JP5678692B2 - Radar equipment - Google Patents

Description

  The present invention relates to a technique for calculating a distance from a target by a radar apparatus.

  A radar device that is mounted in a moving body such as a vehicle or a fixed public facility and that calculates (measures) a distance from a target (obstacle or target) using electromagnetic waves in the millimeter wave band is known. Yes. The radar apparatus includes a transmission antenna and a reception antenna, or a single antenna for both transmission and reception, radiates a predetermined transmission wave to space, and receives a reflected wave from a target as a reception wave. At this time, in the radar apparatus, the reflected energy (that is, the reception level of the received wave) from the target in the direction in which the main lobe faces (main lobe direction; the direction in which the maximum radiation energy is emitted) is set to a predetermined threshold. When it is above, it detects as a target.

  Here, because the side lobe has a lower radiation intensity than the main lobe due to the directional characteristics of the antenna, it is unlikely that the target will be detected by the side lobe. Large reflected energy may be obtained. In this case, in the radar apparatus, the target detected based on the received wave obtained from the direction in which the side lobe faces (side lobe direction) is in the main lobe direction or in the side lobe direction. The target may be detected incorrectly because it cannot be determined. That is, when the system is operated with the desired detection direction of the target (for example, the monitoring direction) aligned with the main lobe direction of the antenna, the side lobe direction is actually present even though no object is present in the monitoring direction. It may be recognized that an object is present in the monitoring direction based on the detection result of.

  With respect to the above-described viewpoint, a radar apparatus is known that determines whether a detected object (target) is in the main lobe direction or the side lobe direction. According to this known radar device, the antenna is displaced at a predetermined speed perpendicular to the center line of the main lobe. Based on whether or not level fluctuations caused by the Doppler velocity that occur when the detected object is detected by the side lobe appears in the received signal, whether the detected object is in the main lobe direction or in the side lobe direction. Determine if it exists.

JP-A-6-174821

  By the way, the above-described known radar apparatus requires a driving mechanism for repeatedly displacing the antenna at a predetermined speed at a right angle to the center line of the main lobe, and is complicated in configuration. From the point of view, it is not preferable.

  Accordingly, an object of one aspect of the present invention is to provide a radar device that can determine whether a target is in the main lobe direction or the side lobe direction of an antenna with a relatively simple configuration. And

The first aspect is
A transmitting antenna for radiating the transmitted wave to space;
A first receiving antenna for receiving a reflected wave by a target of the transmitted wave as a received wave;
A reception antenna for receiving a reflected wave of a target of the transmission wave as a reception wave, and compared with the first reception antenna, an azimuth angle of a null point in a reference plane based on a direction of a main lobe A second receiving antenna having different directivity characteristics;
A distance calculator that calculates the distance to the target based on the transmitted wave and the received wave;
Each receiving antenna that is selectively switched between the first and second receiving antennas and that the distances calculated by the distance calculating unit are equal when the first and second receiving antennas are selected and is the basis for calculating the distance. When the reception levels of the reception antennas are the first and second reception levels, respectively, the calculated distance is based on the difference between the first reception level and the second reception level. A control unit for determining whether or not
Is a radar apparatus.

The second aspect is
A transmitting antenna for radiating the transmitted wave to space;
A first receiving antenna for receiving a reflected wave by a target of the transmitted wave as a received wave;
A reception antenna for receiving a reflected wave of a target of the transmission wave as a reception wave, and compared with the first reception antenna, an azimuth angle of a null point in a reference plane based on a direction of a main lobe A second receiving antenna having different directivity characteristics only in the first rotation direction in the reference plane;
A receiving antenna for receiving a reflected wave of a target of the transmitted wave as a received wave, and an orientation of a null point in the reference plane based on a direction of a main lobe compared to the first receiving antenna A third receiving antenna having a directional characteristic whose angle is different only in a second rotation direction opposite to the first rotation direction in the reference plane;
A distance calculator that calculates the distance to the target based on the transmitted wave and the received wave;
When the first, second and third receiving antennas are selectively switched and the first, second and third receiving antennas are selected, the distances calculated by the distance calculation unit are all equal, and the distance is calculated. Difference between the first reception level and the second reception level, and between the first reception level and the third reception level A control unit for determining whether the calculated distance is due to reception of the main lobe of the receiving antenna, the side lobe in the first rotation direction, or the side lobe in the second rotation direction based on the difference;
Is a radar apparatus.

  According to the disclosed radar device, it is possible to determine whether the target is in the main lobe direction or the side lobe direction of the antenna with a relatively simple configuration.

It is a figure which shows the example of use of the radar apparatus of 1st Embodiment, Comprising: The figure which shows notionally the operation state of the system which monitors a level crossing using a radar apparatus. The figure which shows schematic structure of the radar apparatus of 1st Embodiment. The figure which shows an example of the directivity of a transmission antenna and a 1st receiving antenna, and (b) a receiving level when the 1st receiving antenna is selected. The figure which shows an example of the reception level when the (a) directivity characteristic of a transmitting antenna and a 2nd receiving antenna and (b) the 2nd receiving antenna are selected. The figure which contrasts and shows the reception level when the 1st receiving antenna is selected, and the receiving level when the 2nd receiving antenna is selected. The figure which shows the relationship between the distance calculated and the reception level by the case where the 1st receiving antenna is selected, and the case where the 2nd receiving antenna is selected. The block diagram which shows the structure of the FM-CW radar apparatus of 1st Embodiment. The block diagram which shows the detailed structure of the digital circuit part of the FM-CW radar apparatus of 1st Embodiment. The figure which shows an example of operation | movement of the switch controlled in 1st Embodiment. The flowchart which shows the target detection operation | movement of the FM-CW radar apparatus of 1st Embodiment. The figure which shows notionally the operation state of the system which monitors a pedestrian crossing using the radar apparatus of 2nd Embodiment. The block diagram which shows the structure of the FM-CW radar apparatus of 2nd Embodiment. The figure which shows an example of operation | movement of the switch controlled in 2nd Embodiment. In 2nd Embodiment, (a) An example of the directional characteristic of a 2nd receiving antenna, (b) The figure which shows an example of the directional characteristic of a 3rd receiving antenna. In 2nd Embodiment, (a) The reception level when the 2nd receiving antenna is selected, (b) The figure which shows the receiving level when the 3rd receiving antenna is selected. In the second embodiment, (a) the difference between the reception levels when the first and second reception antennas are selected, and (b) the reception level when the first and third reception antennas are selected. The figure which contrasts and shows a difference.

(1) First Embodiment Hereinafter, a radar apparatus according to a first embodiment will be described. Note that the scales in the diagrams showing the azimuth angle, antenna gain, or reception level associated with the following embodiments are the same in all the drawings.

(1-1) Application Example of Radar Device of Embodiment First, the application of the radar device of this embodiment is illustrated in FIG. FIG. 1 is a diagram conceptually illustrating an operation state of a system that monitors a crossing using the radar apparatus of the present embodiment. In FIG. 1, the radar apparatus is provided in the vicinity of the level crossing barrier bar and monitors the area between the level crossing bar and the track in the level crossing monitoring area. That is, the radar device antenna is arranged so that its main lobe direction is substantially parallel to the longitudinal direction of the railroad crossing fence, and the area of the main lobe covers as much as possible the area between the railroad crossing fence and the track. It has become. The side lobe direction of the antenna of the radar device is directed obliquely by a predetermined angle corresponding to the antenna directivity based on the main lobe direction. At this time, the radar apparatus may detect a target in the side lobe direction. For example, in the system shown in FIG. 1, the radar device can detect a vehicle that stops in the side lobe direction as a target.

In the system illustrated in FIG. 1, if the radar apparatus cannot recognize that the target has been detected by the side lobe, it cannot be distinguished from other targets at the same distance in the main lobe direction. The mark will be erroneously detected. In other words, the vehicle is recognized as being in the level crossing monitoring area even though it is outside the level crossing monitoring area, and a malfunction such as issuing an alarm to a train or the like passing through the level crossing is made. sell.
On the other hand, the radar apparatus of the present embodiment can recognize whether the target is in the main lobe direction or the side lobe direction of the antenna, as will be described later. Operation can be performed.

(1-2) Schematic Configuration of Radar Device and Target Detection Method of Embodiment Hereinafter, a schematic configuration of the radar device and a target detection method of the embodiment will be described with reference to FIGS.

FIG. 2 is a diagram illustrating a schematic configuration of the radar apparatus according to the present embodiment. As shown in FIG. 2, the radar apparatus according to the present embodiment includes a transmission antenna TA, two reception antennas RA1 and RA2, a switch SW for switching the reception antenna, and a signal processing unit 100. The transmission antenna TA radiates a transmission wave to space. The receiving antennas RA1 and RA2 receive a reflected wave of a transmission wave as a received wave as a received wave. The reception is selectively performed according to switching of the switch SW based on the control of the signal processing unit 100. The configurations of the transmission antenna and the reception antenna are not particularly limited, but for example, a patch array antenna or the like may be used.
The receiving antennas RA1 and RA2 are examples of first and second receiving antennas, respectively.

  In FIG. 2, the signal processing unit 100 includes an analog circuit and a digital circuit, generates a transmission wave, calculates a distance to a target based on the transmission wave and the reception wave, and controls switching of the switch SW (that is, a reception antenna). Switching control) and interface processing with a host system (not shown). Any calculation principle (that is, radar system) in the distance calculation processing in the signal processing unit 100 may be used. For example, as a millimeter wave radar system, a pulse system, an FM-CW (Frequency Modulated-Continuous Wave) system, a 2-frequency CW (Continuous Wave) system, and a spread spectrum system are known. May apply.

  The transmission antenna TA may be shared with either of the two reception antennas RA1 and RA2, but is described separately here. In the following description, it is assumed that the directivity characteristics of the transmission antenna TA and the reception antenna RA1 are equal (for example, the transmission antenna TA and the reception antenna RA1 are configured by a single antenna shared). The two receiving antennas RA1 and RA2 have directivity characteristics in which azimuth angles of null points (zero points) in the reference plane based on the direction of the main lobe are different from each other. In the example shown in FIG. 1, the reference plane is equal to the plane of the monitoring area.

  FIG. 3 shows an example of the directivity characteristics of (a) the transmission antenna TA and the reception antenna RA1, and (b) an example of the reception level (for example, reception power) when the reception antenna RA1 is selected. 4A shows an example of the directivity characteristics of the reception antenna RA2 (solid line) (for reference, the directivity characteristics of the reception antenna RA1 are indicated by dotted lines), and FIG. 4B shows the reception level when the reception antenna RA2 is selected. An example (for example, received power) is shown. 3 and 4 is assumed to be logarithmic (dB), and the horizontal axis is an azimuth (+/−) based on the main lobe direction (“0”).

  Here, based on the following equation (1) known as a radar equation, the reception level (reception power) when each reception antenna is selected is logarithmically the antenna gain of the transmission antenna TA and the antenna gain of the reception antenna. It turns out that it becomes a thing proportional to the value which added.

_{S = P t G t G r} λ 2 σ / (4π) 3 R 4 ... formula (1)
In addition,
S: reception power P _t : transmission power G _t : antenna gain of the transmission antenna G _r : antenna gain of the reception antenna λ: wavelength of the transmission wave σ: effective reflection area of the target R: distance to the target.

Therefore, when the receiving antenna RA1 is selected, since the antenna gains of the transmitting antenna TA and the receiving antenna RA1 are both equal, the reception level is obtained by doubling each antenna gain as shown in FIG. With the same characteristics.
Further, as described above, the reception antenna RA2 has a directivity different from the directivity characteristic of the reception antenna RA1 (that is, the directivity characteristic of the transmission antenna TA) in terms of the azimuth angle of the null point in the reference plane based on the direction of the main lobe. It has characteristics. Thereby, when the reception antenna RA2 is selected, as shown in FIG. 4B, the reception level in the side lobe is lower than in the case of FIG. 3B.
FIG. 5 is a diagram for easy comparison of FIG. 3B and FIG. 4B, and the solid line indicates the reception level when the reception antenna RA1 is selected (FIG. 3B). The dotted line indicates the reception level (FIG. 4B) when the reception antenna RA2 is selected. From FIG. 5, it can be seen that there is no change in the reception level in both directions in the main lobe direction, but there is a difference in the reception level in both directions in the side lobe direction.

The signal processing unit 100 performs a distance calculation process to the target based on the transmission wave and the reception wave. In the distance calculation process, the reception antenna RA1 and the second reception antenna RA2 are selected in order. That is, for example, the signal processing unit 100 first selects the reception antenna RA1, and calculates the distance to the target based on the transmission wave and the reception wave from the reception antenna RA1. Next, the signal processing unit 100 selects the reception antenna RA2, and calculates the distance to the target based on the transmission wave and the reception wave by the reception antenna RA2.
Then, the signal processing unit 100 has the same distance calculated when the reception antennas RA1 and RA2 are selected, and sets the reception levels (for example, reception power) of the respective reception antennas that are the basis of the calculation of the distances to P1, respectively. When P2 is set, it is determined whether the calculated distance is due to reception of the main lobe or the side lobe of the receiving antenna based on the difference between P1 and P2.

This determination will be further described with reference to FIG. FIG. 6 is a diagram illustrating the relationship between the calculated distance and the reception level when the reception antenna RA1 is selected (solid line) and when the reception antenna RA2 is selected (dotted line).
As shown in the radar equation of the above equation (1), if the same transmission power and the same distance are assumed, the receiving antennas RA1 and RA2 having different side lobe directivity characteristics are selected. At the same distance obtained by receiving the lobe, a difference occurs in the reception level. On the other hand, the receiving antennas RA1 and RA2 have the same main lobe directivity characteristics, and therefore there is no difference in the reception level at the same distance obtained by receiving the main lobe. Therefore, when the reception level difference is equal to or greater than a predetermined threshold value, it can be determined that the detection of the target at the same distance is obtained by reception of the side lobe.

  In FIG. 6, it is assumed that distances d1 and d2 are calculated based on the transmission wave and the reception waves of reception antennas RA1 and RA2. At this time, the distance d1 has a difference in reception level between when the reception antenna RA1 is selected and when the reception antenna RA2 is selected (for example, | P1-P2 |> threshold), and the distance d1 is It can be determined that the received wave is obtained from the side lobe of the antenna. On the other hand, there is no difference in the reception level between the distance d2 when the reception antenna RA1 is selected and when the reception antenna RA2 is selected (for example, | P1-P2 | ≦ threshold), and the distance d2 is the reception It can be determined that the received wave is obtained by the main lobe of the antenna.

(1-3) Configuration and Operation of Radar Device in Case of FM-CW System FIG. 2 shows a schematic configuration of a radar device when the radar system is not limited. In the following, the radar system is FM-CW system. The configuration of the radar apparatus (hereinafter referred to as FM-CW radar apparatus) and the target detection method will be described with reference to FIGS.
The FM-CW radar device radiates a frequency-modulated (FM-modulated) transmission wave so as to include a frequency rising section (hereinafter referred to as UP section) and a frequency falling section (hereinafter referred to as DOWN section), and reflects it from the target. The received wave is received as a received wave. The modulation signal in frequency modulation is typically a triangular wave, but may be a signal other than a triangular wave such as a sawtooth wave or a trapezoidal wave. The FM-CW radar device acquires a beat signal of a transmission wave and a reception wave obtained by reflection from a target, and performs a frequency analysis by applying a fast Fourier transform (FFT) to the beat signal. Do. The beat signal subjected to frequency analysis has a peak with increased intensity, and the peak frequency corresponding to this peak has information on the distance of the target.

  FIG. 7 is a block diagram showing the configuration of the radar apparatus (FM-CW radar apparatus 1) of the present embodiment. FIG. 7 is a diagram in which the configuration of the radar apparatus shown in FIG. 2 is specialized for the FM-CW system. FIG. 8 is a block diagram showing a detailed configuration of the digital circuit unit of the FM-CW radar apparatus 1 of the present embodiment.

  Referring to FIG. 7, the FM-CW radar apparatus 1 includes a voltage controlled oscillator (VCO) 11, a directional coupler 12, an amplifier 13, a switch 14 (corresponding to the switch SW in FIG. 2), an amplifier 15, A mixer 16, a filter (BPF) 17, a digital circuit unit 18, a transmitting antenna TA, and receiving antennas RA1 and RA2 are provided.

The voltage controlled oscillator 11 changes the frequency of the transmission wave based on the control voltage V _CONT given from the digital circuit unit 18. The transmission wave of the FM-CW radar apparatus 1 uses a frequency band such as 60 GHz or 76 GHz in Japan, but the voltage-controlled oscillator 11 generates a frequency-modulated transmission wave in a frequency band defined in the system. . The voltage controlled oscillator (VCO) 11 is constituted by, for example, a MESFET and a varactor diode, and its output frequency (frequency-modulated output signal) is f _OUT in FIG.

The transmission wave of the voltage controlled oscillator 11 is given to the mixer 16 via the directional coupler 12 and sent to the amplifier 13.
The transmission antenna TA radiates the transmission wave amplified to a predetermined level by the amplifier 13 into space. The receiving antennas RA1 and RA2 selectively receive a reflected wave from the target as a received wave. This received wave is amplified to a predetermined level by the amplifier 15.

  The mixer 16 mixes the transmission wave obtained from the directional coupler 12 and the reception wave obtained from the amplifier 15 to generate a beat signal having a frequency equal to the frequency difference between the transmission wave and the reception wave. The filter 17 is a band-pass filter (BPF) that passes only the components in the frequency range planned as the beat signal for the beat signal generated by the mixer 16 and removes the noise included in the other components. The beat signal that has passed through the filter 17 is sent to the digital circuit unit 18. The received wave obtained from the amplifier 15 is sent to the digital circuit unit 18 for detection of the reception level.

  As shown in FIG. 8, the digital circuit unit 18 includes a signal generator 181, a D / A (Digital / Analogue) converter 182, an A / D (Analogue / Digital) converter 183, and an FFT (Fast Fourier Transform) processing unit. 184, a distance calculation unit 185, an interface (I / F) unit 186, an A / D converter 187, and a switching control unit 188. The digital circuit unit 18 is configured mainly with a microcontroller, but may include a chip set or a DSP (Digital Signal Processor) for realizing specific functions and processing. A part of the digital circuit unit 18 including the distance calculation unit 185 and the switching control unit 188 is an example of a control unit.

The signal generator 181 generates a digital signal corresponding to a control voltage V _CONT (for example, a triangular wave) _supplied to the voltage controlled oscillator 11.
The interface unit 186 includes, for example, an interface circuit for communication with the host system, and reports the calculated distance to the host system, receives a specific command from the host system, and the like.

The FFT processing unit 184 performs FFT processing on the digitized beat signal, and calculates the analysis result (FFT data) of the frequency component (spectral distribution) of the beat signal.
Based on the frequency component (FFT data) of the beat signal acquired from the FFT processing unit 184, the distance calculation unit 185 calculates the peak frequency of the beat signal obtained in the UP section and the peak frequency of the beat signal obtained in the DOWN section. Pairing is performed, and the target component corresponding to the target is specified. Further, the distance calculation unit 185 calculates the distance to the target based on the pairing result. Specifically, the distance calculation unit 185 determines the distance to the target as α _{up when} the peak frequency in the UP section is F _up and the peak frequency in the DOWN section is F _down among the specified target component pairs. It is calculated by the formula x (F _up + F _down ) / 2 (α: constant). Α is a value determined by the radio wave propagation speed (light speed) of the transmission wave, the center frequency, the modulation frequency width, and the like.

  For example, the switching control unit 188 controls the switch 14 so that the reception wave is received by alternately selecting the reception antenna RA1 and the reception antenna RA2. FIG. 9 shows an example of the operation of the switch 14 controlled by the switching control unit 188. In the example shown in FIG. 9, after the radar apparatus 1 is activated (after time t0), the switch 14 is set so that the period T1 during which the receiving antenna RA1 is selected and the period T2 during which the receiving antenna RA2 is selected alternately occur. Be controlled. However, this operation example is only an example, and it is only necessary that the receiving antenna RA1 and the receiving antenna RA2 are selected at least once.

The distance calculation unit 185 calculates the distance and detects the reception level of the reception wave by the reception antenna RA1 during the period T1 when the reception antenna RA1 is selected. The distance calculation unit 185 also calculates the distance and detects the reception level of the received wave by the reception antenna RA2 during the period T2 when the reception antenna RA2 is selected. The distance calculation unit 185 has the same distances calculated when the reception antennas RA1 and RA2 are selected, and the reception levels of the reception antennas that are the basis for calculating the distances are P1 and P2, respectively. In addition, based on the difference between P1 and P2, it is determined whether the calculated distance is due to reception of the main lobe or the side lobe of the receiving antenna.
The distance calculation unit 185 and the switching control unit 188 may operate in synchronization. That is, after the switching control unit 188 selects the receiving antenna RA1, the distance calculation unit 185 sends a control signal to the switching control unit 188 when the processing for the received wave by the receiving antenna RA1 is completed. Then, the switching control unit 188 performs switching from the receiving antenna RA1 to the receiving antenna RA2 in synchronization with this control signal.

  Next, the operation (target detection operation) by the FM-CW radar apparatus 1 shown in FIGS. 7 and 8 will be described with reference to FIG. FIG. 10 is a flowchart showing the target detection operation of the FM-CW radar apparatus of this embodiment, and is mainly executed in the digital circuit unit 18. Note that the operation of the switch 14 follows the example of the timing chart shown in FIG.

  First, in the period T1, the switching control unit 188 controls the switch 14 so as to select the receiving antenna RA1. Thereby, the reception level (output level of the amplifier 15) of the reception wave obtained by the reception antenna RA1 is detected by the distance calculation unit 185 (step S100). The distance calculation unit 185 calculates all distances D1 from the target based on the beat signal (output of the filter 17) obtained from the transmission wave and the reception wave of the reception antenna RA1 (step S110).

  Next, the switching control unit 188 shifts to the period T2, switches the state of the switch 14, and controls the switch 14 to select the receiving antenna RA2. Thereby, the reception level (output level of the amplifier 15) of the reception wave obtained by the reception antenna RA2 is detected by the distance calculation unit 185 (step S120). The distance calculation unit 185 calculates all distances D2 from the target based on the beat signal (output of the filter 17) obtained from the transmission wave and the reception wave of the reception antenna RA2 (step S130).

The processing of steps S100 to S130 may be performed at least once, but the accuracy of the reception level and distance may be improved by performing statistical processing on the reception level and distance of a plurality of samples obtained by performing a plurality of times. .
Next, the distance calculation unit 185 compares all the distances D1 with the target obtained in the period T1 and all the distances D2 with the target obtained in the period T2, and D1 = D2. It is determined whether there is a distance (step S140). If there is no distance that satisfies D1 = D2, no appropriate result is obtained, and the process returns to step S100.

If there is a distance D1 = D2 in step S140, | P1-P2 | and P _TH (P _TH : predetermined) for the reception levels P1 and P2 of the reception antennas RA1 and RA2 that are the basis for calculating the distance. The threshold value is determined (step S150). As a result, when | P1-P2 |> _PTH , as described with reference to FIG. 6, the target at the distance is calculated by the side lobe of the receiving antenna (that is, the target). Is present in the side lobe direction) (step S160). Conversely, if | P1-P2 | ≦ _PTH, it is determined that the target at the distance is calculated by the main lobe of the receiving antenna (that is, the target exists in the main lobe direction). (Step S170).

  As described above, according to the radar apparatus of the present embodiment, two reception antennas having different side lobe directivity characteristics are selectively switched, and a difference in reception level between the reception antennas at the calculated same distance is determined. This makes it possible to determine whether the calculated distance to the target is obtained by receiving the main lobe or the side lobe. That is, according to the radar apparatus of this embodiment, it can be determined whether the target is in the main lobe direction or the side lobe direction of the antenna. According to the radar apparatus of the present embodiment, it is only necessary to add one reception antenna substantially as hardware for realizing the discrimination function, and the discrimination function is realized with a relatively simple configuration. be able to.

(2) Second Embodiment Hereinafter, a radar apparatus according to a second embodiment will be described.

(2-1) Application Example of Radar Device of Embodiment First, the application of the radar device of this embodiment is illustrated in FIG. FIG. 11 is a diagram conceptually showing an operating state of a system for monitoring a pedestrian crossing using the radar apparatus of the present embodiment. In FIG. 11, the radar apparatus is provided at the end of a pedestrian crossing, and mainly monitors an area within the pedestrian crossing. That is, the antenna of the radar apparatus is arranged so that the main lobe direction is substantially parallel to the traveling direction of the pedestrian crossing, and the main lobe area covers the pedestrian crossing area as much as possible. Further, the side lobe direction of the antenna of the radar apparatus is directed obliquely by a predetermined angle corresponding to the directivity characteristic of the antenna based on the main lobe direction, and monitors the vehicle and the pedestrian.

The application example of the radar apparatus illustrated in FIG. 11 is an example of positively detecting a target in the side lobe direction in addition to the antenna main lobe direction. In this system, since the target in the side lobe direction is detected, the detection range is expanded as compared with the case where only the main lobe direction is detected, but the detection is performed by the main lobe and the two side lobes on both sides thereof. It is preferable to sever. For example, in the arrangement example of the radar apparatus of FIG. 11, a pedestrian or the like entering the pedestrian crossing can be detected in the main lobe. In addition, on the right side lobe on the basis of the main lobe direction, a stopped vehicle or the like can be detected, while on the left side lobe on the basis of the main lobe direction, a pedestrian crossing or the like can be detected. Therefore, if the detection by the main lobe and each of the two side lobes on both sides of the main lobe can be separated, it is considered that an appropriate alarm or control according to the detection target (vehicle, pedestrian) can be performed.
From this point of view, the radar apparatus according to the present embodiment will be disclosed below with respect to a radar apparatus that can separate the detection of a target by each of the main lobe and the two side lobes on both sides thereof.

(2-2) Configuration and Operation of Radar Device in Case of FM-CW Method Hereinafter, the configuration of the radar device and the target detection method of this embodiment when the radar method is the FM-CW method will be described with reference to FIGS. Will be described with reference to FIG.

FIG. 12 is a block diagram showing the configuration of the radar apparatus (FM-CW radar apparatus 2) of the present embodiment. Since this block diagram has a configuration similar to that shown in FIG. 7, only the differences will be described, and redundant description will be omitted. The digital circuit unit 18a described later is an example of a distance calculation unit and a control unit.
As shown in FIG. 12, the radar apparatus 2 includes three receiving antennas RA1 to RA3. The receiving antennas RA1 to RA3 are examples of first to third receiving antennas, respectively.
The reception antenna RA1 has the same directivity characteristics as the transmission antenna TA1, for example. The receiving antenna RA2 has a directivity characteristic in which the azimuth angle of the null point in the reference plane based on the main lobe direction is different only in the first rotation direction in the reference plane, as compared with the receiving antenna RA1. . Receiving antenna RA3 has an azimuth angle of a null point in the reference plane based on the direction of the main lobe, only in a second rotation direction opposite to the first rotation direction in the reference plane, as compared with receiving antenna RA1. It has different directivity characteristics.
Here, in the example shown in FIG. 11, the reference plane is equal to the plane of the monitoring area (crosswalk). The first rotation direction is a direction rotating from the main lobe toward the one side lobe on the reference plane, and the second rotation direction is a direction rotating from the main lobe toward the other side lobe on the reference plane. is there.

For example, the digital circuit unit 18a controls the switch 14a so that the reception wave is received by selecting the reception antennas RA1 to RA3 in order.
The digital circuit unit 18a has the same configuration as the digital circuit unit 18 described above, but differs in the following points. That is, the digital circuit unit 18a has the same distances calculated when the receiving antennas RA1 to RA3 are selected, and the reception levels of the receiving antennas serving as the basis for calculating the distances are P1 to P3, respectively. Then, the difference between P1 and P2 and the difference between P1 and P3 are calculated. Then, the digital circuit unit 18a determines whether the calculated distance is due to reception of the main lobe of the reception antenna, the side lobe in the first rotation direction, or the side lobe in the second rotation direction based on each difference.

  FIG. 13 shows an example of the operation of the switch 14a controlled by the digital circuit unit 18a. In the example shown in FIG. 13, after the radar apparatus 2 is activated (after time t0), a period T1 in which the receiving antenna RA1 is selected, a period T2 in which the receiving antenna RA2 is selected, and a period in which the receiving antenna RA3 is selected. The switch 14a is controlled so that T3 occurs alternately. However, this operation example is merely an example, and the receiving antennas RA1 to RA3 may be selected at least once each.

The target detection method of this embodiment is demonstrated below with reference to FIGS. In the following description, the directivity characteristics of the reception antenna RA1 and the transmission antenna TA are the same as those shown in FIG.
14A shows an example of the directivity characteristic of the reception antenna RA2 (solid line) (note that the directivity characteristic of the reception antenna RA3 is indicated by a dotted line), and FIG. 14B shows an example of the directivity characteristic of the reception antenna RA3 (solid line). The dotted line indicates the directivity characteristic of the receiving antenna RA2.) In FIG. 14A, the directivity characteristic of the reception antenna RA2 coincides with the directivity characteristic of the reception antenna RA1 at a minus azimuth angle (angle in the second rotation direction), and a positive azimuth angle (angle in the first rotation direction). , The azimuth angle of the null point in the reference plane has a directivity characteristic different from that of the receiving antenna RA1. In FIG. 14B, the directivity characteristic of the reception antenna RA3 coincides with the directivity characteristic of the reception antenna RA1 at the positive azimuth angle (angle in the first rotation direction), and the negative azimuth angle (in the second rotation direction). In the angle), the azimuth angle of the null point in the reference plane has a directivity characteristic different from that of the receiving antenna RA1.

  As in the first embodiment, when the receiving antenna RA1 is selected, the antenna gains of the transmitting antenna TA and the receiving antenna RA1 are both equal, and therefore, as shown in FIG. The antenna gain is doubled.

FIG. 15 shows (a) a reception level when the reception antenna RA2 is selected, and (b) a reception level when the reception antenna RA3 is selected.
As shown in FIG. 15A, when the reception antenna RA2 is selected, the directivity characteristic of the reception antenna RA2 is the same as the directivity characteristic of the reception antenna RA1 at the minus azimuth angle (angle in the second rotation direction). Therefore, the reception level is the same as that when the reception antenna RA1 is selected (the same level as in FIG. 3B). On the other hand, the directivity characteristic of the reception antenna RA2 has a directivity characteristic in which the azimuth angle of the null point in the reference plane is different from that of the reception antenna RA1 at the + azimuth angle (the angle in the first rotation direction). The reception level in the side lobe is lower than when the reception antenna RA1 is selected.

  As shown in FIG. 15B, when the reception antenna RA3 is selected, the directivity characteristic of the reception antenna RA3 is the directivity characteristic of the reception antenna RA1 at the positive azimuth angle (the angle in the first rotation direction). Therefore, the reception level is the same as that when the reception antenna RA1 is selected (the same level as in FIG. 3B). On the other hand, the directivity characteristic of the reception antenna RA3 has a directivity characteristic in which the azimuth angle of the null point in the reference plane is different from that of the reception antenna RA1 at the minus azimuth angle (angle in the second rotation direction). The reception level in the side lobe is lower than when the reception antenna RA1 is selected.

  FIG. 16 is a diagram in which FIG. 3B and FIG. 15 are easily compared. In FIG. 16A, the solid line indicates the reception level when the reception antenna RA2 is selected (same as FIG. 15A), and the dotted line indicates the reception level when the reception antenna RA1 is selected (FIG. 3B). The same). In FIG. 16B, the solid line indicates the reception level when the reception antenna RA3 is selected (same as FIG. 15B), and the dotted line indicates the reception level when the reception antenna RA1 is selected (FIG. 3B). The same).

  Here, with respect to a target having the same distance calculated by the receiving antennas RA1 to RA3, the difference between the receiving levels P1 and P2 of the receiving antennas RA1 and RA2 that are the basis of the calculation of the distance is shown in FIG. It can be seen that this occurs only at the azimuth angle (angle in the first rotation direction). Similarly, with respect to a target having the same distance calculated by the receiving antennas RA1 to RA3, the difference between the reception levels P1 and P3 of the receiving antennas RA1 and RA3, which is the basis for calculating the distance, is shown in FIG. It can be seen that this occurs only at the azimuth angle (angle in the second rotation direction). Therefore, by comparing the reception levels obtained by the reception antennas RA1 to RA3, it is possible to determine in which rotational direction the side lobe has detected the target.

The digital circuit unit 18a (see FIG. 12) performs a distance calculation process to a target based on a transmission wave and a reception wave. In the distance calculation process, the reception antennas RA1 to RA3 are sequentially selected and performed. When the distances calculated when the reception antennas RA1 to RA3 are all equal, the digital circuit unit 18a sets the reception levels (for example, reception power) of the reception antennas that are the basis for calculating the distances to P1 to P1, respectively. When P3 is set, the following processing is performed.
That is, when P1 and P2 are compared, and | P1-P2 |> _PTH ( _PTH : predetermined threshold), the side lobe of the positive azimuth (angle in the first rotation direction) of the receiving antenna It is determined that it is calculated (that is, the target is present in the side lobe direction with a positive azimuth angle). When P1 and P3 are compared, and | P1-P3 |> _PTH ( _PTH : predetermined threshold), it is calculated by the side lobe of the negative azimuth (angle in the second rotation direction) of the receiving antenna. (That is, the target exists in the side lobe direction of the azimuth angle of-). If there is no difference between the reception levels P1 to P3 that is the basis for calculating the distance, it is determined that the calculation is based on the main lobe (that is, the target exists in the main lobe direction).

  As described above, according to the radar apparatus of this embodiment, in addition to the effects described in the first embodiment, the detection of the target by each of the main lobe of the antenna and the two side lobes on both sides thereof is performed. Can be carved.

  Regarding the above embodiment, the following additional notes are disclosed.

(Appendix 1)
A transmitting antenna for radiating the transmitted wave to space;
A first receiving antenna for receiving a reflected wave by a target of the transmitted wave as a received wave;
A reception antenna for receiving a reflected wave of a target of the transmission wave as a reception wave, and compared with the first reception antenna, an azimuth angle of a null point in a reference plane based on a direction of a main lobe A second receiving antenna having different directivity characteristics;
A distance calculator that calculates the distance to the target based on the transmitted wave and the received wave;
Each receiving antenna that is selectively switched between the first and second receiving antennas and that the distances calculated by the distance calculating unit are equal when the first and second receiving antennas are selected and is the basis for calculating the distance. When the reception levels of the reception antennas are the first and second reception levels, respectively, the calculated distance is based on the difference between the first reception level and the second reception level. A control unit for determining whether or not
A radar apparatus comprising:

(Appendix 2)
A transmitting antenna for radiating the transmitted wave to space;
A first receiving antenna for receiving a reflected wave by a target of the transmitted wave as a received wave;
A reception antenna for receiving a reflected wave of a target of the transmission wave as a reception wave, and compared with the first reception antenna, an azimuth angle of a null point in a reference plane based on a direction of a main lobe A second receiving antenna having different directivity characteristics only in the first rotation direction in the reference plane;
A receiving antenna for receiving a reflected wave of a target of the transmitted wave as a received wave, and an orientation of a null point in the reference plane based on a direction of a main lobe compared to the first receiving antenna A third receiving antenna having a directional characteristic whose angle is different only in a second rotation direction opposite to the first rotation direction in the reference plane;
A distance calculator that calculates the distance to the target based on the transmitted wave and the received wave;
When the first, second and third receiving antennas are selectively switched and the first, second and third receiving antennas are selected, the distances calculated by the distance calculation unit are all equal, and the distance is calculated. Difference between the first reception level and the second reception level, and between the first reception level and the third reception level A control unit for determining whether the calculated distance is due to reception of the main lobe of the receiving antenna, the side lobe in the first rotation direction, or the side lobe in the second rotation direction based on the difference;
A radar apparatus comprising:

(Appendix 3)
A transmitting antenna for radiating the transmitted wave to space;
A first receiving antenna for receiving a reflected wave by a target of the transmitted wave as a received wave;
A reception antenna for receiving a reflected wave of a target of the transmission wave as a reception wave, and compared with the first reception antenna, an azimuth angle of a null point in a reference plane based on a direction of a main lobe Is a target detection method in a radar apparatus comprising: a second receiving antenna having different directivity characteristics in at least one rotation direction in the reference plane,
Select the first receiving antenna, calculate the distance to the target based on the transmitted wave and the received wave by the first receiving antenna,
Select the second receiving antenna, calculate the distance to the target based on the transmitted wave and the received wave by the second receiving antenna,
When the distances calculated when the first and second receiving antennas are selected are equal, and the reception level of each receiving antenna that is the basis for calculating the distance is the first and second reception levels, respectively, Based on the difference between the first reception level and the second reception level, it is determined whether the calculated distance is due to reception of the main lobe or the side lobe of the reception antenna.
A target detection method.

DESCRIPTION OF SYMBOLS 1, 2 ... Radar apparatus 11 ... Voltage controlled oscillator 12 ... Directional coupler 13 ... Amplifier 14, 14a ... Switch 15 ... Amplifier 16 ... Mixer 17 ... Filter 18, 18a ... Digital circuit part 181 ... Signal generator 182 ... D / A converter 183 ... A / D converter 184 ... FFT processing unit 185 ... distance calculation unit 186 ... interface unit 187 ... A / D converter 188 ... switch control unit 100 ... signal processing unit TA ... transmitting antenna RA1, RA2, RA3 ... Receiving antenna

Claims (2)

A transmitting antenna for radiating the transmitted wave to space;
A first receiving antenna for receiving a reflected wave by a target of the transmitted wave as a received wave;
A reception antenna for receiving a reflected wave of a target of the transmission wave as a reception wave, and compared with the first reception antenna, an azimuth angle of a null point in a reference plane based on a direction of a main lobe A second receiving antenna having different directivity characteristics;
A distance calculator that calculates the distance to the target based on the transmitted wave and the received wave;
Each receiving antenna that is selectively switched between the first and second receiving antennas and that the distances calculated by the distance calculating unit are equal when the first and second receiving antennas are selected and is the basis for calculating the distance. When the reception levels of the reception antennas are the first and second reception levels, respectively, the calculated distance is based on the difference between the first reception level and the second reception level. A control unit for determining whether or not
A radar apparatus comprising: A transmitting antenna for radiating the transmitted wave to space;
A first receiving antenna for receiving a reflected wave by a target of the transmitted wave as a received wave;
A reception antenna for receiving a reflected wave of a target of the transmission wave as a reception wave, and compared with the first reception antenna, an azimuth angle of a null point in a reference plane based on a direction of a main lobe A second receiving antenna having different directivity characteristics only in the first rotation direction in the reference plane;
A receiving antenna for receiving a reflected wave of a target of the transmitted wave as a received wave, and an orientation of a null point in the reference plane based on a direction of a main lobe compared to the first receiving antenna A third receiving antenna having a directional characteristic whose angle is different only in a second rotation direction opposite to the first rotation direction in the reference plane;
A distance calculator that calculates the distance to the target based on the transmitted wave and the received wave;
When the first, second and third receiving antennas are selectively switched and the first, second and third receiving antennas are selected, the distances calculated by the distance calculation unit are all equal, and the distance is calculated. Difference between the first reception level and the second reception level, and between the first reception level and the third reception level A control unit for determining whether the calculated distance is due to reception of the main lobe of the receiving antenna, the side lobe in the first rotation direction, or the side lobe in the second rotation direction based on the difference;
A radar apparatus comprising:

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