JPS6035632B2 - Staggered trigger MTI radar - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a moving target detection device (hereinafter referred to as MT) in a seeder.
(referred to as I), particularly relates to staggered trigger type MTI.

[Prior Art] MTI is used in air traffic control radars and the like to erase signals from fixed targets and display only moving targets.

Comparing the phase of the transmitted RF pulse and the phase of the received RF pulse, we find that signals from a fixed target always have a constant phase relationship, whereas signals from a moving target generally have a different phase relationship for each pulse repetition period. . Therefore, when the difference between the video signals obtained by phase detection of signals from the same distance in two consecutive pulse repetition periods is taken, the video signal of the fixed target is erased, and only the moving target remains. However, such a simple MTI
If the radial component of the relative velocity of the moving target is
When it is equal to the product of the half wavelength and the pulse repetition frequency, or when it is equal to an integral multiple thereof, the phase of the received signal becomes constant, and even the reflected wave component from the moving target is eliminated.

This undetectable speed is called blind speed, and the stagger trigger method is widely used to eliminate blind speed. In the staggered trigger method, pulses are transmitted at two or more different repetition periods. However, if the high-voltage DC power supply of a radar transmitter employing a staggered trigger method is an unregulated power supply, the output DC voltage will fluctuate due to the difference in repetition period.

Therefore, the voltage amplitude of the trigger pulse that drives the high voltage RF generating means also fluctuates. When this transmission tube drive pulse voltage fluctuates, the voltage and phase fluctuations of the transmission RF pulse signal (when the load is an amplifier tube such as a traveling wave tube, klystron, and crossfield amplifier) or the frequency fluctuation of the output signal (when the load is (in the case of an oscillator tube such as a magnetron), which deteriorates the erasure degree of MTI.

In order to prevent this deterioration of erasure performance, conventional methods have been devised to suppress voltage fluctuations in the output pulses of the high-voltage DC power supply supplied to the transmitting tube and the like. For example, there is a method in which a high-voltage DC power source is used as a stabilizing power source, or a method in which charging operation in a high-voltage pulse generation circuit is forcibly stopped midway to perform a stabilizing operation.
[Problems to be Solved by the Invention] However, since all of the above conventional methods control the high voltage in the transmitter, the devices are large and heavy, and are also expensive.
Furthermore, it also caused a decrease in reliability.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a staggered trigger type MTI radar that compensates on the receiving side for phase fluctuations in a transmitted signal that are unavoidable in the staggered trigger type.

[Means to solve the problem]

According to the present invention, a transmitted signal obtained by modulating a signal obtained from a phase reference signal with a staggered trigger pulse is radiated into the air, and a phase detector detects the phase difference between the received reflected wave and the phase reference signal. In a staggered trigger MTI radar that receives this phase difference signal, eliminates a fixed target reflected wave signal, and outputs only a moving target signal, means for obtaining an intermediate frequency signal from the transmitted signal, and a means for obtaining an intermediate frequency signal from the transmitted signal, and a means for obtaining an intermediate frequency signal from the transmitted signal; a phase comparator that outputs a signal corresponding to the magnitude of the phase difference with a reference signal; and a gate signal generator that generates a gate signal synchronized with each pulse of the staggered trigger determined in accordance with the output of the phase comparator. and a phase shifter that controls the phase of the phase reference signal in response to the gate signal, and the phase detector detects a phase difference between the output of the phase shifter and the received reflected wave. Staggered trigger method MTI
You can get radar.

In the phase compensation according to the present invention, a part of the transmitted signal is sampled and attached for phase monitoring, and the amplitude of the gate signal is controlled using phase shift information obtained from this sample signal.

Phase shift information can be obtained using a method similar to phase detection in a receiver. The phase reference signal handled by the staggered trigger MTI radar according to the present invention has the same frequency as the intermediate frequency of the receiver and uses low power, making it possible to make the device smaller, lighter, cheaper, and more reliable. .

〔Example〕

The present invention will be described in detail below with reference to the drawings.

FIG. 4 is a block circuit diagram of an MTI radar device having a conventional amplification type transmitter.

The coho 6 generates a signal (coho signal) that serves as a phase reference in the radar. The coho signal is mixed with the output signal of the local oscillator 7 in the mixer A5 and converted into a high frequency signal having a frequency equal to the sum of both signals. This signal is subjected to pulse fluctuation in the pulse modulator 4, and then sent to the transmitter 3 and transmitted to the R
It becomes an F pulse signal and is radiated through the transmitter/receiver switch 2 and the antenna 1. This transmitted signal is reflected by a fixed target and a moving target and is received by the antenna 1. The received reflected signal passes through the transmitter/receiver switch 2, is amplified by the high frequency amplifier 8, and is then mixed with the output signal of the local oscillator 7 by the mixer B9, and converted to an intermediate frequency. The frequency-converted reflected signal is sent to a phase detector 10, where it is compared with the Coho signal and subjected to phase detection, resulting in a video signal having only phase information.
This video signal is sent to the fire extinguisher 11. Now, referring to FIG. 5, FIG. 5A shows the broken intermediate frequency signal output from the mixer B9, and FIG. has been done.

As shown in FIG. 5b, the phase of the reflected signal from the fixed target is always the same for all repetition periods, so the amplitude of the video signal is constant. On the other hand, since the reflected signals from the moving target have different phase relationships for each repetition period, the amplitudes of these video signals differ for each repetition period.

Therefore, if we take the difference between the signal delayed by one period and the signal not delayed, only the moving target will remain due to the above-mentioned properties of each target. FIG. 5c is a diagram showing the erasing process. Referring to FIG. 6, the output a of the phase detector 10 and the output b of the canceler 11 are shown when the radar apparatus shown in FIG. 4 is operated with a staggered trigger.

As mentioned above, when using the staggered trigger method, the phase of each transmitted pulse is not uniform, and it is common for phase fluctuations to occur between successive RF pulses. The phase relationship for each cycle is not constant.

Therefore, the amplitude of the output (video signal) of the phase detector 10 obtained by comparison with the phase of the coho signal also differs for each repetition period, as shown in FIG. 6a. Therefore, when a video signal delayed by one period is generated and passed through the eraser 11 as described above, even the fixed target reflection component remains in the output, resulting in deterioration of MTI performance, as shown in FIG. Referring to FIG. 1, which shows an embodiment of the present invention, there is shown a block diagram of an MTI radar that employs a phase compensation method according to the present invention that constantly monitors the amount of phase fluctuation.

The coho signal from the coho oscillator 6 and the local oscillator signal from the local oscillator 7 are combined in a wave combiner A5, and the resulting CW signal is a trigger pulse from the trigger pulse generator 15 that specifies the stagger period (Fig. 2a). The signal is pulse-modulated by a pulse modulator 4 based on the signal, and is transmitted from the antenna 1 via a transmitter 3 and a transmitter/receiver switch 2. A part of the transmission signal sent from the transmitter 3 is sent to the mixer CI3, where it is mixed with the local signal from the local oscillator and converted into an intermediate frequency signal. This intermediate frequency signal is compared with the Coho signal from the Coho oscillator 6 by a phase comparator 14 and phase-detected. The amplitude of this phase detection signal is proportional to the amount of phase fluctuation of the transmitted signal. A gate signal generator 16 generates a gate signal proportional to the amplitude of this phase detection signal. The gate signal is synchronized with the trigger pulse of FIG. 2a, as shown in FIG. 2b, and its amplitude is proportional to the amplitude of the phase detection signal. The Coho signal from the Coho oscillator 6 is controlled by a phase shifter 12 by an amount corresponding to the amplitude of the gate signal, and then supplied to the phase detector 10'. An example of this phase shifter is published in the American technical magazine ``ELECTRONI''.
CS'' March 18, 1964 issue, page 38. Its specific configuration is shown in FIG. In the figure, the gate signal is applied to the variable capacitance diode CR,
Since the capacitance can be changed depending on the amplitude voltage of the gate signal, the amount of phase shift of the input coho signal can be changed. In the method shown in this figure, the phase of each transmitted pulse is monitored and the phase reference signal on the receiving side is controlled according to the amount of phase variation. Therefore, the amount of phase variation for each green return period may vary due to changes in the temperature of the equipment, etc. Even if the phase changes, complete phase compensation can be achieved. In the embodiment shown in FIG.
A trigger pulse from 5 is applied to the gate signal generator 16 to facilitate synchronization of the gate signal, but this signal is not absolutely necessary and can be used to synchronize the gate signal with the output of the phase comparator 14. There is no problem. Although the case of the staggered trigger method with two types of pulse repetition periods has been described above, phase compensation can be similarly performed by the method of the present invention in a staggered trigger method with three or more different pulse repetition periods. The structure of the eraser 11 in this case was published in 1970 by McGraw-Hill (McGRAW-mLL) in the United States.
), a technical book Radar Handbook published by
It is detailed on pages 17-28 to 17-31 of "Handbook". [Effects of the Invention] As described above, the present invention eliminates the phase fluctuation caused by the staggered trigger to be actually transmitted in order to eliminate the deterioration in the cancellation degree of MTI caused by the phase fluctuation of the transmission signal that occurs when the staggered trigger method is adopted. The phase variation of the transmitted signal is obtained by constantly measuring the phase difference between a Coho signal (phase reference signal) serving as a phase reference of the transmitted signal and the transmitted signal using a phase comparator.

Since the obtained phase difference indicates a phase variation mainly due to the staggered trigger, the phase of the phase reference signal is shifted in accordance with this phase difference. As a result, a phase signal with the above-mentioned phase variation corrected is always obtained at the output of the phase detector. The present invention is configured as described above, and in particular monitors the phase of each transmitted pulse and controls the phase reference signal on the receiving side according to the amount of phase fluctuation. Complete phase compensation is possible even when the amount of phase fluctuation changes. Further, as is clear from the above-described embodiments, since the phase compensation according to the present invention can be performed at the intermediate frequency stage, the configuration can be simplified, and the device can be made compact, lightweight, and highly reliable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the MTI radar according to the present invention, FIG. 2 is a diagram showing staggered trigger pulse train a and gate signal waveform b, FIG. 3 is a phase shifter circuit diagram, and FIG.
The figure is a block diagram of a conventional MTI radar, and Figure 5 is a block diagram of a conventional MTI radar.
FIG. 6 is a signal waveform diagram of each part for explaining the principle of the radar, and FIG. 6 is a signal waveform diagram for explaining the conventional staggered trigger method.

1... Antenna, 2... Transmission/reception switch, 3...
...Transmitter, 4...Pulse modulator, 5, 9, 13...
...Mixer, 6...Coho oscillator, 7...
... Local oscillator, 8 ... High frequency amplifier, 10
... Phase detector, 11 ... Eraser, 1
2... Phase shifter, 14... Phase comparator,
15...Trigger pulse generator, 16...Gate signal generator.

Development diagram 2nd box Figure 3 Traditional illustration Brother's drawing bag diagram

Claims (1)

[Claims] 1. A transmission signal obtained by modulating a signal obtained from a phase reference signal with a staggered trigger pulse is radiated into the air, a phase difference between the received reflected wave and the phase reference signal is detected by a phase detector, and this phase difference is detected by a phase detector. A staggered trigger type MT that receives a signal, eliminates the fixed target reflected wave component, and outputs only the moving target signal.
In the I radar, means for obtaining an intermediate frequency signal from the transmitted signal; a phase comparator that outputs a signal corresponding to the magnitude of the phase difference between the intermediate frequency signal and the phase reference signal;
a gate signal generator that generates a gate signal synchronized with each pulse of the staggered pulse determined in response to the output of the phase separator; and a phase shifter that controls the phase of the phase reference signal in response to the gate signal. A staggered trigger type MTI radar, characterized in that the phase difference between the output of the phase shifter and the received reflected wave is detected by the phase detector.