JP4727311B2 - Radar equipment - Google Patents

Description

  The present invention relates to a radar device that suppresses clutter and detects a moving small target.

  Radar equipment that implements a moving small target detection method is installed on aircraft and other platforms, and it observes the surface of the earth and the sea surface by transmitting and receiving radio waves from the sky, and exists near the earth surface and the sea surface. A small target is detected. Here, the small target means a target having a low radio wave reflection intensity, and is not necessarily a target having a small physical size. When this type of radar observes the ground surface or the sea surface, it is generally a strong echo from the ground surface or sea surface (referred to as ground clutter and sea clutter, respectively. In the description of the present invention, from the background as ground clutter or sea clutter. Are collectively referred to simply as clutter). Therefore, it is necessary to suppress clutter in advance in order to detect an echo from a target (referred to as a target signal) existing near the ground surface or the sea surface from the received radar signal.

As a conventional clutter suppression technique in a radar apparatus, there is a technique called MTI (Moving Target Indicator) that suppresses clutter by using a Doppler frequency difference between a target signal and a clutter (see Non-Patent Document 1, for example). This is a method of suppressing clutter by determining a clutter and a target signal based on the speed difference between the background and the target assuming a small target that moves like a vehicle or a ship.
Further, as a clutter suppression method for detecting a stationary target, there is a method for detecting a target by suppressing the clutter while paying attention to the difference between the polarization characteristics of the target and the background (see, for example, Non-Patent Document 2). . This method measures the background and target polarization characteristics by transmitting and receiving radio waves with a combination of two orthogonal polarizations (for example, horizontal polarization (H polarization) and vertical polarization (V polarization)). Then, a portion corresponding to the polarization characteristic of the clutter in the received signal is suppressed.

  Further, there is a method of analyzing the Doppler frequency and polarization characteristic of the received signal and suppressing a portion corresponding to the Doppler frequency and polarization characteristic of the clutter (see Non-Patent Document 3, for example). In this method, an adaptive filter is generated in the polarization / time signal to suppress clutter. Therefore, when this method is compared with a method such as MTI for moving targets, the clutter suppression performance and target detection performance are improved by the amount that the clutter can be suppressed by the difference in the polarization characteristics of the target and the clutter. There are advantages.

An example of a functional configuration for realizing the method of suppressing clutter using information on the Doppler frequency and polarization characteristics described in Non-Patent Document 3 will be described with reference to FIG.
In the figure, a received signal 101 is obtained by transmitting and receiving a plurality of pulses by a radar device, and is stored in a temporary memory. The structure of the received signal 101 is a form in which signals of a plurality of polarization channels and a plurality of hits are arranged for each range cell. When the number of hits is M and the number of polarization channels is P, the signal of each range cell is M × It is a P-dimensional vector signal. The structure of received signal 101 will be described in detail in Embodiment 1 of the present invention. In order to suppress the clutter of the test cell, the clutter covariance matrix is estimated by the covariance matrix estimation means 102 from the signals of the reference cells before and after the test cell. Using this clutter covariance matrix, the filter generation unit 103 generates a clutter suppression filter, and the clutter suppression unit 104 applies the clutter suppression filter to the observation value in the test cell to suppress the clutter. Next, the determination unit 105 performs target detection determination by comparing the clutter-suppressed signal output from the clutter suppression unit 104 with a threshold value.

M.I.Skolnik, “Introduction to Radar Systems,” Second Edition, McGraw-Hill, 1980. L.M.Novak, M.C.Burl, W.W.Irving, “Optimal polarimetric processing for enhanced target detection,” IEEE Transactions on Aerospace and Electronic Systems, Vol. 29, No. 1, pp.234-244, Jan. 1993 D. Pastina et al. “Aptive Polarimetric Target Detection with Coherent Radar,” IEEE International Radar Conf. 2000, pp93-97

The conventional radar apparatus suppresses clutter in advance by various methods as described above in order to detect an echo (target signal) from the target from the received radar signal. However, there are the following problems. is there.
In the method described in Non-Patent Document 1, when the Doppler frequency of the target signal matches the Doppler frequency of the clutter, such as a vehicle stationary on the ground surface or a ship floating on the sea surface, Even if the target is moving, if the Doppler frequency of the clutter spreads and overlaps with the Doppler frequency of the target signal, the target signal is also suppressed and cannot be determined. Further, when the target signal intensity is extremely small, there may be a problem that the target signal cannot be sufficiently detected even if clutter is suppressed.

Further, in the method described in Non-Patent Document 2, if the background and target polarization characteristics match, or if the difference in polarization characteristics is small, the target signal is sufficiently obtained even if clutter is suppressed. It may not be detected.
Furthermore, in the method described in Non-Patent Document 3, it is necessary to prepare information related to the target polarization characteristics in advance. Further, the filter generation means needs to perform eigenvalue analysis of the covariance matrix. However, since the covariance matrix is a matrix of (M × P) × (M × P), there is a problem that the amount of calculation becomes very large. is there.

  The present invention has been made to solve the above-described problems. By using Doppler information and polarization information, the SCR (Signal to Clutter Ratio) for a moving target can be improved and the target detection probability can be improved. An object of the present invention is to obtain a radar device that can be used.

  A radar apparatus according to the present invention calculates a Doppler spectrum in each range cell from received signals obtained by transmitting and receiving a plurality of pulses, and detects a moving small target by suppressing clutter from the calculated Doppler spectrum. A clutter band estimating means for calculating a Doppler frequency band of the clutter, a clutter band signal extracting means for extracting a signal existing in the Doppler frequency band of the clutter from the Doppler spectrum of the received signal, and a Doppler of the extracted clutter Clutter polarization characteristic estimation means for estimating the polarization characteristic of clutter based on a signal existing in the frequency band, and a clutter for generating a clutter suppression filter for suppressing the component of the estimated clutter polarization characteristic Suppression filter generation means and received signal Doppler spectrum A clutter suppression unit that applies a clutter suppression filter to a Doppler spectrum existing in the Doppler frequency band of the clutter to suppress a component corresponding to the polarization characteristics of the clutter, and a clutter suppression unit by the clutter suppression unit. And a target detection means for performing target detection determination by comparing the suppressed Doppler spectrum with a threshold value.

  According to this invention, since the clutter is suppressed using the information on the polarization characteristics of the clutter and the Doppler frequency, there is an effect of improving the target detection performance. In addition, since the signal of the Doppler frequency band of the clutter is first extracted from the Doppler spectrum of the received signal, and the polarization characteristics of the clutter are estimated using the extracted signal, the estimation accuracy of the polarization characteristics of the clutter is estimated. There is an effect of improving. In general, since the correlation between the polarization characteristics of clutter and the Doppler frequency is low on the sea surface or a uniform ground surface, the order of the matrix used for matrix calculation can be determined by applying Doppler frequency analysis and polarization characteristics analysis in sequence. The amount of calculation can be reduced accordingly.

Embodiment 1 FIG.
1 is a block diagram showing a configuration of a radar apparatus according to Embodiment 1 of the present invention.
In FIG. 1, a transmitter (transmission means) 1 generates a pulse signal, and a transmission / reception switch 2 sends the pulse signal to a polarization switch 3. The polarization switch 3 radiates the pulse signal from the first polarization transmitting / receiving antenna 4 to the space by driving the first polarization transmitting / receiving antenna 4. The pulse signal radiated into space is scattered by the observation target. The polarization switching unit 3 drives both the first polarization transmission / reception antenna 4 and the second polarization transmission / reception antenna 5, and receives the scattered waves scattered by the observation target by each antenna. Here, the polarization characteristics of the first polarized wave transmitting / receiving antenna 4 and the second polarized wave transmitting / receiving antenna 5 are orthogonal to each other. Note that as the combinations in which the polarization characteristics of the first polarization transmitting / receiving antenna 4 and the second polarization transmitting / receiving antenna 5 are orthogonal, for example, a combination of vertical polarization and horizontal polarization, right-handed circular polarization and left-handed circular polarization, and the like. A combination of waves can be considered. Each reception signal of the scattered wave from the observation target is sent to the receiver (reception means) 6 via the transmission / reception switch 2.

In the receiver 6, phase detection processing, A / D conversion processing, and range compression processing are performed on each of the received signals of the scattered waves received by the first polarization transmitting / receiving antenna 4 and the second polarization transmitting / receiving antenna 5. , each of the received signal amplitude and the digital reception signal x _1mn indicating the phase, and outputs a x _2mn. Output from the receiver 6 the received signal x _1mn, x _2mn is transmitted to a memory 7, is temporarily stored. Note that x _pmn is the nth received signal of the p-th polarization channel (p = 1, 2, 3, 4, details will be described later) and the m-th (m = 0, 1,..., M−1) pulse. It is the value in the range cell of the th (n = 0, 1,..., N−1). Here, M is the number of pulses, and N is the number of range cells. The timing for transmitting and receiving M pulses will be described later.
Similarly, the broadband pulse generated by the transmitter 1 is sent to the polarization switching unit 3 via the transmission / reception switching unit 2, and is irradiated to the observation target from the second polarization transmitting / receiving antenna 5. The reception signal x _3mn , x _4mn is obtained by repeating the same processing for the reception signal of the scattered wave received by the first polarization transmission / reception antenna 4 and the second polarization transmission / reception antenna 5 by the receiver 6. . The received signals x _3mn and x _4mn are also sent to the memory 7 and temporarily stored.

  Here, the reception signal of the first polarization channel is a signal transmitted by the first polarization transmission / reception antenna 4 and received by the first polarization transmission / reception antenna 4, and the reception signal of the second polarization channel is It is defined as a signal transmitted by the first polarization transmitting / receiving antenna 4 and received by the second polarization transmitting / receiving antenna 5. Further, the received signal of the third polarization channel is a signal transmitted by the second polarization transmitting / receiving antenna 5 and received by the second polarization transmitting / receiving antenna 5, and the received signal of the fourth polarization channel is the second polarized wave. It is defined as a signal transmitted by the transmission / reception antenna 5 and received by the first polarization transmission / reception antenna 4.

FIG. 2 shows operation modes of the first polarized wave transmitting / receiving antenna 4 and the second polarized wave transmitting / receiving antenna 5 at each time. Interval in the figure, the received signal _{x 1mn, x 2mn, x 3mn} , a lump of processing required to obtain a set of x _4mn. The interval time is T [seconds]. By repeating this interval M times, signals of each polarization channel are acquired for M pulses. Radar apparatus, when the position of the transmitting and receiving antennas is equal monostatic configuration, it x _2mn and x _4mn are equal, the literature "Radar polarimetry for geoscience applications" ( Ulaby et al, Artech House Inc., 1990), etc. It is shown and is well known. Therefore, in the following description, the received signal x _4mn without using the received signal x _1mn three polarized channel, x _2mn, x _{3 mn} only used. It should be noted that expansion in the case where the number of polarization channels is other than three is easy. The signals for the M pulses and N range cells of the polarization channel 3 channels acquired as described above are temporarily stored in the memory 7.

（ｐ＝１，２，３； ｎ＝０，…，Ｎ−１） The Doppler processing means 8 _applies (1) to the received signal x _pmn (p = 1, 2, 3; m = 0,..., M−1; n = 0,..., N−1) read from the memory 7. The Doppler spectrum X _pkn (k = 0,..., M−1) in the polarization channel p and the range cell n is calculated by performing the processing of the discrete Fourier transform of the _equation (1).

(P = 1, 2, 3; n = 0,..., N−1)

Here, the discrete Fourier transform of equation (1) can be calculated at high speed by FFT (Fast Fourier Transform). The spectrum X _pkn obtained by the equation (1) is a component of the Doppler frequency f _k = k / (M × T) in the polarization channel p and the range cell n. It should be noted that the Doppler resolution can be improved by increasing the number M of transmission pulses, which can improve the clutter suppression performance in the clutter suppression means 14 described later, but the observation time is extended by increasing the number of pulses. In some cases, the range migration compensation process may be required based on the information from the own position information measuring unit 10 before the Doppler process of the equation (1). This is a process used in the conventional synthetic aperture radar technology, for example, a well-known technology described in Ouchi's book "Basics of Synthetic Aperture Radar for Remote Sensing" (Tokyo Denki University Press). For example, an inertial navigation device or a GPS (Global Positioning System) receiver is used as the own position information measuring means 10.

The Doppler spectrum X _pkn (p = 1, 2, 3; k = 0,..., M−1; n = 0,..., N−1) output from the Doppler processing means 8 is sent to the clutter band signal extraction means 9. It is done. The clutter band signal extraction unit 9 performs processing for extracting the Doppler frequency band of the clutter estimated by the clutter band estimation unit 11 from the Doppler spectrum X _pkn of the received signal.
Here, before explaining the details of the operation of the clutter band signal extraction means 9, the operation of the clutter band estimation means 11 will be explained. FIG. 3 is a schematic diagram showing an observation state by a radar device mounted on the platform. If the background is stationary like the ground surface, the clutter Doppler frequency is determined only by the observation parameters such as the moving speed and altitude and beam width of the platform, but if the background is moving like the sea surface, The moving speed also contributes to the magnitude of the clutter Doppler frequency. In the following, however, the clutter is assumed to be stationary first. By doing so, the area where the clutter exists in the Doppler spectrum X _pkn is as follows.

In FIG. 3, it is considered that a platform 16 such as an aircraft equipped with a radar device is moving at a constant linear velocity at an altitude H at a speed _Vpf . At this time, the beam pattern of the antenna faces downward in front of the traveling direction. Let θ be the off-nadir angle at the center of the beam, and let ψ be the 3 dB width of the beam. The range irradiated by the 3 dB wide beam is the footprint 17. The Doppler frequency f _d of the reflected signal from the point P in the direction perpendicular to the traveling direction by an off-nadir angle θ and a prospective angle ψ from the front in the traveling direction is expressed by the equation (2).

ここで、θ_rはプラットフォームの位置から、スラントレンジｒの点までのオフナディア角であり、（４）式の関係を満たす。

Let r be the distance to the nth range cell (this is called the slant range distance r of range cell n). In the slant range r, if the size of the prospective angle in the direction orthogonal to the traveling direction (azimuth direction) is ψ _r (see FIG. 3), the Doppler frequency band in which clutter exists in the Doppler spectrum of the nth range cell. Is a range represented by equation (3).

Here, θ _r is the off-nadir angle from the position of the platform to the point of the slant range r, and satisfies the relationship of equation (4).

The prospective angle Ψ _r of the footprint is a function of the antenna beam pattern and the position of the aircraft and the position of the clutter. Therefore, in the clutter band estimation means 11, the footprint in each range cell n is first determined based on the information on the own position obtained from the own position information measuring means 10 and the speed information, and the beam pattern information of the antenna measured in advance. The prospective angle Ψ _{r of} is calculated. Next, the Doppler frequency band of the clutter in each range cell n is calculated and output by the equation (3). Even in the case where the aircraft does not perform a horizontal uniform linear motion, the Doppler band of the clutter is calculated by the same method as described above by obtaining accurate trajectory information from the accurate own position information measuring means 10. It is possible. In addition, here, the case where the beam pattern of the antenna is directed downward in front of the traveling direction has been described as an example, but even if the beam is directed obliquely forward or sideward with respect to the traveling direction, The Doppler frequency band can be calculated. The clutter band estimation means 11 outputs the Doppler frequency band of the clutter calculated as described above (hereinafter referred to as the clutter band).

The clutter band signal extraction means 9 is a clutter band estimation means 11 from the Doppler spectrum X _pkn (p = 1, 2, 3; k = 0,..., M−1; n = 0,..., N−1). The signal existing in the clutter band calculated in step (1) is extracted as follows.
Since the Doppler spectrum X _pkn in a certain range cell n and Doppler cell k is a _component of Doppler frequency f _k = k / (M × T), the comparison using the formula (5) is performed in each range cell and each Doppler cell. . When the inequality sign in equation (5) is satisfied, the Doppler spectrum X _pkn to be compared is extracted as a signal within the clutter band. On the other hand, when the inequality sign is not satisfied, it is determined that it is outside the clutter band ( However, appropriate end point processing is necessary in the equation (3).)

Note that when the interval period T is wide and the Doppler spectrum of the clutter is folded and observed, the folded region is extracted by, for example, the comparison operation of Equation (6). That is, if the inequality sign in equation (6) holds, the Doppler spectrum X _pkn is extracted as a signal within the clutter band, and if not, it is determined that it is outside the clutter band.
FIG. 4 is a schematic diagram showing the concept of the clutter band in the Doppler spectrum X _pkn of the received signal. The rectangular parallelepiped in the figure is a conceptual model expressing the Doppler spectrum X _pkn as a three-dimensional matrix. An elliptical region indicates that a part of the Doppler spectrum of the received signal is a clutter band. The signal extracted according to the criterion of equation (5) corresponds to the part surrounded by this ellipse.

ここで、ｍｏｄ（ａ，ｂ）は、ａをｂで除算したときの剰余である。クラッタ帯域信号抽出手段９は、以上によってクラッタ領域として抽出された（レンジセル番号ｎ、ドップラーセル番号ｋ）の集合ＣＣを出力する。

Here, mod (a, b) is a remainder when a is divided by b. The clutter band signal extraction means 9 outputs a set CC of (range cell number n, Doppler cell number k) extracted as a clutter region as described above.

The clutter polarization characteristic estimation unit 12 performs the process of estimating the polarization characteristic of the clutter based on the signal included in the clutter band extracted by the clutter band signal extraction unit 9 as follows.
The polarization characteristics of the Doppler spectrum X _pkn in a certain range cell n and Doppler cell k can be expressed by a vector quantity Y _kn as shown in equation (7). Y _kn is a quantity whose direction in the vector space represents the polarization characteristic and whose length represents the signal intensity. Call this vector as a "scattering vector", following equation (7) is a definition equation of the scattering vector.

ただし、上付きの＊Ｔはベクトルおよび行列の共役転置を表し、ＣＣはクラッタのドップラー周波数帯域内に含まれる分解能セルのインデックス番号の集合である。 It is known that the clutter scattering vector can generally be treated as a random vector, and its distribution follows a multivariate normal distribution with a mean of zero (in addition, as the resolution improves, it will follow a multivariate K distribution or Weibull distribution). Has been reported.) The clutter polarization characteristic estimation means 12 performs a process of calculating the average property of the scattering vector in the range cell and the Doppler cell of the signal determined to be within the clutter band by the clutter band estimation means 9. This can be realized by calculating the covariance matrix Σ _c of the scattering vector as in equation (8). That is, the clutter polarization characteristic estimation means 12 calculates the covariance matrix Σ _c according to the equation (8) and outputs it as the polarization characteristic of the clutter. That is, what is expressed by this covariance matrix Σ _c is the clutter polarization characteristic, and calculating this covariance matrix Σ _c by equation (8) is to estimate the clutter polarization characteristic.

However, superscript * T will display the conjugate transpose of a vector and a matrix, CC is a set of index number of resolution cells included in the Doppler frequency band of the clutter.

ただし、λ₁≧λ₂≧λ₃はΣ_cの固有値とする。 Clutter suppression filter generating unit 13, a clutter suppression filter for suppressing the components of the polarization characteristics represented by the covariance matrix sigma _c, is generated as follows.
Here, a polarimetric notch filter (hereinafter referred to as PNF) disclosed in Japanese Patent Laid-Open No. 2003-185733 is used as a clutter suppression filter . Therefore, the clutter suppression filter generation unit 13 first performs a process (eigenvalue decomposition) for diagonalizing the covariance matrix Σ _c using the unitary matrix V as shown in the following equation.

_{However, λ 1 ≧ λ 2 ≧ λ} 3 are the eigenvalues of sigma _c.

（１０）式によって算出されるＰＮＦは、クラッタ偏波特性のうち、その第１主成分をゼロに抑圧して、残りの第２、第３主成分については、白色化するフィルタである。なお、クラッタ抑圧フィルタ生成手段１３の処理で使用されるフィルタはＰＮＦに限定されるものではなく、例えば非特許文献２に示されているＰＷＦ（Polarimetric Whitening Filter）などをはじめとして、従来から知られている偏波情報を用いたクラッタ抑圧用フィルタなどを用いてもよい。 Next, using the eigenvalue of the covariance matrix Σ _c obtained by the processing of equation (9) and the unitary matrix V, the filter coefficient F of PNF is determined as in equation (10) and output.

The PNF calculated by the equation (10) is a filter that suppresses the first principal component of the clutter polarization characteristics to zero and whitens the remaining second and third principal components. Note that the filter used in the processing of the clutter suppression filter generation unit 13 is not limited to PNF, and has been conventionally known, such as PWF (Polarimetric Whitening Filter) shown in Non-Patent Document 2. Alternatively, a clutter suppression filter using polarization information may be used.

（１１）式および（１２）式の処理に従って算出されたＺ_kn（ｋ＝０，…，Ｍ−１；ｎ＝０，…，Ｎ−１）は、クラッタ帯域内についてはクラッタの偏波特性成分が抑圧されており、クラッタ帯域外については雑音電力で正規化された信号である。 The clutter suppression unit 14 first converts a signal existing in the clutter band extracted by the clutter band signal extraction unit 9 from the Doppler spectrum calculated by the Doppler processing unit 8 using the generated clutter suppression filter. On the other hand, the clutter suppression processing by the equation (11) is applied. That is, the vector coefficient Y _kn of the Doppler spectrum is multiplied by the filter coefficient F.

Z _kn = FY _kn (k, n) ∈CC (11)

Also, the clutter suppression unit 14 performs normalization on the signal outside the clutter band using the receiver noise power value σ _N according to the equation (12).

Z _kn (k = 0,..., M−1; n = 0,..., N−1) calculated according to the processing of equations (11) and (12) is the polarization characteristics of the clutter within the clutter band. The sex component is suppressed, and the signal outside the clutter band is a signal normalized by noise power.

ここで、レンジセルｎにおけるストラントレンジはｒであるものとして、オフナディア角は（４）式の定義に従って、θｒとしている。また、ドップラーセルｋにおけるドップラー周波数ｆ_kに対応するアジマス角度ψ_kは（１４）式で表される。

Next, the clutter suppression unit 14 corrects the antenna pattern on the Doppler spectrum. If the arrival direction of the signals of the range cell n and the Doppler cell k is the off-nadir angle θr and the azimuth angle ψ _k and the gain of the antenna pattern in this direction is G (θr, ψ _k ), The antenna pattern can be corrected.

Here, it is assumed that the strain range in the range cell n is r, and the off-nadir angle is θr according to the definition of the equation (4). Further, the azimuth angle [psi _k corresponding to the Doppler frequency f _k of the Doppler cell k is expressed by equation (14).

The clutter suppression unit 14 performs the process of applying the clutter suppression filter as described above, and outputs a signal W _kn (k = 0,..., M−1; n = 0,..., N−1) in which the clutter is suppressed. . Note that W _kn is a vector quantity having the dimension of the scattering vector.

（ｎ＝０，…，Ｎ−１）
次に、電力和Ｐ_nを予め設定した閾値Ｔと比較し、（１６）式の規則に従って目標の検出判定を行い、目標と判定されたレンジセルｎの値を出力する。

Ｐ_n≧Ｔ（目標有りと判定）
Ｐ_n＜Ｔ（目標無しと判定） （１６）
（ｎ＝０，…，Ｎ−１）
The target detection unit 15 performs target detection determination by comparing the Doppler spectrum in which clutter is suppressed by the clutter suppression unit 14 with a threshold as follows.
First, after calculating the power sum of all polarization channels in each range cell and each Doppler cell from the Doppler spectrum W _kn in which the clutter is output, which is output from the clutter suppression means 14, the power sum P _n of each range cell n is calculated. calculate. This calculation formula is expressed by (15).

(N = 0, ..., N-1)
Next, the power sum P _n is compared with a preset threshold value T, a target detection determination is performed according to the rule of equation (16), and the value of the range cell n determined as the target is output.

P _n ≧ T (determines that there is a target)
P _n <T (determined that there is no target) (16)
(N = 0, ..., N-1)

  As described above, according to the first embodiment, since the clutter is suppressed using information on the polarization characteristics of the clutter and the Doppler frequency, the target detection performance can be improved. In addition, since the signal of the Doppler frequency band of the clutter is first extracted from the Doppler spectrum of the received signal, and the polarization characteristics of the clutter are estimated using the extracted signal, the estimation accuracy of the polarization characteristics of the clutter is estimated. Can be improved. In the conventional method of Non-Patent Document 3, when the number of hits is M and the number of polarization channels is P, eigenvalue analysis of a covariance matrix of (M × P) × (M × P) is necessary. In Embodiment 1, since the size of the covariance matrix for performing eigenvalue analysis is P × P, the amount of calculation can be reduced. Therefore, the radar apparatus according to the first embodiment can be applied to any moving body such as an aircraft and an automobile.

It is a block diagram which shows the structure of the radar apparatus by Embodiment 1 of this invention. It is a time chart shown about the operation mode of each time of the 1st polarization transmission / reception antenna which concerns on Embodiment 1 of this invention, and a 2nd polarization transmission / reception antenna. It is a schematic diagram which shows the observation condition by the radar apparatus mounted in the platform which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the concept of the clutter area | region in the Doppler spectrum which concerns on Embodiment 1 of this invention. It is a block diagram explaining the conventional method of suppressing clutter using the information of a Doppler frequency and a polarization characteristic simultaneously.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmitter (transmission means), 2 Transmission / reception switch, 3 Polarization switch, 4 1st polarization transmission / reception antenna, 5 2nd polarization transmission / reception antenna, 6 Receiver (reception means), 7 Memory, 8 Doppler processing means , 9 Clutter band signal extraction means, 10 Own position information measurement means, 11 Clutter band estimation means, 12 Clutter polarization characteristic estimation means, 13 Clutter suppression filter generation means, 14 Clutter suppression means, 15 Target detection means.

Claims (2)

In a radar apparatus that calculates a Doppler spectrum in each range cell from received signals obtained by transmitting and receiving a plurality of pulses, suppresses clutter from the calculated Doppler spectrum, and detects a moving small target.
A clutter band estimating means for calculating the Doppler frequency band of the clutter;
A clutter band signal extraction means for extracting a signal present in the Doppler frequency band of the clutter from the Doppler spectrum of the received signal;
Clutter for estimating the clutter polarization characteristic expressed by the covariance matrix Σ _c based on the signal existing in the Doppler frequency band of the extracted clutter by calculating the covariance matrix Σ _c by the following equation (8) Polarization characteristic estimation means;
The filter F coefficients of clutter suppression filter for suppressing the components of the estimated clutter polarization characteristics, by using the unitary matrix V diagonalizing eigenvalues and covariance matrix sigma _c of the covariance matrix sigma _c A clutter suppression filter generating means that is generated by calculation according to the following equation (10);
Clutter suppression means for applying the clutter suppression filter to the Doppler spectrum existing in the Doppler frequency band of the clutter among the Doppler spectrum of the received signal to suppress a component corresponding to the polarization characteristic of the clutter. ,
Radar comprising target detection means for calculating a power sum of a range cell from the following equation (15) from the Doppler spectrum in which clutter is suppressed by the clutter suppression means, and comparing the result with a threshold value to determine target detection. apparatus.

However, CC is Ri set der index numbers resolution cell contained within the Doppler frequency range of the clutter, Y _kn is the scattering vector in resolution cell k, n. Further, λ ₂ and λ ₃ are two of the three eigenvalues of the covariance matrix Σ _c excluding the largest one.
Further, W _kn is a scattering vector obtained by performing the following processing on the scattering vector Y _kn . That is, the scattering vector Y _kn in the resolution cell included in the Doppler frequency band of the clutter is subjected to a process of suppressing the clutter by multiplying by the clutter suppression filter coefficient given by the equation (10). Further, the scattering vector Y _kn in the resolution cell outside the Doppler frequency band of the clutter is subjected to a process of normalizing with the receiver noise power. Thereafter, an appropriate antenna pattern correction process is performed on all resolution cells.   The clutter band estimation means is based on the position information and speed information of the own apparatus given from the own apparatus position information measuring means of the platform on which the radar device is mounted, and the beam pattern information of the antenna measured in advance. The radar apparatus according to claim 1, wherein a Doppler frequency band of clutter is calculated.

Images