Patent Publication Number: US-11381003-B2

Title: Antenna device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is based on PCT filing PCT/JP2018/038662, filed Oct. 17, 2018, which claims priority to JP 2018-011301, filed Jan. 26, 2018, the entire contents of each are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an antenna device. 
     BACKGROUND ART 
     In a mobile communication system based on the communication standard called LTE/LTE-A (advanced), a wireless signal called an ultrashort wave with a frequency of 700 MHz to 3.5 GHz is mainly used for communication. 
     Furthermore, in the communication using an ultrashort wave like the communication standard described above, by adopting a technology called so-called multiple-input and multiple-output (MIMO), it is possible to further improve the communication performance by using a reflected wave in addition to a direct wave for transmitting and receiving signals even in a fading environment. Since a plurality of antennas is used in MIMO, various methods for disposing a plurality of antennas in a terminal device for mobile communication such as a smartphone and the like in a more preferred mode have been studied. 
     Furthermore, in recent years, various studies have been made on a fifth generation (5G) mobile communication system following LTE/LTE-A. For example, in the mobile communication system, the use of communication using a wireless signal called a millimeter wave with a frequency such as 28 GHz or 39 GHz (hereinafter, also simply referred to as “millimeter wave”) has been studied. 
     CITATION LIST 
     Patent Document 
     
         
         Patent Document 1: Japanese Patent Application Laid-Open No. 2005-72653 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In that connection, generally, a millimeter wave has relatively large spatial attenuation, and in a case where a millimeter wave is used for communication, there is a tendency for an antenna having a high gain to be required. To fulfill such a requirement, a technology called so-called beam forming may be used. Specifically, by controlling a beam width of an antenna by beam forming and improving directivity of the beam, it is possible to further improve the gain of the antenna. One example of an antenna system that can implement such control is a patch array antenna. For example, Patent Document 1 discloses one example of the patch array antenna. 
     Meanwhile, as a plurality of antenna elements is arrayed (for example, patch antenna), a distortion may occur in a radiation pattern of at least some of the antenna elements. In contrast, a method for inhibiting occurrence of such a distortion by providing a sufficiently large ground area can be cited. In this case, the size of the antenna device may become larger. 
     Therefore, the present disclosure proposes one example of a technology that enables miniaturization of a device in a more preferred mode in a case where a plurality of antenna elements is arrayed. 
     Solutions to Problems 
     According to the present disclosure, there is provided an antenna device including: a substrate; a plurality of antenna elements supported by the substrate, each of the antenna elements having a feeding point; and a parasitic element supported by the substrate and having no feeding point, in which the plurality of antenna elements is disposed to be spaced apart from each other along a predetermined direction, the parasitic element is mutually spaced apart in the direction from a first antenna element located on an end side in the direction among the plurality of antenna elements, and a first element interval between the parasitic element and the first antenna element is equal to or less than twice a second element interval between the first antenna element and a second antenna element located on an opposite side of the parasitic element with respect to the first antenna element. 
     Effects of the Invention 
     As described above, the present disclosure proposes a technology that enables miniaturization of a device in a more preferred mode in a case where a plurality of antenna elements is arrayed. 
     Note that above effects are not necessarily restrictive, and in addition to or instead of the effects described above, any of the effects indicated in the present specification or other effects that can be determined from the present specification may be produced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory diagram for describing one example of a schematic configuration of a system according to one embodiment of the present disclosure. 
         FIG. 2  is a block diagram showing one example of a configuration of a terminal device according to the embodiment. 
         FIG. 3  is an explanatory diagram for describing one example of a configuration of a communication device assuming the use of a millimeter wave. 
         FIG. 4  is an explanatory diagram for describing one example of a schematic configuration of an antenna device applied to the communication device assuming the use of a millimeter wave. 
         FIG. 5  is an explanatory diagram for describing a technical problem of the antenna device applied to the communication device assuming the use of a millimeter wave. 
         FIG. 6  is an explanatory diagram for describing one example of the schematic configuration of the antenna device according to the embodiment. 
         FIG. 7  is an explanatory diagram for describing one example of the configuration of the antenna device according to the embodiment. 
         FIG. 8  is an explanatory diagram for describing one example of the configuration of the antenna device according to the embodiment. 
         FIG. 9  is an explanatory diagram for describing another example of the configuration of the antenna device according to the embodiment. 
         FIG. 10  is an explanatory diagram for describing another example of the configuration of the antenna device according to the embodiment. 
         FIG. 11  is a diagram showing one example of a schematic configuration of an antenna device according to a comparative example. 
         FIG. 12  is a diagram showing one example of a simulation result of a radiation pattern of an antenna element in the antenna device according to the comparative example. 
         FIG. 13  is a diagram showing one example of the simulation result of the radiation pattern of the antenna element in the antenna device according to the comparative example. 
         FIG. 14  is a diagram showing one example of the schematic configuration of the antenna device according to the embodiment. 
         FIG. 15  is a diagram showing one example of a simulation result of a radiation pattern of an antenna element in the antenna device according to the embodiment. 
         FIG. 16  is a diagram showing one example of the simulation result of the radiation pattern of the antenna element in the antenna device according to the embodiment. 
         FIG. 17  is a diagram showing one example of the simulation result of reflection characteristics of the antenna device according to the comparative example. 
         FIG. 18  is a diagram showing one example of the simulation result of reflection characteristics of the antenna device according to the embodiment. 
         FIG. 19  is an explanatory diagram for describing one example of a configuration of an antenna device according to a first modification. 
         FIG. 20  is an explanatory diagram for describing another example of the configuration of the antenna device according to the first modification. 
         FIG. 21  is an explanatory diagram for describing another example of the configuration of the antenna device according to the first modification. 
         FIG. 22  is an explanatory diagram for describing one example of a configuration of an antenna device according to a second modification. 
         FIG. 23  is an explanatory diagram for describing one example of the configuration of the antenna device according to the second modification. 
         FIG. 24  is an explanatory diagram for describing one example of the configuration of the antenna device according to the second modification. 
         FIG. 25  is an explanatory diagram for describing one example of the configuration of the antenna device according to the second modification. 
         FIG. 26  is an explanatory diagram for describing one example of a configuration of an antenna device according to a third modification. 
         FIG. 27  is an explanatory diagram for describing one example of the configuration of the antenna device according to the third modification. 
         FIG. 28  is an explanatory diagram for describing an application example of the communication device according to the embodiment. 
         FIG. 29  is an explanatory diagram for describing an application example of the communication device according to the embodiment. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     A preferred embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that in the present specification and the drawings, components having substantially the same functional configuration are denoted with the same reference symbol, and redundant description thereof will be omitted. 
     Note that the description will be made in the following order. 
     1. Schematic configuration 
     1.1. One example of system configuration 
     1.2. Configuration example of terminal device 
     2. Overview of communication using millimeter wave 
     3. Configuration example of communication device assuming use of millimeter wave 
     4. Technical problem 
     5. Technical advantage 
     5.1. Configuration 
     5.2. Characteristics of antenna device 
     5.3. Modifications 
     5.4. Application example 
     6. Conclusion 
     1. SCHEMATIC CONFIGURATION 
     &lt;1.1. One Example of System Configuration&gt; 
     To begin with, with reference to  FIG. 1 , one example of a schematic configuration of a system  1  according to one embodiment of the present disclosure will be described.  FIG. 1  is an explanatory diagram for describing one example of the schematic configuration of the system  1  according to one embodiment of the present disclosure. As shown in  FIG. 1 , the system  1  includes a wireless communication device  100  and a terminal device  200 . Here, the terminal device  200  is also called a user. The user may also be called UE. The wireless communication device  100 C is also called UE-relay. The UE here may be UE defined in LTE or LTE-A, the UE-relay may be prose UE to network relay discussed in 3GPP, more generally may mean a communication device. 
     (1) Wireless Communication Device  100   
     The wireless communication device  100  is a device that provides a wireless communication service to a subordinate device. For example, the wireless communication device  100 A is a base station of a cellular system (or mobile communication system). The base station  100 A performs wireless communication with a device located inside a cell  10 A of the base station  100 A (for example, terminal device  200 A). For example, the base station  100 A transmits a downlink signal to the terminal device  200 A and receives an uplink signal from the terminal device  200 A. 
     The base station  100 A is logically connected to another base station by, for example, an X2 interface, and can transmit and receive control information and the like. Furthermore, the base station  100 A is logically connected to a so-called core network (not shown) by, for example, an S1 interface, and can transmit and receive control information and the like. Note that communication between these devices can be physically relayed by various devices. 
     Here, the wireless communication device  100 A shown in  FIG. 1  is a macro cell base station, and the cell  10 A is a macro cell. Meanwhile, the wireless communication devices  100 B and  100 C are master devices that operate the small cells  10 B and  10 C, respectively. As one example, the master device  100 B is a fixedly installed small cell base station. The small cell base station  100 B establishes a wireless backhaul link with the macro cell base station  100 A, and establishes an access link with one or more terminal devices in the small cell  10 B (for example, terminal device  200 B). Note that the wireless communication device  100 B may be a relay node defined by 3GPP. The master device  100 C is a dynamic access point (AP). The dynamic AP  100 C is a mobile device that dynamically operates the small cell  10 C. The dynamic AP  100 C establishes a wireless backhaul link with the macro cell base station  100 A, and establishes an access link with one or more terminal devices in the small cell  10 C (for example, terminal device  200 C). The dynamic AP  100 C may be, for example, a terminal device equipped with hardware or software that can operate as a base station or a wireless access point. In this case, the small cell  10 C is a dynamically formed localized network/virtual cell. 
     The cell  10 A may be operated according to an a wireless communication scheme such as, for example, LTE, LTE-A (LTE-advanced), LTE-ADVANCED PRO, GSM (registered trademark), UMTS, W-CDMA, CDMA200, WiMAX, WiMAX2 or IEEE802.16. 
     Note that the small cell is a concept that can include various types of cell that is smaller than the macro cell and is placed to overlap with or not overlap with the macro cell (for example, femtocell, nanocell, picocell, microcell, and the like). In one example, the small cell is operated by a dedicated base station. In another example, the small cell is operated by a terminal serving as a master device temporarily operating as a small cell base station. The so-called relay node can also be regarded as a form of the small cell base station. The wireless communication device functioning as a master station of the relay node is also referred to as a donor base station. The donor base station may mean DeNB in LTE, or may more generally mean a master station of a relay node. 
     (2) Terminal Device  200   
     The terminal device  200  can perform communication in a cellular system (or mobile communication system). The terminal device  200  performs wireless communication with a wireless communication device of the cellular system (for example, base station  100 A, master device  100 B or  100 C). For example, the terminal device  200 A receives a downlink signal from the base station  100 A and transmits an uplink signal to the base station  100 A. 
     Furthermore, the terminal device  200  is not limited to only so-called UE. For example, a so-called low cost terminal (low cost UE) such as an MTC terminal, an enhanced MTC (eMTC) terminal, or an NB-IoT terminal may be applied. 
     (3) Supplement 
     The schematic configuration of the system  1  has been described above. However, the present technology is not limited to the example shown in  FIG. 1 . For example, as the configuration of the system  1 , a configuration not including a master device, a small cell enhancement (SCE), a heterogeneous network (HetNet), an MTC network, and the like can be adopted. Furthermore, as another example of the configuration of the system  1 , a master device may be connected to a small cell, and a cell may be constructed under the small cell. 
     One example of the schematic configuration of the system  1  according to one embodiment of the present disclosure has been described above with reference to  FIG. 1 . 
     &lt;1.2. Configuration Example of Terminal Device&gt; 
     Next, one example of the configuration of the terminal device  200  according to the embodiment of the present disclosure will be described with reference to  FIG. 2 .  FIG. 2  is a block diagram showing one example of the configuration of the terminal device  200  according to the embodiment of the present disclosure. As shown in  FIG. 2 , the terminal device  200  includes an antenna part  2001 , a wireless communication unit  2003 , a storage unit  2007 , and a communication control unit  2005 . 
     (1) Antenna Part  2001   
     The antenna part  2001  radiates a signal output by the wireless communication unit  2003  into space as an electromagnetic wave. Furthermore, the antenna part  2001  converts an electromagnetic wave in space into a signal, and outputs the signal to the wireless communication unit  2003 . 
     (2) Wireless Communication Unit  2003   
     The wireless communication unit  2003  transmits and receives signals. For example, the wireless communication unit  2003  receives a downlink signal from the base station and transmits an uplink signal to the base station. 
     (3) Storage Unit  2007   
     The storage unit  2007  temporarily or permanently stores a program and various data for operating the terminal device  200 . 
     (4), Communication Control Unit  2005   
     The communication control unit  2005  controls communication with another device (for example, base station  100 ) by controlling the operation of the wireless communication unit  2003 . As one specific example, the communication control unit  2005  may generate a transmission signal by modulating data to be transmitted on the basis of a predetermined modulation method, and cause the wireless communication unit  2003  to transmit the transmission signal to the base station  100 . Furthermore, as another example, the communication control unit  2005  may acquire a reception result of a signal from the base station  100  (that is, received signal) from the wireless communication unit  2003 , and demodulate the data transmitted from the base station  100  by performing predetermined demodulation processing on the received signal. 
     One example of the configuration of the terminal device  200  according to the embodiment of the present disclosure has been described above with reference to  FIG. 2 . 
     2. OVERVIEW OF COMMUNICATION USING MILLIMETER WAVE 
     In a communication system based on the standard such as LTE/LTE-A and the like, a wireless signal called an ultrashort wave with a frequency from about 700 MHz to 3.5 GHz is used for communication. In contrast, in the fifth generation (5G) mobile communication system following LTE/LTE-A, the use of communication using a wireless signal called a millimeter wave with a frequency such as 28 GHz or 39 GHz (hereinafter, also simply referred to as “millimeter wave”) has been studied. Therefore, after describing the overview of communication using a millimeter wave, a technical problem of the communication device according to one embodiment of the present disclosure will be summarized. 
     In the communication using an ultrashort wave like LTE/LTE-A, by adopting the technology called so-called multiple-input and multiple-output (MIMO), even under a fading environment, the communication performance can be further improved by using a reflected wave in addition to a direct wave for transmitting and receiving signals. 
     In contrast, while a millimeter wave can increase an amount of information transmitted more than an ultrashort wave, a millimeter wave has a tendency to have high straightness and increased propagation loss and reflection loss. Therefore, in an environment where no obstacle exists on a path directly connecting antennas that transmit and receive wireless signals (so-called line of site (LOS)), the direct wave mainly contributes to communication characteristics with almost no influence of the reflected wave. From such characteristics, in the communication using a millimeter wave, for example, a communication terminal such as a smartphone and the like receives a wireless signal (that is, millimeter wave) transmitted directly from a base station (that is, receives a direct wave), thereby making it possible to further improve communication performance. 
     Furthermore, as described above, in the communication using a millimeter wave, the direct wave mainly contributes to communication characteristics, and the influence of the reflected wave is small. From such characteristics, in the communication using a millimeter wave between the communication terminal and the base station, a study has been made into introduction of a technology called polarization MIMO that implements MIMO by using a plurality of polarized waves with polarization directions different from each other (for example, horizontally polarized wave and vertically polarized wave) among wireless signals transmitted as direct waves. 
     3. CONFIGURATION EXAMPLE OF COMMUNICATION DEVICE ASSUMING USE OF MILLIMETER WAVE 
     Subsequently, as a configuration example of a communication device assuming the use of a millimeter wave, one example of a configuration in a case where a so-called patch array antenna in which patch antennas (planar antennas) are arrayed is applied to a communication device such as the terminal device  200  described above will be described. For example,  FIG. 3  is an explanatory diagram for describing one example of the configuration of the communication device assuming the use of a millimeter wave. Note that in the following description, the communication device shown in  FIG. 3  may be referred to as “communication device  211 .” 
     The communication device  211  includes a plate-shaped housing  209  having a front surface and a rear surface having a substantially rectangular shape. Note that in this description, a surface on a side where a display unit such as a display and the like is provided is referred to as a front surface of the housing  209 . That is, in  FIG. 3 , a reference sign  201  indicates the rear surface of an outer surface of the housing  209 . Furthermore, reference signs  203  and  205  each correspond to one end surface located around the rear surface  201  out of the outer surfaces of the housing  209 . More specifically, the reference signs  203  and  205  each indicate an end surface extending in a longitudinal direction of the rear surface  201 . Furthermore, reference signs  202  and  204  each correspond to one end surface located around the rear surface  201  out of the outer surfaces of the housing  209 . More specifically, the reference signs  202  and  204  each indicate an end surface extending in a lateral direction of the rear surface  201 . Note that illustration is omitted in  FIG. 3 , a front surface located on an opposite side of the rear surface  201  is also referred to as “front surface  206 ” for convenience. 
     Furthermore, in  FIG. 3 , each of reference signs  2110   a  to  2110   f  indicates an antenna device for transmitting and receiving a wireless signal (for example, millimeter wave) to and from a base station. Note that in the following description, the antenna devices  2110   a  to  2110   f  may be simply referred to as “antenna device  2110 ” in a case where the antenna devices  2110   a  to  2110   f  are not particularly distinguished. 
     As shown in  FIG. 3 , in the communication device  211 , the antenna device  2110  is held (installed) inside the housing  209  so as to be located near at least a part of each of the rear surface  201  and the end surfaces  202  to  205 . 
     Furthermore, the antenna device  2110  includes a plurality of antenna elements  2111 . More specifically, the antenna device  2110  is configured as an array antenna by arraying the plurality of antenna elements  2111 . For example, the antenna elements  2111   a  are provided to be held so as to be located near the end on the end surface  204  side of the rear surface  201  such that the plurality of antenna elements  2111  is arranged along a direction in which the end extends (that is, longitudinal direction of the end surface  204 ). Furthermore, the antenna elements  2111   d  are provided to be held so as to be located near a part of the end surface  205  such that the plurality of antenna elements  2111  is arranged along a longitudinal direction of the end surface  205 . 
     Furthermore, in the antenna device  2110  held so as to be located near a certain surface, each antenna element  2111  is held such that a normal direction of a flat element substantially agrees with a normal direction of the surface. As more specific one example, in a case where attention is paid to the antenna device  2110   a , the antenna element  2111  provided in the antenna device  2110   a  is held such that the normal direction of the flat element substantially agrees with the normal direction of the rear surface  201 . This is similar for the other antenna devices  2110   b  to  2110   f.    
     With the above-described configuration, each antenna device  2110  controls the phase and power of a wireless signal transmitted or received by each of the plurality of antenna elements  2111 , thereby making it possible to control directivity of the wireless signal (that is, perform beam forming). 
     Subsequently, with reference to  FIG. 4 , one example of the schematic configuration of the antenna device applied to the communication device  211  assuming the use of a millimeter wave will be described.  FIG. 4  is an explanatory diagram for describing one example of the schematic configuration of the antenna device applied to the communication device  211  assuming the use of a millimeter wave. 
     The antenna device  2140  shown in  FIG. 4  has a configuration in which two antenna devices  2130  different from each other are connected by a connection part  2141 . Note that in the example shown in  FIG. 4 , the antenna devices  2130   a  and  2130   f  correspond to, for example, the antenna devices  2110   a  and  2110   f  in the example shown in  FIG. 3 , respectively. That is, the antenna elements shown by a reference sign  2131  in  FIG. 4  correspond to the antenna elements  2111  shown in  FIG. 3 . Note that in the example shown in  FIG. 4 , for convenience, a direction in which the plurality of antenna elements  2131  is arranged may be referred to as an x direction, and a thickness direction of the antenna device  2140  may be referred to as a z direction. Furthermore, a direction orthogonal to both the x direction and the z direction may be referred to as a y direction. 
     As shown in  FIG. 4 , the antenna devices  2130   a  and  2130   f  are placed such that, out of ends of the antenna devices  2130   a  and  2130   f , one of the ends extending in the direction in which the plurality of antenna elements  2131  is arranged is located near each other. At this time, the antenna element  2131  of the antenna device  2130   a  and the antenna element  2131  of the antenna device  2130   f  are placed such that the normal directions of the flat elements intersect each other (for example, orthogonal), or the normal directions are at positions twisted around each other. Furthermore, the connection part  2141  is provided to be constructed between ends of the antenna device  2130   a  and the antenna device  2130   f  located near each other. The antenna device  2130   a  and the antenna device  2130   f  are connected by the connection part  2141 . 
     The antenna device  2140  having the above-described configuration is preferably held along a plurality of surfaces (outer surfaces) connected to each other out of the outer surfaces of the housing  209 , for example, like the rear surface  201  and the end surface  204  shown in  FIG. 3 . With such a configuration, a wireless signal arriving from a direction substantially perpendicular to each of the plurality of surfaces connected to each other can be transmitted or received in a more preferred mode. 
     One example of the schematic configuration of the antenna device applied to the communication device  211  assuming the use of a millimeter wave has been described above with reference to  FIG. 4 . 
     4. TECHNICAL PROBLEM 
     Subsequently, with reference to  FIG. 5 , the technical problem of the antenna device applied to the communication device  211  assuming the use of a millimeter wave will be described.  FIG. 5  is an explanatory diagram for describing the technical problem of the antenna device applied to the communication device  211  assuming the use of a millimeter wave. An antenna device  3010  shown in  FIG. 5  corresponds to one example of the configuration of the antenna device  2110  in the communication device  211  described with reference to  FIG. 3 . That is, the example shown in  FIG. 5  shows one example of the configuration of the patch array antenna in which patch antennas are arrayed. 
     As shown in  FIG. 5 , the antenna device  3010  includes antenna elements  3011   a  to  3011   d  and a dielectric substrate  3018 . In the antenna device  3010  shown in  FIG. 5 , each of the antenna elements  3011   a  to  3011   d  is configured as a patch antenna (planar antenna). Note that in the example shown in  FIG. 5 , for convenience, the normal direction of the flat element constituting each of the plurality of antenna elements  3011   a  to  3011   d  is defined as a z direction. Furthermore, the direction in which the plurality of antenna elements  3011   a  to  3011   d  is arranged may be referred to as an x direction, in particular, the right direction of the drawing may be referred to as “+x direction”, and the left direction of the drawing may be referred to as “−x direction.” 
     Furthermore, a direction orthogonal to both the x direction and the z direction is defined as a y direction. That is, in the example shown in  FIG. 5 , the antenna elements  3011   a  to  3011   d  are disposed on a surface of the dielectric substrate  3018  so as to be spaced apart from each other in this order along the x direction. Furthermore, in the following, the antenna elements  3011   a  to  3011   d  may be referred to as “antenna element  3011 ” unless particularly distinguished. Furthermore, in the following description, like the antenna elements  3011   a  to  3011   d , the direction in which a plurality of antenna elements constituting an array antenna is arranged may be simply referred to as “arrangement direction.” For example, in the example shown in  FIG. 5 , the arrangement direction of the plurality of antenna elements  3011  is the x direction. 
     As shown in  FIG. 5 , in the antenna device in which a plurality of antenna elements constitutes a so-called array antenna, a distortion may occur in a radiation pattern of some antenna elements. As one specific example, in the example shown in  FIG. 5 , in each of the antenna elements  3011   a  to  3011   d  arranged along the x direction, a distortion of the radiation pattern may occur in the arrangement direction (x direction) because a current is pulled by another antenna element  3011  disposed adjacent to each other (that is, another antenna element  3011  located nearby). 
     As one more specific example, the antenna element  3011   b  is disposed so as to be mutually adjacent to the other antenna elements  3011   a  and  3011   c  in both the arrangement directions. Therefore, a distortion of the radiation pattern occurs in both the arrangement directions (that is, +x direction and −x direction). Note that in this case, symmetry of the arrangement direction of the radiation pattern of the antenna element  3011   b  is maintained. This is similar for the antenna element  3011   c.    
     Meanwhile, for the antenna elements  3011   a  and  3011   d  located at the ends in the arrangement direction (x direction), the other antenna elements  3011  are disposed only in one of the arrangement directions. Therefore, for example, in the antenna element  3011   a , since a current is pulled by the antenna element  3011   b  disposed adjacent to each other, a distortion of the radiation pattern may occur in the direction in which the antenna element  3011   b  is located, and symmetry of the radiation pattern along the arrangement direction may be impaired. Similarly, in the antenna element  3011   d , because of an influence of the antenna element  3011   c  disposed adjacent to each other, a distortion of the radiation pattern may occur in the direction in which the antenna element  3011   c  is located, and symmetry of the radiation pattern along the arrangement direction may be impaired. 
     As described above, for the antenna element  3011  located on the end side in the arrangement direction, as a method for securing symmetry of the radiation pattern in the arrangement direction, for example, as shown in  FIG. 5 , a method for providing a sufficiently large ground area around the antenna element  3011  can be cited. As one specific example, for the antenna element  3011   a , on the −x direction side where no other antenna element  3011  is disposed in the arrangement direction, a ground area having a length equal to or longer than a wavelength λ of the wireless signal transmitted or received by the antenna element  3011   a  is provided. That is, in this case, for example, the dielectric substrate  3018  is further extended from the position where the antenna element  3011   a  is disposed in the −x direction by the length of the wavelength λ or more. Similarly, for the antenna element  3011   d , on the +x direction side where no other antenna element  3011  is disposed in the arrangement direction, a ground area having a length equal to or longer than the wavelength λ of the wireless signal transmitted or received by the antenna element  3011   d  is provided. That is, in this case, for example, the dielectric substrate  3018  is further extended from the position where the antenna element  3011   d  is disposed in the +x direction by the length of the wavelength λ or more. 
     However, in a case where the ground area as shown in  FIG. 5  is provided to secure symmetry of the radiation pattern of the antenna element  3011  located on the end side in the arrangement direction (for example, antenna elements  3011   a  and  3011   d ), the size of the antenna device (particularly, the size in the arrangement direction described above) becomes larger due to characteristics thereof. 
     In light of such a situation, the present disclosure proposes a technology that enables miniaturization of the antenna device to be achieved in a more preferred mode in a case where the plurality of antenna elements is arrayed. Specifically, the present disclosure proposes a technology that enables both securing symmetry of the radiation pattern of each antenna element (particularly, antenna element located on the end side in the arrangement direction) and miniaturizing the antenna device in a more preferred mode in a case where the plurality of antenna elements is arrayed. 
     5. TECHNICAL ADVANTAGE 
     The following describes technical features of the antenna device according to one embodiment of the present disclosure. 
     &lt;5.1. Configuration&gt; 
     To begin with, one example of the configuration of the antenna device according to one embodiment of the present disclosure will be described. For example,  FIG. 6  is an explanatory diagram for describing one example of the schematic configuration of the antenna device according to the present embodiment, and shows one example of the configuration of the patch array antenna in which patch antennas are arrayed. Note that in the following description, the antenna device shown in  FIG. 6  may be referred to as “antenna device  3110 ” in order to distinguish the antenna device from other antenna devices. 
     As shown in  FIG. 6 , in the antenna device  3110 , antenna elements  3111   a  to  3111   d  are disposed to be spaced apart from each other in this order along a predetermined direction on one surface of a dielectric substrate  3118 . Each of the antenna elements  3111   a  to  3111   d  includes a flat element  3112  and a feeding point  3113 . Note that in the following description, the antenna elements  3111   a  to  3111   d  may be referred to as “antenna element  3111 ” unless particularly distinguished. Furthermore, in the following description, the normal direction of the flat element  3112  constituting the antenna element  3111  is a z direction, in particular, the front surface (upper surface) side of the element  3112  may be referred to as “+z direction”, and the rear surface (lower surface) side may be referred to as “−z direction.” Furthermore, the arrangement direction of the antenna elements  3111   a  to  3111   d  is referred to as a −x direction, in particular the antenna element  3111   a  side is referred to as “−x direction”, and the antenna element  3111   d  side is referred to as “+x direction.” 
     Furthermore, a direction orthogonal to both the x direction and the z direction is defined as a y direction. 
     On the other surface of the dielectric substrate  3118  (that is, surface on the −z direction side), a substantially flat ground plate  3119  is provided so as to cover substantially the entire surface. The feeding point  3113  of each of the antenna elements  3111   a  to  3111   d  is provided to penetrate the dielectric substrate  3118  along the normal direction (z direction) of the corresponding element  3112  and electrically connects the element  3112  to the ground plate  3119  described above. 
     Furthermore, on one surface of the dielectric substrate  3118  (that is, surface on the +z direction side), out of the antenna elements  3111   a  to  3111   d  arranged in the x direction, a parasitic element  3115  is disposed so as to be mutually adjacent in the arrangement direction to the antenna element  3111  located on the end side in the arrangement direction (that is, x direction). More specifically, the parasitic element  3115   a  is disposed so as to be mutually spaced apart from the antenna element  3111   a  in the arrangement direction described above (x direction) on the opposite side of the antenna element  3111   b  (that is, −x direction) with respect to the antenna element  3111   a . Similarly, the parasitic element  3115   b  is disposed so as to be mutually spaced apart from the antenna element  3111   d  in the arrangement direction described above (x direction) on the opposite side of the antenna element  3111   c  (that is, +x direction) with respect to the antenna element  3111   d.    
     The parasitic element  3115  includes a flat element  3116 . The element  3116  may be formed so as to have substantially the same shape as the element  3112  of the antenna element  3111 . Furthermore, the element  3116  may be formed to have substantially the same size as the element  3112 . Meanwhile, the parasitic element  3115  is different from the antenna element  3111  in that the parasitic element  3115  does not have a feeding point for transmitting or receiving a wireless signal via the element  3116 . 
     Furthermore, the element  3116  of the parasitic element  3115  may be used as a pad for another sensor to detect various states. Therefore, various circuits for causing the element  3116  to function as the pad for the sensor described above may be electrically connected to the element  3116  of the parasitic element  3115 . Note that examples of the sensor described above include a proximity sensor for detecting proximity of an object (for example, capacitive sensor), and the like. 
     Subsequently, with reference to  FIG. 7 , out of the antenna device  3110  according to the present embodiment, a more detailed configuration of a portion in which the plurality of antenna elements  3111  constitutes the array antenna will be described with attention particularly paid to the size of each part.  FIG. 7  is an explanatory diagram for describing one example of the configuration of the antenna device  3110  according to the present embodiment, and shows one example of the schematic configuration of the antenna device  3110  in a case where the antenna device  3110  is viewed from vertically above (+z direction). Note that the x direction, y direction, and z direction in  FIG. 7  correspond to the x direction, y direction, and z direction in  FIG. 6 , respectively. 
     In  FIG. 7 , a reference sign d 1  indicates a width of each of the plurality of antenna elements  3111  in the arrangement direction (x direction) (that is, size of the antenna element  3111 ). Here, when a relative permittivity of a resin frame constituting the antenna device  3110  (that is, dielectric substrate  3118 ) is εr and a wavelength of a wireless signal transmitted or received by the antenna device  3110  is λ, a width calculated on the basis of a relational expression shown below as (Equation 1) is a guideline for the width d 1 . 
     
       
         
           
             
               [ 
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 1 
               
               ] 
             
             ⁢ 
             
                 
             
           
         
       
       
         
           
             
               
                 
                   
                     d 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   = 
                   
                     λ 
                     
                       2 
                       ⁢ 
                       
                         
                           ɛ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           r 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     EQUATION 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
     Since the relative permittivity of the resin generally used for the resin frame described above is about 4, in a case where the relative permittivity εr=4, the width d 1  is calculated on the basis of the relational expression shown below as (Equation 2). 
     
       
         
           
             
               [ 
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 2 
               
               ] 
             
             ⁢ 
             
                 
             
           
         
       
       
         
           
             
               
                 
                   
                     d 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   = 
                   
                     λ 
                     4 
                   
                 
               
               
                 
                   ( 
                   
                     EQUATION 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
     Of course, it is also possible to use a resin having a higher dielectric constant as the resin used for the resin frame described above. In this case, as shown in (Equation 1) described above, the width d 1  can be made shorter, that is, an element having a smaller size can be applied as the antenna element  3111 . Note that the width d 1  of the antenna elements  3111  in the arrangement direction corresponds to one example of a “second width.” 
     Furthermore, a reference sign d 2  indicates an element interval between two antenna elements  3111  adjacent to each other among the plurality of antenna elements  3111  constituting the array antenna. Note that in the present disclosure, the “element interval” indicates an interval between centers of the two antenna elements  3111  adjacent to each other. 
     From the viewpoint of further reducing a distortion of the radiation pattern, as the element interval d 2 , the two antenna elements  3111  adjacent to each other are preferably disposed so as to be spaced apart as far as possible. 
     Meanwhile, when d 2 ≥λ, an operation as an array antenna may cause unwanted emission called grating lobes and lower the gain in a predetermined direction. In contrast, in the range of λ/2&lt;d 2 &lt;λ, the element interval d 2  at which the grating lobes occur depends on the required beam scanning angle. 
     In view of the above conditions, each antenna element  3111  is preferably disposed such that the element interval d 2  satisfies the condition shown below as (Equation 3). 
     
       
         
           
             
               [ 
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 3 
               
               ] 
             
             ⁢ 
             
                 
             
           
         
       
       
         
           
             
               
                 
                   
                     λ 
                     2 
                   
                   ≤ 
                   d 
                   &lt; 
                   λ 
                 
               
               
                 
                   ( 
                   
                     EQUATION 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
     Therefore, as the element interval d 2 , for example, an interval calculated on the basis of a relational expression shown below as (Expression 4) may be used as a guideline. Note that the element interval d 2  between the two antenna elements  3111  adjacent to each other in the arrangement direction corresponds to one example of a “second element interval.” 
     
       
         
           
             
               [ 
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 4 
               
               ] 
             
             ⁢ 
             
                 
             
           
         
       
       
         
           
             
               
                 
                   
                     d 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   = 
                   
                     λ 
                     2 
                   
                 
               
               
                 
                   ( 
                   
                     EQUATION 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ) 
                 
               
             
           
         
       
     
     Subsequently, with reference to  FIG. 8 , after describing in detail the size and installation position of the parasitic elements  3115 , the features of the antenna device  3110  according to the present embodiment will be described with attention paid to the size of the antenna device  3110 .  FIG. 8  is an explanatory diagram for describing one example of the configuration of the antenna device  3110  according to the present embodiment, and shows one example of the schematic configuration of the antenna device  3110  in a case where the antenna device  3110  is viewed from vertically above (+z direction). Note that the x direction, y direction, and z direction in  FIG. 8  correspond to the x direction, y direction, and z direction in  FIG. 6 , respectively. 
     For example, the parasitic element  3115  may be formed to be substantially identical to the antenna element  3111  in size. That is, in a case where the width of the parasitic element  3115  in the x direction (that is, width of each of the plurality of antenna elements  3111  in the arrangement direction) is d 3 , the parasitic element  3115  is preferably formed such that the width d 3  is substantially equal to the width d 2  indicated by (Formula 1) or (Formula 2) described above. Furthermore, the parasitic element  3115  is preferably formed so as to have substantially the same shape as the antenna element  3111 . Note that the width d 3  of the parasitic element  3115  in the arrangement direction described above corresponds to one example of the “first width.” 
     Furthermore, d 4  is the element interval between the parasitic element  3115  and the antenna element  3111  mutually adjacent to the parasitic element  3115  (that is, antenna element  3111  located on the end side in the arrangement direction). The parasitic element  3115  is preferably disposed such that the element interval d 4  is equal to or less than the wavelength λ of the wireless signal transmitted or received by the antenna element  3111  described above. In other words, in view of (Equation 4) described above, the parasitic element  3115  is preferably disposed such that the element interval d 4  is equal to or less than twice the element interval d 2  (d 4 ≤2×d 2 ). Note that the element interval d 4  between the parasitic element  3115  and the antenna element  3111  mutually adjacent to the parasitic element  3115  corresponds to one example of the “first element interval.” 
     For example, the example shown in  FIG. 8  shows one example of the configuration of the antenna device  3110  in a case where the width d 3 =d 1 =λ/4 and the element interval d 4 =d 2 =λ/2. Note that in the example shown in  FIG. 8 , with respect to the antenna element  3111  that is mutually adjacent (that is, antenna element  3111  located at the end in the arrangement direction), the parasitic element  3115  is disposed at a position symmetrical to another antenna element  3111  mutually adjacent to the antenna element  3111 . More specifically, the parasitic element  3115   a  is disposed at a position symmetrical to the antenna element  3111   b  with respect to the antenna element  3111   a . Similarly, the parasitic element  3115   b  is disposed at a position symmetrical to the antenna element  3111   c  with respect to the antenna element  3111   d . Note that the antenna element  3111  located at the end in the arrangement direction (for example, antenna elements  3111   a  and  3111   d  shown in  FIG. 8 ) corresponds to one example of the “first antenna element.” Furthermore, another antenna element  3111  mutually adjacent to the first antenna element (for example, antenna elements  3111   b  and  3111   c  shown in  FIG. 8 ) corresponds to one example of the “second antenna element.” 
     Furthermore, the example shown in  FIG. 8  also shows the antenna device  3010  described with reference to  FIG. 5  as a comparison target. As shown in  FIG. 8 , since the parasitic elements  3115  (that is, parasitic elements  3115   a  and  3115   b ) are provided, the antenna device  3110  according to the present embodiment does not need to extend the dielectric substrate  3118  from the parasitic elements  3115  toward the outside of the plurality of antenna elements  3111  in the arrangement direction (x direction). Therefore, it is possible to miniaturize the size of the antenna device  3110  in the arrangement direction described above more than the antenna device  3010 . 
     Note that in the antenna device  3110  described with reference to  FIGS. 6 and 8 , the parasitic element  3115  (that is, parasitic elements  3115   a  and  3115   b ) is provided so as to be mutually adjacent, in the arrangement direction, to each of the antenna elements  3111   a  and  3111   d  located on the end side in the arrangement direction. Meanwhile, the parasitic element  3115  may be provided so as to be mutually adjacent, in the arrangement direction of the antenna element  3111 , to only either antenna element  3111  out of the antenna elements  3111   a  and  3111   d  located on the end side in the arrangement direction. 
     For example,  FIGS. 9 and 10  are each an explanatory diagram for describing another example of the configuration of the antenna device according to the present embodiment. Specifically,  FIG. 9  shows one example of the configuration in a case where the parasitic element  3115   a  is provided so as to be mutually adjacent, out of the antenna elements  3111   a  and  3111   d  described above, to only the antenna element  3111   a  in the arrangement direction. Furthermore,  FIG. 10  shows one example of the configuration in a case where the parasitic element  3115   b  is provided so as to be mutually adjacent, out of the antenna elements  3111   a  and  3111   d  described above, to only the antenna element  3111   d  in the arrangement direction. Note that in the following description, the antenna device shown in  FIG. 9  may be referred to as “antenna device  3130 ” in order to distinguish the antenna device from other antenna devices. Furthermore, the antenna device shown in  FIG. 10  may be referred to as “antenna device  3150 ” in order to distinguish the antenna device from other antenna devices. Furthermore, the antenna device shown in each of  FIGS. 6, 9, and 10  may be simply referred to as “antenna device  3110 ” unless particularly distinguished. That is, in the following description, simple description of “antenna device  3110 ” can include the antenna devices  3130  and  3150  as long as there is no inhibiting factor caused by a difference in a method for disposing the parasitic element  3115 . 
     One example of the configuration of the antenna device according to one embodiment of the present disclosure has been described above with reference to  FIGS. 6 to 10 . 
     &lt;5.2. Characteristics of Antenna Device&gt; 
     Subsequently, a simulation result of characteristics of the antenna device according to the present embodiment will be described. 
     (Simulation Result of Radiation Pattern) 
     To begin with, as the characteristics of the antenna device according to the present embodiment, one example of the simulation result of the radiation pattern of each antenna element constituting the antenna device will be described. Note that in order to make the characteristics of the antenna device  3110  according to the present embodiment easier to understand, to begin with, as a comparative example, one example of the radiation pattern of the antenna element in a case where the configuration corresponding to the parasitic element  3115  in the antenna device  3110  is not provided will be described. For example,  FIG. 11  is a diagram showing one example of the schematic configuration of the antenna device according to the comparative example, and shows one example of the schematic configuration of the antenna device in a case where the antenna device is viewed from vertically above (+z direction). Note that the x direction, y direction, and z direction in  FIG. 11  correspond to the x direction, y direction, and z direction in  FIG. 6 , respectively. Furthermore, in the following description, the antenna device shown in  FIG. 11  is also referred to as “antenna device  3910 ” for convenience. 
     As shown in  FIG. 11 , in the antenna device  3910  according to the comparative example, in a similar manner to the antenna device  3110  according to the present embodiment described above, a plurality of antenna elements  3111  is disposed to be spaced apart from each other along the x direction, and the plurality of antenna elements  3111  constitutes an array antenna. Meanwhile, in the antenna device  3910 , a configuration corresponding to the parasitic element  3115  is not disposed as in the antenna device  3110 , and does not have a configuration to extend the dielectric substrate in the arrangement direction (x direction) as in the antenna device  3010  described above with reference to  FIG. 5 . Under such a configuration, a simulation of the radiation pattern has been performed, out of the plurality of antenna elements  3111 , on each of the antenna element  3111   a  located on the end side in the −x direction and the antenna element  3111   b  mutually adjacent to the antenna element  3111   a  in the +x direction. 
     For example,  FIGS. 12 and 13  are each a diagram showing one example of a simulation result of the radiation pattern of the antenna element in the antenna device  3910  according to the comparative example. 
     Specifically,  FIG. 12  shows one example of the radiation pattern of the antenna element  3111   a  in a case where the radiation pattern is cut along the I-I′ plane (xz plane) of  FIG. 11 .  FIG. 12  shows that a distortion occurs in the radiation pattern of the antenna element  3111   a  on the +x direction side. It is presumed that the distortion is caused by the influence of the antenna element  3111   b  mutually adjacent to the antenna element  3111   a . In contrast, no distortion occurs in the radiation pattern of the antenna element  3111   a  on the −x direction side. That is, as shown in  FIG. 12 , in the antenna device  3910  according to the comparative example, the shape of the radiation pattern of the antenna element  3111   a  is asymmetric in the x direction. 
     Furthermore,  FIG. 13  shows one example of the radiation pattern of the antenna element  3111   b  in a case where the radiation pattern is cut along the I-I′ plane (xz plane) of  FIG. 11 . Other antenna elements  3111  are disposed mutually adjacent to the antenna element  3111   b  in both the +x direction and the −x direction. Therefore, as shown in  FIG. 13 , a distortion occurs in the radiation pattern of the antenna element  3111   b  in both the +x direction and the −x direction. With this arrangement, as a result, the shape of the radiation pattern of the antenna element  3111   b  is targeted in the x direction. 
     Subsequently, the characteristics of the antenna device  3110  according to the present embodiment will be described. For example,  FIG. 14  is a diagram showing one example of the schematic configuration of the antenna device  3110  according to the present embodiment, and shows one example of the schematic configuration of the antenna device  3110  in a case where the antenna device  3110  is viewed from vertically above (+z direction). Note that the x direction, y direction, and z direction in  FIG. 14  correspond to the x direction, y direction, and z direction in  FIG. 6 , respectively. Under such a configuration, a simulation of the radiation pattern has been performed, out of the plurality of antenna elements  3111 , on each of the antenna element  3111   a  located on the end side in the −x direction (that is, antenna element  3111  mutually adjacent to the parasitic element  3115   a ) and the antenna element  3111   b  mutually adjacent to the antenna element  3111   a  in the +x direction. 
     For example,  FIGS. 15 and 16  are each a diagram showing one example of the simulation result of the radiation pattern of the antenna element in the antenna device  3110  according to the present embodiment. 
     Specifically,  FIG. 15  shows one example of the radiation pattern of the antenna element  3111   a  in a case where the radiation pattern is cut along the II-II′ plane (xz plane) of  FIG. 14 . As can be seen by comparing  FIG. 15  with  FIG. 12 , in the antenna device  3110  according to the present embodiment, the distortion on the +x direction side generated in the radiation pattern of the antenna element  3111   a  is smaller than in the antenna device  3910  according to the comparative example. That is, with the antenna device  3110  according to the present embodiment, it can be seen that symmetry of the shape of the radiation pattern of the antenna element  3111   a  in the x direction has become better than in the antenna device  3910  according to the comparative example. 
     Furthermore,  FIG. 16  shows one example of the radiation pattern of the antenna element  3111   b  in a case where the radiation pattern is cut along the II-II′ plane (xz plane) of  FIG. 14 . In the simulation result of the radiation pattern shown in  FIG. 16 , in a similar manner to the simulation result shown in  FIG. 13 , a distortion occurs in both the +x direction and the −x direction, and as a result, the shape of the radiation pattern of the antenna element  3111   b  is targeted in the x direction. 
     (Simulation Result of Reflection Characteristics) 
     Subsequently, as the characteristics of the antenna device according to the present embodiment, about one example of the simulation result of reflection characteristics of the antenna device, in particular, each of the antenna device  3910  according to the comparative example (see  FIG. 11 ) and the antenna device  3110  according to the present embodiment (see  FIG. 14 ) will be described. 
     For example,  FIG. 17  is a diagram showing one example of the simulation result of the reflection characteristics of the antenna device  3910  according to the comparative example. In  FIG. 17 , the horizontal axis indicates frequency (GHz), and the vertical axis indicates gain (dB). Furthermore, the example shown in  FIG. 17  shows the simulation result of each of S parameters S 11  and S 22  for the antenna elements  3111   a  and  3111   b  of the antenna device  3910  shown in  FIG. 11 . 
     Furthermore,  FIG. 18  is a diagram showing one example of the simulation result of the reflection characteristics of the antenna device  3110  according to the present embodiment. The horizontal axis and the vertical axis in  FIG. 18  are similar to the example shown in  FIG. 17 . Furthermore, the example shown in  FIG. 18  shows the simulation result of each of S parameters S 11  and S 22  for the antenna elements  3111   a  and  3111   b  of the antenna device  3110  shown in  FIG. 14 . 
     As can be seen by comparing  FIG. 17  with  FIG. 18 , there is no change in the reflection characteristics between the antenna device  3110  according to the present embodiment and the antenna device  3910  according to the comparative example. This indicates that even if the parasitic element  3115  is provided as in the antenna device  3110  according to the present embodiment, the reflection characteristics of the antenna device are not affected. 
     The simulation result of the characteristics of the antenna device according to the present embodiment has been described above with reference to  FIGS. 11 to 18 . 
     &lt;5.3. Modifications&gt; 
     Subsequently, modifications of the antenna device according to the present embodiment will be described. 
     (First Modification) 
     To begin with, as a first modification, one example in a case where one antenna device is configured by connecting two antenna devices in an L-shape will be described. For example,  FIG. 19  is an explanatory diagram for describing one example of the configuration of the antenna device according to the first modification, and is a schematic perspective view of the antenna device. Note that in the following description, the antenna device shown in  FIG. 19  may be referred to as “antenna device  3210 ” in order to distinguish the antenna device from other antenna devices. 
     As shown in  FIG. 19 , an antenna device  3250  includes antenna parts  3110   a  and  3110   b , and a connection part  3212 . Each of the antenna parts  3110   a  and  3110   b  corresponds to the antenna device  3110  described with reference to  FIGS. 6 and 8 . Therefore, detailed description of the configuration of each of the antenna parts  3110   a  and  3110   b  will be omitted. Note that in the antenna device  3210  shown in  FIG. 19 , one of the antenna parts  3110   a  and  3110   b  corresponds to one example of “first antenna part”, and the other corresponds to one example of “second antenna part.” That is, the dielectric substrate  3118  of the first antenna part corresponds to one example of “first substrate”, and the dielectric substrate  3118  of the second antenna part corresponds to one example of “second substrate.” 
     As shown in  FIG. 19 , the antenna parts  3110   a  and  3110   b  are placed such that, out of ends of the antenna parts  3110   a  and  3110   b , one of the ends extending in the arrangement direction of the plurality of antenna elements  3111  is located near each other. At this time, the antenna element  3111  of the antenna part  3110   a  and the antenna element  3111  of the antenna part  3110   b  are placed such that the normal directions of the flat elements intersect each other (for example, orthogonal), or the normal directions are at positions twisted around each other. Furthermore, the connection part  3212  is provided to be constructed between ends of the antenna part  3110   a  and the antenna part  3110   b  located near each other. The antenna part  3110   a  and the antenna part  3110   b  are connected by the connection part  3212 . That is, the antenna part  3110   a  and the antenna part  3110   b  are held by the connection part  3212  such that the antenna part  3110   a  and the antenna part  3110   b  form a substantial L-shape. 
     With such a configuration, in the antenna device  3210 , the plurality of antenna elements  3111  constituting the array antenna is disposed in the area indicated by a reference sign R 11 , and the parasitic element  3115  is disposed in the area indicated by reference signs R 13  and R 15 . 
     The antenna device  3210  having the above-described configuration is preferably held along a plurality of surfaces (outer surfaces) of the outer surface of the housing  209  of the communication device  211  that are connected to each other, for example, like the rear surface  201  and the end surface  204  of the communication device  211  shown in  FIG. 3 . With such a configuration, a wireless signal arriving from a direction substantially perpendicular to each of the plurality of surfaces connected to each other can be transmitted or received in a more preferred mode. 
     Note that as a configuration corresponding to the antenna parts  3110   a  and  3110   b  constituting the L-shaped antenna device  3210 , it is also possible to apply the antenna device  3130  described with reference to  FIG. 9  and the antenna device  3150  described with reference to  FIG. 10 . 
     For example,  FIG. 20  is an explanatory diagram for describing another example of the configuration of the antenna device according to the first modification. Note that in the following description, the antenna device shown in  FIG. 20  may be referred to as “antenna device  3230 ” in order to distinguish the antenna device from other antenna devices. 
     The antenna device  3230  shown in  FIG. 20  has a configuration corresponding to the antenna parts  3110   a  and  3110   b  in the antenna device  3210  shown in  FIG. 19 , and corresponds to one example in a case where the antenna device  3130  shown in  FIG. 9  is applied. That is, the antenna parts  3130   a  and  3130   b  shown in  FIG. 20  correspond to the antenna device  3130  shown in  FIG. 9 . Furthermore, on the basis of an idea similar to the antenna device  3210  shown in  FIG. 19 , connection of the antenna parts  3130   a  and  3130   b  by the connection part  3232  constitutes the L-shaped antenna device  3230 . 
     With such a configuration, in the antenna device  3230 , the plurality of antenna elements  3111  constituting the array antenna is disposed in the area indicated by the reference sign R 11 , and the parasitic element  3115  is disposed in the area indicated by the reference sign R 13 . 
     Furthermore, in the antenna device  3230  shown in  FIG. 20 , one of the antenna parts  3130   a  and  3130   b  corresponds to one example of “first antenna part”, and the other corresponds to one example of “second antenna part.” That is, the dielectric substrate  3118  of the first antenna part corresponds to one example of “first substrate”, and the dielectric substrate  3118  of the second antenna part corresponds to one example of “second substrate.” 
     For example,  FIG. 21  is an explanatory diagram for describing another example of the configuration of the antenna device according to the first modification. Note that in the following description, the antenna device shown in  FIG. 21  may be referred to as “antenna device  3250 ” in order to distinguish the antenna device from other antenna devices. 
     The antenna device  3250  shown in  FIG. 21  has a configuration corresponding to the antenna parts  3110   a  and  3110   b  in the antenna device  3210  shown in  FIG. 19 , and corresponds to one example in a case where the antenna device  3150  shown in  FIG. 10  is applied. That is, the antenna parts  3150   a  and  3150   b  shown in  FIG. 21  correspond to the antenna device  3530  shown in  FIG. 10 . Furthermore, on the basis of an idea similar to the antenna device  3210  shown in  FIG. 19 , connection of the antenna parts  3150   a  and  3150   b  by the connection part  3252  constitutes the L-shaped antenna device  3250 . 
     With such a configuration, in the antenna device  3250 , the plurality of antenna elements  3111  constituting the array antenna is disposed in the area indicated by the reference sign R 11 , and the parasitic element  3115  is disposed in the area indicated by the reference sign R 15 . 
     Furthermore, in the antenna device  3250  shown in  FIG. 21 , one of the antenna parts  3150   a  and  3150   b  corresponds to one example of “first antenna part”, and the other corresponds to one example of “second antenna part.” That is, the dielectric substrate  3118  of the first antenna part corresponds to one example of “first substrate”, and the dielectric substrate  3118  of the second antenna part corresponds to one example of “second substrate.” 
     As the first modification, with reference to  FIGS. 19 to 21 , one example in a case where one antenna device is configured by connecting two antenna devices in an L-shape has been described above. 
     (Second Modification) 
     Subsequently, as a second modification, one example of the configuration of the antenna device according to the present embodiment will be described with attention particularly paid to the configuration of the array antenna. 
     The above-described embodiment has described a case of configuring a so-called one-dimensional array in which the plurality of antenna elements  3111  is disposed to be spaced apart from each other along the predetermined direction. Meanwhile, the arrangement of the plurality of antenna elements  3111  is not necessarily limited to only the arrangement in a case where the so-called one-dimensional array is configured as in the embodiment described above. 
     For example,  FIGS. 22 to 24  are each an explanatory diagram for describing one example of the configuration of the antenna device according to the second modification, and show one example in a case where an array antenna (so-called two-dimensional array) is configured by arranging the plurality of antenna elements  3111  two-dimensionally. Note that in  FIGS. 22 to 24 , a part indicated as “feeding element” corresponds to the antenna element  3111  in the antenna device  3110  (that is, antenna element having a feeding point) according to the present embodiment. Furthermore, a part indicated as “parasitic element” corresponds to the parasitic element  3115  in the antenna device  3110  according to the present embodiment. Furthermore, in  FIGS. 22 to 24 , for convenience, the normal direction of the flat element constituting the feeding element (that is, configuration corresponding to the element  3112  of the antenna element  3111 ) is defined as a z direction, and directions that are orthogonal to each other and horizontal to a plane of the element are defined as an x direction and a y direction. That is, in the examples shown in  FIGS. 22 to 24 , a plurality of feeding elements is disposed so as to be spaced apart from each other along each of the x direction and the y direction. 
     To begin with, the example shown in  FIG. 22  will be described. In the example shown in  FIG. 22 , among the feeding elements arranged two-dimensionally on an xy plane, parasitic elements are disposed so as to be mutually adjacent, in the x direction, to the feeding elements located on the end sides in the x direction. That is, in the example shown in  FIG. 22 , each of parts indicated by reference signs R 21  and R 22  has a configuration similar to the configuration of the antenna device  3110  described with reference to  FIGS. 6 and 8 . With such a configuration, in the example shown in  FIG. 22 , in each of the parts indicated by the reference signs R 21  and R 22 , in a similar manner to the antenna device  3110 , it is possible to expect effects of improving symmetry of the shape of the radiation pattern of the feeding elements (in this case, symmetry of the shape in the x direction). 
     Then, the example shown in  FIG. 23  will be described. In the example shown in  FIG. 23 , among the feeding elements arranged two-dimensionally on an xy plane, parasitic elements are disposed so as to be mutually adjacent, in the y direction, to the feeding elements located on the end sides in the y direction. That is, in the example shown in  FIG. 23 , each of parts indicated by reference signs R 23  and R 24  has a configuration similar to the configuration of the antenna device  3110  described with reference to  FIGS. 6 and 8 . With such a configuration, in the example shown in  FIG. 23 , in each of the parts indicated by the reference signs R 23  and R 24 , in a similar manner to the antenna device  3110 , it is possible to expect effects of improving symmetry of the shape of the radiation pattern of the feeding elements (in this case, symmetry of the shape in the y direction). 
     Then, the example shown in  FIG. 24  will be described. In the example shown in  FIG. 24 , among the feeding elements arranged two-dimensionally on an xy plane, in each of the x direction and the y direction, parasitic elements are disposed so as to be mutually adjacent to the feeding elements located on the end sides in the direction. That is, in the example shown in  FIG. 24 , each of parts indicated by reference signs R 25  and R 26  has a configuration similar to the configuration of the antenna device  3110  described with reference to  FIGS. 6 and 8 . With such a configuration, in the example shown in  FIG. 24 , in each of the parts indicated by the reference signs R 25  and R 26 , in a similar manner to the antenna device  3110 , it is possible to expect effects of improving symmetry of the shape of the radiation pattern of the feeding elements (in this case, symmetry of the shape in the x direction). Similarly, in the example shown in  FIG. 24 , each of parts indicated by reference signs R 27  and R 28  has a configuration similar to the configuration of the antenna device  3110 . With such a configuration, in the example shown in  FIG. 25 , in each of the parts indicated by the reference signs R 27  and R 28 , in a similar manner to the antenna device  3110 , it is possible to expect effects of improving symmetry of the shape of the radiation pattern of the feeding elements (in this case, symmetry of the shape in the y direction). 
     Furthermore,  FIG. 25  is an explanatory diagram for describing one example of the configuration of the antenna device according to the second modification, and show one example in a case where an array antenna (so-called radial array) is configured by arranging the plurality of antenna elements  3111  radially. Note that in  FIG. 25 , a part indicated as “feeding element” corresponds to the antenna element  3111  in the antenna device  3110  (that is, antenna element having a feeding point) according to the present embodiment. Furthermore, a part indicated as “parasitic element” corresponds to the parasitic element  3115  in the antenna device  3110  according to the present embodiment. Furthermore, in  FIG. 25 , the x direction, y direction, and z direction correspond to the x direction, y direction, and z direction in the example shown in  FIGS. 22 to 24 , respectively. That is, in the example shown in  FIG. 25 , a plurality of feeding elements is disposed so as to be spaced apart from each other in the xy plane. 
     In the example shown in  FIG. 25 , among the feeding elements radially arranged on the xy plane (in other words, feeding elements arranged concentrically), for each of the plurality of feeding elements arranged in the radial direction, the parasitic elements are disposed so as to be mutually adjacent, in the radial direction, to the feeding elements located on the end sides in the radial direction. That is, in the example shown in  FIG. 25 , each of parts indicated by reference signs R 31  to R 37  has a configuration similar to the configuration of the antenna device  3110  described with reference to  FIGS. 6 and 8 . With such a configuration, in the example shown in  FIG. 25 , in each of the parts indicated by the reference signs R 31  to R 37 , in a similar manner to the antenna device  3110 , it is possible to expect effects of improving symmetry of the shape of the radiation pattern of the feeding elements (in this case, symmetry of the shape in the radial direction). 
     Note that the examples shown in  FIGS. 22 to 25  are just one example, and do not necessarily limit the configuration of the antenna device  3110  according to the present embodiment. That is, the configuration of the antenna device according to the present embodiment is not particularly limited if parasitic elements are disposed on the basis of the above-described idea, for at least some two or more antenna elements arranged along a desired direction among the plurality of antenna elements constituting the array antenna. 
     Furthermore, the shape of the feeding element and the parasitic element is not particularly limited, and may be, for example, a circle, a square, and the like. Therefore, as the feeding element, for example, antenna elements including an E-type patch antenna, a patch antenna with a slot, a patch antenna with a circularly-polarized perturbation element, and the like can be applied. Furthermore, the shape of the parasitic element may be set according to the antenna element applied as the feeding element. Furthermore, as another example, the shape of the feeding element or the parasitic element may be determined according to an arrangement pattern of the plurality of feeding elements constituting the array antenna constituting the antenna device. This is not limited to the present modification, but is also similar for the embodiment and other modifications described above. 
     As the second modification, with reference to  FIGS. 22 to 25 , one example of the configuration of the antenna device according to the present embodiment has been described above with attention particularly paid to the configuration of the array antenna. 
     (Third Modification) 
     Subsequently, as a third modification, another example of the configuration of the antenna device according to the present embodiment will be described. 
     The embodiment and the modifications described above have described one example in a case where the substrate on which the antenna element and the parasitic element are disposed is formed in a flat shape. Meanwhile, if it is possible to dispose the antenna element and the parasitic element described above, the shape of the substrate on which the antenna element and the parasitic element are disposed (that is, configuration corresponding to the above-described substrate) is not necessarily limited to a flat shape. 
     For example,  FIGS. 26 and 27  are each an explanatory diagram for describing one example of a configuration of an antenna device according to the third modification. The examples shown in  FIGS. 26 and 27  show one example in a case where an antenna element is disposed on a resin frame formed as some member of a desired mechanism (for example, mechanical frame). 
     Specifically, in the antenna device  3310  shown in  FIG. 26 , a reference sign  3318  indicates a resin frame, and a reference sign  3311  indicates an antenna element. That is, in the example shown in  FIG. 26 , the antenna element and the parasitic element (for example, antenna element  3111  and parasitic element  3115  shown in  FIG. 6 ) may be disposed in an area where the antenna element  3311  is disposed in the resin frame  3318  in order to be substantially similar to the embodiment and the modifications described above. That is, in the example shown in  FIG. 26 , the resin frame  3318  corresponds to the “substrate” in the embodiment and the modifications. 
     Furthermore, in an antenna device  3320  shown in  FIG. 27 , a reference sign  3328  indicates a resin frame and a reference sign  3321  indicates an antenna element. That is, in the example shown in  FIG. 27 , the antenna element and the parasitic element (for example, antenna element  3111  and parasitic element  3115  shown in  FIG. 6 ) may be disposed in an area where the antenna element  3321  is disposed in the resin frame  3328  in order to be substantially similar to the embodiment and the modifications described above. That is, in the example shown in  FIG. 26 , the resin frame  3318  corresponds to the “substrate” in the embodiment and the modifications. 
     As described above, in the antenna device according to the present embodiment, the configuration corresponding to the substrate on which the antenna element and the parasitic element are disposed is not necessarily limited to a flat shape, and the configuration may have a three-dimensional shape as shown in  FIGS. 26 and 27 , for example. That is, the part described as “substrate” in the present disclosure is not limited to only a flat substrate, but also includes a base material on which the antenna element can be disposed, like the resin frame described above (for example, a base material having a three-dimensional shape). 
     As the third modification, another example of the configuration of the antenna device according to the present embodiment has been described above. 
     &lt;5.4. Application Example&gt; 
     Subsequently, as an application example of the communication device to which the antenna device according to one embodiment of the present disclosure is applied, one example of applying the technology according to the present disclosure to devices other than a communication terminal such as a smartphone will be described. 
     In recent years, the technology of connecting various things to a network, which is called internet of things (IoT), has attracted attention. It is assumed that devices other than smartphones and tablet terminals can be used for communication. Therefore, for example, application of the technology according to the present disclosure to movably configured various devices enables the devices to perform communication using a millimeter wave. 
     For example,  FIG. 28  is an explanatory diagram for describing an application example of a communication device according to the present embodiment, and shows one example in a case where the technology according to the present disclosure is applied to a camera device. Specifically, in the example shown in  FIG. 28 , the antenna device according to one embodiment of the present disclosure is held so as to be located near each of surfaces  301  and  302  facing directions different from each other, out of outer surfaces of a housing of a camera device  300 . For example, a reference sign  311  schematically shows the antenna device according to one embodiment of the present disclosure. With such a configuration, for example, in each of the surfaces  301  and  302 , the camera device  300  shown in  FIG. 28  can transmit or receive a wireless signal that propagates in a direction that substantially agrees with the normal direction of the surface. Note that it is needless to say that the antenna device  311  may be provided not only on the surfaces  301  and  302  shown in  FIG. 28  but also on other surfaces. 
     Furthermore, the technology according to the present disclosure can be applied to an unmanned aerial vehicle called a drone, and the like. For example,  FIG. 29  is an explanatory diagram for describing an application example of the communication device according to the present embodiment, and shows one example in a case where the technology according to the present disclosure is applied to a camera device installed on a bottom of a drone. Specifically, it is preferable that a drone flying at a high altitude can mainly transmit or receive a wireless signal (millimeter wave) coming from various directions on the lower side. Therefore, for example, in the example shown in  FIG. 29 , the antenna device according to one embodiment of the present disclosure is held so as to be located near respective portions facing directions different from each other, out of an outer surface  401  of a housing of a camera device  400  installed on the bottom of the drone. For example, a reference sign  411  schematically shows the antenna device according to one embodiment of the present disclosure. Furthermore, although illustration is omitted in  FIG. 29 , the antenna device  411  may be provided not only in the camera device  400  but also, for example, in respective portions of the housing of the drone itself. Also in this case, in particular, the antenna device  411  is preferably provided on the lower side of the housing. 
     Note that as shown in  FIG. 29 , in a case where at least part of outer surfaces of the housing of the target device is configured as a curved surface (that is, surface having curvature), out of respective partial areas in the curved surface, the antenna device  411  is preferably held near each of the plurality of partial areas where the normal directions intersect each other or the normal directions are at positions twisted around each other. With such a configuration, the camera device  400  shown in  FIG. 29  can transmit or receive a wireless signal that propagates in a direction that substantially agrees with the normal direction of each partial area. 
     Note that the example described with reference to  FIGS. 28 and 29  is merely one example, and a device to which the technology according to the present disclosure is applied is not particularly limited as long as the device performs communication using a millimeter wave. 
     As described above, as the application example of the communication device to which the antenna device according to one embodiment of the present disclosure is applied, with reference to  FIGS. 28 and 29 , one example of applying the technology according to the present disclosure to devices other than a communication terminal such as a smartphone has been described. 
     6. CONCLUSION 
     As described above, the antenna device according to the present embodiment includes a substrate (dielectric substrate), a plurality of antenna elements each having a feeding point, and a parasitic element having no feeding point. Each of the plurality of antenna elements and the parasitic element are supported by the substrate. Specifically, the plurality of antenna elements is disposed so as to be spaced apart from each other along a predetermined direction. At this time, the plurality of antenna elements constitutes an array antenna. Furthermore, among the plurality of antenna elements described above, the parasitic element is disposed so as to be mutually spaced apart, in an arrangement direction, from a first antenna element located on the end side of the arrangement direction of the plurality of antenna elements. That is, the parasitic element is disposed so as to be mutually adjacent to the first antenna element in the arrangement direction described above. Furthermore, a first element interval between the parasitic element described above and the first antenna element described above is equal to or less than twice a second element interval between the first antenna element and a second antenna element located on the opposite side of the parasitic element with respect to the first antenna element. 
     With the above configuration, the antenna device according to the present embodiment makes it possible to reduce the influence of the distortion that occurs in the radiation pattern of the first antenna element described above, and to secure symmetry of the radiation pattern in the arrangement direction described above. Furthermore, the antenna device according to the present embodiment makes it possible to make the size in the arrangement direction smaller than in a case where symmetry of the radiation pattern described above in the arrangement direction described above is secured without providing a parasitic element. That is, the antenna device according to the present embodiment enables both securing symmetry of the radiation pattern of each antenna element (particularly, antenna element located on the end side in the arrangement direction) and miniaturizing the antenna device in a more preferred mode in a case where the plurality of antenna elements is arrayed. 
     The preferred embodiment of the present disclosure has been described in detail above with reference to the accompanying drawings, but the technical scope of the present disclosure is not limited to such an example. It is obvious that persons of ordinary skill in the technical field of the present disclosure can conceive various modifications or alterations within the scope of the technical idea described in the claims, and it is of course understood that these also fall within the technical scope of the present disclosure. 
     Furthermore, effects described in the present specification are merely descriptive or illustrative and not restrictive. That is, the technology according to the present disclosure can produce other effects obvious to those skilled in the art from the description in the present specification, in addition to or instead of the effects described above. 
     Note that the following configurations also belong to the technical scope of the present disclosure. 
     (1) 
     An antenna device including: 
     a substrate; 
     a plurality of antenna elements supported by the substrate, each of the antenna elements having a feeding point; and 
     a parasitic element supported by the substrate and having no feeding point, 
     in which the plurality of antenna elements is disposed to be spaced apart from each other along a predetermined direction, 
     the parasitic element is mutually spaced apart in the direction from a first antenna element located on an end side in the direction among the plurality of antenna elements, and 
     a first element interval between the parasitic element and the first antenna element is equal to or less than twice a second element interval between the first antenna element and a second antenna element located on an opposite side of the parasitic element with respect to the first antenna element. 
     (2) 
     The antenna device according to (1) described above, in which the parasitic element is disposed at a position symmetrical to the second antenna element with respect to the first antenna element. 
     (3) 
     The antenna device according to (1) or (2) described above, in which the first element interval is equal to or less than a wavelength of a wireless signal transmitted or received by the plurality of antenna elements. 
     (4) 
     The antenna device according to (3) described above, in which the first element interval is substantially equal to a half of the wavelength. 
     (5) 
     The antenna device according to any one of claims (1) to (4) described above, in which a first width of the parasitic element along the direction is substantially equal to a second width of each of the antenna elements along the direction. 
     (6) 
     The antenna device according to (5) described above, in which the first width d 1  satisfies a conditional expression shown below, in a case where a relative permittivity of a resin frame of the antenna elements is εr, and a wavelength of a wireless signal transmitted or received by the plurality of antenna elements is λ. 
     
       
         
           
             
               [ 
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 5 
               
               ] 
             
             ⁢ 
             
                 
             
           
         
       
       
         
           
             
               d 
               ⁢ 
               
                   
               
               ⁢ 
               1 
             
             = 
             
               λ 
               
                 2 
                 ⁢ 
                 
                   
                     ɛ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     r 
                   
                 
               
             
           
         
       
     
     (7) 
     The antenna device according to (6) described above, in which the first width is substantially equal to λ/4. 
     (8) 
     The antenna device according to any one of claims (1) to (7) described above, in which the parasitic element is used as a pad for a predetermined sensor. 
     (9) 
     The antenna device according to any one of claims (1) to (7) described above, in which the parasitic element has a shape substantially identical to a shape of each of the antenna elements. 
     (10) 
     The antenna device according to (9) described above, in which each of the antenna elements has a configuration as a patch antenna, an E-type patch antenna, a patch antenna with a slot, or a patch antenna with a circularly polarized perturbation element. 
     (11) 
     The antenna device according to any one of claims (1) to (10) described above, in which the plurality of antenna elements is at least a part of antenna elements constituting an array antenna in which a plurality of antenna elements is disposed in one or more directions. 
     (12) 
     The antenna device according to (11) described above, in which the array antenna is a one-dimensional array antenna, a two-dimensional array antenna, or a radial array antenna. 
     (13) 
     The antenna device according to any one of claims (1) to (12) described above, further including, as the substrate, a first substrate and a second substrate each supporting the plurality of antenna elements and the parasitic element, 
     in which the first substrate and the second substrate are each held such that normal directions intersect each other or the normal directions are at positions twisted around each other. 
     REFERENCE SIGNS LIST 
     
         
           200  Terminal device 
           2001  Antenna part 
           2003  Wireless communication unit 
           2005  Communication control unit 
           2007  Storage unit 
           211  Communication device 
           3110  Antenna device 
           3111  Antenna element 
           3112  Element 
           3113  Feeding point 
           3115  Parasitic element 
           3116  Element 
           3118  Dielectric substrate 
           3119  Ground plate 
           3210  Antenna device 
           3110   a ,  3110   b  Antenna part 
           3212  Connection part