JP2003279642A - Device and method for restraining clutter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that a computing load gets remarkably larger when real-time processing is carried out in the prior art. <P>SOLUTION: This device is provided with a clutter center-frequency estimating means 1 for estimating the center frequency of a clutter, a filter coefficient calculating means for calculating a filter coefficient for an estimated value estimated therein by cascade-connecting the two filters to form the zero point of a frequency characteristic of the whole filter, a multiple zero point processing means 4 for calculating a filter coefficient to form the multiple zero point when the estimated value is same to a clutter center-frequency estimation value transmitted to the filter coefficient calculating means, a filter means 3a for restraining the clutter in a received signal using the filter coefficient from the filter coefficient calculating means, and a filter means 3b for restraining the clutter in the received signal using the filter coefficient transmitted from the multiple zero point processing means. The computation volume concerned in the filter coefficient calculation can be reduced to a half or less, while securing clutter restraining performance. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clutter suppressing device and a clutter suppressing method using a filter, for example, eliminating unnecessary reflection echo such as clutter other than a target signal in a signal received by a radar. The present invention relates to a clutter suppressing device and a clutter suppressing method.

[0002]

2. Description of the Related Art When a moving target (such as an aircraft) is detected by a radar, a fixed target is often included at the same distance in the same beam depending on the shape of the antenna and the position of the target. . In such cases, the reflected wave from the fixed target may be much larger than the reflected wave from the moving target. Therefore, it is difficult to distinguish the moving target and the fixed target only from the intensity of the reflected wave. Therefore, it is possible to extract only the reflected wave of the moving target by using the Doppler effect without impairing the function of the pulse radar.

Such a method is used for moving target instruction processing (Mo
ving Target Indication; MT
I). That is, when the transmission pulse from the radar transmitter is reflected from the moving target, the frequency of the reflected wave changes due to the Doppler effect, but the reflected wave from the fixed target does not undergo frequency shift. Therefore, it is possible to detect only the moving target by detecting only the frequency shift or the phase shift corresponding thereto due to the Doppler effect, or by detecting the amplitude change accompanying it. In order to realize this, after converting the received signal into an intermediate frequency signal, the intermediate frequency signal is phase-detected by the reference signal from the reference signal generator to generate a video signal. Further, the difference between the signal obtained by delaying this video signal by one cycle and the video signal generated from the next received signal is calculated. This makes it possible to cancel a fixed target such as clutter.

As described above, in the MTI process, only the moving target can be extracted from the state in which the fixed target and the moving target are mixed by taking the difference between the video signal and the video signal one cycle before. However, when the Doppler frequency is an integral multiple of the pulse repetition frequency, there is a problem that a so-called blind speed in which the speed response becomes zero occurs, and it becomes impossible to detect the target of the speed. Therefore, in the MTI processing, a stagger trigger method is used in which irregularly spaced pulses are periodically transmitted in order to narrow the blind velocity region. This is to prevent the blind speed condition from always being satisfied by continuously switching two or more types of pulse repetition periods.

Conventionally, as a clutter suppressing device for removing clutter received by a pulse radar using the stagger trigger method, the Institute of Electronics, Information and Communication Engineers, IEICE Technical Report SAN
E99-115, pp. 57-62 (February 2000)
Sekiguchi et al., "Suppressing bimodal clutter by a single filter having zeros at two frequencies in a stagger trigger system" is known.

Generally, the received signal of the radar includes a range bin indicating a radio wave propagation distance corresponding to one sampling time when a received signal at a pulse repetition interval is sampled at a predetermined time considerably shorter than the interval, and a transmission signal. It is treated as two-dimensional data of a pulse hit indicating a pulse received with respect to a pulse, but here, unless otherwise specified, an arbitrary one range bin or a process of multiple range bin units performing the same process will be described. To do.

A conventional clutter suppression device will be described with reference to the drawings. FIG. 15 is a block diagram showing the configuration of a conventional clutter suppression device.

In FIG. 15, 1 is a clutter center frequency estimating means for estimating the clutter center frequency in the received signal from the received signal, 2 is a filter coefficient calculating means for calculating a filter coefficient, and 3 is a filter from the filter coefficient calculating means 2. It is a filter means that performs clutter suppression processing using a coefficient.

Next, the operation of the conventional clutter suppressing device will be described with reference to the drawings.

For example, as a method of estimating the number of clutters to be received in a radar such as a search radar that has a small number of pulse hits for performing frequency analysis by discrete Fourier transform or the like, AR (Auto Regressive) described below is used.
A method using the coefficient a _ij of the model can be considered, but here it is assumed that the clutter number is known.

First, the clutter center frequency estimating means 1 estimates the center frequency of the clutter from the received signal.
The clutter center frequency can be estimated by performing frequency analysis using discrete Fourier transform or the like and performing peak detection processing, if a sufficient pulse hit number can be secured.
However, in a radar in which the pulse repetition frequency is not high such that the staggered trigger method needs to be used, it is not possible to secure the number of pulse hits enough to perform a sufficient frequency analysis by the discrete Fourier transform.

Therefore, in the conventional clutter suppressing apparatus, the clutter center frequency is estimated by using the maximum entropy method that is effective when performing spectrum estimation even with a small number of data. For this maximum entropy method,
"S. Haykin," Nonlinear Methods of Spectral Analysi
s ", Springer-Verlag (1983)". For single-peak clutter with one clutter spectrum peak,
It can be approximated by a first-order AR model, and the coefficients of this AR model are
If it is a ₁₁ , the clutter center frequency f ₀ (value normalized by the pulse repetition frequency) can be estimated by the equation (1) by calculating the first-order pole.

[0013]

[Equation 1]

In the case of a bimodal clutter with two clutter spectrum peaks, it can be approximated by a second-order AR model, the coefficient of this AR model is a ₁₁ , the zero-order forward prediction error is e ₀ (n),
The 0th backward prediction error is b ₀ (n) and the ith forward prediction error is e
_{If i} (n) and the i-th backward prediction error are b _i (n), the clutter center frequencies f ₀₁ and f ₀₂ can be estimated by Expression (3) by calculating the second-order pole.

[0015]

[Equation 2]

Next, the clutter center frequency estimated by the above equation is sent to the filter coefficient calculation means 2.
In the filter coefficient calculation means 2, the filter coefficient changes with time so that a deep notch of the filter can be formed even in the case of the stagger trigger method. That is, the filter coefficient changes every pulse interval. The filter is a FIR (Finite Impulse Re).
The impulse response corresponds to the filter coefficient.

Since the case where the clutter is bimodal is included in the case where it is bimodal, it is assumed here that the clutter is bimodal having two spectral peaks. The amplitude square characteristic of the stagger trigger method is defined as the following equation.

[0018]

[Equation 3]

Where N is the impulse response length of the filter, h _ln is the impulse response of the filter, L is the number of staggers,
τ _i (i = 1,2, ..., L) is the pulse interval.

Time δT is defined as in the following equation, and the delay operator z ⁻¹ is an element that gives a delay of δT. At this time, the transfer function C _l (z) is expressed as in Expression (12).

[0021]

[Equation 4]

Two estimated clutter center frequencies f ₀₁ , f
_{In 02} , it is assumed that the coefficients of a filter having k ₁ double zeros and k ₂ double zeros are generated. With l fixed, C _l (z),
And its first to (k ₁ -1) derivative with respect to z so that it becomes 0 when z ₁ = exp [j2πf ₀₁ δT].

[0023]

[Equation 5]

For C _l (z) and its first-order (k ₂ -1) derivative with respect to z, it is set to 0 when z ₂ = exp [j2πf ₀₂ δT].

[0025]

[Equation 6]

From the above, k ₁ + k ₂ = (N-1) equations are formed. There is one less equation for the coefficient, but h ₁₀ can be set arbitrarily. Solving the (N-1) -element system of simultaneous equations created in this way gives the filter coefficient for a specific l. By repeatedly executing this for l = 0, 1, ..., L-1, all filter coefficients can be obtained.

The filter coefficient h _ln generated by the filter coefficient calculation means 2 is sent to the filter means 3. The filter means 3 performs the convolution operation shown in the following equation, and the output signal y (t _k ) suppresses clutter in the received signal x (t _k ).

[0028]

[Equation 7]

In the above description, the case of the bimodal clutter has been shown. However, in the case of the unimodal clutter, the condition regarding the derivative of C _l (z) may be considered only in, for example, the equation (13).

[0030]

In the conventional clutter suppressing device in the radar using the stagger trigger method, the coefficient of the clutter suppressing filter becomes a time-varying coefficient, and the filter coefficient is formed so as to form the notch of the filter with respect to the estimated center frequency of the clutter. In order to adjust the value, it is necessary to solve the "filter impulse response length N-1" original linear simultaneous equations several times for each clutter suppression process, and the calculation load becomes significantly large when performing the real-time processing. , There was a problem.

The present invention has been made in order to solve the above-mentioned problems. By dividing the clutter suppression filter into a plurality of filters and connecting them in cascade, the number of filters increases but the impulse response length of each filter increases. Therefore, the number of simultaneous equations that had to be solved for each clutter suppression process to calculate the filter coefficient is reduced, and a clutter suppression device and a clutter suppression method that can reduce the calculation load are provided. And

[0032]

According to a first aspect of the present invention, there is provided a clutter suppression device for a clutter center frequency estimating means for estimating a center frequency of clutter, and an estimated value sent from the clutter center frequency estimating means. A filter coefficient calculating means for calculating filter coefficients so that two filters are cascaded to form a zero point of the frequency characteristic of the entire filter; and an estimated value sent from the clutter center frequency estimating means is the filter coefficient calculating means. If it is the same as the clutter center frequency estimation value sent to the multi-zero point, the multi-zero point processing means for calculating the filter coefficient so as to form the multi-zero point, and the filter sent from the filter coefficient calculation means for each different pulse interval by the stagger trigger method. First filter means for suppressing clutter in the received signal using a coefficient, It is obtained by a second filter means for suppressing clutter in the received signal using the filter coefficient sent from point processing unit.

In the clutter suppressing apparatus according to claim 2 of the present invention, whether the multiple zero point processing means matches the zero point frequency set by the filter coefficient calculating means with the estimated value sent from the clutter center frequency estimating means. Zero-point frequency determining means for determining whether or not, switching means for switching the processing path according to the determination result of the zero-point frequency determining means,
The present invention has a filter coefficient calculating means for multiple zeros, which allows two filters to form multiple zeros at the same frequency, and a filter coefficient calculating means for calculating filter coefficients having different zero point frequencies of the two filters.

A clutter suppressing device according to a third aspect of the present invention comprises a clutter center frequency estimating means for estimating the center frequency of the clutter, and two filter coefficients cascade-connected so as to form a notch for a specific frequency. Is calculated in advance, filter coefficient selection means for selecting from the filter coefficient storage means a filter coefficient corresponding to a frequency closest to the estimated value sent from the clutter center frequency estimation means, and the selected And a second filter means for suppressing clutter in the received signal by using the selected filter coefficient, and a second filter means for suppressing clutter in the received signal by using the selected filter coefficient. .

A clutter suppressing apparatus according to a fourth aspect of the present invention comprises a clutter center frequency estimating means for estimating the center frequency of the clutter, and at least three filters for the estimated value sent from the clutter center frequency estimating means. The filter coefficient calculation means for calculating filter coefficients so as to form a zero point of the frequency characteristic of the entire filter by cascade connection, and the estimated value sent from the clutter center frequency estimation means are sent to the filter coefficient calculation means before that. If it is the same as the estimated clutter center frequency, the first multiple zero processing means for calculating the filter coefficient so that multiple zeros can be formed, and the estimated value sent from the clutter center frequency estimation means Multiple zeros can be formed if they are the same as the clutter center frequency estimation values sent to the filter coefficient calculation means Second multiple zero point processing means for calculating the filter coefficient, and first filter means for suppressing clutter in the received signal using the filter coefficient sent from the filter coefficient calculation means for each different pulse interval by the stagger trigger method , A second filter means for suppressing clutter in the received signal using the filter coefficient sent from the first multiple zero processing means, and a received signal using the filter coefficient sent from the second multiple zero processing means And third filter means for suppressing the clutter inside.

A clutter suppressing apparatus according to a fifth aspect of the present invention is a clutter center frequency estimating means for estimating a center frequency of clutter, and at least three filters cascaded so as to form a notch for a specific frequency. Filter coefficient storage means for calculating coefficients in advance, and filter coefficient selection means for selecting from the filter coefficient storage means the filter coefficient corresponding to the closest frequency for each of the plurality of estimated values sent from the clutter center frequency estimation means. A first filter means for suppressing clutter in the received signal by using the filter coefficient sent from the filter coefficient calculating means; and a clutter in the received signal by using the filter coefficient sent by the filter coefficient calculating means. And second filter means for transmitting from the filter coefficient calculation means That is the filter coefficient using that a third filter means for suppressing clutter in the received signal.

According to a sixth aspect of the present invention, in the clutter center frequency estimating step of estimating the center frequency of the clutter, and the estimated value of the clutter center frequency, two filters are connected in series for the entire filter. If a filter coefficient calculation step of calculating a filter coefficient so as to form a zero point of the frequency characteristic of, and the clutter center frequency estimation value is the same as the clutter center frequency estimation value in the filter coefficient calculation step, multiple zero points A multiple zero point processing step for calculating a filter coefficient so that the filter coefficient can be formed, and a first filter step for suppressing clutter in the received signal by using the filter coefficient from the filter coefficient calculation step for each different pulse interval depending on the stagger trigger method, , Using the filter coefficients from the multi-zero processing step It is intended to include a second filter step of suppressing clutter in the signal.

According to a seventh aspect of the present invention, in the clutter suppression method, whether the zero point frequency set in the filter coefficient calculation step matches the estimated value from the clutter center frequency estimation step in the multiple zero point processing step. Determining a zero point frequency, a switching step for switching a processing path according to the determination result of the zero point frequency determining step, and a filter coefficient calculation for a multiple zero point that allows two filters to form a multiple zero point at the same frequency. And a filter coefficient calculation step of calculating filter coefficients having different zero-point frequencies of the two filters.

The clutter suppressing method according to claim 8 of the present invention comprises a clutter center frequency estimating step of estimating the center frequency of the clutter, and two filter coefficients cascaded so as to form a notch for a specific frequency. A filter coefficient storing step for calculating in advance, a filter coefficient selecting step for selecting a filter coefficient corresponding to a frequency closest to the estimated value from the clutter center frequency estimating step from the filter coefficient storing step,
A first filter step for suppressing clutter in the received signal using the selected filter coefficient, and a second filter step for suppressing clutter in the received signal using the selected filter coefficient. .

A clutter suppressing method according to claim 9 of the present invention cascades at least three filters with respect to a clutter center frequency estimating step for estimating the clutter center frequency and an estimated value from the clutter center frequency estimating step. The filter coefficient calculation step of connecting and calculating the filter coefficient so as to form the zero of the frequency characteristic of the entire filter, and the estimated value from the clutter center frequency estimation step are sent to the filter coefficient calculation step before that. If it is the same as the clutter center frequency estimate, the first multiple zero processing step of calculating the filter coefficient so that multiple zeros can be formed, and the estimated value from the clutter center frequency estimating step are the filter coefficients before that. If it is the same as the clutter center frequency estimate sent to the calculation step, then multiple zeros A second multiple zeros processing step for calculating the filter coefficient so as to form a filter coefficient, and a first coefficient for suppressing clutter in the received signal by using the filter coefficient from the filter coefficient calculation step for each pulse interval different depending on the stagger trigger method. A filter step, a second filter step for suppressing clutter in the received signal using the filter coefficient from the first multiple zero processing step, and a reception using the filter coefficient from the second multiple zero processing step A third filter step for suppressing clutter in the signal.

According to a tenth aspect of the clutter suppressing method of the present invention, a clutter center frequency estimating step of estimating the center frequency of the clutter and at least three filters cascaded so as to form a notch for a specific frequency. A filter coefficient storing step of pre-calculating coefficients, and a filter coefficient selecting step of selecting a filter coefficient corresponding to the closest frequency from the filter coefficient storing step for each of a plurality of estimated values from the clutter center frequency estimating step, A first filter step for suppressing clutter in the received signal using the filter coefficient from the filter coefficient calculation step, and a second filter step for suppressing clutter in the received signal using the filter coefficient from the filter coefficient calculation step Filter step, and said filter It is intended to include a third filter step of suppressing clutter in the received signal using the filter coefficient sent from several calculation steps.

[0042]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. A clutter suppressing device according to Embodiment 1 of the present invention will be described with reference to the drawings. 1 is a block diagram showing the configuration of a clutter suppression device according to Embodiment 1 of the present invention. In each figure, the same reference numerals indicate the same or corresponding parts.

In FIG. 1, 1 is a clutter center frequency estimating means for estimating a clutter center frequency in a received signal from a received signal, 2 is a filter coefficient calculating means for calculating a filter coefficient, and 4 is a zero-point frequency of cascaded filters. Multiple zero point processing means for determining whether or not there are overlaps and calculating the filter coefficient, 3a is first filter means for performing clutter suppression processing using the filter coefficient from the filter coefficient calculation means 2, and 3b is multiple zero point processing. It is a second filter means for performing clutter suppression processing using the filter coefficient from the means 4.

FIG. 2 is a diagram showing an internal configuration of the multiple zero point processing means of the clutter suppressing device according to the first embodiment of the present invention.

In FIG. 2, reference numeral 10 denotes zero-point frequency determining means for selecting a coefficient calculation method when calculating filter coefficients so as to form a notch for the estimated frequency sent from the clutter center frequency estimating means 1, 11a, Reference numeral 11b is a switching means for changing the processing path based on the determination result of the zero-point frequency determination means 10, 12 is a filter coefficient calculation means for calculating a filter coefficient so as to form a zero point at a frequency different from the zero-point frequency of the preceding filter, 13 Is a multiple-zero-point filter coefficient calculating means for calculating a filter coefficient so that a zero point is formed at the same frequency as the zero point frequency of the preceding filter.

Next, the operation of the clutter suppressing device according to the first embodiment will be described with reference to the drawings.

FIG. 3 is a diagram for explaining the operation of the clutter suppressing device according to the first embodiment of the present invention.

In FIG. 3, 1 is a clutter center frequency estimating means for estimating the clutter center frequency in the received signal from the received signal, and 2a is a notch of the filter with respect to the estimated value transferred from the clutter center frequency estimating means 1. The first filter coefficient calculation means 3a for adjusting the filter coefficient so as to form the filter coefficient 3a, the first filter means 2a for performing the clutter suppression processing using the filter coefficient calculated by the filter coefficient calculation means 2a, and the reference numeral 2b the clutter center. With respect to the estimated value transferred from the frequency estimating means 1, the second filter coefficient calculating means 3b for adjusting the filter coefficient so as to form the notch of the filter, 3b outputs the filter coefficient calculated by the filter coefficient calculating means 2b. It is a second filter means for performing clutter suppression processing.

FIG. 4 is a diagram showing a filter amplitude square characteristic of a conventional (single filter) clutter suppressing device.

FIG. 5 is a diagram showing a filter amplitude square characteristic of a clutter suppressing device when two time-varying filters are connected in cascade (when a zero point is assigned to the same −600 Hz in each filter).

FIG. 6 is a diagram showing a filter amplitude square characteristic of a conventional (single filter) clutter suppressing device.

FIG. 7 is a diagram showing the filter amplitude squared characteristic (filter design method of the first embodiment) of the clutter suppression device when two time-varying filters are cascade-connected.

Clutter is assumed to be unimodal. First,
In FIG. 1, the received signal is a clutter center frequency estimation means 1
Then, the clutter center frequency is estimated in the same manner as in the conventional clutter suppression device.

Next, the clutter suppression filter coefficient is calculated according to the estimated value transferred from the clutter center frequency estimating means 1. The difference from the conventional clutter suppression device is that
In order to reduce the amount of calculation, clutter suppression processing that was conventionally performed with a single filter is configured by dividing one filter and connecting two filters in cascade, and notching with multiple filters at the same frequency. This is to devise the filter coefficient calculation of the second stage so that the zero point multiplicity for that frequency can be secured when forming the.

For example, when a monomodal clutter is received, a D-th order clutter suppression filter is used with D being an integer of 2 or more (impulse response length is D + 1). In the conventional clutter suppression device, it is necessary to solve the D-element first-order simultaneous equations L times in order to calculate the coefficient of the filter used for one clutter suppression process. This means obtaining an inverse matrix of a matrix of size D × D regarding the filter coefficient, and if the Gaussian elimination method is used as the solution method of the inverse matrix, approximately L × D ² multiplications are required.

On the other hand, in the clutter suppressing apparatus according to the first embodiment of the present invention, by dividing the D-order filter into two,
It is possible to reduce the total calculation amount related to the filter coefficient calculation. For example, if the D-th order filter has a cascade connection configuration of two D / 2-order filters, the required number of multiplications is 2
^{× L × (D / 2)} 2 = L × D 2/2 , and the be half of the conventional clutter suppression device.

Further, when D is 6th or less, the clutter suppressing apparatus according to the first embodiment of the present invention uses the filter 1
Since the degree per order can be set to 3 or less, the inverse matrix can be directly obtained instead of the method such as the Gaussian elimination method, and the amount of calculation can be dramatically reduced.

In the staggered trigger method, the pulses are unequal intervals. Therefore, in order to realize a filter having a notch frequency other than 0 and a deep and wide notch, a time-varying coefficient filter whose filter coefficient changes according to the pulse interval is used. The impulse response when such time-varying coefficient filters are connected in cascade is not a simple convolution of the impulse responses of the two filters. In the subsequent filtering process that is cascaded,
This is because the sample at the present time and the sample before that in the input signal of the filter of the subsequent stage have different filter coefficients of the previous stage used for calculating those samples. The impulse response when such time-varying coefficient filters are cascaded is shown below.

FIG. 3 is a configuration diagram in which one filter is simply divided into two filters and cascaded. Let t _k be the time corresponding to the pulse hit number. The input signal of the first filter means 3a is u (t _k ), the input signal of the second filter means 3b is x (t _k ), and the output signal of the second filter means is y (t _k ).
_k ). Now, stagger number L is 3, first coefficient calculation means 2
Let the filter coefficients calculated by a be h _k0 , h _k1 , h _k2 , h _k3 , and the filter coefficients calculated by the second coefficient calculating means 2b.
Let g _k0 , g _k1 , and g _k2 . The output signal y (t _k ) at a certain time can be expressed by the following equation.

[0060]

[Equation 8]

From this, when * is a convolution operation of two vectors, the impulse response when two time-varying filters are connected in cascade is as follows.

[0062]

[Equation 9]

With the order of the first filter means 3a as K ₁ and the order of the second filter means 3b as K ₂ , the above equation is expanded to the general form. The resulting convolution operation result is e _lk (l = 0,1,
, L-1, k = 0, 1, ..., K ₁ + K ₂ ) can be expressed as the following equation.

[0064]

[Equation 10]

In the above equation, since the pulse interval changes periodically with the stagger number L, g ₀₀ , g at times t ₀ , t _L , t _2L , ...
₀₁ , ..., g _{0, K2} correspond, and at times t ₀ , t _{L + 1} , t _{2L + 1} , ...
g ₁₀ ,, g ₁₁ , ..., g _{1, K2} correspond, and at times t ₀ , t _{L + 2} , t _{2L + 2} , ..., g ₂₀ , g ₂₁ , ..., g _{2, K 2} correspond ( Repeat thereafter). The amplitude square characteristic E (f) at this time is expressed by the following equation.

[0066]

[Equation 11]

When the notch frequency of the filter having the notch frequency of 0 is moved to an arbitrary frequency, the filter coefficient to be calculated in advance used by the first filter coefficient calculating means 2a is h _lk ′, and the notch frequency thereof is f ₀₁ .
Further, it is assumed that the filter coefficient used in the second filter coefficient calculation means 2b and calculated in advance is g _lk ′ and the notch frequency thereof is f ₀₂ . At this time, considering the filter alone, h _lk and g _lk are _{recalculated as} in the following equation.

[0068]

[Equation 12]

However, in the case of the cascade connection of time-varying filters, the coefficient g _lk recalculated by the second filter coefficient calculation means 2b does not result in the shift of the notch frequency of the simple notch filter as in the above equation. . This is because the coefficient calculated by the second filter coefficient calculation means 2b depends on the coefficient calculated by the first filter coefficient calculation means 2a.

Below, the second filter coefficient calculation means 2b
The method of calculating the filter coefficient, which is carried out in step 1, will be described. The time δT is defined as shown in equation (10), and the delay z
Be delayed by ΔT. At this time, the transfer function at the time of the time-varying filter cascade connection can be expressed as the following equation.

[0071]

[Equation 13]

When the exponent part of equation (24) is replaced by equation (26), equation (25) is obtained.

[0073]

[Equation 14]

Substituting equation (19) into equation (25) and rearranging yields the following equation.

[0075]

[Equation 15]

In the transfer function E _l (z), the derivative with respect to z is obtained, and it becomes 0 when the equation (28) is obtained, that is,
If so equation (29) holds, it is possible to have a K ₂ double zeros in f = f _02.

[0077]

[Equation 16]

The derivative of E _l (z) in the above equation can be obtained by the following equation.

[0079]

[Equation 17]

In this way, 1 is obtained from the number of filter coefficients.
There are as few as K ₂ equations, but you can set g _l0 arbitrarily. Also, with two filters connected in cascade,
In order to prevent the receiver noise power before and after the filter input / output from changing, g _l0 may be multiplied by a constant c _{l in the} following equation.

[0081]

[Equation 18]

In order to express the above relationship in a matrix, the vector is defined as in equation (32), and the simultaneous equations in equation (33) are obtained.

[0083]

[Formula 19]

In the above equation, A _{1 of} K ₂ × K ₂ matrix, vector
b _l is expressed by the following equation.

[0085]

[Equation 20]

By solving the equation (33), the coefficient relating to a specific l can be obtained. Therefore, l =
0,1, ..., by solving L times for L-1, can be obtained filter coefficient of the second stage with K ₂ double zeros in f = f _02.

In this way, the coefficient calculated by the first filter coefficient calculating means 2a is applied to the first filter means 3a, and the coefficient calculated by the second filter coefficient calculating means 2b is applied to the second filter coefficient. By applying the means 3b, notches can be formed at f = f ₀₁ and f = f ₀₂ as characteristics of the entire filter.

From the above, it was shown that notches can be formed at two frequencies even if two time-varying filters are connected in cascade. In the first embodiment, since the single-peaked clutter is assumed, the clutter center frequency estimation value transferred to the first filter coefficient calculation means 2a and the second filter coefficient calculation means 2b are transferred. The clutter center frequency estimate has the same frequency. That is, when the estimated value of the clutter center frequency is f _0, the filter coefficients are computed as _{f 01 = f 02 = f 0} .

However, in the method described above,
The frequency (f ₀₁ and
If f ₀₂ ) is set to the same frequency, only the multiplicity K _{2 of} zeros assigned by the filter in the subsequent stage becomes dominant, and (K ₁
The notch corresponding to the filter to which + K ₂ ) zeros are assigned should be formed at f = f ₀ , but in reality, the notch characteristic corresponds to the filter to which K ₂ zeros are assigned. The clutter suppressing performance is deteriorated as compared with the conventional clutter suppressing device.

In order to explain this phenomenon, consider a structure in which two first-order time-varying FIR filters are connected in cascade.
The former stage is filter # 1 and the latter stage is filter # 2, and the impulse response is {h _lk : l = 0,1, k = 0,1}, {g _lk : l = 0,1, k = 0,
1}. The number of sugata triggers is 2 here for simplicity.

The total second-order filter has two staggers.
Therefore, the transfer function E of the entire filter is_l(z) is E₀(z), E
₁Think about (z). Impulse of the whole filter
Reply e _lkThen, from equation (27), E_l(z) is as follows
become.

[0092]

[Equation 21]

Each filter is designed so that a notch is formed at the frequency f = f ₁ in the cascade connection structure of the filter # 1 and the filter # 2. First, for the filter coefficient h _lk of the first stage, the coefficient h ′ _lk having a notch at frequency 0 designed in advance is used,
The following calculation is performed to form a notch at the frequency f ₁ .

[0094]

[Equation 22]

Next, the coefficient of the filter # 2 is the filter # 1.
When the coefficient of is given as above, the amplitude square characteristic of the entire filter is designed so as to form a notch at f = f ₁ . E ₁ (z) has a zero point when z = z ₁ = exp [j2πf ₁ δT]. That is, E ₁ (z ₁ ) = 0 may be set. Substitute z = z ₁ into equation (36).

[0096]

[Equation 23]

Using g ₁₁ of the equation (41), E ₁ (z) is given by the following equation.

[0098]

[Equation 24]

[0099] than the process of deriving g _11, the E ₁ (z) is obviously to have a zero point f = f _1, it can be seen that equation (42) forms a notch on f = f _1. Furthermore, filter # 1 and the filter # 2 in setting the zero point f = f ₁ respectively, if it is to form a double zeros, E ₁ (z) of the first derivative E _'1 (z) _{respect, E '1 (z 1)} = 0 should hold. First, E ₁
Differentiating (z) with respect to z gives:

[0100]

[Equation 25]

From the above, it can be seen that the transfer function E ₁ (z) of the entire filter does not have double zeros at f = f ₁ because E ′ ₁ (z ₁ ) does not always become 0. Therefore, when zero points are set at the same frequency in a configuration in which time-varying filters are connected in cascade, the filter order and the zero point multiplicity do not match.

Next, a filter design example showing this phenomenon is shown in FIGS. The calculation condition at this time is the number of staggers L
3, stagger ratio 4: 3: 5, average PRI 400 μs, δ
T is 100 μs, clutter center frequency estimation value f ₀ is -600H
As z, a notch frequency of -600 Hz was assigned a six-fold zero. When two time-varying filters are connected in cascade, the first stage filter has a triple zero at -600 Hz,
A triple zero is assigned to -600 Hz in the second-stage filter.

FIG. 4 is a filter equivalent amplitude squared characteristic of a conventional clutter suppression device at a certain time, and FIG. 5 shows two time-varying filters connected in cascade, and zero points are assigned to the same frequency in each filter. It is a filter amplitude square characteristic of a clutter suppression device in the case. As can be seen from FIGS. 4 and 5, when two time-varying filters are connected in cascade, the stopband width of the notch formed is narrower, and the clutter suppression performance is better for clutter with a wider stopband width. It will deteriorate.

Therefore, in the first embodiment of the present invention, as shown in FIG. 1, the multiple zero point processing means 4 is provided, and the center frequency of the unimodal clutter to which the zero point is assigned by the first filter coefficient calculation means 2. With respect to the estimated value f ₀ , the filter coefficient is calculated so that the zero-point multiplicity can be secured in the filter means 3b in the subsequent stage.

In the time-varying filter, if one filter is simply divided and cascaded as shown in FIG. 3,
Zero multiplicity is not saved. The zero multiplicity of the filter is
How much the derivative of the filter transfer function shown in Expressions (28) to (29) is used at the time of design has an influence.

For example, if a 5th-order time-varying filter is divided into a 2nd-order and a 3rd-order time-varying filter, the filter coefficients are calculated using the 1st to 4th derivatives of the transfer function before the division. After that, only the first to second derivatives are used. Calculating the filter coefficient so that the high-order differential coefficient relating to the transfer function becomes 0 has the effect that the frequency characteristic is close to flat with respect to the frequency, that is, the notch width of the notch filter increases. As it is, even if the total of the filter orders is the same as before the filter division, the frequency characteristics of the filters do not match.

Therefore, the zero-point frequency determining means 10 of FIG. 2 determines whether or not the estimated value sent from the clutter center frequency estimating means 1 coincides with the frequency at which the zero point is set by the filter in the preceding stage, and they coincide with each other. If not, the filter coefficient is calculated by the usual design method when the time-varying filters are connected in cascade. If they match, the zero point multiplex filter coefficient calculation means 13 is used to secure the zero point multiplicity.
In, the filter calculation is performed based on the following calculation.

When the orders of the filter # 1 and the filter # 2 are K ₁ and K ₂ , respectively, in the coefficient calculation of the filter # 2, the K ₁ to (K ₁ + K ₂ −1) th derivative of the filter transfer function is calculated. To use.

The basic design method is the same as the case where the zero-point frequencies do not overlap. Therefore, the matrix A of equation (34),
The vector b in the formula (35), respectively equation (45), replaced as shown in equation (46), determines the coefficient vector g _l filter # 2 by solving simultaneous linear equations shown in equation (47).

[0110]

[Equation 26]

By the above calculation method, a zero point of (K ₁ + K ₂ ) weight is equivalently formed with respect to the frequency f ₀ , so that an amplitude square characteristic equivalent to that of the filter in the conventional clutter suppression device is obtained. be able to.

This state is shown in FIGS. 6 and 7. Figure 6
Filter amplitude 2 of a conventional clutter suppression device at a certain time
The power-law characteristic, FIG. 7 is the amplitude square-law characteristic of the filter in the clutter suppression device according to the first embodiment of the present invention. The calculation conditions of FIGS. 6 and 7 are the same as those of FIGS. 4 and 5.
6 and 7 that the filter of the clutter suppression device according to the first embodiment of the present invention exhibits an amplitude square characteristic equivalent to that of the conventional clutter suppression device, that is, equivalent clutter suppression performance is obtained. .

As described above, for one estimated clutter center frequency value, two filters are connected in cascade, and the filter coefficient of the second stage is calculated in a form dependent on the filter coefficient of the first stage. When the zero-point frequencies overlap, the derivative of the filter transfer function equal to or higher than the filter order of the preceding stage is used to secure the zero-point multiplicity when calculating the filter coefficient of the second stage. It is possible to reduce the amount of calculation related to the filter coefficient calculation to half or less while ensuring the clutter suppression performance equivalent to that of the suppression device.

Embodiment 2. In the first embodiment described above,
It is necessary to calculate the filter coefficient in real time. Considering clutter suppression processing of received signals from all distances up to the maximum detection distance for received signals with different sample intervals, the filter is divided to reduce the calculation amount, but the calculation related to the filter coefficient calculation is performed. It turns out that the amount is still large.

Therefore, in the clutter suppressing apparatus according to the second embodiment, the clutter center frequency estimated value is approximated to a discrete numerical value to form a table, and the filter coefficient for the value is calculated and held in advance. Thus, the amount of calculation related to the filter coefficient calculation is significantly reduced.

A clutter suppressing device according to Embodiment 2 of the present invention will be described with reference to the drawings. Figure 8
It is a block diagram which shows the structure of the clutter suppression apparatus which concerns on Embodiment 2 of this invention.

In FIG. 8, 1 is a clutter center frequency estimating means for estimating the clutter center frequency in the received signal from the received signal, 21 is a filter coefficient storing means for storing the filter coefficient patterns in a table, and 20 is a clutter. According to the estimated value sent from the center frequency estimating means 1,
Filter coefficient selecting means 3a and 3b for selecting a filter coefficient to be extracted from the filter coefficient storage means 21 are filter means for performing clutter suppression processing using the filter coefficient sent from the filter coefficient storage means 21.

Next, the operation of the clutter suppressing device according to the second embodiment will be described with reference to the drawings.

FIG. 9 is a diagram showing patterns stored in the filter coefficient storage means of the clutter suppression device according to the second embodiment of the present invention.

Clutter is assumed to be unimodal. In the stagger trigger method, the transmission pulse interval is not constant, so the clutter suppression filter is a time-varying filter. In the second embodiment, the filter coefficient is not calculated in real time, but the coefficient is stored in the filter coefficient storage means 21, and the filter coefficient selection means 2 is used according to the estimated clutter center frequency.
Select 0 to select an appropriate filter coefficient.

Assuming that the clutter center frequency does not change, at least (total pulse hit number-filter order) kinds of filter coefficients are required for clutter suppression processing of one range bin, but the search radar does not have many pulse hit numbers. Therefore, only one type needs to be prepared.

However, the moving clutter, which is the reflection echo from the moving object, has a high possibility that the center frequency of the clutter will also change because the clutter center frequency always changes. Therefore, discrete frequency values are set within the range of the assumed clutter center frequency, and the filter coefficient is calculated in advance only for the set frequency value. FIG. 7 shows an example of a pattern stored in the filter coefficient storage means 21. In the table, the normalized frequency is the clutter center frequency estimated value normalized by the pulse repetition frequency. DF is a frequency step size for which the filter coefficient is calculated in advance. Although the step size is constant here, it is also effective to change the step size according to the distribution of clutter center frequency estimated values. Q _ij is a vector that stores the filter coefficients, and as shown in the following equation, the number of filter coefficients q corresponding to the impulse response length of the filter
_{have ij} .

[0123]

[Equation 27]

In the filter coefficient selecting means 20, the estimated value sent from the clutter center frequency estimating means 1 is standardized,
This value and the step size D assumed in the filter coefficient storage means 21
The normalized frequency values for each F are compared, and the filter coefficient group corresponding to the closest normalized frequency value is selected. The selected filter coefficient is sent to the filter means 3a and 3b, and the clutter suppression process is performed.

As described above, in the radar clutter suppression device to which the stagger trigger method is applied, when a time-varying filter is required as the clutter suppression filter, the clutter center frequency estimation value is set to a limited number and the frequency is set. Since the time-varying filter coefficient for is designed in advance, it is not necessary to calculate the filter coefficient in real time, and the amount of calculation related to clutter suppression processing can be reduced.

Third embodiment. In the above-described first embodiment, the case where the clutter in the received signal is unimodal is assumed, but next, an embodiment is assumed that is bimodal or when a plurality of clutters are received.

A clutter suppressing device according to Embodiment 3 of the present invention will be described with reference to the drawings. Figure 10
FIG. 6 is a block diagram showing a configuration of a clutter suppression device according to Embodiment 3 of the present invention.

In FIG. 10, 1 is a clutter center frequency estimating means for estimating the clutter center frequency in the received signal from the received signal, and 2 is a filter coefficient by judging whether or not the zero-point frequencies of the cascade-connected filters overlap. The filter coefficient calculation means 3a for calculating is a first filter means for performing clutter suppression processing using the filter coefficient calculated by the filter coefficient calculation means 2, and 4a is for an estimated value sent from the clutter center frequency estimation means 1. The first multiple zero point processing means 3b for adjusting the filter coefficient so as to form the zero point of the filter, and the second filter means 3b for performing the clutter suppression process using the filter coefficient calculated by the multiple zero point processing means 4a. 4y is the zero-point frequency of the cascaded filters with respect to the estimated value sent from the clutter center frequency estimation means 1. Nth multiple zero-point processing means for determining the filter coefficient by determining whether or not overlap, and 3z is an Mth filter means for performing clutter suppression processing using the filter coefficient calculated by the multiple-zero point processing means 4y. .

The internal configurations of the multiple zero point processing means 4a and the multiple zero point processing means 4y are the same as those shown in FIG.

Next, the operation of the clutter suppressing device according to the third embodiment of the present invention will be described with reference to the drawings.

FIG. 11 is a diagram showing a filter amplitude square characteristic of a conventional clutter suppressing device.

FIG. 12 is a diagram showing the filter amplitude square characteristic of the clutter suppressing device when four time-varying filters are simply cascaded.

FIG. 13 is a diagram showing a filter amplitude square characteristic (filter designing method of the third embodiment) of the clutter suppressing device when four time-varying filters are connected in cascade.

The parts of which description is omitted are the same as the operations of the clutter suppressing device in the first embodiment of the present invention.

Although the clutter suppressing apparatus shown in FIG. 10 can theoretically deal with M or less clutters having different center frequencies, the present invention divides a high-order filter into a plurality of low-order filters. Since the aim is to reduce the amount of calculation, the clutter number << M in general.

For example, when two clutters having different center frequencies are received, in order to suppress these clutters from the expected power and bandwidth of each clutter, in order to suppress these clutters, a 6th order is added to each clutter. Fifth-order notch filter (here, 6 times for clutter center frequency,
Alternatively, it means a filter for setting the quintuple zero). Since it is a bimodal clutter, it can be suppressed even if two time-varying filters of the 6th order and the 5th order are cascade-connected, but consider dividing each filter to reduce the amount of calculation. Each filter is 3rd, 3rd, 3rd
When the filter is divided into two filters, that is, the secondary filter and the secondary filter, four time-varying filters are cascaded. Center frequency estimating means 1
Let f ₀₁ and f ₀₂ be the clutter center frequencies estimated in.

Considering FIG. 10 as an example, the time-varying filter # 1 and the time-varying filter # 2 are the filter coefficient calculation means 2,
In the multiple zero point processing means 4a, the frequencies f ₀₁ and f ₀₂ are respectively set to 3
The filter coefficient with double zeros is calculated,
# 3 and time-varying filter # 4 are multiple zero point processing means 4b and 4c.
Then, filter coefficients having triple zeros and double zeros at the frequencies f ₀₁ and f ₀₂ are calculated. The order of the filters is described as an example above, but there is no particular limitation.

As described above, when I number of clutters having different center frequencies are received, the respective clutters are separated by J.
Assuming that the filters are used for suppression, the clutter suppression device according to the third embodiment of the present invention has a cascade connection configuration of I × J time-varying filters. Actually, the number of filters used for one clutter is arbitrarily determined, and the total number of filters is calculated by a more complicated formula than I × J.

As an actual operation, the number of filters to be assigned to the estimated center frequency of each clutter and the order of each filter are determined in advance or from the result of processing the received signal.

Next, the order of filters to be cascaded is determined. For example, a reflected echo from an object such as a ground or a building that does not move like ground clutter does not generate a Doppler frequency, and thus the notch frequency for this clutter may be zero. The fact that the notch frequency is 0 means that it is possible to use the filter coefficient calculated in advance by the ordinary filter design method as it is, so such a filter should be brought to the frontmost stage of the cascade connection configuration. Is more convenient for processing.

11 to 13 show examples of calculation of the filter amplitude square characteristic in the clutter suppressing device according to the third embodiment.

As an example, it is assumed here that the radar receives bimodal clutter. The estimated value transferred from the clutter center frequency estimating means 1 in FIG. 10 is -600H.
z, 400 Hz. That is, there is a clutter having peaks at these two frequencies. At this time, with the conventional clutter suppression device of FIG.
It is considered that a notch is formed by assigning a 6-zero point to 00 Hz and a 5-zero point to a frequency of 400 Hz, respectively. The calculation conditions are: the stagger number L is 3, the stagger ratio is 4: 3: 5, the average PRI is 400 μs, and δT is 100 μs. FIG. 11 shows the equivalent amplitude square characteristic of the filter in the conventional clutter suppression device at this time. -600Hz and 400H
A wide notch is formed in z.

In the clutter suppressing apparatus according to the third embodiment of the present invention, two filters are cascade-connected to each clutter. That is, four filters are connected in cascade, and M = 4 in the configuration of FIG.
The frequencies to which the zero points are assigned and the zero point multiplicities in the four filters are as follows, and different filter coefficient calculation methods are performed for the duplicate zero point frequencies.

First-stage filter: -600 Hz (triple zero), second-stage filter: -570 Hz (triple zero),
Third stage filter: 400 Hz (triple zero), fourth stage filter: 420 Hz (double zero).

The amplitude square characteristic of the filter at this time is shown in FIG.
3 shows. Since it has almost the same filter equivalent amplitude squared characteristic as the conventional clutter suppression device, by connecting four filters in cascade while securing the clutter suppression performance,
It is possible to reduce the calculation amount related to the filter coefficient calculation.

As a reference, FIG. 12 shows a calculation example in a clutter suppressing device in which four filters are simply connected in cascade without having the multiple zero point processing means. In this case, since the zero point multiplex processing means for overlapping frequencies is not provided, the stop band width of the notch for the frequency at which the clutter peak exists is considerably narrower than the characteristic of the clutter suppressing device according to the third embodiment of the present invention. It can be seen that the clutter suppression performance deteriorates.

As described above, for a plurality of clutters,
When multiple filters are connected in cascade, the filter coefficients of the second and subsequent stages are calculated in a form that depends on the filter coefficients of the previous stages, and when the zero-point frequencies overlap, the filter coefficients of the second and subsequent stages are calculated. Sometimes, to ensure zero multiplicity, the derivative of the filter transfer function higher than the previous filter order is used, so while maintaining the same clutter suppression performance as the conventional clutter suppression device, it is possible to calculate the filter coefficient. The calculation amount can be reduced to half or less.

Fourth Embodiment In the second embodiment described above,
The clutter center frequency estimation value is made into a table by approximating it to a discrete value, and the filter coefficient for that value is calculated and stored in advance, thereby significantly reducing the amount of calculation involved in the filter coefficient calculation. . Fourth Embodiment
Relates to a clutter suppressing device that can handle a plurality of clutters.

A clutter suppressing device according to Embodiment 4 of the present invention will be described with reference to the drawings. 14
FIG. 9 is a block diagram showing a configuration of a clutter suppression device according to Embodiment 4 of the present invention.

In FIG. 14, 1 is a clutter center frequency estimating means for estimating the clutter center frequency in the received signal from the received signal, 23 is a filter coefficient storage means for storing the filter coefficient patterns in a table, and 22 is a clutter. Filter coefficient selecting means 3a, 3b for selecting a filter coefficient to be extracted from the filter coefficient storing means 23 according to a plurality of estimated values sent from the center frequency estimating means 1.
3z are first, second, and Mth filter means for performing clutter suppression processing using the filter coefficients sent from the filter coefficient storage means 23, respectively.

Next, the operation of the clutter suppressing device according to the fourth embodiment of the present invention will be described with reference to the drawings.

The basic operation is the second embodiment of the present invention.
Therefore, the description is omitted here.

The difference is that there are a plurality of clutter center frequency estimation values sent to the filter selection means 22, and the number of types of filter coefficients in the filter coefficient storage means 23 correspondingly increases. That is, the number of filter coefficients received in the table in FIG.
The type of coefficient corresponding to the number of filters assigned to one clutter is stored.

With such a configuration, it is possible to realize a clutter suppressing device which does not need to calculate the time-varying filter coefficient in real time even for a plurality of clutters.

As described above, in the radar clutter suppressing device to which the stagger trigger method is applied, when a time-varying filter is required as the clutter suppressing filter, the clutter center frequency estimation value is set to a limited number and the frequency is set. Since the time-varying filter coefficient for is designed in advance, it is not necessary to calculate the filter coefficient in real time, and the amount of calculation related to clutter suppression processing can be reduced.

[0156]

As described above, the clutter suppressing apparatus according to the first aspect of the present invention is based on the clutter center frequency estimating means for estimating the center frequency of the clutter and the estimated value sent from the clutter center frequency estimating means. Then, the filter coefficient calculation means for calculating the filter coefficient so as to form the zero point of the frequency characteristic of the entire filter by connecting the two filters in cascade, and the estimated value sent from the clutter center frequency estimation means are the filter coefficient calculation means. If it is the same as the clutter center frequency estimation value sent to the means, the filter coefficient calculation means calculates the filter coefficient so that multiple zero points can be formed, and the filter coefficient calculation means transmits the filter coefficient at different pulse intervals depending on the stagger trigger method. First filter means for suppressing clutter in the received signal using filter coefficients, and Since the second filter means for suppressing the clutter in the received signal by using the filter coefficient sent from the multiple zero point processing means is provided, the filter coefficient calculation is performed while securing the clutter suppression performance equivalent to that of the conventional clutter suppression device. It is possible to reduce the amount of calculation related to the above by half or less.

As described above, in the clutter suppressing apparatus according to claim 2 of the present invention, the multiple zero point processing means is
Zero-point frequency determining means for determining whether the zero-point frequency set by the filter coefficient calculating means and the estimated value sent from the clutter center frequency estimating means match, and processing is performed according to the determination result of the zero-point frequency determining means. Switching means for switching the path, filter coefficient calculation means for multiple zeros capable of forming multiple zeros at the same frequency with two filters, and filter coefficient calculation means for calculating filter coefficients having different zero frequencies of the two filters are provided. Therefore, it is possible to secure the same clutter suppression performance as that of the conventional clutter suppression device and reduce the amount of calculation related to the filter coefficient calculation to half or less.

As described above, the clutter suppressing apparatus according to the third aspect of the present invention has the clutter center frequency estimating means for estimating the center frequency of the clutter and the cascade connection so as to form a notch for a specific frequency. And a filter coefficient selecting means for selecting from the filter coefficient storing means a filter coefficient corresponding to a frequency closest to the estimated value sent from the clutter center frequency estimating means. A first filter means for suppressing clutter in the received signal by using the selected filter coefficient, and a second filter means for suppressing clutter in the received signal by using the selected filter coefficient. Since it is provided, it is not necessary to calculate the filter coefficient in real time, and the calculation amount related to clutter suppression processing can be reduced An effect that can be.

As described above, the clutter suppressing apparatus according to the fourth aspect of the present invention includes: a clutter center frequency estimating means for estimating the center frequency of the clutter; and an estimated value sent from the clutter center frequency estimating means. Filter coefficient calculation means for calculating filter coefficients so that at least three filters are connected in cascade to form a zero point of the frequency characteristic of the entire filter, and the estimated value sent from the clutter center frequency estimation means is a filter before that. If it is the same as the clutter center frequency estimation value sent to the coefficient calculation means, first multiple zero processing means for calculating the filter coefficient so as to form multiple zeros, and the estimated value sent from the clutter center frequency estimation means. Is the same as the clutter center frequency estimate sent to the previous filter coefficient calculation means, Second multiple zero point processing means for calculating a filter coefficient so that a double zero point can be formed, and clutter in a received signal is suppressed by using a filter coefficient sent from the filter coefficient calculation means at each pulse interval different depending on the stagger trigger method. First filter means, second filter means for suppressing clutter in the received signal using the filter coefficient sent from the first multiple zero point processing means, and filter sent from the second multiple zero point processing means Since the third filter means for suppressing clutter in the received signal by using the coefficient is provided, the clutter suppression performance equivalent to that of the conventional clutter suppression device is ensured, and the amount of calculation related to the filter coefficient calculation is reduced to half or less. There is an effect that can be done.

As described above, the clutter suppressing apparatus according to the fifth aspect of the present invention includes the clutter center frequency estimating means for estimating the center frequency of the clutter and the cascade connection so as to form a notch for a specific frequency. With respect to each of the plurality of estimated values sent from the clutter center frequency estimating means, a filter coefficient storing means for preliminarily calculating at least three filter coefficients is selected from the filter coefficient storing means. Filter coefficient selecting means, first filter means for suppressing clutter in the received signal using the filter coefficient sent from the filter coefficient calculating means, and received signal using the filter coefficient sent from the filter coefficient calculating means Second filter means for suppressing internal clutter, and said filter Since the third filter means for suppressing the clutter in the received signal by using the filter coefficient sent from the number calculation means is provided, it is not necessary to calculate the filter coefficient in real time, and the calculation amount related to the clutter suppression processing can be calculated. The effect that it can reduce is produced.

As described above, the clutter suppressing method according to the sixth aspect of the present invention includes a clutter center frequency estimating step for estimating the center frequency of the clutter, and two filters connected in series for the estimated value of the clutter center frequency. A filter coefficient calculation step of connecting and calculating a filter coefficient so as to form a zero of the frequency characteristic of the entire filter;
If the estimated value of the clutter center frequency is the same as the estimated value of the clutter center frequency in the filter coefficient calculation step, the multiple zero point processing step of calculating the filter coefficient so that multiple zero points can be formed, and different pulses depending on the stagger trigger method A first filter step for suppressing clutter in the received signal using the filter coefficient from the filter coefficient calculation step for each interval, and a clutter in the received signal using the filter coefficient from the multiple zero point processing step Since it includes a second filter step,
It is possible to reduce the amount of calculation related to the filter coefficient calculation to half or less while ensuring the clutter suppression performance equivalent to that of the conventional clutter suppression device.

As described above, in the clutter suppressing method according to claim 7 of the present invention, the multiple zero point processing step includes the zero point frequency set in the filter coefficient calculating step and the estimated value from the clutter center frequency estimating step. , A zero-point frequency determination step for determining whether or not they match, a switching step for switching a processing path in accordance with the determination result of the zero-point frequency determination step, and a multiplex unit capable of forming multiple zero points at the same frequency with two filters. Since the method includes a zero-point filter coefficient calculation step and a filter coefficient calculation step for calculating filter coefficients in which two filters have different zero-point frequencies, the filter coefficient calculation is performed while securing the clutter suppression performance equivalent to that of the conventional clutter suppression device. There is an effect that the calculation amount can be reduced to half or less.

As described above, the clutter suppressing method according to claim 8 of the present invention includes a clutter center frequency estimating step for estimating the center frequency of the clutter, and a cascade connection for forming a notch for a specific frequency. And a filter coefficient selecting step of selecting from the filter coefficient storing step a filter coefficient corresponding to a frequency closest to the estimated value from the clutter center frequency estimating step. , A first filter step for suppressing clutter in the received signal using the selected filter coefficient, and a second filter step for suppressing clutter in the received signal using the selected filter coefficient Therefore, it is not necessary to calculate the filter coefficient in real time, and the clutter suppression processing is An effect that it is possible to reduce the amount of computation involved in.

As described above, the clutter suppressing method according to claim 9 of the present invention, at least for the clutter center frequency estimating step for estimating the center frequency of the clutter and the estimated value from the clutter center frequency estimating step. A filter coefficient calculation step of calculating a filter coefficient so that three filters are cascaded to form a zero point of the frequency characteristic of the entire filter, and an estimated value from the clutter center frequency estimation step is before the filter coefficient calculation step. If it is the same as the clutter center frequency estimate sent to the step, the first multiple zero processing step of calculating the filter coefficient so that multiple zeros can be formed, and the estimated value from the clutter center frequency estimation step are The clutter center frequency estimate sent to the previous filter coefficient calculation step and If the same, the second multiple zero processing step of calculating the filter coefficient so that multiple zeros can be formed, and the received signal using the filter coefficient from the filter coefficient calculation step for each pulse interval different depending on the stagger trigger method. From a first filter step for suppressing clutter, a second filter step for suppressing clutter in a received signal using the filter coefficient from the first multiple zero processing step, and a second multiple zero processing step And a third filter step for suppressing clutter in the received signal by using the filter coefficient of, the clutter suppression performance equivalent to that of the conventional clutter suppression device is ensured, and the calculation amount related to the filter coefficient calculation is reduced to half or less. There is an effect that can be.

As described above, the clutter suppressing method according to the tenth aspect of the present invention includes a clutter center frequency estimating step for estimating the center frequency of the clutter, and a cascade connection so as to form a notch for a specific frequency. For each of the plurality of estimated values from the clutter center frequency estimating step and the filter coefficient storing step in which at least three filter coefficients are calculated in advance, the filter coefficient corresponding to the closest frequency is selected from the filter coefficient storing step. A filter coefficient selection step, a first filter step for suppressing clutter in the received signal using the filter coefficient from the filter coefficient calculation step, and a clutter in the received signal using the filter coefficient from the filter coefficient calculation step The second filter step that suppresses Because it contains a flop, and a third filter step of suppressing clutter in the received signal using the filter coefficients sent from the filter coefficient calculation step,
There is an effect that it is not necessary to calculate the filter coefficient in real time, and the amount of calculation related to clutter suppression processing can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a clutter suppressing device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of multiple zero point processing means of the clutter suppression device according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram for explaining the operation of the clutter suppression device according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a filter amplitude squared characteristic of a conventional clutter suppression device.

FIG. 5 is a diagram showing a filter amplitude square characteristic of a clutter suppression device when two time-varying filters are simply cascaded.

FIG. 6 is a diagram showing a filter amplitude square characteristic of a conventional clutter suppression device.

FIG. 7 is a diagram showing a filter amplitude square characteristic of a clutter suppression device when two time-varying filters are connected in cascade.

FIG. 8 is a block diagram showing a configuration of a clutter suppression device according to Embodiment 2 of the present invention.

FIG. 9 is a diagram showing a table of a filter coefficient storage unit of the clutter suppression device according to the second embodiment of the present invention.

FIG. 10 is a block diagram showing a configuration of a clutter suppression device according to Embodiment 3 of the present invention.

FIG. 11: Filter amplitude 2 of a conventional clutter suppression device
It is a figure which shows a riding characteristic.

FIG. 12 is a diagram showing a filter amplitude square characteristic of a clutter suppression device when four time-varying filters are simply cascaded.

FIG. 13 is a diagram showing a filter amplitude squared characteristic of a clutter suppression device when four time-varying filters are cascade-connected.

FIG. 14 is a block diagram showing a configuration of a clutter suppression device according to Embodiment 4 of the present invention.

FIG. 15 is a block diagram showing a configuration of a conventional clutter suppression device.

[Explanation of symbols]

1 Clutter Center Frequency Estimating Means, 2 Filter Coefficient Calculating Means, 3a First Filter Means, 3b Second Filter Means, 4, 4a, 4y Multiple Zero Point Means, 20
Filter coefficient selecting means, 21 filter coefficient storing means,
22 filter coefficient selecting means, 23 filter coefficient storing means.

Claims (10)

[Claims] 1. A clutter center frequency estimating means for estimating the center frequency of the clutter, and two filters connected in cascade with respect to the estimated value sent from the clutter center frequency estimating means to determine a zero point of the frequency characteristic of the entire filter. If the estimated value sent from the filter coefficient calculation means for calculating the filter coefficient so as to form the clutter center frequency estimation means is the same as the clutter center frequency estimated value sent to the filter coefficient calculation means, the multiple zero point Multiple zero point processing means for calculating a filter coefficient so as to form a filter coefficient, and a first filter means for suppressing clutter in the received signal by using the filter coefficient sent from the filter coefficient calculation means at each pulse interval different depending on the stagger trigger method. And using a filter coefficient sent from the multiple zero point processing means, Clutter suppression apparatus characterized by comprising a second filter means for suppressing Latta. 2. The multiple zero point processing means, and a zero point frequency determination means for determining whether or not the zero point frequency set by the filter coefficient calculation means and the estimated value sent from the clutter center frequency estimation means match. The switching means for switching the processing path according to the determination result of the zero-point frequency determining means, the filter coefficient calculating means for multiple zeros capable of forming multiple zeros at the same frequency by two filters, and the zero-point frequency of the two filters are The clutter suppressing apparatus according to claim 1, further comprising a filter coefficient calculating unit that calculates different filter coefficients. 3. A clutter center frequency estimating means for estimating a center frequency of the clutter, and a filter coefficient storing means for preliminarily calculating two cascaded filter coefficients so as to form a notch for a specific frequency. A filter coefficient selecting means for selecting from the filter coefficient storing means a filter coefficient corresponding to a frequency closest to the estimated value sent from the clutter center frequency estimating means; and a clutter in a received signal using the selected filter coefficient. A clutter suppressing device comprising: a first filter unit for suppressing the above; and a second filter unit for suppressing the clutter in the received signal by using the selected filter coefficient. 4. A clutter center frequency estimating means for estimating the center frequency of the clutter, and at least three filters connected in cascade with respect to the estimated value sent from the clutter center frequency estimating means. A filter coefficient calculating means for calculating a filter coefficient so as to form an estimated value sent from the clutter center frequency estimating means is the same as the clutter center frequency estimated value sent to the preceding filter coefficient calculating means. For example, the first multiple zero point processing means for calculating the filter coefficient so that multiple zero points can be formed, and the estimated value sent from the clutter center frequency estimating means are the clutter centers sent to the preceding filter coefficient calculating means. A second multiple zero that computes the filter coefficients to form multiple zeros if they are the same as the frequency estimate Processing means, first filter means for suppressing clutter in the received signal by using filter coefficients sent from the filter coefficient calculation means at different pulse intervals depending on the stagger trigger method, and sending from the first multiple zero-point processing means. Second filter means for suppressing clutter in the received signal by using the filter coefficient, and third filter means for suppressing clutter in the received signal by using the filter coefficient sent from the second multiple zero point processing means And a clutter suppression device characterized by including. 5. A clutter center frequency estimating means for estimating the center frequency of the clutter, and a filter coefficient storing means for preliminarily calculating at least three filter coefficients connected in series so as to form a notch for a specific frequency. A filter coefficient selecting means for selecting a filter coefficient corresponding to the closest frequency from the filter coefficient storing means for each of a plurality of estimated values sent from the clutter center frequency estimating means, and a filter sent from the filter coefficient calculating means. First filter means for suppressing clutter in the received signal using a coefficient, second filter means for suppressing clutter in the received signal using the filter coefficient sent from the filter coefficient calculation means, and the filter coefficient The filter coefficient sent from the calculation means is used to determine the class in the received signal. Clutter suppression apparatus characterized by comprising a third filter means for suppressing the data. 6. A clutter center frequency estimation step for estimating the center frequency of the clutter, and a filter for connecting the two filters in cascade with respect to the estimated value of the clutter center frequency so as to form a zero point of the frequency characteristic of the entire filter. A filter coefficient calculation step of calculating a coefficient, and an estimated value of the clutter center frequency is the same as the clutter center frequency estimated value in the filter coefficient calculation step, a multiplex for calculating a filter coefficient so that a multiple zero point can be formed. A zero point processing step, a first filter step for suppressing clutter in the received signal by using the filter coefficient from the filter coefficient calculation step for each pulse interval different depending on the stagger trigger method, and a filter coefficient from the multiple zero point processing step A second fill that uses to suppress clutter in the received signal Clutter suppression method which comprises the steps. 7. The zero-point frequency determination step of determining whether or not the zero-point frequency set in the filter coefficient calculation step and the estimated value from the clutter center frequency estimation step match in the multiple zero-point processing step, The switching step that switches the processing path according to the determination result of the zero-point frequency determination step, the multiple-zero-point filter coefficient calculation step that allows two filters to form multiple zeros at the same frequency, and the two filters have different zero-point frequencies. 7. The clutter suppressing method according to claim 6, further comprising a filter coefficient calculating step of calculating a filter coefficient. 8. A clutter center frequency estimating step of estimating a center frequency of the clutter, and a filter coefficient storing step of preliminarily calculating two cascaded filter coefficients so as to form a notch for a specific frequency. A filter coefficient selecting step of selecting a filter coefficient corresponding to a frequency closest to an estimated value from the clutter center frequency estimating step from the filter coefficient storing step; and a clutter in a received signal using the selected filter coefficient. A clutter suppression method comprising: a first filter step for suppressing; and a second filter step for suppressing clutter in a received signal using the selected filter coefficient. 9. A clutter center frequency estimation step for estimating the center frequency of the clutter, and at least three filters are cascade-connected to the estimated value from the clutter center frequency estimation step to determine a zero point of the frequency characteristic of the entire filter. A filter coefficient calculation step of calculating a filter coefficient so as to form, the estimated value from the clutter center frequency estimation step,
If it is the same as the clutter center frequency estimation value sent to the previous filter coefficient calculation step, a first multiple zero processing step of calculating a filter coefficient so as to form multiple zeros, and the clutter center frequency estimation step The estimated value from
If it is the same as the clutter center frequency estimate sent to the previous filter coefficient calculation step, the second multiple zero processing step to calculate the filter coefficient so that multiple zeros can be formed, and the pulse interval that differs depending on the stagger trigger method A first filter step for suppressing clutter in the received signal using the filter coefficient from the filter coefficient calculation step for each, the clutter in the received signal using the filter coefficient from the first multiple zero processing step A clutter suppression method comprising: a second filter step for suppressing; and a third filter step for suppressing clutter in a received signal using the filter coefficient from the second multiple zero point processing step. 10. A clutter center frequency estimating step of estimating a center frequency of a clutter, and a filter coefficient storing step of preliminarily calculating at least three filter coefficients cascaded so as to form a notch for a specific frequency. A plurality of estimated values from the clutter center frequency estimating step, a filter coefficient selecting step of selecting a filter coefficient corresponding to the closest frequency from the filter coefficient storing step, and a filter coefficient from the filter coefficient calculating step. A first filter step for suppressing clutter in the received signal using, a second filter step for suppressing clutter in the received signal using the filter coefficient from the filter coefficient calculation step, from the filter coefficient calculation step Filter coefficient sent Clutter suppression method which comprises a third filter step of suppressing clutter in the received signal by using.