Array antenna and radar equipment

Abstract

To avoid the occurrence of a grating lobe.SOLUTION: An antenna element is arranged so as to satisfy a condition 1 and a condition 2. The condition 1: the combination of a first straight line group formed of mutually-parallel straight lines and a second straight line group formed of mutually-parallel straight lines and straight lines intersecting the straight lines of the first straight line group at the position of the antenna element is defined such that the straight lines of the first straight line group and the straight lines of the second straight line group pass through the positions of the largest number of antenna elements, and the total of the number of line groups and the number of antenna elements not located on the line of the line group is equal to or greater than the number of observation objects L+1 when the straight lines included in the first straight line group and second straight line group are distributed to one or more line groups respectively formed of two or more straight lines intersecting with each other at the position of the antenna element. The condition 2: the second greatest common factor Dgcd_U and the fourth greatest common factor Dgcd_V for an interval of the antenna elements between the groups satisfy at least one of a formula (5) and a formula (6).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This disclosure relates to array antennas and radar equipment. [Background technology]

[0002] Patent Document 1 describes a technique for determining the arrangement of elements in an unequal-spacing array antenna to avoid the occurrence of grating lobes, which are undesirable peaks. In the technique disclosed in Patent Document 1, the antenna elements are divided into two groups, and the greatest common divisor of the antenna element spacing between the groups is determined from the greatest common divisor of the antenna element spacing between the two groups. Then, for all combinations of dividing the antenna elements into two groups, the spacing of the antenna elements is determined such that the greatest common divisor obtained for each group does not exceed a predetermined value. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-241702 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, while the technology disclosed in Patent Document 1 describes the arrangement of elements in a one-dimensional array antenna, it does not mention the arrangement of elements in a two-dimensional array antenna. [Means for solving the problem]

[0005] This disclosure can be implemented in the following forms:

[0006] According to one embodiment of the present disclosure, an array antenna is provided. This array antenna is a receiving array antenna (210) including a plurality of antenna elements arranged two-dimensionally at unequal intervals, wherein the plurality of antenna elements are arranged such that conditions 1 and 2 are satisfied when the number of objects to be observed is L (where L is an integer of 2 or more). Condition 1: The first process is, A first group of parallel lines, each passing through the positions of two or more antenna elements, and consisting of lines that are inclined with respect to a first direction and a second direction, A second group of lines, which are parallel to each other and have an inclination with respect to the first and second directions, and which are not parallel to the lines of the first group of lines, but which intersect with any of the lines of the first group of lines at the position of the antenna element, combination A first process that defines such that the lines of the first group of lines and the lines of the second group of lines pass through the positions of the most antenna elements, A second process involves distributing all the lines included in the first group of lines and all the lines included in the second group of lines into one or more groups of lines, each consisting of two or more lines that intersect each other at the position of the antenna element. The number of the line groups and one or more antenna elements not located on the lines of the line groups are determined through the process described above. The sum of the number of the aforementioned wire groups and the number of the aforementioned one or more antenna elements is (L+1) or greater. Condition 2: Assuming that each group contains at least one antenna element, when all combinations of dividing the plurality of antenna elements into L groups are generated, in all combinations, The greatest common divisor of the first greatest common divisor, which is the greatest common divisor of the spacing between the antenna elements in the first direction of each of the aforementioned groups, is the second greatest common divisor D. gcd_U As requested, The greatest common divisor of the third greatest common divisor, which is the greatest common divisor of the spacing between the antenna elements in the second direction of each of the aforementioned groups, is the fourth greatest common divisor D.gcd_V when obtained as at least one of Formula (5) or Formula (6) is satisfied (the wavelength of the received signal is λ, A system capable of detecting the observed object in the horizontal direction. the upper limit of the range is U max , In the aforementioned horizontal direction, the object to be observed can be detected. the lower limit of the range is U min , A system capable of detecting the observed object in the vertical direction. the upper limit of the range is V max , A system capable of detecting the observed object in the vertical direction. the lower limit of the range is V min , and let it be like this), D gcd_U (U max -U min ) < L·λ ··· (5) D gcd_V (V max -V min ) < L·λ ··· (6) Array antenna.

[0007] According to the above form, in a two-dimensional non-uniform array antenna, when the number of incoming wave frequencies is L, the generation of grating lobes can be avoided.

[0008] According to another form of the present disclosure, a radar device is provided. This radar device includes a transmitting antenna (140) that transmits a transmission signal composed of a continuous wave, a receiving antenna (210) that is an array antenna including a plurality of antenna elements two-dimensionally arranged at unequal intervals, a mixer (230) that mixes the received signal received by the plurality of antenna elements and the transmission signal to obtain a beat signal, an A / D converter (250) that samples the beat signal at a preset sampling frequency to obtain received data for a plurality of channels corresponding to the plurality of antenna elements, and a direction detection unit (320) that detects the distance to the observation target and the direction in which the observation target is located based on the received data. In the radar device, when the number of observation targets is L (L is an integer of 2 or more), the plurality of antenna elements are arranged so as to satisfy Condition 1 and Condition 2. Condition 1: The first process is A first group of parallel lines, each passing through the positions of two or more antenna elements, and consisting of lines that are inclined with respect to a first direction and a second direction, A second group of lines, which are parallel to each other and have an inclination with respect to the first and second directions, and which are not parallel to the lines of the first group of lines, but which intersect with any of the lines of the first group of lines at the position of the antenna element, combination A first process that defines such that the lines of the first group of lines and the lines of the second group of lines pass through the positions of the most antenna elements, A second process involves distributing all the lines included in the first group of lines and all the lines included in the second group of lines into one or more groups of lines, each consisting of two or more lines that intersect each other at the position of the antenna element. The number of the line groups and one or more antenna elements not located on the lines of the line groups are determined through the process described above. The sum of the number of the aforementioned wire groups and the number of the aforementioned one or more antenna elements is (L+1) or greater. Condition 2: Assuming that each group contains at least one antenna element, when all combinations of dividing the plurality of antenna elements into L groups are generated, in all combinations, The greatest common divisor of the first greatest common divisor, which is the greatest common divisor of the spacing between the antenna elements in the first direction of each of the aforementioned groups, is the second greatest common divisor D. gcd_U As requested, The greatest common divisor of the third greatest common divisor, which is the greatest common divisor of the spacing between the antenna elements in the second direction of each of the aforementioned groups, is the fourth greatest common divisor D. gcd_V When calculated as follows, At least one of equation (5) or equation (6) is satisfied (where the wavelength of the received signal is λ, A system capable of detecting the observed object in the horizontal direction. Set the upper limit of the range to U max , In the aforementioned horizontal direction, the object to be observed can be detected. Lower limit of range U min , A system capable of detecting the observed object in the vertical direction. Set the upper limit of the range to V max , A system capable of detecting the observed object in the vertical direction. The lower limit of the range is Vmin , let's assume), D gcd_U (U max -U min ) <L·λ···(5) D gcd_V (V max -V min ) <L·λ···(6) Radar device.

[0009] According to the above configuration, in a two-dimensional array antenna with unequal spacing, the occurrence of grating lobes can be avoided when the number of arriving waves is L. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows the relative positions of a vehicle equipped with radar equipment and other vehicles. [Figure 2] This is a block diagram illustrating the schematic configuration of a radar system. [Figure 3] This diagram illustrates the path difference of the signals received by the antenna elements. [Figure 4] This diagram shows an example of the positional relationship between the object being observed and the antenna element. [Figure 5] This figure shows an example of antenna element arrangement. [Figure 6] This figure shows the spectrum in the configuration shown in Figure 5. [Figure 7] This figure shows an example of an antenna element arrangement that does not meet the conditions. [Figure 8] This figure shows the spectrum in the configuration shown in Figure 7. [Figure 9] This figure shows another example of an antenna element arrangement that does not meet the conditions. [Figure 10] This figure shows the spectrum in the configuration shown in Figure 9. [Figure 11] This figure shows the spectrum in the arrangement shown in Figure 5 when there are three objects to be observed. [Figure 12] This figure shows an example of antenna element arrangement. [Figure 13]This figure shows the spectrum in the configuration shown in Figure 12. [Figure 14] This figure shows an example of antenna element arrangement. [Figure 15] This figure shows the spectrum in the configuration shown in Figure 14. [Figure 16] This figure shows the spectra in the arrangement shown in Figure 14 when there are five objects to be observed. [Modes for carrying out the invention]

[0011] A. Embodiment A1. Overview of Radar Equipment As shown in Figure 1, the radar device 1 according to this embodiment is an in-vehicle radar mounted on the vehicle M1. The radar device 1 is installed, for example, in the front grille of the vehicle M1. The radar device 1 detects the distance to another vehicle M2, which is an observation target located in front of the vehicle M1, the bearing of the other vehicle M2, and the relative speed of the other vehicle M2 with respect to the vehicle M1. The detection results of the radar device 1 are used to inform the driver about the surrounding environment while driving. Specifically, the radar device 1 emits radio waves as a transmitted wave IL. The transmitted wave is a millimeter wave. The transmitted wave IL is reflected by an observation target outside the vehicle M1, such as the other vehicle M2, and becomes a reflected wave RL. The radar device 1 estimates the distance to the observation target from the delay time obtained from the transmission time of the transmitted wave IL and the reception time of the reflected wave RL. The radar device 1 also estimates the relative speed of the observation target from the Doppler shift amount of the reflected wave RL with respect to the transmitted wave IL.

[0012] Furthermore, the radar device 1 estimates the direction of the observed object by utilizing the fact that a phase difference occurs in the reflected wave RL received by each antenna element of the receiving antenna, depending on the direction of arrival. As a calculation algorithm for estimating the direction with high accuracy and high resolution, there is, for example, MUSIC (Multiple Signal Classification).

[0013] The azimuth estimation algorithm is used in combination with an array antenna. To improve the azimuth resolution of multiple observation targets, the aperture area of ​​the antenna should be increased. Array antennas include equally spaced array antennas, where multiple antenna elements are arranged at equal intervals, and unequally spaced array antennas, where multiple antenna elements are arranged at unequal intervals. In equally spaced array antennas, the spacing between antenna elements needs to be reduced to suppress the occurrence of grating lobes. For example, in an equally spaced antenna, reducing the spacing between antenna elements and increasing the aperture area of ​​the antenna increases the number of antenna elements. Therefore, it has been proposed to use an unequally spaced array antenna to reduce the number of antenna elements in order to suppress the occurrence of grating lobes.

[0014] As shown in Figure 2, the radar device 1 comprises a transmitting unit 100, a receiving unit 200, and a processing unit 300. In this embodiment, the radar device 1 is an FMCW (Frequency Modulated Continuous Wave) radar.

[0015] The transmitting unit 100 comprises an oscillator 110, an amplifier 120, a distributor 130, and a transmitting antenna 140. The oscillator 110 is, for example, a voltage-controlled oscillator (VCO). When a triangular wave voltage signal is input to the oscillator 110 from the transmit / receive control unit 330 of the processing unit 300, the oscillator 110 outputs a frequency-modulated high-frequency signal as a transmit signal to the amplifier 120. The amplifier 120 amplifies the transmit signal and outputs the amplified signal to the distributor 130. The distributor 130 distributes the amplified transmit signal to the transmitting antenna 140 and the mixer 230 of the receiving unit 200. A portion of the transmit signal distributed to the mixer 230 is used for detection of the received signal. The transmitting antenna 140 radiates the transmit signal supplied via the distributor 130 as radio waves to the outside of the vehicle M1.

[0016] The receiving unit 200 comprises an array antenna 210, an amplifier 220, a mixer 230, a low-pass filter 240, and an A / D (Analog Digital) converter 250. The array antenna 210 is a two-dimensional array antenna. The array antenna 210 is an unequal spacing array antenna in which K antenna elements are arranged at unequal intervals on a plane. K is an integer greater than or equal to 2. The K antenna elements correspond to each channel from the 1st channel to the Kth channel. The array antenna 210 receives the reflected wave reflected from the object being observed as a received signal and outputs the received signal to the amplifier 220.

[0017] The amplifier 220 amplifies the received signal and outputs the amplified signal to the mixer 230. The mixer 230 mixes the distributed transmitted signal and the received signal to generate a beat signal for phase detection. Phase detection is the extraction of amplitude and phase information from the received signal. The beat signal output by the mixer 230 is supplied to the A / D converter 250 via a low-pass filter 240 that cuts out high-frequency noise. The A / D converter 250 converts the beat signal into a digital signal by sampling and quantizing it at the sampling frequency. The converted digital signal is supplied to the processing unit 300.

[0018] The processing unit 300 comprises a frequency processing unit 310, an orientation detection unit 320, and a transmission / reception control unit 330. The processing unit 300 is composed of a computer including a CPU (Central Processing Unit), memory, etc. The frequency processing unit 310 calculates zero or more beat frequencies from the supplied digital signal. The orientation detection unit 320 estimates the orientation of the observed object using MUSIC or the like for each calculated beat frequency. The transmission / reception control unit 330 controls the transmission unit 100 and the reception unit 200.

[0019] A2. Regarding the occurrence of grating groves As shown in Figure 3, assume that reflected waves are incident on antenna elements A0 and A1 at the same angle Φ. If we use the reflected wave signal received by antenna element A0 as the reference, the signal received by antenna element A1 will be out of phase by a path difference Δd. That is, a phase difference corresponding to the path difference Δd occurs between the signal received by antenna element A0 and the signal received by antenna element A1.

[0020] When the phase difference between the received signal of antenna element A0 and the received signal of antenna element A1 is an integer multiple of the wavelength λ, which is the wavelength of the signal received by radar device 1, the received signal of antenna element A0 and the received signal of antenna element A1 are said to be in phase. When the received signals of multiple antenna elements are in phase, in high-resolution techniques known as subspace techniques such as MUSIC, the received signals of multiple antenna elements are treated as a single signal.

[0021] For example, suppose an array antenna 210 has six antenna elements, and three of the six antenna elements are divided into group 1 and the remaining three into group 2. Suppose the received signals of the three antenna elements belonging to group 1 are in the same phase, and the received signals of the three antenna elements belonging to group 2 are in the same phase. In this case, the three antenna elements belonging to group 1 become equivalent antenna elements. The three antenna elements belonging to group 2 also become equivalent antenna elements.

[0022] In this case, the number of signals that can be separated and received by the array antenna 210 is effectively two. In this case, the size of the correlation matrix obtained from the received signals is a 2x2 matrix, and the maximum number of eigenvectors obtained from the correlation matrix is ​​two. When there are two eigenvectors, the space spanned by the eigenvectors is two-dimensional. In this situation, if there are arriving waves from two observation targets, and furthermore, there is an direction in which no observation target exists but satisfies the conditions, the direction vector for the direction in which no observation target exists is not independent, but is linearly dependent on the respective direction vectors representing the two observation targets. Direction vectors are also called mode vectors or steering vectors. The radar device 1 mounted on the vehicle is required to separate and detect at least two signal sources. A signal source is an observation target from which radio waves are reflected. Here, since there are two observation targets, the antenna elements included in the array antenna 210 are divided into two groups. The number of groups is selected according to the number of arriving waves. Generally, when there are L objects to observe, the antenna elements contained in the array antenna 210 need to be divided into L groups. L is a positive integer.

[0023] Direction estimation using subspace methods such as MUSIC involves obtaining noise vectors from the eigenvectors of the correlation matrix of the array antenna 210's output, and then using the property that the noise subspace spanned by the noise vectors is orthogonal to the signal subspace to determine the direction of the incoming wave. If the direction vector indicating the direction of the incoming wave from the observed object and the direction vector indicating the direction where the observed object does not exist are linearly dependent, then the direction vector indicating the direction where the observed object does not exist is also orthogonal to the noise vector. For this reason, when performing direction estimation using high-resolution methods known as subspace methods such as MUSIC, a grating lobe indicating a direction different from the actual observed object may occur, depending on the spacing of the antenna elements and the conditions of the incoming wave's direction of arrival. As a result, the direction where the observed object does not exist is incorrectly estimated as the direction of the incoming wave.

[0024] As shown in Figure 4, the positional relationship between the observation target T1, the observation point P1 where the observation target T1 is observed, and the antenna elements A0 to A5 is represented in a Cartesian coordinate system. The origin where the X, Y, and Z axes intersect is defined as observation point P1. In this embodiment, the X-axis direction is also called the U-axis direction, and the Y-axis direction is also called the V-axis direction. The antenna elements A0 to A5 are arranged at unequal intervals in the U-axis and V-axis directions.

[0025] For example, the distance between two antenna elements in the U-axis direction is the distance between a point on the U-axis representing the position of one antenna element when that antenna element is projected onto the U-axis, and a point on the U-axis representing the position of the other antenna element when that antenna element is projected onto the U-axis. The distance between two antenna elements in the V-axis direction is the distance between a point on the V-axis representing the position of one antenna element when that antenna element is projected onto the V-axis, and a point on the V-axis representing the position of the other antenna element when that antenna element is projected onto the V-axis. In this embodiment, multiple antenna elements are said to be arranged at unequal intervals, meaning that the antenna elements are arranged such that the distance between them in the U-axis direction is unequal, and the distance between them in the V-axis direction is unequal. As shown in Figure 4, the directions indicated by the X-axis, Y-axis, and Z-axis are mutually orthogonal. Here, orthogonal means that the angle that one direction makes with another direction is within the range of plus or minus 10 degrees from a right angle. The U-axis direction is also called the first direction. The V-axis direction is also called the second direction.

[0026] If the direction of the observed object T1 is represented by a unit vector, then the direction t of the observed object T1 is t = (U t ,V t ,√(1-U t 2 -V t 2 This is expressed as ). The detectable range on the U-axis of radar device 1 is -1 ≤ U t The range of detection on the V-axis of radar device 1 is -1 ≤ V. t The limit is +1.

[0027] Furthermore, when there are two antenna elements, the two antenna elements are aligned on a straight line, so the path difference Δd of the received signal can be expressed by the following equation (1). In equation (1), D u D is the spacing between the antenna elements in the U-axis direction. v This is the spacing between the antenna elements in the V-axis direction. Δd=D u ·U t +D v ·V t ...(1)

[0028] When there are three or more antenna elements, the multiple antenna elements are not necessarily aligned in a straight line. Therefore, in order to adjust the phase difference between the antenna elements, the spacing between the antenna elements in a two-dimensional array antenna needs to be considered in both the U-axis direction and the V-axis direction. Accordingly, in this embodiment, Δd = n·λ is assumed to hold when (a) and (b) below are satisfied, or when (c) is satisfied. n1 is an integer other than zero. n2 is an integer including zero. (a)D u ·U t =n1·λ (b)D v ·V t =n1·λ (c)D u ·U t +D v ·V t =n²·λ

[0029] A3. Antenna element placement conditions First, we will explain an example where the received signals of multiple antenna elements have the same phase, in the antenna element arrangement shown in Figure 4. First, we will explain A0, A1, and A3. In the following explanation, the basic unit representing the distance between elements is d. d = λ / 2, where λ is the wavelength of the received signal. Hereafter, antenna element A0 may be simply referred to as A0. The same applies to antenna elements A1 to A5.

[0030] The distance between A0 and A1 in the U-axis direction is 2d, and the distance in the V-axis direction is 2d. t = 1 / 2, V t When = 1 / 2, D u ·U t =λ / 2, D v ·V t =λ / 2. Therefore, D u ·U t +D v ·V t =λ U t = 1 / 2, V t When = 1 / 2, as shown in equation (c) above, the path difference Δd between A0 and A1 is an integer multiple of the wavelength λ, so the received signal of A0 and the received signal of A1 are in phase. The distance between A0 and A3 in the U-axis direction is 4d, and the distance in the V-axis direction is 4d. t = 1 / 2, V t When = 1 / 2, D u ·U t =λ, D v ·V t =λ. Therefore, D u ·U t +D v ·V t = 2λ U t = 1 / 2, V t When = 1 / 2, the path difference Δd between A0 and A3 is an integer multiple of the wavelength λ, so the received signal at A0 and the received signal at A3 are in phase. The distance between A1 and A3 in the U-axis direction is 2d, and the distance in the V-axis direction is 2d, so D u ·U t =λ / 2, D v ·V t =λ / 2. Therefore, D u ·U t +D v ·V t =λ U t = 1 / 2, V t When = 1 / 2, the path difference Δd between A1 and A3 is an integer multiple of the wavelength λ, so the received signal of A1 and the received signal of A3 are in phase.

[0031] Thus, U t = 1 / 2, Vt When it is 1 / 2, the path difference Δd between A0, A1, and A3 is an integer multiple of the wavelength λ, so the received signals of A0, A1, and A3 have the same phase. Therefore, it can be said that the three antenna elements A0, A1, and A3 are equivalent antenna elements.

[0032] Also, in the arrangement of antenna elements as shown in FIG. 4, another example where the received signals of a plurality of antenna elements have the same phase will be described. Hereinafter, A0, A1, and A2 will be described. The interval between A0 and A1 in the U-axis direction is 2d, and the interval in the V-axis direction is 2d, so U t = 1, V t = 1, when D u ·U t = λ, D v ·V t = λ. As represented by the above formulas (a) and (b), since the path difference Δd between A0 and A1 is an integer multiple of the wavelength λ, the received signal of A0 and the received signal of A1 have the same phase. The interval between A0 and A2 in the U-axis direction is 6d, and the interval in the V-axis direction is 4d, so U t = 1, V t = 1, when D u ·U t = 3λ, D v ·V t = 2λ. The received signal of A0 and the received signal of A2 have the same phase. The interval between A1 and A2 in the U-axis direction is 4d, and the interval in the V-axis direction is 2d, so U t = 1, V t = 1, when D u ·U t = 2λ, D v ·V t = λ. The received signal of A1 and the received signal of A2 have the same phase.

[0033] Thus, when U t = 1, V t = 1, the path difference Δd between A0, A1, and A2 is an integer multiple of the wavelength λ, and the received signals of A0, A1, and A2 have the same phase. Therefore, it can be said that the three antenna elements A0, A1, and A2 are equivalent antenna elements.

[0034] As mentioned above, in the arrangement of antenna elements shown in Figure 4, U t = 1 / 2, V t When = 1 / 2, A0, A1, and A3 have the same phase. Also, A0, A1, and A3 are arranged so as to lie on the same straight line. In this way, the received signals of multiple antenna elements arranged on the same straight line may have the same phase depending on the spacing between the antenna elements and the direction of arrival of the incoming wave. Assume that this straight line has an arbitrary slope K. In this case, D v =K·D u It can be expressed as follows. By rearranging equation (1), the path difference Δd for A0, A1, and A3 can be expressed as shown in equation (2) below. Δd=D u ·U t +K·D u ·V t ...(2)

[0035] Furthermore, in cases where the antenna elements can be connected by a straight line, such as A0, A1, and A3, the absolute value of n when Δd=n·λ holds is smaller compared to cases where the antenna elements cannot be connected by a straight line, such as A0, A1, and A2. In other words, when the antenna elements can be connected by a straight line, U is smaller compared to cases where the antenna elements cannot be connected by a straight line. t The value and V t The values ​​of and take small values. This means that when antenna elements can be connected by a straight line, the detection range in which grating lobes do not occur is narrower compared to when they cannot be connected by a straight line. Therefore, it is preferable that not all antenna elements belonging to the same group are located on the same straight line.

[0036] As mentioned above, the radar device 1 mounted on the vehicle is required to detect at least two signal sources separately. Therefore, the radar device 1 needs to detect at least two objects to be observed. First, let's consider the case where there are two objects to be observed. In the antenna arrangement shown in Figure 4, for example, A1 and A3 are group 1, and A4 and A5 are group 2. In this case, antenna elements A0 and A2 are not used.

[0037] Let A1 and A3, which belong to Group 1, be connected by a straight line, and let the slope of that line be K1. In the antenna arrangement shown in Figure 4, K1 = V / U = 1. The spacing of the antenna elements in the U-axis direction is given by D in equation (2). u Substitute it into the variable. Δd=D u ·U t +K1·D U ·V t =2d·U t +2d·V t ...(3)

[0038] Let A4 and A5, which belong to Group 2, be connected by a straight line, and let the slope of that line be K2. K2 = V / U = -2 / 3. The spacing of the antenna elements in the U-axis direction is given by D in equation (2). u Substitute it into the variable. Δd=D u ·U t +K2·D U ·V t =3d·U t +(-2 / 3)·3d·V t ...(4)

[0039] Here, U t =2 / 5, V tWhen = 3 / 5, in equation (3), Δd = λ, and Δd takes an integer multiple of the wavelength λ. In this case, the received signal of A1 and the received signal of A3, which belong to group 1, have the same phase. Also, in equation (4), Δd = 0, and Δd takes an integer multiple of the wavelength λ. In this case, the received signal of A4 and the received signal of A5, which belong to group 2, have the same phase. Furthermore, since both the Δd shown in equation (3) and the Δd shown in equation (4) take an integer multiple of the wavelength λ, the received signals of A1 and A3, which belong to group 1, and the received signals of A4 and A5, which belong to group 2, can be in phase. In this way, in multiple groups, the received signals of the antenna elements included in each group can be in phase. This can reduce the effective number of antenna elements and cause a grating lobe that points in a different direction from the actual observed object.

[0040] Next, we will discuss the case where antenna elements other than A2 are used in the antenna arrangement shown in Figure 4. Let's consider the case where A0, A1, A3, A4, and A5 belong to the same group. Let's call this group Group 1. When there are three or more antenna elements, as described in Patent Document 1, a phase difference in the received signals of multiple antenna elements occurs depending on the greatest common divisor of the spacing between the multiple antenna elements. In this case, in equations (1) and (2), D u D is the greatest common divisor of the spacing between multiple antenna elements in the U-axis direction, and v This is the greatest common divisor of the spacing between multiple antenna elements in the V-axis direction.

[0041] As mentioned above, U t =2 / 5, V t When = 3 / 5, the received signals of A1 and A3, which are positioned so as to lie on a straight line with slope K1, have the same phase. A0 has slope K1 and is positioned so as to lie on a straight line passing through the positions of A1 and A3. Therefore, U t =2 / 5, V t When =3 / 5, the received signals of A0, A1, and A3 have the same phase. Also, U t =2 / 5, V tWhen = 3 / 5, the received signals of A4 and A5, which are located on a straight line with slope K2, have the same phase. A0 is located on a straight line with slope K2 that passes through the positions of A4 and A5. Therefore, U t =2 / 5, V t When the phase is 3 / 5, the received signals A0, A4, and A5 have the same phase.

[0042] U t =2 / 5, V t When = 3 / 5, the Δd obtained for A0, A1, and A3, which are arranged on a straight line with slope K1, takes an integer multiple of the wavelength λ. t =2 / 5, V t When = 3 / 5, the Δd obtained for A0, A4, and A5, which are arranged on a straight line with slope K2, takes an integer multiple of the wavelength λ. Therefore, the received signals at A0, A1, and A3, and the received signals at A0, A4, and A5, have the same phase. In this way, even if antenna elements belonging to the same group are located on two different straight lines, the received signals can be in phase.

[0043] When antenna elements belonging to the same group are located on two different lines, it can be determined as follows whether the received signals can be in phase. Even if antenna elements belonging to the same group are located on two different lines, the received signals can be in phase if the two lines intersect at the position where either antenna element is placed. In the example shown in Figure 4, the line with slope K1 and the line with slope K2 intersect at the position where A0 is placed. Therefore, the received signals at A0, A1, A3, A4, and A5 can be in phase.

[0044] Furthermore, if A0, A1, A3, A4, and A5 belong to the same group, then assume that there are multiple antenna elements not shown in Figure 4, and that these multiple antenna elements belong to a different group, Group 2. Group 2 includes antenna elements other than A0, A1, A3, A4, and A5. For the sake of ease of understanding the technology, A2 shown in Figure 4 will not be considered. If all the antenna elements in Group 2 are arranged so as to be aligned on a straight line with inclination K1 or a straight line with inclination K2, then the received signals of the antenna elements in Group 1 and the received signals of the antenna elements in Group 2 may be in phase. This can result in a reduction in the effective number of antenna elements and the generation of a grating lobe that indicates a different direction from the actual observed object.

[0045] In the example above, multiple antenna elements were arranged along two straight lines with different slopes. Now, let's consider the case where multiple antenna elements are arranged along three straight lines with different slopes. Let the slopes of the three lines be K1, K2, and K3, respectively. In this case, assume the following situation holds: For the antenna elements arranged along the first straight line with slope K1, Δd = D u ·U t +K1·D u ·V t The equation =n11·λ holds. For antenna elements arranged to be aligned on a second straight line with slope K2, Δd=D u ·U t +K2·D u ·V t The equation =n12·λ holds. For antenna elements arranged to be aligned on the third straight line with slope K3, Δd=D u ·U t +K3·D u ·V t The equation = n13·λ holds true. Note that n11, n12, and n13 are all integers. In this case, since there are three independent equations, generally there are two independent variables U t and V t It is not possible to determine this. Therefore, the slope of the line will not have three or more values, but only two.

[0046] Furthermore, the embodiments assume a two-dimensional array antenna, and do not assume a one-dimensional array antenna. An array antenna in which the antenna elements are arranged on a line parallel to the U-axis is a one-dimensional array antenna. Similarly, an array antenna in which the antenna elements are arranged on a line parallel to the V-axis is also a one-dimensional array antenna. Therefore, array antennas in which the antenna elements are arranged on a line parallel to the U-axis and array antennas in which the antenna elements are arranged on a line parallel to the V-axis are excluded.

[0047] Furthermore, if the antenna elements are arranged so as to be aligned on a straight line having an inclination K1, or on a straight line having an inclination K2 different from inclination K1, and the straight line having inclination K1 or K2 is parallel to the U-axis, then when the antenna elements are not aligned on a straight line, the above (a) and (b) are satisfied, Δd = n·λ holds, but since the straight line having inclination K1 or K2 is parallel to the U-axis, D v = 0, meaning (b) is not satisfied. Therefore, (a) and (b) are not satisfied.

[0048] Furthermore, if the antenna elements are arranged so as to be aligned on a straight line having an inclination K1, or on a straight line having an inclination K2 different from inclination K1, and the straight line having inclination K1 or K2 is parallel to the V-axis, then D u = 0, meaning (a) is not satisfied. Therefore, (a) and (b) are not satisfied.

[0049] Based on the above, in the embodiment, the antenna elements are arranged as follows. When the antenna elements are arranged so as to be aligned on a straight line having an inclination K1, or on a straight line having an inclination K2 different from inclination K1, the straight line having inclination K1 and the straight line having inclination K2 must be straight lines that are not parallel to the U axis and the V axis. A straight line that is not parallel to the U axis is a straight line that has an inclination with respect to the U axis. A straight line that is not parallel to the V axis is a straight line that has an inclination with respect to the V axis.

[0050] Based on the above considerations, in this embodiment, the conditions for the arrangement of antenna elements are as follows. First, in an array antenna including multiple antenna elements arranged two-dimensionally at unequal intervals, the multiple antenna elements are arranged so as to satisfy conditions 1 and 2 described below. Let the number of objects to be observed be L (where L is an integer of 2 or more).

[0051] Condition 1: The first process is, A first group of parallel lines, each passing through the positions of two or more antenna elements and having an inclination with respect to the U-axis and V-axis directions, A combination of a second group of lines consisting of lines that are parallel to each other, have an inclination with respect to the U-axis and V-axis, are not parallel to the lines of the first group of lines, and intersect with any of the lines of the first group of lines at the position of the antenna element, A first process that defines the lines of the first set of lines and the lines of the second set of lines so that they pass through the positions of the most antenna elements, A second process involves distributing all lines included in the first group of lines and all lines included in the second group of lines into one or more groups of lines, each consisting of two or more lines that intersect each other at the position of the antenna element. The number of line groups and one or more antenna elements not located on the lines of the line groups are determined through the following process. The sum of the number of wire groups and the number of antenna elements (one or more) is (L+1) or greater. Condition 2: Assuming that each group contains at least one antenna element, when generating all possible combinations of dividing multiple antenna elements into L groups, in all combinations, The second greatest common divisor D is the greatest common divisor of the first greatest common divisor, which is the greatest common divisor of the spacing in the U-axis direction of the antenna elements included in each group. gcd_U As requested, The greatest common divisor of the third greatest common divisor, which is the greatest common divisor of the spacing in the V-axis direction of the antenna elements included in each group, is the fourth greatest common divisor D. gcd_V When calculated as follows, At least one of equation (5) or equation (6) is satisfied (where the wavelength of the received signal is λ, A system capable of detecting the observed object in the horizontal direction. Set the upper limit of the range to U max , In the aforementioned horizontal direction, the object to be observed can be detected. Lower limit of range U min , A system capable of detecting the observed object in the vertical direction. Set the upper limit of the range to V max , In the aforementioned vertical direction, the object of observation can be detected. The lower limit of the range is V min , let's assume), D gcd_U (U max -U min ) <L·λ···(5) D gcd_V (V max -V min ) <L·λ···(6)。

[0052] Equations (5) and (6) of condition 2 are two-dimensional extensions of the equations that the spacing of antenna elements must satisfy, as described in Patent Document 1. When the arrangement of antenna elements is one-dimensional, the occurrence of grating lobes could be suppressed by adjusting the spacing of the antenna elements.

[0053] However, when the antenna elements are arranged in two dimensions, as mentioned above, adjusting the spacing between the antenna elements alone is not enough to suppress the occurrence of grating lobes. More specifically, false images may occur within the range defined by condition 2. Condition 1 is set to suppress this. Condition 1 is a necessary condition to be satisfied in order to resolve the problem of false images occurring when the technology disclosed in Patent Document 1 is applied to a two-dimensional array antenna. By selecting an antenna element arrangement that satisfies conditions 1 and 2, it is possible to prevent the occurrence of grating lobes in each range obtained by dividing the detectable range of the radar device 1 equally by the number of arriving waves, similar to Patent Document 1.

[0054] The following describes the process for checking whether condition 1 is satisfied. For ease of understanding, we assume that the number of observed objects L is 2. The process described below is performed, for example, by a computer equipped with a processor and memory.

[0055] First, a set of parallel lines is generated, each passing through the positions of two or more antenna elements. The generated set of lines does not include any lines parallel to the U-axis or V-axis. Note that the number of lines in the generated set of lines is not necessarily multiple; it may be just one. One or more sets of lines are generated. Of the generated sets of lines, the set that passes through the positions of the most antenna elements is determined to be the first set of lines.

[0056] Next, a second set of lines is determined, consisting of lines that are parallel to each other, are not parallel to any of the lines in the first set of lines, and intersect any of the lines in the first set of lines at the positions of the antenna elements. The lines in the second set of lines do not include lines parallel to the U-axis or V-axis. Note that the number of lines in the second set of lines is not necessarily multiple; it may be just one. Also, if there are multiple sets of lines that could form the second set of lines, the set of lines that passes through the positions of the most antenna elements is determined as the second set of lines. The process of defining the combination of the first set of lines and the second set of lines is also called the first process.

[0057] Next, all the lines in the first group of lines and all the lines in the second group of lines are divided into one or more groups of lines, each consisting of two or more lines that intersect each other at the positions of the antenna elements. One group of lines identifies a set of antenna elements in which the received signals can be in phase. The received signals of multiple antenna elements located on a line included in one group of lines can be in phase.

[0058] Next, confirm that the sum of the number of line groups and the number of antenna elements not on the line groups is 3 or greater, which is obtained by adding 1 to the number of observed objects. If the sum of the number of line groups and the number of antenna elements not on the line groups is 3 or greater, then condition 1 is satisfied.

[0059] Next, we will explain the process for checking whether condition 2 is satisfied. In an arrangement of antenna elements that satisfies condition 1, all combinations of dividing the antenna elements into two groups are generated. Each group is assumed to contain at least one antenna element. Suppose the number of generated combinations is C, where C is an integer greater than or equal to 1.

[0060] First, the following process is performed on the first combination: The two groups are designated as Group 1 and Group 2. The greatest common divisor (gcd1) is the spacing between the antenna elements in the U-axis direction within Group 1. U Similarly, the greatest common divisor gcd2 of the spacing between antenna elements in the U-axis of group 2 is required. U The greatest common divisor (GCD1) is required. U , gcd2 U This is also called the first greatest common divisor (GCD1). U and the greatest common divisor gcd2 U The second greatest common divisor D is the greatest common divisor of the two numbers. gcd_U This is required.

[0061] Furthermore, the greatest common divisor gcd1 is the spacing in the V-axis direction of the antenna elements included in group 1. VSimilarly, the greatest common divisor gcd2 of the spacing between antenna elements in the V-axis included in group 2 is required. V The greatest common divisor (GCD1) is required. V , gcd2 V This is also called the third greatest common divisor. Greatest common divisor gcd1 V and the greatest common divisor gcd2 V The fourth greatest common divisor is D, which is the greatest common divisor of these two numbers. gcd_V This can be calculated. Furthermore, if equation (5) is satisfied, the greatest common divisor gcd1 V , gcd2 V , the fourth greatest common divisor D gcd_V The calculation of is unnecessary. It is determined whether at least one of equation (5) or equation (6) in condition 2 is satisfied. D gcd_U (U max -U min ) <L·λ···(5) D gcd_V (V max -V min ) <L·λ···(6)

[0062] Next, the same process is performed to check whether at least one of equation (5) or equation (6) is satisfied in the second combination. Then, the same process is performed for the third combination, ..., and the Cth combination, respectively.

[0063] If, among the combinations from the first to the Cth, there is one or more combinations that do not satisfy either equation (5) or equation (6), then the antenna element arrangement being considered is not effective in suppressing grating lobes. Therefore, other antenna element arrangements will be reconsidered. In this way, for antenna arrangements that satisfy condition 1, all possible combinations that can be grouped together are checked to see if they satisfy condition 2. After the above process, an antenna arrangement that satisfies both condition 1 and condition 2 is determined.

[0064] In this way, by determining the spacing of the antenna elements, it is possible to avoid the occurrence of grating lobes in a radar system having a two-dimensional unequal-spacing array antenna when the number of arriving waves is L or less.

[0065] A4. Examples that meet the placement requirements Figure 5 shows an example of antenna element arrangement. Assume the number of objects to be observed is 2.

[0066] First, a set of parallel lines is generated, each passing through the positions of two or more antenna elements. The generated set of lines does not include any lines parallel to the U-axis or V-axis. From the generated set of lines, we look for the set of lines that passes through the positions of the most antenna elements. In the example shown in Figure 5, the parallel lines L11, L21, and L31 each pass through the positions of two or more antenna elements, and the number of antenna elements they pass through is 6, which is the maximum. Therefore, the set of lines consisting of lines L11, L21, and L31 is determined to be the first set of lines. The slope K1 of the lines in the first set of lines is -2 / 3.

[0067] Next, we look for a second group of lines that are parallel to each other, are not parallel to the lines in the first group of lines, and intersect with one of the lines in the first group of lines at the position of the antenna element. The lines in the second group of lines do not include lines parallel to the U-axis and V-axis. In the example shown in Figure 5, the group of lines consisting of the parallel lines L12, L22, L32, and L42 is not parallel to the first group of lines. Also, line L12 intersects with line L11 of the first group of lines at position A1. Line L12 intersects with line L21 of the first group of lines at position A2. Line L32 intersects with line L31 of the first group of lines at position A6. Line L42 intersects with line L31 of the first group of lines at position A8. Furthermore, the number of antenna elements through which lines L12, L22, L32, and L42 pass is 7, which is the largest number among the groups of lines that intersect with any of the lines in the first group of lines at the positions of the antenna elements. Therefore, the group of lines consisting of lines L12, L22, L32, and L42 is determined to be the second group of lines. The slope K2 of the lines in the second group of lines is 1.

[0068] Subsequently, all the lines included in the first group of lines and all the lines included in the second group of lines are divided into one or more groups of lines, each consisting of two or more lines that intersect each other at the position of the antenna element.

[0069] As shown in Figure 5, line L11 of the first line group and line L12 of the second line group intersect at position A1. Line L11 of the first line group and line L22 of the second line group intersect at position A5. Line L21 of the first line group intersects with line L12 of the second line group at position A2, and further intersects with line L22 of the second line group at position A7. Therefore, lines L11, L12, L21, and L22 form a single line group. Let this line group be called line group LG1.

[0070] Furthermore, line L31 of the first line group and line L32 of the second line group intersect at position A6. In addition, line L31 of the first line group and line L42 of the second line group intersect at position A8. Therefore, line L31, line L32, and line L42 form a single line group. Let this line group be called line group LG2.

[0071] As described above, each line group identifies a set of antenna elements whose received signals can be in phase. Here, A1, A2, A4, A5, and A7, which lie on line group LG1, can have their received signals in phase. The antenna elements on line group LG1 are grouped together as antenna element group AG1. Similarly, A6 and A9, which lie on line group LG2, can have their received signals in phase. The antenna elements on line group LG2 are grouped together as antenna element group AG2.

[0072] Furthermore, there is an antenna element A3 that is not located on the lines of line groups LG1 and LG2. Therefore, the sum of the number of line groups and the number of antenna elements not located on the lines of line groups is 3. Note that the number of line groups and the number of antenna element groups are the same. Here, the number of observation targets L is 2. Therefore, the antenna arrangement shown in Figure 5 satisfies condition 1.

[0073] Antenna element A3 is not included in either antenna element group G1 or G2. Therefore, the received signal of antenna element A3 cannot be in phase with the received signal of the antenna element in antenna element group AG1. Furthermore, the received signal of antenna element AG3 cannot be in phase with the received signal of the antenna element in antenna element group AG2. As mentioned above, when there are two observation targets, if there are two effective signals, a grating lobe may occur that indicates a different direction from the actual observation target. However, in the example shown in Figure 5, three effective signals can be secured. Therefore, in the antenna configuration shown in Figure 5, if condition 2, which will be described later, is met, a grating lobe will not occur.

[0074] Next, we check if condition 2 is met. Assume that the number of observed objects L is 2. First, we generate all possible combinations of dividing them into two groups. Each group is assumed to contain at least one antenna element. For example, suppose the antenna elements are divided such that group g1 contains A1, A2, A3, A4, A5, and A7, and group g2 contains A6 and A8. In Figure 5, the antenna elements of group g1 are represented by white circles, and the antenna elements of group g2 are represented by black circles.

[0075] We will find the greatest common divisor (GCD) of the spacing between the antenna elements in group g1 in the U-axis direction. The spacing between the antenna elements in group g1 in the U-axis direction is as follows: The spacing between A1 and A2 is 2d. The spacing between A1 and A3 is 3d. The spacing between A1 and A4 is 4d. The spacing between A1 and A5 is 6d. The spacing between A2 and A3 is 1d. The spacing between A2 and A4 is 2d. The spacing between A2 and A5 is 4d. The spacing between A2 and A7 is 6d. The spacing between A3 and A5 is 3d. The spacing between A4 and A5 is 2d. The spacing between A4 and A7 is 4d. The spacing between A5 and A7 is 2d. Therefore, the greatest common divisor (GCD) of the spacing between the antenna elements in group g1 in the U-axis direction is gcd1. U It is 1d.

[0076] We will find the greatest common divisor (GCD) of the spacing in the U-axis direction for group g2. The spacing of the antenna elements in group g2 in the U-axis direction is as follows: The spacing between A6 and A8 is 3d. Therefore, the greatest common divisor of the spacing of the antenna elements in group g2 in the U-axis direction is gcd2. U It is 3D.

[0077] Greatest common divisor (gcd1) U If d is 1d, then the greatest common divisor is gcd2. U Since it is 3D, the greatest common divisor is gcd1 U and the greatest common divisor gcd2 U The second greatest common divisor D is the greatest common divisor of the two numbers. gcd_U =1d=λ / 2. Here, the radar's detection range is assumed to be omnidirectional. In this case, expressed as a unit direction vector, the radar's detection range is -1≦U t ≤ +1, -1 ≤ V t It can be expressed as ≤ +1. Therefore, U max -U min =2, V max -V min = 2. L = 2. In this case, the second greatest common divisor D is gcd_U This satisfies equation (5).

[0078] Let's consider another example of antenna element combinations. For example, suppose we divide the antenna elements so that group g1 contains A1, A2, A3, and A5, and group g2 contains A4, A6, A7, and A8. We find the greatest common divisor of the spacing in the U-axis direction for group g1. The spacing in the U-axis direction for the antenna elements of group g1 is as follows: The spacing between A1 and A2 is 2d. The spacing between A1 and A3 is 3d. The spacing between A1 and A5 is 6d. The spacing between A2 and A3 is 1d. The spacing between A2 and A5 is 4d. The spacing between A3 and A5 is 3d. Therefore, the greatest common divisor of the spacing in the U-axis direction for the antenna elements of group g1 is gcd1. U It is 1d.

[0079] We will find the greatest common divisor (GCD) of the spacing in the U-axis direction for group g2. The spacing of the antenna elements in group g2 in the U-axis direction is as follows: The spacing between A4 and A6 is 3d. The spacing between A4 and A7 is 4d. The spacing between A4 and A8 is 6d. The spacing between A6 and A7 is 1d. The spacing between A6 and A8 is 3d. The spacing between A7 and A8 is 2d. Therefore, the greatest common divisor of the spacing of the antenna elements in group g2 in the U-axis direction is gcd2. U It is 1d.

[0080] Greatest common divisor (gcd1) U If d is 1d, then the greatest common divisor is gcd2. U Since 1d, the greatest common divisor is gcd1 U and the greatest common divisor gcd2 U The second greatest common divisor D is the greatest common divisor of the two numbers. gcd_U =1d=λ / 2. Here, the radar's detection range is assumed to be omnidirectional. In this case, expressed as a unit direction vector, the radar's detection range is -1≦U t ≤ +1, -1 ≤ V t It can be expressed as ≤ +1. Therefore, U max -U min =2, V max -V min = 2. L = 2. In this case, the second greatest common divisor D is gcd_U This satisfies equation (5).

[0081] Let's consider yet another example of antenna element combinations. For example, suppose we divide the antenna elements so that group g1 contains A1, A2, A4, A5, A7, and A8, and group g2 contains A3 and A6.

[0082] Find the greatest common divisor (GCD) of the spacing in the U-axis direction for group g1. (GCD1 is the greatest common divisor of the spacing in the U-axis direction for antenna elements in group g1.) U It is 2d. Also, the greatest common divisor of the spacing of the antenna elements in the U-axis direction of group g2 is gcd2. U It is 4d. The greatest common divisor is gcd1. U and the greatest common divisor gcd2 U The second greatest common divisor D is the greatest common divisor of the two numbers. gcd_U=2d=λ. The second greatest common divisor is D. gcd_U This does not satisfy equation (5). Therefore, we find the greatest common divisor of the spacing in the V-axis direction. The greatest common divisor of the spacing in the V-axis direction of the antenna elements of group g1 is gcd1. V It is 1d. Also, the greatest common divisor of the spacing in the V-axis direction of the antenna elements of group g2 is gcd2. U It is 6d. The greatest common divisor is gcd1. U and the greatest common divisor gcd2 U The second greatest common divisor D is the greatest common divisor of the two numbers. gcd_U =1d=λ / 2. Therefore, the second greatest common divisor is D. gcd_U This satisfies equation (5).

[0083] So far, we have explained three examples of grouping combinations. Now, let's assume that the above process is performed for all grouping combinations, and that in all combinations, at least one of equation (5) or equation (6) is satisfied. Therefore, condition 2 is satisfied. As mentioned above, condition 1 is satisfied. In this case, the arrangement of antenna elements shown in Figure 5 can be said to be an arrangement that can suppress the generation of grating lobes.

[0084] Figure 6 shows the spectral image (hereinafter referred to as the MUSIC spectrum) output when two observation targets were observed using the array antenna configuration shown in Figure 5, and the direction of the observation targets was detected using MUSIC. The detected directions of the observation targets (hereinafter referred to as the target direction) are (U,V) = (2 / 5,3 / 5) and (-2 / 5,-3 / 5), respectively. In Figure 6, the observation targets are circled. As shown in this figure, no false images were generated.

[0085] A5. Position of separated antenna elements In condition 1 described above, the number of antenna elements not located on the line group is taken into consideration. Hereafter, antenna elements not located on the line group will be referred to as separated antenna elements. The desirable distance between separated antenna elements and the straight line will be explained below.

[0086] Let's consider the distance s1 between A3 in Figure 5 and the nearest straight line L11. In the following explanation, we assume Ut=1 and Vt=1. In this case, the path difference Δd between antenna elements placed on the straight line L11 is given by equation (1) as Δd=D u ·U t +D v ·V t =D u ·1+D v The equation becomes 1 = Du + Dv. In this case, if the sum of the distance Du in the U-axis direction between antenna elements and the distance Dv in the V-axis direction between antenna elements is shifted by 1 / 2 wavelength, the phase of the received signal will be shifted by 180°. A 180° phase shift means that the received signals of A1 and A5, which are arranged to be aligned on the line L11, and A3, which is not located on the line of the group of wires, will have opposite phases. In such a case, the received signals are so different that the generation of grating lobes is suppressed.

[0087] Suppose A3 is positioned 0.5d in the V-axis direction, closer to the line L11 than its current position. In this case, the phase difference between the received signal of A3 and the received signals of A1 and A5, which are aligned on the line L11, is 1 / 4 wavelength. If the phase difference between the received signal of A3 and the received signals of A1 and A5, which are aligned on the line L11, falls below 1 / 2 wavelength, the spectral values ​​in areas without signals will increase, approaching the grating lobe.

[0088] Therefore, it is desirable that the phase difference between the received signal of a separated antenna element not located on a line group and the received signal of an antenna element positioned on a straight line passing through the position closest to the separated antenna be 1 / 2 wavelength or more. The straight line passing through the position closest to the separated antenna is a straight line included in any of the line groups. For this reason, it is desirable that the separated antenna elements be positioned at a distance of 1 / 2 wavelength or more from the straight line passing through the position closest to the separated antenna, in the U-axis or V-axis direction. In the example shown in Figure 5, the distance s1 in the V-axis direction between line L11 and A3 is set to 1 / 2 wavelength. By positioning them in this way, the phase difference between the received signal of an antenna element on the straight line passing through the position closest to the separated antenna and the received signal of the separated antenna element can be widened. This can suppress the generation of grating lobe. However, since this is premised on satisfying condition 2, it is not the case that the greater the distance between the separated antenna element and the straight line passing through the position closest to the separated antenna, the more grating lobe can be suppressed.

[0089] A6. Examples that do not meet the placement requirements Figure 7 shows an example of an antenna element arrangement that does not satisfy the arrangement conditions. First, the first group of lines is determined. The first group of lines is determined to include a line that passes through positions A1, A2, A4, and A6 and has a slope of 1. The lines in the first group of lines do not include lines parallel to the U-axis and V-axis. In the arrangement shown in Figure 7, it is not possible to draw a line parallel to the line that passes through positions A1, A2, A4, and A6, so the number of lines in the first group of lines is 1. Next, the second group of lines is determined to consist of lines that are not parallel to the lines in the first group of lines, but intersect with one of the lines in the first group of lines at the position of the antenna element. The lines in the second group of lines do not include lines parallel to the U-axis and V-axis. For example, the second group of lines is determined to include a line that passes through A4 and A5 and has a slope of -1 / 2. Lines with a slope of -1 / 2 that pass through A1, A2, and A6, respectively, which are located on the lines of the first group of lines, may also be included in the second group of lines. However, these lines only pass through the positions of the antenna elements that lie on the lines of the first group of lines. Here, the lines included in the second group of lines are limited to those that pass through A4 and A5 and have a slope of -1 / 2.

[0090] All lines in the first line group and all lines in the second line group are distributed into one or more line groups, each consisting of two or more lines that intersect each other at the position of the antenna element. In the example shown in Figure 7, there is one line in the first line group and one line in the second line group, so these two line groups form one line group. Also, A3 is not located on this line group. Therefore, the sum of the number of line groups and the number of antenna elements not located on the line groups is 2. Thus, condition 1 is not satisfied.

[0091] Here, condition 1 is intended to ensure that at least three substantial signals are secured, given that the radar device 1 mounted on the vehicle is required to detect at least two signal sources separately.

[0092] Whether or not at least three substantial signals can be secured can be checked by the following method. In the example shown in Figure 7, A1, A2, A4, and A6 can be connected by one straight line. Additionally, A3 and A5 can be connected by another straight line with a different slope. All antenna elements are positioned so that they lie on one of the two straight lines with different slopes. No antenna elements are positioned anywhere other than on these two straight lines. In this case, it is not possible to secure three substantial signals.

[0093] Depending on the number and arrangement of antenna elements, this method allows us to determine whether three substantial signals can be secured before checking condition 1. If it is determined that three substantial signals cannot be secured using this method, then it can be determined that condition 1 is not met without having to perform the check process for condition 1.

[0094] Figure 8 shows the MUSIC spectrum output when two targets were observed using the array antenna configuration shown in Figure 7, and the target direction was detected using MUSIC. In Figure 8, the target direction is circled, and false images are circled. From this figure, it can be seen that a large number of false images are generated.

[0095] The antenna element arrangement shown in Figure 7 does not satisfy condition 1, so normally, checking condition 2 is unnecessary. However, in order to explain the necessity of condition 1, we will check here whether condition 2 is satisfied for Figure 7. For example, suppose the antenna elements are divided so that group g1 contains A1, A2, A4, and A6, and group g2 contains A3 and A5. The greatest common divisor of the spacing of the antenna elements in the U-axis direction of group g1 is gcd1. U The greatest common divisor of the spacing between antenna elements in the U-axis direction of group g2 is gcd2. U It is 3D. The greatest common divisor is gcd1. U and the greatest common divisor gcd2 U The second greatest common divisor D is the greatest common divisor of the two numbers. gcd_U =1d=λ / 2. Therefore, the second greatest common divisor is D.gcd_U This satisfies equation (5). Assume that at least one of equations (5) or (6) is satisfied in any other combination of grouping. Thus, in the antenna arrangement shown in Figure 7, condition 1 is not satisfied, but condition 2 is. Therefore, if condition 2 is satisfied alone, false images may occur, leading to misjudgment of the target direction. For this reason, it is important to consider condition 1 in addition to condition 2.

[0096] Figure 9 shows another example of an antenna element arrangement that does not satisfy the arrangement conditions. Assume the number of observation targets L is 2. The arrangement shown in Figure 9 is obtained by moving the position of A3 in Figure 5 from (U,V)=(-2,-4) to (-3,-3).

[0097] The first and second line groups defined to determine condition 1 are the same as in the example shown in Figure 5. Similar to the example in Figure 5, line group LG1 includes line L11, line L12, line L21, and line L22. Antenna element group AG1 consists of A1, A2, A4, A5, and A7. Line group LG2 includes line L31, line L32, and line L42. Antenna element group AG2 consists of A3, A6, and A8. The number of antenna elements not located on the lines of line groups LG1 and LG2 is 0. Therefore, the sum of the number of line groups and the number of antenna elements not located on the lines of the line groups is 2. Thus, the antenna configuration shown in Figure 9 does not satisfy condition 1.

[0098] Figure 10 shows the MUSIC spectrum output when two observation targets were observed using the array antenna configuration shown in Figure 9, and the target direction was detected using MUSIC. In Figure 10, the target direction is circled, and false images are circled. From this figure, it can be seen that false images are occurring.

[0099] The antenna element arrangement shown in Figure 9 does not satisfy condition 1, so normally, checking condition 2 is unnecessary. However, in order to explain the necessity of condition 1, we will check here whether the arrangement shown in Figure 9 satisfies condition 2. For example, suppose the antenna elements are divided so that group g1 contains A1, A2, A4, A5, and A7, and group g2 contains A3, A6, and A8. The greatest common divisor of the spacing of the antenna elements in the U-axis direction of group g1 is gcd1. U The greatest common divisor of the spacing between antenna elements in the U-axis direction of group g2 is gcd2. U It is 1d. The greatest common divisor is gcd1. U and the greatest common divisor gcd2 U The second greatest common divisor D is the greatest common divisor of the two numbers. gcd_U =1d=λ / 2. Therefore, the second greatest common divisor is D. gcd_U This satisfies equation (5). Assume that at least one of equations (5) or (6) is satisfied in any other combination of grouping. Thus, in the antenna arrangement shown in Figure 9, condition 1 is not satisfied, but condition 2 is. Therefore, if condition 2 is satisfied alone, false images may occur, leading to misjudgment of the target direction. For this reason, it is important to consider condition 1 in addition to condition 2.

[0100] A7. Number of groups The number of groups is selected according to the number of incoming waves. For example, if there are two objects to observe, there are two incoming waves. In this case, when determining condition 2, the antenna elements are divided into two groups. If there are three objects to observe, there are three incoming waves. In this case, when determining condition 2, the antenna elements are divided into three groups.

[0101] Below, we will check whether condition 1 is satisfied with the antenna configuration shown in Figure 5 when there are 3 observation targets L. The first and second line groups are the same. Therefore, antenna element group AG1 consists of A1, A2, A4, A5, and A7, and antenna element group AG2 consists of A6 and A8. There is an antenna element A3 that is not located on the lines of line groups LG1 and LG2. The sum of the number of line groups and the number of antenna elements not located on the lines of line groups is 3. Since there are 3 observation targets, condition 1 is not satisfied.

[0102] In the antenna element arrangement shown in Figure 5, condition 1 is not satisfied when there are three objects to observe, so normally, checking condition 2 is unnecessary. However, in order to explain the necessity of condition 1, we will check here whether the arrangement shown in Figure 5 satisfies condition 2 when there are three objects to observe. Next, let's consider condition 2. Assume that the antenna elements are divided so that group g1 contains A1, A3, A4, A5, and A7, group g2 contains A6 and A8, and group g3 contains A2. The greatest common divisor of the spacing of the antenna elements in the U-axis direction of group g1 is gcd1. U The greatest common divisor of the spacing between antenna elements in group g2 in the U-axis direction is gcd2. U The value is 3d. As described in Patent Document 1, if there is only one antenna element in a group, the greatest common divisor is 0. Therefore, the greatest common divisor of the spacing of the antenna elements in the U-axis direction of group g3 is gcd3. U It is 0d. The greatest common divisor is gcd1. U and the greatest common divisor gcd2 U and the greatest common divisor gcd3 U The second greatest common divisor D is the greatest common divisor of the two numbers. gcd_U =1d=λ / 2. Therefore, the second greatest common divisor is D. gcd_U This satisfies equation (5). Assume that at least one of equations (5) or (6) is also satisfied with any other grouping combination. In other words, condition 2 is satisfied.

[0103] Figure 11 shows the MUSIC spectra output when three observation targets were observed using the array antenna configuration shown in Figure 5, and the target direction was detected using MUSIC. The target directions are (U,V)=(2 / 5,3 / 5), (-2 / 5,-3 / 5), and (0,0). In Figure 11, the observation targets are circled, and false images are circled. As shown, a large number of false images are generated. Thus, when the number of observation targets L is 3, condition 1 is not met with the antenna configuration shown in Figure 5, but condition 2 is met. Therefore, if condition 2 is met alone, false images may be generated, leading to misjudgment of the target direction. For this reason, it is important to check condition 1 in addition to condition 2.

[0104] Next, we check condition 1 when the antenna elements are arranged as shown in Figure 12. There are three objects to observe. The antenna arrangement shown in Figure 12 is the same as the arrangement shown in Figure 5, with A9 added. The first and second line groups are the same. Line group LG1 includes lines L11, L12, L21, and L22. Antenna element group AG1 consists of A1, A2, A4, A5, and A7. Line group LG2 includes lines L31, L32, and L42. Antenna element group AG2 consists of A6 and A8. The antenna elements that are not located on the lines of line groups LG1 and LG2 are A3 and A9. The sum of the number of line groups and the number of antenna elements not located on the lines of line groups is 4. Therefore, when there are three objects to observe, the antenna arrangement shown in Figure 12 satisfies condition 1.

[0105] Next, let's consider condition 2. Suppose the antenna elements are divided such that group g1 contains A1, A2, A4, A5, and A7, group g2 contains A6 and A8, group g3 contains A2, and group g4 contains A9. The greatest common divisor of the spacing between the antenna elements in group g1 in the U-axis direction is gcd1. U The greatest common divisor of the spacing between antenna elements in the U-axis direction of group g2 is gcd2. U The value is 3d. The greatest common divisor of the spacing in the U-axis direction of the antenna elements of group g3 is gcd3. UIt is 0d. The greatest common divisor of the spacing of the antenna elements in the U-axis direction of group g4 is gcd3. U It is 0d. The greatest common divisor is gcd1. U and the greatest common divisor gcd2 U and the greatest common divisor gcd3 U and the greatest common divisor gcd4 U The second greatest common divisor is D, which is the greatest common divisor of the two numbers. gcd_U =1d=λ / 2. Therefore, the second greatest common divisor is D. gcd_U This satisfies equation (5). Assume that at least one of equations (5) or (6) is also satisfied with any other grouping combination. In other words, condition 2 is satisfied.

[0106] Figure 13 shows the MUSIC spectra output when three observation targets were observed using the array antenna configuration shown in Figure 12, and the target direction was detected using MUSIC. In Figure 13, the target direction is circled. As shown in the figure, no false images were generated.

[0107] Figure 14 shows another example of antenna element arrangement. First, a set of lines is generated consisting of parallel lines that pass through the positions of two or more antenna elements. The lines in the generated set of lines do not include lines parallel to the U-axis and V-axis. From the generated set of lines, we find the set of lines that passes through the positions of the most antenna elements. In the example shown in Figure 14, no line of any slope connects more than two antenna elements. For example, line L11 with a slope of -2 / 3 that passes through positions A1 and A5 is determined as the first set of lines. Here, the first set of lines contains only one line. Next, we find a second set of lines consisting of parallel lines that are not parallel to the lines in the first set of lines, but that intersect with one of the lines in the first set of lines at the positions of the antenna elements. The lines in the second set of lines do not include lines parallel to the U-axis and V-axis. For example, line L12 with a slope of 1 that intersects with line L11 in the first set of lines at the position where A1 is located is determined as the second set of lines.

[0108] Subsequently, all the lines in the first line group and all the lines in the second line group are divided into one or more line groups, each consisting of two or more lines that intersect each other at the position of the antenna element. In the example shown in Figure 14, line L11 of the first line group and line L12 of the second line group intersect at position A1. Therefore, line L11 and line L12 form one line group. This line group is called line group LG1.

[0109] Furthermore, the antenna elements that are not located on the line group LG1 are A2, A3, A6, and A7. Therefore, the sum of the number of line groups and the number of antenna elements not located on the line groups is 5. In this case, the maximum value of the observation target L for which no false image occurs is 4, which is obtained by subtracting 1 from the sum of 5.

[0110] Next, we will check if the arrangement shown in Figure 14 satisfies condition 2 when the number of observed objects L is 4. For example, suppose the antenna elements are divided such that group g1 contains A1, A4, and A5, group g2 contains A2 and A3, group g3 contains A6, and group g4 contains A7. The greatest common divisor of the spacing of the antenna elements in the U-axis direction of group g1 is gcd1. U The greatest common divisor of the spacing between antenna elements in the U-axis direction of group g2 is gcd2. U 4d. The greatest common divisor of the spacing in the U-axis direction of the antenna elements in groups g3 and g4 is gcd3. U and gcd4 U Each of these values ​​is 0d. The greatest common divisor is gcd1. U and the greatest common divisor gcd2 U and the greatest common divisor gcd3 U and the greatest common divisor gcd4 U The second greatest common divisor D is the greatest common divisor of the two numbers. gcd_U =2d=λ. L=4. Therefore, the second greatest common divisor is D. gcd_U This satisfies equation (5). Assume that at least one of equations (5) or (6) is also satisfied with other grouping combinations. Condition 2 is satisfied.

[0111] Figure 15 shows the MUSIC spectra output when four observation targets were observed using the array antenna configuration shown in Figure 14, and the target orientation was detected using MUSIC. The target orientations are (U,V)=(2 / 5,3 / 5), (-2 / 5,-3 / 5), (-2 / 5,3 / 5), and (2 / 5,-3 / 5), respectively. In Figure 15, the observation targets are circled. As shown in this figure, no false images were generated.

[0112] Next, we check whether the arrangement shown in Figure 14 satisfies conditions 1 and 2 when there are five objects to observe. As mentioned above, the sum of the number of line groups and the number of antenna elements not located on the lines of the line groups is 5. Therefore, condition 1 is not satisfied.

[0113] Since condition 1 is not satisfied, checking condition 2 is not normally necessary. However, in order to explain the necessity of condition 1, we will check condition 2 here. For example, suppose the antenna elements are divided so that group g1 contains A1, A4, and A5, group g2 contains A2, group g3 contains A6, group g4 contains A7, and group g5 contains A3. The greatest common divisor of the spacing of the antenna elements in the U-axis direction of group g1 is gcd1. U is 2d. For the greatest common divisor of the spacing in the U-axis direction of the antenna elements of groups g2, g3, g4, and g5, let gcd2 U , gcd3 U , gcd4 U , gcd5 U Each of these values ​​is 0d. The greatest common divisor is gcd1. U and the greatest common divisor gcd2 U and the greatest common divisor gcd3 U and the greatest common divisor gcd4 U and the greatest common divisor gcd5 U The second greatest common divisor D is the greatest common divisor of the two numbers. gcd_U =2d=λ. Since L=5, the second greatest common divisor is D. gcd_U This satisfies equation (5). Assume that at least one of equations (5) or (6) is also satisfied with any other grouping combination. In other words, condition 2 is satisfied.

[0114] Figure 16 shows the MUSIC spectra output when five observation targets were observed using the array antenna configuration shown in Figure 14, and the target orientation was detected using MUSIC. The target orientations are (U,V)=(2 / 5,3 / 5), (-2 / 5,-3 / 5), (0,0), (-2 / 5,3 / 5), and (2 / 5,-3 / 5). In Figure 16, the observation targets are circled, and false images are circled. As shown in this figure, a large number of false images are generated.

[0115] Thus, when the number of observed objects L is 5, the arrangement shown in Figure 14 does not satisfy condition 1, but condition 2 is satisfied. Therefore, if condition 2 is satisfied alone, false images may occur, leading to misjudgment of the target direction. For this reason, it is important to consider condition 1 in addition to condition 2.

[0116] B. Other Embodiments In the embodiment, an example was described in which the basic unit representing the distance between elements is d = λ / 2, but the embodiment is not limited to this. It is preferable that the basic unit representing the distance between elements is a value greater than 1 / 10 of the wavelength λ of the received signal.

[0117] This disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from its spirit. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-described problems, or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate. [Explanation of Symbols]

[0118] 1...Radar device, 140...Transmitting antenna, 200...Receiver, 210...Array antenna, 220...Amplifier, 230...Mixer, 250...A / D converter, 320...Directional detection unit

Claims

1. A receiving array antenna (210) including a plurality of antenna elements arranged two-dimensionally at unequal intervals, When the number of objects to be observed is L (where L is an integer of 2 or more), the plurality of antenna elements are arranged such that conditions 1 and 2 are satisfied. Condition 1: The first process is, A first group of parallel lines, each passing through the positions of two or more antenna elements, and consisting of lines that are inclined with respect to a first direction and a second direction, A second group of lines, which are parallel to each other and have an inclination with respect to the first and second directions, and which are not parallel to the lines of the first group of lines, but which intersect with any of the lines of the first group of lines at the position of the antenna element, The combinations, A first process that defines such that the lines of the first group of lines and the lines of the second group of lines pass through the positions of the most antenna elements, A second process involves distributing all the lines included in the first group of lines and all the lines included in the second group of lines into one or more line groups, each consisting of two or more lines that intersect each other at the position of the antenna element. The number of the line groups and one or more antenna elements not located on the lines of the line groups are determined through the process, The sum of the number of the aforementioned wire groups and the number of the aforementioned one or more antenna elements is (L+1) or greater. Condition 2: Assuming that each group contains at least one antenna element, when all combinations of dividing the plurality of antenna elements into L groups are generated, in all combinations, The greatest common divisor of the first greatest common divisor, which is the greatest common divisor of the spacing between the antenna elements in the first direction of each of the aforementioned groups, is the second greatest common divisor D. ｇｃｄ＿Ｕ As requested, The greatest common divisor of the third greatest common divisor, which is the greatest common divisor of the spacing between the antenna elements in the second direction of each of the aforementioned groups, is the fourth greatest common divisor D. ｇｃｄ＿Ｖ When calculated as follows, At least one of equation (5) or equation (6) is satisfied (where the wavelength of the received signal is λ and the upper limit of the range in which the observed object can be detected in the horizontal direction is U). ｍａｘ , the lower limit of the range in which the observed object can be detected in the horizontal direction is U ｍｉｎ , the upper limit of the range in which the observed object can be detected in the vertical direction is V ｍａｘ , the lower limit of the range in which the observed object can be detected in the vertical direction is V ｍｉｎ , let's assume), D ｇｃｄ＿Ｕ (U) ｍａｘ -U ｍｉｎ )<L・λ・・・(5) D ｇｃｄ＿Ｖ (V ｍａｘ -V ｍｉｎ )<L・λ・・・(6) Array antenna.

2. The array antenna according to claim 1, L is 2. Array antenna.

3. An array antenna according to claim 1 or 2, The distance in the first direction and the distance in the second direction between a separation antenna element, which is an antenna element that is deviated from any of the aforementioned straight lines, and the straight line located closest to the separation antenna element are set to be at least half a wavelength apart. Array antenna.

4. Radar device (1), The radar system includes a transmitting antenna (140) that transmits a transmission signal consisting of a continuous wave, a receiving antenna (210) which is an array antenna including a plurality of antenna elements arranged two-dimensionally at unequal intervals, a mixer (230) that mixes the received signal received by the plurality of antenna elements with the transmitted signal to obtain a beat signal, an A / D converter (250) that samples the beat signal at a preset sampling frequency to obtain received data for a plurality of channels corresponding to the plurality of antenna elements, and an orientation detection unit (320) that detects the distance to the object of observation and the direction in which the object of observation is located based on the received data. In the radar device described above, when the number of objects to be observed is L (where L is an integer of 2 or more), the plurality of antenna elements are arranged such that conditions 1 and 2 are satisfied. Condition 1: The first process is, A first group of parallel lines, each passing through the positions of two or more antenna elements, and consisting of lines that are inclined with respect to a first direction and a second direction, A second group of lines, which are parallel to each other and have an inclination with respect to the first and second directions, and which are not parallel to the lines of the first group of lines, but which intersect with any of the lines of the first group of lines at the position of the antenna element, combination A first process that defines such that the lines of the first group of lines and the lines of the second group of lines pass through the positions of the most antenna elements, A second process involves distributing all the lines included in the first group of lines and all the lines included in the second group of lines into one or more line groups, each consisting of two or more lines that intersect each other at the position of the antenna element. The number of the line groups and one or more antenna elements not located on the lines of the line groups are determined through the process, The sum of the number of the aforementioned wire groups and the number of the aforementioned one or more antenna elements is (L+1) or greater. Condition 2: Assuming that each group contains at least one antenna element, when all combinations of dividing the plurality of antenna elements into L groups are generated, in all combinations, The greatest common divisor of the first greatest common divisor, which is the greatest common divisor of the spacing between the antenna elements in the first direction of each of the aforementioned groups, is the second greatest common divisor D. ｇｃｄ＿Ｕ As requested, The greatest common divisor of the third greatest common divisor, which is the greatest common divisor of the spacing between the antenna elements in the second direction of each of the aforementioned groups, is the fourth greatest common divisor D. ｇｃｄ＿Ｖ When calculated as follows, At least one of equation (5) or equation (6) is satisfied (where the wavelength of the received signal is λ and the upper limit of the range in which the observed object can be detected in the horizontal direction is U). ｍａｘ , the lower limit of the range in which the observed object can be detected in the horizontal direction is U ｍｉｎ , the upper limit of the range in which the observed object can be detected in the vertical direction is V ｍａｘ , the lower limit of the range in which the observed object can be detected in the vertical direction is V ｍｉｎ , let's assume), D ｇｃｄ＿Ｕ (U) ｍａｘ -U ｍｉｎ )<L・λ・・・(5) D ｇｃｄ＿Ｖ (V ｍａｘ -V ｍｉｎ )<L・λ・・・(6) Radar device.

5. A radar device according to claim 4, L is 2. Radar device.

6. A radar device according to claim 4 or 5, The distance in the first direction and the distance in the second direction between a separation antenna element, which is an antenna element that is deviated from any of the aforementioned straight lines, and the straight line located closest to the separation antenna element are set to be at least half a wavelength apart. Radar device.

Images