Patent Publication Number: US-2022221554-A1

Title: Electronic device, method for controlling electronic device, and program for controlling electronic device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. 2019-84494 filed in Japan on Apr. 25, 2019, the entire disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an electronic device, a method for controlling an electronic device, and a program for controlling an electronic device. 
     BACKGROUND ART 
     For example, in fields such as automobile-related industries, a technology for measuring a distance or the like between a vehicle of interest and a predetermined object is regarded as important. In recent years, various studies, have been conducted particularly on a radar (Radio Detecting and Ranging) technology for measuring a distance or the like to an object such as an obstacle by transmitting a radio wave such as a millimeter wave and receiving a reflected wave reflected off the object. Such a technology for measuring a distance or the like expectedly becomes more important in the future with progresses of a technology for assisting drivers in driving and a technology related to automated driving for partially or entirely automating driving. 
     It is known that in the above-described radar technology, when a transmission wave is reflected off a particular object, the direction of the plane of polarization (polarization direction) of a radio wave changes. Some techniques using such a property have been proposed. For example, PTL 1 discloses a radar apparatus that receives a second radio wave having a plane of polarization different from a first radio wave that has been transmitted. A radio wave reflector used along with this radar apparatus reflects, as the second radio wave, the first radio wave received from the radar apparatus. For example, PTL 2 discloses a configuration in which a same polarization reflector that reflects an incident first radio wave as a second radio wave and a different polarization reflector that reflects the incident first radio wave as a third radio wave having a plane of polarization changed from that of the first radio wave are alternately arranged. PTL 2 has proposed to virtually make the resolution fine by such a radar transceiver. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Unexamined Patent Application Publication No. 2006-133108 
         PTL 2: Japanese Unexamined Patent Application Publication No. 2007-17356 
       
    
     SUMMARY OF INVENTION 
     In one embodiment, an electronic device includes a transmission antenna that transmits a transmission wave, a reception antenna that receives a reflected wave that is the reflected transmission wave, and a control unit. 
     The control unit detects an object that reflects the transmission wave, based on a transmission signal transmitted as the transmission wave and a reception signal received as the reflected wave. 
     The transmission antenna includes a first transmission antenna that transmits a transmission wave of a first polarization direction, and a second transmission antenna that transmits a transmission wave of a second polarization direction different from the first polarization direction. 
     In one embodiment, a method for controlling an electronic device includes steps as follows: 
     a step of transmitting a transmission wave of a first polarization direction from a first transmission antenna; 
     a step of transmitting a transmission wave of a second polarization direction different from the first polarization direction from a second transmission antenna; 
     a step of receiving, from a reception antenna, a reflected wave that is the reflected transmission wave; and 
     a step of detecting an object that reflects the transmission wave, based on a transmission signal transmitted as the transmission wave and a reception signal received as the reflected wave. 
     In one embodiment, a program for controlling an electronic device causes a computer to perform steps as follows: 
     a step of transmitting a transmission wave of a first polarization direction from a first transmission antenna; 
     a step of transmitting a transmission wave of a second polarization direction different from the first polarization direction from a second transmission antenna; 
     a step of receiving, from a reception antenna, a reflected wave that is the reflected transmission wave; and 
     a step of detecting an object that reflects the transmission wave, based on a transmission signal transmitted as the transmission wave and a reception signal received as the reflected wave. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram for describing how an electronic device according to one embodiment is used. 
         FIG. 2  is a functional block diagram schematically illustrating a configuration of the electronic device according to the one embodiment. 
         FIG. 3  is a diagram for describing a configuration of a transmission signal according to the one embodiment. 
         FIG. 4  is a diagram illustrating an example of arrangement of transmission antennas and reception antennas of an electronic device to be compared with the electronic device according to the one embodiment. 
         FIG. 5  is a diagram illustrating an example of a configuration of transmission antennas and reception antennas of the electronic device according to the one embodiment. 
         FIG. 6  is a diagram illustrating another example of the configuration of the transmission antennas and the reception antennas of the electronic device according to the one embodiment. 
         FIG. 7  is a diagram for describing switch of the transmission antennas in the electronic device according to the one embodiment. 
         FIG. 8  is a diagram illustrating an example of detection of an object performed by the electronic device according to the one embodiment. 
         FIG. 9  is a flowchart for describing an operation of the electronic device according to the one embodiment. 
         FIG. 10  is a conceptual diagram for describing spatial arrangement of the antennas of the electronic device according to the one embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The detection accuracy is desirably improved in a technology for detecting a predetermined object by receiving a reflected wave that is a transmitted transmission wave reflected off the object. An object of the present disclosure is to provide an electronic device, a method for controlling an electronic device, and a program for controlling an electronic device that contribute to improvement of the object detection accuracy. According to one embodiment, an electronic device, a method for controlling an electronic device, and a program for controlling an electronic device that contribute to improvement of the object detection accuracy can be provided. One embodiment is described in detail below with reference with the drawings. 
     An electronic device according to one embodiment is mounted in a vehicle (mobility device) such as an automobile, for example, and thus is capable of detecting a predetermined object located around the mobility device. To this end, the electronic device according to the one embodiment is capable of transmitting a transmission wave to an area around the mobility device from a transmission antenna installed on the mobility device. The electronic device according to the one embodiment is also capable of receiving a reflected wave that is the reflected transmission wave, from a reception antenna installed on the mobility device. At least one of the transmission antenna and the reception antenna may be included in a radar sensor or the like installed on the mobility device, for example. 
     A configuration in which the electronic device according to the one embodiment is mounted in an automobile such as a passenger car is described below as a typical example. However, the mobility device in which the electronic device according to the one embodiment is mounted is not limited to an automobile. The electronic device according to the one embodiment may be mounted in various mobility devices such as a bus, a track, a motorcycle, a bicycle, a ship, an aircraft, a farm vehicle such as a tractor, a snowplow, a garbage truck, a police car, an ambulance, and a drone. The mobility device in which the electronic device according to the one embodiment is mounted is not necessarily limited to a mobility device that moves by its own motive power. For example, the mobility device in which the electronic device according to the one embodiment is mounted may be a trailer towed by a tractor. The electronic device according to the one embodiment is capable of measuring a distance or the like between the sensor and a predetermined object when at least one of the sensor and the object is movable. The electronic device according to the one embodiment is also capable of measuring the distance or the like between the sensor and the object even when both the sensor and the object are stationary. 
     An example of how the electronic device according to the one embodiment detects an object is described first. 
       FIG. 1  is a diagram for describing how the electronic device according to the one embodiment is used.  FIG. 1  illustrates an example in which a sensor including a transmission antenna and a reception antenna according to the one embodiment is installed on a mobility device. 
     A sensor  5  including a transmission antenna and a reception antenna according to the one embodiment is installed on a mobility device  100  illustrated in  FIG. 1 . It is assumed that an electronic device  1  according to the one embodiment is also mounted (for example, built) in the mobility device  100  illustrated in  FIG. 1 . A specific configuration of the electronic device  1  is described later. The sensor  5  may include at least one of the transmission antenna and the reception antenna, for example. The sensor may also appropriately include at least any of other functional units, such as at least part of a control unit  10  ( FIG. 2 ) included in the electronic device  1 . The mobility device  100  illustrated in  FIG. 1  may be an automotive vehicle such as a passenger car but may be a mobility device of any type. In  FIG. 1 , the mobility device  100  may move (travel or slowly travel), for example, in a positive Y-axis direction (traveling direction) illustrated in  FIG. 1  or in another direction, or may be stationary without moving. 
     As illustrated in  FIG. 1 , the sensor  5  including the transmission antenna is installed on the mobility device  100 . In the example illustrated in  FIG. 1 , only one sensor  5  including the transmission antenna and the reception antenna is installed at a front portion of the mobility device  100 . The position where the sensor  5  is installed on the mobility device  100  is not limited to the position illustrated in  FIG. 1  and may be another appropriate position. For example, the sensor  5  illustrated in  FIG. 1  may be installed on a left side, on a right side, and/or on a rear side of the mobility device  100 . The number of such sensors  5  may be any number equal to or greater than 1 depending on various conditions (or requirements) such as a range and/or an accuracy of measurement performed by the mobility device  100 . The sensor  5  may be installed inside the mobility device  100 . The inside the mobility device  100  may be, for example, a space inside a bumper, a space inside a body, a space inside a headlight, or a space such as a driver&#39;s space. 
     The sensor  5  transmits an electromagnetic wave as a transmission wave from the transmission antenna. For example, when a predetermined object (for example, an object  200  illustrated in  FIG. 1 ) is located around the mobility device  100 , at least part of to transmission wave transmitted from the sensor  5  is reflected off the object to become a reflected wave. For example, the reception antenna of the sensor  5  receives such a reflected wave. In this manner, the electronic device  1  mounted in the mobility device  100  can detect the object. 
     The sensor  5  including the transmission antenna may be typically a radar (Radio Detecting and Ranging) sensor that transmits and receives a radio wave. However, the sensor is not limited to a radar sensor. The sensor  5  according to the one embodiment may be, for example, a sensor based on the LIDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) technology that uses an optical wave. Each of these sensors can include, for example, a patch antenna. Since the technologies such as RADAR and LIDAR are already known, detailed description may be appropriately simplified or omitted. 
     The electronic device  1  mounted in the mobility device  100  illustrated in  FIG. 1  receives, from the reception antenna, the reflected wave of the transmission wave transmitted from the transmission antenna of the sensor  5 . In this manner, the electronic device  1  can detect the predetermined object  200  located within a predetermined distance from the mobility device  100 . For example, as illustrated in  FIG. 1 , the electronic device  1  can measure a distance L between the mobility device  100 , which is a vehicle of interest, and the predetermined object  200 . The electronic device  1  can also measure a relative velocity between the mobility device  100 , which is the vehicle of interest, and the predetermined object  200 . The electronic device  1  can further measure a direction (an angle of arrival θ) from which the reflected wave from the predetermined object  200  arrives at the mobility device  100 , which is the vehicle of interest. 
     The object  200  may be, for example, at least any of an oncoming automobile traveling in a lane adjacent to a lane of the mobility device  100 , an automobile traveling side by side with the mobility device  100 , an automobile traveling in front of or behind the mobility device  100  in the same lane, and the like. The object  200  may also be any object located around the mobility device  100 , such as a motorcycle, a bicycle, a stroller, a person such as a pedestrian, an animal, an insect, other forms of life, a guardrail, a median strip, a road sign, a step on a sidewalk, a wall, or an obstacle. The object  200  may be in motion or stationary. For example, the object  200  may be an automobile or the like that is parked or stationary around the mobility device  100 . 
     In  FIG. 1 , a ratio between a size of the sensor  5  and a size of the mobility device  100  does not necessarily indicate an actual ratio.  FIG. 1  illustrates the sensor  5  installed on an outer portion of the mobility device  100 . However, in the one embodiment, the sensor  5  may be installed at various positions of the mobility device  100 . For example, in one embodiment, the sensor  5  may be installed inside a bumper of the mobility device  100  so as not to be seen in the appearance of the mobility device  100 . 
     Description is given below on the assumption that the transmission antenna of the sensor  5  transmits a radio wave in a frequency band, such as a millimeter wave (equal to or higher than 30 GHz) or a quasi-millimeter wave (for example, around 20 GHz to 30 GHz) as a typical example. For example, the transmission antenna of the sensor  5  may transmit a radio wave having a frequency bandwidth of 4 GHz such as from 77 GHz to 81 GHz. 
       FIG. 2  is a functional block diagram schematically illustrating an example of a configuration of the electronic device  1  according to the one embodiment. An example of the configuration of the electronic device  1  according to the one embodiment is described below. 
     When a distance or the like is measured by using a millimeter-wave radar, a frequency-modulated continuous wave radar (hereinafter, referred to as an FMCW radar) is often used. The FMCW radar sweeps a frequency of a to-be-transmitted radio wave to generate a transmission signal. Thus, a frequency of the radio wave used by such a millimeter-wave FMCW radar, which uses a radio wave of a frequency band of 79 GHz, for example, is in a frequency bandwidth of 4 GHz such as from 77 GHz to 81 GHz, for example. The radar of the frequency bandwidth of 79 GHz has a characteristic that the usable frequency bandwidth is wider than another millimeter-wave and/or quasi-millimeter-wave radar of a frequency band of 24 GHz, 60 GHz, or 76 GHz, for example. Such an embodiment is described below. 
     As illustrated in  FIG. 2 , the electronic device  1  according to the one embodiment is constituted by the sensor  5  and an ECU (Electronic Control Unit)  50 . The ECU  50  controls various operations of the mobility device  100 . The ECU  50  may be constituted by at least one or more ECUs. The electronic device according to the one embodiment includes the control unit  10 . The electronic device  1  according to the one embodiment may also appropriately include another functional unit such as at least any of a transmission unit  20 , reception units  30 A to  30 D, and a storage unit  40 . As illustrated in  FIG. 2 , the electronic device  1  may include a plurality of reception units such as the reception units  30 A to  30 D. When the reception units  30 A,  30 B,  30 C, and  30 D are not distinguished from one another, the reception units  30 A,  30 B,  30 C, and  30 D are simply referred to as “reception units  30 ” below. 
     The control unit  10  may include a distance FFT processing unit  11 , a velocity FFT processing unit  12 , an angle-of-arrival estimating unit  13 , an object detecting unit  14 , a detection range determining unit  15 , and a parameter setting unit  16 . These functional units included in the control unit  10  are further described later. 
     As illustrated in  FIG. 2 , the transmission unit  20  may include a signal generating unit  21 , a synthesizer  22 , phase control units  23 A,  23 B, and  23 C, amplifiers  24 A,  24 B, and  24 C, and transmission antennas  25 A,  25 B, and  25 C. When the phase control units  23 A,  23 B, and  23 C are not distinguished from one another, the phase control units  23 A,  23 B, and  23 C are simply referred to as “phase control units  23 ” below. When the amplifiers  24 A,  24 B, and  24 C are not distinguished from one another, the amplifiers  24 A,  24 B, and  24 C are simply referred to as “amplifiers  24 ” below. When the transmission antennas  25 A,  25 B, and  25 C are not distinguished from one another, the transmission antennas  25 A,  25 B, and  25 C are simply referred to as “transmission antennas  25 ” below. 
     As illustrated in  FIG. 2 , each of the reception units  30  may include a respective one of reception antennas  31 A to  31 D. When the reception antennas  31 A,  31 B,  31 C, and  31 D are not distinguished from one another, the reception antennas  31 A,  31 B,  31 C, and  31 D are simply referred to as “reception antennas  31 ” below. As illustrated in  FIG. 2 , each of the plurality of reception units  30  may include an LNA  32 , a mixer  33 , an IF unit  34 , and an AD conversion unit  35 . The reception units  30 A to  30 D may have the same and/or similar configuration.  FIG. 2  schematically illustrates the configuration of only the reception unit  30 A as a representative example. 
     The sensor  5  described above may include, for example, the transmission antennas  25  and the reception antennas  31 . The sensor  5  may also appropriately include at least any of other functional units such as the control unit  10 . 
     The control unit  10  included in the electronic device  1  according to the one embodiment is capable of controlling various functional units of the electronic device  1  and also controlling operations of the entire electronic device  1 . To provide control and processing capabilities for executing various functions, the control unit  10  may include at least one processor, for example, a CPU (Central Processing Unit). The control unit  10  may be collectively implemented by one processor, may be implemented by some processors, or may be implemented discrete individual processors. The processor may be implemented as one IC. The IC is also referred to as an integrated circuit. The processor may be implemented as a plurality of ICs and discrete circuits connected to be able to perform communication. The processor may be implemented on the basis of various other known technologies. In the one embodiment, the control unit  10  may be configured as, for example, a CPU and a program executed by the CPU. The control unit  10  may appropriately include a memory required for operations of the control unit  10 . 
     The storage unit  40  may store a program executed by the control unit  10 , a result of processing performed by the control unit  10 , etc. The storage unit  40  may function as a work memory of the control unit  10 . The storage unit  40  may be constituted, for example, by a semiconductor memory, a magnetic disk, or the like. However, the storage unit  40  is not limited to these, and can be any storage device. The storage unit  40  may be, for example, a storage medium such as a memory card inserted to the electronic device  1  according to the present embodiment. The storage unit  40  may be an internal memory of the CPU used as the control unit  10  as described above. 
     In the one embodiment, the storage unit  40  may store various parameters for setting a range in which an object is detected on the basis of a transmission wave T transmitted from each transmission antenna  25  and a reflected wave R received from each reception antenna  31 . Such parameters are further described later. 
     In the electronic device  1  according to the one embodiment, the control unit  10  is capable of controlling at least one of the transmission unit  20  and the reception units  30 . In this case, the control unit  10  may control at least one of the transmission unit  20  and the reception units  30  on the basis of various kinds of information stored in the storage unit  40 . In the electronic device  1  according to the one embodiment, the control unit  10  may instruct the signal generating unit  21  to generate a signal or may control the signal generating unit  21  to generate a signal. 
     In accordance with control performed by the control unit  10 , the signal generating unit  21  generates a signal (transmission signal) to be transmitted as the transmission wave T from each transmission antenna  25 . When generating the transmission signal, the signal generating unit  21  may allocate a frequency of the transmission signal in accordance with control performed by the control unit  10 , for example. Specifically, the signal generating unit  21  may allocate a frequency of the transmission signal in accordance with a parameter set by the parameter setting unit  16 . For example, the signal generating unit  21  receives frequency information from the control unit  10  (the parameter setting unit  16 ) and generates a signal having a predetermined frequency in a frequency band such as from 77 GHz to 81 GHz, for example. The signal generating unit  21  may include a functional unit such as a voltage control oscillator (VCO), for example. 
     The signal generating unit  21  may be configured as hardware having the function, as a microcomputer for example, or as a processor such as a CPU and a program or the like executed by the processor for example. Each functional unit described below may also be configured as hardware having the function, as a microcomputer for example if possible, or as a processor such as a CPU and a program or the like executed by the processor for example. 
     In the electronic device  1  according to the one embodiment, the signal generating unit  21  may generate a transmission signal such as a chirp signal (transmission chirp signal), for example. In particular, the signal generating unit  21  may generate a signal (linear chirp signal) whose frequency changes linearly and periodically. For example, the signal generating unit  21  may generate a chirp signal whose frequency linearly and periodically increases from 77 GHz to 81 GHz as time elapses. For example, the signal generating unit  21  may generate a signal whose frequency periodically repeats a linear increase (up-chirp) from 77 GHz to 81 GHz and a decrease (down-chirp) as time elapses. The signal to be generated by the signal generating unit  21  may be set in advance by the control unit  10 , for example. The signal generated by the signal generating unit  21  may be stored in advance in the storage unit  40  or the like, for example. Since chirp signals used in a technical field such as a radar are known, more detailed description is appropriately simplified or omitted. The signal generated by the signal generating unit  21  is supplied to the synthesizer  22 . 
       FIG. 3  is a diagram for describing an example of chirp signals generated by the signal generating unit  21 . 
     In  FIG. 3 , the horizontal axis represents the elapsed time and the vertical axis represents the frequency. In the example illustrated in  FIG. 3 , the signal generating unit  21  generates linear chirp signals whose frequency linearly changes periodically. In  FIG. 3 , the individual chirp signals are denoted by c 1 , c 2 , . . . , c 8 . As illustrated in  FIG. 3 , the frequency of each chirp signal linearly increases as time elapses. 
     In the example illustrated in  FIG. 3 , eight chirp signals c 1 , c 2 , . . . , c 8  constitute one subframe. That is, each of subframes such as a subframe  1  and a subframe  2  illustrated in  FIG. 3  includes eight chirp signals c 1 , c 2 , . . . , c 8 . In the example illustrated in  FIG. 3 , 16 subframes such as the subframes  1  to  16  constitute one frame. That is, each of frames such as a frame  1  and a frame  2  illustrated in  FIG. 3  includes 16 subframes. As illustrated in  FIG. 3 , a frame interval of a predetermined length may be included between frames. One frame illustrated in  FIG. 3  may have a length of about 30 ms to 50 ms, for example. 
     In  FIG. 3 , the frame  2  and subsequent frames may have the same and/or similar configuration. In  FIG. 3 , the frame  3  and subsequent frames may have the same and/or similar configuration. In the electronic device  1  according to the one embodiment, the signal generating unit  21  may generate a transmission signal as any number of frames. In  FIG. 3 , an illustration of some chirp signals is omitted. As described above, a relationship between time and a frequency of the transmission signal generated by the signal generating unit  21  may be stored in the storage unit  40  or the like, for example. 
     As described above, the electronic device  1  according to the one embodiment may transmit a transmission signal constituted by subframes each including a plurality of chirp signals. The electronic device  1  according to the one embodiment may transmit a transmission signal constituted by frames each including a predetermined number of subframes. 
     Description is given below on the assumption that the electronic device  1  transmits a transmission signal having a frame structure illustrated in  FIG. 3 . However, the frame structure illustrated in  FIG. 3  is an example. For example, the number of chirp signals included in one subframe is not limited to eight. In the one embodiment, the signal generating unit  21  may generate a subframe including any number (for example, a plurality) or chirp signals. A subframe structure illustrated in  FIG. 3  is also an example. For example, the number of subframes included in one frame is not limited to 16. In the one embodiment, the signal generating unit  21  may generate a frame including any number (for example, a plurality) of subframes. The signal generating unit  21  may generate signals having different frequencies. The signal generating unit  21  may generate a plurality of discrete signals of bandwidths in which frequencies f are different from each other. 
     Referring back to  FIG. 2 , the synthesizer  22  increases the frequency of the signal generated by the signal generating unit  21  to a frequency in a predetermined frequency band. The synthesizer  22  may increase the frequency of the signal generated by the signal generating unit  21  to a frequency selected as a frequency of the transmission wave T to be transmitted from each transmission antenna  25 . The frequency selected as the frequency of the transmission wave T to be transmitted from each transmission antenna  25  may be set by the control unit  10 , for example. For example, the frequency selected as the frequency of the transmission wave T to be transmitted from each transmission antenna  25  may be a frequency selected by the parameter setting unit  16 . The frequency selected as the frequency of the transmission wave T to be transmitted from each transmission antenna  25  may be stored in the storage unit  40 , for example. The signal whose frequency has been increased by the synthesizer  22  is supplied to the phase control unit  23  and the mixer  33 . When the plurality of phase control units  23  are present, the signal whose frequency has been increased by the synthesizer  22  may be supplied to each of the plurality of phase control units  23 . When the plurality of reception units  30  are present, the signal whose frequency has been increased by the synthesizer  22  may be supplied to each of the mixers  33  of the plurality of reception units  30 . 
     Each of the phase control units  23  controls a phase of the transmission signal supplied from the synthesizer  22 . Specifically, for example, in accordance with control performed by the control unit  10 , each of the phase control units  23  may appropriately advance or delay the phase of the signal supplied from the synthesizer  22  to adjust the phase of the transmission signal. In this case, on the basis of a difference between paths of the transmission waves T to be transmitted from the plurality of transmission antennas  25 , the phase control units  23  may adjust the phases of the respective transmission signals. The phase control units  23  appropriately adjust the phases of the respective transmission signals. Consequently, the transmission waves T transmitted from the plurality of transmission antennas  25  enhance with each other in a predetermined direction to form a beam (beamforming). In this case, a correlation between a direction of beamforming and amounts of phase by which the respective transmission signals transmitted by the plurality of transmission antennas  25  are controlled may be stored in the storage unit  40 , for example. The transmission signal whose phase is controlled by each of the phase control units  23  is supplied to a respective one of the amplifiers  24 . 
     The amplifier  24  amplifies power (electric power) of the transmission signal supplied from the phase control unit  23  in accordance with control performed by the control unit  10 , for example. When the sensor  5  includes the plurality of transmission antennas  25 , each of the plurality of amplifiers  24  may amplify power (electric power) of the transmission signal supplied from a respective one of the plurality of phase control units  23  in accordance with control performed by the control unit  10 , for example. Since the technology for amplifying power of a transmission signal is already known, more detailed description is omitted. Each of the amplifiers  24  is connected to a respective one of the transmission antennas  25 . 
     The transmission antenna  25  outputs (transmits), as the transmission wave T, the transmission signal amplified by the amplifier  24 . When the sensor  5  includes the plurality of transmission antennas  25 , each of the plurality of transmission antennas  25  may output (transmit), as the transmission wave T, the transmission signal amplified by a respective one of the plurality of amplifiers  24 . Since the transmission antennas  25  can be configured in a manner that is the same as and/or similar to the manner of transmission antennas for use in the known radar technology, more detailed description is omitted. 
     The electronic device  1  according to the one embodiment, which includes the transmission antennas  25 , is capable of transmitting transmission signals (for example, transmission chirp signals) as the transmission waves T from the respective transmission antennas  25  in this manner. At least one of the functional units constituting the electronic device  1  may be housed in one housing. In this case, the one housing may have a hard-to-open structure. For example, the transmission antennas  25 , the reception antennas  31 , and the amplifiers  24  are desirably housed in one housing, and this housing desirably has a hard-to-open structure. When the sensor is installed on the mobility device  100  such as an automobile, each of the transmission antennas  25  may transmit the transmission wave T to outside the mobility device  100  through a cover member such as a radar cover, for example. In this case, the radar cover may be made of a material, for example, a synthetic resin or rubber, that allows an electromagnetic wave to pass therethrough. This radar cover may also serve as a housing of the sensor  5 , for example. The transmission antennas  25  are covered with a member such as the radar cover, so that a risk of the transmission antennas  25  being damaged or malfunctioning because of a contact with an external object can be reduced. The radar cover and the housing may also be referred to as a radome. 
       FIG. 2  illustrates an example in which the electronic device  1  includes three transmission antennas  25 . However, in the one embodiment, the electronic device  1  may include any number of transmission antennas  25 . On the other hand, in the one embodiment, the electronic device  1  may include the plurality of transmission antennas  25  in the case where the transmission waves T transmitted from the respective transmission antennas  25  form a beam in a predetermined direction. In the one embodiment, the electronic device  1  may include the plurality of phase control units  23  and the plurality of amplifiers  24  to correspond to the plurality of transmission antennas  25 . Each of the plurality of phase control units  23  may control the phase of a respective one of the plurality of transmission waves supplied from the synthesizer  22  and to be transmitted from the plurality of transmission antennas  25 . Each of the plurality of amplifiers  24  may amplify power of a respective one of the plurality of transmission signals to be transmitted from the plurality of transmission antennas  25 . In this case, the sensor  5  may include the plurality of transmission antennas. As described above, when the electronic device  1  illustrated  FIG. 2  includes the plurality of transmission antennas  25 , the electronic device  1  may include a plurality of functional units necessary for transmitting the transmission waves T from the plurality of transmission antennas  25 . 
     The reception antenna  31  receives the reflected wave R. The reflected wave R is the transmission wave T reflected off the predetermined object  200 . As the reception antenna  31 , a plurality of antennas such as the reception antennas  31 A to  31 D, for example, may be included. Since the reception antennas  31  can be configured in a manner that is the same as and/or similar to the manner of reception antennas for use in the known radar technology, more detailed description is omitted. Each of the reception antennas  31  is connected to the LNA  32 . A reception signal based on the reflected wave R received by each of the reception antennas  31  is supplied to the LNA  32 . 
     The electronic device  1  according to the one embodiment can receive, from each of the plurality of reception antennas  31 , the reflected wave R that is the transmission wave T that has been transmitted as the transmission signal such as a chirp signal (transmission chirp signal), for example, and has been reflected off the predetermined object  200 . When the transmission chirp signal is transmitted as the transmission wave T in this manner, the reception signal based on the received reflected wave R is referred to as a reception chirp signal. That is, the electronic device  1  receives the reception signal (for example, the reception chirp signal) as the reflected wave R from each of the reception antennas  31 . When the sensor  5  is installed on the mobility device  100  such as an automobile, each of the reception antennas  31  may receive the reflected wave R from outside the mobility device  100  through a cover member such as a radar cover, for example. In this case, the radar cover may be made of a material, for example, a synthetic resin or rubber, that allows an electromagnetic wave to pass therethrough. This radar cover may also serve as a housing of the sensor  5 , for example. The reception antennas  31  are covered with a member such as the radar cover, so that a risk of the reception antennas  31  being damaged or malfunctioning because of a contact with an external object can be reduced. The radar cover and the housing may also be referred to as a radome. 
     When the reception antennas  31  are installed near the transmission antennas  25 , these may be collectively included in one sensor  5 . That is, for example, one sensor  5  may include at least one transmission antenna  25  and at least one reception antenna  31 . For example, one sensor  5  may include the plurality of transmission antennas  25  and the plurality of reception antennas  31 . In such a case, one radar sensor may be covered with a cover member such as one radar cover, for example. 
     The LNA  32  amplifies, with low noise, the reception signal based on the reflected wave R received by a respective one of the reception antennas  31 . The LNA  32  may be a low-noise amplifier and amplifies, with low noise, the reception signal supplied from a respective one of the reception antennas  31 . The reception signal amplified by the LNA  32  is supplied to the mixer  33 . 
     The mixer  33  mixes (multiplies) the reception signal having an RF frequency supplied from the LNA  32  and the transmission signal supplied from the synthesizer  22  to generate a beat signal. The beat signal obtained by the mixer  33  through mixing is supplied to the IF unit  34 . 
     The IF unit  34  performs frequency conversion on the beat signal supplied from the mixer  33  to reduce the frequency of the beat signal to an intermediate frequency (IF). The beat signal whose frequency has been reduced by the IF unit  34  is supplied to the AD conversion unit  35 . 
     The AD conversion unit  35  digitizes the analog beat signal supplied from the IF unit  34 . The AD conversion unit  35  may be constituted by any analog-to-digital conversion circuit (Analog to Digital Converter (ADC)). The digitized beat signal obtained by the AD conversion unit  35  is supplied to the distance FFT processing unit  11  of the control unit  10 . In the case where the plurality of reception units  30  are present, the beat signals each digitized by a respective one of the plurality of AD conversion units  35  may be supplied to the distance FFT processing unit  11 . 
     The distance FFT processing unit  11  estimates a distance between the mobility device  100  equipped with the electronic device  1  and the object  200  on the basis of the beat signals supplied from the respective AD conversion units  35 . The distance FFT processing unit  11  may include a processing unit that performs fast Fourier transform, for example. In this case, the distance FFT processing unit  11  may be configured as any circuit, any chip, or the like that performs fast Fourier transform (FFT) processing. 
     The distance FFT processing unit  11  performs FFT processing (hereinafter, appropriately referred to as “distance FFT processing”) on the beat signal that has been digitized by each of the AD conversion units  35 . For example, the distance FFT processing unit  11  may perform the FFT processing on a complex signal supplied from each of the AD conversion units  35 . The beat signal that has been digitized by each of the AD conversion units  35  can be represented as a temporal change in signal intensity (power). The distance FFT processing unit  11  performs FFT processing on such a beat signal, so that the beat signal can be represented as signal intensity (power) for each frequency. If a peak in a result obtained by the distance FFT processing is equal to or greater than a predetermined threshold, the distance FFT processing unit  11  may determine that the predetermined object  200  is located at the distance corresponding to the peak. For example, a method for determining that there is an object (reflecting object) that reflects a transmission wave when a peak value that is equal to or greater than a threshold is detected from the average power or amplitude of a disturbance signal, such as a constant false alarm rate (CFAR) detection process, known. 
     As described above, the electronic device  1  according to the one embodiment can detect the object  200  that reflects the transmission wave T on the basis of the transmission signal transmitted as the transmission wave T and the reception signal received as the reflected wave R. 
     The distance FFT processing unit  11  can estimate a distance to a predetermined object on the basis of one chirp signal (for example, c 1  illustrated in  FIG. 3 ). That is, the electronic device  1  can measure (estimate) the distance L illustrated in  FIG. 1  by performing the distance FFT processing. Since a technique for measuring (estimating) a distance to a predetermined object by performing FFT processing on a beat signal is known, more detailed description is appropriately simplified or omitted. Results (for example, distance information) of the distance FFT processing performed by the distance FFT processing unit  11  may be supplied to the velocity FFT processing unit  12 . The results of the distance FFT processing performed by the distance FFT processing unit  11  may also be supplied to the object detecting unit  14 . 
     The velocity FFT processing unit  12  estimates a relative velocity between the mobility device  100  equipped with the electronic device  1  and the object  200  on the basis of the beat signals on which the distance FFT processing has been performed by the distance FFT processing unit  11 . The velocity FFT processing unit  12  may include a processing unit that performs fast Fourier transform, for example. In this case, the velocity FFT processing unit  12  may be configured by any circuit, any chip, or the like that performs fast Fourier transform (FFT) processing. 
     The velocity FFT processing unit  12  further performs FFT processing (hereinafter, appropriately referred to as “velocity FFT processing”) on each beat signal on which the distance FFT processing has been performed by the distance FFT processing unit  11 . For example, the velocity FFT processing unit  12  may perform the FFT processing on each complex signal supplied from the distance FFT processing unit  11 . The velocity FFT processing unit  12  can estimate a relative velocity to the predetermined object on the basis of a subframe (for example, the subframe  1  illustrated in  FIG. 3 ) including chirp signals. When the distance FFT processing is performed on the beat signal in the above-described manner, a plurality of vectors can be generated. The velocity FFT processing unit  12  can estimate a relative velocity to the predetermined object by determining a phase of a peak in a result of the velocity FFT processing performed on the plurality of vectors. That is, the electronic device  1  can measure (estimate) a relative velocity between the mobility device  100  and the predetermined object  200  illustrated in  FIG. 1  by performing the velocity FFT processing. Since a technique for measuring (estimating) a relative velocity to a predetermined object by performing velocity FFT processing on a result of distance FFT processing is known, more detailed description is appropriately simplified or omitted. Results (for example, velocity information) of the velocity FFT processing performed by the velocity FFT processing unit  12  may be supplied to the angle-of-arrival estimating unit  13 . The results of the velocity FFT processing performed by the velocity FFT processing unit  12  may also be supplied to the object detecting unit  14 . 
     The angle-of-arrival estimating unit  13  estimates a direction from which the reflected wave R arrives from the predetermined object  200  on the basis of the results of the velocity FFT processing performed by the velocity FFT processing unit  12 . The electronic device  1  can estimate the direction from which the reflected wave R arrives by receiving the reflected wave R from the plurality of reception antennas  31 . For example, the plurality of reception antennas  31  are arranged at a predetermined interval. In this case, the transmission wave T transmitted from each of the transmission antennas  25  is reflected off the predetermined object  200  to become the reflected wave R. Each of the plurality of reception antennas  31  arranged at the predetermined interval receives the reflected wave R. The angle-of-arrival estimating unit  13  can estimate the direction from which the reflected wave R arrives at each of the plurality of reception antennas  31  on the basis of the phase of the reflected wave R received by the reception antenna  31  and a difference in path of the reflected wave R That is, the electronic device  1  can measure (estimate) the angle of arrival θ illustrated in  FIG. 1  on the basis of the results of the velocity FFT processing. 
     Various techniques for estimating a direction from which the reflected wave R arrives on the basis of a result of velocity FFT processing have been proposed. For example, MUSIC (MUltiple SIgnal Classification), ESPRIT (Estimation of Signal. Parameters via Rotational invariance Technique), and the like are known as known arriving direction estimation algorithms. Thus, more detailed description of the known techniques is appropriately simplified or omitted. Information (angle information) of the angle of arrival θ estimated by the angle-of-arrival estimating unit  13  may be supplied to the object detecting unit  14 . 
     The object detecting unit  14  detects an object located in a range in which the transmission wave T is transmitted, on the basis of the information supplied from at least any of the distance FFT processing unit  11 , the velocity FFT processing unit  12 , and the angle-of-arrival estimating unit  13 . The object detecting unit  14  may perform detection of an object by performing, for example, clustering processing on the basis of the supplied distance information, velocity information, and angle information. For example, DBSCAN (Density-based spatial clustering of applications with noise) or the like is known as an algorithm used in clustering of data. In the clustering processing, for example, average power of points constituting the detected object may be calculated. The distance information, the velocity information, the angle information, and power information of the object detected by the object detecting unit  14  may be supplied to the detection range determining unit  15 . The distance information, the velocity information, the angle information, and the power information of the object detected by the object detecting unit  14  may be supplied to the ECU  50 . In this case, when the mobility device  100  is an automobile, communication may be performed using a communication interface such as a CAN (Controller Area Network), for example. 
     The detection range determining unit  15  determines a range (hereinafter, also referred to as an “object detection range”) in which an object that reflects the transmission wave T is detected on the basis of the transmission signal and the reception signal. The detection range determining unit  15  may determine a plurality of object detection ranges on the basis of an operation performed by a driver or the like of the mobility device  100  equipped with the electronic device  1 , for example. For example, the detection range determining unit  15  may determine a plurality of object detection ranges suitable for parking assist when a parking assist button is operated by a driver or the like of the mobility device  100 . The detection range determining unit  15  may determine a plurality of object detection ranges on the basis of an instruction from the ECU  50 , for example. For example, when the ECU  50  determines that the mobility device  100  is to travel backward, the detection range determining unit  15  may determine, on the basis of an instruction from the ECU  50 , a plurality of object detection ranges suitable when the mobility device  100  travels backward. The detection range determining unit  15  may determine a plurality of object detection ranges on the basis of a change in an operation state of a steering wheel, an accelerator pedal, a transmission lever, or the like of the mobility device  100 , for example. The detection range determining unit  15  may determine a plurality of object detection ranges on the basis of a result or detection of an object performed by the object detecting unit  14 . 
     The parameter setting unit  16  sets various parameters that define a transmission signal and a reception signal with which an object that reflects the transmission wave T as the reflected wave R is to be detected. That is, the parameter setting unit  16  sets various parameters for transmitting the transmission wave T from each transmission antenna  25  and various parameters for receiving the reflected wave R from each reception antenna  31 . 
     In particular, in the one embodiment, the parameter setting unit  16  may set various parameters related to transmission of the transmission wave T and reception of the reflected wave R in order to detect an object in the object detection range described above. For example, the parameter setting unit  16  may define a range or the like in which the reflected wave R is desirably received in order to detect the object in the object detection range by receiving the reflected wave R. For example, the parameter setting unit  16  may define a range or the like to which a beam of the transmission wave T is desirably directed in order to transmit the transmission wave T from each of the plurality of transmission antennas  25  and detect an object in the object detection range. The parameter setting unit  16  may also set various parameters for transmitting the transmission wave T and receiving the reflected wave R. 
     The various parameters set by the parameter setting unit  16  may be supplied to the signal generating unit  21 . Thus, the signal generating unit  21  can generate the transmission signal to be transmitted as the transmission wave T on the basis of the various parameters set by the parameter setting unit  16 . The various parameters set by the parameter setting unit  16  may be supplied to the object detecting unit  14 . Thus, the object detecting unit  14  can perform object detection processing in the object detection range determined on the basis of the various parameters set by the parameter setting unit  16 . 
     The ECU  50  included in the electronic device according to the one embodiment is capable f controlling the functional units of the mobility device  100  and also controlling operations of the entire mobility device  100 . To provide control and processing capabilities for executing various functions, the ECU  50  may include at least one processor, for example, a CPU (Central Processing Unit). The ECU  50  may be collectively implemented by one processor, may be implemented by some processors, or may be implemented discrete individual processors. The processor may be implemented as one IC. The IC is also referred to as an integrated circuit. The processor may be implemented as a plurality of ICs and discrete circuits connected to be able to perform communication. The processor may be implemented on the basis of various other known technologies. In the one embodiment, the ECU  50  may be configured as, for example, a CPU and a program executed by the CPU. The ECU  50  may appropriately include a memory required for operations of the ECU  50 . At least part of the functions of the control unit  10  may be functions of the ECU  50 , or at least part of the functions of the ECU  50  may be functions of the control unit  10 . 
     The electronic device  1  illustrated in  FIG. 2  includes the three transmission antennas  25  and the four reception antennas  31 . However, the electronic device  1  according to the one embodiment may include any number of transmission antennas  25  and any number of reception antennas  31 . For example, by including the two transmission antennas  25  and the four reception antennas  31 , the electronic device  1  can be regarded to include a virtual antenna array that is virtually constituted by eight antennas. As described above, the electronic device  1  may receive the reflected wave R of 16 subframes illustrated in  FIG. 3  by using, for example, the eight virtual antennas. 
     An operation of the electronic device  1  according to the one embodiment is described next. 
     A direction in which the electric field oscillates in an electromagnetic wave constituted by the electric field and the magnetic field is, hereinafter referred to as a “polarization direction” with respect to the ground. A plane in which the electric field oscillates in the electromagnetic wave is referred to as a “plane of polarization”. Among polarized waves, a radio wave for which the oscillation direction of the electric field is horizontal to the ground is referred to as a horizontally polarized wave, and a radio wave for which the oscillation direction of the electric field is vertical to the ground is referred to as a vertically polarized wave. A linearly polarized wave that propagates without any change in the plane of polarization is described below. The present disclosure may also be applied to a circularly polarized wave and an elliptically polarized wave in addition to a linearly polarized wave. 
     When the transmission wave transmitted from the transmission antenna  25  of the electronic device  1  according to the one embodiment hits and is reflected off an object, the direction (polarization direction) of the plane of polarization of the radio wave of the reflected wave may change. This is because the directions of the electric field and the magnetic field rotate or the like when the transmission wave is reflected off the object. Such a change in the polarization direction may vary depending on various conditions such as the inclination, the shape, and/or the material of the reflecting surface of the object, for example. In general, the reflected wave obtained as a result of a radio wave transmitted as a horizontally polarized wave from a transmission antenna being reflected off an object does not entirely become a horizontally polarized wave. The reflected wave obtained as a result of the radio wave transmitted as a horizontally polarized wave being reflected off the object may include a vertically polarized wave. 
     An example of arrangement of transmission antennas and reception antennas of an electronic device is described as a comparative example to be compared with the electronic device according to the one embodiment. 
       FIG. 4  is a diagram illustrating an example of arrangement of transmission antennas and reception antennas of an electronic device to be compared with the electronic device according to the one embodiment.  FIG. 4  illustrates only the transmission antennas  25  and the reception antennas  31  among the members of the electronic device  1  illustrated in  FIG. 2 . The transmission antennas  25  and the reception antennas  31  according to the comparative example illustrated in  FIG. 4  may be configured as, for example, a patch antenna (microstrip antenna). 
     As illustrated in  FIG. 4 , each of the transmission antennas  25  and the reception antennas  31  may include four conductors (radiating elements), each side of which has a length of λ/2 (where λ denotes the wavelength of the transmission wave), that are connected to each other by a microstrip line (feeder). 
     In the example illustrated in  FIG. 4 , the transmission antennas  25 A,  25 B, and  25 C are included as the transmission antennas  25 . In the example illustrated in  FIG. 4 , the reception antennas  31 A,  31 B,  31 C, and  31 D are included as the reception antennas  31 . In  FIG. 4 , a direction of a dash line at the bottom indicates the horizontal direction. 
     All of the transmission antennas  25  and the reception antennas  31  illustrated in  FIG. 4  are configured in the same manner. Thus, the polarization directions of transmission waves transmitted from the three transmission antennas  25  are the same direction. The polarization directions of reflected waves received from the four reception antennas  31  are the same direction. The polarization directions of the transmission antennas  25  and the reception antennas  31  are indicated by respective arrows at the top of  FIG. 4 . Angles with respect to the polarization directions of the transmission antennas  25  and the reception antennas  31  are illustrated at the top of  FIG. 4 . That is, all the polarization directions of the transmission antennas  25  and the reception antennas  31  illustrated in  FIG. 4  are denoted as 0°. This angle may be set, for example, such that the angle is 0° when the polarization direction of the electric field is horizontal to the ground and changes with the counterclockwise direction being a positive direction. 
     In the configuration illustrated in  FIG. 4 , the polarization directions (0°) of the transmission waves transmitted from the three transmission antennas  25  and the polarization directions (0°) of the reflected waves received by the four reception antennas  31  are equal to each other. Thus, by receiving, with the reception antennas  31 , radio waves that are obtained as a result of the transmission waves output from the transmission antennas  25  being reflected off an object and that are returning in the same polarization direction, detection of the object can be performed. Among the polarization directions of the reflected waves received by the reception antennas  31 , the polarization direction in which the reception intensity of the reception antennas  31  is the highest is referred to as a most preferable polarization direction. 
     On the other hand, as described above, when the transmission waves transmitted from the transmission antennas  25  hit and are reflected off an object, the polarization directions of the reflected waves may change from the polarization directions of the transmission waves. Thus, the reflected waves obtained as a result of the radio waves transmitted as vertically polarized waves being reflected off the object may include a horizontally polarized wave. 
     For example, radio waves (the polarization direction of 0°) output from the transmission antennas  25  illustrated in  FIG. 4  hit a detection target and are reflected off the detection target. The polarization directions of at least some of reflected waves obtained as a result of the transmission waves being reflected may change. In this case, the reception antennas  31  illustrated in  FIG. 4  mainly receive a component of the polarization direction of 0° among the reflected waves. The reception antennas  31  also receive a component of the polarization direction of 90° among the reflected waves. However, since the reception level of the reflected waves of the component of the polarization direction of 90° is low, such a component is buried in noise components and consequently may not be detected. 
     In such a circumstance, when the object that reflects the transmission waves is located at a short distance or has a large reflection cross section, the reception power of the reflected waves received by the reception antennas  31  increases. Thus, in such a case, any particular inconvenience is unlikely to occur. However, when the object that reflects the transmission waves is located at a long distance or has a small reflection cross section, the reception power of the reflected waves received by the reception antennas  31  decreases depending on the change in the polarization direction. In such a case, a probability of the reception power being buried in noise increases, which leads to non-detection of the object. 
     As for a single object that reflects a transmission wave, the polarization direction of a reflected wave may expectedly vary depending on the portion of the object. For example, an object is assumed in which a change in the polarization direction is small at the center and is large around an end portion. In this case, the presence of the object can be detected by receiving the reflected wave. However, the end portion of the object may not be detected. In this case, there may be a risk that the width of the object is not accurately detected. 
     Accordingly, the electronic device according to the one embodiment enables a reflecting object to be appropriately detected even if the polarization direction of the reflected wave changes. Such an electronic device  1  is described below. 
       FIG. 5  is a diagram illustrating an example of arrangement of the transmission antennas and the reception antennas of the electronic device according to the one embodiment. As in  FIG. 4 ,  FIG. 5  illustrates only the transmission antennas  25  and the reception antennas  31  among the members of the electronic device  1  illustrated in  FIG. 2 . Description of  FIG. 5  that is the same as and/or similar to that of  FIG. 4  is appropriately simplified or omitted. 
     The transmission antenna  25 A illustrated in  FIG. 5  may be the same as and/or similar to the transmission antenna  25 A illustrated in  FIG. 4 . On the other hand, a transmission antenna  25 B′ illustrated in  FIG. 5  is changed from the transmission antenna  25 B illustrated in  FIG. 4 . A transmission antenna  25 C′ illustrated in  FIG. 5  is also changed from the transmission antenna  25 C illustrated in  FIG. 4 . The reception antennas  31  illustrated in  FIG. 5  may be the same as and/or similar to the reception antennas  31  illustrated in  FIG. 4 . 
     The polarization direction of the transmission antenna  25 B′ illustrated in  FIG. 5  is changed from that of the transmission antenna  25 B illustrated in  FIG. 4  by 45°. The polarization direction of the transmission antenna  25 C′ illustrated in  FIG. 5  is changed from that of the transmission antenna  25 C illustrated in  FIG. 4  by 90°. The changes in the polarization direction of the transmission antennas  25 B′ and  25 C′ are not necessarily limited to 45° or 90°. The polarization directions of the transmission antennas  25 B′ and  25 C′ may be set to be different from at least one of to transmission antenna  25 A and the reception antennas  31 . 
     A difference in the polarization direction between the most adjacent transmission antenna  25  and reception antenna  31 , that is, between the transmission antenna  25 C′ and the reception antenna  31 A, may be set to be large such as, for example, 90°. By setting the difference between the polarization direction of the transmission antenna  25  and the polarization direction of the adjacent reception antenna  31  to be large in this manner, isolation can be highly maintained even if the transmission antenna and the reception antenna are arranged closer to each other. Thus, such a configuration can reduce the size of the antennas. 
       FIG. 6  is a diagram illustrating another example of the arrangement of the transmission antennas and the reception antennas of the electronic device  1  according to the one embodiment. As in  FIGS. 4 and 5 ,  FIG. 6  also illustrates only the transmission antennas  25  and the reception antennas  31  among the members of the electronic device  1  illustrated in  FIG. 2 . Description of  FIG. 6  that is the same as and/or similar to that of  FIG. 4  and/or  FIG. 5  is appropriately simplified or omitted. A transmission antenna  25 B″ illustrated in  FIG. 6  is changed from the transmission antenna  25 B′ illustrated in  FIG. 5  in a configuration of a microstrip line. The configuration illustrated in  FIG. 6  can also provide an effect that is the same as and/or similar to the effect provided by the configuration illustrated in  FIG. 5 . 
     As described above, the electronic device  1  according to the one embodiment includes the transmission antennas  25  that transmit respective transmission waves, the reception antennas  31  that receive respective reflected waves that are the reflected transmission waves, and the control unit  10 . The control unit  10  detects an object that reflects the transmission waves, based on a transmission signal transmitted as the transmission waves and a reception signal received as the reflected waves. 
     In the electronic device  1  according to the one embodiment, the transmission antennas  25  may include a first transmission antenna and a second transmission antenna. Specifically, the transmission antennas  25  include any two of the transmission antennas  25 A,  25 B′, and  25 C′. The first transmission antenna transmits a transmission wave of a first polarization direction. The second transmission antenna transmits a transmission wave of a second polarization direction different from the first polarization direction. 
     In the electronic device  1  according to the one embodiment, the reception antennas  31  may include the plurality of reception antennas  31 A to  31 D that receive reflected waves of an identical polarization direction among the reflected waves that are the reflected transmission waves. 
     The electronic device  1  according to the one embodiment may include a third transmission antenna between the first transmission antenna and the second transmission antenna Specifically, the electronic device  1  according to the one embodiment may include the transmission antenna  25 B′ between the transmission antenna  25 A and the transmission antenna  25 C′. The third transmission antenna transmits a transmission wave of a third polarization direction. An angle between the third polarization direction (45°) and the first polarization direction (for example, 0°) may be smaller than an angle between the first polarization direction (for example, 0°) and the second polarization direction (for example, 90°). The plurality of transmission antennas  25  may be arranged such that the first polarization direction (for example, 0°) and the second polarization direction (for example, 90°) are orthogonal to each other. 
     In the electronic device  1  according to the one embodiment, the polarization direction of the transmission wave transmitted by the transmission antenna  25  that is closer to the reception antennas  31  among the plurality of transmission antennas  25  may be set to be different from the polarization direction of the reflected waves received by the reception antennas  31 . For example, the polarization direction (for example, 90°) of the transmission wave transmitted by the transmission antenna  25  (that is, the transmission antenna  25 C′) that is closer to the reception antennas  31  among the plurality of transmission antennas  25 A to  25 C′ may be set to be different from the polarization direction (for example, 0°) of the reflected waves received by the reception antennas  31 . 
     In the electronic device  1  according to the one embodiment, the polarization direction of the transmission wave transmitted by the transmission antenna  25  that is farther from the reception antennas  31  among the plurality of transmission antennas  25  may be set to be identical to the polarization direction of the reflected waves received by the reception antennas  31 . For example, the polarization direction (for example, 0°) of the transmission wave transmitted by the transmission antenna  25  (that is, the transmission antenna  25 A) that is father from the reception antennas  31  among the plurality of transmission antennas  25 A to  25 C′ may be set to be identical to the polarization direction (for example, 0°) of the reflected waves received by the reception antennas  31 . 
     An operation of transmitting a transmission wave by switching between the plurality of transmission antennas  25  in the electronic device  1  according to the one embodiment is described. The electronic device  1  according to the one embodiment transmits a transmission wave by switching between the plurality of transmission antennas  25  arranged in the above-described manner. 
       FIG. 7  is a diagram for describing switching of the transmission antennas in the electronic device  1  according to the one embodiment. In  FIG. 7 , the horizontal axis represents the elapsed time.  FIG. 7  illustrates a state of transmitting a transmission wave by sequentially switching between the plurality of transmission antennas  25  having different polarization directions with an elapse of time (that is, in a time-division manner). 
     As illustrated in  FIG. 7 , the electronic device  1  according to the one embodiment may transmit a transmission wave from the transmission antenna  25  (for example, the transmission antenna  25 A) of the polarization direction of 0° in the first time interval. The electronic device  1  according to the one embodiment may transmit a transmission wave from the transmission antenna  25  (for example, the transmission antenna  25 B′) of the polarization direction of 45° in the next time interval. The electronic device  1  according to the one embodiment may transmit a transmission wave from the transmission antenna  25  (for example, the transmission antenna  25 C′) of the polarization direction of 90° in the next time interval. The electronic device  1  according to the one embodiment may repeat the above-described switching of the transmission antennas  25  in the next time interval. 
     An operation in the case where the electronic device  1  according to the one embodiment detects an object located at a short distance or detects an object having a large reflection cross section is described as an example below. 
     For example, suppose that the transmission wave is transmitted from the transmission antenna  25 A of the polarization direction of 0° in the first time interval illustrated in  FIG. 7 . In this case, the reception antennas  31  receive a component of the polarization direction of 0° among returning signals that have been reflected off the detection target. The reception antennas  31  also receive a component of the polarization direction of 90° but the reception level is so low. Thus, the component of the polarization direction of 90° is buried in noise components and is not to be detected. 
     Suppose that the transmission wave is transmitted from the transmission antenna  25 B′ of the polarization direction of 45° in the next time interval illustrated in  FIG. 7 . In this case, the reception antennas  31  receive a component of the polarization direction of 0° among returning signals that have been reflected off the detection target. The reception antennas  31  also receive a component of the polarization direction of 45° but the reception level is so low. Thus, the component of the polarization direction of 45° is buried in noise components and is not to be detected. 
     Suppose that the transmission wave is transmitted from the transmission antenna  25 C′ of the polarization direction of 90° in the next time interval illustrated in  FIG. 7 . In this case, the reception antennas  31  receive a component of the polarization direction of 0° among returning signals that have been reflected off the detection target. The reception antennas  31  also receive a component of the polarization direction of 90° but the reception level is so low. Thus, the component of the polarization direction of 90° is buried in noise components and is not to be detected. That is, in the present disclosure, by transmitting a radio wave according to the scheme illustrated in  FIG. 7 , a target having various reflected wave polarization characteristics can be appropriately detected. The reflected wave polarization characteristics are characteristics of how an incident wave is polarized and reflected as a reflected wave. 
     Switching of the transmission antennas illustrated in  FIG. 7  is illustrative. In one embodiment, the transmission antennas may be switched in an order different from the switching order of the transmission antennas illustrated in  FIG. 7 . In one embodiment, the transmission antennas may be switched at random instead of regular repetition as in the switching of the transmission antennas illustrated in  FIG. 7 . The time intervals illustrated in  FIG. 7  may have any time length. All the time intervals illustrated in  FIG. 7  need not have the same time length. 
     As described above, to electronic device  1  according to the one embodiment may transmit a transmission wave by switching between the first transmission antenna and the second transmission antenna. In this case, the electronic device  1  according to the one embodiment may switch between the first transmission antenna and the second transmission antenna at a predetermined timing. Specifically, the electronic device  1  according to the one embodiment may transmit the transmission wave by switching between any two of the transmission antennas  25 A,  25 B′, and  25 C′. 
     The electronic device  1  according to the one embodiment may transmit the transmission wave by switching between the first transmission antenna, the second transmission antenna, and the third transmission antenna. In this case, the electronic device  1  according to the one embodiment may switch between the first transmission antenna, the second transmission antenna, and the third transmission antenna at predetermined timings. Specifically, the electronic device  1  according to the one embodiment may transmit the transmission wave by switching between the transmission antennas  25 A,  25 B′, and  25 C′. 
     An operation in the case where the electronic device  1  according to the one embodiment detects an object having a non-uniform reflection cross section is described as an example next. 
       FIG. 8  is a diagram illustrating an object having a non-uniform reflection cross section. Suppose that the object  200  illustrated in  FIG. 8  has a relatively large reflection cross section at a central portion thereof but has a relatively small reflection cross section at a peripheral portion thereof. That is, the central portion of the object  200  hardly changes the polarization direction when reflecting the transmission wave. For example, the transmission wave transmitted from the transmission antenna  25 A of the polarization direction of 0° is reflected off the central portion of the object  200  such that the polarization direction is maintained substantially at 0°. In this case, the electronic device  1  determines, as the width of the object  200 , a range “a” illustrated in  FIG. 8  at a timing at which the transmission wave of the polarization direction of 0° is transmitted from the transmission antenna  25 A. 
     On the other hand, suppose that the peripheral portion of the object  200  illustrated in  FIG. 8  largely changes the polarization direction when reflecting the transmission wave. For example, the transmission wave transmitted from the transmission antenna  25 A of the polarization direction of 0° is reflected off the peripheral portion of the object  200  such that the polarization direction is changed to 90°. In this case, the electronic device  1  determines, as the width of the object  200 , a range “b” illustrated in  FIG. 8  at a timing at which the transmission wave of the polarization direction of 90° is transmitted from the transmission antenna  25 C′. 
     As described above, by transmitting a plurality of transmission waves having different polarization directions, the electronic device  1  according to the one embodiment can combine the reception results of reflected waves of the transmission waves. By transmitting a plurality of transmission waves having different polarization directions, even if the polarization directions of reflected waves largely change, the electronic device  1  according to the one embodiment can be more likely to receive such reflected waves. The electronic device  1  according to the one embodiment is also effective in detection of an object that is intended to largely change the plane of polarization such as a stealth object, for example. The electronic device  1  according to the one embodiment can complement a range not to be detected with a transmission wave of a single polarization direction. Thus, the electronic device  1  according to the one embodiment can operate to have diversity of the plane of polarization. The electronic device  1  according to the one embodiment can reduce the range not to be detected. 
     A specific example of a procedure of the operation of the electronic device  1  according to the one embodiment is described next. 
       FIG. 9  is a flowchart for describing the operation of the electronic device according to the one embodiment. The operation illustrated in  FIG. 9  may start when the electronic device  1  according to the one embodiment detects an object located around the electronic device  1  (or the sensor  5 ). 
     In response to the start of the operation illustrated  FIG. 9 , the control unit  10  of the electronic device  1  performs control so that a transmission wave is transmitted from the transmission antenna  25  (step S 1 ). It is assumed that the switching order of the plurality of transmission antennas  25  that transmit transmission waves having different polarization directions in step S 1  is previously determined. For example, the transmission antenna  25  that transmits the transmission wave first may be the transmission antenna  25 A (the polarization direction of 0°). 
     After the transmission wave is transmitted in step S 1 , the control unit  10  performs control so that the reflected wave R is received from the reception antennas  31  (step S 2 ). 
     After the reception wave is received in step S 2 , the control unit  10  determines whether a timing at which the electronic device  1  performs detection of an object has come (step S 3 ). The timing at which the electronic device  1  performs detection of an object in step S 3  may be appropriately set depending on the required resolution or the like of the electronic device  1 . 
     If it is determined in step S 3  that it is the timing at which the electronic device performs detection of an object, the control unit  10  detects an object located around the electronic device  1  (or the sensor  5 ) (step S 4 ). In step S 4 , the object detecting unit  14  of the control unit  10  may detect the presence of an object on the basis of an estimation result obtained by at least any of the distance FFT processing unit  11 , the velocity FFT processing unit  12 , and the angle-of-arrival estimating unit  13 . 
     In the electronic device  1  according to the one embodiment, the object detecting unit  14  of the control unit  10  may perform, for example, object detection (for example, clustering) processing from angle information, velocity information, and distance information obtained for each of the plurality of transmission antennas  25  that transmit transmission waves of different polarization directions, for example. The object detecting unit  14  may calculate average power of points constituting the object from the angle information, the velocity information, and the distance information obtained for each of the plurality of transmission antennas  25  that transmit transmission waves of different polarization directions, for example. In the electronic device  1  according to the one embodiment, the object detecting unit  14  may notify an upper-level control CPU such as the ECU  50 , for example, of object detection information or point cloud information obtained for each of the plurality of transmission antennas  25 . 
     Since detection of an object in step S 4  can be performed on the basis of various algorithms or the like by using a known technology of a millimeter wave radar, more detailed description is omitted. After step S 4  illustrated in  FIG. 9 , the control unit  10  may start the processing of step S 1  again. As described above, in the electronic device  1  according to the one embodiment, the control unit  10  may detect an object that reflects the transmission wave on the basis of the transmission signal transmitted as the transmission wave and the reception signal received as the reflected wave. 
     On the other hand, it is determined in step S 3  that it is not the timing at which detection of an object is performed, the control unit  10  determines whether it is a timing at which the transmission antenna  25  that transmits the transmission wave is switched (step S 5 ). The timing at which the transmission antenna  25  is switched in step S 5  may be the timing corresponding to the end of each time interval described in  FIG. 7 . 
     If it is determined in step S 5  that it is not the timing at which the transmission antenna  25  is switched, the process returns to step S 1  and the control unit  10  continues the process. That is, this case, the process is continued without switching the transmission antenna  25 . 
     On the other hand, if it is determined in step S 5  that it is the timing at which the transmission antenna  25  is switched, the control unit  10  switches the transmission antenna  25  that transmits the transmission wave (step S 6 ). For example, if the transmission antenna  25  that has transmitted the transmission wave first is the transmission antenna  25 A. (the polarization direction of 0°), the transmission antenna  25  to which the transmission antenna  25 A is switched in step S 6  may be, for example, the transmission antenna  25 B′ (the polarization direction of 45°). If the transmission antenna  25  that has transmitted the transmission wave is the transmission antenna  25 B′ (the polarization direction of 45°), the transmission antenna  25  to which the transmission antenna  25 B′ is switched in step S 6  may be, for example, the transmission antenna  25 C′ (the polarization direction of 90°). If the transmission antenna  25  that has transmitted the transmission wave is the transmission antenna  25 C′ (the polarization direction of 90°), the transmission antenna  25  to which the transmission antenna  25 C′ is switched in step S 6  may be, for example, the transmission antenna  25 A (the polarization direction of 0°). 
     After the transmission antenna  25  is switched in step S 6 , the process returns to step S 1  and the process is continued. That is, in this case, the process is continued after the transmission antenna  25  is switched. 
     Spatial arrangement of the antennas of the electronic device  1  according to the one embodiment is now described with reference to  FIG. 10 ,  FIG. 10  is a conceptual diagram for describing an example of spatial arrangement of the antennas of the electronic device according to the one embodiment. 
     In  FIG. 10 , three antennas  1001 ,  1003 , and  1005  are arranged on a surface S 2  of an antenna substrate  1010 . These antennas  1001 ,  1003 , and  1005  may be any of the transmission antennas and the reception antennas. In the present disclosure, the number of antennas arranged on the antenna substrate  1010  may be any number other than three. 
     The antenna substrate  1010  is a rectangular parallelepiped having three surfaces S 1 , S 2 , and S 3 . In the present disclosure, the antenna substrate  1010  may have any shape other than a rectangular parallelepiped. 
     As illustrated in  FIG. 10 , a plane parallel to a surface of ground G is denoted as an XY plane. A direction perpendicular to the XY plane is denoted as a Z axis. The surface S 1  of the antenna substrate  1010  is parallel to the XY plane. The surface S 2  of the antenna substrate  1010  is parallel to an XZ plane. The surface S 3  of the antenna substrate  1010  is parallel to a YZ plane. 
     It is assumed that the mobility device  100  equipped with the antenna substrate  1010  travels in the Y-axis direction. In the present disclosure, it may be assumed that the mobility device  100  may travel in a direction other than the Y-axis direction. 
     The three antennas  1001 ,  1003 , and  1005  arranged on the surface S 2  of the antenna substrate  1010  are arranged side by side in the Z-axis direction. In the present disclosure, the three antennas  1001 ,  1003 , and  1005  may be arranged in a direction other than the Z-axis direction. 
     While the present disclosure has been described on the basis of the various drawings and the embodiments, it should be noted that a person skilled in the art can easily make various variations or corrections on the basis of the present disclosure. Therefore, it should be noted that these variations or corrections are within the scope of the present disclosure. For example, functions and the like included in each functional unit can be rearranged without any logical contradiction. A plurality of functional units or the like may be combined into one or may be divided. The embodiments according to the present disclosure described above are not limited to strict implementation according to the respective embodiments described above, and may be implemented by appropriately combining the features or omitting part thereof. That is, a person skilled in the art can make various variations and corrections to the contents of the present disclosure on the basis of the present disclosure. Thus, these variations and corrections are within the scope of the present disclosure. For example, in each embodiment, each functional unit, each means, each step, or the like can be added to another embodiment or replaced with each functional unit, each means, each step, or the like in another embodiment without any logical contradiction. In each embodiment, a plurality of functional units, means, steps, or the like may be combined to one or may be divided. The embodiments according to the present disclosure described above are not limited to strict implementation according to the respective embodiments described above, and may be implemented by appropriately combining the features or omitting part thereof. 
     The embodiments described above are not limited only to implementation as the electronic device  1 . For example, the embodiments described above may be implemented as a method for controlling a device such as the electronic device  1 . For example, the embodiments described above may be implemented as a program for controlling a device such as the electronic device  1 . 
     The electronic device  1  according to one embodiment may include, as the minimum configuration, at least part of at least one of the sensor  5  and the control unit  10 , for example. On the other hand, the electronic device  1  according to one embodiment may appropriately include at least any of the signal generating unit  21 , the synthesizer  22 , the phase control units  23 , the amplifiers  24 , and the transmission antennas  25  illustrated in  FIG. 2  in addition to the control unit  10 . The electronic device  1  according to the one embodiment may appropriately include at least any of the reception antennas  31 , the LNAs  32 , the mixers  33 , the IF units  34 , and the AD conversion units  35  instead of or along with the functional units described above. The electronic device  1  according to the one embodiment may further include the storage unit  40 . As described above, the electronic device  1  according to the one embodiment can employ various configurations. When the electronic device  1  according to the one embodiment is mounted in the mobility device  100 , for example, at least any of the functional units described above may be installed at an appropriate place such as the inside of the mobility device  100 . On the other hand, in one embodiment, for example, at least any of the transmission antennas  25  and the reception antennas  31  may be installed outside the mobility device  100 . 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  electronic device 
               5  sensor 
               10  control unit 
               11  distance FFT processing unit 
               12  velocity FFT processing unit 
               13  angle-of-arrival estimating unit 
               14  object detecting unit 
               15  detection range determining unit 
               16  parameter setting unit 
               20  transmission unit 
               21  signal generating unit 
               22  synthesizer 
               23  phase control unit 
               24  amplifier 
               25  transmission antenna 
               30  reception unit 
               31  reception antenna 
               32  LNA 
               33  mixer 
               34  IF unit 
               35  AD conversion unit 
               40  storage unit 
               50  ECU 
               100  mobility device 
               200  object