JPH095424A - Clutter suppression circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] Even if the clutter signal dispersion is not constant with respect to time (distance), cell averaging L
It is possible to prevent the clutter signal from disappearing or the target signal from disappearing after the OG / CFAR processing. An input signal X obtained by a radar device is supplied to a cell averaging circuit 10 and an average deviation calculating circuit 20. The cell average calculated by the cell averaging circuit 10 is supplied to the average deviation calculating circuit 20,
The average deviation of the clutter signal for a predetermined period before and after is calculated. After the processing delay is compensated by the delay circuit 21, the average deviation is added to the cell average by the addition circuit 22 to determine the threshold value. After the processing delay is compensated by the delay circuit 11, the threshold value is subtracted from the input signal X from the radar device by the subtraction circuit 13, amplified by the amplification circuit 14, and then supplied as the output signal Y to the subsequent stage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clutter suppressing circuit for suppressing clutter signals contained in radar signals.

[0002]

2. Description of the Related Art Received signals from radar devices (radar signals)
Usually includes a reflection signal from a target (target signal) and a reflection signal from another object (clutter signal). For example, in the case of a radar device for ships, the required target signal is a reflection signal from another ship, etc., but actually the sea surface reflection signal (sea clutter), rain cloud reflection signal (weather clutter), etc. are included in the radar signal. Be done. If these clutter signals are kept, problems such as usability will occur when it is difficult to capture a target image when displaying based on radar signals. Therefore, various clutter suppression methods have been conventionally developed.

As one of the methods, a method called cell averaging LOG / CFAR (Constant False Alarm Rate) is known. This method focuses on the fact that the clutter signal in the logarithmically amplified radar signal generally has a certain variance with respect to the average value of the radar signal. That is, normally, as shown in FIG. 1 (a), the clutter signal dispersion is constant regardless of time or distance. Therefore, the radar signal shown in FIG. 1 (a) is multiplied by a constant value of the average value of the radar signal. By reducing the value of
The clutter signal can be removed as shown in (b).

FIG. 2 shows the configuration of a clutter suppression circuit using this method. The clutter suppression circuit in this figure is a cell averaging (signal average value calculation) circuit 1
0, a delay circuit 11, a multiplication circuit 12, a subtraction circuit 13 and an amplification circuit 14.

The cell averaging circuit 10 inputs a logarithmically amplified radar signal as an input signal X, and a time series of the input signal X { _Xk : k = ... -n, -n + 1, ...- 1 ,,
The moving average is calculated by the equation (2) based on 0, +1, ... N-1, n, ...}, and the average value A _k of the radar signal level at the time k is _obtained . However, N is the number of data of the input signal X to be averaged.

[0006]

[Equation 2] If the average value A _k is directly used as the threshold value of the input signal X _k , the variance of the clutter signal included in A _k cannot be removed. Therefore, A _k obtained by the cell averaging circuit 10 is multiplied by a constant in the multiplication circuit 12 by the calculation of C × A _k as shown in Expression (3), and the level is increased by the amount of the clutter signal dispersion. It is a threshold value T _k things. Note that C is a fixed constant that does not depend on time k.

[0007]

(Equation 3) In addition to the threshold value T, the subtraction circuit 13 includes a delay circuit 1
The input signal X delayed by 1 is also input. The delay circuit 11 includes a cell averaging circuit 10 and a multiplying circuit 12.
Is a circuit for compensating the processing delay due to the delay time in the delay circuit 11 and the threshold value T input to the subtraction circuit 13 and the input signal X at the same time value (T _k , X _k ).
Becomes The subtraction circuit 13 calculates X _k −T _k and supplies the result to the amplification circuit 14 as an output signal Y _k at time k. The amplifier circuit 14 outputs the amplified output signal Y.

[0008]

However, when clutter suppression is attempted by such a method, in a situation where the variance from the average value of the clutter signal is not constant as shown in FIG. 3A, an appropriate threshold value is set. Can't get
That is, since the fixed constant C is multiplied by A _k in the calculation according to the equation (3), the threshold level is insufficient and the clutter signal disappears in the range in which the clutter signal varies greatly as shown in FIG. In the remaining range, or in the range where the fluctuation of the clutter signal is small, the threshold value becomes unnecessarily large, and the level of the target signal is further lowered, which makes it difficult to detect the target signal.

The present invention has been made to solve the above problems, and detects the degree of fluctuation of the clutter signal and calculates a threshold value in consideration of the fluctuation to detect the clutter signal. The objective is to suppress it optimally and to detect the target signal well.

[0010]

In order to achieve such an object, the clutter suppression circuit of the present invention uses a time k (k:
Radar signal X at times k-i to k-1 and k + 1 to k + i (i: natural number) belonging to a predetermined range before and after (integer)
A cell averaging means for obtaining a cell average A _k at time k by averaging the levels of _{ki to} X _k−1 and X _{k + 1 to} X _{k + i} , and k−i to k−1 and k + 1.
A means for obtaining an average deviation D _k for estimating an average variation of the clutter signal around time k using the radar signal and the cell average A _k at ~ k + i is provided, and the threshold value T _k is _obtained by the equation (1). Characterize.

[0011]

(Equation 4)

[0012]

According to the present invention, the level of the radar signal in the predetermined range before and after the time k is averaged by the cell averaging means, whereby the cell average A at the time k is obtained.
_k is obtained. Further, in the present invention, the average deviation D _k is obtained by the calculation shown in the equation (5), for example. That is, the cell average is subtracted from the radar signal at each time within the predetermined range, the absolute values thereof are added for the predetermined range, and this is divided by the number of data to obtain the average deviation D _k . This makes it possible to grasp at what level the input signal fluctuates on the basis of the cell average A _k . That is, it is possible to estimate the fluctuation degree of a signal whose level randomly changes, such as a clutter signal. By using the cell average A _k and the average deviation D _k , an appropriate threshold value T _k according to the fluctuation of the clutter signal can be obtained. Therefore, the threshold value T _k can be calculated from the radar signal X _{k at the} time k. By reducing it, the clutter signal can be removed well.

[0013]

(Equation 5)

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. The same components as those of the conventional example shown in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 4 shows a clutter suppressing circuit showing an embodiment of the present invention. The circuit shown in this figure is
The multiplication circuit 12 of the circuit shown in FIG. 2 is replaced with an addition circuit 22, and an average deviation calculation circuit 20 and a delay circuit 21 are further added.

The average deviation calculating circuit 20 first subtracts the average value (cell average) A _k of the input signal obtained by the cell averaging circuit 10 from the input signal X _k , as shown in equation (5). doing, a deviation (absolute value of the difference between X _k and a _k) from the a _k of the input signal X _k at time k. Next, this deviation is added in a predetermined range and averaged to calculate an average deviation D _k of the input signal X from the cell average A. Therefore, this D _k has a larger value as the fluctuation of the input signal X in the predetermined range is larger, and has a smaller value as the fluctuation of the input signal X is smaller.

The delay circuit 21 is a circuit for compensating the processing delay by the average deviation calculating circuit 20, and the delay circuit 2
Due to the delay at 1, the average deviation D and the cell average A input to the adder circuit 22 have the same value (D _k , A _k ) at the time k.

The adder circuit 22 calculates A _k + D _k , and the result is the threshold value T for the input signal X _k at time k.
_It is supplied to the subtraction circuit 13 as _k . The subtraction circuit 13 removes the clutter signal by subtracting the threshold value T from the input signal X supplied via the delay circuit 11.

Therefore, according to this embodiment, since the appropriate threshold value T can be obtained according to the fluctuation of the input signal X, it is possible to prevent the clutter signal from remaining unerased and the input signal from being suppressed more than necessary. , Enables good target detection.

[0020]

As described above, according to the present invention,
By determining the threshold value using the deviation, an appropriate threshold value can be obtained according to the fluctuation of the radar signal, so that the clutter signal does not have a certain variance with respect to the average value of the radar signal. However, the clutter signal can be suppressed well and the target signal can be detected.

[Brief description of drawings]

FIG. 1 is a diagram showing the contents of cell averaging LOG / OFAR, in particular, (a) shows a radar signal before subtraction,
(B) is a figure which shows the signal after a subtraction.

FIG. 2 is a block diagram showing a configuration of a clutter suppression circuit according to a conventional example.

FIG. 3 is a diagram showing a problem of cell averaging LOG / CFAR, showing an influence when a variance from an average value of a radar signal is not constant, and particularly, (a) shows a radar signal before subtraction. , (B) are diagrams showing signals after subtraction.

FIG. 4 is a block diagram showing a configuration of a clutter suppression circuit according to an embodiment of the present invention.

[Description of Reference Signs] 10 cell averaging circuit, 11, 21 delay circuit, 13 subtracting circuit, 14 amplifying circuit, 20 average deviation calculating circuit, 22 adding circuit.

Claims (1)

[Claims] 1. Radar signals X _{ki to} X _k-1 and X _{k + at} times k-i to k-1 and k + 1 to k + i (i: natural number) belonging to a predetermined range before and after time k (k: an integer). ₁ ~
A cell averaging means for averaging the level of the X k _{+ i,} means for determining the threshold value T _k at time k based on cell average A _k obtained by averaging, the time threshold T _k k and means for removing the clutter signals from the radar signal X _k by subtracting from the radar signal X _k, the clutter suppressing circuit comprising, by using the radar signals and cell average in k-i to k-1 and k + 1 to k + i time A clutter suppression circuit comprising means for obtaining an average deviation D _k of the clutter signal before and after _k, and obtaining a threshold value T _k by equation (1). [Equation 1]