Patent Publication Number: US-10784581-B2

Title: Antenna device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Application No. PCT/JP2017/016672 filed on Apr. 27, 2017. This application is based on and claims the benefit of priority from Japanese Patent Application No. 2016-098991 filed on May 17, 2016. The entire disclosures of all of the above applications are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an antenna device having a flat plate structure. 
     BACKGROUND ART 
     Conventionally, as disclosed in Patent Literature 1, there is an antenna device equipped with a metal conductor having a plate shape that provides a ground electric potential by being connected with a power supply line (hereinafter, ground part), a metal conductor having a plate shape disposed to oppose the ground plate and on which a power supply point is provided at any position (hereinafter, patch part), and a short-circuit part that electrically connects the ground part and the patch part. 
     The antenna device disclosed in Patent Literature 1 generates parallel resonance by a capacitance formed between the ground part and the patch part, and an inductance equipped in the short-circuit part. The inductance can be adjusted by the length and the shape of the short-circuit part, and an electrostatic capacity formed between the patch part and the ground part is determined depending on the area of the patch part and the distance between the patch part and the ground plate (hereinafter, distance between opposed conductors). 
     Accordingly, the antenna device having the above-mentioned structure enables to obtain desired frequency for a frequency that is target of transmission and reception (hereinafter, operating frequency) in the antenna device by adjusting the separation between the patch part and the ground plate and the area of the patch part. 
     PRIOR ART LITERATURE 
     Patent Literature 
     
         
         Patent Literature 1: U.S. Pat. No. 7,911,386 B1 
       
    
     SUMMARY OF INVENTION 
     The antenna device is desired to be further downsized. One approach to downsize the antenna device employing the operating principle disclosed in Patent Literature 1 is a method that reduces the area of the patch part as well as cancels a decrease in the capacitance generated due to the area reduction by increasing the inductance. The inductance can be provided by, for example, lengthening the short-circuit part, or connecting one end of a linear conductor to the short-circuit part. 
     However, when the capacitance included in the antenna device is reduced and the inductance included therein is increased, Q value indicating sharpness of the peak of resonance becomes large, robustness as the antenna device is lowered. This is because Q value becomes larger as the inductance becomes larger and the capacitance becomes smaller as shown in the following formula. R denotes a pure resistance value, L denotes the inductance, and C denotes the capacitance in the formula. 
     
       
         
           
             
               
                 
                   Q 
                   = 
                   
                     
                       1 
                       R 
                     
                     ⁢ 
                     
                       
                         L 
                         C 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     It is an object of the present disclosure to provide an antenna device capable of being downsized while suppressing increase of Q value. 
     According to a first aspect of the present disclosure, an antenna device includes a ground part, a patch part, a short-circuit part, a patch area expansion part and a ground area expansion part. The ground part is a conductive member having a plate shape. The patch part is a conductive member having a plate shape disposed parallel to the ground part to oppose the ground part. The short-circuit part is a conductive member electrically connecting the patch part and the ground part. 
     The patch area expansion part is provided on a patch-side opposing surface that is a surface of the patch part opposing the ground part. The patch area expansion part expands an effective surface area that is an apparent area of the patch-side opposing surface with respect to the ground part. The ground area expansion part is provided in a region opposing the patch area expansion part on a ground-side opposing surface that is a surface of the ground part opposing the patch part. The ground area expansion part expands an effective surface area of the ground-side opposing surface with respect to the patch part. 
     The effective surface area of the patch-side opposing surface expanded by the patch area expansion part is equal to an area for providing a necessary capacitance that is a capacitance necessary to generate parallel resonance with an inductance provided by the short-circuit part at a predetermined operating frequency. 
     According to the first aspect of the present disclosure, by being provided with the patch area expansion part on the patch-side opposing surface, an apparent area of the patch-side opposing surface with respect to the ground part (that is, effective surface area) is expanded. In addition, by being provided with the ground area expansion part on the ground-side opposing surface, an effective surface area of the ground-side opposing surface with respect to the patch part is expanded. That is, a capacitance greater than a capacitance corresponding to an original area equipped in the patch part is formed. 
     Accordingly, when operating frequency is fixed, the first aspect of the present disclosure makes it possible to reduce the size of the patch part as compared with a conventional structure. Herein, the conventional structure denotes a structure where conductive fiber layers are not provided on each of the patch-side opposing surface and the ground-side opposing surface. 
     According to the first aspect of the present disclosure, an inductance need not be increased for downsizing. Accordingly, the first aspect makes it possible to downsize the antenna device while suppressing increase of Q value. 
     According to a second aspect of the present disclosure, an antenna device includes a ground-side conductive fiber part, a patch-side conductive fiber part and a short-circuit part. The ground-side conductive fiber part is a plate member having conductive fibers that are fibers having conductivity. The patch-side conductive fiber part is a plate member having the conductive fibers. The patch-side conductive fiber part is disposed parallel to the ground-side conductive fiber part to oppose the ground-side conductive fiber part. The short-circuit part is a conductive member electrically connecting the patch-side conductive fiber part and the ground-side conductive fiber part. 
     A size of the patch-side conductive fiber part is equal to a size for providing a necessary capacitance that is a capacitance necessary to generate parallel resonance with an inductance provided by the short-circuit part at a predetermined operating frequency. 
     In the antenna device according to the second aspect of the present disclosure, a capacitance greater than a capacitance corresponding to an actual area of the patch-side conductive fiber part in top view is also formed due to the same operating principle as that of the antenna device according to the first aspect of the present disclosure described above. Therefore, the second aspect of the present disclosure provides the same advantageous effect as that of the first aspect of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic exterior perspective view of an antenna device; 
         FIG. 2  is a cross sectional view of the antenna device along the line II-II illustrated in  FIG. 1 ; 
         FIG. 3  is an enlarged view of a portion surrounded by sign III illustrated in  FIG. 2 ; 
         FIG. 4  is a diagram illustrating a modification of a fiber direction of a conductive fiber equipped in a conductive fiber layer; 
         FIG. 5  is a diagram illustrating a modification of a patch area expansion part; 
         FIG. 6  is a diagram illustrating a schematic structure of an antenna device according to a third modification; 
         FIG. 7  is a diagram illustrating a schematic structure of an antenna device according to a fourth modification; 
         FIG. 8  is a diagram illustrating a schematic structure of the antenna device according to the fourth modification; 
         FIG. 9  is a diagram illustrating a mode where the antenna devices are periodically disposed in single dimensional manner; 
         FIG. 10  is a diagram illustrating a mode where the antenna devices are periodically disposed in two dimensional manner; and 
         FIG. 11  is a diagram illustrating a schematic structure of an antenna device according to a second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     Hereinafter, a first embodiment of the present disclosure will be described using the drawings.  FIG. 1  is an exterior perspective view illustrating an example of a schematic structure of an antenna device  100  according to the present embodiment.  FIG. 2  is a cross sectional view of the antenna device  100  along the line II-II illustrated in  FIG. 1 . 
     The antenna device  100  is configured to transmit and receive a radio wave having a predetermined operating frequency. Of course, as another mode, the antenna device  100  may be used for only either one of transmission and reception. 
     Herein, the operating frequency shall be 5.9 GHz as an example. Of course, the operating frequency is enough to be appropriately designed, and for example, it may be 300 MHz, 760 MHz, 900 MHz, or the like as another mode. The antenna device  100  can transmit and receive a radio wave having not only the operating frequency but also a frequency within a predetermined range around the operating frequency. For convenience, a frequency band that enables the antenna device  100  to perform transmission and reception will be hereinafter also described as operating band. 
     The antenna device  100  is connected to a radio via, for example, a coaxial cable, and a signal received by the antenna device  100  is sequentially output to the radio. The antenna device  100  converts an electric signal input from the radio into a radio wave and radiates it in a space. The radio uses the signal received by the antenna device  100  as well as supplies to the antenna device  100  high frequency power depending on a transmission signal. 
     In the present embodiment, description is made on the assumption that the antenna device  100  and the radio is connected by the coaxial cable, but another known communication cable such as a feeder line may be used for connection. The antenna device  100  and the radio may be connected via a known matching circuit, a filter circuit, or the like besides the coaxial cable. 
     Hereinafter, a specific structure of the antenna device  100  will be described. The antenna device  100  includes, as illustrated in  FIGS. 1 and 2 , a ground part  10 , a patch part  20 , a patch-side conductive fiber layer  30 , a ground-side conductive fiber layer  40 , a supporting part  50 , and a short-circuit part  60 . 
     The ground part  10  is a conductive member having a plate shape (including a foil) whose material is a conductor such as copper. The ground part  10  is electrically connected to an external conductor that is the coaxial cable and provides a ground electrical potential (in other words, earth potential) in the antenna device  100 . Note that, it is sufficient that the ground part  10  is larger than the patch part  20 , and that the shape in its top view (hereinafter, planar shape) is appropriately designed. 
     Herein, as an example, the planar shape of the ground part  10  shall be a square shape, but the planar shape of the ground part  10  may be a rectangular shape or another polygonal shape as another mode. Alternatively, it may be a circular (including ellipse) shape. Of course, it may be a shape combining a straight line part and a curved line part. 
     The patch part  20  is a conductive member having a plate shape whose material is a conductor such as copper. The patch part  20  is disposed to oppose the ground part  10  via the patch-side conductive fiber layer  30 , the ground-side conductive fiber layer  40 , and the supporting part  50 . Herein, as an example, the planar shape of the patch part  20  shall be a square shape, but it may be a rectangular shape or another shape other than a rectangular shape (e.g., a circular shape, an octagon shape, or the like). 
     The patch-side conductive fiber layer  30  is a layer of conductive fiber (hereinafter, conductive fiber layer). The patch-side conductive fiber layer  30  is provided on a surface on a side opposing the ground part  10  in the patch part  20  (hereinafter, patch-side opposing surface). Note that, as an example in the present embodiment, the patch-side conductive fiber layer  30  shall be provided in the entire region of the patch-side opposing surface except the portion where the short-circuit part  60  is provided. 
       FIG. 3  is an enlarged view of the region surrounded by a broken line of  FIG. 2 , and illustrates a schematic structure of the patch-side conductive fiber layer  30 . As illustrated in  FIG. 3 , the patch-side conductive fiber layer  30  in the present embodiment shall be formed such that fibers having conductive property (hereinafter, conductive fibers) erect with respect to the patch-side opposing surface. The erection herein is not limited to perfect erection, and includes a mode in which the angle with respect to the patch-side opposing surface is inclined in a rage of greater than a predetermined angle (e.g., 60 degrees). In other words, in the patch-side conductive fiber layer  30 , the conductive fibers are extended toward the ground part  10  from the patch-side opposing surface. 
     Although omitted in the drawing, a dielectric substance having a predetermined dielectric constant is filled in each gap between the conductive fibers. As the conductive fiber, a known element can be employed such as carbon nanotube or silver nanowire. Herein, the conductive fiber providing the conductive fiber layer shall be a silver nanowire as an example. The patch-side conductive fiber layer  30  corresponds to a patch area expansion part due to the reason described below. 
     The ground-side conductive fiber layer  40  is also a conductive fiber layer, and its specific structure is the same as that of the patch-side conductive fiber layer  30 . The ground-side conductive fiber layer  40  is provided on a surface on a side opposing the patch part  20  in the ground part  10  (hereinafter, ground-side opposing surface). It is sufficient that the ground-side conductive fiber layer  40  is provided at a portion opposing the patch-side conductive fiber layer  30  on the ground-side opposing surface. That is, in the ground-side conductive fiber layer  40 , the conductive fiber is extended toward the patch part  20  from the ground-side opposing surface. The ground-side conductive fiber layer  40  corresponds to a ground area expansion part. 
     Hereinafter, when the patch part  20  and the patch-side conductive fiber layer  30  are collectively denoted, they are described as a patch-side unit for convenience. In addition, when the ground part  10  and the ground-side conductive fiber layer  40  are collectively denoted, they are described as a ground-side unit for convenience. By being oppositely disposed, the patch-side unit and the ground-side unit function as a capacitor for providing a capacitance corresponding to the area of the patch-side unit. 
     The supporting part  50  is a member for disposing the ground-side unit and the patch-side unit to be oppositely disposed with a predetermined distance. It is sufficient that the supporting part  50  be provided by using a dielectric substance such as a resin. 
     In the present embodiment, the supporting part  50  shall be a member having a plate shape having a thickness of H 1 . Adjustment of the thickness H 1  of the supporting part  50  makes it possible to adjust a distance H 2  between opposed conductors as a separation between the patch part  20  and the ground part  10 . This is because the value obtained by adding the thicknesses of the respective conductive fiber layers to the thickness H 1  corresponds to the distance H 2  between opposed conductors. 
     The distance H 2  between opposed conductors functions as an element for adjusting the length of the short-circuit part  60 , in other words, the inductance provided by the short-circuit part  60  as described below. Furthermore, the distance H 2  between opposed conductors also functions as an element for adjusting the capacitance formed by the ground-side unit and the patch-side unit opposed. 
     It is sufficient that the distance H 1  is sufficiently smaller than the wavelength of the radio wave of the operating frequency (hereinafter, target wavelength), and that its specific value is appropriately determined by a simulation or an experiment. The distance H 1  is preferably at least not more than one tenth of the target wavelength. For example, it is sufficient that the distance H 1  be one fiftieth, one hundredth, or the like of the target wavelength. 
     It is sufficient that the supporting part  50  play the above-described role, and that the shape of the supporting part  50  be appropriately designed. For example, the supporting part  50  may be a plate member that supports the ground part  10  and the patch part  20  so as to be opposed with the predetermined distance H 1 , or may be a plurality of pillars. 
     In addition, in the present embodiment, the structure is employed in which the resin (that is, supporting part  50 ) is filled between the ground-side unit and the patch-side unit as an example, but the structure is not limited thereto. The space between the ground-side unit and the patch-side unit may be a hollow, or a plurality of types of dielectric substances may be laminated in the space. In addition, the structures exemplified above may be combined. 
     The short-circuit part  60  is conductive and electrically connects the patch part  20  and the ground part  10 . It is sufficient that the short-circuit part  60  is provided by using a conductive pin (hereinafter, short pin). Adjustment of the length or the like of the short pin as the short-circuit part  60  makes it possible to adjust the inductance equipped in the short-circuit part  60 . 
     Note that, when the antenna device  100  is provided by using a print wiring board as a base, a via provided on the print wiring board may be made to function as the short-circuit part  60 . In any case, the short-circuit part  60  is a linear member electrically connected with the ground part  10  at its one end and electrically connected with the patch part  20  at the other end. Note that, electrical connection with the patch part  20  also includes electromagnetic connection described below as a third modification. 
     The short-circuit part  60  is provided at a position that becomes the center of the patch part  20  in the top view (hereinafter, patch center point). It is sufficient that the patch center point is a point corresponding to the gravity center of the patch part  20 . Since the patch part  20  of the present embodiment has a square shape, the patch center point corresponds to the intersection point of the diagonal lines of the square. 
     Note that the short-circuit part  60  is not necessarily arranged at the patch center point. Arrangement at a position other than the patch center point generates deviation of directivity depending on deviation amount from the patch center point. In the range where the deviation of directivity is included in a predetermined acceptable range, the short-circuit part  60  may be disposed at a position deviated from the patch center point. 
     Functions of Conductive Fiber Layer 
     The various conductive fiber layers have a surface area of greater than a plane area because of assemble of conductive fiber. The plane area herein is an area in the top view. For example, when number density of the silver nanowire is 10 9  [number/cm 2 ], wire radius thereof is 20 [nm], and wire length thereof (in other words, thickness of conductive fiber layer) is 32 [μm], the surface area per 1 [cm 2 ] becomes 40 [cm 2 ]. 
     The ground-side conductive fiber layer  40  and the patch-side conductive fiber layer  30  are respectively disposed on the ground part  10  and the patch part  20  to be opposed with each other. This expands an apparent area of the patch-side opposing surface with respect to the ground part  10  (hereinafter, effective surface area) due to the principle similar to that of electrolytic capacitor. 
     That is, by introducing the ground-side conductive fiber layer  40  and the patch-side conductive fiber layer  30 , as compared with the structure where no conductive fiber layer is included as a conventional structure, the capacitance per a unit area provided by the patch-side unit can be increased. The effective surface area is a notion corresponding to electrode area in the field of electrolytic capacitor. 
     In other words, the conductive fiber layers provided on each of the patch-side opposing surface and the ground-side opposing surface so as to be opposed to each other function as members for expanding the area of the patch part  20  that contributes to formation of capacitance (that is, effective surface area) so as to be a value larger than the actual area of the patch part  20 . 
     Therefore, the above structure makes it possible to provide a capacitance larger than the capacitance corresponding to the area intrinsically equipped in the patch part  20 . Accordingly, when the operating frequency is made constant, the area of the patch part  20  can be reduced as compared with the conventional one. 
     Furthermore, downsizing of the antenna device by the above structure is achieved by increasing the capacitance per unit area provided by the patch-side unit. That is, according to the above structure, the inductance component need not be increased. Accordingly, the antenna device  100  can be downsized without increasing Q value indicating sharpness of peak of the operating band. 
     Note that the capacitance provided by disposing the patch-side unit so as to oppose the ground-side unit is necessary to have a magnitude that allows parallel resonance with the inductance formed by the short-circuit part  60  in the operating frequency. The capacitance per unit area provided by disposing the patch-side unit to oppose the ground-side unit (hereinafter, unit capacitance) can be changed also by the separation H 1 . It is sufficient that the unit capacitance depending on the separation H 1  is specified by measurement by an experiment or the like. Using the unit capacitance depending on the separation H 1  makes it possible to determine the area that should be equipped in the patch part  20 . 
     It is sufficient that the size or the like of each part equipped in the above-mentioned antenna device  100  is designed by, for example, the following procedure. First, the length of the short-circuit part  60  originated from the separation H 1  is determined depending on the height allowable as the antenna device  100 . This determines the inductance provided by the short-circuit part  60 . 
     Next, the capacitance that should be provided by the patch-side unit is determined based on the inductance provide by the short-circuit part  60  and the operating frequency. Then, the planer shape and the size (in other words, area) of the patch part  20  are determined based on the capacitance that should be formed by the patch-side unit and the unit capacitance depending on the separation H 1 . 
     Note that when the antenna device  100  is manufactured, it is sufficient that the ground-side conductive fiber layer  40 , the supporting part  50 , the patch-side conductive fiber layer  30 , the patch part  20 , and the like are sequentially formed on the ground part  10 . It is sufficient that the short-circuit part  60  is disposed in the middle of the processes or after the processes. 
     It is sufficient that a power feeding point is provided at an appropriately designed position, for example, a position at which impedance matching can be obtained. Power feeding method may be a direct coupling power feeding method or may be an electromagnetic coupling power feeding method. The direct coupling power feeding method includes a mode where a short pin as the short-circuit part  60  is directly connected to an external conductor that is a coaxial cable, and a mode where the short pin is indirectly connected via a predetermined impedance matching circuit. 
     The antenna device  100  described above can be used for, for example, a moving body such as a vehicle. When the antenna device  100  is used for a vehicle, it is sufficient that the antenna device  100  is set such that the ground part  10  is substantially horizontal and the direction toward patch part  20  from the ground part  10  substantially matches the zenith direction on a roof part of the vehicle. 
     Although the embodiment of the present disclosure is described hereinabove, the present disclosure is not limited to the embodiment. 
     Following modifications may be included in the technical scope of the present disclosure, and the present disclosure may be changed in various other ways other than the following modifications without departing from the gist of the present disclosure. 
     Members having the same functions as the members described in the above embodiment will be denoted by the same reference numerals, and descriptions thereof will be omitted. Further, when only a partial configuration is described, the configuration of the above-described embodiment may be applied to the other portions. 
     First Modification 
     In the first embodiment described above, the mode is exemplified in which the patch-side conductive fiber layer  30  is formed such that its conductive fibers erect with respect to the patch-side opposing surface, but this is not limited thereto. For example, as illustrated in  FIG. 4 , orientations of the conductive fibers with respect to the patch-side opposing surface may be random (in other words, irregular). In addition, in this case, a dielectric substance having a predetermined dielectric constant shall be filled in each of gaps between the conductive fibers. 
     Second Modification 
     In the above, the mode is exemplified in which the area that contributes to formation of the capacitance (hereinafter, effective area) is expanded by providing the conductive fiber layer on each of the ground-side opposing surface and the patch-side opposing surface, but this is not limited thereto. 
     For example, by providing an asperity part  30 A with respect to the ground-side opposing surface and the patch-side opposing surface as illustrated in  FIG. 5 , the effective area may be expanded. Such a mode also provides the same effect as that of the above-mentioned embodiment. The asperity part  30 A provided on the patch-side opposing surface corresponds to the patch area expansion part, and the asperity part  30 A provided on the ground-side opposing surface corresponds to the ground area expansion part. 
     The asperity part  30 A can be provided by, for example, subjecting the ground-side opposing surface and the patch-side opposing surface to etching or the like. The concrete shape of the asperity part  30 A may be any shape in a range providing the above-mentioned effect, and for example, may be a cone shape such as a triangular pyramid shape or a four-sided pyramid shape, or may be a frustum shape. Like the conductive fiber layer, a dielectric substance having a predetermined dielectric constant (e.g. resin) shall be filled in a gap of each of asperities equipped in the asperity part  30 A. 
     Third Modification 
     In the above, the mode is disclosed in which the short-circuit part  60  and the patch part  20  are directly connected, but this is not limited thereto. For example, as illustrated in  FIG. 6 , a predetermined separation may be provided between the short-circuit part  60  and the patch part  20  to be electromagnetically joined with each other. That is, among the ends equipped in the short-circuit part  60 , the end  61  on which the patch part  20  exists (hereinafter, patch-side end) may be an open end. The separation between the patch-side end  61  and the patch part  20  is preferably a sufficiently small value with respect to the target wavelength. For example, the separation between the patch-side end  61  and the patch part  20  shall be one hundredth of the target wavelength. 
     Fourth Modification 
     In the third modification described above, the patch-side end  61  may be electrically connected to one end of a linear pattern  70  that is conductive and formed in a plane parallel to the patch part  20  as illustrated in  FIGS. 7 and 8 . 
       FIG. 7  is a cross sectional view corresponding to  FIG. 2  of the antenna device  100  according to a fourth modification, and  FIG. 8  is a schematic top view of the antenna device  100 . It should be noted here that the size of each part in  FIG. 8  does not perfectly match that of  FIG. 7  for convenience. 
     It is sufficient that the linear pattern  70  is provided on, for example, a resin layer  80  laminated on an upper side surface of the patch part  20 . Herein, the upper direction is a direction toward patch part  20  from the ground part  10 . The upper side surface of the patch part  20  is a surface that is not opposed to the ground-side opposing surface. An end that is not connected to the patch-side end  61  among ends equipped in the linear pattern  70  shall be an open end. As another mode, the linear pattern  70  need not necessarily be a spiral shape as illustrated in  FIG. 8 , and may be a straight line. Alternatively, it may be a curved line. 
     Fifth Modification 
     In the first embodiment described above, the mode is exemplified in which the patch-side conductive fiber layer  30  is provided on the entire area of the patch-side opposing surface, but this is not limited thereto. A mode may be employed in which the patch-side conductive fiber layer  30  is provided on only a part of the patch-side opposing surface. For convenience, a region on which the patch-side conductive fiber layer  30  is provided in the patch-side opposing surface is described as an effective surface area expansion part. 
     In this case, the effective surface area expansion part shall be provided so as to provide a part of a capacitance necessary for generating parallel resonance with the inductance provided by the short-circuit part  60  in the operating frequency (hereinafter, necessary capacitance). 
     Furthermore, it is sufficient that an area of the part where no effective surface area expansion part is provided on the patch-side opposing surface has an area providing a capacitance that compensates deficiency of the capacitance provided by the effective surface area expansion part with respect to the necessary capacitance. 
     The mode in which the conductive fiber layer is provided on only a part of the patch-side opposing surface in this manner also makes it possible to downsize the antenna device  100  while suppressing increase of Q value. 
     Sixth Modification 
     Using the antenna device  100  described above as one unit structure, a plurality of the unit structures may be periodically disposed in one dimension as illustrated in  FIG. 9 . In addition, as illustrated in  FIG. 10 , a plurality of the unit structures may be periodically disposed in two dimensions. Note that the supporting part  50  and the like are omitted in  FIGS. 9 and 10 . A broken line in  FIGS. 9 and 10  denotes a cut line (in other words, a border line) of the unit structures. 
     The structures in which the unit structures illustrated in  FIGS. 9 and 10  are periodically disposed are known as an electromagnetic band gap (EGB) structure. In other words, the structures disclosed in  FIGS. 9 and 10  can be provided by using a known method of providing the EGB structure. 
     Second Embodiment 
     In the first embodiment described above, the mode is disclosed in which the ground part  10  and the patch part  20  are included in addition to the conductive fiber layers opposed to each other, but this is not limited thereto. The conductive fiber layers opposed to each other may be treated as members corresponding to the ground part  10  and the patch part  20 . In other words, no ground part  10  and no patch part  20  may be included. Hereinafter, a schematic structure of an antenna device  200  according to a second embodiment as such a mode will be described using  FIG. 11 . 
       FIG. 11  is a diagram corresponding to  FIG. 2 , and is a cross sectional view of the antenna device  200 . The antenna device  200  includes, as illustrated in  FIG. 11 , a ground-side conductive fiber layer  40  also serves the function as the ground part  10 , a patch-side conductive fiber layer  30  also serves the function as the patch part  20 , a supporting part  50 , and a short-circuit part  60 . 
     The supporting part  50  in the second embodiment supports the ground-side conductive fiber layer  40  and the patch-side conductive fiber layer  30  to be opposed with a predetermined distance H 1 . The short-circuit part  60  electrically connects the ground-side conductive fiber layer  40  and the patch-side conductive fiber layer  30 . Such a structure also makes it possible to achieve the same effect as that of the first embodiment. The patch-side conductive fiber layer  30  in the second embodiment corresponds to a patch-side conductive fiber part and the ground-side conductive fiber layer  40  therein corresponds to a ground-side conductive fiber part. 
     The idea disclosed as various modifications with respect to the first embodiment disclosed above can be also applied to the second embodiment. For example, the end of the short-circuit part  60  on which the patch-side conductive fiber layer  30  exists (that is, patch-side end  61 ) may be an open end. In addition, the linear pattern  70  may be connected to the patch-side end  61 . In addition, as disclosed as the sixth modification, using the antenna device  200  as a unit structure, a plurality of the unit structures may be periodically disposed in one dimension or two dimensions. 
     Although the present disclosure is described based on the above embodiments, the present disclosure is not limited to the embodiments and the structures. Various changes and modification may be made in the present disclosure. Furthermore, various combination and formation, and other combination and formation including one, more than one or less than one element may be made in the present disclosure.