JP3463747B2 - FM-CW radar device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM-CW radar device which can obtain at least a distance of a target from a beat frequency between a received signal and the transmission signal by using a transmission signal in which a continuous wave is frequency-modulated. It is a thing.

[0002]

2. Description of the Related Art An FM-CW radar device is suitable for detecting an object (target) at a relatively short distance as compared with a pulse radar device. Therefore, in recent years, development has been promoted as a means for detecting the preceding automobile etc. by mounting it on the automobile.

Triangular wave frequency modulation is generally used for frequency modulation in the FM-CW radar device. Triangular wave frequency modulation is frequency modulation in which a section in which the frequency linearly increases and a section in which the frequency linearly decreases are alternately repeated. The beat frequency and the modulation frequency in the modulation frequency increasing section (hereinafter, simply referred to as an up section) The target distance and the relative speed can be calculated from the beat frequency of the decreasing section (hereinafter, simply referred to as the down section).

The direction of the target can be obtained by scanning an antenna beam narrowed to a desired width.

Generally, the scanning system can be roughly divided into a mechanical scanning system and an electronic scanning system, and one of the electronic scanning systems is a digital beam forming (DBF) scanning system.

In the DBF scanning method, an array antenna having a plurality of element antennas is used as a receiving antenna, and a beat signal obtained for each element antenna is subjected to a phase shift by digital signal processing and synthesized to obtain a desired signal. This is a method of scanning an antenna beam by using a DBF synthesis technique capable of forming an antenna beam in the azimuth direction.

According to the DBF scanning method, it is not necessary to rotate the antenna as in the mechanical scanning method. Therefore,
A drive mechanism for rotating the antenna is not required, which is advantageous in that it is resistant to vibration and can be made smaller and lighter. Utilizing such advantages, research has been conducted on its use as a vehicle-mounted radar device.

On the other hand, the calculation load of the DBF synthesis processing is generally large. Therefore, in order to reduce the calculation load, it has been considered to perform the DBF synthesis only in the beat frequency corresponding to the distance where the target is likely to exist (Japanese Patent Laid-Open No. 11-133142).

As a method of detecting the beat frequency corresponding to the distance where the target is likely to exist, DBF is used.
There is a method of detecting a peak frequency (peak frequency) from the beat frequency spectrum before the synthesis processing.

[0010]

However, the peak level in the beat frequency spectrum before the DBF synthesis processing becomes lower as the target becomes farther away, that is, as the value of the beat frequency increases. Therefore, it is considered that the peak frequency cannot be detected for the long range target.

[0011]

The FM-CW radar device of the present invention has been made in order to solve such a problem, and uses a transmission signal in which a continuous wave is frequency-modulated and a reception signal In an FM-CW radar device capable of obtaining a target distance from a beat frequency of a transmission signal, a reception array antenna having a plurality of element antennas and a DBF synthesis for a beat signal obtained for each of the plurality of element antennas Target detection means for detecting the distance and direction of the target by performing processing to form and scan the antenna beam, and peak frequency detection means for detecting a peak frequency from the beat frequency spectrum before the DBF synthesis processing , The target detection means, the peak frequency below the predetermined frequency detected by the peak frequency detection means Then, the distance and direction of the target are detected by the DBF synthesis processing at that frequency or a frequency in the vicinity thereof, and for beat frequencies higher than a predetermined frequency, the DBF synthesis processing is performed over the entire frequency range up to the maximum frequency of the detection range. It is characterized in that the target distance and direction are detected by.

Comparing the beat frequency spectrum when the antenna beam is formed by the DBF synthesis processing with the beat frequency spectrum before the DBF synthesis processing,
When the target exists in the antenna beam direction, the former causes a sharper peak due to the target. In other words, in the beat frequency spectrum before the DBF synthesis processing, when the beat frequency is large, that is,
When the target is at a long distance, it is difficult to detect the peak caused by the target.

According to the present invention, for beat frequencies higher than the predetermined frequency, the DBF synthesis processing is performed over the entire frequency range up to the maximum frequency of the detection range, so the peak of the beat frequency spectrum caused by the target. Is easy to detect.

Further, for a target at a relatively short distance, the peak frequency is detected from the beat frequency spectrum before the DBF synthesis processing, and the distance and direction of the target are detected by the DBF synthesis processing at or near that frequency. , DB over the entire frequency range
The calculation load is smaller than that in the case where the F synthesis processing is performed.

The FM-CW radar device of the present invention comprises lane shape acquisition means for acquiring the shape of the lane in which the vehicle is traveling when mounted on the vehicle, and the target detection means detects the distance and direction. When it is determined that the target exists on the lane obtained by the lane shape obtaining means, the DBF synthesis processing at the beat frequency higher than the beat frequency corresponding to the target is stopped until a new beat frequency is obtained. Is desirable.

When an FM-CW radar device is mounted on a vehicle and the FM-CW radar device is used to detect the behavior of a preceding vehicle traveling on its own lane, the preceding vehicle traveling on its own lane can be detected. At that time, it becomes less necessary to detect a vehicle ahead of that.

According to this FM-CW radar device, when the target on the own lane is detected, the detection of the target in front of it is stopped, so that the amount of calculation for the DBF synthesis processing is greatly reduced. You can

[0018]

1 is a block diagram showing a radar apparatus according to an embodiment of the present invention. This radar device is an FM-CW radar device that uses a transmission signal obtained by multiplying a continuous wave (CW) by frequency modulation (FM). Further, the antenna beam is formed and scanned by the digital beam forming technique in order to detect the target direction.
It is also a BF radar device.

Prior to describing the specific configuration and operation of this embodiment, the detection principle of the FM-CW radar device will be described.

First, the detection principle of the FM-CW radar will be described with reference to the graphs of FIGS. 2 and 3. Figure 2 (A)
Is a graph showing a change in the transmission frequency by a solid line, and a change in the reception frequency reflected by a target object (target) having a relative speed of zero at the position of the distance R by a broken line, and the vertical axis represents the frequency, The horizontal axis shows time.

As can be seen from this graph, a modulation signal obtained by multiplying a continuous wave by triangular frequency modulation is used as the transmission signal. The center frequency of the transmission signal, that is, the carrier frequency is f0, the frequency shift width is ΔF, and the repeating frequency of the triangular wave is fm.

FIG. 3A is a graph showing the change in the received signal and the change in the transmitted signal when the relative speed of the target is not zero but the speed V (V ≠ 0), and the solid line shows the frequency of the transmitted signal. And the broken line shows the received signal frequency. The meanings of the transmission signal and the coordinate axes are the same as those in FIG.

From FIG. 2A and FIG. 3A, when the relative speed of the target is zero, the received signal when radiating such a transmitted signal has a time delay T depending on the distance.
(T = 2R / C: C is the speed of light), and it can be seen that when the relative speed of the target object is V, a time delay T corresponding to the distance and a frequency shift D corresponding to the relative speed are received. In addition,
In the example shown in FIG. 3A, the received signal frequency is shifted upward in the graph, and the target approaches.

A beat signal can be obtained by mixing a part of the transmission signal with the reception signal. FIGS. 2B and 3B are graphs showing the beat frequency when the relative velocity of the target is zero and when the velocity is V, respectively, and the time axis (horizontal axis) is shown in FIGS. Figure 3
The timing is matched with that of (A).

Now, the beat frequency when the relative speed is zero is fr, the Doppler frequency based on the relative speed is fd, and the beat frequency in the section where the frequency increases (up section) is fb.
1. If the beat frequency in the frequency decreasing section (down section) is fb2, then fb1 = fr-fd (1) fb2 = fr + fd (2)

Therefore, by separately measuring the beat frequencies fb1 and fb2 in the up section and the down section of the modulation cycle, fr and fd can be obtained from the following equations (3) and (4).

Fr = (fb1 + fb2) / 2 (3) fd = (fb2-fb1) / 2 (4) If fr and fd are obtained, the distance R and speed V of the target object are calculated as follows (5) ( It can be obtained by the equation 6).

[0028] R = (C / (4 · ΔF · fm)) · fr (5) V = (C / (2 · f0)) · fd (6) Here, C is the speed of light.

In this way, the target distance R and velocity V can be obtained. This is the detection principle of the FM-CW radar device.

An FM according to an embodiment of the present invention shown in FIG.
An array antenna having a plurality of element antennas is used as a reception antenna in a CW radar device, and the reception signals received by the respective element antennas are subjected to appropriate phase shift processing and combined to form an antenna beam in a desired direction. Can be formed. Then, beam scanning can be achieved by sequentially shifting the desired azimuth. The received signal phase shift processing and combination processing for each element antenna are performed by digital calculation. That is, the antenna beam is formed and scanned using the digital beam forming (DBF) technique. The DBF technology is already known,
For example, it is disclosed in JP-A-11-133142.

In a general radar apparatus to which the DBF technique is applied, a high frequency analog device such as an RF amplifier for amplifying a received signal or a mixer for synthesizing a received signal and a transmitted signal to obtain a beat signal is an element antenna. Although provided for each radar device, this radar device is configured to include one set as a whole by using a high-speed changeover switch.

This radar device comprises a transmitter 1, an array antenna 2, a changeover switch 3, a receiver 4, and a digital signal processor 5. Further, the lane shape acquisition means 6 is provided as an additional component.

The transmitting section 1 includes a voltage controlled oscillator (VCO) 11 having a center frequency of f0 (eg, 76 GHz), a buffer amplifier 12, a transmitting antenna 13, and an RF amplifier 14. The VCO 11 is controlled to f0 ± by the control voltage output from the DC power supply for modulation (not shown).
A modulated wave (transmission signal) of ΔF / 2 is output. The modulated wave is amplified by the buffer amplifier 12 and radiated from the transmitting antenna 13 as an electromagnetic wave over a wide range. A part of the transmission signal is amplified by the RF amplifier 14 and output as a local signal for reception detection.

The receiving array antenna 2 is provided with n element antennas, and a selector switch 3 is provided behind the receiving array antenna 2. The changeover switch 3 has n input terminals and one output terminal, and n element antennas are connected to each input terminal. That is,
Between each element antenna and the changeover switch 3, independent first to n-th channels are formed for each element antenna.

The output terminal of the changeover switch 3 is connected to any one of the n input terminals, and its connection is periodically changed over by a changeover signal (clock signal). The connection switching is performed electrically on the circuit.

The receiving section 4 includes an RF amplifier 41 and a mixer 4
2, an amplifier 43, a filter 44, an A / D converter 45, and a switching signal oscillator 46. Changeover switch 3
The signal output from the output terminal of R, that is, the signal received by one of the element antennas of the array antenna 2 is R
Amplified by the F amplifier 41, and the RF amplifier 14 by the mixer 42.
It is mixed with part of the transmitted signal from. The received signal is down-converted by this mixing, and a beat signal which is a difference signal between the transmitted signal and the received signal is generated.

The reception signal received in parallel for each channel is time-divided by the change-over switch 3 in a time much shorter than the beat signal cycle and converted into serial. Therefore, the beat signals output from the mixer 42 are serial beat signals for each channel. This beat signal is input to the A / D converter 45 via the amplifier 43 and the low-pass filter 44, and converted into a digital signal at the timing of the output signal of the oscillator 46, that is, the clock signal for switching the connection by the change-over switch 3. To be done.

The digital signal processing section 5 inputs the digital beat signal from the A / D converter 45. Here, the serialized digital beat signal is separated for each channel and temporarily stored. Various processing is performed on the digital beat signal for each channel thus obtained to obtain target information, that is, target distance, relative velocity, direction, and width.

For the distance and the relative speed, the above-mentioned F is used.
It is acquired by the detection principle of the M-CW radar device. Also,
The direction is acquired by a method of forming and scanning an antenna beam by the DBF synthesis technique.

The lane shape acquisition means 6 is additionally provided in the FM-CW radar device, and when mounted on a vehicle, acquires the shape of the lane in which the vehicle is traveling. For example, the curvature of the traveling lane can be obtained from the speed and the yaw rate obtained from the speed sensor and the yaw rate sensor mounted on the vehicle. If the curvature of the traveling lane is known, the lane shape can be known under the assumption that the lane width has a predetermined value.

Next, the processing procedure in the digital signal processing section 5 will be described with reference to the flowchart of FIG.

First, in step S11, the digital beat signal input from the A / D converter 45 is divided into channels and stored. At this time, the digital beat signal is stored for both the up section where the transmission signal frequency increases and the down section where the transmission signal frequency decreases.

In step S12, fast Fourier transform processing (FFT processing) is performed on the digital beat signal in the up section for one or more appropriate channels. Thereby, the beat frequency spectrum of the up section is acquired.

FIG. 5 shows an example of the obtained beat frequency spectrum with a solid line. As can be seen from this figure, as the beat frequency increases, the power level of the peak frequency due to the target decreases, and it becomes difficult to distinguish it from noise and the sharpness of the peak becomes dull. In the figure, fx and fy are preset values, fx is the upper limit value of the beat frequency at which the peak is considered to be detected without error, and fy is the distance of the farthest target to be detected. It is the corresponding beat frequency. Note that fx and fy do not necessarily have to be fixed values, but may be variable values depending on the situation.

In step S13, a peak search is performed on the beat frequency spectrum obtained in step S12 in a frequency range of fx or less, and the peak frequency fi (i
, 1, 2, ..., N) are detected. Here, the peak frequency fi means the beat frequency corresponding to the peak of the beat frequency spectrum. The peak frequency fi is a subscript i from the smaller beat frequency to the larger beat frequency i.
= 1, 2, ..., N are sequentially attached. Therefore, the peak frequency fn is the largest peak frequency of fx or less.

The peak search in step S13 may be performed for an appropriate single channel or a plurality of channels. When performing on a plurality of channels, the frequency detected on any channel is adopted as the frequency to be combined in the next step S15.
For example, when frequencies f1, f2, f3 are detected on channel ch1 and frequencies f1, f2, f4 are detected on channel ch2, fi = f1, f2, f3, f4.

By doing so, the reception power of reflected waves from a distance is small, and the threshold value for frequency detection is close. Therefore, even if it cannot be detected by a single channel within the range of detection variations. In some cases, it may be detected in another channel, and the frequency to be synthesized in step S15 will not be missed.

As can be seen from the above description, step S1
2 and step S13 constitute a peak frequency detecting means for detecting a peak frequency from the beat frequency spectrum before the DBF synthesis processing.

Since the beat frequency spectrum in the up section is acquired in step S12, the peak frequency fi is fb1 (= fr-f in the above equation (1).
This corresponds to d). When the beat frequency spectrum of the down section is acquired instead of the up section, the peak frequency fi is fb2 (= fr + f in the above equation (2)).
This corresponds to d).

When the present FM-CW radar device is used for a vehicle, that is, when it is mounted on a vehicle and used to detect a preceding vehicle, the beat frequency fr is generally sufficiently higher than the Doppler frequency fd. , Peak frequency f
It can be said that i is approximately proportional to the distance at which the target exists.

The target detecting means is constituted from steps S14 to S25. In step S14,
For the subscript i of the peak frequency fi, i = 1 is set. After adding 1 to the value of the subscript i in step 21, it is determined in step S23 whether the value of "i" is larger than "n". As described above, “n” is a subscript added to the highest frequency among the peak frequencies fi of fx or less detected in step S13.

As a result of these steps S14, 21, 23, "i" from 1 to n, steps S15-
The target detection process in step S18 is executed. However, if the stop condition in step S22, which will be described later, is satisfied on the way, step S is performed before i reaches n.
The target detection process from 15 to step S18 is stopped.

In step S15, DBF synthesis is performed at the peak frequency fi to obtain a power distribution having the target direction θ as a variable. As will be described later, DBF synthesis is performed for a long-distance target over the entire range of frequencies corresponding to the distance range to be searched, but here, the target is closer than the distance corresponding to the beat frequency fx. Since the approximate distance, that is, the distance including the error due to the relative speed has already been clarified by the peak frequency fi, the DBF synthesis is limited to the peak frequency fi. FIG. 6 is a graph showing an example of the power distribution having the target direction θ at the peak frequency fi (for example, the frequency peak f1) as a variable.

In step S16, the target central direction θ and the width W are obtained from the power distribution obtained in step S15.

The center direction θ of the target is obtained from the direction showing the peak exceeding the threshold value in the power distribution.
For example, in the example of FIG. 6, peaks in a range exceeding the threshold value T appear at two points in the direction θ1 and the direction θ2. Peaks below the threshold T are treated as noise. From this figure, at an approximate distance corresponding to the peak frequency fi, 2
It can be seen that there are two targets in directions θ1 and θ2, respectively.

The target width W is obtained from the width at the position where the power has decreased by a predetermined amount from the peak position. In the example of FIG. 6, the width of the target in the direction θ1 is W1, and the width of the target in the direction θ2 is W2.

In step S17, the beat signal in the down section is used to perform the DBF synthesis processing for the range near the beat frequency fi including the peak frequency fi, and the power distribution having the target direction as a variable in the frequency range is obtained. . Then, the center direction and width of the target are detected from the power distribution.

Next, in step S18, step S
Target information in the same direction and width as the target information of the up section acquired in 16 is searched from the target information of the down section acquired in step S17, and both are paired. This is because if the target information has beat frequencies, directions, and widths that are substantially equal to each other, it can be determined that they are caused by the same target.

By applying the above equations (5) and (6) to the paired target information, the accurate distance and relative velocity of the target can be obtained. With this, all the information about the target distance, relative velocity, direction, and width is gathered, and the target is effectively recognized.

When step S18 is completed, step S
After 21, the process proceeds to step S22. Step S22
Then, it is determined whether or not the target recognized at the end of step S18 exists on the lane acquired by the lane shape acquisition means 6.

FIG. 7 is a schematic plan view showing an example of a running state of an automobile equipped with the FM-CW radar device. In this example, an automobile 61 equipped with the present FM-CW radar device
Is traveling on the central lane 64 of the three-lane road 62. The road 62 curves sharply to the right, and another vehicle 63 is driving in front of the central lane 64. In such a state, it is not always necessary to know the behavior of the vehicle located further ahead of the vehicle 63.

Thus, when the preceding vehicle is present on the own lane, the affirmative determination is made in step S22, and the target recognition in steps S15 to S18, which is repeatedly executed, is stopped. After that, the process returns to step S11, and a new beat signal is acquired.

Own lane, that is, central lane 64 here
The shape of is acquired by the lane shape acquisition means 6 as described above.

If the target recognized in step S18 is not on its own lane, the process proceeds to step S23,
The target recognition in steps S15 to S18 is repeated until the target recognition for the peak frequency fn is performed.

When the target recognition for the peak frequency fn is completed, the process moves from step S23 to step S24. In step S24, DBF synthesis processing is performed for the up section and the down section in the beat frequency range that is higher than the beat frequency fx and lower than the beat frequency fy. When the antenna beam is formed in the direction in which the target exists, for example, the peak P1 in FIG.
From P to P3, a peak due to the target appears in the frequency region where a clear peak was not formed before the DBF synthesis processing.

In step S25, the target information in the up section is compared with the target information in the down section,
Recognize the target by pairing those with the same direction and width and close beat frequencies, and detecting the accurate distance and relative velocity of the target.

After step S25 is completed, the process returns to step S11, and the same target recognition is continued based on the new beat signal.

[0068]

As described above, according to the FM-CW radar device of the present invention, for a beat frequency higher than a predetermined frequency, the DBF synthesis processing is performed over the entire frequency range up to the maximum frequency of the detection range. Therefore, it is easy to detect the peak of the beat frequency spectrum due to the target. Moreover, for a target at a relatively short distance, the peak frequency is detected from the beat frequency spectrum before the DBF synthesis processing, and the distance and direction of the target are detected by the DBF synthesis processing at or near that frequency. DBF over the range
The calculation load is smaller than that in the case of performing the combining process.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an FM-CW radar device according to an embodiment of the present invention.

FIG. 2 is a graph for explaining the detection principle of FM-CW radar.

FIG. 3 is a graph for explaining the detection principle of the FM-CW radar.

FIG. 4 is a flowchart showing the first embodiment of the present invention.

FIG. 5 is a graph showing an example of a beat frequency spectrum in an up section.

FIG. 6 is a graph showing a power distribution after the DBF synthesis processing.

FIG. 7 is a plan view showing an example of a running state of an automobile equipped with the FM-CW radar device of this embodiment.

[Explanation of symbols]

1 ... Transmitter, 2 ... Array antenna, 3 ... Changeover switch,
4 ... Receiving part, 5 ... Digital signal processing part, 6 ... Lane shape acquisition means, 11 ... Voltage controlled oscillator, 13 ... Transmission antenna, 41 ... RF amplifier, 42 ... Mixer, 45 ... A / D
Converter, 46 ... Switching signal generator.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01S ⁷ /00-7/42 G01S 13/00-13/95 B60R 11/02 G08G 1/16

Claims (2)

(57) [Claims] 1. An FM-CW radar device capable of obtaining a target distance from a beat frequency between a reception signal and the transmission signal by using a transmission signal obtained by subjecting a continuous wave to frequency modulation, and having a plurality of element antennas. An array antenna for reception; target detection means for detecting the distance and direction of the target by performing DBF synthesis processing on the beat signals obtained for each of the plurality of element antennas to form and scan an antenna beam; Peak frequency detecting means for detecting a peak frequency from the beat frequency spectrum before the DBF synthesizing process, wherein the target detecting means has a peak frequency less than a predetermined frequency detected by the peak frequency detecting means. Alternatively, the target obtained by the DBF synthesis processing at a frequency close to that The distance and the direction of the target are detected, and for the beat frequency higher than the predetermined frequency, the distance and the direction of the target are detected by the DBF synthesis processing over the entire frequency range up to the maximum frequency of the detection range. An FM-CW radar device characterized by the above. 2. A lane shape acquisition means for acquiring the shape of a lane in which the vehicle is traveling when mounted on the vehicle, wherein the target detection means acquires the lane shape by a target whose distance and direction are detected. When it is determined that the DBF is present on the lane obtained by the means, the DBF synthesis processing is stopped at a beat frequency higher than the beat frequency corresponding to the target until a new beat frequency is acquired. Item 2. The FM-CW radar device according to Item 1.