JPH04121682A - Radar apparatus - Google Patents

Abstract

PURPOSE:To conduct pulse compression without deteriorating an amplitude value of a reception signal even when it is subjected to Dopper shift, by a method wherein a band width of a reference signal to be used for the pulse compression is made wider by a width corresponding to a Doppler frequency than the band width of a transmission signal. CONSTITUTION:A digital complex video signal outputted by a signal means 4 is taken in a signal processing means 102 and subjected to correlative computation with a reference signal read out from a reference signal storage means 18 by a correlative computation means 17. Thereby pulse compression (demodulation processing) is executed. The aforesaid reference signal is obtained by sampling a chirp signal discretely. While this chirp signal is given by the same formula as a usual example, the pulse width of the reference signal is made wider than the width of a transmission pulse (the pulse width before compression) so as to make the band width thereof wider than that of a transmission signal. By this method, a reception signal of a sufficient amplitude value can be obtained by the pulse compression even when the frequency of the reception signal is shifted by a Doppler effect.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radar device that applies demodulation processing that prevents a decrease in pulse compression rate.

[Prior Art] FIG. 7 is a block diagram of the configuration of a conventional radar device. (
1) is an antenna, (2) is a transmitting means, (3) is a transmitting/receiving switch, (4) is a receiving means, (12) is a chirp signal generating means, (23) is a signal processing means, and (22) is a display. It is.

Next, an outline of the operation will be explained.

In the above transmitting means (2), the chirp signal generating means (1
2) Generates a high frequency signal modulated by the chirp signal sent from. The high frequency signal is radiated to the target via a transmitter/receiver switch (3) and an antenna (1).

In the receiving means (4), as shown in FIG. 8, the high frequency signal inputted from the element antenna (1) is inputted to the mixer (5), and the product with the output of one local oscillator (11) is calculated. and converted to an intermediate frequency signal.

The output of the mixer (5) is an IF (intermediate frequency) amplifier (6)
After being amplified by
8) The phase of the output signal is changed to 90° using the 90° shifter (9).
The product is taken with the delayed signal.

Each phase is detected. The output of each phase detector is the real part (I +
It is converted into a digital complex video signal by a converter (10).

The digital complex video signal is processed by signal processor E (23).
The correlation calculation means (17) performs a correlation calculation with the reference signal read out from the reference signal storage means (18), thereby performing pulse compression. The correlation calculating means (17) converts the digital complex video signal into F F T (
Regarding the reference signal sent from the first FF7 means (13) that performs Fast Fourier Transform (Fast Fourier Transform) and the reference signal storage means (18),
A second FFT means (14) that performs FT, a multiplier (15) that performs complex multiplication of the outputs of the first FFT means (3) and the second FFT means (14), and an inverse FFT of the output of the first multiplier (15).
It is composed of an inverse FFT means (16) that performs the following steps. The reference signal is generated by the chirp signal generating means (12) (
This is a discrete sample of the chirp signal.

The output of the correlation calculation means (17) is stored in a buffer not specified in FIG. 7 corresponding to the number of coherent integrals N hits, and is then processed by the third FFT means (19).

FFT is performed in the pulse hit direction (time direction). An amplitude value is calculated by an amplitude detector (20) based on the output of the third FFT 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 device (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 a waveform as shown in FIG. 2 (aJ), and is given by equation (1).

5l) = exp(j2πat2) ・==-(1) where 5(t): Chirp signal t: Time -τ/2≦t≦τ/2 α: Frequency change rate τ: The pulse width before compression (201) in FIG. 2(a) is a chirp signal that is the basis of the transmission signal and the reference signal. Chirp signal (2
01) changes as shown by the frequency (202) of the chirp signal in FIG. 2(b). This frequency f (t)
is expressed by equation (2).

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

Figure 3 (a) and (b) show the reference signal and the received signal (
indicates the frequency of the digital complex video signal).

(301) is the frequency of the reference signal, (302)
is the frequency of the received signal from the stationary target. The reflected wave from the stationary target does not generate a Doppler frequency and becomes a signal in the same band as shown in Figure 3 (a), and when correlated with the reference signal, the pulse compression decoded waveform (401) in Figure 4 (a) is obtained.
As shown, the amplitude value becomes the pulse of rdll. However, in the case of a moving target, as shown by the frequency (303) of the received signal from the moving target in Figure 3(b), the received signal is shifted by the Doppler frequency fd, so the correlation with the reference signal is taken. As shown in the pulse compression decoded waveform (402) in FIG. 4(b), there is a problem that the amplitude value is less than I (27 mm).

[Problems to be Solved by the Invention] Conventional radar devices of this type have a configuration of 9 or more, and when the target is not moving, they receive signals in the same band and use pulse compression to 7 "1" of the received signal of
It is possible to obtain 11 times more signal. But if the target is moving.

Due to the Doppler effect, the received signal is shifted from the transmitting frequency by the Doppler frequency, so even if pulse compression is performed, the received signal cannot be accumulated sufficiently.

This invention was made in order to solve the above-mentioned problems, and aims to provide a radar device that can obtain a received signal with a sufficient amplitude value by pulse compression even if the frequency of the received signal is shifted due to the Doppler effect. purpose.

[Means for Solving the Problems] In order to achieve the above object, a radar device of the present invention has the following features:
a transmitter that generates a transmission pulse; a receiver that receives radio waves reflected by a target via an antenna; amplifies and phase-detects the received signal; and then converts the received signal into a digital complex video signal; A radar device comprising a signal processing means for detecting a target after performing coherent integration, and a display for displaying the detected target, wherein the signal processing means has a width larger than that at the time of transmission as a reference signal used for pulse compression. The present invention is characterized in that it includes a reference signal generating means capable of generating a chirb waveform of a bandwidth.

[Effect] In a radar device configured as described above.

Since the signal processing means is equipped with a reference signal generation means that can generate a chirp waveform with a wider bandwidth than that during transmission as a reference signal used for pulse compression, the amplitude value can be maintained without deterioration even when the received signal has undergone Doppler shift. , the pulse is compressed.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of the main parts of a radar device according to the present invention.

The antenna (1), transmitting means (2), transmitting/receiving switch (3), receiving means (4), chirp signal generating means (12), and display (22), which have the same configuration as the conventional example shown in Fig. 9, have already been described. Since this is just an explanation, the explanation will be omitted here.

In Figure 1, (1) is an antenna, (2) is a transmitter that outputs a chirp-modulated high frequency wave, (3) is a transmitter/receiver switch that switches between transmitting and receiving, and (4) is a digital device that receives reflected waves. receiving means for converting into a complex video signal, (1
2) is a chirp signal generating means for generating a chirp signal for modulation; and (17) is a correlation calculation means for pulse compressing a digital complex video signal. Correlation calculation means (17)
A first FFT means (13) that performs FFT on a digital complex video signal, and a second FF that performs FFT on a reference signal.
a T means (14), a first FFT means (13) and a second FFT means (13);
A multiplier (I5) that performs complex multiplication of the output of the FFT means (14).
) and an inverse FFT means (16) that performs inverse FFT on the output of the 1 multiplier (15). (101) is a reference signal generation means for generating a reference signal used for pulse compression.

(18) is a reference signal storage means for storing the generated reference signal and sending it to the correlation calculation means (17);
(19) is a third FFT means for performing FFT on the output of the correlation calculating means (17) in the pulse hit direction; (20) is an amplitude detector for determining the amplitude value of the output of the third FFT means (19); (21) is an amplitude detector (20) a threshold detector that determines a target when the signal sent from the source exceeds a predetermined threshold level and outputs a detection signal;
(22) is a display that displays the target in response to the detection signal of the threshold detector (21); (102) is the correlation calculation means (17) and the reference signal storage means (1);
8), a reference signal generating means (ioi), and a third
FFT means (19) and an amplitude detector (20).

The signal processing means consists of a threshold detector (21).

The digital complex video signal outputted from the signal means (4) is taken into the signal processing means (102), and is converted into a reference signal storage means (18) by the correlation calculation means (17).
) Pulse compression (demodulation processing) is performed by performing a correlation calculation with a reference signal read from the reference signal. The above reference signal is the reference signal (
501) is obtained by discretely sampling the chirb signal shown in FIG. The equation for the chirb signal above is given by equation (1), which is the same as in the conventional example, but the pulse width τ' of the reference signal is wider than the transmission pulse width (pulse width before compression) τ in order to make the band wider than the transmission signal. Take. For example, if the maximum value of the target Doppler frequency is fd, .

α where α : Frequency change rate τ : Transmission pulse width (502) in FIG. 5(b) represents the frequency of the reference signal. If the bandwidth of the reference signal is widened (if
Even if the frequency of the target signal is Doppler-shifted, the amplitude value after pulse compression by correlation calculation with the reference signal will be the same amplitude value as the received signal from the stationary target, and no deterioration will occur. FIG. 6 shows the relationship between the frequencies of the reference signal and the received signal from the moving target. In the figure, (601) is the frequency of the reference signal, and (602) is the frequency of the received signal from the moving target. As shown in FIG. 6, the bandwidth of the reference signal must be wider than the bandwidth of the received signal shifted by the Doppler frequency.

[Effects of the Invention] As explained above, according to the present invention, the bandwidth of the reference signal used for pulse compression is made wider than the bandwidth of the transmission signal by an amount corresponding to the Doppler frequency. Even with puller-shifted received signals, the amplitude value does not deteriorate.

Pulse compression can be performed.

[Brief explanation of the drawing]

Fig. 1 is a configuration block diagram showing an embodiment, Fig. 2 fa)
, (b) are diagrams showing the chirp signal sent to the transmitting means, Figures 3 (a) and (b) are diagrams showing the relationship between the reference signal and the received signal in the conventional example, and Figures 4 (a) and (b). 5 is a diagram showing the waveform after pulse compression, FIG. 8 is a block diagram showing a conventional example, and FIG. 8 is a block diagram showing a receiving means. In the figure, (1) is an antenna, (2) is a transmitting means, (4) is a receiving means, and (102) is a signal. Processing means, (22) is a display, and (ioi) is a reference signal generation means.In the figure.The same reference numerals are the same or indicate corresponding parts.

Claims (1)

[Claims] A transmitting means that generates a chirp-modulated transmission pulse that is radiated toward a target via an antenna, and a digital complex video signal that receives radio waves reflected from the target via the antenna, amplifies the received signal, and performs phase detection. In a radar device comprising a receiving means for converting into a signal, a signal processing means for performing pulse compression and coherent integration of the received signal and then detecting a target, and a display for displaying the detected target, the signal processing means comprises: 1. A radar device comprising reference signal generation means capable of generating a chirp waveform with a wider bandwidth than that during transmission as a reference signal used for pulse compression.