JPH09145826A - Fm-cw radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent relative speed accuracy from being degraded too much even in an oscillator not very good in its oscillating frequency characteristic to voltage of a milli-wave band regarding an FM-CW (frequency modulation continuous wave) radar device. SOLUTION: A modulation amplitude adjusting means 12 is provided behind a modulation signal generating means 11 so as to be able to switch to a normal radar mode with large frequency deviation by setting large amplitude to a modulation signal to be supplied to a voltage control oscillating means 13 or to a highly accurate measuring mode high in relative speed measuring accuracy by limiting amplitude to reduce frequency deviation. In the highly accurate measuring mode, only the linear area of an output frequency characteristic to input voltage of the voltage control oscillating means 13 is used so as to be able to reduce a measuring error caused by nonlinearity as to the measurement of relative speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver by frequency-modulating (FM-modulating) a high-frequency signal with a modulation signal and transmitting it, receiving a reflection signal from a target object, and branching a part of the transmission signal. FM-CW (Frequency Modulation Continuous Wav)
e) A radar device (frequency-modulated continuous wave radar device), and more particularly, to an FM-CW radar device that is suitable for being mounted on a vehicle to measure a relative speed and a distance to a target object and prevent a collision. .

In recent years, with the increase in the number of vehicles owned, the number of accidents due to collisions of vehicles has been increasing year by year. Therefore, in order to reduce the number of vehicle collision accidents, it is necessary to inexpensively install a safety device such as an inter-vehicle distance monitoring system for notifying a driver of a collision in advance.

[0003]

2. Description of the Related Art Conventionally, an FM-CW radar system has been used as a radar system capable of measuring a relative speed and a distance to a target object. This radar system can measure the relative speed and distance to the target object with a simple signal processing circuit,
Further, since the transceiver can be easily configured, it is used as an on-vehicle collision prevention radar which is particularly required to be downsized and low priced.

FIG. 6 is a diagram showing the principle configuration of a conventional FM-CW radar device. The FM-CW radar device includes a modulation signal generator 1 that generates a modulation signal, an oscillator 2 that generates a signal whose frequency is modulated by the modulation signal, and an oscillator output that is connected to the output of the oscillator 2 to a target object. A transmitting antenna 3 for transmitting toward the receiving antenna, a receiving antenna 4 for receiving a reflected signal reflected by a target object, and an oscillating signal for receiving the received signal received by the receiving antenna 4 by branching a part of the output of the oscillator 2. And a frequency converter 5 that mixes and converts the frequency.

The modulation signal generator 1 generates a triangular wave modulation signal of, for example, several hundred Hz. The oscillator 2 generates a signal that is FM-modulated by a modulation signal centered at, for example, several tens GHz, and the FM-modulated wave is transmitted from the transmission antenna 3. The reflected signal from the target object is received by the receiving antenna 4
And is input to the frequency converter 5. The frequency converter 5 FM-detects the received signal by using the FM modulated wave of the oscillator 2 as a local oscillation signal. At this time, the reflection signal from the target object is shifted in frequency (beat) from the transmission signal according to the distance between the radar and the target object and the Doppler shift due to the relative velocity between the radar and the target object. A) and generate a beat signal. The frequency component of this beat signal is represented by the frequency deviation between the distance frequency that depends on the distance and the speed frequency that depends on the relative speed, and the distance and the relative speed to the target object can be measured from this frequency deviation. .

Here, the measurement of the distance to the target object and the measurement of the relative speed when the relative speed is zero will be described. FIG. 7 is an explanatory view of the principle of measuring the distance by the FM-CW radar device.

In this figure, (A) shows the time change of the transmission / reception frequency, in which the solid line shows the transmission wave and the broken line shows the reception wave. Further, f ₀ is the transmission center frequency, T is the period of the modulated wave, ΔΩ is the modulation width, and fr is the distance frequency depending on the distance. (B) is the beat frequency fb that has been frequency-converted by the frequency converter 5.
Shows the change over time, and (C) shows an example of the actual waveform of the beat signal.

When the frequency of the transmitted wave changes in a triangular wave shape with time, the received wave reflected and returned by the target object has a delay corresponding to the distance to the target object.
It will be delayed from the transmitted wave by the amount of delay.
Here, since the difference between the transmitted wave and the received wave becomes a beat signal, the beat frequency fb changes in a trapezoidal frequency. This beat frequency directly becomes a frequency component that correlates with the distance to the target object. Here, the distance frequency fr depending on the distance is

[0009]

## EQU1 ## fr = (4ΔΩT / c) R (1) Here, R is the distance to the target object, and c is the speed of light. From this equation, distance frequency fr, modulation width ΔΩ,
Since the period T of the modulated wave and the speed of light c are known, the distance R to the target object can be obtained.

FIG. 8 is an explanatory view of the principle of measuring the relative speed by the FM-CW radar device. In this figure,
(A) shows a time change of the transmission / reception frequency, (B) shows a time change of the beat frequency fb, and (C) shows an example of an actual waveform of the beat signal.

The relative velocity with respect to the target object is converted into the beat frequency of the radar as a Doppler frequency component. The beat frequency shifts to the higher side when the target object approaches, and to the lower side when the target object moves away. The amount of shift was such that when the relative speed was zero as described above, the height of the trapezoid was constant when the beat frequency changed to a trapezoid, but when the relative speed changed, the transmission frequency was changed to a triangular shape. Due to the wavy change, when the frequency is raised,
When the frequency is lowered, the beat frequencies are represented by frequency change components fr-fd and fr + fd, respectively. Where fd is the velocity frequency that depends on velocity,

[0012]

[Expression 2] fd = (2f ₀ / c) v (2) Here, v is a relative velocity with respect to the target object.

The expression fr ± fd representing the beat frequency fb,
The distance component to the target object and the relative velocity v to the target object can be obtained by separating the distance component and the velocity component from the respective expressions of the distance frequency fr and the velocity frequency fd. As described above, the FM-CW radar system can simultaneously measure the distance R to the target object and the relative speed v.

When this system is used as an on-vehicle radar, the measuring distance is 100 m at the maximum and the relative speed is 100 m.
Since it is about km / h, in order to secure a sufficient distance measurement accuracy, the period of the modulated wave is about T = 1 × 10 ⁻³ s, the modulation width is about ΔΩ = 100 MHz, and the relative speed is sufficient. To ensure measurement accuracy, the millimeter wave band must be used as the transmission frequency band. For example, the period of the modulated wave is T = 1.33 × 10 ⁻³ s, the modulation width is ΔΩ = 75.
If the MHz and the transmission frequency f ₀ are 60 GHz, the distance resolution is 1 m and the velocity resolution is 6.75 km / h.
Becomes

[0015]

By the way, the conventional FM
In the CW radar device, the oscillator that generates the transmission wave is realized by a voltage-controlled oscillator. As shown in FIG. 9, the voltage-controlled oscillator ideally has an output frequency linearly varying with respect to an input voltage (triangular wave voltage of a modulation signal) as indicated by a broken line. However, as shown by the solid line in the figure, the input / output characteristics of an actual voltage-controlled oscillator show a non-linearity such that the modulation sensitivity is high on the low input voltage side and becomes low when the input voltage is high. Have Moreover, the variation width (modulation width ΔΩ) of the input triangular wave voltage is very large (100 M
Therefore, it is affected by nonlinearity on the low and high output frequency sides. Therefore, the change in the oscillated frequency does not form a clean triangle, but changes toward the end of the modulation width. This change causes an error in detecting the distance frequency fr depending on the distance and the velocity frequency fd depending on the relative velocity, and there is a problem that the measurement accuracy is deteriorated. Especially, speed resolution (6.75 km /
h) is usually the maximum relative speed (100 km / h) of 1
Since it has only a resolution of about 1/5, there is a problem that the accuracy is further deteriorated due to the occurrence of an error.

The present invention has been made in view of the above points, and is an FM-CW radar device that is inexpensive and does not significantly deteriorate the relative speed measurement accuracy even with an oscillator having a slightly bad millimeter-wave band voltage-oscillation frequency characteristic. The purpose is to provide.

[0017]

FIG. 1 is a block diagram showing the principle of the present invention for achieving the above object. The FM-CW radar device of the present invention includes a modulation signal generating means 11 for generating a modulation signal of a triangular wave, a modulation amplitude varying means 12 for variably controlling the amplitude of the modulation signal, and an FM by a modulation signal whose amplitude is variably controlled.
A voltage controlled oscillator 13 for oscillating the modulated signal, and F
A directional coupling means 14 for branching a part of the M-modulated wave, and an FM
Transmitting antenna 15 for transmitting the modulated wave toward the target object
A receiving antenna 16 for receiving the signal reflected by the target object, a frequency converting means 17 for FM detecting the received signal using the signal branched by the directional coupling means 14 as a local oscillation signal source, and an FM detection. The signal processing means 18 for obtaining information on the distance to the target object and the relative velocity from the signal, and the display means 19 for displaying the obtained information. That is, the FM-CW radar device of the present invention is characterized in that the modulation amplitude varying means 12 is newly inserted between the modulation signal generating means 11 and the voltage controlled oscillation means 13.

The amplitude of the modulation signal can be variably controlled, and the amplitude of the modulation signal is changed depending on whether the measurement accuracy is prioritized in relative speed or normal. As a result, when the amplitude of the modulation signal is limited, the measurement can be performed using only the linear region of the input / output characteristic of the voltage controlled oscillator 13, and the relative speed with high measurement accuracy can be obtained. Further, if the amplitude of the modulation signal is not limited, it is possible to perform the conventional measurement using the non-linear region.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the outline of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the basic configuration of the FM-CW radar device of the present invention.

The FM-CW radar device of the present invention variably controls the modulation signal generating means 11 for generating a triangular wave signal for FM modulation, and the amplitude of the triangular wave signal generated by the modulation signal generating means 11. Modulation amplitude changing means 12
A voltage-controlled oscillator 13 for generating a millimeter-wave band FM-modulated signal output from a radar, and a directional coupler 14 for branching the signal from the voltage-controlled oscillator 13.
A transmitting antenna 15 that efficiently emits an FM-modulated signal output from the voltage controlled oscillator 13 into space, a receiving antenna 16 that efficiently receives a signal reflected from a target object, and a directional coupling. The signal of the voltage controlled oscillating means 13 branched by the means 14 and the signal received by the receiving antenna 16 are mixed to generate a signal component including relative velocity information and distance information between the target object and the FM-CW radar device. Frequency conversion means 17 for generating, and signal processing means 18 for extracting relative speed information and distance information from a signal component including relative speed information and distance information from the frequency conversion means 17 and outputting data necessary for display. Display means 1 for displaying the data output from the signal processing means 18.
9. Here, the signal of the voltage controlled oscillation means 13 branched by the directional coupling means 14 is used as a local oscillation signal source in the frequency conversion means 17.

The modulation amplitude varying means 12 inserted between the modulation signal generating means 11 and the voltage control oscillating means 13 does not perform amplitude control on the triangular wave signal generated by the modulation signal generating means 11. It has two operation modes: a radar mode and a high-precision measurement mode for controlling amplitude. Therefore, the modulation amplitude varying means 12 outputs the input triangular wave signal without the amplitude control in the normal radar mode, and outputs the amplitude of the triangular wave signal in the high precision measurement mode with respect to the input voltage of the voltage controlled oscillator 13. The output is limited to the linear region of frequency characteristics. Voltage controlled oscillator 13
Causes a frequency shift necessary for satisfying the required resolution of distance and relative velocity in the normal radar mode with respect to the signal from the modulation amplitude varying means 12, and in the high precision measurement mode, Generates a signal with a smaller frequency shift than in radar mode. This output signal is emitted into space via the transmitting antenna 15.

The emitted output signal hits the target object and is accompanied by a frequency difference due to the Doppler frequency shift corresponding to the relative velocity of the radar and the target object and the delay time corresponding to the distance to the target object. Receiving antenna 1
Received at 6. In the frequency conversion means 17, the received signal is mixed with a part of the output signal from the voltage controlled oscillation means 13, and the Doppler frequency shift corresponding to the relative velocity with the target object and the delay corresponding to the distance to the target object are mixed. A signal including a frequency component due to time is output. The signal processing unit 18 detects the distance information to the target object using the output signal from the frequency conversion unit 17 in the normal radar mode, and detects the distance information to the target object using the output signal in the high precision measurement mode. The relative speed information of is detected.
Thereby, even if the linearity of the input voltage-output frequency characteristic of the voltage controlled oscillator 13 is not good, the relative speed can be measured with high accuracy.

Next, a case where the embodiment of the present invention is applied to an inter-vehicle distance monitoring system will be described as an example. FIG. 2 is a block diagram showing a first embodiment of the FM-CW radar device of the present invention.

The FM-CW radar device shown in the figure has a modulation signal generator 21 as a transmission system and a variable gain amplifier (VGA: Variable Gain Amplifier) for variably controlling the modulation amplitude.
22 and a voltage-controlled oscillator (VCO)
Oscillator) 23, a directional coupler 24, and a transmitting antenna 25. As a receiving system, a receiving antenna 26
And a frequency converter 27, and as a signal processing system, a signal processing unit 28, a display unit 29, and a measurement mode switching unit 30.
It is comprised including. The signal processing unit 28 includes a low-pass filter 28a that receives the output signal of the frequency converter 27.
And an analog / digital converter (A / D) 28b,
It is composed of a digital signal processor (DSP) 28c dedicated to calculation of distance and speed, and a processor (CPU) 28d for passing distance data and speed data from the digital signal processor 28c to display unit 29 as display data. Has been done.

The modulation signal generator 21 is for generating a triangular wave signal for FM modulation. The gain of the variable gain amplifier 22 is switched in accordance with an instruction from the measurement mode switching unit 30 to set the normal radar mode or the high-precision measurement mode, and the amplitude of the triangular wave signal from the modulation signal generator 21 is set to two levels. Change. The voltage controlled oscillator 23 generates a millimeter wave band FM-modulated signal output from the radar. The directional coupler 24 extracts the signal from the voltage controlled oscillator 23 as a local oscillation wave of the local oscillation signal source in the frequency converter 27 in addition to the transmission antenna 25. The transmitting antenna 25 is attached to, for example, a bumper at the front or the rear of the vehicle and emits the signal output from the directional coupler 24 toward the front or the rear of the vehicle.
The receiving antenna 26 is also attached to, for example, a bumper in front of or behind the vehicle and receives signals reflected from the vehicle traveling in front of or behind the vehicle. The frequency converter 27 receives the signal from the directional coupler 24 and the receiving antenna 2
The signal received by 6 is mixed to generate a signal component including distance information and relative speed information between the own vehicle and a vehicle traveling in the front and rear.

In the signal processing section 28, the low pass filter 2
At 8a, the signal output from the frequency converter 27 is transmitted to remove high-frequency components unnecessary for calculation of distance and relative velocity, and the transmitted analog signal is converted to a digital signal by an analog / digital converter 28b. The digital signal processor 28c calculates the distance and the relative speed in the measurement mode according to the instruction of the measurement mode switching unit 30, and the processor 28d displays the distance data and the speed data from the digital signal processor 28c as display data. Output to 29. The display unit 29 is provided on, for example, a dashboard in a vehicle and is provided in the signal processing unit 2
The measurement data of the distance and the relative speed output from 8 are displayed.

The measurement mode switching unit 30 is provided, for example, on a dashboard in an automobile, and when it is desired to know a highly accurate relative speed between the vehicle and a vehicle traveling forward or backward, the measurement mode is a normal radar mode. To a high-precision measurement mode by a manual switch, or in synchronization with the triangular wave signal from the modulation signal generator 21, the measurement mode is set to a normal radar mode or a high-precision measurement mode every predetermined period or each period. It is possible to use a circuit for outputting an instruction signal for alternately switching to, but here, the latter circuit will be described as a circuit for automatically switching between measurement modes.

The operation of the FM-CW radar device having the above structure will be described with reference to the waveform chart of the main part shown in FIG. First, a triangular wave signal is generated by the modulation signal generator 21 for FM modulation as shown in FIG. 3A, and this triangular wave signal is input to the variable gain amplifier 22. Here, in the case where the measurement mode is switched to the normal radar mode for the period of two cycles and the high-accuracy measurement mode for the period of one cycle by the instruction from the measurement mode switching unit 30, these are switched alternately. Is controlled to a gain capable of ensuring a modulation width necessary to realize the range resolution required for the FM-CW radar device in a normal radar mode, for example, a gain of 1, and a gain smaller than 1 in a high precision measurement mode. Controlled by. Variable gain amplifier 22 at this time
The change in the gain is shown in FIG. Voltage controlled oscillator 23
The input voltage vs. output frequency characteristic of is not a straight line generally represented by a broken line as shown in FIG. 9, but has a characteristic represented by a solid line. It deviates greatly from the straight line at both ends of the frequency. Therefore, the gain of the variable gain amplifier 22 in the high precision measurement mode is controlled to a value such that the modulation width falls within the linear portion near the center of the input voltage-output frequency characteristic of the voltage controlled oscillator 23. The output signal of the variable gain amplifier 22 is as shown in FIG.
As shown in (C), the triangular wave signal has a large voltage change width in the normal radar mode, and the triangular wave signal has a small voltage change width in the high-precision measurement mode. When the signal from the variable gain amplifier 22 whose amplitude is controlled in this way is input to the voltage control input terminal of the voltage control oscillator 23, the voltage control oscillator 23 outputs a signal having a frequency corresponding to the input voltage of the triangular wave, that is, radar. An output millimeter-wave band FM-modulated signal is generated. This signal is
As shown in (D), in the normal radar mode section, due to the nonlinearity of the input voltage vs. output frequency characteristic of the voltage controlled oscillator 23, the waveform of the triangular wave is changed in the vicinity where the increasing and decreasing directions of the frequency change at both ends of the modulation width. , The frequency changes in a blunt manner. On the other hand, in the high-precision measurement mode section, since the modulation width is in the almost linear region of the input voltage-output frequency characteristic of the voltage controlled oscillator 23, the frequency changes in a triangular wave shape. ing. Then, such an output signal is transmitted to the transmitting antenna 2
5 is released into the space.

The emitted signal collides with a vehicle running ahead or behind, which is a target object, and when a part of the signal is reflected by the target object and returns, the signal is efficiently received by the receiving antenna 26. The received signal includes a signal component including distance information and relative velocity information between the target object and the FM-CW radar device, and is input to the frequency converter 27. In the frequency converter 27, the received signal is mixed with a part of the output of the voltage controlled oscillator 23, converted into a beat signal and sent to the signal processing unit 28. In the signal processing unit 28, the beat signal from the frequency converter 27 is transmitted by the low-pass filter 28a, and the analog / digital converter 2
8b converts the analog signal into a digital signal, the digital signal processor 28c calculates the distance and speed, and passes the obtained distance data and speed data to the processor 28d. The processor 28d displays these distance data and speed data. And output to the display unit 29.

Since the signal processing unit 28 performs signal processing based on the FM modulated signal generated by the voltage controlled oscillator 23, a processing error is generated when the demodulated wave is far from the triangular wave shape. . Therefore, in the normal radar mode, an error in the processed signal occurs. However, in the high-accuracy measurement mode, the FM modulated wave also has a triangular wave shape, and the signal demodulated by the frequency converter 27 also has a triangular wave shape. Therefore, relative speed detection with a small error becomes possible, and the conventional FM can be detected. -The relative velocity can be measured with higher measurement accuracy than that of the CW radar device. However, in the high-precision measurement mode that measures the relative speed with high accuracy, the frequency modulation width is narrowed, so the distance measurement accuracy when measuring the distance is reduced. When it is not needed, it returns to normal radar mode.

FIG. 4 is a block diagram showing another embodiment of the modulation amplitude varying means. A modulation amplitude varying section 40, which is another embodiment of the modulation amplitude varying means, includes a relay 41 that receives a modulation signal at a movable contact, attenuators 42 and 43 connected to fixed contacts of this relay 41, and these attenuators 42. , 43
And a relay 44 which outputs a modulated signal whose amplitude is controlled by a movable contact.
Further, the modulation amplitude varying section 40 has a control terminal 45 for simultaneously switching the relay contacts of the relays 41 and 44 according to the measurement mode.

In the two attenuators 42 and 43, for example, the attenuator 42 changes the modulation width of the modulation signal from the modulation signal generator 21 into the modulation width in the normal radar mode, that is, FM.
-The CW radar is set to a value that attenuates to a modulation width required to realize the required distance and relative velocity resolution, and the attenuator 43 is set to a value that further attenuates to the modulation width in the high precision measurement mode. ing. Therefore, the control positions of the relays 41 and 44 shown in the figure show the connection positions in the normal radar mode, and when the control terminal 45 receives the measurement mode switching command, the movable contacts of the relays 41 and 44 are controlled. The high-precision measurement mode is switched to, and the modulated signal is attenuated by the attenuator 43.

FIG. 5 is a block diagram showing a second embodiment of the FM-CW radar device of the present invention. FM-shown
The CW radar device uses a modulated signal generator 51 as a transmission system.
A modulation amplitude varying section 52, a voltage controlled oscillator 53, a directional coupler 54, and a transmitting antenna 55, a receiving antenna 56 and a frequency converter 57 as a receiving system, and a signal processing system. , Signal processing unit 58 and display unit 59
It is comprised including. The signal processing unit 58 receives the output signal of the frequency converter 57, and is a low-pass filter 58a.
, Analog / digital converter 58b, and digital signal processor 58c for calculating distance and velocity
And a processor 58d that determines whether or not to switch the measurement mode based on the distance data and velocity data from the digital signal processor 58c and notifies the modulation amplitude varying unit 52 and the digital signal processor 58c of the result, and the measurement mode. Read-only memory (ROM) 58 holding condition data for
e. Although the read-only memory 58e is used as the storage means for holding the condition data here, it may be a random access memory.

Here, the signal processing unit 58 is in an environment in which there is a sufficient vehicle-to-vehicle distance to the target vehicle, and the relative speed with the vehicle does not change so much that there is a relatively low risk of collision. For example, the measurement mode is automatically switched depending on the situation, for example, when the inter-vehicle distance is sufficient but the negative relative speed is large, that is, in the case of an emergency when the vehicle is rapidly approaching. It is configured. In particular, when measuring in the normal radar mode, if the relative speed suddenly increases in the approaching direction, the measured value of the relative speed is not a reliable value, so it is really close. It is not possible to judge whether or not the error is caused by the accuracy error and is large in the calculation. In such a case, it is necessary to switch the measurement mode from the normal radar mode to the high precision measurement mode and obtain the high precision relative velocity.

The processor 58d analyzes the distance data and the speed data passed from the digital signal processor 58c, reads the data which is stored in the read-only memory 58e and serves as a reference for switching judgment, and compares the data with the analysis result. For example, the processor 58d checks whether the inter-vehicle distance is shorter than the reference distance set in the read-only memory 58e, and if the distance is shorter,
For example, activate an alarm device (not shown),
Control is performed to shift to brake operation. Further, if the negative relative speed is large even if the inter-vehicle distance is large, the processor 58d reads the value of the relative speed with respect to the inter-vehicle distance from the read-only memory 58e to satisfy the determination criterion, and the modulation amplitude variable The modulation width is controlled to be small for the unit 52, and a switching signal for notifying the digital signal processor 58c that the measurement mode is the high precision measurement mode is output. The distance and relative velocity data obtained as a result of the measurement in the high precision measurement mode are compared with the judgment reference data set in the read-only memory 58e in the processor 58d,
When it is determined that the predetermined determination criteria are satisfied, the distance and relative velocity data at that time are passed to the display unit 59 and displayed, and an unillustrated alarm device, for example,
An alarm signal is output to the brake control device or the like.

As described above, the signal processing unit 58 stores various kinds of data for determining the measurement mode switching, compares the data of the distance and the relative speed measured in the normal radar mode with the stored data, and determines a predetermined value. When the criterion of (1) is satisfied, the measurement mode is switched to the high-accuracy measurement mode to obtain a highly accurate relative speed. The relative speed with high measurement accuracy obtained here is displayed on the display unit 59.

[0037]

As described above, according to the first aspect of the present invention, the modulation amplitude varying means is newly inserted between the modulation signal generating means and the voltage controlled oscillating means. As a result, the modulation width of the voltage controlled oscillator is
Normally, the modulation width required to realize the distance and the relative velocity resolution required by the FM-CW radar and the modulation width narrower than this modulation width are modulated in a region where the input voltage vs. output frequency characteristic of the voltage controlled oscillator has good linearity. Since it is possible to switch to a modulation width capable of performing, it is possible to reduce the measurement error of the relative speed measurement due to the non-linearity of the input voltage-output frequency characteristic of the voltage controlled oscillator, especially when the modulation width is narrowed. Therefore, the accuracy of speed display of the radar device can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the basic configuration of an FM-CW radar device of the present invention.

FIG. 2 is a block diagram showing a first embodiment of an FM-CW radar device of the present invention.

FIG. 3 is a main part waveform diagram for explaining the operation of the FM-CW radar device.

FIG. 4 is a block diagram showing another embodiment of the modulation amplitude varying means.

FIG. 5 is a block diagram showing a second embodiment of an FM-CW radar device of the present invention.

FIG. 6 is a diagram showing a principle configuration of a conventional FM-CW radar device.

FIG. 7 is an explanatory diagram of the principle of measuring the distance by the FM-CW radar device.

FIG. 8 is an explanatory view of the principle of measuring a relative speed by an FM-CW radar device.

FIG. 9 is a diagram showing input / output characteristics of a voltage controlled oscillator.

[Explanation of symbols]

 11 Modulation Signal Generating Means 12 Modulation Amplitude Changing Means 13 Voltage Control Oscillating Means 14 Directional Coupling Means 15 Transmitting Antennas 16 Receiving Antennas 17 Frequency Converting Means 18 Signal Processing Means 19 Displaying Means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Teruhisa Ninomiya 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited (72) Inventor, Osamu Isaji 1-22 Gosho-dori, Hyogo-ku, Hyogo Prefecture Within Fujitsu Ten Limited

Claims (5)

[Claims] 1. A signal obtained by frequency-modulating a high-frequency signal by a voltage-controlled oscillation means by a modulation signal from a modulation signal generation means is transmitted, a reflection signal from a target object is received, and a part of the transmitted signal is branched. In the FM-CW radar device, the received signal is frequency-converted as a local oscillation signal source of the receiver, and the signal processing means measures the distance to the target object and the relative speed. 2. An FM-CW radar device comprising: a modulation amplitude varying means for limiting the input voltage versus output frequency characteristic in a linear region. 2. The FM-C according to claim 1, wherein the amplitude control of the modulation amplitude varying means is performed in a predetermined cycle.
W radar device. 3. The signal processing means stores the data serving as a judgment reference for switching the presence or absence of amplitude control of the modulation amplitude varying means, and the measured distance and relative velocity data as the judgment reference. 2. The FM according to claim 1, further comprising a mode switching judging means for judging whether or not the amplitude control should be carried out by comparing the data with the following data.
-CW radar device. 4. The FM-CW according to claim 1, wherein the modulation amplitude varying means comprises a variable gain amplifier.
Radar equipment. 5. The modulation amplitude varying means includes two attenuators having different attenuation values and a relay for switching the attenuator through which the modulation signal passes depending on the presence / absence of amplitude limitation. The FM-CW radar device according to 1.