JP2012202955A - Holographic radar - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that when a target is moving, difference in a total path length difference occurs and holographic synthesis cannot be performed.SOLUTION: The holographic radar has: a transmission part (S) for transmitting first and second transmission waves; a reception part (R) for receiving first and second reflection waves; a transmission wave control unit (50) for controlling first and second transmission antenna to change a transmission cycle which is a time interval from transmission of the first transmission wave to transmission of the second transmission wave so as to transmit the first and second transmission waves a plurality of times; and an azimuth operation part (11) which, on the basis of a relative speed of targets included in respective frequency peaks obtained according to detection situations of reflection waves from the target when the transmission waves are transmitted a plurality of times, selects a transmission cycle of an optimal transmission time interval from the relative speed difference when there are a plurality of targets, synthesizes the first and the second reflection waves when the first and second transmission waves are transmitted in the selected transmission cycle, and detects the target.

Description

  The present invention relates to a holographic radar, and more particularly to a holographic radar that detects a plurality of targets.

  A holographic radar is known as a radar that is mounted on a vehicle and detects other vehicles traveling in front of the vehicle. In holographic radar, the measurement accuracy can be increased by increasing the number of receiving antennas. However, when applied to in-vehicle devices, etc., a plurality of transmitting antennas and receiving antennas are arranged substantially for miniaturization. A configuration equivalent to that having a plurality of receiving antennas has been reported (for example, Patent Document 1). As shown in FIG. 1, such a conventional holographic radar transmits a radio wave by sequentially switching a plurality of transmission antennas 101 to 103, and a plurality of reflected waves from a target of the radio wave transmitted from each transmission antenna. Are received by the receiving antennas 104 and 105.

  The transmission antennas 101 to 103 of the conventional holographic radar 100 shown in FIG. 1 are connected to an oscillator 110 that oscillates and outputs a high-frequency signal and a transmission-side switch 114 that outputs one input and three switching outputs via a distributor 112. By switching the switch 114, the high-frequency signal output from the oscillator 110 is supplied to the transmission antennas 101 to 103 in a time division manner.

  On the other hand, the receiving antennas 104 and 105 are connected to a receiving side switch 116 having 1 input and 2 switching output. By switching the switch 116, the reception signals obtained by the two reception antennas 104 and 105 are supplied to the mixer 118 in a time division manner.

  A part of the transmission high-frequency signal from the distributor 112 is supplied to the mixer 118, and an A / D converter 120 is connected to the mixer 118. The beat signal supplied from the mixer 118 is converted into a digital signal. The signal processing circuit 122 connected to the A / D converter 120 performs data processing on the beat signal and obtains desired information such as the distance to the target, the relative speed, and the angle.

  In the conventional holographic radar, the three transmitting antennas 101 to 103 are switched, and the receiving antennas 104 and 105 are switched corresponding to each transmitting antenna, so that the relationship between the transmitting antenna and the receiving antenna pair is in six positional relationships. Data equivalent to the arrangement can be obtained.

  Here, a holographic synthesis method for synthesizing received signals by switching a plurality of transmission antennas and a plurality of reception antennas constituting the holographic radar will be described with reference to the drawings. The holographic synthesis method is a method of virtually increasing the number of reception antennas by arranging transmission antennas in consideration of radio wave paths. FIG. 2 shows a configuration diagram of a transmission antenna and a reception antenna constituting the holographic radar. FIG. 2A shows two transmission antennas Tx1 and Tx2 arranged at an interval 3d and four reception antennas Rx1 to Rx4 arranged at an interval d. By performing holographic synthesis, as shown in FIG. 2B, data equivalent to the arrangement of one receiving antenna Tx1 and seven receiving antennas Rx1 to Rx7 can be obtained. Such a configuration is equivalent to a radar having a total of eight antennas consisting of one transmission antenna and seven reception antennas using a total of six antennas consisting of two transmission antennas and four reception antennas. Data can be obtained and the radar apparatus can be miniaturized. By virtually increasing the number of receiving antennas, the number of targets that can be separated, the separation performance, and the angle accuracy of the target position can be improved.

  Next, a holographic synthesis method will be described with reference to FIG. FIGS. 3A and 3B show an example in which two transmitting antennas and four receiving antennas are arranged. FIG. 3A shows a state in which radio waves are transmitted from the transmission antenna Tx1, and FIG. 3B shows a state in which radio waves are transmitted from the transmission antenna Tx2. First, as shown in FIG. 3A, the radio wave 212 is transmitted from the transmission antenna Tx1 in the direction of the arrow 211, and the reflected waves 213 to 216 from the target are received by the reception antennas Rx1 to Rx4. Next, as shown in FIG. 3B, the radio wave 219 is transmitted from the transmission antenna Tx2 in the direction of the arrow 218, which is the same direction as the arrow 211, and the reflected waves 220 to 223 from the target are received by the reception antennas Rx1 to Rx4. Receive at. Here, it is assumed that the target is stationary.

  Here, the path length difference of the radio wave in each receiving antenna in the case of FIG. 3 (a), (b) is shown to FIG. 3 (c), (d), respectively. As shown in FIG. 3C, if the path length difference per antenna interval d is α, the path length differences of the receiving antennas Rx1 to Rx4 when radio waves are transmitted from the transmitting antenna Tx1 are all 0α. On the other hand, since the distances between the receiving antennas with respect to the transmitting antenna Tx1 are 4d, 5d, 6d, and 7d, respectively, the path length differences at the time of reception are 4α, 5α, and 6α in consideration of the equiphase plane 217. 7α. Here, if the distance from the receiving antennas Rx1 to Rx4 to the target is r, the total path length differences of the receiving antennas Rx1 to Rx4 are 2r + 4α, 2r + 5α, 2r + 6α, and 2r + 7α, respectively.

  On the other hand, as shown in FIG. 3D, the path length difference between the receiving antennas Rx1 to Rx4 when radio waves are transmitted from the transmitting antenna Tx2 is all 3α because the distance between the transmitting antennas Tx1 and Tx2 is 3d. It is. Further, since the distances between the receiving antennas with respect to the transmitting antenna Tx1 are 4d, 5d, 6d, and 7d, respectively, the path length differences at the time of reception are 4α, 5α, and 6α in consideration of the equiphase plane 224, respectively. 7α. Here, if the distance from the receiving antennas Rx1 to Rx4 to the target is r, the total path length differences of the receiving antennas Rx1 to Rx4 are 2r + 7α, 2r + 8α, 2r + 9α, and 2r + 10α, respectively.

  Here, the total path length difference of the reflected wave received by the receiving antenna Rx4 when the radio wave is transmitted from the transmitting antenna Tx1, and the total path length of the reflected wave received by the receiving antenna Rx1 when the radio wave is transmitted from the transmitting antenna Tx2. Since both the differences are 2r + 7α, if the magnitudes of the total path length differences are arranged in ascending order, the total path length differences can be arranged so as to increase by α from (2r + 4α) to (2r + 10α).

  On the other hand, as shown in FIG. 4A, the total path length difference when seven receiving antennas Rx1 to Rx7 having a distance d are arranged at a distance from one transmitting antenna Tx1 and the distance 4d is shown in FIG. Thus, the total path length difference is arranged so as to increase by α from (2r + 4α) to (2r + 10α). This is because, as shown in FIGS. 3A and 3B, the reception data of the radar comprising the two transmission antennas Tx1 and Tx2 and the four reception antennas Rx1 to Rx4 is transmitted as one transmission as shown in FIG. It shows that the antenna Tx1 and the received data of the radar in which the seven receiving antennas Rx1 to Rx7 are arranged match. In this way, the number of reception antennas can be virtually increased by switching the transmission antennas.

  In the above description, it is assumed that the target is stationary. Next, a method of holographic synthesis when the target is moving will be described with reference to FIG. FIGS. 5A to 5D correspond to FIGS. 3A to 3D, and FIG. 5 considers that the target is moving. When radio waves are transmitted by switching the transmission antennas Tx1 and Tx2, radio waves from Tx1 and Tx2 are not transmitted at the same time, and radio waves are transmitted from Tx2 after a predetermined time t from transmission by Tx1. Therefore, it is assumed that the target moves toward the radar by a distance s during time t. FIG. 5C shows the total path length difference when radio waves are transmitted from the transmission antenna Tx1. This is the same as that shown in FIG. FIG. 5D shows the total path length difference when radio waves are transmitted from the transmission antenna Tx2. Since the target approaches the radar side by the distance s during the time t, the distance from the radar to the target is 2r-2s. Therefore, the total path length differences in the receiving antennas Rx1 to Rx4 are (2r-2s + 7α), (2r-2s + 8α), (2r-2s + 9α), and (2r-2s + 10α), respectively.

  Here, when only the total path length difference when radio waves are transmitted from the transmitting antennas Tx1 and Tx2 is arranged in the order of the receiving antennas Rx1 to Rx4, it is as shown in FIG. To simplify the explanation, FIG. 6 shows the total path length difference when the radio wave transmitted from the transmitting antenna Tx1 is received by the receiving antenna Rx1 (“Tx1 → Rx1”), where the total path length difference is 0α. ("Tx1 → Rx1 standard total path length difference") is also shown.

  As described above, in order to perform holographic synthesis, the total path length differences in a plurality of receiving antennas must be arranged at equal intervals. In particular, the reception data of the reflected wave from the target transmitted from the transmitting antenna Tx1 and received by the receiving antenna Rx4 and the reception of the reflected wave of the target transmitted from the transmitting antenna Tx2 and received by the receiving antenna Rx1 The total path length difference of data needs to match. However, when the target is moving, a time t is required for switching between the transmission antennas Tx1 and Tx2, and a difference 2s due to the movement of the target occurs in the total path length difference. However, even if the target is moving, if there is only one target at the frequency peak, holographic synthesis can be established without any problem by simple phase offset correction. However, when there are a plurality of targets present at the frequency peak and the relative velocities of the targets are different from each other, the value of the deviation 2s due to the movement of each target is different, so that the phase offset cannot be corrected and holographic Combining is no longer possible.

  Here, for example, even if two targets exist at the same frequency peak and the shift due to the movement of the target of the total path length difference is 2 s and 2 s ′, respectively, this changes the phase of the received signal. Otherwise, holographic synthesis can be performed. That is, when the wavelength of the transmission wave is λ, no problem arises if (2s−2s ′) = nλ (n is an integer) is satisfied. Further, if the absolute value of the differential movement distance (2s-2s ′) of the target is about λ / 12 (within ± 60 ° in terms of angle), a large error occurs in the target angle estimation. Experience has shown that there is no.

  Here, since the magnitudes of the movement distances s and s ′ vary depending on the transmission period of the radio wave to be transmitted and the movement speed of the target, the allowable movement distance range depends on the transmission period. FIG. 7 shows a temporal change in the frequency of a radio wave to be transmitted in an FM-CW radar. Waveforms 35 and 36 respectively show the waveform of the up period and the waveform of the down period of the radio wave transmitted from the transmission antenna Tx1. Similarly, waveforms 37 and 38 respectively indicate a waveform during an up period and a waveform during a down period of the radio wave transmitted from the transmission antenna Tx2. Since the waveforms 35 and 37 are used in the holographic synthesis, the distance that the target moves during the time interval T between them is s and s'.

Here, the relationship between the relative speed difference and the phase difference between the two targets when the difference moving distance (2s-2s ′) using the moving distances s and s ′ of the target is converted into a phase difference indicates a transmission frequency of 266 Hz. A plot of this case is shown in FIG. In FIG. 8, a similar straight line appears with a period of 360 °. If the phase difference is φ, holographic synthesis is possible within the range of −60 ° ≦ φ ≦ 60 °, but the relative speed difference between two targets that satisfy such conditions is 0 to 0.33 [km / The speed V _{11 of} h], the speed V ₁₂ of 1.67 to 2.33 [km / h], the speed V _{13 of} 3.67 to 4.33 [km / h], and discontinuous values. For example, when the relative speed difference is 3 [km / h], the phase difference is −180 ° and holographic synthesis is not established.

JP 2000-155171 A

  As described above, when there are multiple targets at one frequency peak and there is a relative speed difference, the target is from the time of transmission of radio waves from the transmitting antenna Tx1 to the time of transmission of radio waves from Tx2. Since the distances traveled differed, there was a difference in the total path length difference, resulting in a problem that holographic synthesis was not possible. Furthermore, even if a certain allowable range is set for the total path length difference caused by the movement of the target, the allowable range may be exceeded depending on the magnitude of the relative speed difference, and holographic synthesis cannot be performed. There was a problem.

  The holographic radar according to the present invention includes: a transmission unit that transmits a first transmission wave from a first transmission antenna to a target, and transmits a second transmission wave from the second transmission antenna to the target; A first reflected wave that is a reflected wave from the target of the first transmission wave, and a second reflected wave that is a reflected wave from the target of the second transmission wave, using a plurality of receiving antennas; And a plurality of first transmission waves and second transmission waves by changing a transmission cycle that is a time interval from transmission of the first transmission wave to transmission of the second transmission wave. Transmission wave control unit for controlling the first transmission antenna and the second transmission antenna so as to transmit twice, and the detection status so far, that is, the detection status of the reflected wave from the target when the transmission wave is transmitted a plurality of times The relative speed of the target contained in each frequency peak is calculated from the A transmission cycle of the most suitable transmission time interval is selected from the speed difference, and the first reflected wave and the second reflected wave are transmitted when the first transmission wave and the second transmission wave are transmitted in the selected transmission period. And an azimuth calculation unit for detecting a target.

  The holographic radar according to the present invention has an advantage that even if a plurality of targets are moving at different speeds, the possibility that holographic synthesis is realized can be increased.

It is a block diagram of the conventional holographic radar. It is a block diagram of the transmitting antenna and receiving antenna which comprise a holographic radar. It is explanatory drawing of the holographic synthesis method. It is explanatory drawing of the holographic synthesis method. It is explanatory drawing of the holographic synthesis method in case a target moves. It is a table | surface which shows the total path length difference in the holographic synthesis in case the target moves. FIG. 6 is a waveform diagram of a transmission wave in an FM-CW radar. It is a figure which shows the relationship between a relative speed difference and a phase difference in case a transmission frequency is 266 Hz. It is a block diagram of the holographic radar of this invention. It is the figure which showed the time dependence of the frequency of the transmission wave and reception wave in the radar of FM-CW system, and the figure which showed the time dependence of the beat signal which is a difference signal of a transmission wave and a reception wave. It is the figure which showed the frequency spectrum of UP side and DOWN side, and the figure which shows the angle spectrum obtained based on the peak information in a frequency spectrum. It is a flowchart of the operating method of the holographic radar of Example 1 of this invention. It is a figure which shows the relationship between a relative speed difference in case a transmission frequency is 450 Hz, and a phase difference. It is a figure which shows the relationship between the relative speed difference and phase difference in case transmission frequency is 650Hz. It is a wave form chart of a transmission wave at the time of changing a transmission cycle. It is a flowchart of the operating method of the holographic radar which concerns on Example 2 of this invention. It is a wave form chart of a transmission wave at the time of changing transmission timing.

  Hereinafter, a holographic radar according to the present invention will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 9 shows a configuration diagram of the holographic radar according to the first embodiment of the present invention. The transmission unit S includes an oscillator 5 and a signal generation unit 15 that generate a transmission signal that is an FM-CW wave. A target (not shown) is sent from the first transmission antenna 1a using the generated transmission signal. The first transmission wave 2a is transmitted to the target, and the second transmission wave 2b is transmitted from the second transmission antenna 1b to the target. Switching of radio wave transmission between the first transmission antenna 1a and the second transmission antenna 1b is performed by a switch SW. The switch SW is controlled by a switching signal output from the transmission wave control unit 50 at a cycle T (see FIG. 7). The first reflected waves 4a, 4b,..., 4n, which are reflected waves from the target of the first transmission wave 2a, and the second reflection, which is a reflected wave from the target of the second transmission wave 2b. The waves 4a, 4b,..., 4n are received by the receiving antenna group 3 including the receiving antennas 3a, 3b,. For example, as shown in FIG. 10A, the first transmission antenna 1a and the second transmission antenna 1b are switched for each period of the triangular wave output from the signal generation unit 15, and the first transmission wave 2a and the second transmission wave 2 Are transmitted alternately.

  A signal received by the receiving antenna group 3 is input to the receiving unit R. The receiving unit R includes mixers 7a, 7b,..., 7n, and A / D converters 8a, 8b,. The mixers 7a, 7b,..., 7n mix the reception signal from the reception antenna group 3 with the transmission signal from the oscillator 5, and generate a beat signal that is a difference signal between the transmission signal and the reception signal. The A / D converters 8 a, 8 b,..., 8 n convert the beat signals from the mixers 7 a, 7 b,.

  The signal processing unit 10 includes a fast Fourier transform (FFT) circuit 9, an azimuth calculation unit 11, and a distance / relative speed calculation unit 12. The digital received signal of each receiving antenna supplied to the FFT circuit 9 is subjected to frequency analysis by FFT processing, that is, fast Fourier transform, for each receiving antenna and for each of the UP and DOWN sections of the triangular wave. The frequency spectrum of UP side and DOWN side as shown in b) is obtained. Since the reflected waves of the same target are received for the other receiving antennas, the shape of the frequency spectrum and the peak frequency are the same as those in FIGS. 11A and 11B on both the UP side and the DOWN side. A frequency spectrum with the same power value at the position is obtained. However, since the phase of the reflected wave of the target differs depending on the receiving antenna, the phase information of the peaks located at the same frequency between the receiving antennas is different.

Each peak information obtained by the FFT circuit 9 for each receiving antenna, that is, information such as frequency, power, and phase is supplied to the azimuth calculation unit 11. Normally, each peak shown in FIGS. 11A and 11B includes information on a plurality of targets. The azimuth calculation unit 11 performs synthesis using the holographic synthesis method of the present invention, and then estimates the angle by separating the target from the frequency peak information using a maximum likelihood estimation method, a MUSIC (Multiple Signal Classification) method, or the like. To do. That is, holographic synthesis is performed based on n pieces of peak information having the same frequency in each frequency spectrum obtained from each receiving antenna, and an angle spectrum as shown in FIG. 11C is calculated by a predetermined angle estimation method. Ask. Then, the angle of the peak above a predetermined level in the angle spectrum is calculated as the angle of the target, and the target information (angle and power in the angle spectrum and peak frequency in the frequency spectrum) is supplied to the distance / relative speed calculator 12. FIG. 11C shows that there are two targets located at angles θ ₁ and θ _{2 in} the down-side peak Pd ₁ . In FIG. 11C, the angle spectrum of the UP side peak corresponding to the angle spectrum of the down side peak Pd1 is displayed in an overlapping manner.

  In this embodiment, frequency peak information for two periods obtained for the continuous first transmission wave 2a and second transmission wave 2b shown in FIG. 10A is used as frequency peak information used for angle estimation. Then, the angle of the target is estimated by the holographic synthesis method described with reference to FIGS.

  Through the above processing, each of the UP-side and DOWN-side frequency peaks is separated into one or a plurality of targets and output to the distance / relative speed calculation unit 12 as target information having an angle, power, and frequency.

  The distance / relative speed calculation unit 12 performs pairing between the target information on the UP side and the target information on the DOWN side, and those that are close in angle and power, and the distance and speed of the target from the UP frequency and the DOWN frequency are The angle of the target is obtained from the average value of the UP side angle and the DOWN side angle, and is output as target target information.

  The transmission wave control unit 50 changes the transmission cycle, which is the time interval from when the first transmission wave is transmitted to when the second transmission wave is transmitted, to generate a plurality of first transmission waves and second transmission waves. A transmission wave control signal for controlling the first transmission antenna and the second transmission antenna is output so as to transmit twice. For example, the first transmission frequency is 266 Hz, the second transmission frequency is 450 Hz, and the third transmission frequency is 650 Hz. The transmission wave control unit 50 transmits continuously while switching these three types of transmission frequencies.

  The azimuth calculation unit 11 calculates the relative velocity of the target included in each frequency peak obtained from the detection status so far, that is, the detection status of the reflected wave from the target when the transmission wave was transmitted a plurality of times in the previous time. When there are a plurality of targets at one frequency peak, the most suitable transmission period of the transmission time interval is selected from the relative speed difference. For example, as a result of calculating a phase error occurring at each transmission frequency based on the calculated relative speed difference, the absolute value of the phase difference when transmitted at a transmission frequency of 266 Hz is 75 ° and transmitted at a transmission frequency of 450 Hz. If the absolute value of the phase difference is 30 ° and the absolute value of the phase difference is 130 ° when transmitting at a transmission frequency of 650 Hz, the transmission frequency of 450 Hz with the smallest phase difference is selected. To do.

  The azimuth calculation unit 11 combines the first reflected wave and the second reflected wave when the first transmission wave and the second transmission wave are transmitted in the selected transmission cycle, and uses the holographic synthesis method described above. Detects the target.

  Next, an operation method of the holographic radar of the present invention will be described using the flowchart of FIG. FIG. 12 shows processing performed by the azimuth calculation unit 11. This process is performed for each peak frequency shown in FIG. First, in step S101, the relative speed of the target obtained by the previous corresponding frequency peak (selecting the previous frequency peak closest to the current peak frequency) with respect to the current frequency peak for which the angle is estimated is calculated as the distance · Read from the relative speed calculator 12. In other words, the relative velocity of the target included in each frequency peak is obtained from the detection status thus far, that is, the detection status of the reflected wave from the target when the transmission wave is transmitted a plurality of times.

  The reason why the data of the target calculated last time is used in this calculation is that there is almost no difference in the relative speed of the target between the previous time and this time. In this calculation, angle estimation may be performed without using the holographic synthesis method, and the relative velocity of the target may be obtained by pairing.

In step S102, it is determined whether or not there is a plurality of targets at the previous one frequency peak. If there are a plurality of targets, the relative speed difference is calculated in step S103. In the case of a single unit, it is not necessary to select a transmission frequency, and therefore, for example, a transmission frequency of 266 Hz may be selected in step S108. Next, in step S104, based on the characteristics indicating the relationship between the relative speed difference and the phase difference when radio waves are transmitted from the first transmission antenna 1a and the second transmission antenna 1b toward the target at a transmission frequency of 266 Hz. In addition, the difference moving distance is calculated from the relative speed difference calculated in step S103 and converted into a phase difference. FIG. 15 shows waveforms of radio waves transmitted from the first and second transmission antennas. The period transmitted at the transmission frequency 266 Hz is a period indicated by 61, and is transmitted from the up-chirp signal 61a, the down-chirp signal 61b, and the second transmission antenna 1b of the radio wave transmitted from the first transmission antenna 1a. It consists of an up-chirp signal 61c and a down-chirp signal 61d. First transmitting antenna 1a and the time interval T ₁₁ the transmission of the radio wave of the second transmitting antenna 1b corresponds to the inverse of the transmission frequency 266Hz. FIG. 8 shows the relationship between the relative speed difference and the phase difference when the transmission frequency is 266 Hz. Data representing the characteristics shown in FIG. 8 is stored in advance in a memory (not shown). The range of phase difference φ capable of holographic synthesis is empirically -60 ° ≦ φ ≦ 60 °, but the relative speed difference satisfying such conditions is 0 to 0.33 [km / h]. V ₁₁ takes a discontinuous value with a speed V ₁₂ of 1.67 to 2.33 [km / h], a speed V _{13 of} 3.67 to 4.33 [km / h].

Next, in step S105, based on the characteristic indicating the relationship between the relative speed difference and the phase difference when radio waves are transmitted from the first transmission antenna 1a and the second transmission antenna 1b toward the target at a transmission frequency of 450 Hz. In addition, the difference moving distance is calculated from the relative speed difference calculated in step S103 and converted into a phase difference. FIG. 15 shows waveforms of radio waves transmitted from the first and second transmission antennas. The period transmitted at a transmission frequency of 450 Hz is a period indicated by 62, and is transmitted from the up-chirp signal 62a, the down-chirp signal 62b, and the second transmission antenna 1b of the radio wave transmitted from the first transmission antenna 1a. The radio wave is composed of an up-chirp signal 62c and a down-chirp signal 62d. Telecommunications time interval T ₁₂ the transmissions from the first transmitting antenna 1a and the second transmit antenna 1b corresponds to the inverse of the transmission frequency 450 Hz. FIG. 13 shows the relationship between the relative speed difference and the phase difference when the transmission frequency is 450 Hz. Data representing the characteristics shown in FIG. 13 is stored in advance in a memory (not shown). The range of phase difference φ capable of holographic synthesis is empirically a range of −60 ° ≦ φ ≦ 60 °, but the relative speed difference satisfying such conditions is a speed of 0 to 0.67 [km / h]. V ₂₁ takes a discontinuous value with a speed V ₂₂ of 3.33 to 4.67 [km / h], a speed V _{23 of} 7.33 to 8.67 [km / h].

Next, in step S106, based on the characteristics indicating the relationship between the relative speed difference and the phase difference when radio waves are transmitted from the first transmission antenna 1a and the second transmission antenna 1b toward the target at a transmission frequency of 650 Hz. Then, the difference moving distance is calculated from the relative speed difference and converted into a phase difference. FIG. 15 shows waveforms of radio waves transmitted from the first and second transmission antennas. The period transmitted at the transmission frequency of 650 Hz is a period indicated by 63, and is transmitted from the up-chirp signal 63a, down-chirp signal 63b, and second transmission antenna 1b of the radio wave transmitted from the first transmission antenna 1a. It consists of an up-chirp signal 63c and a down-chirp signal 63d. First transmitting antenna 1a and the second radio time interval T ₁₃ the transmission from the transmitting antenna 1b of corresponds to the inverse of the transmission frequency 650 Hz. FIG. 14 shows the relationship between the relative speed difference and the phase difference when the transmission frequency is 650 Hz. Data representing the characteristics shown in FIG. 14 is stored in advance in a memory (not shown). The range of the phase difference φ that can be holographically synthesized is empirically a range of −60 ° ≦ φ ≦ 60 °, but the relative speed difference that satisfies such a condition is a speed of 0 to 1.0 [km / h]. V ₃₁ takes a discontinuous value with a speed V ₃₂ of 5.0 to 7.0 [km / h], a speed V _{23 of} 7.33 to 8.67 [km / h].

  Next, in step S107, the transmission frequency that minimizes the magnitude of the absolute value of the phase difference is determined. For example, a case will be described in which two targets exist at a frequency peak for which angle estimation is to be performed and the relative speed difference is 11 [km / h]. First, it is examined whether or not the received data when transmitted at a transmission period of 266 Hz can be used for holographic synthesis. As can be seen from FIG. 8, the phase difference at the relative speed difference 11 [km / h] is 180 ° (or −180 °). When transmission is performed at a transmission period of 450 Hz, the relative speed difference 11 [ The phase difference at km / h] is 90 °, and when transmission is performed at a transmission period of 650 Hz, referring to FIG. 14, the phase difference at relative speed difference 11 [km / h] is 60 °. Data when transmission is performed at a transmission period of 650 Hz with a value of 60 ° or less is determined as data to be used for holographic synthesis. When there are a plurality of data whose absolute value of phase difference is 60 ° or less (or −60 ° or more), the data closer to 0 ° is adopted.

  Next, in step S109, holographic synthesis is performed using data received at a transmission frequency of 650 Hz, and angle estimation processing is performed by a method similar to the conventional method.

  According to the present invention, radio waves are transmitted by changing the transmission frequency to 266 Hz, 450 Hz, and 650 Hz, so if the allowable range of the absolute value of the phase difference capable of holographic synthesis is 60 ° or less, the whole The holographic synthesis can be performed in the range of 76.7% of the relative speed difference, and the range in which the holographic synthesis can be performed can be increased by 42% compared to the case of 266 Hz alone.

  In the present embodiment, an example is shown in which radio waves are transmitted by changing the transmission frequency three times. However, the number of transmissions is not limited to three, and may be two or four or more. Further, in the present embodiment, an example in which the transmission frequency is changed to 266, 450, and 650 Hz is shown, but the value of the frequency is not limited to these.

  In the present embodiment, the transmission wave control unit 50 transmits the first transmission wave and the second transmission wave a plurality of times by changing the frequencies of the first transmission wave and the second transmission wave. In the above example, the first transmission antenna and the second transmission antenna are controlled. However, the transmission wave control unit 50 moves the frequencies of the first transmission wave and the second transmission wave at different speeds. You may make it determine with the relative speed difference of a mark. For example, when transmitting at a transmission frequency of 266 Hz, it is assumed that the relative speed difference between the two targets is 11 [km / h]. In this case, as can be seen from FIG. 8, the phase difference φ is 180 ° at 266 Hz, and does not fall within the range of −60 ° ≦ φ ≦ 60 ° where holographic synthesis is possible. Next, considering transmission at a transmission frequency of 450 Hz, the phase difference φ at the relative speed difference of 11 [km / h] is 90 ° from FIG. 13, and holographic synthesis is still impossible. Next, considering transmission at a transmission frequency of 650 Hz, the phase difference φ at the relative speed difference of 11 [km / h] is 60 ° from FIG. 14, and −60 ° ≦ φ ≦ 60 ° that allows holographic synthesis. It can be seen that holographic synthesis is possible. In this way, when the relative speed difference between a plurality of targets is known, the transmission frequency may be determined from the relative speed difference.

Next, an operation method of the holographic radar according to the second embodiment of the present invention will be described with reference to the flowchart of FIG. This embodiment is characterized in that radio waves are transmitted by changing the transmission timing instead of changing the transmission frequency. Also in the second embodiment, steps S101 and S103 in FIG. 12 are the same, and the processing in FIG. 16 is executed after step S103. First, in step S201, a characteristic indicating a relationship between a relative speed difference and a phase difference when radio waves are transmitted from the first transmission antenna 1a and the second transmission antenna 1b toward the target at the first transmission timing. Based on the relative speed difference, the difference moving distance is calculated and converted into a phase difference. FIG. 17 shows waveforms of radio waves transmitted from the first and second transmission antennas. The period transmitted at the first transmission timing is a period indicated by 71, and is transmitted from the up-chirp signal 71a, down-chirp signal 71b, and second transmission antenna 1b of the radio wave transmitted from the first transmission antenna 1a. Radio wave up chirp signal 71c and down chirp signal 71d. Time interval of a radio wave transmission of the first transmitting antenna 1a and the second transmitting antenna 1b is T _21. Here, the frequency obtained from the inverse of the T ₂₁ is assumed to be 650 Hz, the relationship between the relative speed difference and the phase difference becomes similar to the waveform of FIG. 14, conditions -60 ° holographic synthesis possible phase difference φ The relative speed difference satisfying ≦ φ ≦ 60 ° is a speed V _{31 of} 0 to 1.0 [km / h], a speed V ₃₂ of 5.0 to 7.0 [km / h], and a speed V _{33 of} 7.33 to 8.67 [km / h]. ... and discontinuous values.

Next, in step S202, the characteristic indicating the relationship between the relative speed difference and the phase difference when radio waves are transmitted from the first transmission antenna 1a and the second transmission antenna 1b toward the target at the second transmission timing. Based on the above, the difference moving distance is calculated from the relative speed difference and converted into a phase difference. FIG. 17 shows waveforms of radio waves transmitted from the first and second transmission antennas. The period transmitted at the second transmission timing is a period indicated by 72, and is transmitted from the up-chirp signal 72a, down-chirp signal 72b, and second transmission antenna 1b of the radio wave transmitted from the first transmission antenna 1a. Radio wave up chirp signal 72c and down chirp signal 72d. Time interval of a radio wave transmission of the first transmitting antenna 1a and the second transmitting antenna 1b is T _22. Here, the waveform 72a~72d is similar to waveform 71a~71d in Example 1, by providing a period 72e not to transmit radio waves, and has a T _22> T _21. Here, the frequency obtained from the inverse of the T ₂₂ is assumed to be 450 Hz, the relationship between the relative speed difference and the phase difference becomes similar to the waveform of FIG. 13, conditions -60 ° holographic synthesis possible phase difference φ The relative speed difference satisfying ≦ φ ≦ 60 ° is a speed V ₂₁ of 0 to 0.67 [km / h], a speed V ₂₂ of 3.33 to 4.67 [km / h], and a speed V _{23 of} 7.33 to 8.67 [km / h]. ... and discontinuous values.

Next, in step S203, the characteristics indicating the relationship between the relative speed difference and the phase difference when radio waves are transmitted from the first transmission antenna 1a and the second transmission antenna 1b toward the target at the third transmission timing. Based on the above, the difference moving distance is calculated from the relative speed difference and converted into a phase difference. FIG. 17 shows waveforms of radio waves transmitted from the first and second transmission antennas. The period transmitted at the third transmission timing is a period indicated by 73, and is transmitted from the up-chirp signal 73a, down-chirp signal 73b, and second transmission antenna 1b of the radio wave transmitted from the first transmission antenna 1a. Radio wave up chirp signal 73c and down chirp signal 73d. Time interval of a radio wave transmission of the first transmitting antenna 1a and the second transmitting antenna 1b is T _23. Here, the waveform 73a~73d is similar to waveform 71a~71d in Example 1, by providing a period 73e not to transmit radio waves, and has a T _23> T _21. Here, the frequency obtained from the inverse of the T ₂₃ is assumed to be 266Hz, the relationship between the relative speed difference and the phase difference becomes similar to the waveform of FIG. 8, the conditions -60 ° holographic synthesis possible phase difference φ The relative speed difference satisfying ≦ φ ≦ 60 ° is a speed V ₁₁ of 0 to 0.33 [km / h], a speed V ₁₂ of 1.67 to 2.33 [km / h], and a speed V _{13 of} 3.67 to 4.33 [km / h]. ... and discontinuous values.

  Next, in step S204, the transmission frequency that minimizes the magnitude of the absolute value of the phase difference is determined. For example, the case where the relative speed difference of the target is 11 [km / h] will be described. First, it is examined whether or not the received data transmitted at the first transmission timing can be adopted for holographic synthesis. When transmitted at the first transmission timing, the phase difference at the relative speed difference 11 [km / h] is 60 ° from FIG. 14, and when transmitted at the second transmission timing, the relative speed difference 11 from FIG. The phase difference at [km / h] is 90 °, and when transmitted at the third transmission timing, the phase difference at relative speed difference 11 [km / h] is 180 ° (or −180 °) from FIG. Yes, data transmitted at the first transmission timing at which the phase difference is minimized is determined as data to be used for holographic synthesis.

  Next, in step S205, holographic synthesis is performed using data received at the first transmission timing, and angle estimation processing is performed by a method similar to the conventional method.

  According to the present invention, since the transmission timing is changed in three ways and radio waves are transmitted, compared with the case where the transmission timing is not changed, by performing holographic synthesis in a wide range of relative speed differences, The probability that detection can be performed accurately can be increased.

  In the present embodiment, an example in which transmission is performed while changing the transmission timing three times has been described, but the number of times of changing the transmission timing is not limited to three, and may be two or four or more.

  In the present embodiment, the transmission wave control unit 50 transmits the first transmission wave and the second transmission wave a plurality of times by changing the transmission timing of the first transmission wave and the second transmission wave. In this example, the first transmission antenna and the second transmission antenna are controlled as described above, but the transmission wave control unit 50 moves the transmission timings of the first transmission wave and the second transmission wave at different speeds. It may be determined by the relative speed difference between a plurality of targets. For example, when transmitting at the first transmission timing (corresponding to a transmission frequency of 650 Hz), it is assumed that the relative speed difference between the two targets is 10 [km / h]. In this case, as can be seen from FIG. 14, the phase difference φ is 120 ° and does not fall within the range of −60 ° ≦ φ ≦ 60 ° where holographic synthesis is possible. Next, considering transmission at the second transmission timing (corresponding to a transmission frequency of 450 Hz), the phase difference φ at a relative speed difference of 10 [km / h] is 180 ° from FIG. . Next, considering transmission at the third transmission timing (corresponding to a transmission frequency of 266 Hz), the phase difference φ at the relative speed difference of 10 [km / h] is 0 ° from FIG. 8, and holographic synthesis is possible. It can be seen that holographic synthesis is possible within the range of −60 ° ≦ φ ≦ 60 °. In this way, when the relative speed difference between a plurality of targets is known, the transmission timing may be determined from the relative speed difference.

DESCRIPTION OF SYMBOLS 1a 1st transmission antenna 1b 2nd transmission antenna 2a 1st transmission wave 2b 2nd transmission wave 3 Reception antenna group 3a, 3b, ..., 3n Reception antenna 4a, 4b, ..., 4n Reflection wave 5 Oscillators 7 a, 7 b,..., 7 n Mixers 8 a, 8 b,..., 8 n A / D converter 9 FFT circuit 10 Signal processor 11 Direction calculator 12 Distance / relative speed calculator 15 Signal generator 50 Transmission Wave controller S Transmitter R Receiver

Claims (5)

A transmission unit that transmits a first transmission wave to a target from a first transmission antenna and transmits a second transmission wave to the target from a second transmission antenna;
Using a plurality of receiving antennas, a first reflected wave that is a reflected wave from the target of the first transmitted wave and a second reflected wave that is a reflected wave from the target of the second transmitted wave A receiver for receiving the reflected wave;
The first transmission wave and the second transmission wave are transmitted a plurality of times by changing a transmission cycle, which is a time interval from the transmission of the first transmission wave to the transmission of the second transmission wave. A transmission wave control unit for controlling the first transmission antenna and the second transmission antenna,
Based on the relative speed of the target included in each frequency peak obtained from the detection status of the reflected wave from the target when the transmission wave is transmitted a plurality of times, the relative speed when the target is plural A transmission cycle having the most suitable transmission time interval is selected from the difference, and the first reflected wave and the second reflected wave are transmitted when the first transmission wave and the second transmission wave are transmitted in the selected transmission period. Azimuth calculation unit for detecting the target by combining
A holographic radar comprising:   The holographic radar according to claim 1, wherein the transmission wave control unit changes the transmission cycle by changing frequencies of the first transmission wave and the second transmission wave.   The holographic radar according to claim 1, wherein the transmission wave control unit changes the transmission cycle by changing a transmission timing of the first transmission wave and the second transmission wave.   The holographic radar according to claim 1, wherein the transmission wave control unit determines the frequencies of the first transmission wave and the second transmission wave based on a relative speed difference between a plurality of targets moving at different speeds.   2. The holographic device according to claim 1, wherein the transmission wave control unit determines a transmission timing of the first transmission wave and the second transmission wave based on a relative speed difference between a plurality of targets moving at different speeds. Radar.

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