JPS58779A - Radar device - Google Patents

Abstract

PURPOSE:To elliminate an interference wave without deteriorating an erase performance of an MTI filter, by inputting a mean value of period signals before and after the previous signal to the MTI instead of the latter, in case when it has been decided to be an interference wave. CONSTITUTION:The third shift register 8 for recording a prescribed range signal of an output digital signal of an A/D converter 1 is inserted in front of the first shift register 3. Also, an averaging circuit 9 for averaging an output D of the A/D converter 1, that is to say, the present receiving signal, and an output B of the first shift register 3, that it to say, the signal of the last time but one is provided on the input side of a selecting circuit 7. As a result, a mean value of period signals before and after an interference wave is inputted to an MTI filter 2, therefore, a sudden change of an input of the filter 2 is removed, and an erase leftover is prevented. Accordingly, in this way, the interference wave can be elliminated without deteriorating an erase performance of the MTL.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radar device with an improved method of removing interference waves.

A conventional device of this type is shown in FIG. In the figure, (1) is an A/D converter that converts a video signal into a digital signal, (3) +41 is an A/D converter (1
) in which signals in a predetermined range of output digital signals are recorded for each transmission pulse period. The second shift register (5@) (5b) detects the force where the absolute value of the difference between the two input signals is greater than or equal to the set value. The second comparator (6) consists of both comparators (5a) (sb),
Correlation circuit that determines interference waves by correlating signals in the same range over multiple periods, (7) includes both comparators +51 +6
Depending on the state of the signal from 1, A / DI = converter (1
) or the output of the $1 shift register (3), the selection (2) path deletes the fixed target signal from the output of the selection circuit (7) ~ ITI (
Moving Target Indicator H
moving target instruction) filter.

In FIG. 1, the first shift register (3) stores the data from the previous transmission, and the second shift register (4) stores the data from the previous transmission. Now, assume that a signal in a certain range is converted into a digital signal by the A/D converter (1), and at the same time, a signal in the same range from the previous time was output from the shift register 131+41. The output of the A/D converter (1) is A,
The output of the If shift register (3) is B, and the output of the 12 shift register (4) is C.

! The $1 comparator (5) is a circuit (7) that selects the output signal when the absolute value of the difference between the signals A and B is greater than a certain set value X.
The comparator (6) of IJ2 sends its output signal to the selection circuit (7) when the absolute value of the difference between the B and C signals is less than or equal to the set value X. In the selection circuit (7), both comparators (5) (
6), that is, if it is determined to be an interference wave, the B signal is input to the MTI filter (2), and in other cases, the human signal is input to the MTI filter (2).

The set value X is set to a value slightly larger than the maximum value within the range in which the signal from a normal fixed target changes each time it is transmitted. Here, even if a normal signal is a target with a large level, the signal size changes smoothly due to the influence of the antenna pattern.

Next, the operation of this circuit will be explained using FIG. 2.

Note that the explanation will be about the correlation between the previous time and the time before the previous time. In FIG. 2, →- indicates that the difference between the value of A and the previous value in the same range is less than or equal to the set value, and -1 indicates that the difference is greater than or equal to the set value. Further, the upper side of the ward indicates the value of A, and the lower side indicates the output of the selection circuit (7). If the arrow is vertical, the value of A will be the output of the selection circuit (7), and if it is diagonal, the value of B will be the output of the selection circuit (7).

FIG. 2(a) shows the case where no interference waves enter. At this time, the value of A becomes the output of the selection circuit (7).

FIG. 2(b) shows the case where an interference wave enters at time tI.

At this time, since the value of B becomes the output of the selection circuit (7), the output of the selection circuit (7) changes smoothly. At this time, B
If the output of the selection circuit (7) is eliminated without outputting the value of , if there is a fixed target, the output of the selection circuit (7) will be discontinuous, resulting in a residual value in the MTI.

In Figure 1142(c), a large moving target moves from time t3 to t4.
Indicates when the point has been reached. At this time, the value of B or the selection circuit (
7), there is a delay corresponding to the selection period from time t1 to time 14, but there is no practical problem. The same thing will happen if the interference waves enter continuously, but the probability that the interference waves will enter the same range continuously is very small.

On the other hand, if the selection circuit (7) is placed after the MTI filter (2), and the MTI filter has multiple feedbacks, the influence of interference will last longer than the transient number, and this influence can be expressed as follows: Adversely affects the detection of moving targets.

Conventional equipment is configured as described above, so when the radar moves or the elevation angle of the antenna changes, the signal from a large fixed target may change or exceed the set value X, and in this case the signal Since the signal that is determined to be an interference wave and is input to the MTI filter misses one cycle, the change in the signal from pulse to pulse becomes larger than in the normal case, and there is a problem that only residual MTI may be output.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and when it is determined that it is an interference wave, the average value of the signals of the periods before and after the previous signal is used as the MTI.
It is an object of the present invention to provide a filter device that can eliminate abrupt transitions in the MTI filter input and reduce residuals by inputting it to the filter.

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

In FIG. 3, the same reference numerals as in FIG. 1 indicate the same components as in FIG. A shift register, which is inserted before the first shift register (3). Also, (is the output D of the A/D converter (1)
That is, this is an averaging process in which the current received signal and the output B of the first shift register (3), that is, the received signal from the time before the previous time, are averaged.

The difference in the operation of the circuit of this embodiment from that of the conventional circuit is as follows.
In this example circuit, a third shift register (8) is added, so the entire operation is performed using a signal delayed by one cycle of the received signal, and when it is determined that it is an interference wave, conventionally The signal (B in Figure 1) is passed through the MTI filter (2)
In this embodiment, the average value of the signals B and D of the periods before and after the interference wave A is input. As a result, in this embodiment, the signal to be processed is delayed by one cycle of the received signal, but there is no problem in practical use. Also, since the average value of the signals before and after the interference wave is input, the MTI
By eliminating sudden changes in the filter input, it is possible to prevent unerased images.

In addition, the shift registers f31 +41 in the above embodiment
+81 may be substituted by memory.

As described above, according to the radar device according to the present invention, when an interference wave is determined, the average value of the signals of the cycles before and after the previous signal is input to the MTI filter instead of the previous signal. By eliminating sudden changes in the MTI filter input, it is possible to reduce residual erasure, which degrades the erasure performance of the MTI even if there is a signal from a fixed target that is larger than expected when determining the set value X. This has the effect of eliminating interference waves without causing interference.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a conventional radar device, FIG. 2 is an explanatory diagram of the operation of the conventional device, and FIG. 3 is a configuration diagram of a radar device according to an embodiment of the present invention. (1)...A/D converter, (2)...MTI filter, (3)...shift register, (4)...shift register, (6)...correlation circuit, (7 )... Selection circuit, (8)... Shift register, (9)... Average circuit. In the figure on the right, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] (1) A/A converting the received video signal into a digital signal
A D converter, a plurality of shift registers that store signals in a predetermined range of the output of the A/D converter for each period of the transmission pulse, and a plurality of shift registers that store signals in a predetermined range of the output of the A/D converter for each period of the transmission pulse; A correlation circuit that determines the interference wave by correlating the received signals, an averaging circuit that averages the received signals in cycles before and after the output reception signal of a predetermined shift register among the plurality of shift registers, and the correlation circuit detects the interference wave. When the above predetermined shift register output is not determined,
A radar device comprising: a selection circuit that selects and outputs the output of the averaging circuit when an interference wave is determined; and a moving target indicating filter that removes a fixed target component from the output of the selection circuit.