JP7150641B2 - antenna system - Google Patents

Description

Embodiments of the present invention relate to antenna systems.

If the number of antenna elements is increased in order to improve transmission/reception performance using an array antenna, the size of the array antenna will increase and the size of the circuit that performs signal processing will also increase. Also, forming a plurality of beams increases the circuit scale. Thus, if the performance of the array antenna is improved by simply increasing the number of antenna elements, the manufacturing cost will increase as the circuit scale increases. As a technique for suppressing an increase in circuit size due to an increase in the number of antenna elements, there is an array antenna that applies a space feeding system. By applying the space feeding method, it is possible to suppress an increase in circuit size due to an increase in the number of antenna elements. However, when forming a plurality of beams, phase control corresponding to each beam formation is required on the secondary array side, and an increase in circuit scale may not be suppressed.

Japanese Patent No. 4005949

Yoshida, "Revised Radar Technology", The Institute of Electronics, Information and Communication Engineers, 1996, pp. 289-291 Yoshida, "Revised Radar Technology", The Institute of Electronics, Information and Communication Engineers, 1996, pp. 119-123 Yoshida, "Revised Radar Technology", The Institute of Electronics, Information and Communication Engineers, 1996, pp. 134-135 Tanahagi, "Digital Filter and Signal Processing", Corona Publishing, 2001, pp. 120-165 Yoshida, "Revised Radar Technology", The Institute of Electronics, Information and Communication Engineers, 1996, pp. 144-145 Merrill I. Skolnik, "Introduction to radar systems," McGRAW-HILL Inc., 1980, pp.428-430 Yoshida, "Revised Radar Technology", The Institute of Electronics, Information and Communication Engineers, 1996, pp. 260-264 Jian Li, Petre Stoica, "MIMO Radar Signal Processing," John Wiley & Sons, Inc., 2009, pp.1-5

A problem to be solved by the present invention is to provide an antenna system capable of forming a plurality of beams and reducing an increase in circuit size due to an increase in the number of antenna elements.

An antenna system according to an embodiment has a first array antenna, a transmission section, a second array antenna, and a transmission weight determination section. The first array antenna has a plurality of first antenna elements. The transmitter supplies to each of the plurality of first antenna elements a transmission signal obtained by multiplying a signal by a transmission weight corresponding to each of the plurality of first antenna elements. The second array antenna has a plurality of second antenna elements for receiving the transmission signal supplied from the first array antenna and transmitting the input transmission signal in a direction different from the direction to the first array antenna. . The transmission weight determination unit determines a plurality of determine transmit weights for each of the first antenna elements of .

The figure which shows the structural example of the antenna system in 1st Embodiment. 4 is a diagram showing a configuration example of a primary antenna in the first embodiment; FIG. 4 is a diagram showing a configuration example of an antenna module according to the first embodiment; FIG. 4 is a diagram showing the relationship between the beam angle of the primary antenna and the weight (amplitude and phase) of the aperture plane of the secondary antenna in the first embodiment; FIG. The figure which shows an example of the coordinate system which concerns on the secondary antenna in 1st Embodiment. FIG. 4 is a diagram showing a procedure for calculating transmission weights in the first embodiment; FIG. 4 is a diagram showing an operation example of a primary antenna when forming a plurality of transmission beams in the antenna system according to the first embodiment; FIG. 5 is a diagram showing another operation example of the primary antenna when forming a plurality of transmission beams in the antenna system according to the first embodiment; The figure which shows the structural example of the antenna system in 2nd Embodiment. The figure which shows the structural example of the antenna module in 2nd Embodiment. The figure which shows the structural example of the primary antenna in 2nd Embodiment. The figure which shows the structural example of the antenna system in 3rd Embodiment. The figure which shows the structural example of the primary antenna in 3rd Embodiment. The figure which shows the structural example of the antenna module in 3rd Embodiment. The figure which shows the structural example of the antenna system in 4th Embodiment. The figure which shows the structural example of the antenna system in 5th Embodiment. The figure which shows the structural example of the antenna system in 6th Embodiment.

An antenna system according to an embodiment will be described below with reference to the drawings. In the following embodiments, it is assumed that constituent elements with the same reference numerals perform the same operations, and overlapping descriptions will be omitted as appropriate.

(First embodiment)
FIG. 1 is a diagram showing a configuration example of an antenna system according to the first embodiment. The antenna system of the first embodiment comprises a primary antenna 1 and a secondary antenna 2 having multiple antenna elements. A primary antenna 1 performs transmission using a DBF (Digital Beam Forming) method toward a secondary antenna 2 (Non-Patent Document 1). The secondary antenna 2 transmits a signal supplied from the primary antenna 1 by spatial feeding. The secondary antenna 2 has a plurality of antenna modules 21 (21-1, 21-2, . . . , 21-Ns). The shape of the transmission beams (b1, b2, . . . , bBt) formed by the secondary antenna 2 is determined by controlling the signal transmitted by the primary antenna. The shape of the transmit beam may include mainlobe directional and angular response, sidelobe directional and angular response. Configuration examples of the primary antenna 1 and the secondary antenna 2 will be described below.

FIG. 2 is a diagram showing a configuration example of the primary antenna 1 in the first embodiment. The primary antenna 1 includes a signal generator 11 and a plurality of antenna elements 16 (16-1, 16-2, . . . , 16-Np). Np may be a value smaller than Ns. That is, the number of antenna elements 16 of primary antenna 1 may be less than the number of antenna elements of secondary antenna 2 . The Np antenna elements 16 are arranged regularly to form an array antenna (first array antenna). Further, the primary antenna 1 includes DA (Digital-Analog) converters 12 (12-1, 12-2, . . . , 12-Np), frequency converters 13 (13-1, . 13-2, . . . , 13-Np) and HPA (High Power Amplifier) 14 (14-1, 14-2, . The signal generator 11 includes a signal generator 111, a transmission weight determiner 112, and a multiplier 113 (113-1, 113-2, . . . , 113-Np) corresponding to each antenna element 16. FIG.

The signal generator 111 generates a signal including pulses or continuous waves, and supplies the generated signal to each multiplier 113-1 to 113-Np. The frequency and amplitude of the signal generated by the signal generator 111 are given by an externally input beam control signal. If a signal containing pulses is generated, the pulse width and pulse interval are also provided in the beam control signal. The signal generated by the signal generator 111 may be a pulse-modulated signal. Note that the parameters that define the signal to be generated may be determined in advance.

Transmission weight determination section 112 determines each of the plurality of antenna elements 16-1 to 16-Np based on the transmission beam shape formed in secondary antenna 2 and the positions of the plurality of antenna elements provided in secondary antenna 2. determine the transmission weights corresponding to A transmission beam shape formed in the secondary antenna 2 is given by a beam control signal. Transmission weight determination section 112 supplies the transmission weight determined for each antenna element 16 to corresponding multiplier 113 . A procedure for determining each transmission weight by transmission weight determining section 112 will be described later.

Multiplier 113-1 multiplies the signal supplied from signal generator 111 by a transmission weight corresponding to antenna element 16-1 to calculate a transmission signal. The multiplier 113-1 supplies the calculated transmission signal to the DA converter 12-1. Similar to multiplier 113-1, multipliers 113-2 to 113-Np multiply transmission weights of corresponding antenna elements 16 to calculate transmission signals, and convert the transmission signals to DA converters 12-2 to 12-Np. supply each.

The operations of the signal generator 111, the transmission weight determination unit 112, and the plurality of multipliers 113 provided in the signal generation unit 11 are performed using digital circuits, or by using a DSP (Digital Signal Processor) or a DSP (Digital Signal Processor) as a program that instructs each operation. It may be realized by executing it with a general-purpose CPU (Central Processing Unit). ASICs (Application Specific Integrated Circuits), FPGAs (Field Programmable Gate Arrays), and the like may be used as hardware that implements digital circuits.

The DA converter 12-1 converts the digital transmission signal supplied from the multiplier 113-1 into an analog transmission signal, and supplies the analog transmission signal to the frequency converter 13-1. The frequency converter 13-1 converts the frequency of the transmission signal supplied from the DA converter 12-1 into an RF (Radio Frequency) band, and supplies the RF band transmission signal to the HPA 14-1. HPA 14-1 amplifies the transmission signal supplied from frequency converter 13-1 and supplies the amplified transmission signal to antenna element 16-1. A transmission signal is sent out from the antenna element 16-1.

DA converters 12-2 to 12-Np, frequency converters 13-2 to 13-Np and HPAs 14-2 to 14-Np are connected to DA converter 12-1, frequency converter 13-1 and HPA 14-1 respectively. works similarly. Transmission signals multiplied by transmission weights corresponding to antenna elements 16-2 to 16-Np are transmitted from antenna elements 16-2 to 16-Np, respectively.

FIG. 3 is a diagram showing a configuration example of the antenna module 21 in the first embodiment. Antenna module 21 has two antenna elements 211 , 215 and HPA 213 . The directivity direction of the antenna element 211 is directed toward the array antenna formed by the plurality of antenna elements 16 . Antenna element 211 receives a signal obtained by synthesizing transmission signals transmitted from each antenna element 16 of the primary antenna in transmission space. A signal received by antenna element 211 is amplified by HPA 213 and sent out from antenna element 215 . The directivity direction of antenna element 215 is directed in a direction different from that of antenna element 211 . The antenna module 21 acquires the transmission signal supplied from each antenna element 16 of the primary antenna 1 with the antenna element 211, amplifies the acquired signal, and transmits the transmission signal in a direction different from the direction toward the primary antenna 1. do.

The secondary antenna 2 has a plurality of antenna modules 21, as shown in FIG. The antenna modules 21 are arranged regularly, and the plurality of antenna elements 215 form an array antenna (second array antenna). A plurality of antenna elements 211 form an array antenna directed toward the primary antenna 1 side. As shown in FIG. 1, a plurality of antenna elements 211 and a plurality of antenna elements 215 may be arranged such that the directivity directions of these two array antennas are opposite to each other. Also, the plurality of antenna elements 211 and the plurality of antenna elements 215 may be arranged such that the directivity directions of the two array antennas have an arbitrary angular difference.

Each antenna module 21 of the secondary antenna 2 obtains a signal obtained by spatially combining the transmission signals transmitted from each antenna element 16 of the primary antenna 1 . The amplitude and phase of the signal that each antenna module 21 acquires from the primary antenna 1 differ according to the position of the antenna element 211 of the antenna module 21 and the position of the primary antenna 1 . The amplitude and phase of the signal acquired by the antenna element 211 serve as weights for the amplitude and phase of each antenna element 215 of the secondary antenna.

FIG. 4 is a diagram showing the relationship between the beam angle of the primary antenna 1 and the weight (amplitude and phase) of the aperture plane of the secondary antenna 2 in the first embodiment. The aperture plane of the secondary antenna is the aperture plane of the array antenna formed by each antenna element 215 . As shown in FIG. 4, when the array antenna formed by the plurality of antenna elements 16 of the primary antenna 1 forms a beam in the direction of angle Θ, the signal obtained at the position of each antenna element 211 of the secondary antenna 2 is becomes the weight of the antenna element 215 connected to the antenna element 211 . The secondary antenna 2 forms transmission beams determined by weights according to the positions of the antenna elements 211 . Thus, the transmission beam of the array antenna formed by the antenna element 215 of the secondary antenna 2 is formed according to the transmission beam of the array antenna formed by the antenna element 16 of the primary antenna 1 . That is, the shape of the transmission beam in the secondary antenna 2 can be controlled by the transmission weight in the primary antenna 1. FIG.

Here, a method for determining transmission weights for primary antenna 1, that is, a method for forming transmission beams for primary antenna 1 will be described. Considering the scanning of the transmission beam in the secondary antenna 2, the power of the transmission beam in the secondary antenna 2 is represented by Equation (1). Although FIGS. 1 and 4 show the case where the antenna elements 215 of the secondary antenna 1 form a linear array, Equation (1) expresses the case where the antenna elements 215 form a planar array.

式（１）に示すように、送信ビームの角度応答（ＡＺｐ，ＥＬｐ）は、２次アンテナ２の各素子の信号に、素子に対応する複素ウェイトを乗じた総和となる（非特許文献２）。式（１）において、ＡＺｐ及びＥＬｐは、送信ビームの指向方向の方位角及び仰角を表す。Ｗｓｎは、２次アンテナ２のｎ（ｎ＝１，２，…，Ｎｓ）番目のアンテナ素子２１５の複素ウェイトを表す。Ｘｓｎは、２次アンテナ２のｎ番目のアンテナ素子２１５で送信される信号を表す。

As shown in Equation (1), the angular response (AZp, ELp) of the transmission beam is the sum of the signals of each element of the secondary antenna 2 multiplied by the complex weight corresponding to the element (Non-Patent Document 2). . In Equation (1), AZp and ELp represent the azimuth and elevation of the direction of transmission beam. Wsn represents the complex weight of the n-th (n=1, 2, . . . , Ns) antenna element 215 of the secondary antenna 2 . Xsn represents the signal transmitted at the n-th antenna element 215 of the secondary antenna 2;

A complex weight vector Ws whose element is the complex weight Wsn is represented by Equation (2) in the coordinate system shown in FIG. FIG. 5 is a diagram showing an example of a coordinate system related to the secondary antenna 2 in the first embodiment. A three-dimensional coordinate system of the XYZ axes is set with the phase center of the array antenna in the secondary antenna 2 as the origin.

式（２）において、Ａｓｎは、２次アンテナ２のｎ番目のアンテナ素子２１５に対応するサイドローブ低減用ウェイトを表す。サイドローブ低減用ウェイトとして、例えばテーラー分布を用いてもよい（非特許文献３）。ｊは、虚数単位を表す。ｘｓｎ、ｙｓｎ及びｚｓｎは、ｎ番目のアンテナ素子２１５の位置座標を表す。図５に示すように、アレイアンテナの位相中心が位置座標における原点である。ｋｐｘ、ｋｐｙ及びｋｐｚは、式（３）で与えられる。

In equation (2), Asn represents the side lobe reduction weight corresponding to the nth antenna element 215 of the secondary antenna 2 . Taylor distribution, for example, may be used as the side lobe reduction weight (Non-Patent Document 3). j represents an imaginary unit. xsn, ysn and zsn represent the position coordinates of the nth antenna element 215 . As shown in FIG. 5, the phase center of the array antenna is the origin of the position coordinates. kpx, kpy and kpz are given by equation (3).

式（３）において、λは送信される信号の波長である。ＡＺｐ及びＥＬｐは、２次アンテナ２におけるアレイアンテナの位相中心からみたＡＺ軸及びＥＬ軸のビーム指向角を表す。

In equation (3), λ is the wavelength of the transmitted signal. AZp and ELp represent the beam directivity angles of the AZ axis and the EL axis of the secondary antenna 2 viewed from the phase center of the array antenna.

The weight vector Ws of amplitude and phase for each of the Ns antenna elements 215 is determined at each position of the antenna element 211 of the secondary antenna 2, as shown in FIG. Transmission weights for the antenna elements 16-1 to 16-Np of the primary antenna 1 are calculated based on the weight vector Ws. Transmission weight calculation is performed by transmission weight determination section 112 .

FIG. 6 is a diagram showing a procedure for calculating transmission weights in the first embodiment. First, transmission weight determination section 112 determines angles Θ corresponding to the positions of Ns antenna elements 211 in secondary antenna 2, which are formed by antenna elements 16-1 to 16-Np in primary antenna 1. An angle Θ on the sin Θ axis (spatial frequency axis) viewed from the phase center of the array antenna is calculated. Transmission weight determination section 112 uses angle Θ corresponding to each position to convert weights Wsn (n=1, 2, . The reason why the weight Wsn is converted to the weight Wsn' on the sin Θ axis is that when calculating the aperture distribution of the array antenna of the primary antenna 1 by inverse Fourier transform, signals at equal intervals on the sin Θ axis are required. The aperture distribution of the array antenna and the orthogonal beams equidistantly spaced along the sin Θ axis have a Fourier transform relationship.

Next, in order to calculate the aperture distribution of the array antenna formed by the antenna elements 16-1 to 16-Np, the transmission weight determination unit 112 arranges the Ns weights Wsn' at regular intervals by an interpolation method. Extract the weight Wsconv at each of the Np points obtained. A known interpolation method such as spline interpolation is used as the interpolation method. Transmission weight determination section 112 calculates Np complex weights by performing inverse Fourier transform on the extracted weight Wsconv. Np complex weights calculated by inverse Fourier transform are obtained as transmission weights for each of the Np antenna elements 16-1 to 16-Np. A transmission weight vector Wp whose elements are the transmission weights of the antenna elements 16-1 to 16-Np is expressed by Equation (4).

式（４）において、ＦＦＴ［・］はフーリエ変換を表し、ＩＦＦＴ［・］は逆フーリエ変換を表す。Ｗｓｃｏｎｖは、２次アンテナ２の各アンテナ素子２１５に対するウェイトベクトルＷｓを変換して得られる複素ウェイトベクトルを表す。

In equation (4), FFT[·] represents Fourier transform and IFFT[·] represents inverse Fourier transform. Wsconv represents a complex weight vector obtained by transforming the weight vector Ws for each antenna element 215 of the secondary antenna 2 .

The method of obtaining the transmission weight vector Wp of the primary antenna 1 from the complex weight vector Wsconv is the same as the method of obtaining tap coefficients when designing a frequency filter for FIR (Finite Impulse Response) (Non-Patent Document 4). That is, a method of calculating the amplitude and phase tap coefficients on the time axis that satisfy a desired frequency response can be used as a method of calculating the transmission weight vector Wp corresponding to the complex weight vector Wsconv. Therefore, transmission weight determining section 112 may use the above-described method of calculating tap coefficients or other methods instead of the method using inverse Fourier transform.

The method of obtaining the transmission weight vector Wp described above is a case where the far-field condition that the primary antenna 1 and the secondary antenna 2 are sufficiently separated is satisfied (Non-Patent Document 5). If the far-field condition is not satisfied, transmission weight determination section 112 determines transmission weight vector Wp that determines the shape of the transmission beam of primary antenna 1, including near-field conditions. In other words, a method that considers changes in amplitude and phase due to the signal transmitted from each antenna element 16 of the primary antenna 1, the path length to each antenna element 211 of the secondary antenna 2, and the angular response of the antenna element 211. use. In the method using the inverse Fourier transform shown in Equation (4), Wsconv and Wp are expressed in vector form. However, when the near-field conditions are taken into consideration, the vector element (n, n2) is used for the sake of clarity. In this case, the complex weight vector Wsconv is represented by Equation (5).

式（５）において、Ｗｓｃｏｎｖ（ｎ２）は、ウェイトベクトルＷｓを変換して得られる複素ウェイトベクトルのｎ２（ｎ２＝１，２，…，Ｎｐ）番目の要素を表す。Ｘｐｓ（ｎ，ｎ２）は、１次アンテナ１のｎ（ｎ＝１，２，…，Ｎｐ）番目のアンテナ素子１６と、補間手法により得られる２次アンテナ２のｎ２番目の仮想のアンテナ素子との位置から決まる振幅及び位相を表す。仮想のアンテナ素子は、ウェイトＷｓｃｏｎｖを抽出する際に補間手法により等間隔に配置されるＮｐ個の点に仮想的に設けられたアンテナ素子である。仮想のアンテナ素子の位置は、ｓｉｎΘ軸における位置である。振幅及び位相を表すＸｐｓ（ｎ，ｎ２）は、式（６）で得られる。

In Equation (5), Wsconv(n2) represents the n2 (n2=1, 2, . . . , Np)-th element of the complex weight vector obtained by transforming the weight vector Ws. Xps(n,n2) is the n (n=1, 2, . represents the amplitude and phase determined from the position of . The virtual antenna elements are antenna elements that are virtually provided at Np points that are evenly spaced by an interpolation method when extracting the weight Wsconv. The position of the virtual antenna element is the position on the sin Θ axis. Xps(n, n2) representing amplitude and phase is obtained by equation (6).

式（６）において、Ａ１２（・）は、アンテナ素子１６と仮想のアンテナ素子との位置関係と互いの角度応答とにより決まる振幅及び位相を表す。Ｌ１２（・）は、アンテナ素子１６と仮想のアンテナ素子との位置により定まる経路長を表す。ｘｐｎ、ｙｐｎ及びｚｐｎはアンテナ素子１６の位置を表し、ｘｓｎ２、ｙｓｎ２及びｚｓｎ２は仮想のアンテナ素子の位置を表す。ｋは（２π／λ）であり、λは送信される信号の波長である。

In equation (6), A12(·) represents the amplitude and phase determined by the positional relationship and mutual angular response between the antenna element 16 and the virtual antenna element. L12(·) represents the path length determined by the positions of the antenna element 16 and the virtual antenna element. xpn, ypn and zpn represent the positions of the antenna elements 16, and xsn2, ysn2 and zsn2 represent the positions of virtual antenna elements. k is (2π/λ) and λ is the wavelength of the signal to be transmitted.

Transmission weight determination section 112 numerically calculates a transmission weight vector Wp in which the values of the right and left sides of equation (5) are equal or the difference is equal to or less than a certain value at each of the Np points. By using the vector obtained by the formula (4) under the far-field condition as the initial value of the transmission weight vector Wp in the numerical calculation, the calculation time of the numerical calculation can be reduced.

As described above, the transmission weight determination unit 112 determines transmission weights for the antenna elements 16-1 to 16-Np from the phases and amplitudes of the antenna elements 211 and 215 determined according to the beam shape formed by the secondary antenna 2. Determine the vector Wp. Although the case where the transmission weights include weights for amplitude and phase has been described, transmission weights may not include weights for amplitude.

7 and 8 are diagrams showing an operation example of the primary antenna 1 when forming a plurality of transmission beams b1 to bBt in the antenna system according to the first embodiment. When the antenna system forms a plurality of transmission beams b1 to bBt as shown in FIG. Section 112 determines transmission weight vectors Wp corresponding to transmission beams b1 to bBt, and supplies the transmission weights to multipliers 113-1 to 113-Np. By these operations, as shown in FIG. 7, the primary antenna 1 switches transmission beams in a time division manner, thereby allowing the secondary antenna 2 to form a plurality of transmission beams b1 to bBt.

When the primary antenna 1 simultaneously forms a plurality of transmission beams b1 to bBt, the signal generator 111 divides the frequency band of the transmission signal into Bt frequency bands to generate signals for each frequency band. In this case, transmission weight determination section 112 determines transmission weight vectors Wp corresponding to transmission beams b1 to bBt, respectively, and supplies the transmission weights to multipliers 113-1 to 113-Np. Each of multipliers 113-1 to 113-Np multiplies each divided frequency band signal by a transmission weight according to the transmission beam to calculate a transmission beam signal for each frequency band signal. Each multiplier 113-1 to 113-Np synthesizes the calculated signal of each transmission beam and supplies it to the DA converters 12-1 to 12-Np. Through these operations, the primary antenna 1 allocates transmission beams to the divided frequency bands, respectively, so that the secondary antenna 2 forms a plurality of transmission beams b1 to bBt, as shown in FIG. Since the antenna system uses different frequency bands for each transmission beam when forming a plurality of transmission beams, it is possible to form independently controllable multiple transmission beams while maintaining isolation between the transmission beams.

Note that in the example shown in FIG. 8, the operation of dividing the frequency band in order to simultaneously form a plurality of transmission beams has been described. However, the primary antenna 1 may maintain isolation between transmission beams by using different code sequences with less mutual interference instead of dividing the frequency band. As a code sequence with little mutual interference, an M sequence may be used (Non-Patent Document 6).

The antenna system of the first embodiment has a simple configuration in which each antenna module 21 of the secondary antenna 2 does not perform phase control. By changing the transmission beam of the primary antenna 1, each antenna element of the secondary antenna 2 215 can be controlled in amplitude and phase. As a result, it is possible to form a plurality of transmission beams in the array antenna of the secondary antenna 2 with high performance and low cost. In addition, since the antenna module 21 in the secondary antenna 2 has a simple configuration, even when the aperture of the secondary antenna 2 is widened, an increase in circuit scale can be reduced, and manufacturing costs can be suppressed.

In addition, since the primary antenna 1 controls the transmission beam of the array antenna formed by the antenna elements 16-1 to 16-Np with the DBF, the degree of freedom in weight setting for each antenna element 215 of the secondary antenna 2 is high. It is possible to form a transmit beam with an angular response that depends on the usage situation. Also, as described above, the antenna system can change the number of transmit beams formed without changing the antenna module 21 of the secondary antenna 2 .

(Second embodiment)
In the first embodiment, an antenna system for transmitting signals was described. In a second embodiment, an antenna system for receiving signals will be described. FIG. 9 is a diagram showing a configuration example of an antenna system according to the second embodiment. The antenna system of the second embodiment comprises a secondary antenna 3 and a primary antenna 4 having multiple antenna elements. The secondary antenna 3 has a plurality of antenna modules 31 (31-1, 32-2, . . . , 32-Ns). A signal received by each antenna module 31 is supplied to the primary antenna 4 by spatial feeding. The primary antenna 4 applies the DBF method to the spatially-fed signal to form a plurality of reception beams (b1, b2, . . . , bBr) at the secondary antenna 3. FIG. The shape of the receive beam may include mainlobe direction and angular response, sidelobe direction and angle response. Configuration examples of the secondary antenna 3 and the primary antenna 4 will be described below.

FIG. 10 is a diagram showing a configuration example of the antenna module 31 in the second embodiment. The antenna module 31 has two antenna elements 311 and 313 and an LNA (Low Noise Amplifier) 312 . The directivity direction of the antenna element 311 is directed in a direction different from the direction toward the first antenna 4 . Antenna element 311 provides a received signal to LNA 312 . The antenna element 313 supplies the signal amplified by the LNA 312 to the primary antenna 4 by spatial feeding. The directivity direction of antenna element 313 is directed in a direction different from the directivity direction of antenna element 311 . The antenna module 31 receives a signal arriving from a direction different from the direction toward the primary antenna 4 with the antenna element 311 , amplifies the signal, and supplies the amplified signal to the primary antenna 4 .

The secondary antenna 3 has a plurality of antenna modules 31 as shown in FIG. The antenna modules 31 are regularly arranged, and the plurality of antenna elements 311 form an array antenna. A plurality of antenna elements 313 form an array antenna directed toward the primary antenna 4 side. As shown in FIG. 9, a plurality of antenna elements 311 and a plurality of antenna elements 313 may be arranged such that the directivity directions of these two array antennas are opposite to each other. Also, the plurality of antenna elements 311 and the plurality of antenna elements 313 may be arranged such that the directivity directions of the two array antennas have an arbitrary angular difference.

FIG. 11 is a diagram showing a configuration example of the primary antenna 4 in the second embodiment. The primary antenna 4 comprises a plurality of antenna elements 41 (41-1, 41-2, . . . , 42-Np). Np antenna elements 41 are arranged regularly to form an array antenna. The primary antenna 4 includes LNAs 42 (42-1, 42-2, ..., 42-Np) and frequency converters 43 (43-1, 43-2, ..., 43-Np) corresponding to the respective antenna elements 41. and AD (Analog-Digital) converters 44 (44-1, 44-2, . . . , 44-Np). Further, the primary antenna 4 comprises a beamformer 45 . The beam forming unit 45 includes a reception weight determining unit 451, multipliers 452 (452-1, 452-2, . . . , 452-Np) corresponding to the antenna elements 41, and an adder 453.

LNA 42-1 amplifies the signal received by antenna element 41-1 and supplies the amplified signal to frequency converter 43-1. The frequency converter 43-1 converts the frequency of the signal supplied from the LNA 42-1 from the RF band to a baseband signal, and supplies the baseband signal to the AD converter 44-1. The AD converter 44-1 converts the signal supplied from the frequency converter 43-1 into a digital signal and supplies the digital signal to the multiplier 452-1.

LNAs 42-2 to 42-Np, frequency converters 43-2 to 43-Np, and AD converters 44-2 to 44-Np are LNA 42-1, frequency converter 43-1, and AD converter 44-1, respectively. behaves similarly to Signals received by the antenna elements 41-2 to 41-Np are amplified, frequency-converted, and AD-converted, and supplied to multipliers 452-2 to 452-Np.

Reception weight determination section 451 determines a plurality of antenna elements 41-1 to 41-Np based on the reception beam shape formed in secondary antenna 3 and the respective positions of a plurality of antenna elements 313 provided in secondary antenna 2. Determine the receive weight corresponding to each. A receive beam shape formed in the secondary antenna 3 is given by a beam control signal. The reception weight determining section 451 supplies the reception weight determined for each antenna element 41 to the corresponding multiplier 452 . The procedure for determining each reception weight by the reception weight determining unit 451 is the same as the procedure for determining each transmission weight by the transmission weight determining unit 112 in the first embodiment, so description of the procedure is omitted.

The multiplier 452-1 calculates a received signal by multiplying the digital signal supplied from the AD converter 44-1 by the reception weight corresponding to the antenna element 41-1. Multiplier 452 - 1 supplies the calculated received signal to adder 453 . Similar to the multiplier 452-1, the multipliers 452-2 to 452-Np correspond to the digital signals supplied from the AD converters 44-2 to 44-Np to the antenna elements 41-2 to 41-Np. Received signal is calculated by multiplying by the received weight. Each of multipliers 452 - 2 to 452 -Np supplies the calculated received signal to adder 453 . The adder 453 adds and synthesizes the reception signals supplied from the multipliers 452-1 to 452-Np, and outputs a signal obtained by the synthesis to the outside as a reception beam signal.

The operations of the reception weight determination unit 451, the plurality of multipliers 452, and the adders 453 provided in the beam forming unit 45 are performed by using digital circuits or by executing programs instructing the respective operations by a DSP or a general-purpose CPU. It may be realized by ASIC, FPGA, or the like may be used as hardware for realizing the digital circuit.

In the antenna system according to the second embodiment, the reception weight determining unit 451 calculates the reception weight of each antenna element 41 corresponding to each of a plurality of reception beams, and the adder 453 adds and combines the reception signals for each reception beam. . By these operations, the primary antenna 4 can simultaneously form a plurality of reception beams b1 to bBr in the secondary antenna 3, as shown in FIG. Even if the secondary antenna 3 is not provided with a phase shifter or the like, the receiving beam shape of the array antenna of the secondary antenna 3 can be controlled by changing the receiving beam of the primary antenna 4 . As a result, the secondary antenna 3 can form a plurality of reception beams with high performance and low cost. In addition, since the antenna module 31 in the secondary antenna 3 has a simple configuration, even when the aperture of the secondary antenna 3 is widened, an increase in circuit scale can be reduced, and manufacturing costs can be suppressed.

When the aperture plane of the secondary antenna 3 is divided into four and monopulse beams of Σ, ΔAZ, and ΔEL (Non-Patent Document 7) are formed based on the signals of the divided aperture planes, the antenna of the primary antenna 4 The aperture plane of the array antenna formed by the elements 41 may be divided into four to form monopulse beams of Σ, ΔAZ and ΔEL. By applying a monopulse beam to the antenna system of the second embodiment, it is possible to use a reception beam with a high degree of freedom and an improved angular resolution.

(Third embodiment)
The antenna system for transmitting signals has been described in the first embodiment, and the antenna system for receiving signals has been described in the second embodiment. In the third embodiment, an antenna system that can be used as a radar device by combining these antenna systems will be described. FIG. 12 is a diagram showing a configuration example of an antenna system according to the third embodiment. The antenna system of the third embodiment comprises a primary antenna 5 and a secondary antenna 6 with multiple antenna elements. The secondary antenna 6 has a plurality of antenna modules 61 (61-1, 61-2, . . . , 61-Ns).

The primary antenna 5 spatially feeds each antenna module 61 of the secondary antenna 6 by transmission using the DBF method. Each antenna module 61 of the secondary antenna 6 transmits the signal supplied by the primary antenna 5 . Further, the secondary antenna 6 supplies the signal received by each antenna module 61 to the primary antenna 5 by spatial feeding. The primary antenna 5 applies the DBF scheme to the spatially-fed signals to form a plurality of transmission/reception beams (b1, b2, . . . , bBr) in the secondary antenna 6 .

FIG. 13 is a diagram showing a configuration example of the primary antenna 5 in the third embodiment. The primary antenna 5 comprises a plurality of antenna elements 16-1 to 16-Np. The Np antenna elements 16 are arranged regularly to form an array antenna. Further, the primary antenna 5 includes circulators 15 (15-1, . . . , 15-Np), DA converters 12 (12-1, . (13-1, ..., 13-Np), HPA 14 (14-1, ..., 14-Np), LNA 42 (42-1, ..., 42-Np), frequency converter 43 (43-1, ..., 43 -Np) and AD converters 44 (44-1, . . . , 44-Np). Since transmission and reception are performed using a plurality of antenna elements 16-1 to 16-Np, the antenna elements 16-1 to 16 are connected via circulators 15-1 to 15-Np that separate the transmission system and the reception system. -Np, HPAs 14-1 to 14-Np and LNAs 42-1 to 42-Np are connected.

FIG. 14 is a diagram showing a configuration example of the antenna module 61 in the third embodiment. The antenna module 61 comprises two antenna elements 211, 215, an HPA 213, an LNA 321, and two circulators 212, 214. As with the primary antenna 5, since the antenna element 211 is used for transmission and reception, the antenna element 211, the HPA 213 and the LNA 312 are connected via a circulator 212 that separates the transmission system and the reception system. there is Also, the antenna element 215 is connected to the HPA 213 and the LNA 312 via the circulator 214 .

The antenna system in the third embodiment forms a plurality of transmission/reception beams b1 to bBtr as shown in FIG. A transmit and receive beam is a combination of a transmit beam and a receive beam. When using the antenna system as a radar device, a reception beam is formed according to the direction of the transmission beam. When the antenna system forms multiple transmit and receive beams, it forms multiple transmit beams by time division or frequency division as described in the first embodiment. For reception, the need to detect signals reflected by unknown targets requires the antenna system to form multiple receive beams simultaneously.

Specifically, the beam forming unit 45 determines reception weights for forming a co-directional reception beam with each transmission beam. In addition, the beam forming unit 45 separates the frequency band of the digital signal supplied from each AD converter 44 according to the frequency band used in each transmission beam, and multiplies the separated signals by corresponding reception weights. Calculate the received signal of the receive beam. The beam forming unit 45 synthesizes received signals for each frequency band to obtain a received beam signal of each received beam. The beam forming section 45 may use the transmission weight of each transmission beam determined by the transmission weight determination section 112 as the reception weight.

By combining the antenna systems of the first and second embodiments like the antenna system of the third embodiment, even if the secondary antenna 6 is not provided with a circuit for scanning the transmission and reception beams, the transmission of the primary antenna 5 can be performed. By changing the beam and the reception beam, the shape of the transmission and reception beam in the array antenna of the secondary antenna 6 can be controlled. As a result, it is possible to form a plurality of transmission/reception beams in the secondary antenna 6 with high performance and low cost.

In addition, in the antenna system of the third embodiment, the configuration in which the plurality of antenna elements 16 provided in the primary antenna 5 are used for transmission and reception has been described. However, without being limited to this configuration, the primary antenna 5 may include a transmitting antenna element used for transmission and a receiving antenna element (third antenna element) used for reception. If the primary antenna 5 has a transmitting antenna element and a receiving antenna element, the primary antenna 5 may not have the circulators 15-1 to 15-Np. Also in this case, the beam forming unit 45 performs the same operation as described above. The transmitting antenna elements and receiving antenna elements are arranged regularly to form an array antenna. The transmit antenna elements and receive antenna elements may be arranged alternately or arranged in any pattern in the array antenna. Further, when the transmitting antenna element used for transmission and the receiving antenna element used for reception are separated, the antenna system includes the primary antenna 1 of the first embodiment and the second antenna instead of the primary antenna 5. It may be provided with the primary antenna 4 of the embodiment. The antenna system may also use some of the antenna elements 16 for transmission and reception, and may comprise the aforementioned transmit and receive antenna elements.

Also, in the antenna system of the third embodiment, the configuration in which the plurality of antenna modules 61 provided in the secondary antenna 6 perform transmission and reception has been described. However, without being limited to this configuration, the secondary antenna 6 may include the antenna module 21 of the first embodiment and the antenna module 31 (fourth antenna element) of the second embodiment. When the secondary antenna 6 comprises antenna modules 21, 31, the antenna modules 21, 31 are arranged regularly to form an array antenna. Also in this case, the primary antenna 5 performs the same operation as described above. The antenna modules 21 and 31 may be alternately arranged or arranged in an arbitrary pattern in the array antenna. The secondary antenna 6 may also include an antenna module 61 for transmission and reception, an antenna module 21 for transmission, and an antenna module 31 for reception.

(Fourth embodiment)
In the antenna system of the third embodiment, according to the distance between the antenna elements 16-1 to 16-Np provided in the primary antenna 5 and each antenna module 61 provided in the secondary antenna 6 and the angular response of each antenna element, , the level of the signal space-fed between the primary antenna 5 and the secondary antenna 6 may drop. A drop in the level of the space-fed signal can cause degradation of the transmit and receive beams. In the fourth embodiment, an antenna system that compensates for such signal level drop will be described.

FIG. 15 is a diagram showing a configuration example of an antenna system according to the fourth embodiment. The antenna system of the fourth embodiment has the same configuration as the antenna system of the third embodiment. As shown in FIG. 15, the antenna modules 61-1 and 61-Ns located farther from the array antenna formed by the antenna elements 16-1 to 16-Np than the other antenna modules 61 have The level of the space-fed transmitted signal is reduced. This drop in level is due to the path loss increasing with spatial path length. In addition, the angle between the orientation of each antenna element 16 and the orientation of the antenna element 211 of the antenna module 61 is different for each antenna module 61, resulting in a difference in angular response characteristics, which causes a difference in transmission signal level.

In the antenna module 61 according to the fourth embodiment, in order to compensate for the above-described level reduction and level difference of the transmission signal, the amplification factor of the HPA 213 is adjusted according to the position of the antenna module 61 in the secondary antenna 6 and the difference in the angular response characteristics. raise the The amplification factor of the HPA 213 of each antenna module 61 is determined so as to reduce the level difference of the transmission signal caused by the difference in path loss and angular response characteristics. That is, the longer the spatial path length and the greater the path loss, the greater the amplification factor, and the smaller the angular response characteristic, the greater the amplification factor of the HPA 213 . By determining the amplification factor of the HPA 213 (first amplifier) in this way, the transmission power of each antenna element 215 can be made uniform, and the precision of the transmission beam formed by the secondary antenna 6 can be improved.

When the level of the transmission signal falls below the allowable input range of the HPA 213 due to the level drop and level difference of the transmission signal, the HPA 213 may not operate. In such a case, an amplifier that includes the level of the transmission signal within its allowable input range is provided in the preceding stage of the HPA 213, or an amplifier having an allowable input range suitable for the level of the transmission signal in each antenna module 61 is used as the HPA 213. may

When a signal space-fed from the secondary antenna 6 is received by the primary antenna 5 as well, the level of the signal may drop, as in the case of the transmission signal. This is because the amplitude distribution in the aperture plane of the array antenna formed by the antenna elements 16 of the primary antenna 5 is uniform, whereas the amplitude distribution in the aperture plane of the spatially-fed signal varies. This is because the amplitude of is deviated from the desired amplitude.

The amplification factor of the LNA 312 of the antenna module 61 is increased in accordance with the decrease in signal level so as to make the amplitude distribution in the aperture plane of the array antenna of the primary antenna 5 uniform. By determining the amplification factor of the LNA 312 (second amplifier) in this way, the amplitude distribution in the array antenna of the primary antenna 5 becomes uniform, and the accuracy of the reception beam formed by the beam forming unit 45 by the DBF method is improved. can be made

In addition, the amplification factor of the HPA 213 and LNA 312 of each antenna module 61 may be determined according to the path loss (path distance).

(Fifth embodiment)
In the fourth embodiment, the antenna compensates for the difference in path loss and angular response characteristics between each antenna element of the primary antenna and each antenna element of the secondary antenna by signal amplification in the antenna module of the secondary antenna. explained the system. In a fifth embodiment, an antenna system is described that reduces the difference in path loss and angular response characteristics by another technique.

FIG. 16 is a diagram showing a configuration example of an antenna system according to the fifth embodiment. The antenna system of the fifth embodiment comprises a primary antenna 5 and a secondary antenna 6a. The secondary antenna 6a has a plurality of antenna modules 61 (61-1, 61-2, . . . , 61-Ns) like the secondary antenna 6 of the third embodiment. In the secondary antenna 6a, the surface on which the plurality of antenna modules 61 are regularly arranged is curved so that the beam pattern of the array antenna formed by the antenna elements 16 of the primary antenna 5 is uniform. is different from the secondary antenna 6 . That is, in the secondary antenna 6a, the aperture surface of the array antenna formed by the plurality of antenna elements 211 is curved so that the distance difference from the antenna element 211 of each antenna module 61 to the array antenna of the primary antenna 5 is small. is doing.

As described above, by bringing the end of the secondary antenna 6 closer to the primary antenna 5 side and curving the aperture surface toward the primary antenna 5, the path loss at the end of the secondary antenna 6a is suppressed and the angle It is possible to change the level of the response and suppress the drop in the signal level. By curving the surface on which the antenna elements 211 of each antenna module 61 are arranged (the aperture surface of the array antenna), the difference in path loss and angular response characteristics between the primary antenna 5 and the secondary antenna 6a can be reduced. , the accuracy of the transmission beam formed by the secondary antenna 6a can be improved.

In addition, by forming the aperture surface of the array antenna into a curved surface, it is possible to increase the number of antenna modules 61 to be arranged compared to a flat surface. As a result, the transmission power can be increased when forming a transmission beam with the secondary antenna 6a. While the aperture plane of the array antenna formed by the plurality of antenna elements 211 of the secondary antenna 6a is curved as described above, the aperture plane of the array antenna formed by the plurality of antenna elements 215 is not curved. It may be flat.

(Sixth embodiment)
In the first to fifth embodiments, the case where the antenna system has one primary antenna and one secondary antenna has been described. In this case, if an attempt is made to increase the aperture of the secondary antenna, it is necessary to increase the separation distance between the primary and secondary antennas in consideration of the difference in path loss and angular response characteristics. Therefore, when trying to increase the aperture of the secondary antenna, the size of the antenna system increases not only in the aperture direction but also in the depth direction with respect to the aperture. In the sixth embodiment, an antenna system that suppresses an increase in dimension in the depth direction when the aperture of the secondary antenna is increased will be described.

FIG. 17 is a diagram showing a configuration example of an antenna system according to the sixth embodiment. The antenna system of the sixth embodiment includes a plurality of primary antennas 5 (5-1, 5-2, . . . , 5-P) and a plurality of secondary antennas 6 (6-1, 6-2, . 6-P). The primary antenna 5 and the secondary antenna 6 are associated one-to-one. In the sixth embodiment, the aperture required for the antenna system is divided into P parts, a secondary antenna 6 is installed for each divided aperture, and a primary antenna 5 is installed for each secondary antenna 6 . Even if the beam width (beam angle width) of the beam pattern of the array antenna formed by the plurality of antenna elements 16 provided in each primary antenna 5 is constant, by installing the secondary antenna 6 for each divided aperture, , the increase in dimension in the depth direction can be reduced.

Once the depth dimension D and the beam angle θbw of the primary antenna 5 that are permissible in the antenna system are determined, the aperture length L of the secondary antenna 6 is determined by Equation (7). The number of divisions P is determined by dividing the aperture length Lall required for the antenna system by the aperture length L calculated by Equation (7) and rounding up to the nearest whole number.

The antenna system in the sixth embodiment not only mitigates the increase in depth dimension when increasing the aperture of the secondary antenna 6, but also transmits for each pair of primary antenna 5 and secondary antenna 6 Robust operation corresponding to various targets and usage environments is made possible by changing the polarization and frequency of the signal. Also, by changing the modulation scheme for each secondary antenna 6, MIMO (Multiple-Input Multiple-Output) can be configured (Non-Patent Document 8). When MIMO is configured, the degree of freedom in combining the secondary antennas 6 used for transmission and the secondary antennas 6 used for reception in the plurality of secondary antennas 6 is increased, and multi-beam formation and unwanted wave suppression performance in the antenna system are improved. It is possible to improve performance such as improvement.

In each of the embodiments described above, the configuration in which transmission weight determination section 112 determines transmission weights by calculation has been described. However, without being limited to this configuration, transmission weight determination section 112 has a table storing transmission weights for each transmission beam formed by the secondary antenna, and determines transmission weights corresponding to transmission beams designated by beam control signals. You can choose from the table. Also, transmission weight determination section 112 may be provided outside signal generation section 11 . Similarly, the reception weight determination unit 451 may also have a table storing reception weights for each reception beam, and select reception weights corresponding to reception beams designated by beam control signals from the table. Also, the reception weight determining unit 451 may be provided outside the beam forming unit 45 .

According to at least one embodiment described above, according to the transmission beam shape formed by the second array antenna (secondary antennas 2 and 6) and the position of each of the second antenna elements (antenna element 215) The transmission weight is changed by having a transmission weight determination unit that determines the transmission weight of each of the plurality of first antenna elements (antenna element 16) based on the determined phase or phase and amplitude of each of the second antenna elements. , the amplitude and phase of the second antenna element can be controlled. By controlling the amplitude and phase, it is possible to form a plurality of transmission beams in the second array antenna without phase control in the second array antenna, and reduce the increase in the circuit size due to the increase in the number of the second antenna elements. can.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

1, 4, 5... Primary antenna; 2, 3, 6, 6a... Secondary antenna; 11... Signal generator; 12... DA converter; 13, 43... Frequency converter; 212,214...circulator;16,41,211,215,311,313...antenna element;21,31,61...antenna module;42,312...LNA;44...AD converter;45...beam former;111... Signal generator; 112...Transmission weight determination section; 113, 452...Multiplier; 451...Reception weight determination section; 453...Adder

Claims (10)

a first array antenna having a plurality of first antenna elements;
a transmitter that supplies to each of the plurality of first antenna elements a transmission signal obtained by multiplying a signal by a transmission weight corresponding to each of the plurality of first antenna elements;
a second antenna element having a plurality of second antenna elements for receiving the transmission signal supplied from the first array antenna and transmitting the input transmission signal in a direction different from the direction toward the first array antenna; an array antenna;
Based on the phase or the phase and amplitude of each of the second antenna elements determined according to the transmission beam shape formed by the second array antenna and the position of each of the second antenna elements, the plurality of second antenna elements a transmission weight determination unit that determines the transmission weight for each of one antenna element;
An antenna system comprising: a beam forming unit that acquires signals received by the second array antenna by each of the plurality of first antenna elements, and combines the acquired signals by multiplying them by corresponding reception weights;
The reception weight based on the phase or the phase and amplitude of each of the plurality of second antenna elements determined according to the reception beam shape formed by the second array antenna and the position of each of the second antenna elements. a reception weight determination unit that determines
2. The antenna system of claim 1, further comprising: The first array antenna has a plurality of third antenna elements,
a beam forming unit that acquires signals supplied from the second array antenna by each of the plurality of third antenna elements, and combines the acquired signals by multiplying them by reception weights corresponding to the signals;
Based on the phase or the phase and amplitude of each of the plurality of second antenna elements determined according to the reception beam shape formed by the second array antenna and the position of each of the second antenna elements, the reception a reception weight determination unit that determines the weight;
2. The antenna system of claim 1, further comprising: The second array antenna supplies signals received by each of the plurality of second antenna elements toward the first array antenna,
Antenna system according to claim 2 or claim 3. The second array antenna has a plurality of fourth antenna elements,
The second array antenna supplies signals received by each of the plurality of fourth antenna elements toward the first array antenna,
Antenna system according to claim 2 or claim 3. The transmission signal includes signals in a plurality of frequency bands,
wherein the transmission weight determination unit calculates the transmission weights for the signals in each of the plurality of frequency bands according to a plurality of transmission beam shapes formed by the second array antenna;
Antenna system according to any one of claims 1 to 5. The second array antenna includes a first amplifier for amplifying the transmission signal transmitted by each of the plurality of second antenna elements, and a signal received by each of the plurality of second antenna elements to amplify the a second amplifier feeding towards the first array antenna;
The amplification factors of the first and second amplifiers increase as the distance between the second antenna element and the first array antenna increases.
Antenna system according to claim 2 or claim 3. A surface of the second array antenna on which each of the plurality of second antenna elements is arranged is curved so as to reduce a difference in distance between each of the second antenna elements and the first array antenna. ,
Antenna system according to claim 2 or claim 3. a plurality of the first array antennas;
The transmission unit, the transmission weight determination unit, the beam formation unit, the reception weight determination unit, and the second array antenna corresponding to each of the plurality of first array antennas,
Antenna system according to claim 2 or claim 3. a first array antenna having a plurality of first antenna elements;
a beam forming unit that combines signals received by each of the plurality of first antenna elements by multiplying them by reception weights;
a second array antenna having a plurality of second antenna elements for receiving signals in a direction different from the direction to the first array antenna and for supplying received signals to the first array antenna;
The reception weight based on the phase or the phase and amplitude of each of the plurality of second antenna elements determined according to the reception beam shape formed by the second array antenna and the position of each of the second antenna elements. a reception weight determination unit that determines
An antenna system comprising:

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