JP4771166B2 - FM-CW radar equipment - Google Patents

Description

The present invention, FM-CW using microwaves - relates (Frequency Modulated continuous wave) radar, for example, relates to the FM-CW radar device capable Detection of distance and speed suitable for slow moving object such as a walking person.

Conventionally, a method using a Doppler effect of a reflected wave from a moving object is well known for measuring a moving speed using radio waves. Further, as a method of measuring from a point away from a moving object using radio waves, a method of measuring using a transmission pulse wave and a delay time of a reflected wave from the moving object of the transmission wave is known.
However, in the measurement method according to the delay time, the radio wave speed is fast damage, in short distance measurement, it is required to detect the pulse wave at nanosecond precision, in order to detect with high accuracy, the device scale It gets bigger.
As a prior art proposed to solve this problem, the following Patent Document 1 can be cited. The method for measuring the distance and speed of a moving body described in Patent Document 1 is based on a Doppler radar apparatus using microwaves or millimeter waves, and a transmission wave is subjected to FM modulation of a triangular wave. It is shown that a method of detecting a Doppler frequency during a frequency rising period and a falling period by FM modulation of a triangular wave and calculating a distance based on this frequency is shown.

However, in the FM-CW radar system that applies FM modulation of a triangular wave described in Patent Document 1, symmetry of the rising period and falling period of the triangular wave (that is, even if there is a difference between rising and falling, the slope: the rate of change is an absolute value. Since it directly affects the detection accuracy, it is necessary to maintain symmetry, but it is difficult to maintain this with high accuracy.
Further, when the moving body is at a low speed, the Doppler frequency difference between the rising period and the falling period becomes small, so that highly accurate detection becomes difficult.
Therefore, the present invention has been made in order to solve the above-described problems in the measurement of the distance and speed of a moving body by the conventional FM-CW radar system, and the object thereof is to provide the above-described symmetry for FM modulation. An FM-CW radar system that does not require high speed is capable of detecting a distance / speed suitable not only for a high-speed moving object but also for a low-speed moving object such as a walking person.

The invention of claim 1 is an FM-CW radar apparatus, wherein a variable frequency oscillator whose output frequency is changed by a control input, and a radar wave transmitting means for transmitting a CW radar wave based on an output signal of the variable frequency oscillator; A radar wave receiving means for receiving the CW radar wave reflected by a moving object, a mixer for mixing a received signal of the radar wave receiving means with a transmission signal of the variable frequency oscillator, and a frequency difference component from the output of the mixer A filter for detecting the frequency of the signal filtered by the filter, means for generating a sawtooth wave as a control input for changing the output frequency of the variable frequency oscillator, and the sawtooth wave The distance from the moving object is determined based on the frequency detected by the frequency detection circuit at one detection point in the inclined portion and the inclination of the inclined portion of the sawtooth wave. When calculating the speed of the distance calculating means for obtaining the separation and the speed of the low-speed moving body, the distance of the two detection points of the moving object and the time obtained by the distance calculating means at time intervals that are multiple times the period of the sawtooth wave, respectively. And the distance of the two detection points of the moving object obtained at predetermined time intervals within the same inclined portion of the sawtooth wave by the distance calculation means and the time And a speed calculating means for determining the speed based on the above .

According to the present invention, the time over a plurality of periods of the sawtooth wave that changes the output frequency of the CW radar wave is set as the detection time point, and the speed is obtained based on the obtained distance, so the speed of the low-speed moving object is detected with high accuracy. can do.
Further, since the speed is obtained based on the distance obtained by using the time within one cycle of the sawtooth wave that changes the output frequency of the CW radar wave as the detection time point, the speed of the high-speed moving object can be detected with high accuracy.

Hereinafter, an embodiment according to the FM-CW radar equipment of the present invention.
Device described below as an embodiment according to the FM-CW radar apparatus, since the operation according to the distance and speed method for detecting moving objects, described also with METHODS in the form of aggregated to an embodiment of the FM-CW radar apparatus .
The FM-CW radar device of this example is aimed at a device that can measure a distance and speed to a moving object that is not so far, such as a person who walks or runs. For example, a microwave is used as a radar wave. This apparatus performs a radar operation in which a radio wave such as a microwave is transmitted from an antenna toward a moving object to be detected, and a wave reflected and returned from the moving object is received.
Here, the operation as the FM-CW radar is performed. The CW radar wave transmitted from the antenna is subjected to modulation whose frequency changes in proportion to time. When this CW radar wave reflected and returned by the moving object is received, the FM modulated wave signal continuously transmitted from the apparatus and the received signal are mixed. The reflected wave has a time delay corresponding to the distance from the moving object compared to the transmitted wave, and the frequency difference between the signals to be mixed is shifted accordingly, so this frequency difference is detected as the Doppler frequency. As will be described later, this frequency difference has a predetermined relationship with the distance.

FIG. 1 shows a schematic configuration of an embodiment according to the FM-CW radar apparatus of the present invention.
The apparatus shown in FIG. 1 has a configuration capable of performing the basic operation as the FM-CW radar described above.
As a configuration on the transmission side, since a FM modulated wave is transmitted, the transmitter has a signal source including a VCO (Voltage Controlled Oscillator) 12 and a control voltage generation circuit 11 that generates a control input signal for controlling the VCO 12. In addition, it includes a power amplifier 13 that amplifies the output of the VCO 12, a filter 14 that filters unnecessary signal components, a circulator 15, and an antenna 19.
As a configuration on the receiving side, the receiving circuit includes an antenna 19 that captures a reflected wave from a target object, a circulator 15, a filter 20 that filters only necessary signal components, and an amplifier 21 that amplifies the output of the filter 20. The antenna 19 and the circulator 15 are elements common to transmission and reception. The circulator 15 transmits a signal from the internal circuit at the time of transmission from the antenna 19 and receives a signal received by the antenna 19 at the time of reception. Incorporate into the circuit. Further, since the difference frequency between the transmission wave signal and the reception wave signal is detected, it is necessary from the demultiplexer 22 that demultiplexes the VCO output signal on the transmission side, the mixer 23 that mixes the reception signal and the demultiplexer output signal, and the mixer output. A filter 24 for filtering only the Doppler frequency (difference frequency) signal component, and a frequency detection circuit 25 for detecting the difference frequency based on the filter output.
The control circuit 10 controls the operation of the control voltage generation circuit 11 and calculates calculating means for calculating the distance and speed based on the difference frequency acquired as a detection result from the frequency detection circuit 25 (the calculation method will be described in detail later). Has a description).

An outline of the operation of the FM-CW radar apparatus shown in FIG. 1 will be described below.
Since the control circuit 10 applies FM modulation to the VCO 12 and changes the output frequency in a sawtooth shape as will be described later, the control voltage generation is performed based on the control conditions such as the generation timing of the control signal that changes in the sawtooth shape at the beginning of the operation. Set to circuit 11. In accordance with this setting condition, the control voltage generation circuit 11 applies a voltage to the frequency control terminal of the VCO 12. With this control voltage, the output frequency of the VCO 12 becomes a signal that changes in a sawtooth shape.
Next, a part of the output signal of the VCO 12 is demultiplexed by the demultiplexer 22, but the transmitted signal passes through the power amplifier 13, the filter 14 for filtering unnecessary signal components, the circulator 15 and the antenna 19. Then, a moving object as a target is irradiated.
The outgoing wave from the antenna 19 is reflected by the moving object and returns as a reflected wave, and is received by the antenna 19. The received signal is input to the mixer 23 after passing through the circulator 15, the filter 20 that filters only necessary signal components, and the amplifier 21 that amplifies the output of the filter 20.

Since the transmission signal demultiplexed by the demultiplexer 22 from the transmission side circuit is input to the other input terminal of the mixer 23 to which the reception signal is input, it is reflected by this transmission signal and the moving object on the reception side. The mixed signal is mixed.
Between the signals to be mixed, the reception signal of the reflected wave with respect to the transmission signal is reflected by the moving object, and there is a time delay that occurs while going back and forth. Therefore, the mixing output has a frequency difference associated with the time delay. appear. The output after mixing also includes a sum frequency component, but since this component is not necessary, the filter 24 is an LPF (low-pass filter) that filters only the required Doppler frequency (difference frequency) signal component. Removed.
Since the output signal from the filter 24 is a signal corresponding to the difference frequency, a signal indicating the difference frequency is sampled at a predetermined timing by the frequency detection circuit 25 and detected as frequency data.
Next, the control circuit 10 that receives the data of the detected Doppler frequency performs an operation for obtaining the distance and the speed based on this data.

Next, a method for obtaining the distance and speed based on the Doppler frequency will be described.
In the distance and speed detection based on the Doppler frequency of the present invention, as mentioned in the description of the apparatus configuration described above, FM modulation is performed so that the frequency of the transmission output signal is changed in a sawtooth shape.
The transmitted wave and reflected wave signals that are FM-modulated in a sawtooth shape are shown in FIGS. In both figures, the horizontal axis represents time and the vertical axis represents frequency, and the frequency of the transmission output signal is periodically changed in a sawtooth shape. The period of change is given by Tm. In this example, the frequency change width is Δf, and the frequency is modulated at a constant change rate (slope). Therefore, the change rate (slope) can be expressed by Δf / Tm at any time point. .
2, the rate of change in FIG. 2 is larger than that in FIG. 3. However, as described later, by changing the rate of change in this way, the rate of change varies depending on the speed of the moving object to be detected. By using the detection method, the detection accuracy can be increased.

First, a method for detecting the distance of a moving object using a radar wave that is FM-modulated in a sawtooth shape will be described with reference to FIG.
A method of detecting the distance of the moving object can be obtained based on the result of detecting one Doppler frequency at a certain time. For example, as shown in FIG. 2, an appropriate timing such as A1 in the first sawtooth wave section avoiding a sawtooth wave switching point that may cause an unstable operation is selected as a detection point.
In A1 of FIG. 2, the reflected wave from the moving object with respect to the transmission wave is captured with a deviation caused by a time delay corresponding to the distance of the moving object. This shift appears in the output of the mixer 23 as the difference between the frequency of the reflected wave and the frequency of the transmitted wave, that is, the Doppler frequency fa.
Between the Doppler frequency fa and the distance Ra of the moving object,
Ra = c · (Tm / Δf) · fa / 2 Formula (1)
There is a relationship. In the above formula (1), c: speed of light (constant).
Here, Tm / Δf is data managed by the control circuit 10 as a value set in the control voltage generation circuit 11 as a control condition. That is, c · (Tm / Δf) is given as a known amount before detection.
The Doppler frequency fa is output to the control circuit 10 by the frequency detection circuit 25. Therefore, the control circuit 10 can calculate the distance Ra of the moving object at the point A1 in the first sawtooth wave section based on the data of the Doppler frequency fa according to the above equation (1).

Next, a method for detecting the velocity of a moving object using a radar wave that is FM-modulated in a sawtooth shape will be described.
The speed detection method of the present plan is a method based on the above-described distance detection method, and detects the distances Ra and Rb with respect to the moving object at a time T based on the above-described distance detection method.
Speed V = (Ra−Rb) / T Formula (2)
In this way, the velocity V of the moving object is obtained. The time T has a timer in the control circuit 10 and a method for defining the detection point at a time set in advance in the timer in consideration of avoiding a sawtooth wave switching point that may cause an unstable operation. Can be implemented. In addition, after detecting the distance Ra, the moving body is displaced during the time T, but the error can be reduced when there is a condition in which the speed can be regarded as not changing during this time.
As a method according to the above speed detection process, the present method shows two detection methods of the following methods 1 and 2.
Method 1: Time T is a time spanning a plurality of periods in which the modulation frequency of the transmission output signal is changed in a sawtooth shape.
Method 2: The time T is set to a time within one cycle of changing the modulation frequency of the transmission output signal in a sawtooth shape.
Each of the above methods 1 and 2 will be described below with reference to FIGS.

"Speed detection by method 1"
In this method, when the distances Ra and Rb to the moving object are detected at intervals of time T, the first detection point is selected, and then the next detection point is a time spanning a plurality of periods of the sawtooth wave, that is, the above-described time. The time interval is set to be a multiple of the period of the sawtooth wave, and is intended to provide a detection accuracy of the speed of an object moving at a low speed.
The A1 time point and B1 time point illustrated in FIG. 2 are detection points according to the method 1, and the B1 time point is set with a plurality of sawtooth wave cycles from the A1 time point.
The distance detection at the time A1 is as described above. The distance detection at time B1 is basically performed in the same manner as at time A1. That is, based on the Doppler frequency fb at time B1 in FIG.
Rb = c · (Tm / Δf) · fb / 2 Formula (3)
The distance Rb is obtained according to In the case of FIG. 2, since the object moving in the direction away from the radar device is targeted, the Doppler frequency fb at the time B1 increases (the frequency difference increases) and the distance also increases. The timing for detecting the distance at the time point B1 can also be implemented by managing the timer in the control circuit 10 as described above.
The speed V is obtained according to the above formula (2) based on the distances Ra and Rb.

"Speed detection by method 2"
In this method, when the distances Ra and Rb to the moving object are detected at a time T, the first detection point is selected, and then the next detection point is set within a predetermined slope portion of the sawtooth wave. This time interval is set to be intended to provide a detection accuracy of the speed of an object moving at high speed.
The point A2 and the point B2 illustrated in FIG.
In the case of high speed, even if the time T is shortened, the difference between the Doppler frequencies fa and fb at the time A2 and the time B2 can be made large, so two detection points within the same inclined portion of the sawtooth wave should be selected. It is possible to reduce errors. However, it is necessary to avoid the vicinity of the sawtooth switching point where unstable operation may occur.
The distances Ra and Rb at the time A2 and the time B2 are detected in accordance with the equations (1) and (3), respectively, as in the method 1. Further, the timing for detecting the distance at the time point B2 can also be implemented by managing with the timer as described above.
The speed V is obtained according to the above formula (2) based on the distances Ra and Rb.

"Application example of FM-CW radar equipment"
Next, as an application example of the FM-CW radar apparatus of the present proposal, an example of a detection system using this radar apparatus as an element constituting a system for detecting the position / velocity of an object moving on a plane will be shown.
The above-mentioned FM-CW radar device basically detects the distance and speed between the device and the target in one dimension. When used alone, the distance from the observation point (device installation point) is required. However, it is impossible to specify in which direction of the detectable area the position on the plane is present. Therefore, an example in which this FM-CW radar apparatus is extended to elements constituting a system that enables two-dimensional detection using an object moving on a plane as a detection target will be described below.
A first application example to a two-dimensional detection system is a system in which a direction detection device capable of detecting a direction (angle) is combined with the FM-CW radar device of the present invention.
This system can detect in which direction the moving object to be detected exists on the observation point where the FM-CW radar device is installed. For example, the direction (angle) of a camera or a scanning beam method with strong directivity The system is configured by using a direction detection device such as a sensor as another detection means.
In this system, the position of the moving object on the plane can be specified by detecting the distance from the observation point by the FM-CW radar device and the direction by the direction detection device, and the position data can be obtained.
Further, the velocity vector of the moving object can be obtained by detecting the position on the plane of the moving object at two time points separated by a predetermined time.

A second application example to a two-dimensional detection system is to combine two FM-CW radar devices of the present invention according to the principle of triangulation, or to detect the direction (angle) in the FM-CW radar device of the present invention. It is a system that uses a combination of direction detection devices that can perform the above.
This system constitutes a system by setting another FM-CW radar device or direction detection device on another observation point that is spaced a predetermined distance from one observation point where the FM-CW radar device is installed. . The direction detection device uses, for example, a camera or a scanning beam type direction (angle) sensor having strong directivity.
This system specifies the position of a moving object according to the principle of triangulation that works on a triangle formed by a moving object to be detected and two observation points. However, when following this principle, if the detectable area becomes large, the triangles with the same distance and direction (angle) obtained as the detection value may not be uniquely determined. There is a need.
In a system in which FM-CW radar devices are provided at two observation points, the three sides of a triangle formed by the moving object to be detected and the two observation points are determined. Therefore, the position of the moving object on the plane is specified and its position data is obtained. be able to. In a system in which an FM-CW radar device and a direction detection device are provided at two observation points, the condition for determining the angle on the FM-CW radar device side among the angles sandwiching one side of a triangle formed by the two observation points is as follows. Since the triangle formed by the moving object to be detected and the two observation points is uniquely determined, the position of the moving object on the plane can be specified and the position data can be obtained.
Further, the velocity vector of the moving object can be obtained by detecting the position on the plane of the moving object at two time points separated by a predetermined time.

The schematic structure of embodiment which concerns on the FM-CW radar apparatus of this invention is shown. FIG. 5 is a diagram for explaining the operation principle (method 1) of the FM-CW radar of the present invention, and shows the relationship between a sawtooth FM modulated transmission wave, a reflected wave signal, and detection points. FIG. 2 is a diagram for explaining the operation principle (method 2) of the FM-CW radar of the present invention, and shows the relationship between a transmission wave, a reflected wave signal, and detection points that are FM-modulated in a sawtooth shape.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Control circuit, 11 ... Control voltage generation circuit, 12 ... VCO (Voltage Controlled Oscillator), 14, 20 ... Filter, 15 ... Circulator, 19 ... Antenna , 22 ... demultiplexer, 23 ... mixer, 24 ... low-pass filter (LPF), 25 ... frequency detection circuit.

Claims (1)

A variable frequency oscillator whose output frequency changes according to the control input;
Radar wave transmitting means for transmitting a CW radar wave based on the output signal of the variable frequency oscillator;
Radar wave receiving means for receiving the CW radar wave reflected by the moving object;
A mixer for mixing the reception signal of the radar wave receiving means with the transmission signal of the variable frequency oscillator;
A filter for filtering frequency difference components from the output of the mixer;
A frequency detection circuit for detecting the frequency of the signal filtered by the filter;
Means for generating a sawtooth wave as a control input for changing the output frequency of the variable frequency oscillator;
Distance calculating means for obtaining a distance from a moving object based on the frequency detected by the frequency detection circuit at one detection point in the inclined portion of the sawtooth wave and the inclination of the inclined portion of the sawtooth wave;
When determining the speed of the low-speed moving body, the distance calculation means moves at a high speed based on the distance between the two detection points of the moving object and the time obtained at time intervals that are multiple times the period of the sawtooth wave. When calculating the speed of the body, the distance calculation means calculates the speed based on the distance between the two detection points of the moving object obtained at a predetermined time interval within the same inclined portion of the sawtooth wave and the time. An FM-CW radar apparatus comprising: a speed calculation means to be obtained.

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