JPH10142320A - Radar apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize characteristics of both superior detection efficiency at a far distance without narrowing a detection area and superior detection efficiency at a near distance in a radar apparatus. SOLUTION: A transmission wave changing a modulating frequency F every repetition cycle Tm is generated at an oscillation source 14. A part of the transmission wave is supplied to a frequency shift circuit 26. The frequency shift circuit 26 outputs, depending on whether or not a modulation oscillator 30 generates a shift signal, a reference signal changing with a frequency F+F0 or the transmission wave of a frequency F. A mixer 34 generates a beat frequency fb as a frequency difference of the transmission wave and a reflection wave, or a conversion frequency fb+F0 corresponding to a frequency difference of the reference signal and the reflection wave. A signal-processing part 30 detects a target on the basis of the fb or fb+F0 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar device, and more particularly to a radar device suitable for detecting a target located in front of a vehicle.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent No. 86, an FM-CW type radar device is known. The above-mentioned conventional radar apparatus includes a transmission antenna for transmitting a frequency-modulated transmission wave. The modulation frequency f of the transmission wave is increased or decreased at a predetermined repetition cycle Tm with a predetermined value f ₀ as a center value and a shift width ΔF.

Further, the above radar device includes a receiving antenna for receiving a reflected wave of a transmission wave, and a signal processing device for detecting a difference between the frequency of the transmission wave and the frequency of the reception wave, that is, a beat frequency fb. ing. The beat frequency fb includes information on the relative distance R between the target that reflected the transmission wave and the radar device, and the relative speed V of both. The signal processing device described above uses the beat frequency fb
Distance R to the target and relative velocity V based on
Is calculated.

[0004] The range of the beat frequency fb that can be processed by the signal processing device is limited to a predetermined range. Here, it is assumed that the range satisfies f _MIN ≦ fb ≦ f _MAX . As described above, the relative distance R and the relative velocity V between the radar device and the target are reflected in the beat frequency fb. A target that can be detected by the above-described conventional apparatus has a relative distance R and a relative velocity V of the above-described f.
It is limited to generating a satisfying beat frequency fb of the _MIN ≦ fb ≦ f _MAX. As described above, in the above-described conventional radar apparatus, the relation between the relative velocity V and the relative distance R among the targets existing in the area irradiated with the transmission wave is as follows.
Only those that satisfy a predetermined relationship determined according to the range of frequencies that can be processed by the signal processing device can be detected.

[0005] The conventional radar device, the period of the modulation frequency is increased or decreased transmission wave, that is, a function of changing the repetition period T ₀ in two steps. When the repetition period T ₀ is changed in the above conventional device, the above f _MIN ≦≦
The relationship between the relative speed V and the relative distance R that satisfies the condition of fb ≦ f _MAX changes. Therefore, when the repetition period T ₀ is long, a wide detectable range with respect to the relative speed V can be obtained in a region where the relative distance R is long. When the repetition period T ₀ is short, a wide detectable range for the relative speed V can be obtained in a region where the relative distance is short.

[0006]

However, in the conventional radar apparatus, when the repetition period T ₀ is changed, the detectable range for the relative distance R and the detectable range for the relative speed V are both extremely large. It has the characteristic of changing to For this reason, according to the above-mentioned conventional radar apparatus, when the repetition period T ₀ is set to a short time, a large detectable range for the relative speed V can be ensured in an area where the relative distance R is short. On the other hand, there is a disadvantage that the detectable range of the relative distance R is extremely reduced. As described above, with the conventional radar device, it has not been possible to increase the detection capability of a target existing at a short distance while securing a large detectable range for the relative distance R.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and provides an excellent detection method for a target at a short distance while securing a large detectable range for a relative distance R and a detectable range for a relative speed V. It is an object of the present invention to provide a radar device exhibiting its ability.

[0008]

The above object is achieved by the present invention.
As described in the above, a transmission wave transmitting means for transmitting a transmission wave for increasing or decreasing the modulation frequency by one cycle for each predetermined repetition cycle in a predetermined direction, a reflected wave receiving means for receiving a reflected wave of the transmission wave, In a radar apparatus for measuring a relative distance to a target based on a frequency of a transmitted wave and a frequency of the reflected wave, a relative distance to the target is a beat which is a deviation between the frequency of the transmitted wave and the frequency of the reflected wave. This is achieved by a radar device that is calculated based on a converted frequency shifted by a predetermined shift frequency with respect to the frequency.

In the present invention, the relative distance R of the target
Is calculated based on the conversion frequency fb + F ₀ shifted by the shift frequency F _{0 with} respect to the beat frequency fb.
Assuming that the minimum and maximum frequencies at which signal processing is possible are f _MIN and f _MAX , respectively, the relative distance R can be calculated when the conversion frequency fb + F ₀ satisfies the following equation.

[0010] f_MIN≦ fb + F₀≤ f_MAX (1) The above equation (1) can be rewritten as the following equation. f_MIN-F₀≦ fb ≦ f_MAX-F₀ (2) The beat frequency fb includes the relative distance R of the target and
The relative speed V is reflected. Therefore, beat frequency f
b is any of the relative distance R and the relative velocity V of the target.
It changes as things change. The relative speed V is a predetermined value V
₀Is fixed, the above equation (2) is related to the relative distance R.
This is a conditional expression that determines the detectable range. Defined by the conditional expression
The detectable range for the relative distance R
Frequency F ₀, Regardless of the value of
You. And the detectable range is that the relative distance R is equal to the beat.
As compared with the case where the calculation is performed based on the frequency fb, the shift
Frequency F₀Shift to the decreasing side, that is,
To

If the detectable range for the relative distance R always has a constant width with respect to a predetermined relative speed V ₀ ,
The detection area of the target is maintained as wide as when the relative speed R is calculated based on the beat signal. Further, if the detectable range for the relative distance R is shifted to the short distance side, excellent detection capability can be exhibited for a target existing at a short distance. Therefore, in the present invention, the ability to detect a short-range target is improved without narrowing the target detection area.

[0012] The above object is also achieved by the radar apparatus according to the first aspect, wherein the conversion frequency is a reference frequency shifted by the shift frequency with respect to the frequency of the transmission wave; This is also achieved by a radar device determined as a deviation from the frequency of the reflected wave.

In the present invention, the conversion frequency fb + F
₀Is calculated as the deviation between the reference frequency and the frequency of the reflected wave.
Can be The reference frequency is shifted with respect to the frequency of the transmitted wave
Frequency F ₀Frequency shifted by Also, the transmitted wave
Between the frequency of the reflected wave and the frequency of the reflected wave is the beat frequency fb
It is. Therefore, the deviation between the reference frequency and the frequency of the reflected wave
Is the shift frequency F with respect to the beat frequency fb.₀Only
Frequency fb + F₀Becomes

[0014] The object of the present invention is as described in claim 3.
3. The radar device according to claim 2, wherein the reference frequency is also achieved by a radar device generated by adding the shift frequency to the frequency of the transmission wave.

[0015] In the present invention, the reference frequency is generated by adding the shift frequency F ₀ to the frequency of the transmitted wave. According to the above configuration, using the frequency of the transmission wave,
It is possible to generate the reference frequency with high accuracy. According to a fourth aspect of the present invention, the above object is also achieved by the radar apparatus according to the first aspect, wherein the shift frequency can be changed within a predetermined range including 0.

In the present invention, when the shift frequency F ₀ is changed, the distance from the radar device to the position where the best detection ability is exhibited is changed while the target detection area is maintained at the same size. Is done. The above object is achieved by a transmission wave transmitting means for transmitting a transmission wave for increasing or decreasing a modulation frequency by one cycle in a predetermined repetition cycle in a predetermined direction, and a reflected wave of the transmission wave. And a signal obtained by separating and capturing a part of the signal supplied to the transmission wave transmitting means, and a signal that fluctuates at a predetermined shift frequency are combined to obtain a frequency of the transmission wave. And a reference signal generating means for generating a reference signal that fluctuates at a frequency higher by the shift frequency, and calculates a relative distance to a target based on a deviation between the frequency of the reflected wave and the frequency of the reference signal. And a relative distance calculating means.

In the present invention, the transmission wave transmitted from the transmission wave transmitting means is reflected by the target and then received by the reflected wave receiving means. A part of the signal supplied to the transmission wave transmitting means, that is, a part of the signal having the same modulation frequency as the transmission wave, is used as the basis of the reference signal without being transmitted to the target. The reference signal has a frequency shifted by the shift frequency F _{0 with} respect to the frequency of the transmission wave. The relative distance R of the target is determined by the frequency of the reference signal,
Deviation from the frequency of the reflected wave, that is, frequency fb + F shifted by shift frequency F _{0 with} respect to beat signal fb
It is calculated based on ₀ . In this case, similarly to the first aspect of the invention, a target detection area having an appropriate size is secured at a position close to the radar device.

[0018]

FIG. 1 is a block diagram showing a radar apparatus according to an embodiment of the present invention. The radar apparatus according to the present embodiment is an FM-CW type radar apparatus, which is mounted on a vehicle and used to detect a target (a preceding vehicle or the like) existing in front of the vehicle.

The radar device of the present embodiment has a signal processing unit 10
It has. An oscillation source 14 is connected to the signal processing unit via a microstrip line 12. The microstrip line 12 is a conductive line that can transmit a high-frequency signal with high accuracy. The signal processing unit 10 includes an oscillation source 14
Supplies a modulation command signal to the The oscillation source 14 generates a transmission wave that fluctuates at a modulation frequency F according to a modulation command signal supplied from the signal processing unit 10.

A directional coupler 18 is connected to the oscillation source 14 via a microstrip line 16. The directional coupler 18 has a microstrip line 2.
The transmission antenna 24 and the frequency shift circuit 26 are connected via 0 and 22. The directional coupler 18 converts the transmission wave supplied from the oscillation source 14 into a microstrip line 20 and a microstrip line 22 at a predetermined ratio.
Device to distribute to The transmission wave supplied to the transmission antenna 24 is then transmitted forward of the vehicle.

A modulation oscillator 30 is connected to the frequency shift circuit 26 via a microstrip line 28. The modulation oscillator 30 can supply a shift signal to the frequency shift circuit 26 when a command signal is supplied from outside. Shift signal is a signal that varies at a predetermined shift frequency F _0. When no command signal is supplied to the modulation oscillator 30, the frequency shift circuit 2
No signal is supplied to 6.

The frequency shift circuit 26 includes a modulation oscillator 30
If the transmission signal supplied from the directional coupler 18 is not received, the transmission wave supplied from the directional coupler 18 is passed without changing its frequency. On the other hand, the frequency shift circuit 26
When the shift signal is supplied from the modulation oscillator 30, the transmission wave supplied from the directional coupler 18 and the shift signal are combined, and the modulation frequency F and the shift frequency F _{0 of the} transmission wave are combined. And a reference signal that varies at a reference frequency F + F ₀ equal to the sum of

In this embodiment, the frequency shift circuit 26
Is constituted by a mixer using a nonlinear element.
Note that the configuration of the frequency shift circuit 26 is not limited to this, but may be any as long as it can convert the modulation frequency F to the reference frequency F + F ₀ . In the frequency shift circuit 26,
A mixer 34 is connected via a microstrip line 32. The mixer 34 also has a receiving antenna 40 via microstrip lines 36 and 38, respectively.
And an amplifier 42 are connected. Receiving antenna 40
Is an antenna for receiving the reflected wave of the transmission wave transmitted from the transmission antenna 24. The reflected wave received by the receiving antenna 40 is supplied to the mixer 34.

The mixer 34 includes a transmission wave or a reference signal supplied from the frequency shift circuit 26 and a reception antenna 40.
Are combined with the reflected waves supplied from the above to generate a signal that fluctuates at a frequency equal to the frequency deviation of those signals. Specifically, when a transmission wave is supplied from the frequency shift circuit 26, the mixer 34 sets the deviation | F−F ′ | between the frequency F ′ of the reflected wave and the modulation frequency F of the transmission wave as the fluctuation frequency. Generate a beat signal. On the other hand, the frequency shift circuit 2
6 is supplied with the reference signal, the mixer 34
Deviation between frequency F ′ of reflected wave and reference frequency F + F ₀ | F
A converted signal having a variable frequency of −F ′ + F ₀ | is generated. The beat signal and the converted signal generated by the mixer 34 are supplied to the amplifier 42.

In an FM-CW radar device,
Conventionally, the modulation frequency F of the transmitted wave and the frequency F ′ of the reflected wave
In general, a method of detecting a target based on a beat frequency fb obtained as a deviation | F−F ′ | In the present embodiment, the frequency | F−F ′ + F ₀ | of the converted signal generated by the mixer 34 is equal to the beat frequency f.
b = | F-F '| if the use can be rewritten as fb + F _0. Hereinafter, this frequency fb + F ₀ is referred to as a conversion frequency.

The amplifier 42 has a microstrip line
The signal processing unit 10 is connected via 44. Amplifier
42 is a beat signal or a variable supplied from the mixer 34.
The replacement signal is amplified and supplied to the signal processing unit 10. Signal processing
The section 10 controls the frequency of the signal supplied from the amplifier 42,
That is, beat frequency fb or conversion frequency fb + F ₀
Of the target that reflected the transmitted wave and the vehicle based on the
The distance R and the relative speed V are calculated.

Next, with reference to FIG. 2, the principle of detecting a target by the radar apparatus of the present embodiment will be described. The waveform shown by the solid line in FIG. 2 indicates a change in the modulation frequency F of the transmission wave. The waveform shown by the broken line in FIG. 2 indicates a change in the frequency F 'of the reflected wave. As shown in FIG. 2, the modulation frequency F of the transmission wave emitted from the oscillation source 14 repeatedly increases and decreases within a range of a shift width ΔF with a predetermined value f ₀ as a center value. The modulation frequency F of the transmission wave continuously increases for a predetermined period at a constant rate of change, and then decreases at a constant rate for a predetermined period of time. Hereinafter, a section where the modulation frequency F rises is a rising section, a section where the modulation frequency F falls is a falling section,
A cycle in which the modulation frequency F is increased or decreased by one cycle is referred to as a repetition cycle Tm.

When a target is irradiated with a transmission wave transmitted from the transmission antenna 24, a reflected wave is generated by the target. The reflected wave generated by the target is received by the receiving antenna 40 with a time delay corresponding to the relative distance R between the vehicle and the target and a Doppler shift corresponding to the relative speed V between the vehicle and the target.

The time delay Δt generated in the reflected wave is calculated by using the relative distance R and the propagation speed c ₀ of the transmitted wave as Δt = 2R / c
It can be represented as ₀ . Also, the frequency change rate d of the transmitted wave
F / dt is calculated using a repetition period Tm and a shift width ΔF, and dF / dt = ΔF / (Tm / 2) = 2ΔF / Tm
It can be expressed as. Therefore, when the reflected wave is received, Δt · dF / dt = ｛4ΔF / (c ₀ · T) between the transmitted wave and the reflected wave due to the time delay of the reflected wave.
m) A frequency difference represented by｝ · R occurs.

Further, if the direction in which the vehicle and the target approach each other is the positive direction of the relative velocity V, the Doppler shift frequency generated in the reflected wave can be expressed as (2F / c) · V. The frequency difference caused by the above-mentioned time delay occurs such that the frequency F ′ of the reflected wave becomes higher than the modulation frequency F in the falling section of the modulation frequency F. Therefore, the beat frequency fbdn in the descending section can be expressed by the following equation.

Fbdn = {4ΔF / (c ₀ · Tm)} · R + (2F / c) · V (3) Further, the frequency difference due to the above-mentioned time delay is caused in the rising section of the modulation frequency F. Is generated such that the frequency F ′ of the reflected wave becomes lower than the modulation frequency F. Therefore,
The beat frequency fbup in the rising section can be expressed as the following equation.

F bup = {4ΔF / (c ₀ · Tm)} · R− (2F / c) · V (4) In the above equations (3) and (4), (2F / c) and ｛ 4ΔF / (c ₀ · Tm)｝ is α or β, respectively.
Then, these expressions can be rewritten as the following expressions.

Fbdn = α · V + β · R (5) fbup = −α · V + β · R (6) The relative distance R and the relative velocity V are expressed by the above equations (5) and (6). Thus, the following equation can be obtained.

R = (fbdn + fbup) / 2β (7) V = (fbdn−fbup) / 2α (8) As described above, in the system according to the present embodiment, the transmission wave frequency F By detecting the beat frequency fb, which is the deviation from the frequency F 'of the reflected wave, in both the rising section and the falling section, the relative speed V and the relative distance R between the target reflecting the transmission wave and the vehicle can be obtained. it can.

In the system of this embodiment, the frequency that can be processed by the signal processing unit 10 is _{equal to} or higher than f _MIN and f _MAX
It is limited to the following frequencies. Therefore, in order for the signal processing unit 10 to obtain the relative distance R and the relative velocity V based on the beat frequency fd (fbup and fbdn), it is necessary that fbup and fbdn satisfy the following conditional expressions, respectively. Become.

F _MIN ≦ f bdn ≦ f _MAX (9) f _MIN ≦ f bup ≦ f _MAX (10) In the conditional expression of the above expression (9), substitute the relationship of the above expression (5). Can be rewritten into the following two conditional expressions.

F _MIN ≦ α · V + β · R (11) f _MAX ≧ α · V + β · R (12) Further, these two conditional expressions (11) and (12) are as follows. Can be organized.

V ≧ − (α / β) · R + f _MIN / β (13) V ≦ − (α / β) · R + f _MAX / β (14) Similarly, the above equation (10) The conditional expressions can be arranged into the following two conditional expressions using the relationship of the above expression (6).

V ≦ (α / β) · R−f _MIN / β (15) V ≧ (α / β) · R−f _MAX / β (16) FIG. And two-dimensional coordinates of the relative velocity V.
The hatched region in FIG. 3 corresponds to the above (13)
It is an example of the area | region limited by the conditions of (16). The region that satisfies all of the above conditions (13) to (16) is a region where the signal processing unit 10 can detect a target based on the beat frequency fb. Hereinafter, this region is referred to as a long-distance detection region.

As shown in FIG. 3, the long-distance detection area is limited to have a rhombic shape on the two-dimensional coordinates of the relative distance R and the relative velocity V. The rhombus shape of the detection area changes according to the set values of the modulation frequency F, the shift width ΔF, the repetition period Tm, etc., which are the bases of α and β.

[0041] In the far side detection region shown in FIG. 3, the detectable range for the relative distance R is the predetermined value R ₁ or more, and is limited to a predetermined value R ₃ or less. The detection range of the relative speed V, the relative distance R is smallest when a predetermined value R ₁ or R _3, the relative distance R increases nears a predetermined value R _2. According to such a setting, the target detection capability of the radar device, becomes the best in the vicinity of a point spaced from the vehicle by a distance R _2.

In order to reflect the detection result of the radar device in vehicle control, it may be necessary to accurately detect a target having a short relative distance R from the vehicle. In order to accurately detect a target having a short relative distance R, it is necessary to secure a wide detectable range for the relative speed V in an area where the relative distance R is short.

As described above, the shape of the detection area shown in FIG. 3 can be changed by changing the modulation frequency F or the like. Specifically, for example, the modulation frequency F of the transmission wave
Is set to twice the value for obtaining the long-distance detection area shown in FIG. 3, α in the above equations (13) to (16) is doubled to separate the target detection area. The inclination of the four straight lines can be twice as large as the straight lines separating the long-distance detection areas. Hereinafter, the setting condition for realizing the long-distance detection area shown in FIG. 3 is referred to as a basic setting condition, and the condition for setting the modulation frequency F to a value twice the basic setting condition is referred to as a trial setting condition.

FIG. 4 shows a detection area realized by the basic setting conditions (an area indicated by a broken line in FIG. 4) and a detection area realized by the trial setting conditions (an area indicated by hatching in FIG. 4). FIG. As shown in FIG. 4, according to the trial setting condition, the detectable range related to the relative distance R can be moved to a short distance side as compared with the detectable range realized under the basic setting condition. Further, according to the trial setting condition, the relative distance R that can realize the widest detectable range with respect to the relative speed V can be moved closer to the distance than the position obtained under the basic setting condition. Therefore, according to the trial setting condition, it is possible to enhance the target detection capability at a position at a short distance from the vehicle as compared with the basic setting condition.

As described above, when the signal processing unit 10 detects a target based on the beat frequency fb, by increasing the modulation frequency F, it is possible to enhance the detection capability of the radar device in a short distance region. Therefore,
According to the radar device of the present embodiment, the target detection process is performed based on the beat frequency fb, and the modulation frequency F of the transmission wave is appropriately changed, so that excellent detection can be performed in both the long-distance region and the short-distance region. You can gain the ability.

However, as shown in FIG. 4, the detectable range of the relative distance R is extremely large in the detection area realized under the trial setting condition, as compared with the long-distance detection area realized by the basic setting condition. Has been reduced to. For this reason, when the trial setting condition is set in the radar device of the present embodiment, the detection capability of the radar device in the short-distance region can be improved, but the detection capability of the radar device in the middle-distance region is extremely reduced. Inconvenience occurs. In this regard, the above method is not always an optimal method for changing the distance from the vehicle to the detection area of the radar device.

The system of the present embodiment is characterized in that excellent detection capability can be realized in a short-distance region without such inconvenience. Hereinafter, the characteristic portions will be described. In the radar device of the present embodiment, when no command signal is supplied to the modulation oscillator 30, the modulation oscillator 30 does not generate a shift signal. In this case, a beat signal having the beat frequency fb as a variation frequency is supplied to the signal processing unit 10. Therefore, in such a situation, a long-distance detection range indicated by hatching in FIG. 3 is realized.

In the radar device of this embodiment, when a command signal is supplied to the modulation oscillator 30, a shift signal is generated from the modulation oscillator 30. In this case, the signal processing unit 10 is supplied with a conversion signal having the conversion frequency fb + F ₀ as the fluctuation frequency. In this case, the signal processing unit 1
0 calculates the relative distance R and the relative speed V of the target based on the conversion frequency fb + F ₀ . Hereinafter, a condition under which such processing is executed is referred to as a short distance setting condition.

The frequency of the converted signal supplied to the signal processing unit 10 under the short-distance setting condition is, specifically, f
bdn + F _0, can be in rising section represents a fbup + F _0. If converted signal to the signal processing section 10 is supplied, the signal processing unit 10, these converted frequency fbdn + F ₀ and the relative when fbup + F ₀ satisfies the condition below the distance R
And the relative speed V can be calculated.

F _MIN ≦ f bdn + F ₀ ≦ f _MAX (17) f _MIN ≦ f bup + F ₀ ≦ f _MAX (18) The above equations (17) and (18) are obtained by the above equation (5). The following four conditional expressions can be rewritten using the relationship of the expressions (6) and (6).

V ≧ − (α / β) · R + (f _MIN −F ₀ ) / β (19) V ≦ − (α / β) · R + (f _MAX −F ₀ ) / β (19) (20) V ≦ (α / β) · R− (f _MIN −F ₀ ) / β (21) V ≧ (α / β) · R− (f _MAX −F ₀ ) / β (22) FIG. 5 shows a long-distance-side detection region (region indicated by a dashed line denoted by reference numerals (13) to (16) in FIG. 5) realized by the basic setting condition and a short-distance setting condition. FIG. 6 is a diagram illustrating a detection region to be realized (a region indicated by hatching in FIG. 5) in comparison. Hereinafter, the detection area realized by the short distance setting condition is referred to as a short distance side detection area.

Four straight lines separating the short-distance detection area,
That is, the straight lines (19) to (22) forming the boundaries of the regions satisfying the conditions (19) to (22) are four straight lines separating the long-distance detection region, that is, the lines (13) to (13).
A straight line (19) forming the boundary of the region satisfying the condition (16)
(22). The V-axis intercepts of the four straight lines (19) to (22) that separate the short-distance detection area are V-intercepts of the four straight lines (13) to (16) that separate the long-distance detection area. Compared to the axis intercept, the magnitude is changed to the R-axis side by a magnitude F ₀ / β corresponding to the shift frequency F ₀ .

Therefore, as shown in FIG. 5, the short-distance side detection area maintains the same rhombic shape as the long-distance side detection area, that is, the detectable range for the relative distance R and the detection for the relative velocity V. While maintaining both of the possible ranges at the same values as those in the far-side detection area, the area is displaced to an area with a small relative distance R. in this way,
According to the radar apparatus of the present embodiment, by setting the short-distance setting condition, the detection capability of the radar apparatus in the short-distance area can be increased without reducing the size of the detection area. Therefore, according to the radar apparatus of the present embodiment, by switching between the long-distance setting condition and the short-distance setting condition, that is, a command signal is appropriately supplied to the modulation oscillator 30 as necessary or cut off. Thus, it is possible to generate a detection area having an appropriate size and an excellent detection capability in both the short distance area and the long distance area.

By the way, the short distance detection area shown in FIG.
This is a region that is realized by setting the shift frequency F ₀ to almost the same value as f _MIN . According to the radar device of the present embodiment, by setting the shift frequency F ₀ to a larger value, the near-distance detection area can be made closer to the vehicle.

In FIG. 5, a straight line indicated by a dashed line and a V-axis
The region to be separated is the shift frequency F ₀To f_MINCompared to
Short distance detection realized by setting a sufficiently large value
4 shows an example of a region. Set the near-side detection area to this range
, The relative distance R from the vehicle is very small,
In addition, a target having a large relative velocity
Detection is possible.

On the other hand, the target is always detected on the basis of the beat frequency fb, and the slope of the four straight lines separating the detection area of the target is made sharp to bring the detection area closer to the vehicle. Depending on the method, a target having a very small relative distance R from the vehicle and a large relative speed V cannot be detected with high accuracy. The radar device of the present embodiment is also superior in this respect to the radar device using the above method.

In the above embodiment, the modulation oscillator 30
Is configured to selectively generate a shift signal that fluctuates at the same shift frequency F ₀ , but the present invention is not limited to this. it may be configured to change the shift frequency F ₀ linearly. In this case, it is possible to linearly change the distance between the target detection area and the vehicle.

In the above embodiment, the reference signal having the reference frequency F + F ₀ as the variation frequency is generated by combining the transmission wave and the shift signal, but the present invention is not limited to this. Instead, the reference signal may be generated independently in a system different from the transmission wave.

[0059] Further, the deviation between in the above-mentioned embodiment, generates a reference frequency F + F ₀ shifted by shift frequency F ₀ for the frequency F of the transmission wave, the frequency F of the reference frequency F + F ₀ and a reflected wave ' To obtain the conversion frequency f
b + F ₀ is obtained, but the conversion frequency fb + F
_The method of generating ₀ is not limited to this. That is, the conversion frequency fb + F ₀ is equal to the frequency F ′ of the reflected wave.
F′-F, which is reduced by the shift frequency F _0
It may be obtained as a deviation between ₀ and the modulation frequency F of the transmission wave.

In the above-described embodiment, the "transmitting wave transmitting means" according to claim 5 is configured by the signal processing unit 10, the oscillating source 14, the directional coupler 18, and the transmitting antenna 24 to form the receiving antenna. 40, the "reflected wave receiving means" according to the fifth aspect, the frequency shift circuit 26 and the modulation oscillator 30 are the "reference signal generating means" according to the fifth aspect, and the mixer 34 and the signal processing unit 10 are the same. The "relative distance calculation means" described in 5 is realized respectively.

[0061]

As described above, according to the first aspect of the present invention, a target existing at a short distance can be detected without narrowing both the detectable range for the relative speed V and the detectable range for the relative distance R. The detection ability can be improved.

According to the second aspect of the present invention, the beat frequency fb is accurately determined using the reference frequency and the frequency of the reflected wave.
, The converted frequency fb + F ₀ shifted by the shift frequency F ₀ can be generated. According to the third aspect of the present invention, the reference frequency can be accurately obtained by a simple method using the frequency of the transmission wave.

According to the fourth aspect of the present invention, the position exhibiting high detection capability can be set on both the long distance side and the short distance side without narrowing the target detection area. For this reason, according to the radar device of the present invention, it is possible to ensure excellent detection capability over a wide area.

According to the fifth aspect of the present invention, similarly to the first aspect of the present invention, a target detection area having an appropriate size can be secured at a position close to the radar device.

[Brief description of the drawings]

FIG. 1 is a block diagram of a radar apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a change in a modulation frequency of a transmission wave transmitted from the radar apparatus according to the embodiment and a change in a frequency of a reflected wave received by the radar apparatus according to the embodiment.

FIG. 3 is a diagram illustrating a long-distance detection area realized under basic setting conditions in the radar apparatus of the present embodiment.

FIG. 4 is a diagram illustrating a detection area realized when a trial setting condition is set in the radar device of the present embodiment.

FIG. 5 is a diagram illustrating a short-distance side detection area realized under a short-distance side setting condition in the radar apparatus of the present embodiment.

[Explanation of symbols]

Frequency F of 10 signal processing unit 14 oscillation source 18 directional coupler 24 transmitting antenna 26 frequency shift circuit 30 modulates the oscillator 34 mixer 36 receiving antenna 42 amplifier F transmitted wave modulation frequency F 'reflected wave ₀ shift frequency F + F ₀ reference frequency fb Beat frequency fbdn Beat frequency in falling section fbup Beat frequency in rising section fb + F ₀ conversion frequency

Claims (5)

[Claims] 1. A modulation frequency of 1 for each predetermined repetition period.
A radar device that transmits a transmission wave whose cycle is to be increased / decreased in a predetermined direction, receives a reflected wave of the transmission wave, and measures a relative distance to a target based on the frequency of the transmission wave and the frequency of the reflected wave. Wherein the relative distance to the target is calculated based on a conversion frequency shifted by a predetermined shift frequency with respect to a beat frequency which is a deviation between the frequency of the transmission wave and the frequency of the reflected wave. Radar equipment. 2. The radar device according to claim 1, wherein the conversion frequency is obtained as a deviation between a reference frequency shifted by the shift frequency with respect to a frequency of the transmission wave and a frequency of the reflected wave. Characteristic radar device. 3. The radar device according to claim 2, wherein the reference frequency is generated by adding the shift frequency to a frequency of the transmission wave. 4. The radar device according to claim 1, wherein the shift frequency can be changed within a predetermined range including 0. 5. A modulation frequency of one for each predetermined repetition period.
Transmitting wave transmitting means for transmitting a transmitting wave to be increased / decreased in a predetermined direction, reflected wave receiving means for receiving a reflected wave of the transmitting wave, and separating a part of a signal supplied to the transmitting wave transmitting means. A reference signal generating unit that combines the captured signal and a signal that fluctuates at a predetermined shift frequency to generate a reference signal that fluctuates at a frequency higher than the frequency of the transmission wave by the shift frequency, A radar apparatus comprising: a relative distance calculator that calculates a relative distance to a target based on a deviation between a frequency of a reflected wave and a frequency of the reference signal.