JPH05249227A - Clutter signal suppression device for radar - Google Patents

Abstract

PURPOSE:To suppress an erroneous alarm probability for a clutter signal to be equal to or less than a certain value by converting an input signal to a normal distribution signal and then dividing the standard deviation value by a value which is obtained by subtracting an average value from a signal which is converted to the normal distribution signal. CONSTITUTION:A normal distribution signal Y where a radar signal Z is subjected to logarithmic conversion 1 is delayed 2 through N stages, an output signal of each delay tap is added 3 and then is divided 4 by the number of data N to obtain an average value signal (Y), and it is subtracted from the signal Y to obtain a denominator Y-muy. Then, square average values of the signal (Y) are calculated 6-9, the square values of the signal (Y) which is obtained by a square circuit 10 is subtracted 11 from the values to obtain a dispersion value of the signal Y and furthermore a square root of the dispersion value is obtained for calculating a standard deviation sigmay of the signal Y 12. Then, the standard deviation sigmay is divided by the denominator Y-muy 13 to obtain a standard normal distribution signal V with a constant error alarm provability (CFAR) and to output it after inverse logarithmic conversion, thus obtaining the CFAR signal from a radar signal which follows the lognormal distribution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clutter signal suppressing device for radar which suppresses clutter signals mixed in radar signals as unnecessary signals from the sea surface, drizzle, ground and the like.

[0002]

2. Description of the Related Art A radar, as the name implies, is a radio device for emitting a radio wave and knowing the existence of a target and the distance to the target from the reflected wave. Radar uses the characteristics of radio waves to work that the human eye cannot function: darkness, clouds,
It is an indispensable device for detecting a target object through fog and rain and for accurately measuring the position of the target object, so that ships and aircraft can navigate safely.

Such radar signals include necessary signals from targets such as ships and aircraft called targets,
Clutter is mixed with unnecessary signals from the sea surface, rain, clouds, ground, etc. The purpose of radar signal processing is to suppress clutter as low as possible and detect the target. Further, the false alarm probability indicating the probability that clutter is erroneously determined as a target is suppressed to a certain value or less, and a constant false alarm probability CFAR (Constant False A
The process of obtaining the larm rate) is very important.

A Log-CFA shown in FIG. 2 is used as a signal processing method for suppressing clutter signals in a conventional radar device.
The R processing method is known. In FIG. 2, reference numeral 200 is a logarithmic amplifier, which performs logarithmic conversion of the input signal X. Reference numeral 201 denotes a delay circuit, which converts the logarithmically converted radar video signal into N
Delay by a step. Reference numeral 202 denotes an adder circuit, which is a delay circuit 2
The total sum of the individual output signals output from the delay taps of N stages of 01 is calculated. Reference numeral 203 denotes an average value calculation circuit, which calculates the average value signal by 1 / N the sum signal from the addition circuit 202. Reference numeral 204 denotes a subtraction circuit, which calculates the log-CFAR output signal W by subtracting the average value signal by the average value 203 from the radar video signal that has passed through the delay circuit 201.

In the Log-CFAR processing, when the radar video signal follows the Lilly distribution signal shown in equation (1), the probability density function of the output signal does not depend on b of the Lilly distribution signal as shown in equation (2). Become a signal. (2)
In the equation, γ is the Euler constant.

[0006]

[Equation 1]

Considering the probability when the Log-CFAR output signal of the clutter signal is above a certain threshold value T as the false alarm probability, the value of the false alarm probability is obtained by integrating equation (2) from T to infinity. Be done. As a result of this calculation, the false alarm probability becomes the formula (3) and becomes a constant value regardless of the variance value b of the Lerry distribution signal, and the Log-CFAR output signal is CA.
It means that it is FR.

[0008]

[Equation 2]

[0009]

However, in the radar signal, not only the clutter signal follows the Lilly distribution, but especially the sea surface reflection signal is a log normal distribution (L
It is also well known that it follows an og-Normal distribution). Thus, even if the Log-CFAR processing of FIG. 2 is applied to the clutter signal according to the lognormal distribution, the output signal is not converted to CFAR, and the clutter signal remains unerased. There is a problem that it becomes difficult to detect.

The present invention has been made in view of such conventional problems, and a false alarm probability is set for a clutter signal due to a log-normal distribution, which has been difficult to achieve CFAR by the conventional log-CFAR processing. An object of the present invention is to provide a clutter signal suppression device for radar that can be made constant and converted to CFAR.

[0011]

In order to achieve this object, in a radar clutter signal suppressing apparatus of the present invention, a logarithmic amplification means for inputting a radar signal and performing logarithmic conversion, and the logarithmic conversion. The average value calculating means for inputting a signal and calculating the average value thereof, the standard deviation calculating means for calculating the standard deviation value of the radar signal, and the average value obtained from the radar signal by the average value calculating means It is characterized by further comprising subtraction means and division means for obtaining an output signal by dividing the standard deviation value obtained by the standard deviation calculation means by the output signal of the subtraction means.

[0012]

According to the radar clutter signal suppressing device of the present invention having such a configuration, the radar signal according to the lognormal distribution is logarithmically converted into a normal distribution signal,
The average value and standard deviation value are calculated, and the standard deviation value is converted into a signal that does not depend on the parameters of the input radar signal by dividing the average value from the signal converted to a normal distribution signal by the subtraction value. , Conventional Log-CFAR
A CFAR-converted signal can be obtained from a radar signal that follows a log-normal distribution that cannot be obtained by processing.

[0013]

First, the principle of the present invention will be described. When the input signal Z according to the lognormal distribution is passed through the logarithmic amplifier, the output signal Y is converted into the normal distribution represented by the equation (4). Here, μy represents the average value of Y, and the square of σy represents the variance value. When the processing of the equation (5) is performed on the Y signal, the probability density function of the output signal V has a constant distribution shown by the equation (6). That is, V is a CFA with a constant false alarm probability.
An R output will be obtained.

[0014]

[Equation 3]

Here, the threshold value T which determines the false alarm probability value can be easily determined by using a standard normal distribution table. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, 1 is a logarithmic amplifier, 2 is a first delay circuit that delays the logarithmically converted signal Y by N stages, and 3 is output from each delay tap of N stages of the first delay circuit 2. Is a first adder circuit for calculating the sum of the individual output signals. 4 is the summation signal from the first adder circuit 1 / N
And a first average value calculation circuit for calculating the average value signal Y. 5 is the first from the signal Y logarithmically converted by the logarithmic amplifier 1.
2 is a first subtraction circuit for subtracting the average value signal <Y> obtained by the average value calculation circuit 4.

Reference numeral 6 is a first squaring circuit for obtaining a squared value of the signal Y logarithmically converted by the logarithmic amplifier 1, and 7 is a squared signal from the first squaring circuit 6 for N stages. Numeral 8 is a second delay circuit for delaying, 8 is a second adder circuit for calculating the sum of the individual squared output signals output from the delay taps of N stages of the second delay circuit 7, and 9 Is a second average value calculation circuit for obtaining the root mean square value signal by 1 / N the output signal from the second addition circuit 8.

Reference numeral 10 is a second square circuit for calculating the square value of the average value signal <Y> output from the first average value calculation circuit 4, and 11 is the square of the second square circuit 10. A second subtraction circuit for calculating a variance value by subtracting the average value from the average value of the second average value operation circuit 9, and 12 is a standard by taking the square root of the variance value from the second subtraction circuit 11. This is a square calculation circuit for obtaining a deviation value σy. 13 is a square root calculation circuit 12
From the output signal of the first subtraction circuit 5 (Y
-Μy) is a division circuit for obtaining the CFAR output signal V by division, and 14 in the final stage is an inverse logarithmic conversion circuit that inversely logarithmically transforms the CFAR output signal V to transform the dynamic range in the same manner as the input signal. is there.

In operation, the radar signal Z according to the lognormal distribution signal is converted into the normal distribution signal Y by the logarithmic amplifier 1. The normal distribution signal Y is delayed by N stages by the first delay circuit 2 and the sum of the output signals of the delay taps is obtained by the first adder circuit 3. Further, the average value signal <Y> is calculated by dividing the number of data N by the first average value calculation circuit 4. The first delay circuit 2, the first addition circuit 3 and the first average value calculation circuit 4 constitute the average value calculation means according to claim 1.

By subtracting the average value signal <Y> obtained by the first average value calculation circuit 4 from the normal distribution signal Y by the first subtraction circuit 5, the denominator (Y-
μy) is realized. Next, the calculation of the standard deviation σy will be described. Generally, the standard deviation of a signal is defined as the square root of the variance. The variance value can be calculated by subtracting the square of the average value from the average value of the square values of the signal.

That is, the square value of the normal distribution signal Y is obtained by the first square circuit 6, and the square signal is calculated by the second delay circuit 7, the second adder circuit 8 and the second average value calculation circuit 9. The root mean square value of the signal Y is calculated. Second
The square value of the average value signal <Y> calculated by the first average value calculation circuit 4 is calculated by the square circuit 10 of FIG.
By subtracting the signal obtained by squaring the mean value <Y> from the square mean value by 1, the variance value of the normal distribution signal Y can be obtained. Further, the standard deviation σy of the signal Y can be calculated by taking the square root of the variance value by the square root calculation circuit 12.

The first delay circuit 2, the first adder circuit 3, the first averaging circuit 4, the first squaring circuit 6, and the second delay circuit necessary for calculating these standard deviations σy. 7,
The second adder circuit 8, the second average value calculation circuit 9, the second 2
Power circuit 10, second subtraction circuit and square root operation circuit 12
Constitutes the standard deviation computing means according to claim 1. Finally, the division circuit 13 performs the operation of the equation (5), and CF
The AR-normalized standard normal distribution signal V is calculated and output via the inverse logarithmic conversion circuit 14.

[0022]

As described above, according to the present invention,
The radar signal that follows the lognormal distribution is logarithmically converted into a normal distribution signal, then the average value and standard deviation value are calculated, and this standard deviation value is subtracted from the signal converted into the normal distribution signal. It is possible to obtain a CFAR-converted signal from a radar signal according to a lognormal distribution, which is not obtained by the conventional Log-CFAR processing, by converting the signal into a signal that does not depend on the parameter of the input radar signal by dividing by a value. it can.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing the configuration of an apparatus that performs conventional Log-CFAR processing.

[Explanation of symbols]

 1: Logarithmic amplifier 2: 1st delay circuit 3: 1st addition circuit 4: 1st average calculation circuit 5: 1st subtraction circuit 6: 1st square circuit 7: 2nd delay circuit 8 : Second addition circuit 9: Second average value calculation circuit 10: Second square circuit 11: Second subtraction circuit 12: Square root calculation circuit 12 13: Division circuit 14: Inverse logarithmic conversion circuit

Claims (1)

[Claims] 1. A logarithmic amplifying means for inputting a radar signal and performing logarithmic conversion, an average value calculating means for inputting the logarithmically converted signal and calculating an average value thereof, and a standard of the radar signal. Standard deviation calculation means for calculating a deviation value, subtraction means for subtracting the average value obtained by the average value calculation means from the radar signal, and standard deviation value obtained by the standard deviation calculation means for the subtraction means And a dividing means for obtaining an output signal by dividing the clutter signal suppressing device for a radar.