Abstract:
A hinge portion is formed on the base portion. An antenna portion is attached to the hinge portion so as to be pivotable thereabout. The hinge portion includes a hinge base having a first shaft formed on one end thereof, a second shaft formed on the other end thereof, and a first protrusion formed on an outer periphery of the second shaft, and a hinge bush rotatably mounted on the first shaft and engaged with the antenna portion. The antenna portion is formed with a hole surrounding the outer periphery of the second shaft. A projection is formed on an inner periphery of the hole. The first protrusion is brought into contact with the projection when the antenna portion is pivoted so as to define a predetermined angle with respect to the base portion.

Description:
[0001]     The disclosure of Japanese Patent Application Nos. 2006-0009362 filed Jan. 18, 2006, 2006-009382 filed Jan. 18, 2006, and 2006-009434 filed Jan. 18, 2006, including specifications, drawings and claims is incorporated herein by reference in their entirety.  
       BACKGROUND  
       [0002]     The present invention relates to an antenna device operable to receive an electric wave of digital radio broadcasting.  
         [0003]     A digital radio receiver which is operable to receive a satellite wave or ground wave and allows a person to hear digital radio broadcasting has been developed, and has been put to practical use in United States. The digital radio receiver can be mounted on a mobile station, such as a vehicle, or can be installed inside a building to receive an electric wave the frequency band of which is about 2.3 GHz and to allow a person to hear the radio broadcasting. Since the frequency of the received electric wave is about 2.3 GHz, a received wavelength (resonant wavelength) λ is about 128.3 mm. In addition, once the satellite wave is received at the earth station, the frequency thereof is shifted a little and is retransmitted as a linearly polarized wave that is the ground wave.  
         [0004]     Since an electric wave having a frequency band of about 2.3 GHz is used in the digital radio broadcasting, it is preferable that an antenna device receiving the electric wave is installed outdoors. Therefore, when the digital radio receiver is mounted on a vehicle or the like, it is provided, for example, in the outside of the vehicle such as a roof thereof in many cases. On the other hand, when the digital radio receiver is used inside a building, the antenna device is installed in a roof, a balcony or the like in many cases.  
         [0005]     Here, the directional sensitivity of this type of antenna device is omni-directional. However, in order to ensure the best sensitivity, the antenna device is required to be constructed such that the wave angle of the antenna device is adjusted to avoid an electric wave shielding object. The related-art antenna device for home use which has an angle adjustment function is disclosed in, for example, Japanese Patent Publication No. 2004-289514A. The related-art antenna device disclosed in Japanese Patent Publication No. 2004-289514A includes a base portion, and an antenna portion the angle of which is adjustable with respect to the base portion via a hinge portion. The hinge portion has a hinge base, two hinge bushes, two coil springs, two washer, and two screws. The hinge base is formed on an end of a ceiling surface of the base case of the base portion, and has two tapered shafts protruding from both ends of the hinge base, respectively. Each of the hinge bushes has a tapered inner peripheral surface and is fitted into each of the shafts of the hinge base. The coil spring is fitted into each of the shafts on which the hinge bush is mounted. A screw is fastened via the washer to an end surface of each of the shafts on which the hinge bush and the coil spring are mounted. The biasing force of the spring generates a frictional force between the outer peripheral surface of the shaft of the hinge base and the inner peripheral surface of the hinge bush when the hinge bush rotates. The antenna portion is joined to the hinge bush and is capable of being opened and closed at an arbitrary angle relative to the base portion. The frictional force between the shaft of the hinge base and the hinge bush causes the antenna device to be fixed at a constant angle without rotation when an external force is not applied thereto. On the other hand, when an external force larger than the frictional force between the shaft of the hinge base and the hinge bush is applied to the antenna portion, the antenna portion rotates, and can be adjusted to an arbitrary angle. The angle adjustment is performed as follows, for example. A user manually adjusts the angle of the antenna portion such that the best level of a broadcasting signal or the best sound quality of audio information received by a digital radio receiver is maintained, while confirming the level or the sound quality.  
         [0006]     As described above, in the related-art antenna device including the example described in Japanese Patent Publication No. 2004-289514A, the number of the hinge bush, the coil spring, the washer, and the screw is two, respectively. For this reason, it is disadvantageous in decreasing the size and the weight of the antenna device. Also, since the cost of parts is high and since a number of manufacturing processes are required, it is disadvantageous the decreasing the cost thereof.  
         [0007]     A satellite wave, especially a circularly polarized wave is used for digital radio broadcasting. As disclosed in Japanese Patent Publication No. 2005-20644A, an related-art antenna device including an antenna module corresponding to the circularly polarized wave has a ground plate, an antenna plate disposed to face the ground plate at a distance therefrom, an antenna probe disposed between the ground plate and the antenna plate, and a probe holder made of resin for holding the antenna probe. The probe holder is formed with a groove portion in which the antenna probe is to be disposed. A member made of an insulating material, such as a tape, for electrically insulating the antenna probe and the antenna plate is attached onto the ceiling surface of the probe holder in which the antenna probe is to be disposed.  
         [0008]     For the purpose of realizing miniaturization, lightness, reliability, and cost reduction of the antenna device including the related-art antenna device disclosed Japanese Patent Publication No. 2005-20644A, it is effective to realize miniaturization, lightness, reliability, and cost reduction of the antenna module. Specifically, it is considered that, for example, the ground plate and the antenna plate is miniaturized. However, in a case where the ground plate and the antenna plate are miniaturized, there is a possibility that an electrostatic capacitance of the antenna module, which is required for the antenna device to exhibit a sufficient gain, may decrease.  
         [0009]     An antenna device used for a GPS (global positioning system) using a satellite wave similarly to a digital radio broadcasting system, particularly an antenna device suitable for being installed on a roof of a vehicle is disclosed in Japanese Patent Publication No. 2005-109688A. The related-art antenna device disclosed in Japanese Patent Publication No. 2005-109688A includes a top cover, a bottom cover, an antenna module, a packing member, and a signal line. Since the packing member is disposed in a connecting portion between the bottom plate and the top plate to ensure adherence therebetween to perform a water-proof function, it is also called as a water-proof packing. The packing member has a generally angular-shaped plate part including a wide angular-shaped frame part and a bush part covering the periphery of the signal line in the position of a cut-out portion formed in the top cover. Since the frame part and the bush part are integrally formed with each other, the number of parts and manufacturing processes is small compared to a case in which the both members are separately formed. The water-proof function is realized as follows. A water-proof rib having an angular and frame shape is formed inside the top cover to correspond to the angular-shaped frame part of the plate part of the packing member. The-packing member and the bottom plate are fastened to the top cover with a plurality of screws. The fastening pressure at this time causes the leading end of the water-proof rib of the top cover to be pressed against the angular-shaped frame part of the packing member, thereby realizing the water-proof function.  
         [0010]     As described above, in the antenna device including the related-art antenna device disclosed in Japanese Patent Publication No. 2005-109688A, when the fastening pressures by the plurality of screws are different from one another or the fastening pressures by the screws are too large, there is a possibility that a gap may be formed between the water-proof rib formed in the top cover and the packing member. As a result, there is a possibility that the water-proof property realized by the packing member may deteriorate.  
       SUMMARY  
       [0011]     It is therefore an object of the present invention to provide an antenna device which is small in size and light in weight, and which is low in cost because the cost of parts and the number of manufacturing processes is small.  
         [0012]     It is also an object of the invention to provide an antenna device which is small in size, light in weight and low in cost, while the antenna device can exhibit a high gain.  
         [0013]     It is also an object of the invention to provide an antenna device having an excellent water-proof property.  
         [0014]     In order to achieve the above described objects, according to the invention, there is provided an antenna device, comprising:  
         [0015]     a base portion;  
         [0016]     a hinge portion formed on the base portion;  
         [0017]     an antenna portion attached to the hinge portion so as to be pivotable thereabout, wherein:  
         [0018]     the hinge portion includes: 
        a hinge base having a first shaft formed on one end thereof, a second shaft formed on the other end thereof, and a first protrusion formed on an outer periphery of the second shaft; and     a hinge bush rotatably mounted on the first shaft and engaged with the antenna portion;        
 
         [0021]     the antenna portion is formed with a hole surrounding the outer periphery of the second shaft;  
         [0022]     a projection is formed on an inner periphery of the hole; and  
         [0023]     the first protrusion is brought into contact with the projection when the antenna portion is pivoted so as to define a predetermined angle with respect to the base portion.  
         [0024]     According to the invention, there is also provided antenna device, comprising:  
         [0025]     an antenna portion;  
         [0026]     a hinge portion formed on the antenna portion;  
         [0027]     a base portion attached to the hinge portion so as to be pivotable thereabout, wherein:  
         [0028]     the hinge portion includes: 
        a hinge base having a first shaft formed on one end thereof, a second shaft formed on the other end thereof, and a first protrusion formed on an outer periphery of the second shaft; and     a hinge bush rotatably mounted on the first shaft and engaged with the base potion;        
 
         [0031]     the base portion is formed with a hole surrounding the outer periphery of the second shaft;  
         [0032]     a projection is formed on an inner periphery of the hole; and  
         [0033]     the first protrusion is brought into contact with the projection when the base portion is pivoted so as to define a predetermined angle with respect to the antenna portion.  
         [0034]     The antenna portion may be operable to pivot about the hinge portion in a first direction.  
         [0035]     The hinge base may have a second protrusion formed on the outer periphery of the second shaft.  
         [0036]     The antenna portion may have a wall portion formed on the inner periphery of the antenna portion.  
         [0037]     The wall portion may be brought into contact with the second protrusion so that the antenna portion is not pivot in the first direction when the antenna portion defines a right angle with respect to the base portion.  
         [0038]     The base portion may be operable to pivot about the hinge portion in a first direction.  
         [0039]     The base portion may have a wall portion formed on the inner periphery of the base portion.  
         [0040]     The wall portion is brought into contact with the second protrusion so that the base portion is not pivot in the first direction when the base portion defines a right angle with respect to the antenna portion.  
         [0041]     The hinge bush may be comprised of at least one of ABS resin, ASA resin, and PC resin.  
         [0042]     With this configuration, the antenna device is small in size and is light in weight, and the antenna device is low in cost the cost of parts is low and the number of manufacturing processes is small.  
         [0043]     According to the invention, there is also provided an antenna device, comprising:  
         [0044]     a ground plate adapted to be electrically grounded;  
         [0045]     an antenna plate;  
         [0046]     an antenna probe feeding to the antenna plate;  
         [0047]     a probe holder which is comprised of resin, interposed between the ground plate and the antenna plate, and holding the antenna probe, wherein:  
         [0048]     an area of the probe holder is equal to or larger than at least one of an area of the ground plate and an area of the antenna plate.  
         [0049]     A face of the probe holder, which opposes the antenna plate may be formed with a groove.  
         [0050]     The antenna probe may be inserted into the groove.  
         [0051]     A projection may be formed in the groove so as to hold the antenna probe in the groove  
         [0052]     A depth of the groove and a position in the groove where the projection is formed may be set so that the antenna probe is disposed at a predetermined distance from the antenna plate so as to be electrically insulated from the antenna plate.  
         [0053]     The antenna device may further comprise:  
         [0054]     a ground member which is comprised of metal, disposed under the ground plate, and an area of which is equal to or larger than the ground plate, wherein:  
         [0055]     electric potential of the ground member is equal to electric potential of the ground plate.  
         [0056]     The ground member may include at least one of a metal sheet, a metal sheet adhered on a bottom cover of the antenna device, and conductive coating material coating the bottom cover of the antenna device.  
         [0057]     With this configuration, the antenna device is small in size, is light in weight and is low in cost, while the antenna device can exhibit a high gain. Further, the antenna device exhibits an excellent shielding effect against both an incoming noise and a radiation noise.  
         [0058]     According to the invention, there is also provided An antenna device, comprising:  
         [0059]     a first cover;  
         [0060]     a second cover coupled to the first cover and defining a space therebetween;  
         [0061]     an antenna module accommodated in the space;  
         [0062]     a signal line electrically connected to the antenna module and led out from the space;  
         [0063]     a packing member interposed between the first cover and the second cover so as to close the space in a waterproofing manner, wherein:  
         [0064]     the packing member includes a frame portion formed with a groove and a bush portion into which the signal line fitted; and  
         [0065]     the second cover includes a rib fitted into the groove.  
         [0066]     A width of the groove may be substantially equal to a thickness of the rib.  
         [0067]     The antenna module may be accommodated within the frame.  
         [0068]     The packing member may be comprised of silicone rubber.  
         [0069]     The rib may include a rib end portion disposed in the vicinity of the bush portion.  
         [0070]     The groove may include a groove end portion disposed in the vicinity of the bush portion.  
         [0071]     The rib end portion may be fitted into the groove end portion.  
         [0072]     The antenna device according to the present invention has an excellent water-proof property. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0073]     The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:  
         [0074]      FIG. 1  is a schematic exploded view showing an antenna device according to an embodiment of the present invention;  
         [0075]      FIGS. 2A and 2B  are respectively a perspective view and a partially enlarged view showing a packing member of the antenna device shown in  FIG. 1 ;  
         [0076]      FIGS. 3A  to  3 D are respectively a plan view, a cross-sectional view, another cross-sectional view, and a partially enlarged view showing the packing member shown in  FIG. 1 ;  
         [0077]      FIGS. 4A  to  4 E are respectively a bottom view, a cross-sectional view, a plan view, another bottom view, and a partially enlarged view showing the top cover of the antenna device shown in  FIG. 1 ;  
         [0078]      FIG. 5  is a partial cross-sectional view showing a water-proof structure of the antenna device according to the embodiment of the present invention;  
         [0079]      FIGS. 6A and 6B  are views showing an angle adjusting structure of the antenna device according to the embodiment of the present invention;  
         [0080]      FIGS. 7A and 7B  are alternative views showing an angle adjusting structure of the antenna device according to the embodiment of the present invention;  
         [0081]      FIGS. 8A and 8B  are further alternative views showing an angle adjusting structure of the antenna device according to the embodiment of the present invention; and  
         [0082]      FIGS. 9A  to  9 C are respectively a plan view, a cross-sectional view, and another cross-sectional view showing a probe holder of the antenna device according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0083]     Hereinafter, an embodiment of an antenna device according to the invention will be discussed with reference to the accompanying drawings.  
         [0084]     An antenna device according to the present invention is an antenna device for a digital radio receiver, and particularly an antenna device for home use assuming that the antenna device is also installed in outdoor places, such as a roof and a balcony, in addition to indoors, and is connected to a digital radio receiver installed indoors.  
         [0085]     The directional sensitivity of the antenna device is omni-directional. However, in order to ensure best sensitivity, it is desirable that the antenna device is constructed such that the attachment angle of the antenna device is adjusted to avoid an electric wave shielding object. For this reason, the present antenna for home use has an angle adjustment function.  
         [0086]     As shown in  FIG. 1 , the antenna device according to the present invention has the angle adjustment function. Specifically, the present antenna device has a base portion  20  which can be attached to a wall surface or the like, an antenna portion  10  accommodating an antenna module  13 , and a hinge portion  30  for connecting the antenna portion  10  to the base portion  20  such that the angle therebetween can be adjusted.  
         [0087]     The base portion  20  includes a base case  21  and a base plate  22 . The base case  21  and the base plate  22  are coupled together using a plurality of screws  23 . Four rubber pads  24  are adhered to the base plate  22 . The present antenna device can be mounted inside an oriel window of a building. Further, the base plate  22  is provided with hooking holes  222 , the present antenna device can be hooked and attached to screws or hooks provided in a wall.  
         [0088]     The antenna portion  10  includes a top cover  11 , a bottom cover  12 , an antenna module  13  which is mounted inside the top cover, a packing member  14 , and a ground sheet  17  (the detailed description thereof will be made below). The top cover  11  and the bottom cover  12  are coupled together by a plurality of screws  18 .  
         [0089]     The packing member  14  is made of, for example, a resin material, such as silicone rubber or EPDM rubber(ethylene propylene rubber). Since the packing member  14  is arranged at a connecting portion between the bottom cover  12  and the top cover  11  to ensure the adherence therebetween to perform a water-proof function, it is also called as a water-proof packing. As shown in  FIG. 2A , the packing member  14  has a frame part  141  having a rectangular frame shape with large width, and a bush part  142  covering the periphery of a signal line (not shown) at the position of a cut-out part  123  formed at the top cover  11 . Since the packing member  14  is constructed such that the frame part  141  and the bush part  142  are integrally formed, the number of parts and manufacturing processes is small compared to the case in which both the members are separately formed. The packing member  14  is useful in terms of miniaturization, lightness, reliability, and cost reduction.  
         [0090]     The present antenna device has a water-proof structure realizing a water-proof function between the top cover  11  and the bottom cover  12 . As shown in  FIGS. 4A  to  4 E, a water-proof lib  113  protruding in a generally rectangular frame shape is formed inside the top cover  11 . On the other hand, as shown in  FIGS. 2B, 3A  to  3 D, the generally rectangular-shaped frame part  141  of the packing member  14  is provided with a generally rectangular and frame-shaped groove  141   a  which corresponds to the protruded water-proof rib  113  having the generally rectangular frame shape. When the bottom cover  12  and the top cover  11  are assembled together with the packing member  14  therebetween, a leading end of the water-proof lib  113  of the top cover  11 , as shown in  FIG. 5 , fits into the groove  141   a  of the frame part  141  of the packing member  14 . Further, when the top cover  11  and the bottom cover  12  are fastened together using the plurality of screws  18 , the water-proof rib  113  is pressed against the groove  141   a , thereby realizing the water-proof function. The width of the groove  141   a  is substantially equal to the thickness of the water-proof rib  113 .  
         [0091]     Further, in the generally rectangular-shaped frame part  141  of the packing member  14 , as shown in  FIG. 3D , a groove end  141   b  which continues from the groove  141   a  is formed to the vicinity of the bush part  142 . The groove end  141   b  has a pocket shape. On the other hand, as shown in  FIG. 4E , a rib end  114  which continues from the water-proof rib is formed inside the top cover  11 . In the protruded portion of the signal line, the bush part  142  is fitted into a bush accommodating portion of the top cover  11 , thereby exhibiting a water-proof effect, as well as the rib end  114  is fitted into the groove end  141   b , thereby increasing a water-proof property.  
         [0092]     In the water-proof structure of the present antenna device, the contact area between the packing member  14  and the water-proof rib  113  is large. For this reason, any gap is not created between the water-proof rib  113  of the top cover  11  and the packing member  14 , even in a case in which the fastening pressures by the plurality of screws  18  are different from one another, or the fastening pressures by the screws  18  are relatively large. Therefore, the present antenna device has an excellent water-proof property. Further, when the water-proof rib  113  of the top cover  11  fits into the groove  141   a  of the packing member  14 , the packing member  14  is not dislocated in the horizontal direction.  
         [0093]     In the present antenna device, the angle of the antenna portion  10  with respect to the base portion  20  can be adjusted via the hinge portion  30 . As shown in  FIGS. 1, 6A  and  6 B, the hinge portion  30  includes a hinge base  31 , a hinge bush  32 , a coil spring  33 , a washer  34  and a screw  35 . The hinge base  31  is provided at an end of a ceiling surface of a base case  21  of the base portion  20 , and extends parallel to the ceiling surface of the base case  21 . An end of the hinge base  31  is formed with a first shaft  312 . The first shaft  312  has a base  312   a  having a tapered outer peripheral surface and a shaft-body-shaped leading end  312   b  extending from the base  312   a . The hinge bush  32  is made of a low frictional resin material, such as ABA, ASA, or PC, has a tapered inner peripheral surface, and is fitted around the base  312   a  of the first shaft  312  such that it can rotate with friction. The coil spring  33  is fitted onto the leading end  312   b  on which the hinge bush  32  is mounted. The screw  35  is fastened via the washer  34  to an end surface of the first shaft  312  on which the hinge bush  32  and the coil spring  33  is mounted. The biasing force of the coil spring  33  generates a frictional force between the outer peripheral surface of the base  312   a  of the first shaft  312  and the inner peripheral surface of the hinge bush  32  to cause the hinge bush  32  to slide with respect to the first shaft  312 .  
         [0094]     The hinge bush  32  is sandwiched and fixed between the top cover  11  and the bottom cover  12 . The frictional force between the base  312   a  of the first shaft  312  and the hinge bush  32  causes the antenna portion  10  to be fixed at a constant angle without rotation when an external force is not applied thereto. On the other hand, the antenna portion  10  can be rotated and adjusted to an arbitrary angle when an external force larger than the frictional force between the base  312   a  of the first shaft  312  and the hinge bush  32  is applied thereto.  
         [0095]     In the present invention, the angle of the hinge portion  30  can be adjusted within a range of 0 to 90 degrees. The angle adjustment is performed as follows, for example. A user manually adjusts the angle of the antenna portion  10  such that the best level of a broadcasting signal or the best sound quality of audio information received by a digital radio receiver via the present antenna device is maintained, while confirming the level or the sound quality.  
         [0096]     Further, in the present invention, the hinge base may be formed at an end of the antenna, and the hinge bush may be fixed to an end of the base portion.  
         [0097]     In the angle adjusting structure of the present antenna device, the number of the hinge bush  32  of the hinge portion  30 , the coil spring  33 , the washer  34 , and the screw  35  is one, respectively. Therefore, the antenna device is small in size and is light in weight, and the antenna device is low in cost since the cost of parts is low and the number of manufacturing processes is small.  
         [0098]     Further, As shown in  FIGS. 7A and 7B  and  FIGS. 8A and 8B , the other end of the hinge base  31  is formed with a second shaft  313 . The second shaft  313  has a pair of cantilever pieces  313   a  formed by splitting the end of a shaft body of the second shaft, and a convex portion  313   b  formed on an outer peripheral surface of one of the cantilever pieces. The cantilever piece  313   a  functions as a cantilever spring. On the other hand, inner peripheral surface portions  122  are formed at ends of the top cover  11  and the bottom over  12  so as to surround the second shaft. Each inner peripheral surface portion  122  has a protrusion  122   a  formed corresponding to a predetermined position of the convex portion  313   b  when the antenna portion  10  is opened and closed with respect to the base portion  20 . In the present embodiment, the predetermined position of the convex portion  313   b  is a position just before the angle of the antenna portion  10  with respect to the base portion  20  becomes 0 degree. When the antenna portion  10  is closed toward 0 degree as shown in  FIGS. 8A and 8B  from a state where the antenna device is opened as shown in  FIGS. 7A and 7B , the convex portion  313   b  supported by the cantilever piece  313   a  rides over the protrusion  122   a . At this time, a click feeling is created. Further, when the antenna portion  10  is completely closed at 0 degree, the convex portion  313   b  supported by the cantilever piece  313   a  is regulated by the protrusion  122   a . Therefore, the antenna portion  10  is not inadvertently opened (floated) as long as an external force exceeding the elastic force of the cantilever piece  313   a  is not applied thereto.  
         [0099]     The second shaft  313  further includes a second convex portion  313   c  formed on an outer peripheral surface of the root thereof. On the other hand, the inner peripheral surface portion  122  further has a wall portion  122   b  which abuts on the second convex portion  313   c  to prevent the antenna portion  10  from having an angle larger than 90 degrees when the antenna portion  10  forms an angle of 90 degrees with respect to the base portion  20 .  
         [0100]     In addition, in the present invention, the second shaft along with the hinge base may be formed in the antenna portion, while the inner peripheral surface portion may be formed in the base portion. Further, any one of the convex portion formed in the second shaft and the protrusion formed in the inner peripheral portion has preferably a low frictional property.  
         [0101]     As shown in  FIG. 1 , the antenna module  13  includes a ground plate  134 , an antenna plate  131 , an antenna probe  132 , a probe holder  133 , an LNA (low noise amplifier)  137 , and a shielding case  138 .  
         [0102]     The ground plate  134  is made of metal, and has a generally square shape. The antenna plate  131  is made of metal, has a generally square shape, and is arranged to face the ground plate  134  with a distance therebetween. The antenna probe  132  is made of metal and is located between the ground plate  134  and the antenna plate  131 . The probe holder  133  is made of ABS resin, has a generally cubic shape, and holds the antenna probe  132  in a fixed position.  
         [0103]     The plate surface area of each of the ground plate  134  and the antenna plate  131  is made smaller than that of the related-art antenna device. When the ground plate and the antenna plate are miniaturized, there is a possibility that the electrostatic capacitance of the antenna module decreases and the antenna device does not exhibit a sufficient gain. However, the present antenna device increases a specific dielectric constant between the ground plate  134  and the antenna plate  131  to ensure a sufficient electrostatic capacitance. For this reason, the present antenna device can exhibit a high gain. Specifically, the probe holder  133  provided between the ground plate  134  and the antenna plate  131  has a size equal to or lager than the facing area between the ground plate  134  and the antenna plate  131 . That is, most of the space between the ground plate  134  and the antenna plate  131  is filled with resin member (probe holder  133 ). Since the resin has a specific dielectric constant larger than that of air, the antenna module  13  has a sufficient electrostatic capacitance.  
         [0104]     As shown in  FIG. 9A  to  9 C, a generally L-shaped groove  133   b  is formed in a ceiling surface of the probe holder  133 . The antenna probe  132  is inserted into the groove  133   b . Since a protrusion  133   c  is formed in the groove  133   b , the antenna probe  132  inserted into the groove  133   b  is securely held within the groove  133   b  without being removed unnecessarily. The depth of the groove  133   b  and the height of the protrusion  133   c  are set such that the antenna probe  132  held by the probe holder  133  and the antenna plate  131  are spaced from each other with a predetermined distance therebetween and are electrically insulated from each other. For this reason, an insulating member needs not to be mounted on the antenna probe held by the probe holder, whereby the number of parts of the antenna device may be reduced.  
         [0105]     An end of the antenna probe  132  and a signal line (not shown) are electrically connected to the LNA  137 . The shielding case  138  is soldered to the LNA  137 . The LNA  137  covered with the shielding case  138  is adhered to the ground plate  134  with an insulating tape  136 . The ground plate  134  to which the LNA  137  is adhered is attached to the inside the top cover  11  with a plurality of screws  135 . The signal line is led out of the antenna portion  10  via the bush part  142  of the packing member  14  located in the cut-out position formed in the bottom cover  12 .  
         [0106]     As described above, the plate surface area of each of the ground plate  134  and the antenna plate  131  is smaller than that of the conventional one. When the ground plate is miniaturized, there is a possibility that the shielding effect against an incoming noise and a radiation noise may deteriorate. However, since the present antenna device includes an additional ground means, it has a shielding effect against the incoming noise and the radiation noise. That is, the ground means is composed of a ground sheet  17  shown in  FIG. 1 . The ground sheet  17  is composed of an aluminum adhesive seal, has a size equal to or larger than the area of the ground plate  134 , and is adhered to an inner bottom surface of the bottom cover  12 . The ground sheet  17  is arranged in a state in which it is spaced with a predetermined distance from the ground plate  134  and the shielding case  138 . The additional ground means according to the present invention may be a metal plate or conductive paint applied onto the inner bottom surface of the bottom cover  12 . The conductive paint may contain, for example, copper or aluminum.  
         [0107]     The present invention has been described with reference to the preferred embodiment, but the present invention is not limited the above-described embodiment. For example, the present invention is not limited to a home antenna for a digital radio receiver and may be applied to an antenna device for receiving a GPS signal, and an antenna device for mobile communication for receiving satellite waves and ground waves.