JP2003227871A - Clutter suppression circuit for radar apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make image display performable, even a target continued long in a distance direction, so as to match with an actual target in a clutter suppression circuit for a radar apparatus in which a cell-averaging log CFAR processing operation is performed to a first received video signal to an n-th received video signal (V<SB>in</SB>=X<SB>1</SB>to X<SB>n</SB>) (where n represents an integer of 2 or more) in one transmission period of the radar apparatus. <P>SOLUTION: The clutter suppression circuit for the radar apparatus is provided with monotonously reducing threshold-value generation means (2, 3, 4) by which a first threshold value to an n-th threshold value with reference to the first received video signal to the n-th received video signal are monotonously reduced as distances used to obtain the first received video signal to the n-th received video signal are away; and a subtraction means (6) by which the first threshold value to the n-th threshold value generated by the monotonously reducing threshold-value generation means are subtracted from the first received video signal to the n-th received video signal so as to output a first subtracted- result signal to an n-th subtracted-result signal. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clutter suppression circuit for radar equipment.

[0002]

Conventionally, as the clutter suppressing circuit of the radar apparatus, the radar receives a video signal (hereinafter, simply referred to as the received video _signal) Cell-Averaging the _{V in}
LogCFAR (Constant False Al
Arm-Rate) Cell-Averag for processing
There is an ing Log CFAR circuit.

This Cell-Averaging Lo
The g CFAR circuit branches the received video signal that has passed through the logarithmic amplifier into a delay circuit and a low-pass filter, outputs the average value of the received video signal by this low-pass filter, and delays the received video signal through the delay circuit. This average value is subtracted from the video signal to eliminate the clutter average level. If the received video signal contains clutter, use the fact that the signal passing through the logarithmic amplifier generally has a constant amplitude from the average value, and subtract the average value as a threshold value from the received video signal. The clutter amplitude level is suppressed by.

Now, considering X _{1 to} X _n (n = 2, 3, ...) Time-series signals as received video signals in one transmission period of the radar, a certain k-th (k is time, that is, up to a reflection target) is considered. The threshold value T _k for the signal X _{k (} variable indicating distance) is

[Equation 1] It is represented by.

Therefore, the Cell for the _kth input X _k
-Output Y of Averaging Log CFAR circuit
_k is the _{Y k =} X k -T k.

That is, since the logarithmic amplifier keeps the variation of the output video signal constant regardless of the magnitude (average value) of the received video signal, the low frequency component is subtracted, so that the characteristic of the received video signal is obtained. Is known to exhibit excellent CFAR characteristics against weather clutter due to the Rayleigh distribution caused by rain and clouds and sea clutter due to sea surface reflection.

[0007]

[Problems to be Solved by the Invention]
In a clutter suppression circuit of a conventional radar device using an averaging log CFAR circuit, a low frequency component is subtracted from a long continuous target in the distance direction, such as a land image in an ocean radar image. When observing them, there is a problem that only the edge part of the image is displayed and the expression becomes unclear. That is, Cell-Averaging Log CFA
Since the R circuit acts as a high-pass filter, it is easy to detect small targets for which a sharp reflection signal is obtained, but for targets that are long and continuous in the distance direction, the image becomes an actual target due to the filter effect. It makes a big difference.

Further, as described above, when the amplitude characteristics of the clutter follow the Rayleigh distribution, excellent CFAR characteristics are exhibited, while when the characteristics deviate from the Rayleigh distribution, the fluctuation amount of the clutter is not constant and the CFAR characteristics are When the target is deteriorated and consequently the target is observed on the radar image display, the remaining clutter image remains to prevent the correct target detection.

The present invention has been made in order to solve these two problems, and Cell-Averagin
While having the excellent effect of the g Log CFAR circuit,
A radar device capable of displaying an image along an actual target even in a long continuous target in the distance direction, and capable of correcting the deterioration of the CFAR characteristic even when the amplitude characteristic of the clutter deviates from the Rayleigh distribution. The purpose of the present invention is to provide a clutter suppression circuit.

[0010]

According to a first aspect of the present invention, the first to nth (n is an integer of 2 or more) received video signals (V _in = X ₁ to) in one transmission period of the radar.
X _n ), for Cell-Averaging Lo
In a clutter suppression circuit of a radar device that performs g CFAR processing, the first to nth threshold values for the first to nth received video signals are obtained from the first to nth received video signals. A monotonically decreasing threshold value generating means (2, 3, 4) for monotonically decreasing as the distance is increased, and the monotonically decreasing threshold value from the first to nth received video signals. Means for subtracting the first to nth threshold values generated by the respective means, and outputting the first to nth subtraction result signals, the radar apparatus comprising: The clutter suppression circuit of is obtained.

According to a second aspect of the present invention, in the clutter suppression circuit of the radar device according to the first aspect described above, another threshold value (H _m ) from the first to n-th subtraction result signals. Another subtracting means (7) for performing subtraction and outputting another 1st to nth subtraction result signal, and how many signals among the 1st to nth subtraction result signals are different from the other subtraction means (7). Counting whether the threshold value is exceeded, and the first to nth
The counter means (8) for outputting the count result indicating the number N _m of signals of the subtraction result signals exceeding the another threshold value and the count result N _m are compared with a predetermined comparison value to obtain the optimum value. An optimum threshold value calculating means (9, 10) for calculating a threshold value and outputting the calculated threshold value to the different subtracting means as the different threshold value is further provided. A clutter suppression circuit for a radar device, which is characterized in that the output is the final output.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

Of the above-mentioned two problems, first, a means for solving the processing for a target that is long and continuous in the distance direction will be described.

According to the principle of the radar, the received video signal of the radar is attenuated as the distance thereof increases, even if the distance is long. This tendency is the same for sea clutter, and generally the reflection intensity of sea clutter is 3
It is known to be inversely proportional to the power.

Therefore, the present invention utilizes the fact that the reflection intensity of the sea clutter decreases according to the distance, and the conventional C
Threshold (average value of received video signal) T _k output from theell-Averaging Log CFAR circuit
However, processing is performed so that the distance decreases monotonically as the distance increases. _{'If k, T'} the threshold of making this process T _k is

[Equation 2] That is, the current threshold value T _k is the previous threshold value T ′ _k−1.
Is greater than, the previous threshold value T ′ is set as T ′ _k.
k-1 is output, and the current threshold value T _k is the previous threshold value T ′.
For _k-1 or less, and outputs the current threshold _{T k} as T _'k.

In this way, the threshold C is monotonically decreased.
A FAR circuit (hereinafter, referred to as a threshold monotonically decreasing CFAR circuit) is provided by a conventional Cell-Av.
At the threshold value output from the erasing Log CFAR circuit, it decreases monotonically as the distance increases until the reflection of the sea clutter disappears, but the strong reflection intensity of the land itself raises the average value of the signal from the moment it approaches the land. Therefore, it is possible to solve the problem that the threshold value is increased and only the edge portion of the image is displayed, resulting in an unclear expression.

Next, a means for solving the case where the amplitude characteristic of clutter deviates from the Rayleigh distribution will be described.

As described above, the clutter signal whose amplitude characteristic deviates from the Rayleigh distribution is detected by the conventional Cell-Averag.
When the signal is passed through the ing Log CFAR circuit, the fluctuation of the clutter is not constant, the CFAR characteristics are deteriorated, and the remaining clutter is increased (the false alarm probability is increased.) This is the Cell-Averaging Log CFAR.
It indicates that the threshold value output from the circuit is not high enough and the threshold value must be increased.

In the present invention, the threshold monotonically decreasing CFAR is used.
The output signal of the circuit is passed through the threshold subtraction circuit of another block,

[Equation 3] As shown in, the number of signals N _m (m = 1, 2, 3, ...) That has exceeded the threshold value and is output during a predetermined period (for example, one transmission cycle) is counted.

N _m is compared with a reference value for the upper limit R _t and the lower limit R _b , giving a threshold value H _m for each case. For example: Case 1: N _m > R _t H _m = H _m-1 + ΔH Case 2: R _t ≧ N _m ≧ R _b H _m = H _m-1 Case 3: N _m <R _b H _m = H _m-1 −ΔH (where ΔH is a threshold difference, and a constant ΔH ≧ 0) is performed every predetermined period. Thereby, it is possible to feed back an appropriate threshold value for this period based on the threshold value H _{m- 1} obtained in the previous period.

In this way, the output signal subjected to the threshold value subtraction processing is passed through the counter circuit to measure how many signals N _m are output in excess of the threshold value. By setting ΔH such that N _m converges, an appropriate threshold value H _m is obtained, and when the clutter amplitude characteristic deviates from the Rayleigh distribution, the CFAR characteristic deteriorates.
It is possible to solve the problem that the leftover clutter image hinders correct target detection.

According to the present invention, the threshold value that monotonically decreases as the distance increases is calculated. Therefore, in the range where sea clutter exists, the conventional Cell-Avera is used.
While inheriting the good clutter suppression characteristics of the ging Log CFAR circuit, the threshold is not raised for continuous signals with a large reception level such as land, and the signals are filtered to the actual signal. Can express images.

Further, regarding the sea clutter suppression characteristic,
Even when the amplitude characteristic deviates from the Rayleigh distribution, the signal exceeding the threshold value is directly counted, so that the remaining degree of the sea clutter signal can be grasped and an appropriate threshold value for the input signal is given. As a result, the degree of suppression of the sea clutter signal can be kept constant, so that it becomes easy to detect the target signal mixed in the sea clutter signal.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an outline of an embodiment of a clutter suppressing circuit of a radar device of the present invention, and FIG.
FIG. 3 is a waveform diagram showing waveforms at various parts of the circuit shown in FIG.

The clutter suppression circuit of FIG. 1 will be described with reference to FIG.

1 is a received video signal (V_in= X₁，
X_Two, X_Three,…) 2 is Cell-Averaging
Circuit, the received video signal X_kMoving average value T_kOut
Force 3 is the ratio for calculating the monotonically decreasing threshold
In the comparison circuit, the threshold value T ′ output from the delay circuit 4
_k-1And T_kAre compared in level, and the smaller value is T ′_kWhen
And output. To be more precise, as mentioned above,
Threshold T_kIs the previous threshold T ' _k-1If greater than
T '_kAs the previous threshold T ′_k-1And output this time
Threshold T_kIs the previous threshold T '_k-1In the following case, T '
_kAs the threshold T this time _kIs output. Received video signal
V_inPasses through the delay circuit 5 and reaches the threshold value T '._kAnd time
After being matched, the subtraction circuit 6 outputs V_in-T '_kof
Calculation is performed, and the result of this calculation is Y_kOutput as.

Next, the subtraction circuit 7, to the output from the subtraction circuit 6 _{Y k,} is further conducted subtraction threshold _{H m (Y} k -H _m) is the result Y _'k Output as. With respect to the output Y ′ _k of the subtraction circuit 7, the counter circuit 8 counts the output _satisfying Y ′ _k > 0 for each predetermined period as shown in the above equation (3), and counts the count N.
_m (m = 1, 2, 3, ...) Is output every predetermined period.

The comparison circuit 9 outputs the output N _{m of the} counter circuit 8.
Is compared with the upper limit R _t and the lower limit R _b of the comparison value, and the determination result is output. The threshold value generation circuit 10 sets the optimized threshold value H _m based on the determination result of the comparison circuit 9.

[Equation 4] It outputs in the form like. For example, when N _m > R _t , the threshold value acts to increase, and when N _m <R _b ,
On the contrary, the threshold value acts to decrease. 11 is the final output V
_out, which is a general term for the time-series signals Y ′ _k . Output V
_out for the incoming video signal _{V in} as a result, the input,

[Equation 5] The processing indicated by is performed.

[0030]

As described above, the clutter suppression circuit of the radar device according to the present invention has the conventional Cell-Averag.
Solving the problems caused by the ing Log CFAR circuit,
There is an effect that it is possible to display a video that matches the actual target even if the target is long in the distance direction, and to realize a circuit that can obtain an effective clutter suppression effect even if the amplitude characteristics of the clutter deviate from the Rayleigh distribution. .

[Brief description of drawings]

FIG. 1 is a block diagram of a clutter suppression circuit of a radar device of the present invention.

FIG. 2 is a waveform diagram showing each waveform of the clutter suppression circuit shown in FIG.

[Explanation of symbols]

2 Cell-Averaging circuit 3 comparison circuit 4 delay circuits 5 delay circuit 6 Subtraction circuit 7 Subtraction circuit 8 counter circuits 9 Comparison circuit 10 Threshold generation circuit

Claims (2)

[Claims] 1. The first to nth (n is an integer of 2 or more) received video signals (V _in = X) in one transmission period of the radar.
_{1- Xn} ), Cell-Averaging
In a clutter suppression circuit of a radar device that performs Log CFAR processing, the first to nth received video signals are obtained from the first to nth threshold values for the first to nth received video signals. The monotonically decreasing threshold value generating means (2,
3 and 4), and subtracting the first to nth threshold values generated by the monotonically decreasing threshold value generation means from the first to nth received video signals, respectively. A clutter suppressing circuit for a radar device, comprising: a subtracting means (6) for outputting an nth subtraction result signal. 2. The clutter suppression circuit of the radar device according to claim 1, wherein another threshold value (H _m ) is subtracted from the first to n-th subtraction result signals, and the first to n-th different ones are subtracted. Another subtraction means (7) for outputting the subtraction result signal of (1), and counting how many signals among the first to nth subtraction result signals exceed the another threshold value, Counter means (8) for outputting a count result indicating the number N _m of signals of the 1 to n-th subtraction result signals exceeding the another threshold value, and comparing the count result N _m with a predetermined comparison value. By further comprising: calculating an optimum threshold value, and outputting the calculated threshold value to the another subtraction means as the another threshold value, further comprising: The output of another subtraction means is the final output. Clutter suppression circuit of da apparatus.