JP2005181018A - Radar device and radar signal analysis method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniaturizable radar device and a radar signal analysis method, capable of shortening the time required for frequency analysis of a beat signal. <P>SOLUTION: In this radar device 1, radar wave is transmitted from a transmitting antenna 5, and a reflected wave from a target is received by two receiving antennas A1, A2 installed at different positions, and frequency analysis is performed, to thereby discriminate the target azimuth. The device 1 is constituted of a voltage control oscillator 3 for generating a transmitting signal; a mixer 7 for mixing received signals by each receiving antenna A1, A2 respectively with the transmitting signal, and generating two beat signals I, Q comprising frequency differences; and a complex signal processing part 19 for generating a frequency complex spectrum, based on a complex signal having a real part formed from either of the beat signals I, Q and an imaginary part formed from the other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a radar apparatus and a radar signal analysis method, and more specifically, receives a reflected wave from a target by a plurality of receiving antennas installed at different positions, and identifies a target direction from a phase difference of received signals. The present invention relates to an improvement of a radar apparatus such as a phase monopulse radar.

As a radar apparatus that is mounted on a moving body such as a vehicle and identifies a target direction of a preceding vehicle, for example, there is a phase monopulse radar. Phase monopulse radar transmits radar waves from a transmitting antenna, receives reflected waves from a target by a plurality of receiving antennas installed at different positions, and identifies a target direction based on the phase difference of received signals. Yes. The phase difference of the received signal is calculated based on the frequency analysis for each received signal. That is, the reception signal from each reception antenna is mixed with the transmission signal, and a beat signal composed of a frequency difference is generated. A phase difference is obtained by performing frequency analysis such as Fast Fourier Transform (FFT) for each of these beat signals (for example, Patent Documents 1 and 2).
JP-A-9-152478 Japanese Patent Laid-Open No. 11-271434

  In the conventional radar apparatus as described above, since frequency analysis must be performed for each beat signal, there is a problem that it is difficult to shorten the time required for the analysis processing. Therefore, in order to reduce the time required for the analysis processing, if the frequency analysis for each beat signal is to be processed in parallel, the processing load increases, and thus there is a problem that it is difficult to reduce the size of the radar apparatus. In addition, if the frequency analysis for each beat signal is to be processed in parallel, the configuration of the radar apparatus becomes complicated, resulting in an increase in manufacturing cost.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a radar device and a radar signal analysis method that can reduce the time required for frequency analysis of beat signals and can be miniaturized. Yes. It is another object of the present invention to provide a radar apparatus that can reduce the time required for frequency analysis of beat signals and reduce the manufacturing cost.

  A radar apparatus according to the present invention is a radar apparatus that transmits a radar wave from a transmission antenna and receives a reflected wave from a target by two reception antennas installed at different positions, and a transmission signal generation means for generating a transmission signal And the beat signal generating means for mixing the received signals from the receiving antennas with the transmission signal to generate two beat signals composed of frequency differences, and one of the beat signals as a real part and the other as an imaginary part. The frequency analysis means generates a frequency complex spectrum based on the complex signal.

  According to such a configuration, since the frequency complex spectrum is generated based on one complex signal composed of two beat signals, the frequency analysis processing related to spectrum generation can be completed only once. Therefore, the time required for the frequency analysis can be shortened as compared with a conventional radar apparatus that performs frequency analysis for each beat signal. Moreover, since the increase in processing load is suppressed as compared with parallel processing of frequency analysis for each beat signal, the radar apparatus can be reduced in size and the manufacturing cost can be reduced.

  In addition to the above-described configuration, the radar apparatus according to the present invention includes a spectral component extracting unit that extracts a complex spectral component having the maximum amplitude from the frequency complex spectrum, and an azimuth identifying unit that identifies a target direction based on the complex spectral component. It consists of. According to such a configuration, since the time required for frequency analysis is shortened, it is possible to realize a small radar apparatus that can identify the target direction in a short time.

  The radar apparatus according to the present invention further includes signal phase shifting means for shifting the phase of the transmission signal by π / 2 in addition to the above-described configuration, and the beat signal generation means is based on transmission signals having phases different from each other by π / 2. Configured to generate each beat signal. According to such a configuration, since the relational expression between the complex spectrum component and the phase difference between the received signals can be easily obtained, the configuration of the radar apparatus can be simplified when the target direction is obtained from the complex spectrum.

  A radar signal analysis method according to the present invention is a signal analysis method in a radar apparatus that transmits a radar wave from a transmission antenna and receives a reflected wave from a target by two reception antennas installed at different positions. A transmission signal generation step to generate, a beat signal generation step of generating two beat signals each consisting of a frequency difference by mixing a reception signal from each reception antenna with the transmission signal, and one of the beat signals as a real part, A frequency analysis step of generating a frequency complex spectrum based on a complex signal having the other as an imaginary part.

  According to the radar apparatus of the present invention, the frequency complex spectrum is generated based on one complex signal composed of two beat signals, so that the frequency analysis processing related to spectrum generation can be performed only once. Accordingly, the time required for frequency analysis can be shortened and an increase in processing load is suppressed, so that the radar apparatus can be reduced in size. Further, since the configuration of the radar apparatus is prevented from becoming complicated, the manufacturing cost can be reduced.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing an example of a schematic configuration of a radar apparatus according to Embodiment 1 of the present invention. The radar apparatus 1 according to the present embodiment transmits a radar wave from the transmitting antenna 5 and receives reflected waves from the target by the two receiving antennas A1 and A2, and performs frequency analysis to obtain the target azimuth and the target. A target detection radar that identifies a distance and a target speed, and is a small electronic device that can be mounted on a moving body such as a vehicle.

  The radar apparatus 1 includes a voltage generation circuit 2, a voltage controlled oscillator (VCO) 3, a distribution circuit 4, a transmission antenna 5, reception antennas A1 and A2, a mixer 7, an amplifier 8, a band pass filter (BPF). ) 9, an A / D converter 10, a memory 11, a phase shift circuit 12, a control unit 18, and a complex signal processing unit 19. Here, the receiving antennas A1 and A2 are installed at different positions, and a mixer 7, an amplifier 8, a band pass filter 9, and an A / D converter 10 are provided for each of the receiving antennas A1 and A2.

  The voltage generation circuit 2 is a voltage source that generates a predetermined voltage based on the control of the control unit 18, and generates a voltage signal whose voltage temporally changes in a triangular wave shape. Here, the period in which the voltage increases is referred to as an up-phase period T1, and the period in which the voltage decreases is referred to as a down-phase period T2, and these periods are alternately repeated. The time widths of these periods are the same (T1 = T2). The generated voltage signal is sequentially output to the voltage controlled oscillator 3.

  The voltage controlled oscillator 3 generates a transmission signal based on the voltage signal from the voltage generation circuit 2. The transmission signal is a high-frequency signal whose frequency changes with time in proportion to the applied voltage, and is called a so-called frequency-modulated continuous wave (FMCW). That is, the frequency of the transmission signal continuously increases in the up phase period T1 and decreases in the down phase period T2. This frequency change width Δf is the same in the up-phase period and the down-phase period. The generated transmission signals are sequentially output to the distribution circuit 4, are distributed in power, and are output to the transmission antenna 5, the mixer 7, and the phase shift circuit 12. A part of the transmission signal transmitted as a radar wave by the transmitting antenna 5 is reflected by a target such as a preceding vehicle, and a part of the reflected wave propagates through the space and is received by the receiving antennas A1 and A2.

  The mixer 7 mixes the reception signal with the transmission signal from the distribution circuit 4 and generates a beat signal composed of a frequency difference. That is, the mixer 7 connected to one receiving antenna A 1 mixes the transmission signal and the reception signal input from the distribution circuit 4 as the local signal I, and sequentially outputs the beat signal I to the amplifier 8. The mixer 7 connected to the other receiving antenna A2 mixes the transmission signal (local signal Q) input from the distribution circuit 4 via the phase shift circuit 12 and the reception signal, and sequentially sends the beat signal Q to the amplifier 8. Output. The phase shift circuit 12 is a signal phase shift means for shifting the phase of the transmission signal by π / 2, and includes a delay circuit and the like. The local signals I and Q are different in phase from each other by π / 2. That is, the beat signal Q is generated based on the local signal Q after phase shift by π / 2.

  The two beat signals I and Q are each amplified by the amplifier 8 at a predetermined amplification rate, and the pass band is limited to a predetermined band by the band pass filter 9. By this band limitation, unnecessary frequency components can be removed in frequency analysis. The beat signals I and Q after the band limitation are converted into digital data by the A / D converter 10 at a predetermined sampling speed, and written into the memory 11. The digital data is written in synchronization with the up-phase period T1 and the down-phase period T2 under the control of the control unit 18, and the memory 11 is in a writable state based on the start of each period, and is read when the period ends. It becomes possible.

  The complex signal processing unit 19 is composed of a CPU and a DSP (Digital Signal Processor), performs frequency analysis on the complex signal composed of digitized beat signals I and Q, and identifies the target direction, the distance to the target, and the target speed. Is going. This frequency analysis is performed in synchronization with the up phase period T1 and the down phase period T2 under the control of the control unit 18.

  FIG. 2 is a block diagram showing a detailed configuration example of the main part of the radar apparatus of FIG. 1, and shows a complex signal processing unit 19 that performs frequency analysis based on a complex signal. The complex signal processing unit 19 includes a frequency analysis processing unit 13, a complex spectrum component extraction unit 14, an orientation identification unit 15, a beat frequency extraction unit 16, and a distance / speed calculation unit 17.

  The frequency analysis processing unit 13 performs frequency analysis based on a complex signal composed of beat signals I and Q. As this frequency analysis, for example, complex FFT (Fast Fourier Transform) processing is performed on a complex signal having the beat signal I as a real part and the beat signal Q as an imaginary part. A frequency complex spectrum is generated by such frequency analysis processing. The generation of the frequency complex spectrum is performed for each of the up phase period T1 and the down phase period T2, and is output to the complex spectrum component extraction unit 14 and the beat frequency extraction unit 16, respectively.

  The complex spectrum component extraction unit 14 extracts a complex spectrum component having the maximum amplitude from the frequency complex spectrum from the frequency analysis processing unit 13. The direction identifying unit 15 identifies a target direction based on the extracted complex spectrum component. Since the receiving antennas A1 and A2 are installed at different positions, the phases of the received signals, that is, the beat signals I and Q are different depending on the target orientation viewed from the receiving antennas A1 and A2. Therefore, the target azimuth can be calculated by obtaining this phase difference (phase shift) from the complex spectral component. Here, the azimuths calculated for each of the up-phase period T1 and the down-phase period T2 are compared, and if the comparison result exceeds a predetermined allowable range, this identification process is terminated because an identification error has occurred. On the other hand, if the comparison result is within the allowable range, one or both of the calculated directions are output as the identification result.

  The beat frequency extraction unit 16 extracts a frequency (beat frequency f) having the maximum amplitude from the frequency complex spectrum from the frequency analysis processing unit 13. The distance / speed calculating unit 17 identifies the distance r to the target and the target speed v based on the extracted beat frequency f. Due to the delay time T3 generated between the transmission and reception signals according to the distance (relative distance) r to the target viewed from the radar apparatus 1 and the frequency shift due to the Doppler effect according to the target speed (relative speed) v viewed from the radar apparatus 1. The beat frequency f in each up-phase period T1 and down-phase period T2 is different. Therefore, the distance r and the target speed v can be calculated by extracting the beat frequency in each of the up phase period T1 and the down phase period T2.

  FIGS. 3A to 3E are diagrams illustrating an example of a temporal change in the output state of various signals generated in the radar apparatus of FIG. 1. FIG. 3A illustrates a voltage generation circuit. 2 shows the generated voltage in the voltage signal generated by 2, and FIG. 3B shows the output voltage in the transmission signal (local signal I) generated by the voltage controlled oscillator 3. 3C shows the frequency of the transmission signal transmitted from the transmission antenna 5 and the frequency of the reception signal from the reception antennas A1 and A2, and FIG. 3D shows the frequency generated by the mixer 7. The frequency of the beat signal to be played is shown. FIG. 3E shows the output voltage of the beat signal I generated from the local signal I.

  The frequency of the local signal I increases uniformly by Δf in the up phase period T1, and decreases uniformly by Δf in the down phase period. On the other hand, the frequency of the received signal rises and falls with a delay time T3 and is shifted by the Doppler effect. For this reason, the frequency of the beat signal is different in each up-phase period T1 and down-phase period T2. Here, the beat frequency in the up phase period T1 is set to fu, and the beat frequency in the down phase period T2 is set to fd (> fu).

  FIGS. 4A and 4B are diagrams showing an example of the state of time change in the output state of various signals generated in the radar apparatus of FIG. 1, and FIG. 4A shows a phase shift circuit. 12 shows the output voltage of the local signal Q generated by 12, and FIG. 4B shows the output voltage of the beat signal Q generated from the local signal Q. The phase of the local signal Q is shifted from that of the local signal I by π / 2. For this reason, the phase of the beat signal Q is also shifted from the beat signal I by π / 2.

  FIG. 5 is a diagram illustrating an example of a reception state of reflected waves in the radar apparatus of FIG. When the receiving antennas A1 and A2 are installed at a distance d, when a reflected wave is incident at an incident angle θ, the path difference between the receiving antennas A1 and A2 is d × sin θ. Here, the front direction perpendicular to the antenna surface is used as a reference, and the clockwise direction is the positive direction. Further, it is assumed that the path difference is a path difference between the reception antenna A2 and the reception antenna A1. A target azimuth (azimuth angle θ) can be calculated by obtaining a phase difference corresponding to such a path difference by frequency analysis.

  Hereinafter, a mechanism for calculating the target azimuth angle θ, the distance r, and the target speed v by frequency analysis of the complex signal will be described.

When the target exists at the azimuth angle θ, the beat signal I (t) from the receiving antenna A1 can be expressed by the following equation (1).

At this time, the beat signal Q (t) from the receiving antenna A2 takes into account the phase difference δ (θ) caused by the path difference with respect to the phase and the phase shift (π / 2) by the phase shift circuit 12, and the amplifier with respect to the amplitude. Considering the variation between individuals in the amplification factor of 8, it can be expressed by the following equations (2) and (3).

  In equations (2) and (3), α is the amplitude ratio and λ is the wavelength of the received signal. When a frequency complex spectrum is obtained for a complex signal having such a beat signal I (t) as a real part and a beat signal Q (t) as an imaginary part, when δ (θ) = 0, the real part and the imaginary part are obtained. Are orthogonal, so that a peak (real image) of a complex spectral component appears only at the actual beat frequency f.

  6 (a) and 6 (b) are diagrams showing an example of a frequency complex spectrum generated by the frequency analysis processing unit in FIG. 2, and FIG. 6 (a) shows the position between the receiving antennas A1 and A2. The real part of the complex spectral component when the phase difference is δ (θ) = 0 is shown, and FIG. 6B shows the imaginary part thereof. In this case, one beat frequency at which the amplitude of the complex spectral component is maximum appears on the positive side. That is, peaks B1 and B2 of the complex spectral component appear at the beat frequency f.

  On the other hand, when δ (θ) = 0 is not true, the real part and the imaginary part are not orthogonal, so that a peak (virtual image) of a complex spectral component appears at the beat frequency −f in addition to the actual beat frequency f.

  FIGS. 7A and 7B are diagrams illustrating an example of a frequency complex spectrum generated by the frequency analysis processing unit in FIG. 2. FIG. 7A illustrates a phase difference of δ (θ) = The real part of the complex spectral component when it is not 0 is shown, and FIG. 7B shows the imaginary part thereof. In this case, one beat frequency at which the amplitude of the complex spectral component is maximum appears on each of the positive side and the negative side. That is, the peaks B1 and B2 of the complex spectral component appear at the beat frequency f, and the peaks C1 and C2 appear at the beat frequency -f.

When the phase difference is not δ (θ) = 0, that is, when the azimuth angle θ ≠ 0, the complex spectral component S0 at the actual beat frequency f is expressed by the following equation (4).

Further, the complex spectral component S1 at the beat frequency -f of the virtual image is expressed by the following equation (5).

Here, the product MX of the two complex spectral components S0 and S1, the spectral power P0 of the complex spectral component at the actual beat frequency f, and the spectral power P1 of the complex spectral component at the beat frequency −f of the virtual image are expressed by the formula ( It can be expressed by the following formulas (6) to (8) based on 4) and (5).

From the equations (6) to (8), the phase difference δ (θ) and the amplitude ratio α can be expressed by the following equations (9) and (10).

From the equations (3) and (9), the azimuth angle θ is expressed by the following equation (11).

  Accordingly, by extracting the complex spectral components S0 and S1 from the frequency complex spectrum and obtaining the product MX and the spectral powers P0 and P1, the target azimuth angle θ can be calculated by the equation (11).

Further, the distance r to the target and the target speed v can be calculated from the beat frequencies fu and fd with the speed of light as c by the following equations (12) and (13).

  Steps S101 to S109 in FIG. 8 are flowcharts showing an example of the analysis operation in the complex signal processing unit in FIG. First, the frequency analysis processing unit 13 reads the digital voltage values of the beat signals I and Q in the up phase period T1 from the memory 11, respectively, and performs complex processing on the complex signal having the beat signal I as a real part and the beat signal Q as an imaginary part. Perform FFT. Next, the complex spectrum component extraction unit 14 extracts the complex spectrum components S0u and S1u from the frequency complex spectrum generated by the complex FFT, and the beat frequency extraction unit 16 extracts the beat frequency fu (steps S101 and S102). ).

  The azimuth identifying unit 15 calculates a target azimuth angle θu from the extracted complex spectrum components S0u and S1u (step S103).

  Next, the frequency analysis processing unit 13 similarly performs a complex FFT on the complex signal composed of the beat signals I and Q in the down phase period T2 to generate a frequency complex spectrum. The complex spectrum component extraction unit 14 extracts the complex spectrum components S0d and S1d from the generated frequency complex spectrum, and the beat frequency extraction unit 16 extracts the beat frequency fd (steps S104 and S105).

  The azimuth identifying unit 15 calculates a target azimuth angle θd from the extracted complex spectrum components S0d and S1d (step S106). At this time, if the difference between the calculated azimuth angles θu and θd is less than a predetermined threshold value θe, the azimuth identifying unit 15 outputs one or both of the calculated azimuth angles. Further, the distance / speed calculating unit 17 calculates the distance r and the target speed v from the beat frequencies fu and fd to the target (steps S107 and S108).

  On the other hand, if the difference between the azimuth angles θu and θd is greater than or equal to the threshold value θe, the analysis process in the up-phase period T1 and the down-phase period T2 is terminated because an identification error has occurred (step S109).

  According to the present embodiment, the frequency complex spectrum is generated based on the complex signal composed of the beat signals I and Q. Therefore, the time required for frequency analysis is higher than that of a conventional radar apparatus that performs frequency analysis for each beat signal. Can be shortened, and an increase in processing load in the frequency analysis is suppressed, so that the radar apparatus 1 can be downsized. Further, since the configuration of the radar apparatus 1 is prevented from being complicated, the manufacturing cost can be reduced.

  In the present embodiment, an example in which Equation (9) is used to calculate the azimuth angle θ has been described, but the present invention is not limited to this. For example, in order to calculate the target azimuth angle θ from the complex spectral components S0 and S1, a numerical table composed of complex spectral components for each target azimuth is created in advance by experiments, and the complex spectrum is calculated based on the numerical table. The azimuth angle θ corresponding to the components S0 and S1 may be calculated. In this way, the time required to calculate the target direction can be further shortened, and the processing load is suppressed, so that the radar apparatus can be further downsized.

Embodiment 2. FIG.
In the first embodiment, the example in which the phase of the transmission signal is shifted by π / 2 by the phase shift circuit 12 has been described. On the other hand, in the present embodiment, a case will be described in which the phase shift circuit 12 shifts the phase of the transmission signal by a predetermined phase shift amount x (rad).

  FIG. 9 is a block diagram showing a detailed configuration example of the main part of the radar apparatus according to Embodiment 2 of the present invention, in which a complex signal processing unit 19a having a new numerical value table 22 is shown. In this radar apparatus, a local signal Q is generated by shifting the phase of the transmission signal by a predetermined phase shift amount x (rad) different from π / 2 by the phase shift circuit 12, and the numerical value table 22 is generated by the direction identification unit 21. Based on the above, the target azimuth angle θ is obtained.

  This numerical table 22 stores in advance the complex spectral components for each target orientation obtained by experiments or the like. That is, in the present embodiment, in order to calculate the target azimuth angle θ from the complex spectrum component, the azimuth angle corresponding to the complex spectrum component is calculated based on the numerical value table 22. Even with such a configuration, it is possible to reduce the time required for frequency analysis and to realize a small radar apparatus that can identify a target direction in a short time.

It is the block diagram which showed an example of schematic structure of the radar apparatus by Embodiment 1 of this invention. FIG. 2 is a block diagram illustrating a configuration example of details of a main part in the radar apparatus of FIG. 1. It is the figure which showed an example of the mode of the time change in the output state of the various signals produced | generated in the radar apparatus of FIG. It is the figure which showed an example of the mode of the time change in the output state of the various signals produced | generated in the radar apparatus of FIG. It is the figure which showed an example of the reception state of the reflected wave in the radar apparatus of FIG. It is the figure which showed an example of the frequency complex spectrum produced | generated by the frequency analysis process part of FIG. It is the figure which showed an example of the frequency complex spectrum produced | generated by the frequency analysis process part of FIG. 3 is a flowchart illustrating an example of an analysis operation in the complex signal processing unit in FIG. 2. It is the block diagram which showed the structural example of the principal part detail in the radar apparatus by Embodiment 2 of this invention.

Explanation of symbols

1 radar device, 2 voltage generation circuit, 3 voltage controlled oscillator (VCO), 4 distribution circuit, 5 transmission antenna, 7 mixer, 8 amplifier, 9 band pass filter (BPF),
10 A / D converter, 11 memory, 12 phase shift circuit, 13 frequency analysis processing unit,
14 Complex spectral component extraction unit, 15, 21 Direction identification unit, 16 Beat frequency extraction unit, 17 Distance / speed calculation unit, 18 Control unit, 19, 19a Complex signal processing unit,
22 Numerical table, A1, A2 receiving antenna

Claims (7)

In a radar apparatus that transmits a radar wave from a transmitting antenna and receives a reflected wave from a target by two receiving antennas installed at different positions,
A transmission signal generating means for generating a transmission signal;
Beat signal generation means for mixing the reception signals from the respective reception antennas with the transmission signal, and generating two beat signals composed of frequency differences;
A radar apparatus comprising: frequency analysis means for generating a frequency complex spectrum based on a complex signal in which one of the beat signals is a real part and the other is an imaginary part. Spectral component extraction means for extracting a complex spectral component having a maximum amplitude from the frequency complex spectrum;
The radar apparatus according to claim 1, further comprising an azimuth identifying unit that identifies a target azimuth based on the complex spectrum component. Comprising signal phase shifting means for shifting the phase of the transmission signal by π / 2,
The radar apparatus according to claim 1, wherein the beat signal generation unit generates each beat signal based on transmission signals having phases different from each other by π / 2.   The radar apparatus according to claim 2, wherein the azimuth identifying means identifies a target azimuth based on a numerical table composed of complex spectral components for each target azimuth.   2. The transmission signal generating means generates a transmission signal whose frequency changes continuously, and an up phase period in which the frequency increases and a down phase period in which the frequency increases are alternately repeated. Radar equipment. A frequency extracting means for extracting a beat frequency having a maximum amplitude from the frequency complex spectrum;
6. Distance speed calculation means for calculating a distance from the beat frequency extracted during the up-phase period and a beat frequency extracted during the down-phase period to a target and a target speed. The radar device described in 1. A signal analysis method in a radar apparatus that transmits a radar wave from a transmitting antenna and receives a reflected wave from a target by two receiving antennas installed at different positions,
A transmission signal generating step for generating a transmission signal;
A beat signal generation step of mixing a reception signal from each reception antenna with the transmission signal, and generating two beat signals each having a frequency difference;
A radar signal analysis method comprising: a frequency analysis step of generating a frequency complex spectrum based on a complex signal having one of the beat signals as a real part and the other as an imaginary part.

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