JP2006226955A - Radar installation and its signal processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radar installation and its signal processing method capable of reducing the mistakes in dealiasing and thereby computing the speeds of targets with high accuracy and high reliability. <P>SOLUTION: On the basis that the amount of phase rotation for each PRF is proportional to the Doppler speeds (PRF) of targets. the PRF-switchable radar installation corrects the amount of phase rotation of received pulse echoes to a value based on PRFs, a reference value, under a plurality of dealiasing conditions. Vector composition is performed on velocity vectors, based on correction phase angle data acquired thereby. A state, in which its absolute value is maximum, is adopted as a state in which speed dealiasing has occurred. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radar apparatus such as a weather radar or a mobile tracking radar and a signal processing method in this type of radar apparatus.

A Doppler radar is used to calculate a wind speed or a moving target speed (see, for example, Patent Documents 1 to 3). In this type of radar apparatus, the velocity is calculated from the phase rotation amount (phase angle) of the echo reflected by the target.
There is also a technique for changing the detection distance of the target and the expansion of the observation speed by switching the transmission repetition period (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, see Non-Patent Document 1)
JP-A-6-34752 JP-A-11-94932 JP 2000-230976 A Toshiba Review Vol.55 No.5 (2000)

  By the way, if the moving speed of the target is high, the received phase signal may exceed one cycle of the transmission wavelength, and the return of the speed occurs in the detection of the Doppler speed. Since this phenomenon greatly fluctuates the speed calculation result, the aliasing correction process is required. In the existing technology, the speed is calculated for each different PRF, and the speed folding correction process is performed based on the speed difference.

  However, if there is a large variation in echo reflection intensity from the target, the accuracy of the speed data itself that causes the aliasing correction deteriorates, so that an error occurs in the aliasing correction. If a return correction error occurs, the reliability of the detection speed is impaired, and some countermeasure is desired.

  The present invention has been made under the circumstances described above, and an object of the present invention is to make it possible to reduce aliasing correction errors due to variations in echo reflection intensity, and thereby to calculate a target speed with high accuracy and high reliability. An apparatus and a signal processing method thereof are provided.

  In order to achieve the above object, according to one aspect of the present invention, a transmission / reception unit that transmits a radar pulse and receives a radar echo, and a switching unit that switches the pulse repetition frequency of the radar pulse stepwise with respect to a reference value; A signal processing unit that calculates the velocity of the target based on phase angle data observed from the radar echo, and the signal processing unit has a phase rotation amount of the radar echo proportional to the velocity of the target. A value corresponding to the observation value at the pulse repetition frequency of the reference value of the phase angle data of the radar echo based on the radar pulse transmitted under a pulse repetition frequency different from the reference value based on being inversely proportional to the pulse repetition frequency. By correcting each of the above, it corresponds to the state of occurrence of speed folding for each of the plurality of pulse repetition frequencies. Based on the correction phase angle data calculated for each pulse repetition frequency for each of the plurality of conditions, correction means for calculating correction phase angle data based on the pulse repetition frequency of the reference value for each number of conditions, A calculation unit that calculates a target velocity vector for each pulse repetition frequency for each of the plurality of conditions, and a velocity vector calculated for each of the pulse repetition frequencies is mutually vector-synthesized for each of the plurality of conditions, and the combined vector And a verification means for verifying the state of occurrence of the speed return based on the absolute value of the radar apparatus.

  In general, the phase difference between pulse hits of radar echoes based on radar pulses transmitted at different PRFs is different for each PRF even if the target velocity is constant. On the other hand, since the difference in phase difference for each PRF is corrected according to the above configuration, it is possible to generate phase angle data as if they were transmitted and received under the same PRF.

  That is, the inventor has focused on the fact that the phase shift amount is proportional to the target velocity, and has invented that the phase angle data can be corrected based on this fact. Furthermore, the inventor has conceived that if the phase angle of the velocity vector that correctly reflects the state of occurrence of velocity folding for each PRF is corrected by the above method, the velocity vectors for each PRF overlap each other in the vector space. By utilizing this fact, it can be concluded that the state in which the absolute value of the combined velocity vector is maximum is a state that correctly reflects the state of occurrence of velocity folding. Therefore, the speed folding correction can be more reliably performed by evaluating the magnitude of the absolute value of the combined vector.

  That is, according to the above configuration, it is possible to determine the presence or absence of speed wrapping based on a new index called the magnitude of a vector instead of the existing method that has determined the presence or absence of speed wrapping based only on the speed difference. . Accordingly, it is possible to reduce the influence of variations in echo reflection intensity, reduce aliasing correction errors, and calculate the target speed with high accuracy and high reliability.

  According to the present invention, there is provided a radar apparatus and a signal processing method thereof capable of reducing aliasing correction errors regardless of variations in echo reflection intensity and thereby calculating a target speed with high accuracy and high reliability. Can be provided.

  FIG. 1 is a functional block diagram showing an embodiment of a radar apparatus according to the present invention. In FIG. 1, a modulation unit 12 generates a digital value of an intermediate frequency signal of a specified modulation system under the control of a signal processing unit 11 given through an interface (I / F). This digital value is converted into an analog signal 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 having 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) that reflects the moving speed of the target, and the reception frequency is expressed as (f0 + fd). The radar echo reaches 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 Q component (real number component) and I component (imaginary number component) reception data obtained in this way is provided 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 Doppler velocity of the target can be calculated from the phase angle data observed from the received data.

  The signal processing unit 11 includes a switching processing unit 11a, a correction processing unit 11b, a speed calculation processing unit 11c, and a verification processing unit 11d as processing functions according to this embodiment. The switching processing unit 11a switches the transmission repetition frequency (PRF) of the radar pulse 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 corrects the phase angle data of the radar echo based on the radar pulse transmitted under the PRF different from the reference value to the phase angle data corresponding to the observation value in the reference value PRF. For this correction processing, the correction processing unit 11b uses the fact that the phase rotation amount of the radar echo is proportional to the target velocity (PRF). Data generated by the correction process is referred to as corrected phase angle data. The corrected phase angle data is calculated for each different PRF (however, it is not necessary to calculate for the reference value PRF). The corrected phase angle data is calculated for each condition indicating whether or not the speed is turned back. For example, there is a condition that there is no folding in PRF1 and PRF2, but only in PRF3. A plurality of such conditions can be considered, and the correction processing unit 11b calculates corrected phase angle data for each condition.

  The velocity calculation processing unit 11c calculates the velocity vector of the target for each PRF for each of the plurality of conditions based on the corrected phase angle data calculated for each of the plurality of conditions and for each PRF. The verification processing unit 11d verifies the occurrence state of speed folding based on the calculated speed vector. Specifically, the verification processing unit 11d synthesizes the speed vectors with each other for each condition, and concludes that speed folding occurs under the condition where the absolute value of the combined vector is the maximum.

  If the signal processor 11 verifies the occurrence state of speed folding, the speed of the target can be calculated more accurately based on that. For example, by statistically averaging the velocity vectors for a plurality of PRF data under the verified state, the velocity of the target having a large variation in echo intensity can be obtained more accurately. If the velocity vector is larger than the number of radar pulses transmitted under the same PRF, it is more preferable because data of different PRFs can be used. It is also preferable for the averaging process to use a velocity vector based on a plurality of PRF data.

  The correction process makes it possible to calculate the speed using the phase angle data uniformly regardless of the PRF. Therefore, the number of data relating to the speed calculation is not limited by the number of pulse hits in each PRF, and the target speed can be calculated using a larger number of phase angle data than the number of radar pulses transmitted by the same PRF. it can. By using as many phase angle data as possible, it is possible to average the variation in echo reflection intensity and increase the accuracy of the calculation amount. Next, the operation of the above configuration will be described in detail.

FIG. 2 is a flowchart showing a processing procedure of the radar apparatus of FIG. In the reference value PRF1, the received signal is subjected to I / Q detection after A / D conversion. Then, the phase difference between successive pulse hits is calculated. Here, PRF1> PRF2.
On the other hand, the phase difference between pulse hits is also calculated in the same procedure for PRF2 having a smaller value than PRF1. Thereafter, in the folding correction step, the phase difference at PRF2 is corrected to a value corresponding to the phase difference at PRF1. As a result, the phase difference between PRF1 and PRF2 can be handled uniformly. Further, in the folding correction step, the folding condition is verified by the vector, and the speed is calculated. That is, in this step, the loopback determination and the speed calculation are performed simultaneously. That is, in this step, in addition to the calculation of the speed, a speed return correction process is performed, and the presence or absence of the return is verified. Then, after the folding correction is performed, the target speed is finally calculated.

  FIG. 3 is a schematic diagram showing a process performed for verifying the speed return in this embodiment. In FIG. 3, a three-stage PRF (PRF1> PRF2> PRF3) is taken as an example. As indicated by the phase circle in FIG. 3, the phase angle centered on the origin increases as PRF1, PRF2, PRF3, and PRF change. Of these, PRF1 and PRF2 are assumed to be unfolded and PRF3 is unknown. In PRF 3, since it cannot be determined whether the phase angle exceeds π or whether there is no return and a negative phase is indicated, the return is determined.

FIG. 3A corresponds to a state without folding. In this state, when the correction phase angle for each PRF is calculated to obtain the velocity vector, the velocity vectors of PRF1 and PRF2 overlap, but only the velocity vector of PRF3 is shifted on the phase circle.
FIG. 3B shows a state in which the PRF 3 is folded from the + side. This corresponds to a state in which folding occurs in PRF3. When the correction phase angle for each PRF is calculated in this state and the velocity vector is obtained, the velocity vectors in all PRFs overlap on the phase circle. Thus, the states of FIGS. 3A and 3B can be distinguished by vector-combining the velocity vectors on the phase circle and comparing the lengths (absolute values) of the combined vectors. That is, when the phase angle of the velocity vector for each PRF is correctly corrected, the angular velocity vectors overlap on the phase circle. By utilizing this fact and finding a condition that maximizes the absolute value of the combined vector, it is possible to reduce speed folding correction errors.

Table 1 is a table summarizing the conditions under which speed folding can occur. If the PRF has three stages, for example, seven conditions as shown in Table 1 can be considered. For each PRF, “0” is set for no return, “1” is set for return from the + side, and “−1” is set for return from the − side, so that 3 × 3 × 3 = Although 27 conditions can be considered, it is sufficient to consider the seven conditions in Table 1 from the magnitude relationship of PRF1 to PRF3.

  For each condition in Table 1, a corrected phase angle and velocity vector can be calculated for each PRF. For each of these conditions, there is only one condition that maximizes the absolute value of the combined velocity vector. In Table 2, the condition (condition 2) is (PRF1, PRF2, PRF) = (0, 0, 1). This corresponds to FIG. Condition 1 in Table 1 corresponds to FIG. Next, a method for calculating the corrected phase angle data and the velocity vector in the present embodiment will be described using mathematical expressions. First, for each of PRF1 to PRF3, the phase angle θ is obtained from the received data of the pulse echo.

<Calculation for PRF1>
When the pulse pair method is used, the real part and the imaginary part of the pulse echo of PRF1 are expressed by the following equations (1) and (2).

The phase angle of the pulse echo of PRF1 is expressed as the following equation (3).

The maximum speed of the pulse echo of PRF1 is expressed by the following equation (4).

  In Equation (4), C is the speed of light, and f0 is the frequency of the transmission pulse.

<Calculation for PRF2>
Similarly, the real part and imaginary part of the pulse echo of PRF2 are expressed by the following equations (5) and (6). Further, the phase angle of the pulse echo of PRF2 is expressed by the following equation (7). Further, the maximum speed of the pulse echo of PRF2 is expressed by the following equation (8).

<Calculation for PRF3>
Similarly, the real part and imaginary part of the pulse echo of PRF3 are expressed by the following equations (9) and (10). In addition, the phase angle of the pulse echo of PRF 3 is expressed by the following equation (11). Further, the maximum speed of the pulse echo of PRF3 is expressed as the following equation (12).

  In equations (8) and (12), C is the speed of light, and f0 is the frequency of the transmission pulse.

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 expressed by equation (13) and the imaginary part is expressed by equation (14).

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 (15), and the imaginary part is expressed by Expression (16).

Next, when the values of each PRF are synthesized for each real part and imaginary part, the following equations (17) and (18) are obtained.

Using equations (17) and (18), a corrected velocity vector on the phase circle can be calculated by the following equation (19).

The magnitude (scalar amount) of the velocity vector is expressed as in the following equation (20) using equations (17) and (18).

  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. As a result, even if the number of pulse hits in each PRF is finite, data can be used across different PRFs, so the number of data related to speed calculation can be significantly increased.

  FIG. 4 is a flowchart showing a processing procedure in an existing radar apparatus for comparison. In the existing apparatus, as shown in FIG. 4, the Doppler speed is calculated for each PRF, and the target speed is obtained through the aliasing correction process. However, this method has a weak point in that it tends to cause a mistake in the aliasing correction processing for a target having a large variation in echo reflection intensity.

  On the other hand, in this embodiment, in the radar apparatus capable of switching the PRF, the phase rotation amount of the received pulse echo is based on the fact that the phase rotation amount for each PRF is proportional to the Doppler velocity (PRF) of the target. Is corrected to a value based on the reference value PRF. The velocity vectors based on the corrected phase angle data thus obtained are vector-synthesized, and the presence / absence of velocity folding in each PRF is verified based on the magnitude relationship between the absolute values.

  That is, as shown in FIG. 3, the velocity vector obtained with different PRFs is corrected to an amount corresponding to the data obtained with the same PRF, and the condition that maximizes the resultant vector is adopted as the state of occurrence of folding. . Accordingly, more data can be used than in the existing apparatus, and the aliasing correction process can be performed based on a new index such as the magnitude of the vector, so that correction errors can be reduced.

  In addition, since the received data related to the speed calculation can be handled uniformly regardless of the PRF, the target Doppler speed can be calculated using more received data. Therefore, the effect of averaging variations in echo reflection intensity can be enhanced, and the accuracy of speed calculation can be improved. As described above, it is possible to reduce the aliasing correction error regardless of the variation in the echo reflection intensity, thereby providing a radar apparatus capable of calculating the target speed with high accuracy and high reliability and its signal processing method. It becomes possible to do.

  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 the above embodiment, the presence / absence of speed folding is determined based on the absolute value of the combined vector. Of course, this can be combined with the conventional determination based on the speed difference. Further, the present invention is not limited to the weather radar, but can be applied to other Doppler radars.

  In the above embodiment, not only PRF 1 but also other PRFs such as PRF 2 and PRF 3 may be used as reference values. Further, the present technology can be applied not only to three stages but also to two stages, or conversely, four stages or more. 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.

  Furthermore, 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. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

1 is a functional block diagram showing an embodiment of a radar apparatus according to the present invention. The flowchart which shows the process sequence of the radar apparatus of FIG. The schematic diagram which shows the process implemented in order to verify speed return 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 ... Speed calculation processing part, 11d ... Verification processing part, 12 ... Modulation part, 13 ... D / A conversion part, 14 ... Transmission / reception part, 15 ... Antenna, 16 ... A / D converter, 17 ... Demodulator

Claims (8)

A transmission / reception unit for transmitting radar pulses and receiving radar echoes;
Switching means for stepwise switching the pulse repetition frequency of the radar pulse with respect to a reference value;
A signal processing unit for calculating a target velocity based on phase angle data observed from the radar echo,
This signal processor
Based on the fact that the phase rotation amount of the radar echo is proportional to the velocity of the target and inversely proportional to the pulse repetition frequency, the phase of the radar echo based on the radar pulse transmitted under a pulse repetition frequency different from the reference value By correcting the angle data to a value corresponding to the observed value at the pulse repetition frequency of the reference value, the pulse repetition of the reference value for each of a plurality of conditions corresponding to the state of occurrence of speed folding for each of the plurality of pulse repetition frequencies. Correction means for calculating correction phase angle data based on the frequency;
Calculation means for calculating the velocity vector of the target for each pulse repetition frequency for each of the plurality of conditions based on corrected phase angle data calculated for each pulse repetition frequency for each of the plurality of conditions;
And verifying means for combining the speed vectors calculated for each pulse repetition frequency with each other for each of the plurality of conditions and verifying the occurrence state of the speed wrapping based on the absolute value of the combined vector. Radar equipment. The radar apparatus according to claim 1, wherein the signal processing unit calculates the velocity of the target using a velocity vector in a state of occurrence of velocity folding verified by the verification unit over a plurality of PRF data. . The radar apparatus according to claim 2, wherein the signal processing unit calculates the speed of the target by using a larger number of speed vectors than the number of radar pulses transmitted at the same pulse repetition frequency. The radar apparatus according to claim 2, wherein the signal processing unit calculates the speed of the target using a speed vector based on a plurality of PRF data. In a signal processing method used in a radar apparatus that transmits radar pulses and receives radar echoes,
A switching step of stepwise switching the pulse repetition frequency of the radar pulse with respect to a reference value;
A signal processing step of calculating a target velocity based on phase angle data observed from the radar echo,
This signal processing step consists of
Based on the fact that the phase rotation amount of the radar echo is proportional to the velocity of the target and inversely proportional to the pulse repetition frequency, the phase of the radar echo based on the radar pulse transmitted under a pulse repetition frequency different from the reference value By correcting the angle data to a value corresponding to the observed value at the pulse repetition frequency of the reference value, the pulse repetition of the reference value for each of a plurality of conditions corresponding to the state of occurrence of speed folding for each of the plurality of pulse repetition frequencies. A correction step for calculating corrected phase angle data based on the frequency;
A calculation step of calculating a velocity vector of the target for each pulse repetition frequency for each of the plurality of conditions based on corrected phase angle data calculated for each of the pulse repetition frequencies for each of the plurality of conditions;
And verifying the velocity vectors calculated for each of the pulse repetition frequencies with each other for each of the plurality of conditions, and verifying the occurrence state of the velocity folding based on the absolute value of the synthesized vector. A signal processing method. 6. The signal processing step according to claim 5, wherein the velocity of the target is calculated using a velocity vector in a state of occurrence of velocity folding verified in the verification step over a plurality of PRF data. Signal processing method. 7. The signal processing according to claim 6, wherein the signal processing step is a step of calculating the speed of the target using a number of speed vectors larger than the number of radar pulses transmitted at the same pulse repetition frequency. Method. The signal processing method according to claim 6, wherein the signal processing step is a step of calculating a velocity of the target using a velocity vector based on a plurality of PRF data.

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