JP2013088273A - Fmcw radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an FMCW radar device capable of measuring a distance to each detected target and a relative speed by detecting a plurality of targets over a wide range.SOLUTION: The FMCW radar device includes means (101) for setting a plurality of range observation periods, means (101) for setting a plurality of modulation frequency widths different in each range observation period, means (107) for generating a beat signal for each range observation period from a transmission signal and a reception signal, means (109, 111) for setting a passing band width of the generated beat signal, means (110, 112) for amplifying the beat signal passing through the passing band width setting means, means (113) for converting the amplified beat signal into digital data, and means (108a, 108b) for switching the passing band width setting means and the amplification means in each range observation period.

Description

  The present invention is an apparatus that detects a target object (hereinafter referred to as a target) and measures the distance and relative speed thereof. More specifically, a plurality of targets are detected in a wide distance range, and the detected target is detected. The present invention relates to an FMCW (Frequency Modulated Continuous Wave) radar apparatus capable of measuring the distance and relative speed of a target.

An FMCW radar device (hereinafter simply referred to as FMCW radar) that can handle short-range targets of several hundred meters or less with a cheap and simple configuration compared to a pulse radar or the like radiates a specific transmission signal as an electromagnetic wave (transmitted wave) And receiving the electromagnetic wave reflected by the target, using the received electromagnetic wave as a reception signal, and generating a beat signal from the transmission signal and the reception signal.
In recent years, beat signals are converted into digital data by an A / D converter, and then input to a CPU (Central Processing Unit). Measurement of relative speed between distance and target is performed.

The intensity (power) of the electromagnetic wave received by the FMCW radar varies greatly depending on the distance to the target and the like, and the voltage value of the beat signal also varies greatly accordingly. For this reason, when the dynamic range of the receiving circuit is insufficient, various problems occur.
For example, the intensity of the electromagnetic wave received from the target is small, and the absolute value of the generated beat signal voltage of the target or the relative change is the 1-bit (minimum) voltage of the A / D converter. If it is smaller than the value, it cannot be handled as digital data, or the original correct signal information is lost.
If the intensity of the electromagnetic wave received from the target is large and the absolute value of the generated beat signal voltage of the target is greater than the maximum voltage value that can be converted by the A / D converter, the original correct signal information is obtained. It will be lost.
Furthermore, even if the intensity of the received electromagnetic wave from the target is large and the absolute value of the generated beat signal voltage of the target is smaller than the maximum voltage value that can be converted by the A / D converter, the signal is saturated in the receiving circuit. If this happens, the generated beat signal of the target will have a “distorted waveform” that is different from the actual one, and the original correct signal information may not be obtained, or unnecessary information such as harmonics may appear. .

Japanese Unexamined Patent Publication No. 2001-228240 (Patent Document 1) is known as a conventional technique related to a reception circuit for a received electromagnetic wave whose intensity greatly varies in such an FMCW radar.
In Japanese Patent Laid-Open No. 2001-228240, “a radio wave is transmitted to one target (target), a reflected wave from the target is received, and a distance to the target or a relative speed with the target is obtained. In a reception signal amplifying apparatus for FMCW radar, a plurality of amplifiers connected in cascade to amplify a reception signal, and the output voltage of the amplifiers is adapted to the input voltage range of the A / D conversion means, and And selecting an amplifier having the highest level and providing an output selection means for guiding the output to the A / D conversion means ”.
That is, in Japanese Patent Laid-Open No. 2001-228240, a reception signal amplifying apparatus for an FMCW radar that transmits radio waves to one target, including a plurality of amplifiers connected in cascade to amplify the reception signal, each amplifier The optimum amplifier is selected with reference to the output voltage level.

JP 2001-228240 A

In an environment where the FMCW radar is operated, there is not necessarily only one target.
For example, in an in-vehicle FMCW radar used for ACC (Adaptive Cruise Control) and collision mitigation (or prevention), as shown in FIG. 5, a target traveling in front of a vehicle 510 on which an FMCW radar 511 is mounted. 520 is the most notable target (vehicle), but there may be a plurality of other targets that reflect electromagnetic waves.
In the lane adjacent to the lane in which the vehicle 510 is traveling, there is a target 530 that is closer than the target 520 ahead of the traveling direction of the vehicle 510, and the beat signal of the target 530 is detected by the FMCW radar 511 mounted on the vehicle 510. Assume that the best output (ie, the optimum amplifier output) is selected.
At this time, the beat signal of the target 520 to which attention should be paid is lower in voltage than the beat signal of the target 530. Therefore, if the dynamic range of the receiving circuit is narrow, the beat signal of the target 520 is sufficiently amplified at the selected amplifier output. In some cases, the data cannot be handled as digital data, or a part of the signal information is lost.

  The present invention has been made to solve such a conventional problem, and in a situation where a plurality of targets are present and the dynamic range of the receiving circuit is narrow, An object of the present invention is to provide an FMCW radar apparatus capable of detecting a plurality of targets over a wide distance range and measuring the distance to each detected target and the relative velocity with the detected target.

An FMCW radar apparatus according to the present invention is an FMCW radar apparatus that detects a plurality of targets over a wide distance range and measures the distance and relative velocity with the detected targets.
Distance range observation period setting means to set multiple distance range observation periods consisting of up-chirp period and down-chirp period by changing the measurable distance range, and multiple modulation frequency widths that are different for each distance range observation period Modulation frequency width setting means, beat signal generating means for generating a beat signal for each distance range observation period from a transmission signal and a received signal, and a beat signal for each distance range observation period generated by the beat signal generating means Pass bandwidth setting means for setting the pass bandwidth of the signal, amplification means for amplifying the beat signal passing through the pass bandwidth setting means, and conversion means for converting the beat signal amplified by the amplification means into digital data And a switching means for switching the passband width setting means and the amplification means for each distance range observation period. It is.

  According to the present invention, each of a plurality of targets existing over a wide distance range is detected even in a situation where a plurality of targets are present and the dynamic range of the receiving circuit is narrow, It is possible to measure the distance to each detected target and the relative speed with the detected target.

1 is a block diagram showing a configuration of an FMCW radar apparatus according to Embodiment 1. FIG. 6 is a diagram showing a transmission signal when there are two distance range observation periods in the FMCW radar apparatus according to Embodiment 1. FIG. It is a figure which shows the characteristic of the 1st and 2nd band pass filter in the FMCW radar apparatus which concerns on Embodiment 1. FIG. FIG. 6 is a diagram for explaining that a beat signal can be obtained in a desired distance range even when the dynamic range of a receiving circuit is narrow in the FMCW radar device according to the first embodiment. It is a figure which shows an example of the driving | running state of a FMCW radar apparatus mounting vehicle and multiple targets.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing the configuration of the FMCW radar apparatus according to the first embodiment.
In FIG. 1, 101 is a control and signal processing unit, 102 is a voltage controlled oscillator (hereinafter referred to as VCO: Voltage Controlled Oscillator), 103 is a distribution circuit, 104 is a high frequency amplifier, 105 is a transmitting antenna, and 106 is a receiving antenna. , 107 are mixers, 108a and 108b are interlocking switches, 109 is a first band-pass filter (hereinafter referred to as BPF), 110 is a first amplifier, 111 is a second BPF, and 112 is a first Reference numeral 113 denotes an A / D converter (hereinafter referred to as ADC: Analog-Digital Converter).

The control and signal processing unit 101 includes, for example, a dedicated logic circuit, a general-purpose CPU, a program in a DSP (Digital Signal Processor), or a combination thereof and a data storage circuit (memory). The operation timing of each component (for example, VCO 102, interlocking switches 108a and 108b, ADC 113, etc.) is controlled.
In addition, the control and signal processing unit 101 performs signal processing on a beat signal converted into digital data, which will be described later, determines the presence or absence of the target, measures the distance to the target, Measure the relative speed.

The VCO 102 generates a transmission signal whose frequency changes with time according to the applied voltage under the control of the signal processing unit 101.
The transmission signal includes an up-chirp period in which the frequency increases in time for each of M types of distance ranges from the first distance range to the Mth (> 1) distance range, and the frequency in time. A distance range observation period consisting of a down-chirp period in which is low.

Here, how to change the distance range will be described based on the principle of the FMCW radar.
When the length of each chirp period is T [s], the modulation frequency width is B [Hz], the center frequency of the modulation width is F [Hz], and the velocity of the electromagnetic wave is C [m / s], the distance is R [m]. ] For a target with a relative velocity of V [m / s] (defined as a negative value when approaching)
The beat frequency (U [Hz]) observed during the up-chirp period is
U [Hz] =-{(2 * B) / (C * T)} * R-{(2 * F) / C} * V (1)
The beat frequency (D [Hz]) observed during the down chirp period is
D [Hz] = {(2 * B) / (C * T)} * R-{(2 * F) / C} * V (2)
It is represented by
In recent years, a beat signal converted into digital data by an A / D converter is converted into a frequency power spectrum by FFT (Fast Fourier Transform) in a CPU, DSP, etc., and the power is a maximum and a threshold set in advance. The beat frequency U and beat frequency D are obtained by extracting a frequency larger than the value.

In FFT, the discrete frequency width (step) is 1 / T [Hz] because the chirp period is T [s].
Therefore, when N pieces of sample data of the chirp period T (where N is a power of 2) are FFTed, the frequency range obtained is
-(N / 2) x (1 / T) [Hz] to (N / 2-1) x (1 / T) [Hz] (3)
It is.

Here, the maximum distance Ru at which the beat frequency during the up-chirp period becomes the limit frequency on the negative value side is
− (N / 2) × (1 / T) = − {(2 × B) / (C × T)} × Ru−
{(2 × F) / C} × V (4)
By transforming the formula of
Ru [m] = {(C × N) / (4 × B)} − {(T × F) / B} × V (5)
And
By changing the modulation frequency width B included in both the first term and the second term, the maximum distance Ru within the frequency range obtained by FFT can be changed.
Note that the maximum distance Ru can be changed by changing the chirp period T.

Similarly, the maximum distance Rd at which the beat frequency during the down chirp period becomes the limit frequency on the plus value side is
(N / 2-1) × (1 / T) = {(2 × B) / (C × T)} × Rd−
{(2 × F) / C} × V (6)
By transforming the formula of
Rd [m] = {C / (2 × B)} × (N / 2-1) + {(T × F) / B} × V (7), both in the first term and the second term By changing the modulation frequency width B included, the maximum distance Rd within the frequency range obtained by FFT can be changed.
Note that the maximum distance Rd can be changed by changing the chirp period T.

  However, in general, the relative speed V with respect to the target to be measured has a range from a negative value to a positive value. Therefore, Ru in the above formula (5) obtained within the relative speed range, the above formula (7) ) Of Rd is the minimum value in operation.

Based on the above, by providing different modulation frequency widths B for each distance range observation period composed of an up-chirp period and a down-chirp period, a plurality of distance ranges in which a frequency can be obtained by FFT can be set for each distance range observation period.
Hereinafter, in order to simplify the description, a case where there are two distance range observation periods (that is, a case where M = 2) will be described as an example.
When there are two distance range observation periods, as shown in FIG. 2, the chirp period includes an up chirp period in the first distance range observation period, a down chirp period in the first distance range observation period, and a second distance range. An up chirp period for the observation period and a down chirp period for the second distance range observation period are provided.
However,
The modulation frequency width B1 for the first distance range and the modulation frequency width for the second distance range so that the relationship of the maximum distance R1 in the first distance range <the maximum distance R2 in the second distance range is satisfied. Assume that B2 is set.

For example, when the relative speed V of the target to be measured is “−Vx to + Vx”,
The minimum value of Equation (5) and Equation (7) is
{C / (2 × B)} × (N / 2-1) − {(T × F) / B} × Vx (8)
As
{C / (2 × B1)} × (N / 2-1) − {(T × F) / B1} × Vx <
{C / (2 × B2)} × (N / 2-1) − {(T × F) / B2} × Vx (9)
B1 and B2 satisfying the above condition are set.
The first distance range is “Rmin [m] to R1 [m]”, and the second distance range is “R1 [m] to R2 [m]”.

Under the control and control of the signal processing unit 101, the VCO 102 generates an up-chirp period transmission signal of the first distance range observation period whose modulation frequency width is B1.
A part of the transmission signal generated by the VCO 102 is input to the high-frequency amplifier 104 and the rest to the mixer 107 via the distribution circuit 103.
The high frequency amplifier 104 amplifies the transmission signal to a predetermined size and inputs the amplified signal to the transmission antenna 105.
The transmission antenna 105 transmits the transmission signal amplified by the high-frequency amplifier 104 to space as an electromagnetic wave.
The transmitted electromagnetic wave is applied to a target (not shown), and the electromagnetic wave reflected by the target is received by the receiving antenna 106.
The electromagnetic wave received by the receiving antenna 106 is input to the mixer 107 as a received signal.
The mixer 107 generates a beat signal from the reception signal and the transmission signal input via the distribution circuit 103.
The generated beat signal is input to the first BPF 109 via the interlocking switch 108a switched to the terminal P1 side by the control and control of the signal processing unit 101.

The first BPF 109 has the characteristics shown in FIG. 3A, and a beat signal in which an unnecessary low frequency component and a component higher than the frequency F1 corresponding to the maximum distance R1 in the first distance range are suppressed. Input to the first amplifier 110.
Here, the frequency F1 corresponding to the maximum distance R1 in the first distance range is, for example, “−Vx” in V of Expression (1) when the relative speed V of the target to be measured is “−Vx to + Vx”. Is set by the following equation as a value obtained by substituting for the absolute value of the right side or a value obtained by substituting “+ Vx” for V in Equation (2) to obtain the absolute value of the right side.
F1 = {(2 * B1) / (C * T)} * R1-{(2 * F) / C} * Vx (10)
At this time, a beat signal having a component higher than the frequency F1 corresponding to the maximum distance R1 in the first distance range is suppressed.
That is, the beat signal voltage of the target farther than the distance R1 that is outside the first distance range is suppressed.

The first amplifier 110 amplifies the beat signal voltage to a magnitude set in advance for the first distance range, and the amplified beat signal is switched to the terminal P1 side by control and control of the signal processing unit 101. It is input to the ADC 113 via the interlocking switch 108b.
The ADC 113 converts the voltage value of the input beat signal into digital data and inputs the digital data to the control and signal processing unit 101.
The control and signal processing unit 101 extracts and stores the beat frequency U1 of the up-chirp period by FFT for the digital data of the input beat signal.
At this time, since frequency components higher than F1 are suppressed, “so-called aliasing” in which unnecessary high frequency components are folded back and appear at low frequencies can be prevented.
When there are a plurality of targets, a plurality of beat frequencies are extracted during the up-chirp period and all are stored.

Subsequently, the VCO 102 generates a down-chirp period transmission signal of the first distance range observation period whose modulation frequency width is B1 under the control of the signal processing unit 101.
With respect to the generated transmission signal, distribution circuit 103, high frequency amplifier 104, transmission antenna 105, reception antenna 106, and mixer 107 operate in the same manner as described above to generate a beat signal.
The generated beat signal is input to the first BPF 109 via the interlocking switch 108a switched to the terminal P1 side by the control and control of the signal processing unit 101.
The first BPF 109, the first amplifier 110, the interlock switch 108b, and the ADC 113 operate in the same manner as described above, and the digital data of the beat signal voltage value is input to the control and signal processing unit 101.

The control and signal processing unit 101 extracts the beat frequency D1 of the down chirp period from the digital data of the input beat signal by FFT, and uses a known FMCW with the stored beat frequency U1 of the up chirp period. The distance and relative speed of the target are calculated based on the radar principle.
When there are a plurality of targets, a predetermined constraint condition or the like (for example, publicly known) is used with a plurality of beat frequencies extracted in the down-chirp period and a plurality of beat frequencies extracted in the stored up-chirp period. Based on the above, a distance and a relative speed are calculated for each of a plurality of targets.

Subsequently, the VCO 102 generates an up-chirp period transmission signal in the second distance range observation period whose modulation frequency width is B2 under the control of the signal processing unit 101.
With respect to the generated transmission signal, distribution circuit 103, high frequency amplifier 104, transmission antenna 105, reception antenna 106, and mixer 107 operate in the same manner as described above to generate a beat signal.
The generated beat signal is input to the second BPF 111 via the interlocking switch 108a switched to the terminal P2 side by the control and control of the signal processing unit 101.
The second BPF 111 has the characteristics shown in FIG. 3B, and corresponds to a component lower than the frequency F2L corresponding to the maximum distance R1 in the first distance range and the maximum distance R2 in the second distance range. A beat signal in which a component higher than the frequency F2H is suppressed is input to the second amplifier 112.

Here, for the frequency F2L corresponding to the maximum distance R1 in the first distance range and the frequency F2H corresponding to the maximum distance R2 in the second distance range, for example, the relative velocity V of the target to be measured is “−Vx˜ In the case of + Vx ″, the minimum value of the absolute values on the right side in Expressions (1) and (2) is set by the following expression.
F2L = {(2 × B2) / (C × T)} × R1 − {(2 × F) / C} × Vx (11)
F2H = {(2 × B2) / (C × T)} × R2 − {(2 × F) / C} × Vx (12)
At this time, a beat signal having a component lower than the frequency F2L corresponding to the maximum distance R1 in the first distance range is suppressed. That is, since the beat signal voltage of the target at a distance shorter than the distance R1, which is outside the second distance range, is suppressed, saturation does not occur in the receiving circuit composed of the interlock switch, BPF, amplifier, etc. Unnecessary unnecessary information never appears.
In addition, a beat signal having a component higher than the frequency F2H corresponding to the maximum distance R2 in the second distance range is suppressed. That is, the beat signal voltage of the target farther than the distance R2 that is outside the second distance range is suppressed.

The second amplifier 112 is preset for the second distance range, amplifies the beat signal with a degree of amplification larger than that of the first amplifier 110, and is switched to the terminal P2 side by control and control of the signal processing unit 101. Is input to the ADC 113 via the interlock switch 108b.
The ADC 113 converts the voltage value of the beat signal into digital data and inputs the digital data to the control and signal processing unit 101.
The control and signal processing unit 101 extracts the beat frequency U2 of the up-chirp period from the digital data of the input beat signal by FFT.
At this time, since the frequency component higher than F2H is suppressed, the aliasing that appears at the lower frequency by folding the unnecessary higher frequency component can be prevented.
When there are a plurality of targets, a plurality of beat frequencies are extracted during the up-chirp period and all are stored.

Finally, the VCO 102 generates a down-chirp period transmission signal of the second distance range observation period whose modulation frequency width is B2 under the control of the signal processing unit 101.
With respect to the generated transmission signal, distribution circuit 103, high frequency amplifier 104, transmission antenna 105, reception antenna 106, and mixer 107 operate in the same manner as described above to generate a beat signal.
The generated beat signal is input to the second BPF 111 via the interlocking switch 108a switched to the terminal P2 side by the control and control of the signal processing unit 101.
The second BPF 111, the second amplifier 112, the interlock switch 108b, and the ADC 113 operate in the same manner as described above, and digital data of the beat signal voltage value is input to the control and signal processing unit 101.

The control and signal processing unit 101 extracts the beat frequency D2 of the down-chirp period from the input digital data of the beat signal by FFT, and the known FMCW with the stored beat frequency U2 of the up-chirp period The distance and relative speed of the target are calculated based on the radar principle.
In addition, when there are a plurality of targets, a plurality of beat frequencies extracted in the down chirp period and a plurality of beat frequencies extracted in the stored up chirp period, based on a predetermined constraint condition, etc. For each target, the distance and relative speed are calculated.

  By changing the degree of amplification by the amplifier for each distance range set as described above, the power of the target that varies depending on the distance as shown in FIG. Even if the dynamic range that can be handled by the receiving circuit is narrowed, a signal cannot be obtained at a long distance of the hatched portion as shown in FIG. 4B, and the hatched portion as shown in FIG. Signals can be obtained in all desired distance ranges, as shown in FIG. 4D, without obtaining correct signal information at close distances.

  As described above, the FMCW radar apparatus according to the present embodiment is an FMCW radar apparatus that detects a plurality of targets over a wide distance range and measures the distance and relative velocity with the detected targets, and can be measured. Distance range observation period setting means for setting a plurality of distance range observation periods (for example, a first distance range observation period and a second distance range observation period) composed of an up-chirp period and a down-chirp period by changing the distance range (Control and signal processing unit 101), modulation frequency width setting means (control and signal processing unit 101) for setting a plurality of different modulation frequency widths (for example, B1 and B2) for each distance range observation period, and a transmission signal Generated by the beat signal generating means (mixer 107) for generating a beat signal for each distance range observation period from the received signal and the beat signal generating means. Pass bandwidth setting means (for example, first BPF 109, second BPF 111) for setting the pass bandwidth of the beat signal for each distance range observation period, and amplification for amplifying the beat signal passing through the pass bandwidth setting means Means (eg, first amplifier 110, second amplifier 112), conversion means (ADC 113) for converting the beat signal amplified by the amplifying means into digital data, and pass bandwidth setting for each distance range observation period And switching means (interlocking switches 108a and 108b) for switching the amplification means.

  In addition, the FMCW radar apparatus according to the present embodiment has another distance range observation period (for example, the second distance range) depending on the maximum distance that can be measured in a certain distance range observation period (for example, the first distance range observation period). The low-frequency side suppression frequency of the bandpass filter for the observation period) is determined.

In the description of the first embodiment described above, the configuration using the first BPF and the first amplifier with the filter gain = 1.0, and the second BPF and the second amplifier with the filter gain = 1.0. However, each of the first BPF and the second BPF has an amplification function of a preset size for each distance range in the passband, and there is no first amplifier or second amplifier. May be.
In the present invention, the embodiments can be modified or omitted as appropriate within the scope of the invention.

  The present invention is useful not only for realizing an FMCW radar apparatus suitable for being mounted on a vehicle but also for realizing an FMCW radar apparatus suitable for being mounted on a ship or an aircraft other than the vehicle.

101 Control and Signal Processing Unit 102 Voltage Controlled Oscillator (VCO)
103 distribution circuit,
104 high frequency amplifier 105 transmitting antenna 106 receiving antenna 107 mixer 108a, 108b interlocking switch 109 first band pass filter (first BPF)
110 First amplifier 111 Second band pass filter (second BPF)
112 Second amplifier 113 A / D converter (ADC)
510 Vehicle equipped with FMCM radar 520, 530 Target

Claims (2)

An FMCW radar device that detects a plurality of targets over a wide distance range and measures the distance and relative velocity with the detected targets,
Distance range observation period setting means for setting a plurality of distance range observation periods consisting of up-chirp period and down-chirp period by changing the measurable distance range;
Modulation frequency width setting means for setting a plurality of different modulation frequency widths for each distance range observation period;
Beat signal generating means for generating a beat signal for each distance range observation period from a transmission signal and a reception signal;
A pass bandwidth setting means for setting a pass bandwidth of a beat signal for each of the distance range observation periods generated by the beat signal generating means;
Amplifying means for amplifying the beat signal passing through the pass bandwidth setting means;
Conversion means for converting the beat signal amplified by the amplification means into digital data;
An FMCW radar apparatus comprising switching means for switching between the pass bandwidth setting means and the amplification means for each distance range observation period.   2. The FMCW radar apparatus according to claim 1, wherein a low-frequency side suppression frequency of a band pass filter for another distance range observation period is determined by a maximum distance measurable in a certain distance range observation period.

Images