JP2011064567A - Radar system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radar system which can reduce the detection of ghosts and suppress the degree of cross correlation. <P>SOLUTION: The radar system includes: a transmitting antenna group; a receiving antenna group; a transmission switching means; a virtual correlation value obtaining means; and a target detection means. The transmitting antenna group is included in the receiving antenna group. The transmission switching means allows part of or all the receiving antennas included in the receiving antenna group to function as a transmitting antenna successively. The transmitting antenna group and the receiving antenna group are arranged symmetrically and in a line at unequal spacings. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radar apparatus that detects a target.

  Conventionally, in a radar apparatus having an array antenna with antennas arranged at equal intervals, the result of transmitting and receiving while switching the antenna to be used as a transmission antenna is holographically synthesized, so that the number of virtual antennas exceeds the number of actual antennas. There is a technique for obtaining a reception result (see, for example, Patent Documents 1 to 4).

  Moreover, in a radar apparatus using an adaptive antenna such as a synthetic aperture radar apparatus, a technique that suppresses the influence of an interference wave having a correlation with a desired wave (correlation interference wave) is a spatial averaging method (spatial smoothing method). There is processing technology. This spatial averaging process is based on the fact that the phase relationship of correlated waves is different at the receiving position, and the degree of cross-correlation is calculated by weighted averaging the correlation values between the waves obtained by translating the receiving position. It is a technology to suppress. For example, Patent Documents 5 to 8 disclose spatial averaging processing in a synthetic aperture radar apparatus.

JP 2004-198312 A JP 2005-195491 A JP 2006-91028 A JP 2006-98181 A Patent No. 3678946 Japanese Patent No. 3595220 JP 2001-194454 A JP 2002-181930 A

  FIG. 1 shows a ghost detection situation in an array antenna when six antennas are installed at equal intervals. A conventional electronic scanning radar device uses an equally spaced array antenna, and as shown in FIG. 1, the target is located outside the angular range (FOV: Field of View) where the target can be detected according to the antenna spacing. Phase wrapping occurs, and it is detected as if the target is present in the direction where the target does not actually exist. In the present specification, the presence of the false target may be referred to as “ghost”. As a countermeasure against the ghost, it is conceivable that the beam is narrowed by the antenna and the radio wave intensity outside the FOV is rapidly reduced. However, an electronic scanning radar device uses a plurality of antennas, and by antenna design, it is possible to form a flat beam as much as possible inside the FOV and to form a beam that rapidly reduces the radio field intensity outside the FOV. Impossible. Further, in the electronic scanning radar apparatus, it is difficult for all the antennas to form the same beam by the shape of the transmission port or the radio wave absorber, and the beam range changes for each antenna.

Further, in the electronic scanning radar device, the antenna of the receiving antenna, which is a structural correlation of the receiving antenna, can be regarded as parallel, using the unequally spaced antennas, and the reflected signals reaching the receiving antennas from the target can be regarded as parallel. When attention is paid to the ratio of the intervals and the ratio is used, detection of ghost may be suppressed by accurately calculating the number of phase folds in the signal received by the receiving antenna. However, the spatial average processing generally used to suppress the degree of cross-correlation existing between the desired wave and the interference wave is a sub-carrier that is cut out as a part of an actual antenna group in an equally spaced antenna. The antenna group is used as a subarray, and the correlation values of a plurality of subarrays whose positions are shifted are weighted and averaged. For example, as shown in FIG. 2, the spatial averaging process uses nine to six antennas as subarrays, and uses a total of four subarrays. Therefore, when the spatial averaging processing that is generally used is used for an unequal interval antenna, as shown in FIG. 3, when the position is shifted from subarray 1 to subarray 2, antennas # 3 to # 5 of subarray 2 are used. There is a problem that the degree of cross-correlation cannot be suppressed by the normal spatial averaging method.

  In view of the above-described problems, an object of the present invention is to provide a radar apparatus that can suppress detection of ghosts and further suppress the degree of cross-correlation.

  The present invention devised the arrangement of the antenna group in order to solve the above-described problems. As a result, it is possible to provide a radar apparatus that can suppress detection of ghosts and further suppress the degree of cross-correlation.

  Specifically, a radar apparatus according to the present invention transmits a transmission antenna group having a plurality of transmission antennas, a reception antenna group having a plurality of reception antennas, and sequentially switching transmission waves from each transmission antenna of the transmission antenna group. A transmission switching means that transmits the transmission wave of each of the transmission antennas when the transmission switching means sequentially performs transmission wave transmission by the transmission switching means, and receives the reflected wave from the transmission antenna. The virtual correlation value is acquired corresponding to the number of transmission antennas that transmitted the transmission wave, using the correlation value in the spatial averaging process corresponding to the virtual subarray as a virtual correlation value. And a virtual correlation value corresponding to the plurality of virtual subarrays acquired by the virtual correlation value acquiring means, By applying a spatial averaging process based on the relative position of each of the transmission antennas whose transmission has been switched by the transmission switching unit with respect to the reception antenna group, the transmission antenna is virtually switched from the reception antenna group by the transmission switching of the transmission switching unit. Target detection means for calculating an average virtual correlation value corresponding to the virtual antenna group derived in step (b) and detecting the target based on the average virtual correlation value, wherein the transmission antenna group includes the reception antenna And the transmission switching means sequentially causes some or all of the reception antennas included in the reception antenna group to function as transmission antennas, and the transmission antenna group and the reception antenna group are symmetrical and non-symmetric. They are arranged in a line at equal intervals.

  In the radar apparatus, when the virtual correlation value acquisition unit acquires a virtual correlation value, a plurality of reception antennas included in the reception antenna group are caused to function as a virtual subarray. That is, the radar apparatus according to the present invention virtually treats the entire reception antenna group as a subarray in the spatial averaging process, and the actual reception antenna as in the case of the spatial averaging process in the prior art. The process of cutting out a part of the antenna group as a subarray is not performed. However, in order to apply spatial averaging processing, it is necessary to perform weighted averaging processing on the cross-correlation between the desired wave and the interference wave, so the subarrays are arranged so that the reception positions of some of the receiving antennas of the subarray overlap. Although it is necessary to move in parallel, if the entire group of reception antennas that exist as described above is a virtual subarray, the virtual subarray cannot be physically moved for spatial averaging.

Therefore, a transmission antenna switching technique for sequential transmission of transmission waves performed by the holographic synthesis technique is used. Even when the position of the reception antenna group does not change, the relative position of the transmission antenna with respect to the reception antenna group changes by switching transmission of the transmission wave by the transmission antenna. In other words, the parallel movement of the subarray when the spatial averaging process is applied can be realized without actually moving the reception antenna group. That is, there is a change in the relative position of the transmission antenna with respect to the reception antenna group due to transmission wave switching at the transmission antenna, which means that the reception antenna group moves relatively in parallel with respect to the transmission antenna. If some of the receiving antenna groups overlap during the movement, spatial averaging processing can be realized.

  Furthermore, in the above radar apparatus, the virtual correlation value acquisition means corresponds to the transmission antenna that has transmitted the transmission wave from the reception antenna group that is not actually moved in parallel by the transmission antenna being switched by the transmission switching means. As many virtual correlation values as the number of transmission antennas are obtained. This virtual correlation value is associated with each of the transmission antennas and, as described above, takes into account the change in the relative position of the transmission antenna with respect to the reception antenna group due to transmission wave switching at the transmission antenna. Thus, even from a received wave received by a receiving antenna group that is not actually translated, it can be derived and acquired as a correlation value corresponding to the correlation value in the spatial averaging process.

  Therefore, in the above radar apparatus, the transmission antenna group is included in the reception antenna group, and the transmission switching unit is configured to sequentially function a part or all of the reception antennas included in the reception antenna group as the transmission antenna. Then, the target detection unit performs a spatial averaging process on the virtual correlation value acquired by the virtual correlation value acquisition unit based on the relative position of the transmission antenna with respect to the associated reception antenna group. That is, it is assumed that the receiving antenna group is virtually moving from the change in the relative position caused by the sequential switching of the transmitting antenna, and the spatial averaging process is performed, and the weighted average of each virtual correlation value is applied. An average virtual correlation value is calculated and used for target detection.

  Note that the transmission antenna group and the reception antenna group are arranged in a line with unequal spacing and left-right symmetry. The transmission antenna group and the reception antenna group are arranged in a line symmetrically in a line means that the transmission antenna group and the reception antenna group are arranged in a line symmetrically in a line. As a result, the radar apparatus according to the present invention can prevent erroneous detection due to phase folding and suppress ghost detection. Further, along with transmission wave switching at the transmission antenna, at least one antenna of the reception antenna group is arranged at the same position, a part of the reception antenna group overlaps, and Forward-Backward spatial averaging (FBSS) is performed. It is possible. As a result, the radar apparatus according to the present invention can suppress the degree of cross-correlation. In addition, the radar apparatus according to the present invention can reduce the size of the radar apparatus by using a part of the reception antenna group also as the transmission antenna. Such spatial average processing in the radar apparatus according to the present invention is hereinafter referred to as “virtual space average processing”.

  In addition, the radar apparatus does not synthesize a plurality of received waves into one received wave based on the phase at the reference receiving antenna as in the holographic synthesis technique of the prior art. Since the transmission antenna is switched for this purpose, even if the target moves at the time of switching the transmission antenna, there is no influence of the phase shift caused thereby, and the target detection can be realized more accurately.

  Here, in the radar apparatus, the transmission antenna group and the reception antenna group may be formed separately, and at least the reception antenna group may be arranged in a line symmetrically and unequally spaced. With this configuration, it becomes easy to form a transmission antenna adapted to the transmission purpose of the transmission wave, for example, transmitting a stronger transmission wave.

  The radar apparatus according to the present invention directs a directional null to other incoming waves when directing the main lobe to a certain incoming wave, and arrives when no main lobe is directed to any incoming wave. The direction of arrival of the target can be estimated by the Capon method in which nulls are directed to all the waves.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the radar apparatus which can suppress the detection of a ghost and can also suppress the grade of a cross correlation.

The ghost detection situation in an array antenna when six antennas are installed at equal intervals is shown. It is the schematic which shows the space average process generally utilized when an antenna is installed at equal intervals. It is the schematic which shows the spatial average process generally utilized when the antenna is installed in unequal intervals. 1 is a schematic diagram illustrating a configuration of a radar apparatus according to a first embodiment. FIG. 3 is a schematic diagram illustrating virtual space averaging processing executed in the radar apparatus according to the first embodiment. 3 is a flowchart showing a flow of virtual space averaging processing executed by the radar apparatus according to the first embodiment. FIG. 6 is a diagram illustrating a calculation result of a target position based on a calculation result of an angle spectrum by performing a virtual space averaging process in the radar apparatus according to the first embodiment. FIG. 6 is a diagram illustrating an angular spectrum calculation result obtained by estimating a target arrival direction by the Capon method and a target position calculation result based on the calculation result in the radar apparatus according to the first embodiment. FIG. 7 is a diagram illustrating a calculation result of an angle spectrum obtained by estimating a direction of arrival of a target using DBF and a calculation result of a target position based on the calculation result in the radar apparatus according to the first embodiment. In the radar apparatus according to the first embodiment, two objects are stationary, and n (n = 1, 2, 3, 4, 5, 6) objects move at an equal speed and an equal frequency BIN. It is a figure which shows the calculation result of the target position based on the calculation result of an angle spectrum in the case of performing virtual space average process. In the radar apparatus according to the first embodiment, it is a diagram illustrating a calculation result of an angle spectrum when two objects are stationary and seven objects are moving at an equal speed and an equal frequency BIN. In the radar apparatus according to the first embodiment, when the same one-antenna transmission is averaged six times without performing virtual space averaging processing, two objects are stationary, and n (n = 1, 2, 3, It is a figure which shows the calculation result of the target position based on the calculation result of an angle spectrum in case the object of 4) moves by equal velocity and equal frequency BIN. In the radar apparatus according to the first embodiment, it is a diagram illustrating the calculation result of the target position based on the calculation result of the angle spectrum when the distance between the antennas is narrower as the antenna is installed on the outside. In the radar apparatus which concerns on the present Example 2, it is a figure which shows another arrangement | positioning form of a transmission / reception antenna.

  Hereinafter, embodiments of a radar apparatus according to the present embodiment will be described with reference to the drawings. The radar apparatus according to the present embodiment is mounted on a vehicle and can be used to detect targets around the vehicle such as other vehicles. The target detection result is output to an in-vehicle storage device, an ECU (Electrical Control Unit), or the like, and can be used for vehicle control or the like. However, the radar apparatus according to the present embodiment may be used for purposes other than the in-vehicle radar apparatus.

  FIG. 4 is a schematic diagram illustrating the configuration of the radar apparatus 1 according to the first embodiment. FIG. 5 is a schematic diagram illustrating virtual space averaging processing executed in the radar apparatus 1 according to the first embodiment. The radar apparatus 1 according to the first embodiment includes antennas ch1 to ch6, a distributor 19, a transmission unit 11, a reception unit 12, a preprocessing unit 14, a detection unit 15, and an output unit 16 having different antenna intervals, and includes a preprocessing unit. 14, the detection unit 15 and the output unit 16 form a control unit 13 of the radar apparatus 1. The control unit 13 can be realized by a computer, for example, and a general-purpose or dedicated processor can be used for each component such as the preprocessing unit 14, the detection unit 15, and the output unit 16. Further, a combination of a plurality of processors may be included in one configuration, or a single processor having multiple functions in a plurality of configurations may be used.

  The transmission unit 11 will be described. The transmission unit 11 controls switching of the transmission / reception state of each antenna so as to transmit a radar transmission wave using any one of the antennas ch1 to ch6 as a transmission antenna. In the radar apparatus 1 according to the first embodiment, any of the antennas ch1 to ch6 can be used for transmission. However, when implementing the radar apparatus 1 according to the present invention, a plurality of antennas in the array antenna are used. Of these, at least two or more antennas may be used as transmitting antennas. In the first embodiment, an FM-CW (Frequency Modulated Continuous Wave) radar transmission wave is used for radio waves transmitted and received by the radar apparatus 1. According to the FM-CW method, since the relative phase based on the target arrival direction estimation, the time delay due to the target distance, and the Doppler shift due to the target speed can be obtained from the reflected radio wave, the target arrival direction, distance, Relative speed can be measured.

  The receiving unit 12 will be described. The receiving unit 12 receives a reflected radio wave from the target using an antenna that is not transmitting a radar transmission wave among the antennas ch1 to ch6 as a reception antenna. The radar apparatus 1 according to the first embodiment switches the transmission antenna to the reception antenna in a time-sharing manner immediately after transmitting the radar transmission wave from the transmission antenna, and receives the reflected radio wave of the radar transmission wave transmitted by the own antenna. Is possible. For example, even when the antenna ch1 is used as a transmission antenna, the reflected radio wave of the radar transmission wave transmitted from the antenna ch1 can be obtained by switching the antenna ch1 to the reception mode immediately after transmission of the radar transmission wave from the antenna ch1. The antenna ch1 is also received. That is, in the first embodiment, even when each antenna is used as a transmission antenna, all six antennas ch1-ch6 are used as reception antennas. In addition, as a specific configuration of the reception unit 12, a dedicated reception circuit may be provided for each antenna, but a reception circuit that collectively receives reception signals from all reception antennas may be provided. In the latter case, control for sequentially switching the receiving antennas corresponding to the receiving circuit in time division is required, but the circuit configuration in the radar apparatus 1 can be made compact.

  In the first embodiment, the preprocessing unit 14, the detection unit 15, and the output unit 16 are realized by a computer as the control unit 13 executing a control program. The control unit 13 used here includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a CPU (Central Processing Unit) that controls the entire system by processing instructions and data expanded in the RAM, and the like. A computer having an EEPROM (Electrical Erasable and Programmable Read Only Memory) or the like in which various data used by the system such as various programs loaded on the computer and calculation results obtained by the target detection process are stored.

The control unit 13 will be described. The control unit 13 controls each component provided in the radar apparatus 1. Specifically, the control unit 13 switches the transmission / reception mode of each antenna by controlling the distributor 19 according to the transmission timing of the radar transmission wave and the reception timing of the reflected radio wave from the target. In the first embodiment, the transmission antenna receives the reflected radio wave of the radar transmission wave transmitted from the own antenna by switching the transmission mode and the reception mode at high speed in a time division manner.

  The preprocessing unit 14 will be described. The preprocessing unit 14 can suppress the correlation between the desired wave and the interference wave by so-called spatial averaging processing by performing virtual space averaging processing. Details of the operation of the preprocessing unit will be described later.

  The detection unit 15 will be described. The detection unit 15 calculates the estimated arrival direction, distance, and speed of the target by the Capon method based on the received signal subjected to the virtual space averaging process by the preprocessing unit 14. The Capon method directs a directional null to other incoming waves when directing the main lobe to one incoming wave, and directs nulls to all incoming waves when the main lobe is not directed to any incoming wave As a result, it is possible to suppress the beam of the antenna that has caused the phase folding. Further, the output unit 16 determines the target detection result (information including the estimated arrival direction, distance, and speed of the target) by the detection unit 15, and sends the determined detection result to an ECU or the like connected to the radar device 1. Output. In the first embodiment, since the output unit 16 outputs a highly accurate target detection result, the in-vehicle ECU can control the engine, the in-vehicle navigation device, and the like based on the highly accurate target detection result. Become.

  Here, based on FIG. 5, the principle of the virtual space averaging process executed by the preprocessing unit 14 of the radar apparatus 1 will be described. The virtual space averaging process is a target detection pre-process for accurately detecting a target by suppressing the degree of cross-correlation between a desired wave and an interference wave in target detection. As shown in FIG. 4, in the radar device 1 in which the virtual space averaging process is executed, six antennas ch1 to ch6 that are physically present function as a transmission antenna and a reception antenna. Therefore, in the radar apparatus 1, the antennas ch1 to ch6 are a reception antenna group and a transmission antenna group according to the present invention. Here, the antenna shown in FIG. 5 is given an antenna number together with “#”. The antenna number with the # symbol corresponds to a virtual antenna different from the actual antenna.

  The antennas ch1-ch6 are arranged in a line symmetrically and unequally spaced. Specifically, as shown in FIG. 4, the distance between the antennas ch1 and ch2 and between the antennas ch5 and ch6 is 2.8λ. The distance between the antennas ch2-ch3 and the antenna ch4-ch5 is 2.2λ. The distance between the antennas ch3 and ch4 is 1.8λ. That is, the antennas ch1-ch6 are arranged at unequal intervals, and are further arranged symmetrically about the antenna ch3-ch4. In the radar apparatus 1 according to the first embodiment, six antennas are installed in a line, but the number is not limited to six.

  Here, when the virtual space averaging process executed by the radar apparatus 1 is performed, the antenna ch1 functions as a transmission antenna and the antennas ch1-ch6 function as reception antennas. Therefore, the antenna ch1 functions as a transmission / reception antenna. The reception signal received by the reception antenna group at this time corresponds to the transmission wave from the antenna ch1, and is referred to as a first reception signal. Similarly, the received signal received by the receiving antenna group when the antenna ch2 functions as a transmitting antenna is the second received signal, and the received signal received by the receiving antenna group when the antenna ch3 functions as the transmitting antenna is the first received signal. Three received signals and a received signal received by the receiving antenna group when the antenna ch4 functions as a transmitting antenna are referred to as a fourth received signal.

Thus, when the transmission antenna is sequentially switched from antenna ch1 to ch4,
Considering the received signals (first received signal to fourth received signal) received by the receiving antenna group, each received signal is received by the same receiving antenna group, that is, the actual receiving antennas ch1-ch6. However, if it is assumed that the transmission antennas are transmitted from the same transmission antenna with the position of the transmission antenna overlapped in one place, each received signal has a moving distance when the transmission antenna is sequentially switched and the position moves. This is equivalent to the signal received by the virtual receiving antenna group moved by the amount. In other words, even when the receiving antenna group is not actually moving, by sequentially switching the transmitting antenna, it is possible to virtually form a configuration that receives the reflected wave from the target by moving the receiving antenna group. It is possible. Therefore, the virtual space averaging process according to the first embodiment performs the space averaging process using the movement of the virtual reception antenna group.

  Therefore, in the virtual space averaging process described above, as shown in FIGS. 4 and 5, the reception antenna group sequentially moves by the transmission movement distance of the transmission antenna (the same value as the interval of each antenna) in correspondence with the switching of the transmission antenna. It becomes possible to handle it virtually. A group of reception antennas treated as virtually moving is referred to as a virtual subarray, and the number of the transmission antenna that has transmitted the transmission wave is assigned to each virtual subarray as a reference number. For example, a virtual reception antenna group that has received the first reception signal when the antenna ch1 functions as a transmission antenna is referred to as a virtual subarray 1 and receives the fourth reception signal when the antenna ch4 functions as a transmission antenna. The virtual receiving antenna group is referred to as a virtual subarray 4 (see FIG. 5). In this case, since the distance between the antennas ch1 and ch2 is 2.8λ (see FIG. 4), the virtual subarray 2 is located at a position moved by a distance 2.8λ with respect to the virtual subarray 1. Furthermore, since the antennas ch1 to ch6 are not evenly spaced and arranged symmetrically, one antenna in the virtual subarray 2 overlaps with one antenna in the virtual subarray 1 at the position of the virtual antenna # 6. However, the three antennas in the virtual sub-array 2 do not overlap with the three antennas in the virtual sub-array 1 at the positions of the virtual antennas # 3- # 5 (see FIG. 5). Further, the remaining one antenna of the virtual sub-array 2 is a virtual seventh virtual antenna # 7. In addition, since the spacing between the antennas ch2-ch3 is 2.2λ (see FIG. 4), the virtual subarray 3 moves by a distance 2.2λ with respect to the virtual subarray 2, and the spacing between the antennas ch3-ch4 is 1.. Since it is 8λ (see FIG. 4), the virtual subarray 4 moves relative to the virtual subarray 3 by a distance of 1.8λ. The virtual sub-array 3 and the virtual sub-array 4 have an overlapping relationship at the position of the virtual antenna # 6 included in a part thereof. The sixth antenna of the virtual subarray 1 is the virtual reception antenna # 6, the sixth antenna of the virtual subarray 2 is the virtual reception antenna # 7, the sixth antenna of the virtual subarray 3 is the virtual reception antenna # 8, and the virtual subarray 4 The sixth antenna becomes the virtual reception antenna # 9. Therefore, in the virtual space averaging process, the radar apparatus 1 actually has only six antennas ch1 to ch6, but six of the virtual nine antennas # 1 to # 9 are partially included. Can be used as a virtual sub-array.

  As described above, the direction-of-arrival estimation according to the first embodiment is such that even if the antennas ch1 to ch6 are unequally spaced, the antennas ch1 to ch6 are arranged in a line in a symmetrical manner, so that each virtual subarray has one virtual subarray. It becomes a relationship which overlaps at the position of the antenna, and it is possible to perform the spatial averaging process by the Forward-Backward spatial averaging method (FBSS). It should be noted that the spatial averaging process is not uniform as compared with the case where the antennas ch1 to ch6 are not evenly spaced, and the effect of suppressing the degree of cross-correlation can be sufficiently expected. Furthermore, in the laser apparatus 1 according to the first embodiment, the antennas ch1 to ch6 are arranged in a line at unequal intervals, so that it is possible to prevent erroneous detection due to phase folding and suppress detection of ghosts. .

Further, when performing the spatial averaging process, the wider the sub-array movement range, the more significant the suppression effect of the degree of cross-correlation between the desired wave and the interference wave by the process. Therefore, in the radar apparatus 1 according to the first embodiment, as illustrated in FIG. 5, it is possible to further increase the virtual subarray by sequentially transmitting the antennas ch5 and ch6 (the increased virtual subarray is illustrated in FIG. 5). Middle, indicated by dotted lines). Therefore, it is possible to enjoy the effect of the spatial averaging process more effectively without increasing the size of the radar apparatus 1.

  As described above, the radar apparatus 1 according to the first embodiment switches the transmission antenna in order to execute the virtual space averaging process. Therefore, FIG. 6 shows a specific processing flow for virtual space averaging processing executed in the radar apparatus 1 and target detection based on the processing. The target detection process illustrated in FIG. 6 is executed by the control unit 13 that executes the control program after the radar apparatus 1 is started, particularly the virtual space averaging process, by the preprocessing unit 14. Note that the processing start timing may be in accordance with a target detection request by a computer or ECU connected to the outside of the radar device 1. Further, the processing order shown in each drawing is an example, and the processing order may be appropriately rearranged according to the embodiment.

  In S101, as shown in FIG. 5, the signal reception by the virtual subarray is performed by sequentially switching the transmission antennas. That is, as described above, even though the actual reception antenna group does not move, the transmission antenna is switched, and the relative position between the transmission antenna and the reception antenna group is shifted. Thus, a state in which the reception antenna group is moving is created, and a reception state by the virtual subarray is formed. In the first embodiment, the reception result by the virtual subarray 1-4 is obtained by sequentially functioning the antennas ch1 to ch4 as transmission antennas in accordance with FIG. Note that the received signal by the virtual subarray is simply referred to as a virtual subarray signal. When the process of S101 ends, the process proceeds to S102.

  In S102, a virtual correlation value for each virtual subarray is acquired based on each virtual subarray signal obtained in S101. The virtual correlation value is a correlation value in the virtual space average process, and is physically the same quality as the correlation value in the conventional space average process, and therefore the specific calculation is simply kept. That is, in S102, the correlation value for the spatial averaging process is calculated based on the received signal received by the virtual subarray that is considered to exist virtually by switching the transmission antenna.

従って、仮想サブアレーｎの仮想相関値である相関行列は、以下の式で表される。

Ｓ１０２の処理が終了すると、Ｓ１０３へ進む。 Specifically, the input vector Xn (t) of the virtual subarray n is expressed by the following equation.

Therefore, the correlation matrix that is the virtual correlation value of the virtual sub-array n is expressed by the following equation.

When the process of S102 ends, the process proceeds to S103.

In S103, the virtual correlation values for each virtual subarray calculated in S102 are based on the relative positions of the transmitting antenna and the receiving antenna group that are sequentially switched, that is, as shown in FIG. Based on the fact that the state is moved at each switching, spatial averaging processing is performed by FBSS to suppress the degree of cross-correlation between the desired wave and the interference wave. Even if the antennas ch1 to ch6 are unequally spaced, the antennas ch1 to ch6 are arranged in a line symmetrically in the left-right direction, so that each virtual subarray overlaps at the position of one virtual antenna. Averaging can be performed. S
Since the spatial average processing itself for suppressing cross-correlation performed in 103 is substantially the same as the conventional spatial average processing, its description is omitted. When the process of S103 ends, the process proceeds to S104.

  In S104, the estimated arrival direction of the target is calculated by the detection unit 15 using the Capon method based on the results of the virtual space averaging process executed in S101 to S103. Since the technique for calculating the target arrival direction based on the relative phase of the reflected radio waves received by the array antenna is a conventional technique, a detailed description thereof is omitted. Further, since the radar apparatus 1 according to the first embodiment transmits the radar transmission wave by the FM-CW method, the time delay of the received radio wave due to the distance of the target and the Doppler shift due to the speed of the target, The distance and speed can also be calculated. The target detection result obtained in S104 is output to the ECU or the like connected to the radar apparatus 1 by the output unit 16. Thereafter, by repeating the processing from S101 to S104, the radar apparatus 1 according to the first embodiment periodically detects the target and outputs the detection result to the ECU or the like.

  The target detection result by the target detection control will be described with reference to FIGS. First, the case where six antennas are installed at unequal intervals and the case where six antennas are installed at equal intervals are compared. A case where six antennas are installed at unequal intervals will be described. FIG. 7 shows the calculation result of the target position based on the calculation result of the angle spectrum by installing six antennas at unequal intervals, performing the virtual space averaging process, estimating the arrival direction of the target by the Capon method. As shown in FIG. 7, the calculation result of the target position when six antennas are installed at unequal intervals is FOV = 16.12 degrees when the distance between the antennas is 1.8λ which is the minimum distance. A ghost is not detected even at an outside position, and the object position can be specified. The six antennas installed at unequal intervals are symmetrical as shown in FIG.

  Next, a case where six antennas are installed at equal intervals will be described. As shown in FIG. 1, the calculation result of the target position when six antennas are installed at equal intervals is such that phase wrapping occurs at a position where the target is beyond the angular range where the target can be detected according to the antenna interval. Is detected.

  As described above, the radar apparatus 1 according to the first embodiment can prevent erroneous detection due to phase folding and suppress detection of ghosts when antennas are installed at unequal intervals.

  Next, the case where the arrival direction estimation of the target is performed by the Capon method and the case where the arrival direction estimation of the target is performed by DBF (Digital Beam Forming) are compared. Note that DBF is a method that performs not only amplitude / phase control but also calculation of directivity by digital signal processing. First, the case where the direction of arrival of the target is estimated by the Capon method will be described. The left side of FIG. 8A is an angular spectrum calculation result obtained by installing six antennas at unequal intervals, performing a virtual space averaging process, and estimating the arrival direction of the target by the Capon method. The right side of FIG. It is the calculation result of the target position based on a calculation result. As shown on the right side of FIG. 8A, when the direction of arrival of the target is estimated by the Capon method, the ghost is not detected, and the object position can be specified. Note that the six antennas installed at unequal intervals are symmetrical.

Next, a case where the direction of arrival of the target is estimated by DBF will be described. The left side of FIG. 8B is an angular spectrum calculation result obtained by installing six antennas at unequal intervals, performing virtual space averaging processing, and estimating the arrival direction of the target by DBF, and the right side of FIG. It is the calculation result of the target position based on a result. As shown on the right side of FIG. 8B, when the direction of arrival of the target is estimated by DBF, phase wrapping occurs and a ghost is detected. Even when DBF is used, the object position can be normally specified when the FOV is within ± 10 degrees. Note that the six antennas installed at unequal intervals are symmetrical.

  As described above, when estimating the arrival direction of the target, the radar apparatus 1 according to the first embodiment prevents erroneous detection due to phase wrapping and suppresses detection of ghosts when the Capon method is used. Can be estimated.

  Next, the case where the virtual space averaging process is performed is compared with the case where the same one-antenna transmission is averaged six times without performing the virtual space averaging process. First, the case where the virtual space averaging process is performed will be described. In this case, the distance between antennas ch1-ch2 and between antennas ch5-ch6 is 2.9λ, the distance between antennas ch2-ch3 and between antennas ch4-ch5 is 2.3λ, and between antennas ch3-ch4 Six antennas are installed at unequal intervals so that the distance is 1.8λ, two objects are stationary, and n (n = 1, 2, 3, 4, 5, 6) objects are A target position is calculated based on the calculation result of the angular spectrum when moving at an equal speed and an equal frequency BIN and performing a virtual space averaging process. Note that the six antennas installed at unequal intervals are symmetrical. (1) in FIG. 9 shows that when two objects are stationary and one object moves at a constant speed, the virtual space averaging process is performed, the direction of arrival of the target is estimated by the Capon method, and the angle spectrum It is the calculation result of the target position based on a calculation result. 9 (2) to 9 (6) show a Capon method in which virtual space averaging processing is performed when two objects are stationary and two to six objects move at a constant speed, respectively. The target arrival direction is estimated by the above, and the target position is calculated based on the angular spectrum calculation result. As shown in FIG. 9 (6), when two objects are stationary and six objects are moving at the same speed and the same frequency BIN, the calculation limit is exceeded. FIG. 10 shows calculation results of the angle spectrum when two objects are stationary and seven objects are moving at the same speed and the same frequency BIN. As shown in FIGS. 9 (1) to 9 (3), when two objects are stationary and one to three objects are moving at the same speed and equal frequency BIN, It is possible to prevent erroneous detection due to aliasing, suppress detection of ghosts, and estimate the direction of arrival of the target. As shown in FIG. 10, when the number of objects exceeding the calculation limit moves at a constant speed and a constant frequency BIN, there is almost no amplitude difference and the spectrum value becomes large.

  Next, a case where the same one-antenna transmission is averaged six times without performing the virtual space averaging process will be described. FIG. 11 shows that when the same one-antenna transmission is averaged six times without performing virtual space averaging processing, two objects are stationary, and n (n = 1, 2, 3, 4) objects are equal. The calculation result of the target position based on the calculation result of the angle spectrum when moving at the speed and the equal frequency BIN is shown. (1) in FIG. 11 shows the calculation result of the target position based on the calculation result of the angle spectrum without performing the virtual space averaging process when two objects are stationary and the one object moves at a constant speed. It is. 11 (2) to FIG. 11 (4) show that when two objects are stationary and two to four objects move at a constant speed, the virtual space averaging process is not performed and the angle is It is the calculation result of the target position based on the calculation result of a spectrum. As shown in (1) and (2) of FIG. 11, when two objects are stationary and up to two objects are moving at the same speed and equal frequency BIN, detection of ghost is suppressed, The direction of arrival of the target can be estimated. However, as shown in (3) and (4) of FIG. 11, when two objects are stationary and three or more objects move at the same speed and the same frequency BIN, the objects should be detected. It is impossible to identify the object position. This indicates that the degree of cross-correlation cannot be suppressed.

  As described above, when performing the virtual space averaging process, the radar device 1 according to the first embodiment prevents erroneous detection due to phase wrapping, suppresses ghost detection, and estimates the arrival directions of a large number of targets. Is possible.

  Next, when six antennas are installed at unequal intervals and symmetrically, when the distance between the antennas is wider as the antennas are installed outside, and when the distance between the antennas is narrower as the antennas are installed outside. Compare First, the case where the distance between the antennas is greater as the antenna is installed on the outside will be described. In this case, the distance between antennas ch1-ch2 and between antennas ch5-ch6 is 2.9λ, the distance between antennas ch2-ch3 and between antennas ch4-ch5 is 2.3λ, and between antennas ch3-ch4 Six antennas are installed at unequal intervals and symmetrically so that the distance becomes 1.8λ. FIG. 7 shows the calculation result of the target position based on the calculation result of the angle spectrum by performing the virtual space averaging process, estimating the arrival direction of the target by the Capon method when six antennas are installed as described above. .

  Next, the case where the distance between the antennas is shorter as the antenna is installed on the outside will be described. In this case, the distance between the antennas ch1 and ch2 and between the antennas ch5 and ch6 is 1.8λ, the distance between the antennas ch2 and ch3, and between the antennas ch4 and ch5 is 2.3λ, and between the antennas ch3 and ch4. Six antennas are installed at unequal intervals and symmetrically so that the distance becomes 2.9λ. FIG. 12 shows the calculation result of the target position based on the calculation result of the angle spectrum by performing the virtual space averaging process and estimating the arrival direction of the target by the Capon method when six antennas are installed as described above. .

  As shown in FIG. 7 and FIG. 12, the distance between the antennas is the smallest when the distance between the antennas is larger as the antennas are installed on the outside and the distance between the antennas is narrower as the antennas are installed on the outside. Even at a position outside FOV = 16.12 degrees when 1.8λ is, the ghost is not detected, and the object position can be specified. In this case, there is no other object in the equal frequency BIN. When there are three or more objects in the equal frequency BIN, it is considered that a ghost is detected by using three types of antenna intervals. Also, when the distance between the antennas is larger for the antennas installed on the outside, the targets arranged side by side are separated farther than when the distance between the antennas is narrower for the antennas installed on the outside. It is possible to obtain a high angular separation performance that can be detected.

  A radar apparatus 1 according to Embodiment 2 of the present invention will be described. The antenna in the radar apparatus 1 shown in FIG. 4 has a configuration in which a part or all of the reception antenna group also functions as a transmission antenna. Here, as shown in FIG. 13, the reception antenna group and the transmission antenna group may have different configurations. The receiving antenna is provided with six antennas at unequal intervals and symmetrically, and the transmitting antennas are provided at equal intervals. The virtual space averaging process is performed based on the relationship between the relative positions of the transmission antenna group and the reception antenna group, and virtual reception that is considered to have virtually moved when the transmission antennas are sequentially switched. If the antenna groups overlap with each other in part, they can function as the above-described virtual subarray. Also, by setting the transmission antenna interval in a manner not constrained by the reception antenna interval, it becomes easy to form a transmission wave antenna adapted to the transmission purpose of the transmission wave, such as transmitting a stronger transmission wave.

DESCRIPTION OF SYMBOLS 1 ... Radar apparatus 11 ... Transmission part 12 ... Reception part 13 ... Control part 14 ... Pre-processing part 15 ... Detection part 16 ... Output part 19 ... Distributor ch1 -Ch6 ... antenna # 1- # 11 ... virtual receiving antenna

Claims (4)

A transmission antenna group having a plurality of transmission antennas;
A receiving antenna group having a plurality of receiving antennas;
Transmission switching means for sequentially switching and transmitting transmission waves from each transmission antenna of the transmission antenna group;
When transmission waves are sequentially transmitted by the transmission switching unit, the transmission antenna of each transmission antenna is reflected by a target and the reception antenna group that receives the reflected wave is defined as a virtual antenna corresponding to the transmission antenna. A virtual correlation value acquisition unit that functions as a virtual subarray and acquires a correlation value in a spatial averaging process corresponding to the virtual subarray as a virtual correlation value, corresponding to the number of transmission antennas that have transmitted transmission waves;
Relative position of each of the transmission antennas whose transmission has been switched by the transmission switching unit with respect to the virtual correlation values corresponding to the plurality of virtual subarrays acquired by the virtual correlation value acquisition unit with respect to the reception antenna group To calculate an average virtual correlation value corresponding to a virtual antenna group that is virtually derived from the reception antenna group by transmission switching of the transmission switching means, and performing the average virtual correlation value And target detection means for detecting the target based on
The transmitting antenna group is included in the receiving antenna group,
The transmission switching means sequentially causes some or all of the reception antennas included in the reception antenna group to function as transmission antennas,
The transmitting antenna group and the receiving antenna group are arranged in a line with left-right symmetry and unequal intervals.
Radar device. A transmission antenna group having a plurality of transmission antennas;
A receiving antenna group having a plurality of receiving antennas;
Transmission switching means for sequentially switching and transmitting transmission waves from each transmission antenna of the transmission antenna group;
When transmission waves are sequentially transmitted by the transmission switching unit, the transmission antenna of each transmission antenna is reflected by a target and the reception antenna group that receives the reflected wave is defined as a virtual antenna corresponding to the transmission antenna. A virtual correlation value acquisition unit that functions as a virtual subarray and acquires a correlation value in a spatial averaging process corresponding to the virtual subarray as a virtual correlation value, corresponding to the number of transmission antennas that have transmitted transmission waves;
Relative position of each of the transmission antennas whose transmission has been switched by the transmission switching unit with respect to the virtual correlation values corresponding to the plurality of virtual subarrays acquired by the virtual correlation value acquisition unit with respect to the reception antenna group To calculate an average virtual correlation value corresponding to a virtual antenna group that is virtually derived from the reception antenna group by transmission switching of the transmission switching means, and performing the average virtual correlation value And target detection means for detecting the target based on
The transmitting antenna group and the receiving antenna group are formed separately,
At least the receiving antenna group is arranged in a line symmetrically and unequally spaced,
Radar device. The spatial averaging process is performed by a Forward-Backward spatial averaging method.
The radar apparatus according to claim 1 or 2. The direction of arrival estimation of the target is performed by the Capon method.
The radar device according to any one of claims 1 to 3.

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