Patent Publication Number: US-2013249759-A1

Title: Antenna, dipole antenna, and communication apparatus  using the same

Description:
TECHNICAL FIELD 
     The present invention relates to an antenna having a strip-shaped conductor, a dipole antenna having the antenna, and a communication apparatus using the same. 
     BACKGROUND ART 
     As one of antennas which perform transmitting and receiving of electromagnetic waves in a communication apparatus, a dipole antenna or a monopole antenna is known, for example, as disclosed in Japanese Unexamined Patent Publication JP-A 5-259728 (1993). 
     SUMMARY OF INVENTION 
     The dipole antenna is basically required to have a conductor having a length of ½ wavelength, and the monopole antenna is basically required to have a conductor having a length of ¼ wavelength and a ground surface. Therefore, there is a problem that shapes thereof are large-sized. 
     The invention has been made in light of the problem in the related art, and an object thereof is to provide an antenna which can be miniaturized and has a strip-shaped conductor, a dipole antenna having the antenna, and a communication apparatus using the same. 
     An antenna of the invention comprises a strip-shaped conductor in which a plurality of strip-shaped m-th order elements, where m is an integer of 3 or more, are sequentially connected to one another, wherein n-th order elements constituting the strip-shaped conductor, where n is all integers equal to or more than 2 and equal to or less than m, are configured to be p n-th order elements into which an (n−1)-th order element is divided, where p is an integer of 3 or more, and the n-th order elements divided into p have bent shapes at respective boundary parts between the n-th order elements and are located along a straight line parallel to a line segment connecting one end of the (n−1)-th order element to the other end thereof. 
     A dipole antenna of the invention comprises a first antenna and a second antenna which are the antenna mentioned above, wherein a shape of the conductor of the first antenna and a shape of the conductor of the second antenna are the same, each of first order elements of the strip-shaped conductors being linear, and line segments connecting both ends of each of the strip-shaped conductors are located on a same straight line. 
     A dipole antenna of the invention comprises a first antenna and a second antenna which are the antenna mentioned above, wherein a shape of the strip-shaped conductor of the first antenna and a shape of the strip-shaped conductor of the second antenna are line-symmetric, each of first order elements of the strip-shaped conductors being linear, and line segments connecting both ends of each of the strip-shaped conductors are located on a same straight line. 
     A communication apparatus of the invention comprises the antenna mentioned above, and at least one of a receiving circuit and a transmitting circuit which are connected to the antenna. 
     A communication apparatus of the invention comprises the dipole antenna mentioned above, and at least one of a receiving circuit and a transmitting circuit which are connected to the dipole antenna. 
     In addition, an angle between the n-th order elements adjacent to each other means an angel which is made between a line segment connecting both ends of one adjacent n-th order element and a line segment connecting both ends of the other adjacent n-th order element, and is smaller than 180°. 
     According to the invention, it is possible to obtain an antenna and a dipole antenna which can be miniaturized. In addition, it is possible to obtain a communication apparatus which has the antennas and can be miniaturized. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view schematically illustrating an antenna (dipole antenna) according to an embodiment of the invention; 
         FIG. 2  is a schematic top view of the antenna (dipole antenna) shown in  FIG. 1 ; 
         FIG. 3  is a schematic plan view illustrating a shape of a conductor  20  in the antenna shown in  FIGS. 1 and 2 ; 
         FIG. 4  is a top view schematically illustrating an antenna according to an embodiment of the invention; 
         FIG. 5  is a top view schematically illustrating an antenna according to an embodiment of the invention; 
         FIG. 6  is a top view schematically illustrating an antenna according to an embodiment of the invention; 
         FIG. 7  is an enlarged view illustrating a shape of a conductor  320  of a region A of the antenna shown in  FIG. 6 ; 
         FIG. 8  is a schematic plan view illustrating a modified example of a shape of a conductor in the antenna of the invention; 
         FIG. 9  is a schematic plan view illustrating a modified example of a shape of a conductor in the antenna of the invention; 
         FIG. 10  is a top view schematically illustrating a modified example of the dipole antenna of the invention; 
         FIG. 11  is a perspective view schematically illustrating a modified example of the antenna (dipole antenna) of the invention; 
         FIG. 12  is a block diagram schematically illustrating an example of a communication apparatus according to an embodiment of the invention; 
         FIG. 13  is a schematic diagram illustrating a coordinate system in a simulation; 
         FIG. 14  is a graph illustrating a radiation pattern of a directional gain on an xy plane; 
         FIG. 15  is a graph illustrating a radiation pattern of a directional gain on a zx plane; 
         FIG. 16  is a graph illustrating a radiation pattern of a directional gain on a zy plane; and 
         FIG. 17  is a graph illustrating a radiation pattern of a directional gain on the zy plane. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an antenna, a dipole antenna, and a communication apparatus using the same of the invention will be described in detail with reference to the accompanying drawings. In addition, in the present specification, a conductor having a bent shape is described using expression of folding the conductor; however, this expression is used for convenience in order to describe a shape of a pattern, and there may no process of practically folding the conductor in manufacturing an antenna. 
     First Embodiment 
       FIG. 1  is a perspective view schematically illustrating an antenna according to a first embodiment of the invention.  FIG. 2  is a schematic top view of the antenna shown in  FIG. 1 .  FIG. 3  is a schematic plan view illustrating a shape of the conductor  20  in the antenna in this embodiment shown in  FIGS. 1 and 2 . 
     The antenna of this embodiment, as shown in  FIGS. 1 and 2 , includes a dielectric substrate  10 , and a strip-shaped conductor  20  having a predetermined shape, disposed on the upper surface of the dielectric substrate. In addition, the strip-shaped conductor  20  is divided into a conductor  20   a  and a conductor  20   b  at the center, and a terminal portion  30  includes terminals  30   a  and  30   b  provided at divided locations. The conductor  20  is supplied with power at the terminal portion  30 , and functions as a dipole antenna which has the conductors  20   a  and  20   b  as elements. 
     In addition, in the following description, the conductor  20  will be described assuming that the conductor  20   a  and the conductor  20   b  are not divided but are connected to each other. 
     The left part of  FIG. 3  shows a first order element  41 , the central part thereof shows second order elements  42   a  to  42   d , and the right part thereof shows third order elements  43   a  to  43   s .  FIG. 3  shows a design method of a pattern of the conductor  20  through schematic decomposition. 
     First, the first order element  41  is divided into four second order elements  42   a  to  42   d . In addition, each of the four second order elements is divided into four third order elements, and thus there are a total of sixteen third order elements  43   a  to  43   s . As a result, the conductor  20  in the antenna of this embodiment has a structure formed by sequentially connecting the sixteen strip-shaped third order elements  43   a  to  43   s.    
     The linear first order element  41  is divided into the four second order elements  42   a  to  42   d . In addition, respective boundary parts of the second order elements  42   a  to  42   d  have a folded shape along a straight line (indicated by the dotted line;  52   w  to  52   x ) parallel to a line segment which connects one end  41   w  of the first order element  41  to the other end  41   x  thereof. In other words, the boundary parts of the respective second order elements  42   a  to  42   d  are folded and have a bent shape such that a vector direction from one end of the first order element  41  to the other end thereof does not vary. 
     In addition, each of the second order elements  42   a  to  42   d  is divided into four third order elements. At this time, respective boundary parts of the third order elements  43   a  to  43   d  have a folded shape along a straight line (indicated by the dotted line) parallel to a line segment which connects one end of the second order element  42   a  to the other end thereof. This is also the same for the other three second order elements  42   b  to  42   d . In other words, the boundary parts of the respective third order elements  43   a  to  43   s  are folded and have a bent shape such that a vector direction from one end of each of the second order elements  42   a  to  42   d  to the other end thereof does not vary. 
     In addition, in this embodiment, the first order element  41  is linear, the first order element  41  is divided into the four second order elements  42   a  to  42   d  having the same length and has a shape in which the boundary parts of the respective second order elements  42   a  to  42   d  in the first order element  41  are sequentially bent in a reverse direction such that an angle between the second order elements  42   a  to  42   d  adjacent to each other is 90°. 
     In addition, each of the second order elements  42   a  to  42   d  is divided into the four third order elements having the same length, and has a shape in which the boundary parts of the respective third order elements in each of the second order elements  42   a  to  42   d  are sequentially bent in a reverse direction such that an angle between the third order elements adjacent to each other is 90°. 
     Here, the length of the first order element  41 , the length of the second order shape  52  in which the four second order elements are connected to each other, and the length of the third order shape  53  in which the sixteen third order elements are connected to each other, are all the same. Here, when the sizes in a z direction of  FIG. 3  are compared, the second order shape  52  is 2½ times the size of the first order element  41 , and since the third order shape  53  is 2½ times the size of the second order shape  52 , the third order shape  53  is ½ of the first order element  41 . In other words, according to the antenna of this embodiment, it is possible to obtain a miniaturized antenna whose length in the longitudinal direction (z direction in the figure) is reduced to ½ as compared with a basic antenna having a linear conductor such as the first order element  41 . 
     In a design of this antenna, the following procedures may be performed such that a length in the longitudinal direction (z direction in the figure) is a desired length. 
     (Procedure 1) A linear first order element is divided into four second order elements having the same length, and boundary parts of the second order elements are sequentially folded in a reverse direction such that an angle formed between the second order elements adjacent to each other is 90°. At this time, a straight line connecting both ends of the first order element before being folded is made to be parallel to a straight line connecting both ends of the first order element after being folded. 
     (Procedure 2) Each of the second order elements is divided into four third order elements having the same length, and boundary parts of the third order elements are folded such that an angle formed between the third order elements adjacent to each other is 90°. At this time, the third order elements are sequentially folded in a reverse direction in each second order element, and a straight line connecting both ends of each second order element before being folded is made to be parallel to a straight line connecting both ends of each second order element after being folded. 
     (Procedure 3) The order of elements increases by one as necessary, and an operation of the previous procedure is performed. 
     (Procedure 4) The operation of the procedure 3 is repeatedly performed until the order of elements arrives at a desired order as necessary. 
     When generally expressed, the antenna of this embodiment includes the conductor  20  in which a plurality of strip-shaped m-th order elements (where m is an integer of 3 or more) are sequentially connected, and, n-th order elements constituting the conductor  20  (where n is all integers equal to or more than 2 and equal to or less than m), are configured to be p n-th order elements into which an (n−1)-th order element is divided (where p is an integer of 3 or more). In addition, the n-th order elements divided into p have bent shapes at respective boundary parts between the n-th order elements and are located along a straight line parallel to a line segment connecting one end of the (n−1)-th order element to the other end thereof. In other words, the respective boundary parts of the n-th order elements have folded shapes such that a vector direction from one end of the (n−1)-th order element to the other end thereof does not vary. At this time, a straight line connecting both ends of the (n−1)-th order element before being folded is parallel to a straight line connecting both ends of the p n-th order elements after being folded into which the (n−1)-th order element is divided. In addition, in the embodiment shown in  FIGS. 1 to 3 , the maximum order m is 3, and the division number p is 4. 
     In the antenna of this embodiment having the configuration, since the boundary parts of the n-th order elements are folded such that a vector direction from one end of the (n−1)-th order element to the other end thereof does not vary, a vector sum of a current flowing through the respective m-th order elements is approximately the same as a vector from one end  53   w  of the conductor  20  to the other end  53   x  thereof. In other words, a direction of the vector sum of the current flowing through the respective m-th order elements is approximately the same as a direction when a current flowing through the conductor  20  formed only by the original first order element  41  is represented by a vector. Therefore, according to the antenna of this embodiment, it is possible to obtain a miniaturized antenna which maintains approximately the same antenna characteristics also including directivity as compared with a linear antenna having the conductor  20  which is formed only by the original first order element  41 . Therefore, an antenna which is miniaturized, has a high performance, and is easily designed is obtained. 
     In addition, it is preferable to satisfy a condition in which the divided p n-th order elements have the same length, and angles formed by the n-th order elements adjacent to each other in each of the (n−1)-th order elements are all the same. With this configuration, symmetry of an antenna increases, and thus an antenna having desired characteristics is easily designed. 
     In addition, a bent shape is preferable in which an angle between the n-th order elements adjacent to each other is θ (90°≦θ&lt;180°). With this configuration, there is no reverse component in current vectors of the n-th order elements adjacent to each other, and overlapping between the n-th order elements can be simply prevented. Therefore, it is possible to obtain an antenna which has a higher performance and is easily designed. 
     Next, an embodiment of the dipole antenna of the invention exemplified in  FIGS. 1 to 3  will be described. The dipole antenna of this embodiment has two antennas including a first antenna (the conductor  20   a ) and a second antenna (the conductor  20   b ) having the same shape. The antennas are antennas having the above-described configuration of the invention. In addition, a line segment connecting both ends of the first antenna (the conductor  20   a ) and a line segment connecting both ends of the second antenna (the conductor  20   b ) are located on the same straight line. 
     This is exactly a state in which the antenna according to an embodiment of the invention, designed to maintain characteristics and to be reduced such as the first order element  41 -&gt;the second order shape  52 -&gt;the third order shape  53  in  FIG. 3 , is equally divided into two at the center in the longitudinal direction, and forms a dipole antenna by being supplied with power at the division parts. Therefore, according to the dipole antenna of this embodiment, it is possible to easily obtain, without using an electromagnetic simulation, a dipole antenna which maintains approximately the same characteristics also including directivity and is further miniaturized, without using an electromagnetic field simulation, as compared with a dipole antenna which is divided at the center of the linear first order element  41  and has power supply points at the division parts. 
     In the antenna of this embodiment, the dielectric constant of the dielectric substrate  10  is, for example, about 2 to 20. A material of the dielectric substrate  10  is not particularly limited, and may use a resin such as glass epoxy. In addition, dielectric ceramics are preferably used from the viewpoint of accuracy when the dielectric substrate  10  is formed and easiness of manufacturing. The conductor  20  is made of metal having good conductivity such as, for example, gold, silver, copper, and an alloy thereof, and, a thickness thereof is, for example, about 3 μm to 50 μm. The conductor may be formed using either a thick film method such as printing or a thin film method such as a PVD method or a CVD method. 
     Second Embodiment 
       FIG. 4  is a top view schematically illustrating an antenna according to a second embodiment of the invention. In addition, in this embodiment, a difference from the above-described first embodiment will be described, and repeated description of the same element will be omitted. When this embodiment is generally expressed, the maximum order m is 4, and the division number p is 4. 
     As shown in  FIG. 4 , a conductor  120  of the antenna of this embodiment is provided on a dielectric substrate  110  and is formed by sequentially connecting  64  fourth order elements having a strip-shape. The fourth order elements have a shape in which each of the third order elements  43   a  to  43   s  having the third order shape  53  shown in  FIG. 3  is divided into four fourth order elements having the same length, and boundary parts of the fourth order elements in each of the third order elements  43   a  to  43   s  are sequentially bent in a reverse direction such that a vector direction from one end of each of the third order elements  43   a  to  43   s  to the other end thereof does not vary and an angle between the fourth order elements adjacent to each other is 90°. 
     According to the antenna of this embodiment, it is possible to obtain a miniaturized antenna which maintains approximately the same antenna characteristics also including directivity and has a length in the longitudinal direction (z direction in the figure) reduced to a length multiplied by 2 3/2 as compared with a basic antenna having a linear conductor such as the first order element  41  of  FIG. 3 . 
     In addition, as shown in  FIG. 4 , the conductor  120  of the antenna may be equally divided into two at the center in the longitudinal direction, and may function as a dipole antenna by providing power supply points  130   a  and  130   b  at the division part  130 . A line segment connecting both ends of a first antenna (on which the power supply point  130   a  is located) and a line segment connecting both ends of a second antenna (on which the power supply point  130   b  is located) are located on the same straight line, which thus can be regarded as an embodiment of the dipole antenna of the invention. 
     Third Embodiment 
       FIG. 5  is a top view schematically illustrating an antenna according to a third embodiment of the invention. In addition, in this embodiment, a difference from the above-described embodiments will be described, and repeated description of the same element will be omitted. When this embodiment is generally expressed, the maximum order m is 5, and the division number p is 4. 
     As shown in  FIG. 5 , a conductor  220  of the antenna of this embodiment is provided on a dielectric substrate  210  and is formed by sequentially connecting  256  fifth order elements having a strip-shape. The fifth order elements have a shape in which each of the fourth order elements of the conductor  120  of the antenna shown in  FIG. 4  is divided into four fifth order elements having the same length, and boundary parts of the fifth order elements in each of the fourth order elements are sequentially bent in a reverse direction such that a vector direction from one end of each of the fourth order elements to the other end thereof does not vary and an angle between the fifth order elements adjacent to each other is 90°. 
     According to the antenna of this embodiment, it is possible to obtain a miniaturized antenna which maintains approximately the same antenna characteristics including directivity and has a length in the longitudinal direction (z direction in the figure) reduced to a length multiplied by ¼ as compared with a basic antenna having a linear conductor such as the first order element  41  of  FIG. 3 . 
     In addition, as shown in  FIG. 5 , the conductor  220  of the antenna may be equally divided into two at the center in the longitudinal direction, and may function as a dipole antenna by providing power supply points  230   a  and  230   b  at the division part  230 . A line segment connecting both ends of a first antenna (on which the power supply point  230   a  is located) and a line segment connecting both ends of a second antenna (on which the power supply point  230   b  is located) are located on the same straight line, which thus can be regarded as an embodiment of the dipole antenna of the invention. 
     Fourth Embodiment 
       FIG. 6  is a top view schematically illustrating an antenna according to a fourth embodiment of the invention. In addition,  FIG. 7  is an enlarged view illustrating a conductor state of the region A of  FIG. 6 . In addition, in this embodiment, a difference from the above-described embodiments will be described, and repeated description of the same element will be omitted. When this embodiment is generally expressed, the maximum order m is 6, and the division number p is 4. 
     As shown in  FIGS. 6 and 7 , a conductor  320  of the antenna of this embodiment is provided on a dielectric substrate  310  and is formed by sequentially connecting  1024  sixth order elements having a strip-shape. The sixth order elements have a shape in which each of the fifth order elements of the conductor  220  of the antenna shown in  FIG. 5  is divided into four sixth order elements having the same length, and boundary parts of the sixth order elements in each of the fifth order elements are sequentially bent in a reverse direction such that a vector direction from one end of each of the fifth order elements to the other end thereof does not vary and an angle between the sixth order elements adjacent to each other is 90°. 
     According to the antenna of this embodiment, it is possible to obtain a miniaturized antenna which maintains approximately the same antenna characteristics including directivity and has a length in the longitudinal direction (z direction in the figure) reduced to a length multiplied by 2 5/2 as compared with a basic antenna having a linear conductor such as the first order element  41  of  FIG. 3 . 
     In addition, as shown in  FIG. 6 , the conductor  320  of the antenna may be equally divided into two at the center in the longitudinal direction, and may function as a dipole antenna by providing power supply points  330   a  and  330   b  at the division part  330 . A line segment connecting both ends of a first antenna (on which the power supply point  330   a  is located) and a line segment connecting both ends of a second antenna (on which the power supply point  330   b  is located) are located on the same straight line, which thus can be regarded as the dipole antenna according to an embodiment of the invention. 
     Modified Example 1 
     Although a description has been made that the division number p is 4, and an angle between the n-th order elements adjacent to each other is 90° in the embodiments, the invention is not limited thereto.  FIG. 8  is a schematic plan view illustrating a modified example of the shape of the conductor. In addition, in this embodiment, a difference from the first embodiment described with reference to  FIG. 3  will be described, and repeated description of the same element will be omitted. When this embodiment is generally expressed, the maximum order m is 3, and the division number p is 5. In addition, an angle of the n-th order elements adjacent to each other is 90°. 
     A first order element  440  is divided into five second order elements  441   a  to  441   e . In addition, since each of the five second order elements is divided into five third order elements, there are twenty-five third order elements  442   a  to  442   z  in total. As a result, the conductor in the antenna of this embodiment has a structure formed by sequentially connecting the twenty-five strip-shaped third order elements  442   a  to  442   z.    
     The linear first order element  440  is divided into the five second order elements  441   a  to  441   e . In addition, respective boundary parts of the second order elements  441   a  to  441   e  have a bent shape along a straight line (indicated by the dotted line;  451   w  to  451   x ) parallel to a line segment which connects one end  440   w  of the first order element  440  to the other end  440   x  thereof. In other words, the boundary parts of the respective second order elements  441   a  to  441   e  have a folded shape such that a vector direction from one end of the first order element  440  to the other end thereof does not vary. 
     In addition, each of the five second order elements  441   a  to  441   e  is divided into five third order elements. At this time, respective boundary parts of the third order elements  442   a  to  442   e  have a bent shape along a straight line (indicated by the dotted line) parallel to a line segment which connects one end of the second order element  441   a  to the other end thereof. In the same manner for the other four second order elements  441   b  to  441   e , boundary parts of the respectively corresponding third order elements have a bent shape. In other words, the boundary parts of the respective third order elements  442   a  to  442   z  have a folded shape such that a vector direction from one end of each of the second order elements  441   a  to  441   e  to the other end thereof does not vary. 
     Modified Example 2 
       FIG. 9  is a schematic plan view illustrating a modified example of the shape of the conductor. In addition, in this embodiment, a difference from the first embodiment described with reference to  FIG. 3  will be described, and repeated description of the same element will be omitted. When this embodiment is generally expressed, the maximum order m is 3, and the division number p is 4, which is the same as in the first embodiment, but an angle between the n-th order elements adjacent to each other is greater than 90°, which is different from in the first embodiment. 
     A first order element  540  is divided into four second order elements  541   a  to  541   d . In addition, each of the four second order elements is divided into four third order elements, and thus there are a total of sixteen third order elements  542   a  to  542   s . As a result, the conductor in the antenna of this embodiment has a structure formed by sequentially connecting the sixteen strip-shaped third order elements  542   a  to  542   s.    
     Here, an angle formed between the second order elements  541   a  to  541   d  adjacent to each other is greater than 90°. In addition, an angle formed between the third order elements  542   a  to  542   s  adjacent to each other is also greater than 90°. 
     As mentioned above, both the antennas of the modified examples 1 and 2 shown in  FIGS. 8 and 9  have a length which is reduced in the longitudinal direction (z direction in the figure) as compared with an antenna having a linear conductor shown in each first order element. In addition, since the above-described operations and effects of an antenna of the invention are achieved, it is possible to obtain an antenna which maintains approximately the same antenna characteristics and is miniaturized as compared with a linear antenna having the same length. 
     Modified Example 3 
     Next, a modified example of the dipole antenna will be described. In the above-described first to fourth embodiments, a central part of a conductor is divided and is provided with power supply points so as to form a first antenna and a second antenna having the same shape, and thereby a line segment connecting both ends of the first antenna and a line segment connecting both ends of the second antenna are made to be located on the same straight line so as to form a dipole antenna; however, the invention is not limited thereto. 
       FIG. 10  shows a modified example of the dipole antenna of the invention. A conductor  620   a  of the first antenna and a conductor  620   b  of the second antenna have shapes which are line-symmetric to each other with respect to a straight line passing through the power supply point  630  of the dipole antenna, which is an axis of symmetry. In addition, the first order element of each conductor is linear, and two line segments connecting both ends of the respective conductors are located on the same straight line. In addition, the axis of symmetry of line symmetry is perpendicular to the straight line. 
     According to the dipole antenna having this configuration, in the two conductors  620  ( 620   a  and  620   b ), magnitudes of currents flowing through the m-th order elements located at an equal distance from the power supply point are the same, and a component in a direction perpendicular to the line segment connecting both ends of the conductors  620  is in a reverse direction. Therefore, current components in the direction perpendicular to the line segment connecting both ends of the conductors  620  ( 620   a  and  620   b ) cancel out each other between the two conductors  620   a  and  620   b , and thus a direction of a vector sum of currents flowing through the respective parts of the two conductors  620   a  and  620   b  conforms to a direction of a vector from the one end of the conductors  620  ( 620   a  and  620   b ) to the other end thereof. Therefore, according to the dipole antenna having this configuration, it is possible to obtain a dipole antenna which maintains approximately the same characteristics also including directivity and is miniaturized, as compared with a dipole antenna which has a linear conductor. 
     Modified Example 4 
       FIG. 11  is a perspective view schematically illustrating a modified example of the antenna of the invention. The antenna of this embodiment, as shown in  FIG. 11 , has a configuration in which a conductor  720  and a dielectric substrate  710  are folded with respect to an axis, which is a straight line parallel to a straight line connecting one end of the conductor  720  to the other end thereof in the antenna of the first embodiment shown in  FIGS. 1 and 2 . This axis is an axis parallel to the z axis shown in each figure. 
     According to the antenna with this configuration, a size in the width direction can be reduced in addition to the longitudinal direction, and thus it is possible to obtain a further miniaturized antenna. In addition, since the conductor  720  is folded with respect to the axis, which is the straight line parallel to the straight line connecting one end of the conductor  720  to the other end thereof, a state is preserved in which components of currents flowing through the respective parts of the conductor  720 , perpendicular to the straight line connecting the one end of the conductor  720  to the other end thereof, cancel out each other. Therefore, antenna characteristics including directivity are almost not changed as compared with the conductor before being folded. In other words, according to this embodiment, it is possible to obtain an antenna which has dimensions reduced in both the longitudinal direction and the width direction, is miniaturized, has a high performance, and is easily designed, almost without changing the antenna characteristics including directivity. 
     This is exactly the same for a case of the dipole antenna, and folding can be performed with respect to an axis, which is a straight line parallel to a straight line on which a line segment connecting both ends of each of the conductor  720   a  of the first antenna and the conductor  720   b  of the second antenna is located. 
     In addition,  FIG. 11  shows an example in which the conductor  720  is folded only once at a predetermined angle with respect to the axis, which is the straight line parallel to the straight line connecting one end of the conductor to the other end thereof; however, the invention is not limited thereto. A folded angle may be small or large, and folding may be performed multiple times. In addition, the conductor may be folded smoothly, in a cylindrical shape, or in a spiral shape. In addition, there may be any number of axes when the conductor is folded. Particularly, by providing the antenna (dipole antenna) of the invention on a flexible substrate made of a material such as polyimide, the conductor can be freely folded with respect to the above-described predetermined axis (for example, a straight line parallel to a straight line connecting one end of the conductor to the other end thereof), and thus it is possible to easily accommodate the miniaturized antenna in a small communication apparatus such as a mobile phone which is a communication apparatus having a limitation of an internal volume. 
     Next,  FIG. 12  is a block diagram schematically illustrating a communication apparatus according to an embodiment of the invention. The communication apparatus of this embodiment includes an antenna  81  of the invention, and a receiving circuit  83  and a transmitting circuit  84  which are connected to the antenna  81  via an antenna sharing machine  82 . The antenna or the dipole antenna of any of the above-described embodiments may be employed as the antenna  81  of the invention. 
     According to the communication apparatus of this embodiment with this configuration, transmitting and receiving of a communication signal are performed using the antenna  81  of the invention which is miniaturized and has good electrical characteristics, and thus it is possible to obtain a communication apparatus which is miniaturized and good electrical characteristics. 
     The invention is not limited to the above-described embodiments, and may be variously modified or changed without departing from the scope of the invention. In addition, the examples shown in the respective embodiments and the modified examples may be combined. 
     For example, in the above-described embodiments, the examples in which the dipole antenna is configured have been described; however, the invention is not limited thereto. For example, a monopole antenna may be configured by supplying power to one end of a conductor. In addition, in the above-described embodiments, the examples in which a maximum of 1024 sixth order elements having a strip-shaped is configured have been described; however, the invention is not limited thereto. It is possible to obtain an antenna which is further miniaturized by further increasing the order of elements. 
     In addition, in the above-described embodiments, the examples in which the (n−1)-th order element is equally divided into four or five have been described; however, the (n−1)-th order element may be equally divided into three or more, or may not be equally divided. Further, in the above-described embodiments, the examples in which the boundary parts of the n-th order elements adjacent to each other are sequentially folded in a reverse direction have been described; however, the invention is not limited thereto, and the boundary parts of the n-th order elements adjacent to each other may not be sequentially folded in a reverse direction. In addition, although the example in which an angle at which a pattern is folded is 90° or more has been described, an angle may be smaller than this angle, and the pattern may be bent smoothly. 
     EXAMPLES 
     Next, Examples of the invention will be described. 
     First, a radiation characteristic of the antenna of the third embodiment (the maximum order m=5, and the division number p=4) shown in  FIG. 5  was calculated through a simulation. In addition, as Comparative Example, a radiation characteristic of a linear dipole antenna having the linear conductor  20  such as the first order element  41  of  FIG. 3  was simulated together. In these simulations, the dielectric constant of the dielectric substrate  10  was set to 1, the width of the conductor  20  was set to 0.2 mm, the overall length of the conductor  20  was set to 750 mm, and the central frequency thereof was set to 200 MHz. 
     A coordinate system in these simulations is shown in  FIG. 13 , and simulation results are shown in  FIGS. 14 to 16 .  FIG. 14  shows a radiation pattern of a directional gain on an xy plane,  FIG. 15  shows a radiation pattern of a directional gain on a zx plane, and  FIG. 16  shows a radiation pattern of a directional gain on a zy plane. In addition, in  FIGS. 9 to 11 , the radiation pattern of the directional gain of the antenna of Example is indicated by the solid line, and the radiation pattern of the directional gain of the antenna of Comparative Example is indicated by the broken line. 
     In the graphs shown in  FIGS. 14 to 16 , the solid line and the broken line draw approximately the same trajectory, and thus it can be seen that the antenna of Example has a ¼ length in the longitudinal direction (z direction in the figure) as compared with the antenna of Comparative Example but has approximately the same characteristics also including directivity as compared with the antenna of Comparative Example. 
     Next, a radiation characteristic of the antenna of the second embodiment (the maximum order m=4, and the division number p=4) shown in  FIG. 4 , and an antenna in which the antenna of the second embodiment shown in  FIG. 4  is folded at 90° with respect to an axis parallel to the z axis as in  FIG. 11 , was calculated through simulations. In these simulations, the dielectric constant of the dielectric substrate  10  was set to 1, the width of the conductor  20  was set to 0.2 mm, the overall length of the conductor  20  was set to 750 mm, and the central frequency thereof was set to 270 MHz. In addition, a coordinate system in these simulations was the same as in  FIG. 13 . 
     A simulation result thereof is shown in  FIG. 17 .  FIG. 17  shows a radiation pattern of a directional gain on the zy plane. The radiation pattern of the directional gain of the antenna which is folded at 90° is indicated by the solid line, and the radiation pattern of the directional gain of the antenna which is shown in  FIG. 4  and is not folded is indicated by the broken line. It can be seen from the graph shown in  FIG. 17  that the solid line and the broken line draw the same line in an overlapping manner, and radiation characteristics also including directivity almost do not vary before and after folding. 
     As described above, the advantages of the invention can be confirmed from the simulation results shown in  FIGS. 14 to 17 . 
     REFERENCE SIGNS LIST 
     
         
         
           
               10 : Dielectric substrate 
               20 : Conductor 
               41 : First order element 
               42   a  to  42   d : Second order element 
               43   a  to  43   s : Third order element 
               81 : Antenna 
               83 : Receiving circuit 
               84 : Transmitting circuit