GB2573909A

GB2573909A - Adaptive array antenna device

Info

Publication number: GB2573909A
Application number: GB1910715.0A
Authority: GB
Inventors: Takahashi Ryuhei
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2017-03-17
Filing date: 2017-03-17
Publication date: 2019-11-20
Anticipated expiration: 2037-03-17
Also published as: GB201910715D0; JP6573745B2; GB2573909B; WO2018167952A1; JPWO2018167952A1

Abstract

The present invention is provided with a null offset estimation unit (11) for estimating a null offset, which is a change between a direction of arrival of interference in a listening period and a direction of arrival of interference in a beam transmission period, from a plurality of signals respectively received by a number M of sub-array antennas (1-m) during the listening period and a plurality of signals respectively received by the M sub-array antennas (1-m) during the beam transmission period. On the basis of the null offset estimated by the null offset estimation unit (11), a compensation weight calculation unit (12) calculates a compensation weight for compensating for null offset, the compensation weight serving as a weighting factor for the plurality of signals respectively received by the M sub-array antennas (1-m) during the beam transmission period.

Description

TITLE OF INVENTION: AD APTIVE ARRAY ANTENNA DEVICE

TECHNICAL FIELD [0001] The present invention relates to an adaptive array antenna device for multiplying a plurality of signals each received by a plurality of subarray antennas by a weight coefficient and combining the plurality of signals after multiplication by the weight coefficient.

BACKGROUND ART [0002] Radar devices are mounted on a platform such as an aircraft and are sometimes operated under the environment in which interfering waves are incoming.

An antenna device included in a radar device forms an adaptive beam by an array antenna in which a plurality of subarray antennas is arranged.

At this time, in order to suppress interfering waves included in reception signals of the array antenna to improve the signal to jamming and noise ratio (SJNR) of a target signal related to a target to be observed, the antenna device determines an adaptive weight such that a null is formed in an incoming direction of an interfering wave. The adaptive weight is a weight coefficient for a plurality of signals each received by the plurality of subarray antennas.

[0003] The determination of the adaptive weight by the antenna device is performed, for example, by the following method.

First, the antenna device temporarily stops the beam transmitted from the array antenna and acquires, as signals of an interfering wave, a plurality of signals each received by the plurality of subarray antennas during a listening period in which no beam is transmitted.

Next, the antenna device determines the adaptive weight such that a null is formed in the incoming direction of the interfering wave from the acquired signals of interfering wave.

[0004] In a case where the radar device including the antenna device is installed in a base or the like on the land and the radar device does not move, unless the transmission source of the interfering wave is moving, the incoming direction of the interfering wave does not change.

However, in a case where the radar device including the antenna device or the transmission source of the interfering wave is moving, the incoming direction of the interfering wave changes.

Therefore, even when the antenna device determines the adaptive weight for forming a null in the incoming direction of the interfering wave during the listening period, the incoming direction of the interfering wave changes during a short time before transmission of a beam from the array antenna is resumed.

That is, the incoming direction of the interfering wave in the listening period and the incoming direction of the interfering wave in the beam transmission period during which the beam is transmitted after the end of the listening period become different.

[0005] As the incoming direction of the interfering wave changes, a shift (hereinafter referred to as a “null shift”) occurs between the direction of the null formed by the adaptive weight determined during the listening period and the actual incoming direction of the interfering wave during the beam transmission period.

Since the occurrence of the null shift deteriorates the suppression performance of the interfering wave by the antenna device, the target detection performance by the radar device deteriorates.

The following Non-Patent Literature 1 discloses an antenna device for performing processing of expanding the width of a null formed by an adaptive weight determined during a listening period in order to avoid the influence of a null shift. CITATION LIST NON-PATENT LITERATURE [0006] Non-Patent Literature 1: J. R. Guerci, Theory and application of covariance matrix tapers for robust adaptive beamforming, IEEE Transactions on Signal Processing, vol. 47, no. 4, pp. 977-985, Apr 1999.

SUMMARY OF INVENTION

TECHNICAL PROBLEM [0007] Although the processing for expanding the width of the null formed by the adaptive weight is performed in the conventional antenna device, this does not properly set the expanded width of the null width on the basis of a change in the incoming direction of the interfering wave. Therefore, there are cases where the incoming direction of the interfering wave changes greatly such that the expanded null width is exceeded. As described above, there is a disadvantage that an interfering wave included in reception signals of the array antenna cannot be suppressed in a case where a change in the incoming direction of the interfering wave is large.

[0008] The present invention has been devised in order to solve the disadvantage as described above, and it is an object of the present invention to provide an antenna device capable of suppressing an interfering wave included in reception signals of an array antenna even when the incoming direction of the interfering wave drastically changes.

SOLUTION TO PROBLEM [0009] An antenna device according to the present invention includes: an array antenna in which a plurality of subarray antennas is arrayed, each of the plurality of subarray antennas including one or more element antennas; a null shift estimating unit for estimating a null shift from a plurality of signals each received by the plurality of subarray antennas during a listening period during which no beam is transmitted from the array antenna and a plurality of signals each received by the plurality of subarray antennas during a beam transmission period during which the beam is transmitted after an end of the listening period, the null shift being a shift between an incoming direction of an interfering wave during the listening period and an incoming direction of an interfering wave during the beam transmission period; and a compensation weight calculating unit for calculating, as a weight coefficient for the plurality of signals each received by the plurality of subarray antennas, a compensation weight for compensating for the null shift during the beam transmission period on the basis of the null shift estimated by the null shift estimating unit, and a beam forming unit for multiplying the plurality of signals each received by the plurality of subarray antennas by the compensation weight calculated by the compensation weight calculating unit and combining the plurality of signals after multiplication by the compensation weight.

ADVANTAGEOUS EFFECTS OF INVENTION [0010] According to the present invention, included is a null shift estimating unit for estimating a null shift, which is a shift between an incoming direction of an interfering wave during a listening period and an incoming direction of an interfering wave during a beam transmission period, from a plurality of signals each received by a plurality of subarray antennas during the listening period and a plurality of signals each received by the plurality of subarray antennas during the beam transmission period, and a compensation weight calculating unit calculates, as a weight coefficient for the plurality of signals each received by the plurality of subarray antennas, a compensation weight for compensating for the null shift during the beam transmission period on the basis of the null shift estimated by the null shift estimating unit. Therefore, the interfering wave included in the reception signals of the array antenna can be suppressed even when the incoming direction of the interfering wave drastically changes.

BRIEF DESCRIPTION OF DRAWINGS [0011] FIG. 1 is a configuration diagram illustrating an adaptive array antenna device according to a first embodiment of the present invention.

FIG. 2 is a hardware configuration diagram illustrating a signal processing device 2 of the adaptive array antenna device according to the first embodiment of the present invention.

FIG. 3 is a hardware configuration diagram of a computer in the case where the signal processing device 2 is implemented by software, firmware, or the like.

FIG. 4 is a configuration diagram illustrating a null shift estimating unit 11 of the adaptive array antenna device according to the first embodiment of the present invention.

FIG. 5 is a configuration diagram illustrating a compensation weight calculating unit 12 of the adaptive array antenna device according to the first embodiment of the present invention.

FIG. 6 is a flowchart illustrating a processing procedure in the case where the signal processing device 2 is implemented by software, firmware, or the like.

FIG. 7 is a configuration diagram illustrating a compensation weight calculating unit 12 of an adaptive array antenna device according to a second embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS [0012] To describe the present invention further in detail, embodiments for carrying out the present invention will be described below with reference to the accompanying drawings.

[0013] First Embodiment

FIG. 1 is a configuration diagram illustrating an adaptive array antenna device according to a first embodiment of the present invention.

In FIGS. 1 and 2, in an array antenna 1, M subarray antennas 1-m (m = 1, 2,..., M) are arrayed.

A subarray antenna 1-m includes at least one element antenna.

[0014] The signal processing device 2 includes a null shift estimating unit 11, a compensation weight calculating unit 12, and a beam forming unit 13 and is a device that multiplies a plurality of signals each received by the M subarray antennas 1-m by a weight coefficient and combines the plurality of signals after multiplication by the weight coefficient.

In FIG. 1, in order to simplify the drawing, a receiver for detecting a signal received by a subarray antenna 1-m and a converter for converting the reception signal of the receiver from an analog signal to a digital signal are omitted; however, in fact, receivers and converters are included.

Therefore, digital reception signals corresponding to the signals received by the M subarray antennas 1-m are provided to the null shift estimating unit 11 and the beam forming unit 13.

In FIG. 1, reception signal vectors including M digital reception signals are illustrated.

[0015] The null shift estimating unit 11 is implemented by a null shift estimating circuit 21 illustrated in FIG. 2, for example.

The null shift estimating unit 11 acquires M digital reception signals corresponding to M signals each received by the M subarray antennas 1-m during a listening period which is a period during which no beam is transmitted from the array antenna 1.

The null shift estimating unit 11 also acquires M digital reception signals corresponding to M signals each received by the M subarray antennas 1-m during a beam transmission period which is a period during which a beam is transmitted after the end of the listening period.

From the M digital reception signals during the listening period and the M digital reception signals during the beam transmission period, the null shift estimating unit 11 performs processing for estimating a null shift which is a shift between an incoming direction of an interfering wave during the listening period and an incoming direction of an interfering wave during the beam transmission period.

Note that the beam transmission period includes a period during which the array antenna 1 receives a beam in addition to the period during which the array antenna 1 transmits a beam.

[0016] The compensation weight calculating unit 12 is implemented by a compensation weight calculating circuit 22 illustrated in FIG. 2, for example.

The compensation weight calculating unit 12 performs processing for calculating, as a weight coefficient for the M digital reception signals corresponding to the M signals each received by the M subarray antennas 1-m, a compensation weight for compensating for a null shift during the beam transmission period on the basis of the null shift estimated by the null shift estimating unit 11.

[0017] The beam forming unit 13 is implemented by a beam forming circuit 23 illustrated in FIG. 2, for example.

The beam forming unit 13 includes M multipliers 14-m and an adder 15 and performs processing for, during the beam transmission period, multiplying the M digital reception signals corresponding to the M signals each received by the M subarray antennas 1-m by the compensation weight calculated by the compensation weight calculating unit 12 and combining the M digital reception signals after multiplication by the compensation weight.

During the beam transmission period, the multipliers 14-m multiply the digital reception signals corresponding to the signals received by the subarray antennas 1-m by the compensation weight calculated by the compensation weight calculating unit 12 and output the digital reception signals after multiplication by the compensation weight to the adder 15.

The adder 15 combines the M digital reception signals after multiplication by the compensation weight each output from the M multipliers 14-m and outputs the combined digital reception signal as a reception beam.

[0018] In FIG. 1, it is assumed that each of the null shift estimating unit 11, the compensation weight calculating unit 12, and the beam forming unit 13, which are components of the signal processing device 2, is implemented by dedicated hardware as illustrated in FIG. 2. That is, implementation by the null shift estimating circuit 21, the compensation weight calculating circuit 22, and the beam forming circuit 23 is assumed.

The null shift estimating circuit 21, the compensation weight calculating circuit 22, and the beam forming circuit 23 correspond to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination thereof.

[0019] Note that the components of the signal processing device 2 are not limited to those implemented by dedicated hardware, and the signal processing device 2 may be implemented by software, firmware, or a combination of software and firmware.

The software or the firmware is stored in a memory of a computer as a program. Here, a computer refers to hardware for executing the program and corresponds to, for example, a central processing unit (CPU), a central processing device, a processing device, an arithmetic device, a microprocessor, a microcomputer, a processor, a digital signal processor (DSP), or the like.

[0020] FIG. 3 is a hardware configuration diagram of a computer in the case where the signal processing device 2 is implemented by software, firmware, or the like.

In the case where the signal processing device 2 is implemented by software, firmware, or the like, it is only required that a program for causing the computer to execute processing procedures of the null shift estimating unit 11, the compensation weight calculating unit 12, and the beam forming unit 13 be stored in a memory 31 of the computer and that a processor 32 of the computer execute the program stored in the memory 31.

Note that the memory 31 of the computer may be a nonvolatile or volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable read only memory (EPROM), or an electrically erasable programmable read only memory (EEPROM); a magnetic disc, a flexible disc, an optical disc, a compact disc, a mini disc, a digital versatile disk (DVD), or the like.

[0021] FIG. 4 is a configuration diagram illustrating the null shift estimating unit 11 of the adaptive array antenna device according to the first embodiment of the present invention.

In FIG. 4, a first correlation matrix calculating unit 41 performs processing for calculating a correlation matrix of the interfering wave from the M digital reception signals corresponding to the M signals each received by the M subarray antennas 1-m during the listening period.

[0022] A vector calculating unit 42 performs processing for calculating a weight vector for scanning in the scan direction of the interfering wave by using a weight constraint vector for scanning in the main beam direction of the beam and the correlation matrix of the interfering wave calculated by the first correlation matrix calculating unit 41.

That is, the vector calculating unit 42 performs processing for calculating the weight vector by multiplying a diagonal matrix, which has, as elements on a diagonal line, path difference phase components due to the difference between the main beam direction and the scan direction, the weight constraint vector, and the correlation matrix of the interfering wave calculated by the first correlation matrix calculating unit 41.

A second correlation matrix calculating unit 43 performs processing for calculating a correlation matrix of reception signals of the array antenna 1 from the M digital reception signals corresponding to the M signals each received by the M subarray antennas 1-m during the beam transmission period.

[0023] An evaluation function calculating unit 44 performs processing for calculating an evaluation function used for estimation of the null shift by using the weight vector calculated by the vector calculating unit 42 and the correlation matrix of reception signals calculated by the second correlation matrix calculating unit 43.

A null shift estimation processing unit 45 performs processing for estimating a null shift by using the evaluation function calculated by the evaluation function calculating unit 44.

[0024] FIG. 5 is a configuration diagram illustrating the compensation weight calculating unit 12 of the adaptive array antenna device according to the first embodiment of the present invention.

In FIG. 5, a CMT matrix calculating unit 51 performs processing for calculating a covariance matrix taper (CMT) matrix which is a matrix for setting a null width from the null shift estimated by the null shift estimation processing unit 45 of the null shift estimating unit 11.

A weight calculation processing unit 52 includes a compensating correlation matrix calculating unit 53 and a compensating weight calculating unit 54.

The weight calculation processing unit 52 performs processing for calculating a compensation weight that compensates for the null shift from the CMT matrix calculated by the CMT matrix calculating unit 51 and the correlation matrix of the interfering wave calculated by the first correlation matrix calculating unit 41 of the null shift estimating unit 11.

[0025] The compensating correlation matrix calculating unit 53 performs processing for calculating a null shift compensating correlation matrix from the CMT matrix calculated by the CMT matrix calculating unit 51 and the correlation matrix of the interfering wave calculated by the first correlation matrix calculating unit 41 of the null shift estimating unit 11.

The compensating weight calculating unit 54 performs processing for calculating the compensation weight that compensates for the null shift from the weight constraint vector and the null shift compensating correlation matrix calculated by the compensating correlation matrix calculating unit 53.

[0026] Next, the operation will be described.

First, the signal processing device 2 temporarily stops the beam transmitted from the array antenna 1 and acquires, as signals of an interfering wave, M signals each received by the M subarray antennas 1-m (m = 1, 2, ..., M) during the listening period in which no beam is transmitted.

The signal processing device 2 detects the M signals each received by the M subarray antennas 1-m and converts each of the detected M signals from an analog signal to a digital signal.

The null shift estimating unit 11 and the beam forming unit 13 of the signal processing device 2 are provided with a reception signal vector including the digital reception signals which are the converted M digital signals.

[0027] During the listening period, the reception signal vector xo(t) expressed in the following equation (1) is provided to the null shift estimating unit 11 and the beam forming unit 13.

^<Y · - \ jMO+MO (i)

In equation (1), t represents time, aj(uo^(k)) represents a steering vector for the incoming direction uo^(k) = [uo^(k), vo^(k)]^T of a k-th interfering wave. Symbol T represents transposition.

Symbol jk(t) represents the complex amplitude of the k-th interfering wave, and no(t) represents the receiver noise vector.

[0028] When provided with the reception signal vector xo(t) during the listening period, the first correlation matrix calculating unit 41 of the null shift estimating unit 11 calculates a correlation matrix Ro of the interfering wave from the reception signal vector xo(t) during the listening period as expressed in the following equation (2) (step STI in FIG. 6).

In equation (2), E[·] is a symbol representing the ensemble average for “·.” Symbol H represents Hermitian transpose.

In equation (2), a finite number of reception signal vectors xo(t) at different times t in the listening period are used.

The first correlation matrix calculating unit 41 outputs the calculated correlation matrix Ro of the interfering wave to the vector calculating unit 42 and the compensating correlation matrix calculating unit 53 of the compensation weight calculating unit 12.

[0029] The vector calculating unit 42 acquires a scan direction u of the interfering wave and obtains a diagonal matrix D(u - u_s) having, as elements on a diagonal line, path difference phase components due to a difference between the scan direction u and the main beam direction u_s.

The main beam direction u_s is the direction of the main beam in the beam transmitted from the array antenna 1 during the beam transmission period after the end of the listening period.

The vector calculating unit 42 further acquires a weight constraint vector a(u_s) for scanning in the main beam direction u_s of the beam transmitted from the array antenna 1 during the beam transmission period after the end of the listening period. [0030] The vector calculating unit 42 calculates a weight vector w(u) for scanning in the scan direction u of the interfering wave by multiplying the diagonal matrix D(u - u_s), the weight constraint vector a(u_s), and the correlation matrix Ro of the interfering wave output from the first correlation matrix calculating unit 41 as expressed in the following equation (3) (step ST2 in FIG. 6).

w(u)-aD{u~u,)R_e'a(u_s) (3)

In equation (3), a represents a preset normalization coefficient.

The vector calculating unit 42 outputs the calculated weight vector w(u) to the evaluation function calculating unit 44.

Note that the weight vector w(u) calculated by the vector calculating unit 42 is a vector for forming a null in the incoming direction uo^(k) of the interfering wave and corresponds to a weight vector for scanning a weight vector w(us) = aRo^_1a(us) in the main beam direction u_s in the scan direction u of the interfering wave.

[0031] During the beam transmission period after the end of the listening period, the reception signal vectors x(t) expressed in the following equation (4) are provided to the null shift estimating unit 11 and the beam forming unit 13.

A' / ’ X x(/) = ⁺ (u^ + διι_έ (0 + »(0 ( 4 )

In equation (4), s(t) represents a target signal, a_s represents a steering vector with respect to the incoming direction of the target signal s(t), n(t) represents the receiver noise vector, and the characteristic of the receiver noise vector n(t) is the same as the characteristic of the receiver noise vector no(t) in the listening period.

An expression of uo^(k) + 5uk represents the incoming direction of the k-th interfering wave in the beam transmission period, which is shifted from the incoming direction of the k-th interfering wave in the listening period.

An expression of 6uk = [5uk, 5vk]^T is a shift between the incoming direction of the k-th interfering wave in the beam transmission period and the incoming direction of the k-th interfering wave in the listening period.

[0032] When provided with the reception signal vectors x(t) during the beam transmission period after the end of the listening period, the second correlation matrix calculating unit 43 of the null shift estimating unit 11 calculates a correlation matrix R_xof reception signals of the array antenna 1 from the reception signal vectors x(t) during the beam transmission period as expressed in the following equation (5) (step ST3 in FIG. 6).

R, = E[xO)x^H(i)] (5)

The second correlation matrix calculating unit 43 outputs the calculated correlation matrix R_x of reception signals to the evaluation function calculating unit 44. [0033] The evaluation function calculating unit 44 of the null shift estimating unit 11 calculates an evaluation function P(u) used for estimation of the null shift as illustrated in the following equation (6) by using the weight vector w(u) output from the vector calculating unit 42 and the correlation matrix R_x of reception signals output from the second correlation matrix calculating unit 43 (step ST4 in FIG. 6).

ti) - --1------------------ .

^} w ^H(u)R_xw(u) (6.)

The denominator of equation (6), wh(u)R_xw(u), is the scanning output power of the beam by the weight vector w(u).

Since the weight vector w(u) is a weight vector for scanning the weight vector w(u_s) in the main beam direction u_s in the scan direction u of the interfering wave as described above, the null formed by the weight vector w(u) in the incoming direction u of the interfering wave is also scanned.

[0034] Therefore, when the scan direction u is u_s + 5uk, the weight vector w(u) results in a null formed in a direction of uo^(k) + 5uk.

Since the direction uo^(k) + 5uk forming this null coincides with the incoming direction uo^(k) + 5uk of the k-th interfering wave included in the correlation matrix Rx of reception signals, the power of the k-th interfering wave included in w^H(us + 5uk)R_xw(u_s+ 6uk) is minimized.

Therefore, with the evaluation function P(u) calculated by the evaluation function calculating unit 44, the function value reaches a peak in the scan direction u = u_s + 5uk, and 6uk which is u corresponding to the peak function value is obtained as a candidate null shift.

Since there are a total of K candidate null shifts, the candidate having the largest function value among the K candidates is obtained as the estimated value 6u-hat of the null shift. In the description of the specification, the symbol “^Λ” cannot be placed over a letter due to limitation of the electronic patent application, and thus it is noted as “6u-hat.”

The evaluation function calculating unit 44 outputs the calculated evaluation function P(u) to the null shift estimation processing unit 45.

[0035] The null shift estimation processing unit 45 of the null shift estimating unit 11 estimates the null shift using the evaluation function P(u) output from the evaluation function calculating unit 44 and outputs the estimated value 6u-hat of the null shift to the compensation weight calculating unit 12 (step ST5 in FIG. 6).

[0036] Although the power of the k-th interfering wave is minimized in this example, the power of the target signal included in the correlation matrix R_x of reception signals and the power of the interfering waves other than the k-th interfering wave still remain.

Since the power of the target signal included in w^H(u_s + 5uk)R_xw(u_s + 5uk) is unnecessary power when the estimated value 5u-hat of the null shift is calculated, reducing the power of the target signal in advance can improve the accuracy of estimation of the null shift using the evaluation function P(u).

Therefore, the vector calculating unit 42 may calculate the weight vector w(u) for scanning in the scan direction u of interfering wave by the following equation (7) instead of equation (3).

w(u) aD(ii-u_s )R/D_Aa(ii_s) (7)

In equation (7), Da is a diagonal matrix having a taper for forming a difference beam as elements on a diagonal line.

The symbol w(u) represents a weight vector for forming a null in the incoming direction u of the interfering wave and in the main beam direction u_s.

In order to form a null in the main beam direction u_s, the target signal incoming from the vicinity of the main beam direction u_s is suppressed, and the power of the target signal included in w^H(u_s + 5uk)R_xw(u_s + 5uk) is reduced.

[0037] Although the shift between the incoming direction of the k-th interfering wave in the listening period and the incoming direction of the k-th interfering wave in the beam transmission period is defined as 6uk = [5uk, 5vk]^T in the description above, in a case where the differences in the shifts of the K interfering waves are small enough to be negligible, the shift may be regarded as 6u = [6u, δν]^τ.

— Δχ,.Δί-ί sine | —Δν,,Δν | fl Λ* 1 ί λ ' »I J

Λ J X ?

[Tmt 1., ^sinc

In this case, since the function value of the evaluation function P(u) reaches a peak in the scan direction u = u_s + 5u, 6u which is u corresponding to the peak function value is obtained as a candidate null shift, and 6u which is u corresponding to the peak function value is obtained as the estimated value 6u-hat of the null shift.

[0038] When receiving the estimated value 6u-hat of the null shift output from the null shift estimation processing unit 45 of the null shift estimating unit 11, the CMT matrix calculating unit 51 of the compensation weight calculating unit 12 calculates a CMT matrix Tcmt for setting a null width by using the estimated value 6u-hat of the null shift as expressed in the following equation (8) (step ST6 in FIG. 6).

In equation (8), i and j are matrix element numbers, where i = 1, 2,..., M and j = 1,2,..., M.

In equation (8), coordinates of an m-th subarray antenna 1-m are defined as Pm = [xk, yk]^T, and each of Axy and Ayy is a relative coordinate.

Where, Axy = xi - xj and Ayy = yi - yj. Symbol λ represents the transmission wavelength.

In equation (8), the setting null width by the CMT matrix Tcmt is defined as Au = [Au, Δν]^τ.

The setting null width Au by the CMT matrix Tcmt is determined on the basis of the estimated value 6u-hat of the null shift as in the following equation (9).

r - ^A iT

Au = l&u&u,UA-l ( 9 )

In equation (9), k_u and k_v are arbitrary coefficients, values of which are preset depending on a taper used for beam formation irrespective of the estimated value 6u-hat of the null shift.

The CMT matrix calculating unit 51 outputs the calculated CMT matrix Tcmt to the compensating correlation matrix calculating unit 53.

[0039] The compensating correlation matrix calculating unit 53 of the compensation weight calculating unit 12 calculates a null shift compensating correlation matrix R from the CMT matrix Tcmt output from the CMT matrix calculating unit 51 and the correlation matrix Ro of the interfering wave output from the first correlation matrix calculating unit 41 of the null shift estimating unit 11 as illustrated in the following equation (10) (step ST7 of FIG. 6).

R ~ T_CMT O ( 1 θ )

In equation (10), a double circle is a symbol indicating the Hadamard product obtained by performing multiplication of matrix elements of the CMT matrix Tcmt and the correlation matrix Ro of the interfering wave.

The compensating correlation matrix calculating unit 53 outputs the calculated null shift compensating correlation matrix R to the compensating weight calculating unit 54.

[0040] During the beam transmission period after the end of the listening period, the compensating weight calculating unit 54 of the compensation weight calculating unit 12 acquires the weight constraint vector a(u_s) for scanning in the main beam direction u_s of the beam transmitted from the array antenna 1.

Using the weight constraint vector a(u_s) and the null shift compensating correlation matrix R output from the compensating correlation matrix calculating unit 53, the compensating weight calculating unit 54 calculates compensation weight vectors wa each representing a compensation weight that compensates for the null shift as expressed in the following equation (11) (step ST8 in FIG. 6).

w_A J (1 1)

In equation (11), β represents a normalization coefficient.

The compensating weight calculating unit 54 outputs the calculated compensation weight vectors wa to the beam forming unit 13.

[0041] When provided with the reception signal vectors x(t) during the beam transmission period after the end of the listening period, the beam forming unit 13 calculates a reception beam y(t) by multiplying the reception signal vectors x(t) by the compensation weight vectors wa as expressed in the following equation (12) and combining the reception signal vectors x(t) after multiplication by the compensation weight (step ST9 in FIG. 6).

(1 2) [0042] That is, the M multipliers 14-m in the beam forming unit 13 multiply the digital reception signals from the subarray antennas 1-m included in the reception signal vectors x (t) by the compensation weights for the subarray antennas 1-m included in the compensation weight vectors wa and output the digital reception signals after multiplication by the compensation weight to the adder 15.

The adder 15 of the beam forming unit 13 combines the M digital reception signals each output from the M multipliers 14-m and outputs the combined digital reception signal as the reception beam y(t).

Since the reception signal vectors x(t) are multiplied by the compensation weight vectors wa, a null having a setting null width of Au is formed in the reception beam y(t) with the incoming direction uo of the interfering wave as a center.

[0043] As is clear from the above description, according to the first embodiment, included is the null shift estimating unit 11 for estimating a null shift, which is a shift between an incoming direction of an interfering wave during a listening period and an incoming direction of an interfering wave during a beam transmission period, from a plurality of signals each received by the M subarray antennas 1-m during the listening period and a plurality of signals each received by the M subarray antennas 1-m during the beam transmission period, and the compensation weight calculating unit 12 calculates, as a weight coefficient for the plurality of signals each received by the M subarray antennas 1-m, a compensation weight for compensating for the null shift during the beam transmission period on the basis of the null shift estimated by the null shift estimating unit 11. Therefore, the interfering wave included in the reception signals of the array antenna 1 can be suppressed even when the incoming direction of the interfering wave drastically changes.

[0044] Second Embodiment

In the first embodiment, the example is described in which the compensation weight calculating unit 12 includes the CMT matrix calculating unit 51 and calculates the compensation weight vectors wa representing a compensation weight that compensates for the null shift by using the CMT matrix Tcmt calculated by the CMT matrix calculating unit 51.

In a second embodiment, an example will be described in which a compensation weight calculating unit 12 calculates compensation weight vectors wa representing compensation weights that compensate for a null shift without using the CMT matrix Tcmt.

[0045] FIG. 7 is a configuration diagram illustrating the compensation weight calculating unit 12 of an adaptive array antenna device according to the second embodiment of the present invention. In FIG. 7, the same symbol as that in FIG. 5 represents the same or a corresponding part and thus descriptions thereof are omitted.

A weight calculation processing unit 55 includes a compensating correlation matrix calculating unit 56 and a compensating weight calculating unit 54.

The compensating correlation matrix calculating unit 56 performs processing for calculating a null shift compensating correlation matrix from a null shift estimated by a null shift estimation processing unit 45 of a null shift estimating unit 11 and a correlation matrix of an interfering wave calculated by a first correlation matrix calculating unit 41 of the null shift estimating unit 11.

[0046] Next, the operation will be described.

In the first embodiment, a shift between the incoming direction of the k-th interfering wave in the listening period and the incoming direction of the k-th interfering wave in the beam transmission period is defined as 6uk = [5uk, 5vk]^T.

In the second embodiment, it is assumed that the differences of shifts of K interfering waves are negligibly small, and an example in which the shifts are deemed as 5u = [6u, δν]^τ will be described.

[0047] Therefore, in the second embodiment, during a beam transmission period after the end of a listening period, reception signal vectors x(t) expressed by the following equation (13) are provided to the null shift estimating unit 11 and a beam forming unit

13.

x(i) - a_s5’(f) + (u/ + ou j 4 (/) + n(/) (i 3 ) b·!

In equation (13), uo^(k) + 5u represents an incoming direction of a k-th interfering wave in the beam transmission period, which is shifted from the incoming direction of the k-th interfering wave in the listening period.

[0048] When provided with the reception signal vectors x(t) during the beam transmission period expressed in equation (13), a second correlation matrix calculating unit 43 of the null shift estimating unit 11 calculates a correlation matrix R_x of reception signals of an array antenna 1 from the reception signal vectors x(t) during the beam transmission period like in the first embodiment.

The second correlation matrix calculating unit 43 outputs the calculated correlation matrix R_x of reception signals to the evaluation function calculating unit 44. [0049] An evaluation function calculating unit 44 of the null shift estimating unit 11 calculates an evaluation function P(u) used for estimation of the null shift like in the first embodiment by using a weight vector w(u) output from a vector calculating unit 42 and the correlation matrix R_x of reception signals output from the second correlation matrix calculating unit 43.

[0050] Therefore, when the scan direction u is u_s + 5u, the weight vector w(u) forms a null in a direction of uo^(k) + 5u.

Since the direction uo^(k) + 5u in which the null is formed coincides with the incoming direction uo^(k) + 5u of the k-th interfering wave included in the correlation matrix Rx of reception signals, the power of the k-th interfering wave included in w^H(us + 6u)R_xw(us + 5u) is minimized.

Therefore, with the evaluation function P(u) calculated by the evaluation function calculating unit 44, the function value reaches a peak in the scan direction of u = u_s + 5u, and 6u which is u corresponding to the peak function value is obtained as an estimated value 6u-hat of the null shift.

[0051] The null shift estimation processing unit 45 of the null shift estimating unit 11 estimates the null shift using the evaluation function P(u) output from the evaluation function calculating unit 44 and outputs the estimated value 6u-hat of the null shift to the compensation weight calculating unit 12 like in the first embodiment.

[0052] The compensating correlation matrix calculating unit 56 of the compensation weight calculating unit 12 calculates a null shift compensating correlation matrix Ro' from the estimated value 6u-hat of the null shift output from the null shift estimation processing unit 45 of the null shift estimating unit 11 and the correlation matrix Ro of the interfering wave output from the first correlation matrix calculating unit 41.

The compensating correlation matrix calculating unit 56 outputs the calculated null shift compensating correlation matrix Ro' to the compensating weight calculating unit 54.

[0053] In this example, the correlation matrix Ro of the interfering wave calculated by the first correlation matrix calculating unit 41 can be expressed by the following equation (14).

R_e-£[x_e(z)x_e“(/)]-A_e4A_a ^M+«r²I (14)

In equation (14), Ao represents a matrix in which K steering vectors aj(uo^(k)) are aligned, J represents a correlation matrix of jk(t), and σ² represents receiver noise power.

Meanwhile, the correlation matrix Ro' of the interfering wave during the beam transmission period can be expressed by the following equation (15). The correlation matrix Ro' of the interfering wave during the beam transmission period corresponds to the null shift compensating correlation matrix.

R' - A'JA;^h +σ²Ι u 5)

In equation (15), Ao¹ represents a matrix in which K steering vectors aj(uo^(k) + 6u) are aligned.

[0054] In this example, in the case where a diagonal matrix having path difference phase components due to the shift 6u as elements on a diagonal line is defined as D(6u), the following equation (16) holds.

a, + Sa) -D(Sa)aj (u^^!) (1 6 )

Therefore, equation (15) can be expressed as the following equation (17).

R’ = »^H (Sa) D(Sa) + σΤ ^U/)

From the relationship of equation (17), Ro¹ can be calculated as a null shift compensating correlation matrix from the estimated value 6u-hat of the null shift and the correlation matrix Ro of the interfering wave as in the following equation (18).

R'_o D^H(S_u)R₀D(5_a) ( i 8) [0055] During the beam transmission period after the end of the listening period, the compensating weight calculating unit 54 of the compensation weight calculating unit 12 acquires the weight constraint vector a(u_s) for scanning in the main beam direction u_s of the beam transmitted from the array antenna 1.

The compensating weight calculating unit 54 calculates compensation weight vectors wa each representing a compensation weight that compensates for the null shift as expressed in the following equation (19) by using the weight constraint vector a(u_s) and the null shift compensating correlation matrix Ro¹ output from the compensating correlation matrix calculating unit 53.

w_A = ^Rj“^fa(u,) (1 9)

[0056] When provided with the reception signal vectors x(t) during the beam transmission period after the end of the listening period, the beam forming unit 13 calculates a reception beam y(t) by multiplying the reception signal vectors x(t) by the compensation weight vectors wa and combining the reception signal vectors x(t) after multiplication by the compensation weight like in the first embodiment.

Since the reception signal vectors x(t) are multiplied by the compensation weight vectors wa, a null having a setting null width of Au is formed in the reception beam y(t) with the incoming direction uo of the interfering wave as a center. [0057] As is apparent from the above description, like in the first embodiment, interfering waves included in reception signals of the array antenna 1 can be suppressed according to the second embodiment even when incoming directions of the interfering waves drastically change.

[0058] Note that, within the scope of the present invention, the present invention may include a flexible combination of the respective embodiments, a modification of any component of the respective embodiments, or an omission of any component in the respective embodiments.

INDUSTRIAL APPLICABILITY [0059] The present invention is suitable for an adaptive array antenna device for multiplying a plurality of signals each received by a plurality of subarray antennas by a weight coefficient and combining the plurality of signals after multiplication by the weight coefficient.

REFERENCE SIGNS LIST [0060] 1: Array antenna, 1-1 to 1-M: Subarray antenna, 2: Signal processing device, 11: Null shift estimating unit, 12: Compensation weight calculating unit, 13: Beam forming unit, 14-1 to 14-M: Multiplier, 15: Adder, 21: Null shift estimating circuit, 22: Compensation weight calculating circuit, 23: Beam forming circuit, 31: Memory, 32: Processor, 41: First correlation matrix calculating unit, 42: Vector calculating unit, 43: Second correlation matrix calculating unit, 44: Evaluation function calculating unit, 51: CMT matrix calculating unit, 52: Weight calculation processing unit, 53: Compensating correlation matrix calculating unit, 54: Compensating weight calculating unit, 55: Weight calculation processing unit, 56: Compensating correlation matrix calculating unit.

Claims

1. An adaptive array antenna device comprising:

an array antenna in which a plurality of subarray antennas is arrayed, each of the plurality of subarray antennas comprising one or more element antennas;

a null shift estimating unit for estimating a null shift from a plurality of signals each received by the plurality of subarray antennas during a listening period during which no beam is transmitted from the array antenna and a plurality of signals each received by the plurality of subarray antennas during a beam transmission period during which the beam is transmitted after an end of the listening period, the null shift being a shift between an incoming direction of an interfering wave during the listening period and an incoming direction of an interfering wave during the beam transmission period;

a compensation weight calculating unit for calculating, as a weight coefficient for the plurality of signals each received by the plurality of subarray antennas, a compensation weight for compensating for the null shift during the beam transmission period on a basis of the null shift estimated by the null shift estimating unit; and a beam forming unit for multiplying the plurality of signals each received by the plurality of subarray antennas by the compensation weight calculated by the compensation weight calculating unit and combining the plurality of signals after multiplication by the compensation weight.

2. The adaptive array antenna device according to claim 1, wherein the null shift estimating unit comprises:

a first correlation matrix calculating unit for calculating a correlation matrix of the interfering wave from the plurality of signals each received by the plurality of subarray antennas during the listening period;

a vector calculating unit for calculating a weight vector for scanning in a scan direction of the interfering wave by using a weight constraint vector for scanning in a main beam direction of the beam and the correlation matrix of the interfering wave calculated by the first correlation matrix calculating unit;

a second correlation matrix calculating unit for calculating a correlation matrix of reception signals of the array antenna from the plurality of signals each received by the plurality of subarray antennas during the beam transmission period;

an evaluation function calculating unit for calculating an evaluation function used for estimation of the null by using the weight vector calculated by the vector calculating unit and the correlation matrix of the reception signals calculated by the second correlation matrix calculating unit; and a null shift estimation processing unit for estimating the null shift by using the evaluation function calculated by the evaluation function calculating unit.

3. The adaptive array antenna device according to claim 2, wherein the vector calculating unit calculates the weight vector by multiplying a diagonal matrix, which has, as elements on a diagonal line, path difference phase components due to a difference between the main beam direction and the scan direction, the weight constraint vector, and the correlation matrix of the interfering wave calculated by the first correlation matrix calculating unit.

4. The adaptive array antenna device according to claim 2, wherein the compensation weight calculating unit comprises;

a CMT matrix calculating unit for calculating a CMT matrix for setting a null width from the null shift estimated by the null shift estimation processing unit; and a weight calculation processing unit for calculating a compensation weight, which compensates for the null shift, from the CMT matrix calculated by the CMT matrix calculating unit and the correlation matrix of the interfering wave calculated by the first correlation matrix calculating unit.

5. The adaptive array antenna device according to claim 2, wherein the compensation weight calculating unit comprises:

a weight calculation processing unit for calculating a compensation weight, which compensates for the null shift, from the null shift estimated by the null shift estimation processing unit and the correlation matrix of the interfering wave calculated by the first correlation matrix calculating unit.