JP2003161775A - Target detecting method and radar device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a radar device that enables the detection of a near target even under a condition that an unnecessary component exists. <P>SOLUTION: The radar device is provided with transmitting means (101-104), outputting a continuous wave to which a prescribed non-linear frequency modulation is applied as a transmission signal, a receiving means (105), receiving the transmitting signal reflected by the target as a receiving signal, power spectrum means (106-111), determining a beat signal based on the transmitting and the receiving signals and converting the beat signal into a power spectrum, and a detecting means (113) for the presence of the object, determining a frequency width of a range that the power value of the power spectrum is larger than a prescribed magnitude, to detect the presence of the target from the magnitude of the frequency width. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a target detecting method and a radar device, and more particularly, to a target to be detected (hereinafter referred to as a target) which is mounted on a moving body such as a vehicle and exists at a short distance. The present invention relates to a target detection method and a radar device.

[0002]

2. Description of the Related Art A radar device mounted on a vehicle or the like is described in the document "Introduction to Radar Systems" MI SKOLNIK,
McGRAW-HILL BOOK COMPANY, INC. (1962) and other references "RADAR HANDBOOK" MI SKOLNIK, McGRAW
-FMC known in HILL BOOK COMPANY, INC. (1970) etc.
The W (Frequency Modulated Continuous Wave) method is often used.

In such an FMCW radar, frequency modulation is often performed with a triangular wave. FIG. 12 shows the frequency with respect to time of each signal in the triangular wave modulation FMCW radar. In FIG. 12, 1a is a transmission signal transmitted toward the target by the radar, 2a is a reception signal reflected back from the target, and 3a is a beat signal. The frequency difference between the transmission signal 1a and the reception signal 2a is
It becomes the frequency of the beat signal 3a.

At this time, the frequency U of the beat signal in the modulation period (up phase) in which the frequency rises with time, and the frequency D of the beat signal in the modulation period (down phase) in which the frequency falls with time.
Is represented by the following equations (1) and (2).

[0005]

[Equation 1]

Based on these relationships, the target relative distance r and relative velocity v can be obtained by using the results of subtraction and addition of U and D shown in equations (3) and (4), and equations (5) and (6). Obtained from

[0007]

[Equation 2]

However, since an unnecessary signal other than the beat signal corresponding to the target is generated in an actual device, it is general to use a frequency filter for the beat signal. For this reason, the measurement range of the target relative distance and relative velocity is limited. For example, when an HPF (High Pass Filter) is used to remove the offset component (DC component),
Frequency components in the range of direct current (0 Hz) to HPF cutoff frequency (Fh Hz) are not measured. At this time, as can be seen from the equations (1) and (2), there may be a case where the measurement result cannot be obtained for a long-distance target having a large relative speed and a short-distance target having a small relative speed. this house,
In particular, dealing with short-range targets with a small relative speed has been a problem.

To solve this problem, Japanese Patent Laid-Open No. 50-7358
In JP 6 and JP 59-79176 A, the relationship between the beat frequency and the target relative distance is calculated by changing the frequency modulation from a triangular wave to a sine wave as shown in FIG. ), The following equations (7) and (8) are used.

[0010]

[Equation 3]

That is, for targets with the same relative distance,
The beat frequency is set higher than in the case of triangular wave modulation, and H
The limit range by PF is made relatively small.

FIG. 14 is a diagram of Japanese Patent Laid-Open No. 59-59, which is based on the above principle.
FIG. 4 is a diagram showing a configuration of an FMCW radar of Japanese Patent No. 79176, wherein 4 is a triangular wave modulation signal generation circuit, 5 is a sine wave modulation signal generation circuit, 6 is a selection circuit, 7 is a transmission circuit, 8 is a reception circuit, and 9 is a frequency. The filter 10 is a beat frequency measuring unit,
Reference numeral 11 is a control means.

Either the triangular wave output from the triangular wave modulation signal generation circuit 4 or the sine wave output from the sine wave modulation signal generation circuit 5 is selected by the selection circuit 6 and input to the transmission circuit 7, where it is frequency-modulated. Sent. The output of the receiving circuit 8 which detects the beat signals of the received wave and the transmitted wave is input to the beat frequency counter 10 via the frequency filter 9 capable of switching the pass band frequency, and the beat frequency is counted. The control means 11 calculates the distance to the target from the count value, switches the selection circuit 6 to the triangular wave modulation signal generation circuit 4 side when it is relatively far, and sets the frequency filter 9 to a frequency of about 3 times the modulation frequency or more. To allow passage of signals, and when the target is close, the selection circuit 6 is switched to the side of the sine wave modulation signal generation circuit 5 and the frequency filter 9 can pass signals of a frequency slightly higher than the modulation wave frequency. To change.

In the FMCW radar of FIG. 14, the control means 1
1, the current beat frequency measurement result fb is compared with a preset frequency fmin, and if fb> fmin, the selection circuit 6 is controlled so that the triangular wave modulation signal generation circuit 4 causes the transmission circuit 7 A continuous wave modulated with a triangular wave is emitted. On the other hand, if fb ≦ fmin, the selection circuit 6 is controlled to cause the sine wave modulation signal generation circuit 5 to
The transmission circuit 7 radiates a continuous wave subjected to sine wave modulation.

[0015]

The conventional radar apparatus is constructed as described above, and even under the condition that the unnecessary component exists, the beat frequency is made larger than that in the case of the triangular wave modulation, so that the limit range by the HPF is increased. Can be made small, and the measurement results of the relative distance and the relative velocity can be obtained even for a short-range target. However, in the prior art, HP
The limit of measurable range due to the influence of F still remains,
There has been a problem that a measurement result of a target existing in a short distance may not be obtained.

The present invention has been made to solve the above problems, and in a radar device, even under the condition that an unnecessary component exists, without using a frequency filter,
An object of the present invention is to obtain a target detection method and a radar device capable of detecting a target existing at a short distance.

[0017]

According to the present invention, there is provided a transmitting step of outputting a continuous wave which is frequency-modulated based on a predetermined non-linear function as a transmitting signal, and a receiving step of receiving the transmitting signal reflected by a target as a receiving signal. Step, and obtain a beat signal based on the transmission signal and the reception signal,
A power spectrum conversion step of converting the beat signal into a power spectrum, a frequency width in a range in which the power value of the power spectrum is larger than a predetermined threshold value, and a target for detecting the presence or absence of a target from the size of the frequency width. A target detection method including a presence / absence detection step.

An even power function is used as the predetermined nonlinear function.

A sine wave function is used as the predetermined non-linear function.

Further, the method further comprises a step of obtaining a center value of the frequency width and measuring a target speed from the center value.

Further, the target presence / absence detecting step compares the power value of the power spectrum at an arbitrary frequency with a preset first threshold value, and has a power value larger than the first threshold value. Obtaining a range in which the frequency exists continuously as a frequency width, comparing the obtained frequency width with a preset second threshold value, the frequency width is equal to or more than the second threshold value. If it is, it is determined that the target exists.

The present invention further includes a transmitting means for outputting as a transmission signal a continuous wave subjected to frequency modulation based on a predetermined non-linear function, a receiving means for receiving the transmission signal reflected by a target as a reception signal, Obtaining a beat signal based on the transmission signal and the received signal, a power spectrum converting means for converting the beat signal into a power spectrum, and obtaining a frequency width in a range in which the power value of the power spectrum is larger than a predetermined threshold value, The radar apparatus is provided with a target presence / absence detecting means for detecting the presence / absence of a target from the magnitude of the frequency width.

An even power function is used as the predetermined non-linear function.

A sine wave function is used as the predetermined non-linear function.

Further, there is further provided speed measuring means for obtaining a center value of the frequency width and measuring a target speed from the center value.

Further, the target presence / absence detecting means compares the power value of the power spectrum at an arbitrary frequency with a preset first threshold value, and has a power value larger than the first threshold value. Obtaining a range in which the frequency exists continuously as a frequency width, comparing the obtained frequency width with a preset second threshold value, the frequency width is equal to or more than the second threshold value. If it is, it is determined that the target exists.

Further, F using a continuous wave of linear frequency modulation
Used in combination with MCW radar.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 is a configuration diagram of a radar device according to a first embodiment of the present invention.

In FIG. 1, 100 is a control unit, 101 is a voltage generation circuit for generating a predetermined non-linear modulation voltage, and 10 is a voltage generation circuit.
A VCO (Voltage Co) 2 generates and outputs a transmission signal composed of a non-linear frequency modulation continuous wave by a modulation voltage.
ntrolled Oscillator), 103 is a distribution circuit that distributes the transmission signal, 104 is a transmission antenna that radiates the transmission signal into the air, 105 is a reception antenna that receives the transmission signal reflected by the target as a reception signal, and 106 is the transmission signal and reception A mixer for generating a beat signal based on the signal, 107a,
107b and 107c are switches, 108 is an HPF for removing offset components (direct current components), and 109 is analog /
ADC (Analog to Digital Conv)
erter), 110 is a memory, 111 is a frequency spectrum conversion unit that converts a beat signal for each modulation period into a power spectrum, and 112 is a distance / distance for obtaining a target relative distance and relative velocity using the power spectrum of a predetermined modulation period. The velocity measuring unit 113 is a target presence / absence detecting unit that detects the presence / absence of a short-distance target using the power spectrum of another predetermined modulation period.

The operation will be described. Under the control of the control unit 100, the voltage generation circuit 101 outputs a modulation voltage as shown in FIG. As shown in FIG. 2, the first modulation period T
Is a linear up-phase (modulation period in which the frequency rises with time), and the next modulation period T
Is a non-linear modulation period, and the last modulation period T
Is a linear down phase (modulation period in which the frequency decreases as time passes). In the following description, it is assumed that a quadratic function is applied as the nonlinear modulation shown in FIG.

The VCO 102 receives the modulation voltage of FIG.
The transmission signal 201 of FIG. 3 is generated. At this time, the frequency Fc (t) of the non-linear modulation period (hereinafter referred to as the quadratic function modulation period) is expressed by the equation (9).

[0032]

[Equation 4]

The transmission signal 201 of FIG. 3 is radiated into the air from the transmission antenna 104 through the distribution circuit 103. At this time, a part of the transmission signal is input to the mixer 106 by the distribution circuit 103. The transmission signal 201 radiated into the air from the transmission antenna 104 is reflected by a target (not shown) having a relative distance r and a relative velocity v, and is received by the reception antenna 105 as a reception signal 202 in FIG. The mixer 106 receives the transmission signal 201 from the distribution circuit 103 and the reception signal 202 from the reception antenna 105, and generates the beat signal 203 in FIG. Beat signal 2
As shown in FIG. 3, 03 is a constant value in the up phase and the down phase, and is time-varying (linearly changing with the passage of time) in the quadratic function modulation period.

The switch 10 is controlled by the control unit 100.
7a and 107b are connected to the L terminal for the beat signals of the up phase and the down phase, output the beat signal to the ADC 109 via the HPF 108, and are connected to the S terminal for the beat signal of the quadratic function modulation period. , And outputs the beat signal directly to the ADC 109. Beat signal 2
03 is converted into digital data by the ADC 109 and recorded in the memory 110.

Under the control of the control unit 100, the frequency spectrum conversion unit 111 outputs the beat signal for each modulation period,
For example, it is converted into a power spectrum by FFT (Fast Fourier Transform) or the like.

The switch 10 is controlled by the control unit 100.
7c is connected to the L terminal for the up-phase and down-phase power spectra, outputs the power spectrum to the distance / velocity measuring unit 112, and is connected to the S terminal for the power spectrum of the quadratic function modulation period. The power spectrum is output to the target presence / absence detection unit 113.

The distance / speed measuring unit 112 is a conventional FMC.
Based on the measurement principle of the W radar, the beat frequencies in the up phase and the down phase are calculated, and equation (5),
By (6), the target relative distance and relative velocity are obtained.

The characteristics of the power spectrum input to the target presence / absence detecting unit 113 during the quadratic function modulation period will be described. Since the frequency modulation of the transmission signal is the quadratic function of Expression (9), the frequency Fb (t) of the beat signal is time-varying as in Expression (10).

[0039]

[Equation 5]

However, in the equation (10), it is assumed that the influence of the Doppler shift due to the target relative velocity is small. From Expression (10), it can be seen that the fluctuation range increases as the target relative distance changes, as shown in FIG.
Therefore, the power spectrum in each case where the relative distance is r1 <r2 <r3 is as shown in FIG.

Assuming that there is a component that leaks directly from the transmitting antenna 104 to the receiving antenna 105 in the radar apparatus of FIG. 1, a beat signal of approximately 0 Hz, that is, an unnecessary DC component is reflected as reflection at a distance of approximately 0 m. Occurs. At this time, the power spectrum in the quadratic function modulation period when the target does not exist is as shown in FIG. 6, while the power spectrum when the target exists at the relative distances r1, r2, r3 is as shown in FIG. become. That is,
When the frequency width in which the power value of the power spectrum becomes equal to or larger than the predetermined threshold value Tp is Fw, the value of the frequency width Fw becomes larger than that in FIG. 6 in the case where no target exists. The target presence / absence detection unit 113 detects the presence / absence of a short-range target by utilizing the property of the power spectrum during the quadratic function modulation period.

For example, the target presence / absence detection unit 113 detects the presence / absence of a target according to the processing procedure shown in FIG. First, in step S1, the power spectrum of the quadratic function modulation period is input. Subsequently, in step S2, the power value P (f) at an arbitrary frequency f is compared with a preset threshold value Tp, and if it is large, it is set to P (f) as it is, and if it is small, it is set to 0 (zero). In step S3, a range in which the spectrum whose power value is not 0 continuously exists in the frequency direction is obtained, and this range is set as the frequency width Fw. In step S4, the frequency width Fw obtained in step S3 is compared with a preset threshold value Tw, and it is determined that a target exists if Fw ≧ Tw. If Fw <Tw, no target exists. To determine.

By adjusting the parameters and threshold values of the quadratic function to be used, it is possible to leave a target with a relatively large relative distance undetected as shown in FIG. Such targets can be detected by conventional methods). As a result, the distance / speed measuring unit 11
2 and the target presence / absence detection unit 113 can avoid handling the same target, and wasteful processing can be omitted.

Further, even if an even power function or a sine function other than the above-mentioned quadratic function is applied as the non-linear modulation, the power spectrum thereof has the same property as in the case of the above quadratic function. You may apply these.

As described above, in the present embodiment,
By using a non-linear frequency-modulated continuous wave as the transmission signal, the frequency of the transmitted / received beat signal is time-varying, the power spectrum of the beat signal is spread, and the presence or absence of the target is determined from the spread width. Since the detection is performed, it is possible to detect a target existing at a short distance without using a frequency filter even under the condition that an unnecessary component exists.

Embodiment 2. Hereinafter, another embodiment of the present invention will be described with reference to the drawings. FIG. 9 is a configuration diagram of the radar device according to the second embodiment of the present invention.

In FIG. 9, reference numeral 301 denotes a second target presence / absence detecting unit which performs the same operation as the above-mentioned target presence / absence detecting unit 113, and further obtains the minimum frequency and the maximum frequency with respect to the frequency width obtained in step S3. Reference numeral 302 denotes a velocity measuring unit that obtains the center of the frequency width from the minimum frequency and the maximum frequency, and thereby obtains the target relative velocity.
The other constituent elements are the same as those shown in FIG. 1 of the first embodiment, and therefore, the same reference numerals are given here,
The description is omitted.

The operation will be described. First, in the radar device shown in FIG. 9, the control unit 100 and the voltage generation circuit 10
1, VCO 102, distribution circuit 103, transmission antenna 10
4, receiving antenna 105, mixer 106, switch 10
7a to 107c, HPF 108, ADC 109, memory 110, spectrum conversion unit 111, distance / speed measurement unit 1
12 operates similarly to the first embodiment. However, here, the influence of the Doppler shift due to the target relative speed is seen, and the frequency Fb (t) of the beat signal is represented by the equation (11).

[0049]

[Equation 6]

The second target presence / absence detecting unit 301 and the speed measuring unit 302 detect the presence / absence of a target and measure the speed in accordance with the processing procedure shown in FIG. In FIG. 10, step S
From 1 to S4, the target presence / absence detection unit 11 of the first embodiment
The operation is the same as 3. In step S10, the second target presence / absence detection unit 301 determines the frequency width F obtained in step S3.
The minimum frequency Fx and the maximum frequency Fy of w are obtained and output to the speed measurement unit 302. Assuming that the frequency modulation width B and the frequency modulation time T are set so that the relationship of Expression (12) is established at a short distance of several meters or less, step S
11, the speed measurement unit 302 determines that the center of the frequency width obtained in step S3 corresponds to the target Doppler frequency as shown in FIG. 11, and obtains F obtained in step S10.
The target relative velocity Vn is calculated from x and Fy by the equation (13).

[0051]

[Equation 7]

As described above, in the present embodiment,
Since the speed measurement unit 302 that measures the target speed from the center of the spread width of the power spectrum of the beat signal is added, it is possible to detect the relative speed of the short-range target of several meters or less.

[0053]

According to the present invention, there is provided a transmitting step of outputting a continuous wave which is frequency-modulated based on a predetermined nonlinear function as a transmitting signal, a receiving step of receiving the transmitting signal reflected by a target as a receiving signal, Obtaining a beat signal based on the transmission signal and the received signal, a power spectrum conversion step for converting the beat signal into a power spectrum, and obtaining a frequency width in a range in which the power value of the power spectrum is larger than a predetermined threshold value, Since it is a target detection method comprising a target presence detection step for detecting the presence or absence of a target from the size of the frequency width, even under conditions where unnecessary components exist, without using a frequency filter,
A target existing at a short distance can be detected.

Since an even power function is used as the predetermined non-linear function, the frequency of the transmitted / received beat signal can be changed with time.

Since the sine wave function is used as the predetermined non-linear function, the frequency of the transmitted / received beat signal can be changed with time.

Since the method further includes the step of obtaining the center value of the frequency width and measuring the target speed from the center value, the speed of the short-range target can also be detected.

In the target presence / absence detecting step, the power value of the power spectrum at an arbitrary frequency is compared with a preset first threshold value, and the power value is larger than the first threshold value. Obtaining a range in which the frequency exists continuously as a frequency width, comparing the obtained frequency width with a preset second threshold value, the frequency width is equal to or more than the second threshold value. If it is, it is determined that the target exists, so that the target at a short distance can be detected with high accuracy.

The present invention further includes a transmitting means for outputting as a transmission signal a continuous wave subjected to frequency modulation based on a predetermined non-linear function, a receiving means for receiving the transmission signal reflected by the target as a reception signal, Obtaining a beat signal based on the transmission signal and the received signal, a power spectrum converting means for converting the beat signal into a power spectrum, and obtaining a frequency width in a range in which the power value of the power spectrum is larger than a predetermined threshold value, Since the radar device is provided with a target presence / absence detection unit that detects the presence / absence of a target from the magnitude of the frequency width, even under the condition that an unnecessary component exists, a frequency filter is not used and a short range is achieved. It is possible to detect existing targets.

Since an even power function is used as the predetermined non-linear function, the frequency of the transmitted / received beat signal can be time-varying.

Since the sine wave function is used as the predetermined non-linear function, the frequency of the transmitted / received beat signal can be time-varying.

Further, since the speed measuring means for obtaining the center value of the frequency width and measuring the target speed from the center value is further provided, the speed of the short-range target can also be detected.

Further, the target presence / absence detecting means compares the power value of the power spectrum at an arbitrary frequency with a preset first threshold value and has a power value larger than the first threshold value. Obtaining a range in which the frequency exists continuously as a frequency width, comparing the obtained frequency width with a preset second threshold value, the frequency width is equal to or more than the second threshold value. If it is, it is determined that the target exists, so that the target at a short distance can be detected with high accuracy.

Further, F using a continuous wave of linear frequency modulation
When used in combination with the MCW radar, it is possible to detect short-range and long-range targets with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a radar device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a modulation voltage output by a voltage generation circuit provided in the radar device according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a transmission / reception frequency and a beat frequency in the radar device according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing the relationship between the fluctuation range of the beat frequency and the target relative distance.

FIG. 5 is an explanatory diagram showing a variation of a power spectrum at each target relative distance.

FIG. 6 is an explanatory diagram showing a power spectrum in a quadratic function modulation period when a target does not exist in consideration of a leakage component.

FIG. 7 is an explanatory diagram showing a variation of a power spectrum at each relative distance in the case where a target is present in consideration of a leakage component.

FIG. 8 is a flowchart showing a processing flow of a target presence / absence detection unit provided in the radar device according to the first embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration of a radar device according to a second embodiment of the present invention.

FIG. 10 is a flowchart showing a processing flow of a target presence / absence detection unit provided in the radar device according to the second embodiment of the present invention.

FIG. 11 is an explanatory diagram showing a relationship between a frequency width and a target Doppler frequency.

FIG. 12 is an explanatory diagram showing frequencies with respect to time of each signal in a conventional triangular wave modulation FMCW radar.

FIG. 13 is an explanatory diagram showing the frequency of each signal with respect to time in a conventional sine wave modulation FMCW radar.

FIG. 14 is a block diagram showing a configuration of a conventional FMCW radar.

[Explanation of symbols]

1a transmission signal, 2a reception signal, 3a beat signal,
4 triangular wave modulation signal generation circuit, 5 sine wave modulation signal generation circuit, 6 selection circuit, 7 transmission circuit, 8 reception circuit, 9
Frequency filter, 10 beat frequency counter, 11
Control means, 100 control unit, 101 voltage generation circuit, 1
02 VCO, 103 distribution circuit, 104 transmitting antenna, 105 receiving antenna, 106 mixer, 107
a, 107b, 107c switch, 108 HPF,
109 ADC, 110 memory, 111 frequency spectrum conversion unit, 112 distance / speed measurement unit, 113 target presence / absence detection unit, 301 second target presence / absence detection unit, 302
Speed measurement unit.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shigeki Morita             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F-term (reference) 5J070 AB17 AC02 AC06 AF03 AH14                       AH35 AK02

Claims (11)

[Claims] 1. A transmission step of outputting as a transmission signal a continuous wave subjected to frequency modulation based on a predetermined nonlinear function, a reception step of receiving the transmission signal reflected at a target as a reception signal, the transmission signal and the above Obtaining a beat signal based on the received signal, a power spectrum conversion step for converting the beat signal into a power spectrum, and obtaining a frequency width of a range in which the power value of the power spectrum is larger than a predetermined threshold, A target presence / absence detection step of detecting the presence / absence of a target from the size of the target. 2. The target detecting method according to claim 1, wherein an even power function is used as the predetermined nonlinear function. 3. The target detecting method according to claim 1, wherein a sine wave function is used as the predetermined nonlinear function. 4. The target detecting method according to claim 1, further comprising a step of obtaining a center value of the frequency width and measuring a target speed from the center value. 5. The target presence / absence detecting step compares a power value of a power spectrum at an arbitrary frequency with a preset first threshold value, and has a power value larger than the first threshold value. The range in which the frequency exists continuously is obtained as the frequency width, the obtained frequency width is compared with the preset second threshold value, and the frequency width is equal to or more than the second threshold value. The target detection method according to any one of claims 1 to 4, wherein the target is determined to be present when it is. 6. A transmission means for outputting as a transmission signal a continuous wave subjected to frequency modulation based on a predetermined non-linear function, a reception means for receiving the transmission signal reflected at a target as a reception signal, the transmission signal and the above. A beat signal is obtained based on the received signal, a power spectrum conversion means for converting the beat signal into a power spectrum, and a frequency width in a range where the power value of the power spectrum is larger than a predetermined threshold value are obtained. A radar apparatus comprising: a target presence / absence detection unit for detecting the presence / absence of a target from the size. 7. The radar device according to claim 6, wherein an even power function is used as the predetermined nonlinear function. 8. The radar device according to claim 6, wherein a sine wave function is used as the predetermined nonlinear function. 9. The radar device according to claim 6, further comprising speed measuring means for determining a center value of the frequency width and measuring a target speed from the center value. 10. The target presence / absence detecting means compares a power value of a power spectrum at an arbitrary frequency with a preset first threshold value, and has a power value larger than the first threshold value. The range in which the frequency exists continuously is obtained as the frequency width, the obtained frequency width is compared with the preset second threshold value, and the frequency width is equal to or more than the second threshold value. 10. The radar device according to claim 6, wherein the target is determined to be present when the above condition. 11. The radar device according to claim 6, wherein the radar device is used in combination with an FMCW radar that uses a continuous wave of linear frequency modulation.