JPH04188089A - Radar equipment - Google Patents

Abstract

PURPOSE:To prevent range bin movement even for a target signal shifted by the Doppler effect and prevent decay of amplitude by giving reference signal used for pulse compression after compensating in accordance with the target Doppler frequency obtained from the result of coherence integration. CONSTITUTION:The output of an amplitude detector 20 is input to a threshold detector 21 and if it exceeds a determined threshold, it is judged to be a target. A frequency change rate alpha and a pre-compression pulse width tau are given by a chirp signal generator 12 and a Doppler frequency fd is obtained from the output of the amplitude detector 20. The recalculation of the reference signal is executed by a reference signal calculation means 101. Since the pulse compression is done with the use of the recalculated reference signal for the coherent integration after the second time, the signal after the pulse compression never have a range bin movement. Also for the amplitude width, decay due to Doppler frequency is never caused.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radar device that applies demodulation processing that prevents range bin movement of a target signal after pulse compression and deterioration of pulse compression ratio.

[Conventional technology] FIG. 8 is a block diagram of a conventional radar device.

) is the antenna, (2) is the transmitting means, (3) is the transmitting/receiving switch, (4) is the receiving means, (12) is the chirp signal generating means, +231 is the signal processing means, and (22) is the display. .

Next, an outline of the operation will be explained.

In the above transmitting means (2), the chirp signal generating means 2
) generates a high-frequency signal modulated by a chirp signal sent from the The high frequency signal is radiated to the target via a transmitter/receiver switch (3) and an antenna.

In the receiving means (4), as shown in FIG. 9, the high frequency signal reflected by the target is input to the mixer (5) via the antenna (9), and the product of the signal and the output of the local oscillator (11) is and converted to an intermediate frequency signal. The output of the mixer (5) is amplified by an IP (intermediate frequency) amplifier (6), then divided into two parts, each input to a phase detector (A), and outputted from a coherent (8) by a phase detector (7). The product of the signal and the signal obtained by delaying the phase of the pressure signal from the coherent oscillator (8) by 90° by a 90° phase shifter (9) are taken, and the phases are detected. The output of each phase detector is converted into a digital complex video signal by an A/D converter (10) as the real part m and imaginary part iQ) of the received complex video signal. The digital complex video signal is taken into the signal processing means (23), and the correlation calculation means (17)
) by performing a correlation calculation with the reference signal read out from the reference signal storage means (18),
Pulse compression is performed. The correlation calculation means (17) performs FFT fFastFourier Trans on the digital complex video signal in the range bin direction (distance direction).
a first FF7 means (13) that performs FFT on the reference signal sent from the reference signal storage means (18), a first FF7 means (13) and a second FF7 means ( 14
) and a multiplier (15) that performs complex multiplication of the output of
5) comprises an inverse FFT means (16) which performs an inverse FFT on the output of step 5).

The above reference signal is a chirp signal generating means (12)
This is a discrete sample of the chirp signal generated by The output of the correlation calculation means (I7) is stored in a buffer not specified in FIG. 8 corresponding to the number of coherent integrals N hits, and is subjected to FFT in the pulse hit direction (time direction) by the third FFT means (19). . An amplitude value is calculated by an amplitude detector (20) based on the output of the third FF7 means (19) and sent to a threshold detector (21). The threshold detector (21) determines that the signal sent from the amplitude detector (20) is a target when it exceeds a predetermined threshold level, and sends a detection signal to the display (22). The display (22) receives the target detection signal and displays the target.

The chirp signal used for modulating the transmission signal and as a reference signal has the waveform shown in FIG.
It is given by Equation 11.

s (t) = exp (j2παt 2 ) ・
(1) Here, 5 (t): Chirp signal t: Time -te/2≦t≦te/2 α: Frequency change rate τ: Pulse width before compression.

Fig. 3 (f2011 in al is a chirp signal that is the basis of the transmission signal and reference signal. Chirp signal (2
01) changes as shown by the frequency (202) of the chirp signal in FIG. 3(b). This frequency f (tl
is expressed by equation (2).

f(t)=a-t ・・・・・・・・・・・・ (
2) Here, α: Frequency change rate t: Time −te/2≦t≦τ/2.

FIGS. 4(a) and 4(b) show the frequencies of the reference signal and the received signal (digital complex video signal). (3
01) is the frequency of the reference signal, (3021 is the frequency of the received signal from the stationary target. The reflected wave from the stationary target does not generate a Doppler frequency.

As shown in Figure 4 (a), the signal is in the same band as the transmission signal, and is correlated with the reference signal as shown in Figure 5 (a).
The pulse compression decoded waveform (the amplitude value indicated by 4011 is Jατ2
becomes the pulse. However, in the case of a moving target, the fourth
The frequency of the received signal from the moving target in Figure tbl (3031
As shown in Figure 5 (
As shown in the pulse compressed decoded waveform (402) of bl, there is a problem in that a shift in the pulse waveform in the time direction proportional to the distance (range) and a deterioration in the amplitude value of the pulse waveform occur.

[Problems to be Solved by the Invention] Conventional radar devices of this type are configured in one or more ways, and when the target is not moving, they receive signals in the same band and perform pulse compression. The compressed pulse does not move the range bin, and the received signal before compression is J at the target position.
(It accumulates as a 212 times signal.

However, when the target is moving, the received signal is shifted from the transmitted frequency by the Doppler frequency due to the Doppler effect, resulting in range bin movement after pulse compression, which does not correctly indicate the target position. Further, there is a problem that a sufficient compression effect cannot be obtained for the signal after pulse compression.

This invention was made to solve the above-mentioned problems, and provides a radar device that does not cause range bin movement even if the frequency of the received signal shifts due to the Doppler effect, and that can obtain a sufficient compression effect. The purpose is to obtain.

[Means for Solving the Problems] fl) To achieve the above object, the radar device of the present invention includes a transmitting means for generating a transmitting pulse.

A receiving means receives radio waves reflected by a target via an antenna, amplifies the received signal, performs phase detection, and then converts it into a digital complex video signal, and a receiving means that performs pulse compression and coherent integration of the received signal before detecting the target. The radar apparatus includes a signal processing means for detecting a detected target, and a display for displaying a detected target.

The signal processing means is characterized in that it includes a reference signal calculation means capable of calculating a reference signal used for pulse compression according to a target Doppler frequency determined from a result of coherent integration.

(2) The signal processing means includes a plurality of reference storage means used for pulse compression, and a control means capable of switching the reference storage means according to the target Doppler frequency determined from the coherent integration result. shall be.

[Function] In the radar device configured as described above, the signal processing means includes reference signal calculation means capable of compensating and calculating the reference signal used for pulse compression according to the target Doppler frequency determined from the coherent integration result. As a result, range bin movement does not occur even in the received signal that has undergone Doppler shift, and the amplitude value does not deteriorate (pulse compression of the target signal can be performed).

(2) In the radar device configured as described above, the signal processing means can switch between the plurality of reference storage means used for pulse compression and the reference storage means according to the target Doppler frequency determined from the coherent integration result. By providing a control means that can control the range bin movement, even if the received signal undergoes Doppler shift, the range bin movement is small.

Furthermore, the pulse compression of the target signal can be performed while suppressing the deterioration of the amplitude value.

[Embodiment 1 of the Invention An embodiment of each of claims (1) and (2) will be described with reference to the drawings.

FIG. 1 is a block diagram of main parts showing an embodiment of claim (1).

Antenna (1), transmitting means (2), transmitting/receiving switch (3), receiving means (4), chirp signal generating means f12), and first FF7 means (13) having the same configuration as the conventional example shown in FIG.
.

Second FF7 means (14), multiplier (151, inverse FF
T means (16), correlation calculation means (171, third FFT
Means (191° amplitude detector (20), threshold detector (21).

The display device (22) has already been explained.

The explanation will be omitted here.

In FIG. 1, reference signal calculation means (101) calculates and outputs a reference signal used for pulse compression; (181 stores the output reference signal;
Reference signal storage means for sending to the correlation calculation means (17), (102+ is the correlation calculation means (17), the reference signal storage means (18), the reference signal calculation means (101), and the third FF7 means (19) , an amplitude detector (20), and a threshold detector (21).

Next, the operation will be explained.

The digital complex video signal outputted from the receiving means (4) is taken into the signal processing means f102), and the reference signal storage means (18) is processed by the correlation calculating means (17).
), pulse compression is performed by performing a correlation calculation with a reference signal read from the reference signal. The initial value of the above reference signal is the chirp signal (201) in Figure 3 fa).
This is a discrete sample of the transmitted signal shown in . The output of the above-mentioned correlation calculation means (17) is stored in a buffer not specified in FIG. 1 for a coherent integral number N hits9, and is subjected to FFT in the pulse hit direction (time direction) by the third FF7 means (19). . The output of the third FF7 means (19) is an amplitude detector (2G)
and amplitude detection is performed. In Fig. 6 (6011) shows the output of the amplitude detector (20).
The output of 20) is input to a threshold detector (21), and when it exceeds a predetermined threshold level, it is determined to be a target. The received signal determined to be the target is sent to the amplitude detector (2
The Doppler frequency fd is measured from the output of 0). The value of the Doppler frequency fd is fed back to the reference signal calculation means (101). When the Doppler frequency ° is fd, the true frequency of the received signal is fb in Figure 7.
) is estimated to have changed as shown in The vertical axis in FIG. 7(b) represents frequency, and the horizontal axis represents time. (702
) indicates the time change in the frequency of the received signal. When the frequency (702) of the received signal changes as shown in the figure, the received signal has the waveform shown by (701) in FIG. 7(a), for example. (201) of the received signal waveform in Fig. 7(a) and the chirp signal in Fig. 3 Fa) used as the initial value of the reference signal.
When the correlation is taken, the two bands are different, so the peak value will not be obtained where the centers of both signals coincide. In other words, range bin movement occurs in which the peak value deviates in the range bin direction, and the exact position of the target cannot be determined. In order to prevent this range bin movement in the second and subsequent coherent integrations, we recalculate the reference signal used in pulse compression.
The received signal in FIG. 7(a) is made to have the same waveform as the waveform (701). The recalculated reference signal is
3) Formula % Formula % r(t): Reference signal t: Time -t/2≦t≦τ/2 α: Frequency change rate T: Pulse width before compression fd: Doppler frequency.

The frequency change rate α and the pre-compression pulse width are given by the chirp signal generating means 2), and the Doppler frequency fd is determined from the output of the amplitude detector (20). The calculation of equation (3) is performed by the reference signal calculation means (101).

In the second and subsequent coherent integrations, pulse compression is performed using the recalculated reference signal, so no range bin movement occurs in the signal after pulse compression. Also, the amplitude value does not deteriorate due to the influence of Doppler frequency.

Next, FIG. 2 is a block diagram of essential parts showing an embodiment of claim (2).

Since the same components as those of the conventional example shown in FIG. 8 have already been explained, their explanation will be omitted here.

In FIG. 2, (2001) is a control means for selecting a reference signal used for pulse compression, +20031 is a plurality of correlation signal storage means for storing reference signals, and +20021 is a correlation calculation means (17).
, a reference signal processing means (2003), a control means (2001), a third FF7 means (19), an amplitude detector (20), and a threshold detector (21). be.

Next, the operation will be explained.

The digital complex video signal output from the receiving means (4) is taken into the signal processing means +20021, and the reference signal storage means (20021) is processed by the correlation calculation means (17).
Pulse compression is performed by performing a correlation calculation with the reference signal read from 001. The initial value of the reference signal is selected by the control means +20011 from among the plurality of reference signal storage means, which stores data obtained by discretely sampling the transmission signal shown by the chirp signal (201) in FIG. 3(a). give it. The output of the correlation calculating means (17) is stored in a buffer not specified in FIG. will be held. The output of the third FFT means (19) is sent to the amplitude detector (20), where amplitude detection is performed.

(601) in FIG. 6 shows the output of the amplitude detector (20). Furthermore, the output of the amplitude detector (20) is input to a threshold detector (21), and when it exceeds a predetermined threshold level, it is judged as a target. The Doppler frequency fd of the received signal determined to be the target is measured from the output of the amplitude detector (20). The value of the Doppler frequency fd is fed back to the control means (2001). When the Doppler frequency is fd, it is estimated that the true frequency of the received signal changes as shown in Figure 7 (bl. Figure 7 fb), the vertical axis represents frequency and the horizontal axis represents time. . (702) indicates a time change in the frequency of the received signal. When the frequency of the received signal (702+ changes as shown in the figure,
The received signal has a waveform shown, for example, at (701) in FIG. 7(a). The received signal waveform in FIG. 7(a) and the chirp signal in FIG. 3(a) used as the initial value of the reference signal (
201), the two bands are different, so the peak value does not occur where the centers of both signals coincide. In other words, range bin movement occurs in which the peak value deviates in the range bin direction, and the exact position of the target cannot be determined. In order to suppress this range bin shift in the second and subsequent coherent integrations, the control means (2001) switches the reference signal used in pulse compression and selects data close to the received signal waveform (701) in FIG. 7(a). The reference signal calculated in advance and stored in a plurality of reference signal storage means is given by equation (4).

y (t) =:exp(j2u (a ・t+ f
'd) ・t)...(4) Here γ(t): Reference signal t: Time -t/2≦t≦τ/2α: Frequency change rate τ: Pulse width before compression f'd: Doppler Frequency f. +L+fz+...

f.

M: Total number of reference signal storage means (2003).

The frequency change rate α and the pre-compression pulse width are determined by the chirp signal output from the chirp signal generating means (I2). The Doppler frequency f'd, which is assumed in advance, is determined according to the expected speed of the target. It is assumed that the plurality of reference signal storage means (2003) respectively store values obtained by calculating equation (4) with the Doppler frequencies f'd"fo, f+, fz, . . . , 9. The control means (20011) selects the f'd closest to fd according to the Doppler frequency fd of the received signal obtained from the output of the amplitude detector (20), and correlates the reference signal storage means (200) corresponding to the f'd. Connected to the calculation means (17).Since the second and subsequent coherent integrations perform pulse compression using a reference signal approximated to the received signal, the signal after pulse compression can suppress range bin movement and amplitude value deterioration. can.

[Effects of the Invention] As explained above, according to the present invention, by compensating and providing a reference signal used for pulse compression according to the target Doppler frequency determined from the coherent integration result, Pulse compression of the target signal can be performed without range bin movement occurring in the signal and without deterioration of the amplitude value.

In addition, in the above, according to the target Doppler frequency determined by the coherent integration result, the most matching reference signal is selected from a plurality of reference signal recording/listening means in which different reference signals are recorded/superimposed, and is provided to the interpolation calculation means. As a result, even if the target signal has undergone Doppler shift, there is little range bin movement, and the pulse compression of the target signal can be performed while suppressing deterioration of the amplitude value.

[Brief explanation of drawings]

Figure 1 shows claim 1. Main part configuration showing one embodiment of the present invention); Figure 2. Claim 2. A main part configuration diagram showing an example of
Figures 3(a) and fb) are diagrams showing the chirp signal sent to the transmitting means, Figures 4a) and [b) are diagrams showing the relationship between the reference signal and the received signal in the conventional example, and Figure 5(a).
, (b) is a diagram showing the waveform after pulse compression, FIG. 6 is a diagram showing the waveform after coherent integration, FIG. 7 is a diagram showing the reference signal of the embodiment, and FIG. 8 is a configuration block showing the conventional example. 9 are block diagrams showing the structure of the receiving means. In addition, in FIG. 9, the same reference numerals indicate the same or equivalent parts. Fig. 3 Fig. 4vA 302: Frequency 1d of receiving signal 3 of stationary eye barrel; Figure 701--The output of 1) ≧ (20) No. 7 % Raif+5.7
02: I of Hokkaido! 'l-tribe Mukuro 703: Inside the Yakuka-go! (point,

Claims (2)

[Claims] (1) A transmitter that generates a chirp-modulated transmission pulse that is radiated toward a target via an antenna, receives radio waves reflected by the target via the antenna, amplifies the received signal, and performs phase detection, and then A radar apparatus comprising a receiving means for converting into a digital complex video signal, a signal processing means for detecting a target after pulse compression and coherent integration of the received signal, and a display for displaying the detected target. A radar device characterized in that the means comprises reference signal calculation means capable of calculating a reference signal used for pulse compression according to a target Doppler frequency determined from a coherent integration result. (2) The signal processing means is configured to include a plurality of reference storage means used for pulse compression, and a control means capable of switching the reference storage means according to a target Doppler frequency determined from the coherent integration result. A radar device according to claim (1), characterized in that: