JP2015036628A - Passive radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a passive radar device capable of depressing a clutter in addition to a direct wave.SOLUTION: A receiving signal vector forming portion 9 forms a receiving signal vector from a frequency spectrum obtained by an SUR system FFT portion 5 and an REF system FFT portion 8. An unnecessary wave suppressing portion 10 carries out unnecessary wave suppression from the receiving signal vector of the receiving signal vector forming portion 9 and the frequency spectrum from the REF system FFT portion 8, and obtains a receiving signal vector after unnecessary wave suppression. An IFFT portion 11 applies inverse fast discrete Fourier transform to the receiving signal after unnecessary wave suppression, thereby obtaining correlation output after unnecessary wave suppression.

Description

  The present invention relates to a passive radar device that does not transmit radio waves and that receives a transmission signal from another transmission source operating in an uncooperative manner with itself and performs target detection and the like.

The passive radar itself does not transmit radio waves but receives transmission signals from other transmission sources operating in an uncooperative manner with itself, and performs target detection and the like. As a transmission source, an artificial satellite, a radio tower, or the like is used, and a television broadcast wave or the like is used as a transmission signal. The target signal is detected by obtaining the cross-correlation between the direct wave of the transmission signal from the transmission source and the target scattered wave that is reflected and arrives at the target, etc., and the estimated value of the propagation distance and the arrival angle is further obtained. Perform position estimation.
The passive radar is composed of two reception systems, a REF system that receives direct waves and a SUR system that receives target scattered waves, and a signal processing unit that performs target detection and the like using these outputs. Since the direct wave power received by the passive radar is generally sufficiently larger than the target signal power, the REF system is designed to selectively receive only the direct wave using a relatively low gain antenna. The SUR system uses a relatively high gain antenna so as to receive a weak target signal power, and is designed to suppress the reception power of the direct wave in order to avoid degradation of the target detection capability.
When a direct wave is received by the SUR system, the cross-correlation output includes a cross-correlation component of the direct wave. In particular, when direct wave suppression is not sufficient, there is a problem that the cross-correlation component of the weak target signal is buried in the cross-correlation side lobe of the direct wave, and the target detection capability deteriorates.
When detecting a low altitude target, the SUR antenna beam is directed in the low elevation direction. At this time, the SUR system also receives clutter reflected by a plurality of fixed objects such as buildings, mountains, and seas existing in the same direction. When the clutter reception power is large, the cross-correlation component of the weak target signal is buried in the cross-correlation side lobe of the clutter, and there is a problem that the target detection capability deteriorates as in the case of the direct wave.

  Therefore, as a method for solving the problem of target detection capability degradation caused by such direct waves and clutter (hereinafter, sometimes referred to as unnecessary waves collectively), for example, a passive radar device as shown in Patent Document 1 is used. there were.

JP 2013-44642 A

  The conventional passive radar device disclosed in Patent Document 1 is intended to selectively suppress only direct waves that cause degradation of target detection capability. Therefore, when the influence of clutter is negligible, such as when detecting a relatively high target, it is possible to improve target detection capability degradation due to direct waves. However, when the influence of clutter cannot be ignored, such as when detecting a low altitude target, there has been a problem that target detection capability deterioration cannot be sufficiently improved.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a passive radar device capable of suppressing not only direct waves but also clutter.

  A passive radar device according to the present invention includes a SUR system receiving unit that receives a reflected wave from a target and a direct wave from a clutter and a transmission station by a signal transmitted from a transmitting station that operates uncoordinated with itself, and a SUR system receiving A SUR-based FFT unit that obtains a frequency spectrum by applying a fast discrete Fourier transform to the received signal of the signal receiving unit, a REF-based receiving unit that receives a direct wave of the signal transmitted from the transmitting station, and a reception of the REF-based receiving unit A REF FFT unit that obtains a frequency spectrum by applying a fast discrete Fourier transform to the signal, a received signal vector formation unit that forms a received signal vector from the frequency spectrum obtained by the SUR system FFT unit and the REF system FFT unit, Received by the SUR receiving unit from the received signal vector of the received signal vector forming unit and the frequency spectrum from the REF FFT unit. An unnecessary wave suppression unit that suppresses unnecessary waves and obtains a reception signal vector after unnecessary wave suppression, and an IFFT that calculates an inverse correlation after unnecessary wave suppression by applying an inverse fast discrete Fourier transform to the reception signal vector after unnecessary wave suppression Part.

  The passive radar device according to the present invention suppresses unnecessary waves received by the SUR system reception unit from the reception signal vector of the reception signal vector forming unit and the frequency spectrum from the REF system FFT unit, and receives signal vectors after unnecessary wave suppression. Therefore, a passive radar device capable of suppressing not only direct waves but also clutter can be obtained.

It is a block diagram which shows the passive radar apparatus by Embodiment 1 of this invention. It is a block diagram which shows the unnecessary wave suppression part of the passive radar apparatus by Embodiment 1 of this invention. It is a block diagram which shows an example of the unnecessary wave delay time estimation part of the passive radar apparatus by Embodiment 1 of this invention. It is a block diagram which shows the other example of the unnecessary wave delay time estimation part of the passive radar apparatus by Embodiment 1 of this invention. ^B passive radar apparatus according to Embodiment 1 of the present invention (h) ^[j], is an explanatory diagram showing a relationship between _{^{b (h) [j-i}} s]. It is a block diagram which shows the unnecessary wave suppression part of the passive radar apparatus by Embodiment 2 of this invention. It is a block diagram which shows the unnecessary wave suppression part of the passive radar apparatus by Embodiment 3 of this invention. It is a block diagram which shows the passive radar apparatus by Embodiment 4 of this invention.

Embodiment 1 FIG.
In the first embodiment, unnecessary waves that arrive at the SUR system are suppressed.
1 to 4 are configuration diagrams showing Embodiment 1 of the passive radar device of the present invention.
First, FIG. 1 will be described.
In FIG. 1, a transmission station 1 is a transmission source that generates a transmission signal by operating in a coordinated manner with a passive radar. The transmission antenna 2 is an antenna that spatially radiates a transmission signal generated by the transmission station 1. Further, in FIG. 1, a SUR system antenna 3, a SUR system receiver 4, a SUR system FFT unit 5, a REF system antenna 6, a REF system receiver 7, a REF system FFT unit 8, a received signal vector forming unit 9, an unnecessary wave suppression. Unit 10 and IFFT unit 11 represent the passive radar device according to the first embodiment.

  The SUR antenna 3 propagates directly from the transmission antenna 2, the target scattered wave reflected from the target 100 such as an aircraft, the clutter reflected from the building, mountain, sea, etc. It is an antenna that receives direct waves. The SUR receiver 4 is a device that digitizes a signal received at the SUR antenna 3 by predetermined frequency conversion and AD conversion, and constitutes a SUR receiver together with the SUR antenna 3. The SUR system FFT unit 5 is a processing unit that obtains a frequency spectrum by applying a fast discrete Fourier transform to a received signal from the SUR system receiver 4. The REF antenna 6 is an antenna that receives a direct wave in which a transmission signal spatially radiated from the transmission antenna 2 is directly propagated. The REF receiver 7 is a device that digitizes a signal received by the REF antenna 6 by predetermined frequency conversion and AD conversion, and constitutes a REF receiver together with the REF antenna 6. The REF FFT unit 8 is a processing unit that obtains a frequency spectrum by applying a fast discrete Fourier transform (FFT) to the received signal from the REF receiver 7. The received signal vector forming unit 9 is a processing unit that forms a received signal vector from the frequency spectrum from the SUR-based FFT unit 5 and the REF-based FFT unit 8. The unnecessary wave suppression unit 10 suppresses unnecessary waves received by the SUR system reception unit from the reception signal vector from the reception signal vector formation unit 9 and the frequency spectrum from the REF system FFT unit 8, and receives the signal after unnecessary wave suppression. A processing unit for obtaining a signal vector. The IFFT unit 11 is a processing unit that applies an inverse fast discrete Fourier transform (IFFT: Inverse FFT) to the reception signal vector after unnecessary wave suppression from the unnecessary wave suppression unit 10 to obtain a cross-correlation output after unnecessary wave suppression.

  Next, the configuration of the unnecessary wave suppression unit 10 will be described with reference to FIG. The unnecessary wave suppression unit 10 shown in FIG. 2 includes an unnecessary wave delay time estimation unit 20, an unnecessary wave FFT unit 21, a complex power spectrum estimation unit 22, a first orthogonal projection matrix calculation unit 23, and a first orthogonal projection unit 24. I have. The unnecessary wave delay time estimation unit 20 is a processing unit that estimates the delay time of the unnecessary wave arrival time from the reception signal vector from the reception signal vector formation unit 9 to the REF system with respect to the SUR system. The unnecessary wave FFT unit 21 is a processing unit that obtains a frequency spectrum in which an FFT based on an unnecessary wave delay time is applied to a received signal from the REF receiver 7. The complex power spectrum estimation unit 22 is a processing unit that obtains a complex power spectrum from the frequency spectra of the REF system and the unnecessary wave FFT unit 21. The first orthogonal projection matrix calculation unit 23 generates an orthogonal projection matrix for unnecessary wave suppression from the complex power spectrum from the complex power spectrum estimation unit 22 and the unnecessary wave delay time from the unnecessary wave delay time estimation unit 20. This is a processing unit to be obtained. The first orthogonal projection unit 24 multiplies the reception signal vector from the reception signal vector formation unit 9 by the orthogonal projection matrix from the first orthogonal projection matrix calculation unit 23 to obtain a reception signal vector after unnecessary wave suppression. It is.

Next, the configuration of the unnecessary wave delay time estimation unit 20 in FIG. 2 will be described.
FIG. 3 is a block diagram illustrating an example of the unnecessary wave delay time estimation unit 20. In this example, the unnecessary wave delay time estimation unit 20 includes a delay time estimation system IFFT unit 30, an amplitude detection unit 31, a direct wave delay time sample number estimation unit 32, and a clutter delay time sample number estimation unit 33. The delay time estimation system IFFT unit 30 is a processing unit that obtains a cross-correlation output by applying inverse fast discrete Fourier transform to the received signal vector from the received signal vector forming unit 9. The amplitude detection unit 31 is a processing unit that obtains an amplitude detection signal of a cross-correlation output from the delay time estimation system IFFT unit 30. The direct wave delay time sample number estimation unit 32 is a processing unit that estimates a sample number corresponding to the direct wave delay time from the amplitude detection signal output from the amplitude detection unit 31. The clutter delay time sample number estimation unit 33 calculates the clutter from the amplitude detection signal output from the amplitude detection unit 31, the direct wave delay time sample number output from the direct wave delay time sample number estimation unit 32, and the number of clutters. It is a processing unit that estimates a delay time sample number.

  FIG. 4 is a block diagram illustrating another example of the unnecessary wave delay time estimation unit 20. In this example, the unnecessary wave delay time estimation unit 20 includes a delay time estimation system IFFT unit 30, an amplitude detection unit 31, and an unnecessary wave delay time sample number estimation unit 34. The delay time estimation system IFFT unit 30 and the amplitude detection unit The unit 31 has the same configuration as that shown in FIG. The unnecessary wave delay time sample number estimation unit 34 estimates the unnecessary wave delay time sample number for the amplitude detection signal output from the amplitude detection unit 31 based on one of the number of clutters, the threshold, and the cumulative power ratio. Is a processing unit.

  Next, the flow of processing in the passive radar device according to the first embodiment will be described with reference to FIGS. In the description, the theory of the unnecessary wave suppression method in the passive radar device of the present invention is first described, and then the flow of the processing is clarified by showing the correspondence with each processing shown in FIGS.

ＳＵＲ系には、直接波がＲＥＦ系に到達した時間を基準とする遅延時間ｔ_０を伴う直接波ｂ（ｔ−ｔ_０）に加え、同遅延時間ｔ_ｋ（ｋ＝１，…，Ｋ）を伴うＫ個のクラッタ、および同遅延時間ｔ_Ｓの目標散乱波が到来する。これらを含む受信信号をｚ_ｓｕｒ（ｔ）とすると、そのサンプリング後の受信信号ｚ_ｓｕｒ［ｉ］は以下のように与えられる。

ただし、○はアダマール積である。また，ｉ_０，ｉ_ｋ，ｉ_Ｓはそれぞれ遅延時間ｔ_０，ｔ_ｋ，ｔ_ｓに対応するサンプリング番号である。
ＲＥＦ系には直接波を含む受信信号ｚ_ｒｅｆ（ｔ）が受信される。そのサンプリング後の受信信号ｚ_ｒｅｆ［ｉ］とすると、以下のように与えられる。ただし、β_０，ｎ_ｒｅｆ［ｉ］はそれぞれ距離等による減衰係数、ＲＥＦ系受信機雑音である。

さらに以降の説明では、ＲＥＦ系アンテナの受信機雑音は直接波に比べて無視できるものとし、以降では次式のように扱う。

Now, when a transmission signal received by the REF system, that is, a direct wave is b (t) and this is sampled at a constant interval Δt, the direct wave b [i] after sampling can be expressed as follows. However, i is a sampling number.

In the SUR system, the delay time t _k (k = 1,..., K) is added to the direct wave b (t−t ₀ ) with a delay time t ₀ based on the time when the direct wave reaches the REF system. And K target clutters with the same delay time t _S arrive. If a received signal including these is z _sur (t), the received signal z _sur [i] after sampling is given as follows.

However, (circle) is a Hadamard product. _Further, a _{i 0,} i _k, i _S the delay time _{t 0,} t k, a sampling number corresponding to the _{t s.}
The REF system receives a reception signal z _ref (t) including a direct wave. If the received signal z _ref [i] after the sampling is given, it is given as follows. Here, β ₀ , n _ref [i] are an attenuation coefficient due to distance and the like, and REF receiver noise, respectively.

Further, in the following description, the receiver noise of the REF antenna is assumed to be negligible compared to the direct wave, and is handled as follows in the following.

さらにサンプリング後の受信信号で表すと以下のようになる。

実際の相互相関は±∞で定義されたｚ_ｓｕｒ（ｔ），ｚ_ｒｅｆ（ｔ）に対して有限な区間を設け、区間毎に処理を行う。本稿ではこの区間のことをＰＲＩ（Ｐｕｌｓｅ Ｒｅｐｅｔｉｔｉｏｎ Ｉｎｔｅｒｖａｌ）と呼ぶことにする。以降では、ＰＲＩ毎の相互相関処理の定式化を行う。
式（１）にて、サンプリング後の直接波ｂ［ｉ］を定義したが、インパルス信号δ［ｉ］を用いれば、以下のように表すことができる。

次に、各ＰＲＩ内での受信信号のサンプル数をＲＢとし、サンプル番号をｊ＝１，…，ＲＢとすると、ｉは次式のようなｊとｈの関数となる。ただし、ｈはＰＲＩに与えるインデックス番号である。

よって、直接波ｂ［ｉ］は以下のように表すことができる。

Cross-correlation is a correlation process with received signals z _sur (t) and z _ref (t) according to the following equation.

Further, the received signal after sampling is expressed as follows.

In actual cross-correlation, a finite interval is provided for z _sur (t) and z _ref (t) defined by ± ∞, and processing is performed for each interval. In this paper, this section is referred to as PRI (Pulse Repeat Interval). Thereafter, the cross-correlation process for each PRI is formulated.
Although the direct wave b [i] after sampling is defined by the expression (1), if the impulse signal δ [i] is used, it can be expressed as follows.

Next, assuming that the number of received signal samples in each PRI is RB and the sample numbers are j = 1,..., RB, i is a function of j and h as shown in the following equation. Here, h is an index number given to PRI.

Therefore, the direct wave b [i] can be expressed as follows.

式（１１）および式（１０）より、第ｈ番目のＰＲＩにて処理する直接波ｂ^（ｈ）［ｊ］が以下のように導かれる。

Next, consider the correlation processing in the h-th PRI. The target received signals are only those received by the PRI, and the received signals other than the PRI are not processing targets. Therefore, the received signals z _ref ^(h) [j] and z _sur ^(h) [j] processed in the h-th PRI are defined as follows. Here, j = 1,..., RB is a sample number in the PRI, and RB is the number of samples of the received signal. z _ref ^(h) [j], z _sur ^(h) [j] is defined under the condition of j = 1,..., RB, h = h to be processed.

From the equations (11) and (10), the direct wave b ^(h) [j] processed by the h-th PRI is derived as follows.

よって、式（１３）および式（１４）の関係を用いると、式（１１）および式（１２）の受信信号ｚ_ｒｅｆ ^（ｈ）［ｊ］，ｚ_ｓｕｒ ^（ｈ）［ｊ］はそれぞれ以下のように表される。

Further, a direct wave b ^(h) [j−i _s ] with a delay processed in the h-th PRI is defined as follows. FIG. 5 shows the relationship between b ^(h) [j] and b ^(h) [j−i _s ].

Therefore, using the relationship of Expression (13) and Expression (14), the received signals z _ref ^(h) [j] and z _sur ^(h) [j] in Expression (11) and Expression (12) are respectively It is expressed as follows.

よって、ＰＲＩ内の受信信号ｚ_ｒｅｆ［ｊ］，ｚ_ｓｕｒ［ｊ］の相互相関出力ｙ［ｊ］は以下のように表される。

Hereinafter, the generality is not lost, and the PRI corresponding to the index number h = 0 will be described.
When h = 0, the equations (15) and (16) are as follows. However, in order to simplify the description, z _ref ⁽⁰⁾ [j] and z _sur ⁽⁰⁾ [j] are represented as z _ref [j] and z _sur [j], respectively.

Therefore, the cross-correlation output y [j] of the received signals z _ref [j] and z _sur [j] in the PRI is expressed as follows.

よって、ＳＵＲ系とＲＥＦ系の受信信号の周波数スペクトルをそれぞれ離散フーリエ変換（通常はＦＦＴを用いる）により求め、これらのスペクトル積を逆離散フーリエ変換（通常はＩＦＦＴを用いる）することにより、相互相関出力ｙ［ｊ］を求めることができる。 Here, since the calculation of Expression (19) is a convolution calculation, it is often performed in the frequency domain instead of the time domain to increase the speed. This is because the discrete Fourier transform of Equation (19) is the product of the frequency spectrum z _sur [m] of the received signal z _sur [j] and the complex conjugate z _ref ^* [m] of the frequency spectrum of the received signal z _ref [j]. Based on the correlation theorem of equality. That is, the following relationship is established. Arrow ⇔ represents discrete Fourier transform and inverse discrete Fourier transform operations. Here, m = 1,..., M is a frequency spectrum number, and M (≧ 2 · RB−1) is a frequency spectrum score.

Therefore, the cross-correlation is obtained by obtaining the frequency spectra of the received signals of the SUR system and the REF system by discrete Fourier transform (usually using FFT) and inverse discrete Fourier transform (usually using IFFT) of these spectral products. The output y [j] can be determined.

Here, when B [m] is a frequency spectrum of the direct wave b [j] of the PRI of interest, it can be expressed as follows.

以上の説明に基づき、式（１７）および式（１８）によるｚ_ｒｅｆ［ｊ］，ｚ_ｓｕｒ［ｊ］の周波数スペクトルは以下のように表せる。

よって、スペクトル乗算値Ｘ（ｍ）は以下のように表される。ただし、Ｎ［ｍ］＝Ｂ^＊［ｍ］Ｎ_ｓｕｒ［ｍ］である。

Next, a direct wave in the SUR system with a delay will be considered using b [j−i _s ]. b [j−i _s ] is expressed as follows, and the first term on the right side is obtained by delaying the _s samples of the latter half of the direct wave received by the REF system in the PRI immediately before the PRI of interest by _s samples. There, the second term is a _{RB-i s} samples of the direct wave front half of interest PRI.

Based on the above description, the frequency spectra of z _ref [j] and z _sur [j] according to the equations (17) and (18) can be expressed as follows.

Therefore, the spectrum multiplication value X (m) is expressed as follows. However, N [m] = B ^* [m] N _sur [m].

式（３０）より、以下のように変形できる。ただし、以降の議論に関係のないβ_０ ^＊は省略した（β_０ ^＊＝１とした）。

A single snapshot received signal vector x in which X [m] are arranged is defined.

From the equation (30), it can be modified as follows. However, β ₀ ^{* which} is not related to the following discussion was omitted (β ₀ ^* = 1).

Ａ_ｕｕここで、ｙ_ＩＦＦＴ，Ｗはそれぞれ以下のとおりである。

このとき、従来の相互相関出力は、Ｍサンプルで構成されるｙ_ＩＦＦＴからＲＢサンプルを取り出したｙとなる。

Subsequently, in order to obtain the cross-correlation output y [j] of the conventional method, IFFT is performed on the received signal vector. The m-th coefficient vector of FFT is set to w _m , and the following y _IFFT is obtained.

A _u u where y _IFFT and W are as follows.

At this time, the conventional cross-correlation output is y obtained by extracting the RB sample from the y _IFFT composed of M samples.

式（４９）による射影行列Ｐ_ｎｕｌｌを受信信号ベクトルｘに乗じると、以下のように不要波抑圧後受信信号ベクトルｘ_ｎｕｌｌが得られる。

次いで、不要波抑圧後の相互相関出力ｙ_ｎｕｌｌ［ｊ］を得るために不要波抑圧後受信信号ベクトルｘ_ｎｕｌｌに対するＩＦＦＴを行い、以下のｙ_{ＩＦＦＴ，ｎｕｌｌ}を求める。

このとき、不要波抑圧後の相互相関出力は、Ｍサンプルで構成されるｙ_{ＩＦＦＴ，ｎｕｌｌ}からＲＢサンプルを取り出したｙ_ｎｕｌｌとなる。 The unnecessary wave included in the received signal vector x is A _u u in Expression (35). Therefore, the following projection matrix P _null is obtained.

By multiplying the reception signal vector x by the projection matrix P _null according to Equation (49), a reception signal vector x _null after unnecessary wave suppression is obtained as follows.

Next, in order to obtain the cross-correlation output y _null [j] after unnecessary wave suppression, IFFT is performed on the reception signal vector x _null after unnecessary wave suppression to obtain the following y _{IFFT, null} .

At this time, the cross-correlation output after unnecessary wave suppression is y _null obtained by extracting the RB sample from y _{IFFT, null} composed of M samples.

As described above, the theory of the unwanted wave suppression method in the passive radar device of the present invention has been described. In the following, the correspondence between the above theory and each process shown in FIGS. 1 to 4 will be shown, and the flow of the process will be clarified.
First, processing of the components shown in FIG. 1 will be described. A transmission signal b (t) generated by the transmission station 1 operating in a non-cooperative manner with the passive radar is spatially radiated from the transmission antenna 2 and reflected by the target 100, K clutters, and the transmission antenna 2. The direct wave directly propagated from the SUR system antenna 3 and the SUR system receiver 4 is received. The REF antenna 6 and the REF receiver 7 receive direct waves. These received signals z _sur [i] and z _ref [i] are expressed as shown in equations (2) and (3), respectively. Next, in the SUR system FFT unit 5 and the REF system FFT unit 8, the frequency spectra Z _sur [m] and Z _ref [m] are obtained from the received signals z _sur [i] and z _ref [i], respectively, and the equations ( 25) and equation (26). From the frequency spectra Z _sur [m] and Z _ref [m], the received signal vector forming unit 9 forms an M-dimensional received signal vector x shown in Expression (35). The unwanted wave suppression unit 10 receives the received signal vector x, the REF system frequency spectrum Z _ref [m], and the REF system received signal z _ref [i], and outputs the unwanted signal suppressed received signal vector x _null . IFFT section at 11 _{x null} is entered, the cross-correlation output _{y null} after unnecessary wave suppression is obtained by the equation (51).

Next, FIG. 2 will be described. In the unnecessary wave delay time estimation unit 20, the sample numbers i ₀ and i _k corresponding to the delay time estimation values of the direct wave and K clutters from the waveform obtained by amplitude detection of the normal cross-correlation output y shown in the equation (48). Ask for. The method for obtaining the sample numbers i ₀ and i _k will be described later. Next, the unnecessary wave FFT unit 21 first converts b [j−i ₀ ] and b [j−i _k ] according to Expression (23) from the sample numbers i ₀ and i _{k of the} unnecessary wave delay time to the REF system received signal. Take out from z _ref [i]. Subsequently, FFT is applied to b [j−i ₀ ] and b [j−i _k ], and unnecessary wave frequency spectra B ₀ [m] and B _k [m] according to Expressions (27) and (28) are applied. Ask. The complex power spectrum estimation unit 22 obtains complex power spectrum vectors c ₀ and c _{k according} to the equations (31), (32), (36), and (37) from the frequency spectrum of the REF system and unnecessary waves. In the first orthogonal projection matrix calculation unit 23, the sample number _i 0, _{i k} delay time by Equation (39) and (40) from the steering vector _a 0, seeking _{a k,} the delay time steering vector _a 0, a _The projection matrix P _{null according} to the equation (49) is obtained from _k and the complex power spectrum vectors c ₀ and c _k . The first orthogonal projection unit 24 obtains a reception signal vector x _null after unnecessary wave suppression from the projection matrix P _null and the reception signal vector x according to Expression (50).

FIG. 3 shows an example of how to obtain the sample numbers i ₀ and i _k . The delay time estimation system IFFT unit 30 obtains a cross-correlation output based on the equations (45) to (48) from the received signal vector. The amplitude detector 31 obtains an amplitude detection signal from the cross-correlation output. The direct wave delay time sample number estimation unit 32 outputs the sample number corresponding to the maximum value of the amplitude detection signal as the sample number i ₀ corresponding to the direct wave delay time. The clutter delay time sample number estimation unit 33 selects K amplitude detection signal peaks corresponding to a far distance from the sample number i ₀ based on the sample number i ₀ and a preset number of clutters K, and responds to this. and outputs the sample number as sample number i _k corresponding to the clutter delay time. Alternatively, it may be output to the K adjacent sample number corresponding than the sample number i ₀ to far range as sample number i _k corresponding to the clutter delay time.

FIG. 4 shows another example of how to obtain the sample numbers i ₀ and i _k as in FIG. The delay time estimation system IFFT unit 30 and the amplitude detection unit 31 are the same as the operations described in FIG. The unnecessary wave delay time sample number estimation unit 34 selects the top K + 1 amplitude detection values or peaks having a value larger than that of the amplitude detection signal based on the sample number i ₀ and the preset number K of clutters, and samples corresponding thereto. The numbers are output as sample numbers i ₀ and i _k corresponding to the unnecessary wave delay time. Alternatively, a threshold for the amplitude detection value may be set without using the number K of clutters, and the sample number of the amplitude detection value exceeding the threshold may be output as the sample numbers i ₀ and i _k corresponding to the unnecessary wave delay time. Further, without using the number of clutters K or the threshold, the amplitude detection value of the unnecessary wave is selected based on the preset cumulative power ratio, and the corresponding sample number is set to the sample number i ₀ , corresponding to the unnecessary wave delay time. It may be output as i _k . The cumulative power ratio is the ratio of the sum of these detection values to the sum of all detection values when the detection values of the amplitude detection signal are sorted in descending order and an appropriate number of detection values are selected in this order. .

  As described above, according to the passive radar device of the first embodiment, the SUR that receives the reflected wave from the target and the direct wave from the clutter and the transmitting station by the signal transmitted from the transmitting station that operates in cooperation with itself. System receiving unit, SUR system FFT unit for obtaining a frequency spectrum by applying a fast discrete Fourier transform to the received signal of the SUR system receiving unit, and a REF system receiving unit for receiving a direct wave of a signal transmitted from a transmitting station A REF FFT unit for obtaining a frequency spectrum by applying a fast discrete Fourier transform to the received signal of the REF receiving unit, and a received signal vector from the frequency spectrum obtained by the SUR FFT unit and the REF FFT unit The received signal vector forming unit, the received signal vector of the received signal vector forming unit, the frequency spectrum from the REF FFT unit, etc. Suppression of unwanted waves received by the SUR system receiver, unnecessary wave suppression unit for obtaining a received signal vector after unnecessary wave suppression, and unnecessary fast wave suppression by applying inverse fast discrete Fourier transform to the received signal vector after unnecessary wave suppression Since the IFFT unit for obtaining the post-correlation output is provided, the direct wave and the clutter can be suppressed even when not only the direct wave but also the influence of the clutter cannot be ignored.

  In addition, according to the passive radar device of the first embodiment, the unnecessary wave suppression unit estimates the delay time of the unnecessary wave arrival time from the received signal vector to the REF system relative to the SUR system, A complex power spectrum is obtained from an unnecessary wave FFT unit for obtaining a frequency spectrum to which a fast discrete Fourier transform based on an unnecessary wave delay time is applied to a reception signal from a REF system receiver, and a frequency spectrum of the REF system and the unnecessary wave FFT unit. Complex power spectrum estimation unit, first orthogonal projection matrix calculation unit for obtaining orthogonal projection matrix for unnecessary wave suppression from complex power spectrum and unnecessary wave delay time, and reception signal vector multiplied by orthogonal projection matrix Since the first orthogonal projection unit for obtaining the received signal vector after wave suppression is provided, direct waves and clutter can be efficiently suppressed. That.

  Further, according to the passive radar device of the first embodiment, the unnecessary wave delay time estimation unit applies the inverse fast discrete Fourier transform to the received signal vector from the received signal vector forming unit to obtain the cross correlation output. An estimation system IFFT unit, an amplitude detection unit for obtaining an amplitude detection signal of a cross-correlation output from the delay time estimation system IFFT unit, and a direct wave delay time sample number for estimating a sample number corresponding to the direct wave delay time from the amplitude detection signal Equipped with an estimation unit and a clutter delay time sample number estimation unit that estimates the clutter delay time sample number from the amplitude detection signal, direct wave delay time sample number, and the number of clutters, so that direct waves and clutters can be efficiently suppressed. be able to.

  Further, according to the passive radar device of the first embodiment, the unnecessary wave delay time estimation unit applies the inverse fast discrete Fourier transform to the received signal vector from the received signal vector forming unit to obtain the cross correlation output. An estimation system IFFT unit, an amplitude detection unit for obtaining an amplitude detection signal of a cross-correlation output from the delay time estimation system IFFT unit, and an unnecessary wave delay based on any of the number of clutters, a threshold, and a cumulative power ratio with respect to the amplitude detection signal Since the unnecessary wave delay time sample number estimation unit for estimating the time sample number is provided, direct waves and clutter can be efficiently suppressed.

Embodiment 2. FIG.

FIG. 6 is a configuration diagram of the unnecessary wave suppression unit 10 according to the second embodiment. The basic configuration of the second embodiment is the same as that of the passive radar device shown in FIG. 1, and will be described with reference to FIG. However, in the second embodiment, a connection line from the REF receiver 7 in FIG. 1 to the unnecessary wave suppression unit 10 is not necessary.
The unnecessary wave suppression unit 10 illustrated in FIG. 6 includes an unnecessary wave delay time estimation unit 20, a second orthogonal projection matrix calculation unit 23a, a second orthogonal projection unit 24a, and a power spectrum estimation unit 25. Here, the unnecessary wave delay time estimation unit 20 is the same as the unnecessary wave delay time estimation unit 20 shown in FIG. 3 and FIG. The power spectrum estimation unit 25 is a processing unit that obtains the power spectrum of the REF system frequency spectrum. The second orthogonal projection matrix calculation unit 23a is a processing unit that obtains an orthogonal projection matrix for suppressing unnecessary waves from the power spectrum obtained by the power spectrum estimation unit 25 and the delay time steering vector. The second orthogonal projection unit 24a is a processing unit that obtains a reception signal vector after unnecessary wave suppression by multiplying the reception signal vector by the orthogonal projection matrix from the second orthogonal projection matrix calculation unit 23a.

Next, the flow of processing in the passive radar device of the second embodiment will be described. However, the description of the same flow as the process described in the first embodiment is omitted.

  As described above, according to the passive radar device of the second embodiment, the unnecessary wave suppression unit estimates the unnecessary wave delay time estimation that estimates the delay time of the unnecessary wave arrival time from the received signal vector to the REF system with respect to the SUR system. And an unnecessary wave FFT unit for obtaining a frequency spectrum obtained by applying a fast discrete Fourier transform based on an unnecessary wave delay time to a received signal from the REF receiver, and complex power from the frequency spectrum of the REF system and the unnecessary wave FFT unit. A complex power spectrum estimation unit for obtaining a spectrum, a first orthogonal projection matrix calculation unit for obtaining an orthogonal projection matrix for suppressing unnecessary waves from the complex power spectrum and unnecessary wave delay time, and an orthogonal projection matrix for a received signal vector Since the first orthogonal projection unit that multiplies and obtains the received signal vector after unnecessary wave suppression is provided, unnecessary wave suppression can be performed efficiently. .

Embodiment 3 FIG.
In the third embodiment, the projection matrix P _null is not obtained every processing cycle in the second embodiment, but is obtained in advance, thereby reducing the calculation load. The basic configuration in the third embodiment is the same as that in FIG. 1, and the configuration of the unwanted wave suppression unit 10 is different.

FIG. 7 is a configuration diagram illustrating the unwanted wave suppressing unit 10 according to the third embodiment.
The unnecessary wave suppression unit 10 according to the third embodiment includes an unnecessary wave delay time estimation unit 20, a third orthogonal projection matrix calculation unit 23 b, a third orthogonal projection unit 24 b, and a power spectrum estimation unit 25. Since the unnecessary wave delay time estimation unit 20 and the power spectrum estimation unit 25 are the same as those in the configuration of the second embodiment, description thereof will be omitted. The third orthogonal projection matrix calculation unit 23b is a processing unit that obtains an orthogonal projection matrix for unnecessary wave suppression from the delay time steering vector. The third orthogonal projection unit 24b multiplies the reception signal vector by the power spectrum vector obtained by the power spectrum estimation unit 25 and the orthogonal projection matrix obtained by the third orthogonal projection matrix calculation unit 23b, and receives the received signal after suppressing unnecessary waves. A processing unit for obtaining a vector.

ここで、以下のような射影行列Ｐ_ｎｕｌｌを求める。

式（５９）から不要波が抑圧されていることがわかる。 Next, the operation of the passive radar device according to the third embodiment will be described.

Here, the following projection matrix P _null is obtained.

It can be seen from the equation (59) that unnecessary waves are suppressed.

Next, the operation of the unwanted wave suppression unit 10 shown in FIG. 7 will be described. The third orthogonal projection matrix calculation unit 23b obtains the delay time steering vectors a ₀ and a _{k according} to the equations (39) and (40) from the sample numbers i ₀ and i _k, and the projection matrix P _null according to the equation (58). Ask for.

As described above, in the third embodiment, the projection matrix P _null is not obtained for each processing cycle in the second embodiment, but is obtained in advance, thereby reducing the calculation load and enabling unnecessary wave suppression. be able to.

  As described above, according to the passive radar device of the third embodiment, the unnecessary wave suppression unit estimates the unnecessary wave delay time of the unnecessary wave arrival time from the received signal vector to the REF system with respect to the SUR system. A time estimation unit; a third orthogonal projection matrix calculation unit for determining an orthogonal projection matrix for unnecessary wave suppression from the unnecessary wave delay time; a power spectrum estimation unit for determining a power spectrum of a REF frequency spectrum; and a received signal vector Since the third orthogonal projection unit for multiplying the power spectrum by the orthogonal projection matrix to obtain the received signal vector after unnecessary wave suppression is provided, unnecessary wave suppression can be performed efficiently.

Embodiment 4 FIG.
The fourth embodiment is an example in which the received signal vector is divided into subbands and unnecessary wave suppression shown in any of the first to third embodiments is performed for each subband. By subband division, the number of dimensions of the received signal vector is reduced for each subband, and the calculation load is reduced. At the same time, it is also for reducing the deterioration of unnecessary wave suppression performance due to the difference in frequency characteristics between the REF and SUR receivers.

FIG. 8 is a configuration diagram illustrating a passive radar device according to the fourth embodiment.
The passive radar device shown in FIG. 8 includes a SUR system antenna 3, a SUR system receiver 4, a SUR system FFT unit 5, a REF system antenna 6, a REF system receiver 7, a REF system FFT unit 8, a received signal vector forming unit 9, A first subband dividing unit 12, a second subband dividing unit 13, a subband unnecessary wave suppressing unit 10a, a subband combining unit 14, and an IFFT unit 11 are provided. Here, since the SUR system antenna 3 to the received signal vector forming unit 9 and the IFFT unit 11 are the same as the configuration of the first embodiment shown in FIG. 1, their description is omitted.

  The first subband dividing unit 12 is a processing unit that divides the received signal vector from the received signal vector forming unit 9 into L subbands. The second subband splitting unit 13 is a processing unit that splits the frequency spectrum from the REF-based FFT unit 8 into L subbands. The subband unnecessary wave suppressing unit 10a is provided for each subband from the received signal vector after subband division from the first subband dividing unit 12 and the frequency spectrum after subband division from the second subband dividing unit 13. This is a processing unit that performs unnecessary wave suppression and obtains a received signal vector after subband division after suppressing L unnecessary waves. The subband synthesizing unit 14 is a processing unit that synthesizes the reception signal vectors after subband division after suppressing the L unnecessary waves from the subband unnecessary wave suppressing unit 10a and obtaining the reception signal vectors after suppressing the unnecessary waves.

Next, the difference of the operation of the passive radar device according to the fourth embodiment from the first embodiment will be described.
The first subband splitting unit 12 in FIG. 8 divides the received signal vector from the received signal vector forming unit 9 into L subbands. The second subband dividing unit 13 divides the frequency spectrum from the REF-based FFT unit 8 into L subbands. L is an integer of 2 or more. In the subband unnecessary wave suppressing unit 10a, the subband-divided received signal vector from the first subband dividing unit 12 and the subband-divided frequency spectrum from the second subband dividing unit 13 are used for each subband. In addition, unnecessary wave suppression similar to that in any one of the first to third embodiments is performed, and a subband divided received signal vector after L unnecessary wave suppression is obtained. However, in the case where the unnecessary wave suppression unit 10 of FIG. 2 is used, the unnecessary wave FFT unit 21 performs subband division at the preceding stage to obtain the frequency spectrum of the unnecessary wave in a desired subband.

  Thus, in the fourth embodiment, the passive radar device divides the received signal vector into subbands, and performs unnecessary wave suppression shown in any of the first to third embodiments for each subband. By subband division, the number of dimensions of the received signal vector is reduced for each subband, and the calculation load can be reduced. At the same time, it is possible to reduce the deterioration of unnecessary wave suppression performance due to the difference in frequency characteristics between the REF and SUR receivers.

  As described above, according to the passive radar device of the fourth embodiment, the SUR that receives the reflected wave from the target and the direct wave from the clutter and the transmitting station by the signal transmitted from the transmitting station that operates in uncoordinated manner with itself. System receiving unit, SUR system FFT unit for obtaining a frequency spectrum by applying a fast discrete Fourier transform to the received signal of the SUR system receiving unit, and a REF system receiving unit for receiving a direct wave of a signal transmitted from a transmitting station A REF FFT unit for obtaining a frequency spectrum by applying a fast discrete Fourier transform to the received signal of the REF receiving unit, and a received signal vector from the frequency spectrum obtained by the SUR FFT unit and the REF FFT unit Received signal vector forming section, and a first subband that divides the received signal vector from the received signal vector forming section into a plurality of subbands. A sub-band division unit, a second sub-band division unit that divides the frequency spectrum from the REF FFT unit into a plurality of sub-bands, a received signal vector after sub-band division from the first sub-band division unit, and 2 Suppress unnecessary waves received by the previous SUR receiving unit for each subband from the frequency spectrum after subband division from the subband division unit of the subband, and obtain a received signal vector after subband division after suppressing a plurality of unnecessary waves. A subband unnecessary wave suppression unit to be obtained; and a subband combining unit for combining a plurality of unnecessary wave-suppressed subband divided reception signal vectors from the subband unnecessary wave suppression unit to obtain a reception signal vector after unnecessary wave suppression; And an IFFT unit that performs inverse fast discrete Fourier transform on the received signal vector after unnecessary wave suppression and obtains a cross-correlation output after unnecessary wave suppression. The jitter can be efficiently suppressed.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  1 transmitting station, 2 transmitting antenna, 3 SUR system antenna, 4 SUR system receiver, 5 SUR system FFT unit, 6 REF system antenna, 7 REF system receiver, 8 REF system FFT unit, 9 received signal vector forming unit, 10 , 10a Unnecessary wave suppression unit, 11 IFFT unit, 12 First subband division unit, 13 Second subband division unit, 14 Subband synthesis unit, 20 Unnecessary wave delay time estimation unit, 21 Unnecessary wave FFT unit, 22 Complex power spectrum estimation unit, 23 1st orthogonal projection matrix calculation unit, 23a 2nd orthogonal projection matrix calculation unit, 23b 3rd orthogonal projection matrix calculation unit, 24 1st orthogonal projection unit, 24a 2nd orthogonal projection , 24b Third orthogonal projection unit, 25 Power spectrum estimation unit, 30 Delay time estimation system IFFT unit, 31 Amplitude detection unit, 32 Direct wave delay time sample number Tough, 33 clutter delay sample number estimation section, 34 unnecessary wave delay sample number estimating unit, 100 target.

Claims (8)

A SUR system receiver that receives a reflected wave and a clutter from a target by a signal transmitted from a transmitting station that operates in an uncoordinated manner with itself, and a direct wave from the transmitting station;
A SUR system FFT unit that obtains a frequency spectrum by applying a fast discrete Fourier transform to the received signal of the SUR system reception unit;
A REF system receiver that receives a direct wave of a signal transmitted from the transmitter station;
A REF FFT unit that obtains a frequency spectrum by applying a fast discrete Fourier transform to a received signal of the REF system receiver;
A received signal vector forming unit that forms a received signal vector from the frequency spectrum obtained by the SUR system FFT unit and the REF system FFT unit;
An unnecessary wave that suppresses unnecessary waves received by the SUR receiving unit from the received signal vector from the received signal vector forming unit and the frequency spectrum from the REF FFT unit and obtains a received signal vector after suppressing unnecessary waves. The repressor,
A passive radar device comprising: an IFFT unit that obtains a cross-correlation output after suppressing unnecessary waves by applying inverse fast discrete Fourier transform to the received signal vector after suppressing unnecessary waves. The unnecessary wave suppression unit is
An unnecessary wave delay time estimation unit that estimates a delay time of an unnecessary wave arrival time to the REF system with respect to the SUR system from the received signal vector;
An unnecessary wave FFT unit for obtaining a frequency spectrum obtained by applying a fast discrete Fourier transform based on the unnecessary wave delay time to a reception signal from the REF system receiving unit;
A complex power spectrum estimation unit for obtaining a complex power spectrum from the frequency spectrum of the REF system and the unwanted wave FFT unit;
A first orthogonal projection matrix calculation unit for obtaining an orthogonal projection matrix for unnecessary wave suppression from the complex power spectrum and the unnecessary wave delay time;
The passive radar device according to claim 1, further comprising a first orthogonal projection unit that multiplies the reception signal vector by the orthogonal projection matrix to obtain a reception signal vector after unnecessary wave suppression. The unnecessary wave suppression unit is
An unnecessary wave delay time estimation unit that estimates an unnecessary wave delay time of an unnecessary wave arrival time to the REF system with respect to the SUR system from the received signal vector;
A power spectrum estimation unit for obtaining a power spectrum of the REF system frequency spectrum;
A second orthogonal projection matrix calculation unit for obtaining an orthogonal projection matrix for unnecessary wave suppression from the power spectrum and the unnecessary wave delay time;
The passive radar device according to claim 1, further comprising: a second orthogonal projection unit that multiplies the reception signal vector by the orthogonal projection matrix to obtain a reception signal vector after unnecessary wave suppression. The unnecessary wave suppression unit is
An unnecessary wave delay time estimation unit that estimates an unnecessary wave delay time of an unnecessary wave arrival time to the REF system with respect to the SUR system from the received signal vector;
A third orthogonal projection matrix calculation unit for obtaining an orthogonal projection matrix for unnecessary wave suppression from the unnecessary wave delay time;
A power spectrum estimation unit for obtaining a power spectrum of the REF system frequency spectrum;
The passive radar device according to claim 1, further comprising: a third orthogonal projection unit that obtains a reception signal vector after unnecessary wave suppression by multiplying the reception signal vector by the power spectrum and the orthogonal projection matrix. The unnecessary wave delay time estimation unit is
A delay time estimation system IFFT unit for obtaining a cross-correlation output by applying an inverse fast discrete Fourier transform to the received signal vector from the received signal vector forming unit;
An amplitude detector for obtaining an amplitude detection signal of a cross-correlation output from the delay time estimation system IFFT unit;
A direct wave delay time sample number estimation unit that estimates a sample number corresponding to a direct wave delay time from the amplitude detection signal;
The clutter delay time sample number estimation part which estimates a clutter delay time sample number from the said amplitude detection signal, the said direct wave delay time sample number, and the number of clutters is provided. The passive radar device according to any one of the above. The unnecessary wave delay time estimation unit is
A delay time estimation system IFFT unit for obtaining a cross-correlation output by applying an inverse fast discrete Fourier transform to the received signal vector from the received signal vector forming unit;
An amplitude detector for obtaining an amplitude detection signal of a cross-correlation output from the delay time estimation system IFFT unit;
3. An unnecessary wave delay time sample number estimation unit that estimates an unnecessary wave delay time sample number based on any one of the number of clutters, a threshold, and a cumulative power ratio for the amplitude detection signal. The passive radar device according to claim 4. A SUR system receiver that receives a reflected wave and a clutter from a target by a signal transmitted from a transmitting station that operates in an uncoordinated manner with itself, and a direct wave from the transmitting station;
A SUR system FFT unit that obtains a frequency spectrum by applying a fast discrete Fourier transform to the received signal of the SUR system reception unit;
A REF system receiver that receives a direct wave of a signal transmitted from the transmitter station;
A REF FFT unit that obtains a frequency spectrum by applying a fast discrete Fourier transform to a received signal of the REF system receiver;
A received signal vector forming unit that forms a received signal vector from the frequency spectrum obtained by the SUR system FFT unit and the REF system FFT unit;
A first subband splitting unit for splitting a received signal vector from the received signal vector forming unit into a plurality of subbands;
A second subband splitting unit for splitting the frequency spectrum from the REF-based FFT unit into a plurality of subbands;
Unnecessary signal received by the SUR receiver for each subband from the received signal vector after subband division from the first subband divider and the frequency spectrum after subband division from the second subband divider. A subband unnecessary wave suppression unit that performs wave suppression and obtains a received signal vector after subband division after a plurality of unnecessary wave suppressions;
A subband combining unit that synthesizes a reception signal vector after subband division after suppression of a plurality of unnecessary waves from the subband unnecessary wave suppression unit and obtains a reception signal vector after suppression of unnecessary waves;
A passive radar device comprising: an IFFT unit that performs inverse fast discrete Fourier transform on the received signal vector after suppressing the unnecessary wave to obtain a cross-correlation output after suppressing the unnecessary wave. The subband unnecessary wave suppression unit is
8. The passive radar device according to claim 7, wherein the unnecessary wave suppression unit according to any one of claims 2 to 6 is configured using a number equal to the number of subband divisions.

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