Patent Publication Number: US-2022224015-A1

Title: Antenna unit and wireless communication device including the same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of International Application No. PCT/JP2020/037890 filed on Oct. 6, 2020 which claims priority from Japanese Patent Application No. 2019-197528 filed on Oct. 30, 2019. The contents of these applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND ART 
     Technical Field 
     The present disclosure relates to an antenna unit and a wireless communication device including the antenna unit. 
     Background Art 
     For example, the Patent Document 1 discloses a bow-tie antenna whose size is downsized while keeping wideband characteristics thereof. Because each of a pair of antenna conductors has a shape extending in a direction away from a feed point and having the width that expands as the distance from the feed point increases, the bow-tie antenna has wideband characteristics.
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2010-263524   

     BRIEF SUMMARY 
     A downsized antenna unit for communicating in a first frequency band having wide band width is desirable to be also usable in a second frequency band, which is another frequency band. That is to say, such a downsized antenna unit is desirable to be dual-band compatible. However, in the case where the second frequency band is a low frequency band compared with the first frequency band, it is required to extend the antenna length in order to become compatible with that second frequency band. As a result, the size of the antenna unit increases. 
     The present disclosure is to enable an antenna unit communicating in a higher frequency band having wide band width to communicate also in a lower frequency band while suppressing an increase in the size of the antenna unit. 
     In order to resolve foregoing technical issues, according to one aspect of the present disclosure, there is provided an antenna unit including: a feed point; a first antenna conductor extending from the feed point in a direction away from the ground conductor and having a width that expands as a distance from the feed point increases; a second antenna conductor facing a top end edge of the first antenna conductor with a gap formed therebetween; a first connection part connecting the top end edge of the first antenna conductor and the second antenna conductor via a capacitor; and a second connection part connecting the top end edge of the first antenna conductor and the second antenna conductor via an inductor or a zero-ohm resistor, wherein a first connection point between the first connection part and the first antenna conductor is closer to a center of the top end edge of the first antenna conductor compared with a second connection point between the second connection part and the first antenna conductor. 
     Moreover, according to a different aspect of the present disclosure, there is provided a wireless communication device including the foregoing antenna unit, and a feed circuit that supplies power to the feed point of the antenna unit. 
     The present disclosure enables an antenna unit communicating in a higher frequency band having wide band width to communicate also in a lower frequency band while suppressing an increase in the size of the antenna unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a wireless communication device including an antenna unit according to an embodiment 1 of the present disclosure. 
         FIG. 2  is a partially enlarged view of the wireless communication device. 
         FIG. 3  is a partially enlarged view of a wireless communication device including an antenna unit of a comparative example. 
         FIG. 4  is a diagram illustrating frequency characteristics (matching completed) of return loss of the antenna unit according to the embodiment 1 (working example 1) and the antenna unit of the comparative example. 
         FIG. 5  is a partially enlarged view of a wireless communication device including an antenna unit according to an embodiment 2 of the present disclosure. 
         FIG. 6  is a diagram illustrating frequency characteristics of return loss (matching completed) of the antenna unit according to the embodiment 1 (working example 1) and the antenna unit according to the embodiment 2 (working example 2). 
         FIG. 7  is a partially enlarged view of a wireless communication device including an antenna unit according to an embodiment 3 of the present disclosure. 
         FIG. 8  is a diagram illustrating relationships between the band width of frequency band and the inductor&#39;s inductance value for an inductor arranged between a short-circuit conductor and a ground conductor and an inductor arranged between the short-circuit conductor and a first antenna conductor. 
         FIG. 9  is a partially enlarged view of a wireless communication device including an antenna unit according to an embodiment 4 of the present disclosure. 
         FIG. 10  is a partially enlarged view of a wireless communication device including an antenna unit according to an embodiment 5 of the present disclosure. 
         FIG. 11  is a partially enlarged view of a wireless communication device including an antenna unit according to an embodiment 6 of the present disclosure. 
         FIG. 12  is a partially enlarged view of a wireless communication device including an antenna unit according to an embodiment 7 of the present disclosure. 
         FIG. 13  is a partially enlarged view of a wireless communication device including an antenna unit according to an embodiment 8 of the present disclosure. 
         FIG. 14  is a partially enlarged view of a wireless communication device including an antenna unit according to an embodiment 9 of the present disclosure. 
         FIG. 15  is a partially enlarged view of a wireless communication device including an antenna unit according to an embodiment 10 of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     An antenna unit of one aspect of the present disclosure includes a feed point; a first antenna conductor extending from the feed point in a direction away from the ground conductor and having a width that expands as a distance from the feed point increases; a second antenna conductor facing a top end edge of the first antenna conductor with a gap formed therebetween; a first connection part connecting the top end edge of the first antenna conductor and the second antenna conductor via a capacitor; and a second connection part connecting the top end edge of the first antenna conductor and the second antenna conductor via an inductor or a zero-ohm resistor, wherein a first connection point between the first connection part and the first antenna conductor is closer to a center of the top end edge of the first antenna conductor compared with a second connection point between the second connection part and the first antenna conductor. 
     Such an aspect enables an antenna unit communicating in a higher frequency band having wide band width to communicate also in a lower frequency band while suppressing an increase in the size of the antenna unit. 
     For example, the first connection point may be positioned at the center of the top end edge of the first antenna conductor, and the second connection point may be positioned at one end of the top end edge of the first antenna conductor. 
     For example, the antenna unit may further include a ground conductor connected to the feed point. In this case, the first antenna conductor extends in a direction away from the ground conductor. 
     For example, the antenna unit may further include a short-circuit conductor, one end portion of the short-circuit conductor being connected to the first antenna conductor, another end portion of the short-circuit conductor being connected to the ground conductor. In this case, a third connection point between the short-circuit conductor and the first antenna conductor can be closer to the second connection point than to the first connection point. 
     For example, the one end portion of the short-circuit conductor may be connected to the first antenna conductor via an inductor, and the another end portion of the short-circuit conductor may be connected to the ground conductor via an inductor. 
     For example, a width of the second antenna conductor may be equal to or greater than a length of the top end edge. 
     For example, the first antenna conductor may have a triangular shape whose base is the top end edge, and the second antenna conductor may have a rectangular shape. 
     For example, the first antenna conductor may have a triangular shape whose two sides have different lengths. 
     A wireless communication device according to another aspect of the present disclosure includes the antenna unit and a feed circuit that supplies power to the feed point of the antenna unit. 
     Such an aspect enables an antenna unit communicating in a higher frequency band having wide band width to communicate also in a lower frequency band while suppressing an increase in the size of the antenna unit. 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. 
     Embodiment 1 
       FIG. 1  is a top view of a wireless communication device including an antenna unit according to an embodiment 1 of the present disclosure. Further,  FIG. 2  is a partially enlarged view of the wireless communication device. Note that the X-Y-Z orthogonal coordinate illustrated in the drawings is provided to facilitate understanding of the present disclosure and is not intended to limit the present disclosure. Further, in the present specification, the X-axis direction is the width direction, and the Y-axis direction is the length direction. 
     As illustrated in  FIG. 1 , a wireless communication device  50  including an antenna unit  10  according to the present embodiment 1 is used by being installed in an electronic device capable of wireless communication. Further, the antenna unit  10  is a dual-band antenna unit capable of communicating at a frequency of a relatively high frequency band (HB band) and a frequency of a relatively low frequency band (LB band). In the case of the present embodiment 1, the high frequency band is a 5 GHz band (for example, 5.15 to 5.85 GHz), and the low frequency band is a 2.4 GHz band (for example, 2.4 to 2.484 GHz). Further, the high frequency band has a wider band width compared with the low frequency band. 
     As illustrated in  FIG. 1 , in the case of the present embodiment 1, the antenna unit  10  includes a ground conductor  12  provided on a base board  52  of the wireless communication device  50 , a first antenna conductor  14  and a second antenna conductor  16  connected to the ground conductor  12  provided on the base board  52 , and a first connection part  18  and a second connection part  20  that connect the first antenna conductor  14  and the second antenna conductor  16 . 
     Further, in the case of the present embodiment 1, the antenna unit  10  includes a feed point  22  and a matching circuit  24  that are provided between the ground conductor  12  and the first antenna conductor  14 . Note that a feed circuit (not illustrated) provided in the wireless communication device  50  is connected to this feed point  22 . The antenna unit  10  receives power from the feed circuit via the feed point  22 . Further, the matching circuit  24  is, for example, a LC resonant circuit including a chip inductor and a chip capacitor. 
     In the case of the present embodiment 1, the ground conductor  12  of the antenna unit  10  has a rectangular shape and is, for example, a conductor pattern of copper or the like formed on the base board  52  fabricated from an insulating material. 
     In the case of the present embodiment 1, the first antenna conductor  14  and the second antenna conductor  16  of the antenna unit  10  are, for example, conductor patterns of copper or the like formed on the base board  52 . 
     The first antenna conductor  14  has a shape extending from the feed point  22  in a direction (Y-axis direction) moving away from the ground conductor  12  and having the width (size in X-axis direction) that expands as the distance from the feed point  22  increases. 
     Specifically, the first antenna conductor  14  extends from the feed point  22  in the length direction (Y-axis direction) in such a manner as to move away from an end edge  12   a  of the ground conductor  12  in which the feed point  22  is provided. Further, the width (size in X-axis direction) expands linearly as the distance from the feed point  22  increases, that is to say, the width (size in X-axis direction) expands linearly as the distance to a top end edge  14   a  which is an edge of a distal end portion away from the feed point  22  decreases. In the case of the present embodiment 1, the first antenna conductor  14  has a triangular shape whose base is the top end edge  14   a  and whose two sides  14   b  and  14   c  have different lengths. Further, the top end edge  14   a  of the first antenna conductor  14  is linear and extends in the width direction (X-axis direction) in parallel to the end edge  12   a  of the ground conductor  12 . 
     The second antenna conductor  16  is provided in such a manner as to face the top end edge  14   a  of the first antenna conductor  14  with a gap formed therebetween. 
     Specifically, the second antenna conductor  16  is arranged in such a manner as to face the top end edge  14   a  of the first antenna conductor  14  with the gap formed therebetween in the length direction (Y-axis direction). Further, in the case of the present embodiment 1, the second antenna conductor  16  has a rectangular shape that extends in the length direction (Y-axis direction) while maintaining the width (size in X-axis direction) equal to the length of the top end edge  14   a  of the first antenna conductor  14 . The second antenna conductor  16  having such rectangular shape has the length (size in Y-axis direction) smaller than the width (size in X-axis direction). 
     The first connection part  18  connects the first antenna conductor  14  and the second antenna conductor  16  via a capacitor. In the case of the present embodiment 1, the first connection part  18  connects the first antenna conductor  14  and the second antenna conductor  16  via a chip capacitor  26  having a desired capacitance. Note that instead of the chip capacitor  26 , a capacitor may be formed by using a gap formed between a protruding part that protrudes from the first antenna conductor  14  toward the second antenna conductor  16  and a protruding part that protrudes from the second antenna conductor  16  toward the first antenna conductor  14 . 
     The second connection part  20  connects the first antenna conductor  14  and the second antenna conductor  16  via an inductor. In the case of the present embodiment 1, the second connection part  20  connects the first antenna conductor  14  and the second antenna conductor  16  via a chip inductor  28  having a desired inductance. Note that instead of the chip inductor  28 , the first antenna conductor  14  and the second antenna conductor  16  may be connected via a conductor pattern having a shape (for example, a meander shape) that has a desired inductance. Alternatively, instead of the chip inductor  28 , the second connection part  20  may connect the first antenna conductor  14  and the second antenna conductor  16  via a zero-ohm resistor. 
     Further, the first connection part  18  and the second connection part  20  are provided between the first antenna conductor  14  and the second antenna conductor  16  in such a way that a connection point (first connection point)  18   a  between the first connection part  18  and the first antenna conductor is closer to the center of the top end edge  14   a  of the first antenna conductor  14  compared with a connection point (second connection point)  20   a  between the second connection part  20  and the first antenna conductor. 
     In the case of the present embodiment 1, the connection point  18   a  between the first connection part  18  and the first antenna conductor  14  is positioned at the center of the top end edge  14   a  of the first antenna conductor  14 . In contrast, the connection point  20   a  between the second connection part  20  and the first antenna conductor  14  is positioned at one end of the top end edge  14   a  of the first antenna conductor  14 . 
     According to the antenna unit  10  such as this, as illustrated in  FIG. 2 , in the case where communication is performed at a frequency in the high frequency band (5 GHz band), a current I HB  flows from the feed point  22  along a width center part of the first antenna conductor  14  toward the first connection part  18 , then flows through the first connection part  18 , and flows in the second antenna conductor  16  in the length direction (Y-axis direction). This current path is formed because, for a relatively high frequency current, it is easier to flow through the capacitor (chip capacitor  26 ) in the first connection part  18  compared with the inductor (chip inductor  28 ) in the second connection part  20 . The path length of this current I HB  substantially corresponds to ¼ of wavelength of a frequency in the high frequency band. 
     On the other hand, in the case where communication is performed at a frequency in the low frequency band (2.4 GHz band), a current I LB  flows from the feed point  22  along the side  14   b  of the first antenna conductor  14  toward the second connection part  20 , then flows through the second connection part  20 , and flows in the second antenna conductor  16  in the width direction (X-axis direction). This current path is formed because, for a relatively low frequency current, it is easier to flow through the inductor (chip inductor  28 ) of the second connection part  20  compared with the capacitor (chip capacitor  26 ) of the first connection part  18 . The path length of this current I LB  substantially corresponds to ¼ of wavelength of a frequency in the low frequency band. 
     Advantageous effects of the antenna unit  10  having such configuration are now described. Table 1 describes efficiencies of the antenna unit  10  according to the present embodiment 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Average Band Width Efficiency (dB) 
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Frequency Band 
                 LB 
                 HB 
               
               
                   
                   
               
               
                   
                 Working Example 1 
                 −0.7 
                 −0.9 
               
               
                   
                 Comparative Example 
                 −2.2 
                 −0.4 
               
               
                   
                   
               
            
           
         
       
     
     Table 1 describes the average band width efficiency in a frequency band ranging from 2.4 to 2.484 GHz (LB band) and the average band width efficiency in a frequency band ranging from 5.15 to 5.85 GHz (HB band) of the antenna unit  10  (working example 1) according to the present embodiment 1. 
     As illustrated in  FIG. 1 , the mounting area of the first antenna conductor  14  and the second antenna conductor  16  of the antenna unit  10  of the working example 1 is an area having a length L 1  of 9.5 mm and a width W 1  of 11.5 mm. For reference, the base board has a length L 2  of 35 mm and a width W 2  of 25 mm. Further, the capacitance of the chip capacitor  26  of the first connection part  18  is 0.1 pF, and the inductance of the chip inductor  28  of the second connection part  20  is 1.1 nH. 
     Further, for reference, Table 1 describes the average band width efficiency in the LB band and the average band width efficiency in the HB band of an antenna unit of a comparative example. 
       FIG. 3  is a partially enlarged view of a wireless communication device including the antenna unit of the comparative example. 
     As illustrated in  FIG. 3 , an antenna unit  110  of a wireless communication device  150  of the comparative example includes an antenna conductor  114  having a triangular shape whose width expands as the distance from a feed point  122  increases. The footprint of the antenna conductor  114  is substantially equal to the footprint of the first antenna conductor  14  and the second antenna conductor  16  of the antenna unit  10  according to the present embodiment 1 (working example 1). Further, the antenna unit  110  of the comparative example includes a matching circuit  124  that provides matching between the feed point  122  and the antenna conductor  114  in a low frequency band LB and a high frequency band HB, which are similar to those in the antenna unit  10  of the working example 1. 
       FIG. 4  illustrates frequency characteristics (matching completed) of return loss of the antenna unit according to the embodiment 1 (working example 1) and the antenna unit of the comparative example. 
     As illustrated in  FIG. 4 , in both the antenna unit  10  of the working example 1 (dashed line) and the antenna unit  110  of the comparative example (solid line), in the range where the return loss is at a practical level of 10 dB or higher, the matching is provided in both the low frequency band LB and the high frequency band HB. 
     As described in Table 1 described above, the antenna unit  110  of the comparative example has a higher average efficiency value compared with −1.0 dB (practical level) in the high frequency band HB, and thus has a favorable efficiency. However, in the low frequency band LB, the average efficiency value is −2.2 dB and thus unfavorable. 
     On the other hand, in the case of the working example 1, the average efficiencies in the high frequency band HB and the low frequency band LB are both higher than −1.0 dB. Accordingly, the antenna unit  10  of the working example 1 has favorable efficiency because the efficiency is high in both the high frequency band HB and the low frequency band LB. 
     Accordingly, by dividing the antenna conductor  114  of the comparative example capable of communicating in the high frequency band having wide band width into the first antenna conductor  14  and the second antenna conductor  16  such as the ones described in the working example 1 and connecting these using the first connection part  18  and the second connection part  20 , it becomes possible to achieve favorable efficiency in both the high frequency band and the low frequency band without necessarily substantially expanding the footprint of the antenna conductor. 
     The present embodiment 1 described above enables an antenna unit communicating in a higher frequency band having wide band width to communicate also in a lower frequency band while suppressing an increase in the size of the antenna unit. 
     Embodiment 2 
     The present embodiment 2 is an improved embodiment of the foregoing embodiment 1. Accordingly, the present embodiment 2 is described, focusing on points different from the foregoing embodiment 1. Note that the same reference symbol is given to the constituent element of the present embodiment 2 that is substantially identical to the constituent element of the foregoing embodiment 1. 
       FIG. 5  is a partially enlarged view of a wireless communication device including an antenna unit according to the embodiment 2 of the present disclosure. 
     As illustrated in  FIG. 5 , in an antenna unit  210  of a wireless communication device  250  according to the present embodiment 2, in addition to be connected to the ground conductor  12  via the feed point  22 , the first antenna conductor  14  is connected to the ground conductor  12  via a short-circuit conductor  230 . That is to say, the first antenna conductor  14  is short-circuited to the ground conductor  12  via the short-circuit conductor  230 . 
     Specifically, the short-circuit conductor  230  is a conductor having one end portion connected to the first antenna conductor  14  and the other end portion connected to the ground conductor  12 . Further, a connection point (third connection point)  230   a  between the short-circuit conductor  230  and the first antenna conductor  14  is away from the connection point (first connection point)  18   a  between the first connection part  18  and the first antenna conductor  14  and is closer to the connection point (second connection point)  20   a  between the second connection part  20  and the first antenna conductor  14 . That is to say, in the case of the present embodiment 2, the ground conductor  12 , the first antenna conductor  14 , and the short-circuit conductor  230  are unified as a single constituent element (for example, a single conductor pattern). Note that the connection point  20   a  and the connection point  230   a  can be closer to each other as in the present embodiment 2. 
       FIG. 6  is a diagram illustrating frequency characteristics of return loss (matching completed) of the antenna unit according to the embodiment 1 (working example 1) and the antenna unit according to the embodiment 2 (working example 2). 
     As illustrated in  FIG. 6 , by providing the short-circuit conductor  230  (working example 2), in the range where the return loss is at a practical level of 10 dB or higher, the band width of the low frequency band expands about twofold. This is because, in frequencies of the low frequency band, the antenna unit  10  of the foregoing embodiment 1 (working example 1) functions as a monopole antenna while the antenna unit  210  of the present embodiment (working example 2) functions as an inverted-F antenna. 
     Note that as described in Table 2, even when the band width of the low frequency band expands, the efficiency does not change drastically. As is the case with the foregoing embodiment 1 (working example 1), also in the present embodiment 2 (working example 2), it becomes possible to achieve favorable efficiency in both the high frequency band and the low frequency band. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Average Band Width Efficiency (dB) 
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Frequency Band 
                 LB 
                 HB 
               
               
                   
                   
               
               
                   
                 Working Example 2 
                 −1.0 
                 −1.0 
               
               
                   
                 Working Example 1 
                 −0.7 
                 −0.9 
               
               
                   
                   
               
            
           
         
       
     
     Further, as illustrated in  FIG. 5 , the short-circuit conductor  230  can be arranged in such a manner as to extend along an end edge  52   a  of the base board  52  fabricated from an insulating material. Such arrangement of the short-circuit conductor  230  facilitates flowing of a current into part of the ground conductor  12  along the end edge  52   a  of the base board  52  in the case of the low frequency band. As a result, compared with the case where the short-circuit conductor  230  is provided at a location away from the end edge  52   a  of the base board  52 , in the low frequency band, the efficiency increases as the band width thereof expands. 
     As is the case with the foregoing embodiment 1, the present embodiment 2 described above enables an antenna unit communicating in a higher frequency band having wide band width to communicate also in a lower frequency band while suppressing an increase in the size of the antenna unit. Further, it becomes possible to expand the band width of the lower frequency band. 
     Embodiment 3 
     The present embodiment 3 is an improved embodiment of the foregoing embodiment 2. Accordingly, the present embodiment 3 is described, focusing on points different from the foregoing embodiment 2. Note that the same reference symbol is given to the constituent element of the present embodiment 3 that is substantially identical to the constituent element of the foregoing embodiment 2. 
       FIG. 7  is a partially enlarged view of a wireless communication device including an antenna unit according to the embodiment 3 of the present disclosure. 
     As illustrated in  FIG. 7 , in an antenna unit  310  of a wireless communication device  350  according to the present embodiment 3, the first antenna conductor  14  is short-circuited to the ground conductor  12  via a short-circuit conductor  330 . However, the short-circuit conductor  330  is an independent conductor different from the ground conductor  12  and the first antenna conductor  14 . Therefore, one end portion of the short-circuit conductor  330  is connected to the first antenna conductor  14  via an inductor, for example, a chip inductor  332 , and the other end portion of the short-circuit conductor  330  is connected to the ground conductor  12  via a chip inductor  332 . In the case of the present embodiment 3, the chip inductor  332 , which is arranged between the short-circuit conductor  330  and the ground conductor  12 , and the chip inductor  332 , which is arranged between the short-circuit conductor  330  and the first antenna conductor  14 , have the same inductance. Note that two chip inductors  332  may have different inductances. 
       FIG. 8  is a diagram illustrating relationships between the band width of frequency band and the inductor&#39;s inductance value for the inductor arranged between the short-circuit conductor and the ground conductor and the inductor arranged between the short-circuit conductor and the first antenna conductor. 
     As illustrated in  FIG. 8 , the band width of a high frequency band (HB band) expands as the inductance of the chip inductor  332  increases. Accordingly, by adjusting the inductance of the chip inductor  332 , it becomes possible to have a desired band width in the high frequency band. 
     Note that instead of using the connection via the chip inductors  332 , one end portion and the other end portion of the short-circuit conductor  330  may be changed in such a manner as to have different widths from the width of the part between the one end portion and the other end portion, that is to say, may be configured in such a manner as to have desired inductances, and the one end portion and the other end portion of the short-circuit conductor  330  that have been changed may be connected to the ground conductor  12  and the first antenna conductor  14 . 
     As is the case with the foregoing embodiment 2, the present embodiment 3 described above enables an antenna unit communicating in a higher frequency band having wide band width to communicate also in a lower frequency band while suppressing an increase in the size of the antenna unit. Further, it becomes possible to expand the band width of the lower frequency band. Moreover, it also becomes possible to expand the band width of the higher frequency band. 
     Thus far, the present disclosure has been described using a plurality of the embodiments 1 to 3. However, embodiments of the present disclosure are not limited thereto. 
     For example, in the case of the foregoing embodiment 1, as illustrated in  FIG. 2 , the second antenna conductor  16  has a rectangular shape. Specifically, the second antenna conductor  16  has a rectangular shape that extends in the length direction (Y-axis direction) with the width (size in X-axis direction) being a constant state and has the length (size in Y-axis direction) smaller than the width. Further, the width of the second antenna conductor  16  has the dimension equal to the length of the top end edge  14   a  of the first antenna conductor  14 . However, in embodiments of the present disclosure, the shape of the second antenna conductor is not limited to a rectangular shape. 
     Each of  FIG. 9  to  FIG. 13  is a partially enlarged view of a wireless communication device including an antenna unit according to embodiments 4 to 8 of the present disclosure. 
     As illustrated in  FIG. 9 , a second antenna conductor  416  of an antenna unit  410  of a wireless communication device  450  according to the embodiment 4 has a shape whose length (size in Y-axis direction) increases as the distance from the second connection part  20  in the width direction (X-axis direction) increases. Note that the width (size in X-axis direction) of the second antenna conductor  416  is equal to the length of the top end edge  14   a  of the first antenna conductor  14 . 
     Further, as illustrated in  FIG. 10 , a second antenna conductor  516  of an antenna unit  510  of a wireless communication device  550  according to the embodiment 5 has a shape that has a greater length (size in Y-axis direction) at the center in the width direction (X-axis direction) compared with the lengths at both ends thereof. Note that a back end edge  516   a  of the second antenna conductor  516 , which faces the top end edge  14   a  of the first antenna conductor  14 , is linear and in parallel to the top end edge  14   a . Further, the width (size in X-axis direction) of the second antenna conductor  516  is equal to the length of the top end edge  14   a  of the first antenna conductor  14 . 
     Moreover, as illustrated in  FIG. 11 , a second antenna conductor  616  of an antenna unit  610  of a wireless communication device  650  according to the embodiment 6 has a shape that has a smaller length (size in Y-axis direction) at the center in the width direction (X-axis direction) compared with the lengths at both ends thereof. Note that a top end edge  616   b  of the second antenna conductor  616 , which is the opposite side of a back end edge  616   a  of the second antenna conductor  616  that faces the top end edge  14   a  of the first antenna conductor  14 , is linear and in parallel to the top end edge  14   a  of the first antenna conductor  14 . Further, the width (size in X-axis direction) of the second antenna conductor  616  is equal to the length of the top end edge  14   a  of the first antenna conductor  14 . 
     As is the case with the foregoing embodiment 1, the embodiments 4 to 6 such as those enable an antenna unit communicating in a higher frequency band having wide band width to communicate also in a lower frequency band while suppressing an increase in the size of the antenna unit. 
     Still further, as illustrated in  FIG. 12 , a second antenna conductor  716  of an antenna unit  710  of a wireless communication device  750  according to the embodiment 7 has a trapezoidal shape in which a back end edge  716   a  and a top end edge  716   b  are in parallel to each other and the length of the back end edge  716   a  is greater than the length of the top end edge  716   b . The back end edge  716   a  has a greater length than the top end edge  14   a  of the first antenna conductor  14 . 
     As is the case with the foregoing embodiment 1, the embodiment 7 such as this enables an antenna unit communicating in a higher frequency band having wide band width to communicate also in a lower frequency band while suppressing an increase in the size of the antenna unit. Moreover, it becomes possible to expand the band width of the higher frequency band. 
     As illustrated in  FIG. 13 , a second antenna conductor  816  of an antenna unit  810  of a wireless communication device  850  according to the embodiment 8 is different from that of the antenna unit  710  according to the embodiment 7 in that the second antenna conductor  816  has a rectangular shape in which a back end edge  816   a  and a top end edge  816   b  are parallel to each other and have an equal length. The length of the back end edge  816   a  and the top end edge  816   b  is smaller than the length of the top end edge  14   a  of the first antenna conductor  14 . 
     As is the case with the foregoing embodiment 1, the embodiment 8 such as this also enables an antenna unit communicating in a higher frequency band having wide band width to communicate also in a lower frequency band while suppressing an increase in the size of the antenna unit. 
     Further, for example, in the case of the foregoing embodiment 1, as illustrated in  FIG. 2 , the first antenna conductor  14  has a triangular shape whose base is the top end edge  14   a . However, in embodiments of the present disclosure, the shape of the first antenna conductor is not limited to a triangular shape. 
       FIG. 14  and  FIG. 15  are partially enlarged views of wireless communication devices including antenna units according to embodiments 9 and 10 of the present disclosure, respectively. 
     As illustrated in  FIG. 14 , a first antenna conductor  914  of an antenna unit  910  of a wireless communication device  950  according to the embodiment 9 has a so-called bowl shape which is a shape that extends from the feed point  22  in a direction (Y-axis direction) away from the ground conductor  12  and has the width (size in X-axis direction) that expands in a quadratic fashion as the distance from the feed point  22  increases. 
     Further, as illustrated in  FIG. 15 , a first antenna conductor  1014  of an antenna unit  1010  of a wireless communication device  1050  according to the embodiment 10 has a so-called trapezoidal shape which is a shape that extends from the feed point  22  in a direction (Y-axis direction) away from the ground conductor  12  and has the width (size in X-axis direction) that expands in a linear fashion as the distance from the feed point  22  increases. 
     As is the case with the foregoing embodiment 1, the embodiments 9 and 10 also enable an antenna unit communicating in a higher frequency band having wide band width to communicate also in a lower frequency band while suppressing an increase in the size of the antenna unit. 
     Moreover, in the case of the foregoing embodiment 1, as illustrated in  FIG. 2 , the first antenna conductor  14  extends from the feed point  22  in the direction away from the ground conductor  12 . However, embodiments of the present disclosure is not limited thereto. For example, as in a self-complementary antenna such as a bow-tie antenna or the like, while extending the first antenna conductor from the feed point, another antenna conductor may extend from the feed point in the opposite direction. 
     That is to say, an antenna unit according to an embodiment of the present disclosure is, in a broader sense, an antenna unit including a feed point; a first antenna conductor extending from the feed point in a direction away from the ground conductor and having a width that expands as a distance from the feed point increases; a second antenna conductor facing a top end edge of the first antenna conductor with a gap formed therebetween; a first connection part connecting the top end edge of the first antenna conductor and the second antenna conductor via a capacitor; and a second connection part connecting the top end edge of the first antenna conductor and the second antenna conductor via an inductor or a zero-ohm resistor, wherein a first connection point between the first connection part and the first antenna conductor is closer to a center of the top end edge of the first antenna conductor compared with a second connection point between the second connection part and the first antenna conductor. 
     Thus far, the present disclosure has been described using a plurality of embodiments. However, it is apparent to those skilled in the art that still another embodiment according to the present disclosure may be formed by combining an embodiment and part or whole of at least one other embodiment. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to dual-band antenna units.