Radar device and method for setting the antenna array of the radar device

Abstract

When the human body is the target of detection by millimeter-wave radar, the generation of virtual images on the radar image created from the received signal is suppressed even if the distance between adjacent receiving antenna elements exceeds half a wavelength of the radar. [Solution] The radar device of the present invention comprises a plurality of receiving antenna elements arranged based on the relative positions of a plurality of reflection points of electromagnetic waves in a specific detection target, a transmitting antenna element that emits electromagnetic waves, and a radar image creation unit that creates a radar image based on the received signals received by the plurality of receiving antenna elements.

Description

Technical Field

[0001] The present invention relates to a radar device in a millimeter wave band and a method for setting an antenna array of the radar device.

Background Art

[0002] Millimeter wave radars can sense even in adverse environments such as dust, thick smoke, and bad weather, and are promising as, for example, vehicle-mounted radars and human detection sensors in the field of disaster relief. Therefore, conventionally, in the technical field of millimeter wave radars, techniques for optimizing the array of a plurality of antenna elements included in a millimeter wave radar have been proposed (see, for example, Non-Patent Documents 1 and 2). Non-Patent Document 1 proposes a sparse array optimization technique using simulated annealing and compressed sensing applicable to near-field millimeter wave imaging. Further, Non-Patent Document 2 proposes a technique for optimizing a planar phased array by introducing a gradient method in a millimeter wave radar sensor mounted on a vehicle.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Non-Patent Document 2

[0004] Incidentally, conventional methods for imaging received signals from millimeter-wave radar (radar imaging methods) can be broadly classified into two types: coherent processing and incoherent processing. Examples of coherent processing include synthetic aperture processing (SAR: Synthetic Aperture Radar) and beamforming, while an example of incoherent processing is the RPM (Range Points Migration) method. Coherent processing can improve azimuth resolution and achieve high noise immunity, but it has the problem that if the distance between adjacent receiving antenna elements exceeds half the radar wavelength, a virtual image based on the phase uncertainty of the received signal occurs in the radar image.

[0005] The present invention was made to solve the above problems. The object of the present invention is to provide a radar device and a method for setting the antenna array thereof that can suppress the generation of virtual images on the radar image created from the received signal, even when the human body is the target of detection by millimeter-wave radar, for example, when the distance between adjacent receiving antenna elements exceeds half a wavelength of the radar. [Means for solving the problem]

[0006] To solve the above problems, the radar device of the present invention comprises a plurality of receiving antenna elements arranged based on the relative positions of a plurality of reflection points of electromagnetic waves in a specific detection target, a transmitting antenna element that emits electromagnetic waves, and a radar image creation unit that creates a radar image based on the received signals received by the plurality of receiving antenna elements.

[0007] Furthermore, in order to solve the above problems, the antenna array setting method of the radar device of the present invention includes setting the arrangement positions of a plurality of receiving antenna elements based on the relative positions of a plurality of reflection sites of electromagnetic waves at a specific detection target of the radar device. [Effects of the Invention]

[0008] According to the present invention with the above configuration, when the target of detection by millimeter-wave radar is the human body, for example, even if the distance between adjacent receiving antenna elements exceeds half a wavelength of the radar, the generation of a virtual image on the radar image created from the received signal can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an overview of the numerical calculation model used in the antenna array setting method for a radar device according to the first embodiment of the present invention. [Figure 2] This flowchart shows the procedure for setting the antenna array of a radar device according to the first embodiment of the present invention. [Figure 3] This figure shows an example of the phase interference intensity distribution of a received signal obtained when applying the antenna array setting method of a radar device according to the first embodiment of the present invention. [Figure 4] This figure shows an example of a radar image (Example 1-1) obtained when a receiving antenna element is placed at the arrangement position set by the antenna array setting method of the radar device according to the first embodiment of the present invention, and a simulated human body detection is performed. [Figure 5]This figure shows another example of a radar image (Example 1-2) obtained when a receiving antenna element is placed at the arrangement position set by the antenna array setting method of the radar device according to the first embodiment of the present invention, and a simulated human body detection is performed. [Figure 6] This is a schematic diagram of a radar device according to the first embodiment of the present invention. [Figure 7] This figure shows the arrangement of antenna elements in a radar device according to the first embodiment of the present invention. [Figure 8] This figure shows an overview of the numerical calculation model used in the antenna array setting method for a radar device according to the second embodiment of the present invention. [Figure 9] This figure shows an example of the phase interference intensity distribution of a received signal obtained when applying the antenna array setting method of a radar device according to the second embodiment of the present invention. [Figure 10] This figure shows an example of a radar image (Example 2-1) obtained when a receiving antenna element is placed at the arrangement position set by the antenna array setting method of the radar device according to the second embodiment of the present invention, and a simulated human body detection is performed. [Figure 11] This figure illustrates the principle of a method for suppressing virtual images in a radar image, performed by a radar device according to a second embodiment of the present invention. [Figure 12] This figure shows the effect of suppressing the virtual image of a detection target by the virtual image suppression method of a radar device according to the second embodiment of the present invention. [Figure 13] This figure shows an example of a composite radar image (Example 2-2) created using the virtual image suppression method for a radar device according to a second embodiment of the present invention. [Figure 14] This figure shows an example of a composite radar image (Example 2-3) created using the virtual image suppression method for a radar device according to the second embodiment of the present invention. [Figure 15] This figure shows an example of a composite radar image (Example 2-4) created using the virtual image suppression method for a radar device according to the second embodiment of the present invention. [Figure 16]This figure shows the evaluation results of the correlation coefficient of a composite radar image created using the virtual image suppression method of a radar device according to the second embodiment of the present invention. [Figure 17] This figure shows the evaluation results of the noise immunity of a synthesized radar image created using the virtual image suppression method of a radar device according to the second embodiment of the present invention. [Figure 18] This is a schematic diagram of a radar device according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0010] The following will specifically describe, with reference to the drawings, the methods for setting the arrangement of antenna elements in a radar device according to various embodiments of the present invention, and the configuration of a radar device in which the antenna elements are arranged at the positions set by the arrangement setting method. In the following, the target of detection by the radar device will be the human body.

[0011] 1. First Embodiment [Numerical computation model] In the antenna element arrangement setting method of the first embodiment, first, when a radar device simulates irradiating a human body model with millimeter-wave electromagnetic waves (transmitted signals), the phase interference intensity distribution (hereinafter referred to as the "phase interference pattern") of the reflected waves (received signals) incident on a planar region (hereinafter referred to as the "planar array region") where multiple antenna elements are arranged from the human body model is calculated. Then, based on the calculated phase interference pattern of the reflected waves in the planar array region, the arrangement configuration (position and number) of the receiving antenna elements is set.

[0012] Figure 1 shows the configuration of the human body model to be detected and the positional relationship between the human body model and the planar array region in three-dimensional space, which are used when numerically calculating the phase interference pattern of reflected waves in the planar array region in the antenna element arrangement setting method of the first embodiment.

[0013] In this embodiment, as shown by the dashed lines in Figure 1, the human body to be detected is represented by 11 elliptical parts that simulate the head, chest, waist, left upper arm, left lower arm, right upper arm, right lower arm, left thigh, left shin, right thigh, and right shin, respectively. In the simulation that was actually performed, as shown by the black circles in Figure 1, each of the 11 elliptical parts (targets) that make up the human body model to be detected is approximated by an electromagnetic wave reflection point TG. That is, the human body model consisting of 11 elliptical parts is approximated by 11 reflection points TG (point cloud). For the sake of simplicity, the specific coordinates of each reflection point TG of the human body model in the 3D spatial coordinate system in Figure 1 are omitted here. Furthermore, the configuration of the human body model is not limited to the example shown in Figure 1; any human body model that can be detected as a human body can be used.

[0014] Furthermore, the calculation conditions for the phase interference pattern of the reflected wave are as follows: The distance (distance in the y-direction in Figure 1) between the human body model consisting of 11 reflection points TG (point cloud) to be detected and the planar array region PA where multiple antenna elements are arranged is 5m. Therefore, in the three-dimensional spatial coordinate system in Figure 1, the human body model consisting of 11 reflection points TG is placed on the xz plane at y=5000mm, and the planar array region PA is placed on the xz plane at y=0mm. Note that the distance from the planar array region PA to the human body model can be appropriately changed according to the specifications of the actual device to which the antenna element arrangement setting method of this embodiment is applied (e.g., an in-vehicle radar).

[0015] The planar array region PA is defined as a rectangular region. The dimensions of the planar array region PA are set to a width of 21 cm in the x-direction and a width of 10 cm in the z-direction as shown in Figure 1. The center position of the planar array region PA is (x,y,z)=(0[mm],0[mm],1000[mm]) in the three-dimensional spatial coordinate system shown in Figure 1.

[0016] The transmitting antenna element is assumed to be one, positioned in the center of the planar array region PA. The center frequency of the electromagnetic wave (transmitted signal) emitted from the transmitting antenna element is assumed to be 79 GHz (wavelength: approximately 3.8 mm), and the bandwidth is assumed to be 4 GHz. The reflected waves (received signals) reaching the planar array region PA from each reflection point TG of the human body model are calculated using a geometrical optics approximation that does not consider multiple scattered waves.

[0017] [Method for setting the arrangement of receiving antenna elements] Next, we will describe a method for setting the array of receiving antenna elements in a planar array region PA using the numerical calculation model described above. Figure 2 is a flowchart showing the procedure for setting the array of receiving antenna elements in this embodiment. Note that the process shown in the flowchart below can be performed, for example, using a computer or the like in a program.

[0018] First, the reception position of the reflected wave within the planar array region PA is set (S1). In this process, the coordinates of the reception position of the reflected wave within the planar array region PA are set at small intervals. For example, within the planar array region PA, the coordinates of the reflected wave reception position are set at intervals corresponding to the pixel spacing of the phase interference pattern image (see Figure 3 below). Specifically, the coordinates of the reflected wave reception position AP within the planar array region PA are set according to Equation 1 below. j,k Set it.

[0019]

number

[0020] In the above equation 1, indices j and k are the identification indices for the x and z coordinates of the reflected wave reception position within the planar array region PA, respectively. Furthermore, in the three-dimensional spatial coordinate system shown in Figure 1, any reception position AP of the reflected wave within the planar array region PA is... j,k x coordinate x j The value will be within the range of -105mm to 105mm, and the z coordinate z kIt becomes a value within the range of 950 mm to 1050 mm (see FIG. 3 described later). In the example shown in FIG. 1, since the planar array region PA is arranged on the x-z plane where y = 0 mm, the y coordinate in Equation 1 above becomes 0 mm.

[0021] Next, the number NT of reflection points TG of the human body model to be detected and the positions of each reflection point TG are set (S2). In the example shown in FIG. 1, in the process of step S2, the number NT of reflection points TG (targets) is set to "11", and the position coordinates of each reflection point TG are set by Equation 2 below.

[0022]

Equation

[0023] The index i in Equation 2 above is an index for identifying the part of the human body model, that is, the type of reflection point TG, and becomes a value within the range of "1" to "11". Also, xt i , yt i and zt i are respectively the x coordinate, y coordinate, and z coordinate of the reflection point TG of index i (any one of 1 to 11) in the three-dimensional space coordinates in FIG. 1. In the example shown in FIG. 1, since the distance from the planar array region PA to the human body model is 5 m, yt i in Equation 2 above becomes 5000 mm regardless of the index i.

[0024] Next, when the electromagnetic wave (transmission signal) is simulatedly irradiated from the transmission antenna element to each reflection point TG, the phase rotation amount φ of the reflected wave (received signal) incident on each reception position AP j,k in the planar array region PA from each reflection point TG is calculated (S3). Specifically, the phase rotation amount φ of the reflected wave incident from each reflection point TG is calculated using Equation 3 below.

[0025]

Equation

[0026] φ in the above number 3 i,j,k This is index i (position coordinate TP) i ) From the reflection point TG to the receiving position AP within the planar array region PA. j,k This is the phase rotation amount φ of the reflected wave incident on the element. Also, in equation 3 above, λ is the center wavelength of the transmitted signal (approximately 3.8 mm).

[0027] Next, a phase interference pattern of the reflected waves within the planar array region PA is created (S4). In this process, first, the following equation 4 is used to create a phase interference pattern of each receiving position AP within the planar array region. j,k Phase interference intensity I(x) of the reflected wave j ,z k ) is calculated. Then, each calculated receiving position AP j,k Phase interference intensity I(x) of the reflected wave j ,z k Based on this, the phase interference intensity I(x) of the reflected wave within the planar array region PA. j ,z k This creates a distribution of the absolute values ​​of ), i.e., a phase interference pattern.

[0028]

number

[0029] Figure 3 shows the phase interference pattern of reflected waves within the planar array region PA created by the processing in step S4. In Figure 3, the maximum points of the phase interference pattern are indicated by white circles. For comparison, Figure 3 also shows the positions of each receiving antenna element when four receiving antenna elements are arranged at equal intervals in both the x and z directions within the planar array region PA, i.e., when 16 receiving antenna elements are arranged at equal intervals in a 4 (z direction) × 4 (x direction) array configuration, indicated by black circles.

[0030] Next, based on the phase interference pattern of reflected waves within the planar array region PA created by the processing in step S4 (see Figure 3), the coordinate positions of the maximum points of the phase interference pattern, i.e., the points where the reflected waves from each reflection point TG reinforce each other, are extracted (S5). In the example shown in Figure 3, the coordinate positions of 15 points, represented by white circles in Figure 3, are extracted as the coordinate positions of the maximum points.

[0031] While any method can be used to extract (select) the maximum points of the phase interference pattern, the following methods can be used, for example. • Extract the local maximum point where the value is greater than or equal to a predetermined value (as adopted in this embodiment). • Extract a predetermined number of local maxima starting with the largest values. - A predetermined number of local maximums are extracted, taking into account the specifications such as the size of the receiving antenna element installed in the actual device (e.g., a vehicle-mounted radar). • Extract a predetermined number of local maximums according to user requests, etc.

[0032] Next, the coordinate positions of the local maximums extracted by the process in step S5 are set as the optimal placement positions for the receiving antenna elements within the planar array region PA (S6). That is, in the example shown in Figure 3, the coordinate positions of the 15 local maximums represented by the white circles in Figure 3 are set as the optimal placement positions for the receiving antenna elements. Therefore, in the example shown in Figure 3, the number of receiving antenna elements installed within the planar array region PA is 15, and their optimal placement positions are unequal. After the process in step S6, the process of setting the arrangement of the receiving antenna elements is completed.

[0033] [Radar image] Next, we will explain an example of a radar image obtained from the received signal when a simulated human body detection is performed by placing multiple receiving antenna elements at the positions set by the receiving antenna element arrangement setting method described in Figures 1 to 3.

[0034] (Example 1-1) In Example 1-1, a simulation was performed to calculate a radar image obtained from the received signal when simulating human body detection was performed using 15 receiving antenna elements positioned at the 15 white circles within the planar array region PA shown in Figure 3. In Example 1-1, the positional relationship between the planar array region PA and each reflection point TG of the human body model is configured as shown in Figure 1. That is, the distance between the planar array region PA and each reflection point TG of the human body model is set to 5m.

[0035] In Example 1-1, as shown in Figure 3, within the planar array area PA (size: 10 cm (z direction) × 21 cm (x direction)), the spacing between adjacent receiving antenna elements (indicated by white circles in the figure) is approximately 20 mm at its narrowest point, which is longer than half a wavelength of the transmitted signal (wavelength: approximately 3.8 mm). Furthermore, while any method can be used to create a radar image based on the received signals from the 15 receiving antenna elements, here we will describe an example using an existing predetermined coherent processing method (e.g., DAS (Delay And Sum)).

[0036] In addition, as Comparative Example 1-1, we also calculated the radar image obtained from the received signal when 16 receiving antenna elements were arranged at equal intervals in a 4 (z direction) × 4 (x direction) array (indicated by black circles in Figure 3) within a planar array area PA to simulate human body detection. In Comparative Example 1-1, as shown in Figure 3, the spacing between adjacent receiving antenna elements (indicated by black circles in the figure) within the planar array area PA (size: 10 cm (z direction) × 21 cm (x direction)) is approximately 33 mm at its narrowest interval, which is longer than half a wavelength of the transmitted signal (wavelength: approximately 3.8 mm). Furthermore, in Comparative Example 1-1, the calculation conditions other than the arrangement of the multiple receiving antenna elements are the same as in Example 1-1.

[0037] Furthermore, as Reference Example 1, we also calculated the radar image obtained from the received signal when 8192 receiving antenna elements were arranged at equal intervals in a 64 (z direction) × 128 (x direction) array within a planar array area PA to simulate human body detection. In Reference Example 1, within the planar array area PA (size: 10 cm (z direction) × 21 cm (x direction)), the spacing between adjacent receiving antenna elements in both the x and z directions is approximately 1.6 mm, which is shorter than half a wavelength of the transmitted signal (wavelength: approximately 3.8 mm). In Reference Example 1, the calculation conditions other than the arrangement of the multiple receiving antenna elements are the same as in Example 1-1.

[0038] Figure 4A is the radar image obtained in Comparative Example 1-1, Figure 4B is the radar image obtained in Example 1-1, and Figure 4C is the radar image obtained in Reference Example 1. The white circles in each figure indicate the positions of the 11 reflection points TG (targets) that make up the human body model shown in Figure 1.

[0039] In Comparative Example 1-1, the distance between adjacent receiving antenna elements is longer than half a wavelength of the transmitted signal, so, as shown in Figure 4A, a virtual image of the human body model (detection target) appears on the radar image due to the phase uncertainty of the reflected wave. In contrast, in Example 1-1, although the distance between adjacent receiving antenna elements is longer than half a wavelength of the transmitted signal, similar to Comparative Example 1-1 (see Figure 3), the virtual image of the human body model (detection target) is sufficiently suppressed on the radar image, and it can be seen that images corresponding to the corresponding parts of the human body model appear at positions corresponding to the 11 reflection points TG that constitute the human body model.

[0040] Furthermore, in Reference Example 1, the distance between adjacent receiving antenna elements is shorter than half a wavelength of the transmitted signal, so as shown in Figure 4C, no virtual image of the human body model (detection target) is generated in the radar image. Comparing the radar image of Reference Example 1 shown in Figure 4C with the radar image of Example 1-1 shown in Figure 4B, it can be seen that in Example 1-1, almost the same resolution (azimuth resolution) is obtained with a much smaller number of receiving array elements compared to Reference Example 1.

[0041] In other words, from the calculation results of the radar image described above, it was found that when the arrangement positions of multiple receiving antenna elements are set using the receiving antenna element arrangement setting method of this embodiment, even if the spacing between adjacent receiving antenna elements is wider than half a wavelength of the transmitted signal, the illusion of a human body model on the radar image can be sufficiently suppressed, and high azimuth resolution can be obtained in human body detection.

[0042] (Examples 1-2) In Example 1-2, similar to Example 1-1, multiple receiving antenna elements were placed at their optimal positions (indicated by white circles in Figure 3) with a distance of 5m between the planar array area PA and the human body model. The radar image obtained when simulating human body detection with a distance of 6m between the planar array area PA and the human body model was then calculated through simulation. Note that in Example 1-2, the calculation conditions other than the distance between the planar array area PA and the human body model were the same as in Example 1-1.

[0043] Furthermore, as Comparative Example 1-2, we also calculated the radar image obtained when simulating human body detection was performed by arranging 16 receiving antenna elements at equal intervals in a 4(z direction) × 4(x direction) array (indicated by black circles in Figure 3) within the planar array region PA, with a distance of 6m between the PA and the human body model. In Comparative Example 1-2, the calculation conditions other than the distance between the PA and the human body model were the same as in Comparative Example 1-1.

[0044] Figure 5A shows the radar image obtained in Comparative Example 1-2, and Figure 5B shows the radar image obtained in Example 1-2. The white circles in each figure indicate the positions of the 11 reflection points TG (targets) that make up the human body model shown in Figure 1.

[0045] As is clear from comparing the radar image of Comparative Example 1-2 shown in Figure 5A with the radar image of Example 1-2 shown in Figure 5B, in Comparative Example 1-2, a virtual image of the human body model appears on the radar image due to the phase uncertainty of the reflected wave, but in Example 1-2, this virtual image is suppressed. Furthermore, in the radar image of Example 1-2, it can be seen that images corresponding to the corresponding parts of the human body model appear to some extent at positions corresponding to the 11 reflection points TG that constitute the human body model. In other words, even if the distance between the planar array region PA and the human body model differs slightly from the distance used when determining the placement positions of the multiple receiving antenna elements, it was found that the virtual image of the human body model (detection target) is suppressed on the radar image, and images corresponding to the corresponding parts of the human body model appear.

[0046] [Radar equipment configuration] Figure 6 shows an example of a radar system configuration in which receiving antenna elements are arranged at the positions determined by the receiving antenna element arrangement setting method of this embodiment described above. Here, as an example, we will describe a configuration in which 15 receiving antenna elements are placed at the positions of 15 local maximums (marked with white circles) within the phase interference pattern of the reflected wave shown in Figure 3.

[0047] As shown in Figure 6, the radar device 10 comprises a transmission processing unit 11, a reception processing unit 12, a control processing unit 13, one transmitting antenna element Tx, and 15 receiving antenna elements Rx1 to Rx15. The radar device 10 is a radar that emits electromagnetic waves in the millimeter-wave band. For example, the center frequency of the electromagnetic wave (transmitted signal) emitted from the transmitting antenna element Tx can be set to 79 GHz (wavelength approximately 3.8 mm), and the bandwidth can be set to 4 GHz.

[0048] In the radar device 10, the transmission processing unit 11 and the reception processing unit 12 are electrically connected to the control processing unit 13. The transmission processing unit 11 is electrically connected to the transmitting antenna element Tx. The reception processing unit 12 is electrically connected to each of the receiving antenna elements Rx1 to Rx15.

[0049] The transmission processing unit 11 creates a transmission signal based on the signal input from the control processing unit 13 and outputs the created transmission signal to the transmitting antenna element Tx. The reception processing unit 12 performs processing, such as demodulation, on the electromagnetic waves (received signals) received by each of the receiving antenna elements Rx1 to Rx15.

[0050] The control processing unit 13 controls the overall operation of the radar device 10. In this embodiment, the control processing unit 13 also performs radar image creation processing based on the received signal. That is, the control processing unit 13 has a radar image creation unit. Any method can be used for creating the radar image by the radar image creation unit, but in this embodiment, an existing predetermined coherent processing method (e.g., DAS) is used. In this embodiment, since the arrangement positions of the multiple receiving antenna elements are determined by adopting the receiving antenna element arrangement setting method described above, even if a radar image is created using coherent processing, the generation of virtual images based on the phase uncertainty of reflected waves on the radar image can be suppressed.

[0051] One transmitting antenna element Tx and fifteen receiving antenna elements Rx1 to Rx15 are arranged within a planar array region PA (see Figure 1). Figure 7 is a plan view showing the arrangement of the transmitting antenna element Tx and receiving antenna elements Rx1 to Rx15 in the radar device 10 (planar array region PA) of this embodiment.

[0052] In this embodiment, the arrangement of the 15 receiving antenna elements Rx1 to Rx15 is determined based on the arrangement setting method for multiple receiving antenna elements described above. Therefore, in the example shown in Figure 7, within the planar array region PA, the 15 receiving antenna elements Rx1 to Rx15 are arranged at 15 points (white circles in Figure 7) corresponding to the positions of the maximum points of the reflected wave phase interference pattern shown in Figure 3. The transmitting antenna element Tx is positioned in the center of the planar array region PA (black circle in Figure 7).

[0053] In the example shown in Figure 7, the placement of the transmitting antenna element Tx does not overlap with the placement of the receiving antenna element. However, if they overlap, for example, one or both of the transmitting antenna element Tx and the receiving antenna element may be slightly offset in their placement. Alternatively, for example, the transmitting antenna element Tx and the receiving antenna element whose placements overlap may be configured as a single antenna element used for both transmission and reception, with the operation switching between signal transmission and reception.

[0054] [effect] As described above, when multiple receiving antenna elements are arranged in the array configuration set by the receiving antenna element arrangement setting method in the planar array region PA of this embodiment, and reflected waves are received, and a radar image of a human body model is created based on the received signal, even if the distance between adjacent receiving antenna elements is longer than half a wavelength of the transmitted signal, virtual images based on the phase uncertainty of reflected waves can be sufficiently suppressed on the radar image.

[0055] Furthermore, when using the receiving antenna element arrangement method in the planar array region PA of this embodiment described above, it becomes possible to achieve radar imaging with high azimuth resolution while sufficiently suppressing virtual images based on the phase uncertainty of reflected waves, even with a small number of receiving antenna elements. Therefore, the receiving antenna element arrangement method of this embodiment, and a radar device in which multiple receiving antenna elements are arranged in the arrangement configuration set by this arrangement method, are suitable for applications such as automotive radar where the array aperture area is limited.

[0056] 2. Second Embodiment In the second embodiment, a radar device in which a plurality of receiving antenna elements are arranged in a planar array region PA based on the antenna element arrangement setting method of the first embodiment will be described, and which will have a function that can further suppress the illusion of a detection target (human body) in the radar image.

[0057] [Overview of virtual image suppression techniques in radar images] In this embodiment, in order to suppress the illusion of the detected target (human body) in the radar image, first, in the same manner as in the first embodiment, a plurality of receiving antenna elements are arranged in the planar array region PA in an array configuration set based on the phase interference pattern of the reflected waves incident on the planar array region PA. Next, the radar device equipped with the planar array region PA is moved a predetermined distance toward the detected target (human body model in the numerical calculation model) while irradiating it with electromagnetic waves. Then, while moving the predetermined distance, radar images are created at predetermined time intervals, and the plurality of created radar images are coherently combined, that is, synthetic aperture processing is performed on the plurality of radar images. In the radar image obtained by this synthetic aperture processing (hereinafter referred to as the "synthesized radar image"), the illusion of the detected target is suppressed. The specific details of the illusion suppression method in the synthesized radar image described above will be described in detail later.

[0058] [Numerical calculation model for determining the arrangement of receiving antenna elements] In the antenna element arrangement setting method of the second embodiment, similar to the first embodiment, first, when a radar device simulates irradiating a human body model with millimeter-wave electromagnetic waves (transmitted signals), the phase interference intensity distribution (phase interference pattern) of the reflected waves (received signals) incident from the human body model into the planar array region PA is calculated. Then, based on the calculated phase interference pattern of the reflected waves in the planar array region PA, the arrangement configuration (placement position and number) of receiving antenna elements within the planar array region PA is set.

[0059] Figure 8 shows the configuration of the human body model to be detected and the positional relationship between the human body model and the planar array region PA in three-dimensional space, which are used when numerically calculating the phase interference pattern of reflected waves in the planar array region PA in the antenna element arrangement setting method of the second embodiment. The configuration of the human body model in this embodiment is the same as that of the first embodiment (see Figure 1) as shown in Figure 8, and the human body model consisting of 11 elliptical parts (parts enclosed by dashed lines in the figure) is approximated by 11 reflection points TG (point cloud).

[0060] Furthermore, the calculation conditions for the phase interference pattern of the reflected wave are as follows (basically the same as those for the first embodiment described above).

[0061] The distance between the human body model, consisting of 11 reflection points TG (point cloud) to be detected, and the planar array region PA where multiple antenna elements are arranged (distance in the y-direction in Figure 8) is set to 5m, as in the first embodiment described above. Therefore, in the three-dimensional spatial coordinate system in Figure 8, if the planar array region PA is placed on the xz plane at y=0mm, the human body model consisting of 11 reflection points TG is placed on the xz plane at y=5000mm. The distance from the planar array region PA to the human body model can be appropriately changed depending on the specifications of the actual device to which the antenna element arrangement setting method of this embodiment is applied (e.g., an in-vehicle radar).

[0062] The planar array region PA is a rectangular region, similar to the first embodiment described above. The size of the planar array region PA is 20 cm in the x-direction and 10 cm in the z-direction in Figure 8. The center position of the planar array region PA is (x, y, z) = (0 [mm], 0 [mm], 1000 [mm]) in the three-dimensional spatial coordinate system shown in Figure 8, similar to the example shown in Figure 1. In the numerical calculation model (Figure 8) used to calculate the phase interference pattern of the reflected wave, the number of transmitting antenna elements within the planar array region PA is assumed to be one. Note that the placement position (coordinate position) of the transmitting antenna element can be arbitrarily set in the numerical calculation model.

[0063] The center frequency of the electromagnetic wave (transmitted signal) emitted from the transmitting antenna element is set to 79 GHz (wavelength: approximately 3.8 mm), as in the first embodiment described above, and the bandwidth is set to 4 GHz (distance resolution: approximately 37.5 mm). The reflected waves (received signals) reaching the planar array region PA from each reflection point TG of the human body model are calculated using a geometrical optics approximation that does not consider multiple scattered waves.

[0064] [Method for setting the arrangement of receiving antenna elements] Next, in this embodiment, the method for setting the array of receiving antenna elements in the planar array region PA using the numerical calculation model described above (see Figure 8) will be explained. The specific processing details of the receiving antenna element array setting method in this embodiment are the same as those of the receiving antenna element array setting method in the first embodiment described in the flowchart shown in Figure 2, and can be implemented using a computer or the like.

[0065] First, within the planar array region PA (see Figure 8), the reception position r of the reflected wave A , and the transmission position r of the electromagnetic wave (transmitting antenna element) T Set this (processing S1 in Figure 2). Note that the reception position r of the reflected wave A For example, within the planar array region PA, the interval is set to correspond to the pixel spacing of the phase interference pattern image. Specifically, the reception position r of the reflected wave is determined by the following equation 5. A , and the transmission position r of the electromagnetic wave T Set it.

[0066]

number

[0067] In this embodiment, the receiving position r of the reflected wave in the planar array region PA is one of the five numbers above. A x coordinate x A In the three-dimensional spatial coordinate system shown in Figure 8, the value is within the range of -100mm to 100mm, and the z-coordinate is z A The value should be within the range of 950mm to 1050mm (see Figure 9 below).

[0068] Next, the number NT of reflection points TG of the human body model to be detected and the position coordinates TP of each reflection point TG are determined. i The following is set (processing S2 in Figure 2). In this embodiment, the number NT of reflection points TG (targets) is set to "11", as in the first embodiment described above. The position coordinates TP of each reflection point TG. iThis is set by the number 2 above, similar to the first embodiment described above. Note that the position coordinates TP of each reflection point TG are i The index i in the above is an index for identifying the part of the human body model, i.e., the type of reflection point TG, as in the first embodiment described above, and is a value within the range of "1" to "11". Also, in the example shown in Figure 8, the distance from the planar array region PA to the human body model is 5m, so the yt in the above number 2 i This will be 5000mm regardless of the value of index i.

[0069] Next, from the transmitting antenna element to each reflection point TG, any wavelength λ within the bandwidth of the transmitted signal is set. l When electromagnetic waves of type (l=1,2,…,Nλ) are simulated and irradiated, the distance from each reflection point TG to each receiving position r within the planar array region PA is measured. A The phase rotation amount φ of the reflected wave (received signal) incident on the point is calculated (processing S3 in Figure 2). Specifically, the phase rotation amount φ of the reflected wave incident on each reflection point TG is calculated using equation 6 below. Note that φ(r) in equation 6 below A TP i ,λ l ) is index i (position coordinate TP i ) From the reflection point TG to the receiving position r within the planar array region PA A Wavelength λ incident on it l This is the phase rotation amount φ of the reflected wave.

[0070]

number

[0071] Next, a phase interference pattern of the reflected waves within the planar array region PA is created (processing S4 in Figure 2). In this process, first, the following equation 7 is used to determine each receiving position r within the planar array region PA. A Phase interference intensity I(r) of the reflected wave A ) is calculated, and the phase interference intensity I(r) of the reflected wave within the planar array region PA is calculated. A This creates a distribution of the absolute values ​​of ), i.e., a phase interference pattern.

[0072]

number

[0073] Figure 9 shows an example of a phase interference pattern of reflected waves within a planar array region PA created in this embodiment. In Figure 9, the maximum points of the phase interference pattern are indicated by white circles.

[0074] Next, based on the phase interference pattern of reflected waves within the planar array region PA created by the above process (see Figure 9), the coordinate positions of the maximum points of the phase interference pattern, that is, the points where reflected waves from each reflection point TG reinforce each other, are extracted in the same manner as in the first embodiment (processing S5 in Figure 2). In the example shown in Figure 9, the coordinate positions of 40 points, represented by white circles in Figure 9, are extracted as the coordinate positions of the maximum points. Then, the extracted coordinate positions of the maximum points are set as the optimal placement positions for the receiving antenna elements within the planar array region PA (processing S6 in Figure 2). Hereafter, the arrangement of multiple antenna elements in the planar array region PA set in this manner will be referred to as the "optimized array".

[0075] [Radar image] Next, we will describe various examples of radar images obtained from the received signal when a simulated human body detection is performed by arranging multiple receiving antenna elements in a planar array region PA using the optimized array configuration set by the receiving antenna element arrangement setting method of this embodiment described above. In the numerical calculation model used to calculate the radar image in the simulation (when creating the radar image), the number of transmitting antenna elements is set to be the same as the number of receiving antenna elements, resulting in a multi-point transmission / multi-point reception configuration. Furthermore, in the numerical calculation model used to create the radar image, the placement positions of the multiple transmitting antenna elements are also set to be the same as the placement positions of the multiple receiving antenna elements. In other words, here we will describe an example in which the arrangement configuration of the receiving and transmitting antenna elements in the planar array region PA is MIMO (Multiple-Input and Multiple-Output) and an optimized array.

[0076] (Example 2-1) In Example 2-1, a radar device was used to simulate human body detection, with 40 receiving antenna elements and 40 transmitting antenna elements positioned at each of the 40 white circles within the planar array area PA shown in Figure 9. The radar image obtained from the received signal was then calculated through simulation. In Example 2-1, within the planar array area PA (size: 20 cm (x direction) × 10 cm (x direction)), the shortest spacing between adjacent receiving antenna elements is approximately 10 mm, which is longer than half a wavelength of the transmitted signal (wavelength: approximately 3.8 mm).

[0077] In Example 2-1, the center frequency of the electromagnetic wave (transmitted signal) emitted from the transmitting antenna element is 79 GHz (wavelength: approximately 3.8 mm), the same as in the first embodiment, and the bandwidth is 4 GHz (distance resolution: approximately 37.5 mm). The distance between the planar array area PA and each reflection point TG of the human body model is 5 m, the reflection coefficient of the TGs in the upper and lower torso parts of the human body model is set to "1", and the reflection coefficient of the TGs in the other parts is set to "0.5". The method for creating radar images based on the received signals from the 40 receiving antenna elements in the planar array area PA in Example 2-1 is the same as that in Examples 1-1 and 1-2.

[0078] Furthermore, in order to compare with Example 2-1, Comparative Example 2-1 was also prepared, in which 40 receiving antenna elements were arranged in an 8 (x direction) × 5 (z direction) configuration (not shown) at equal intervals within a planar array region PA to simulate human body detection, and the radar image obtained from the received signal was calculated. In the following, the arrangement configuration of multiple antenna elements arranged at equal intervals within the planar array region PA, as in Comparative Example 2-1, will be referred to as an "equally spaced array." In Comparative Example 2-1, the calculation conditions other than the arrangement configuration of the multiple receiving antenna elements are the same as those in Example 2-1. In Comparative Example 2-1, the shortest spacing between adjacent receiving antenna elements within the planar array region PA is approximately 28.6 mm, which is longer than half a wavelength of the transmitted signal (wavelength: approximately 3.8 mm).

[0079] Furthermore, in comparison with Example 2-1, as Reference Example 2, we also calculated the radar image obtained from the received signal when 8192 receiving antenna elements were arranged in a 128 (x direction) × 64 (z direction) equally spaced array within the planar array region PA to simulate human body detection. In Reference Example 2, the calculation conditions other than the arrangement of the multiple receiving antenna elements are the same as those in Example 2-1. In Reference Example 2, the spacing between adjacent receiving antenna elements in the x and z directions is approximately 1.6 mm, which is shorter than half a wavelength of the transmitted signal (wavelength: approximately 3.8 mm).

[0080] Figure 10A is the radar image obtained in Reference Example 2, Figure 10B is the radar image obtained in Comparative Example 2-1, and Figure 10C is the radar image obtained in Example 2-1. The white circles in each figure indicate the positions of the 11 reflection points TG (targets) that make up the human body model shown in Figure 8.

[0081] In Reference Example 2, the distance between adjacent receiving antenna elements is shorter than half a wavelength of the transmitted signal, so as shown in Figure 10A, no virtual image of the human body model (detection target) is generated in the radar image. On the other hand, in Comparative Example 2-1, the distance between adjacent receiving antenna elements is longer than half a wavelength of the transmitted signal, so as shown in Figure 10B, a virtual image of the human body model appears in the radar image based on the phase uncertainty of the reflected wave.

[0082] In contrast, in Example 2-1, although the spacing between adjacent receiving antenna elements is longer than half a wavelength of the transmitted signal (see Figure 9), similar to Comparative Example 2-1, it can be seen that the virtual image of the human body model is sufficiently suppressed in the radar image compared to Comparative Example 2-1. Furthermore, it can be seen that in Example 2-1, almost the same resolution (azimuth resolution) is obtained with a much smaller number of receiving array elements compared to Reference Example 2.

[0083] From the calculation results of the radar image described above, it was found that, in this embodiment as well, similar to the first embodiment, when the arrangement of multiple receiving antenna elements (arrangement position and number) within the planar array region PA is set using the receiving antenna element arrangement setting method of this embodiment described above, even if the distance between adjacent receiving antenna elements is wider than half a wavelength of the transmitted signal, it is possible to sufficiently suppress the virtual image of the human body model (detection target) on the radar image, and high azimuthal resolution can be obtained in human body detection.

[0084] [Techniques for suppressing false images in radar images] Next, we will describe a method for further suppressing the virtual image of the detected object (human body model) in the radar image obtained when multiple receiving antenna elements are arranged in the form of an optimized array in the planar array region PA. Figure 11 is a diagram illustrating the principle of the method (processing) for further suppressing the virtual image in the radar image obtained with the optimized array.

[0085] In the example numerical calculation model for virtual image suppression processing in the radar image shown in Figure 11, it is assumed that in the planar array region PA, multiple receiving antenna elements are arranged in the manner of an optimized array, and multiple transmitting antenna elements are also arranged in the same position as the multiple receiving antenna elements. Furthermore, in the example numerical calculation model shown in Figure 11, the distance L between the initial position of the planar array region PA (position at time t=t1 in the figure) and the human body model (reflection point TG) is set to 5000 mm. The configuration of the electromagnetic waves irradiated onto the human body model (reflection point TG) is the same as that in Example 2-1 above, and it is assumed that the human body model (reflection point TG) does not move.

[0086] In the radar image suppression method of this embodiment, first, as shown in Figure 11, a planar array region PA (radar device) equipped with antenna elements arranged in an optimized array configuration is moved at a constant velocity va toward a human body model (target) (along the y-axis in the figure) for a predetermined distance (hereinafter referred to as "SA length") from its initial position, while emitting electromagnetic waves (dashed arrows in the figure). In the example numerical calculation model shown in Figure 11, the SA length can be set to a distance within the range of, for example, 100 mm to 500 mm.

[0087] Furthermore, the radar device receives reflected waves (received signals: dashed arrows in the figure) from the human body model (TG) at predetermined time intervals while the planar array region PA (optimized array antenna elements) moves over a distance of SA length, thereby creating radar image RI. As a result, as shown in Figure 11, multiple radar image RIs (r,t) are generated during the period in which the planar array region PA moves over a distance of SA length. k A radar image RI (r: imaging position, k=1~N) is created. The index k is an index for identifying the time t at which the radar image RI is created at a predetermined time interval, and the maximum value N of the index k is the number of radar image RI samples obtained by the travel distance (SA length) of the planar array region PA.

[0088] For example, if the SA length is 100 mm, the constant speed va is 10 m / s, and the reception interval for the received signal (reflected wave) (the predetermined time interval above) is 2 ms, the radar device will receive the received signal 6 times during the period it travels the distance of the SA length and create radar images RI. That is, at each timing t=t1, t2, ..., t6 (N=6), the radar device will receive the received signal and create radar images RI(r,t1), RI(r,t2), ..., RI(r,t6), respectively.

[0089] Then, as shown in Figure 11, the radar device generates multiple radar images RI(r,t) at the reception interval of the received signal (reflected wave). k ) are coherently combined to create a composite radar image RI SAThe radar device generates multiple radar images RI(r,t) at predetermined time intervals (determined distance intervals) while moving. k Synthetic aperture processing is performed on ) and the synthesized radar image RI SA (r) is created. Specifically, the radar device creates a composite radar image RI according to the following equation 8. SA Find (r).

[0090]

number

[0091] Multiple radar images RI(r,t k By performing synthetic aperture processing on ), the signal values ​​of the positions of the real images of the detected object (human body model) in each radar image RI are superimposed in phase with each other, so the synthetic radar image RI SA Within (r), the signal value of the real image becomes larger. On the other hand, the phase of the position of the virtual image of the detected object (human body model) within the radar image RI shifts for each radar image RI, so the combined radar image RI SA When they are superimposed in (r), the signal values ​​at the virtual image positions cancel each other out and become smaller. Therefore, the composite radar image RI SA Within (r), the illusion can be suppressed even further.

[0092] Figure 12 shows the effect of the virtual image suppression method in radar images according to this embodiment. The white circles in each radar image RI shown in Figure 12 indicate the positions of the 11 reflection points TG (targets) that make up the human body model shown in Figure 8.

[0093] Radar images RI(r,t1), RI(r,t2), ..., RI(r,t) in Figure 12 N ) are, respectively, the periods during which the planar array region PA (antenna elements of the optimized array) of this embodiment is moved toward the human body model (detection target) by a distance of SA length, at times t1, t2, ..., t N These are radar images obtained from RI(r,t1), RI(r,t2), ..., RI(r,tN When these are coherently combined (synthetic aperture processing is performed), the synthesized radar image RI in Figure 12 is obtained. SA (r) is obtained.

[0094] As is clear from Figure 12, each radar image RI(r,t) before synthesis k Even in this case, the illusion of the human body model is suppressed to the extent that the human body model can be identified, but in the synthetic radar image RI SA In (r), it can be seen that the virtual image is further suppressed. That is, by combining the virtual image suppression method in the radar image of this embodiment described above with the receiving antenna element arrangement setting method of this embodiment (receiving antenna element arrangement method based on the phase interference pattern of reflected waves), the virtual image of the detected object (human body model) can be further suppressed on the radar image (synthetic radar image).

[0095] [Various examples of the illusion suppression technique] Next, the composite radar image RI obtained by combining the receiving antenna element arrangement method of this embodiment (receiving antenna element arrangement method based on the phase interference pattern of reflected waves) and the virtual image suppression method in the radar image of this embodiment described above. SA Various examples of (r) (Examples 2-2 to 2-4) will be explained.

[0096] In the following Examples 2-2 to 2-4, the radar image RI(r,t kThe numerical calculation model used to calculate the ) in the simulation is the same as that of the numerical calculation model shown in Figure 11, with the distance between the initial position of the planar array region PA (position at time t=t1 in Figure 11) and the human body model (reflection point TG) being 5m. The reflection coefficient of the TGs of the upper and lower torso parts of the human body model is set to "1", and the reflection coefficient of the TGs of the other parts is set to "0.5". The center frequency of the electromagnetic wave (transmitted signal) emitted from the transmitting antenna element is set to 79GHz (wavelength: approximately 3.8mm), and the bandwidth is set to 4GHz (distance resolution: approximately 37.5mm). Furthermore, the number of receiving antenna elements placed within the planar array region PA is set to 40, and their arrangement is the optimized array shown by the white circles in Figure 9. The arrangement (placement position and number) of the transmitting antenna elements is the same as that of the receiving antenna elements.

[0097] (Example 2-2) In Example 2-2, in the numerical calculation model shown in Figure 11, the SA length is set to 100 mm, and within the interval of the SA length, radar images RI(r,t) are obtained at six equally spaced points (positions at time t=t1, t2, ..., t6 (N=6) in Figure 11). k Create (k=1~6) radar images and combine these six radar images to create a composite radar image RI SA (r) was created.

[0098] Furthermore, for comparison, a radar device of Comparative Example 2-2, in which 40 receiving antenna elements and 40 transmitting antenna elements are arranged in an 8 (x direction) × 5 (z direction) equally spaced array (not shown) within the planar array region PA, was also subjected to the same procedure as in Example 2-2 to produce a composite radar image RI. SA (r) was created. Note that in the simulation of Comparative Example 2-2, the calculation conditions other than the arrangement of the receiving antenna elements and transmitting antenna elements (equally spaced array) are the same as those of Example 2-2.

[0099] Figure 13A shows the composite radar image RI obtained in Comparative Example 2-2. SA (r) is shown in Figure 13B, which is the synthesized radar image RI obtained in Example 2-2. SA(r) In Example 2-2, similar to Comparative Example 2-2, the spacing between adjacent receiving antenna elements is longer than half the wavelength of the transmitted signal, but as is clear from the comparison between Figure 13A and Figure 13B, the composite radar image RI SA (r) Above, it can be seen that the illusion of the human body model (detection target) is sufficiently suppressed compared to that of Comparative Example 2-2.

[0100] Furthermore, in Example 2-2, the radar image RI(r,t1) obtained when the planar array region PA (antenna elements of the optimized array) is positioned at the initial position (position at time t=t1) is the same as the radar image RI of Example 2-1 shown in Figure 10C. Comparing Figure 13B and Figure 10C, it can be seen that in Example 2-2, by using the virtual image suppression method in the radar image of this embodiment, the virtual image of the human body model (detection target) on the radar image can be suppressed even more effectively.

[0101] (Examples 2-3) In Example 2-3, in the numerical calculation model shown in Figure 11, the SA length is set to 200 mm, and within the SA length, radar images RI(r,t) are obtained at six equally spaced points (positions at time t=t1, t2, ..., t6 (N=6) in Figure 11). k Create (k=1~6) radar images and combine these six radar images to create a composite radar image RI SA (r) was created.

[0102] Furthermore, for comparison, a radar device of Comparative Example 2-3, in which 40 receiving antenna elements and 40 transmitting antenna elements are arranged in an 8 (x direction) × 5 (z direction) equally spaced array (not shown) within the planar array region PA, was also subjected to the same procedure as in Example 2-3 to produce a composite radar image RI. SA (r) was created. Note that in the simulation of Comparative Example 2-3, the calculation conditions other than the arrangement of the receiving antenna elements and transmitting antenna elements (equally spaced array) are the same as those of Example 2-3.

[0103] Figure 14A shows the composite radar image RI obtained in Comparative Example 2-3. SA(r) is shown in Figure 14B, which shows the synthesized radar image RI obtained in Example 2-3. SA (r) As is clear from the comparison of Figure 14A and Figure 14B, in Example 2-3 as well, the synthesized radar image RI SA (r) It can be seen that the virtual image of the human body model (detection target) is suppressed more effectively than in comparative examples 2-3.

[0104] Furthermore, in Example 2-3, the radar image RI(r,t1) obtained when the planar array region PA (antenna elements of the optimized array) is positioned at the initial position (position at time t=t1) is the same radar image RI as in Example 2-1 shown in Figure 10C. Comparing Figure 14B and Figure 10C, it can be seen that in Example 2-3 as well, by using the virtual image suppression method in the radar image of this embodiment, the virtual image of the human body model (detection target) on the radar image can be further suppressed.

[0105] (Examples 2-4) In Example 2-4, in the numerical calculation model shown in Figure 11, the SA length is set to 500 mm, and within the SA length, radar images RI(r,t) are calculated at six equally spaced points (positions at time t=t1, t2, ..., t6 (N=6) in Figure 11). k Create (k=1~6) radar images and combine these six radar images to create a composite radar image RI SA (r) was created.

[0106] Furthermore, for comparison, a radar device of Comparative Example 2-4, in which 40 receiving antenna elements and 40 transmitting antenna elements are arranged in an 8 (x direction) × 5 (z direction) equally spaced array (not shown) within the planar array region PA, was also subjected to the same procedure as in Example 2-4 to produce a composite radar image RI. SA (r) was created. Note that in the simulation of Comparative Example 2-4, the calculation conditions other than the arrangement of the receiving antenna elements and transmitting antenna elements (equally spaced array) are the same as those of Example 2-4.

[0107] Figure 15A shows the composite radar image RI obtained in Comparative Example 2-4. SA(r) is shown in Figure 15B, which is the composite radar image RI obtained in Example 2-4. SA (r) As is clear from the comparison of Figure 15A and Figure 15B, in Example 2-4 as well, the synthesized radar image RI SA (r) It can be seen that the virtual image of the human body model (detection target) is suppressed more effectively than in Comparative Example 2-4.

[0108] Furthermore, in Example 2-4, the radar image RI(r,t1) obtained when the planar array region PA (antenna elements of the optimized array) is positioned at the initial position (position at time t=t1) is the same radar image RI as in Example 2-1 shown in Figure 10C. Comparing Figure 15B and Figure 10C, it can be seen that in Example 2-4 as well, by using the virtual image suppression method in the radar image of this embodiment, the virtual image of the human body model (detection target) on the radar image can be further suppressed.

[0109] [Evaluation results based on correlation coefficient] Furthermore, in this embodiment, each of the synthesized radar images RI obtained in Examples 2-2 to 2-4 above is also used. SA The correlation coefficient between (r) and the reference radar image was evaluated. The reference radar image used was the radar image from Reference Example 2 shown in Figure 10A (where 8192 receiving antenna elements were arranged in a 128 (x direction) × 64 (z direction) equally spaced array within the planar array region PA to simulate human body detection). For comparison, the composite radar image RI obtained in Comparative Examples 2-2 to 2-4 was also used in this evaluation. SA Similarly, the correlation coefficient was evaluated for (r).

[0110] Figure 16 shows the composite radar images RI obtained in Examples 2-2 to 2-4 and Comparative Examples 2-2 to 2-4. SA This is a table summarizing the evaluation results of the correlation coefficient for (r). In the figure, "equally spaced array" refers to the arrangement of multiple receiving antenna elements in Comparative Examples 2-2 to 2-4, and "optimized array" refers to the arrangement of multiple receiving antenna elements in Examples 2-2 to 2-4.

[0111] Specifically, in the table in Figure 16, the upper column shows the evaluation results of the correlation coefficients for Comparative Example 2-2 (SA length 100 mm), Comparative Example 2-3 (SA length 200 mm), and Comparative Example 2-4 (SA length 500 mm). The lower column of the table in Figure 16 shows the evaluation results of the correlation coefficients for Example 2-2 (SA length 100 mm), Example 2-3 (SA length 200 mm), and Example 2-4 (SA length 500 mm). Note that the evaluation results of the correlation coefficient for SA length = 0 mm in Figure 16 are the evaluation results of the correlation coefficient calculated for radar image RI when the virtual image suppression method in the radar image of this embodiment described above is not implemented, specifically for the radar image RI of Comparative Example 2-1 shown in Figure 10B and Example 2-1 shown in Figure 10C.

[0112] As is clear from the evaluation results in Figure 16, the correlation coefficient is higher in the examples (Examples 2-2 to 2-4) than in the comparative examples (Comparative Examples 2-2 to 2-4) for each SA length. From these results, it was found that in this embodiment, the effect of suppressing the illusion of the human body model (detection target) on the radar image (synthetic radar image) is improved. Furthermore, as is clear from the evaluation results in Examples 2-2 to 2-4, it was found that as the SA length increases, the correlation function increases, and the effect of suppressing the illusion of the human body model on the radar image improves.

[0113] [Sensitivity analysis for additive noise] Furthermore, in this embodiment, the composite radar image RI obtained in Example 2-2 (SA length = 100 mm) is also obtained. SA As an evaluation of (r), the composite radar image RI when noise is added to the received signal. SA We performed a sensitivity analysis to the effect on (r), i.e., to additive noise.

[0114] In this evaluation, Gaussian white noise generated by a normal random number is added to the received signal, and the SNR (Signal-Noise-Ratio) level is changed to 10 dB, 0 dB, or -10 dB. The resulting composite radar image RI obtained under the simulation conditions of Example 2-2 above is then displayed. SAThe correlation coefficient of (r) was calculated. In this evaluation, the radar image from Reference Example 2 shown in Figure 10A was used as the reference radar image for the correlation coefficient. Furthermore, for comparison, the composite radar image RI obtained in Comparative Example 2-2 was also used in this evaluation. SA Similarly, sensitivity analysis to additive noise was performed for (r).

[0115] Figure 17 shows the composite radar images RI obtained in Example 2-2 and Comparative Example 2-2. SA This table summarizes the evaluation results of the sensitivity analysis for additive noise in (r).

[0116] As is clear from the evaluation results shown in Figure 17, at all SNR levels, Example 2-2 (optimized array in the figure) showed a higher correlation coefficient than Comparative Example 2-2 (equally spaced array in the figure). Furthermore, the evaluation results for Example 2-2 shown in Figure 17 showed that almost the same correlation coefficient was obtained regardless of the noise level. This is because the virtual image suppression method (synthetic aperture processing) in the radar image of this embodiment can suppress not only virtual images of the human body model but also noise based on the same principle as the virtual image suppression principle.

[0117] [Radar equipment configuration] Figure 18 shows an example configuration of a radar device 20 in which a plurality of receiving antenna elements are arranged in a planar array region PA in the form of an optimized array set by the receiving antenna element arrangement setting method of this embodiment described above. In the configuration of the radar device 20 of this embodiment shown in Figure 18, the same reference numerals are used for the same components as those of the radar device 10 of the first embodiment shown in Figure 6, and the explanation of those components is omitted. Furthermore, as an example, a configuration example in which 40 receiving antenna elements are arranged at the positions of 40 maximum points (indicated by white circles) within the reflected wave phase interference pattern shown in Figure 9 will be described.

[0118] As shown in Figure 18, the radar device 20 comprises a transmission processing unit 11, a reception processing unit 12, a control processing unit 23, 40 transmitting antenna elements Tx1 to Tx40, and 40 receiving antenna elements Rx1 to Rx40. In other words, the configuration of the receiving and transmitting antenna elements within the planar array region PA of the radar device 20 in this embodiment is MIMO. Furthermore, the radar device 20 is a radar that emits electromagnetic waves in the millimeter-wave band, and for example, the center frequency of the electromagnetic waves (transmitted signals) emitted from each transmitting antenna element Tx can be set to 79 GHz (wavelength is approximately 3.8 mm), and the bandwidth can be set to 4 GHz.

[0119] Within the radar device 20, the transmission processing unit 11 and the reception processing unit 12 are electrically connected to the control processing unit 23. The transmission processing unit 11 is electrically connected separately to each of the 40 transmission antenna elements Tx1 to Tx40, and the reception processing unit 12 is electrically connected to each of the reception antenna elements Rx1 to Rx40.

[0120] The control processing unit 23 controls the overall operation of the radar device 20. Furthermore, similar to the control processing unit 13 in the first embodiment, the control processing unit 23 includes a radar image creation unit that performs radar image creation processing based on the received signal. The radar image creation unit also has the function of performing the virtual image suppression processing (synthetic aperture processing) within the radar image described in Figure 11. However, the present invention is not limited thereto, and the function unit for performing the virtual image suppression processing within the radar image described above may be provided separately from the radar image creation unit.

[0121] The 40 receiving antenna elements Rx1 to Rx40 are positioned within the planar array region PA at the optimized array locations, specifically at the 40 maximum points (indicated by white circles) within the reflected wave phase interference pattern shown in Figure 9.

[0122] Furthermore, in this embodiment, the 40 transmitting antenna elements Tx1 to Tx40 are also arranged in an optimized array manner within the planar array region PA. In this case, for example, each of the 40 transmitting antenna elements Tx1 to Tx40 may be placed near the 40 receiving antenna elements Rx1 to Rx40 (see Figure 7). Alternatively, for example, if the transmitting and receiving antenna elements are composed of a single antenna element that serves both transmitting and receiving, and the operation is switched between transmitting and receiving signals, then the 40 antenna elements that serve both transmitting and receiving may be placed at the positions of the 40 maximum points (indicated by white circles) within the reflected wave phase interference pattern shown in Figure 9.

[0123] [effect] As described above, in the radar device 20 of this embodiment, similar to the first embodiment, multiple receiving antenna elements are arranged in an optimized array configuration set by a receiving antenna element arrangement setting method based on the phase interference pattern of the reflected wave to receive the reflected wave, and a radar image of a human body model is created based on the received signal. Therefore, in this embodiment as well, the same effects as those obtained in the first embodiment can be obtained.

[0124] Furthermore, the radar device 20 of this embodiment is equipped with a function to create multiple radar images during a period of movement over a predetermined distance (SA length) while irradiating the detection target (human body) with electromagnetic waves, and to create a composite radar image by coherently combining (synthetic aperture processing) the multiple radar images that have been created. This function further suppresses the illusion of the detection target (human body) within the composite radar image. Therefore, in this embodiment, the detection sensitivity and detection accuracy of the detection target (human body) by the radar device 20 can be further improved.

[0125] 3. Various variations The above describes the antenna array setting method for radar devices according to various embodiments of the present invention and radar devices in which antenna elements are arranged according to the antenna element arrangement determined based on the method. However, the above examples of embodiments are described in detail and specifically to explain the configuration of the device in an easy-to-understand manner, and are not necessarily limited to devices that have all the configurations described. The present invention can be modified in various ways as long as it does not depart from the gist of the present invention as described in the claims. For example, the following various modifications can be adopted, and the same effects as the above embodiments can be obtained in the following various modifications.

[0126] (Variation 1) In the first embodiment described above, an example was explained in which the arrangement of the receiving antenna elements is set to the center of the planar array region PA in the numerical calculation model for calculating the phase interference pattern of reflected waves within the planar array region PA. However, the present invention is not limited to this. For example, in the numerical calculation model for calculating the phase interference pattern of reflected waves, the arrangement of the transmitting antenna elements may be set to a position other than the center of the planar array region PA. In this case, the phase interference pattern of reflected waves within the planar array region PA changes depending on the arrangement of the transmitting antenna elements. However, the optimal arrangement position of the receiving antenna elements can be set based on the maximum value of the phase interference pattern of reflected waves, similar to the receiving antenna element arrangement setting method described in Figure 2 above.

[0127] (Modification 2) In the above embodiments, an example was described in which one transmitting antenna element and multiple receiving antenna elements are provided within the planar array region PA (a one-point transmission / multi-point reception configuration) in the numerical calculation model for calculating the phase interference pattern of reflected waves within the planar array region PA. However, the present invention is not limited to this. For example, a configuration comprising multiple transmitting antenna elements and multiple receiving antenna elements, i.e., a multi-point transmission / multi-point reception configuration, may also be used in the numerical calculation model for calculating the phase interference pattern of reflected waves. As an example of a method for setting the arrangement of receiving antenna elements in a multi-point transmission / multi-point reception configuration (numerical calculation model), the following various methods can be considered.

[0128] One approach is to calculate the phase interference pattern of reflected waves simulated from a human body model into a planar array region for each transmitting antenna element, and then determine the placement positions of multiple receiving antenna elements based on the calculated phase interference patterns. In this case, for example, the multiple phase interference patterns calculated for each transmitting antenna element may be superimposed, and the placement positions of the multiple receiving antenna elements may be determined based on the maximum point of the superimposed phase interference pattern. Alternatively, for example, the multiple phase interference patterns calculated for each transmitting antenna element may be processed using a predetermined optimization algorithm to find the optimal placement positions of the multiple receiving antenna elements.

[0129] Alternatively, one method involves first performing a predetermined process, such as a convolution operation, based on the arrangement of multiple transmitting antenna elements and multiple receiving antenna elements, to separate the transmitted signal for each transmitting antenna element and calculate an equivalent (virtual) array of receiving antenna elements that can receive the signal. Next, a phase interference pattern of reflected waves simulated from a human body model is generated in the region of the calculated equivalent array (planar array region), and the maximum points of the phase interference pattern are extracted. Then, specific processing (such as deconvolution) is applied to the extracted maximum points to calculate the placement positions of multiple receiving antenna elements.

[0130] In other words, in the method for setting the arrangement of receiving antenna elements in a multi-point transmission / multi-point reception configuration (numerical calculation model), although the planar array region of the receiving antenna elements may become the equivalent array region depending on the method used, basically, similar to the various embodiments described above, the placement positions of the multiple receiving antenna elements are determined based on the maximum points of the phase interference pattern of the reflected waves calculated in the planar array region.

[0131] (Variation 3) In the various embodiments described above, the multiple receiving antenna elements were arranged based on the maximum points of the phase interference intensity distribution of electromagnetic waves calculated when electromagnetic waves are simulated to be incident from multiple reflection points constituting a human body model. However, the present invention is not limited thereto. The multiple receiving antenna elements only need to be arranged based on the relative positions of the multiple reflection points constituting the human body. For example, multiple reflection points may be set based on the values ​​of the phase interference intensity distribution of electromagnetic waves actually transmitted and received to and from the human body, and the multiple receiving antenna elements may be arranged based on the relative positions of these multiple reflection points.

[0132] (Modification 4) In the second embodiment described above, the method for suppressing false images in radar images involves simply summing up multiple radar images created at predetermined time intervals (predetermined distance intervals) during a period in which a planar array region is moved toward a human body model by a predetermined distance (SA length), thereby suppressing false images of the detected target (human body) in the radar image. However, the present invention is not limited to this. For example, predetermined parameters representing the false image suppression effect of the synthesized radar image relative to a reference radar image may be set, and weights and the like may be appropriately set for each radar image obtained at predetermined time intervals so that the predetermined parameters are optimal (the false image suppression effect is maximized).

[0133] (Variation 5) In the various embodiments described above, the multiple receiving antenna elements were arranged to detect the human body, but the present invention is not limited thereto. The multiple receiving antenna elements only need to be arranged to set a specific detection target, and for example, the specific detection target may be something other than the human body. [Explanation of Symbols]

[0134] 10,20...Radar device, 11...Transmission processing unit, 12...Reception processing unit, 13,23...Control processing unit, Tx,Tx1~Tx40...Transmitting antenna elements, Rx1~Rx15,Rx1~Rx40...Receiving antenna elements, TG...Reflection point, PA...Planar array area,Radar image RI(r,t k ), synthetic radar image RI SA (r)

Claims

1. Multiple receiving antenna elements arranged based on the relative positions of multiple reflection points of electromagnetic waves in a specific detection target, The transmitting antenna element that emits the aforementioned electromagnetic waves, The system includes a radar image creation unit that creates a radar image based on the received signals received by the plurality of receiving antenna elements. Radar device.

2. The plurality of receiving antenna elements are arranged based on the maximum point of the phase interference intensity distribution of the electromagnetic waves reflected from the plurality of reflection sites. The radar device according to claim 1.

3. The plurality of receiving antenna elements are positioned based on the maximum point of the phase interference intensity distribution of the electromagnetic waves in the planar array region where the plurality of receiving antenna elements are arranged, when the electromagnetic waves are simulated to be incident on the planar array region where the plurality of receiving antenna elements are arranged from the plurality of reflection points that constitute a model simulating the specific detection target. The radar device according to claim 2.

4. The plurality of receiving antenna elements are arranged at unequal intervals. The radar device according to claim 1.

5. The radar image creation unit creates the radar image by applying a predetermined coherent processing to the received signal. The radar device according to claim 1.

6. The radar image creation unit creates a radar image based on the received signals received by the plurality of receiving antenna elements at predetermined time intervals while moving the plurality of receiving antenna elements a predetermined distance toward the specific detection target, and combines the plurality of radar images created at the predetermined time intervals. The radar device according to claim 1.

7. The radar image creation unit combines a plurality of radar images such that the real images of the specific detection target in each radar image created at predetermined time intervals are combined in phase with each other. The radar device according to claim 6.

8. This includes setting the placement positions of multiple receiving antenna elements based on the relative positions of multiple reflection points of electromagnetic waves at a specific detection target of the radar device. Method for configuring the antenna array of a radar system.

9. The arrangement positions of the multiple receiving antenna elements are set based on the maximum point of the phase interference intensity distribution of the electromagnetic waves reflected from the multiple reflection sites. A method for setting the antenna array of a radar device according to claim 8.

Images