JP4836496B2 - Radar apparatus and signal processing method thereof - Google Patents

Description

  The present invention relates to a radar apparatus used in a Doppler weather radar that captures dynamic conditions of rain and clouds, for example, and a signal processing method thereof.

In Doppler radar, when detecting a meteorological echo having a high moving speed, the received phase signal may exceed one cycle of the transmission wavelength, and the return of the speed occurs when the Doppler speed is detected. On the other hand, there is a technique for expanding the maximum speed detection range of the target by switching the transmission repetition frequency (PRF) of the radar pulse. For example, the upper limit of the observation speed depends on the value of the PRF, but a speed exceeding the upper limit of the observation speed of each PRF can be calculated by combining speed data obtained in different PRFs (for example, non-patent literature). 1).
Toshiba Review, Volume 55, Issue 5, May 1, 2000, “Doppler Weather Radar”, p. 28

  By the way, in general, the Doppler radar deteriorates the speed calculation accuracy for a target having a large speed distribution variation. This tendency is particularly significant in radar devices that observe natural phenomena, such as weather radar. In order to cope with this, it is effective to average the variation by increasing the number of observation data, that is, the number of pulse hits.

However, it is not easy to change the PRF and the number of pulse hits in the existing radar apparatus. Also, the target velocity can only be calculated for each individual PRF. For this reason, the number of pulse echoes that can be used for speed calculation does not exceed the number of pulse hits in each PRF, and the amount of data that can be used for speed calculation inevitably reaches a limit, and the observation accuracy is limited. I understand. In addition, in a radar apparatus with a small number of pulses transmitted for each PRF, the influence of variations in velocity distribution is even greater, and the observation accuracy is degraded.
The present invention has been made paying attention to the above circumstances, and its object is to provide a radar apparatus capable of calculating the speed of an observation target with high accuracy even when there is a large variation in the speed distribution of the observation target, and its signal processing method Is to provide.

In order to achieve the above object, a radar apparatus according to the present invention selectively transmits and receives a radar pulse based on a pulse repetition frequency and receives a radar echo, and selectively selects the pulse repetition frequency from a plurality of frequencies. A switching unit for switching, and a signal processing unit that calculates a velocity of the target based on a velocity spectrum observed from the radar echo. The signal processing unit expresses the velocity spectrum obtained for each pulse repetition frequency in a Doppler velocity region by a phase angle so that a positive aliasing velocity hits + π and a negative aliasing velocity hits −π. Based on the conversion means for converting to a phase difference vector represented by a polar coordinate system by replacing the region with a vector and by converting the phase angle obtained by the phase difference vector proportional to the speed of the target, Correction means for correcting a phase difference vector of the pulse repetition frequency to a phase difference vector corresponding to the reference pulse repetition frequency on the basis of one of the repetition frequencies, and a plurality of the phase difference vectors including the corrected phase difference vector A phase difference vector is synthesized, and the target velocity is calculated from the synthesized phase difference vector. The

The signal processing method according to the present invention is a signal processing method used in a radar apparatus that transmits a radar pulse and receives a radar echo based on a pulse repetition frequency, wherein the pulse repetition frequency is selected from a plurality of frequencies. And a signal processing step of calculating the target velocity based on the velocity spectrum observed from the radar echo. In the signal processing step , the Doppler velocity region is expressed by a phase angle so that the velocity spectrum obtained for each pulse repetition frequency corresponds to + π and the negative aliasing velocity corresponds to −π. Based on the conversion step of converting to a phase difference vector represented by a polar coordinate system by replacing the region with a vector, and the phase angle obtained by the phase difference vector being proportional to the speed of the target, the pulse repetition A correction step of correcting a phase difference vector having a pulse repetition frequency different from the reference value to a phase difference vector corresponding to the reference pulse repetition frequency with reference to one of the frequencies, and the corrected phase difference vector is A plurality of phase difference vectors including the target, and the target phase is calculated from the synthesized phase difference vector. The speed of the robot is calculated.

  In the radar device having the above configuration, a velocity spectrum is observed from radar echoes based on radar pulses transmitted at different pulse repetition frequencies, the velocity spectrum is converted into a phase difference vector, and a phase difference corresponding to a reference pulse repetition frequency is obtained. The vector is corrected to a vector, and the velocity is calculated by uniformly using the velocity spectrum observed at different pulse repetition frequencies regardless of the pulse repetition frequency.

  According to the above configuration, the number of data related to the speed calculation is not limited by the number of pulse hits in each PRF, and the target speed is obtained using a larger number of received data than the number of radar pulses transmitted by the same PRF. Can be calculated. By using as many received data as possible, it is possible to average the variation in the velocity distribution and increase the accuracy of the calculated value. Therefore, according to the present invention, it is possible to provide a radar apparatus and its signal processing method capable of calculating the speed of the observation target with high accuracy even when the variation in the speed distribution of the observation target is large.

FIG. 1 is a functional block diagram showing an embodiment of a radar apparatus according to the present invention.
The modulation unit 12 generates a digital value of the intermediate frequency signal of the designated modulation system under the control given from the signal processing unit 11 via the interface (I / F). This digital value is converted into an analog value by the D / A converter 13 to generate a transmission intermediate frequency signal (fi). This transmission intermediate frequency signal is up-converted to the transmission frequency of the radar pulse in the transmission / reception device 14, and after power amplification, is transmitted from the antenna 15 to the space.

  The radar pulse with the frequency f0 transmitted from the antenna 15 is reflected by a target such as raindrops, and the radar echo returns. This radar echo is accompanied by a Doppler frequency (fd) reflecting the moving speed of the target, and the reception frequency is represented as (f0 + fd). The radar echo arrives at the transmitter / receiver 14 via the antenna 15 and is amplified and then down-converted to generate a reception intermediate frequency signal of (fi + fd). This received intermediate frequency signal is converted into a digital value by the A / D converter 16 and then subjected to quadrature detection by the demodulator 17.

  The quadrature-detected signal is demodulated by the demodulator 17 using a plurality of modulation methods. The received data of the I component (in-phase component) and Q component (quadrature phase component) obtained in this way is given to the signal processing unit 11 via the interface (I / F). The signal processing unit 11 calculates observation data such as echo reflection intensity, target velocity and velocity width from the received data. In particular, the target Doppler velocity can be calculated from the velocity spectrum observed from the received data.

  The signal processing unit 11 includes a switching processing unit 11a, a correction processing unit 11b, and a calculation processing unit 11c as processing functions according to this embodiment. The switching processing unit 11a switches the transmission repetition frequency (PRF) of radar pulses stepwise, for example, for every fixed number of pulses. A method is conceivable in which the lowest value of the PRF is used as a reference value, and the pulse interval is shortened for every 30 shots, for example. Conversely, the maximum value of the PRF may be used as a reference value, and the pulse interval may be extended in descending order from the reference value for every fixed number of pulses. After the PRF reaches the maximum value (or the minimum value), pulse transmission from the PRF having the minimum value (or the maximum value) is repeated again.

  The correction processing unit 11b converts velocity spectra obtained by different PRFs into phase difference vectors, and further corrects the converted phase difference vectors into phase difference vectors corresponding to the reference PRF. This correction process utilizes the property that the phase angle obtained from the phase difference vector is proportional to the target speed. In addition, the calculation processing unit 11c combines the phase difference vectors corrected by the correction processing unit 11b, and calculates the target speed based on the combined vector.

Next, target speed calculation processing of the radar apparatus having the above configuration will be described.
FIG. 2 is a flowchart showing a processing procedure of the radar apparatus of FIG. In the reference value PRF1, the received signal is A / D converted and subjected to I / Q detection, and then subjected to FFT processing to obtain a velocity spectrum. This velocity spectrum is further converted into a phase difference vector. On the other hand, in PRF2, the received signal is converted into a phase difference vector by the same procedure as PRF1, but thereafter, the phase difference in PRF2 is corrected to a value corresponding to the phase difference in PRF1. As a result, the phase differences in PRF1 and PRF2 can be handled uniformly, and the Doppler velocity of the target is calculated using these phase differences.

FIG. 3 shows a method of converting the velocity spectra of different PRFs into phase difference vectors of the respective PRFs. Here, PRF1>PRF2> PRF3 is assumed by taking a three-stage PRF as an example. For the velocity spectrum of each PRF , the intensity and Doppler velocity are replaced with the vector length and phase angle, respectively , and a phase difference vector is obtained by a vector synthesis method . Since the folding speeds (Vmax (PRF1), Vmax (PRF2), Vmax (PRF3)) of each PRF have different values depending on the PRF, the phase angle differs depending on the PRF even if the same Doppler speed is observed. As shown in FIG. 3, the phase angles with respect to PRF1 to PRF3 are θ1 to θ3, respectively, which are different values.

  The phase difference for each PRF is proportional to the target Doppler velocity. Therefore, in this embodiment, the phase difference is once calculated among PRF1, PRF2, and PRF3, and the magnitude of the phase to be corrected is determined from the value. This will be described below using mathematical formulas. First, the phase angle θ is obtained from the velocity spectrum for each of PRF1 to PRF3.

<Calculation for PRF1>
First, the real part and the imaginary part of the phase difference vector (R _PRF1 ) obtained by the vector synthesis method are obtained from the velocity spectrum of _PRF1 .

Further, the maximum speed V _maxPRF1 of _{PRF 1} is obtained as follows.

In equation (3), C is the speed of light, and f ₀ is the frequency of the transmission pulse.

<Calculation for PRF2>
Similar to PRF1, the real and imaginary parts of the phase difference vector (R _PRF2 ) obtained by the vector synthesis method from the velocity spectrum of PRF2 and the maximum velocity V _maxPRF2 of _PRF2 are obtained.

<Calculation for PRF3>
Similarly, the real part and imaginary part of the phase difference vector (R _PRF3 ) obtained by the vector synthesis method from the speed spectrum of PRF 3 and the maximum speed V _maxPRF3 of _{PRF 3} are obtained.

In equations (6) and (9), C is the speed of light, and f ₀ is the frequency of the transmission pulse.

<Correction of PRF2 data to PRF1 data>
Next, the IQ data in PRF2 is corrected to data corresponding to the value of the radar pulse transmitted in PRF1. (') Is added to the correction value, and the real part is represented by the equation (10) and the imaginary part is represented by the equation (11).

<Correction of PRF2 data to PRF1 data>
Similarly, the IQ data in PRF3 is corrected to data corresponding to the value obtained by transmitting the radar pulse in PRF1. The real part of the correction value is expressed by Expression (12), and the imaginary part is expressed by Expression (13).

Next, when the values of each PRF are synthesized for each real part and imaginary part, the following equations (14) and (15) are obtained.

Using equations (14) and (15), the Doppler velocity can be calculated by the following equation (16).

  FIG. 4 is a schematic diagram showing the correction of the phase angle by the above arithmetic processing. According to the arithmetic processing described above, the phase angles at PRF2 and PRF3 are both corrected to a value corresponding to the phase angle at PRF1. That is, according to the present embodiment, received waves based on pulses transmitted with different PRFs are corrected to received waves with the same PRF. Thereby, even if the number of pulse hits in each PRF is small, the data can be used across different PRFs, so that the speed can be calculated using more data.

  FIG. 5 is a flowchart showing a processing procedure in an existing radar apparatus for comparison. In the existing technology, the Doppler speed is calculated for each same PRF. For this reason, there is an upper limit on the number of data related to the speed calculation, and there is a problem in that the accuracy of calculation tends to deteriorate for a target having a large variation in speed distribution.

  On the other hand, in the present embodiment, the radar apparatus capable of switching the PRF converts the velocity spectrum observed from the radar echo into a phase difference vector. Then, based on the fact that the phase angle for each PRF is proportional to the Doppler velocity of the observation target, the phase angle obtained from the phase difference vector of each PRF is corrected to a value based on the reference value PRF. As a result, reception data related to speed calculation can be handled uniformly regardless of PRF, and the Doppler speed of the target is calculated using more reception data. Therefore, the effect of averaging the variation in the speed distribution can be enhanced, and the speed calculation accuracy can be improved. From the above, it is possible to provide a radar apparatus and a signal processing method thereof that can reduce the variation in the velocity distribution and calculate the target velocity with high accuracy.

  The present invention is not limited to the above embodiment. For example, in FIG. 1, the functions of the D / A conversion unit 13 and the A / D conversion unit 16 can be combined with other functional blocks. In addition, the present invention is not limited to the weather radar but can be applied to other Doppler radars. Further, not only PRF1, but other PRFs such as PRF2 and PRF3 may be used as reference values. Further, the PRF is not limited to three stages, and the disclosed technique can be applied to more PRFs. Furthermore, the present invention can be applied to a so-called radar system in which a plurality of radar devices having different PRFs are combined, instead of switching the PRF in a single radar device.

  In short, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

The block diagram which shows the function structure of one Embodiment of the radar apparatus concerning this invention. The flowchart which shows the process sequence of the radar apparatus of FIG. The schematic diagram for demonstrating a mode that the phase angle of the echo from the same target changes with the values of PRF. The schematic diagram which shows correction | amendment of the phase angle by the arithmetic processing in embodiment of this invention. The flowchart which shows the process sequence in the existing radar apparatus for a comparison.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Signal processing part, 11a ... Switching processing part, 11b ... Correction processing part, 11c ... Calculation processing part, 12 ... Modulation part, 13 ... D / A conversion part, 14 ... Transmission / reception part, 15 ... Antenna, 16 ... A / D converter, 17... Demodulator.

Claims (2)

A transmission / reception unit that repeatedly transmits radar pulses and receives radar echoes based on the pulse repetition frequency; and
Switching means for selectively switching the pulse repetition frequency from a plurality of frequencies;
A signal processing unit that calculates a target velocity based on a velocity spectrum observed from the radar echo,
The signal processing unit
The velocity spectrum obtained for each pulse repetition frequency is vector-synthesized by replacing the Doppler velocity region with a region represented by a phase angle so that the positive folding rate corresponds to + π and the negative folding rate corresponds to −π. Conversion means for converting into a phase difference vector represented by a polar coordinate system,
Based on the fact that the phase angle obtained by the phase difference vector is proportional to the velocity of the target, the phase difference vector of the pulse repetition frequency is set to the reference pulse repetition frequency based on one of the pulse repetition frequencies. Correction means for correcting to a corresponding phase difference vector;
A radar apparatus comprising: a calculating unit that combines a plurality of phase difference vectors including the corrected phase difference vector, and calculates the velocity of the target from the combined phase difference vector. In a signal processing method used in a radar apparatus that transmits a radar pulse and receives a radar echo based on a pulse repetition frequency,
A switching step of selectively switching the pulse repetition frequency from a plurality of frequencies;
A signal processing step of calculating a target velocity based on a velocity spectrum observed from the radar echo,
The signal processing step includes
Velocity spectrum obtained for each pulse repetition frequency is vector-synthesized by replacing the Doppler velocity region with a region represented by a phase angle so that the positive folding velocity hits + π and the negative folding velocity hits −π. A conversion step of converting into a phase difference vector represented in a polar coordinate system by
Based on the fact that the phase angle obtained by the phase difference vector is proportional to the velocity of the target, a phase difference vector having a pulse repetition frequency different from the reference value is set as a reference with respect to one of the pulse repetition frequencies. A correction step for correcting the phase difference vector corresponding to the pulse repetition frequency;
A signal processing method comprising: combining a plurality of phase difference vectors including the corrected phase difference vector, and calculating a velocity of the target from the combined phase difference vector.

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