JP3865761B2 - Radar equipment - Google Patents

Description

  The present invention relates to a radar apparatus that measures at least a direction in which a target object exists using signals received by a plurality of element antennas.

  Conventionally, various types of radar devices for detecting a target are known. Among them, a holographic radar device having a plurality of receiving antennas is known. In this holographic radar device, a target direction is usually obtained by monopulse angle measurement using two adjacent beams.

FIG. 7 shows a holographic radar device of Patent Document 1. The transmission unit 1 includes an oscillator 1a and a transmitter 1b. A transmission signal obtained by the oscillator 1a is supplied to the transmission antenna 2 via the transmitter 1b, and a radio wave of a predetermined frequency is transmitted from the transmission antenna 2 to the front of the vehicle. To be emitted. The reflected wave reflected by the target 3 is received by the array antenna 4 composed of n element antennas A _{# 1 to} A _#n . This array antenna 4, n pieces of being connected to the receiving unit 5 composed of individual reception unit RM # ₁ ~RM _#n, the reception wave from the antenna elements A _{# 1} to A _#n corresponding Signal processing is performed by the individual receivers RM _{# 1 to} RM _#n . The individual receivers RM _{# 1 to} RM _#n respectively obtain a difference signal between the transmission signal and the reflected signal by mixing the reception signal from the low noise amplifier 5a for amplifying the received wave and the amplified signal with the transmission signal from the oscillator 1b. It comprises a synthesizer 5b and an A / D converter 5c that converts an analog difference signal from the synthesizer 5b into a digital signal.

In each of the individual receiving units RM _{# 1 to} RM _#n , the demodulated digital signal is supplied to FFTs 6-1 to 6-n that perform frequency analysis by fast Fourier transform, and all the processing results are digital multi-beam forming means. 7 is supplied. The multi-beam forming unit 7 forms a multi-beam to the target 3, and the multi-beam angle measuring unit 8 detects the angle of the target 3 for each multi-beam.

JP-A-63-186176

  Here, the multi-beam angle measuring means in FIG. 7 performs monopulse angle measurement continuously in a plurality of directions, and the basic principle is the monopulse angle measurement method.

  This monopulse angle measurement is an effective method in terms of calculation speed and accuracy for a radar apparatus that detects a single target angle. However, when there are a plurality of targets in the same beam, the detection angle error of the target is large and the detection accuracy is deteriorated.

  The monopulse angle measurement includes a phase monopulse method and an amplitude monopulse method. In phase monopulse angle measurement, two beams having the same beam direction are used, and the arrival direction of the radio wave is detected from the phase difference. On the other hand, in the amplitude monopulse, two beams having different beam directions are used, and the radio wave arrival direction is estimated from the ratio of the amplitude sum and the difference.

  Therefore, when there are two targets in the same beam, the received wave is a composite of the reflected waves from the two targets, and these are separated to detect the correct direction for each of the two targets. It was difficult to do.

  For example, in an in-vehicle radar, there are two or more preceding vehicles when traveling on a road with multiple lanes, and reflected waves from each of them often arrive. In such a case, there was a problem that correct target detection could not be performed in monopulse angle measurement.

  An object of the present invention is to solve the above-described problems and to obtain an angle in a target direction efficiently with a small angle detection error in a situation where a plurality of targets exist in the same beam.

The radar apparatus according to the present invention uses a signal received by a plurality of element antennas to form a multi-beam forming means for forming a multi-beam, and a peak for detecting a reception level peak after the multi-beam forming by the multi -beam forming means. A high-resolution angle measurement process that performs a high-resolution angle measurement process by applying a maximum likelihood estimation method to the detection means and the azimuth around the reception level detected by the peak detection means for the received signal. And a matrix from the relationship between the reception signals X1 to Xn (n is a natural number) of the plurality of element antennas and the complex amplitude information S1 to Sm (m is a natural number) from the plurality of element antennas. Using the expressed X = AS, the combination max [tr [A (A ^H A) ^{−1 of the} received wave arrival directions θ1 to θm that minimizes the error between the actual measurement value and the theoretical value. A ( A ^H XX ^H ]], A (A ^H A) ⁻¹ A ^H is tabulated in advance, and angle measurement processing is performed with high resolution using the table.

  In this way, since the high-resolution processing calculation is performed on the received signal using the peak detection result after multi-beam formation, the high-resolution processing calculation can be limited to the periphery of the peak. Therefore, it is possible to reduce the amount of high resolution processing calculation and perform efficient target detection with high resolution. Note that, as the high-resolution processing calculation, a maximum likelihood estimation method, a MUSIC method, or the like is preferable.

  Further, monopulse calculation is performed on the received signal to form a Σ signal and a Δ signal, and a monopulse angle measuring unit that detects a target direction from the obtained Σ signal and Δ signal, and an angle calculated by the monopulse angle measuring unit It is preferable to further comprise selection means for determining the target number of presence from the error result and selecting whether or not to use the high-resolution angle measuring means based on the determination result. Thus, monopulse angle measurement can be used when high-resolution processing calculation is not required. That is, by selecting a high resolution processing means when there are a plurality of target existence numbers, it is possible to reduce the amount of calculation and perform efficient target angle detection.

  As described above, according to the present invention, the high resolution processing operation is performed on the received signal using the detection result of the peak detecting means. Accordingly, high-resolution processing can be efficiently performed, and a plurality of targets in one beam can be efficiently separated.

  Further, the high resolution processing means can perform the high resolution processing more efficiently by performing the high resolution processing only in the vicinity of the peak detected by the peak detecting means.

  In addition, by performing high resolution processing by the maximum likelihood estimation method with a limited processing range, highly accurate angle measurement can be performed while suppressing a calculation load.

  In addition, monopulse calculation is performed on the received signal to form a Σ signal and a Δ signal, and a monopulse angle measuring unit that detects a target direction from the obtained Σ signal and Δ signal, and an angle calculated by the monopulse angle measuring unit Selecting a target presence number from the error result, and selecting means for selecting whether or not to use the high-resolution angle measuring means based on the determination result. Means can be used, and efficient target direction detection can be performed.

  The selection means selects the angle measurement result of the monopulse angle measurement means when the target existence number determined by the monopulse angle measurement means is 1, and selects the high resolution processing means when the target existence number is plural. Thus, when there is only one target, the direction of the target can be detected with a simple calculation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 shows the configuration of the first embodiment of the present invention. The transmission unit 11 includes an oscillator 11a and a transmitter 11b, and a transmission signal (an FMCW wave whose frequency increases and decreases at a predetermined repetition frequency) obtained by the oscillator 11a is output via the transmitter 11b. In this embodiment, the FMCW method is used, and the oscillator 11a generates a transmission signal having a transmission frequency fRF that is frequency-modulated at a constant repetition period. The transmission signal is amplified by the transmitter 11b, and then transmitted to the transmission antenna 12, and is emitted toward the target from here. The radar apparatus according to this embodiment is mounted on a vehicle and radiates toward the front of the vehicle.

Target 13 in front of the transmitting antenna 12 (in this example, two target 1 and target 2) is present, constituting a reflected wave reflected by the target 13 from the n antenna elements A _{# 1} to A _#n Received by the array antenna 14. The array antenna 14, n-number of which is connected to the configured receiver unit 15 from the individual reception unit RM # ₁ ~RM _#n, the reception wave from the antenna elements A _{# 1} to A _#n corresponding Signal processing is performed by the individual receivers RM _{# 1 to} RM _#n . The individual receivers RM _{# 1 to} RM _#n each have a low noise amplifier 15a that amplifies the received wave, and a beat signal that is a difference signal between the transmission signal and the reflected signal by mixing the amplified signal with the transmission signal from the oscillator 11b. Synthesizer 15b and A / D converter 15c for converting the beat signal from synthesizer 15b into a digital received signal.

In each of the individual receiving units RM _{# 1 to} RM _#n , the obtained beat signal is converted into digital signals X _{1 to} X _n by the A / D converter 15c. Digital signal X ₁ to X _n from the A / D converter 15c is supplied to FFT16-1~16-n, wherein the frequency analysis by fast Fourier transform is performed.

  Here, this embodiment is an FMCW radar device, and when the target 13 is moving, the Doppler frequency appears in the reflected signal. In addition, when linear chirp frequency modulation generally performed in FM-CW radar is applied, a frequency corresponding to a distance delay is included in addition to the Doppler frequency. That is, as shown by a solid line in FIG. 2A, the transmission signal repeats a period in which the frequency increases linearly (up chirp) and a period in which the frequency decreases (down chirp). Then, as shown by a broken line in FIG. 2A, the reflected signal is shifted in frequency by the Doppler frequency depending on the relative speed and delayed according to the relative distance, as compared with the transmission signal.

  Accordingly, the frequency difference (beat signal) between the transmission signal and the reflected signal is fb1 in the up chirp period and fb2 in the down chirp period. That is, a signal in which the Doppler frequency is superimposed on the frequency difference based on the delay time is obtained. In the case of FIG. 2A, the reflected signal has a higher frequency than the transmission signal, and indicates the relative speed in the direction in which the relative distance decreases (the approach direction).

  Then, in the FFTs 16-1 to 16-n, beat signals as shown in FIG. 2B are obtained. Therefore, this signal is supplied to the distance / velocity calculating means 30, where the target distance and speed are determined by the principle of FM-CW radar.

Here, in this embodiment, the digital signals X ₁ , X ₂ ,... X _n regarding the frequency components of the beat signals from the FFTs 16-1 to 16-n are supplied to the target signal extraction unit 17. The target signal extraction unit 17 extracts a complex data of the frequency fb1, fb2 signal is the peak of the beat signal for each antenna element A _{# 1} ~A _#n. Then, the obtained complex data (X _{1 to} X _n ) of the frequency fb 1 or fb 2 is collected for the number of element antennas and supplied to the multi-beam forming means 18 and the high resolution processor 19.

  Multi-beam forming means 18 directs a plurality of antenna beams in all directions. That is, assuming that only one radio wave arrives with two antennas, the distance between the two antennas is d, the arrival direction of the received wave with respect to the direction perpendicular to the line connecting the two antennas is θ, and the wavelength of the received wave is λ. In this case, as shown in FIG. 3, the phase difference φ between the received signals obtained by both antennas is φ = (2π / λ) dsin (θ). Therefore, assuming that the amplitude of the received wave at a certain point in time at the first antenna is A (t), the amplitude at the second antenna at the same point is A (t) exp [j (2π / λ) dsin (θ). ].

Accordingly, if each element antenna A _{# 1} is used as a reference and the distance between each element antenna A _{# 2 to} A _#n is id (the distance between all elements is d), each element antenna A _{# 2 to} A _#n Is A (t) exp [j (2π / λ) (1-i) dsin (θ)].

If radio waves arrive from two directions of arrival directions θ1 and θ2, and the amplitude at antenna A _{# 1} is A (t) and B (t), the amplitude at element antenna A _{# 2} at the same point is A (t) exp amplitude at [j (2π / λ) dsin (θ)], B (t) exp [j (2π / λ) dsin (θ)] , and the antenna elements A _#n is, A (t) exp [J (2π / λ) ndsin (θ)], B (t) exp [j (2π / λ) ndsin (θ)].

The actual received signals X _{1 to} X _n of the element antennas A _{# 1 to} A _#n are obtained by adding noise to these reflected waves.

Therefore, the multi-beam forming means multiplies the received signals X _{1 to} X _n by exp [−j (2π / λ) (i−1) dsinψ] while sequentially changing this ψ as the beam direction ψ. , Output sequentially.

  The output of the multi-beam forming means 18 is supplied to the peak detecting means 20. The peak detecting means 20 arranges the outputs of the multi-beam forming means 18 in the angular direction and detects a maximum point. That is, when the beam direction ψ coincides with the reception wave arrival directions θ1 and θ2, the exponent term of exp becomes 0 in calculation and the amplitude is output as it is.

  The peak detection means 20 supplies the direction to the high resolution processor 19 when the local maximum point is found.

  The high-resolution processor 19 assumes the arrival direction of the target at several points on the left and right of the maximum point, and uses the maximum likelihood estimation method, the MUSIC (Multiple Signal Classification) method, and the like to generate reflected waves from multiple targets at a high resolution. Perform the separation process.

When the maximum likelihood estimation method is used, the calculation is performed as follows. For example, it is assumed that there are m received waves, the distance between the element antennas is d, and the received signals of the element antennas are X _{1 to} X _n . In this case, if the complex amplitude information from each element antenna obtained by FFT is S _{1 to} S _m , each received signal is expressed as follows.

These are expressed in matrix as follows.

となるようなθ₁〜θ_mの組合せを求めればよい。 Thus, the combination of all conceivable theta ₁ through? _M, by obtaining a combination of the measured values and the error epsilon ² is minimized theta ₁ through? _M of theory, the resulting, separated for a plurality of incoming waves Can be detected. That is,

What is necessary is just to obtain | require the combination of (theta) _{1- (} theta) _m which becomes.

となる。従って、楕円で囲ったＡ（Ａ^HＡ）−¹Ａ^Hの部分は、考え得るθ₁〜θ_mの組合せにおいて、予め計算しテーブルに持っておくことができ、これによって高分解能処理器１９における演算を効率的に行える。 If you expand the expression,

It becomes. Accordingly, the portion of A (A ^H A) ^-1 A ^H surrounded by an ellipse can be calculated in advance and held in a table in a possible combination of θ _{1 to} θ _m , and thereby the high resolution processor 19. Can be performed efficiently.

In this embodiment, a peak signal is supplied from the peak detecting means 20 to the high resolution processor 19. Therefore, it is possible to perform processing for θ _{1 to} θ _m only in the vicinity of the peak. As a result, the amount of calculation can be reduced and efficient detection can be performed for all detection ranges of the target as compared to the case where θ _{1 to} θ _m are changed.

  Even when the MUSIC method is used, efficient high-resolution processing can be performed by limiting the detection to the periphery of the peak.

  As described above, according to this embodiment, a plurality of antenna beams are directed in all directions based on the received signals received by the element antennas, the antenna beam that the target signal receives most strongly is searched, and the periphery of the antenna beam The angle measurement method applying the maximum likelihood estimation method is applied. This makes it possible to perform highly accurate angle measurement while suppressing the calculation load. That is, in this method, the angle can be obtained for each of two or more targets within the antenna beam width.

Embodiment 2. FIG.
FIG. 4 shows the configuration of the second embodiment of the present invention. In the above-described first embodiment, the maximum likelihood estimation method is applied to the antenna beam directions of all peaks. However, in the second embodiment, before applying the maximum likelihood estimation method, whether or not one target is obtained by monopulse calculation. If it is 1 target, the monopulse angle measurement is applied, and if it is 2 targets or more, the maximum likelihood estimation method is applied. Since the maximum likelihood estimation method takes much longer time than the monopulse angle measurement, the calculation time can be shortened by using the two methods in combination. In addition, about the member same as Embodiment 1 of FIG. 1, the same name is attached | subjected and description is abbreviate | omitted.

The output of the multi-beam forming means 18 is supplied to the monopulse calculator 21. In this monopulse computing unit 21, based on the outputs X _{1 to} X _n of the multi-beam forming means 18, the Σ signal which is the sum of signals from all the element antennas A _{# 1 to} A _#n and the element antennas are divided into two groups from the middle. In other words, a Δ signal is calculated by subtracting the sum of the other group from the sum of the other group.

That is, the element antennas A _{# 1 to} A _#n are divided into two groups (antenna 1 and antenna 2), and Σ signals A and B are obtained separately. For example, A and B are expressed as follows.

  The two signals A and B obtained by integrating the two signals in this way are substantially the same as the two received signals obtained from the two antennas. Therefore, if the arrival direction of one received wave is θ, the phase difference between the two signals φ = (2π / λ) dsin θ as described above.

  Therefore, if the output A (t) of the antenna 1 is assumed, the output of the antenna 2 is A (t) exp [jφ]. Therefore, the sum of both Σ = A (t) exp [jφ] + A (t), The difference between them is Δ = A (t) exp [jφ] −A (t).

  Then, Σ and Δ are supplied to the angle detector 22. The angle detector 22 obtains the ratio Δ / Σ of Σ and Δ, and obtains the arrival angle from the value.

That is, in the case of the incoming wave from the antenna boresight, the amplitude values of the antenna 1 and the antenna 2 in which the boresight becomes large in the Σ signal are maximized in the directions shifted from the respective boresights. From this relationship, Δ / Σ (error voltage) is as shown in FIG. 5B, and the deviation from the boresight of the target antenna 4 as a whole (target angle Δε _m ) from the value of Δ / Σ. Can be detected. That is, the ratio between the output Σ signal and the Δ signal is calculated to obtain an error voltage, the deviation from the antenna boresight is calculated, and the angle measurement value is calculated.

  At this time, when there is only one target in the curve of the Σ signal in FIG. 5 (a), the target direction is uniquely determined, but when there are two or more targets, the reflected signals from the respective targets are synthesized. The angle cannot be specified. Accordingly, paying attention to the characteristics of the error signal Δ / Σ calculated by the Σ signal and the Δ signal, it is determined whether the target is one target or two targets or more.

Here, consider a case where two targets exist in the same beam as shown in FIG. When two radio waves arrive from the angles θa and θb and are received by two antennas having an inter-element distance d, the amplitude at one antenna at a certain point in time is A (t) and B (t). The amplitude at the other antenna at the same point is A (t) exp [j (2π / λ) dsin (θ)], B (t) exp [j (2π / λ) dsin (θ)]. Here, when φ ₁ = (2π / λ) dsin (θ) and φ ₂ = (2π / λ) dsin (θ), the error voltage Δ / Σ is expressed as follows.

Therefore, the real part disappears only when cos (φ ₁ −φ ₂ ) = 1, that is, φ ₁ −φ ₂ = 2πn (n = 0, 1, 2,...). Means radio waves coming from the same direction.

  Therefore, it is possible to determine whether the incoming radio wave is one wave or two or more by obtaining Δ / Σ of two beams in the phase monopulse and examining whether or not the result has a real part.

  Therefore, the angle detector 22 supplies this intermediate data to the target number determiner 23. The target number determination unit 23 determines that one target is obtained if the value is near zero based on the value of the imaginary part of the error voltage Δ / Σ calculated by the angle detector, and that two or more targets are provided if the value is large.

  If it is determined that there are two or more targets, the target signal extraction means 17 collects the complex data of the target frequency fb1 or fb2 for the number of element antennas and sends it to the high resolution processor. In the high resolution processor 19, the target orientation is obtained as in the case of the first embodiment.

  Further, the selector circuit 24 selects angle measurement data from the angle detector 22 when the target number is 1 based on the signal from the target number determiner 23, and the high resolution processor when the target number is 2 or more. Angle measurement data from 19 is selected and output.

  In this embodiment, when there is a single target, it can be switched to the conventional monopulse angle measurement method, and when there are multiple targets, it can be switched to a high resolution angle measurement method that improves the angle resolution. It is possible to detect a small number of angle detection errors for a plurality of targets existing inside. Furthermore, since the two types of angle measurement methods are switched and operated, it is not necessary to always use the high-resolution angle measurement method which requires a processing load, and the radar device can be efficiently operated.

  In the above-described embodiment, the FMCW method is adopted, but the same effect can be obtained by another method such as a spread spectrum method.

1 is a block diagram illustrating a configuration of a radar apparatus according to Embodiment 1. FIG. It is a figure which shows the time change of the transmission / reception wave of a FMCW system, and the frequency of a beat signal. It is a figure which shows the principle of a phase monopulse. FIG. 6 is a block diagram showing a configuration of a radar apparatus according to a second embodiment. It is a figure which shows the relationship between the amplitude value with respect to an angle, and error voltage (DELTA) / Σ with respect to an angle. It is a figure which shows an amplitude value when two or more targets enter in one beam. It is a block diagram which shows the structure of the radar apparatus which concerns on a prior art example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 Transmitter, 12 Transmit antenna, 13 Target, 14 Array antenna, 15 Receiver, 16-1-16-n FFT, 17 Target signal extraction means, 18 Multi-beam formation means, 19 High-resolution processor, 20 Peak detection means , 21 Monopulse calculator, 22 Angle detector, 23 Target number determiner, 24 Selector circuit, 30 Distance / speed calculating means.

Claims (3)

Multi-beam forming means for forming a multi-beam using signals received by a plurality of element antennas;
Peak detection means for detecting a peak of a reception level after multi-beam formation by the multi-beam forming means;
High-resolution angle measurement processing means for limiting the received signal to the vicinity of the azimuth at which the reception level detected by the peak detection means is high, and performing angle measurement processing at high resolution by applying a maximum likelihood estimation method. ,
X = AS represented by a matrix from the relationship between the reception signals X1 to Xn (n is a natural number) of the plurality of element antennas and the complex amplitude information S1 to Sm (m is a natural number) from the plurality of element antennas was used. Among the combinations max [tr [A [A (A ^H A) ⁻¹ A ^H XX ^H ]] of the arrival directions θ1 to θm of the received waves that minimize the error between the measured value and the theoretical value,
A radar apparatus characterized in that A (A ^H A) ⁻¹ A ^H is tabulated in advance and angle measurement processing is performed with high resolution using the table. Monopulse angle measuring means for performing monopulse angle measurement after multi-beam formation by the multi-beam forming means;
A selection means for determining a target existence number from the angle error result calculated by the monopulse angle measurement means, and selecting whether to perform high-resolution angle measurement processing on the received signal based on the determination result;
The selection means selects the angle measurement result of the monopulse angle measurement means when the target existence number determined by the monopulse angle measurement means is 1, and selects the high resolution processing means when the target existence number is plural. The radar apparatus according to claim 1. A transmission antenna for transmitting FMCW waves;
The radar apparatus according to claim 1, wherein at least a direction in which the target object exists is measured using a signal transmitted from the transmission antenna, reflected by a target and received by a plurality of element antennas. .

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