Patent ID: 12204045

DETAILED DESCRIPTION

A technique (beamforming) of forming a beam of transmission waves transmitted from a plurality of transmission antennas is conventionally known in technical fields such as wireless communication. With beamforming, a beam of transmission waves transmitted from a plurality of transmission antennas can be formed in a predetermined direction to, for example, extend the reaching distance of radio waves. When forming the beam of the transmission waves transmitted from the plurality of transmission antennas, if the beam can be accurately aimed in a predetermined direction, the measurement accuracy (detection accuracy) of the distance from a surrounding object and the like can be improved. As an example of a technique of improving object detection accuracy, JP 2015-155883 A (PTL 1) proposes preventing erroneous estimation by a side lobe and a grating lobe when estimating the azimuth angle of an object using a reception array antenna. It could be helpful to provide an electronic device, a control method of an electronic device, and a control program of an electronic device that improve object detection accuracy. According to an embodiment, it is possible to provide an electronic device, a control method of an electronic device, and a control program of an electronic device that improve object detection accuracy. Some of the disclosed embodiments will be described in detail below, with reference to the drawings.

An electronic device according to an embodiment can be mounted in a vehicle (mobile body) such as a car (automobile) to detect a certain object around the mobile body. The electronic device according to the embodiment can transmit transmission waves to the surroundings of the mobile body from transmission antennas installed in the mobile body. The electronic device according to the embodiment can also receive reflected waves resulting from reflection of the transmission waves, by reception antennas installed in the mobile body. The transmission antennas and/or the reception antennas may be included in, for example, a radar sensor installed in the mobile body.

The following will describe a structure in which the electronic device according to the embodiment is mounted in a car (an example of a mobile body) such as a passenger car, as a typical example. The electronic device according to the embodiment is, however, not limited to being mounted in a car. The electronic device according to the embodiment may be mounted in various mobile bodies such as a self-driving car, a bus, a truck, a motorcycle, a bicycle, a ship, an airplane, a drone, a robot, and a pedestrian. The electronic device according to the embodiment is not limited to being mounted in a mobile body that moves with its own power. For example, the mobile body in which the electronic device according to the embodiment is mounted may be a trailer portion towed by a tractor. In a situation in which at least one of a sensor part and an object can move, the electronic device according to the embodiment can detect the object present around the sensor part and measure, for example, the distance between the sensor part and the object. The electronic device according to the embodiment can also measure, for example, the distance between the sensor part and the object when both the sensor part and the object are stationary.

An example of object detection by the electronic device according to the embodiment will be described below.

FIG.1is a diagram illustrating a use state of the electronic device according to the embodiment.FIG.1illustrates an example in which a sensor including transmission antennas and reception antennas according to the embodiment is installed in a mobile body.

A sensor5including transmission antennas and reception antennas according to the embodiment is installed in a mobile body100illustrated inFIG.1. An electronic device1according to the embodiment is mounted (e.g. included) in the mobile body100illustrated inFIG.1. A specific structure of the electronic device1will be described later. For example, the sensor5may include the transmission antennas and/or the reception antennas. The sensor5may include at least one of the other functional parts as appropriate, such as at least part of a controller10(FIG.2) included in the electronic device1. The mobile body100illustrated inFIG.1may be a vehicle of a car such as a passenger car. The mobile body100illustrated inFIG.1may be any type of mobile body. InFIG.1, for example, the mobile body100may move (run or slow down) in the Y-axis positive direction (direction of travel) in the drawing, move in other directions, or be stationary without moving.

As illustrated inFIG.1, the sensor5including a plurality of transmission antennas and a plurality of reception antennas is installed in the mobile body100. In the example illustrated inFIG.1, only one sensor5including transmission antennas and reception antennas is installed at the front of the mobile body100. The position at which the sensor5is installed in the mobile body100is not limited to the position illustrated inFIG.1, and may be any other position as appropriate. For example, the sensor5illustrated inFIG.1may be installed at the left, the right, and/or the back of the mobile body100. The number of sensors5may be any number greater than or equal to 1, depending on various conditions (or requirements) such as the range and/or accuracy of measurement in the mobile body100.

The sensor5transmits electromagnetic waves from the transmission antennas, as transmission waves. For example, in the case where there is a certain object (e.g. an object200illustrated inFIG.1) around the mobile body100, at least part of the transmission waves transmitted from the sensor5is reflected off the object to become reflected waves. As a result of the reflected waves being received by, for example, a reception antenna of the sensor5, the electronic device1mounted in the mobile body100can detect the object.

The sensor5including the transmission antennas may be typically a radar (radio detecting and ranging) sensor that transmits and receives radio waves. The sensor5is, however, not limited to a radar sensor. For example, the sensor5according to the embodiment may be a sensor based on a technique of lidar (light detection and ranging, laser imaging detection and ranging) by lightwaves. Such sensors may include, for example, patch antennas and the like. Since the techniques of radar and lidar are already known, detailed description is simplified or omitted as appropriate.

The electronic device1mounted in the mobile body100illustrated inFIG.1receives reflected waves of transmission waves transmitted from the transmission antennas in the sensor5, by the reception antennas. Thus, the electronic device1can detect the object200present within a predetermined distance from the mobile body100. For example, the electronic device1can measure the distance L between the mobile body100as the own vehicle and the object200, as illustrated inFIG.1. The electronic device1can also measure the relative speed of the mobile body100as the own vehicle and the object200. The electronic device1can further measure the direction (arrival angle θ) in which the reflected waves from the object200reaches the mobile body100as the own vehicle.

The object200may be, for example, at least one of an oncoming car running in a lane adjacent to the mobile body100, a car running parallel to the mobile body100, and a car running ahead or behind in the same lane as the mobile body100. The object200may be any object around the mobile body100, such as a motorcycle, a bicycle, a stroller, a pedestrian, a guardrail, a median strip, a road sign, a sidewalk step, a wall, a manhole, and an obstacle. The object200may be moving or stopped. For example, the object200may be a car parked or stopped around the mobile body100. In the present disclosure, examples of the object200detected by the electronic device1include not only non-living objects but also living objects such as humans and animals. In the present disclosure, the object200detected by the electronic device1includes a target such as a human, a thing, or an animal detected by radar technology.

For example, the sensor5installed at the front of the mobile body100can form a beam of transmission waves in front of the mobile body100(i.e. beamforming). Here, the electronic device1controls the phase of the transmission waves transmitted from each of the plurality of transmission antennas so that the transmission waves of the plurality of transmission antennas will be in phase with each other in the front direction of the mobile body100(Y-axis positive direction). Consequently, the plurality of transmission waves intensify each other in the front direction of the mobile body100(Y-axis positive direction) and form the radio wave beam. As mentioned above, the use of the beamforming technique can improve, for example, the accuracy in the measurement of the distance from the object detected using the transmission waves. Moreover, with beamforming, the reaching distance of the transmission waves can be extended.

The electronic device1can, by appropriately controlling the phases of the transmission waves transmitted from the plurality of antennas, change the direction of the beam of the transmission waves. The electronic device1can aim the beam of the transmission waves transmitted from the transmission antennas40in any of various directions, by appropriately changing the phases of the transmission waves. Thus, the electronic device1can measure the direction (arrival angle θ) in which the reflected waves from the object200reach the mobile body100as the own vehicle. With beamforming, the radiation direction of the transmission waves can be controlled to improve the measurement accuracy of the angle toward the object.

FIG.2is a functional block diagram schematically illustrating an example of the structure of the electronic device1according to the embodiment. The structure of the electronic device1according to the embodiment will be described below.

As illustrated inFIG.2, the electronic device1according to the embodiment includes the sensor5and the controller10. In the electronic device1illustrated inFIG.2, one sensor5is connected to one controller10. However, the electronic device1according to the embodiment may include any number of controllers10and any number of sensors5. For example, in the electronic device1according to the embodiment, a plurality of sensors5may be connected to one controller10. InFIG.2, only one sensor5is illustrated in detail as a typical example of a plurality of sensors5that can be connected to the controller10.

The electronic device1according to the embodiment may also include a signal generator22, a frequency synthesizer24, a transmission controller30, power amplifiers36A and36B, and transmission antennas40A and40B. The sensor5may include at least the transmission antennas40A and40B. The sensor5may include one or more other functional parts such as the controller10, the transmission controller30, and the power amplifiers36A and36B. In the example illustrated inFIGS.1and2, the sensor5and the controller10are illustrated as separate functional parts. Alternatively, the sensor5may include part or whole of the controller10. The members included in the sensor5are not limited to the example illustrated inFIG.2, and any of the members illustrated inFIG.2may be not included in the sensor5. The transmission antennas40A and40B, reception antennas50A and50B, and the power amplifiers36A and36B may be contained in one housing as the sensor5. It is assumed herein that the number of transmission antennas is 2 and the number of reception antennas is 2. In an embodiment, however, any number of two or more transmission antennas and any number of two or more reception antennas may be provided.

The electronic device1illustrated inFIG.2includes two transmission antennas40A and40B. Hereafter, in the case where the transmission antennas40A and40B are not distinguished from each other in the electronic device1according to the embodiment, they are collectively referred to as “transmission antenna40”. The electronic device1illustrated inFIG.2may include two functional parts of any of the other types (e.g. the power amplifiers36A and36B). In the case where such a plurality of functional parts of the same type are not distinguished from each other, the functional parts are collectively referred to by omitting symbols such as A and B.

The electronic device1according to the embodiment may further include the reception antennas50A and50B, LNAs52A and52B, mixers54A and54B, IF units56A and56B, AD converters58A and58B, a distance estimation unit62, an angle estimation unit64, and a relative speed estimation unit66. For these functional parts, too, in the case where a plurality of functional parts of the same type are not distinguished from each other, the functional parts are collectively referred to by omitting symbols such as A and B. The sensor5may include the reception antennas50A and50B. The sensor5may include other functional parts such as the LNAs52A and52B.

The controller10included in the electronic device1according to the embodiment can control overall operation of the electronic device1, including control of each of the functional parts included in the electronic device1. The controller10may include at least one processor such as a central processing unit (CPU), to provide control and processing capacity for achieving various functions. The controller10may be implemented by one processor, by several processors, or by respective separate processors. Each processor may be implemented as a single integrated circuit (IC). Each processor may be implemented as a plurality of integrated circuits and/or discrete circuits communicably connected to one another. Each processor may be implemented based on any of other various known techniques. In an embodiment, the controller10may be implemented, for example, by a CPU and a program executed by the CPU.

As illustrated inFIG.2, the controller10may include a memory12, a detection range determination unit14, and a frequency selector16. The detection range determination unit14and the frequency selector16may each be configured as hardware having the function, configured as a microcomputer or the like, or configured as a processor such as a CPU and a program executed by the processor.

The memory12may store the program executed by the controller10, results of processes performed by the controller10, and the like. The memory12may function as a work memory of the controller10. The memory12may be implemented, for example, by a semiconductor memory, a magnetic disk, or the like. The memory12is, however, not limited to such, and may be any storage device. For example, the memory12may be a storage medium such as a memory card inserted in the electronic device1according to the embodiment. The memory12may be an internal memory of the CPU used as the controller10as described above.

The detection range determination unit14determines a range of object detection by the transmission waves T transmitted from the transmission antennas40and the reflected waves R received by the reception antennas50. In an embodiment, the detection range determination unit14may determine the object detection range based on estimation by at least one of a distance estimation unit62and an angle estimation unit64. The determination of the object detection range by the detection range determination unit14will be described in detail later. The detection range determination unit14may notify the frequency selector16of the determined object detection range.

The frequency selector16determines the frequency of the transmission waves T transmitted from the transmission antennas40. In an embodiment, for example, the frequency selector16selects a predetermined band part used to transmit the transmission waves T, in a predetermined frequency band prepared as a frequency band usable for detection. In an embodiment, the frequency selector16may select the predetermined band part used to transmit the transmission waves T, based on the detection range determined by the detection range determination unit14. The selection of the predetermined band part by the frequency selector16will be described in detail later. The frequency selector16may notify the frequency synthesizer24of the selected frequency. In this case, the frequency synthesizer24can increase the frequency of the transmission waves T to a frequency in the predetermined frequency band selected by the frequency selector16.

In the electronic device1according to the embodiment, the controller10can control the transmission controller30. In this case, the controller10may control the transmission controller30based on various information stored in the memory12. In the electronic device1according to the embodiment, the controller10may instruct the signal generator22to generate a signal, or control the signal generator22to generate a signal.

In the case where the mobile body100is a car, communication between electronic control units (ECUs) can be performed using a communication interface such as CAN (Controller Area Network). In this case, the controller10can acquire control information of the mobile body100from an ECU (e.g. a mobile body controller) or the like. Hence, in the electronic device1according to the embodiment, the controller10may determine a transmission wave transmission mode based on the acquired control information and the like. For example, the transmission wave transmission mode may be any of an operation mode (BF mode) in which beamforming is performed and an operation mode (normal mode) in which beamforming is not performed. The transmission wave transmission mode may be various settings in each of the modes. For example, the transmission wave transmission mode may define the number of transmission antennas (the number antennas) that transmit transmission waves in each of the modes. For example, the transmission wave transmission mode may define whether to perform beamforming and/or the angle of beamforming. Herein, the angle of beamforming may be an angle for increasing the gain of the beam for the installation location (position) of the transmission antennas40in the mobile body100in the case of performing beamforming.

Having determined the transmission mode, the controller10supplies setting information in the transmission mode to the transmission controller30. The setting information in the transmission mode may include, for example, information of the number of transmission antennas that transmit transmission waves in the transmission mode. The setting information in the transmission mode may include, for example, information of the power with which the transmission antennas transmit transmission waves in the transmission mode. The setting information in the transmission mode may include, for example, information of the phase of transmission waves transmitted from each of the plurality of transmission antennas40in the case of performing beamforming.

For such operation, for example, a table or the like in which each transmission mode is associated with setting information necessary for operation in the transmission mode may be stored in the memory12beforehand. For example, transmission wave phase information when performing beamforming in a transmission mode may be stored in the memory12in association with the installation location (position) and installation angle of the transmission antenna40in the mobile body100. In such a case, having determined the transmission mode, the controller10can read setting information corresponding to the determined transmission mode from the memory12and supply the setting information to the transmission controller30.

To change the reaching distance of transmission waves T transmitted from the transmission antenna40, for example, the transmission power of the transmission waves T may be adjusted to change the gain of the transmission antenna40and/or the gain of beamforming. In this case, the transmission power of the transmission waves T transmitted from the transmission antenna40and the gain of the transmission antenna40and/or the gain of beamforming may be stored in the memory12in association with each other.

The foregoing transmission modes and the setting information corresponding to each transmission mode may be generated as appropriate based on various conditions. In such a case, having determined the transmission mode, the controller10can supply the setting information corresponding to the determined transmission mode to the transmission controller30, even when the setting information is not stored in the memory12.

The signal generator22generates a signal (transmission signal) transmitted from the transmission antenna40as the transmission waves T, based on control by the controller10. When generating the transmission signal, for example, the signal generator22assigns the frequency of the transmission signal based on control by the controller10. For example, the signal generator22receives frequency information from the controller10, and generates a signal of a predetermined frequency in a frequency band of 77 GHz to 81 GHz. The signal generator22may include a functional part such as a voltage controlled oscillator (VCO). Herein, “a GHz to b GHz” denotes a GHz or more and less than b GHz, where a and b are any numbers. Herein, “a GHz to b GHz” may denote more than a GHz and b GHz or less, where a and b are any numbers.

The signal generator22may be configured as hardware having the function, configured as a microcomputer or the like, or configured as a processor such as a CPU and a program executed by the processor. Each functional part described below may be configured as hardware having the function, or, if possible, configured as a microcomputer or the like or configured as a processor such as a CPU and a program executed by the processor.

In the electronic device1according to the embodiment, the signal generator22may generate a transmission signal such as a chirp signal. In particular, the signal generator22may generate a signal (linear chirp signal) whose frequency linearly changes periodically. For example, the signal generator22may generate a chirp signal whose frequency linearly increases periodically from 77 GHz to 81 GHz with time. For example, the signal generator22may generate a signal whose frequency periodically repeats a linear increase (up-chirp) and decrease (down-chirp) from 77 GHz to 81 GHz with time. The signal generated by the signal generator22may be, for example, set by the controller10beforehand. The signal generated by the signal generator22may be, for example, stored in the memory12beforehand. Since chirp signals used in technical fields such as radar are already known, more detailed description is simplified or omitted as appropriate. The signal generated by the signal generator22is supplied to the frequency synthesizer24.

The frequency synthesizer24increases the frequency of the signal generated by the signal generator22to a frequency in a predetermined frequency band. The frequency synthesizer24may increase the frequency of the signal generated by the signal generator22to a frequency selected as the frequency of the transmission waves T transmitted from the transmission antenna40. The frequency selected as the frequency of the transmission waves T transmitted from the transmission antenna40may be, for example, set by the controller10. In an embodiment, the frequency synthesizer24may increase the frequency of the signal generated by the signal generator22to the frequency selected by the frequency selector16. The frequency selected as the frequency of the transmission waves T transmitted from the transmission antenna40may be, for example, stored in the memory12. The signal increased in frequency by the frequency synthesizer24is supplied to the transmission controller30and each mixer54.

The transmission controller30performs control to transmit the transmission signal supplied from the frequency synthesizer24as the transmission waves T from at least one of the plurality of transmission antennas40. As illustrated inFIG.2, the transmission controller30may include phase controllers32and power controllers34. As illustrated inFIG.2, the transmission controller30may perform control to transmit the transmission signal from the transmission antenna40as the transmission waves T, based on control by the controller10. Various information necessary for the controller10to control the transmission controller30may be stored in the memory12.

Each phase controller32controls the phase of the transmission signal supplied from the frequency synthesizer24. Specifically, the phase controller32may adjust the phase of the signal supplied from the frequency synthesizer24by advancing or delaying the phase of the signal as appropriate, based on control by the controller10. In this case, based on the path difference between the respective transmission waves T transmitted from the plurality of transmission antennas40, the phase controllers32may adjust the phases of the respective transmission signals. As a result of the phase controllers32adjusting the phases of the respective transmission signals as appropriate, the transmission waves T transmitted from the plurality of transmission antennas40intensify each other and form a beam in a predetermined direction (i.e. beamforming).

For example, in the case of transmitting the transmission waves T without beamforming in the normal mode, the phase controller32does not need to control the phase of the transmission signal transmitted as the transmission waves T from the transmission antenna40. For example, in the case of performing beamforming of the transmission waves T in the BF mode, the phase controller32may control the phase of a corresponding one of the plurality of transmission signals transmitted from the plurality of transmission antennas40as the transmission waves T, depending on the beamforming direction. In this case, the correlation between the beamforming direction and the amount of phase to be controlled in the transmission signal transmitted from each of the plurality of transmission antennas40may be stored in, for example, the memory12. The signal phase-controlled by the phase controller32is supplied to the corresponding power amplifier36.

Each power controller34is connected to the corresponding power amplifier36, as illustrated inFIG.2. The power controller34controls the amplification of power by the power amplifier36connected to the power controller34. By controlling the power amplifier36, the power controller34controls the transmission power of the transmission waves T transmitted from the transmission antenna40connected to the power amplifier36. For example, the power controller34can switch on and off the transmission power of the power amplifier36connected to the power controller34. That is, the power controller34can switch whether to transmit the transmission waves T from the transmission antenna40connected to the power amplifier36.

For example, the power controller34A can switch on and off the transmission power of the transmission waves T transmitted from the transmission antenna40A. The power controller34B can switch on and off the transmission power of the transmission waves T transmitted from the transmission antenna40B. Thus, the electronic device1can freely control whether to transmit the transmission waves T from the transmission antenna40A and/or the transmission antenna40B, based on control by both of the power controllers34A and34B. The power controller34may adjust the transmission power of the power amplifier36connected to the power controller34, as appropriate. Thus, the power controller34can define the number of transmission antennas40from which the transmission waves T are transmitted from among the plurality of transmission antennas40, for example based on the setting in the transmission mode. Various information necessary for control by the power controller34may be, for example, stored in the memory12. For example, the memory12may store the correlation between the control by each power controller34and the transmission power of the transmission waves T transmitted from the corresponding transmission antenna40. The memory12may store such correlation for each transmission mode.

The electronic device1according to the embodiment can set various transmission conditions of the transmission waves T transmitted from at least one of the plurality of transmission antennas40, based on control by the phase controllers32and/or the power controllers34in the transmission controller30. Specifically, the electronic device1according to the embodiment can set whether to perform beamforming, the beam direction in the case of performing beamforming, etc. In this case, for example, the memory12may store control information of the phase controllers32and/or the power controllers34corresponding to various transmission conditions of the transmission waves T. By reading the control information corresponding to the transmission conditions of the transmission waves T from the memory12, the controller10enables the control of the transmission waves T by the phase controllers32and/or the power controllers34. For example, in the case where the electronic device1operates in the normal mode (e.g. not performing beamforming), each power controller34controls the power when transmitting the transmission waves T depending on the antenna radiation gain of the corresponding transmission antenna40. For example, in the case where the electronic device1operates in the BF mode (e.g. performing beamforming), each phase controller32appropriately changes the phase of the transmission signal transmitted from the transmission antenna used from among the plurality of transmission antennas40. In an embodiment, when performing beamforming for the transmission waves T transmitted from a plurality of transmission antennas40, the number of beams, the beam shape, etc. can be variously set based on control by the phase controllers32and the power controllers34.

Each power amplifier36amplifies the power of the transmission signal supplied from the phase controller32, based on control by the power controller34. Since techniques of amplifying power of transmission signals are already known, more detailed description is omitted. The power amplifier36is connected to the transmission antenna40.

Each transmission antenna40outputs (transmits) the transmission signal amplified by the power amplifier36, as the transmission waves T. The sensor5may include a plurality of transmission antennas such as the transmission antennas40A and40B, as mentioned above. Since each transmission antenna40can be configured in the same way as transmission antennas used in known radar techniques, more detailed description is omitted.

Thus, the electronic device1according to the embodiment can transmit the transmission signal such as a chirp signal from the plurality of transmission antennas40as the transmission waves T. At least one of the functional parts included in the electronic device1may be contained in one housing having a structure that cannot be opened easily. For example, the transmission antennas40A and40B, the reception antennas50A and50B, and the power amplifiers36A and36B may be contained in one housing having a structure that cannot be opened easily. In the case where the sensor5is installed in the mobile body100such as a car, each transmission antenna40may transmit transmission waves T to outside the mobile body100through a member such as a radar cover. In this case, the radar cover may be made of a material that allows electromagnetic waves to pass through, such as synthetic resin or rubber. For example, the radar cover may be a housing of the sensor5. By covering the transmission antennas40with a member such as a radar cover, the risk that the transmission antennas40break or become defective due to external contact can be reduced. The radar cover and the housing are also referred to as “radome” (the same applies hereafter).

The electronic device1illustrated inFIG.2includes two transmission antennas40, e.g. the transmission antennas40A and40B, and transmits the transmission waves T by the two transmission antennas40. Hence, the electronic device1illustrated inFIG.2includes two functional parts of the same type necessary for transmitting the transmission waves T from the two transmission antennas40, for each type of functional part. Specifically, the transmission controller30includes two phase controllers32, e.g. the phase controllers32A and32B. The transmission controller30also includes two power controllers34, e.g. the power controllers34A and34B. The electronic device1illustrated inFIG.2also includes two power amplifiers36, e.g. the power amplifiers36A and36B.

Although the electronic device1illustrated inFIG.2includes two transmission antennas40, the number of transmission antennas40included in the electronic device1according to the embodiment may be any number greater than or equal to 2, e.g. three or more transmission antennas40. In this case, the electronic device1according to the embodiment may include the same number of power amplifiers36as the plurality of transmission antennas40. The electronic device1according to the embodiment may also include the same number of phase controllers32and the same number of power controllers34as the plurality of transmission antennas40.

Each reception antenna50receives reflected waves R. The reflected waves R result from reflection of the transmission waves T off the object200. The reception antennas50may include a plurality of antennas such as the reception antennas50A and SOB. Since each reception antenna50can be configured in the same way as reception antennas used in known radar techniques, more detailed description is omitted. The reception antenna50is connected to the LNA52. A reception signal based on the reflected waves R received by the reception antenna50is supplied to the corresponding LNA52.

The electronic device1according to the embodiment can receive the reflected waves R as a result of the transmission waves T transmitted as the transmission signal such as a chirp signal being reflected off the object200, by the plurality of reception antennas50. At least one of the functional parts included in the electronic device1, such as the plurality of reception antennas50, may be contained in one housing having a structure that cannot be opened easily. In the case where the sensor5is installed in the mobile body100such as a car, each reception antenna50may receive the reflected waves R from outside the mobile body100through a member such as a radar cover. In this case, the radar cover may be made of a material that allows electromagnetic waves to pass through, such as synthetic resin or rubber. For example, the radar cover may be a housing of the sensor5. By covering the reception antennas50with a member such as a radar cover, the risk that the reception antennas50break or become defective due to external contact can be reduced.

The sensor5may include, for example, all transmission antennas40and all reception antennas50. In the case where a reception antenna50is installed near a transmission antenna40, these antennas may be included in one sensor5in combination. For example, one sensor5may include at least one transmission antenna40and at least one reception antenna50. For example, one sensor5may include a plurality of transmission antennas40and a plurality of reception antennas50. In such a case, for example, one radar sensor may be covered with one member such as a radar cover.

Each LNA52amplifies a reception signal based on the reflected waves R received by the reception antenna50, with low noise. The LNA52may be a low-noise amplifier, and amplifies the reception signal supplied from the reception antenna50with low noise. The reception signal amplified by the LNA52is supplied to the corresponding mixer54.

Each mixer54mixes (multiplies) the reception signal of RF frequency supplied from the LNA52and the transmission signal supplied from the frequency synthesizer24, to generate a beat signal. The beat signal generated by the mixer54is supplied to the corresponding IF unit56.

Each IF unit56performs frequency conversion on the beat signal supplied from the mixer54, to lower the frequency of the beat signal to intermediate frequency (IF). The beat signal lowered in frequency by the IF unit56is supplied to the corresponding AD converter58.

Each AD converter58digitizes the analog beat signal supplied from the IF unit56. The AD converter58may include any analog-to-digital converter (ADC). The beat signal digitized by the AD converter58is supplied to the distance estimation unit62in the case where the number of reception antennas50is one, and supplied to the distance estimation unit62and the angle estimation unit64in the case where the number of reception antennas50is two or more.

The distance estimation unit62estimates the distance between the mobile body100having the electronic device1mounted therein and the object200, based on the beat signal supplied from the AD converter58. The distance estimation unit62may include, for example, a FFT processor. The FFT processor may be composed of any circuit, chip, or the like for performing fast Fourier transform (FFT) processing. The FFT processor performs FFT processing on the beat signal digitized by the AD converter58. For example, the distance estimation unit62may perform FFT processing on the complex signal supplied from the AD converter58. In the case where the peak of the result obtained by the FFT processing is greater than or equal to a predetermined threshold, the distance estimation unit62may determine that the object200is present at distance corresponding to the peak. Information of the distance estimated by the distance estimation unit62may be, for example, supplied to the controller10.

The angle estimation unit64estimates the direction from the mobile body100having the electronic device1mounted therein toward the object200(i.e. the direction in which the reflected waves R reach the reception antenna50), based on the beat signal supplied from the AD converter58. The angle estimation unit64may include, for example, a FFT processor, as with the distance estimation unit62. As mentioned above, the distance estimation unit62may perform FFT processing on the complex signal supplied from the AD converter58, and, in the case where the peak of the result obtained by the FFT processing is greater than or equal to the predetermined threshold, determine that the object200is present at distance corresponding to the peak. In this case, the angle estimation unit64may estimate the direction in which the reflected waves R reach the reception antenna50(i.e. the direction from the object200toward the reception antenna50), based on the result of receiving the reflected waves R from the object200by the plurality of reception antennas50. The direction in which the reflected waves R reach the reception antennas50, which is estimated by the angle estimation unit64, may be the direction from the object200toward the reception antennas50. Information of the direction (the direction of arrival or the angle of arrival) estimated by the angle estimation unit64may be, for example, supplied to the controller10.

The relative speed estimation unit66estimates the relative speed of the object200and the mobile body100, based on the beat signal.

Typically, a frequency spectrum can be obtained by performing FFT processing on the beat signal. From such a frequency spectrum, the FFT processor can estimate whether the object200is present within the range of the beam of the transmission waves T transmitted from the transmission antenna40. That is, the FFT processor can estimate whether the object200is present within the range of the beam emitted from the sensor5including the transmission antenna40, based on the FFT-processed beat signal. In the case where the object200is present, the FFT processor can estimate the distance between the sensor5including the transmission antenna40and the object200, based on the FFT-processed beat signal. Further, in the case where the object200is present, the FFT processor can estimate the positional relationship between the sensor5including the transmission antenna40and the object200, based on the FFT-processed beat signal. In the distance estimation unit62, the angle estimation unit64, and the relative speed estimation unit66, a Fourier transform other than a fast Fourier transform (FFT) may be performed.

Thus, the electronic device1according to the embodiment may measure (estimate) the distance between the object200and the mobile body100, based on the beat signal obtained from the signal transmitted as the transmission waves T and the signal received as the reflected waves R. The electronic device1according to the embodiment may also measure (estimate) the positional relationship between the object200and the mobile body100(e.g. the angle of arrival at which the reflected waves R reach the mobile body100from the object200), based on the beat signal. The electronic device1according to the embodiment may further measure (estimate) the relative speed of the object200and the mobile body100, based on the beat signal. The controller10may perform various computation, estimation, control, and the like, using the information of the distance supplied from the distance estimation unit62, the information of the direction (angle) supplied from the angle estimation unit64, and the like. Since the technique of estimating the distance, direction, etc. to a certain object from which reflected waves are reflected based on a beat signal acquired using millimeter wave radar of 79 GHz band or the like is known, more detailed description is omitted.

The electronic device1illustrated inFIG.2includes two reception antennas50, e.g. the reception antennas50A and50B, and receives the reflected waves R by the two reception antennas50. Hence, the electronic device1illustrated inFIG.2includes two functional parts of the same type necessary for receiving the reflected waves R by the two reception antennas50. Specifically, the transmission controller30includes two LNAs52, two mixers54, two IF units56, and two AD converters58.

Although the electronic device1illustrated inFIG.2includes two reception antennas50, the number of reception antennas50included in the electronic device1according to the embodiment may be any number greater than or equal to 2. In this case, the electronic device1according to the embodiment may include the same number of LNAs52, the same number of mixers54, the same number of IF units56, and the same number of AD converters58as the plurality of reception antennas50.

Transmission waves transmitted and reception waves received in the operation of the electronic device1according to the embodiment will be described below.

When measuring distance or the like by millimeter-wave radar, frequency-modulated continuous wave radar (hereafter, “FMCW radar”) is often used. FMCW radar sweeps the frequency of transmitted radio waves to generate a transmission signal. Therefore, for example, in millimeter-wave FMCW radar using radio waves in a frequency band of 79 GHz, the radio waves used have a frequency bandwidth of 4 GHz, e.g. 77 GHz to 81 GHz. Radar of 79 GHz in frequency band has a feature that its usable frequency bandwidth is broader than that of millimeter wave/submillimeter wave radar of 24 GHz, 60 GHz, 76 GHz, etc. in frequency band.

The transmission signal generated by the electronic device1according to the embodiment may be a chirp signal. The chirp signal is a signal whose frequency changes continuously with time. The chirp signal is also referred to as “frequency-modulated continuous wave (FMCW)”. The change in frequency of the chirp signal may be increasing or decreasing, or a combination of increasing and decreasing. The chirp signal may include a linear chirp signal whose frequency changes linearly with time, an exponential chirp signal whose frequency changes exponentially with time, or the like. In the case where the transmission signal is a chirp signal, as information for generating a chirp signal in each operation mode, parameters such as start frequency, end frequency, and duration may be stored in the memory12as information relating to the operation mode.

The signal generated by the signal generator22is not limited to a FMCW signal. The signal generated by the signal generator22may be a signal of any of various systems such as a pulse system, a pulse compression system (spread spectrum system), and a frequency continuous wave (CW) system. When measuring distance or the like by millimeter wave radar, frequency-modulated continuous wave radar (hereafter, “FMCW radar”) is often used. FMCW radar sweeps the frequency of transmitted radio waves to generate a transmission signal. Therefore, for example, in millimeter-wave FMCW radar using radio waves in a frequency band of 79 GHz, the radio waves used have a frequency bandwidth of 4 GHz, e.g. 77 GHz to 81 GHz. Radar of 79 GHz in frequency band has a feature that its usable frequency bandwidth is broader than that of other millimeter wave/submillimeter wave radar of 24 GHz, 60 GHz, 76 GHz, etc. in frequency band. This embodiment will be described below.

The FMCW radar system used in the present disclosure may include a fast-chirp modulation (FCM) system that transmits a chirp signal in a cycle shorter than normal. The signal generated by the signal generator22is not limited to a FM-CW signal. The signal generated by the signal generator22may be a signal of any of various systems other than FM-CW. A transmission signal sequence stored in the memory12may be different depending on the system used. For example, in the case of a FM-CW radar signal, a signal whose frequency increases and a signal whose frequency decreases for each time sample may be used. Well-known techniques can be appropriately applied to the foregoing various systems, and therefore more detailed description is omitted.

As described above, as a result of forming a beam of radio waves transmitted from a plurality of transmission antennas40(i.e. beamforming), transmission waves in a predetermined direction can intensify each other. In this way, the electronic device1can improve the accuracy in measuring the distance between the mobile body100having the electronic device1mounted therein and the object200, the direction to the object200, and the like. Hence, the electronic device1according to the embodiment uses, as transmission waves, radio waves that change in frequency with time as in FMCW radar, and performs beamforming for such transmission waves when necessary. This embodiment will be described in more detail below.

A state in which the electronic device1according to the embodiment receives the reflected waves R by the plurality of reception antennas50will be described below.

FIG.3is a diagram illustrating an example of the reception waves received by the electronic device1. An example in which two reception antennas50A and50B are arranged as the plurality of reception antennas50will be described below, as illustrated inFIG.3. In an embodiment, however, any number of two or more reception antennas50may be arranged.

The electronic device1according to the embodiment includes the plurality of reception antennas50as illustrated inFIG.3, and thus can estimate (measure) the direction of an object. Specifically, the electronic device1according to the embodiment receives the reflected waves R generated as a result of the transmission waves T transmitted from the transmission antennas40being reflected off the object, by the plurality of reception antennas50. The electronic device1according to the embodiment estimates the direction of the object reflecting the transmission waves T, based on the path difference D between the plurality of reflected waves R received by the plurality of reception antennas50.

In an embodiment, the direction (Y-axis direction) perpendicular to the direction (X-axis direction) in which the plurality of reception antennas50are arranged is a reference direction, as illustrated inFIG.3. In an embodiment, the angle between a straight line parallel to the reference direction (Y-axis direction) and a straight line corresponding to the direction in which the reflected waves R are incident on the reception antennas50is an incidence angle θ, as illustrated inFIG.3.

In the electronic device1, the reception antennas50A and50B are arranged with a spacing W, as illustrated inFIG.3. The following will describe the case where radio waves (reflected waves R) in a direction α (incidence angle of 30°) illustrated inFIG.3are received by the plurality of reception antennas50arranged in this manner. That is, the following will describe the case where the reflected waves R in the direction α that is inclined 30° to the right with respect to the Y-axis positive direction are received by the reception antennas50A and50B.

The spacing W between the reception antennas50A and50B illustrated inFIG.3is λ/2, where λ is the wavelength of the transmission waves. Consider the case where reflected waves R of radio waves transmitted at 79 GHz which is the center frequency of the frequency band of 77 GHz to 81 GHz are received by the plurality of reception antennas50. In this case, the wavelength λ (=c/f=3.0×108[m/s]/79×109) of the reflected waves is 3.7975 [mm], where the light speed is c=3.0×108[m/s]. Hence, the spacing W=λ/2 between the reception antennas50A and50B is 1.8987 [mm].

There is a path difference between the reflected waves R received in the direction α by the two reception antennas50arranged with the spacing W=1.8987 [mm]. As illustrated inFIG.3, the reception waves received by the reception antenna50A in the direction α are referred to as reflected waves Ra, and the reception waves received by the reception antenna50B in the direction α are referred to as reflected waves Rb. Herein, in the case where the reflected waves Ra and the reflected waves Rb are not distinguished from each other, they are collectively referred to as “reflected waves R”. In the example illustrated inFIG.3, the path of the reflected waves Ra is longer than the path of the reflected waves Rb by the path difference D.

As illustrated inFIG.3, the path difference D between the reflected waves Ra and the reflected waves Rb received in the direction α can be expressed as W·sin 30°, using the spacing W between the reception antennas50. Accordingly, the path difference D=W/2 is 0.9494 [mm]. Using the wavelength λ, the path difference D=W/2 can be expressed as D=λ/4, because W=λ/2. This expression reveals that the path difference D corresponds to a phase of ¼ of the wavelength λ, i.e. a phase of 90° (π/2). Therefore, in the case where the frequency of the transmission waves T is 79 GHz, the phase difference between the reflected waves Ra (incidence angle of) 30° received by the reception antenna50A and the reflected waves Rb (incidence angle of 30°) received by the reception antenna50B is 90° (π/2). Moreover, the phase of the reflected waves Ra (incidence angle of 30°) received by the reception antenna50A is delayed by 90° (π/2) with respect to the phase of the reflected waves Rb received by the reception antenna50B, as illustrated inFIG.3. It can be presumed fromFIG.3that, in the case where the phase of the reflected waves Ra is delayed by 90° (π/2) with respect to the phase of the reflected waves Rb, the direction of the object reflecting the transmission waves T is inclined at an angle of 30° to the right (clockwise) from the reference direction.

Next, consider the case where the incidence angle θ of the reflected waves R is larger.FIG.4is a diagram illustrating another example of the reception waves received by the electronic device1.

The following will describe the case where radio waves (reflected waves R) in a direction α′ (incidence angle of 90°) are received as illustrated inFIG.4. That is, the following will describe the case where the reflected waves R in the direction α′ that is inclined 90° to the right with respect to the Y-axis positive direction, i.e. in an approximately directly horizontal direction, are received by the reception antennas50A and50B.

The spacing W between the reception antennas50A and50B illustrated inFIG.4is 1.8987 [mm], as inFIG.3. Consider the case where reflected waves R of radio waves transmitted at 79 GHz are received by the plurality of reception antennas50, as in the foregoing situation.

In the situation illustrated inFIG.4, too, there is a path difference between the reflected waves R received in the direction α′ by the two reception antennas50arranged with the spacing W, as in the situation illustrated inFIG.3. InFIG.4, too, the reception waves received by the reception antenna50A in the direction α′ are referred to as reflected waves Ra, and the reception waves received by the reception antenna50B in the direction α′ are referred to as reflected waves Rb. In the example illustrated inFIG.4, too, the path of the reflected waves Ra is longer than the path of the reflected waves Rb by the path difference D.

As illustrated inFIG.4, the path difference D between the reflected waves Ra and the reflected waves Rb received in the direction α′ can be expressed as W·sin 90°, using the spacing W between the reception antennas50. Accordingly, the path difference D=W is 1.8988 [mm]. Using the wavelength λ, the path difference D (=W) can be expressed as D=λ/2, because W=λ/2. This expression reveals that the path difference D corresponds to a phase of ½ of the wavelength λ, i.e. a phase of 180° (π). Therefore, in the case where the frequency of the transmission waves T is 79 GHz, the phase difference between the reflected waves Ra (incidence angle of) 90° received by the reception antenna50A and the reflected waves Rb (incidence angle of 90°) received by the reception antenna50B is 180° (π). Moreover, the phase of the reflected waves Ra (incidence angle of 90°) received by the reception antenna50A is delayed by 180° (π) with respect to the phase of the reflected waves Rb received by the reception antenna50B, as illustrated inFIG.4. It can be presumed fromFIG.4that, in the case where the phase of the reflected waves Ra is delayed by 180° (π) with respect to the phase of the reflected waves Rb, the direction of the object reflecting the transmission waves T is inclined at an angle of 90° to the right (clockwise) from the reference direction. Thus, the direction of the object reflecting the transmission waves T can be estimated based on the phase difference between the reflected waves Ra and the reflected waves Rb.

Next, consider the case where the frequency of the transmission waves T is higher in the situation illustrated in each ofFIGS.3and4.

Consider the case where, in the situation illustrated inFIG.3, reflected waves R of radio waves transmitted at 81 GHz which is the maximum frequency of the frequency band of 77 GHz to 81 GHz are received by the plurality of reception antennas50. In this case, the wavelength λ (=c/f=3.0×108[m/s]/81×109) of the reflected waves is 3.7037 [mm]. The spacing between the reception antennas50A and50B is W=1.8987 [mm], as in the foregoing situation. In this case, the path difference D inFIG.3is 1.8987×sin(30°). Hence, the phase difference between the reflected waves Ra received by the reception antenna50A and the reflected waves Rb received by the reception antenna50B is (1.8987 [mm]/3.7037 [mm])×360°×sin(30°)=92.28°. That is, in the case where the frequency of the transmission waves T is 81 GHz, the phase of the reflected waves Ra (incidence angle of 30°) received by the reception antenna50A is delayed by 92.28° with respect to the phase of the reflected waves Rb (incidence angle of 30°) received by the reception antenna50B. Thus, when the frequency of the transmission waves T is higher, the phase difference between the plurality of reflected waves R is greater.

Consider the case where, in the situation illustrated inFIG.4, reflected waves R of radio waves transmitted at 81 GHz which is the maximum frequency of the frequency band of 77 GHz to 81 GHz are received by the plurality of reception antennas50. In this case, the wavelength λ (=c/f=3.0×108[m/s]/81×109) of the reflected waves is 3.7037 [mm]. The spacing between the reception antennas50A and50B is W=1.8987 [mm], as in the foregoing situation. In this case, the path difference D (=W) inFIG.4is 1.8987×sin(90°). Hence, the phase difference between the reflected waves Ra received by the reception antenna50A and the reflected waves Rb received by the reception antenna50B is (1.8987 [mm]/3.7037 [mm])×360°×sin(90°=184.55°). That is, in the case where the frequency of the transmission waves T is 81 GHz, the phase of the reflected waves Ra (incidence angle of 90°) received by the reception antenna50A is delayed by 184.55° with respect to the phase of the reflected waves Rb (incidence angle of 90°) received by the reception antenna50B. Thus, when the frequency of the transmission waves T is higher in such a situation in which the incidence angle θ is larger, the phase difference between the reflected waves Ra received by the plurality of reception antennas50can exceed 180°.

In the case where the phase difference between the reflected waves Ra received by the plurality of reception antennas50exceeds 180°, however, a problem may arise in the detection of the object reflecting the transmission waves T. For example, in the case where the phase of the reflected waves Ra is delayed by 184.55° with respect to the phase of the reflected waves Rb, this state cannot be distinguished from the case where the phase of the reflected waves Ra is advanced by 175.45° (=360°-184.55°) with respect to the phase of the reflected waves Rb. For example, in the case of defining the phase difference to be −180° to +180° as in a normal process performed when detecting an object by radar, the foregoing phase difference is determined to be not a delay of 184.55° but an advance of 175.45°. In this case, even when the reception antennas50receive the reflected waves R at around an incidence angle θ=90° (i.e. from the right side of the reception antenna50B) as illustrated inFIG.4, it is determined that the reception antennas50receive the reflected waves R at around an incidence angle θ=−90° (i.e. from the left side of the reception antenna50A). There is thus the possibility that, if the phase difference between the reflected waves Ra received by the plurality of reception antennas50exceeds 180°, the object reflecting the transmission waves T is not detected accurately.

When the reception antennas50receive the reflected waves R at around an incidence angle θ=30° as illustrated inFIG.3, on the other hand, the phase difference (about 92.28°) between the reflected waves R received by the plurality of reception antennas50does not exceed 180°. Thus, the foregoing problem does not occur in a situation in which the incidence angle θ is not relatively large. The threshold of the incidence angle θ that is determined to be relatively large may be, for example, an angle at which the incidence direction is higher than when the incidence angle θ is around 90° inFIG.4. For example, the threshold of the incidence angle θ may be 80° or more.

As described above, in a situation in which the incidence angle θ is large, if the frequency of the transmission waves T is high, the phase difference between the reflected waves Ra received by the plurality of reception antennas50may exceed 180° and cause the problem. In view of this, the electronic device1according to the embodiment controls the frequency of the transmission waves T to be not high, in a situation in which the incidence angle θ is large.

The example described above concerns the case where the reflected waves R of the radio waves transmitted at 79 GHz which is the center frequency of the frequency band of 77 GHz to 81 GHz are received by the plurality of reception antennas50. For example, one conceivable method for avoiding the foregoing problem is to set the antenna spacing W (=λ/2) with respect to the wavelength of 81 GHz which is the upper limit of the frequency usable for the transmission of the transmission waves T.

However, in the case of using the entire frequency band usable for the transmission of the transmission waves T, the entire frequency band of 77 GHz to 81 GHz is used. In such a case, the average of the phase differences at the frequencies of 77 GHz to 81 GHz is the phase difference at 79 GHz which is the center frequency. Hence, the phase difference between the reflected waves R received by the plurality of reception antennas50is represented by the phase difference at 79 GHz which is the center frequency. In the above-described avoidance method, the antenna spacing W is based on the frequency of 81 GHz, whereas the phase difference between the reflected waves R is based on the frequency of 79 GHz. This causes incompatibility between the antenna spacing W and the phase difference between the reflected waves R, as a result of which the object detection property may degrade. In object detection, it is desirable to set the antenna spacing W (=λ/2) so as to maximize the property, using the entire frequency band usable for the transmission of the transmission waves T. Accordingly, the antenna spacing W is typically determined based on the wavelength of 79 GHz which is the center frequency of 77 GHz to 81 GHz.

Operation of the electronic device1according to each of some embodiments will be described below.

FIG.5is a diagram illustrating an example of the frequency band of the transmission waves transmitted by the electronic device1according to each embodiment. InFIG.5, the horizontal axis represents the frequency f [GHz], and the vertical axis represents the transmission power P [W] of the transmission waves T. It is assumed that the electronic device1according to each embodiment described below can use the frequency band of 77 GHz to 81 GHz for the transmission of the transmission waves T, as illustrated inFIG.5. In detail, when transmitting the transmission waves T, the electronic device1according to each embodiment described below can assign the frequency band of 77 GHz to 81 GHz and transmit the transmission waves T from the transmission antennas40. The center frequency in the frequency band of 77 GHz to 81 GHz usable for the transmission of the transmission waves T is 79 GHz, as illustrated inFIG.5.

Embodiment 1

The electronic device1according to the embodiment controls the frequency of the transmission waves T to be not high in a situation in which the incidence angle θ is large, as mentioned above. In detail, in the case where the incidence angle θ when receiving the reflected waves R is less than a predetermined angle, the electronic device1according to Embodiment 1 transmits the transmission waves T using a frequency of a relatively high band part in the frequency band usable for the transmission of the transmission waves T. In the case where the incidence angle θ when receiving the reflected waves R is greater than or equal to the predetermined angle, the electronic device1according to Embodiment 1 transmits the transmission waves T using a frequency of a relatively low band part in the frequency band usable for the transmission of the transmission waves T. Herein, the “frequency of a relatively high band part” may be, for example, a frequency higher than the center frequency in the frequency band usable for the transmission of the transmission waves T. The “frequency of a relatively low band part” may be, for example, a frequency lower than the center frequency in the frequency band usable for the transmission of the transmission waves T. The operation of the electronic device1according to Embodiment 1 will be described in more detail below.

FIG.6is a diagram illustrating an example in which the sensor according to Embodiment 1 is provided in the mobile body. In the case where the electronic device1includes a plurality of sensors5, the sensor5may be installed in a plurality of parts of the mobile body100, as illustrated inFIG.6.

In the example illustrated inFIG.6, a sensor5ais located in a front left part of the mobile body100, a sensor5bis located in a front right part of the mobile body100, a sensor5cis located in a back right part of the mobile body100, and a sensor5dis located in a back left part of the mobile body100. The sensor5ccan detect an object in a detection range S1or S2, as illustrated inFIG.6. The detection ranges S1and S2are schematically illustrated inFIG.6.

In the case where the sensor5cperforms object detection in the detection range S1, the electronic device1may cause the transmission waves T transmitted by the transmission antennas40to be included in the detection range S1. In the case where the sensor5cperforms object detection in the detection range S1, the electronic device1may cause the incidence angle when the reception antennas50receive the reflected waves R to be included in the detection range S1. Likewise, in the case where the sensor5cperforms object detection in the detection range S2, the electronic device1may cause the transmission waves T transmitted by the transmission antennas40to be included in the detection range S2. In the case where the sensor5cperforms object detection in the detection range S2, the electronic device1may cause the incidence angle when the reception antennas50receive the reflected waves R to be included in the detection range S2.

The sensor5a,5b, and/or5cmay transmit the transmission waves T, too, although illustration is omitted for simplicity's sake. The following will describe only one sensor5c. Hereafter, in the case where a plurality of sensors such as the sensors5a,5b,5c, and5din the electronic device1according to Embodiment 1 are not distinguished from each other, they are collectively referred to as “sensor5”.

The electronic device1according to the embodiment is capable of controlling the plurality of sensors5individually. For example, the electronic device1may control the on/off state of each of the plurality of sensors5independently. For example, the electronic device1may control at least one of the beam width and the reaching distance of the transmission waves transmitted from each of the plurality of sensors5independently. For example, the electronic device1may control the operation mode (e.g. normal mode/BF mode) of each of the plurality of sensors5independently. For example, the electronic device1may control the beamforming direction of the transmission waves transmitted from each of the plurality of sensors5independently. By appropriately controlling, for example, the beam width and/or the reaching distance of the transmission waves transmitted from each of the plurality of sensors5, the electronic device1according to the embodiment can perform object detection substantially all around the mobile body10inFIG.6.

The direction perpendicular to the direction in which the plurality of reception antennas50are arranged in the sensor5cis a reference direction Dn, as illustrated inFIG.6. The reference direction Dn inFIG.6may correspond to the reference direction (the Y-axis direction) inFIG.3.

For example, in the case of the detection range S1in which the incidence angle θ1when the reception antennas50receive the reflected waves R is relatively large, the electronic device1according to Embodiment 1 selects the frequency used to transmit the transmission waves T from a relatively low band part in the usable frequency band. Herein, the case where the incidence angle θ1is relatively large may be the case where the incidence angle θ1is greater than or equal to the predetermined angle. The predetermined angle may be set as appropriate based on the threshold beyond which the phase advance and delay described with reference toFIGS.3and4are indistinguishable. For example, the predetermined angle is 80°.

In such a case, for example, the electronic device1may transmit the transmission waves T using a frequency of a relatively low band part fr1in the frequency band of 77 GHz to 81 GHz usable for the transmission of the transmission waves T, as illustrated inFIG.7.FIG.7is a diagram illustrating an example of the frequency band of the transmission waves transmitted by the electronic device1according to Embodiment 1. InFIG.7, the horizontal axis represents the frequency f [GHz], and the vertical axis represents the transmission power P [W] of the transmission waves T, as inFIG.6. The relatively low band part may be, for example, a band part lower than the center frequency of 79 GHz in the frequency band of 77 GHz to 81 GHz usable for the transmission of the transmission waves T, such as the band part fr1(77 GHz to 78 GHz) inFIG.7. The relatively low band part may be, for example, a band part whose center frequency is lower than the center frequency of 79 GHz. In other words, the center frequency of the band part fr1may be lower than the center frequency of 79 GHz in the frequency band (77 GHz to 81 GHz) usable for the transmission of the transmission waves T.

For example, in the case of the detection range S2in which the incidence angle θ2when the reception antennas50receive the reflected waves R is relatively small, the electronic device1according to Embodiment 1 selects the frequency used to transmit the transmission waves T from a relatively high band part in the usable frequency band. Herein, the case where the incidence angle θ2is relatively small may be the case where the incidence angle θ2is less than the predetermined angle. The predetermined angle may be set as appropriate based on the threshold beyond which the phase advance and delay described with reference toFIGS.3and4are indistinguishable, as in the foregoing case. For example, the predetermined angle is 80°.

In such a case, for example, the electronic device1may transmit the transmission waves T using a frequency of a relatively high band part fr2in the frequency band of 77 GHz to 81 GHz usable for the transmission of the transmission waves T, as illustrated inFIG.7. The relatively high band part may be, for example, a band part higher than the center frequency of 79 GHz in the frequency band of 77 GHz to 81 GHz usable for the transmission of the transmission waves T, such as the band part fr2(80 GHz to 81 GHz) inFIG.7. The relatively high band part may be, for example, a band part whose center frequency is higher than the center frequency of 79 GHz. In other words, the center frequency of the band part fr2may be higher than the center frequency of 79 GHz in the frequency band (77 GHz to 81 GHz) usable for the transmission of the transmission waves T.

The relatively high band part may be a band part higher in frequency than the band part fr1. In this case, the band part fr2inFIG.7may not overlap in frequency with the band part fr1. The relatively high band part may be, for example, a band part whose center frequency is higher than the center frequency of the band part fr1. In other words, the center frequency of the band part fr2may be higher than the center frequency of the band part fr1. In this case, the band part fr2and the band part fr1may partially overlap with each other.

In the case where the incidence angle θ is greater than or equal to the predetermined angle, the electronic device1according to Embodiment 1 controls the frequency of the transmission waves T to be not high. The electronic device1according to Embodiment 1 thus prevents the frequency of the transmission waves T from being high in a situation in which the incidence angle θ is large. Therefore, the electronic device1according to Embodiment 1 can avoid the problem in that the phase advance and delay are indistinguishable, and improve the object detection accuracy.

In the example illustrated inFIG.6, the direction of the axis of symmetry of the detection range S2is the same as the reference direction Dn. Alternatively, the direction of the axis of symmetry of the detection range S2may be different from the reference direction Dn. For example, by controlling the phase of the transmission waves transmitted from at least one of the plurality of transmission antennas40, the direction of the beam can be changed. Accordingly, the direction of the detection range S2can be changed with respect to the sensor5cas the center. In Embodiment 1, the direction of the detection range S2may be any direction as long as the incidence angle θ when the reception antennas50receive the reflected waves R is less than the predetermined angle. In the example illustrated inFIG.6, the direction of the axis of symmetry of the detection range S1may be different from the reference direction Dn, too.

FIG.8is a flowchart illustrating the operation of the electronic device1according to Embodiment 1. The operation illustrated inFIG.8may be started, for example, when the electronic device1starts the detection of the object200around the mobile body100. That is, the operation illustrated inFIG.8may be started when performing object detection using the sensor5in the electronic device1.

After the start of the operation illustrated inFIG.8, the detection range determination unit14in the controller10determines the range of object detection by the transmission waves T and the reflected waves R (step S11). In step S11, the detection range determination unit14may determine, for example, whether the detection range by the sensor5cinFIG.6is to be the detection range S1or the detection range S2.

In step S11, for example, the detection range determination unit14may determine a default range as the detection range. In step S11, for example, the detection range determination unit14may determine the detection range based on the position of an object detected using the transmission waves T of a previous frame. In this case, the detection range determination unit14may determine the detection range based on an object detection result by at least one of the distance estimation unit62, the angle estimation unit64, and the relative speed estimation unit66.

After the detection range is determined in step S11, the controller10determines whether the incidence angle θ of the reflected waves R is greater than or equal to a predetermined angle (step S12). In step S12, the predetermined angle may be set as appropriate based on the threshold beyond which the phase advance and delay described with reference toFIGS.3and4are indistinguishable. For example, the predetermined angle is 80°. That is, in step S12, the predetermined angle may be set so that, if the incidence angle θ of the reflected waves R is greater than or equal to the predetermined angle, the phase advance and delay described with reference toFIGS.3and4are indistinguishable.

In the case where the controller10determines that the incidence angle θ of the reflected waves R is greater than or equal to the predetermined angle in step S12, the frequency selector16selects a frequency of a first band part lower than a predetermined frequency in a predetermined frequency band (step13). The predetermined frequency band may be the frequency band (e.g. 77 GHz to 81 GHz) usable for detection, as mentioned above. The first band part lower than the predetermined frequency may be, for example, the band part fr1inFIG.7. The predetermined frequency may be, for example, the center frequency (79 GHz) illustrated inFIG.5. In step13, the controller10transmits the transmission waves T from the transmission antennas40using the selected frequency.

In the case where the controller10determines that the incidence angle θ of the reflected waves R is less than the predetermined angle in step S12, the frequency selector16selects a frequency of a second band part higher than the predetermined frequency in the predetermined frequency band (step14). The predetermined frequency band may be the frequency band (e.g. 77 GHz to 81 GHz) usable for detection, as mentioned above. The second band part higher than the predetermined frequency may be, for example, the band part fr2inFIG.7. The predetermined frequency may be, for example, the center frequency (79 GHz) illustrated inFIG.5. In step14, the controller10transmits the transmission waves T from the transmission antennas40using the selected frequency.

After the transmission waves T are transmitted in step S13or S14, the electronic device1receives the reflected waves R by the plurality of reception antennas50(step S15). After the reflected waves R are received in step S15, the electronic device1detects an object, such as the object200, around the electronic device1(or the mobile body100) (step S16). In step S16, the controller10may detect an object based on an estimation result of at least one of the distance estimation unit62, the angle estimation unit64, and the relative speed estimation unit66.

Since the object detection in step S16can be performed using a known millimeter wave radar technique according to any of various algorithms, more detailed description is omitted. After step S16inFIG.8, the controller10may perform step S11again.

Thus, in Embodiment 1, the controller10detects the object reflecting the transmission waves T based on the transmission signal transmitted as the transmission waves T and the reception signal received as the reflected waves R. The controller10also determines the band part used to transmit the transmission waves T in the predetermined frequency band (e.g. the frequency band usable for detection), depending on the incidence angle θ when the reception antennas50receive the reflected waves R. Herein, the incidence angle θ may be the angle between a straight line corresponding to the direction in which the reflected waves R are incident on the reception antennas50and a perpendicular line to the direction in which the plurality of reception antennas50are arranged.

In Embodiment 1, in the case where the incidence angle θ is greater than or equal to the predetermined angle, the controller10may set the frequency of the band part used to transmit the transmission waves T to be lower than or equal to the predetermined frequency in the predetermined frequency band. In Embodiment 1, in the case where the incidence angle θ is greater than or equal to the predetermined first angle, the controller10may set the frequency of the band part used to transmit the transmission waves T to be lower than the center frequency of the predetermined frequency band.

In Embodiment 1, in the case where the incidence angle θ is greater than or equal to the first angle, the controller10may set the center frequency of the band part used to transmit the transmission waves T to be lower than the center frequency of the predetermined frequency band. In Embodiment 1, in the case where the incidence angle θ is less than the first angle, the controller10may set the center frequency of the band part used to transmit the transmission waves T to be greater than or equal to the center frequency of the predetermined frequency band.

The electronic device1according to Embodiment 1 controls the frequency of the transmission waves T to be low in a situation in which the incidence angle θ is large. Thus, the electronic device1according to Embodiment 1 can prevent the problem in that the phase advance and delay are indistinguishable, and accurately detect the object reflecting the transmission waves T.

Embodiment 2

The electronic device1according to Embodiment 2 will be described below.

In Embodiment 1 described above, two band parts for transmitting the transmission waves T are set in the usable frequency band depending on the incidence angle θ when the reception antennas50receive the reflected waves R (seeFIGS.6and7).

The electronic device1according to Embodiment 2 sets three band parts for transmitting the transmission waves T in the usable frequency band depending on the incidence angle θ when the reception antennas50receive the reflected waves R, as illustrated inFIGS.9and10. The description of the parts same as or similar to those in Embodiment 1 will be simplified or omitted as appropriate.

FIG.9is a diagram illustrating an example in which the sensor according to Embodiment 2 is provided in the mobile body. The following will describe only one sensor5einFIG.9, while omitting the description of the other sensors5for simplicity's sake.

In the example illustrated inFIG.9, the sensor5eis located at the back center of the mobile body100. The sensor5ecan detect an object in a detection range S1, S2, or S3, as illustrated inFIG.9. The detection ranges S1, S2, and S3are schematically illustrated inFIG.9.

In the case where the sensor5eperforms object detection in the detection range S1, S2, or S3, the electronic device1may cause the transmission waves T transmitted by the transmission antennas40to be included in the detection range. In the case where the sensor5eperforms object detection in the detection range S1, S2, or S3, the electronic device1may cause the incidence angle when the reception antennas50receive the reflected waves R to be included in the detection range.

The direction perpendicular to the direction in which the plurality of reception antennas50are arranged in the sensor5eis a reference direction Dn, as illustrated inFIG.9. The reference direction Dn inFIG.9may correspond to the reference direction (the Y-axis direction) inFIG.3.

For example, in the case of the detection range S1in which the incidence angle θ1when the reception antennas50receive the reflected waves R is relatively large, the electronic device1according to Embodiment 2 selects the frequency used to transmit the transmission waves T from a relatively low band part in the usable frequency band. Herein, the case where the incidence angle θ1is relatively large may be the case where the incidence angle θ1is greater than or equal to a first angle. The first angle may be set as appropriate based on the threshold beyond which the phase advance and delay described with reference toFIGS.3and4are indistinguishable. For example, the first angle is 80°.

In such a case, for example, the electronic device1may transmit the transmission waves T using a frequency of a relatively low band part fr1in the frequency band usable for the transmission of the transmission waves T, as illustrated inFIG.10.FIG.10is a diagram illustrating an example of the frequency band of the transmission waves transmitted by the electronic device1according to Embodiment 2. The relatively low band part fr1may be the same as that in Embodiment 1.

For example, in the case of the detection range S2in which the incidence angle θ2when the reception antennas50receive the reflected waves R is greater than or equal to a second angle that is less than the first angle, the electronic device1according to Embodiment 2 selects the frequency used to transmit the transmission waves T from a second band part whose frequency is higher than or equal to the first band part in the usable frequency band. The second angle may be any angle (e.g. 20°) less than the first angle.

In such a case, for example, the electronic device1may transmit the transmission waves T using a frequency of a second band part fr2higher in frequency than the first band in the frequency band usable for the transmission of the transmission waves T, as illustrated inFIG.10. The second band part may be, for example, a band part around the center frequency of 79 GHz in the frequency band usable for the transmission of the transmission waves T, such as the band part fr2(78.5 GHz to 79.5 GHz) inFIG.10. The second band part fr2may be, for example, a band part whose center frequency is higher than the center frequency of the first band part. In other words, the center frequency of the band part fr2may be higher than the center frequency of 77.5 GHz of the first band part.

For example, in the case of the detection range S3in which the incidence angle θ3when the reception antennas50receive the reflected waves R is less than the second angle, the electronic device1according to Embodiment 2 selects the frequency used to transmit the transmission waves T from a third band part whose frequency is higher than or equal to the second band part in the usable frequency band.

In such a case, for example, the electronic device1may transmit the transmission waves T using a frequency of a third band part fr3higher in frequency than the second band in the frequency band usable for the transmission of the transmission waves T, as illustrated inFIG.10. The third band part may be, for example, a band part around the maximum frequency of 81 GHz in the frequency band usable for the transmission of the transmission waves T, such as the band part fr3(80 GHz to 81 GHz) inFIG.10. The third band part fr3may be, for example, a band part whose center frequency is higher than the center frequency of the first band part. The third band part fr3may be, for example, a band part whose center frequency is higher than the center frequency of the second band part. In other words, the center frequency of the band part fr3may be higher than the center frequency of the first band part and/or the center frequency of the second band part.

As illustrated inFIG.10, the first band part fr1, the second band part fr2, and the third band part fr3may not overlap with one another. Alternatively, the first band part fr1, the second band part fr2, and the third band part fr3may partially overlap with one another.

In the case where the incidence angle θ is greater than or equal to the first angle, the electronic device1according to Embodiment 2 controls the frequency of the transmission waves T to be not high. The electronic device1according to Embodiment 2 thus prevents the frequency of the transmission waves T from being high in a situation in which the incidence angle θ is large. Therefore, the electronic device1according to Embodiment 2 can avoid the problem in that the phase advance and delay are indistinguishable, and improve the object detection accuracy.

FIG.11is a flowchart illustrating the operation of the electronic device1according to Embodiment 2. The differences from the operation illustrated inFIG.8will be mainly described below, while simplifying or omitting the description of the parts same as or similar to those in the operation illustrated inFIG.8.

After the operation illustrated inFIG.11starts and the detection range is determined in step S11, the controller10determines whether the incidence angle θ of the reflected waves R is greater than or equal to the first angle (step S21). The first angle may be the same as or different from the predetermined angle in step S12inFIG.8. The first angle may be set as appropriate based on the threshold beyond which the phase advance and delay described with reference toFIGS.3and4are indistinguishable. For example, the first angle is 80°.

In the case where the controller10determines that the incidence angle θ of the reflected waves R is greater than or equal to the predetermined angle in step S21, the same operation as in step S13onward inFIG.8may be performed. In this case, for example, the frequency selector16may select a frequency (77 GHz to 78 GHz) in the band part fr1illustrated inFIG.10.

In the case where the controller10determines that the incidence angle θ of the reflected waves R is less than the predetermined angle in step S21, the controller10determines whether the incidence angle θ of the reflected waves R is greater than or equal to the second angle (step S22). The second angle may be an angle smaller than the first angle, e.g. 20°.

In the case where the controller10determines that the incidence angle θ of the reflected waves R is greater than or equal to the second angle in step S22, the same operation as in step S14onward inFIG.8may be performed. In this case, for example, the frequency selector16may select a frequency (78.5 GHz to 79.5 GHz) in the band part fr2illustrated inFIG.10.

In the case where the controller10determines that the incidence angle θ of the reflected waves R is less than the second angle in step S22, the frequency selector16transmits the transmission waves T at a frequency in the third band part whose frequency is greater than or equal to the second band part (step S23). In this case, for example, the frequency selector16may select a frequency (80 GHz to 81 GHz) in the band part fr3illustrated inFIG.10.

After step S23, the same operation as in step S15onward inFIG.8may be performed. After step S16inFIG.11, the controller10may perform step S11again.

Thus, in Embodiment 2, in the case where the incidence angle θ is less than the second angle that is less than the first angle, the controller10may set, for example, the center frequency of the band part used to transmit the transmission waves T to be greater than or equal to a predetermined frequency higher than the center frequency of the predetermined frequency band.

The electronic device1according to Embodiment 2 controls the frequency of the transmission waves T to be low in a situation in which the incidence angle θ is large. Thus, the electronic device2according to Embodiment 1 can prevent the problem in that the phase advance and delay are indistinguishable, and accurately detect the object reflecting the transmission waves T. Moreover, the electronic device1according to Embodiment 2 can adaptively change the detection range depending on, for example, the detection purpose and/or detection target of the sensor5, as illustrated inFIG.9.

Embodiment 3

An electronic device1according to Embodiment 3 will be described below.

The electronic device1according to Embodiment 3 variably controls the predetermined angle with which the incidence angle θ of the reflected waves R is compared in the electronic device1according to Embodiment 1 described above. In Embodiment 1, the predetermined angle with which the incidence angle θ of the reflected waves R is compared is set as appropriate in step S12inFIG.8. In Embodiment 3, the predetermined angle with which the incidence angle θ of the reflected waves R is compared is set based on an object detection result.

FIG.12is a diagram illustrating an example in which a sensor according to Embodiment 3 is provided in the mobile body. The following will describe only one sensor5cinFIG.12, as inFIG.6.

For example, in the case where an object200is present around the mobile body, the sensor5ccan detect the object in the detection range S2, as illustrated inFIG.12. In this case, the incidence angle θ when the reception antennas50in the sensor5creceive the reflected waves R is relatively small (i.e. not a large angle). Thus, in the case where the object is detected in the detection range S2, the situation in which the phase advance and delay are indistinguishable as described with reference toFIGS.3and4does not occur.

For example, suppose the object200inFIG.12has moved to the position of an object200′ inFIG.12with time. In this case, the sensor5ccan detect the object in the detection range S1. Then, the incidence angle θ when the reception antennas50in the sensor5creceive the reflected waves R is relatively large. This can cause the situation in which the phase advance and delay are indistinguishable.

In view of this, in Embodiment 3, for example in the case where the incidence angle θ when the reception antennas50receive the reflected waves R is (or is likely to be) greater than or equal to a predetermined angle based on the position of the object that can move, the frequency of the band part used to transmit the transmission waves T may be set to be lower than or equal to a predetermined frequency. For example, if the frequency used to transmit the transmission waves T is a frequency in the band part fr1inFIG.7when detecting the object200′ inFIG.12, the situation in which the phase advance and delay are indistinguishable does not occur. If the frequency used to transmit the transmission waves T is a frequency in the band part fr2inFIG.7when detecting the object200′ inFIG.12, the situation in which the phase advance and delay are indistinguishable can occur. Hence, in Embodiment 3, in the case where the frequency used to transmit the transmission waves T is a frequency in the band part fr2inFIG.7when detecting the object200′ inFIG.12, the frequency is changed to a frequency in the band part fr1. Subsequently, the band part of the frequency used to transmit the transmission waves T may be changed as appropriate according to the movement of the object200(object200′).

FIG.13is a flowchart illustrating the operation of the electronic device1according to Embodiment 3. The differences of the operation of the electronic device1according to Embodiment 3 illustrated inFIG.13from the operation illustrated inFIG.8lie in step S12. The differences from the operation illustrated inFIG.8will be mainly described below, while simplifying or omitting the description of the parts same as or similar to those in the operation illustrated inFIG.8.

After the operation illustrated inFIG.13starts and the detection range is determined in step S11, the controller10determines whether the position of an already detected object is greater than or equal to a predetermined angle (step S31). In step S31immediately after the start of the operation illustrated inFIG.13, there is a possibility that no object has been detected.

In such a case, the operation advances to step S14, where the frequency selector16may transmit the transmission waves T at a relatively high frequency such as a frequency in the band part fr2illustrated inFIG.7.

After step S14, the same operation as in step S15onward inFIG.8may be performed. After step S16inFIG.13, the controller10may perform step S11again.

After the detection range is determined in step S11again, the controller10determines whether the position of the object detected in step S16is greater than or equal to the predetermined angle (step S31). The predetermined angle may be set as appropriate based on the threshold beyond which the phase advance and delay described with reference toFIGS.3and4are indistinguishable, as in step S12inFIG.8. For example, the predetermined angle is 80°. In step S31, for example, whether the angle of the direction from the sensor5cto the object200with respect to the reference direction Dn inFIG.12is greater than or equal to the predetermined angle may be determined.

In the case where the controller10determines that the position of the object is at an angle greater than or equal to the predetermined angle in step S31, the same operation as in step S13onward inFIG.8may be performed. In this case, for example, the frequency selector16may select a frequency (77 GHz to 78 GHz) in the band part fr1illustrated inFIG.7.

In the case where the controller10determines that the position of the object is at an angle less than the predetermined angle in step S31, the same operation as in step S14onward inFIG.8may be performed. In this case, for example, the frequency selector16may select a frequency (80 GHz to 81 GHz) in the band part fr2illustrated inFIG.7.

The electronic device1according to Embodiment 3 repeats the operation illustrated inFIG.13. Hence, for example even when the object200is moving, the electronic device1can dynamically change the band part of the frequency used to transmit the transmission waves T according to the movement of the object200.

Thus, in Embodiment 3, the controller10may determine the band part used to transmit the transmission waves T in the predetermined frequency band, based on the position of the detected object. In Embodiment 3, the controller10may dynamically vary the band part used to transmit the transmission waves T in the predetermined frequency band, according to the position of the detected object.

The electronic device1according to Embodiment 3 controls the frequency of the transmission waves T to be low as the angle of the position of the object increases, i.e. in a situation in which the incidence angle θ increases. Thus, the electronic device1according to Embodiment 3 can prevent the problem in that the phase advance and delay are indistinguishable, and accurately detect the object reflecting the transmission waves T. Moreover, the electronic device1according to Embodiment 3 can dynamically change the band part of the frequency used to transmit the transmission waves T according to the position of the moving object200(object200′), as illustrated inFIG.12.

While some embodiments and examples of the present disclosure have been described above by way of drawings, various changes and modifications may be easily made by those of ordinary skill in the art based on the present disclosure. Such changes and modifications are therefore included in the scope of the present disclosure. For example, the functions included in the functional parts, etc. may be rearranged without logical inconsistency, and a plurality of functional parts, etc. may be combined into one functional part, etc. and a functional part, etc. may be divided into a plurality of functional parts, etc. Moreover, each of the disclosed embodiments is not limited to the strict implementation of the embodiment, and features may be combined or partially omitted as appropriate. That is, various changes and modifications may be made to the presently disclosed techniques by those of ordinary skill in the art based on the present disclosure. Such changes and modifications are therefore included in the scope of the present disclosure. For example, functional parts, means, steps, etc. in each embodiment may be added to another embodiment without logical inconsistency, or replace functional parts, means, steps, etc. in another embodiment. In each embodiment, a plurality of functional parts, means, steps, etc. may be combined into one functional part, means, step, etc., and a functional part, means, step, etc. may be divided into a plurality of each functional parts, means, steps, etc. Moreover, each of the disclosed embodiments is not limited to the strict implementation of the embodiment, and features may be combined or partially omitted as appropriate.

As a modification to the foregoing embodiments, for example, the angle based on the threshold beyond which the phase advance and delay described with reference toFIGS.3and4are indistinguishable may be determined beforehand. In the case where the incidence angle θ is greater than or equal to the determined angle, the electronic device1may set the frequency of the band part used to transmit the transmission waves T to be a relatively low frequency such as a frequency in the band part fr1illustrated inFIG.7.

For example, in the example illustrated inFIG.5, the usable frequency band is the frequency band of 77 GHz to 81 GHz, and the center frequency is f=79 [GHz]. When the center frequency of the usable frequency band is f [GHz], the spacing W between the reception antennas50is typically ½ of the wavelength λ of the frequency f. Accordingly, the spacing W can be expressed as W=λ/2. The light speed c can be expressed as c=f·λ. Therefore, the spacing W between the reception antennas50can be expressed as W=c/2f. In this case, the path difference D between the reflected waves R incident on the reception antennas50A and50B at the incidence angle θ can be expressed as D=W·sin θ, i.e. D=(c/2f)·sin θ.

Suppose the frequency used is f [GHz], where f<f′. For example, f′=81 GHz. The wavelength λ′ of the frequency f′ is λ′=c/f′. When limiting the incidence angle θ, the phase difference resulting from the path difference D needs to be less than or equal to half of λ′ (i.e. less than or equal to 180°). From this relationship, the path difference D between the reflected waves R can be expressed as D=W·sin θ>λ′/2=c/2f′. The relationship sin θ>c/2Wf′ thus holds. Representing this expression using the center frequency f of the usable frequency band without using W yields sin θ>f/f′. Hence, in the case where the reflected waves are received from such an angle that exceeds the incidence angle θ when the frequency f′ is used, the band part of the frequency used to transmit the transmission waves T may be changed.

The foregoing embodiments are not limited to implementation as the electronic device1. For example, the foregoing embodiments may be implemented as a control method of a device such as the electronic device1. For example, the foregoing embodiments may be implemented as a control program of a device such as the electronic device1.

Although the foregoing embodiments describe the case where the number of transmission antennas40and the number of reception antennas50are both2, the number of transmission antennas40and the number of reception antennas50may be any number of 2 or more in an embodiment. In the case where the number of transmission antennas40and the number of reception antennas50are 3 or more, one of the plurality of transmission antennas40and the plurality of reception antennas50may be a reference antenna. In this case, the phase of the transmission waves transmitted from each transmission antenna40may be controlled to perform beamforming, depending on the path difference D in a predetermined direction between the transmission waves transmitted from the reference antenna and the transmission waves transmitted from each of the other transmission antennas40.

The electronic device1according to each of the embodiments may include, for example, only the controller10as a minimum structure. Alternatively, the electronic device1according to the embodiment may include at least one of the signal generator22, the frequency synthesizer24, the transmission controller30, the power amplifier36, and the transmission antenna40illustrated inFIG.2, in addition to the controller10. The electronic device1according to the embodiment may include at least one of the reception antenna50, the LNA52, the mixer54, the IF unit56, the AD converter58, the distance estimator62, the angle estimator64, and the relative speed estimation unit66instead of or together with the foregoing functional parts, in addition to the controller10. The electronic device1according to the embodiment can thus have any of various structures. In the case where the electronic device1according to the embodiment is mounted in the mobile body100, for example, at least one of the foregoing functional parts may be installed in an appropriate location such as the inside of the mobile body100. In an embodiment, for example, at least one of the transmission antenna40and the reception antenna50may be installed on the outside of the mobile body100.

REFERENCE SIGNS LIST

1electronic device5sensor10controller12memory14detection range determination unit16frequency selector22signal generator24frequency synthesizer30transmission controller32phase controller34power controller36power amplifier40transmission antenna50reception antenna52LNA54mixer56IF unit58AD converter62distance estimation unit64angle estimation unit66relative speed estimation unit100mobile body200object