Patent Publication Number: US-7215289-B2

Title: Antenna device and portable radio terminal

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an antenna device incorporated in a small-sized radio terminal, especially to an antenna device showing a good reception characteristic for high-frequency radio signals regardless of direction and a portable radio terminal provided with the antenna. 
   2. Description of the Prior Art 
   In recent years, a portable radio terminal typified by a mobile phone often uses radio signals in a high-frequency band. For instance, the frequency used in the third generation mobile phone goes beyond 2 GHz (gigahertz), and has a tendency to shift to the higher frequencies. 
   While a portable radio terminal is getting smaller and smaller, it has limitations for further miniaturization thereof from the operational point of view. Accordingly, as the higher frequencies are used, the length of a housing of a portable radio terminal often becomes beyond more than half of the wavelength λ, being λ/2. 
   As the length of the housing becomes longer with respect to the frequency, the radiation characteristic changes because of the current of the housing. Therefore, as represented by a half wave dipole antenna, it is not possible to have the uniform field emission pattern characteristic in a horizontal surface, and an abrupt drop (null point) appears in the horizontal surface. 
   In the case where the frequency is around 1 GHz, the wavelength is about 30 centimeter. Accordingly, when the electrical length including that of an antenna is equal to or less than λ/2, that is, when the length of the housing is equal to or less than 7.5 centimeter, and the electrical length of the antenna is equal to or less than λ/4, its field emission pattern characteristic becomes similar to that of the half wave dipole antenna. Thus, it is possible to have a relatively uniform field emission pattern characteristic in the horizontal surface. 
   However, in the case where the frequency is around 2 GHz, the wavelength is about 15 centimeter. Accordingly, even when the length of the housing of a radio terminal is around 10 centimeter, the electrical length including that of an antenna is about the same as or more than the wavelength. Thus, the field emission pattern characteristic does not become uniform because of the current of the housing, and an abrupt drop (null point) arises in the horizontal surface. 
   There has been the problem that it is not possible for a portable radio terminal to stably receive radio signals if the housing thereof has such a field emission characteristic and the reception characteristic changes depending on the direction of the terminal. 
   As a prior art document concerning an antenna of a portable radio terminal, Japanese utility model patent application laid-open No. 62-161410 discloses an antenna for a radio terminal, in which a platy radiating element is disposed parallel to the surface of a metallic housing of a radio terminal, one end of the platy radiating element is connected to the housing of the radio terminal and immobilized, a feeder cable is connected to a designated position on the platy radiating element, and a rod-shaped parasitic element is placed on the housing of the radio terminal. 
   This prior art realizes an antenna of a small size and also broadband characteristic by resonating the reverse F-shaped antenna of the platy radiating element and the rod-shaped parasitic element with each different resonance frequency. 
   Further, Japanese patent application laid-open No. 2004-56319 discloses a null-less antenna intended to fill in a null. 
   In the first prior art, while the radio terminal shows a good radiation characteristic in two frequency bands, the generation of a null has not been conceived. Therefore, when the art is applied to an antenna in a portable radio terminal, radio signals cannot be transmitted and received between a radio terminal and another radio terminal or a base station depending on the aspect of the radio terminal. 
   Also, the second prior art is so-called antenna array having a plurality of antennas, and therefore, it is difficult to apply the art to a portable radio terminal being required to be made smaller and lighter. 
   As above, it has not been provided an antenna device capable of being applied to a portable radio terminal and also showing a good radiation characteristic regardless of the direction of the terminal. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention, in order to overcome the above mentioned problems, to provide an antenna device capable of being applied to a portable radio terminal and showing a good antenna characteristic regardless of direction, and a portable radio terminal provided with the antenna device. 
   To achieve the object mentioned above, in the first aspect of the present invention, an antenna device applied to a portable radio terminal whose housing length is equal to or more than λ/4 with respect to the wavelength λ of transmission-reception signals comprises: 
   an antenna element disposed on one end of the housing in the longitudinal direction in which at least one point of one end is connected to a signal wiring pattern on a substrate and the other end is an open end; and 
   a parasitic element disposed on the same side of housing as the antenna element in which one point of one end is connected to a ground wiring on the substrate and the other end is an open end; 
   wherein the open end of the antenna element and that of the parasitic element are approximated to each other and capacity coupled, and the antenna element, the parasitic element and the substrate are disposed forming a loop. 
   Preferably, in the first aspect of the present invention: 
   the antenna element is L-shaped or F-shaped and the parasitic element is reverse L-shaped or I-shaped; 
   at least one of the antenna element and the parasitic element is meandering-shaped in the vicinity of the open end in any configuration of the above described elements; 
   at least one of the antenna element and the parasitic element is helical-shaped in the vicinity of the open end, and more preferably, the open end of one of the antenna element and the parasitic element is inserted inside the other element whose open end is helical-shaped; or 
   at least one of the antenna element and the parasitic element is configured with tabular conductor in the vicinity of the open end. 
   Preferably, in any configuration of the above described elements: 
   the open ends of the antenna element and the parasitic element are disposed in substantially the same plane as the substrate, and the distances from the substrate to the open end of the antenna element and to the open end of the parasitic element are different; or 
   the open ends of the antenna element and the parasitic element are spaced from the substrate. 
   Preferably, in the first aspect of the present invention: 
   at least one of the antenna element and the parasitic element has two or more open ends; 
   at least one of the antenna element and the parasitic element is helical-shaped in the vicinity of at least one of the open ends, and more preferably, at least one of the open ends of one of the antenna element and the parasitic element is inserted inside the other element whose open end is helical-shaped; or 
   at least one of the open ends of at least one of the antenna element and the parasitic element is configured with a tabular conductor. 
   Preferably, the open ends of the antenna element and the parasitic element are disposed in substantially the same plane as the substrate, and the distances from the substrate to the open end of the antenna element and to the open end of the parasitic element are different, or preferably, the open ends of the antenna element and the parasitic element are spaced from the substrate. 
   Preferably, in any configuration of the first aspect of the present invention: 
   connecting sections of the antenna element and the parasitic element to the substrate are platy; 
   the open ends of the antenna element and the parasitic element are platy; 
   a high dielectric material is disposed around the antenna element and the parasitic element; 
   at least one of the antenna element and the parasitic element is configured with the signal wiring pattern on the substrate; and 
   a capacitive element or an inductive element is disposed between the open end of the antenna element and that of the parasitic element. 
   In the second aspect of the present invention, a portable radio terminal is provided with the antenna device having any one of configurations in the first aspect of the present invention. 
   Preferably in the second aspect of the present invention: 
   two housings are joined by a conjunction mechanism to be openable and closable; 
   the antenna element and the parasitic element contained in the housing are disposed in the vicinity of the conjunction mechanism, or the antenna element and the parasitic element contained in the housing are disposed at the place most distant from the conjunction mechanism; and 
   the antenna element and the parasitic element contained in the housing are disposed alongside of an interior surface of the housing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further objects and novel features of the invention will be more fully understood from the following detailed description when the same is read in connection with the accompanying drawings in which: 
       FIG. 1  is a diagram showing the structure of an antenna device according to the first embodiment of the present invention; 
       FIG. 2  is a diagram showing the operation of the antenna device according to the first embodiment of the present invention; 
       FIG. 3  is a diagram showing the field emission pattern characteristic of the antenna device of the first embodiment of the present invention; 
       FIG. 4  is a graph showing the current distribution of a housing of a portable radio terminal applied by the antenna device according to the first embodiment of the present invention; 
       FIG. 5  is a diagram showing another example of the structure of the antenna device according to the first embodiment of the present invention; 
       FIG. 6  is a diagram showing the structure of an antenna device according to the second embodiment of the present invention; 
       FIG. 7  is a diagram showing the structure of an antenna device according to the third embodiment of the present invention; 
       FIG. 8  is a diagram showing the structure of an antenna device according to the fourth embodiment of the present invention; 
       FIG. 9(   a ) is a diagram showing a disposition example of an antenna element and a parasitic element of the antenna device according to the fourth embodiment of the present invention; 
       FIG. 9(   b ) is a diagram showing another disposition example of the antenna element and the parasitic element of the antenna device according to the fourth embodiment of the present invention; 
       FIG. 10  is a diagram showing the structure of an antenna device according to the fifth embodiment of the present invention; 
       FIG. 11  is a diagram showing another example of the structure of the antenna device according to the fifth embodiment of the present invention; 
       FIG. 12  is a diagram showing the structure of an antenna device according to the sixth embodiment of the present invention; 
       FIG. 13  is a diagram showing the structure of an antenna device according to the seventh embodiment of the present invention; 
       FIG. 14  is a diagram showing a disposition example of high dielectric material in the antenna device according to the seventh embodiment of the present invention; 
       FIG. 15  is a diagram showing the structure of an antenna device according to the eighth embodiment of the present invention; 
       FIG. 16  is a diagram showing the structure of an antenna device according to the ninth embodiment of the present invention; 
       FIG. 17  is a diagram showing the structure of an antenna device according to the tenth embodiment of the present invention; 
       FIG. 18  is a diagram showing the structure of an antenna device according to the eleventh embodiment of the present invention; 
       FIG. 19(   a ) is a diagram showing the structure of an antenna device according to the twelfth embodiment of the present invention; 
       FIG. 19(   b ) is a diagram showing the structure of an antenna device according to the twelfth embodiment of the present invention; 
       FIG. 20(   a ) is a diagram showing the structure of an antenna device according to the thirteenth embodiment of the present invention; 
       FIG. 20(   b ) is a diagram showing the structure of an antenna device according to the thirteenth embodiment of the present invention; 
       FIG. 21  is a diagram showing the structure of an antenna device according to the fourteenth embodiment of the present invention; 
       FIG. 22(   a ) is a diagram showing the structure of an antenna device according to the fifteenth embodiment of the present invention; 
       FIG. 22(   b ) is a diagram showing the structure of an antenna device according to the fifteenth embodiment of the present invention; 
       FIG. 23  is a diagram showing the structure of an antenna device according to the sixteenth embodiment of the present invention; 
       FIG. 24  is a diagram showing the structure of an antenna device according to the seventeenth embodiment of the present invention; 
       FIG. 25  is a diagram showing the structure of an antenna device according to the eighteenth embodiment of the present invention; 
       FIG. 26  is a diagram showing the structure of an antenna device according to the nineteenth embodiment of the present invention; 
       FIG. 27  is a diagram showing the structure of an antenna device according to the twentieth embodiment of the present invention; and 
       FIG. 28  is a diagram showing the structure of an antenna device according to the twenty-first embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A description will be given of the first embodiment of the present invention.  FIG. 1  is a diagram showing the structure of an antenna device according to this embodiment and  FIG. 2  is a diagram showing the operation of the antenna device according to this embodiment. In the antenna device, an antenna element  21  and a parasitic element  31  are attached on one end of a substrate  10 . At least one point of one end of the antenna element  21  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element is an open end. One end of the parasitic element  31  is connected to the ground of the substrate  10  and the other end of the parasitic element  31  is an open end. 
   The antenna element  21  and the parasitic element  31  are substantially L-shaped or reverse L-shaped and both of the open ends are disposed in proximity to each other and their fore-ends are in alignment. 
   When the open ends of the antenna element  21  and the parasitic element  31  are disposed as above, as shown in  FIG. 2 , high-frequency loop current passes through the ground of the substrate  10 , the antenna element  21  and the parasitic element  31 , and operates in the same manner as that of a loop antenna. 
     FIG. 3  is a diagram showing the field emission pattern characteristic of the antenna device of this embodiment. 
   When the antenna device operates only with the L-shaped antenna  21 , an abrupt drop of the field emission pattern characteristic arises in the horizontal surface, and also in the vertical direction. This means that when the antenna device operates only with the antenna element  21 , the transmission-reception of signals could be disturbed depending on the direction. 
   On the other hand, as the antenna device of this embodiment, when the antenna device operates with the parasitic element  31 , the drop in the horizontal direction and the vertical direction becomes smaller, and therefore the uniform field emission pattern characteristic can be obtained. 
     FIG. 4  is a graph showing the current distribution of a housing of a portable radio terminal to which the antenna device of this embodiment is applied. When the antenna device operates without the parasitic element  31 , the current value of the housing reaches a peak at a point distant from the antenna element  21 . That causes the deterioration of the field emission pattern characteristic. On the other hand, in the portable radio terminal to which the antenna device of this embodiment is applied, by placing the parasitic element  31 , the current value of the housing does not reach a peak except at the site of the antenna device. In other words, with the parasitic element  31 , smaller current passes through the ground plane of the substrate  10 , and therefore, it is possible to prevent the deterioration of the field emission pattern characteristic (for example, as described above, the field emission pattern characteristic becomes papilionaceous and a null point arises) because of the influence of the current of the housing. 
   In a portable radio terminal, the direction in which the antenna device is used is depending on a user&#39;s posture for using the portable radio terminal. Therefore, it is necessary for the portable radio terminal to have approximately uniform field emission pattern characteristic in all directions to receive effectively radio waves transmitted from a distance. 
   As shown in  FIG. 3 , the antenna device of this embodiment shows the field emission pattern characteristic similar to that of an omnidirectional antenna. Incidentally, it is apparent that the antenna device of this embodiment has applicability to a portable radio terminal as is the case with a conventional antenna. 
   Here, a description has been given of an example of the case that the ends of the antenna element  21  and the parasitic element  31  are disposed in close proximity to each other in alignment. However, the ends of the antenna element  21  and the parasitic element  31  are not needed to be in alignment, and as shown in  FIG. 5 , it is sufficient for the ends of the antenna element  21  and the parasitic element  31  to be disposed in close proximity to each other. 
   A description will be given of the second embodiment of the present invention.  FIG. 6  is a diagram showing an antenna device of this embodiment. In the antenna device, the antenna element  22  and the parasitic element  32  are attached on one end of the substrate  10 . The antenna element  22  is electrically connected to a signal wiring pattern on the substrate  10  at least at one point of one end and also to a ground pattern, and the other end of the antenna element  22  is an open end. One end of the parasitic element  32  is connected to the ground of the substrate  10  and the other end of the parasitic element  32  is an open end. 
   The antenna element  22  is substantially F-shaped or reverse F-shaped and the parasitic element  32  is substantially L-shaped or reverse L-shaped, and both ends are disposed in proximity in alignment. 
   When the open ends of the antenna element  22  and the parasitic element  32  are disposed as above, as is the case with the antenna device of the first embodiment, high-frequency loop current passes through the ground of the substrate  10 , the antenna element  22  and the parasitic element  32 , and operates in the same manner as that of a loop antenna. 
   The antenna device of this embodiment, same as that of the first embodiment, shows approximately uniform field emission pattern characteristic in all directions, and therefore, the antenna device of this embodiment has applicability to a portable radio terminal. 
   A description will be given of the third embodiment of the present invention.  FIG. 7  is a diagram showing an antenna device of this embodiment. In the antenna device, the antenna element  23  and the parasitic element  33  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  23  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  23  is an open end. One end of the parasitic element  33  is connected to the ground of the substrate  10  and the other end of the parasitic element  33  is an open end. 
   The antenna element  23  is substantially L-shaped or reverse L-shaped and the parasitic element  33  is substantially I-shaped, and both of the open ends are disposed in proximity. 
   When the open ends of the antenna element  23  and the parasitic element  33  are disposed as above, as is the case with the antenna device of the first embodiment, high-frequency loop current passes through the ground of the substrate  10 , the antenna element  23  and the parasitic element  33 , and operates in the same manner as that of a loop antenna. 
   The antenna device of this embodiment, same as that of the first embodiment, has approximately uniform field emission pattern characteristic in all directions, and therefore, the antenna device of this embodiment has applicability to a portable radio terminal. 
   A description will be given of the fourth embodiment of the present invention.  FIG. 8  is a diagram showing an antenna device of this embodiment. In the antenna device, the antenna element  24  and the parasitic element  34  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  24  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  24  is an open end. One end of the parasitic element  34  is connected to the ground of the substrate  10  and the other end of the parasitic element  34  is an open end. 
   The antenna element  24  and the parasitic element  34  are substantially L-shaped or reverse L-shaped and both ends are configured with tabular conductors. The open ends of antenna element  24  and the parasitic element  34  are disposed in proximity to each other. 
   When the open ends of the antenna element  24  and the parasitic element  34  are disposed as above, as is the case with the antenna device of the first embodiment, high-frequency loop current passes through the ground of the substrate  10 , the antenna element  24  and the parasitic element  34 , and operates in the same manner as that of a loop antenna. 
   The antenna device of this embodiment, same as that of the first embodiment, has approximately uniform field emission pattern characteristic in all directions, and therefore, the antenna device of this embodiment has applicability to a portable radio terminal. 
   Incidentally, here, as shown in  FIG. 8(   a ), a description has been given of an example of the case that conductors of the antenna element  24  and the parasitic element  34  and the substrate  10  are disposed in the same plane. On the other hand, as shown in  FIG. 8(   b ), each conductor of the antenna element  24  and the parasitic element  34  may be disposed perpendicular to the substrate  10 . 
   A description will be given of the fifth embodiment of the present invention.  FIG. 10  is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  25  and the parasitic element  35  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  25  is electrically connected to a signal wiring pattern on the substrate  10  and also a ground pattern, and the other end of the antenna element  25  is an open end. One end of the parasitic element  35  is connected to the ground of the substrate  10  and the other end of the parasitic element  35  is an open end. 
   The antenna element  25  and the parasitic element  35  are configured with conductors being meandering-shaped. The open ends of antenna element  25  and the parasitic element  35  are disposed in proximity to each other. 
   When the antenna element  25  and the parasitic element  35  are meandering-shaped, it is possible to lower their natural resonance frequencies. Therefore, the antenna device functions effectively as antenna over such low frequencies as the length of the antenna element  25  or the parasitic element  35  is equal to or less than λ/4 with respect to the wavelength λ. 
   When the open ends of the antenna element  25  and the parasitic element  35  are disposed in close proximity to each other, as is the case with the antenna device of the first embodiment, high-frequency loop current passes through the ground of the substrate  10 , the antenna element  25  and the parasitic element  35 , and operates in the same manner as that of a loop antenna. 
   Incidentally, as shown in  FIG. 11 , there is likely the case that the directions of open ends of the antenna element  25  and the parasitic element  35  are not the same. In this case, if the antenna element  25  and the parasitic element  35  are capacity coupled, it is possible to have the usual effects of the case that the open ends face to the same direction. 
   The antenna device of this embodiment, same as that of the first embodiment, has approximately uniform field emission pattern characteristic in all directions, and therefore, the antenna device of this embodiment has applicability to a portable radio terminal. 
   A description will be given of the sixth embodiment of the present invention.  FIG. 12  is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  26  and the parasitic element  36  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  26  is electrically connected to a signal wiring pattern on the substrate  10  and also a ground pattern, and the other end of the antenna element  26  is an open end. One end of the parasitic element  36  is connected to the ground of the substrate  10  and the other end of the parasitic element  36  is an open end. 
   The antenna element  26  and the parasitic element  36  are configured with L-shaped (reverse L-shaped) coiled conductors and both open ends are disposed in close proximity to each other. 
   When the antenna element  26  and the parasitic element  36  are coiled-shaped, it is possible to lower their natural resonance frequencies. Therefore, the antenna device functions effectively as antenna over such low frequencies as the length of the antenna element  26  or the parasitic element  36  is equal to or less than λ/4 with respect to the wavelength λ. 
   When the open ends of the antenna element  26  and the parasitic element  36  are disposed in close proximity to each other, as is the case with the antenna device of the first embodiment, high-frequency loop current passes through the ground of the substrate  10 , the antenna element  26  and the parasitic element  36 , and operates in the same manner as that of a loop antenna. 
   The antenna device of this embodiment, same as that of the first embodiment, has approximately uniform field emission pattern characteristic in all directions, and therefore, the antenna device of this embodiment has applicability to a portable radio terminal. 
   A description will be given of the seventh embodiment of the present invention.  FIG. 13  is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  27  and the parasitic element  37  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  27  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  27  is an open end. One end of the parasitic element  37  is connected to the ground of the substrate  10  and the other end of the parasitic element  37  is an open end. 
   The antenna element  27  and the parasitic element  37  are substantially L-shaped or reverse L-shaped and the open ends are in close proximity to each other in alignment. A high dielectric material  47  is disposed, by being stuck or formed around the antenna element  27  and the parasitic element  37 . 
   Although the high dielectric material  47  can be disposed at an arbitrary place in the vicinity of the antenna element  27  and the parasitic element  37 , it is desirable to dispose between the substrate  10  and the ends of the antenna element  27  and the parasitic element  37  as shown in  FIG. 13 . 
   When the high dielectric material  47  is disposed between the antenna element  27  and the parasitic element  37 , it is possible to lower their natural resonance frequencies. Therefore, the antenna device functions effectively as antenna over such low frequencies as the length of the antenna element  27  or the parasitic element  37  is equal to or less than λ/4 with respect to the wavelength λ. 
   When the open ends of the antenna element  27  and the parasitic element  37  are disposed in close proximity to each other, as is the case with the antenna device of the first embodiment, high-frequency loop current passes through the ground of the substrate  10 , the antenna element  27  and the parasitic element  37 , and operates in the same manner as that of a loop antenna. 
   The antenna device of this embodiment, same as that of the first embodiment, has approximately uniform field emission pattern characteristic in all directions, and therefore, the antenna device of this embodiment has applicability to a portable radio terminal. 
   A description will be given of the eighth embodiment of the present invention.  FIG. 15  is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  28  is attached on one end of the substrate  10 . At least one point of one end of the antenna element  28  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  28  is an open end. On the substrate  10 , a substantially L-shaped (or reverse L-shaped) ground wiring pattern is formed and configures the parasitic element  38 . One end of the parasitic element  38  is an open end. 
   When the open ends of the antenna element  28  and the parasitic element  38  are disposed in close proximity to each other, as is the case with the antenna device of the first embodiment, high-frequency loop current passes through the ground of the substrate  10 , the antenna element  28  and the parasitic element  38 , and operates in the same manner as that of a loop antenna. 
   Incidentally, here, while a description has been given of an example of the case that the parasitic element  38  is configured with the wiring pattern of the substrate  10 , it is also possible to configure the antenna element  28  or both of the antenna element  28  and the parasitic element  38  from the wiring pattern. 
   The antenna device of this embodiment, same as that of the first embodiment, has approximately uniform field emission pattern characteristic in all directions, and therefore, the antenna device of this embodiment has applicability to a portable radio terminal. 
   A description will be given of the ninth embodiment of the present invention.  FIG. 16  is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  29  and the parasitic element  39  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  29  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  29  is an open end. One end of the parasitic element  39  is connected to the ground of the substrate  10  and the other end of the parasitic element  39  is an open end. 
   The antenna element  29  and the parasitic element  39  are substantially L-shaped or reverse L-shaped, and a capacitor  49  is formed by both open ends. 
   When the open ends of the antenna element  29  and the parasitic element  39  are disposed in close proximity to each other, as is the case with the antenna device of the first embodiment, high-frequency loop current passes through the ground of the substrate  10 , the antenna element  28  and the parasitic element  38 , and operates in the same manner as that of a loop antenna. 
   The antenna device of this embodiment, same as that of the first embodiment, has approximately uniform field emission pattern characteristic in all directions, and therefore, the antenna device of this embodiment has applicability to a portable radio terminal. 
   Further, since the degree of capacity coupling of the capacitor  49  formed with open ends of the antenna element  29  and the parasitic element  39  can be forcibly adjusted, a desirable antenna characteristic can be easily made. In other words, even if the respective ends of the antenna element  29  and the parasitic element  39  cannot approximate each other enough to be capacity coupled by a desirable capacitance value, by disposing capacitive element on the respective ends of the antenna element  29  and the parasitic element  39 , the antenna element  29  and the parasitic element  39  are capacity coupled by a desirable capacitance value. 
   Incidentally, when the antenna element  29  and the parasitic element  39  are capacity coupled by equal to or more than a desirable capacitance value, by disposing an inductive element at the ends of the antenna element  29  and the parasitic element  39 , the antenna element  29  and the parasitic element  39  are forcibly capacity coupled by a desirable capacitance value. 
   A description will be given of the tenth embodiment of the present invention.  FIG. 17  is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  210  and the parasitic element  310  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  210  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  210  is an open end. One end of the parasitic element  310  is connected to the ground of the substrate  10  and the other end of the parasitic element  310  is an open end. 
   According to this embodiment, each open end of the antenna element  210  and the parasitic element  310  forms a coiled element being substantially square-shaped in its cross-sectional surface. The coiled element being substantially square-shaped in its cross-sectional surface can form a longer antenna than a coiled element being substantially round in its cross-sectional surface. In other words, because the coiled element being substantially square-shaped in its cross sectional surface has a longer turn length, it is possible to contain an antenna having the longer electrical length in a housing. Thus, it is possible to mount, on the substrate  10 , the antenna for transmitting and receiving a low-frequency electromagnetic wave. Incidentally, interior spaces of most of portable radio terminals have substantially rectangular solid shape, and therefore, by forming the coil being substantially square-shaped in its cross-sectional surface, the antenna device can be easily contained in the housing without making a dead space. 
   A description will be given of the eleventh embodiment of the present invention.  FIG. 18  is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  211  and the parasitic element  311  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  211  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  211  is an open end. One end of the parasitic element  311  is connected to the ground of the substrate  10  and the other end of the parasitic element  311  is an open end. 
   According to this embodiment, turn sections (in other words, small number of turned portions) are provided in the vicinity of a feeder end of the antenna element  211  and in the vicinity of a ground end of the parasitic element  311 . The open end of each element is linear-shaped, and disposed in close proximity to each other. 
   The configuration as above is effective in the case where there is a structural restriction, for example, in the case where a hole has to be made in the vicinity of the both open ends (in other words, the midsection of a housing). 
   A description will be given of the twelfth embodiment of the present invention.  FIG. 19(   a ) is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  212  and the parasitic element  312  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  212  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  212  is an open end. One end of the parasitic element  312  is connected to the ground of the substrate  10  and the other end of the parasitic element  312  is an open end. 
   According to this embodiment, the open end of the parasitic element  312  is coil-shaped, and the open end of the antenna element  212  is linear-shaped. As shown in  FIG. 19(   b ), the open end of the antenna element  212  is inserted inside a coil formed by the parasitic element  312 . 
   The configuration as above is effective in the case where a longer coil (element) relative to the antenna device has to be made. In other words, with such structure, the longer coil can be made without expanding the width of the antenna device, and further, both coils (elements) are strongly capacity coupled. 
   Incidentally, while the open end of the antenna element  212  is linear-shaped and the open end of the parasitic element  312  is coil-shaped as an example, the open end of the antenna element  212  may be coil-shaped and the open end of the parasitic element  312  may be linear-shaped, and the parasitic element  312  may be inserted inside the coil formed by the antenna element  212 . Additionally, one of the antenna element  212  and the parasitic element  312  may be coil-shaped having longer outside diameter, and the other element may also be coil-shaped having shorter outside diameter, and the coil having the shorter outside diameter may be inserted inside the coil having the longer outside diameter. Consequently, one of the antenna element  212  and the parasitic element  312  is inserted inside the other element, and thus, the same effect as above can be obtained. 
   A description will be given of the thirteenth embodiment of the present invention.  FIG. 20(   a ) is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  213  and the parasitic element  313  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  213  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  213  is an open end. One end of the parasitic element  313  is connected to the ground of the substrate  10  and the other end of the parasitic element  313  is an open end. 
   According to this embodiment, the open end of the parasitic element  313  is meandering-shaped and vertical to the substrate  10 , and the open end of the antenna element  213  is linear-shaped. As shown in  FIG. 20(   b ), the antenna element  213  and the parasitic element  313  are disposed substantially parallel to each other in the substantially same plane as the substrate  10 . 
   According to this embodiment, same as the twelfth embodiment, the longer coil can be made without expanding the width of the antenna device, and the antenna element  213  and the parasitic element  313  are strongly capacity coupled. However, differently from the twelfth embodiment, one element is not inserted inside the other element, and thus, each element can be mounted individually on the substrate  10  in a factory. In other words, the antenna element  213  and the parasitic element  313  can be easily mounted on the substrate  10 . 
   While the open end of the antenna element  213  is linear-shaped and the open end of the parasitic element  313  is meandering-shaped as an example, other shapes may be chosen. 
   A description will be given of the fourteenth embodiment of the present invention.  FIG. 21  is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  214  and the parasitic element  314  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  214  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  214  is an open end. One end of the parasitic element  314  is connected to the ground of the substrate  10  and the other end of the parasitic element  314  is an open end. 
   According to this embodiment, the open end of the antenna element  214  is branched into two parts, and coiled elements ( 214   a ,  214   b ) are formed in the vicinity of respective ends. The open end of the parasitic element  314  is also branched into two parts, and coiled elements ( 314   a ,  314   b ) are formed in the vicinity of respective ends. 
   By forming two or more elements in the antenna element  214  and the parasitic element  314 , a multi-resonance antenna or a wideband antenna can be made. 
   While each of antenna element  214  and parasitic element  314  is provided with two elements by way of example in the structure of this embodiment, three or more elements can of course be provided. Incidentally, the elements are not limited to be coil-shaped. For example, the elements may be meandering-shaped or linear-shaped. 
   A description will be given of the fifteenth embodiment of the present invention.  FIG. 22(   a ) is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  215  and the parasitic element  315  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  215  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  215  is an open end. One end of the parasitic element  315  is connected to the ground of the substrate  10  and the other end of the parasitic element  315  is an open end. A contact plate  215   a  is attached at a feeder end of the antenna element  215  and a contact plate  315   a  is attached at a ground end of the parasitic element  315 , and each element and each corresponding contact plate are electrically connected. Incidentally, shapes of these elements are voluntarily chosen. 
   For the respective elements, the contact plates  215   a  and  315   a  are electrical connection points connecting to the substrate  10 . In order to obtain electrical connection with the substrate  10 , connectors are disposed on the substrate  10  and contact to the contact plates  215   a  and  315   a . By having the electrical connection through the contact plates  215   a  and  315   a , the antenna element  215  and the parasitic element  315  are certainly electrically connected to the substrate  10 . 
   Additionally, when the space between the substrate  10  and a housing is too narrow to dispose the connectors on the substrate  10 , as shown in  FIG. 22(   b ), in order to obtain an electrical connection, one part of each of contact plates  215   a  and  315   a  is formed into a spring shape. 
   A description will be given of the sixteenth embodiment of the present invention.  FIG. 23  is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  216  and the parasitic element  316  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  216  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  216  is an open end. One end of the parasitic element  316  is connected to the ground of the substrate  10  and the other end of the parasitic element  316  is an open end. An open end plate  216   a  is attached at the top of the open end of the antenna element  216  and an open end plate  316   a  is attached at the top of the open end of the parasitic element  316 , and each element and each corresponding open end plate are electrically connected. Incidentally, shapes of these elements are voluntarily chosen. 
   When the space between each top of the elements is the same, the elements are more strongly capacity coupled with the open end plates  216   a  and  316   a . Therefore, even in the case where a space must be made (the open ends cannot be approximated) by the structural reason, the elements are capacity coupled by a desirable capacitance value with the open end plates, and therefore better antenna characteristic is obtained. 
   A description will be given of the seventeenth embodiment of the present invention.  FIG. 24  is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  217  and the parasitic element  317  are attached on one end of the substrate  10 . At least one point of one end of the antenna element  217  is electrically connected to a signal wiring pattern on the substrate  10  and the other end of the antenna element  217  is an open end. One end of the parasitic element  317  is connected to the ground of the substrate  10  and the other end of the parasitic element  317  is an open end. A contact plate  217   a  is attached at a feeder end of the antenna element  217  and a contact plate  317   a  is attached at a ground end of the parasitic element  317 , and each element and each corresponding contact plate are electrically connected. An open end plate  217   b  is attached at the top of the open end of the antenna element  217  and an open end plate  317   b  is attached at the top of the open end of the parasitic element  317 , and each element and each corresponding open end plate are electrically connected. Incidentally, shapes of these elements are voluntarily chosen. 
   The antenna device of this embodiment has both advantages of the antenna devices of the fifteenth embodiment and the sixteenth embodiment. Overlapping explanation of each advantage is omitted here. 
   A description will be given of the eighteenth embodiment of the present invention.  FIG. 25  is a diagram showing the structure of an antenna device of this embodiment. In the antenna device, the antenna element  218  and the parasitic element  318  are attached in the vicinity of one end of the substrate  10 . The antenna element  218  is electrically connected to a signal wiring pattern at a feeder end being in the vicinity of one end of the substrate  10  and the other end of the antenna element  218  is an open end. One end of the parasitic element  318  is connected to the ground of the substrate  10  and the other end of the parasitic element  318  is an open end. 
   Each part of the antenna element  218  and the parasitic element  318  is lengthened from a feeder end and a ground end respectively in the substantially vertical direction relative to the substrate  10 , and both elements are disposed within the projection plane of the substrate  10 . 
   With such structure, it is possible to obtain a good antenna characteristic even when the substrate  10  and the elements cannot be disposed on the substantially same plane in close proximity to each other in a housing. 
   A description will be given of the nineteenth embodiment of the present invention.  FIG. 26  is a diagram showing the structure of an antenna device of this embodiment. A terminal to which the antenna device of this embodiment is applied is assembled by connecting two housings (an upper housing  8  and a lower housing  9 ) by a conjunction mechanism (such as a hinge, a slide mechanism). Incidentally, while the antenna element  219  and the parasitic element  319  whose elements are coil-shaped are shown in the figure, the same shapes of the elements as the above described embodiments may also be applied. 
   As shown in  FIG. 26 , the antenna device is disposed so that the elements are in the vicinity of a conjunction section of the two housings. With this structure, when the terminal is closed, the antenna element  219 , the parasitic element  319  and the upper housing  8  are apart from each other, and therefore a good antenna characteristic can be obtained. On the other hand, when the terminal is opened, the antenna element  219 , the parasitic element  319  and the upper housing  8  are in close proximity with each other, and therefore the antenna characteristic becomes lower in comparison with the closed terminal. Thus, the antenna device of this embodiment is better applied to the portable radio terminal, which is often used in the closed condition. 
   A description will be given of the twentieth embodiment of the present invention.  FIG. 27  is a diagram showing the structure of an antenna device of this embodiment. A terminal to which the antenna device of this embodiment is applied is assembled by connecting two housings (an upper housing  8  and a lower housing  9 ) by a conjunction mechanism (such as a hinge, a slide mechanism). Incidentally, while the antenna element  220  and the parasitic element  320  whose elements are coil-shaped are shown in the figure, the same shapes of the elements as the above described embodiments may also be applied. 
   According to this embodiment, contrary to the nineteenth embodiment, the elements are disposed apart from a conjunction section of the two housings. With this structure, when the terminal is opened, the antenna element  220 , the parasitic element  320  and the upper housing  8  are apart from each other, and therefore a good antenna characteristic can be obtained. On the other hand, when the terminal is closed, the antenna element  220 , the parasitic element  320  and the upper housing  8  are in close proximity with each other, and therefore the antenna characteristic becomes lower in comparison with the opened terminal. Thus, the antenna device of this embodiment is better applied to the portable radio terminal, which is often used in the opened condition. 
   A description will be given of the twenty-first embodiment of the present invention.  FIG. 28  is a diagram showing the structure of an antenna device of this embodiment. According to the structure of the antenna device of this embodiment, the elements are disposed alongside an interior surface of a housing. 
   With this structure, the distance between the substrate  10  and the elements can be secured as long in the housing as possible, and a better antenna characteristic can be obtained. Incidentally, the shape of the elements is voluntarily chosen and the same shapes of the elements as the above described embodiments may also be applied. 
   According to the present invention, it is possible to provide an antenna device capable of being applied to a portable radio terminal and showing a good antenna characteristic regardless of direction, and a portable radio terminal provided with the antenna device. 
   While preferred embodiments of the present invention have been described using specific terms, the description has been for illustrative purpose only. For example, while the antenna element is substantially L-shaped or substantially F-shaped in the above described embodiments, any shape can be applied as long as the antenna element and the parasitic element can be capacity coupled. 
   As above, changes and variations of the present invention may be made without departing from the spirit or scope of the following claims.