Direction-finding system and direction-finding method

Abstract

Effectively suppresses the occurrence of false images under a variety of circumstances. [Solution] A direction-finding system that detects the direction of an object based on target radio waves, which are radio waves arriving from the object, comprises a radio wave fluctuation device that periodically fluctuates the incident radio waves according to predetermined parameters and reflects them as fluctuating waves, an antenna that receives radio waves, and a signal processor that detects the direction of the object based on the radio waves received by the antenna. The signal processor reduces the influence of fluctuating waves on the detection result based on information about the periodic fluctuations contained in the radio waves received by the antenna.

Description

Technical Field

[0001] The present disclosure relates to a direction detection system and a direction detection method.

Background Art

[0002] Conventionally, a radar device mounted on a moving body is known. Patent Document 1 discloses this type of radar device.

[0003] The radar device of Patent Document 1 includes means for detecting and determining the level of artifacts generated by the structure of the moving body, means for storing the detected level and direction, and level adjustment means for reducing the artifact level. Here, an artifact refers to an image that appears on the radar even though the detection target does not exist.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The configuration of Patent Document 1 suppresses the generation of artifacts. However, in order to achieve this, it is necessary to collect reference data related to artifacts in advance. Here, in order to effectively suppress the generation of artifacts, it is necessary to assume various situations and collect a large amount of reference data corresponding thereto. However, it is difficult to assume all situations, and there is a risk of artifacts occurring under unexpected situations.

[0006] The present disclosure has been made in view of the above circumstances, and its object is to effectively suppress the generation of artifacts under various situations.

Means for Solving the Problems

[0007] The problems that this disclosure aims to solve are as described above, and next we will explain the means and effects of solving these problems.

[0008] According to a first aspect of this disclosure, a direction-finding system is provided having the following configuration: a direction-finding system that detects the direction of an object based on target radio waves, which are radio waves arriving from the object. The direction-finding system comprises a radio wave modulation device, an antenna, and a signal processor. The radio wave modulation device modulates the incident radio waves with predetermined parameters for periodic variation and reflects them as a modulated wave. The antenna receives the radio waves. The signal processor detects the direction of the object based on the radio waves received by the antenna. The signal processor reduces the influence of the modulated wave on the detection result based on information about the periodic variation contained in the radio waves received by the antenna.

[0009] If the target radio wave is simply reflected and incident on the antenna at the location where the radio wave modulation device is installed, the incident radio wave will cause false images. In contrast, in the direction-finding system described above, the radio wave modulation device reflects the target radio wave as a fluctuating wave. Even if such a fluctuating wave incident on the antenna, the signal processor reduces the influence of the fluctuating wave on the detection result. This effectively suppresses the occurrence of false images. Furthermore, the signal processor can detect the direction of the object with high accuracy based on the target radio wave that directly incident on the antenna. The aforementioned effects can be applied to a variety of situations if the information on the periodic fluctuations that the radio wave modulation device imparts to the radio wave is known in advance.

[0010] A second aspect of this disclosure provides a direction-finding method, which detects the direction of an object based on a target radio wave, which is a radio wave arriving from the object. The method involves: periodically fluctuating the incident radio wave with predetermined parameters and reflecting it as a fluctuating wave; receiving the radio wave with an antenna; detecting the direction of the object based on the radio wave received by the antenna; and reducing the influence of the fluctuating wave on the detection result based on information about the periodic fluctuation contained in the radio wave received by the antenna.

[0011] In the direction-finding method described above, when reflecting radio waves containing the target radio wave, a periodic fluctuation of predetermined parameters is applied to it, causing it to be reflected as a fluctuating wave. This allows for the distinction between the target radio wave directly incident on the antenna and the radio wave that is incident on the antenna after being reflected as a fluctuating wave. Based on the information of this periodic fluctuation, the influence of the latter on the detection result can be reduced. This effectively suppresses the generation of false images. Furthermore, the direction of the object can be detected with high precision based on the target radio wave directly incident on the antenna. The aforementioned effects can be achieved in a variety of situations if the information of the periodic fluctuations applied to the incident radio wave is known in advance. [Effects of the Invention]

[0012] According to this disclosure, the occurrence of false images can be effectively suppressed under a variety of circumstances. [Brief explanation of the drawing]

[0013] [Figure 1] A diagram schematically showing the overall configuration of the direction-finding system according to the first embodiment. [Figure 2] A conceptual diagram illustrating the reflection of radio waves by the radio wave fluctuation device of the first embodiment. [Figure 3] A graph showing an example of a frequency spectrum corresponding to amplitude modulation. [Figure 4] A diagram schematically showing the functional configuration of the direction-finding system according to the first embodiment. [Figure 5]A diagram showing the functional configuration of a direction detection system according to a first modification of the first embodiment. [Figure 6] A conceptual diagram for explaining the reflection of radio waves by the radio wave fluctuation device of the second modification of the first embodiment. [Figure 7] END]] A conceptual diagram for explaining the reflection of radio waves by the radio wave fluctuation device of the second embodiment. [Figure 8] A conceptual diagram for explaining the reflection of radio waves by the radio wave fluctuation device of a modification of the second embodiment. [Figure 9] A conceptual diagram for explaining the reflection of radio waves by the radio wave fluctuation device of the third embodiment. [Figure 10] A graph showing an example of a frequency spectrum corresponding to phase modulation. [Figure 11] A graph showing another example of a frequency spectrum corresponding to phase modulation. [Figure 12] A conceptual diagram for explaining the reflection of radio waves by the radio wave fluctuation device of a modification of the third embodiment. [Figure 13] A diagram schematically showing the overall configuration of a direction detection system according to the fourth embodiment. [Figure 14] A diagram schematically showing the functional configuration of a direction detection system according to the fourth embodiment.

Embodiments for Carrying Out the Invention

[0014] Next, the first embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a diagram schematically showing the overall configuration of a direction detection system 1 according to the present embodiment. FIG. 2 is a conceptual diagram for explaining the reflection of radio waves by the radio wave fluctuation device 13 of the present embodiment. FIG. 3 is a graph showing an example of a frequency spectrum corresponding to amplitude modulation. FIG. 4 is a diagram schematically showing the functional configuration of the direction detection system 1 according to the present embodiment.

[0015] The direction detection system 1 of this embodiment is a system that detects the direction of the target object 100 based on the target radio wave TW, which is a radio wave arriving from the target object 100, with respect to the radio wave measurement point. The target radio wave TW is a radio wave in a high-frequency band with strong directivity. The frequency band of the target radio wave TW is, for example, a frequency band higher than the UHF (Ultra High Frequency) band. The target radio wave TW may be a radio wave emitted by the target object 100 or a radio wave emitted from the direction detection system 1 and reflected by the target object 100. Here, first, the characteristics of the direction detection system 1 will be briefly described. That is, the direction detection system 1 detects the direction of the target object 100 based on the target radio wave TW. Suppose that the target radio wave TW is reflected by some structure, for example, a structure included in the direction detection system 1, and this reflected wave is incident on the antenna 15 of the direction detection system 1. When the arrival direction of the target radio wave TW is different from the arrival direction of the reflected wave, if the direction of the target object 100 is detected based on the latter reflected wave, the above-mentioned artifact will occur. In contrast, the direction detection system 1 of this embodiment, conceptually speaking, assigns specific identification information to the reflected wave. Thereby, the direction detection system 1 can distinguish between the target radio wave TW that arrives from the target object 100 and directly enters the antenna 15 and the reflected wave that enters the antenna 15, and detect the direction of the target object 100 based only on the former target radio wave TW. Thereby, it is possible to effectively suppress the occurrence of artifacts under various situations and detect the direction of the target object 100 with high accuracy.

[0016] Next, referring to FIGS. 1 to 4, the direction detection system 1 of this embodiment will be described in detail. As shown in FIG. 1, the direction detection system 1 includes a moving body 11, a radio wave fluctuation device 13, an antenna 15, and a signal processor 17. In this embodiment, the radio wave fluctuation device 13, the antenna 15, and the signal processor 17 are provided on the moving body 11. By providing the radio wave fluctuation device 13 on the moving body 11, it becomes possible to suppress the occurrence of artifacts caused by the moving body 11 itself reflecting the target radio wave TW, as will be clear from the following description.

[0017] The mobile body 11 is, for example, an object that can move on land, in the air, or on water. For example, the mobile body 11 may be a car, a motorcycle, a train, an aircraft, or other flying vehicle or ship. In this embodiment, the mobile body 11 is an aircraft that a person can ride on.

[0018] The radio wave modulation device 13 imparts periodic fluctuations to the incident radio waves, including the target radio wave TW, according to predetermined parameters, and reflects them as a fluctuating wave FW. The information of these periodic fluctuations according to predetermined parameters corresponds to the identification information described above. In other words, the target radio wave TW and the fluctuating wave FW can be distinguished based on the information of these periodic fluctuations. The radio wave modulation device 13 may be placed at any part of the mobile body 11.

[0019] The radio wave fluctuation device 13 of this embodiment is a metasurface reflector. A metasurface reflector is a type of metamaterial in which structures that reflect radio waves are periodically arranged on its surface. The relative permittivity of a metasurface reflector can be electrically and dynamically controlled by applying a predetermined control method. By dynamically controlling the relative permittivity of the metasurface reflector, the reflection phase of radio waves at each part of the reflector can be individually adjusted. By such individual adjustment of the reflection phase, it is possible to change the reflection direction of radio waves, switch between specular and diffuse reflection of radio waves, and change the reflection phase of radio waves for the metasurface reflector as a whole. The radio wave fluctuation device 13 of this embodiment applies a control method for changing the reflection direction of radio waves to periodically fluctuate the reflection direction, which is the direction in which the incident target radio wave TW is reflected. In other words, the predetermined parameters in this embodiment are parameters related to the said reflection direction.

[0020] Here, modulation refers to changing the characteristics of a radio wave by applying periodic fluctuations to it. Therefore, the radio wave modulation device 13 modulates the incident radio wave with predetermined parameters. In this sense, the fluctuating wave can also be read as the modulated wave.

[0021] Antenna 15 receives radio waves. The radio waves received by antenna 15 include the target radio wave TW and the fluctuating wave FW. Antenna 15 outputs information about the received radio waves as an electrical signal to the first port 19a of the directional coupler 19, which will be described later. Antenna 15 in this embodiment is a mechanically scanning directional antenna. Antenna 15 may be placed at any part of the mobile body 11.

[0022] The signal processor 17 detects the direction of the object 100 shown in Figure 2 based on the radio waves received by the antenna 15. The signal processor 17 reduces the influence of the fluctuating wave FW on the detection result based on the information of the periodic fluctuations contained in the radio waves received by the antenna 15. The configuration of the signal processor 17 and the processing performed by the signal processor 17 will be described in detail later.

[0023] The direction in which the radio wave modulation device 13 reflects radio waves arriving from a certain object is defined as the reflection direction. As shown in Figure 2, the radio wave modulation device 13 of this embodiment periodically changes the amplitude of the fluctuating wave FW received by the antenna 15 by periodically changing the reflection direction of the target radio wave TW arriving from the object 100. That is, the radio wave modulation device 13, which is configured as a metasurface reflector, periodically changes the reflection direction of the target radio wave TW in three ways in this example by adjusting its reflection phase. The three reflection directions shown in Figure 2, in other words, the propagation directions of the fluctuating wave FW, are merely examples. In order for this disclosure to achieve the aforementioned effects, at least two patterns of reflection directions are necessary in the form in which the reflection direction of the target radio wave TW changes discretely. Furthermore, the reflection direction may change discretely as shown above, or it may change continuously in a way that interpolates between them.

[0024] Of the three reflection directions shown in Figure 2, the one directed towards the antenna 15 of the direction-finding system 1 is the central reflection direction. The fluctuating wave FW corresponding to this central reflection direction is also called the first fluctuating wave FW1. The fluctuating waves FW corresponding to the remaining two reflection directions are also called the second fluctuating wave FW2 and the third fluctuating wave FW3, respectively. The amplitudes of the second fluctuating wave FW2 and the third fluctuating wave FW3 are the same as or approximately the same as the amplitude of the first fluctuating wave FW1. However, the direction of propagation of the second fluctuating wave FW2 and the third fluctuating wave FW3 is offset from the antenna 15. Therefore, the antenna 15 receives each of the fluctuating waves FW1, FW2, and FW3 individually and periodically. For example, in antenna 15, each fluctuating wave FW can be received individually and periodically, repeating in the order described: "first fluctuating wave FW1, second fluctuating wave FW2, first fluctuating wave FW1 and third fluctuating wave FW3." However, the order in which each fluctuating wave FW is received by antenna 15, in other words, the order in which the reflection direction is changed by the radio wave modulation device 13, is not limited to this. In the reception of each fluctuating wave FW in a series, antenna 15 receives the first fluctuating wave FW1 as a radio wave with a relatively large amplitude, while the second fluctuating wave FW2 and the third fluctuating wave FW3 are received as radio waves with a relatively small amplitude. As a result, the fluctuating waves FW received by antenna 15 are observed as radio waves to which amplitude modulation has been applied to the target radio wave TW.

[0025] It is known that the frequency spectrum of a radio wave to which amplitude modulation by a modulation signal is applied to a carrier wave is as shown in Figure 3. The radio wave to which amplitude modulation by a modulation signal is applied to a carrier wave will hereafter be called the amplitude-modulated wave. Here, fc is the frequency of the carrier wave, and fm is the frequency of the modulation signal. As can be seen from Figure 3, the frequency spectrum of the amplitude-modulated wave includes the component of the carrier wave at frequency fc, as well as the components of frequencies fc+fm and fc-fm. Note that both the carrier wave and the amplitude-modulated wave have a constant bandwidth Δf, but this is omitted from the illustration in Figure 3. The carrier wave is a sinusoidal radio wave of a specific frequency, and refers to the radio wave before modulation is applied. The modulation signal refers to a signal that imparts periodic fluctuations to the carrier wave.

[0026] In the direction-finding system 1 of this embodiment, the above-mentioned frequency fc component corresponds to the component corresponding to the target radio wave TW, and the above-mentioned frequency fc+fm component and frequency fc-fm component correspond to the component corresponding to the fluctuating wave FW. Based on the power ratio of the two corresponding components, it is possible to determine whether the radio wave received by antenna 15 in any direction is the target radio wave TW or the fluctuating wave FW. Specifically, in the radio wave received by antenna 15, the larger the power ratio, i.e., Pm / Pc, which is the ratio of the power Pm of the component corresponding to the fluctuating wave FW to the power Pc of the component corresponding to the target radio wave TW, the higher the probability that the received radio wave is a fluctuating wave FW, and direction-finding is performed accordingly. The above-mentioned frequency fm corresponds to the fluctuation period when the radio wave fluctuation device 13 fluctuates the reflection direction of the target radio wave TW.

[0027] Next, the configuration for performing direction finding, which was outlined in the previous paragraph, will be described with reference to Figure 4. As shown in the figure, the direction finding system 1 of this embodiment includes a mobile body 11, a radio wave fluctuation device 13, an antenna 15, and a signal processor 17, as well as a device control unit 33 that controls the radio wave fluctuation device 13 and a display unit 35 that displays the detection results. In this embodiment, the display unit 35 is a display provided on the mobile body 11, but is not limited to this. Also, the device control unit 33 of this embodiment is provided on the mobile body 11.

[0028] As shown in Figure 4, the device control unit 33 receives information regarding at least the modulation parameters of the radio wave modulation device 13, and controls the radio wave modulation device 13 based on this input information. The modulation parameters of the radio wave modulation device 13 are, for example, the fluctuation period of the reflection direction of the radio waves reflected by the radio wave modulation device 13. As a result, the target radio wave TW incident on the radio wave modulation device 13 is reflected as a fluctuating wave FW. In this embodiment, the fluctuating wave FW has a periodically fluctuating direction of propagation, as described above, but is shown by a single arrow in Figure 4. The device control unit 33 may be composed of a known computer equipped with an arithmetic unit and a memory device.

[0029] The signal processor 17 comprises a directional coupler 19, a first bandpass filter 21, a second bandpass filter 23, a power ratio calculation unit 25, a variable attenuator 27, and a control unit 29. The signal processor 17 also includes an arithmetic unit and a memory device that stores a program executable by the arithmetic unit. The program executable by the arithmetic unit is, for example, a program for executing the direction finding method of this embodiment. At least some of the components of the signal processor 17 may be realized through the cooperation of hardware and software, that is, by the arithmetic unit executing a program stored in the memory device. Alternatively or in addition, at least some of the components of the signal processor 17 may be realized by hardware such as electrical components or electrical circuits.

[0030] The directional coupler 19 has a first port 19a, a second port 19b, and a third port 19c. The first port 19a is connected to the antenna 15. The second port 19b is connected to the variable attenuator 27. The third port 19c is connected to the first bandpass filter 21 and the second bandpass filter 23. The directional coupler 19 can extract a portion of the electrical signal that is the subject of information transmitted from the first port 19a to the second port 19b from the third port 19c. In this example, the electrical signal that is the subject of information transmitted from the first port 19a to the second port 19b is an electrical signal based on radio waves received by the antenna 15. Most of the electrical signal input to the first port 19a is input to the variable attenuator 27 via the second port 19b, while a portion of it is input to the first bandpass filter 21 and the second bandpass filter 23 via the third port 19c. In the following description, when explaining the exchange of information, for example, information regarding the frequency components of radio waves, by the components of the direction-finding system 1, such information may sometimes be simply referred to as the components of an electrical signal.

[0031] The first bandpass filter 21 has its input side connected to the third port 19c of the directional coupler 19 and its output side connected to the power ratio calculation unit 25. The first bandpass filter 21 receives input information regarding at least the specifications of the target radio wave TW. The specifications of the target radio wave TW are, for example, its frequency. Based on this input information, the center frequency of the passband of the first bandpass filter 21 is set to be the same as or approximately the same as the frequency of the component corresponding to the target radio wave TW. The stopband of the first bandpass filter 21 is set to include the frequencies of the two components corresponding to the fluctuating wave FW. The first bandpass filter 21 passes the component corresponding to the target radio wave TW from the electrical signal input from the third port 19c of the directional coupler 19 without substantially attenuation, while substantially blocking the component corresponding to the fluctuating wave FW by attenuation. Therefore, the component corresponding to the target radio wave TW is output from the first bandpass filter 21 to the power ratio calculation unit 25.

[0032] The second bandpass filter 23 has its input side connected to the third port 19c of the directional coupler 19 and its output side connected to the power ratio calculation unit 25. Strictly speaking, the second bandpass filter 23 is configured as a band-elimination filter that attenuates only a certain range of frequencies from the input to the output, but it can be considered a type of bandpass filter in a broad sense. At least information regarding the above modulation parameters is input to the second bandpass filter 23. The modulation parameters are, for example, the fluctuation period of the reflection direction. In Figure 4, the input of information regarding the modulation parameters is indicated by an arrow extending from the device control unit 33 to the second bandpass filter 23. Based on this input information, the center frequency of the stopband of the second bandpass filter 23 is set to be the same as or approximately the same as the frequency of the component corresponding to the target radio wave TW. The passband of the second bandpass filter 23 is set to include the frequencies of the two components corresponding to the fluctuating wave FW. The second bandpass filter 23 attenuates and effectively blocks the component of the electrical signal input from the third port 19c of the directional coupler 19 that corresponds to the target radio wave TW, while allowing the component corresponding to the fluctuating wave FW to pass through without substantially attenuation. Therefore, the component corresponding to the fluctuating wave FW is output from the second bandpass filter 23 to the power ratio calculation unit 25.

[0033] The power ratio calculation unit 25 calculates the power ratio, i.e., Pm / Pc, which is the ratio of the power Pm of the electrical signal component corresponding to the fluctuating wave FW to the power Pc of the electrical signal component corresponding to the target radio wave TW, based on the inputs from the first bandpass filter 21 and the second bandpass filter 23. The calculated power ratio information is output to the variable attenuator 27.

[0034] The variable attenuator 27 is a device that attenuates the input signal, and its attenuation rate is variable. The input side of the variable attenuator 27 is connected to the second port 19b of the directional coupler 19, and the output side is connected to the control unit 29. The variable attenuator 27 also receives information regarding the power ratio from the power ratio calculation unit 25. The variable attenuator 27 changes its attenuation rate based on this power ratio information. Specifically, the attenuation rate of the variable attenuator 27 increases as the power ratio increases, that is, as the ratio of the power of the component corresponding to the fluctuating wave FW increases.

[0035] Here, the electrical signal based on the radio waves received by antenna 15 is mostly input to the variable attenuator 27 via the directional coupler 19. When this electrical signal corresponds to the direct incidence of the target radio wave TW, that is, when the power ratio of the component corresponding to the fluctuating wave FW is low or substantially zero, it is input to the control unit 29 with almost no attenuation. On the other hand, when this electrical signal corresponds to the fluctuating wave FW, that is, when the power ratio of the component corresponding to the fluctuating wave FW is high, it is significantly attenuated before being input to the control unit 29.

[0036] The control unit 29 has a function to control the direction of the antenna 15 and a function to display the direction detection result on the display unit 35. The function of the control unit 29 to control the direction of the antenna 15 is also called the direction control function. The function of the control unit 29 to display the direction detection result on the display unit 35 is also called the display control function. The display control function may be provided in any other device that can communicate with the display unit 35. In this case, the output signal of the variable attenuator 27 is input to the other device directly or indirectly.

[0037] The control unit 29 controls the direction of the antenna 15 by mechanically scanning it using its direction control function. In this embodiment, this direction control is achieved by rotating the antenna 15 along a predetermined plane. The control unit 29 also displays information on the display unit 35 that associates the direction of the antenna 15 with the input signal from the variable attenuator 27 using its display control function.

[0038] More specifically, when antenna 15 is oriented as shown in Figure 4, in the illustrated example, the target radio wave TW arriving from the left of antenna 15 is received with high gain. As described above, the electrical signal based on the target radio wave TW is input to the control unit 29 with almost no attenuation, so the control unit 29 displays a large shape A extending to the left on the display unit 35. In Figure 4, the shape A displayed on the display unit 35 is given dot hatching for easier identification. On the other hand, when antenna 15 is pointing to the upper left in Figure 4, in the illustrated example, the fluctuating wave FW arriving from the upper left of antenna 15 is received with high gain. As described above, the electrical signal based on the fluctuating wave FW is significantly attenuated before being input to the control unit 29, so the control unit 29 displays a small shape B extending to the upper left on the display unit 35. In Figure 4, the shape B displayed on the display unit 35 is given diagonal hatching for easier identification. By seeing these displays, the user can recognize that there is a high probability that the target object 100 is located to the left. The small shape extending to the upper left can be omitted.

[0039] Thus, in the signal processor 17, the power ratio Pm / Pc is determined in relation to the radio wave reception direction while the direction of the antenna 15 is controlled by the control unit 29, that is, while the direction of radio wave reception of the antenna 15 is controlled. The display unit 35 then displays the detection results for each radio wave reception direction such that the larger the corresponding power ratio Pm / Pc, the lower the probability of the object 100 being present is recognized. In Figure 4, a dashed line shows a diagram C as a reference, representing the case where the electrical signal based on the fluctuating wave FW is displayed without attenuation. This dashed line diagram C corresponds to the false image described above, and it can be seen that the generation of false images can be effectively suppressed by the direction finding system 1 of this embodiment.

[0040] Next, a direction-finding method that can be performed in the direction-finding system 1 of this embodiment will be briefly described. In this direction-finding method, the radio wave modulation device 13 periodically modulates the radio waves, including the target radio wave TW, that are incident on it, according to predetermined parameters, and reflects them as a modulated wave FW. In this example, the predetermined parameters are the reflection direction in which the radio wave modulation device 13 reflects the target radio wave TW. That is, by periodically varying the reflection direction, the amplitude of the modulated wave FW received by the antenna 15 is periodically varied.

[0041] Then, the signal processor 17 detects the direction of the object 100 based on the radio waves received by the antenna 15, including the target radio wave TW and the fluctuating wave FW. Based on the periodic fluctuation information contained in the received radio waves, the influence of the fluctuating wave FW on the detection result is reduced. More specifically, the first bandpass filter 21 and the second bandpass filter 23 separate the electrical signal based on the received radio waves into a component corresponding to the target radio wave TW and a component corresponding to the fluctuating wave FW. The power ratio Pm / Pc, which is the ratio of the power Pm of the latter component to the power Pc of the former component, is then calculated by the power ratio calculation unit 25 in relation to the radio wave reception direction. For each radio wave reception direction, the detection result is displayed on the display unit 35 such that the larger the corresponding power ratio Pm / Pc, the lower the probability of the object 100 being present.

[0042] As described above, the direction finding system 1 of this embodiment detects the direction of an object 100 based on the target radio wave TW, which is a radio wave arriving from the object 100. The direction finding system 1 comprises a radio wave modulation device 13, an antenna 15, and a signal processor 17. The radio wave modulation device 13 imparts periodic fluctuations to the incident radio wave with predetermined parameters and reflects it as a fluctuating wave FW. The antenna 15 receives the radio wave. The signal processor 17 detects the direction of the object 100 based on the radio wave received by the antenna 15. The signal processor 17 reduces the influence of the fluctuating wave FW on the detection result based on the periodic fluctuation information contained in the radio wave received by the antenna 15.

[0043] If the target radio wave TW is simply reflected by some structure and incident on the antenna 15 at the location where the radio wave modulation device 13 is installed, the incident radio wave will cause false images. In contrast, in the direction finding system 1 described above, the radio wave modulation device 13 reflects the radio wave including the target radio wave TW as a fluctuating wave FW. Even if such a fluctuating wave FW incident on the antenna 15, the signal processor 17 reduces the influence of the fluctuating wave FW on the detection result. This effectively suppresses the occurrence of false images. Furthermore, the signal processor 17 can detect the direction of the object 100 with high accuracy based on the target radio wave TW that directly incident on the antenna 15. Each of the above effects can be applied to a variety of situations if the information on the periodic fluctuations that the radio wave modulation device 13 imparts to the radio waves is known in advance.

[0044] Furthermore, the direction-finding system 1 of this embodiment further comprises a mobile body 11. The mobile body 11 has a radio wave fluctuation device 13, an antenna 15, and a signal processor 17.

[0045] As a result, the user of the direction-finding system 1 can accurately determine the direction of the object 100 while moving if they are on board the mobile body 11, or using the mobile body 11 while moving if they are not on board. Furthermore, in this case, because the mobile body 11 has a radio wave fluctuation device 13, the direction-finding system 1 can suppress the occurrence of false images, particularly when the mobile body 11 itself reflects the target radio wave TW and it enters the antenna 15.

[0046] Furthermore, in the direction-finding system 1 of this embodiment, the radio wave fluctuation device 13 periodically fluctuates the amplitude of the fluctuating wave FW received by the antenna 15.

[0047] As a result, antenna 15 receives a fluctuating wave FW to which amplitude modulation is effectively applied to the target radio wave TW. Based on the difference between the frequency spectrum of the target radio wave TW and the frequency spectrum of the fluctuating wave FW, it becomes possible to reduce the influence of the fluctuating wave FW on the detection result.

[0048] Furthermore, the direction-finding system 1 of this embodiment includes a reflection direction, which is the direction in which the radio wave modulation device 13 reflects the target radio wave TW, as a predetermined parameter. The radio wave modulation device 13 periodically changes the amplitude of the fluctuating wave FW received by the antenna 15 by periodically changing the reflection direction.

[0049] This makes it possible to suppress the generation of false images by a relatively simple control that periodically varies the reflection direction of the radio wave fluctuation device 13.

[0050] Furthermore, the direction-finding system 1 of this embodiment further includes a display unit 35 for displaying the detection results. The signal processor 17 determines the power ratio Pm / Pc, which is the ratio of the power Pm of the component corresponding to the fluctuating wave FW to the power Pc of the component corresponding to the target radio wave TW, in relation to the radio wave reception direction. For each radio wave reception direction, the display unit 35 displays the detection results such that the larger the corresponding power ratio Pm / Pc, the lower the probability of the object 100 being recognized.

[0051] As a result, a user looking at the display unit 35 showing the detection results can easily recognize that the probability of object 100 being present in a radio wave reception direction with a large corresponding power ratio Pm / Pc, i.e., a radio wave reception direction with a high ratio of power Pm corresponding to the fluctuating wave FW. Conversely, by looking at the display unit 35, the user can easily recognize that the probability of object 100 being present in a radio wave reception direction with a small corresponding power ratio Pm / Pc, i.e., a radio wave reception direction with a high ratio of power Pc corresponding to the target radio wave TW.

[0052] Furthermore, in the direction-finding system 1 of this embodiment, the radio wave fluctuation device 13 is composed of a metasurface reflector. The radio wave fluctuation device 13, which is a metasurface reflector, periodically changes the reflection direction, which is the direction in which the radio wave fluctuation device 13 reflects the target radio wave TW, by adjusting the reflection phase.

[0053] This allows for periodic fluctuations in the reflection direction by electrically controlling the radio wave fluctuation device 13, which is a metasurface reflector. Since the metasurface reflector does not undergo physical deformation when adjusting the reflection phase, if it is installed on a mobile body 11, for example, it is possible to avoid an increase in air resistance at the installation site of the radio wave fluctuation device 13.

[0054] Furthermore, in this embodiment, the direction-finding system 1 has a mechanically scanned directional antenna 15. The signal processor 17 controls the direction of the antenna 15 by mechanically scanning it.

[0055] This makes it possible to reduce the cost of the antenna 15, and consequently, to reduce the cost of the direction-finding system 1.

[0056] Furthermore, the direction-finding method of this embodiment is a direction-finding method that detects the direction of an object 100 based on an incoming radio wave TW, which is a radio wave coming from the object 100. The incident radio wave is given a periodic fluctuation with predetermined parameters and reflected as a fluctuating wave FW. The radio wave is received by the antenna 15. The direction of the object 100 is detected based on the radio wave received by the antenna 15. The influence of the fluctuating wave FW on the detection result is reduced based on the periodic fluctuation information contained in the radio wave received by the antenna 15.

[0057] In the direction-finding method described above, when reflecting radio waves including the target radio wave TW, a periodic variation of predetermined parameters is applied to them, causing them to be reflected as a fluctuating wave FW. This allows for the distinction between the target radio wave TW that directly enters the antenna 15 and the radio waves that enter the antenna 15 after being reflected as a fluctuating wave FW. Based on the information of this periodic variation, the influence of the latter on the detection result can be reduced. This effectively suppresses the generation of false images. Furthermore, the direction of the object 100 can be detected with high accuracy based on the target radio wave TW that directly enters the antenna 15. The aforementioned effects can be applied to a variety of situations if the information of the periodic variation applied to the incident radio waves is known in advance.

[0058] Furthermore, the direction-finding method of this embodiment periodically varies the amplitude of the fluctuating wave FW received by the antenna 15.

[0059] As a result, antenna 15 receives a fluctuating wave FW to which amplitude modulation is effectively applied to the target radio wave TW. Based on the difference between the frequency spectrum of the target radio wave TW and the frequency spectrum of the fluctuating wave FW, it becomes possible to reduce the influence of the fluctuating wave FW on the detection result.

[0060] Furthermore, the direction-finding method of this embodiment includes a reflection direction, which is the direction in which the target radio wave TW is reflected, as a predetermined parameter. By periodically varying the reflection direction, the amplitude of the fluctuating wave FW received by the antenna 15 is periodically varied.

[0061] This makes it possible to suppress the generation of false images through a relatively simple operation: periodically varying the direction of reflection.

[0062] Furthermore, the direction finding method of this embodiment determines the power ratio Pm / Pc, which is the ratio of the power Pm of the component corresponding to the fluctuating wave FW to the power Pc of the component corresponding to the target radio wave TW, in relation to the radio wave reception direction. For each radio wave reception direction, the detection results are displayed such that the larger the corresponding power ratio Pm / Pc, the lower the probability of the object 100 being present.

[0063] As a result, a user who sees the display of the detection results can easily recognize that the probability of object 100 being present in a radio wave reception direction with a large corresponding power ratio Pm / Pc, i.e., a radio wave reception direction with a high ratio of power Pm corresponding to the fluctuating wave FW. Conversely, by looking at the display, the user can easily recognize that the probability of object 100 being present in a radio wave reception direction with a small corresponding power ratio Pm / Pc, i.e., a radio wave reception direction with a high ratio of power Pc corresponding to the target radio wave TW.

[0064] Next, a first modified example of the first embodiment will be described. Figure 5 is a diagram showing the functional configuration of the direction-finding system 1 according to this modified example. In the description of this modified example, the same or similar components as those in the previously described embodiment will be denoted by the same reference numerals in the drawings, and their descriptions may be omitted.

[0065] The direction-finding system 1 of this modified version differs from the first embodiment in the configuration of the antenna 15 and the signal processor 17. Specifically, as shown in Figure 5, the antenna 15 of this modified version is an electronically scanning array antenna equipped with a plurality of antenna elements 15a, and the signal processor 17 includes an arrival direction estimation unit 31. In Figure 5, the arrival direction estimation unit 31 and the power ratio calculation unit 25 are shown with displays, but these are for illustrative purposes only, and the display for showing information to the user is limited to the indicator 35. However, this does not preclude visually displaying the estimation results by the arrival direction estimation unit 31 and the calculation results by the power ratio calculation unit 25 to the user by some means. The signal processor 17 has a control unit equipped with a display control function after the variable attenuator 27.

[0066] The direction of arrival estimation unit 31 estimates the direction of arrival of radio waves received by the antenna 15, which is an electronically scanned array antenna. For example, the direction of arrival estimation unit 31 may estimate the direction of arrival of the received radio waves based on the directional direction of the electronically scanned antenna 15 and the magnitude of the output power of the antenna 15 in each directional direction. Alternatively, the direction of arrival estimation unit 31 may estimate the direction of arrival of the received radio waves based on the phase difference of the received signals of the multiple antenna elements 15a provided by the antenna 15. However, the method for estimating the direction of arrival of the received radio waves is not limited to these. The direction of arrival estimation unit 31 may be implemented through the cooperation of hardware and software, that is, by the execution of a program stored in the memory of the signal processor 17 by the arithmetic unit. Alternatively or in addition, the direction of arrival estimation unit 31 may be implemented by hardware such as electrical components or electrical circuits.

[0067] The direction of arrival estimation unit 31 processes the power of electrical signals based on radio waves, including the target radio wave TW and the fluctuating wave FW, and the direction of arrival of the radio waves. In Figure 5, the results of this processing are shown in a manner similar to a display within the block of the direction of arrival estimation unit 31. In the illustrated example, the target radio wave TW arriving from the left is shown by a figure extending to the left, and the fluctuating wave FW arriving from the upper left is shown by a figure extending to the upper left. The size of the two figures is the same or approximately the same. Therefore, at this stage, information is obtained that radio waves with a certain amount of power are arriving from two directions. In other words, in the illustrated example, from the processing results at this stage, it can be recognized that there is a high possibility that the object 100 exists to the left and / or upper left, but the latter is a false image, so it is necessary to eliminate the possibility of its existence.

[0068] To this end, in the direction-finding system 1 of this modified example, similar to the first embodiment described above, the power ratio Pm / Pc, which is the ratio of the power Pm of the component corresponding to the fluctuating wave FW to the power Pc of the component corresponding to the target radio wave TW, is determined in relation to the radio wave reception direction. Then, for each radio wave reception direction, the detection result is displayed on the display unit 35 such that the larger the corresponding power ratio Pm / Pc, the lower the probability of the object 100 being present is perceived.

[0069] To explain the specifics, first, we will describe the case where the target radio wave TW is directly incident on the antenna 15, referring to Figure 5. In this case, as shown in the example, the target radio wave TW arriving from the left is received by the antenna 15. The direction of arrival estimation unit 31 estimates that a radio wave with a certain amount of power arrived from the left. The estimated direction of arrival, that is, the radio wave reception direction information in this modified example, is temporarily stored in the memory device of the signal processor 17. The direction of arrival estimation unit 31 outputs an electrical signal based on the received radio wave to the first port 19a of the directional coupler 19.

[0070] From the third port 19c of the directional coupler 19, which receives an electrical signal based on the received radio wave, the electrical signal based on the received radio wave is output and input to the first bandpass filter 21 and the second bandpass filter 23, respectively. Then, in association with the radio wave reception direction stored in the memory device, the power ratio Pm / Pc is calculated by the power ratio calculation unit 25, as in the first embodiment described above. In this example, the radio wave reception direction stored in the memory device is to the left. In Figure 5, the radio wave arriving from the left is the target radio wave TW, so the power ratio is substantially zero. Therefore, the display in the block of the power ratio calculation unit 25 in the figure does not show a figure extending to the left, indicating that the power ratio corresponding to the left direction is substantially zero.

[0071] Then, most of the electrical signal based on the received radio waves output from the second port 19b of the directional coupler 19 and input to the variable attenuator 27 is output from the variable attenuator 27 without being attenuated, because the power ratio Pm / Pc input to the variable attenuator 27 is substantially zero. Upon receiving this output signal, the signal processor 17 displays a figure A extending far to the left on the display unit 35. In Figure 5, the figure A displayed on the display unit 35 is given dot hatching for easier identification.

[0072] Next, we will explain the case where the target radio wave TW is reflected by the radio wave modulation device 13 and incident on the antenna 15 as a fluctuating wave FW, with reference to Figure 5. In this case, in the illustrated example, the fluctuating wave FW arriving from the upper left is received by the antenna 15. The direction of arrival estimation unit 31 estimates that a radio wave with a certain amount of power arrived from the left. The estimated direction of arrival, i.e., the radio wave reception direction information in this modified example, is temporarily stored in the memory device of the signal processor 17. The direction of arrival estimation unit 31 outputs an electrical signal based on the received radio wave to the first port 19a of the directional coupler 19.

[0073] The electrical signal based on the received radio wave is input to the third port 19c of the directional coupler 19, and the electrical signal based on the received radio wave is output and input to the first bandpass filter 21 and the second bandpass filter 23, respectively. Then, the power ratio Pm / Pc is calculated by the power ratio calculation unit 25 in association with the radio wave reception direction stored in the memory. In this example, the radio wave reception direction stored in the memory is the upper left. In Figure 5, the radio wave arriving from the upper left is a fluctuating wave FW, so the power ratio is large. Therefore, the display in the block of the power ratio calculation unit 25 in the figure shows a figure extending to the upper left to indicate that the power ratio corresponding to the upper left direction is large.

[0074] Then, most of the electrical signal based on the received radio waves output from the second port 19b of the directional coupler 19 and input to the variable attenuator 27 is significantly attenuated because the power ratio Pm / Pc input to the variable attenuator 27 is large, and is output from the variable attenuator 27. Upon receiving this attenuated output signal, the signal processor 17 displays a small figure B extending to the upper left on the display unit 35. In Figure 5, the figure B displayed on the display unit 35 is hatched with diagonal lines for easier identification. By looking at this display and the aforementioned figure extending far to the left, the user can recognize that there is a high probability that the object 100 is located to the left. The display of the small figure extending to the upper left may be omitted. Also, in Figure 5, as in Figure 4, a dashed line is shown for reference to represent the case where the electrical signal based on the fluctuating wave FW is displayed without attenuation.

[0075] As described above, in this modified direction-finding system 1, the antenna 15 is an electronically scanned array antenna. The signal processor 17 controls the direction of the antenna 15 by electronically scanning it.

[0076] This makes it possible to make the antenna 15 smaller, lighter, and more reliable, which in turn makes the direction-finding system 1 smaller, lighter, and more reliable.

[0077] Next, a second modified example of the first embodiment will be described. Figure 6 is a conceptual diagram illustrating the reflection of radio waves by the radio wave fluctuation device 13 of this modified example. In the description of this modified example, the same or similar components as those in the previously described embodiment will be denoted by the same reference numerals in the drawings, and their descriptions may be omitted.

[0078] The direction-finding system 1 of this modified example differs from the first embodiment in the configuration of the radio wave fluctuation device 13. Specifically, as shown in Figure 6, the radio wave fluctuation device 13 of this modified example is composed of a reflector whose orientation or attitude can be mechanically changed, instead of a metasurface reflector. The radio wave fluctuation device 13 is driven by a power source to periodically oscillate in the clockwise and counterclockwise directions shown in Figure 6, as indicated by the solid and dashed lines, thereby periodically changing the reflection direction, which is the direction in which the target radio wave TW arriving from the object 100 is reflected. As a result, the amplitude of the fluctuating wave FW received by the antenna 15 of the direction-finding system 1 periodically fluctuates. Based on the target radio wave TW arriving from the object 100 and directly incident on the antenna 15, and the fluctuating wave FW reflected by the radio wave fluctuation device 13 and incident on the antenna 15, the direction-finding system 1 can detect the direction of the object 100 with high accuracy while suppressing the generation of false images, similar to the first embodiment.

[0079] As described above, in this modified form of the direction-finding system 1, the radio wave fluctuation device 13 is a reflector whose orientation can be changed. The direction-finding system 1 further includes a drive source that periodically oscillates the radio wave fluctuation device 13.

[0080] This allows for the suppression of false images through a relatively simple action: periodically oscillating the reflector.

[0081] Next, a second embodiment will be described. Figure 7 is a conceptual diagram illustrating the reflection of radio waves by the radio wave fluctuation device 13 of this embodiment. In the description of this embodiment, the same or similar components as those in the previously described embodiment will be denoted by the same reference numerals in the drawings, and their descriptions may be omitted.

[0082] The direction-finding system 1 of this embodiment is similar to the first embodiment in that it substantially applies amplitude modulation to the target radio wave TW, but its specific manner differs from the first embodiment. That is, the radio wave modulation device 13 of this embodiment periodically varies the amplitude of the fluctuating wave FW received by the antenna 15 by periodically varying the diffuse reflectance of the radio wave. Here, diffuse reflectance is the ratio of the diffuse reflection component to the specular reflection component in the reflection of the target radio wave TW by the radio wave modulation device 13. The specular reflection component refers to the component of reflected light where the angle of incidence and the angle of reflection are equal. The diffuse reflection component refers to the component of reflected light where the angle of incidence and the angle of reflection are different.

[0083] In the example shown in Figure 7, the radio wave modulation device 13 is composed of a metasurface reflector, and by adjusting its reflection phase, it can be switched between a first state in which it specularly reflects the target radio wave TW and a second state in which it diffusely reflects the target radio wave TW. When the radio wave modulation device 13 is in the first state, the diffuse reflectance is relatively low, and when the radio wave modulation device 13 is in the second state, the diffuse reflectance is relatively high. In this embodiment, the radio wave modulation device 13 is controlled to periodically switch between the first and second states, thereby periodically varying the diffuse reflectance. In Figure 7, the fluctuating wave FW in the first state, i.e., the specularly reflected radio wave, is indicated by a white arrow, and the fluctuating wave FW in the second state, i.e., the diffusely reflected radio wave, is indicated by a black arrow.

[0084] Figure 7 shows an example where the specular reflection component is directed towards antenna 15. When the diffuse reflectance is low, that is, when the ratio of the specular reflection component in the fluctuating wave FW is high, the antenna 15 of the direction-finding system 1 receives the fluctuating wave FW as a radio wave with a relatively large amplitude. On the other hand, when the diffuse reflectance is high, that is, when the ratio of the specular reflection component in the fluctuating wave FW is low, the antenna 15 of the direction-finding system 1 receives the fluctuating wave FW as a radio wave with a relatively small amplitude. Such amplitude changes occur periodically through the control described above. As a result, the fluctuating wave FW received by antenna 15 is observed as a radio wave to which amplitude modulation has been applied to the target radio wave TW. Based on such a fluctuating wave FW and the target radio wave TW that arrives from the object 100 and directly incidents on antenna 15, the direction of the object 100 can be detected with high accuracy while suppressing the generation of false images, similar to the first embodiment.

[0085] The first and second states may be switched discretely, or they may be switched continuously to fill the gap between them. In addition, as long as the diffuse reflectance can be periodically varied, there may be at least one other state having a different diffuse reflectance than the first and second states, either in place of or in addition to them.

[0086] As described above, the direction-finding system 1 of this embodiment includes a predetermined parameter which is the diffuse reflectance, which is the ratio of the diffuse reflection component to the specular reflection component in the reflection of the target radio wave TW at the radio wave fluctuation device 13. The radio wave fluctuation device 13 periodically fluctuates the amplitude of the fluctuating wave FW received by the antenna 15 by periodically fluctuating the diffuse reflectance.

[0087] This makes it possible to suppress the generation of false images by a relatively simple control that periodically varies the diffuse reflectance in the reflection of the radio wave fluctuation device 13.

[0088] Furthermore, the direction-finding method of this embodiment includes a predetermined parameter, which is the diffuse reflectance, which is the ratio of the diffuse reflection component to the specular reflection component in the reflection of the target radio wave TW. By periodically varying the diffuse reflectance, the amplitude of the fluctuating wave FW received by the antenna 15 is periodically varied.

[0089] This makes it possible to suppress the generation of false images through a relatively simple operation: periodically varying the diffuse reflectance in the reflection of the target radio wave TW.

[0090] Next, a modified example of the second embodiment will be described. Figure 8 is a conceptual diagram illustrating the reflection of radio waves by the radio wave fluctuation device 13 of this modified example. In the description of this modified example, the same or similar components as those in the previously described embodiment will be denoted by the same reference numerals in the drawings, and their descriptions may be omitted.

[0091] The direction-finding system 1 of this modified example differs from the second embodiment in the configuration of the radio wave modulation device 13. Specifically, as shown in Figure 8, the radio wave modulation device 13 of this modified example is composed of a reflector whose shape can be mechanically changed, instead of a metasurface reflector. The radio wave modulation device 13 is periodically deformed by a drive source between a shape that is relatively close to a flat surface and a shape that is relatively far from a flat surface. In the example in Figure 8, the shape of the radio wave modulation device 13 that is relatively close to a flat surface is the planar shape shown by the solid line, and the shape of the radio wave modulation device 13 that is relatively far from a flat surface is the curved shape shown by the dashed line. The target radio wave TW is specularly reflected by the radio wave modulation device 13 in the former shape, while the target radio wave TW is diffusely reflected by the radio wave modulation device 13 in the latter shape. As a result, the amplitude of the fluctuating wave FW received by the antenna 15 of the direction-finding system 1 fluctuates periodically. The direction-finding system 1, based on the target radio wave TW arriving from the object 100 and directly incident on the antenna 15, and the fluctuating wave FW reflected by the radio wave fluctuation device 13 and incident on the antenna 15, can detect the direction of the object 100 with high accuracy while suppressing the generation of false images, similar to the first embodiment.

[0092] As described above, in this modified form of the direction-finding system 1, the radio wave fluctuation device 13 is a reflector whose shape can be changed. The direction-finding system 1 further includes a drive source that periodically deforms the radio wave fluctuation device 13 between a shape that is relatively close to a flat surface and a shape that is relatively far from a flat surface.

[0093] This allows for the suppression of false images through a relatively simple operation: periodically deforming the reflector.

[0094] Next, a third embodiment will be described. Figure 9 is a conceptual diagram illustrating the reflection of radio waves by the radio wave modulation device 13 of this embodiment. Figure 10 is a graph showing an example of a frequency spectrum corresponding to phase modulation. Figure 11 is a graph showing another example of a frequency spectrum corresponding to phase modulation. In the description of this embodiment, components identical or similar to those in the previously described embodiments are denoted by the same reference numerals in the drawings, and their descriptions may be omitted.

[0095] As shown in Figure 9, the radio wave modulation device 13 of this embodiment is a metasurface reflector that applies phase modulation to the target radio wave TW arriving from the object 100 and reflects it as a fluctuating wave FW. That is, the predetermined parameters in this embodiment are parameters related to the phase of the target radio wave TW. The radio wave modulation device 13, configured as a metasurface reflector, adjusts its reflection phase, thereby periodically shifting the phase of the target radio wave TW back and forth in time, as conceptually illustrated in Figure 9. In the graph showing the phase of the target radio wave TW in Figure 9, the horizontal axis t represents time. This periodic phase shift may be performed discretely or continuously. The radio wave modulation device 13 may also apply frequency modulation to the target radio wave TW and reflect it as a fluctuating wave FW. In this case, the predetermined parameters are parameters related to the frequency of the target radio wave TW.

[0096] Here, it is known that the frequency spectrum of a radio wave to which phase modulation or frequency modulation by a modulation signal is applied to a carrier wave is as shown in Figures 10 and 11. The radio wave to which phase modulation or frequency modulation by a modulation signal is applied to a carrier wave will hereinafter also be called the angle-modulated wave. Here, fc is the frequency of the carrier wave, and fm is the frequency of the modulation signal. Figure 10 shows a graph for narrowband modulation with a small modulation index, and Figure 11 shows a graph for wideband modulation with a large modulation index. Note that both the carrier wave and the angle-modulated wave have a constant bandwidth Δf, but this is omitted from Figures 10 and 11.

[0097] As can be seen from Figure 10, in the case of narrowband modulation, i.e., narrowband phase modulation or narrowband frequency modulation, the spectrum is spread in a relatively narrow frequency band, centered around the carrier frequency fc, at intervals corresponding to the modulation signal frequency fm. On the other hand, as can be seen from Figure 11, in the case of broadband modulation, i.e., broadband phase modulation or broadband frequency modulation, the spectrum is spread in a relatively wide frequency band, centered around the carrier frequency fc, at intervals corresponding to the modulation signal frequency fm. Here, it is known that the majority of these spread spectra are contained within a predetermined frequency band determined based on the modulation signal frequency fm. The majority of the spectrum here refers to, for example, about 98% of the whole.

[0098] In the direction-finding system 1 of this embodiment, the component with frequency fc corresponds to the component corresponding to the target radio wave TW, and the component obtained by removing the component with frequency fc from the component corresponding to the majority of the spread spectrum corresponds to the component corresponding to the fluctuating wave FW. Based on the power ratio of the two, it is possible to determine whether the radio wave received by the antenna 15 in any direction is the target radio wave TW or the fluctuating wave FW. Specifically, in the radio wave received by the antenna 15, the larger the power ratio Pm / Pc, which is the ratio of the power Pm of the component corresponding to the fluctuating wave FW to the power Pc of the component corresponding to the target radio wave TW, the higher the probability that the received radio wave is a fluctuating wave FW, and direction-finding is performed accordingly. The frequency fm corresponds to the period of the periodic phase shift of the target radio wave TW caused by the radio wave fluctuation device 13.

[0099] The signal processor 17 of this embodiment has substantially the same configuration as that of the first embodiment, but the configuration of the second bandpass filter 23 differs slightly from that of the first embodiment. Specifically, the second bandpass filter 23 of this embodiment is similar to the second bandpass filter 23 of the first embodiment in that it is configured to block the component of the input signal corresponding to the target radio wave TW, while allowing the component excluding the component corresponding to the fluctuating wave FW to pass through. However, as can be seen from Figures 10 and 11, the second bandpass filter 23 of this embodiment requires that its center frequency and attenuation bandwidth be appropriately set according to the magnitude of the modulation index of the phase modulation by the radio wave fluctuation device 13. This setting can be done accordingly because the parameters of the phase modulation by the radio wave fluctuation device 13 are known.

[0100] As described above, the direction-finding system 1 of this embodiment has predetermined parameters that include the phase or frequency of the target radio wave TW.

[0101] This makes it possible to suppress the generation of false images by a relatively simple control method, which involves periodically varying the phase or frequency of the target radio wave TW using the radio wave fluctuation device 13.

[0102] Furthermore, the direction-finding method of this embodiment includes predetermined parameters that include the phase or frequency of the target radio wave TW.

[0103] This makes it possible to suppress the generation of false images by a relatively simple operation of periodically varying the phase or frequency of the target radio wave TW.

[0104] Next, a modified example of the third embodiment will be described. Figure 12 is a conceptual diagram illustrating the reflection of radio waves by the radio wave fluctuation device 13 of the modified example of this embodiment. In this description of the modified example, the same or similar components as those in the previously described embodiment will be denoted by the same reference numerals in the drawings, and their descriptions may be omitted.

[0105] The direction-finding system 1 of this modified example differs from the third embodiment in the configuration of the radio wave modulation device 13. Specifically, as shown in Figure 12, the radio wave modulation device 13 of this modified example is composed of a reflector capable of mechanical vibration operation instead of a metasurface reflector. The radio wave modulation device 13 vibrates periodically in the vertical direction in Figure 12 by a drive source, thereby applying phase modulation to the target radio wave TW arriving from the object 100 and reflecting it as a fluctuating wave FW. Based on the target radio wave TW arriving from the object 100 and directly incident on the antenna 15, and the fluctuating wave FW reflected by the radio wave modulation device 13 and incident on the antenna 15, the direction-finding system 1 can detect the direction of the object 100 with high accuracy while suppressing the generation of false images, similar to the third embodiment.

[0106] As described above, in this modified form of the direction-finding system 1, the radio wave fluctuation device 13 is a reflector capable of vibration. The direction-finding system 1 further includes a drive source that periodically vibrates the radio wave fluctuation device 13.

[0107] This allows for the suppression of false images through a relatively simple operation: periodically vibrating the reflector.

[0108] Next, a fourth embodiment will be described. Figure 13 is a schematic diagram showing the overall configuration of the direction-finding system 1 according to this embodiment. Figure 14 is a schematic diagram showing the functional configuration of the direction-finding system 1 according to this embodiment. In the description of this embodiment, the same or similar components as those in the previously described embodiments will be denoted by the same reference numerals in the drawings, and their descriptions may be omitted.

[0109] The direction-finding system 1 of this embodiment differs from the above embodiment 1 in that it comprises a plurality of moving bodies 11. That is, as shown in Figures 13 and 14, the direction-finding system 1 of this embodiment comprises at least two moving bodies 11. One of these moving bodies 11 is a detection moving body 11A. That is, the direction-finding system 1 of this embodiment comprises one detection moving body 11A and at least one other moving body 11. In this example, there are three moving bodies 11 that are different from the detection moving body 11A.

[0110] The detection mobile unit 11A has an antenna 15 and a signal processor 17. These configurations are the same as those in Embodiment 1 described above, so their explanation is omitted here. In addition, the detection mobile unit 11A may also have a radio wave modulation device 13. In this case, when the target radio wave TW arriving from the target object 100 is reflected by the detection mobile unit 11A, it is reflected as a modulated wave FW by the radio wave modulation device 13, so that the generation of false images due to the reflected wave can be suppressed.

[0111] The three mobile units 11 do not have an antenna 15 and a signal processor 17, but they do have a radio wave fluctuation device 13 and a device control unit 33. Since these configurations are the same as those in Embodiment 1 described above, a detailed explanation is omitted here.

[0112] As shown in Figure 14, the modulation parameters of the radio wave modulation device 13, such as information regarding the fluctuation period of the reflection direction, are shared between the detection mobile body 11A and the three mobile bodies 11. Therefore, when a fluctuating wave FW reflected by the radio wave modulation device 13 of the three mobile bodies 11 is incident on the antenna 15 of the detection mobile body 11A, it is possible to distinguish between the fluctuating wave FW and the target radio wave TW arriving from the target object 100 and directly incident on the antenna 15, based on the information regarding the modulation parameters, and to reduce the influence of the fluctuating wave FW on the direction finding result. This mechanism for reducing the influence is the same as that of Embodiment 1 described above, so a detailed explanation is omitted here.

[0113] As described above, the direction-finding system 1 of this embodiment comprises a plurality of mobile bodies 11. At least one of the plurality of mobile bodies 11 has a radio wave fluctuation device 13. One of the plurality of mobile bodies 11 is a detection mobile body 11A having an antenna 15 and a signal processor 17.

[0114] As a result, even if the target radio wave TW is reflected by the mobile body 11 having the radio wave modulation device 13, it will be incident on the antenna 15 as a fluctuating wave FW with periodic fluctuations. Therefore, the mobile body 11A can distinguish between the fluctuating wave FW and the target radio wave TW that comes from the object 100 and is incident directly on the antenna 15, and can reduce the influence of the former fluctuating wave FW on the detection result. As a result, the generation of false images is effectively suppressed, and the direction of the object 100 can be detected with high accuracy.

[0115] Furthermore, in the direction-finding system 1 of this embodiment, the moving bodies 11 other than the detected moving body 11A have a radio wave fluctuation device 13.

[0116] As a result, even if the target radio wave TW is reflected by any of the moving objects 11, the generation of false images can be effectively suppressed, and the direction of the target object 100 can be detected with high precision.

[0117] Preferred embodiments and modifications of the present disclosure have been described above, but the above configuration can be modified as follows, for example. Modifications may be made individually or in any combination of multiple modifications.

[0118] In the above embodiments and modifications, the radio wave fluctuation device 13 is provided on the mobile body 11, but the radio wave fluctuation device 13 may also be provided on a fixed structure, such as a building.

[0119] At least one of the first bandpass filter 21 and the second bandpass filter 23 can also be implemented using a combination of a high-pass filter and a low-pass filter.

[0120] The antenna 15 is mounted on the mobile unit 11, and the signal processor 17 and display unit 35 may be mounted on a different mobile unit or a fixed structure such as a facility. In this case, the mobile unit 11 stores data, including the radio waves received by the antenna 15 and the direction of radio wave reception, in an appropriate storage medium. The facility acquires the data from the mobile unit 11 and displays the results of the signal processor 17 processing on the display unit 35. Data acquisition may be performed via a removable storage medium, or by wired or wireless communication.

[0121] The power ratio calculation unit 25 of the signal processor 17 may also calculate the ratio of the power of the component corresponding to the fluctuating wave FW to the total power of the target radio wave TW and the fluctuating wave FW combined.

[0122] Two or more of the modulations shown in Figure 2, Figure 7, and Figure 9 may be combined. Two or more of the modulations shown in Figure 6, Figure 8, and Figure 12 may also be combined.

[0123] [Pattern] The embodiments described above are specific examples of the following embodiments. (Aspect 1) A direction-finding system that detects the direction of an object based on target radio waves, which are radio waves arriving from the object, A radio wave fluctuation device that imparts periodic fluctuations to incident radio waves according to predetermined parameters and reflects them as fluctuating waves, An antenna that receives radio waves, A signal processor that detects the direction of the object based on the radio waves received by the antenna, Equipped with, The signal processor is a direction-finding system that reduces the influence of the fluctuating waves on the detection result based on the information of the periodic fluctuations contained in the radio waves received by the antenna. (Aspect 2) A direction-finding system according to Embodiment 1, Equipped with additional mobile components, The mobile unit is a direction-finding system comprising the radio wave fluctuation device, the antenna, and the signal processor. (Aspect 3) A direction-finding system according to Embodiment 1, Equipped with multiple mobile units, At least one of the aforementioned multiple mobile bodies has the radio wave fluctuation device, A direction-finding system in which one of the plurality of moving bodies is a detection moving body having the antenna and the signal processor. (Aspect 4) A direction-finding system according to embodiment 3, The moving body other than the detected moving body is a direction-finding system having the radio wave fluctuation device. (Aspect 5) A direction-finding system according to Embodiment 4, The detected moving object is a direction-finding system having the radio wave fluctuation device. (Aspect 6) A direction-finding system according to any one of embodiments 1 to 5, The aforementioned radio wave fluctuation device is a direction-finding system that periodically changes the amplitude of the fluctuating wave received by the antenna. (Aspect 7) A direction-finding system according to embodiment 6, The predetermined parameters include the reflection direction, which is the direction in which the radio wave fluctuation device reflects the target radio wave. The aforementioned radio wave fluctuation device is a direction-finding system that periodically fluctuates the amplitude of the fluctuating wave received by the antenna by periodically fluctuating the reflection direction. (Pattern 8) A direction-finding system according to embodiment 6, The predetermined parameters include the diffuse reflectance, which is the ratio of the diffuse reflection component to the specular reflection component in the reflection of the target radio wave at the radio wave fluctuation device. The aforementioned radio wave fluctuation device is a direction-finding system that periodically fluctuates the amplitude of the fluctuating wave received by the antenna by periodically fluctuating the diffuse reflectance. (Aspect 9) A direction-finding system according to any one of embodiments 1 to 5, The predetermined parameters include the phase or frequency of the target radio wave, in a direction-finding system. (Aspect 10) A direction-finding system according to any one of embodiments 1 to 9, The device further includes a display for showing the detection results, The signal processor determines the power ratio, which is the ratio of the power of the component corresponding to the fluctuating wave to the power of the component corresponding to the target radio wave, in relation to the radio wave reception direction. The aforementioned display unit is a direction-finding system that displays the detection results for each of the radio wave reception directions such that the larger the corresponding power ratio, the lower the probability of the object being present. (Aspect 11) A direction finding method for detecting the direction of an object based on target radio waves, which are radio waves arriving from the object, By subjecting the incident radio waves to periodic fluctuations according to predetermined parameters, the fluctuating waves are reflected back. The antenna receives radio waves, Based on the radio waves received by the antenna, the direction of the object is detected. A direction-finding method that reduces the influence of the fluctuating waves on the detection result based on the information of the periodic fluctuations contained in the radio waves received by the antenna. (Aspect 12) A direction-finding method described in embodiment 11, A direction-finding method that periodically varies the amplitude of the fluctuating wave received by the antenna. (Aspect 13) A direction-finding method described in embodiment 12, The aforementioned predetermined parameters include the reflection direction, which is the direction in which the target radio wave is reflected. A direction-finding method that periodically varies the amplitude of the fluctuating wave received by the antenna by periodically varying the reflection direction. (Aspect 14) A direction-finding method described in embodiment 12, The predetermined parameters include the diffuse reflectance, which is the ratio of the diffuse reflection component to the specular reflection component in the reflection of the target radio wave. Direction finding method, wherein the amplitude of the fluctuating wave received by the antenna is periodically varied by periodically varying the diffuse reflectance. (Aspect 15) A direction-finding method described in embodiment 11, A direction-finding method in which the predetermined parameters include the phase or frequency of the target radio wave. (Aspect 16) A direction-finding method described in any one of embodiments 11 to 15, The power ratio, which is the ratio of the power of the component corresponding to the fluctuating wave to the power of the component corresponding to the target radio wave, is determined in relation to the radio wave reception direction. Direction finding method, which displays the detection results for each of the aforementioned radio wave reception directions such that the larger the corresponding power ratio, the lower the probability of the object being present. [Explanation of Symbols]

[0124] 1 Direction Finding System 11 Mobile Unit 11A Detected moving object (moving object) 13. Radio wave fluctuation devices 15 Antennas 17 Signal Processors 35 Display 100 Objects TW Target Radio Waves FW fluctuation wave

Claims

1. A direction-finding system that detects the direction of an object based on target radio waves, which are radio waves arriving from the object, A radio wave fluctuation device that imparts periodic fluctuations to incident radio waves according to predetermined parameters and reflects them as fluctuating waves, An antenna that receives radio waves, A signal processor that detects the direction of the object based on the radio waves received by the antenna, Equipped with, The signal processor is a direction-finding system that reduces the influence of the fluctuating waves on the detection result based on the information of the periodic fluctuations contained in the radio waves received by the antenna.

2. A direction-finding system according to claim 1, Equipped with additional mobile components, The mobile unit is a direction-finding system comprising the radio wave fluctuation device, the antenna, and the signal processor.

3. A direction-finding system according to claim 1, Equipped with multiple mobile units, At least one of the aforementioned multiple mobile bodies has the radio wave fluctuation device, A direction-finding system in which one of the plurality of moving bodies is a detection moving body having the antenna and the signal processor.

4. A direction-finding system according to claim 3, The moving body other than the detected moving body is a direction-finding system having the radio wave fluctuation device.

5. A direction-finding system according to claim 4, The detected moving object is a direction-finding system having the radio wave fluctuation device.

6. A direction-finding system according to any one of claims 1 to 5, The aforementioned radio wave fluctuation device is a direction-finding system that periodically changes the amplitude of the fluctuating wave received by the antenna.

7. A direction-finding system according to claim 6, The predetermined parameters include the reflection direction, which is the direction in which the radio wave fluctuation device reflects the target radio wave. The aforementioned radio wave fluctuation device is a direction-finding system that periodically fluctuates the amplitude of the fluctuating wave received by the antenna by periodically fluctuating the reflection direction.

8. A direction-finding system according to claim 6, The predetermined parameters include the diffuse reflectance, which is the ratio of the diffuse reflection component to the specular reflection component in the reflection of the target radio wave at the radio wave fluctuation device. The aforementioned radio wave fluctuation device is a direction-finding system that periodically fluctuates the amplitude of the fluctuating wave received by the antenna by periodically fluctuating the diffuse reflectance.

9. A direction-finding system according to any one of claims 1 to 5, The predetermined parameters include the phase or frequency of the target radio wave, in a direction-finding system.

10. A direction-finding system according to any one of claims 1 to 5, The device further includes a display for showing the detection results, The signal processor determines the power ratio, which is the ratio of the power of the component corresponding to the fluctuating wave to the power of the component corresponding to the target radio wave, in relation to the radio wave reception direction. The aforementioned display unit is a direction-finding system that displays the detection results for each of the radio wave reception directions such that the larger the corresponding power ratio, the lower the probability of the object being present.

11. A direction finding method for detecting the direction of an object based on target radio waves, which are radio waves arriving from the object, By subjecting the incident radio waves to periodic fluctuations according to predetermined parameters, the fluctuating waves are reflected back. The antenna receives radio waves, Based on the radio waves received by the antenna, the direction of the object is detected. A direction-finding method that reduces the influence of the fluctuating waves on the detection result based on the information of the periodic fluctuations contained in the radio waves received by the antenna.

12. A direction-finding method according to claim 11, A direction-finding method that periodically varies the amplitude of the fluctuating wave received by the antenna.

13. A direction-finding method according to claim 12, The aforementioned predetermined parameters include the reflection direction, which is the direction in which the target radio wave is reflected. A direction-finding method that periodically varies the amplitude of the fluctuating wave received by the antenna by periodically varying the reflection direction.

14. A direction-finding method according to claim 12, The predetermined parameters include the diffuse reflectance, which is the ratio of the diffuse reflection component to the specular reflection component in the reflection of the target radio wave. Direction finding method, wherein the amplitude of the fluctuating wave received by the antenna is periodically varied by periodically varying the diffuse reflectance.

15. A direction-finding method according to claim 11, A direction-finding method in which the predetermined parameters include the phase or frequency of the target radio wave.

16. A direction-finding method according to any one of claims 11 to 15, The power ratio, which is the ratio of the power of the component corresponding to the fluctuating wave to the power of the component corresponding to the target radio wave, is determined in relation to the radio wave reception direction. A direction finding method that displays the detection results for each of the aforementioned radio wave reception directions such that the larger the corresponding power ratio, the lower the probability of the object being present.

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