WO2007102308A1

WO2007102308A1 - Radar apparatus

Info

Publication number: WO2007102308A1
Application number: PCT/JP2007/053071
Authority: WO
Inventors: Tomohiro Nagai
Original assignee: Murata Manufacturing Co., Ltd.
Priority date: 2006-03-06
Filing date: 2007-02-20
Publication date: 2007-09-13

Abstract

Receiving antennas (5A to 5F) are arranged in a line at intervals of at least one wavelength of a transmission wave, and the central directions of the directivities of the receiving antennas (5A to 5F) are so set as to be different from one another. A signal processing circuit (1) forms an angular spectrum according to the signal intensity distribution of a signal received at each of the receiving antennas (5A to 5F) and also forms an angular spectrum generated by performing phase difference processing on each received signal. The signal processing circuit (1) compares the peaks of these two angular spectrums with each other and outputs the direction in which the peak positions match each other as a direction in which an object is detected.

Description

Specification

Radar equipment

Technical field

TECHNICAL FIELD [0001] The present invention relates to an FM-CW radar device used for preventing collision of an automobile, and more particularly to a radar device that detects an azimuth using an array antenna.

Background art

[0002] Conventionally, as a vehicle-mounted radar device that detects the orientation of an object using a high-frequency signal in the millimeter wave band, continuous waves reflected by a plurality of arrayed receiving antennas using frequency-modulated continuous waves Various FM-CW radar devices have been devised that receive waves and detect their orientation. For example, the radar apparatus of Patent Document 1 includes one transmitter having one transmission antenna and one receiver having a plurality of reception antennas. The radar device of Patent Document 1 detects the azimuth of the phase difference force detection object of the received signal obtained from each receiving antenna by switching a plurality of receiving antennas at high speed with a switch.

Patent Document 1: Japanese Patent No. 3622565

Disclosure of the invention

Problems to be solved by the invention

In order to perform wide-angle azimuth detection with a radar device that forms a reception beam at a plurality of azimuth angles using the phase difference between the reception signals of each reception antenna as in Patent Document 1, the interval between the reception antennas is reduced. While maintaining this, the number of receiving antennas must be increased tl, or the arrangement interval of receiving antennas must be increased without increasing the number of receiving antennas.

[0004] When the number of receiving antennas is increased, the number of parts cannot be increased to reduce the size! /, And the number of switches for switching receiving antennas and the number of switches increase, resulting in a large switch loss. As a result, reception loss increases. Furthermore, since the number of received signals that make up the receive beam increases, the amount of processing calculations increases, and it takes time to form the receiving beam due to the phase difference, and the calculation processing time becomes longer. .

[0005] When the interval between the receiving antennas is increased without increasing the number of receiving antennas, particularly when the interval between adjacent antennas is one or more wavelengths of the transmission wave, a grating lobe is generated. To be born. Such a grating lobe is a phenomenon in which a peak of the received signal intensity (radiation intensity) occurs in a different direction from the main lobe that occurs in the originally desired direction of the received beam. May be misunderstood.

[0006] In addition, some conventional radar apparatuses perform azimuth detection by comparing received signal strengths of receiving antennas having different detection directions, and this apparatus performs wide-angle detection by widening the receiving antenna interval. However, no grating lobe is generated. However, the direction detection result by this method cannot be as accurate as the direction detection result using the phase difference.

Accordingly, an object of the present invention is to realize a radar apparatus capable of detecting a bearing with high accuracy and high speed without erroneous recognition even when performing wide-angle detection.

Means for solving the problem

[0008] The present invention provides a transmission antenna that transmits a transmission wave subjected to predetermined modulation to a detection region, a plurality of reception antennas that receive a reflected wave of the transmission wave and output a reception signal, and a reception antenna The present invention relates to a radar apparatus including detection means for detecting a direction based on each received signal. The plurality of receiving antennas of the radar apparatus of the present invention include receiving antennas arranged in a straight line and having different directivity center directions, and the detection means calculates based on the signal strength of each received signal. It is characterized in that the amplitude calculation direction is compared with the phase difference calculation direction calculated based on the phase difference of each received signal, and the matching direction is output as the object detection direction.

[0009] With this configuration, a plurality of receiving antennas receive reflected waves from a region having a predetermined width including the central direction of each directivity. In this case, since the directivity of each receiving antenna has a predetermined spread, a reflected wave from one object is received by a plurality of receiving antennas. The reception signals of the respective reception antennas have a phase difference corresponding to the arrangement interval of the reception antennas, and by combining the reception signals based on this phase difference, reception beams having different azimuths as the central directions. Is formed.

[0010] The detection means acquires the azimuth angle distribution (angle spectrum) of the received signal intensity from the signal intensity of each received signal, and determines the azimuth angle distribution of the received beam intensity from each of the formed received beam curves. Get the cloth (angle spectrum). At this time, in the azimuth distribution of the received signal strength, only a peak having a relatively wide azimuth width due to the main lobe exists. On the other hand, in the azimuth distribution of received beam intensity, a peak with a narrow azimuth width due to the main lobe and a peak with a predetermined azimuth width due to a virtual image such as a grating tube are mixed. The detection means compares these two azimuth angle distributions, compares the signal intensity and the beam intensity peak, and outputs this azimuth when it detects that the azimuth coincides.

[0011] Further, the detection means of the radar apparatus according to the present invention is characterized in that the phase difference calculation azimuth is calculated only within a predetermined azimuth angle range including the amplitude calculation azimuth.

In this configuration, when the azimuth is calculated using the phase difference of the received beam, the azimuth angle specific calculation is performed only within a predetermined azimuth angle range including the azimuth obtained by the signal intensity. The calculation amount is small, and the load on the signal processing circuit is reduced.

[0013] In addition, the radar apparatus according to the present invention is characterized in that the arrangement interval of the plurality of receiving antennas is at least one wavelength of the transmission wave! /

[0014] In this configuration, the azimuth angle detection range by the reception beam is expanded by widening the arrangement interval of the reception antennas. In this case, a grating globe is generated by setting the arrangement interval to one or more wavelengths of the transmitted wave, but the azimuth angle detection without being affected by the above-described configuration (method) is performed.

[0015] Further, the radar apparatus according to the present invention is characterized by comprising selection means for switching the output signals of the plurality of reception antennas in synchronization with the modulation period of the transmission wave and giving the detection signals to the detection means.

[0016] With this configuration, since the receiving antenna is switched at the timing when the modulation period, that is, the substantial observation period is switched, noise superposition at the time of switching with respect to the received signal is reduced.

[0017] Further, the radar apparatus according to the present invention is characterized in that there is one transmission antenna and the transmission wave is transmitted to the entire detection region by the one transmission antenna.

[0018] With this configuration, since the transmission antenna power is high, it is easy to reduce the size and cost without having to provide a means for switching the transmission antenna.

The invention's effect According to the present invention, the azimuth distribution is correlated between the received signal intensity of each receiving antenna of the plurality of arranged antennas and the received beam intensity of the plurality of arranged antennas.

By detecting the azimuth angle, the azimuth can be detected reliably and with high accuracy.

At this time, since this method is not affected by the azimuth angle range, the azimuth detection is reliably and highly accurate even in wide-angle detection in which the arrangement interval of the receiving antennas is set to one or more wavelengths of the transmission wave. It can be performed.

[0020] Further, according to the present invention, by performing azimuth detection based on the received beam intensity only within a predetermined range based on the azimuth angle detected based on the received signal strength, the amount of azimuth angle specifying calculation processing can be reduced, and higher speed can be achieved. It is possible to detect the direction.

[0021] Further, according to the present invention, by switching the receiving antenna in synchronization with the modulation period, the switching noise included in the received signal is reduced, and the azimuth detection can be performed more reliably.

[0022] Further, according to the present invention, since it is necessary to switch the transmission antenna, the constituent elements are simplified, and a radar apparatus that performs wide-angle azimuth detection reliably and with high accuracy is realized in a small size and at low cost. be able to.

Brief Description of Drawings

FIG. 1 is a block diagram showing a main part of a radar apparatus according to a first embodiment.

2 is a diagram showing the configuration of each of the receiving antennas 5A to 5F shown in FIG.

FIG. 3 is a diagram showing directivity characteristics 500A to 500F of receiving antennas 5A to 5F.

FIG. 4 is a diagram showing a frequency modulation pattern of a transmission signal and assignment of receiving antennas 5A to 5F that perform reception.

FIG. 5 is a flowchart showing a direction detection process of the signal processing circuit 1.

FIG. 6 is a diagram showing an example of an angle spectrum obtained by the signal processing circuit 1;

FIG. 7 is a diagram showing another example of an angular spectrum obtained by the signal processing circuit 1;

FIG. 8 is a flowchart showing a direction detection process of the signal processing circuit 1 according to the second embodiment.

FIG. 9 is a diagram showing the directivity characteristics of other receiving antennas.

Explanation of symbols [0024] 1 Single signal processing circuit, 2—VCO, 3 branch circuit, 4 Transmitting antenna, 5A to 5F Receiving antenna, 6—Switch circuit, 7—LNA, 8—Mixer, 9—IF amplifier

BEST MODE FOR CARRYING OUT THE INVENTION

A radar apparatus according to the first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a block diagram showing the main part of the radar apparatus of this embodiment.

FIG. 2 is a diagram showing the configuration of each of the receiving antennas 5A to 5F shown in FIG.

FIG. 3 is a diagram showing the directivity characteristics 500A to 500F of the receiving antennas 5A to 5F.

FIG. 4 is a diagram showing the frequency modulation pattern of the transmission signal and the assignment of the receiving antennas 5A to 5F for receiving.

In this embodiment, the number of receiving antennas is six, but the number of receiving antennas is not limited to this and may be set as appropriate.

As shown in FIG. 1, the radar apparatus of this embodiment includes a signal processing circuit 1, a VC02, a branch circuit 3, a transmitting antenna 4, receiving antennas 5A to 5F, a switch circuit 6, an LNA 7, a mixer 8, and an IF. With amplifier 9.

[0027] The signal processing circuit 1 generates a control voltage signal for frequency modulation of the transmission signal and supplies it to VC02. In addition, the signal processing circuit 1 detects an object and detects an object direction by a method described later based on the IF beat signal of the input reception signal.

[0028] VC02 is based on the control voltage signal! A triangular wave modulated transmission signal whose frequency changes in a triangular wave shape over time, as shown in Figs. 4 (A) and (C), and Fig. 4 (B) A sawtooth modulation transmission signal whose frequency changes in a sawtooth shape with time is generated. At this time, the modulation period of the transmission signal is set according to the period of the control voltage signal. In the following description, an example is shown in which a transmission signal whose frequency changes repeatedly with time is used. However, any transmission signal that includes a pulse signal or the like and that is modulated at a predetermined period may be used.

The branch circuit 3 gives the transmission signal output from the VC02 to the transmission antenna 4, and gives a part of the transmission signal to the mixer 8 as a local signal.

[0030] The transmission antenna 4 is formed by a microstrip antenna or the like, and is arranged so as to coincide with the front direction of an automobile or the like on which the antenna front direction force S radar apparatus is mounted. Send The antenna 4 transmits a transmission wave to the entire desired detection area with the front direction as the center of radiation directivity.

[0031] The receiving antennas 5A to 5F are each formed in a structure as shown in FIG. 2, and are arranged in a straight line at intervals d as shown in FIG. Here, the arrangement interval d is set to a length of one or more wavelengths of the transmission signal. Each of the reception antennas 5A to 5F is installed such that the front direction is perpendicular to the arrangement direction and faces the same direction. And the front direction of each receiving antenna 5A-5F corresponds with the front direction of the said motor vehicle.

Each of the receiving antennas 5A to 5F is a microstrip antenna provided with six patch antennas 551 to 556 and 561 to 566 arranged in a straight line on the dielectric substrate 57, respectively. Notch antennas 551 to 556 are connected in series via transmission line 55, and Notch antennas 561 to 566 are connected in series via transmission line 56. These two patch antenna groups connected in series are arranged in parallel to the arrangement direction of the notch antennas, and are connected to the transmission line 53 and the transmission line 54 at one end respectively. The transmission lines 53 and 54 are formed in a shape extending in a direction perpendicular to the arrangement direction of the patch antennas, and are connected to the feed line 51 at the connection point 52. By adjusting the ratio of the lengths of the transmission lines 53 and 54, the phase difference between the reflected waves received by the patch antennas 551 to 556 and the reflected waves received by the patch antennas 561 to 566 is adjusted, and the result shown in FIG. The antenna directivity as shown can be set. That is, the receiving antennas 5A to 5F are configured with the same components, and the directivity is set in different directions by changing the length ratio of the transmission lines 53 and 54 for each receiving antenna 5A to 5F. It is set to be the center position of.

[0033] Here, the length ratio of transmission paths 53 and 54 is reversed between reception antenna 5A and reception antenna 5F, and the length ratio of transmission paths 53 and 54 is reversed between reception antenna 5B and reception antenna 5E. The length ratio of the transmission lines 53 and 54 is reversed between the receiving antenna 5C and the receiving antenna 5D. As a result, the directivity of the receiving antenna 5A and the directivity of the receiving antenna 5F are symmetrical with respect to the front axis of the receiving antenna passing through the center in the arrangement direction. Similarly, the receiving antennas 5B and 5E have symmetric characteristics, and the receiving antennas 5C and 5D have symmetric characteristics. Specifically, if the central orientation of the directivity of the receiving antenna 5A is γ °, the central orientation of the directivity of the receiving antenna 5F is + γ °, and the central orientation of the directivity of the receiving antenna 5Β is | 8 °. so If there is, the central direction of the directivity of the receiving antenna 5E is +. Thus, if the central orientation of the directivity of the receiving antenna 5C is α °, the central orientation of the directivity of the receiving antenna 5D is + α °. With such a configuration, each of the receiving antennas 5A to 5F has directivity characteristics 500A to 500F as shown in FIG.

[0034] The switch circuit 6 connects any one of the receiving antennas 5A to 5F to the LNA 7. Specifically, in the case of the transmission signal of FIG. 4 (A), the reception antennas 5A to 5F are sequentially selected for each triangular wave modulation period, and the reception signals of the reception antennas 5A to 5F are output to the LNA 7. In this way, by switching the receiving antenna at the division of the modulation period, the switching noise generated at the time of switching is generated at the timing corresponding to the end of the modulation period, so the upstream modulation section and the downstream modulation section which are the main observation periods The received signal can be acquired effectively without being affected by noise at intermediate frequencies.

[0035] LNA 7 amplifies the input received signal and outputs it to mixer 8. Mixer 8 mixes the received signal from LNA 7 with the local signal from branch circuit 6 to generate an IF beat signal. To do. The IF amplifier 9 amplifies the IF beat signal and outputs it to the signal processing circuit 1.

Next, a direction detection method in the signal processing circuit 1 will be described. In the following description, the case of using the transmission signal and reception antenna assignment shown in FIG. 4 (A) will be described.

FIG. 5 is a flowchart showing the direction detection processing of the signal processing circuit 1.

6A and 6B are diagrams showing an example of an angle spectrum obtained by the signal processing circuit 1. FIG. 6A shows an angle spectrum based on the received signal intensity, and FIG. 6B shows an angle spectrum based on the received beam intensity. In FIG. 6, the reference direction of the azimuth is the front direction of the receiving antennas 5A to 5F, and this direction is the direction of the azimuth 0 °.

[0038] As described above, the signal processing circuit 1 includes I based on the reception signals of the reception antennas 5A to 5F that are switched for each frequency modulation period of the transmission signal in accordance with the switching of the switch circuit 6.

An F beat signal is input (S101).

[0039] The signal processing circuit 1 performs object detection, distance, and relative velocity calculation using the known FMCW technique using the acquired IF beat signal of the received signal (S102).

[0040] The signal processing circuit 1 receives the reception signals (IF beat signals) of all the reception antennas 5A to 5F. And signal strength is detected. Then, an angle spectrum that is a distribution of the received signal intensity in each direction as shown in FIG. 6A is formed (S103).

[0041] Further, the signal processing circuit 1 acquires the reception signals (IF beat signals) of all the reception antennas 5A to 5F and uses a known beamformer method or the like to detect the signals in all detectable directions. Calculation based on the phase difference of each received signal is performed (S104). Then, an angle spectrum of each direction as shown in FIG. 6 (B) is formed (S105). More specifically, the signal processing circuit 1 uses exp (—j · 2πd · (sin θ) Z) and exp (−ΐ · 2Χ2πά · (sin0 θχρ) for each received signal (IF beat signal). (-ΐ · 3Χ2πά · (sin θ) / λ), exp (-j · 4 X 2 π d- (sin θ) / λ), Θχρ (-) 5Χ2πά · (sin θ) / λ) Where Θ is the azimuth (angle), d is the receiving antenna spacing, λ is the wavelength of the transmission signal, and the wavelength of the transmission signal changes from time to time because the frequency of the transmission signal is modulated. However, for example, while the center frequency of the transmission frequency is 76.5 GHz, the modulation frequency width is about 3 OO MHz, so the wavelength of the transmission signal is set to a wavelength corresponding to the center frequency of the transmission frequency. Then, the signal processing circuit 1 forms an angle spectrum as shown in FIG.

[0042] The signal processing circuit 1 detects the peak of the signal intensity in each angle spectrum formed in this way, and detects the corresponding azimuth (S106). In the case of FIG. 6 (A), the signal processing circuit 1 detects the signal intensity peak P11 and detects the corresponding azimuth angle + 45 °. In the case of FIG. 6 (B), the signal intensity peaks P21 and P22 are detected, and the corresponding azimuth angles + 45 ° and 17 ° are detected.

[0043] From these results, the signal processing circuit 1 determines the direction of the detected object based on the fact that a peak is detected in the direction of the azimuth angle + 45 ° regardless of the received signal strength or the signal strength based on the phase difference. Output as a bearing (S107 → S108 → S109). On the other hand, the signal processing circuit 1 determines that it is a false image due to a grating lobe based on the fact that there is no peak at the azimuth angle 17 ° of the angle spectrum based on the received signal strength, and this azimuth (one 17 °) It is not output as (S107 → S108 → S110).

FIG. 7 is a diagram showing another example of an angular spectrum obtained by the signal processing circuit 1, (A) is an angular spectrum based on received signal strength, and (B) is an angular spectrum based on a phase difference. Indicates. In FIG. 7, the reference direction of the azimuth is the front direction of the receiving antenna 5A 5F, and this direction is the direction with an azimuth of 0 °.

[0045] As shown in Fig. 7 (A), the signal processing circuit 1, when the angle spectrum force formed based on the received signal strength also detects peaks Pl1, P12, the corresponding azimuth + 45 ° Detects 17 °. In addition, as shown in FIG. 7 (B), the signal processing circuit 1 detects the peaks P21 and P22 as the angular spectrum force formed based on the received signal strength, and the corresponding azimuth angle + 45 ° 17 ° Detect.

[0046] As described above, when a peak is detected at an azimuth angle of + 45 ° 17 ° in both the received signal strength and the signal strength based on the phase difference, the signal processing circuit 1 detects objects in directions corresponding to these two peaks, respectively. Therefore, these two directions are output as object detection directions.

[0047] As described above, by using the configuration of the present embodiment, even when wide-angle detection is performed by widening the interval between the receiving antennas, high accuracy that is not affected by the grating lobe is obtained. It is possible to detect the object orientation.

Next, a radar apparatus according to the second embodiment will be described with reference to FIG.

Note that the radar apparatus of the present embodiment has the same configuration as the radar apparatus shown in the first embodiment and differs only in the azimuth detection method.

FIG. 8 is a flowchart showing the direction detection processing of the signal processing circuit 1.

Similarly to the first embodiment, the signal processing circuit 1 acquires an IF beat signal based on the reception signal of each reception antenna 5A 5F (S101), detects an object using a known FMCW method, The distance and relative speed are calculated (S102), and an angle spectrum, which is a distribution of received signal strength in each direction, is formed (S103).

[0050] The signal processing circuit 1 detects the angle spectrum force peak due to the received signal strength, and calculates a direction (corresponding to the "amplitude calculation direction" of the present invention) based on the received signal strength (Sll). The signal processing circuit 1 sets a partial azimuth range having a predetermined angular width centered on the azimuth based on the detected received signal strength (S 112), and performs calculation based on the received signal phase difference within the partial azimuth range (S 113). ). [0051] The signal processing circuit 1 forms an angle spectrum that is a signal intensity distribution based on the phase difference within the partial azimuth range (S114). The signal processing circuit 1 detects the peak of the signal intensity in the angle spectrum due to the received beam signal intensity in the partial direction range thus formed, and detects the corresponding azimuth (S115).

The signal processing circuit 1 outputs the detected azimuth as the azimuth of the detected object from the azimuth detection result (S116).

[0053] Here, processing for comparing the orientations of the detected peaks as in the first embodiment may be performed.

[0054] By using such an azimuth detection method, the calculation angle range for specifying the azimuth can be narrowed, so that the calculation processing is performed rather than performing the calculation for specifying the azimuth for all azimuths. Can be reduced. Thereby, the direction detection processing can be speeded up.

In each of the above-described embodiments, an example in which the reception antenna is switched for each modulation period using a transmission signal whose frequency changes in a triangular wave shape has been shown, but a sawtooth wave shape as shown in FIG. If the transmission antenna is used and the receiving antenna is switched every uplink modulation period, the speed cannot be detected, but the direction can be detected at a higher speed. In addition, as shown in Fig. 4 (C), the direction can be detected at higher speed by using the method of switching the receiving antenna within the uplink modulation period.

[0056] Further, in the above-described embodiment, the power of each of the receiving antennas 5A to 5F is shown as an example in which the spread of directivity is set to be approximately the same as shown in FIG. The antennas may have different directivity spreads. The directivity characteristics shown in FIG. 9 are merely examples, and may be set as appropriate according to the required detection specifications.

[0057] Fig. 9 is a diagram showing the directivity characteristics of the receiving antenna. (A) shows an example in which the directivity of the receiving antenna is concentrated in the front direction (direction 0 ° direction). An example is shown in which the directivity of the receiving antenna is concentrated in the direction (within ± 45 °).

[0058] In the case of Fig. 9 (A), the receiving antennas 5A, 5F (directivity 500A, 500F) are set to have a center of directivity from the front (center) to a predetermined amount (about ± 30 °) toward both sides. Wide directivity range is set. The receiving antennas 5B to 5E are set so that the center of directivity is set within a range of approximately ± 10 ° in the front (center), and the directivity width is set narrow. Such a set of directivity By using matching, it is possible to improve the direction detection accuracy near the center of the front.

[0059] In the case of Fig. 9 (B), the receiving antennas 5C and 5D (directivity 500C and 500D) have a directivity center set near the front (center) (approximately ± 15 °) and the directivity width is Widely set. Receiving antennas 5A, 5B, 5E, and 5F have a directivity center set in the direction of both sides from the front (center) by a predetermined amount (about ± 45 °), and the directivity width is set narrow. By using such a combination of directivities, it is possible to improve the accuracy of azimuth detection on the side surface and obliquely forward in front of the front center.

In the above description, an example in which there is one transmission antenna is shown, but a plurality of transmission antennas may be installed and a transmission signal may be transmitted while switching between them. However, with a single transmission antenna, a simple and small radar device can be configured without the need for a transmission antenna switching circuit.

Claims

The scope of the claims

[1] A transmission antenna that transmits a transmission wave subjected to predetermined modulation to a detection region, a plurality of reception antennas that receive a reflected wave of the transmission wave and output a reception signal, and each reception of the reception antenna In a radar apparatus equipped with detection means for detecting a direction based on a signal,

The plurality of reception antennas include reception antennas arranged in a straight line and having different directivity center directions,

The detection means compares the amplitude calculation azimuth calculated based on the signal strength of each received signal with the phase difference calculated azimuth calculated based on the phase difference of each received signal, and determines the matching direction as the object detection azimuth. Output as a radar device.

2. The radar apparatus according to claim 1, wherein the detection means calculates the phase difference calculation azimuth within a predetermined azimuth angle range including the amplitude calculation azimuth.

[3] The radar device according to claim 1 or 2, wherein an interval between the plurality of reception antennas is one or more wavelengths of the transmission wave.

[4] The radar device according to any one of claims 1 to 3, further comprising a selection unit that switches output signals of the plurality of reception antennas in synchronization with a modulation period of a transmission wave and supplies the switching unit to the detection unit.

[5] The radar device according to any one of [1] to [4], wherein the number of the transmission antenna is one, and the transmission wave is transmitted to the entire detection area by the one transmission antenna.