JP2006226954A - 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 variations in the reflection intensity of echoes and computing the speeds of targets with high accuracy. <P>SOLUTION: The PRF-switchable radar installation corrects the amount of phase rotation of received pulse echoes to a value based on PRFs, a reference value, on the basis that the amount of phase rotation for each PRF is proportional to the Doppler speed of targets. It is thereby possible to unify and handle reception data on speed computations, independently of PRFs for computing the Doppler velocities of the targets through the use of larger amount of reception data. It is thus possible to heighten the effect of averaging variations in the reflection intensity of echoes and improve the accuracy in speed computations. <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 in a meteorological phenomenon or a speed of a target moving in air traffic control (see, for example, Patent Documents 1 to 3 below). 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 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.
JP-A-6-34752 JP-A-11-94932 JP 2000-230976 A

  By the way, as is well known, speed calculation accuracy deteriorates for a target having a large variation in echo reflection intensity. 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 increase the number of observation angle data, that is, the phase angle data observed from the pulse echo and average the variation.

However, in the existing radar apparatus, the target velocity can be calculated only in a manner closed to each PRF. In other words, even if a plurality of radars having different PRFs are used, the speed itself can only be calculated for each PRF using the phase angle data received at each 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 its peak, so the observation accuracy is limited. I understand that. In addition, in a radar apparatus with a small number of pulses transmitted for each PRF, the influence of variations in echo reflection intensity is even greater, and some measures are desired because the observation accuracy deteriorates.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a radar apparatus and a signal processing method thereof capable of calculating a target speed with high accuracy regardless of variations in echo reflection intensity.

  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 a target velocity 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 target velocity. Correction for correcting the phase angle data of the radar echo based on the radar pulse transmitted under a pulse repetition frequency different from the reference value to the phase angle data corresponding to the observation value at the pulse repetition frequency of the reference value And calculation means for calculating the speed of the target using a plurality of phase angle data including the corrected phase angle data Radar apparatus comprising: a is provided.

  In general, the phase difference between pulse hits of radar echoes based on radar pulses transmitted with different PRFs differs for each RPF even if the target velocity is constant. This is the reason why the velocity cannot be obtained using the phase angle data of different PRFs. According to the above configuration, the difference in phase difference for each PRF is corrected, so that it is possible to generate received data as if they were transmitted using the same PRF.

  That is, the inventor noticed that the phase shift amount is inversely proportional to the PRF and proportional to the target speed, and has invented that the phase angle data can be corrected based on this fact. This makes it possible to process the phase angle data uniformly even if the PRFs are different by using the phase angle data observed for each PRF transversely. Therefore, the number of data relating to the speed calculation can be significantly increased as compared with the existing radar apparatus, and the accuracy of the speed calculation can be improved even for a target having a large variation in echo reflection intensity.

  ADVANTAGE OF THE INVENTION According to this invention, the radar apparatus which can reduce the dispersion | variation in echo reflection intensity, and can calculate the speed of a target with high precision, and its signal processing method 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, 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 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 speed and inversely proportional to the PRF. The calculation processing unit 11c calculates the target velocity using a plurality of phase angle data including the phase angle data corrected by the correction processing unit 11b. In particular, the calculation processing unit 11c calculates the target speed using phase angle data based on continuous radar echoes.

  The correction process makes it possible to calculate the speed using the phase angle data uniformly regardless of the RPF. For this reason, the number of data relating to speed calculation is not limited by the number of pulse hits in each PRF, and the target speed is calculated using a larger number of phase angle data than the number of radar pulses transmitted by the same PRF. be able to. 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. The phase difference between the pulse hits is calculated in the same procedure in PRF2 having a smaller value than PRF1, but the phase difference in PRF2 is corrected to a value corresponding to the phase difference in PRF1 by the correction step. 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 is a schematic diagram for explaining how the phase angle of echoes from the same target varies depending on the value of PRF. Taking a three-stage PRF as an example, PRF1> PRF2> PRF3. In general, the phase difference between pulse hits is first obtained in order to obtain the velocity from the received signal of the radar. However, if the PRF is different, the value of the phase difference is different even if the target speed is the same. 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 shift for each PRF is proportional to the target Doppler velocity and inversely proportional to the PRF. 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, 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 combined for each real part and imaginary part, the following equations (17) and (18) are obtained.

Using equations (17) and (18), the Doppler velocity 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).

  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 in the number of data related to the speed calculation, and there is a problem that the accuracy of the calculation tends to deteriorate for a target having a large variation in reflection intensity.

  On the other hand, in this embodiment, the radar apparatus is capable of switching the PRF, and the phase rotation amount of the received pulse echo is used as a reference based on the fact that the phase rotation amount for each PRF is proportional to the Doppler velocity of the target. The value is corrected to a value based on the PRF as a value. As a result, reception data related to velocity calculation can be handled uniformly regardless of PRF, and the Doppler velocity of the target is calculated using more reception data. Therefore, the effect of averaging variations in echo reflection intensity can be enhanced, and the accuracy of speed calculation can be improved. From the above, it is possible to provide a radar apparatus and a signal processing method thereof that can reduce variations in echo reflection intensity and calculate the target speed 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. Further, 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.

  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 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 (6)

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, the phase angle data of the radar echo based on the radar pulse transmitted under a pulse repetition frequency different from the reference value is obtained from the reference value. Correction means for correcting the phase angle data corresponding to the observed value at the pulse repetition frequency;
A radar apparatus comprising: a calculating unit that calculates a velocity of the target using a plurality of phase angle data including the corrected phase angle data. The radar apparatus according to claim 1, wherein the calculating means calculates the velocity of the target using a larger number of phase angle data than the number of radar pulses transmitted at the same pulse repetition frequency. The radar apparatus according to claim 1, wherein the calculation unit calculates the velocity of the target using phase angle data based on continuous radar echoes. 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, the phase angle data of the radar echo based on the radar pulse transmitted under a pulse repetition frequency different from the reference value is obtained from the reference value. A correction step for correcting the phase angle data corresponding to the observed value at the pulse repetition frequency;
And a calculation step of calculating a velocity of the target using a plurality of phase angle data including the corrected phase angle data. 5. The signal processing according to claim 4, wherein the calculating step is a step of calculating the velocity of the target using a larger number of phase angle data than the number of radar pulses transmitted at the same pulse repetition frequency. Method. The signal processing method according to claim 4, wherein the calculating step is a step of calculating a velocity of the target using phase angle data based on continuous radar echoes.

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