Patent Publication Number: US-2020295449-A1

Title: Antenna device

Description:
TECHNICAL FIELD 
     The present disclosure relates to an antenna device. 
     BACKGROUND ART 
     PTL 1 discloses an antenna device using an artificial magnetic conductor (hereinafter, referred to as AMC). 
     CITATION LIST 
     Patent Literature 
     PTL1: Unexamined Japanese Patent Publication No. 2015-70542 
     SUMMARY 
     The present disclosure provides an antenna device that can be miniaturized while a frequency characteristic of the antenna device at a fundamental wave is maintained. 
     An antenna device of the present disclosure includes: a substrate having an artificial magnetic conductor; a plurality of antenna conductors disposed on the substrate; and a parasitic conductor disposed on the substrate. The parasitic conductor is apart from and adjacent to the plurality of antenna conductors. 
     According to the present disclosure, the antenna conductor and a parasitic conductor are disposed to be opposed to an artificial magnetic conductor, so that capacitive coupling between the antenna conductor and the artificial magnetic conductor is enhanced to increase a capacitance, and thus a receivable frequency can be shifted to a low frequency band side. Further, the antenna device can work appropriately at frequencies on the lower frequency band side without increasing the length of the antenna conductor, so that the antenna device can be miniaturized. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing an outer appearance of antenna device  100  according to a first exemplary embodiment. 
         FIG. 2  is a vertical cross sectional view along line II-II of  FIG. 1 . 
         FIG. 3  is an upper surface view of antenna device  100  of  FIG. 1 , where layers upper than AMC  20  are deleted. 
         FIG. 4  is an upper surface view of antenna device  100  of  FIG. 1 , where layers upper than ground conductor  30  are deleted. 
         FIG. 5  is a graph showing frequency characteristics of voltage standing wave ratios of antenna device  100  of  FIG. 1 , where two cases are compared: one has parasitic conductor  6 , and the other has no parasitic conductor  6 . 
         FIG. 6  is a perspective view showing an outer appearance of antenna device  200  according to a second exemplary embodiment. 
         FIG. 7A  is an upper surface view of antenna device  300  according to a third exemplary embodiment, where layers upper than AMC  20  are deleted. 
         FIG. 7B  is a graph showing a frequency at which a voltage standing wave ratio exhibits a minimum with respect to a ratio L 1 /L 2 , which is a ratio of a length L 1  of an antenna conductor to a length L 2  of a parasitic conductor of antenna device  300 . 
         FIG. 7C  is a graph showing a fractional bandwidth with respect to a ratio L 1 /L 2 , which is a ratio of the length L 1  of the antenna conductor to the length L 2  of the parasitic conductor of antenna device  300 . 
         FIG. 8  is a diagram showing a configuration of AMC  26  of antenna device  101  according to a first modified example. 
         FIG. 9  is a diagram showing a configuration of AMC  27  of antenna device  102  according to a second modified example. 
         FIG. 10  is a diagram showing a configuration of AMC  28  of antenna device  103  according to a third modified example. 
         FIG. 11  is a diagram showing a configuration of AMC  29  of antenna device  104  according to a fourth modified example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, with reference to the drawings appropriately, a detailed description will be given on exemplary embodiments specifically showing antenna devices according to the present disclosure (hereinafter, the exemplary embodiments are referred to as the present exemplary embodiments). However, an unnecessarily detailed description will be omitted in some cases. For example, a detailed description of a well-known matter and a duplicated description of substantially the same configuration will be omitted in some cases. This is to avoid the following description from being unnecessarily redundant and thus to help those skilled in the art to easily understand the description. Note that the accompanying drawings and the following description are provided to help those skilled in the art to sufficiently understand the present disclosure, and are not intended to limit the subject matter of the claims. 
     In the following, the present exemplary embodiments preferable to practice the present disclosure will be described in detail with reference to the drawings. 
     Note that, in the following exemplary embodiments, modified example, and comparative example, a description will be given below, taking as an example an antenna device that is for a 2.4 GHz band (for example, 2,400 MHz to 2,500 MHz) and is for Bluetooth (registered trademark), for Wi-Fi, or for various types of electronic equipment. However, an antenna device of the present disclosure can be used also in other frequency bands. 
     First Exemplary Embodiment 
     In the following, with reference to  FIGS. 1 to 4 , a configuration of antenna device  100  according to a first exemplary embodiment will be described. 
       FIG. 1  is a perspective view showing an outer appearance of antenna device  100  according to the first exemplary embodiment, and  FIG. 2  is a vertical cross sectional view along line II-II of  FIG. 1 . Further,  FIG. 3  is an upper surface view of antenna device  100  of  FIG. 1 , where layers upper than AMC  20  are deleted (+x direction correspond the upper side), and  FIG. 4  is an upper surface view of antenna device  100  of  FIG. 1 , where layers upper than ground conductor  30  are deleted. Antenna device  100  of the present exemplary embodiment can be attached to a display device like a television device. 
     In the following exemplary embodiments, comparative example, and modified examples, description will be given, taking a dipole antenna as an example of antenna device  100 . The dipole antenna is formed on a printed wiring board  1  (hereinafter, referred to as substrate  1  in some cases) that is a laminated substrate having a plurality of layers, and a pattern of the dipole antenna is formed by performing etching or other processing on a metal foil on the surface. Each of the plurality of layers is configured with a copper foil or glass epoxy. 
     As shown in  FIGS. 1 and 2 , antenna device  100  includes: printed wiring board  1 ; antenna conductor  2  that is a strip conductor and is an example of a feeding antenna; antenna conductor  3  that is a strip conductor and is an example of a parasitic antenna (grounded antenna); via conductor  4 ; via conductor  5 ; and parasitic conductor  6  disposed on a side of antenna conductors  2 ,  3  (on a +y direction side). Via conductor  4  constitutes a feeding conductor of a power feed line between feeding point Q 1  of antenna conductor  2  and a wireless communication circuit (not shown in the drawing but is assembled on rear surface  1   b  of printed wiring board  1 ). Via conductor  5  constitutes a ground conductor of a power feed line between feeding point Q 2  of antenna conductor  3  and the wireless communication circuit. Parasitic conductor  6  is a parasitic pattern electrically separated from antenna conductors  2 ,  3 . 
     Antenna conductor  2  and antenna conductor  3  constitute, for example, a dipole antenna, and longitudinal directions of antenna conductors  2 ,  3  respectively extend in a straight line in a +z direction and a −z direction. In addition, ends of antenna conductors  2 ,  3  on the side of feeding points Q 1 , Q 2  (hereinafter, referred to as feeding-side ends) are formed on surface  1   a  of printed wiring board  1  so as to be a predetermined space apart from each other. Note that both ends, of antenna conductors  2 ,  3 , on the opposite sides of the feeding-side ends (the both ends are maximally apart from each other in the whole of antenna device  100 ) are hereinafter referred to as tip-side ends of antenna conductors  2 ,  3 . Further, a distance between the tip-side end of antenna conductor  2  and the tip-side end of antenna conductor  3  in the z direction is defined as a length L 1  of the antenna conductor. 
     Via conductors  4 ,  5  are each formed by filling through-holes formed through in a thickness direction from surface  1   a  to rear surface  1   b  of printed wiring board  1  with conductor. Since antenna conductor  2  functions as a feeding antenna, antenna conductor  2  is connected to a feeding terminal of the wireless communication circuit on rear surface  1   b  of printed wiring board  1  via conductor  4 . Further, since antenna conductor  3  functions as a parasitic antenna, antenna conductor  3  is connected to ground conductor  30  in printed wiring board  1  and to the ground terminal of the wireless communication circuit via conductor  5 . 
     In this description, the z direction means the longitudinal directions of antenna device  100  and antenna conductors  2 ,  3  of antenna device  100 . The y direction means width directions of antenna device  100  and antenna conductors  2 ,  3  of antenna device  100 , and is perpendicular to the z direction. The x direction means a thickness direction of antenna device  100  and perpendicular to the yz plane. In printed wiring board  1 , via conductors  4 ,  5  are respectively formed at positions substantially directly under feeding points Q 1 , Q 2 . Note that printed wiring board  1  of antenna device  100  may be assembled, for example, on a printed wiring board of electronic equipment. 
     With reference to  FIG. 2 , printed wiring board  1 , which is a laminated substrate, is configured with dielectric substrate  10 , AMC  20 , dielectric substrate  11 , and ground conductor  30  in this order. In  FIG. 2 , dielectric substrate  10 , dielectric substrate  11 , and ground conductor  30  each has substantially the same shape but each may have different shapes. For example, if ground conductor  30  larger than dielectric substrate  10  and dielectric substrate  11  is used, ground conductor  30  can be shared with other antennas. Dielectric substrates  10 ,  11  are formed of, for example, glass epoxy or other materials. AMC  20  is an artificial magnetic conductor having perfect magnetic conductor (PMC) characteristics and is formed of a predetermined metal pattern. By using AMC  20 , an antenna can be made thinner and can have a higher gain. Printed wiring board  1  is an example of a substrate. 
     Parasitic conductor  6  is disposed on printed wiring board  1  to be opposed to AMC  20  and to be adjacent to antenna conductors  2 ,  3  in the width direction with a predetermined distance secured between parasitic conductor  6  and antenna conductors  2 ,  3 . The predetermined distance is, for example, more than or equal to a quarter of a wavelength of a reception radio wave. In the first exemplary embodiment, parasitic conductor  6  is disposed on one of side surfaces of antenna conductors  2 ,  3  and is in parallel to the z direction in which antenna conductors  2 ,  3  are disposed. Since, in the same manner as antenna conductors  2 ,  3 , parasitic conductor  6  is opposed to and capacitively coupled to AMC  20  via dielectric substrate  10 , a capacitance between antenna conductors  2 ,  3  and AMC  20  can be increased so that a frequency can be shifted to a lower side. 
     In the present exemplary embodiment, as shown in  FIG. 1 , a length L 2  of parasitic conductor  6  in the z direction is shorter than the length L 1  of the antenna conductors. Further, as shown in  FIG. 1 , a distance in the z direction between the tip-side end of antenna conductor  2  and an end of parasitic conductor  6  on the antenna conductor  2  side is a gap G 1 , and a distance in the z direction between the tip-side end of antenna conductor  3  and an end of parasitic conductor  6  on the antenna conductor  3  side is a gap G 2 . In the present exemplary embodiment, antenna conductors  2 ,  3  are formed to be plane-symmetric with respect to the xy plane, and parasitic conductor  6  is also formed to be plane-symmetric with respect to the xy plane. Therefore, the gap G 1  and the gap G 2  are substantially equal to each other. 
     A size, shape, number, and the like of parasitic conductor  6  are not particularly limited, and parasitic conductor  6  only has to be on the same side as antenna conductors  2 ,  3  with respect to AMC  20  and to be capacitively coupled to AMC  20 , however, parasitic conductor  6  does not have to be disposed to be opposed to AMC  20  via dielectric substrate  10 . 
     Via conductor  4  has a columnar shape and is a power feed line to supply electric power to drive antenna conductor  2  as an antenna, and via conductor  4  electrically connects antenna conductor  2  formed on surface  1   a  of printed wiring board  1  to the feeding terminal of the above-described wireless communication circuit. Further, to prevent via conductor  4  from being electrically connected to AMC  20  or ground conductor  30 , via conductor  4  is formed substantially coaxial to via conductor insulating holes  21 ,  31  formed in AMC  20  and ground conductor  30 . A diameter of via conductor  4  is smaller than diameters of via conductor insulating holes  21 ,  31 . 
     On the other hand, via conductor  5  is to electrically connect antenna conductor  3  to the ground terminal of the above-described wireless communication circuit, and via conductor  5  is electrically connected to ground conductor  30  and AMC  20 . 
     AMC  20  of  FIGS. 2 and 3  is provided with: 
     (1) opening  20   a  that has a rectangular shape and is formed to extend in the z direction in a longitudinal direction of antenna conductor  2  from the vicinity of a position that is directly under and substantially opposed to the tip-side end of antenna conductor  2  (opening  20   a  penetrates through the layer of AMC  20  of FIG.  2  in a thickness direction of AMC  20  within the layer of AMC  20 , but is not formed in the vertical direction (+x direction or −x direction) outside the layer of AMC  20 ); 
     (2) opening  20   c  that has a rectangular shape and is formed to extend in the z direction in the longitudinal direction to a left-side end of printed wiring board  1  from a position a predetermined distance apart from opening  20   a  in the z direction (opening  20   c  penetrates through the layer of AMC  20  of  FIG. 2  in the thickness direction of AMC  20  within the layer of AMC  20 , but is not formed in the vertical direction (+x direction or −x direction) outside the layer of AMC  20 ); 
     (3) opening  20   b  that has a rectangular shape and is formed to extend in the −z direction in the longitudinal direction from the vicinity of a position that is directly under and substantially opposed to the tip-side end of antenna conductor  3  (opening  20   b  penetrates through the layer of AMC  20  of  FIG. 2  in the thickness direction of AMC  20  within the layer of AMC  20 , but is not formed in the vertical direction (+x direction or −x direction) outside the layer of AMC  20 ); 
     (4) opening  20   d  that has a rectangular shape and is formed to extend in the −z direction in the longitudinal direction to a right-side end of printed wiring board  1  from a position a predetermined distance apart from opening  20   b  in the −z direction (opening  20   d  penetrates through the layer of AMC  20  of  FIG. 2  in the thickness direction of AMC  20  within the layer of AMC  20 , but is not formed in the vertical direction (+x direction or −x direction) outside the layer of AMC  20 ); and 
     (5) slit  71  that is formed at a central part in the z direction, penetrates through AMC  20  in the thickness direction of AMC  20 , and extends to ends in a width direction of AMC  20 . 
     Each of openings  20   a  to  20   d  and slit  71  (including openings according to the exemplary embodiments and modified examples to be described later) includes, for example, so-called slit, slot, through-hole, notch section, and the like, and is a part where no artificial magnetic conductor is formed in the layer of AMC  20 . AMC  20  is divided into two parts in the longitudinal direction by slit  71  (the parts of AMC are each referred to as “AMC part” in some cases). Note that, such a configuration that AMC is divided in the longitudinal direction by slit  71  is similarly employed also in the second and third exemplary embodiments, modified examples, and comparative example to be described below. 
     A position where opening  20   a  is formed includes a position that is directly under and is substantially opposed to the tip-side end of antenna conductor  2  (the position corresponds to a central part of a left half part of AMC  20  (that is, printed wiring board  1 )) and that extends in the z direction toward a left-side tip of printed wiring board  1 . Further, a position where opening  20   b  is formed includes a position that is directly under and is substantially opposed to the tip-side end of antenna conductor  3  (the position corresponds to a central part of a right half part of AMC  20  (that is, printed wiring board  1 )) and that extends in the −z direction toward a right-side tip of printed wiring board  1 . 
     Openings  20   c ,  20   d  respectively extends, for example, in the longitudinal directions of antenna conductors  2 ,  3  toward tip parts of antenna device  100  from positions that are apart in the longitudinal directions of antenna conductors  2 ,  3  from positions substantially opposed to the tip-side ends of antenna conductors  2 ,  3 , which tip-side ends are opposite to ends on the side of the feeding points of antenna conductors  2 ,  3 , toward the tip parts of antenna device  100  (in other words, one of openings  20   c ,  20   d  is direct under the tip ends of antenna conductors  2 ,  3 ). This arrangement is employed also in other exemplary embodiments. 
     In ground conductor  30  of  FIG. 4 , there are formed two holes: one is via conductor insulating hole  31  through which via conductor  4  penetrates and which is electrically insulated from ground conductor  30 , and the other is a hole through which via conductor  5  penetrates and which is electrically connected to ground conductor  30 . 
     In antenna device  100  according to the first exemplary embodiment, as apparent from  FIGS. 2 to 4 , AMC  20  and ground conductor  30  have substantially the same rectangular planar shape and has substantially a congruent shape, and AMC  20  and ground conductor  30  are formed to be opposed to each other and to be a predetermined distance apart from each other in the thickness direction. Note that AMC  20  is formed to have openings  20   a  to  20   d  and slit  71  but is formed such that a length of AMC  20  in the longitudinal direction is substantially the same as a length of ground conductor  30  in the longitudinal direction. 
       FIG. 5  is a graph showing frequency characteristics of voltage standing wave ratios (VSWRs), where two cases are compared: one is antenna device  100  according to the first exemplary embodiment (the case where parasitic conductor  6  is included), and the other is a comparative example (the case where parasitic conductor  6  is not included). Simulations are conducted under the same conditions except the presence or absence of parasitic conductor  6 . 
     As apparently understood from this graph, the voltage standing wave ratio of antenna device  100  of the present exemplary embodiment including parasitic conductor  6  is shifted to the low frequency side. In particular, when paying attention to the minimum values of the voltage standing wave ratios in the graph, the minimum value for the comparative example (no parasitic conductor) is at 2,430 MHz, but the minimum value for antenna device  100  of the present exemplary embodiment including parasitic conductor  6  is at 2,340 MHz, that is, the low frequency side. As a result, a larger antenna conductor is required for lower frequencies, however, when parasitic conductor  6  is provided, it is possible to achieve antenna device  100  that works appropriately at lower frequencies, without changing the size of the antenna conductor. 
     Second Exemplary Embodiment 
     In the following, a configuration of antenna device  200  according to a second exemplary embodiment will be described with reference to  FIG. 6 . 
       FIG. 6  is a perspective view showing an outer appearance of antenna device  200  according to the second exemplary embodiment. Antenna device  200  has parasitic conductor  7  in addition to parasitic conductor  6  of the first exemplary embodiment. 
     In the second exemplary embodiment, similarly to the first exemplary embodiment, parasitic conductors  6 ,  7  are disposed on printed wiring board  1  to be opposed to AMC  20  and to be adjacent to antenna conductors  2 ,  3  with a predetermined distance secured between parasitic conductors  6 ,  7  and antenna conductors  2 ,  3 . In the second exemplary embodiment, parasitic conductors  6 ,  7  are disposed on both sides (in the y direction) of antenna conductors  2 ,  3  and in parallel to the z direction in which antenna conductors  2 ,  3  are disposed. Two parasitic conductors  6 ,  7  further increase the capacitance, so that the frequency can be further shifted to the lower side. 
     Third Exemplary Embodiment 
     Next, with reference to  FIGS. 7A to 7C , a description will be given on characteristics of antenna device  300  according to a third exemplary embodiment when a length L 1  of antenna conductor and a length L 2  of parasitic conductor  6  are varied.  FIG. 7A  is an upper surface view of antenna device  300 , where layers upper than AMC  25  are deleted. As shown in  FIG. 7A , antenna device  300  is different from antenna device  100  described in the first exemplary embodiment, and openings  20   a ,  20   b ,  20   c ,  20   d  are not formed in AMC  25 . The other configuration is the same as the configuration of antenna device  100  and will not be described. 
       FIG. 7B  is a graph showing a frequency at which a voltage standing wave ratio exhibits a minimum with respect to a ratio L 1 /L 2 , which is a ratio of the length L 1  of the antenna conductor to the length L 2  of parasitic conductor  6  of antenna device  300 .  FIG. 7C  is a graph showing a fractional bandwidth of antenna device  300  with respect to a ratio of the length L 1  of the antenna conductor to the length L 2  of parasitic conductor  6 .  FIGS. 7B and 7C  are each a result of simulations conducted on cases where the length L 1  of the antenna conductor is 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, or 16 mm and the length L 2  of parasitic conductor  6  is 3 mm, 5 mm, or 7 mm. The fractional bandwidth shown in  FIG. 7C  represents a ratio of a band of frequencies at which the voltage standing wave ratio is less than or equal to 3 to a frequency at which the voltage standing wave ratio exhibits a minimum. 
     As shown in  FIG. 7B , there is a tendency that, for any length L 2  of parasitic conductor  6 , the frequency at which the voltage standing wave ratio exhibits a minimum decreases as the length L 1  of the antenna conductor increases, and, at the same time, there is a tendency that the frequency at which the voltage standing wave ratio exhibits a minimum decreases as the length L 2  of parasitic conductor  6  is longer. For example, when paying attention to the case where the frequency at which the voltage standing wave ratio exhibits a minimum is 2,340 MHz, the length L 1  of the antenna conductor needs to be about 14 mm, about 13 mm, and about 11 mm in the case of the length L 2  of parasitic conductor  6  is 3 mm, 5 mm, and 7 mm, respectively, which fact means that the length L 1  of the antenna conductor can be reduced by increasing the length L 2  of parasitic conductor  6 , whereby a shorter antenna device  100  can be achieved. 
     Further, as shown in  FIG. 7C , there is a tendency that the fractional bandwidth increases for any length L 2  of parasitic conductor  6  as the length L 1  of the antenna conductor increases, and, at the same time, there is a tendency that the fractional bandwidth is larger as the length L 2  of parasitic conductor  6  is longer. The fact that the fractional bandwidth is large means that radio waves in a relatively wide frequency range can be received, and means that the effect to reduce manufacturing variation of antenna devices and to reduce fluctuation in characteristics depending on installation position is large. 
     As described above, by providing larger parasitic conductor  6 , an antenna conductor can be made accordingly smaller, whereby antenna device  100  can be made smaller, and, at the same time, it is possible to achieve antenna device  100  capable of stably receiving radio waves. 
     Advantageous Effect and the Like 
     Each of the antenna devices of the first to third exemplary embodiments includes substrate  1  having an artificial magnetic conductor (AMC), antenna conductors  2 ,  3 , disposed on substrate  1 , and a parasitic conductor disposed to be apart from antenna conductors  2 , 3 . 
     With this arrangement, since the parasitic conductor is provided on the same plane as antenna conductors  2 ,  3 , capacitive coupling between antenna conductors  2 ,  3  and the artificial magnetic conductor is enhanced, and a capacitance is increased, whereby the frequency can be shifted to a low frequency band side. Further, the antenna device can work appropriately at frequencies on the lower frequency band side without increasing the length of antenna conductors  2 ,  3 , so that the antenna device can be miniaturized. 
     In each of the antenna devices according to the first to third exemplary embodiments, antenna conductors  2 ,  3  and the parasitic conductor or parasitic conductors are disposed adjacent to each other on substrate  1 . This arrangement enables antenna conductors  2 ,  3  and the parasitic conductor to be easily positioned and manufactured. 
     Further, antenna device  200  of the second exemplary embodiment has at least two parasitic conductors  6 ,  7  disposed on both sides of antenna conductors  2 ,  3 . This arrangement easily enhances the capacitive coupling. 
     Further, in a case where the parasitic conductor is on the top layer of the antenna device as in the first to third exemplary embodiments, the frequency can be easily adjusted by modifying the parasitic conductor. Therefore, manufacturing of an antenna device with the frequency being adjusted, for example, manufacturing of various types of antenna devices is easy. 
     First Modified Example 
       FIG. 8  is an upper surface view of antenna device  101  according to a first modified example, where layers upper than AMC  26  are deleted. Antenna device  101  according to the first modified example has three slits  71  in the layer of AMC  26  as shown in  FIG. 8 , and on this point, antenna device  101  is different from antenna device  100  of the first exemplary embodiment, which has one slit  71  in the layer of AMC  20 , but the other configuration of antenna device  101  is the same as the configuration of antenna device  100 . 
     Antenna device  101  according to the first modified example provides a similar action and effect to antenna device  100  according to the first exemplary embodiment. Note that also in the antenna devices described in the second and third exemplary embodiments, it is possible to employ the layer of AMC  26  of the first modified example. 
     Second Modified Example 
       FIG. 9  is an upper surface view of antenna device  102  according to a second modified example, where layers upper than AMC  27  are deleted. Antenna device  102  according to the second modified example has slit  72  in the layer of AMC  27  as shown in  FIG. 9 , and on this point, antenna device  102  is different from antenna device  100  of the first exemplary embodiment, which has slit  71  in the layer of AMC  20 , but the other configuration of antenna device  102  is the same as the configuration of antenna device  101 . As shown in  FIG. 9 , slit  72  has a slit part having the same shape as one slit  71  shown in  FIG. 3  and has, on the both sides of the slit part, slit parts extending a predetermined length in a width direction but not reaching both ends, and these slit parts are connected to each other at a central part in the width direction. 
     Antenna device  102  according to the second modified example provides a similar action and effect to antenna device  100  according to the first exemplary embodiment. Note that also in the antenna devices described in the second and third exemplary embodiments, it is possible to employ the layer of AMC  27  of the second modified example. 
     Third Modified Example 
       FIG. 10  is an upper surface view of antenna device  103  according to a third modified example, where layers upper than AMC  28  are deleted. Antenna device  103  according to the third modified example has slit  73  in the layer of AMC  28 , and on this point, antenna device  103  is different from antenna device  100  of the first exemplary embodiment, which has slit  71  in the layer of AMC  20 , but the other configuration of antenna device  103  is the same as the configuration of antenna device  100 . As shown in  FIG. 10 , slit  73  has a shape in which three slits  71  shown in  FIG. 8  are connected to each other at the central part in the width direction. 
     Antenna device  103  according to the third modified example provides a similar action and effect to antenna device  100  according to the first exemplary embodiment. Note that also in the antenna devices described in the second and third exemplary embodiments, it is possible to employ the layer of AMC  28  of the third modified example. 
     Fourth Modified Example 
       FIG. 11  is an upper surface view of antenna device  104  according to a fourth modified example, where layers upper than AMC  29  are deleted. Antenna device  104  according to the fourth modified example has slit  74  in the layer of AMC  29 , and on this point, antenna device  104  is different from antenna device  100  of the first exemplary embodiment, which has slit  71  in the layer of AMC  20 , but the other configuration of antenna device  104  is the same as the configuration of antenna device  100 . As shown in  FIG. 11 , slit  74  has a shape in which one slit  71  shown in  FIG. 3  and a slit extending a predetermined length in a width direction but not reaching both end in the width direction are connected to each other at a central part in the width direction. 
     Antenna device  104  according to the fourth modified example provides a similar action and effect to antenna device  100  according to the first exemplary embodiment. Note that also in the antenna devices described in the second and third exemplary embodiments, it is possible to employ the layer of AMC  29  of the fourth modified example. 
     Other Exemplary Embodiments 
     In the above, as an example of techniques disclosed in the present application, a description has been given taking a dipole antenna as an example in the above exemplary embodiments and modified examples. However, other antennas such as a monopole antenna, an inverted-L antenna, and an inverted-F antenna may be used. For example, it is possible to configure a monopole antenna by including only one antenna conductor  2  instead of two antenna conductors  2 ,  3  of antenna device  100  according to the first exemplary embodiment of  FIG. 1 . In this case, a similar action and effect is provided except that a radiation characteristic is different from antenna device  100 . Note that a monopole antenna may be used for the antenna devices described in the second and third exemplary embodiments and the first to fourth modified examples. 
     In the above exemplary embodiments and modified examples, antenna devices for the 2.4 GHz band have been described, but the present disclosure may be applied to antenna devices for other frequency bands. 
     In the above exemplary embodiments and modified examples, printed wiring board  1 , which is a laminated substrate, is used to configure an antenna device. However, the antenna device only needs to be configured in such a manner that antenna conductors  2 ,  3 , an AMC, and a ground conductor are stacked in order and to be a predetermined distance apart from each other. For example, a part or a whole of each dielectric substrate  10 ,  11  may be an air layer. Further, each of the antenna devices according to the above exemplary embodiments and modified examples includes one ground conductor  30 , but may include a plurality of ground conductors. 
     Further, the ground conductor and the AMC may be provided to be opposed to each other, and in addition, may be provided such that, in a plan view, the ground conductor is included in the AMC, or the AMC is included in the ground conductor. This configuration miniaturizes the antenna device in size. 
     In each case described in the exemplary embodiments and modified examples, one to three slits are formed in the AMC; however, four or more slits may be formed, or all or some of the plurality of slits may be connected to each other. 
     Exemplary embodiments of an antenna device according to the present disclosure have been described above with reference to the drawings, but the present discloser is not limited to those examples. It is apparent that those skilled in the art can conceive various modification examples, substitution examples, addition examples, removal examples, equivalent examples, and the like within the scope described in the attached claims, and those examples are of course understood to be within the technical scope of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     An antenna device of the present disclosure is useful in the field where an antenna device is required to work appropriately at frequencies on the lower frequency band side without increasing the length of the antenna conductor. 
     REFERENCE MARKS IN THE DRAWINGS 
     
         
         
           
               1 : substrate (printed wiring board) 
               2 ,  3 : antenna conductor 
               4 ,  5 : via conductor 
               6 ,  7 : parasitic conductor 
               10 ,  11 : dielectric substrate 
               20 ,  25 ,  26 ,  27 ,  28 ,  29 : artificial magnetic conductor (AMC) 
               20   a ,  20   b ,  20   c ,  20   d : opening 
               21 ,  31 : via conductor insulating hole 
               30 : ground conductor 
               71 ,  72 ,  73 ,  74 : slit 
               100 ,  101 ,  102 ,  103 ,  104 ,  200 ,  300 : antenna device 
             Q 1 , Q 2 : feeding point