JPS61164172A - Clutter elimination device - Google Patents

Abstract

PURPOSE:To improve the signal to noise ratio by not eliminating the Doppler frequency of an objective signal even when the Doppler frequency of objective signal is superposed on the part of clutter spectrum where power is larger. CONSTITUTION:Serially connect the plural number of delay elements 1 which correspond to the pulse repeating time is serially connected, and the load is multiplied to the output signal of delay elements 1 by multiplier 2, and add up its outputs by adder 3 to obtain a total. A load calculation means 5a inputs an output signal from each delay element 1 and a target Doppler frequency to identify an objective signal from outside as parameters, and calculates the value of load. The load calculation means 5a controls with conditions that the Doppler frequency shall not be eliminated even though it overlaps with the clutter spectrum where the electric power is larger. By this method, the power of other Doppler frequency is minimized, and the signal to noise ratio is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a signal for removing unnecessary signals other than reflected echoes from a target such as received clutter in a pulsed Dob 2 radar system. It relates to a processing device.

[Conventional technology]

Conventionally, as a signal processing device for removing unnecessary signals other than reflected echoes from a target such as received clutter,
For example, IEEE InternationalC
onference on acoustics,
5peech, and signalProces
Lecture number 47, 8, J, 5itterle et al. Applications of Lin in the Proceedings of the 1984 edition of
ear prediction Filtering
o Small Wavelength I) oppl
er weather radarSignal pr
What is known is what was disclosed by Ocessing J.K. FIG. 3 is a block diagram showing the configuration of a conventional clutter removal device. In the figure, u(0) is the input signal to the clutter removal device, and is a pulse Doppler signal (not shown).
The reflected echo received by the radar is
(in-phase), Q (quadrature)
e) Signal (complex signal) converted (PRT) T
There are four delay elements 1,
Each delay element 1 receives the input signal u(0) as ufil, ut
21, u+3ゝ, u'' (D 4 Converted to a horn input signal group. 2 is a multiplier for complex signals, 3 and 4 are adders for complex signals, and by the device consisting of each component as described above, Output signal 1 y based on the following complex operation
generate.

y=u(0)+v ”'u ”)+(B ”lu(1)+af21u
421 +,%31uf31 +a141u14) )
,,,1. , (1) Further, 5 is a load calculation means and an input signal group U.

Loads afil, , + applied to each multiplier 2 from uf2), ufat, u(41 and output signal y)
21, af31, , +41 are calculated.

The conventional clutter removal device is configured as described above, and eliminates strong frequency components in the Doppler frequency spectrum of the input signal u(0). In other words, focus on the certain range gate (0) fll
, , , , 14+ and the signal sequence ukt"k' l
uk corresponds to unwanted signals such as clutter and movement of the target signal in the range direction, and has a Doppler frequency proportional to their velocity = 3 - Contains signal elements 0 For example, in Figure 5, the input ■ of the signal C1 with a period of 4T and the signal C3 with a period of 3T in the signal
The waveforms of the components are shown. Also.

FIG. 6 shows an input signal sequence u(
The Doppler Φ spectra of 0), u(1ゝ,..., u(4) are shown. Generally, clutter has a signal component containing many frequency components, and its Doppler spectrum also has a 6th Rather than a line spectrum as shown in the figure.

In most cases, the distribution is over a band as shown in FIG. The distribution of such a Doppler spectrum for clutter can be considered approximately constant over multiple consecutive range bins. This is the source of clutter on the ground and sea surface.

This is because rain clouds, chaff, etc. are considered to have constant radio wave reflectance, moving speed, etc. over a wider range than the distance corresponding to the range bin. Now.

In order to efficiently eliminate the clutter distributed as shown in FIG. 7, the load calculation means 5 controls the power of the output signal y to be minimized.

In FIG. 1, which is a block diagram showing the configuration of the load calculation means in detail, 6 is a complex conjugate arithmetic unit, 7 is a complex multiplier, 8 is an amplifier, 9 is a complex adder, and IO is a delay element in the range direction. The delay time of the delay element 10 is assumed to be a time corresponding to one range bin (here, τ3). By using such load calculation means 5, each load H(1), 2(
21, a(81, a(4)) is calculated as follows.

a(A)+x JQ +uy sauce)*(i = 1.2.
3.4) --------(2, but the above (
In equation 2), μ is the amplification factor of the amplifier 8. With the weight calculated in this way, the power of the output signal y becomes a minimum value, which is .

On the Doppler frequency axis, the rack and
Spectrum 5c(z) (z == 6j”gfT)
This corresponds to applying a filter with reciprocal characteristic ξ/8c(Z) to generate an output signal y. For the clutter spectrum 5c (Zl, the reciprocal characteristic ξ/8c(Z)
The fill and the spectrum 8y(Z) of the output signal y are illustrated in FIG. Such a load calculation means 5 eliminates clutter having any Doppler e spectrum so that the output power is minimized. On the contrary,
If the target Doppler spectrum is not superimposed on the clusterer's Doppler spectrum, the target spectrum will appear in the output signal y without being cancelled. Further, the influence of the target signal on the loads a(1), . . . , ao) is small. This is because, as can be seen from the above equation (2), the load is calculated by integrating the input signal u(0) in the range direction, but since the target is only applied to the lunge gate at most, the target signal is This is because even if it is integrated, its value is smaller than that of clutter, and it has almost no effect on the load control in equation (2) above.

[Problem that the invention attempts to solve]

In the conventional clutter removal device as described above, when the Doppler frequency of the target signal is superimposed on the high power part of the clutter spectrum, the target signal is also canceled.
As a result, there was a problem in that the signal-to-noise ratio (Sc) did not improve.

This invention was made to solve this problem, and even if the Doppler frequency of the target signal is superimposed on the high-power part of the clutter spectrum, only the Doppler frequency component where the target signal exists is not erased. It is an object of the present invention to obtain a clutter removal device that can improve the signal-to-noise ratio by minimizing the power of other Doppler frequency components. In such a clutter removal device, the Doppler frequency that the target signal should have is input as a parameter, and the load calculation means calculates the Doppler frequency of the target signal even if the Doppler frequency of the target signal is superimposed on the high power part of the clutter spectrum. The control is performed by attaching constraint conditions so that deletion is not performed.

[Effect]

In the clutter removal device of the present invention, signal cancellation is not performed for the input signal of the Doppler frequency where the target signal is assumed to exist. Therefore, in this clutter removal device, the target signal is not attenuated and is output to the side. As a result, the probability of finding a target signal can be improved in the signal detector, tracking filter, etc. that follow the clutter removal device, and it is possible to realize target detection characteristics with higher accuracy.

〔Example〕

FIG. 1 is a block diagram showing the configuration of a clutter removing device which is an embodiment of the present invention, and each reference numeral 1 to 3 is the same as that of the conventional device. The apparatus shown in FIG.
The difference from the conventional device shown in the figure is that the input signal u(0
) is also multiplied by a complex weight and added by processing equivalent to other delayed signals for each pulse repetition time (PRT) T to create the output signal y. The load calculating means 5a calculates 1 based on the input signal group UΦ), ..., u(4) and the separately given constrained Doppler frequency 1°.
The complex loads a(o), a(1) are calculated as follows:
, ..., a(4) is generated.

However, +1 m ' is a five-dimensional vector and -g
k+1=[α, , , p) or 1. ..., α'F+
x) (T is a symbol representing transposition) I C= (1# e
j2""#e""" e e""'e38xfCT
). Further, Rk is an estimated value of the correlation matrix of the 5×5 input signal.

represents. The inverse matrix Rk of the matrix soul expressed by the above equation (4) can be calculated using the inverse matrix lemma as follows.

is a 5×5 unit matrix multiplied by an appropriate constant.

In the clutter removal device configured as described above, by using the load calculation means 5a, the Doppler frequency fc
Such an input signal u(:u.

[1,ej2ffCT...ej8ffcT) The required output signal U is preserved, and the input signals with other Doppler frequencies are controlled so that the sum of the output powers is minimized. In order to show that, the arbitrary value of the weight vector which is the output of the weight calculation means 5a is set to 1, and the correlation function matrix of the input signal vector η is expressed as follows.

R=E (conspiracy) ・・・・・・
(7) Now, let's find the output power at this time.

B(lyl”)=B(g un g)=g Pi(u
lu )g=gRc +□ ・・・・・・(8)ε*[1
c, and the load vector a is the next optimal load vector.

"1ε*T... .*R-"c °-°-(
9), this power is minimum. Also, regarding direct in this case.

αopt ' ” ' ・
...a[ holds true, so for an input signal ucc having a Doppler frequency fc, the output signal becomes uc and is not removed by this clutter removal device.

Now, as can be seen from the above equation (3), the load calculation means 5a calculates the optimum load vector of the above equation (9). 1. It gives an estimate of . Therefore, if the crack removal device according to the present invention is used, the Doppler spectral distribution will be constant and unchanged over a certain range, and the ratio of component sounds other than a specific Doppler frequency to radar echoes including racks will be reduced. can be increased. An example of the Doppler frequency spectrum of the input signal and the Doppler frequency transfer function of the clutter removal device of the present invention corresponding to the Doppler frequency spectrum are shown in FIG.

Note that in the above embodiment, four delay elements 1 corresponding to the pulse repetition time T are used, and an input signal group u(Oゝ, (1), . . . , u34ゝ) having a total of 5 taps is used. Although a case has been described above, in general, a similar device can be constructed by using any number of delay elements 1 of this type, and the effects can be expected to be accordingly.

Furthermore, the configuration shown in FIG.
30)=1, and the multiplier 2 at the 0th tap may be omitted. The structure of another embodiment of the present invention in such a case is shown in FIG. In the clutter removal device shown in FIG. 2, the load calculation means 5b calculates the load vector by
Tok, which is determined by the following formula.

is used to determine the load value. In this way, multiplier 2
Not only can one be omitted, but also the constrained Doppler frequency f. In the case of the above-mentioned conventional device in which . The device structures of the adders 3 and 4 are the same, and the same functions can be achieved simply by changing the method of the load calculation means 5b.

〔Effect of the invention〕

As described above, in the present invention, the Doppler frequency that the target signal should have is input as a parameter in the clutter removal device, and the load calculation means uses the Doppler frequency as a parameter.

Even if the Doppler frequency of the target signal is superimposed on a high-power part of the clutter spectrum, the Doppler frequency of the target signal is controlled with a constraint so that it will not be canceled, so the signal vs. clutter is always controlled. (noise) without compromising the ratio.

This provides an excellent effect in that clutter can be removed extremely effectively.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a clutter removal device that is an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a clutter removal device that is another embodiment of the invention, and FIG.
The figure is a block diagram showing the configuration of a conventional clutter removal device.
FIG. 4 is a block diagram showing in detail the configuration of the load calculation means in the clutter removal device shown in FIG. 3, and FIGS. A line spectrum diagram expressed in Doppler frequency components, FIG. 7 is a diagram showing the spectrum of arbitrary clutter, and FIGS. FIG. 3 is a diagram showing a frequency transfer function. In the figure, -1, 10... delay element, 2... multiplier. 3.4...Adder, 5, 5a, 5b...Load calculation means. 6... Complex conjugate operator, 7... Complex multiplier, 8...
- Amplifier, 9... is a complex adder. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A plurality of delay elements corresponding to the pulse repetition time are connected in series, and a plurality of multipliers that apply a load to each output signal from each delay element, and an addition that sums up the output signals from each multiplier. and load calculation means for inputting output signals from each of the delay elements and a target Doppler frequency for identifying an externally applied target signal as a value signal, and calculating a load value. Clutter removal device. (2) Instead of inputting the value signal of the target Doppler frequency, a signal obtained by sampling the signal having the target Doppler frequency by the number of delay elements at intervals of the pulse repetition time is input as a vector, and 2. The clutter removing device according to claim 1, wherein the clutter removing device is applied to a load calculation means.