Patent Publication Number: US-8988292-B2

Title: Antenna device and electronic device including antenna device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2011-076288, filed Mar. 30, 2011, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an antenna device and an electronic device including the antenna device. 
     BACKGROUND 
     Recently, the housings of portable terminal devices typified by cellular phones, smart phones, Personal Digital Assistants (PDAs), and tablet type terminals have been required to reduce the dimensions and weight from the viewpoint of compactness and lightweightness. Accordingly, demands have arisen for more compact antenna devices. It has also been required to allow a single portable terminal device to communicate with a plurality of radio systems using different frequency bands. 
     Conventionally, therefore, a multifrequency antenna device has been proposed, which has, for example, the second antenna element formed from a monopole element and provided in a direction opposite to the first antenna element formed from a folded element with a stub at a position near the feeding point of the first antenna element. 
     In these conventionally provided multifrequency antenna devices, although it is possible to independently adjust the first resonance caused by the folded element and the second resonance caused by the monopole element, there occurs a band in which radiation efficiency deteriorates due to parallel resonance between the first resonance and the second resonance, resulting in difficulty in achieving wider bandwidth. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A general architecture that implements the various features of the embodiments will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate the embodiments and not to limit the scope of the invention. 
         FIG. 1  is a view showing the arrangement of an electronic device including an antenna device according to the first embodiment; 
         FIG. 2  is a view showing an example of the antenna device shown in  FIG. 1 ; 
         FIG. 3  is a graph showing the frequency characteristics of the imaginary part of the antenna impedance of the antenna device shown in  FIG. 2 ; 
         FIGS. 4A ,  4 B and  4 C are views showing a plurality of models obtained by changing the length of the parasitic element of the antenna device shown in  FIG. 1 ; 
         FIG. 5  is a graph showing the frequency characteristics of the imaginary parts of the antenna impedances based on the plurality of models shown in  FIGS. 4A ,  4 B and  4 C; 
         FIG. 6  is a graph showing the VSWR frequency characteristics based on the plurality of models shown in  FIGS. 4A ,  4 B and  4 C; 
         FIG. 7  is a view for explaining one of the conditions for the antenna device shown in  FIG. 1 ; 
         FIGS. 8A ,  8 B,  8 C and  8 D are views showing a plurality of models obtained by changing the length of the folded element of the antenna device shown in  FIG. 7 ; 
         FIG. 9  is a graph showing the frequency characteristics of the imaginary parts of antenna impedances based on the plurality of models shown in  FIGS. 8A ,  8 B,  8 C and  8 D; 
         FIG. 10  is a view showing the arrangement of an antenna device according to the second embodiment; 
         FIG. 11  is a view showing the arrangement of an antenna device according to the third embodiment; 
         FIG. 12  is a view showing an example of the antenna device shown in  FIG. 11 ; 
         FIG. 13  is a graph showing the frequency characteristics of the imaginary part of the antenna impedance in the example shown in  FIG. 12 ; 
         FIG. 14  is a graph showing VSWR frequency characteristics in the example shown in  FIG. 12 ; 
         FIG. 15  is a perspective view showing the arrangement of an antenna device according to the fourth embodiment; 
         FIG. 16  is a perspective view showing the arrangement of an antenna device according to the fifth embodiment; 
         FIG. 17  is a cross-sectional view of the antenna device shown in  FIG. 16 ; 
         FIG. 18  is a perspective view showing the arrangement of an antenna device according to the sixth embodiment; 
         FIG. 19  is a graph showing the frequency characteristics of the imaginary part of the antenna impedance of the antenna device shown in  FIG. 18 ; 
         FIG. 20  is a graph showing the VSWR frequency characteristics of the antenna device shown in  FIG. 18 ; 
         FIG. 21  is a perspective view showing the arrangement of an antenna device according to the seventh embodiment; 
         FIG. 22  is a graph showing the frequency characteristics of the imaginary part of the antenna impedance of the antenna device shown in  FIG. 21 ; 
         FIG. 23  is a graph showing the VSWR frequency characteristics of the antenna device shown in  FIG. 21 ; 
         FIG. 24  is a perspective view showing the arrangement of an antenna device according to the eighth embodiment; 
         FIG. 25  is a graph showing the frequency characteristics of the imaginary part of the antenna impedance of the antenna device shown in  FIG. 24 ; 
         FIG. 26  is a graph showing the VSWR frequency characteristics of the antenna device shown in  FIG. 24 ; 
         FIG. 27  is a perspective view showing the arrangement of an antenna device according to the ninth embodiment; 
         FIG. 28  is a graph showing the frequency characteristics of the imaginary part of the antenna impedance of the antenna device shown in  FIG. 27 ; 
         FIG. 29  is a graph showing the VSWR frequency characteristics of the antenna device shown in  FIG. 27 ; 
         FIG. 30  is a perspective view showing the arrangement of an antenna device according to the 10th embodiment; 
         FIG. 31  is a graph showing the frequency characteristics of the imaginary part of the antenna impedance of the antenna device shown in  FIG. 30 ; 
         FIG. 32  is a graph showing the VSWR frequency characteristics of the antenna device shown in  FIG. 30 ; 
         FIGS. 33A ,  33 B,  33 C,  33 D and  33 E are views showing the first modification group of a folded element; 
         FIGS. 34A ,  34 B,  34 C,  34 D and  34 E are views showing the second modification group of a folded element; 
         FIGS. 35A ,  35 B,  35 C,  35 D and  35 E are views showing the first modification group of a monopole element; 
         FIGS. 36A ,  36 B,  36 C and  36 D are views showing the second modification group of a monopole element; 
         FIGS. 37A ,  37 B,  37 C,  37 D and  37 E are views showing the first modification group of a parasitic element; 
         FIGS. 38A ,  38 B,  38 C and  38 D are views showing the second modification group of a parasitic element; and 
         FIGS. 39A and 39B  are views showing a modification group to which the second parasitic element is added. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. 
     In general, according to one embodiment, an antenna device includes a first antenna element formed from a folded monopole element, a second antenna element formed from a monopole element, and a third antenna element formed from a parasitic element. 
     One end of the first antenna element is connected to a feeding terminal, and the other end is connected to a first ground terminal. The first antenna element is folded in the middle, with a stub being provided between the forward and backward portions formed by folding. 
     One end of the second antenna element is connected to the above feeding terminal directly or through part of the first antenna element, and the other end is open. 
     One end of the third antenna element is connected to a second ground terminal provided at a position on the opposite side to the first ground terminal through the feeding terminal, and the other end is open. 
     The electrical length of the first antenna element from the feeding terminal to the first ground terminal through the other end of the folding portion is set to nearly ½ a wavelength corresponding to a predetermined first resonance frequency. 
     The electrical length of the second antenna element from the feeding terminal to the other end is set to nearly ¼ a wavelength corresponding to a predetermined second resonance frequency. 
     The third antenna element is placed parallel to the second antenna element in a state in which at least part of the third antenna element can be capacitively coupled to the second antenna element. The electrical length of the third antenna element from the second ground terminal to the other end is set to nearly ¼ a wavelength corresponding to a predetermined third resonance frequency. 
     The antenna device having the above arrangement can prevent the occurrence of parallel resonance between a plurality of series resonance bands. This can implement wider resonance bands. 
     First Embodiment 
       FIG. 1  is a view showing the arrangement of the main components of an electronic device including an antenna device according to the first embodiment. This electronic device includes a notebook personal computer or television receiver including a radio interface. The housing (not shown) of this device accommodates a printed circuit board  1 . 
     Note that the electronic device may be a portable terminal such as a cellular phone, smart phone, PDA (Personal Digital Assistant), or tablet type terminal other than a notebook personal computer or television receiver. The printed circuit board  1  may be formed as part of the metal housing or formed from a metal member such as a copper foil. 
     The printed circuit board  1  includes a first area  1   a  and a second area  1   b . The first area  1   a  is provided with an antenna device  4 . A ground pattern  3  is formed in the second area  1   b . In addition, first and second ground terminals  31  and  32  are provided in the second area  1   b . Note that a plurality of circuit modules required to constitute an electronic device are mounted on the rear surface side of the printed circuit board  1 . 
     The circuit module includes a radio unit  2 . The radio unit  2  has a function of transmitting and receiving radio signals by using the channel frequency assigned to a radio system as a communication target. The first area  1   a  is provided with a feeding terminal  22 . The radio unit  2  is connected to the feeding terminal  22  through a feeding pattern  21 . 
     The antenna device  4  has the following arrangement. 
     The antenna device  4  includes a folded monopole element  41  as the first antenna element, a monopole element  42  as the second antenna element, and a parasitic element  43  as the third antenna element. The elements  41 ,  42  and  43  are arranged such that the folded monopole element  41  is placed at a position nearest to the ground pattern  3 , and the monopole element  42  and the parasitic element  43  are placed outside the monopole element  41  in increasing order of distance from the ground pattern  3 . 
     The folded monopole element  41  is formed from a conductive pattern having a shape obtained by folding the element in a hairpin form at a position dividing the entire element into almost two equal portions, with one end of the element being connected to the feeding terminal  22 , and the other end being connected to the first ground terminal  31 . A stub  411  is provided between the forward and backward portions formed by folding the element. The element length of the folded monopole element  41 , that is, the electrical length from the feeding terminal  22  to the first ground terminal  31  through the folding position, is set to nearly ½ a wavelength corresponding to a predetermined first resonance frequency f 1 . 
     The monopole element  42  is formed from an L-shaped conductive pattern having a proximal end connected to the feeding terminal  22  through part of the folded monopole element  41 , and a distal end open. The element length of the monopole element  42 , that is, the electrical length from the feeding terminal  22  to the distal end, is set to nearly ¼ a wavelength corresponding to a predetermined second resonance frequency f 2 . 
     The parasitic element  43  is formed from an L-shaped conductive pattern having a proximal end connected to the ground terminal  32 , and a distal end open. The element length of the parasitic element  43 , that is, the electrical length from the ground terminal  32  to the distal end, is set to a length nearly ¼ a wavelength corresponding to a predetermined third resonance frequency f 3 . The parasitic element  43  is also placed parallel to the monopole element  42  such that at least part of the horizontal portion of the parasitic element  43  on the distal end side can be current-coupled to the horizontal portion of the monopole element  42 . 
     The first resonance frequency f 1  is set in the band (700 MHz to 900 MHz) used by, for example, a radio system using LTE (Long Term Evolution). The second resonance frequency f 2  is set in the band (1.7 GHz to 1.9 GHz) used by a radio system based on the 3G standard. The third resonance frequency f 3  is set in a band near the first resonance frequency f 1  or the second resonance frequency f 2  to expand the band used by the above radio system using LTE or the band used by the radio system based on the 3G standard. 
     The element lengths of the folded monopole element  41  with the stub, monopole element  42 , and parasitic element  43  and their relative positions are set to lengths that are necessary to generate the first, second, and third resonance frequencies f 1 , f 2 , and f 3 .  FIG. 2  shows an example of an antenna device configured to satisfy this condition. The numbers in  FIG. 2  represent the dimensions (unit: mm) of the respective antenna element portions. 
     In order to generate the third resonance frequency f 3  on the parasitic element  43 , the parasitic element  43  needs to be placed such that at least part of the distal end horizontal portion of the parasitic element  43  becomes parallel to the horizontal portion of the monopole element  42 . In order to check this condition, the present applicant analyzed the frequency characteristics of the imaginary parts of antenna impedances obtained when setting the distance (d in  FIG. 2 ) between the feeding terminal  22  and the ground terminal  32 , to which the parasitic element  43  is grounded, to 5 mm, 10 mm, 15 mm, and 20 mm.  FIG. 3  shows an example of the analysis result. 
     As is obvious from  FIG. 3 , when the distance d becomes larger than 15 mm, that is, the length of the portion of the parasitic element  43  which is parallel to the monopole element  42  becomes equal to or less than 0 mm, the parasitic element  43  cannot maintain a capacitively coupled state with the monopole element  42 . As a consequence, it becomes impossible to cause resonance, as indicated by “A” in  FIG. 3 . Obviously, therefore, it is necessary to place the parasitic element  43  so as to maintain a state in which at least the distal end portion of the parasitic element  43  is parallel to the horizontal portion of the monopole element  42 . 
     In addition, the antenna device  4  of the first embodiment can independently adjust the third resonance frequency f 3  by changing the element length of the parasitic element  43 . In order to check this effect, the present applicant prepared three kinds of models 01, 02, and 03 obtained by setting the element length of the parasitic element  43  to different lengths as shown in, for example,  FIGS. 4A ,  4 B and  4 C and analyzed the frequency characteristics of the imaginary parts of the antenna impedances of the respective models and frequency characteristics of voltage standing wave ratio (VSWR).  FIGS. 5 and 6  each show an example of each analysis result. 
     As is obvious from the characteristics shown in  FIGS. 5 and 6 , setting the length of the horizontal portion of the parasitic element  43  to a relatively large value (e.g., 40 mm) as shown in  FIG. 4A  can generate the third resonance frequency f 3  in a low band K 31  (e.g., near 1.2 GHz). In addition, setting the length of the horizontal portion of the parasitic element  43  to a value (e.g., 27.5 mm) smaller than 40 mm as shown in  FIG. 4B  can generate the third resonance frequency f 3  in a band K 32  (near 2 GHz) higher than 1.2 GHz. Furthermore, setting the length of the horizontal portion of the parasitic element  43  to a value (e.g., 12.5 mm) shorter than 27.5 mm as shown in  FIG. 4C  can generate the third resonance frequency f 3  in a band K 33  (near 3.2 GHz) higher than 2 GHz. Note that K 1  and K 2  in  FIG. 5  represent the first and second resonance frequencies f 1  and f 2  generated by the folded monopole element  41  and the monopole element  42 . 
     The parasitic element  43  causes no interference with the folded monopole element  41  and the monopole element  42 . This is because the folded monopole element  41 , the monopole element  42 , and the parasitic element  43  are arranged in a positional relationship like that shown in  FIG. 1  so as not to cause parallel resonance in bands between series resonances between the folded monopole element  41 , the monopole element  42 , and the parasitic element  43 , thereby preventing an increase in mismatch loss and deterioration in radiation efficiency. 
     That is, according to the antenna device  4  described above, merely setting the element length of the parasitic element  43  to an arbitrary length can independently set the third resonance frequency f 3  in an arbitrary band near the first or second resonance frequency f 1  or f 2  without causing any interference between the folded monopole element  41  and the monopole element  42 . This can implement wider bands of the first or second resonance frequency f 1  or f 2 . 
     In order to effectively obtain the above effects, a distance C between the first ground terminal  31  and the feeding terminal  22  of the folded monopole element  41  may be set to ⅕ or less a wavelength corresponding to the first resonance frequency f 1  as shown in  FIG. 7 . In order to check this condition, the present applicant prepared four kinds of models, 04 to 07, obtained by changing the distance C as shown in, for example,  FIGS. 8A ,  8 B,  8 C and  8 D and analyzed the frequency characteristics of the imaginary parts of the antenna impedances of the respective models.  FIG. 9  shows an example of the analysis result. 
     As is obvious from the analysis result shown in  FIG. 9 , in the models 04 to 06 with the distance C being set to be relatively short, series resonances K 11 , K 12  and K 13  occur owing to the folded monopole element  41 . However, in the model 07 with the distance C being set to be long, no sufficient series resonance occurs, and hence the first resonance frequency f 1  cannot be set. 
     As described in detail above, according to the first embodiment, the folded monopole element  41  with the stub, the monopole element  42 , and the parasitic element  43  are arranged in increasing order of distance from the ground pattern  3 , and the parasitic element  43  is placed so as to make at least part of its distal end horizontal portion become parallel to the horizontal portion of the monopole element  42 , thereby generating the third resonance frequency f 3  on the parasitic element  43 . 
     Therefore, merely setting the element length of the parasitic element  43  to an arbitrary length in the above manner can independently set the third resonance frequency f 3  in an arbitrary band near the first or second resonance frequency f 1  or f 2  without causing any interference between the folded monopole element  41  and the monopole element  42 . This can implement wider bands of the first or second resonance frequency f 1  or f 2 . 
     Second Embodiment 
       FIG. 10  is a view showing the arrangement of an antenna device according to the second embodiment. The same reference numerals as in  FIG. 10  denote the same parts in  FIG. 1 , and a detailed description of them will be omitted. 
     The section extending from the stub installation position to the folding position of a folded monopole element  41  with a stub is formed from one element  412  having a plate-like shape. Note that the element  412  may have a rod-like shape other than a plate-like shape. 
     This arrangement can increase the structural strength of the section of the folded monopole element  41  which extends from the stub to the folding position, and hence can increase the yield in manufacturing an antenna device  4 . 
     Third Embodiment 
       FIG. 11  is a view showing the arrangement of an antenna device according to the third embodiment. The same reference numerals as in  FIG. 11  denote the same parts in  FIG. 1 , and a detailed description of them will be omitted. 
     A folded monopole element  41  is formed by folding its section extending from the stub installation position to the folding position in a crank shape, with one additional element  44  being provided at a position corresponding to the root portion of the crank shape. 
       FIG. 12  shows a specific arrangement of this monopole element. The numbers in  FIG. 12  represent the dimensions (unit: mm) of the respective antenna element portions.  FIGS. 13 and 14  show the results obtained by analyzing the frequency characteristics of the imaginary part of the antenna impedance and voltage standing wave ratio (VSWR) frequency characteristic.  FIGS. 13 and 14  show also characteristics obtained without using the additional element  44 . 
     As is obvious from  FIGS. 13 and 14 , providing the additional element  44  can also generate a resonance frequency at near 2.5 GHz. This allows the antenna device  4  to cope with a larger number of resonances. In addition, this can continuously expand the multiple resonance band from 2.0 GHz to 2.5 GHz. 
     Fourth Embodiment 
       FIG. 15  is a view showing the arrangement of an antenna device according to the fourth embodiment. The same reference numerals as in  FIG. 15  denote the same parts in  FIG. 1 , and a detailed description of them will be omitted. 
     A ground pattern  3  formed on a printed circuit board  1  has a side in a crank shape which is in contact with a first area  1   a . A feeding cable  23  is placed along a side of the portion on the ground pattern  3  which is formed into the crank shape so as to protrude into the first area  1   a . The feeding cable  23  is formed from a coaxial cable obtained by shielding a conductive line  24 , and the shielded line is grounded to a ground terminal  33  provided on the ground pattern  3 . 
     In addition, a portion of the first area  1   a  which protrudes into a second area  1   b  by forming the ground pattern  3  into a crank shape is provided with a feeding terminal  22 . The distal end portion of the conductive line  24  of the feeding cable  23  is electrically connected to the feeding terminal  22  through a means such as soldering. 
     This arrangement allows to place the feeding cable  23  along a side of the ground pattern  3  without forcibly bending the feeding cable  23 . This can improve the implementation efficiency of electronic components per unit area by effectively using the space of the printed circuit board  1 , thereby further improving the reliability of the device. In addition, this arrangement can prevent the feeding cable  23  from overlapping a parasitic element  43 , and hence can reduce variations in antenna characteristics owing to wiring of the feeding cable  23 . 
     Fifth Embodiment 
       FIG. 16  is a perspective view showing the arrangement of an antenna device according to the fifth embodiment.  FIG. 17  is a cross-sectional view of the antenna device shown in  FIG. 16 . The same reference numerals as in  FIG. 17  denote the same parts in  FIG. 1 , and a detailed description of them will be omitted. 
     The antenna device according to the fifth embodiment includes a resin antenna base material (resin base material)  5 . A folded monopole element  41  with a stub, a monopole element  42 , and a parasitic element  43  are arranged on the circumferential surface of the resin base material  5 . 
     More specifically, a printed circuit board  1  is formed from a flexible board. Conductive patterns respectively forming the folded monopole element  41  with the stub, the monopole element  42 , and the parasitic element  43  are formed in a first area  1   a  of the printed circuit board  1  formed from this flexible board. On the other hand, the resin base material  5  is formed from a prismatic body having a longitudinal cross-section. As shown in  FIG. 17 , the printed circuit board  1  formed from the above flexible board as shown in  FIG. 17  is wound around the circumferential surface of the resin base material  5  formed from this prismatic body. 
     For the sake of illustrative convenience,  FIG. 17  shows that the printed circuit board  1  is spaced apart from the circumferential surface of the resin base material  5 . In practice, however, the printed circuit board  1  is provided in tight contact with the resin base material  5  with an adhesive or bonding material such as a doubled-sided adhesive tape. As the resin base material  5 , a columnar body, an elliptic columnar body, or a plate-like body can be used instead of a prismatic body. 
     This arrangement can decrease the dimensions of the printed circuit board  1  in a planar direction, and hence can downsize the antenna device  4 , that is, the electronic device. In addition, arranging the folded monopole element  41  with the stub, the monopole element  42 , and the parasitic element  43  on the circumferential surface of the resin base material  5  can provide a highly reliable device with structural stability. 
     Sixth Embodiment 
       FIG. 18  is a perspective view showing the arrangement of an antenna device according to the sixth embodiment. The same reference numerals as in  FIG. 18  denote the same parts in  FIGS. 15 ,  16  and  17 , and a detailed description of them will be omitted. 
     Conductive patterns respectively forming a folded monopole element  41  with a stub, a monopole element  42 , and a parasitic element  43  are formed on a printed circuit board  1  formed from a flexible board. Of these elements, the folded monopole element  41  with the stub has a section extending from its stub installation position to the folding position, which is formed from one plate-like element  412 . The middle position of the monopole element  42  is connected to the folded monopole element  41  through a connecting element  424 . The proximal end portion of the parasitic element  43  is formed into a plate-like shape. In addition, power is fed to the folded monopole element  41  with the stub and the monopole element  42  via a feeding cable  23  formed from a coaxial cable. 
       FIGS. 19 and 20  show an example of the results obtained by analyzing the frequency characteristics of the imaginary part of the antenna impedance and frequency characteristics of voltage standing wave ratio (VSWR) of the antenna device having the above arrangement. According to this example, a first resonance K 1  occurs near 800 MHz owing to the folded monopole element  41  with the stub  411 , and a third resonance K 3  occurs near 1.0 GHz at a position near the first resonance K 1  owing to the parasitic element  43 . This can expand the resonance band from 800 MHz to 1.0 GHz. In addition, a resonance K 2  occurs near 1.9 GHz owing to the monopole element  42 . 
     Seventh Embodiment 
       FIG. 21  is a perspective view showing the arrangement of an antenna device according to the seventh embodiment. The same reference numerals as in  FIG. 21  denote the same parts in  FIGS. 15 ,  16 ,  17  and  18 , and a detailed description of them will be omitted. 
     Conductive patterns respectively forming a folded monopole element  41  with a stub, a monopole element  42 , and a parasitic element  43  are formed on the printed circuit board  1  formed from a flexible substrate. Of these elements, the folded monopole element  41  with the stub has a section extending from its stub installation position to the folding position, which is formed from one plate-like element  412 . The plate-like element  412  has a width larger than that of the section extending from the stub installation position to a feeding terminal  22 . The parasitic element  43  has a planar proximal end portion. In addition, power is fed to the folded monopole element  41  with the stub and the monopole element  42  via a feeding cable  23  formed from a coaxial cable. 
       FIGS. 22 and 23  show an example of the results obtained by analyzing the frequency characteristics of the imaginary part of the antenna impedance and frequency characteristics of voltage standing wave ratio (VSWR) by the antenna device having the above arrangement. According to this example, a first resonance K 1  occurs near 900 MHz owing to the folded monopole element  41  with the stub. A second resonance K 2  occurs near 1.9 MHz owing to the monopole element  42 , and a third resonance K 3  occurs near 2.3 GHz at a position adjacent to the second resonance K 2  owing to the parasitic element  43 . This can expand the resonance band from 1.9 GHz to 2.3 GHz. 
     Eighth Embodiment 
       FIG. 24  is a perspective view showing the arrangement of an antenna device according to the eighth embodiment. The same reference numerals as in  FIG. 24  denote the same parts in  FIGS. 15 ,  16  and  17 , and a detailed description of them will be omitted. 
     Conductive patterns respectively forming a folded monopole element  41  with a stub, a monopole element  42 , and a parasitic element  43  are formed on the printed circuit board  1  formed from a flexible substrate. Of these elements, as shown in  FIG. 11 , the folded monopole element  41  with the stub is formed by folding its section extending from the stub installation position to the folding position in a crank shape. The section extending from this stub installation position to the folding position is formed from one element  412 , and the element  412  has a width larger than the section extending from the stub installation position to a feeding terminal  22 . 
     One additional element  44  is provided at a position corresponding to the root portion of the crank shape. The parasitic element  43  has a planar proximal end portion. In addition, power is fed to the folded monopole element  41  with the stub and the monopole element  42  via a feeding cable  23  formed from a coaxial cable. 
       FIGS. 25 and 26  show an example of the results obtained by analyzing the frequency characteristics of the imaginary part of the antenna impedance and frequency characteristics of voltage standing wave ratio (VSWR) of the antenna device having the above arrangement. According to this example, a first resonance K 1  occurs near 900 MHz owing to the folded monopole element  41  with the stub. A second resonance K 2  occurs near 2.0 GHz owing to the monopole element  42 , and a third resonance K 3  occurs near 2.6 MHz at a position adjacent to the second resonance K 2  owing to the parasitic element  43 . This can expand the resonance band from 2.0 GHz to 2.6 GHz. In addition, a fourth resonance K 4  occurs near 3.2 GHz owing to the additional element  44 . 
     That is, this arrangement can provide a multiple resonance antenna device having a wide resonance band ranging from 2.0 GHz to 2.6 GHz. 
     Ninth Embodiment 
       FIG. 27  is a perspective view showing the arrangement of an antenna device according to the ninth embodiment. The same reference numerals as in  FIG. 27  denote the same parts in  FIG. 24 , and a detailed description of them will be omitted. 
     The ninth embodiment differs from the eighth embodiment in that a monopole element  42  has a longer element length. 
       FIGS. 28 and 29  show an example of the results obtained by analyzing the frequency characteristics of the imaginary part of the antenna impedance and frequency characteristics of voltage standing wave ratio (VSWR) of the antenna device having the above arrangement. According to this example, it is possible to decrease the frequency of a second resonance K 2  owing to the monopole element  42  to a frequency near 1.85 GHz. Therefore, the second resonance K 2  owing to the monopole element  42  and a third resonance K 3  owing to a parasitic element  43  can further expand a 2-GHz resonance band. 
     10th Embodiment 
       FIG. 30  is a perspective view showing the arrangement of an antenna device according to the 10th embodiment. The same reference numerals as in  FIG. 30  denote the same parts in  FIG. 18 , and a detailed description of them will be omitted. 
     The 10th embodiment differs from the sixth embodiment in that a parasitic element  43  is branched midway into two elements  4371  and  4372  having different lengths, and the element  4371 , i.e., one of the elements  4371  and  4372 , has a plate-like distal end portion  433 . 
       FIGS. 31 and 32  show an example of the results obtained by analyzing the frequency characteristics of the imaginary part of the antenna impedance and frequency characteristics of voltage standing wave ratio (VSWR) by the antenna device having the above arrangement. According to this example, a first resonance K 1  occurs near 800 MHz owing to a folded monopole element  41  with a stub. A third resonance K 3  occurs near 1.0 GHz at a position near the first resonance K 1  owing to one parasitic element  4371 . This can expand the resonance band from 800 MHz to 1.0 GHz. In addition, a second resonance K 2  occurs near 1.9 GHz owing to a monopole element  42 , and a fourth resonance K 4  occurs near 2.2 GHz at a position near the second resonance K 2  owing to the other parasitic element  4372 . This can expand the resonance band from 1.9 GHz to 2.2 GHz. 
     Other Embodiments 
     (1) Modification of Folded Monopole Element  41  with Stub 
       FIGS. 33A ,  33 B,  33 C,  33 D and  33 E and  FIGS. 34A ,  34 B,  34 C,  34 D and  34 E show various modifications of the folded monopole element  41  with the stub. 
     The antenna device shown in  FIG. 33A  is configured such that the section extending from the installation position of the stub  411  of the folded monopole element  41  with the stub to the folding end is folded. This arrangement can reduce the installation space of the antenna device in the longitudinal direction of the folded monopole element  41  with the stub even if its element length is long. 
     The antenna device shown in  FIG. 33B  has a plurality of (two in the case shown in  FIG. 33B ) stubs  4111  and  4112  provided between the forward and backward portions of the folded monopole element  41  with the stub which are formed by folding. This arrangement can cause a larger number of resonances. 
     The antenna device shown in  FIG. 33C  is configured such that the folded monopole element  41  with the stub has a wide portion near the feeding terminal  22 . 
     The antenna device shown in  FIG. 33D  is configured such that the folded monopole element  41  with the stub has a wide portion near the first ground terminal  31 . 
     The antenna device shown in  FIG. 33E  is configured such that the ground position of the folded monopole element  41  with the stub relative to the ground pattern  3 , i.e., the position of the first ground terminal  31 , is offset in the direction of the distal end of the folded monopole element  41  with the stub. 
     The antenna device shown in  FIG. 34A  is configured such that the section extending from the installation position of the stub  411  of the folded monopole element  41  with the stub to the folding end is formed from one element, which is formed into a meandering shape. 
     The antenna device shown in  FIG. 34B  is configured such that the portion between the middle portion and distal end portion of the section extending from the installation position of the stub  411  of the folded monopole element  41  with the stub to the folding end is formed from one element. 
     The antenna device shown in  FIG. 34C  is configured such that the folded monopole element  41  with the stub and the monopole element  42  have a wide portion near the feeding terminal  22 . 
     The antenna device shown in  FIG. 34D  is configured such that the portion between the middle portion and distal end portion of the section extending from the installation position of the stub  411  of the folded monopole element  41  with the stub to the folding end is formed from a wide plate-like element. 
     The antenna device shown in  FIG. 34E  is configured such that lumped parameter elements  61 ,  62  and  63  are respectively inserted in a portion near the feeding terminal  22  of the folded monopole element  41  with the stub and monopole element  42 , the interval from the branch position between the folded monopole element  41  with the stub and the monopole element  42  to the installation position of the stub  411 , and a portion near the first ground terminal  31  of the folded monopole element  41  with the stub. The lumped parameter elements  61 ,  62  and  63  are formed from inductances and have a function of increasing the electrical length of the folded monopole element  41  with the stub. 
     (2) Modification of Monopole Element  42   
       FIGS. 35A ,  35 B,  35 C,  35 D and  35 E and  FIGS. 36A ,  36 B,  36 C and  36 D show various modifications of the monopole element  42 . 
     The antenna device shown in  FIG. 35A  is configured such that the distal end portion of the monopole element  42  is folded. This makes it possible to reduce the installation space of the antenna device in the longitudinal direction of the monopole element  42  even if it has a long element length. 
     The antenna device shown in  FIG. 35B  is configured such that the monopole element  42  has a wide distal end portion. 
     The antenna device shown in  FIG. 35C  is configured such that the monopole element  42  is connected to the folded monopole element  41  with the stub through the connecting element  424  at a position where they are parallel to each other. 
     The antenna device shown in  FIG. 35D  is configured such that the distal end portion of the monopole element  42  is branched to provide an additional element  425 . Note that the device shown in  FIG. 35D  is provided with only one additional element  425 . However, two or more additional elements may be provided. 
     The antenna device shown in  FIG. 35E  is configured such that the monopole element  42  is branched at the feeding terminal  22  or at its nearby position without being branched midway along the folded monopole element  41  with the stub. 
     The antenna device shown in  FIG. 36A  is configured such that the distal end portion of the monopole element  42  is formed into a meandering shape. 
     The antenna device shown in  FIG. 36B  is configured such that a connecting portion  427  of the monopole element  42  for the folded monopole element  41  with the stub is formed into a wide portion. 
     The antenna device shown in  FIG. 36C  is configured such that a second monopole element  428  is provided on the monopole element  42  in a direction opposite to the bending direction of the monopole element  42 . Although  FIG. 36C  shows a case in which one second monopole element  428  is provided, two or more second monopole elements may be provided. 
     The antenna device shown in  FIG. 36D  is configured such that a lumped parameter element  64  is inserted in a portion near the connecting portion between the monopole element  42  and the folded monopole element  41  with the stub. The lumped parameter element  64  is formed from an inductance and has a function of increasing the electrical length of the monopole element  42 . 
     (3) Modification of Parasitic Element  43   
       FIGS. 37A ,  37 B,  37 C,  37 D and  37 E and  FIGS. 38A ,  38 B,  38 C and  38 D show various modifications of the parasitic element  43 . 
     The antenna device shown in  FIG. 37A  is configured such that the distal end portion of the parasitic element  43  is folded. 
     The antenna device shown in  FIG. 37B  is configured such that the distal end portion of the parasitic element  43  is formed into a meandering shape. This makes it possible to reduce the installation space of the antenna device in the longitudinal direction of the parasitic element  43  even if it has a long element length. 
     The antenna device shown in  FIG. 37C  is configured such that the parasitic element  43  has a wide distal end portion. 
     The antenna device shown in  FIG. 37D  is configured such that the distal end portion of the parasitic element  43  is branched into a plurality of portions to provide a plurality of elements  4341  and  4342 . In the case shown in  FIG. 37D , the distal end portion is branched into two portions. However, the distal end portion may be branched into three or more portions. 
     The antenna device shown in  FIG. 37E  is configured such that a plurality of parasitic elements  43  and  45  are provided between the feeding terminal  22  and the second ground terminal  32 . 
     The antenna device shown in  FIG. 38A  is configured such that the middle portion of the parasitic element  43  is formed into a meandering shape. This arrangement makes it possible to reduce the installation space of the antenna device in the longitudinal direction of the parasitic element  43  even if it has a long element length. 
     The antenna device shown in  FIG. 38B  is configured such that the proximal end portion of the parasitic element  43  which is near the second ground terminal  32  is formed into a wide portion. 
     The antenna device shown in  FIG. 38C  is configured such that the parasitic element  43  is branched into a plurality of portions at a position where it is bent in an L shape, thereby providing a plurality of elements  4371  and  4372 . In the case shown in  FIG. 38C , the parasitic element  43  is branched into two portions. However, the parasitic element  43  may be branched into three or more portions. 
     The antenna device shown in  FIG. 38D  is configured such that a lumped parameter element  65  is inserted in a portion near the connecting position between the parasitic element  43  and the second ground terminal  32 . The lumped parameter element  65  is formed from an inductance and has a function of increasing the electrical length of the parasitic element  43 . 
     (4) When Parasitic Element is Added 
       FIGS. 39A and 39B  each show an example of the arrangement including an additional parasitic element. 
       FIG. 39A  shows an arrangement in which a second parasitic element  46  is placed between the ground pattern  3  and the folded monopole element  41  with the stub independently of the folded monopole element  41  with the stub. 
     Referring to  FIG. 39B , a second parasitic element  47  is placed between the ground pattern  3  and the folded monopole element  41  with the stub, and the ground terminal of the second parasitic element  47  is shared with the first ground terminal  31  of the folded monopole element  41  with the stub. The above arrangement can further increase the number of resonances and expand the band. 
     In addition, the shapes, installation positions, sizes of the folded monopole element with the stub, monopole element, and parasitic element and the types, arrangements, and the like of the electronic device can be variously modified and embodied. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.