JP2021038875A - Target speed detection device and target speed detection method - Google Patents

Abstract

To provide a target speed detection device of which detection accuracy has been improved.SOLUTION: A target speed detection device in accordance with an embodiment is provided with an antenna section capturing radar echo from a target, a receiving section, and a signal processing section. The receiving section generates a received signal from the radar echo. The signal processing section is provided with a converter converting the received signal to a digital signal and a detection processing part processing the digital signal. The detection processing part is provided with a Fourier transformation function, a point detection function, a determination function, and a speed detection function. The Fourier transformation function obtains a spectrum waveform in a direction of a frequency axis by application of the Fourier transformation to the digital signal. The point detection function detects points more than predetermined threshold value on the spectrum waveform. The determination function determines a Doppler frequency of a target by comparing the spectrum waveform with a theoretical waveform of the spectrum waveform. The speed detection function detects a speed of the target based on the Doppler frequency.SELECTED DRAWING: Figure 2

Description

Embodiments of the present invention relate to a target speed detection device and a target speed detection method.

For example, a seeker mounted on a flying object detects a target by the principle of radar using radio waves or the like. Since the radar (antenna) in front of the flying object loses sight of the target when it comes closest to the target, it was common to mount the antenna separately on the side. On the other hand, there is known a method of reducing the weight by using the front antenna for side detection.

Japanese Patent No. 5305955

The antenna in front cannot detect the target passing right next to the flying object. Therefore, the meeting time with the target is predicted from the detection result at the time when the target is captured in the forward direction. Therefore, it is required to detect the target distance and speed with high accuracy.
However, with the existing technology, since the shape of the target becomes wider as the distance from the target becomes shorter, a plurality of reflection points of the radar wave are observed, and as a result, a velocity detection error is likely to occur.

Therefore, an object of the present invention is to provide a target speed detection device and a target speed detection method with improved detection accuracy.

According to the embodiment, the target speed detection device includes an antenna unit, a receiving unit, and a signal processing unit. The antenna section captures the radar echo from the target. The receiving unit generates a received signal from the captured radar echo. The signal processing unit processes the received signal. The signal processing unit includes a conversion unit that converts a received signal into a digital signal, and a detection processing unit that processes the digital signal. The detection processing unit includes a Fourier transform function, a point detection function, a determination function, and a speed detection function. The Fourier transform function Fourier transforms a digital signal to obtain a spectral waveform in the frequency axis direction. The point detection function detects points that exceed a predetermined threshold level in the spectral waveform. The determination function compares the spectral waveform with the theoretical waveform of the spectral waveform to determine the target Doppler frequency. The speed detection function detects the target speed based on the Doppler frequency.

FIG. 1 is a block diagram showing an example of a flying object equipped with a target speed detection device according to an embodiment. FIG. 2 is a functional block diagram showing an example of the target detection unit 5. FIG. 3 is a diagram showing an example of the positional relationship between the flying object 1 and the target 7. FIG. 4 is a flowchart showing an example of the processing procedure of the detection processor 17. FIG. 5 is a diagram showing an example of the Fourier transform waveform of the received signal. FIG. 6 is a diagram showing another example of the Fourier transform waveform of the received signal. FIG. 7 is a diagram showing another example of the positional relationship between the flying object 1 and the target 7. FIG. 8 is a diagram showing an example of the peak position of the Fourier transform waveform observed from each reflection point of FIG. 7. FIG. 9 is a diagram showing a waveform in which the Fourier transform waveforms of the reflection points shown in FIG. 8 are superimposed on the frequency axis. FIG. 10 is a diagram showing an example of the result of a simulation for explaining how the speed spreads. FIG. 11 is a diagram showing a theoretical waveform for the Fourier transform shown in FIG. FIG. 12 is a graph in which the observed waveform and the theoretical waveform of FIG. 11 are superimposed on the frequency axis. FIG. 13 is a graph showing the peak position of the theoretical waveform in the state where the minimum error value is the smallest.

FIG. 1 is a block diagram showing an example of a flying object equipped with the target speed detection device according to the embodiment. The flying object 1 includes a guiding unit 2, a warhead 3, and a steering unit 4. The guidance unit 2 outputs a guidance signal for flying in the direction of the target 7. The steering unit 4 controls the attitude of the flying object 1 toward the target 7 in accordance with this guidance signal. Further, the guidance unit 2 predicts the meeting time with the target, and generates and outputs a detonation signal to detonate the warhead 3 at the meeting time.

The guidance unit 2 includes a target detection unit 5 and a target follow-up unit 6 as target speed detection devices. The target detection unit 5 has a function as a so-called radio wave seeker and detects the target 7. In addition to generating the guidance signal, the target following unit 6 predicts the meeting time with the target 7 and generates a detonation signal based on the meeting time.

FIG. 2 is a functional block diagram showing an example of the target detection unit 5. The target detection unit 5 includes an array antenna unit 13 that transmits radio waves (transmitted waves) in the direction of the target 7 and captures radio waves (reflected waves: radar echo) from the target 7. The target detection unit 5 further includes an antenna controller 11, a transmitter 12, a receiver 14, and a signal processor 15.

The antenna controller 11 indicates the transmission direction of the transmitted wave. The transmitter 12 generates radio waves (transmitted waves). The receiver 14 detects the received wave (radar echo) from the array antenna unit 13.
The signal processor 15 includes an A / D converter 16 and a detection processor 17. The A / D converter 16 converts the analog detection output signal from the receiver 14 into a digital signal. The detection processor 17 detects a target from the digital signal from the A / D converter 16 and obtains the distance, angle, and speed of the target 7. Then, the detection processor 17 passes this information to the target tracking unit 6. Further, the detection processor 17 outputs the direction of the next transmitted wave to the antenna controller 11. Next, the operation in the above configuration will be described.

FIG. 3 is a diagram showing an example of the positional relationship between the flying object 1 and the target 7. In addition, in order to simplify the discussion, the explanation will be given in two dimensions below, but the same argument holds in a three-dimensional space. In FIG. 3, the flying object 1 travels straight at a speed of Vm, and the target 7 exists in the direction of the target relative direction θ1 with respect to the traveling direction. The target goes straight at a speed of Vt and travels in the direction of θ2 with respect to the traveling direction of the flying object. The target relative velocity Vtm at this time is represented by the equation (1).
Vtm = Vm · cos θ1 + Vt · cos (θ2-θ1)… (1)
FIG. 4 is a flowchart showing an example of a processing procedure related to the detection of the target speed by the detection processor 17. In step S1 of FIG. 4, the detection processor 17 performs a Fourier transform process on the digitized received signal to obtain a Fourier transform waveform (power value) as shown in FIG. In order to remove harmonics, it is preferable to multiply the received signal by the window function and then perform the Fourier transform. Here, the vertical axis of the graphs of FIGS. 5 and 6 indicates the power value, and the horizontal axis indicates the point number in the simulation. The horizontal axis is equivalent to frequency.

In step S2 of FIG. 4, the detection processor 17 performs a threshold value determination process on the Fourier transform waveform. For example, assuming that the power value shown by the dotted line in FIG. 5 is the threshold level, the detection processor 17 records three points indicating the power value exceeding the threshold as target detection points. In the next step S3, the detection processor 17 determines the number of target detection points. If the target detection point is 3 or less, it can be considered that there is no variation in the target detection speed. Therefore, the detection processor 17 calculates the target speed from the peak point in step S4.

If there is only one target detection point, the target speed (Doppler speed) can be obtained in step S4 by using the frequency of the detection point as the target Doppler frequency as it is. If the number of target detection points is two or three, the detection processor 17 obtains the target Doppler frequency fd from the weighted average value using the average value of the frequencies of each point or the power value, and formula (2). The target speed Vd is obtained by.

Vd = fd · C / 2f ... (2)
Here, C is the speed of light and f is the transmission frequency.
If the number of target detection points is 0 in step S3, it is assumed that there is no target and the process ends.

The problem here is when four or more target detection points are detected in step S3. That is, as shown in FIG. 6, for example, five target detection points may be detected. This is a phenomenon that occurs when the target seen from the flying object 1 has a spatial expanse, and corresponds to the case shown in FIG. 7.

As shown in FIG. 7, when the target 20 is approached, the number of reflection points of radio waves seems to increase for the flying object 1. When viewed from the flying object 1, for example, if there are a plurality of (three) reflection points in the lateral direction, the Fourier transform waveform (FIG. 6) of the received signal spreads in the frequency direction. In addition, the number of detection points whose received power exceeds the threshold value also increases.

The explanation will be continued by returning to FIG. When four or more target detection points are detected in step S3, the target speeds are also observed to vary. Here, the processing procedure branches to step S5, and the detection processor 17 executes the processing of steps S5 to S10 to obtain the target speed when four or more target detection points are observed. Here, the factor that causes the Fourier transform waveform from the plurality of reflection points to spread in the frequency direction will be described with reference to FIG.

FIG. 8 is a diagram showing an example of the peak position of the Fourier transform waveform observed from each reflection point of FIG. 7. When the signals from the reflection points 1 to 3 are received independently, the waveforms appear to have different relative velocities due to the difference in the angles of the reflection points (FIG. 7), so that the peak position also changes in the frequency direction. In reality, since the reflected waves from each reflection point are received at the same time, the individual waveforms of each reflection point overlap each other as shown in FIG. 9, and the waveform spreads in the frequency direction.

FIG. 10 is a diagram showing an example of the result of a simulation for explaining how the speed spreads. In the calculation, Vm = 500 m / s, Vt = 500 m / s, θ1 = 10.2 °, and θ2 = 20 °, respectively. As shown in FIG. 7, when the flying object 1 and the target 7 move linearly, the velocity is the fastest at the angle of the reflection point corresponding to the meeting point, and the velocity decreases as the distance from the point increases. Therefore, even if the target component spreads in the frequency direction on the Fourier transform waveform, it is sufficient to find the point corresponding to the fastest speed.

As can be seen from FIG. 8, the fastest velocity component appears on the higher frequency side of the entire detection point. Therefore, the peak point corresponding to the fastest speed can be estimated from this part. Specifically, the target speed is calculated assuming that the two detection points from the highest frequency are the components of the signal corresponding to the fastest speed.

FIG. 11 is a diagram showing a theoretical waveform with respect to the waveform of FIG. FIG. 11 (a) corresponds to the observed waveform (FIG. 6), and the theoretical waveform thereof is FIG. 11 (b). The theoretical waveform is a Fourier transform waveform of the window function multiplied by the received signal, and shows the same shape as the ideal waveform when there is no spread of the velocity component (one reflection point). FIG. 11B shows a waveform having a higher frequency resolution than the actual observed waveform.

The explanation will be continued by returning to FIG. 4 again. In step S5 of FIG. 4, the detection processor 17 controls (offsets) the scale of the vertical axis, and as shown in (a) of FIG. 12, the upper second point on the frequency axis of the detection point ( The second point from the highest frequency: (A) in FIG. 11 (a) and the peak of the theoretical waveform are overlapped.
FIG. 12 is a graph in which the observed waveform and the theoretical waveform of FIG. 11 are superimposed on the frequency axis. The horizontal axis is enlarged and the resolution of the theoretical waveform is shown as 8 times. Of course, a higher resolution may be used.

In step S6, the detection processor 17 calculates an error (b) between the first high frequency point ((B) in FIG. 11 (a)) and the theoretical waveform of the detection point, and sets the absolute value as the minimum error value. Remember as. Next, in step S7, the detection processor 17 slides the theoretical waveform by one point with respect to the horizontal axis. If the error (b) between the first high frequency detection point in step S6 and the theoretical waveform is positive, the sliding direction is to the left on the graph. If the error (b) is negative, the slide direction is to the right. In the example of FIG. 12, the theoretical waveform is slid to the left. After the slide, the power value of the theoretical waveform is adjusted so that the power value of the theoretical waveform is the same as that of the second highest frequency of the detection point.

Next, in step S8, the detection processor 17 calculates an error between the first high frequency point of the detected point after sliding and the theoretical waveform. Next, the detection processor 17 compares the minimum error value in step S9 with the absolute value of the error obtained in step S8, and if the absolute value of the error obtained in step S8 is larger, in step S10. Perform processing. If it is smaller, the process returns to step S7 again.

In step S10, the detection processor 17 considers the peak position of the theoretical waveform at the time when the minimum error value is the smallest as the Doppler frequency fd of the fastest velocity component, and sets a target based on the equation (2) from the value of that frequency. Calculate the velocity Vd of. FIG. 13 shows the peak position of the theoretical waveform in the state where the minimum error value is the smallest. FIG. 13 (d) shows the state where the minimum error value is the minimum, and FIG. 13 (c) shows the peak position of the Doppler frequency fd related to the speed calculation.

As described above, in this embodiment, the waveform of the observation result (Fourier transform waveform) and the waveform based on the theoretical value are compared with each other based on the characteristics of the velocity of the target having a lateral spread, so that the echo from the target can be obtained. It becomes possible to determine the peak position of the Doppler frequency with high accuracy. That is, in the target speed detection by the radio wave seeker, the speed detection error due to the target angle spread can be reduced by utilizing the speed characteristics and the characteristics of the observed waveform. This makes it possible to detect the target speed with high accuracy, and by extension, the predicted meeting time with the target can be obtained with high accuracy.
From these facts, according to the embodiment, it is possible to provide a target speed detection device and a target speed detection method with improved detection accuracy.

Although embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. This novel embodiment can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Flying body, 2 ... Guidance unit, 3 ... Bullet head, 4 ... Steering unit, 5 ... Target detection unit, 6 ... Target tracking unit, 7 ... Target, 11 ... Antenna controller, 12 ... Transmitter, 13 ... Array antenna unit, 14 ... receiver, 15 ... signal processor, 16 ... A / D converter, 17 ... detection processor, 20 ... target.

Claims (6)

The antenna part that captures the radar echo from the target,
A receiving unit that generates a received signal from the captured radar echo,
A signal processing unit for processing the received signal is provided.
The signal processing unit
A conversion unit that converts the received signal into a digital signal,
A detection processing unit that processes the digital signal is provided.
The detection processing unit
A Fourier transform function that Fourier transforms the digital signal to obtain a spectral waveform in the frequency axis direction,
A point detection function that detects points that exceed a predetermined threshold level in the spectral waveform, and
A determination function for determining the target Doppler frequency by comparing the spectral waveform with the theoretical waveform of the spectral waveform, and
A target speed detection device including a speed detection function for detecting the target speed based on the Doppler frequency. The Fourier transform function multiplies the received signal by a window function and then performs a Fourier transform on the digital signal.
The target speed detection device according to claim 1, wherein the theoretical waveform is a Fourier transform waveform of the window function. The determination function
Of the plurality of detected points, the upper second point on the frequency axis and the peak of the theoretical waveform are superimposed.
The first aspect of the present invention, wherein the peak position of the theoretical waveform that minimizes the error between the upper first point on the frequency axis and the theoretical waveform among the plurality of points is determined as the target Doppler frequency. Target speed detector. A target speed detection method for a device including an antenna unit that captures a radar echo from a target, a signal processing unit that converts a received signal of the captured radar echo into a digital signal, and a detection processing unit.
A process in which the detection processing unit Fourier transforms the digital signal to obtain a spectral waveform in the frequency axis direction.
The process in which the detection processing unit detects a point exceeding a predetermined threshold level in the spectral waveform, and
A process in which the detection processing unit compares the spectral waveform with the theoretical waveform of the spectral waveform to determine the target Doppler frequency.
A target speed detection method comprising a process in which the detection processing unit detects the target speed based on the Doppler frequency. The detection processing unit multiplies the received signal by a window function and then performs a Fourier transform on the digital signal.
The target speed detection method according to claim 4, wherein the theoretical waveform is a Fourier transform waveform of the window function. The detection processing unit
Of the plurality of detected points, the upper second point on the frequency axis and the peak of the theoretical waveform are superimposed.
The fourth aspect of the present invention, wherein the peak position of the theoretical waveform that minimizes the error between the upper first point on the frequency axis and the theoretical waveform among the plurality of points is determined as the target Doppler frequency. Target speed detection method.