JPH0452585A - Target detection device - Google Patents

Abstract

PURPOSE:To prevent an enemy side to discover it easily and interference by the enemy side from being received easily by using a spectrum-diffused transmission signal and by correlating it inside. CONSTITUTION:A code generator 1 generates spectrum diffusion code, outputs this transmission pulse train signal to a frequency modulator 2, and at the same time outputs it to an exclusive OR circuit 10 and a correlation function operator 11. Then, the modulator 2 performs frequency modulation by FSK (Frequency Shift Keying) by transmission pulse train signal according to spectrum diffusion code from the generator 1. Then, the operator 11 obtains a mutual correlation function between the transmission pulse train signal from the generator 1 and the reception pulse train signal from the circuit 10 and then outputs the correlation signal to a comparator 12. Then, the comparator 12 outputs target detection signal only when the correlation signal exceeds a specified value. On the other hand, since the non-correlated internal noise or interference wave does not exceeds a threshold value, the comparator 12 does not output target detection signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a target detection device, and particularly to a target detection device using radar.

[Conventional technology]

A conventional target detection device is shown in FIG.

An oscillator 21 and a pulse modulator 22 that performs pulse modulation of the outputs of the two oscillators, a circulator 23 that guides the output of the pulse modulator 22 to an antenna, an antenna 24 that transmits the output of the circulator 23 in the target direction, and a It has a receiver 25 that receives reflected waves via an antenna 24 and a circulator 23, and a comparator 26 that detects a target when the output of the receiver 25 exceeds a certain value.

Next, the operation will be explained. The output of the oscillator 21 is modulated by a pulse modulator 22, passes through a circulator 23, and is transmitted from an antenna 24 toward the target. The transmitted waves are reflected by the target.

The antenna 24. is delayed by a time corresponding to the round-trip propagation distance to the target. The signal passes through the circulator 23 and is received by the receiver 25. When the reflected wave received by the receiver 25 exceeds a certain threshold level, the comparator 26 outputs a target detection signal.

[Problem to be solved by the invention]

In this conventional target detection device, since the transmission output is a single frequency, it is easy to detect that the enemy is emitting radio waves, and it is also possible to detect interference waves at frequencies that pass through the frequency band of the receiver. If so, you will continue to be interfered with,
I have no countermeasures. Furthermore, during the time that the transmit pulse is being output, part of the transmit power goes around to the receiver, making it impossible to receive the reflected wave from the target, so the pulse width of the transmit pulse is determined. The disadvantage is that if the target is closer than the target, the target cannot be detected.

[Means to solve the problem]

The device of the present invention is a target detection device that detects a target using radar, and includes a transmitting means for transmitting a transmitting signal frequency-modulated by a spread spectrum code in a target direction, and a receiving device that receives the transmitted signal and the target reflected by the target. After performing homodyne detection with the signal, a detection means detects and outputs a bead frequency component by the homodyne detection, and performs an exclusive OR of the spread spectrum code and the detection output of the detection means to detect the transmitted signal and the detection means. demodulating means for obtaining the transmitted signal as a demodulated signal with a propagation time delayed as indicated by the time difference from the received signal; and a correlation value at a delay time equal to the propagation time by cross-correlating the spread spectrum code and the demodulated signal. and target detection means for detecting a target based on the target information.

Further, the apparatus of the present invention has a configuration in which frequency modulation using the spread spectrum signal is FSX.

Furthermore, the apparatus of the present invention has a configuration in which target detection by the target detection means is determined based on a correlation value of the cross-correlation exceeding a predetermined constant value.

〔Example〕

Next, two aspects of the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

In the embodiment shown in FIG. 1, a code generator 11 a frequency modulator 2. a directional coupler 3° circulator 4 and an antenna 5; a mixer 6 constituting a detection means;
Amplifier 7. It comprises a bandpass filter 8 and a detector 9, an exclusive OR 10 as demodulation means, and a correlation function calculator 11 and a comparator 12 that constitute target detection means.

FIG. 2 is a waveform diagram of main signals in the embodiment of FIG. 1. The operation of the embodiment shown in FIG. 1 will be described below with reference to FIG. 2.

A code generator 1 generates a spread spectrum code and outputs this transmission pulse train signal to a frequency modulator 2 as well as an exclusive OR circuit 10 and a correlation function calculator 11.

The frequency modulator 2 generates F S K (
Frequency modulation using Frequency 5hift Keying) is performed. FIG. 2(a) shows the transmitted pulse train signal.

FIG. 2(b) shows the modulation signal.

The directional coupler 3 branches part of the modulated signal from the nine-frequency modulator 2 and guides it to the mixer 6, and also guides the modulated signal to the circulator 4. The circulator 4 is a directional coupler 3
The transmitted signal from antenna 5 is guided to antenna 5, and at the same time
The reflected wave received from the target is guided to the mixer 6 as a received signal.

FIG. 2(c) shows the received signal. The mixer 6 performs homodyne detection on the branched transmission signal from the directional coupler 3 and the reception signal from the circulator 4 and sends a bead signal as a detection result to the amplifier 7. FIG. 2(d) shows the bead signal. The amplifier 7 amplifies the bead signal from the mixer 6 and sends the amplified signal to the bandpass filter. The bandpass filter 7 passes only the signal frequency component of the amplified signal. The detector 9 detects the signal that has passed through the bandpass filter 8 and sends the detected signal shown in FIG. 2(e) to the exclusive OR circuit 10.

The exclusive OR circuit 10 is constructed as shown in FIG.
Exclusive OR is performed between the transmitted pulse train signal based on the spread spectrum code shown in a) and the detected signal shown in FIG. 2(e) detected by the detector 9, and the received pulse train signal shown in FIG. 2(f) is obtained. is sent to the correlation function calculator 11.

The correlation function calculator 11 receives a transmission pulse train signal based on the spread spectrum code from the code generator 1.

A cross-correlation function with the received pulse train signal of the exclusive OR circuit 10 is determined, and the correlation signal is output to the comparator 12. The comparator 12 outputs the target detection signal shown in FIG. 2(g) only when the correlation signal from the correlation function calculator 11 exceeds a predetermined value.

The above-mentioned spread spectrum code generates a high correlation output for a signal that is in phase with the white code, but generates an extremely low correlation output for a code that is out of phase with the white code by one or more bits. use In this embodiment, when the transmission pulse train signal of the code generator 1 shown in FIG. 2(a) is at a high level, the output frequency of the frequency modulator 2 is high. The frequency (fo) is a low frequency (ft) when it is at a low level, but it may be set to a low frequency (fL) when it is a high level and a high frequency (fn>) when it is a low level.

The received signal shown in FIG. 2(c) is a received signal in which the modulated signal in FIG. 2(b) is reflected from the target, received by the antenna 5, and then guided to the mixer 6 through the circulator 4. Therefore, the received signal reflected from the target becomes a signal received with a delay of propagation time td corresponding to the distance to the target.

The bead signal in FIG. 2(d) is generated by the mixer 6 which performs homodyne detection on the modulated signal in FIG. 2(b) branched by the directional coupler 3 and the received signal in FIG. 2(c). This is the bead signal to be output, and the bead frequency (f
H-fL) and (fLfs) are output.

The detected signal in FIG. 2(e) is a signal obtained by amplifying the bead signal in FIG. 2(d) by an amplifier 7, passing through a bandpass filter 8, and detecting the signal by a pulse detector 9. The bandpass filter 8 is a difference frequency (f) I- between the high frequency (fH) and the low frequency (fL) output from the frequency modulator 2.
Since only the signal of fL) is passed through, only the signal frequency component is detected and output from the detector 9 as a detected signal.

The received pulse train in FIG. 2 (f>) is obtained by exclusive ORing the detected signal in FIG. 2(e) and the transmitted pulse train signal based on the spread spectrum code shown in FIG. This is what I took.

The detected signal detected by the detector 9 is exclusive-ORed with the transmitted pulse train signal using the spread spectrum code, thereby demodulating the pulse train using the same spread spectrum code as the original transmitted pulse train signal delayed by the propagation time ta. .

FIG. 2(g) shows a correlation function calculator 11 between the received pulse train signal demodulated by the exclusive OR circuit 10 and the transmitted pulse train signal based on the spread spectrum code shown in FIG. 2(a).
This is the result of finding the correlation function by. The correlation signal of the correlation function calculator 11 shown in FIG. 2(g) is as shown in FIG. 2(f).
Since the received pulse train signal shown in FIG. 2(a) is a pulse train delayed by the propagation time td corresponding to the distance to the target, the transmitted pulse train signal based on the spread spectrum code shown in FIG. 2(a) has a delay equal to this propagation time td. The comparator 12 shows a strong correlation value only when the correlation value exceeds a predetermined threshold value, and outputs a target detection signal.

On the other hand, since uncorrelated receiver internal noise and external interference waves do not exceed the threshold, the comparator 12 does not output a target detection signal.

〔Effect of the invention〕

As explained above, since the present invention utilizes a spread spectrum transmission signal, it is possible to reduce the transmission power density per unit frequency band, prevent it from being discovered by an enemy, and prevent internal interference from interference. By correlating with , it becomes less susceptible to the influence, and since the received wave is homodyne detected by the transmitted wave, it is possible to transmit and receive at the same time. This has the effect that targets can also be detected.

...Correlation function calculator, 12...Comparator, 21...
Oscillator, 22... Pulse modulator, 23... Circulator, 24... Antenna, 25... Receiver, 26
...Comparator.

Claims (1)

[Claims] 1. A target detection device for detecting a target using radar, which includes a transmitting means for transmitting a transmitting signal frequency-modulated by a spread spectrum code in a target direction, and a transmitting means for transmitting a transmitting signal frequency-modulated by a spread spectrum code in a target direction; After performing homodyne detection with the received signal, a detection means detects and outputs a bead frequency component by the homodyne detection, and performs an exclusive OR of the spread spectrum code and the detection output of the detection means, and performs the transmission. demodulating means for obtaining the transmitted signal as a demodulated signal with a propagation time delayed as indicated by the time difference between the signal and the received signal; and a delay time equal to the propagation time for cross-correlating the spread spectrum code and the demodulated signal. 1. A target detection device comprising: target detection means for detecting a target based on a correlation value. 2. Frequency modulation by the spread spectrum signal is FS
2. The target detection device according to claim 1, wherein the target detection device is K. 3. The target detection device according to claim 1, wherein target detection by the target detection means is determined based on a correlation value of the cross-correlation exceeding a predetermined constant value.