JP5182645B2 - Radar device and obstacle detection method - Google Patents

Description

  The present invention relates to a radar apparatus that verifies an obstacle using a high-frequency radar such as a millimeter wave, and more particularly to a radar apparatus that uses an electronic scanning antenna such as an array antenna that electronically scans an antenna beam.

  Conventionally, a vehicle including a radar device in front or rear in order to detect an obstacle has been put into practical use. This radar device detects obstacles using the reflected wave of the transmitted pulse wave and obtains the inter-vehicle distance and relative speed, so the vehicle avoids collision with obstacles and warns the driver. Can do.

  As a radar apparatus used in this vehicle, for example, an FM-CW radar apparatus that uses a frequency modulation pattern that increases or decreases the frequency of a signal to be transmitted along a triangular wave, or a CW radar apparatus that switches a plurality of frequencies in a time division manner is known. Yes.

FIG. 6 is a diagram for explaining an obstacle detection range of the in-vehicle radar device.
In the vehicles 602, 603, 608, and 609 shown in FIGS. 6A and 6C, there are areas where radio wave interference occurs due to overlapping detection ranges, as shown in the angular areas 602a, 603a, 608a, and 609a. Although the main lobe of the antenna is narrow, the radar detection range of the obstacle is narrow.

  Also, as shown in the vehicles 605, 606, 611, and 612 in FIGS. 6B and 6D, the beam pattern of the directional antenna is changed to suppress the influence of the side lobe and expand the range of the main lobe. There is a radar device.

  By the way, beam scanning is performed by providing a difference in path length from each antenna element to the power distribution point of the transmission signal between adjacent antenna elements without using a phase shifter. A radar apparatus is disclosed in which the directivity of the beam can be changed with a simple configuration without causing an increase in size by controlling the directivity by turning OFF (see, for example, Patent Document 1).

  Further, an FM-CW radar apparatus is disclosed in which a filter for reducing spike noise generated by radio wave interference is provided to efficiently suppress the generated spike-like noise component and improve obstacle detection capability ( For example, see Patent Document 2). In this FM-CW radar apparatus, a complicated processing circuit is required, such as digitally converting a beat signal to obtain a difference for each data.

JP 2007-17294 A JP 2006-242818 A

  However, as shown in the angle regions 605a, 606a, 611a, and 612a in FIGS. 6B and 6D, when the radar detection range of the transmission antenna in the radar apparatus is simply widened, an interference region where the detection ranges overlap is formed. There is a problem that radio interference from other vehicles is caused.

  When radio wave interference occurs, the detection accuracy of the radar apparatus deteriorates, and in the worst case, there is a problem that a target such as a preceding vehicle cannot be recognized. In particular, in the case of an on-vehicle radar device, the measured distance to the partner vehicle and the relative speed are used to prevent a collision with the partner vehicle. However, when radio wave interference occurs between a plurality of radar devices, the distance, relative There is a problem that the speed cannot be detected correctly and the collision prevention function does not operate correctly.

  The present invention has been made in view of the above problems, and even when the detection range of the antenna is widened, it is possible to accurately determine whether or not radio interference with other radar apparatuses has occurred in the received signal. Another object of the present invention is to provide a radar apparatus that can appropriately avoid the detection performance deterioration of the preceding vehicle and the decrease in the recognition level.

  In order to solve the above problems, a radar apparatus according to the present invention is a radar apparatus that detects an obstacle by performing an operation in a signal detection unit based on a transmission signal from a transmission unit and a reception signal received in the reception unit. The transmission unit generates a transmission signal generation unit that generates a plurality of transmission signals using different values of predetermined radio wave characteristics, and generates a composite wave of the plurality of transmission signals generated by the transmission signal generation unit And a transmission antenna unit that includes a plurality of antenna elements, and that changes the directivity of the beam based on the radio wave characteristics of the transmission signal of the combined wave generated by the combined wave generation unit. It is characterized by that.

  With this configuration, the transmission unit can generate a plurality of transmission signals having different radio wave characteristic values in the generation signal generation unit, and can generate a synthetic wave of the transmission signal in the synthetic wave generation unit. It is possible to direct the beam in the direction corresponding to.

  Further, in the radar apparatus according to the present invention, the radio wave characteristic is a frequency, the transmission signal generating unit generates a plurality of transmission signals having different frequencies, and the synthesized wave generating unit is connected to the transmission signal generating unit. A plurality of transmission signals are combined to generate a combined wave, and the transmission antenna unit transmits a beam from the antenna element while changing a beam directivity based on a frequency of the transmission signal of the combined wave. To do.

  With this configuration, the generated signal generating unit generates a plurality of generated signals having different frequencies, the combined wave generating unit combines the plurality of generated signals to generate a combined wave, and generates a combined wave from the transmitting antenna unit at an angle corresponding to the frequency. The beam can be directed and transmitted.

  Further, the signal detection unit of the radar apparatus according to the present invention uses a beat signal that is a difference signal between the transmission signal and the reception signal to detect a frequency of the reception signal received at the reception antenna of the reception unit. Means, an angle detection means for detecting a reception angle of the reception signal with respect to the reception antenna, and a frequency of the transmission signal in the angle region detected by the angle detection means when the reception unit receives the reception signal; Frequency comparison means for comparing the frequency of the received signal detected by the frequency detection means, and obstacle recognition means for performing obstacle recognition processing using output data from the frequency comparison means, the frequency comparison means If the frequency does not match by the comparison, the received signal is determined as an interference signal, and the output data to be processed by the obstacle recognizing means is determined. Characterized in that the exclusion of the received signal from the data.

  With this configuration, the frequency comparison unit compares the frequency assigned to the angle of the transmission wave with the frequency detected by the frequency detection unit, and if the frequency does not match, the received signal is transmitted from the vehicle. Since it can be determined that the signal is not an interference signal and can be excluded from the data to be processed by the obstacle recognizing means, it is possible to appropriately avoid deterioration in detection performance of the preceding vehicle and reduction in recognition level caused by radio wave interference.

  The transmission unit of the radar apparatus according to the present invention further includes a variable phase shifter that adjusts the phase of a transmission signal supplied to the antenna element of the transmission antenna unit, and the variable phase shifter is connected to an adjacent antenna element. It is characterized by adjusting so as to increase the phase difference of the supplied transmission signal.

  With this configuration, it is possible to increase the phase difference between transmission signals supplied to adjacent antenna elements in the variable phase shifter, and to effectively scan in the beam direction using the frequency scanning method.

  The antenna unit of the transmission unit and the reception unit of the radar device according to the present invention is an array antenna in which a plurality of antenna elements are arranged in an array, and the radar device is a CW radar device or an FM-CW radar device. With this configuration, the radar apparatus according to the present invention can be a CW radar apparatus or FM-CW radar apparatus using an array antenna.

  Needless to say, the obstacle detection method according to the present invention can be realized as a program on a computer or the like, or the program can be distributed via a recording medium such as a DVD or CD-ROM or a transmission medium such as a communication network. Yes.

  In the radar apparatus according to the present invention, it is possible to appropriately detect that an interference signal is an interference signal by comparing the frequencies assigned to each angle region even when radio interference occurs with the radar apparatus of another vehicle. It is possible to appropriately avoid the deterioration of the detection performance of the preceding vehicle and the decrease of the recognition level caused by the interference.

Functional block diagram of a transmission unit of a radar apparatus according to an embodiment The flowchart which shows the operation | movement procedure of the transmission part of the radar apparatus which concerns on embodiment Functional block diagram of a receiving unit and a signal processing unit of a radar apparatus according to an embodiment The flowchart which shows the operation | movement procedure of the signal processing part of the radar apparatus which concerns on embodiment Explanatory drawing at the time of radio wave interference between vehicles equipped with a radar device according to an embodiment The figure explaining the detection range of the obstacle of an in-vehicle radar device

Hereinafter, embodiments of a radar apparatus according to the present invention will be described with reference to the drawings.
(Embodiment)
FIG. 1 is a functional block diagram of a transmission unit 100 of a radar apparatus according to the present embodiment.

  The radar apparatus according to the present embodiment is, for example, a millimeter wave radar mounted on a vehicle, and a distance to an obstacle using a millimeter wave with a wavelength of 1 to 10 mm and a very high frequency of 30 to 300 GHz. A distance measuring function for measuring the speed and a speed measuring function for measuring the speed with respect to the obstacle are provided. The purpose of use of the radar apparatus includes pre-crash safety (PCS) and automatic cruise control (ACC), which are controls for assisting warning, display, danger avoidance, and the like. The radio wave used in the radar apparatus is not limited to the above-described millimeter wave. For example, radio waves in the 24 GHz or 26 GHz band may be used.

  Also, the radar apparatus according to the present embodiment uses a frequency scanning method in which a beam is scanned electronically using a plurality of different frequencies in order to expand the radar detection area. This frequency scanning method will be described later.

  As shown in the figure, the transmission unit 100 includes a plurality of transmission signal generation units 101 to 103, a plurality of variable phase shifters 105 corresponding to the combined wave generation units 104 and 1 to K, and a plurality of phase shifters 105 corresponding to the K. Amplitude adjusters 106 and a plurality of antenna elements 107 corresponding to 1 to K.

  The transmission signal generation units 101 to 103 generate a transmission signal that is a signal of a transmission wave used for obstacle detection at a frequency (for example, 75.5 GHz, 76 GHz, 76.5 GHz, etc.) assigned in advance.

  The synthetic wave generation unit 104 generates a synthetic wave (complex wave) obtained by synthesizing the displacements at the respective points of the transmission signals having different frequencies generated by the transmission signal generation units 101 to 103.

  The variable phase shifter 105 supplies a high-frequency signal whose predetermined phase has been changed to the antenna element 107 side. When the main beam is scanned at an arbitrary angle θ using the phase scanning method, the phase can be delayed by using the variable phase shifter 105 by Kdsinθ as the antenna element number (k) of the inter-antenna distance d increases. good. In FIG. 1, the variable phase shifter 105 is shown in order to explain the method of changing the directivity of the antenna by changing the phase of the variable phase shifter 105 in the following. In order to change the directivity of the beam using the scanning method, scanning in the beam direction is not performed using the variable phase shifter 105.

As shown in equation (2) to be described later, by increasing the phase difference δ _k of the transmission signal supplied to the adjacent antenna element 107 in the variable phase shifter 105, the beam can be effectively used by using the frequency scanning method. The direction can be scanned.

  The amplitude adjuster 106 amplifies the amplitude of the transmission signal supplied from the variable phase shifter 105 and supplies the amplified signal to the antenna element 107 side. In the drawing, a processing unit such as a power feeding circuit for amplifying a transmission signal in the transmission unit 100 is omitted.

  A plurality of antenna elements 107 (K in this figure) are provided to form a linear linear array antenna, and each antenna element 107 is a planar dipole antenna or a slot antenna. From this antenna element, the main beam is directed and transmitted in the direction of an angle θ corresponding to the frequency of the transmission signal.

  Here, a frequency scanning method generally used as a beam scanning method of the array antenna will be described. This frequency scanning method is a method of scanning by changing the direction of the beam from each antenna element by changing the frequency of the transmission signal.

  When described using a linear linear array antenna composed of K antenna elements in FIG. 1, the array factor is expressed by the following equation (1).

ここで、Ａ_kは各々の振幅、ｆは周波数、ｄ_kはアンテナ基準点からの距離、ｃは光速、θはビームの角度、δ_kは位相器の位相である。
そして、このアレーアンテナのメインローブをある角度θに向けるための条件は、下記の式（２）で示される。

Here, A _k is the amplitude, f is the frequency, d _k is the distance from the antenna reference point, c is the speed of light, θ is the angle of the beam, and δ _k is the phase of the phase shifter.
The condition for directing the main lobe of the array antenna to a certain angle θ is expressed by the following equation (2).

As shown in this equation (2), the angle θ at which the main lobe of the antenna is directed depends on three phases: phase shifter phase δ _k , frequency f, and distance d _k from the antenna reference point. The frequency scanning method is an electronic scanning method in which the main lobe angle θ is greatly changed by the difference in the frequency f by increasing the phase δ _k between the antenna elements from the equation (2). In the phase scanning method for use in a millimeter-wave radar or the like, changing the angle θ of the main lobe by changing the phase [delta] _k in this.

  In the present invention, based on the characteristics of such an array antenna, the transmission signals are generated by assigning different frequencies to the transmission signals using the plurality of transmission signal generation units 101 to 103, so that the angle assigned to the frequency is set. Each beam is transmitted.

  In the present embodiment, description has been made on the assumption that the transmission signal generators 101 to 103 are configured. However, the number of generated transmission signals having different frequencies is not limited to three. By dividing into a plurality, it is possible to further improve the radio wave interference detection accuracy.

  Further, FIG. 1 illustrates the case where a transmission signal with one frequency characteristic is generated from one transmission signal generation unit, but one transmission signal generation unit generates a plurality of transmission signals having different frequencies. May be output to the combined wave generator. It is also conceivable that the transmission signal generator and the synthesized wave generator are one processing unit.

  In the array antenna, the line length (L) from the power supply to the antenna element is different. The frequency changes due to the difference in the line length (L), and the phase distribution changes with the change in the frequency to change the directivity of the antenna. Therefore, beam scanning by frequency scanning can be performed similarly by changing the line length (L). This is because the scanning sensitivity with respect to frequency can be increased by increasing the line length (L) and the L / d of the antenna interval d. In order to increase the scanning sensitivity, it is necessary to use a snake line, for example, to make the feed line length (L) long.

  FIG. 2 is a flowchart showing an operation procedure of the transmission unit 100 of the radar apparatus according to the present embodiment.

  First, the transmission signal generation units 101 to 103 generate transmission signals having three different frequencies (step S201). Next, a composite wave of three transmission signals is generated in the composite wave generation unit 104 (step S202), and after undergoing amplification processing and the like, the main beam is directed from the antenna element 107 of the antenna unit in an angle direction according to the frequency of the transmission signal. Is directed and transmitted (step S203).

FIG. 3 is a functional block diagram of the receiving unit 300 and the signal processing unit 307 of the radar apparatus according to the present embodiment.
In this figure, the receiving unit 300 includes a receiving antenna element 301, a low noise amplifier circuit 302 (LNA: Low Noise Amplifier), a mixer 303, a local oscillator (OSC: Oscillator) 304, and an A / D converter 306.

  The signal processing unit 307 includes a fast Fourier transform (FFT) 307a, an angle detection unit 307b, a frequency comparison unit 307c, and a target recognition unit 307d.

First, the receiving unit 300 will be described. The receiving unit 300 separates a desired signal from an external interference signal and amplifies the received signal to an intensity required for digital automatic signal processing.
The receiving antenna element 301 receives a received wave transmitted from the transmitting unit 100 and reflected by an obstacle. Note that the antenna element 301 can also be used as the antenna element 107 of the transmission unit 100 by switching between transmission and reception.
The low noise amplifier circuit 302 performs processing for amplifying the received signal and lowering the total noise figure before the mixer 303.

  The mixer 303 is a beat signal 305 that is a difference signal between a transmission signal from a local oscillator 304 provided as a transmission signal generation source and a reception signal input from the low-noise amplifier circuit 302 received by the antenna of the reception unit 300. Is synthesized and output.

  The A / D converter 306 is a processing unit that outputs the amplitude and phase information of the received signal as a digital signal. The input analog format beat signal is quantized and encoded to be converted into a digital format beat signal. The signal is converted and output to the signal processing unit 307 side.

Next, the signal processing unit 307 will be described.
The fast Fourier transform unit 307a performs Fourier transform on the beat signal converted into a digital signal by the A / D converter 306, calculates the frequency spectrum of the received signal, and calculates the distance to the obstacle and the relative speed.

  In the present embodiment, the angle detection unit 307b obtains the direction θ of the received signal from the phase difference of the signals received by the respective antennas using, for example, a phase monopulse method. Here, the phase difference can be obtained by the following expression (3) from the arrival angle, the antenna element interval, and the wavelength λ of the carrier wave. Therefore, the direction θ of the received signal can be calculated using Equation (3).

  The frequency comparison unit 307c compares the frequency of the reception signal calculated by the fast Fourier transform unit 307a with the frequency assigned to the reception direction of the reception signal detected by the angle detection unit 307b, and only when they match. The calculation result is output to the target recognition unit 307d.

In comparison with the frequency in the frequency comparison unit 307c, it is necessary to consider a frequency shift due to the Doppler shift, but the frequency shift amount due to the Doppler shift is relative when a high-frequency millimeter wave is used in a CW radar device or the like. Therefore, it is determined that the minute frequency shift amount is not due to radio wave interference.
The target recognition unit 307d performs target recognition processing using distance data to the obstacle and the like, and outputs a recognition result to the data output unit 308.

  FIG. 4 is a flowchart showing an operation procedure of the signal processing unit 307 of the radar apparatus according to the present embodiment.

First, it is determined whether or not there is a digital signal input from the A / D converter 306 (step S401).
Next, when the digitally converted signal is input to the signal processing unit 307 (YES in step S401), the fast Fourier transform unit 307a detects the frequency of the received signal (step S402). Further, the angle detection unit 307b detects the reception angle of the reception signal (step S403).

  Then, the frequency comparison unit 307c performs a loop process that compares the frequency corresponding to the angular region of the transmitted signal with the frequency corresponding to the angular region of the received signal. That is, the frequency comparison unit 307c compares the frequency of the signal transmitted for each angle region with the frequency of the received signal (step S404), and if the frequencies do not match (NO in step S405), the interference Processing to determine that the signal is excluded from the processing target is performed (step S406). On the other hand, if the frequencies match (YES in step S405), the calculation result is output to the target recognition unit 307d (step S407). Here, a comparison loop process is performed in all angle regions.

  FIG. 5 is an explanatory diagram at the time of radio wave interference between vehicles on which the radar apparatus according to the present embodiment is mounted.

FIG. 5 (a) shows a case where a plurality of vehicles 501 to 503 are running on a road having two or more lanes. A signal transmitted by another vehicle is reflected on a preceding vehicle or the like, and the vehicle receives the signal. It is a figure explaining a case. In other words, the radar device of the vehicle 502 transmits transmission signals having different frequencies corresponding to, for example, the three angular regions 502a , 502b, and 502c.

  And the signal of the frequency allocated to the radar angle area | region 502b which the radar apparatus of the vehicle 502 transmitted is reflected in the vehicle 501, and is received as a received signal. On the other hand, the transmission signal assigned to the radar angle region 503 a transmitted by the radar device of the vehicle 503 is reflected by the vehicle 501 and received by the vehicle 502. That is, the radar device of the vehicle 502 transmits a transmission signal assigned to the angle region 502b transmitted by the host vehicle and reflected by the vehicle 501 and a transmission signal assigned to the angle region 503a transmitted by the vehicle 503 and reflected by the vehicle 501. Will be received as a received signal.

  In the radar apparatus according to the present invention, the frequency comparison unit 307c of the signal processing unit 307 compares the frequency assigned to the angle region of the reception signal with the frequency of the reception signal actually received, and as a result, the frequency Are not matched, they are excluded from the target recognition process as interference signals. That is, in FIG. 5A, the frequency of the signal reflected and received from the angle region 503a of the vehicle 503 to the vehicle 501 is different from the frequency assigned to 502b, and thus is excluded from the target recognition process as an interference signal.

  As described above, the radar apparatus mounted on the vehicle 502 in this figure assigns different frequencies to the reception signal from the front and the reception signal from the oblique direction, and therefore, it is transmitted from the own vehicle and reflected by the obstacle. Whether the signal is a signal or a signal transmitted from another vehicle and reflected by an obstacle can be appropriately distinguished, and erroneous recognition of the obstacle can be prevented appropriately.

  FIG. 5B is an explanatory diagram of radio wave interference of a radar device mounted on a plurality of vehicles 504 to 506 in the oncoming lane. The radar device of the vehicle 505 transmits a transmission signal in the angle regions 505c, 505b, and 505a.

  Then, the transmission signal assigned to the angle region 505 b transmitted by the radar device of the vehicle 505 can be reflected by the vehicle 504 and received. On the other hand, radio wave interference occurs between the transmission signal of the radar angular region 505c transmitted by the radar device of the vehicle 505 and the transmission signal of the radar angular region 506c transmitted by the radar device of the vehicle 506. In this case, since the radar device of the vehicle 505 has the same frequency band, data cannot be excluded in the frequency comparison. However, since the radar device of the vehicle 505 detects the vehicle 504 using the received signal from the angle region 505b, an appropriate brake control or the like can be realized for the vehicle 504.

  As described above, the transmission unit 100 of the radar apparatus according to the present invention generates a plurality of transmission signals having different frequencies and generates a composite wave of these transmission waves. Further, by increasing the phase between adjacent antennas with an array antenna or the like, the transmission signal is transmitted using antennas having different beam directivities for each frequency of the transmission signal. Further, the frequency comparison unit 307c of the signal processing unit 307 compares the frequency corresponding to the angle region of the received radio wave, and if the frequency does not match, it is excluded from the target recognition processing data as an interference signal. For this reason, even if the detection area of the antenna of the radar apparatus is widened, problems such as deterioration in detection performance of the preceding vehicle due to radio wave interference and inability to recognize it can be appropriately avoided.

  Even in the case of receiving broadband spike noise that is an interference signal from an oncoming vehicle, the spike noise becomes low level in the frequency domain in the process of performing fast Fourier transform in the CW radar device or pulse radar device, and thus spikes. The target detection performance of the radar apparatus according to the present invention is not deteriorated by noise.

  The radar apparatus according to the present invention can be applied to, for example, a CW radar apparatus, an FM-CW radar apparatus, and a pulse radar apparatus having a narrow beam width as a vehicle-mounted radar apparatus that is a moving body.

DESCRIPTION OF SYMBOLS 100 Transmission part 101,102,103 Transmission signal generation part 104 Synthetic wave generation part 105 Variable phase shifter 106 Amplitude adjuster 107,301 Antenna element 300 Reception part 302 Low noise amplifier circuit 303 Mixer 304 Local oscillator 305 Beat signal 306 A / D Converter 307 Signal processing unit 307a Fast Fourier transform unit 307b Angle detection unit 307c Frequency comparison unit 307d Target recognition unit 308 Data output unit 501, 502, 503, 504, 505, 506 Vehicle

Claims (6)

Based on the received signal received by the receiver and the transmission signal from the transmitter, a radar device for detecting obstacles,
The transmitter is
Transmission signal generating means for generating a plurality of transmission signals using values having different frequencies ;
Combined wave generating means for generating a combined wave of a plurality of transmission signals generated in the transmission signal generating means;
A transmission antenna unit comprising a plurality of antenna elements, and transmitting by changing the directivity of the beam based on the frequency of the transmission signal of the synthesized wave generated by the synthesized wave generating means ;
A signal detection unit for detecting an obstacle based on the transmission signal and the reception signal;
The signal detector is
Using a beat signal that is a difference signal between at least one transmission signal and a reception signal among the plurality of transmission signals, a frequency detection unit that detects a frequency of the reception signal received at the reception antenna of the reception unit;
Angle detection means for detecting a reception angle of the reception signal with respect to a reception antenna;
A frequency comparison unit that compares the frequency of the transmission signal in the angle region detected by the angle detection unit with the frequency of the reception signal detected by the frequency detection unit when the reception unit receives the reception signal;
Including obstacle recognition means for performing obstacle recognition processing from output data of the frequency comparison means when the frequencies match in the comparison of the frequency comparison means,
Radar device. Before Symbol frequency comparison means, if no frequency is matched by the comparison, the received signal is judged that an interference signal, the received signal from the output data of said frequency comparison means to be processed of the obstacle recognition means excludes claim 1 radar system in accordance. The transmitter further includes:
A variable phase shifter that adjusts a phase of a transmission signal supplied to an antenna element of the transmission antenna unit, and the variable phase shifter adjusts so as to increase a phase difference between transmission signals supplied to adjacent antenna elements. Item 2. The radar device according to item 1 . The antenna unit of the transmitter and the receiver of the radar device is an array antenna in which a plurality of antenna elements are arranged in an array,
The radar device according to any one of claims 1 to 3 , wherein the radar device is a CW (Continuous Wave) radar device or an FM-CW (Frequency Modulation-Continuous Wave) radar device. Based on the received signal received in the transmission signal and the reception section from the transmitting unit, a obstacle detection method for use in a radar apparatus for detecting obstacles,
A transmission signal generation step of generating a plurality of transmission signals using values having different frequencies ;
A synthetic wave generating step for generating a synthetic wave of a plurality of transmission signals generated in the transmission signal generating step ;
A transmission step of transmitting by changing the directivity of the beam based on the frequency of the transmission signal of the synthetic wave generated in the synthetic wave generation step;
A frequency detection step of detecting a frequency of a reception signal received at a reception antenna of the reception unit using a beat signal which is a difference signal between at least one transmission signal and a reception signal among the plurality of transmission signals;
An angle detection step of detecting a reception angle of the reception signal with respect to a reception antenna;
A frequency comparison step of comparing the frequency of the transmission signal in the angle region detected in the angle detection step with the frequency of the reception signal detected in the frequency detection step when the reception unit receives the reception signal;
From the output data of the frequency comparison step when the frequencies match in the comparison of the frequency comparison step, an obstacle recognition step of performing an obstacle recognition process,
Obstacle detection method. In prior Symbol frequency comparison step, if no frequency is matched by the comparison, the received signal is judged that an interference signal, the received signal from the output data of the frequency comparison step to be processed in the obstacle recognition step The obstacle detection method according to claim 5 .

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