JPH0245834B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an MTI (Moving Target Indicator) radar device that eliminates reflected echoes from fixed objects (or bodies) such as buildings or mountains and displays moving targets.

First, a conventional MTI radar device will be explained.

Figure 1 shows the commonly used MTI
This is a block diagram of a radar device, in which signals from a stabilized local oscillator 11 and a reference signal generator 12 are mixed by a mixer 10, amplified by a power amplifier 9, and pulsed by a pulse modulated wave from a pulse modulator 8. The modulated radio waves emitted from the antenna 1 are reflected by a target (not shown) and then received by the antenna 1 again. This received signal is introduced into a mixer 3 through a duplexer 2. The mixer 3 mixes the received signal and the local oscillator signal provided from the stabilizing local oscillator 11, extracts the difference between the intermediate frequencies, and guides it to an intermediate frequency amplifier (hereinafter referred to as IF amplifier) 4 at a predetermined level. is amplified to.

The received signal amplified by the IF amplifier 4 is transferred to the reference signal generator 12 used to generate the transmitted signal.
Phase detection is performed by the phase detector 5 using the reference signal from the target, resulting in a coherent video CV that preserves the Doppler frequency component of the target (not shown).

Delay line canceler 6
By delaying the signal by one period and taking the difference from the coherent video of the next period, the received signal from the fixed target is erased, and only the received signal from the moving target is extracted and displayed on the indicator 7.

In such an MTI radar device, when the Doppler frequency of the target is an integral multiple of the transmission pulse repetition frequency, the speed response of the delay line canceler 6 becomes zero, resulting in so-called blind speed, and the speed cannot be detected. It becomes possible. For this reason, generally a staggered trigger generator 13 is used that continuously switches between two or more types of transmission pulse repetition periods.

However, in the conventional device described above, the so-called secondary echo, which is a reflected wave from a fixed object located further away than the distance corresponding to the transmission pulse repetition period, is received after the next transmission wave is emitted, and is not reflected by the next transmission wave. , the time differs for each reception, and it is not possible to eliminate unnecessary secondary echoes by calculating the difference between successive received signals using the delay line canceler 6 shown in FIG.

The present invention has been made to improve these conventional problems, and provides an MTI radar device that uses two or more types of staggered repetition periods, a pulse width discrimination circuit, and a defruter circuit.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention, and numerals 1 to 13 are the same as those shown in FIG.

14 receives the received signal from the delay line canceler 6, measures its pulse width τ _S , and compares the magnitude with a predetermined time τ _t . If τ _S τ _t (1), then the pulse width τ _S It is a pulse width discriminator that outputs as is, and if τ _S > τ _t (2), narrows the pulse width to a predetermined width τ _t and outputs it. (T is the transmission pulse repetition period)
This is a defruter that detects the correlation between the N-delay line cancelers and controls the output of the N-fold delay line canceler to turn ON/OFF.

The defruter 15 has a threshold circuit that determines the presence or absence of detection at the output of the N-fold delay line canceler 6, a delay circuit that delays the output of the threshold circuit for (N+1)T time, and determines a mismatch between the detection before the delay. It is composed of a mismatch detection circuit for detecting a mismatch, and a gate circuit that turns the output of the N-fold delay line canceler 6 ON and OFF based on the output of the mismatch detection circuit. For example, N=
0, that is, if no eraser is used, defruter 1
5, when it is determined that there is a detection, if there is a similar detection at the same distance one repetition cycle ago, the gate is turned on as a continuous synchronous signal and the signal is passed through, and if there is no signal, a mismatch is detected and it is treated as an asynchronous signal such as an interference wave. Cut off.

Now, similarly to FIG. 1, the coherent video CV phase-detected by the phase detector 5 is canceled by the delay line canceler 6 in the case of a received signal from a fixed target.
In the case of a received signal from a moving target, it passes through the delay line canceler 6 and is output. However, if the above coherent video CV has a transmission pulse repetition period T
In the case of a so-called secondary echo, which is a received signal from a fixed target located further away than the distance corresponding to the distance, the signal is not canceled by the delay line canceler 6, but is outputted and input to the pulse width discriminator 14. If the pulse width τ _S of the secondary echo is less than the predetermined time τ _t as shown in equation (1), the secondary echo passes through the pulse width discriminator 14 as it is, and is detected as a mismatch in the defruter 15. Set the output to "OFF".

If the pulse width τ _S of the secondary echo exceeds a predetermined time τ _t as shown in equation (2), the pulse width of the secondary echo is changed to a predetermined width τ _t by the pulse width discriminator 14.
The defruer 15 detects a mismatch and turns the output "OFF".

The above operation will be explained in more detail on the time axis.

Figure 3 shows an example of signals received from a target when using the above-mentioned staggered trigger generator that continuously switches six types of transmission pulse repetition periods. The primary echo E _F and the secondary echo E _S are shown. In the figure, T ₁ , T ₂ , T ₃ , T ₄ , T ₅ , T ₆ are the six types of transmission pulse repetition periods, T _F is the primary echo reception time,
T _S is the secondary echo reception time and TP is the transmitted pulse.

Figure 4 shows the received signals (echoes) in Figure 3 above for each reception time based on the time of occurrence of the transmission pulse, and (A) is the (K-6)th received signal; (i) indicates the (K-5)th received number, and below (u) to (ki) respectively (K-4),
(K-3), (K-2), (K-1), K-th received signals are shown.

As is clear from this waveform diagram, the primary echo E _F
is always separated by a time T _F from the transmitted pulse TP, whereas the time of the secondary echo E _S differs each time it is received from the transmitted pulse TP.

Therefore, the delay line canceler 6 shown in FIG.
By calculating the difference between successive received signals using , the secondary echo E _S cannot be eliminated and is input to the pulse width discriminator 14 shown in FIG. 2 above.

FIG. 5 shows the output of the delay line canceler 6 when the pulse width τ _S of the secondary echo E _S is smaller than a predetermined time, and the number N of stages of the delay line is two. The part indicated by the broken line in the figure is the transient output of the delay line canceler 6. When a single pulse signal is input to the N-stage delay line canceler, the transient response causes (N+1) transient outputs to be the same distance regardless of whether or not there is a stagger. When the number of stages N is 2, a total of three transient outputs are output for one echo as shown in the figure.
Since the pulse width τ _S of the secondary echo E _S is smaller in the pulse width discriminator 14 , it passes through as is and is inputted to the defruter 15 . The defruter 15 detects a match with the received signal before transmission three times, and turns the output "OFF" at a distance where there is no match.
As shown in FIG. 6, only the primary echo is output.

7, 8, and 9 show the delay line canceler 6, pulse width discriminator 14, and defruter 15 when the pulse width τ _S of the secondary echo E _S is larger than the predetermined time τ _t .
The pulse width of the secondary echo E _S output from the pulse width discriminator 14 is narrowed to τ _t , and the deruter 15 detects a match with the received signal three times before transmission. , since there is no match, no secondary echo is output to the output of the defruter 15, and only the primary echo is output.

As shown in Figs. 5 and 7, the output of the two-stage delay line canceler is 3 transient outputs for one echo, so it takes 3 cycles to detect a mismatch. It is necessary to see the discrepancy in the previous signal. Furthermore, in FIG. 5, the six periods (a) to (f) have different staggered periods in order to prevent the same secondary echo from matching three periods before the secondary echo in (g).

In the above explanation, a fixed object was mentioned as the object of the secondary echo E _S , and a moving target was mentioned as the object of the primary echo E _F , but the secondary echo E _S is also canceled in the case of a moving target. , the primary echo E _F is canceled in the case of a fixed object.

In addition, an example was shown in which the staggered repetition period is 6 types and the number of stages of the delay line canceler 6 is 2, but if the delay line canceler 6 has N stages, (N+1) transient outputs are generated due to transient response, and the defruter is Check the mismatch with the signal from (N+1) periods ago. 2(N+1) so that the (N+1)th transient output of the secondary echo does not match the signal from (N+1) periods ago at the defruer.
Quite the same effect can be achieved by using different types of staggered repetition periods. Here, N is a positive integer.

In addition, in the above explanation, the pulse width discriminator 1
As an example of the judgment condition in step 4, equations (1) and (2) were set, and the pulse width after discrimination was set as τ _t , but there was no equality sign in equation (1).
Exactly the same effect can be obtained when there is an equal sign in equation (2) or when the pulse width after discrimination is smaller than τ _t .

As described above, the present invention uses an N-stage delay line canceler, 2 (N+1) or more types of staggered repetition periods, and uses a pulse width discriminator and a defruter in an MTI radar device having a staggered repetition frequency. It has the advantage of being able to eliminate secondary echoes from fixed objects that cannot be eliminated by conventional MTI radar equipment.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional MTI radar device.
FIG. 2 is a block diagram showing one embodiment of this invention.
3 is a diagram showing received signals for explaining the operation in FIG. 2 on the time axis, and FIG. 4 is a diagram showing received signals for explaining the operation in FIG. 2 in more detail on the time axis. 5 is a diagram showing the output of the delay line canceler when the pulse width of the secondary echo is narrower than a predetermined pulse width, FIG. 6 is a diagram showing the defruter output of the output shown in FIG. 5, and FIG. The figure shows the output of the delay line canceler when the pulse width of the secondary echo is wider than the predetermined pulse width, Figure 8 shows the output of the pulse width discriminator for the output shown in Figure 7, and Figure 9 8 is a diagram showing the defruter output of the output shown in FIG. 8. FIG. In the figure, 1 is an antenna, 2 is a duplexer,
3 is a mixer, 4 is an intermediate frequency amplifier, 5 is a phase detector, 6 is a delay line canceller, 7 is an indicator, 8 is a pulse modulator, 9 is a power amplifier, 10 is a mixer, 11 is a stabilizing local oscillator, 12 is a reference signal generator, 13
is a staggered trigger generator, 14 is a pulse width discriminator,
15 is a defruter, CV is a coherent video,
E _F is the primary echo, E _S is the secondary echo, TP is the transmitted pulse, T _F is the primary echo reception time, T _S is the secondary echo reception time, T ₁ , T ₂ , T ₃ , T ₄ , T ₅ and T ₆ are staggered repetition periods, τ _S is the pulse width of the secondary echo, and τ _t is the judgment pulse width of the pulse width discriminator. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Claims] 1 In an MTI radar device that emits pulse waves with a staggered repetition period of 2 (N+1) types or more (N is a positive integer), the output of an N-stage delay line canceler is introduced, and the pulse width and output pulse are set in advance. a pulse width discriminator that compares the width with the width of the pulse width discriminator and outputs a predetermined pulse width signal according to the magnitude relationship;
(N+1) of the output resulting from the above pulse width discriminator
A signal processing device for an MTI radar, comprising means for detecting correlation between transmission pulse repetition periods and turning on the output of the pulse width discriminator when there is a correlation and turning off when there is no correlation.