Patent Publication Number: US-11385343-B1

Title: Radar device

Description:
On 2020, Ministry of Internal Affairs and Communications, R &amp; D consignment business in the information and communication field (Strategic Information and Communications R&amp;D Promotion Programme strategic information and communication R &amp; D promotion program: SCOPE), patent application subject to Article 17 of the Japanese Industrial Technology Strengthening Law. 
     TECHNICAL FIELD 
     The present invention relates to a radar device. 
     BACKGROUND ART 
     A radar device employs an array antenna having a plurality of antenna elements arranged therein. An array antenna is usable as a phased-array antenna by being configured to be able to control a phase of a radio wave transmitted and received by an antenna element, the phased array antenna being capable of performing a process of changing a direction of the array antenna by controlling the phase of the radio wave transmitted and received. Since a radar device with a phased-array antenna is able to orient an antenna, the radar device may make field intensity (which is also referred to as an “antenna gain”. Hereinafter, the field intensity of radio waves radiated by an antenna is simply referred to as a “gain”.) of radio waves radiated by the antenna in a direction to which the antenna is oriented higher than the field intensity of a radar device that does not orient an antenna. Therefore, a detection available distance of the radar device may be lengthened. 
     The phased-array antenna is able to change the direction of the antenna without using a mechanical structure for changing an antenna direction, the mechanical structure being exemplified by a rotating table to which the antenna is attachable, or the like. Therefore, the phased-array antenna is able to change the direction of the antenna in a shorter time than a case where the antenna direction is changed through the use of the mechanical structure. In addition, since the mechanical structure is not necessary, the phased-array antenna may make an antenna structure simpler than the case where the antenna direction is changed through the use of the mechanical structure. This makes it possible to easily change the direction of antenna, even if an antenna is attached to a device, such as a man-made satellite, etc., that has a wide variety of problems related to changing of the antenna direction through the use of the mechanical structure. 
     By using the phased-array antenna capable of changing the direction of orientation in a short time, a radar device that scans a wide area in a short time may be configured. Therefore, the use of the phased-array antenna may configure the radar device capable of scanning a wide area in a short time and specifying a location of an observed object, or the like, located in the area. 
     For the radar device with the phased-array antenna, a phased-array antenna having antenna elements disposed in a plane (hereinafter, also simply referred to as a “planar phased-array antenna”) is widely used. However, the planar phased-array antenna has a problem that the gain decreases and the detection available distance shortens when receiving a radio wave in a direction away from a direction of a normal of the plane. To solve the problem, various measures have been taken to specify the location of the observed object in the wide area through the use of the phased-array antenna. 
     As an example of the measures, Non-Patent Literature 1 discloses a phased-array antenna that is configured by using eight poles having a multitude of antenna elements. 
     CITATION LIST 
     Non-Patent Literature 
     
         
         Non-Patent Literature 1: Nobuyuki Kaya, “NEW RECEIVING GROUND ANTENNA USING ACTIVE PHASED ARRAY ANTENNA FOR SATELLITES”, (In proceedings of “67 th  International Astronautical Congress (IAC 2016)”), 2016, p. 3159-3162. 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     According to Non-Patent Literature 1, since eight poles having a multitude of antenna elements are used, it is possible to receive radio waves from a wider area than a case where a planar phased-array antenna is used. However, Non-Patent Literature 1 only discloses a receiving phased-array antenna that receives a radio wave and does not disclose a specific method or the like for configuring a radar device using the receiving phased-array antenna. In general, a radar device specifies a location of an observed object by receiving a reflected wave with a receiving antenna, the reflected wave being generated by a transmitting wave illuminating the observed object, and the transmitting wave being transmitted by a transmitting antenna. In order to specify the location of the observed object in a wider area, a configuration of the antenna for transmission to be used in combination with the receiving antenna is important. 
     In a radar device of the prior art, various types of antennae such as a linear antenna, a parabola antenna, and/or a planar phased-array antenna or the like are used as an antenna for transmission for transmitting a transmitting wave. The radar device may further increase a gain in a reflected wave and further lengthen a detection available distance, by orienting the antenna for transmission and the receiving antenna in the same direction. As such, the location of observed object in an even wider area may be estimated. 
     A pole antenna disclosed by Non-Patent Literature 1 is configured by disposing a multitude of antenna elements on poles. The pole antenna (which is also called as a “linear array antenna” because antenna elements are arrayed linearly along the poles, and hereinafter simply referred to as the “linear array antenna”) is used by being oriented to a direction in which the gain of radio waves from a conical surface area to the antenna is large, the conical surface area having a longitudinal direction of the antenna as a central axis. The “conical surface area” used herein is an area that includes a side surface of a cone and an area adjacent to the side surface and that does not include the inside of the cone. In contrast, the aforementioned various types of antennae are used by being oriented to a direction in which the gain of radio waves from a linear range to the antenna is large. As such, it is not easy to orient the aforementioned various types of antennae to the same direction as the direction to which the phased-array antenna of Non-Patent Literature 1 is oriented. Hence, there is a further problem to be solved when the radar device is configured by combining the phased-array antenna of Non-Patent Literature 1 with the antenna for transmission. 
     The present invention has been made in view of such circumstances. An objective of the present invention is to provide a radar device that is able to instantly estimate a location of an observed object in a wide area, by using a phased-array antenna capable of receiving a reflected wave from a wider area than a case where a planar phased-array antenna is used. 
     Means for Solving the Problems 
     As a result of diligent study of the aforementioned problems, the inventors have found that it is possible to achieve the aforementioned objective by making processes feasible, and have completed the present invention, the processes including a linear array antenna transmitting a transmitting wave; the linear array antenna receiving a reflected wave, the reflected wave being generated by the transmitting wave illuminating an observed object; and estimating a location of the observed object by using time from transmission of the transmitting wave to reception of the reflected wave and direction of the transmitting wave, and/or by using a frequency of the transmitting wave, a frequency of the reflected wave, and the direction of the transmitting wave. Specifically, the present invention provides the following. 
     An invention according to a first characteristic provides a radar device that includes one or more linear array antennae and a controller, the controller being able to perform a process of at least the one or more linear array antennae transmitting a transmitting wave; a process of at least the one or more linear array antenna receiving a reflected wave, at least the one or more linear array antenna being the same as and/or different from the linear array antenna that transmits the transmitting wave and the reflected wave being generated by the transmitting wave illuminating an observed object; and a process of estimating a location of the observed object by using time from transmission of the transmitting wave to reception of the reflected wave, and the direction of the transmitting wave, and/or by using a frequency of the transmitting wave and a frequency of the reflected wave, and the direction of the transmitting wave. 
     First, it is described that the linear array antenna is able to receive the reflected wave from a wider area than a planar phased-array antenna or the like. In general, the planar phased-array antenna is controlled so that the gain of reflected wave toward the antenna from a linear range along a direction to which the planar phased-array antenna is oriented is large. This allows the planar phased-array antenna to receive the reflected wave towards the antenna from the linear range in the direction to which the planar phase array antenna is oriented. 
     In contrast to this, it is possible to control the linear array antenna in a direction in which the gain of the reflected wave toward the antenna from a conical surface area having a longitudinal direction of the linear array antenna as a central axis is large. This allows the linear array antenna to receive the reflected wave from the conical surface area in a direction of orientation towards the antenna. Then, the conical surface area is wider than the linear range. Therefore, according to the invention related to the first characteristic, the phased-array antenna may be configured that is able to receive the reflected wave from a wider area than a case where the planar phased-array antenna is used. 
     Subsequently, description is given of a direction of the antenna when transmitting the transmitting wave. The radar device may further increase the gain in the reflected wave and further lengthen the detection available distance, by orienting the antenna for transmission and the receiving antenna to the same direction. As such, the radar device may estimate the location of the observed object in an even wider area. 
     According to the invention related to the first characteristic, since the transmitting wave is transmitted by using the linear array antenna and the reflected wave is received by using the linear array antenna, the direction of the linear array antenna when transmitting the transmitting wave and the direction of the linear antenna when receiving the reflected waves may be made the same as a conical surface direction. Therefore, the gain related to the reflected wave may be increased and the detection available distance of the radar device may be made even longer. Hence, according to the invention related to the first characteristic, the location of the observed object in a wide area may be estimated. 
     Description is given of a process of the radar device estimating the location of the observed object. The direction from the linear array antenna to the location of the observed object where the reflected wave is generated is the same direction as the direction of the transmitting wave. According to the invention related to the first characteristic, the transmitting wave is transmitted by using the linear array antenna oriented to the conical surface direction. Therefore, the location of the observed object is included in this conical surface and a periphery thereof. The time from the transmission of the transmitting wave to the reception of the reflected wave varies depending on a distance from the linear array antenna to the location of the observed object. Therefore, the distance from the linear array antenna to the location of the observed object may be measured by using the time from the transmission of the transmitting wave to the reception of the reflected wave. If the transmitting wave is frequency modulated, a difference between the frequency of the transmitting wave and the frequency of the reflected wave varies depending on the distance from the linear array antenna to the location of the observed object. Therefore, the distance from the linear array antenna to the location of the observed object may be measured by using the difference. 
     A location of the apex of the conical surface is the same as that of the linear array antenna. Therefore, a space that is included in the conical surface and the periphery thereof and where the distance from the linear array antenna satisfies the measured distance is an approximately circular space. Therefore, it is possible to estimate that the location of the observed object is the location included in the aforementioned approximately circular space, by performing the process of estimating the location of the observed object by using the time from the transmission of the transmitting wave to the reception of the reflected wave and the direction of the transmitting wave, and/or by using the frequency of the transmitting wave, the frequency of the reflected wave, and the direction of the transmitting wave. According to the invention related to the first characteristic, the reflected wave from the location of the observed object in the conical surface area may be received approximately simultaneously, without changing the direction of the linear array antenna. Therefore, the location of the observed object in the conical surface area, which is wider than the linear range, may be estimated in a shorter time than a case where the direction of the linear array antenna is changed. As such, the location of the observed object in the wide area may be estimated instantly. 
     Hence, according to the invention related to the first characteristic, it is possible to provide the radar device that is able to instantly estimate the location of the observed object in a wide area, using the phased-array antenna capable of receiving the reflected wave from a wider area than a case where a planar phased-array antenna is used. 
     An invention according to a second characteristic is the invention according to the first characteristic, and provides a radar device in which the linear array antenna that transmits the transmitting wave is also the linear array antenna that receives the reflected wave in the process of receiving the reflected wave. 
     According to the invention related to the second characteristic, it is possible to receive the reflected wave at a location of the linear array antenna that transmits the transmitting wave. As such, the direction of the transmitting wave and the direction of the reflected wave match better than a case where the reflected wave is received at a different location from the linear array antenna that transmits the transmitting wave. Therefore, the gain related to the reflected wave may be increased without changing the direction of the linear array antenna between the transmission of the transmitting wave and the reception of the reflected wave. Consequently, the detection available distance of the radar device may be made even longer. Hence, according to the invention related to the second characteristics, the location of the observed object in a wide area may be estimated. 
     According to the invention related to the second characteristic, it is possible to transmit the transmitting wave without having another antenna for transmitting a transmitting wave. As such, the radar device may be configured to have a simpler structure than the radar having the other antenna for transmitting the transmitting wave. Hence, cost performance and/or maintainability or the like of the radar device may be improved. 
     Hence, according to the invention related to the second characteristic, it is possible to provide the radar device that is able to instantly estimate the location of the observed object in a wide area, using the phased-array antenna capable of receiving the reflected wave from a wider area than a case where a planar phased-array antenna is used. 
     An invention according to a third characteristic is the invention according to the first or second characteristic. The invention according to the third characteristic provides a radar device wherein the number of the linear array antennae is two or more, the two or more linear array antennae being disposed parallel to each other in a longitudinal direction, and wherein the process of receiving the reflected wave includes a process of at least the two or more linear array antennae receiving the reflected wave, and the process of estimating the location of the observed object includes a process of specifying two locations. 
     According to the invention related to the third characteristic, it is possible to specify an approximately circular space by using time until each of the two or more linear array antennae receive the reflected wave and/or each of frequencies of the reflected waves. It is possible to specify two intersecting points by using this approximately circular space, the time from the transmission of the transmitting wave to the reception of the reflected wave, and the direction of the transmitting wave, and/or by using the approximately circular space that is estimated by using the frequency of the transmitting wave, the frequency of the reflected wave, and the direction of the transmitting wave. Therefore, it is possible to configure so that the process of estimating the location of the observed object includes the process of specifying the two locations. 
     According to the invention related to the third characteristic, the two or more linear array antennae are disposed approximately parallel to each other in the longitudinal direction. This makes it possible to orient each of the two or more linear array antennae to the approximately the same direction. Therefore, each of the two or more linear array antennae is able to each increase the gain related to the reflected wave. 
     Hence, according to the invention related to the third characteristic, it is possible to provide the radar device that is able to instantly estimate the location of the observed object in a wide area, using the phased-array antenna capable of receiving the reflected wave from a wider area than a case where a planar phased-array antenna is used. 
     An invention according to a fourth characteristic is the invention according to the third characteristic, and provides a radar device wherein the linear array antenna that transmits the transmitting wave differs from the linear array antenna that receives the reflected wave. 
     According to the invention related to the fourth characteristic, it is possible to transmit the transmitting wave even when receiving the reflected wave. This may cause more transmitting waves to illuminate the observed object and generate more reflected waves. Therefore, more reflected waves may be received and the location of the observed object may be estimated even more reliably. 
     Hence, according to the invention related to the fourth characteristic, it is possible to provide the radar device that is able to instantly estimate the location of the observed object in a wide area, using the phased-array antenna capable of receiving the reflected wave from a wider area than a case where a planar phased-array antenna is used. 
     An invention according to a fifth characteristic is the invention according to the third or fourth characteristic. The invention according to the fifth characteristic provides a radar device wherein the transmitting wave is a frequency modulated transmitting wave, the linear array antenna that receives the reflected wave is the linear array antenna different from the linear array antenna that transmits the transmitting wave, and the controller is further able to perform a process of removing the transmitting wave from the reflected wave and a process of measuring the time using the frequency of the transmitting wave and the frequency of the reflected wave. 
     According to the invention related to the fifth characteristic, it is possible to continuously transmit the frequency modulated transmitting wave, and to receive the reflected wave with the linear array antenna different from the linear array antenna that transmits the transmitting wave. This may cause more transmitting waves to illuminate the observed object and generate more reflected waves. 
     In order to measure the time from the transmission of the transmitting wave to the reception of the reflected wave, it is necessary to identify when the transmitting wave that generates the reflected wave is transmitted. However, if a transmitting wave that is not frequency modulated is transmitted continuously, it is difficult to identify when the transmitting wave that generates the reflected wave is transmitted. Therefore, if the transmitting wave that is not frequency modulated is transmitted continuously, it may be difficult to measure the time from the transmission of the transmitting wave to the reception of the reflected wave. According to the invention related to the fifth characteristic, since the frequency modulated transmitting wave is transmitted, it may be identified when the transmitting wave that generates the reflected wave is transmitted, by using the frequency of the transmitting wave and the frequency of the reflected wave. This makes it possible to measure the time from the transmission of the transmitting wave to the reception of the reflected wave. 
     Therefore, according to the invention related to the fifth characteristic, generation of more reflected waves in the observed object and measurement of the time from the transmission of the transmitting wave to the reception of the reflected wave to may be achieved simultaneously. As such, more reflected waves may be received and the location of the observed object may be estimated even more reliably. 
     If the transmitting wave is transmitted continuously, the linear array antenna may also receive the transmitting wave when receiving reflected wave. The received transmitting wave may become noise in processing using the reflected wave. According to the invention according to the fifth characteristic, the process of removing the transmitting wave from the reflected wave may be performed, thereby preventing the received transmitting wave from becoming noise. 
     Hence, according to the invention related to the fifth characteristic, it is possible to provide the radar device that is able to instantly estimate the location of the observed object in a wide area, using the phased-array antenna capable of receiving the reflected wave from a wider area than a case where a planar phased-array antenna is used. 
     An invention according to a sixth characteristic is the invention according to any of the first to fifth characteristics. The invention according to the sixth characteristic provides a radar device wherein the number of the linear array antennae is three or more, the three or more linear array antennae being disposed to each other in the longitudinal direction, and wherein the process of receiving the reflected wave includes a process of at least the three or more linear array antennae receiving the reflected wave, and the process of estimating the location of the observed object includes the process of specifying the location of the observed object. 
     According to the invention related to the sixth characteristic, it is possible to specify three or more approximately circular spaces by using the reflected waves received by each of the three or more linear array antennae. Then, it is possible to specify the location of the observed object by using an intersecting point of these three or more approximately circular spaces. 
     According to the invention related to the sixth characteristic, the three or more linear array antennae are disposed parallel to each other in the longitudinal direction. This may orient each of the three or more linear array antennae to the approximately the same direction. Therefore, each of the three or more linear array antennae may improve the gain related to the reflected wave. 
     Hence, according to the invention related to the sixth characteristic, it is possible to provide the radar device that is able to instantly estimate the location of the observed object in a wide area, using the phased-array antenna capable of receiving the reflected wave from a wider area than a case where a planar phased-array antenna is used. 
     An invention according to a seventh characteristic is the invention according to any of the first to sixth characteristics, and provides a radar device wherein the controller is further able to perform a process of controlling the phase of the transmitting wave and the phase of the reflected wave to control the direction of the one or more linear array antennae to be a direction from the one or more linear array antennae toward the observed object. 
     According to the invention related to the seventh characteristic, by controlling the direction of the linear array antenna to be the direction from the one or more linear array antennae toward the observed object, the gain of the transmitting wave that illuminates the observed object may be further increased. Furthermore, the gain of the reflected wave to be received may be further increased. Since both the gain of the transmitting wave illuminating the observed object and the gain of the reflected wave may be increased, the detection available distance of the radar device may be made even longer. Therefore, the location of the observed object in an even wider area may be estimated. 
     Hence, according to the invention related to the seventh characteristic, it is possible to provide the radar device that is able to instantly estimate the location of the observed object in a wide area, using the phased-array antenna capable of receiving the reflected wave from a wider area than a case where a planar phased-array antenna is used. 
     An invention according to an eighth invention is the invention according to any of the first to seventh characteristic, and provides a radar device wherein the process of transmitting the transmitting wave includes a process of transmitting the transmitting wave intermittently. 
     According to the invention related to the eighth characteristic, since the transmitting wave is transmitted intermittently, the reflected wave may be easily associated with the transmitting wave that generates the reflected wave. This makes it possible to easily measure the time from the transmission of the transmitting wave to the reception of the reflected wave. 
     According to the invention related to the eighth characteristic, while the linear array antenna is not transmitting the transmitting wave, the reflected wave may be received by that linear array antenna. Therefore, it is possible to receive the reflected wave without having another antenna for receiving the reflected wave. As such, the radar device may be configured to have a simper structure than the radar device having another antenna for receiving the reflected wave. Hence, the cost performance and/or maintainability or the like of the radar device may be improved. 
     Hence, according to the invention related to the eighth characteristic, it is possible to provide the radar device that is able to instantly estimate the location of the observed object in a wide area, using the phased-array antenna capable of receiving the reflected wave from a wider area than a case where a planar phased-array antenna is used. 
     An invention according to ninth characteristic is the invention according to any of the first to eighth characteristics, and provides a radar device wherein the transmitting wave and the reflected wave include radio waves and/or sonic waves. 
     According to the invention related to the ninth characteristic, the transmitting wave including radio waves and/or sonic waves may be transmitted to a wide range without being affected by the atmosphere, clouds, and fog or the like that attenuate visible light rays. Further, the reflected wave including radio waves and/or sonic waves may be received from a wide range without being affected by the atmosphere, the clouds, and the fog or the like that attenuate the visible light rays. Therefore, it is possible to provide the radar device that is able to estimate the location of the observed object in an even wider area. 
     Hence, according to the invention related to the ninth characteristic, it is possible to provide the radar device that is able to instantly estimate the location of the observed object in a wide area, using the phased-array antenna capable of receiving the reflected wave from a wider area than a case where a planar phased-array antenna is used. 
     Effect of the Invention 
     According to the present invention, it is possible to provide a radar device that is able to instantly estimate a location of an observed object in a wide area, by using a phased-array antenna capable of receiving a reflected wave from a wider area than a case where a planar phased-array antenna is used. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a radar device  1  in a first embodiment of the present invention, when it is viewed from diagonally above. 
         FIG. 2  is a conceptual diagram illustrating a transmitting wave T transmitted by an antenna element  44  and a reflected wave R received by the antenna element  44 . 
         FIG. 3  is a flowchart illustrating an example of a flow of a location estimation process to be performed by a controller  2 . 
         FIG. 4  is a conceptual diagram illustrating a transmitting wave T to be transmitted from an antenna for transmission P of the prior art. 
         FIG. 5  is a conceptual diagram illustrating a transmitting wave T that is transmitted from a linear array antenna  4  and oriented in a conical surface shape. 
         FIG. 6  is a conceptual diagram illustrating that a feedback signal F is used to reduce interference Ti of the transmitting wave. 
         FIG. 7  is a conceptual diagram illustrating a process of estimating a location of an observed object O 1 , by using a direction of the transmitting wave T and time until a first linear array antenna  4   a  receives a first reflected wave R 1 . 
         FIG. 8  is a conceptual diagram illustrating a process of specifying two locations including the location of the observed object O 1 , by using the direction of the transmitting wave T, until each of the first linear array antenna  4   a  and a second linear array antenna  4   b  receives the first reflected wave R 1 , and detection of an arrival angle. 
         FIG. 9  is a conceptual diagram illustrating a process of specifying a location of the observed object O 1 , by using the direction of the transmitting wave T, time until each of the first linear array antenna  4   a , the second linear array antenna  4   b , and a third linear array antenna  4   c  receives the first reflected wave R 1 , and the detection of the arrival angle. 
         FIG. 10  is a conceptual diagram of a radar device  101  of a second embodiment of the present invention when viewed from diagonally above. 
         FIG. 11  is a flowchart illustrating an example of a flow of a specification process to be performed by a controller  102 . 
         FIG. 12  is a conceptual diagram illustrating a second transmitting wave T 2  transmitted from a parabola antenna C of the prior art. 
         FIG. 13  is a conceptual diagram illustrating a fourth transmitting wave T 4  and a fifth transmitting wave T 5  transmitted from the radar device  101 . 
         FIG. 14  is a conceptual diagram illustrating a process of specifying a distance to the observed object O 1 , by using time until the first reflected wave R 1  is received. 
         FIG. 15  is a conceptual diagram illustrating a process of specifying an approximately circular region including a location of an observed object O 6 , by using time until a first omni-directional antenna  104   a  and a second omni-directional antenna  104   b  each receive a sixth reflected wave R 6 . 
         FIG. 16  is a conceptual diagram illustrating a process of specifying the two locations including the location of the observed object O 6 , by using time until each of the first omni-directional antenna  104   a , the second omni-directional antenna  104   b , and a third omni-directional antenna  104   c  receives the sixth reflected wave R 6 , and the detection of the arrival angle. 
         FIG. 17  is a conceptual diagram illustrating a process of specifying the location of the observed object O 6 , by using the time until each of the first omni-directional antenna  104   a , the second omni-directional antenna  104   b , the third omni-directional antenna  104   c , and a fourth omni-directional antenna  104   d  receives the sixth reflected wave R 6 , and the detection of the arrival angle. 
         FIG. 18  is a conceptual diagram illustrating a communication system using the radar device  101 . 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     In the following, description is given of an example of a preferred aspect for carrying out the present invention with reference to the figures. It is to be noted that this is merely an example and the technical scope of the present invention is not limited thereto. 
     First Embodiment 
     A radar device of a first embodiment is a radar device in which an antenna is a linear array antenna orientable in a conical surface shape. 
     &lt;Radar Device  1 &gt; 
       FIG. 1  is a schematic diagram of a radar device  1  in the first embodiment of the present invention when viewed from diagonally above. In the following, with reference to  FIG. 1 , description is given of an example of a preferred configuration of the radar device  1  in the first embodiment of the present invention. 
     The radar device  1  includes a controller  2 , a transmitter  3 , and one or more linear array antennae  4  (reference numerals  4   a  to  4   c  in  FIG. 1 ). Each of the one or more linear array antennae  4  is a linear array antenna having antenna elements arranged to be arrayed linearly/in which antenna elements are arranged to be arrayed linearly. 
     It is possible to use a linear array antenna by orienting the antenna to a conical surface area, a central axis of the conical surface being a longitudinal direction of the antenna. The “conical surface area” as used herein is an area that includes a side surface of a cone and an area adjacent to the side surface and that does not include the inside of the cone. By orienting the antenna, it is possible to make intensity (which is also referred to as an “antenna gain”. Hereinafter, the field intensity of radio waves radiated by an antenna is simply referred to as a “gain”.) of waves radiated by the antenna in a direction to which the antenna is oriented. Further, by orienting the antenna, it is possible to improve efficiency of converting into a digital signal the reflected wave received from the direction in which the antenna is oriented. 
     It is preferable that the radar device  1  further include a support structure  5  capable of supporting the one or more linear array antennae  4 , although it is not an essential aspect. Inclusion of the support structure  5  allows the one or more linear array antennae  4  to be supported by the support structure  5  so that each of these one or more linear array antennae  4  maintains a predetermined positional relationship. This makes it possible to easily perform a process of estimating a location of an observed object, which is described below. 
     [Controller  2 ] 
     The controller  2  controls the transmitter  3  and the one or more linear array antennae  4 . The controller  2  also performs a location estimation process for specifying a space that includes the location of the observed object, by using time from when the one or more linear array antennae  4  transmit the transmitting wave until each of the one or more linear array antennae receives the reflected wave. The location estimation process to be performed by the controller  2  is described in detail below with reference to  FIG. 3 . Since the radar device  1  includes the controller  2 , it is possible to perform the location estimation process and estimate the location of the observed object. 
     The controller  2  is not specifically limited. The controller  2  may be a prior-art microcomputer including, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory) or the like. 
     The controller  2  is configured to be able to acquire each piece of reflected wave information regarding the reflected wave received by the one or more linear array antennae  4 . Each piece of the reflected wave information includes information that allows for measurement of the time from when the linear array antenna  4  transmits the transmitting wave until the receiving linear array antenna  4  receives the reflected wave. 
     The controller  2  is configured to be able to change a direction of the linear array antenna  4  by controlling the phase of the transmitting wave and that of the reflected wave. As such, a direction of the transmitting wave may be controlled to be a direction from the linear array antenna  4  toward the observed object, and the efficiency of converting the reflected wave from the observed object into an electric signal in the linear array antenna  4  may be improved. 
     The controller  2  is preferably configured to be able to output the location of the observed object estimated by the location estimation process. Means for outputting the location of the observed object is not specifically limited, and may be various means used by a prior-art radar device to output the location of the observed object. 
     The controller  2  is preferably able to receive various instructions from a user who uses the radar device  1 . Examples of various instructions include an instruction to start transmission of the transmitting wave, an instruction to stop the transmission of the transmitting wave, and/or an instruction to change the direction of the linear array antenna  4 , or the like. Because the controller  2  is able to receive the various instructions from the user who uses the radar device  1 , the radar device  1  may be controlled in response to the user&#39;s instruction. 
     [Transmitter  3 ] 
     The transmitter  3  is a transmitter capable of providing a transmission signal that causes the linear array antenna  4  to transmit the transmitting wave. The transmitter  3  is connected to the controller  2  and the one or more linear array antennae  4 . The transmitter  3  is configured to be able to provide the one or more linear array antennae  4  with the transmission signal in accordance with the control of the controller  2 . The transmitter  3  is not specifically limit and may be a transmitter of the prior art. The transmitter  3  may be a transmitter including, for example, an oscillator that oscillates a transmission signal and a modulator that modulates the transmission signal or the like. The radar device  1  including the transmitter  3  makes it possible to transmit the transmitting wave to the one or more linear array antennae  4  via the transmission signal. 
     The transmitter  3  is preferably able to provide a pulse wave transmission signal that causes transmission of a transmitting wave that is a pulse wave, although it is not an essential aspect. A pulse wave is a transmitting wave that is intermittently transmitted. Since the pulse wave is transmitted intermittently, it is easy to associate the transmitting wave with the reflected wave. As such, the time from the transmission of the transmitting wave to the reception of the reflected wave may be measured, by using time from transmission of the pulse wave to the reception of the reflected wave. 
     The transmitter  3  is preferably able to provide a chirp wave transmission signal that causes transmission of a transmitting wave that is a chirp wave, although it is not an essential aspect. A chirp wave is a transmitting wave that is transmitted intermittently, and that is a transmitting wave a frequency of which increases with time or a transmitting wave a frequency of which decreases with time. Since the frequency of the chirp wave increases or decreases with time, it is possible to measure elapsed time from the transmission of the chirp wave using the frequency of the chirp wave. This makes it possible to measure the time from the transmission of the transmitting wave to the reception of each reflected wave, by using the frequency of the reflected wave. Consequently, even if the chirp wave is transmitted for a longer period of time than the pulse wave, it is possible to accurately measure the time until the reflected wave is received. Therefore, it is possible to cause more transmitting waves to illuminate the observed object. Then, it is possible to cause more reflected waves to be generated in the observed object. Therefore, the linear array antenna  4  is able to receive more reflected waves than a case where the transmitting wave is the pulse wave. As such, the location of the observed object may be estimated more reliably. 
     A frequency modulated continuous wave (also referred to as a FM-CW) is a continuous wave a frequency of which is modulated. Since the frequency of the frequency modulated continuous wave is frequency modulated, it is possible to measure elapsed time from the transmission of the frequency modulated continuous wave, by using the frequency of the frequency modulated continuous wave. 
     The transmitter  3  is preferably able to provide a frequency modulated continuous wave transmission signal that causes the linear array antenna  4  to transmit a transmitting wave which is a frequency modulated continuous wave, although it is not an essential aspect. As such, it is possible to measure the time from the transmission of the transmitting wave to the reception of each reflected wave by using a comparison of the frequency of the transmitting wave and the frequency of the reflected wave. 
     The frequency modulated continuous wave is a continuous wave. Therefore, if the transmitting wave is the frequency modulated continuous wave, more transmitting waves may illuminate the observed object than a case where the transmitting wave is a pulse wave and/or a chirp wave. Then, more reflected waves may be generated in the observed object. Therefore, because the transmitter  3  is able to provide the frequency modulated continuous wave transmission signal, the linear array antenna  4  may receive more reflected ways than a case where the transmitting wave is a pulse wave and/or a chirp wave that is intermittently transmitted. As such, the location of the observed object may be estimated more reliably. 
     The transmitter  3  is preferably able to provide a wireless communication signal that causes the linear array antenna  4  to transmit a transmitting wave which is used in wireless communications, although it is not an essential aspect. This makes it possible to transmit to the linear array antenna  4  the transmitting wave to be used for wireless communications. 
     [Linear Array Antenna  4 ] 
     The linear array antenna  4  is a linear array antenna that is able to transmit a transmitting wave in accordance with a transmission signal provided from the transmitter  3  and to receive a reflected wave that is generated by the transmitting wave illuminating the observed object. Each of the one or more linear array antennae  4  includes a linear array antenna structure  41 , a signal distributor  42 , a plurality of phase shifters  43 , a plurality of antenna elements  44 , and a converter  45 . If there is a plurality of the linear array antennae  4 , the plurality of linear array antennae  4  are disposed so that respective longitudinal directions are approximately parallel to each other. Each of the one or more linear array antennae  4  is connected to the controller  2  and the transmitter  3 . Each of the one or more linear array antennae  4  is configured to be controllable by the controller  2 . 
     Because the radar device  1  includes the one or more linear array antennae  4 , it is possible to receive reflected waves from a wider area than a planar phased-array antenna or the like. Because the radar device  1  includes the one or more linear array antennae  4 , it is possible to perform the process of estimating the location of the observed object by using the time from the transmission of the transmitting wave to the reception of the reflected wave and a direction of the transmitting wave. The process of estimating the location of the observed object is described below in detail with reference to  FIG. 7 . 
     It is preferable that the number of the linear array antennae  4  be two or more, and these two or more linear array antennae  4  be disposed approximately parallel to each other in the longitudinal direction, although it is not an essential aspect. This makes it possible to perform a process of specifying two locations including the location of the observed object. The process of specifying the two locations including the location of the observed object is described below in detail with reference to  FIG. 8 . 
     It is preferable that the number of linear array antennae  4  be three or larger, and these three or more linear array antennae  4  be disposed approximately parallel to each other in the longitudinal direction, although it is not an essential aspect. This makes it possible to perform the process of specifying the location of the observed object. The process of specifying the location of the observed object is described below in detail with reference to  FIG. 9 .  FIG. 1  illustrates a first linear array antenna  4   a , a second linear array antenna  4   b , and a third linear array antenna  4   c  which are disposed approximately parallel to each other in the longitudinal direction. 
     It is described that the linear array antenna  4  is able to receive the reflected waves from a wider area than the planar phased-array antenna or the like. In general, the planar phased-array antenna is controlled to efficiently receive the reflected waves toward the antenna from a linear region along the direction in which the planar phased-array antenna is oriented. As such, the planar phased-array antenna is able to receive the reflected waves towards the antenna from the linear region in the direction in which the planar phased-array antenna is oriented. 
     In contrast, it is possible to control the linear array antenna  4  to a direction in which the reflected waves toward the antenna from a conical surface area are efficiently received, the central axis of the conical surface area being the longitudinal direction of the linear array antenna  4 . As such, the linear array antenna  4  may receive the reflected waves toward the antenna from the conical surface area in the direction in which the linear array antenna  4  is oriented. Then, the conical surface area is wider than the linear range. Therefore, because the radar device  1  includes the linear array antenna  4 , the phased-array antenna may be configured that is able to receive the reflected wave from a wider area than the case where the planar phased-array antenna is used. 
     It is preferable that the number of the phase shifters  43  included in each of the one or more linear array antennae  4  be any of the number being one smaller than the number of the antenna elements  44 , the number being the same as the number of the antenna elements  44 , or the number being larger than the number of the antenna elements  44 , although it is not an essential aspect. Because the number of the phase shifters  43  is any of these numbers, the phase of the transmitting wave transmitted by each of the plurality of the antenna elements  44  may be controlled. In addition, as such, the phase of a reflected wave received by each of the plurality of antenna elements  44  may be controlled. Therefore, the direction of the linear array antenna  4  may be controlled. Hereinafter, description is given as both of the number of the phase shifters  43  included and the number of the antenna elements in each of the one or more linear array antennae  4  being a predetermined number “np”. 
     [Linear Array Antenna Structure  41 ] 
     The linear array antenna structure  41  is configured to be able to support various components included in the linear array antennae  4 , such as the plurality of antenna elements  44 . This makes it possible to dispose each of the plurality of antenna elements  44  so as to configure the linear array antenna. 
     [Signal Distributor  42 ] 
     The signal distributor  42  distributes transmission signals provided from the transmitter  3  and provides them to each of the plurality of phase shifters  43 . Further, the signal distributor  42  synthesizes respective reflected waves provided via the respective phase shifters  43  and provides them to the converter  45 . 
     The signal distributor  42  makes it possible to provide the transmission signal to each of the plurality of phase shifters  43  even when the transmitter  3  is not a transmitter capable of generating a plurality of transmission signals. Even when each of the reflected waves provided via each of the plurality of phase shifters  43  is weak, the signal distributor  42  may provide the converter  45  with a stronger reflected wave in a form of an analog signal, the stronger reflected wave being obtained by synthesizing these reflected waves. 
     The signal distributor  42  is a signal distributor that is also usable as a synthesizer. Hereinafter, a signal distributor also usable as a synthesizer is simply referred to as a “signal distributor” regardless of use thereof. The signal distributor  42  is not specifically limited, and may be a signal distributor of the prior art that is exemplified by, for example, a resistance distributor, a Wilkinson distributor, and a hybrid distributor or the like. The distributor  42  may be a distributor that is a combination of two or more distributors of the prior art. 
     The signal distributor  42  preferably includes a ladder-type distributor, among others. The ladder-type distributor is a distributor having a transformer, a first signal distributor transmission path, and p second signal distributor transmission paths. A characteristic impedance of the ladder-type distributor Z P [Ω] is not specifically limited. 
     The first signal distributor transmission path is a transmission path end of which is connected to the transformer. The first signal distributor transmission path has an impedance of Z P /p[Ω]. 
     The p second signal distributor transmission paths are transmission paths connected to the first signal distributor transmission path with a gap of d P [m] from each other. Each of the p second signal distributor transmission paths is configured to be able to provide the phase shifter  43  for transmission with a transmission signal. Each of the p second signal distributor transmission paths has the impedance of Z P [Ω]. 
     Although the gap d P [m] is not specifically limited, it is preferable that the gap d P [m] be approximately the same as a wavelength λ[m] of the transmission signal. Because the gap d P [m] is approximately the same as λ[m], the phase of the transmission signal provided via the signal distributor  42  may be made approximately the same in the phase shifter  43  for transmission. 
     Although the number p of the second transmission paths is not specifically limited, the number p is preferably a number that satisfies p=n P  or p=n P /2. Because the number p of the second transmission paths is the number that satisfies p=n P , the transmission signals may be distributed to the n P  phase shifters  43  by the ladder type distributor. Further, the reflected wave provided by the n P  phase shifters  43  may be synthesized by the ladder-type distributor. Because the number p of the second transmission paths is the number that satisfies p=n P , the prior-art distributor capable of distributing the transmission signal into two and exemplified by the Wilkinson distributor or the like may be combined with the ladder type distributor to distribute the transmission signal to the n P  phase shifters  43 . Moreover, the prior-art distributor capable of synthesizing two reflected waves and exemplified by the Wilkinson distributor or the like may be combined with the ladder-type distributor to synthesize the reflected waves provided by the n P  phase shifters  43 . 
     The transformer is a transformer capable of changing a voltage and/or a current and is connected to the transmitter  3 . The transformer has the impedance of Z P [Ω]. The transformer includes a signal distributor transmission path connection unit connected to the first signal distributor transmission path, an external connection unit connected to the transmitter  3  and the converter  45 , and a signal distributor intermediate unit connecting the signal distributor transmission path connection unit and the external connection unit. The intermediate unit has a length of d p /p[m]. The impedance Z P0 [Ω] of the signal distributor transmission path connection unit, the impedance Z P1 [Ω] of the signal distributor intermediate unit, and the impedance Z P2 [Ω] of the external connection unit satisfy the following expression (1): 
     [Mathematical Expression (1)] 
     
       
         
           
             
               
                 
                   
                     Z 
                     
                       P 
                       ⁢ 
                       1 
                     
                   
                   = 
                   
                     
                       
                         Z 
                         
                           P 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           0 
                         
                       
                       ⁢ 
                       
                         Z 
                         
                           P 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Because the signal distributor  42  includes the ladder-type distributor, the transmission signals may be distributed to an arbitrary number of the phase shifters  43 , while maintaining impedance matching. As such, if the predetermined number n P  is a large number, the transmission signals may be distributed to the n P  phase shifters  43 , while maintaining the impedance matching. 
     Because the signal distributor  42  includes the ladder-type distributor, the reflected wave provided by the arbitrary number of phase shifters  43  may be synthesized, while maintaining the impedance matching. As such, if the predetermined number n P  is a large number, the reflected waves provided by the arbitrary number of phase shifters  43  may be synthesized, while maintaining the impedance matching. 
     [Phase Shifter  43 ] 
     The phase shifters  43  is a phase shifter that controls the phase of a transmission signal distributed by the signal distributor  42  and provides it to the antenna element  44 . The phase shifter  43  is also a phase shifter that controls the phase of the reflected wave provided from the antenna elements  44 . The phase shifter  43  is configured to be controllable by the controller  2 . The phase shifter  43  is not specifically limited, and may be a phase shifter of the prior art. By the phase shifter  43  controlling the phase of the transmission signal provided to the antenna element  44 , the direction of a transmitting wave may be controlled. Further, by the phase shifter  43  controlling the phase of the reflected wave, the direction of the linear array antenna  4  may be controlled. 
       FIG. 1  illustrates a first phase shifter  43   a , a second phase shifter  43   b , and a third phase shifter  43   c , as the phase shifter  43  included in the linear array antenna  4 . Each of these phase shifters  43  is connected to the signal distributor  42 . 
     [Antenna Element  44 ] 
     The antenna element  44  is an antenna element that transmits the transmitting wave on the basis of the transmission signal the phase of which is controlled by the phase shifter  43 . The antenna element  44  is also an antenna element that receives the reflected wave generated by the transmitting wave illuminating the observed object. The antenna element  44  is able to provide the phase shifter  43  with the received reflected wave in the form of the analog signal. 
     The transmitting wave is not specifically limited as far as it is a wave that generates a reflected wave by illuminating the observed object. The reflected wave is not specifically limited as far as it is a wave that is generated by the transmitting wave illuminating the observed object. The transmitting wave and the reflected wave preferably include radio waves and/or sonic waves. Because the transmitting wave include radio waves and/or sonic waves, i the transmitting wave including radio wave and/or sonic wave may be transmitted to a wide area without being affected by the atmosphere, clouds, and fog or the like that attenuate visible light rays. Because the reflected wave includes radio waves and/or sonic waves, the reflected wave including radio waves and/or sonic waves may be received from a wide area without being affected by the atmosphere, clouds, and fog or the like that attenuate visible light rays. Therefore, it is possible to provide the radar device  1  capable of estimating the location of the observed object in an even wider area. 
     The antenna element  44  is disposed in the linear array antenna structure  41  so as to configure the linear array antenna along the longitudinal direction of the linear array antenna  4 . The antenna element  44  allows for provision of the transmitting wave based on the transmission signal. The antenna element  44  allows for reception of the reflected wave. 
     The antenna element  44  is not specifically limited, and may be an antenna element configured by using a prior-art antenna capable of transmitting the transmitting wave and receiving the reflected wave. If the transmitting wave and the reflected wave include radio waves, the antenna element  44  preferably includes an antenna capable of transmitting and receiving radio waves. This makes it possible to transmit the transmitting wave including radio waves via the antenna element  44 . It is also possible to receive reflected wave including radio waves by using the antenna element  44 . 
     If the transmitting wave and the reflected wave include radio waves, the antenna element  44  preferably includes a speaker capable of generating sonic waves and a sonic wave sensor capable of receiving sonic waves. This makes it possible to transmit the transmitting waves including sonic waves via the antenna element  44 . Further, it is possible to receive the reflected waves including sonic waves by using the antenna element  44 . The speaker and the sonic wave sensor may be configured integrally or configured separately. 
     The antenna element  44  is preferably able to transmit and receive the transmitting wave used in wireless communications. As such, wireless communications may be performed using the radar device  1 . 
       FIG. 2  is a conceptual diagram illustrating transmitting waves T transmitted by the antenna element  44  and reflected waves R received by the antenna element  44 . The antenna element  44  is preferably configured by using an omni-directional antenna capable of transmitting the transmitting waves T to all azimuth directions and receiving the reflected waves R from all azimuth directions. This makes it even easier to control the phase of the transmitting wave so as to direct the direction of the transmitting wave T to all azimuth directions. Further, this makes it possible to receive the reflected wave R regardless of an azimuth direction of the observed object as viewed from the antenna element  44 . 
     The antenna element  44  is preferably a substantially non-directive antenna element, although it is not an essential aspect. The term “substantially no-directive” as used herein indicates that a gain G illustrated in  FIG. 2  is approximately the same regardless of the azimuth direction viewed from the antenna element. If the transmitting wave T includes radio waves, the gain G as used herein is a ratio obtained by dividing the field intensity of the antenna in an azimuth direction viewed from the antenna element by the field intensity in the case of an isotropic antenna element. The upper limit of the gain G in the substantially non-directive antenna element is preferably 1.7 or lower, more preferably 1.5 or lower, and further preferably 1.3 or lower. By setting the upper limit of the gain G as described above, it becomes even easier to transmit the transmitting wave T to all azimuth directions. Further, it is possible to receive the reflected wave even more reliably, regardless of the azimuth direction of the observed object as viewed from the antenna element  44 . 
     It is preferable that each of the plurality of antenna elements  44  be arranged with a predetermined arrangement gap s P [m], although it is not an essential aspect. As such, the direction of the linear array antenna  4  may be controlled, by giving a predetermined phase difference α P  to each of the phase of the transmitting wave T and the phase of the reflected wave R transmitted by the two adjacent antenna elements  44 . 
     [Converter  43 ] 
     The converter  45  converts the reflected wave R in the form of an analog signal provided from the signal distributor  42  into a digital signal. The converter  45  provides the controller  2  with this reflected wave R in the form of the digital signal. This makes it possible to provide the controller  2  with the reflected wave R in the form of the digital signal suitable for the location estimation process performed in the controller  2 . The converter  45  is not specifically limited, and may be a converter capable of converting an analog signal of the prior art into a digital signal. 
     [Amplifier] 
     The linear array antenna  4  preferably includes one or more amplifiers (not illustrated), although it is not an essential aspect. The amplifier may be an amplifier that amplifies the transmission signal and/or the reflected wave R. Inclusion of the amplifier allows stronger transmitting waves T to be transmitted. In general, amplified reflected waves are easier to analyze than reflected waves that are not amplified. Therefore, the amplifier may make it easier to perform analysis of the reflected wave R. The amplifier is not specifically limited, and may be an amplifier of the prior art. 
     The upper limit of a noise factor of the amplifier is preferably 3 or lower, more preferably 2.5 or lower, and further preferably 2 or lower. By setting the upper limit of the noise factor of the amplifier as described above, the transmitting wave with less noise may be transmitted. This may reduce influence of noise in the process of estimating the location of the observed object. By setting the upper limit of the noise factor of the amplifier as described above, it is possible to obtain an amplified reflected wave R with less noise. This may reduce the influence of noise in the process of estimating the location of the observed object. 
     The amplifier is preferably able to amplify the transmission signal provided by the signal distributor  42 . As such, if the intensity of the transmission signal decreases due to the distribution in the signal distributor  42 , the transmission signal may be amplified and provided to the phase shifter. Then, it is possible to transmit a stronger transmitting wave. This makes it possible to make stronger the reflected wave R generated when the transmitting wave T illuminates the observed target. Therefore, it becomes easier to receive the reflected wave R. 
     If the amplifier is able to amplify the transmission signal provided by the signal distributor  42 , the number of amplifiers included in each of the one or more linear array antennae  4  is preferably n P  or more. As such, each of the transmission signals provided by the signal distributor  42  may be amplified and provided to the n P  phase shifters  43 . 
     The amplifier is preferably able to amplify reflected waves R provided by the antenna element  44 . As such, the amplified reflected waves R may be provided to the phase shifter  43 . If the amplifier is able to amplify the reflected waves R provided by the antenna element  44 , the number of amplifiers included in each of the one or more linear array antennae  4  is preferably n P  or more. As such, each of the reflected waves R provided by the n P  antenna elements  44  may be amplified and provided to the n P  phase shifters  43 . 
     [Frequency Converter for Reception] 
     The linear array antenna  4  preferably includes one or more frequency converters (not illustrated), although it is not an essential aspect. The frequency converter is a frequency converter capable of converting the frequency of the transmission signal provided to the antenna element  44  and converting the frequency of the reflected wave R provided from the antenna element  44 . 
     In general, processing an electric signal with a higher frequency makes a configuration of a member that processes the signal more complicated, which thus reduces the cost performance, or the like. With the frequency converter, the frequency of the transmission signal processed by the transmitter  3 , the signal distributor  42 , the phase shifter  43 , and/or the amplifier or the like may be made lower than the frequency of the transmitting wave T. Further, with the frequency converter, the frequency of the reflected wave R processed by the amplifier, the phase shifter  43 , the signal distributor  42 , and/or the converter  45  or the like may be made lower than the frequency of the reflected wave R. Therefore, the configuration of these components may be made simpler and the cost performance or the like of the radar device  1  may be improved. 
     The number of the frequency converters is preferably n P  or more. Because the number of the frequency converters is n P  or more, the frequency of each of transmission signals distributed by the signal distributor  42  may be converted. As such, the transmitter  3  and the signal distributor  42  may be configured to process a frequency lower than the frequency of the transmitting wave T. Further, because the number of the frequency converters is n P  or more, the phase shifter  43  and/or the amplifier may be configured to process a frequency lower than the frequency of the transmitting wave T. Because the number of the frequency converters is n P  or more, each of reflected waves R received by the n P  antenna elements  44  may be converted. As such, the signal distributor  42  and the converter  45  may be configured to process a frequency lower than the frequency of the reflected wave R. Further, the amplifier and/or the phase shifter  43  may be configured to process a frequency lower than the frequency of the reflected wave R. 
     The frequency converter is not specifically limited, and may be a frequency converter of the prior art. The frequency converter may be, for example, a mixer that synthesizes a predetermined periodic signal LO P  (this signal is a signal usually referred to as LO, but is denoted as the predetermined periodic signal LO P  to discriminate it from a specific periodic signal in the second embodiment, to be described below) with the transmitting wave T and/or the reflected wave R, thereby converting the frequency of the transmitting wave T and/or the reflected wave R. By synthesizing the predetermined periodic signal LO P  and the transmission signal, it is possible to convert the frequency of the transmission signal into a frequency of a sum of the frequency of the predetermined periodic signal LO P  and the frequency of the transmission signal. By synthesizing the predetermined periodic signal LO P  and the reflected wave R, it is possible to convert the frequency of the reflected wave R into a frequency of a difference between the frequency of the predetermined periodic signal LO P  and the frequency of the reflected wave R. 
     [Support Structure  5 ] 
     The support structure  5  is able to support the one or more linear array antennae  4 . The support structure  5  is not specifically limited, and may be a support structure of the prior art. The support structure  5  is preferably able to support the one or more linear array antennae  4  so as to maintain a positional relationship of each of the one or more linear array antennae  4  in a predetermined positional relationship. This may make it easier to perform the location estimation process to be described below. 
     [Flowchart] 
       FIG. 3  is a flowchart illustrating an example of a flow of the location estimation process to be performed by the controller  2 . Hereinafter, with reference to  FIG. 3 , description is given of an example of a preferred procedure of the location estimation process performed by the controller  2 . 
     [Step S 1 : Determine Whether or not to Change the Direction of the Linear Array Antenna] 
     The controller  2  determines whether or not to change the direction of the linear array antenna  4  (step S 1 ). If the direction of the linear array antenna  4  is changed, the controller  2  shifts the processing to step S 2 . If the direction of the linear array antenna  4  is not changed, the controller  2  shifts the processing to step S 3 . By determining whether or not to change the direction of the linear array antenna  4 , it is possible to perform a process of changing the direction of the linear array antenna  4  if it is determined that the direction of the linear array antenna  4  is changed. 
     The method of determining whether or not to change the direction of the linear array antenna  4  is not specifically limited. The method of determining whether or not to change the direction of the linear array antenna  4  preferably includes a method of determining that the direction of the linear array antenna  4  is changed, for example, if a direction from the linear array antenna  4  toward the observed object differs from the direction of the linear array antenna  4 . As such, if the direction from the linear array antenna  4  toward the observed object differs from the direction of the linear array antenna  4 , it is possible to control the direction of the linear array antenna  4  to be the direction from the linear array antenna  4  toward the observed object. 
     The method of determining whether or not to change the direction of the linear array antenna  4  preferably includes a method of determining that the direction of the linear array antenna  4  is changed, for example, in response to a user who uses the radar device  1  issuing the instruction to change the direction of orientation. This makes it possible to change the direction of the linear array antenna  4  in response to the instruction from the user who uses the radar device  1 . 
     [Step S 2 : Change the Direction of the Linear Array Antenna] 
     The controller controls the phase of each of the transmitting wave T and the reflected wave R via the plurality of phase shifters  43 , and changes the direction of each of the one or more linear array antennae  4  (Step S 2 ). The controller  2  shifts the processing to step S 3 . 
     The process of controlling the phase of each of the transmitting wave T and the reflected wave R via the plurality of phase shifters  43 , and changing the direction of the linear array antennae  4  is not specifically limited. The process of changing the direction of the linear array antennae  4  preferably includes a process of changing a direction of an array antenna in a phased-array antenna of the prior art. If each of the plurality of antenna elements  44  is disposed with the predetermined arrangement gap s P [m], the process of changing the direction of the linear array antennae  4  may be, for example, a process of giving the predetermined phase αP to each of the phase of the transmitting wave T transmitted by and the phase of the reflected wave R received by the two adjacent antenna elements  44 . With this, the direction of the linear array antenna  4  to a direction towards the conical surface area may be controlled, the central axis of the conical surface area being the longitudinal direction of the linear array antenna  4 . 
     Subsequently, description is given of the direction of the antenna when the transmitting wave T is transmitted. The radar device may further increase the gain in the reflected wave R and further lengthen a detection available distance by orienting the antenna for transmission and the receiving antenna to the same direction. As such, the radar device may estimate a location of the observed object in an even wider area. 
     The one or more linear array antennae  4  which transmit the transmitting wave T, and the one or more linear array antennae that are the same and/or different from the linear array antennae  4  which transmit the transmitting wave T and that receive the reflected wave T are both linear array antennae. Therefore, the process performed in step S 2  may make the direction of the linear array antennae when transmitting the transmitting wave T and the direction of the linear array antenna when receiving the reflected wave R the same conical surface direction. This may increase the gain related to the reflected wave R and make the detection available distance an even longer distance. Therefore, the location of the observed object in the wide area may be estimated. 
     The process of changing the direction of the linear array antennae  4  preferably includes a process of controlling the phases of the transmitting wave T and the reflected wave R to control the direction of the linear array antenna  4  to be a direction from the linear array antenna toward the observed object. To control the direction of the linear array antenna  4  to the direction from the linear array antenna  4  toward the observed object is to orient the linear array antenna  4  in a conical surface shape and make the observed object included in the side surface of the conical surface and/or in the vicinity of the side surface of the conical surface. 
     As such, the direction of the linear array antenna  4  is controlled to be the direction from the linear array antenna  4  to the observed object, which may further increase the gain of the transmitting wave T illuminating the observed object. Further, the gain of the reflected wave R may be further increased. Since both the gain of the transmitting wave T illuminating the observed object and the gain of the reflected wave R may be increased, the detection available distance of the radar device  1  may be made even longer. Therefore, the location of the observed object in an even wider area may be estimated. 
     If the method of determining whether or not to change the direction of the linear array antenna  4  includes the method of determining that the direction of the linear array antenna  4  is changed, in response to the user who uses the radar device  1  issuing the instruction to change the direction of orientation, the process of changing the direction of the linear array antenna  4  preferably includes a process of changing the direction of the linear array antenna  4  to the direction in response to the user&#39;s instruction. This makes it possible to change the direction of the linear array antenna  4  in response to the user&#39;s instruction. 
     [Step S 3 : Determine Whether or not to Transmit the Transmitting Wave] 
     The controller  2  determines whether or not to transmit the transmitting wave T (step S 3 ). If the transmitting wave T is transmitted, the controller  2  shifts processing to step S 4 . If the transmitting wave T is not transmitted, the controller  2  shifts the processing to step S 1  and repeats the processing of steps S 1  to S 8 . By determining whether or not to transmit the transmitting wave T, it is possible to transmit the transmitting wave T only when it is determined that the transmitting wave T is to be transmitted. The process of determining whether or not to transmit the transmitting wave T is not specifically limited. 
     If the transmitter  3  provides the linear array antenna  4  with the pulse wave transmission signal that causes transmission of the transmitting wave T which is the pulse wave, the process of determining whether or not to transmit the transmitting wave T preferably includes a process of determining that the transmitting wave T is to be transmitted when the pulse wave is transmitted and determining that the transmitting wave T is not to be transmitted when the pulse wave is not transmitted. This makes it possible to transmit the pulse wave that is transmitted intermittently. 
     If the transmitter  3  provides the linear array antenna  4  with the chirp wave transmission signal that causes transmission of the transmitting wave T which is the chirp wave, the process of determining whether or not to transmit the transmitting wave T preferably includes a process of determining that the transmitting wave T is to be transmitted when the chirp wave is transmitted and determining that the transmitting wave T is not to be transmitted when the chirp wave is not transmitted. This makes it possible to transmit the chirp wave that is transmitted intermittently in accordance with the chirp signal transmission signal. 
     The process of determining whether or not to transmit the transmitting wave T preferably includes a process of determining that the transmitting wave T is to be transmitted between the time when the user who uses the radar device  1  instructs start of the transmission of the transmitting wave T and the time when the user instructs stop of the transmission of the transmitting wave T, and a process of determining that the transmitting wave T is not to be transmitted between the time when the user who uses the radar device  1  instructs the stop of the transmission of the transmitting wave T and when the user instructs the start of the transmission of the transmitting wave T. This makes it possible to transmit the transmitting wave T in response to the instruction of the user who uses the radar device  1 . 
     [Step S 4 : Control so as to Provide the Transmission Signal] 
     The controller  2  controls the transmitter  3  so as to provide the linear array antenna  4  with the transmission signal that causes the transmitting wave T to be transmitted (step S 4 ). The controller  2  shifts the processing to step S 5 . By controlling the transmitter  3  so as to provide the linear array  4  with the transmission signal that causes the transmitting wave T to be transmitted, it is possible to transmit the transmitting wave T via the linear array antenna  4 . 
     Description is given of a difference between a linearly transmitted transmitting wave T of the prior art and a conically oriented transmitting wave T of the present embodiment.  FIG. 4  is a conceptual diagram illustrating the transmitting wave T transmitted from an antenna for transmission P of the prior art.  FIG. 5  is a conceptual diagram illustrating the transmitting wave T that is transmitted from the linear array antenna  4  and oriented in the conical surface shape. The transmitting wave T transmitted from the prior-art antenna for transmission P is transmitted to the linear range ( FIG. 4 ). However, the transmitting wave T transmitted from the linear array antenna  4  of the present embodiment is transmitted to the conical surface area ( FIG. 5 ). The term conical surface area as used herein is an area along the side surface of the cone and does not include the inside of the cone. 
     Since the transmitting wave T transmitted from the linear array antenna  4  of the present embodiment is transmitted to the conical surface area, it is transmitted to a wider area than the transmitting wave T transmitted to the linear range. Since the transmitting wave T transmitted from the linear array antenna  4  of the present embodiment is transmitted to the conical surface area, it is transmitted to a narrower area than a transmitting wave transmitted to an area (also referred to as a fan-shaped range) that includes the side surface of the cone and the inside of the cone. This makes it possible to make the intensity of the transmitting wave T illuminating the observed object higher than that of the transmitting wave transmitted to the fan-shaped range. 
     The transmission signal is not specifically limited. The transmission signal includes, for example, the pulse wave transmission signal that causes the linear array antenna  4  to transmit the transmitting wave T which is the pulse wave, the chirp transmission signal that causes the linear array antenna  4  to transmit the transmitting wave T which is the chirp wave, and/or the frequency modulated continuous wave transmission signal that causes the linear array antenna  4  to transmit the transmitting wave T which is the frequency modulated continuous wave. 
     In order to measure the time from the transmission of the transmitting wave T to the reception of the reflected wave R, it is necessary to identify the transmitting wave T that generates the reflected wave R. However, if the transmitting wave T that is not frequency modulated is transmitted continuously, it is difficult to identify the transmitting wave that generates the reflected wave R. Therefore, if the transmitting wave T that is not frequency modulated is transmitted continuously, measurement of the time from the transmission of the transmitting wave T to the reception of the reflected wave R may become difficult. 
     Because the transmission signal includes the pulse transmission signal, the linear array antenna  4  is able to transmit the transmitting wave T including the pulse wave. As such, the transmitting wave T that generates the reflected wave R may be identified and the transmitting wave including the pulse wave may be associated with the reflected wave R. Therefore, it is possible to measure the time from the transmission of the transmitting wave T including the pulse wave to the reception of the reflected wave R more accurately than a case where the continuous wave that is not subjected to the frequency modulation is transmitted. 
     Because the transmission signal includes the chirp transmission signal, the linear array antenna  4  is able to transmit the chirp wave. This makes it possible to measure the time from the transmission of the transmitting wave T including the chirp wave to the reception of the reflected wave R, by using the frequency of the reflected wave R, even when the transmitting wave T including the chirp wave is transmitted longer than the pulse wave. 
     Because the transmission signal includes the pulse wave transmission signal and/or the chirp wave transmission signal, the transmitting wave T is transmitted intermittently. Therefore, the reflected wave R may be easily associated with the transmitting wave T that generates the reflected wave R. This makes it possible to easily measure the time from the transmission of the transmitting wave T to the reception of the reflected wave R. 
     In addition, as such, the reflected wave R may be received by the linear array antenna  4  while the linear array antenna  4  is not transmitting the transmitting wave T. Therefore, it is possible to receive the reflected wave R without having another antenna for transmitting the reflected wave R. As such, the radar device  1  may be configured to have a simpler structure than a radar device having another antenna for receiving the reflected wave R. Therefore, the cost performance and/or maintainability or the like of the radar device  1  may be improved. 
     Because the transmission signal includes the frequency modulated continuous wave transmission signal, the linear array antenna  4  is able to transmit the frequency modulated continuous wave. As such, the time from the transmission of the transmitting wave T to the reception of the reflected wave R may be measured by using a comparison of the frequency of the transmitting wave T and the frequency of the reflected wave R. Therefore, even when the transmitting wave T is not the transmitting wave T that is transmitted intermittently, the time from the transmission of the transmitting wave T to the reception of the reflected wave R may be measured. Moreover, because the transmission signal includes the frequency modulated continuous wave transmission signal, more transmitting waves may illuminate the observed object and more reflected wave may be generated. 
     If the transmission signal includes the frequency modulated continuous wave transmission signal, and the linear array antenna  4  for transmitting the transmitting wave T and the linear array antenna  4  for receiving the reflected wave R differ from each other, it is preferable that the controller  2  control the linear array antenna  4  that is different from the linear array antenna  4  for transmitting the transmitting wave T so that that linear array antenna  4  receives the reflected wave R. This makes it possible to transmit the transmitting wave even while receiving the reflected wave. 
     Turn back to  FIG. 3 . If the transmission signal includes the pulse wave transmission signal and/or the chirp wave transmission signal, the controller  2  preferably performs the process of controlling the linear array antenna  4  so as to receive the reflected wave R illustrated in step S 5 . 
     [Step S 5 : Control the Linear Array Antenna so as to Receive the Reflected Wave] 
     The controller  2  controls the linear array antenna  4  so as to receive the reflected wave R (step S 5 ). The controller  2  shifts the processing to step S 6 . This allows the reflected wave R to be received. The process of controlling the linear array antenna  4  so as to receive the reflected wave R is not specifically limited. 
     It is preferable that the process of controlling the linear array antenna  4  so as to receive the reflected wave R include the process of controlling the linear array antenna  4  so as to receive the reflected wave R, that linear array antenna  4  being the same as the linear array antenna that transmits the transmitting wave T in step S 4 . This allows the reflected wave R to be received at a location of the linear array antenna  4  that transmits the transmitting wave T. As such, the direction of the transmitting wave T and the direction of the reflected wave R match better than a case where the reflected wave R is received at a location different from that of the linear array antenna  4  that transmits the transmitting wave T. Therefore, the gain related to the reflected wave R may be increased without changing the direction of the linear array antenna  4  between when the transmitting wave T is transmitted and when the reflected wave R is received. As such, the detection available distance of the radar device  1  may be made even longer. Hence, the location of the observed object in the wide area may be estimated. 
     In addition, because the process of controlling the linear array antenna  4  so as to receive the reflected wave R includes the process of controlling the linear array antenna  4  to transmit the reflected wave R, that linear array antenna  4  being the same as the linear array antenna that transmits the transmitting wave T in step S 4 , it is possible to transmit the transmitting wave T without having another antenna for transmitting the transmitting wave T. As such, the radar device  1  may be configured to have the simpler structure that a radar device having the other antenna for transmitting the transmitting wave T. Therefore, the cost performance and/or maintainability or the like of the radar device  1  may be improved. 
     If the number of the linear array antennae  4  is two or more, it is preferable that the process of controlling the linear array antenna  4  so as to receive the reflected wave R include a process of controlling the linear array antenna  4  so as to receive the reflected wave R, that linear array antenna  4  being different from the linear array antenna  4  that transmits the transmitting wave T in step S 4 . This allows the reflected wave R to be received at the linear array antenna  4  which is different from the linear array antenna  4  that transmits the transmitting wave T, even when the frequency modulated transmitting wave T is transmitted continuously. As such, more transmitting waves T may illuminate the observed object and more reflected waves R may be generated. 
     If the number of the linear array antennae  4  is two or more, it is preferable that the process of controlling the linear array antenna  4  so as to receive the reflected wave R include a process of controlling the two or more linear array antennae  4  so as to receive the reflected wave R. This makes it possible to perform a process of specifying two locations including the location of the observed object. The process of specifying the two locations including the location of the observed object is described below in more detail with reference to  FIG. 8 . 
     If the number of the linear array antennae  4  is three or more, and at least the three or more linear array antennae  4  are disposed non-linearly, it is preferable that the process of controlling the linear array antenna  4  so as to receive the reflected wave include a process of controlling the three or more non-linearly disposed linear array antennae  4  so as to receive the reflected wave R. This makes it possible to perform the process of specifying the location of the observed object. The process of specifying the location of the observed object is described below in more detail with reference to  FIG. 9 . 
     [Step S 6 : Receive the Reflected Wave for a Predetermined Time] 
     The controller  2  controls the one or more linear array antennae  4  so as to receive the reflected wave R for a predetermined time (step S 6 ). By controlling the controller  2  so as to receive the reflected wave  2  for the predetermined time, it is possible to measure the time from the transmission of the transmitting wave until the linear array antenna  4  receives the reflected wave, by using the received reflected wave, and to perform the processing of estimating the location of the observed object. The predetermined time is not specifically limited, and may be, for example, time according to a transmission cycle of the pulse wave and/or the chirp wave or time according to a cycle in which the frequency modulated continuous wave repeats modulation, or the like. 
     [Step S 7 : Measure the Time from the Transmission of the Transmitting Wave to the Reception of the Reflected Wave] 
     For each of the one or more observed objects where reflected waves are generated, the controller  2  measures the time from the transmission of the transmitting wave to the reception of the reflected wave by each of the one or more linear array antennae  4  (step S 7 ). The controller  2  shifts the processing to step S 8 . As such, the time from the transmission of the transmitting wave to the reception of the reflected wave, which is used in the process of estimating the location of the observed object, is obtained. 
     The process of measuring the time from the transmission of the transmitting wave to the reception of the reflected wave by each of the one or more linear array antennae  4  (hereinafter, also simply referred to as a “reflected wave reception time measurement process”) is not specifically limited. 
     If the transmitting wave T includes the pulse wave, it is preferable that the reflected wave reception time measurement process include a process of measuring the time from when the pulse wave is transmitted until each of the one or more linear array antennae  4  receives the reflected wave R. This makes it possible to associate the pulse wave with the reflected wave R and more accurately measure the time until the reflected wave R is received than a case where the continuous wave that is not subjected to frequency modulation is transmitted. 
     If the transmitting wave T includes the chirp wave, it is preferable that the reflected wave reception time measurement process include a process of measuring the time from when the chirp wave is transmitted until each of the one or more linear array antennae  4  receives the reflected wave R, using the phase difference and/or the frequency difference between the chirp wave and the reflected wave R. Use of the phase difference and/or the frequency difference between the chirp wave and the reflected wave R makes it possible to measure the time until the reflected wave R is received, even for the chirp wave that is transmitted for a longer time than the pulse wave. Therefore, more transmitting waves T may illuminate the observed object. Further, more reflected waves R may be generated. As such, more reflected waves R may be received than a case where the transmitting wave T is the pulse wave. Therefore, the location of the observed object may be estimated more reliably. 
     If the transmitting wave T includes the frequency modulated continuous wave, the reflected wave reception time measurement process preferably includes a process of removing the transmitting wave T from the reflected wave R. If the transmitting wave T is transmitted continuously, the linear array antenna  4  may also receive the transmitting wave T when receiving the reflected wave R. The received transmitting wave T may become noise in processing using the reflected wave R. Because the reflected wave reception time measurement process includes the process of removing the transmitting wave T from the reflected wave R, the transmitting wave T may be removed from the reflected wave R, preventing the received transmitting wave T from becoming noise. The process of removing the transmitting wave T from the reflected wave R is not specifically limited, and may be a prior-art process of removing the transmitting wave T from the reflected waves R. 
       FIG. 6  is a conceptual diagram illustrating that a feedback signal F is used to reduce a transmitting wave Ti that interferes with a reflected wave. The process of removing the transmitting wave T from the reflected wave R may be, for example, a process of removing the transmitting wave Ti that interferes with the reflected wave R, by adding the feedback signal F to the reflected wave R, the feedback signal F being generated by using the transmitting wave T whose phase is inverted, as illustrated in  FIG. 6 . 
     If the transmitting wave T includes the frequency modulated continuous wave, it is preferable that the reflected wave reception time measurement process include the process of measuring the time from when the transmitting wave T is transmitted until each of the one or more linear array antennae  4  receives the reflected wave R, by using the comparison of the frequency of the transmitting wave T and the frequency of the reflected wave R. This makes it possible to measure the time until the reflected wave R is received even for the frequency modulated continuous wave that is transmitted continuously. Therefore, more transmitting waves T may illuminate the observed object. As such, then, more reflected waves R may be generated. More reflected waves may be received than a case where the transmitting wave T is the pulse wave and/or the chirp wave that is transmitted intermittently. As such, the location of the observed object may be estimated more reliably. 
     The generation of more reflected waves R in the observed object and the measurement of the time from the transmission of the transmitting wave T to the reflected wave R may be achieved simultaneously by including the process of the reflected wave reception time measurement process removing the transmitting wave T from the reflected wave R when the transmitting wave T includes the frequency modulated continuous wave and the process of measuring the time from when the transmitting wave T is transmitted until each of the one or more linear array antennae  4  receives the reflected wave R by using the comparison of the frequency of the transmitting wave T and the frequency of the reflected wave R. As such, more reflected waves R may be received and the location of the observed object may be estimated even more reliably. 
     [Step S 8 : Estimate the Location of the Observed Object for Each Observed Object] 
     Turn back to  FIG. 3 . For each of the one or more observed objects where the reflected wave R is generated, the controller  2  estimates the location of the observed object by using the time from the transmission of the transmitting wave T until each of the one or more linear array antennae  4  receives the reflected wave R (step S 8 ). The controller  2  shifts the process to step S 1  and repeats the processing of steps S 1  to S 8 . This allows the location of the observed object to be estimated for each of the one or more observed objects where the reflected wave R is generated. The process of estimating the location of the observed object is not specifically limited. 
     The process of estimating the location of the observed object preferably includes a process of specifying an approximately circular space including the location of the observed object. 
     The direction from the linear array antenna  4  to the location of the observed object where the reflected wave R is generated is the same direction as the direction of the transmitting wave T. In the processing of step S 4 , the transmitting wave T is transmitted by using the linear array antenna  4  oriented to the direction of the conical surface. Therefore, the location of the observed object is included in this conical surface and the periphery thereof. The time from the transmission of the transmitting wave T to the reception of the reflected wave R varies depending on the distance from the linear array antenna  4  to the observed object. Therefore, the distance from the linear array antenna  4  to the observed object may be measured by using the time from the transmission of the transmitting wave T to the reception of the reflected wave R. 
     A location of the apex of the conical surface is the same as that of the linear array antenna  4 . Therefore, a space that is included in the conical surface and the periphery thereof and where the distance from the linear array antenna  4  satisfies the measured distance is an approximately circular space. Consequently, use of the time from the transmission of the transmitting wave T to the reception of the reflected wave R and the direction of the transmitting wave T makes it possible to specify the approximately circular space including the observed object. 
     If the number of the linear array antennae  4  is two or more, and the process of controlling the linear array antenna  4  so as to receive the reflected wave R in step S 5  includes the process of controlling the two or more linear array antennae  4  so as to receive the reflected wave R, the process of estimating the location of the observed object preferably includes the process of specifying the two locations including the location of the observed object. 
     Since the process of controlling the linear array antenna  4  so as to receive the reflected wave R in step S 5  includes the process of controlling the two or more linear array antennae  4  so as to receive the reflected wave R, it is possible to specify two or more approximately circular spaces using the respective reflected waves R received by the two or more linear array antennae  4 . Use of these two or more approximately circular spaces makes it possible to specify two intersecting points. Therefore, it is possible to configure so that the processing of estimating the observed object includes the process of specifying the two locations. 
     If the number of the linear array antennae  4  is three or more, and the process of controlling the linear array antenna  4  so as to receive the reflected wave R in step S 5  includes the process of controlling the three or more linear array antennae  4  so as to receive the reflected wave R, the process of estimating the location of the observed object preferably includes the process of specifying the location of the observed object. 
     Since the process of controlling the linear array antenna  4  so as to receive the reflected wave in step S 5  includes the process of controlling that the three or more linear array antennae  4  receive the reflected wave R, it is possible to specify three or more approximately circular spaces by using the respective reflected waves R received by the three or more linear array antennae. Then, use of an intersecting point of these three or more approximately circular spaces makes it possible to specify the location of the observed object. 
     &lt;Usage Examples&gt; 
       FIG. 7  is a conceptual diagram illustrating a process of estimating a location of an observed object O 1 , using the direction of the transmitting wave T and the time until the first linear array antenna  4   a  receives a first reflected wave R 1 .  FIG. 8  is a conceptual diagram illustrating the process of specifying the two locations including the location of the observed object O 1 , by using the direction of the transmitting wave T, time until each of the first linear array antenna  4   a  and the second linear array antenna  4   b  receives the first reflected wave R 1 , and the detection of the arrival angle.  FIG. 9  is a conceptual diagram illustrating the process of specifying the location of the observed object O 1  using the direction of the transmitting wave T, time until each of the first linear array antenna  4   a , the second linear array antenna  4   b , and the third linear array antenna  4   c  receives the first reflected wave R 1 , and the detection of the arrival angle. Hereinafter, description is given of usage examples of the radar device  1  in the present embodiment with reference to  FIG. 7  to  FIG. 9 , where appropriate. 
     [Changing the Direction of the Transmitting Wave] 
     The user who uses the radar device  1  instructs the controller  2  to change the direction of the linear array antenna  4  to the direction from the linear array antenna  4  toward the observed object. The controller  2  controls the first linear array antenna  4   a , the second linear array antenna  4   b , and the third linear array antenna  4   c , controlling the directions of these linear array antennae  4  so as to be the direction from these linear arran antennae  4  toward the observed object. 
     [Transmitting the Transmitting Wave] 
     The user who uses the radar device  1  instructs the controller  2  to transmit the transmitting wave T. The controller  2  controls the transmitter  3  so as to provide the linear array antenna  4  with a transmission signal that causes the transmitting wave T to be transmitted. The transmitter  3  provides the linear array antenna  4  with the transmission signal. Then, the transmitting wave T is transmitted from the linear array antenna  4 . 
     [Receiving the Reflected Wave] 
     The controller  2  controls each of the first linear array antenna  4   a , the second linear array antenna  4   b , and the third linear array antenna  4   c  so as to receive the first reflected wave R 1  that is generated when the transmitting wave T illuminates the first observed object O 1 . Each of the first linear array antenna  4   a , the second linear array antenna  4   b , and the third linear array antenna  4   c  receives the first reflected wave R 1 . 
     [Measuring the Time Until the Reflected Wave is Received] 
     The controller  2  measures the time from when the transmitting wave T is transmitted until each of the first linear array antenna  4   a , the second linear array antenna  4   b , and the third linear array antenna  4   c  receives the first reflected wave R 1 . 
     [Estimating the Location of the Observed Object] 
     The controller  2  estimates the location of the first observed object O 1  by using the time until the measured first reflected wave R 1  is received. 
     [Process of Specifying the Approximately Circular Space] 
     With reference to  FIG. 7 , description is given of a process of specifying the approximately circular space including the first observed object O 1  in a case where the radar device  1  includes only the first linear array antenna  4   a.    
     The transmitting wave T transmitted to the conical direction of the linear array antenna  4   a  illuminates the first observed object O 1 , and then generates the first reflected wave R 1 . The first reflected wave R 1  is received by the linear array antenna  4   a  in the same direction of that of the transmitting wave T. This makes it possible to estimate that the location of the first observed object O 1  is included in the conical surface area to which the linear array antenna  4   a  is oriented. 
     The measured time until the first reflected wave R 1  is received is defined in accordance with a first distance D 1  from the linear array antenna  4   a  to the first observed object O 1 . Therefore, use of the measured time until the first reflected wave R 1  is received allows the first distance D 1  from the first linear arran antenna  4   a  to the first observed object O 1  to be measured. 
     The space that is included in the conical surface area to which the linear array antenna  4   a  is oriented and where the distance from the first linear array antenna  4   a  to the first observed object O 1  is the first distance D 1  is an approximately circular first space A 1  illustrated in  FIG. 7 . Therefore, it is possible to specify the approximately circular first space A 1  including the location of the first observed object O 1  by using the time from the transmission of the transmitting wave T to the reception of the first reflected wave R 1  and the direction of the transmitting wave T. This makes it possible to estimate that the location of the first observed object O 1  is included in the first space A 1 . 
     [Process of Specifying the Two Locations] 
     With reference to  FIG. 8 , description is given of the process of specifying the two locations including the first observed object O 1  in a case where the radar device  1  includes the first linear array antenna  4   a  and the second linear array antenna  4   b.    
     If the radar device  1  includes the first linear antenna  4   a  and the second linear antenna  4   b , it is possible to specify the approximately circular first space A 1  including the first observed object O 1 , by using the first reflected wave R 1  received by the first linear array antenna  4   a.    
     In a three-dimensional space, it is known that a location of a point where respective distances from two points at different locations are known is included in a circular region that has a center on a straight line passing through these two points and that is included in a plane perpendicular to the straight line. It is also known that a location of a point where a distance from a predetermined location and a difference between the distance from the predetermined location and a distance from a location different from the predetermined location are known is included in the circular region that has the center on a straight line passing through these two locations and that is included in the plane perpendicular to the straight line. 
     Therefore, it is possible to specify an approximately circular second space A 2  including the first observed object O 1 , by using information regarding a difference between the time from the transmission of the transmitting wave T until the first linear array antenna  4   a  receives the first reflected wave R 1  and the time from the transmission of the transmitting wave T 1  until the second linear array antenna  4   b  receives the first reflected wave R 1  (for example, the phase difference and/or the frequency difference between the first reflected waves R 1  respectively received by the first linear array antenna  4   a  and the second linear array antenna  4   b , or the like). Therefore, it is possible to specify the two locations (first location L 1  and second location L 2 ) including the first observed object O 1  through a process of finding an intersecting point of two circles on a plane. Therefore, it is possible to estimate the two locations (first location L 1  and second location L 2 ) where the first observed object O 1  may be included. In a case where it is known that the location of the first observed object O 1  lies in an approximately semi-spherical range that centers around the radar device  1 , such as a case where the radar device  1  is installed on the ground, it is possible to estimate that the location of the first observed object O 1  is the first location L 1 . 
     If a process of specifying the second space A 2  includes the process of specifying the second space A 2  by using the phase difference and/or the frequency difference of each of the first reflected waves R 1  each received by the first linear array antenna  4   a  and the second linear array antenna  4   b , the process of specifying the second space A 2  preferably includes, for example, a calculation related to expression (2) illustrated below. A first observed object direction vector denoted by r accompanied by a circumflex ({circumflex over ( )}, also referred to a hat symbol) is a unit vector having the same direction as a direction toward the first observed object A 1  from a predetermined location (The predetermined location is not specifically limited. Hereinafter, description is given on the assumption that the predetermined location is the location of the first linear array antenna  4   a .) exemplified by the location of the first linear array antenna  4   a  or the like. i is a natural number which is equal to or smaller than the number of the linear array antennae  4 . The i th  linear array antenna vector r i  is a position vector related to the location of the i th  linear array antenna (for example, the second linear array antenna  4   b , if i=2) in a case based on the predetermined location. The i th  linear array antenna vector r i  has an X-axis direction component x i , a y-axis direction component y i , and a z-axis direction component z i . A first angle θ is an angle made by the x-axis direction and the vector r. A second angle φ is an angle made a vector obtained by projecting the first observed object vector r on an xy plane and the x-axis direction. The first angle θ and the second angle φ are both angles related to the first reflected wave R 1  received by the first linear array antenna  4   a . An angle related to the direction of the first reflected wave R 1  received by the first linear array antenna  4   a  is also referred to as an arrival angle. 
     [Mathematical Expression (2)] 
     It is known the phase difference and/or the frequency difference of each of the reflected waves received by the plurality of linear array antennae  4  is a difference that depends on a direction towards the observed object from the predetermined location that serves as a reference and the location of each of the plurality of linear array antennae  4  based on the predetermined location. For example, the phase difference and/or the frequency difference of the respective first reflected waves R 1  respectively received by the first linear array antenna  4   a  and the second linear array antenna  4   b  is a difference that depends on the direction from the first linear array antenna  4   a  toward the first observed object A 1  and the location of the second linear array antenna  4   b  in a case based on the location of the first linear array antenna  4   a . Therefore, for example, it is possible to specify a value in the left side of the expression (2) when i=2, based on the location of the first linear array antenna  4   a , by using the phase difference and/or the frequency difference of the respective first reflected waves R 1  respectively received by the first linear array antenna  4   a  and the second linear array antenna  4   b . It is possible to obtain an expression related to the first angle θ and the second angle φ by specifying the value of the left side of the expression (2). 
     Therefore, because the process of specifying the second space A 2  includes the calculation related to the expression (2), it is possible to obtain the expression related to the first angle θ and the second angle φ. More specifically, it is possible to obtain an expression related to the arrival angle of the first reflected wave R 1 . The approximately circular second space A 2  may be specified by using the time from the transmission of the transmitting wave T until the first linear array antenna  4   a  received the first reflected wave R 1  and the expression related to the first angle θ and the second angle φ. Then, it is possible to estimate the two locations (first location L 1  and second location L 2 ) including the first observed object O 1  by using the first space A 1  and the second space A 2 . 
     [Process of Specifying the Location of the Observed Object] 
     With reference to  FIG. 9 , description is given of a process of specifying the first observed object O 1  in a case where the radar device  1  includes the first linear array antenna  4   a , the second linear array antenna  4   b , and the third linear array antenna  4   c.    
     As described in the process of specifying the two locations, it is possible to estimate the two locations (first location L 1  and second location L 2 ) where the location of the first observed object O 1  may be included, by using the time when each of the first linear array antenna  4   a  and the second linear array antenna  4   b  receives the first reflected wave R 1 , or the like. Further, it is possible to specify an approximately circular third space A 3  including the first observed object O 1 , by using a difference between the time from the transmission of the transmitting wave T until the first linear array antenna  4   a  receives the first reflected wave R 1  and the time from the transmission of the transmitting wave T until the third linear array antenna  4   c  receives the first reflected wave R 1 . 
     Therefore, it is possible to specify the location (first location L 1 ) of the first observed object O 1  through a process of determining which of the first location L 1  and the second location L 2  is included in the third space A 3 . 
     [Mounting on a Flight Vehicle] 
     The radar device  1  is usable as a radar device to be mounted on a flight vehicle exemplified by an unmanned aerial vehicle such as a drone, etc., a helicopter, a multicopter, a balloon, an airship, a passenger plane, and a cargo airplane, or the like. 
     If reflected waves are received from a wide azimuth range using the prior-art radar device that is used by being oriented linearly, a rotation mechanism that rotates the radar device may be necessary. Alternatively, it may be necessary to include a plurality of radar devices for each azimuth direction in which the reflected wave is received. Mounting the rotation mechanism and/or the plurality of radar devices on a flight vehicle may increase weight of the flight vehicle. The increased weight of the flight vehicle may degrade the performance of the flight vehicle that is exemplified by a navigation speed, a cruising distance, payload, stability during flight, or the like. 
     Since the radar device  1  is able to receive reflected waves from a wide range, the rotation mechanism is not necessary and it is not necessary to include the plurality of radar devices  1 . This may prevent an increase in the weight of the flight vehicle and prevent a deterioration in the performance of the flight vehicle. 
     [Mounting on a Vehicle] 
     The radar device  1  is usable as a radar device to be mounted on a vehicle exemplified by a passenger car, transport vehicle, and a service vehicle, or the like. 
     A location of an observed object (for example, an oncoming car, a following car, and a preceding car, or the like) in the periphery of a vehicle is estimated by means of a radar device mounted on the vehicle. By estimating the location of the observed object in the periphery of the vehicle, accidents such as a collision between the vehicle and the observed object, or the like may be prevented. 
     In the meantime, if the observed object in the periphery of the vehicle is a traveling vehicle, a direction from the radar device toward the observed object may change significantly in a short time. If such a location of the observed object is estimated by using a device that combines the prior-art radar device, which is used by being oriented linearly, with the rotation mechanism, there may be a case where rotations of the radar device by the rotation mechanism are not able to follow a change in the direction. 
     The radar device  1  may change the direction of the linear array antenna  4  in a short time by controlling the respective phases of the transmitting wave T and the reflected wave R. As such, even if the direction from the radar device toward the observed object changes significantly in a short time, the direction of the linear array antenna  4  may be controlled to be the direction from the linear array antenna  4  toward the observed object. Therefore, even if the observed object is a travelling vehicle in the periphery of the vehicle, the location of the observed object may be estimated. 
     [Mounting on a Man-Made Satellite] 
     The radar device  1  is usable as a radar device to be mounted on a man-made satellite exemplified by a communication satellite, meteorological satellite, or an observation satellite, or the like. 
     If reflected waves are received from a wide azimuth range using the prior-art radar device that is used by being oriented linearly, the rotation mechanism that rotates the radar device may be necessary. Alternatively, it may be necessary to include a plurality of radar devices for each azimuth direction in which the reflected wave is received. If a mechanical rotation mechanism is mounted on the man-made satellite, there may arise a problem that lubricating oil used for rotating parts evaporates due to a vacuum, a problem that reaction accompanying the rotation affects posture control of the man-made satellite, or the like. Moreover, usually, the weight of a man-made satellite to be launched using a rocket is strictly limited. Consequently, if the radar device is mounted on a man-made satellite, improvement of the weight related to the radar device may be called for. 
     By controlling the respective phases of the transmitting wave T and the reflected wave R, the radar device  1  is able to orient the linear array antenna  4  to an arbitrary direction without using the mechanical rotation mechanism or without including the plurality of radar devices  1 . This may solve the problem that the lubricating oil used for the rotating parts evaporates due to the vacuum, the problem that the reaction accompanying the rotation affects the posture control of the man-made satellite, or the like. Further, the weight of the radar device to be mounted on the man-made satellite may be improved. 
     [Use as a Ground Radar Base] 
     The radar device  1  is usable as a ground radar base to be installed on the ground. The radar device  1  may change the direction of the linear array antenna  4  in a short time by controlling the respective phases of the transmitting wave T and the reflected wave R. As such, the radar device  1  is usable as the ground radar device for estimating locations of various high-speed flight vehicles. 
     Second Embodiment 
     A second embodiment is a radar device whose antenna is an omni-directional antenna. 
     &lt;Radar Device  101 &gt; 
       FIG. 10  is a schematic diagram of a radar device  101  in the second embodiment of the present invention when viewed from diagonally above. Hereinafter, with reference to  FIG. 10 , description is given of an example of a preferred configuration of the radar device  101  in the second embodiment of the present invention. 
     The radar device  101  includes a controller  102 , a transmitter  103 , and one or more omni-directional antennae  104  (reference numerals  104   a ,  104   b ,  104   c , and  14   d  in  FIG. 10 ). 
     It is preferable that the radar device  101  further include a support structure  105  capable of supporting the one or more omni-directional antennae  104 , although it is not an essential aspect. Inclusion of the support structure  105  allows the one or more omni-directional antennae  104  to be supported by the support structure  105  so that each of these one or more omni-directional antennae  104  maintains a specific positional relationship. This makes it possible to easily perform a process of estimating a location of an observed object, which is described below. 
     [Controller  102 ] 
     The controller  102  controls the transmitter  103  and the one or more omni-directional antennae  104 . The controller  102  also performs the location estimation process for estimating the location of the observed object, using the time from the transmission of the transmitting wave to the reception of the reflected wave. Since the radar device  101  includes the controller  102 , it is possible to estimate the location of the observed object by performing the location estimation process. 
     The controller  102  is not specifically limited. The controller  102  may be a prior-art microcomputer including, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory), or the like. 
     The controller  102  is configured to be able to acquire each piece of reflected wave information regarding the reflected waves received by the one or more omni-directional antennae  104 . Each piece of reflected wave information includes information that allows for measurement of the time from the transmission of the transmitting wave until the omni-directional antenna  104  receives the reflected wave. 
     The controller  102  is preferably configured to be able to output the location of the observed object that is estimated by the location estimation process. Means for outputting the location of the observed object is not specifically limited, and may be means for outputting a location of an observed object that is used by the prior-art radar device. 
     The controller  102  is preferably able to receive various instructions from a user who uses the radar device  102 . Examples of various instructions include the instruction to start the transmission of the transmitting waves and/or the instruction to stop the transmission of the transmitting waves, or the like. Because the controller  102  is able to receive various instructions from the user who uses the radar device  101 , the radar device  101  may be controlled in response to the user&#39;s instruction. 
     [Transmitter  103 ] 
     The transmitter  103  is similar to the transmitter  3  of the first embodiment. The transmitter  103  is able to provide a transmission signal that causes the omni-directional antenna  104  to transmit the transmitting wave. The transmitter  103  is connected to the controller  102  and the omni-directional antenna  104 . The transmitter  103  is configured to be able to provide the omni-directional antenna  104  with the transmission signal in accordance with the control by the controller  102 . Because the radar device  101  includes the transmitter  103 , it is possible to cause the omni-directional antenna  104  to transmit the transmitting wave via the transmission signal. 
     [Omni-Directional Antenna  104 ] 
     The omni-directional antenna  104  is an omni-directional antenna  104  capable of transmitting the transmitting wave in accordance with the transmission signal provided from the transmitter  103  and of receiving a reflected wave that is generated by the transmitting wave illuminating the observed object. Each of the one or more omni-directional antennae  104  is connected to the controller  102  and the transmitter  103 . Each of the one or more omni-directional antennae  104  is configured to be controllable by the controller  102 . Each of the one or more omni-directional antennae  104  includes an omni-directional antenna element  141  and a converter  142 . 
     Because the radar device  101  includes the one or more omni-directional antennae  104 , it is possible to receive the reflected wave from a wider area than the planar phased-array antenna or the like. The omni-directional antenna  104  transmits the transmitting wave to a wider azimuth range than a case where the planar phased-array antenna is used. Then, the transmitting wave illuminates the observed object in a different direction, generating the reflected wave. This reflected wave is received by the omni-directional antenna  104 . Therefore, the reflected wave may be received from the wider azimuth range than the case where the planar phased-array antenna is used. 
     The number of the omni-directional antennae  104  is not specifically limited. The number of the omni-directional antennae  104  is preferably two or more. This makes it possible to perform the process of specifying the approximately circular space including the location of the observed object. The process of specifying the approximately circular space including the observed object is described below with reference to  FIG. 15 . 
     The number of the omni-directional antennae  104  is three or more, and it is more preferable that the three omni-directional antennae  104  be disposed non-linearly. This makes it possible to perform the process of specifying the two locations including the location of the observed object. The process of specifying the two locations including the observed object is described below with reference to  FIG. 16 . 
     The number of the omni-directional antennae  104  is four or more, and it is further preferable that the four or more omni-directional antennae  104  be disposed so that at least one of the omni-directional antennae  104  is not on the same plane. This makes it possible to perform the process of specifying the observed object. The process of specifying the observed object is described below with reference to  FIG. 17 . 
     If a direction from an observed point toward an observed object and a distance from the observed point to the observed object are determined by using a distance from different two observed points, it is known that when the observed object lies on and around a straight line connecting the two observed points, an accuracy of specifying the direction from the observed point toward the observed object degrades. Therefore, if a straight line connecting two omni-directional antenna  104  and a straight line connecting the observed object and the omni-directional antenna  104  are parallel, the accuracy of specifying the direction from the omni-directional antenna  104  toward the observed object may degrade. For example, if the two omni-directional antennae  104  are arranged along a vertical direction, the accuracy of specifying a direction from the omni-directional antenna  104  toward the observed object located above the omni-directional antenna  104  may degrade. 
     The number of the omni-directional antennae  104  is four or more, and the four or more omni-directional antennas  104  are disposed so that at least the one omni-directional antenna  104  is not on the same plane. As such, a direction of a straight line connecting at least the two omni-directional antennae  104  of the four or more omni-directional antennae  104  differs from the direction from the omni-directional antenna  104  toward the observed object. Therefore, a degradation in the accuracy of specifying the direction from the omni-directional antenna  104  toward the observed object may be prevented. 
     [Omni-Directional Antenna Element  141 ] 
     The omni-directional antenna element  141  (reference numerals  141   a ,  141   b ,  141   c , and  141   d  in  FIG. 10 ) is an omni-directional antenna element that transmits the transmitting wave in response to the transmission signal provided from the transmitter  103  and receives the reflected wave that is generated by the transmitting wave illuminating the observed object. The omni-directional antenna element  141  provides the converter  142  with the received reflected wave in the form of an analog signal. With the omni-directional antenna element  141 , it is possible to transmit the transmitting wave on the basis of the transmission signal. With the omni-directional antenna element  141 , it is possible to receive the reflected wave and provide it to the converter  141  in the form of the analog signal. 
     The transmitting wave is not specifically limited as far as it is a wave that generates a reflected wave by illuminating the observed object. The reflected wave is not specifically limited as far as it is a wave that is generated by the transmitting wave illuminating the observed object. The transmitting wave and the reflected wave preferably include radio waves and/or sonic waves. Because the transmitting wave include radio waves and/or sonic waves, i the transmitting wave including radio wave and/or sonic wave may be transmitted to a wide area without being affected by the atmosphere, clouds, and fog or the like that attenuate visible light rays. Because the reflected wave includes radio waves and/or sonic waves, the reflected wave including radio waves and/or sonic waves may be received from a wide area without being affected by the atmosphere, clouds, and fog or the like that attenuate visible light rays. Therefore, it is possible to provide the radar device  101  capable of estimating the location of the observed object in an even wider area. 
     The omni-directional antenna element  141  is not specifically limited, and may be an omni-directional antenna element configured by using the prior-art antenna capable of transmitting the transmitting wave and receiving the reflected wave. If the transmitting wave and the reflected wave include radio waves, the omni-directional antenna element  141  preferably includes an antenna capable of transmitting and receiving radio waves. As such, it is possible to transmit the transmitting wave including radio waves via the omni-directional antenna element  141 . It is also possible to receive the reflected wave including radio waves by using the omni-directional antenna element  141 . 
     If the transmitting wave and the reflected wave include radio waves, the omni-directional antenna element  141  preferably includes a speaker capable of generating sonic waves and a sonic wave sensor capable of receiving sonic waves. This makes it possible to transmit the transmitting waves including sonic waves via the omni-directional antenna element  141 . Further, it is possible to receive the reflected wave including sonic waves by using the omni-directional antenna element  141 . The speaker and the sonic wave sensor may be configured integrally or configured separately. 
     The omni-directional antenna element  141  is preferably a substantially non-directive antenna element. If the transmitting wave includes radio waves, the upper limit of the gain in the substantially non-directive antenna element is preferably 1.7 or lower, more preferably 1.5 or lower, and further preferably 1.3 or lower. By setting the upper limit of the gain G as described above, it becomes even easier to transmit the transmitting wave to all azimuth directions. Further, it is possible to receive the reflected wave even more reliably, regardless of the azimuth direction of the observed object viewed from the omni-directional antenna element  141 . 
     The omni-directional antenna element  141  is preferably able to transmit and receive the transmitting wave used in wireless communications. As such, the wireless communications may be performed using the radar device  101 . 
     [Converter  142 ] 
     The converter  142  (reference numerals  142   a ,  142   b ,  142   c , and  142   d  in  FIG. 10 ) converts the reflected wave in the form of an analog signal provided from the omni-directional antenna element  141  into a digital signal. The converter  142  provides the controller  2  with this reflected wave in the form of the digital signal. With the converter  142 , it is possible to provide the controller  102  with the reflected wave in the form of the digital signal suitable for the location estimation process performed in the controller  102 . This allows the controller  102  to perform digital beamforming that changes the direction of the antenna by using the digital signal obtained through the conversion of the reflected wave. The converter  142  is not specifically limited, and may be a converter capable of converting an analog signal of the prior art into a digital signal. 
     [Amplifier] 
     The omni-directional antenna  104  preferably includes one or more amplifiers (not illustrated), although it is not an essential aspect. The amplifier is an amplifier that amplifies the transmission signal and/or the reflected wave R. Inclusion of the amplifier allows stronger transmitting waves T to be transmitted. In general, amplified reflected waves are easier to analyze than reflected waves that are not amplified. Therefore, the amplifier may make it easier to perform analysis of the reflected wave. The amplifier is not specifically limited, and may be an amplifier of the prior art. 
     The upper limit of a noise factor of the amplifier is preferably 3 or lower, more preferably 2.5 or lower, and further preferably 2 or lower. By setting the upper limit of the noise factor of the amplifier as described above, the transmitting wave with less noise may be transmitted. This may reduce influence of noise in the process of estimating the location of the observed object. By setting the upper limit of the noise factor of the amplifier as described above, it is possible to obtain an amplified reflected wave R with less noise. This may reduce the influence of noise in the process of estimating the location of the observed object. 
     The amplifier is preferably able to amplify the transmission signal provided by the transmitter  103 . As such, the transmission signal may be amplified and provided to the omni-directional element  141 . Then, it is possible to transmit a stronger transmitting wave. This makes it possible to make stronger the reflected wave generated when the transmitting wave illuminates the observed object. Therefore, it becomes easier to receive the reflected wave. 
     [Frequency Converter] 
     The omni-directional antenna  104  preferably includes a frequency converter (not illustrated), although it is not an essential aspect. The frequency converter is a frequency converter capable of converting the frequency of the transmission signal provided to the omni-directional antenna element  141  and converting the frequency of the reflected wave provided from the omni-directional antenna element  141 . 
     In general, processing an electric signal with a higher frequency makes a configuration of a member that processes the signal more complicated, which thus reduces the cost performance. With the frequency converter, the frequency of the transmission signal processed by the transmitter  103  and/or the amplifier or the like may be made lower than the frequency of the transmitting wave. Therefore, the configuration of these components may be made simpler. This may improve the cost performance or the like of the radar device  101 . With the frequency converter, the frequency of the reflected wave processed by the amplifier and/or the converter  142 , or the like may be made lower than the frequency of the reflected wave. Therefore, the configuration of these components may be made simpler. This may improve the cost performance or the like of the radar device  101 . 
     The frequency converter is not specifically limited, and may be a frequency converter of the prior art. The frequency converter may be, for example, a mixer that synthesizes a specific periodic signal LO C  (this signal is a signal usually referred to as LO, but is denoted as the predetermined periodic signal LO C  to discriminate it from the predetermined periodic signal in the aforementioned first embodiment) with the transmitting wave and/or the reflected wave, thereby converting the frequency of the transmitting wave and/or the reflected wave. By synthesizing the specific periodic signal LO C  and the transmission signal, it is possible to convert the frequency of the transmission signal into a frequency of a sum of the specific periodic signal LO C  and the frequency of the transmission signal. By synthesizing the specific periodic signal LO C  and the reflected wave R, it is possible to convert the frequency of the reflected wave R into a frequency of a difference between the frequency of the specific periodic signal LO C  and the frequency of the reflected wave R. 
     [Support Structure  105 ] 
     The support structure  105  is able to support the one or more omni-directional antennae  104 . The support structure  105  is not specifically limited, and may be a support structure of the prior art. The support structure  105  is preferably able to support the one or more omni-directional antennae  104  so as to maintain a positional relationship of each of them in a predetermined positional relationship. This may make it easier to perform the location estimation process to be described below. 
     The support structure  105  may include one or more omni-directional antennae support structures  151  (reference numerals  151   a ,  151   b ,  151   c , and  151   d  in  FIG. 10 ) and a base structure  152  capable of supporting the one or more omni-directional support structures  151 . The omni-directional antenna support structure  151  is a support structure capable of supporting the one or more omni-directional antennae  104 . As such, it becomes even easier to maintain a positional relationship of each of the plurality of omni-directional antennae in the predetermined positional relationship. 
     [Flowchart] 
       FIG. 11  is a flowchart diagram illustrating an example of a flow of the location estimation process performed by the controller  102 . Hereinafter, with reference to  FIG. 11 , description is given of an example of a preferred procedure of the location estimation process performed by the controller  102 . 
     [Step S 11 : Determine Whether or not to Transmit the Transmitting Wave] 
     First, the controller  102  determines whether or not to transmit the transmitting wave (step S 11 ). If the transmitting wave is transmitted, the controller  102  shifts processing to step S 12 . If the transmitting wave is not transmitted, the controller  102  shifts the processing to step S 11  and repeats the processing of steps S 11  to S 17 . By determining whether or not to transmit the transmitting wave, it is possible to transmit the transmitting wave only when it is determined that the transmitting wave is to be transmitted. The process of determining whether or not to transmit the transmitting wave is not specifically limited. 
     If the transmitter  103  provides the omni-directional antenna  104  with the pulse wave transmission signal that causes transmission of the transmitting wave which is the pulse wave, the process of determining whether or not to transmit the transmitting wave preferably includes the process of determining that the transmitting wave is to be transmitted when the pulse wave is transmitted and determining that the transmitting wave is not to be transmitted when the pulse wave is not transmitted. This makes it possible to transmit the pulse wave that is transmitted intermittently. 
     If the transmitter  103  provides the omni-directional antenna  104  with the chirp wave transmission signal that causes transmission of the transmitting wave which is the chirp wave, the process of determining whether or not to transmit the transmitting wave preferably includes the process of determining that the transmitting wave is to be transmitted when the chirp wave is transmitted and determining that the transmitting wave is not to be transmitted when the chirp wave is not transmitted. This makes it possible to transmit the chirp wave that is transmitted intermittently in accordance with the chirp signal transmission signal. 
     The process of determining whether or not to transmit the transmitting wave preferably includes the process of determining that the transmitting wave is to be transmitted between the time when the user who uses the radar device  101  instructs the start of transmission of the transmitting wave and the time when the user instructs the stop of the transmission of the transmitting wave, and the process of determining that the transmitting wave is not to be transmitted between the time when the user who uses the radar device  101  instructs the stop of the transmission of the transmitting wave and the time when the user instructs the start of the transmission of the transmitting wave. This makes it possible to transmit the transmitting wave in response to the instruction of the user who uses the radar device  101 . 
     [Step S 12 : Control so as to Provide the Transmission Signal] 
     The controller  102  controls the transmitter  103  so as to provide the omni-directional antenna  104  with the transmission signal that causes the transmitting wave to be transmitted (step S 12 ). The controller  102  shifts the processing to step S 5 . By controlling the transmitter  103  so as to provide the omni-directional antenna  104  with the transmission signal that causes the transmitting wave to be transmitted, it is possible to transmit the transmitting wave via the omni-directional antenna  104 . 
     The transmission signal is not specifically limited. The transmission signal includes, for example, the pulse wave transmission signal that causes the omni-directional antenna  104  to transmit the transmitting wave which is the pulse wave, the chirp transmission signal that causes the omni-directional antenna  104  to transmit the transmitting wave which is the chirp wave, and/or the frequency modulated continuous wave transmission signal that causes the omni-directional antenna  104  to transmit the transmitting wave which is the frequency modulated continuous wave. 
     In order to measure the time from the transmission of the transmitting wave to the reception of the reflected wave R, it is necessary to identify when the transmitting wave T that generates the reflected wave is transmitted. However, if the transmitting wave that is not frequency modulated is transmitted continuously, it is difficult to identify when the transmitting wave T that generates the reflected wave is transmitted. Therefore, if the transmitting wave that is not frequency modulated is transmitted continuously, measurement of the time from the transmission of the transmitting wave to the reception of the reflected wave R may become difficult. 
     Because the transmission signal includes the pulse transmission signal, the omni-directional antenna  104  is able to transmit the transmitting wave including the pulse wave. As such, by associating the transmitting wave including the pulse wave with the reflected wave, it is possible to measure the time from the transmission of the transmitting wave including the pulse wave to the reception of the reflected wave more accurately than a case where the continuous wave that is not subjected to the frequency modulation is transmitted. 
     Because the transmission signal includes the chirp transmission signal, the omni-directional antenna  104  is able to transmit the chirp wave. This makes it possible to measure the time from the transmission of the transmitting wave including the chirp wave to the reception of the reflected wave, by using the frequency of the reflected wave, even when the transmitting wave including the chirp wave is transmitted longer than the pulse wave. 
     Because the transmission signal includes the pulse wave transmission signal and/or the chirp wave transmission signal, the transmitting wave is transmitted intermittently. Therefore, the reflected wave may be easily associated with the transmitting wave that generates the reflected wave. This makes it possible to easily measure the time from the transmission of the transmitting wave to the reception of the reflected wave. 
     In addition, as such, the reflected wave R may be received by the omni-directional antenna  104  while the omni-directional antenna  104  is not transmitting the transmitting wave. Therefore, it is possible to receive the reflected wave without having another antenna for transmitting the reflected wave. As such, the radar device  101  may be configured to have a simpler structure than a radar device having the other antenna for receiving the reflected wave. Therefore, the cost performance and/or maintainability or the like of the radar device  101  may be improved. 
     Because the transmission signal includes the frequency modulated continuous wave transmission signal, the omni-directional antenna  104  is able to transmit the frequency modulated continuous wave. As such, the time from the transmission of the transmitting wave to the reception of the reflected wave may be measured by using a comparison of the frequency of the transmitting wave and the frequency of the reflected wave. Therefore, even when the transmitting wave is not a transmitting wave that is transmitted intermittently, the time from the transmission of the transmitting wave to the reception of the reflected wave may be measured. Moreover, because the transmission signal includes the frequency modulated continuous wave transmission signal, more transmitting waves may illuminate the observed object and more reflected wave may be generated. 
     If the transmission signal includes the frequency modulated continuous wave transmission signal, and the omni-directional antenna  104  for transmitting the transmitting wave T and the omni-directional antenna  104  for receiving the reflected wave R differ from each other, it is preferable to control the omni-directional antenna  104  that is different from the omni-directional antenna  104  for transmitting the transmitting wave T so that that omni-directional antenna  104  receives the reflected wave R. This makes it possible to transmit the transmitting wave even while receiving the reflected wave. 
     If the transmission signal includes the pulse wave transmission signal and/or the chirp wave transmission signal, the controller  102  preferably performs the process of controlling the omni-directional antenna  104  so as to receive the reflected wave R illustrated in step S 13 . 
     [Step S 13 : Control the Omni-Directional Antenna so as to Receive the Reflected Wave] 
     The controller  102  controls the omni-directional antenna  104  so as to receive the reflected wave (step S 13 ). The controller  102  shifts the processing to step S 14 . This allows the reflected wave to be received. The process of controlling the omni-directional antenna  104  so as to receive the reflected wave is not specifically limited. 
     It is preferable that the process of controlling the omni-directional antenna  104  so as to receive the reflected wave include a process of controlling the omni-directional antenna  104  so as to receive the reflected wave, that omni-directional antenna  104  being the same as the omni-directional antenna  104  that transmits the transmitting wave in step S 12 . This allows the reflected wave to be received at the location of the omni-directional antenna  104  that transmits the transmitting wave. Therefore, a distance from the omni-directional antenna  104  to the observed object may be specified without regard to a difference between a distance from the omni-directional antenna  104  that transmits the transmitting wave to the observed object and a distance from the omni-directional antenna  104  that receives the reflected wave to the observed object. As such, the distance from the omni-directional antenna  104  to the observed object may be specified even more easily. 
     If the number of the omni-directional antennae  104  is two or more, it is preferable that the process of controlling the omni-directional antenna  104  so as to receive the reflected wave include the process of controlling the omni-directional antenna  104  so as to receive the reflected wave, that omni-directional antenna  104  being different from the omni-directional antenna  104  that transmits the transmitting wave T in step S 12 . This allows the reflected wave to be received at the omni-directional antenna  104  which is different from the omni-directional antenna  104  that transmits the transmitting wave, even when the frequency modulated transmitting wave is transmitted continuously. As such, more transmitting waves T may illuminate the observed object and more reflected waves R may be generated. 
     If the number of the omni-directional antennae  104  is two or more, it is preferable that the process of controlling the omni-directional antenna  4  so as to receive the reflected wave include a process of controlling the two or more omni-directional antennae  104  so as to receive the reflected wave. This makes it possible to perform a process of specifying an approximately spherical space including the location of the observed object. The process of specifying the approximately spherical location including the location of the observed object is described below in more detail with reference to  FIG. 15 . 
     If the number of the omni-directional antennae  104  is three or more, and the three or more omni-directional antennae  104  are disposed non-linearly, it is preferable that the process of controlling the omni-directional antenna  104  so as to receive the reflected wave include a process of controlling the three or more non-linearly disposed omni-directional antennae  104  so as to receive the reflected wave R. This makes it possible to perform the process of specifying the two locations including the location of the observed object. The process of specifying the two locations including the observed object is described below in more detail with reference to  FIG. 16 . 
     If the number of the omni-directional antennae  104  is four or more, and at least the one omni-directional antenna  104  of the four or more omni-directional antennae  104  is disposed so as not to be on the same plane, it is preferable that the process of controlling the omni-directional antenna  104  so as to receive the reflected wave include a process of controlling the four or more omni-directional antennae  104 , of which at least the one omni-directional antenna  104  is not on the same plane, to receive the reflected wave. This makes it possible to perform the process of specifying the approximately circular space including the location of the observed object. The processing of specifying the approximately circular space including the observed object is described below in detail with reference to  FIG. 15 . 
     [Step S 14 : Receive the Reflected Wave for a Predetermined Time] 
     The controller  102  controls the one or more omni-directional antennae  104  so as to receive the reflected wave for a predetermined time (step S 14 ). By controlling the controller  102  so as to receive the reflected wave for the predetermined time, it is possible to measure the time from the transmission of the transmitting wave until the omni-directional antenna  104  receives the reflected wave, by using the received reflected wave, and to perform the processing of estimating the location of the observed object. The predetermined time is not specifically limited, and may be, for example, time according to a transmission cycle of the pulse wave and/or the chirp waves or time according to a cycle in which the frequency modulated continuous wave repeats modulation, or the like. 
     Although this is not an essential aspect, if the number of the omni-directional antennae  104  is two or more, the controller  102  preferably performs a process of selecting a signal for each azimuth direction to the observed target illustrated in step S 15 . 
     [Step S 15 : Select a Signal for Each Azimuth Direction to the Observed Object] 
     The controller  102  selects a signal for each azimuth direction to the observed object (step S 15 ). The controller  102  shifts the processing to step S 16 . 
     If the number of the omni-directional antennae  104  is two or more, it is possible to configure an array antenna by using the two or more omni-directional antennae  104 . Therefore, it is possible to perform digital beamforming for selecting a signal for each azimuth direction to the observed object using a digital signal obtained by converting the reflected wave. As such, the signal may be selected by the digital beamforming to increase the gain related to the reflected wave. Therefore, the reflected wave in the direction from the observed object to the omni-directional antenna  104  may be received more reliably. 
     The digital beamforming for selecting a signal is used for each azimuth direction to the observed object. Therefore, even when a plurality of observed objects is in different azimuth directions, the signal may be selected for each azimuth direction to the observed object and the gain related to the reflected wave may be increased. Therefore, each reflected wave in the direction toward the omni-directional antennae  104  from each of the observed objects at the different azimuth directions may be received more reliably. 
     [Step S 16 : Measure the Time from the Transmission of the Transmitting Wave to the Reception of the Reflected Wave] 
     For each of the one or more observed objects where reflected waves are generated, the controller  102  measures the time from the transmission of the transmitting wave to the reception of the reflected wave by each of the omni-directional antennae  104  (step S 16 ). The controller  102  shifts the processing to step S 17 . As such, the time from the transmission of the transmitting wave to the reception of the reflected wave, which is used in the process of estimating the location of the observed object, is obtained. 
     The process of measuring the time from the transmission of the transmitting wave to the reception of the reflected wave by each of the one or more omni-directional antennae  104  (hereinafter, also simply referred to as a “reflected wave reception time measurement process”) is not specifically limited. 
     If the transmitting wave includes the pulse wave, it is preferable that the reflected wave reception time measurement process include the process of measuring the time from when the pulse wave is transmitted until each of the one or more omni-directional antennae  104  receives the reflected wave. This makes it possible to associate the pulse wave with the reflected wave and more accurately measure the time until the reflected wave is received than a case where the continuous wave that is not subjected to frequency modulation is transmitted. 
     If the transmitting wave includes the chirp wave, it is preferable that the reflected wave reception time measurement process include the process of measuring the time from when the chirp wave is transmitted until each of the one or more omni-directional antennae  104  receives the reflected wave, using the phase difference and/or the frequency difference between the chirp wave and the reflected wave. Use of the phase difference and/or the frequency difference between the chirp wave and the reflected wave R makes it possible to measure the time until the reflected wave R is received, even for the chirp wave that is transmitted for a longer time than the pulse wave. Therefore, more transmitting waves T may illuminate the observed object. Further, more reflected waves R may be generated. As such, more reflected waves may be received than a case where the transmitting wave T is the pulse wave. Therefore, the location of the observed object may be estimated more reliably. 
     If the transmitting wave includes the frequency modulated continuous wave, the reflected wave reception time measurement process preferably includes the process of removing the transmitting wave from the reflected wave. If the transmitting wave is transmitted continuously, the omni-directional antenna  104  may even receive the transmitting wave when receiving the reflected wave. The received transmitting wave may become noise in processing using the reflected wave. Because the reflected wave reception time measurement process includes the process of removing the transmitting wave from the reflected wave, the transmitting wave may be removed from the reflected wave, preventing the received transmitting wave from becoming noise. The process of removing the transmitting wave from the reflected wave is not specifically limited, and may be the prior-art process of removing transmitting waves from reflected waves. The process of removing the transmitting wave from the reflected wave may be, for example, a process of adding a feedback signal to the reflected wave, the feedback signal being generated by using a transmitting wave whose phase is inverted, to remove a transmitting wave that interferes with a reflected wave. 
     If the transmitting wave includes the frequency modulated continuous wave, it is preferable that the reflected wave reception time measurement process include the process of measuring the time from when the transmitting wave is transmitted until each of the one or more omni-directional antennae  104  receives the reflected wave, by using the comparison of the frequency of the transmitting wave and the frequency of the reflected wave. This makes it possible to measure the time until the reflected wave is received even for the frequency modulated continuous wave that is transmitted continuously. Therefore, more transmitting waves may illuminate the observed object. As such, then, more reflected waves may be generated. More reflected waves may be received than a case where the transmitting wave is the pulse wave and/or the chirp wave that is transmitted intermittently. As such, the location of the observed object may be estimated more reliably. 
     The generation of more reflected waves in the observed object and the measurement of the time from the transmission of the transmitting wave to the reflected wave may be achieved simultaneously by including the process of the reflected wave reception time measurement process removing the transmitting wave from the reflected wave when the transmitting wave includes the frequency modulated continuous wave and the process of measuring the time from when the transmitting wave is transmitted until each of the one or more omni-directional antennae  104  receives the reflected wave by using the comparison of the frequency of the transmitting wave and the frequency of the reflected wave. As such, more reflected waves may be received and the location of the observed object may be estimated even more reliably. 
     [Step S 17 : Estimate the Location of the Observed Object] 
     Turn back to  FIG. 3 . For each of the one or more observed objects where the reflected wave is generated, the controller  102  estimates the location of the observed object by using the time from the transmission of the transmitting wave until each of the one or more omni-directional antennae  104  receives the reflected wave R (step S 17 ). The controller  102  shifts the processing to step S 11  and repeats the processing of steps S 11  to S 17 . This allows the location of the observed object to be estimated for each of the one or more observed objects where the reflected wave is generated. The process of estimating the location of the observed object is not specifically limited. 
     The time from the transmission of the transmitting wave to the reception of the reflected wave varies depending on the distance from the omni-directional antenna  104  to the observed object. Therefore, the distance from the omni-directional antenna  104  to the observed object may be measured by using the time from the transmission of the transmitting wave T to the reception of the reflected wave R. 
     If the number of the omni-directional antennae  104  is two or more, and the process of controlling the omni-directional antenna  104  so as to receive the reflected wave in step S 13  includes the process of controlling the two or more omni-directional antennae  104  so as to receive the reflected wave, the process of estimating the location of the observed object preferably includes the process of specifying the approximately circular space including the observed object. 
     In a three-dimensional space, it is known that a location of a point where respective distances from two points at different locations are known is included in a circular region that has a center on a straight line passing through these two points and that is included in a plane perpendicular to the straight line. If the number of the omni-directional antennae  104  is two or more, and the process of controlling the omni-directional antenna  104  so as to receive the reflected wave in step S 13  includes the process of controlling the two or more omni-directional antennae  104  so as to receive the reflected wave, each distance from each of the two or more omni-directional antennae  104  to the observed object may be specified by using the time from the transmission of the transmitting wave until each of the two or more omni-directional antennae  104  receives the reflected wave. Therefore, the approximately circular space including the observed object may be specified by using the positional relationship of the two or more omni-directional antennae  104  and the specified two or more distances. 
     If the number of the omni-directional antennae  104  is three or more, the three or more omni-directional antennae  104  are disposed non-linearly, and the process of controlling the omni-directional antenna  104  so as to receive the reflected wave in step S 13  includes a process of controlling the three or more omni-directional antennae  104  disposed non-linearly so as to receive the reflected wave, it is preferable that the process of estimating the observed object include the process of specifying the two locations including the observed object. 
     In a three-dimensional space, it is known that a location of a point where respective distances from three points at different locations are known is any of two points located mutually symmetrically with respect to a plane defined by these three points. If the number of the omni-directional antennae  104  is three or more, the three or more omni-directional antennae  104  are disposed non-linearly, and the process of controlling the omni-directional antenna  104  so as to receive the reflected wave in step S 13  includes the process of controlling the three or more omni-directional antennae  104  disposed non-linearly so as to receive the reflected wave, each of the distances from each of the three or more omni-directional antennae  104  to the observed object may be specified by using the time from the transmission of the transmitting wave until each of the three or more omni-directional antennae  104  receives the reflected wave. Therefore, the two locations including the observed object may be specified by using the positional relationship of the three or more omni-directional antennae  104  and the specified three or more distances. 
     If the number of the omni-directional antennae  104  is four or more, the four or more omni-directional antennae  104  are disposed so that at least the one omni-directional antenna  104  is not on the same plane, and the process of controlling the omni-directional antenna  104  so as to receive the reflected wave in step S 13  includes a process of controlling the four or more omni-directional antennae  104  disposed so that at least the one omni-directional antenna  104  is not on the same plane so as to receive the reflected wave, it is preferable that the process of estimating the location of the observed object include the process of specifying the location of the observed object. 
     In this case, the four or more omni-directional antennae  104  disposed so that at least the one omni-directional antenna  104  not on the same plane receives the reflected wave. As such, the two locations including the observed object may be specified by using the time from the transmission of the transmitting wave to the reception of the reflected wave by each of the three or more omni-directional antennae  104  on the same plane. The specified two locations are in locations mutually symmetrical with respect to a plane defined by these three or more omni-directional antennae  104 . The one omni-directional antenna  104 , which is not coplanar, is not on this plane. Therefore, each of the distances to the two locations specified by the one omni-directional antenna  104 , which are not on the same plane, are not equal to each other. Therefore, it may be specified which of the specified two locations is the observed object, by using the time from the transmission of the transmitting wave to the reception of the reflected wave by the one omni-directional antenna  104 , which is not on the same plane. 
     &lt;Usage Examples&gt; 
       FIG. 12  is a conceptual diagram illustrating a second transmitting wave T 2  transmitted from a parabola antenna C of the prior art.  FIG. 13  is a conceptual diagram illustrating a fourth transmitting wave T and a fifth transmitting wave T 5  transmitted from the radar device  101 .  FIG. 14  is a conceptual diagram illustrating a process of specifying a distance to the observed object O 1  by using the time until the first reflected wave R 1  is received.  FIG. 15  is a conceptual diagram illustrating a process of specifying an approximately circular region including an observed object O 6  by using time until each of the first omni-directional antenna  104  and the second omni-directional antenna  104   b  receives a sixth reflected wave R 6 .  FIG. 16  is a conceptual diagram illustrating a process of specifying two locations including a location of the observed object O 6  by using the time until each of the first omni-directional antenna  104   a , the second omni-directional antenna  104   b , and a third omni-directional antenna  104   c  receives the sixth reflected wave R 6  and detection of an arrival angle.  FIG. 17  is a conceptual diagram illustrating a process of specifying the location of the observed object O 6  by using time until each of the first omni-directional antenna  104   a , the second omni-directional antenna  104   b , the third omni-directional antenna  104   c , and a fourth omni-directional antenna  104   d  receives the sixth reflected wave R 6  and the detection of the arrival angle. Hereinafter, description is given of usage examples of the radar device  101  in the present embodiment with reference to  FIG. 12  to  FIG. 17 , where appropriate. 
     [Transmitting the Transmitting Wave] 
     The user who uses the radar device  101  instructs the controller  102  to transmit the transmitting wave T. The controller  102  controls the transmitter  103  so as to provide the omni-directional antenna  104  with the transmission signal that causes the transmitting wave T to be transmitted. The transmitter  103  provides the antenna for transmission  104  with the transmission signal. Then, the transmitting wave T is transmitted from the omni-directional antenna  104 . 
     With reference to  FIG. 12  and  FIG. 13 , description is given of a difference between a second transmitting wave T 2  transmitted by the parabola antenna C of the prior art and a fourth transmitting wave T 4  and a fifth transmitting wave T 5  that are transmitted from the radar device  101  of the present embodiment. 
     As illustrated in  FIG. 12 , the prior-art parabola antenna C is used by orienting the parabola antenna C to a linear direction. Therefore, the second transmitting wave T 2  transmitted by the prior-art parabola antenna C is transmitted to a direction from the parabola antenna C toward a second observed object O 2 . At this time, the second transmitting wave T 2  does not illuminate a third observed object located in a direction different from a direction of the parabola antenna C. Therefore, the third observed object O 3  generates no reflected wave. As such, it is not possible to estimate the third observed object O 3 . 
     The radar device  101  of the present embodiment of the present embodiment is able to transmit the transmitting wave in a plurality of directions that are different from each other, by the digital beamforming. Therefore, as illustrated in  FIG. 13 , it is possible to transmit the fifth transmitting wave T 5  in a direction from the radar device  101  toward the fifth observed object O 5 , and simultaneously transmit the fourth transmitting wave T 4  from the radar device  101  toward the fourth observed object O 4 . Therefore, both the fourth observed object O 4  and the fifth observed object O 5  may generate the reflected wave. As such, a location of the fourth observed object O 4  and a location of the fifth observed object may be estimated, respectively. 
     [Receiving the Reflected Wave] 
     The controller  102  controls each of the first omni-directional antenna  104   a , the second omni-directional antenna  104   b , the third omni-directional antenna  104   c , and the fourth omni-directional antenna  104   d  so as to receive the sixth reflected wave R 6  generated when the transmitting wave T illuminates the first observed object O 6 . Each of the first omni-directional antenna  104   a , the second omni-directional antenna  104   b , the third omni-directional antenna  104   c  receives the sixth reflected wave R 6 . 
     [Measuring the Time Until the Reflected Wave is Received] 
     The controller  102  measures the time from when the transmitting wave T is transmitted until each of the first omni-directional antenna  104   a , the second omni-directional antenna  104   b , the third omni-directional antenna  104   c , and the fourth omni-directional antenna  104   d  receives the sixth reflected wave R 6 . 
     [Estimating the Location of the Observed Object] 
     The controller  102  estimates the location of the sixth observed object O 6  by using the time until the measured sixth reflected wave R 6  is received. 
     [Process of Specifying the Distance from the Omni-Directional Antenna to the Observed Object] 
     With reference to  FIG. 14 , description is given of a process of specifying the distance from the omni-directional antenna  104  to the sixth observed object O 6  in a case where the radar device  101  includes only the first omni-directional antenna  104   a.    
     The transmitting wave T enters the sixth observed object O 6 . Then, the sixth reflected wave R 6  is generated. This sixth reflected wave R 6  is received by the omni-directional antenna  104   a  in the same direction as the transmitting wave T. The measured time until the sixth reflected wave R 6  is received is defined in accordance with a first distance D 1  from the first omni-directional antenna  104   a  to the sixth observed object O 6 . Therefore, use of the measured time until the sixth reflected wave R 6  is received makes it possible to measure an a-th distance Da from the first omni-directional antenna  104   a  to the sixth observed object O 6 . 
     [Process of Specifying the Approximately Circular Space] 
     With reference to  FIG. 15 , description is given of a process of specifying an approximately circular fourth space A 4  including the sixth observed object O 6  in a case where the radar device  101  includes the first omni-directional antenna  104   a  and the second omni-directional antenna  104   b.    
     In a three-dimensional space, it is known that a location of a point where respective distances from two points at different locations are known is included in a circular region that has a center on a straight line passing through these two points and that is included in a plane perpendicular to the straight line. It is also known that a location of a point where a distance from a predetermined location and a difference between the distance from the predetermined location and a distance from a location different from the predetermined location are known is included in the circular region that has the center on a straight line passing through these two locations and that is included in the plane perpendicular to the straight line. 
     It is possible to measure the a-th distance Da from the first omni-directional antenna  104   a  to the sixth observed object O 6  by using the time from when the transmitting wave T is transmitted until the first omni-directional antenna  104   a  receives the sixth reflected wave R 6 . It is also possible to measure a distance difference between a b-th distance from the second omni-directional antenna  104   b  to the sixth observed object O 6  and the a-th distance Da, by using information (for example, a phase difference and/or a frequency difference of each of the sixth reflected wave R 6  received by the first omni-directional antenna  104   a  and the sixth reflected wave R 6  received the second omni-directional antenna  104   b , or the like) regarding a difference between the time until the first omni-directional antenna  104   a  receives the sixth reflected wave R 6  and the time until the second omni-directional antenna  104   b  receives the sixth reflected wave R 6 . The first omni-directional antenna  104   a  and the second omni-directional antenna  104   b  have a specific positional relationship. Therefore, by using a first line segment X 1  connecting the first omni-directional antenna  104   a  and the second omni-directional antenna  104   b , the the distance Da, and the aforementioned distance difference, it is possible to specify the approximately circular fourth space A 4  having the first center C 1  on a straight line extended from the line segment X 1 . 
     The process of specifying the fourth space A 4  is not specifically limited, and may be, for example, a process of specifying an arrival angle of the sixth reflected wave R 6  in the first omni-directional antenna  104   a  by using the phase difference and/or the frequency difference of each of the sixth reflected wave R 6  received by the first omni-directional antenna  104   a  and the sixth reflected wave R 6  received the second omni-directional antenna  104   b  as well as a calculation related to the expression (2). By specifying the arrival angle, it is possible to specify the fourth space A 4  using the arrival angle and the a-th distance Da. 
     [Process of Specifying the Two Locations] 
     With reference to  FIG. 16 , description is given of a process of specifying a third location L 3  and a fourth location L 4  that include the sixth observed object O 6  in a case where the radar device  101  includes the first omni-directional antenna  104   a , the second omni-directional antenna  104   b , and the third omni-directional antenna  104   c.    
     Similarly to the process of specifying the approximately circulate space, it is possible to specify the approximately circular fourth space A 4  by using the time until each of the first omni-directional antenna  104   a  and the second omni-directional antenna  104   b  receives the sixth reflected wave R 6 , or the like. It is also possible to specify an approximately circular fifth space A 5  by using the second omni-directional antenna  104   b  and the third omni-directional antenna  104   c . At this time, the fifth space A 5  has a second center C 2  on a straight line extended from a second line segment X 2 , the second line segment X 2  connecting the second omni-directional antenna  104   b  and the third omni-directional antenna  104   c . It is also possible to specify an approximately circular sixth space A 6  by using the time until each of the first omni-directional antenna  104   a  and the third omni-directional antenna  104   c  receives the sixth reflected wave R 6 , or the like. At this time, the sixth space A 6  has a third center C 3  on a straight line extended from a third line segment X 3 , the third line segment X 3  connecting the first omni-directional antenna  104   a  and the third omni-directional antenna  104   c.    
     The fourth space A 4 , the fifth space A 5 , and the sixth space A 6  have two intersecting points. Therefore, it is possible to specify the third location L 3  and the fourth location L 4  that include the sixth observed object O 6 , by using these intersecting points. If it is known that the location where the sixth observed object O 6  is located is in an approximately semi-spherical area centered around the radar device  101 , such as when the radar device  101  is installed on the ground, or the like, it is possible to determine that the location of the sixth observed object O 6  is the third location L 3 . 
     [Process of Specifying the Location of the Observed Object] 
     With reference of  FIG. 17 , description is given of a process specifying the location of the sixth observed object O 6  in a case where the radar device  101  includes the first omni-directional antenna  104   a , the second omni-directional antenna  104   b , the third omni-directional antenna  104   c , and the fourth omni-directional antenna  104   d.    
     As described in the process of specifying the two locations, if the radar device  101  includes the first omni-directional antenna  104   a , the second omni-directional antenna  104   b , and the third omni-directional antenna  104   c , it is possible to specify the third location L 3  and the fourth location L 4  that include the sixth observed object O 6 . It is possible to measure a d-th distance Dd from the fourth omni-directional antenna  104   d  to the observed object, by using the time until the fourth omni-directional antenna  104   d  receives the sixth reflected wave R 6 . 
     The third location L 3  and the fourth location L 4  are in locations that are mutually symmetrical to a plane defined by the first omni-directional antenna  104   a , the second omni-directional antenna  104   b , and the third omni-directional antenna  104   c . The fourth omni-directional antenna  104   d  is not on this plane. Therefore, the d-th distance Dd from the fourth omni-directional antenna  104   d  to the third location L 3  and an e-th distance De from the fourth directional antenna  104   d  to the fourth location L 4  differ from each other. Therefore, it is possible to determine that of the third location L 3  and the fourth location L 4 , the third location L 3  is the location of the sixth observed object O 6 , by using the d-th distance Dd from the fourth omni-directional antenna  104   d  to the observed object. 
     [Mounting on a Flight Vehicle] 
     The radar device  101  is usable as a radar device to be mounted on a flight vehicle exemplified by an unmanned aerial vehicle such as a drone, etc., a helicopter, a multicopter, a balloon, an airship, a passenger plane, and a cargo airplane, or the like. 
     If reflected waves are received from a wide azimuth range using the prior-art radar device that is used by being oriented linearly, a rotation mechanism that rotates the radar device may be necessary. Alternatively, it may be necessary to include a plurality of radar devices for each azimuth direction in which the reflected wave is received. Mounting the rotation mechanism and/or the plurality of radar devices on a flight vehicle may increase weight of the flight vehicle. The increased weight of the flight vehicle may degrade the performance of the flight vehicle that is exemplified by a navigation speed, a cruising distance, payload, stability during flight, or the like. 
     Since the radar device  101  is able to receive reflected waves from a wide azimuth range, the rotation mechanism is not necessary, and it is not necessary to include the plurality of radar devices  101 . This may prevent an increase in the weight of the flight vehicle and prevent a deterioration in the performance of the flight vehicle. 
     [Mounting on a Vehicle] 
     The radar device  101  is usable as a radar device to be mounted on a vehicle exemplified by a passenger car, transport vehicle, and a service vehicle, or the like. 
     A location of an observed object (for example, an oncoming car, a following car, and a preceding car, or the like) in the periphery of a vehicle is estimated by means of a radar device mounted on the vehicle. By estimating the location of the observed object in the periphery of the vehicle, accidents such as a collision between the vehicle and the observed object, or the like may be prevented. 
     In the meantime, if the observed object in the periphery of the vehicle is a traveling vehicle, a direction from the radar device toward the observed object may change significantly in a short time. If such a location of the observed object is estimated by using a device that combines the prior-art radar device, which is used by being oriented linearly, with the rotation mechanism, there may be a case where rotations of the radar device by the rotation mechanism are not able to follow a change in the direction. 
     The radar device  101  may select a signal for each azimuth direction to the observed object by the digital beamforming. As such, the reflected wave may be identified even if the direction from the radar device toward the observed object changes significantly in a short time. Therefore, even if the observed object is a travelling vehicle in the periphery of the vehicle, the location of the observed object may be estimated. 
     [Mounting on a Man-Made Satellite] 
     The radar device  101  is usable as a radar device to be mounted on a man-made satellite exemplified by a communication satellite, meteorological satellite, or an observation satellite, or the like. 
     If reflected waves are received from a wide azimuth range using the prior-art radar device that is used by being oriented linearly, a rotation mechanism that rotates the radar device may be necessary. Alternatively, it may be necessary to include a plurality of radar devices for each azimuth direction in which the reflected wave is received. If a mechanical rotation mechanism is mounted on the man-made satellite, there may arise a problem that lubricating oil used for rotating parts evaporates due to a vacuum, a problem that reaction accompanying the rotation affects posture control of the man-made satellite, or the like. Moreover, usually, the weight of a man-made satellite to be launched using a rocket is strictly limited. As such, if the radar device is mounted on a man-made satellite, improvement of the weight related to the radar device may be called for. 
     The radar device  101  is able to receive the reflected wave from the wide azimuth range without using the mechanical rotation mechanism or without including the plurality of radar devices  101 . This may solve the problem that the lubricating oil used for the rotating parts evaporates due to the vacuum, the problem that the reaction accompanying the rotation affects the posture control of the man-made satellite, or the like. Further, the weight of the radar device to be mounted on the man-made satellite may be improved. 
     [Use as a Ground Radar Base] 
     The radar device  101  is usable as a ground radar base to be installed on the ground. The radar device  101  may receive the reflected wave from the wide azimuth range. As such, the radar device  101  is usable as a ground radar base for estimating the location of the observed object in the wider azimuth range. 
     [Communication System] 
       FIG. 18  is a conceptual diagram illustrating a communication system using the radar device  101 . Hereinafter, with reference to  FIG. 18 , description is given of usage examples in which the radar device  101  of the present embodiment is used in the communication system. 
     A first man-made satellite S 1 , a second man-made satellite S 2 , and an unmanned aerial vehicle A include a radar device  101 S 1 , a radar device  101 S 2 , and a radar device  101 A, respectively, in this order. A radar device  101   b  is used as a base station. A radar device  101   g   1  and a radar device  101   g   2  are used as ground stations. A vehicle V includes the prior-art parabola antenna C. 
     The radar device  101  is able to orient the transmitting wave in an arbitrary direction using the digital beamforming. Therefore, even for the man-made satellite S 1  that goes around in an orbit and whose position is not fixed, the radar device  101   b  used as the base station is able to orient the transmitting wave to the direction of the man-made satellite S 1  from the radar device  101   b . This allows the radar device  101   b  to transmit the transmitting wave to the radar device  101 S 1  included in the man-made satellite S 1 . Further, using the digital beamforming, the radar device  101  is able to receive the reflected wave from an arbitrary direction. Therefore, the radar device  101  is able to receive the transmitting wave from the radar device  101 S 1  by using the digital beamforming. Therefore, the radar device  101   b  is able to establish a communication link Wbs 1  with the radar device  101 S 1 . 
     Since the digital beamforming capable of orienting the array antenna in a plurality of directions is used, the radar device  101   b  is able to establish a communication link Wbs 2  with the radar device  10152  included in the man-made satellite S 2 , while establishing the communication link Wbs 1  with the radar device  10151 . Therefore, the radar device  101   b  may act as a relay station that relays a plurality of communication links. 
     If a mechanical rotation mechanism is mounted on the man-made satellite, there may arise a problem that lubricating oil used for rotating parts evaporates due to a vacuum, a problem that reaction accompanying the rotation affects posture control of the man-made satellite, or the like. The digital beamforming is able to orient the transmitting wave in arbitrary direction without using the mechanical rotation mechanism. The radar device  101  including the four or more omni-directional antennae  104  disposed so that at least the one omni-directional antenna  104  is not on the same plane may orient the omni-directional antenna  104  in an arbitrary direction. Therefore, even if a positional relationship with the radar device  101   b  varies as the man-made satellite S 1  orbits, the radar device  101 S 1  included in the man-made satellite S 1  is able to continuously establish the communication links Wbs 1 , Wss, and Wgs 1 , and a communication link Wcs 1 , respectively, with the radar device  101   b ,  101 S 2 , and  101   g   1 , and with the parabola antenna C. 
     The radar device  101  is also usable as the radar device  101  while establishing the communication link. The radar device  101 S 2  included in the man-made satellite S 2  may transmit the transmitting wave T to debris b and receive the reflected wave R, while establishing the communication links Wss, Sbs 2 , Was 1 , and Wgs 2  respectively with the radar devices  101 S 1 ,  101   b ,  101 A, and  101   g   2 . Therefore, by using the radar device  101 , the estimation of the location of the observed object and the establishment of the communication links may be performed simultaneously, without preparing another antenna for communication. Therefore, a configuration of the man-made satellite S 2  may be simplified. 
     Although the respective embodiments of the present invention have been described above, the present invention is not limited to the aforementioned embodiments. In addition, the effects described in the aforementioned various embodiments merely recite the most preferred effects derived from the present invention, and the effects of the present invention are not limited to those described in the aforementioned various embodiments. In addition, the aforementioned various embodiments have been described in detail to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations. Further, for one embodiment, it is possible to replace some of a configuration thereof with a configuration of another embodiment. Moreover, for one embodiment, it is also possible to add the configuration of another embodiment to the configuration thereof. 
     DESCRIPTION OF THE REFERENCE NUMERALS 
     
         
           1  Radar device 
           2  Controller 
           3  Transmitter 
           4  Linear array antenna 
           41  Linear array antenna structure 
           42  Signal distributor 
           43  Phase shifter 
           44  Antenna element 
           45  Converter 
           5  Support Structure 
           101  Radar device 
           102  Controller 
           103  Transmitter 
           104  Omni-directional antenna 
           141  Omni-directional antenna element 
           142  Converter 
           105  Support structure 
           151  Omni-directional antenna support structure 
           152  Base structure 
         A Unmanned aerial vehicle 
         A 1  First region 
         A 2  Second region 
         A 3  Third region 
         A 4  Fourth region 
         A 5  Fifth region 
         A 6  Sixth region 
         b Debris 
         C Prior-art parabola antenna 
         C 1  First center 
         C 2  Second center 
         C 3  Third center 
         Da a-th distance 
         db b-th distance 
         Dc c-th distance 
         Dd d-th distance 
         De e-th distance 
         L 1  First location 
         L 2  Second location 
         L 3  Third location 
         L 4  Fourth location 
         O 1  First observed object 
         O 2  Second observed object 
         O 3  Third observed object 
         O 4  Fourth observed object 
         O 5  Fifth observed object 
         O 6  Sixth observed object 
         P Prior-art antenna for transmission 
         R Reflected wave 
         R 1  First reflected wave 
         R 6  Sixth reflected wave 
         S 1  First man-made satellite 
         S 2  Second man-made satellite 
         T Transmitting wave 
         V Vehicle 
         X 1  First line segment 
         X 2  Second line segment 
         X 3  Third line segment