JPH023952B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a moving target extractor in a pulse modulation radar.

Pulse radars on the ground and on ships can be roughly divided into pulse Doppler type radar and simple pulse type radar. Conventionally, pulse Doppler radar, which can eliminate fixed targets such as the ground or sea surface and determine the speed relative to the radar device, has been used to gain insight into moving targets such as aircraft. However, this method is very complicated and expensive, so there is a strong desire for a simple and low-cost device to replace it.

The present invention is based on the frequency band used x band, pulse width
In addition to simple pulse radar with a repetition rate of 0.2 to 2 μS and a repetition frequency of 400 to 2000 PPS (pulses per second), it can erase fixed targets such as structures on the ground and mountains, and can also be used to erase fixed targets such as radars and moving targets such as aircraft, ships, and vehicles. The object of the present invention is to provide a moving target extractor that can deeply determine the distance of a moving target, and the speed and direction of a moving target.

FIG. 1 shows an example of the configuration of a simple pulse radar that has been used conventionally. In this figure, a transmitting/receiving antenna 1 is connected to a receiving system mixer 3 or a modulated transmission source 9 via a transmitting/receiving switch 2, and the receiving system includes a mixer 3 and a local oscillator 1.
0, an intermediate frequency amplifier 4, an amplitude detector 5, and a video amplifier 6. A video signal 7 from the video amplifier 6 is output to a display 13. On the other hand, the trigger
The pulse generator 11 outputs a trigger pulse signal 12 to the modulated transmission source 9 and the display 13.

This pulse radar receives radio waves emitted from the device and reflected back from fixed targets on the ground of the aircraft, and the horizontal axis on the A scope as a display shows the distance, and the vertical axis shows the intensity of the reflected radio waves. is displayed. Therefore, as is, it is not possible to erase fixed targets such as the ground and display only moving targets.

The principle of how the present invention allows fixed targets to be deleted and only moving targets to be displayed will be explained below using a concrete example.

Figure 2 shows the reflected wave video signal from an aircraft measured by a pulse radar with a repetition frequency of 1000 PPS, which is converted into a 0.1 μs signal using an analog-to-digital converter.
Multiple sets of data sampled at different times are obtained and visually displayed. This figure has 16 horizontal axis (0.1 μs interval) (distance R to R + 225 m) and 256 horizontal axis
(1ms interval), a total of 4096 data groups. This relationship can be expressed as follows.

〓 ₀ =〓 _0,N-1 ... 〓 _0,0 =X ₀ (N-1) ...X _M-1(N-1) 〓 ...X ₀₍₀₎ ...X _M-1(0) ... (1) However, the vector 〓 _0,N-1 is 〓 _0,N-1 = [X _0(N-1) ,...,X _M-1(N-1) ].

In this example, M=16 and N=256, and in FIG. 2, the closest side corresponds to 〓 ₀ , ₀ , and the farthest side corresponds to 〓 _{0, N-1} .
Note that the vertical axis is the video signal voltage. In this example, you can see that the aircraft (where the video signal voltage is highest) is moving from left to right (from near to far), but in many cases the moving target overlaps the fixed target on the ground and is very close to the ground. It is becoming difficult to identify. Therefore, if fixed targets can be deleted and only moving targets can be displayed, the accuracy of measuring their speed and position should improve.

Furthermore, it is difficult to determine the target speed from FIG. Rearrange Figure 2 as shown in Figure 3. Similarly, equation (1) can be rearranged as follows.

〓 _A ＝〓 _A,M-1 … 〓 _A,0 ＝X _M-1(0) …X _M-1(N-1) 〓 … X ₀₍₀₎ …X _0(N-1) ……( 2) In Figure 3, the depth axis in Figure 2 is the horizontal axis (repetition time), and the horizontal axis is the depth axis (distance R to R +
225m), and the nearest data is 〓 _A,0
, and the innermost one is 〓 _A,M-1 .

In this figure, the video signal voltage at _A,5 is initially high at a constant distance of M-1=5, and as the repetition time passes, the video signal voltage becomes low; and the location at _A,11 is M- At a constant distance of 1=11, the video signal voltage is initially low, and as the repetition time elapses, the video signal voltage becomes higher. Thus, the reason why the video signal voltage changes from high to low (or vice versa) over a certain distance is because the target is moving, and the rate of change is proportional to the speed. If we extract only (〓 _A,5 , 〓 _A,11 ) corresponding to the changing portions of the rising and falling edges of the pulse in the reflected wave video signal in Figure 2 and ignore the noise, Figures 4 and 5 It can be written as shown in the figure.
In addition, in the case of a fixed target, it becomes a horizontal straight line as shown in FIGS. 4 and 5. These two waveforms correspond to the rising and falling pulses in the reflected wave video signal of FIG. 2, so they form a pair, and one set always appears for one moving target. Here, from the formula, the straight line with slope 1 (Y=X) is y≒2 _∞ 〓 ⁿ⁼¹ (-1) ^n-1 sin(nx)/n...(3) (However, -π<x< Since π and n are integers [Iwanami Zensho Mathematics Official Collection, p. 242]) and Fourier series, the slope when the waveform is approximated by a straight line as shown in Figures 4 and 5 is expressed by these Fourier series, It is determined from the largest n=1 component in equation (3). On the other hand, looking at the n=1 component of the rising or falling portion of the pulse, in the waveform group of Fig. 3, does the waveform of Fig. 4 lie on the near side or on the far side of the depth axis indicating distance? can be detected from the fact that the phase of the n=1 component is reversed in FIGS. 4 and 5, and it can be determined whether the moving target is approaching or moving away. (The example in Figure 3 shows that the waveform in Figure 4 is coming closer and moving away.) Here, the slopes of the straight lines in Figures 4 and 5 are found from the digital Fourier transform of equation (2). Think about it. From the formula, the K-th Fourier coefficient is expressed as F _n(K) = 1/N _N-1 〓 ⁿ⁼⁰ X _n(o) exp(-j2πKn/N)...(4). However, m=0, 1,...,M-1
It is.

From F _n(1) in equation (4), |F _n(1) | or I _n {F _n(1) } [imaginary part of F _n(1) ], each broken line in Figure 3 can be drawn as a straight line. The slope of the approximate case can be found, and from the extreme value, the slope of the straight line in FIGS. 4 and 5 can be found.

_Nyquist diagram _{( vector} The locus) and Bode diagrams are shown in FIGS. 6, 7, and 8. From these figures, sequence (5) has extreme values at F _{5 (1)} and F _{11 (1)} ,
It can be seen that this corresponds to the slope of the straight line in FIGS. 4 and 5.

Next, try to find the speed of the moving target from F _{5 (1)} , F _{11 (1)} , or F _{11 (1)} in Figure 6 or Figure 7. 9th
The figure is a diagram depicting the video signal within one repetition of FIG. 2 using a simple broken line approximation. This a (μs),
Using b (volts) to find the target speed V (m/s), approximately V=｜F ₅₍₁₎ ｜×N×C×a×N×T/4π×b ………(6 ) becomes. Here, N is the number of samples, 256, C is the speed of light, 3×10 ⁸ m/s, and T is the transmission pulse interval, 1 ms.
From Figure 2, b = 0.4 volts, a = 0.15
(μs), and reading from FIG. 7 that |F ₅₍₁₎ |=0.14 volts, the velocity V of the moving target is found to be V≒82 m/s. In this example, the velocity was determined using a calculation formula, but the measurement accuracy would be further improved if the display formula was calibrated through simulation or the like.

Next, we will explain how to determine whether the target is approaching or moving away. In the Nyquist diagram shown in Figure 6, if the moving target is moving away, first a waveform with a negative slope as shown in Figure 4 rises, and then a waveform with a positive slope as shown in Figure 5 rises. The trajectory is drawn in the order of F ₅₍₁₎ and F ₁₁₍₁₎ , and if they are close, the trajectory is drawn in the opposite direction. This relationship is the seventh
This can be shown more clearly in FIG. 2
From the phase of F ₅₍₁₎ and F ₁₁₍₁₎ , ∠
If F ₅₍₁₎ ≒−90°, ∠F ₁₁₍₁₎ ≒90°, the target is moving away; if ∠F ₅₍₁₎ ≒90°, ∠F ₁₁₍₁₎ ≒−90°, the target It can be seen that it is approaching. Moreover, the peak and valley portions of FIG. 7 are the center positions of the targets.

To find the target velocity from equations (3), (4), and Figures 6, 7, and 8, the real part of the complex number F _n(1) is smaller than the imaginary part, so |F _{n (1)} Instead of |, the speed and position of the moving target can also be determined from the imaginary part [I _n {F _n(1) }].

FIG. 10 is a graph in which the vertical axis shows the speed determined from I _n {F _n(1) }. In this example, the target is moving away, but if the target is approaching, the plus and minus polarities in the diagram are reversed. From this as well, the direction of movement of the target can be determined.

The above has described the case of display using the A scope, but fixed targets can also be deleted using the same method in the case of the PPI scope. By showing the signals in Figures 7 and 10 that have been described so far on the PPI scope, it is possible to eliminate the fixed target, but in Figure 7, the signal near the center of the target is missing, so There is a possibility of confusing the two goals.No. 10
The diagram has a drawback in that the center position of the target is displayed shifted. On the other hand, when the data in FIG. 2 is differentiated with respect to time, data as shown in FIG. 11 is obtained.
When this data group is subjected to digital Fourier transform, Fourier coefficients as shown in FIGS. 12 and 13 are obtained. This figure 13 corresponds to figure 10 for the data before differentiation, and the waveform width is narrow, and the apex points near the center of the moving target, so
Excellent as a signal for PPI.

Although the above explanation has been made for the case where there is a single goal, a similar argument can be made for multiple goals.

FIG. 14 shows the configuration of an embodiment of a moving target extractor according to the present invention. In this figure, the moving target extractor added to the pulse radar device 15 is a differentiator 16 that differentiates the video signal 7 output from the moving target extractor.
, an analog-to-digital converter 17 that converts the output of the differentiator 16 and the video signal 7 into digital signals, a digital calculator 18, and a moving target signal 19 outputted from this to calculate the distance to the target and the target. The pulse radar device 15 includes a display 20 for displaying the speed and direction of travel, etc., and a pulse generator 21 for recording the operation of the analog-to-digital converter 17 in the trigger pulse signal 12 of the pulse radar device 15. Here, the pulse radar device 15 may have a conventional configuration as shown in FIG. The data is digitized by an analog-to-digital converter 17 and input into a computer 18 in synchronization with the data. By processing this data using the above-mentioned equation (4), etc., it is possible to display the speed of the moving target as shown in FIG. 10 and the position of the target as shown in FIG. 13.

As explained above, according to the present invention, a moving target can be added to a simple pulse radar to eliminate a fixed target and to know the distance from the radar to the moving target and the speed and direction of the moving target. It is possible to obtain an extractor, and in particular, it is possible to easily display a moving target at a low cost.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of a pulse radar device currently in use, Figure 2 is a graph showing a three-dimensional video signal of the target reflected wave, and Figure 3 is a rearranged version of Figure 2. The graphs shown in Figures 4 and 5 are graphs drawn by extracting 〓 _A , ₅ , 〓 _A , ₁₁ from Figure 3, and Figure 6 is the graph obtained by digital Fourier transform of 〓 _A , m in Figure 3. 7 and 8 are Bode diagrams of the Fourier coefficients, and FIG. 9 is a graph showing a waveform obtained by approximating the video signal of the target reflected wave with a broken line.
Figure 10 is a graph that shows the imaginary part of the Fourier coefficient instead of Figure 6, Figure 11 is a graph that shows the time differential waveform of the video signal three-dimensionally instead of Figure 2, and Figure 12 is a graph that shows the imaginary part of the Fourier coefficient in place of Figure 2. A graph displaying the amplitude term of the Fourier coefficient in Figure 1 obtained from the signal of
FIG. 3 is a graph showing the imaginary part, and FIG. 14 is a block diagram showing an embodiment of the moving target extractor according to the present invention. 7... Video signal, 12... Trigger pulse signal, 15... Pulse radar device, 16... Differentiator, 17... Analog-digital converter, 18
...Digital calculator, 19...Moving target signal,
20...Display device, 21...Pulse generator.

Claims (1)

[Claims] 1. In a pulse modulation radar, a video signal of a radar reflected wave from a moving target is digitized by an analog-to-digital converter synchronized with the system trigger pulse of the radar, and the video signal is digitized in the distance direction. M, repeated in the time direction, temporarily stored as a total of M×N data groups, and then digitally Fourier-transformed as a set of N pieces of data located at equal distances. M first-order Fourier coefficients obtained. A moving target extractor characterized in that it obtains a velocity component from the absolute value or imaginary part of and outputs a signal capable of displaying the distance to the target, the speed of the target, and the traveling direction. 2 In a pulse modulation radar, the video signal of the radar reflected wave from a moving target is differentiated with time,
An analog-to-digital converter synchronized with the radar's system trigger pulse digitizes M in the distance direction, N in the repetition time direction, and M in total.
The absolute value of the M first-order Fourier coefficients, or the velocity component from the imaginary part, is obtained by digitally Fourier-transforming a set of N data equidistant after temporarily storing it as a group of ×N data. A moving target extractor characterized in that it outputs a signal capable of displaying the center position value and velocity of the target.