Calibration matrix estimation device, calibration matrix estimation method, and program for calibration matrix estimation method

Abstract

To provide a calibration matrix estimation device and the like that can more accurately estimate a calibration matrix related to mutual coupling between elements of an array antenna.SOLUTION: A calibration matrix estimation device estimates a calibration matrix that represents inter-element mutual coupling between a plurality of antenna elements 400 of an array antenna 40, and includes a pre-calibration inter-element phase difference calculation unit 330 that calculates pre-calibration inter-element phase differences for each installation angle of the array antenna 40 using an autocovariance matrix of received data based on signals received by the respective antenna element 400, an approximation unit 331 that performs polynomial approximation on the basis of the pre-calibration inter-element phase differences and calculates an approximation result obtained by the approximation, a fixed offset calculation unit 333 that calculates a fixed offset value based on the difference between the approximation result and a theoretical value of the inter-element phase difference, and a calibration matrix estimation operation unit 335 that adds the fixed offset value to the theoretical value and estimates a calibration matrix that serves as a matrix component.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This technology relates to a calibration matrix estimation device, a calibration matrix estimation method, and a program for the calibration matrix estimation method, and in particular to estimation of a calibration matrix used for calibration between antenna elements in a communication device that transmits and receives radio signals using a phased array antenna. [Background technology]

[0002] Communication devices that transmit and receive wireless signals, such as radio waves, may use phased array antennas, which are configured by regularly arranging multiple antenna elements. In principle, antennas such as phased array antennas experience electromagnetic mutual coupling (inter-element mutual coupling) between the antenna elements, which can cause errors in the measurement system. For this reason, a calibration matrix is ​​generally estimated, which represents the amount of inter-element mutual coupling between antenna elements in an array antenna in a matrix for all combinations of antenna elements. Then, when transmitting and receiving wireless signals, the values ​​(data) indicated by the signals are corrected using the calibration matrix, reducing the effects of inter-element mutual coupling and improving the accuracy of signal processing.

[0003] For this reason, a calibration device has been proposed that corrects data related to signals received by an array antenna to be calibrated using a calibration matrix estimated based on known radio signals received by an installed array antenna under test (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-257298 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the calibration device in Patent Document 1 estimates the calibration matrix directly using the received data obtained when the array antenna under test receives radio waves. Therefore, if the characteristics of the array antenna are complex, even if the calibration matrix is ​​estimated using the array antenna under test, it may not be possible to accurately estimate the calibration matrix for the array antenna to be calibrated, and when signal processing is performed, it may not be possible to improve the accuracy of the processing results.

[0006] Therefore, there has been a demand for a calibration matrix estimation device, a calibration matrix estimation method, and a program for the calibration matrix estimation method that can more accurately estimate a calibration matrix related to mutual coupling between elements of an array antenna. [Means for solving the problem]

[0007] The calibration matrix estimation device according to this disclosure is a calibration matrix estimation device that estimates a calibration matrix that represents inter-element mutual coupling between multiple antenna elements of a phased array antenna, and includes a pre-calibration inter-element phase difference calculation unit that calculates the inter-element phase difference before calibration for each installation angle of the phased array antenna as a pre-calibration inter-element phase difference using an autocovariance matrix of received data based on signals received by each antenna element; an approximation unit that performs polynomial approximation based on the pre-calibration inter-element phase difference to calculate an approximation result that approximates the inter-element phase difference; a fixed offset calculation unit that calculates a fixed offset value based on the difference between the approximation result and a theoretical value of the inter-element phase difference; and a calibration matrix estimation operation unit that adds the fixed offset value to the theoretical value to estimate a calibration matrix that serves as a matrix component.

[0008] Furthermore, the calibration matrix estimation method according to this disclosure is a calibration matrix estimation method for estimating a calibration matrix that represents inter-element mutual coupling between multiple antenna elements of a phased array antenna, and includes a pre-calibration inter-element phase difference calculation step that calculates the inter-element phase difference before calibration for each installation angle of the phased array antenna as a pre-calibration inter-element phase difference using an autocovariance matrix of received data based on signals received by each antenna element; an approximation value calculation step that performs polynomial approximation based on the pre-calibration inter-element phase difference to calculate an approximation result that approximates the inter-element phase difference; a fixed offset calculation step that calculates a fixed offset value based on the difference between the approximation result and the theoretical value of the inter-element phase difference; and a calibration matrix estimation calculation step that adds the fixed offset value to the theoretical value to estimate a calibration matrix that serves as a matrix component.

[0009] Furthermore, a program for a calibration matrix estimation method according to this disclosure is a program for a calibration matrix estimation method that estimates a calibration matrix that represents inter-element mutual coupling between multiple antenna elements of a phased array antenna, and causes a computer to execute the following steps: a pre-calibration inter-element phase difference calculation step that calculates the inter-element phase difference before calibration for each installation angle of the phased array antenna as a pre-calibration inter-element phase difference using an autocovariance matrix of received data based on signals received by each antenna element; an approximation value calculation step that performs polynomial approximation based on the pre-calibration inter-element phase difference to calculate an approximation result that approximates the inter-element phase difference; a fixed offset calculation step that calculates a fixed offset value based on the difference between the approximation result and the theoretical value of the inter-element phase difference; and a calibration matrix estimation calculation step that adds the fixed offset value to the theoretical value and estimates a calibration matrix that uses the fixed offset value as a matrix component. [Effects of the Invention]

[0010] According to this disclosure, when estimating a calibration matrix based on inter-element mutual coupling between antenna elements, polynomial approximation is performed on the pre-calibration inter-element phase difference, and the calibration matrix is ​​estimated by calculating fixed offset values ​​based on the approximation result and theoretical values ​​obtained based on the steering vector. Therefore, rather than estimating the calibration matrix directly from actual measurement values ​​obtained from signals, by estimating the calibration matrix calculated as fixed offset values ​​and applied to the theoretical values, it is possible to estimate a calibration matrix that cannot be estimated using only actual measurement values. Therefore, a more accurate calibration matrix can be estimated. Then, by using the estimated calibration matrix, it is possible to further improve the accuracy of signal processing. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a configuration of a calibration system including a communication device according to a first embodiment. [Figure 2] 2 is a diagram showing a configuration in which a digital section 30 according to the first embodiment is divided into processing functions. FIG. [Figure 3] FIG. 3 is a diagram showing a functional configuration of a calibration matrix estimation unit 324 according to the first embodiment. [Figure 4] FIG. 3 is a diagram illustrating a procedure for calibrating the communication device 13 in the first embodiment. [Figure 5] 4 is a diagram illustrating a procedure for initializing an RF circuit in the calibration system according to the first embodiment. FIG. [Figure 6] FIG. 3 is a diagram illustrating a procedure for measuring calibration data in the first embodiment. [Figure 7] FIG. 3 is a diagram illustrating a procedure for calibration matrix estimation processing according to the first embodiment. [Figure 8] FIG. 4 is a diagram showing an example of pre-calibration inter-element phase differences according to the first embodiment. [Figure 9] FIG. 4 is a diagram showing an example of an approximate value of a pre-calibration inter-element phase difference according to the first embodiment. [Figure 10] FIG. 10 is a diagram showing an example when a fixed offset value according to the first embodiment is applied. [Figure 11]FIG. 10 is a diagram showing the relationship between the installation angle and the RMSE and switching decision before and after calibration. [Figure 12] 10 is a diagram showing a comparison between a calibration matrix estimated by performing a calibration matrix estimation process in the calibration system according to the first embodiment and a calibration matrix estimated by directly using actual measurement values. FIG. [Figure 13] 5A and 5B are diagrams showing an example of a comparison result of antenna patterns before and after calibration in the calibration system according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] A calibration matrix estimation device according to an embodiment will be described below with reference to the drawings. In the drawings, components with the same reference numerals are identical or equivalent, and this applies throughout the entire description of the embodiments described below. The size relationships between components in the drawings may differ from those in reality. The configurations of components shown throughout the specification are merely illustrative and are not limited to the configurations described in the specification. In particular, the combinations of components are not limited to the combinations in each embodiment, and components described in other embodiments may be applied to other embodiments. Furthermore, when multiple similar devices are distinguished by subscripts, the subscripts may be omitted if there is no need to distinguish or identify them.

[0013] Embodiment 1 FIG. 1 is a diagram illustrating the configuration of a calibration system including a communication device according to a first embodiment. In the first embodiment, a case will be described in which a calibration matrix for array antenna 40 in communication device 13 to be calibrated is estimated. Here, in the first embodiment, as will be described later, digital section 30 in communication device 13 functions as a calibration matrix estimation device. In FIG. 1, the calibration system according to the first embodiment has installation angle adjustment jig 11, measuring device 12, and communication device 13. Here, as shown in FIG. 1, communication device 13, installation angle adjustment jig 11, and reference antenna 200 of measuring device 12, which will be described later, are installed in anechoic chamber 10.

[0014] The communication device 13 to be calibrated is a device that transmits, receives, and processes radio waves. Here, the radio waves transmitted and received by the communication device 13 are assumed to be radio waves and signals. The communication device 13 has a digital section 30, an analog section 50, and an array antenna 40.

[0015] The array antenna 40 emits radio waves based on a transmission signal into the air and receives radio waves from the air. The array antenna 40 is a phased array antenna configured by arranging a plurality of antenna elements 400. The array antenna 40 in the first embodiment has 28 elements, antenna elements 400-01 to 400-28. Although not shown in FIG. 1, the antenna elements 400-01 to 400-28 are arranged in a 4×7 array triangle. The array antenna 40 is adjusted by signal processing in the digital unit 30 so that the outputs related to signal transmission and reception form a beam pattern that directs a main lobe in a specific direction. Each antenna element 400 is connected to an analog unit 50 (analog unit 50-01 to analog unit 50-28).

[0016] Each analog section 50 controls the amplification and modulation of signals transmitted and received via the corresponding antenna element 400. Each analog section 50 includes a transmit / receive switching section 500, a transmitting RF circuit 501, and a receiving RF circuit 502.

[0017] Each transmit / receive switching unit 500 (transmit / receive switching unit 500-01 to transmit / receive switching unit 500-28) switches between transmission and reception. When transmitting a signal via the corresponding antenna element 400, the transmit / receive switching unit 500 electrically connects the antenna element 400 to the transmitting RF circuit 501 and electrically disconnects the antenna element 400 from the receiving RF circuit 502. When transmitting a signal related to a radio wave received by the antenna element 400 to the receiving RF circuit 502, the transmit / receive switching unit 500 electrically connects the antenna element 400 to the receiving RF circuit 502 and electrically disconnects the antenna element 400 from the transmitting RF circuit 501.

[0018] Each transmitting RF circuit 501 (transmitting RF circuit 501-01 to transmitting RF circuit 501-28) is connected to the digital unit 30. The transmitting RF circuit 501 modulates a transmission signal sent from the digital unit 30 into a signal related to, for example, a 5.7 GHz band wireless LAN and sends the modulated signal to the antenna element 400. A radio wave including the modulated signal is emitted into the air from the antenna element 400. Each receiving RF circuit 502 (receiving RF circuit 502-01 to receiving RF circuit 502-28) is also connected to the digital unit 30. The receiving RF circuit 502 demodulates, for example, a 5.7 GHz band wireless LAN signal based on the radio wave received from the antenna element 400. The receiving RF circuit 502 transfers the demodulated signal to the digital unit 30 as a received signal.

[0019] The digital unit 30 processes signals transmitted and received by the communication device 13 and stores data related to the signals. The digital unit 30 in the first embodiment has, as hardware devices, a field-programmable gate array (FPGA) 300, a central processing unit (CPU) 301, and a memory 302. The FPGA 300, the CPU 301, and the memory 302 are connected to each other. The FPGA 300 is also connected to the transmitting RF circuits 501 and the receiving RF circuits 502 of the analog unit 50. The FPGA 300 and the CPU 301 control the analog unit 50 and perform signal processing. In the first embodiment, the FPGA 300 and the CPU 301 particularly perform processing related to calibration. The memory 302, which serves as a storage device, stores various data used by the FPGA 300 and the CPU 301 when performing signal processing, etc. The memory 302 also stores, for example, data related to a program indicating the procedure of processing performed by each unit that realizes the functions of the digital unit 30, which will be described later. The FPGA 300 and the CPU 301 then execute the programs to realize the processing steps of each unit.

[0020] FIG. 2 is a diagram showing a configuration in which digital section 30 according to the first embodiment is divided into processing functions. In digital section 30 according to the first embodiment, FPGA 300, CPU 301, and memory 302 described above cooperate to perform the processing of each section, thereby realizing a function related to calibration matrix estimation. Therefore, digital section 30 according to the first embodiment serves as a calibration matrix estimation device that executes a calibration matrix estimation method. Here, FPGA 300, CPU 301, and memory 302 perform the processing to realize the function of each section, but this is not limited to this, and one or more functions may be realized by independent hardware devices. Hereinafter, when the term "signal" is used, it may include values ​​or data indicated by various signals.

[0021] When the communication device 13 transmits radio waves as signals via the array antenna 40, the transmission processing unit 312 generates transmission signals that form a beam pattern and transfers the generated signals to the transmission array calibration unit 311. The transmission array calibration unit 311 performs correction by multiplying the transmission signals corresponding to each of the 28 antenna elements 400 by a calibration matrix corresponding to the main lobe direction stored in a calibration matrix storage unit 326 (described later), which is to be described later, and transfers the result to the transmission RF calibration unit 310. Here, the transmission array calibration unit 311 switches whether or not to perform correction of the transmission signals based on the calibration matrix according to the installation angle of the array antenna 40, based on a switching threshold. The switching threshold will be described later. The transmission RF calibration unit 310 multiplies the transmission signals corresponding to each of the 28 antenna elements 400 by a transmission RF adjustment value that makes the phase difference between the transmission RF circuits 501 of each analog unit 50 zero, and transfers the result to each transmission RF circuit 501.

[0022] Meanwhile, the receiver RF calibration unit 320 multiplies the pre-calibration received signals related to the received signals received by each of the 28 antenna elements 400 sent from the receiver RF circuits 502 of each analog unit 50 by a receiver RF adjustment value that makes the phase difference between the receiver RF circuits 502 of each analog unit 50 zero. The receiver RF calibration unit 320 then transfers the pre-calibration received signals multiplied by the receiver RF adjustment value to the receiver array calibration unit 321 and the receiver processing unit 322.

[0023] The receiving array calibration unit 321 performs correction by multiplying the pre-calibration received signals corresponding to each of the 28 antenna elements 400 by a calibration matrix corresponding to the main lobe direction stored in a calibration matrix storage unit 326 (described later), and transfers the calibrated received signals to the receiving processing unit 322. Here, the receiving array calibration unit 321 switches whether or not to correct the received signals based on the calibration matrix according to the installation angle of the array antenna 40, based on a switching threshold. The receiving processing unit 322 multiplies data based on the pre-calibration and post-calibration received signals corresponding to each of the 28 antenna elements 400 by weights that form a beam pattern, and calculates received signals to which the beam pattern has been applied. The receiving processing unit 322 stores a value based on the calculated covariance matrix of the received signals in the received data storage unit 323 as received data.

[0024] The received data storage unit 323 stores received data such as the pre-calibration inter-element phase difference and the post-calibration inter-element phase difference obtained by calculation by the reception processing unit 322. When storing the received data, the received data storage unit 323 stores the received data in association with installation angle data indicating the installation angle set by the installation angle adjustment jig 11 with respect to the array antenna 40. The installation angle and pre-calibration inter-element phase difference data stored by the received data storage unit 323 are used by the calibration matrix estimation unit 324 when performing calibration matrix estimation processing.

[0025] 3 is a diagram showing a functional configuration of calibration matrix estimation unit 324 according to the first embodiment. Calibration matrix estimation unit 324 according to the first embodiment performs calibration matrix estimation processing to estimate a calibration matrix related to the calibration of inter-element mutual coupling between antenna elements 400 of array antenna 40. Calibration matrix estimation unit 324 includes pre-calibration inter-element phase difference calculation unit 330, approximation unit 331, steering vector reference unit 332, fixed offset calculation unit 333, theoretical inter-element phase difference calculation unit 334, calibration matrix estimation operation unit 335, and post-calibration inter-element phase difference calculation unit 336. Here, one or more functions of calibration matrix estimation unit 324 may be implemented by independent hardware devices.

[0026] The pre-calibration inter-element phase difference calculation unit 330 performs a pre-calibration inter-element phase difference calculation step using the pre-calibration reception data and installation angle data stored in the reception data storage unit 323. The pre-calibration inter-element phase difference calculation step is a step of calculating the relative phase difference for each of the 28 antenna elements 400 with respect to the installation angle as a pre-calibration inter-element phase difference (actually measured value), which is the inter-element phase difference before calibration. The calculated pre-calibration inter-element phase difference data is transferred together with the installation angle data to the approximation unit 331 and the RMSE calculation unit 325. Here, in an array antenna 40 having N elements, the n-th column element of an N×N covariance matrix for received signals received by each antenna element 400 has the characteristic of indicating the relative phase with respect to antenna element 400-n. For example, in the case of an array antenna 40 having 28 antenna elements 400, the first column element of a 28×28 covariance matrix for received signals received by each antenna element 400 indicates the relative phase with respect to antenna element 400-1. Therefore, the elements in the first column of the stored covariance matrix are the relative phase differences between each antenna element 400 and the antenna element 400-01 as a reference.

[0027] The approximation unit 331 performs an approximation value calculation step of performing polynomial approximation processing using the data of the pre-calibration inter-element phase difference calculated by the pre-calibration inter-element phase difference calculation unit 330 and the installation angle data, and transferring the approximation result data to the fixed offset calculation unit 333. Here, the method of performing polynomial approximation includes, for example, a method of performing fifth-order polynomial approximation by a commonly used method using Vandermonde's determinant.

[0028] Steering vector reference unit 332 stores as data the theoretical values ​​of the steering vectors for each installation angle calculated based on the geometric arrangement of array antenna 40. Then, steering vector reference unit 332 transfers the corresponding steering vector to theoretical inter-element phase difference calculation unit 334 and calibration matrix estimation operation unit 335 based on the installation angle data acquired from received data storage unit 323. Theoretical inter-element phase difference calculation unit 334 performs a theoretical inter-element phase difference calculation step, which uses the theoretical values ​​of inter-element phase differences based on the steering vector and the installation angle data to calculate the theoretical values ​​of relative phase differences for each of the 28 antenna elements 400 with respect to the installation angle. Theoretical inter-element phase difference calculation unit 334 transfers data related to the calculated theoretical values ​​of inter-element phase differences to fixed offset calculation unit 333 and RMSE calculation unit 325.

[0029] The fixed offset calculation unit 333 performs a fixed offset calculation step of calculating a fixed offset value based on the following equation (1) using the approximation result of the inter-element phase difference and the theoretical value data. In equation (1), Δf represents the fixed offset value. Furthermore, M represents the number of measurements related to the measurement of the calibration data. Furthermore, x m represents the mth installation angle. And f(x m ) and p(x m ) are the installation angles x m The fixed offset calculation unit 333 transfers data of the fixed offset value obtained by calculating the average value of the difference between the approximation result by polynomial approximation and the theoretical value to the calibration matrix estimation operation unit 335.

[0030]

number

[0031] Calibration matrix estimation unit 335 performs a calibration matrix estimation calculation step of estimating a calibration matrix using data on the theoretical inter-element phase difference and the fixed offset value. Calibration matrix estimation unit 335 transfers the estimated calibration matrix data to calibration matrix storage unit 326 and calibrated inter-element phase difference calculation unit 336. Here, the calibration matrix, as shown in the following equation (2), represents errors due to inter-element coupling in an N-element array antenna using an N × N complex matrix. The calibration matrix is ​​estimated, for example, based on the least squares method described in "Yamada Hiroyoshi, 'Array Calibration Method for High-Resolution Direction-of-Arrival Estimation,' Institute of Electronics, Information and Communication Engineers Transactions B2009, Vol. J92-B No. 9, pp. 1308-1321." In equation (2), C represents the calibration matrix. Furthermore, N represents the number of antenna elements 400 in array antenna 40.

[0032]

number

[0033] The post-calibration inter-element phase difference calculation unit 336 performs a post-calibration inter-element phase difference calculation step using the pre-calibration inter-element phase difference data and corresponding installation angle data stored in the received data storage unit 323, and the calibration matrix data estimated by the calibration matrix estimation operation unit 335. The post-calibration inter-element phase difference calculation unit 336 calculates the post-calibration relative phase difference for each of the 28 antenna elements 400 with respect to the installation angle as the post-calibration inter-element phase difference (calibration value), which is the inter-element phase difference after calibration. The calculated post-calibration inter-element phase difference data is transferred to the RMSE calculation unit 325 together with the installation angle data.

[0034] 2 performs an RMSE calculation step based on the following equation (3) using data on the inter-element phase differences before and after calibration and the theoretical values ​​from the calibration matrix estimation unit 324. The RMSE calculation step is a step of calculating the error between the inter-element phase differences of each antenna element 400 and the theoretical value as RMSE for each installation angle. Then, based on the calculation results, the RMSE calculation unit 325 determines whether or not there is an improvement effect due to the calibration matrix for each installation angle, and stores the data of the determination results in the calibration matrix storage unit 326. Here, RMSE (Root Mean Squared Error) is a value that indicates how much the estimated value deviates from the theoretical value, and a smaller value indicates a smaller error. In equation (3), RMSE(x m ) is the phase difference between elements and the installation angle x m represents the RMSE with the theoretical value of all elements in the array antenna 40. N represents the number of antenna elements 400 in the array antenna 40. x m represents the mth installation angle. And f(x m ) is the installation angle x m represents the theoretical value at g(x m ) is the installation angle x m The values ​​of the comparison objects (inter-element phase difference before calibration, inter-element phase difference after calibration) are shown.

[0035]

number

[0036] Calibration matrix storage unit 326 stores the calibration matrix from calibration matrix estimator 324 and the data of the determination results for each installation angle from RMSE calculator 325. When communication device 13 performs communication, transmitting array calibration unit 311 and receiving array calibration unit 321 use the calibration matrix and installation angle data from calibration matrix storage unit 326 to perform correction processing in which signals are multiplied by the calibration matrix when the installation angle is such that an improvement in processing accuracy can be expected. Control unit 327 performs processing related to control of communication device 13. In addition, control unit 327 here, for example, sends adjustment instructions to installation angle adjustment jig 11 (described later) to adjust the installation angle of array antenna 40, etc.

[0037] 1 and 2 includes a reference antenna 200, a directional coupler 201, a calibration signal generator 202, and a calibration signal receiver 203. Reference antenna 200 is connected to calibration signal generator 202 and calibration signal receiver 203 via directional coupler 201 via a coaxial cable. Reference antenna 200 is installed 5 m away from array antenna 40 of communication device 13 in anechoic chamber 10. Calibration signal generator 202 generates a continuous wave signal in the 5.7 GHz band. Reference antenna 200 emits a radio wave signal containing calibration data generated by calibration signal generator 202 into the air. Hereinafter, data used to calibrate communication device 13 may be referred to as calibration data. The radio waves emitted by reference antenna 200 are received by array antenna 40 when performing calibration measurements. Calibration signal receiver 203 observes the 5.7 GHz radio waves received by reference antenna 200 from the air and measures the radio wave intensity. The radio waves received by the reference antenna 200 from the air include, for example, radio waves emitted by the array antenna 40 when measurements related to calibration are performed.

[0038] 1 and 2 adjusts the installation angle of the array antenna 40 in the communication device 13. The installation angle adjustment jig 11 in the first embodiment can adjust the installation angle of the array antenna 40 relative to the reference antenna 200, for example, within a range of -180 degrees to +180 degrees in azimuth and a range of -180 degrees to +180 degrees in elevation, in 5-degree increments. The installation angle adjustment jig 11 is connected to the communication device 13 and transfers data on the azimuth and elevation angles of the installation angle to the received data storage unit 323 as installation angle data. As described above, the received data storage unit 323 stores the installation angle data together with the received data. Here, the adjustment of the installation angle by the installation angle adjustment jig 11 in the first embodiment will be described assuming that the control unit 327 of the communication device 13 sends a signal to issue an adjustment instruction, but the present invention is not limited to this. For example, the installation angle may be adjusted manually by the installation angle adjustment jig 11.

[0039] 4 is a diagram illustrating a procedure flow for calibration of communication device 13 in the first embodiment. As a preparation for performing calibration-related measurements, communication device 13 performs RF circuit initialization, which sets the phase difference between transmitting RF circuits 501 in each analog unit 50 to zero and sets the phase difference between receiving RF circuits 502 in each analog unit 50 to zero (step S1001). Then, communication device 13 measures the transmitted signal and the received signal and performs calibration data measurement, which acquires calibration data such as received data for calibration that is required when estimating a calibration matrix (step S1002). Then, communication device 13 performs calibration matrix estimation processing, which estimates a calibration matrix based on the calibration data obtained by measurement (step S1003).

[0040] Fig. 5 is a diagram illustrating the procedure for initializing the RF circuit in the calibration system according to embodiment 1. Here, the procedure for initializing the RF circuit in Fig. 4 will be explained using Fig. 5. First, the antenna plane of array antenna 40 in communication device 13 to be calibrated and the antenna plane of reference antenna 200 in measuring instrument 12 are set to face each other using installation angle adjustment jig 11 (step S1101).

[0041] In digital section 30 of communication device 13, the calibration matrices used in transmit array calibration section 311 and receive array calibration section 321 are set to be unit matrices, which are the initial state (step S1102). Furthermore, transmit RF calibration section 310 sets the initial state of the transmit RF adjustment value for each antenna element 400 (step S1103). The transmit RF adjustment value is set to the complex number 1+j0 (real part+j imaginary part) for all antenna elements 400.

[0042] Then, in each analog unit 50, the transmit / receive switching unit 500 performs switching to electrically connect each antenna element 400 to each transmit RF circuit 501 (step S1104). In order to zero the phase difference between the transmit RF circuits 501 in each analog unit 50, the communication device 13 uses a common REV method (revolution of element electric field vector method) to measure adjustment values ​​between the transmit RF circuits 501 (step S1105). Then, based on the measurement, the transmit RF calibration unit 310 of the digital unit 30 sets a transmit RF adjustment value that will zero the phase difference between the transmit RF circuits 501. Here, the REV method is a method of obtaining the amplitude and phase of each antenna element 400 based on a change in the amplitude of the composite electric field at all antenna elements 400 of the array antenna 40 when the phase of each antenna element 400 is changed.

[0043] Next, in digital section 30, reception RF calibration section 320 sets the initial state of the reception RF adjustment value for each antenna element 400. The reception RF adjustment value is set to the complex number 1+j0 for all antenna elements 400 (step S1106). Also, in each analog section 50, transmit / receive switch 500 performs switching to electrically connect each antenna element 400 to each reception RF circuit 502 (step S1107). Then, calibration signal generator 202 in measuring instrument 12 starts transmitting a signal including calibration data (step S1108).

[0044] Array antenna 40 of communication device 13 receives radio waves associated with a signal containing calibration data transmitted from measuring instrument 12. As a result, received data associated with the received signal before and after calibration is transferred to reception processing unit 322. At this time, reception processing unit 322 temporarily stores received data associated with the received signal before calibration that did not pass through receiving array calibration unit 321 (step S1109). Here, reception processing unit 322 temporarily stores, for example, 1,000 consecutive samples of received data. When reception processing unit 322 finishes temporarily storing the data, calibration signal generator 202 of measuring instrument 12 stops transmitting the calibration signal (step S1110).

[0045] The reception processing unit 322 calculates the autocovariance matrix of the pre-calibration reception signal based on the temporarily stored reception data to obtain a 28 × 28 covariance matrix (step S1111). Then, the reception processing unit 322 extracts 28 complex numbers in the first column of the calculated 28 × 28 covariance matrix. These complex numbers each represent the relative phases of the analog units 50-01 to 50-28 with the analog unit 50-01 as the reference. The reception RF calibration unit 320 sets, for the reception RF circuits 502 of each analog unit 50, the first extracted complex number first as a reception RF adjustment value that will reduce the phase difference between the reception RF circuits 502 to zero (step S1112).

[0046] FIG. 6 is a diagram illustrating the flow of procedures related to calibration data measurement in the first embodiment. Here, the procedure for measuring the calibration data in Fig. 4 will be explained using Fig. 6. In the RF circuit initialization process, the reception RF calibration unit 320 sets the adjustment value of each reception RF circuit 502 calculated by the reception processing unit 322 (step S1201). The transmit / receive switching unit 500 of each analog unit 50 performs switching, and electrically connects each antenna element 400 and each reception RF circuit 502 (step S1202).

[0047] The elevation angle of array antenna 40 is set to −90 degrees by installation angle adjusting jig 11 (step S1203). Then, calibration signal generator 202 of measuring instrument 12 starts transmitting a signal including calibration data (step S1204). Furthermore, for example, control unit 327 causes installation angle adjusting jig 11 to set the azimuth angle of array antenna 40 to −90 degrees (step S1205).

[0048] The array antenna 40 of the communication device 13 receives the radio waves transmitted from the measuring instrument 12. The received signal including the calibration data is transmitted from the analog unit 50 to the digital unit 30. The reception RF calibration unit 320 of the digital unit 30 performs calibration for the reception RF circuit 502. The reception processing unit 322 temporarily stores 1000 consecutive samples of data of the pre-calibration received signal that did not pass through the reception array calibration unit 321 (step S1206). The reception processing unit 322 calculates the autocovariance matrix of the pre-calibration received signal based on the temporarily stored data, and calculates a 28 × 28 covariance matrix (step S1207). The reception processing unit 322 transfers the calculated 28 × 28 covariance matrix data to the reception data storage unit 323. The received data storage unit 323 stores the covariance matrix data from the reception processing unit 322 in association with the installation angle data relating to an azimuth angle of -90 degrees and an elevation angle of -90 degrees from the installation angle adjustment jig 11 (step S1208).

[0049] For example, the control unit 327 uses the installation angle adjustment jig 11 to set the array antenna 40 to increase the azimuth angle by 5 degrees (step S1209). Here, the azimuth angle of the array antenna 40 is increased by +5 degrees to −85 degrees. Then, for example, the control unit 327 determines whether the azimuth angle set by the installation angle adjustment jig 11 is greater than +90 degrees (step S1210). If it determines that the azimuth angle is +90 degrees or less, the control unit 327 returns to step S1206 and performs processes such as calculating and storing the covariance matrix for an azimuth angle of −85 degrees and an elevation angle of −90 degrees. Then, the processes of steps S1206 to S1210 are repeated until it is determined that the azimuth angle exceeds +90 degrees.

[0050] In step S1209, the azimuth angle increases by 5 degrees to +95 degrees, and in step S1210, for example, the control unit 327 determines that the azimuth angle is greater than +90 degrees. At this time, for example, the control unit 327 then sets the elevation angle to increase by 5 degrees using the installation angle adjustment jig 11 (step S1211). Here, the elevation angle increases by +5 degrees to -85 degrees. Then, for example, the control unit 327 determines whether the elevation angle set by the installation angle adjustment jig 11 is greater than +90 degrees (step S1212). If it determines that the elevation angle is less than or equal to +90 degrees, the process returns to step S1205, and processes such as calculating and saving the covariance matrix for an azimuth angle of -90 degrees and an elevation angle of -85 degrees are performed. The processes of steps S1205 to S1212 are then repeated until it is determined that the elevation angle exceeds +90 degrees.

[0051] By performing the above processing, covariance matrices are calculated for the azimuth angle of array antenna 40 from -90 degrees to +90 degrees and for the elevation angle of array antenna 40 from -90 degrees to +90 degrees in 5-degree increments, and are stored as received data in received data storage unit 323. When measurements for all angles have been completed, calibration signal generator 202 of measuring instrument 12 stops transmitting the signal related to calibration (step S1213).

[0052] Fig. 7 is a diagram illustrating the flow of procedures related to the calibration matrix estimation process in Embodiment 1. Here, the procedures of the calibration matrix estimation process in Fig. 4 will be explained using Fig. 7. Pre-calibration inter-element phase difference calculation section 330 calculates the relative phase differences of antenna elements 400-01 to 400-28 with respect to each antenna element 400, using the installation angles corresponding to the covariance matrices stored in received data storage section 323 (step S1301).

[0053] Fig. 8 is a diagram showing an example of pre-calibration inter-element phase differences according to the first embodiment. Fig. 8 shows an example for antenna element 400-13. Pre-calibration inter-element phase difference calculation section 330 extracts the components of the first column of the covariance matrix for the installation angle. The result expressed as a relative phase difference for the installation angle is the pre-calibration inter-element phase difference. The pre-calibration inter-element phase difference is an actually measured value.

[0054] Fig. 9 is a diagram showing an example of an approximate value of the pre-calibration inter-element phase difference according to embodiment 1. Fig. 9 shows an example for antenna element 400-13. Next, approximation unit 331 performs polynomial approximation on the pre-calibration inter-element phase difference in order to reduce the amount of sudden fluctuation due to the pre-calibration inter-element phase difference (step S1302).

[0055] The fixed offset calculation unit 333 calculates a fixed offset value by performing calculation based on the difference between the approximate value of the pre-calibration inter-element phase difference and the theoretical value of the inter-element phase difference due to the steering vector (step S1303).

[0056] Fig. 10 is a diagram showing an example when a fixed offset value according to Embodiment 1 is applied. Fig. 10 shows an example for antenna element 400-13. Calibration matrix estimation operation section 335 adds the fixed offset value calculated by fixed offset calculation section 333 to the theoretical value based on the steering vector, and estimates a calibration matrix using the covariance matrix of the complex number related to the addition (step S1304).

[0057] Then, RMSE calculation unit 325 calculates the RMSE between the theoretical value of the inter-element phase difference based on the steering vector and the pre-calibration inter-element phase difference as the pre-calibration RMSE (step S1305). Furthermore, RMSE calculation unit 325 calculates the RMSE between the theoretical value of the inter-element phase difference and the post-calibration inter-element phase difference as the post-calibration RMSE (step S1306). RMSE calculation unit 325 compares the calculated pre-calibration RMSE with the post-calibration RMSE, and sets, for each installation angle, a switching threshold used by transmitting array calibration unit 311 and receiving array calibration unit 321 when determining whether or not to apply a calibration matrix (step S1307).

[0058] FIG. 11 is a diagram showing the relationship between the installation angle and the RMSE and switching decision before and after calibration. In FIG. 11, the installation angle is adjusted by the installation angle adjustment jig 11 with the elevation angle fixed at 0 degrees and the azimuth angle adjusted from -90 degrees to +90 degrees. In FIG. 11, when a main lobe is formed at an installation angle within the range indicated by ○, the transmit array calibrator 311 and the receive array calibrator 321 perform correction using a calibration matrix based on a switching threshold when the communication device 13 performs communication. On the other hand, in FIG. 11, when a main lobe is formed at an installation angle within the range indicated by ×, the transmit array calibrator 311 and the receive array calibrator 321 do not perform correction using a calibration matrix based on a switching threshold. In this way, the communication device 13 corrects signals related to transmission and reception based on the estimated calibration matrix, and performs signal processing on the transmission signal from the array antenna 40 and the reception signal related to reception.

[0059] As described above, when communication device 13 in the calibration system according to the first embodiment estimates a calibration matrix based on inter-element mutual coupling between antenna elements 400, approximation unit 331 of digital unit 30, which serves as a calibration matrix estimation device, performs polynomial approximation on the pre-calibration inter-element phase differences. Then, fixed offset calculation unit 333 calculates fixed offset values ​​based on the approximation result and theoretical values ​​obtained based on the steering vectors, and calibration matrix estimation operation unit 335 estimates a calibration matrix using the fixed offset values ​​and the theoretical values. Therefore, rather than estimating a calibration matrix directly from actual measurement values ​​obtained from signals, estimating a calibration matrix calculated as fixed offset values ​​and assigned to the theoretical values ​​makes it possible to estimate a calibration matrix that cannot be fully estimated using only the pre-calibration inter-element phase differences, which are actual measurement values. Therefore, a more accurate calibration matrix can be estimated than a calibration matrix estimated directly using actual measurement data of the signals used to estimate the calibration matrix. Furthermore, using the estimated calibration matrix further improves the accuracy of signal processing in communication device 13.

[0060] Furthermore, post-calibration inter-element phase difference calculation unit 336 of digital unit 30, which serves as a calibration matrix estimation device, calculates the post-calibration inter-element phase difference. RMSE calculation unit 325 then compares the pre-calibration inter-element phase difference with a theoretical value, and further compares the post-calibration inter-element phase difference with the theoretical value to set a switching threshold for transmit array calibration unit 311 and receive array calibration unit 321. This makes it possible to set whether or not to perform processing that applies a calibration matrix depending on the set angle of signal processing in communication device 13, thereby further improving accuracy.

[0061] The calibration matrix represents inter-element coupling in each antenna element 400 of the array antenna 40. For this reason, the calibration matrix has the characteristic that the component due to the influence of the element itself is dominant over the components due to the influence of other antenna elements 400. Therefore, when the square of each component of the calibration matrix is ​​calculated, in an appropriately estimated calibration matrix, the diagonal components are large and the other components are small.

[0062] 12 is a diagram showing a comparison between a calibration matrix estimated by performing a calibration matrix estimation process in the calibration system according to Embodiment 1 and a calibration matrix estimated directly using actual measurement values. In Fig. 12, the squared values ​​of each component of the calibration matrix are expressed on a logarithmic scale, with the larger the component, the darker the black color.

[0063] For communication device 13, the calibration matrix estimated using actual measurement values ​​does not have a dominant diagonal component, as shown in Fig. 12(b), and the calibration matrix is ​​not fully estimated. In contrast, the calibration matrix estimated by calculating fixed offset values ​​through the calibration matrix estimation process of embodiment 1 has a dominant diagonal component, as shown in Fig. 12(a). Therefore, the calibration matrix is ​​properly estimated.

[0064] Fig. 13 is a diagram showing an example of a comparison result of antenna patterns before and after calibration in the calibration system according to the first embodiment. Fig. 13 shows the antenna pattern when the main lobe of the array antenna 40 is directed in the direction of an azimuth of +30 degrees and an elevation angle of 0 degrees. Fig. 13(a) shows the antenna pattern before calibration, and Fig. 13(b) shows the antenna pattern after calibration. As shown in Fig. 13, it can be seen that the antenna pattern after calibration is closer to the theoretical value than the antenna pattern before calibration.

[0065] Embodiment 2 In the first embodiment described above, the digital section 30 is configured as hardware including the FPGA 300, the CPU 301, and the memory 302, but this is not limiting. For example, a hardware configuration of the FPGA 300 alone may also be applied as long as it can perform processing that realizes the functions of the digital section 30 in the first embodiment.

[0066] Furthermore, in the configuration system of the first embodiment, digital unit 30 of communication device 13 functions as a calibration matrix estimation device and performs calibration matrix estimation processing and the like. Here, it is not necessary to estimate the calibration matrix in real time while performing signal processing related to calibration. Therefore, an external computer other than communication device 13 to be calibrated may perform calibration matrix estimation processing and the like as a calibration matrix estimation device. Furthermore, the processing executed by calibration matrix estimation unit 324 may be performed by an external computer and the like. [Explanation of symbols]

[0067] 10 Radio Wave Anechoic Chamber 11 Installation angle adjustment jig 12 Measuring instruments 13. Communications equipment 30 Digital Department 40 Array Antenna 50, 50-01 to 50-28 Analog section 200 Reference Antenna 201 Directional coupler 202 Calibration Signal Generator 203 Calibration signal receiver 300 FPGA 301 CPU 302 memory 310 Transmission RF calibration section 311 Transmitting array calibration section 312 Transmission processing unit 320 Receiver RF Calibration Unit 321 Receiving Array Calibration Unit 322 Receiving processing unit 323 Received Data Storage Unit 324 Calibration matrix estimator 325 RMSE calculation section 326 Calibration matrix storage section 327 Control Unit 330 Pre-calibration inter-element phase difference calculation unit 331 Approximation part 332 Steering Vector Reference 333 Fixed Offset Calculation Unit 334 Theoretical Inter-element Phase Difference Calculation Unit 335 Calibration matrix estimation calculation unit 336 Calibrated inter-element phase difference calculation unit 400, 400-01 to 400-28 antenna elements 500, 500-01 to 500-28 Transmission / reception switching unit 501, 501-01 to 501-28 Transmit RF circuit 502, 502-01 to 502-28 Receiver RF circuit

Claims

1. 1. A calibration matrix estimation device that estimates a calibration matrix representing mutual coupling between a plurality of antenna elements of a phased array antenna, comprising: a pre-calibration inter-element phase difference calculation unit that calculates, as a pre-calibration inter-element phase difference, an inter-element phase difference before calibration for each installation angle of the phased array antenna using an autocovariance matrix of received data based on signals received by each of the antenna elements; an approximation unit that performs polynomial approximation based on the pre-calibration inter-element phase difference and calculates an approximation result that approximates the inter-element phase difference; a fixed offset calculation unit that calculates a fixed offset value based on a difference between the approximation result and the theoretical value of the inter-element phase difference; a calibration matrix estimation calculation unit that estimates the calibration matrix by adding the fixed offset value to the theoretical value and using the result as a matrix element; A calibration matrix estimator comprising:

2. a post-calibration inter-element phase difference calculation unit that calculates the post-calibration inter-element phase difference based on the calibration matrix; an RMSE calculation unit that calculates an RMSE value between the pre-calibration inter-element phase difference and the theoretical value and an RMSE value between the post-calibration inter-element phase difference and the theoretical value for each installation angle, and determines whether or not the calibration matrix is ​​applied for each installation angle based on a result of the calculation; The calibration matrix estimation device of claim 1 , comprising:

3. 3. The calibration matrix estimation device according to claim 2, wherein the RMSE calculation unit determines to apply the calibration matrix when a value of RMSE between the post-calibration inter-element phase difference and the theoretical value is smaller than a value of RMSE between the pre-calibration inter-element phase difference and the theoretical value.

4. 4. The calibration matrix estimation device according to claim 1, further comprising a theoretical inter-element phase difference calculation unit that calculates, as the theoretical value, a relative phase difference in each of the antenna elements with respect to the installation angle, using data on the inter-element phase difference and the installation angle based on a steering vector.

5. 1. A calibration matrix estimation method for estimating a calibration matrix representing inter-element mutual coupling between a plurality of antenna elements of a phased array antenna, comprising: a pre-calibration inter-element phase difference calculation step of calculating, as a pre-calibration inter-element phase difference, an inter-element phase difference before calibration for each installation angle of the phased array antenna using an autocovariance matrix of received data based on signals received by each of the antenna elements; an approximation value calculation step of performing polynomial approximation based on the pre-calibration inter-element phase difference and calculating an approximation result obtained by approximating the inter-element phase difference; a fixed offset calculation step of calculating a fixed offset value based on a difference between the approximation result and the theoretical value of the inter-element phase difference; a calibration matrix estimation calculation step of adding the fixed offset value to the theoretical value and estimating the calibration matrix having the fixed offset value as a matrix element; A calibration matrix estimation method having:

6. 1. A program for a calibration matrix estimation method for estimating a calibration matrix representing mutual coupling between a plurality of antenna elements of a phased array antenna, comprising: a pre-calibration inter-element phase difference calculation step of calculating, as a pre-calibration inter-element phase difference, an inter-element phase difference before calibration for each installation angle of the phased array antenna using an autocovariance matrix of received data based on signals received by each of the antenna elements; an approximation value calculation step of performing polynomial approximation based on the pre-calibration inter-element phase difference and calculating an approximation result obtained by approximating the inter-element phase difference; a fixed offset calculation step of calculating a fixed offset value based on a difference between the approximation result and the theoretical value of the inter-element phase difference; a calibration matrix estimation calculation step of adding the fixed offset value to the theoretical value and estimating the calibration matrix having the fixed offset value as a matrix element; A program for a calibration matrix estimation method that causes a computer to execute the above.

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