematic configuration of an antenna holder in this embodiment.  FIGS. 3A and 3A  are drawings illustrating a structure in which an antenna  100  is mounted on a circuit board  10 .  FIG. 3A  is a side view, and  FIG. 3B  is a sectional view. 
   The antenna  100  held by the antenna holder in this embodiment is an antenna  100  so constructed as illustrated in  FIGS. 1A and 1B . More specific description will be given. An external element  110  and an internal element  120  are both constructed using a wire 1.2 mm in diameter. With the height from the board surface set to a predetermined value L 1  (=L 2 ), the external element and the internal element are wound as follows. The external element  10  is plurally wound (e.g. six turns) with a predetermined inside diameter D 1  (e.g. 14 mm) and a predetermined pitch P 1  (e.g. 3 mm) so that an electrical length (half wavelength) for resonance at a predetermined frequency is ensured. The internal element  120  is also plurally wound (e.g. nine turns) with a predetermined inside diameter D 2  (e.g., 1.5 mm) smaller than D 1  and a predetermined pitch P 2  (e.g., 1.3 mm). 
   As illustrated in  FIG. 2  and  FIGS. 3A and 3B , an antenna holder  200  includes at least the following: a distance maintaining section  210  that keeps the opposition distance D 3  between the external element  110  and the internal element  120  at a predetermined value; and an external inclination suppressing section  220  that suppresses the inclination of the central axis of the external element  110  in the direction orthogonal to the surface of the circuit board  10 . 
   Any material can be adopted as the material for constructing the antenna holder  200  as long as it is an electrical insulation material. A material whose relative dielectric constant is as small as possible (the resulting wavelength shortening effect is small) and whose dielectric dissipation factor, which has influence on the antenna performance, is small is more desirable. In this embodiment, the antenna holder is integrally molded using a synthetic resin whose relative dielectric constant is 3 or so. 
   The distance maintaining section  210  is constructed of an external fitting portion  211  and an internal fitting portion  212  disposed on one surface of a flat (disk shape in this embodiment) base portion  201  at a predetermined distance between them. The external fitting portion  211  is fit to part of the spiral of the external element  110 , and the internal fitting portion  212  is fit to part of the spiral of the internal element  120 . For example, the external fitting portion  211  is formed by providing a protruded portion  211   a  formed on the base portion  201  with a groove portion  211   b  in line with the spiral of the corresponding external element  110 . The groove portion  211   b  is so formed that the width (corresponding to the diameter of the external element  110 ) of the opening (upper part) for inserting the external element  110  is slightly smaller than the diameter of the external element  110  as illustrated in  FIG. 2  and  FIG. 3B . At the same time, the groove portion is so formed that the size of its lower part communicating with the insertion opening is substantially equal to or slightly larger than the diameter of the external element  110 . The groove portion  211   b  is provided at a predetermined height from the board surface according to the position in which the external element  110  should be held. For example, by applying a little stress to the external element  110 , the external element  110  is fit into the groove portion  211   b , and thus the external element  110  can be positioned at a predetermined height from the board surface. 
   The internal fitting portion  212  is different only in element  120  to be fit in it, and has the same construction as the external fitting portion  212 . The opposition distance between the external fitting portion  211  and the internal fitting portion  212  is set to a predetermined value at which the antenna can offer a desired antenna characteristic (resonance characteristic). Therefore, when elements  110 ,  120  are fit to the corresponding fitting portions  211 ,  212 , the distance D 3  between the opposite areas of the external element  110  and the internal element  120  can be set to a predetermined value. Also, after the elements are fit, the distance D 3  can be maintained by the fitting portions  211 ,  212 . 
   In this embodiment, three external fitting portions  211  and one internal fitting portion  212  are provided. Provision of multiple fitting portions makes it possible to hold the corresponding element  110  ( 120 ) in different positions in the direction of height from the circuit board  10 . This also contributes to the maintenance of perpendicularity to the circuit board  10 , and the perpendicularity can also be maintained depending on disposition (the distance maintaining section  210  also functions as, for example, the external inclination suppressing section  220 ). However, there is no special limitation on the number of fitting portions  211 ,  212 . With respect to each kind of fitting portion, one or more fitting portions only have to be provided. Also, the configuration of each fitting portion  211 ,  212  is not limited to the foregoing. 
   The external inclination suppressing section  220  is so constructed that the following is implemented: it is protruded from the distance maintaining section formation surface of the base portion  201 ; and it is in contact with the spiral inner circumferential portion or spiral outer circumferential portion of the external element  110  throughout a predetermined range in the direction orthogonal to the circuit board (the direction of height from the surface of the circuit board). In this embodiment, the external inclination suppressing section  220  is so constructed that it includes the following: an annular portion  221  that has a predetermined height from the base portion  201  and the outer circumferential surface of which is in contact with the spiral inner circumferential portion of the external element  110  (that is, the diameter of the outer circumferential surface of which is equal to the inside diameter D 1  of the external element  110 ); and a connecting groove  222  that is provided in the annular portion  221  and connects an inner radius area in which the internal element  120  is disposed and an outer radius area in which the external element  110  is disposed. However, the external inclination suppressing section  220  may be constructed without the connecting groove  222  (with only the annular portion  221  provided). 
   The larger the range (contact length) of contact with the external element  110  in the direction of height is, the more the external inclination suppressing section  220  can suppress the inclination (runout) of the central axis of the external element  110  due to vibration or the like. As mentioned above, however, the relative dielectric constant of a material that constructs the antenna holder  200  has influence on the antenna performance. Specifically, depending on relative dielectric constant, the wavelength of a high-frequency current passed through the external element  110  is shortened and the resonance frequency is shifted to a low value. To return the shifted resonance frequency to a high value, it is required to cut the external element  110  to shorten its overall length. In this case, the electrical length (component perpendicular to the circuit board  10 ) is shortened, and this results in a degraded radiation characteristic. Therefore, it is desirable that the height of the external inclination suppressing section  220  from the base portion  201  should be ⅓ or so of the height L 1  of the external element  110  from the board surface from both the viewpoints of vibration suppression and antenna performance. In this embodiment, the height of the external inclination suppressing section  220  from the base portion  201  is set to ⅓ or so of the height L 1 . 
   In addition to the above-mentioned distance maintaining section  210  and external inclination suppressing section  220 , the antenna holder  200  in this embodiment includes the following: an internal inclination suppressing section  230  that suppresses the inclination of the central axis of the internal element  120  in the direction orthogonal to the surface of the circuit board  10 ; and a connecting position defining section  240  that defines the positional relation between the ends (feeding point  130  and ground point  131 ) of the two elements  110 ,  120  to be connected with the wirings. 
   The internal inclination suppressing section  230  is so formed that the following is implemented: it is protruded from the external inclination suppressing section formation surface of the base portion  201 ; and it is in contact with the internal element  120  throughout a predetermined range in the direction orthogonal to the circuit board  10  (the direction of height from the surface of the circuit board). In this embodiment, the internal inclination suppressing section  230  is formed in a columnar shape so that the following is implemented: it has a predetermined height from the base portion  201 ; and its outer circumferential surface is in contact with the spiral inner circumferential portion of the internal element  120  (that is, the diameter of its outer circumferential surface is substantially equal to the inside diameter D 2  of the internal element  120 ). Further, the internal inclination suppressing section  230  is so formed that the center of the column that constructs it agrees with the center of the above-mentioned annular portion  221  that constructs the external inclination suppressing section  220  in the direction of the plane of the circuit board  10 . That is, when the elements  110 ,  120  are assembled to the antenna holder  200 , the central axis of the external element  110  agrees with the central axis of the internal element  120 . 
   The internal element  120  is disposed inside the spirally extended external element  110  at a predetermined distance between them. For this reason, the internal element  120  is less prone to have an inclination (runout) in the direction orthogonal to the surface of the circuit board due to vibration or the like as compared with the external element  110 . Therefore, the internal inclination suppressing section  230  is not an element indispensable to the antenna holder  200 . However, provision of the internal inclination suppressing section  230  makes it possible to suppress the inclination of the internal element  120  without fail because it is in contact with the circuit board  10  only at one end (e.g., feeding point  130 ). In cases where the shape of the internal element  120  is spiral, an inclination (runout) is especially prone to occur as compared with linear internal elements, as described above in relation to this embodiment. Therefore, it is desirable that the antenna holder should be so constructed that it also includes the internal inclination suppressing section  230 . 
   Also, with respect to the internal inclination suppressing section  230 , the larger the range (contact length) of contact with the internal element  120  in the direction of height is, the more it can suppress the inclination (runout) of the central axis of the internal element  120  due to vibration or the like. From both the viewpoints of vibration suppression and antenna performance, however, it is desirable that the following measure should be taken as with the external inclination suppressing section  220 : the height of the internal inclination suppressing section  230  from the base portion  201  is set to ⅓ or so of the height L 2  of the internal element  120  from the board surface. In this embodiment, the height of the internal inclination suppressing section  230  from the base portion  201  is set to ⅓ or so of the height L 2 . 
   The connecting position defining section  240  is a section that defines the positions of one ends of the two elements  110 ,  120  (feeding point  130  and ground point  131 ) so that they are respectively connected with the corresponding wirings. In this embodiment, an external through hole  241  and an internal through hole  242  are formed in the base portion  201 , and these through holes  241 ,  242  are taken as the connecting position defining section  240 . 
   The following is an example of the procedure for mounting an antenna  100  on a circuit board  10  using an antenna holder  200  constructed as mentioned above. Each of the elements  110 ,  120  is so constructed that its predetermined area extended from the end on the side where it is mounted on the circuit board  10  is linear and the remaining area is spiral. The antenna  100  is assembled to the antenna holder  200  in advance. 
   First, the spiral inner circumferential portion of the internal element  120  is guided along the outer circumferential surface of the internal inclination suppressing section  230 . While this is being done, the end of the internal element  120  to be connected with the wiring of the circuit board  10  as an insertion end is inserted into the internal through hole  242  formed in the base portion  201 . The internal element  120  is inserted until its spiral portion is brought into contact with the surface (external inclination suppressing section formation surface) of the base portion  201 . The length of the linear portion of the internal element  120 , the thickness of the circuit board  10 , and the thickness of the base portion  201  are preset so that the following is implemented: when the antenna is assembled to the circuit board  10  as described later with the spiral portion of the internal element in contact with the surface of the base portion  201 , the end of the internal element  120  is exposed in the back surface of the circuit board  10 . Thus, the end of the internal element can be connected with the wiring by solder. 
   Part of the spiral portion of the internal element  120  is fit to the internal fitting portion  212  by pressure arising from this inserting operation. This completes the assembling of the internal element  120  to the antenna holder  200 . In this state, the spiral inner circumferential portion of the internal element  120  is in contact with the outer circumferential surface of the internal inclination suppressing section  230 . Further, (the central axis of) the internal element  120  is held substantially perpendicular to the surface of the base portion  201 . 
   Next, the spiral inner circumferential portion of the external element  110  is guided along the outer circumferential surface of the external inclination suppressing section  220 . While this is being done, the end of the external element  110  to be connected with the wiring of the circuit board  10  as an insertion end is inserted into the external through hole  241  formed in the base portion  201 . The external element  110  is inserted until its spiral portion is brought into contact with the surface (external inclination suppressing section formation surface) of the base portion  201 . The length of the linear portion of the external element  110 , the thickness of the circuit board  10 , and the thickness of the base portion  201  are preset so that the following is implemented: when the antenna is assembled to the circuit board  10  as described later with the spiral portion of the external element in contact with the surface of the base portion  201 , the end of the external element  110  is exposed in the back surface of the circuit board  10 . Thus, the end of the external element can be connected with the wiring by solder. 
   Part of the spiral portion of the external element  110  is fit to the external fitting portion  211  by pressure arising from this inserting operation. This completes the assembling of the external element  110  to the antenna holder  200 , that is, the assembling of the antenna  100  to the antenna holder  200 . In this state, the spiral inner circumferential portion of the external element  110  is in contact with the outer circumferential surface of the external inclination suppressing section  220 . Further, (the central axis of) the external element  110  is held substantially perpendicular to the surface of the base portion  201 . The external element  110  is fit to the external fitting portion  211  and the internal element  120  is fit to the internal fitting portion  212 , and the distance D 3  between the opposite areas of the two elements  110 ,  120  is kept at a predetermined value. 
   The antenna  100  constructed of the two elements  110 ,  120  assembled into one by the antenna holder  200  is mounted on the circuit board  10  in whole. Specifically, the ends exposed from the base portion  201  are inserted into the corresponding through holes in the circuit board  10  until the back surface of the base portion  210  is brought into contact with the surface of the circuit board  10 . When the back surface of the base portion  201  is in contact with the surface of the circuit board  10 , the ends (feeding point  130 , ground point  131 ) of the individual elements  110 ,  120  are exposed in the back surface of the circuit board  10  opposite the antenna holder mounting surface. The exposed ends and the wirings (lands) provided on the surface of the circuit board around the through holes are joined with each other by solder. This completes the mounting of the antenna  100  on the circuit board  10 . In this mounting state, the central axes of the spirals of the two elements  110 ,  120  are held substantially perpendicular to the surface of the circuit board  10  by the external inclination suppressing section  220  and the internal inclination suppressing section  230 . Further, the distance D 3  between the opposite areas of the two elements  110 ,  120  is kept at a predetermined value by the external fitting portion  211  and the internal fitting portion  212 . 
   According to the invention, as mentioned above, the following is implemented: the antenna  100  can be mounted on the circuit board  10  with the distance D 3  between the two elements  110 ,  120  kept at a predetermined value by the external fitting portion  211  and internal fitting portion  212  that construct the distance maintaining section  210 ; and also after the antenna is mounted, the distance D 3  can be kept at a predetermined value. Further, the antenna  100  can be mounted on the circuit board  10  so that the central axis of the external element  110  is substantially perpendicular to the surface of the circuit board, by the external inclination suppressing section  220 . Also after the antenna is mounted, the perpendicularity can be maintained. Therefore, with the antenna  100  mounted on the circuit board  10 , the two elements  110 ,  120  can be held in desired positional relation. In other words, the certain performance of the antenna can be maintained. 
   Further, it is possible to assemble the antenna  100  constructed of the two elements  110 ,  120  into one by the antenna holder  200 , and to mount the assembly on the circuit board  10  in whole. In other words, the easiness of mounting the antenna  100  on the circuit board  10  can be enhanced. 
   In this embodiment, further, it is possible to mount the antenna  100  on the circuit board  10  so that the central axis of the internal element  120  is substantially perpendicular to the surface of the circuit board, by the internal inclination suppressing section  230 . Also after the antenna is mounted, the perpendicularity can be maintained. Therefore, the certain performance of the antenna can be more reliably maintained. 
   In this embodiment, the positional relation between the ends to be connected with the wirings of the circuit board  10  can be reliably defined by the external through hole  241  and internal through hole  242  that construct the connecting position defining section  240 . Therefore, the easiness of mounting the antenna  100  on the circuit board  10  can be further enhanced. 
   In the description of this embodiment, a case where the antenna holder  200  is disposed in proximity to the ends of the two elements  110 ,  120  to be electrically connected with the wirings of the circuit board  10  has been taken as an example. In an area closer to the joints (feeding point  130 , ground point  131 ) between the ends of the two elements  110 ,  120  and the wirings provided on the circuit board  10 , a more intensive current is passed through the elements  110 ,  120 . Such an area is low in impedance and is electrically stable. That is, though the antenna holder  200  is so constructed that the inclination suppressing sections  220 ,  230  are in contact with the corresponding elements  110 ,  120  throughout a predetermined range in the direction orthogonal to the circuit board  10 , the relative dielectric constant of the holder  200  has less influence on the resonance frequency. With an identical resonance frequency, therefore, the electrical length (e.g., the number of turns of the external element  110 ) of the elements  110 ,  120  can be accordingly earned, and an inductance component that contributes to radiation can be ensured. 
   In the description of this embodiment, a case where the base portion  201  is disposed on the circuit board  10  has been taken as an example. Therefore, when the antenna is mounted, the inclination of the elements  110 ,  120  can be more reliably suppressed than in such a mounting structure that the antenna holder  200  is lifted from the circuit board  10 . In addition to disposing the base portion  201  on the surface of the circuit board  10  in contact, it may be secured using, for example, adhesive. Thus, it is possible to reduce the stress that acts on the joints (feeding point  130 , ground point  131 ) between the ends of the elements  110 ,  120  and the wirings. That is, the reliability of connection can be enhanced. 
   In the description of this embodiment, a case where the inclination suppressing sections  220 ,  230  are so constructed that the central axis of the internal element  120  agrees with the central axis of the external element  110  has been taken as an example. When the antenna is mounted, in this case, the opposite area of the internal element  120  and that of the external element  110  are equal to each other in height in the axial direction when the internal element  120  is positioned in the center; therefore, the antenna gain can be increased. Instead, the external element  110  and the internal element  120  may be disposed with the central axis of the internal element  120  misaligned from the central axis of the external element  110  to the extent that the antenna gain is not significantly reduced. Even to this construction, the antenna holder  200  described in this embodiment can be applied. 
   In the description of this embodiment, a case where the internal element  120  is assembled to the antenna holder  200  before the external element  110  is assembled has been taken as an example. Instead, the internal element  120  may be assembled after the external element  110  is assembled, or they may be simultaneously assembled. 
   Second Embodiment 
   Description will be given to a second embodiment of the invention with reference to  FIGS. 4A and 4B .  FIGS. 4A and 4B  are drawings illustrating a structure in which an antenna  100  in a second embodiment of the invention is mounted on a circuit board  10 .  FIG. 4A  is a side view, and  FIG. 4B  is a sectional view. 
   There are many commonalities between an antenna holder  200  in the second embodiment and the antenna holder  200  described in relation to the first embodiment. Therefore, the detailed description of the commonalities will be omitted below, and description will be given mainly to differences. 
   In this embodiment, as illustrated in  FIGS. 4A and 4B , the antenna holder  200  described in relation to the first embodiment is so disposed that it holds the ends of the two elements  110 ,  120  on the side where they are not connected with the wirings of the circuit board  10 . That is, the antenna holder in this embodiment holds the antenna  100  in such a state that the antenna is lifted from the circuit board  10 . 
   Unlike the two elements  110 ,  120  described in relation to the first embodiment, the two elements  110 ,  120  in this embodiment are so constructed that the following is implemented: not only their predetermined areas extended from the ends on the side where they are connected with the wirings of the circuit board  10  are linear. But also their predetermined areas extended from the ends on the side where they are not connected with the wirings are constructed as linear portions  111 ,  121  as illustrated in  FIG. 4B . The remaining areas are constructed as spiral portions  112 ,  122  as illustrated in the same drawing. 
   The assembling of the antenna  100  to the antenna holder  20  is different from that in the first embodiment in the following: the end of each element on the side where it is not connected with the corresponding wiring is inserted as an insertion end into an external through hole  241  (internal through hole  242 ) formed in a base portion  201 . The end of each element is inserted until its spiral portion is brought into contact with the surface (external inclination suppressing section formation surface) of the base portion  201 . Then, the antenna  100  constructed of the two elements  110 ,  120  assembled into one by the antenna holder  200  is mounted on the circuit board  10  in whole. Specifically, the ends that are not held by the antenna holder  200 , on the side where the elements are connected with the wirings are respectively inserted into corresponding through holes formed in the circuit board  10 . The antenna holder is so constructed that when the spiral portions  112 ,  122  are inserted and brought into contact with the surface of the circuit board  10 , the individual ends are exposed in the back surface of the circuit board  10 . The spiral portions  112 ,  122  of the two elements  110 ,  120  are substantially perpendicular to the linear portions  111 ,  121  at their portions bent from the linear portions  111 ,  121  inserted into the through holes in the circuit board  10 . Therefore, by bringing the spiral portions  112 ,  122  into contact with the surface of the circuit board  10 , the perpendicularity of the antenna  100  to the circuit board  10  can be ensured. With the perpendicularity ensured, the ends exposed in the back surface of the circuit board  10  and the wirings (lands) provided on the surface of the circuit board around the through holes are joined with each other by solder. 
   Also, with the construction in this embodiment, as mentioned above, the same or similar effect as with the construction described in relation to the first embodiment can be expected. 
   In the description of this embodiment, a case where the two elements  110 ,  120  are held by the antenna holder  200  in proximity to their ends that are not connected with the wirings of the circuit board  10  has been taken as an example. Instead, the antenna holder  200  may be so constructed that the two elements  110 ,  120  are held in their intermediate areas. 
   Although the present invention has been fully described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. 
   For example, the internal element  120  may be in a linear shape or other shape instead of the spiral shape. The distance maintaining section  210  (the internal fitting portion  212 ) and the internal inclination suppressing section  230  may accordingly be formed. That is, the internal element  120  having the linear shape may be supported at its external surface by a part that serves as the internal inclination suppressing section  230 , and the same part may serve as the external inclination suppressing section  210  by supporting the spiral inner circumferential portion of the external element  110  with its external surface. 
   Further, the internal inclination suppressing section  230  may be in contact with the spiral external circumferential portion of the internal element  120  instead of the spiral internal circumferential portion thereof for suppressing the runout of the internal element  120 . 
   Furthermore, the external inclination suppressing section  220  may be in contact with the spiral external circumferential portion of the external element  110  instead of the spiral internal circumferential portion thereof for suppressing the runout of the external element  110 . 
   Furthermore, the total electrical length of the external element  110  and the internal element  120  may be different from the half wavelength of the radio wave in use. That is, the total electrical length may be a length that can resonate with the radio wave in use. 
   Furthermore, the external element  110  and the internal element  120  may have different height as opposed to the case shown in the above embodiment. 
   Furthermore, the antenna  100  may be applied to a different apparatus such as a transmitter or the like beside being applicable to the keyless receiver. 
   Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.

Technology Category: 5