Antenna calibration system, antenna calibration method, and antenna calibration program

Abstract

To provide an antenna calibration system for calibrating the amplitude and phase differences between antenna elements constituting an array antenna capable of executing antenna calibration without repeating signal transmission and reception between the array antenna and a calibration station.SOLUTION: An antenna calibration system 1 calibrates the difference in transmission characteristics between antenna element systems of an array antenna that has a DBF function based on a calibration signal. The system includes an estimation value calculation unit 9 and a calibration value calculation unit 10. The estimation value calculation unit 9 calculates an estimated difference in transmission characteristics and an estimated signal arrival direction by solving an optimization problem based on an evaluation function related to the design value of the radiation pattern, the calibration signal, the estimated pass characteristic difference, and the estimated signal arrival direction. The calibration value calculation unit 10 calculates the calibration value based on either the calculated estimated transmission characteristic difference, the calculated estimated signal arrival direction, and the radiation pattern design value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a system for calibrating an amplitude difference and a phase difference generated between antenna elements constituting an array antenna.

Background Art

[0002] Array antennas composed of a plurality of antenna elements are widely used in, for example, radar and communication systems. In recent years, an array antenna having a function called DBF (Digital Beam Forming) (hereinafter referred to as a DBF antenna), which realizes advanced beam forming and signal multiplexing by converting a high-frequency signal received by each antenna element into a digital signal on a per-antenna-element basis (in the case of transmission, converting from a digital signal to a high-frequency signal to be transmitted), has become widespread. DBF antennas have also begun to be used for antennas mounted on artificial satellites.

[0003] In a receiving DBF antenna, generally, a high-frequency signal received by each antenna element is amplified by a low-noise amplifier, the amplified signal is frequency-converted to an intermediate frequency band by a frequency converter, and the frequency-converted signal is converted into a digital signal by an analog-to-digital converter (hereinafter referred to as an AD converter). The digital signal is input to a DBF signal processing unit that performs predetermined beam forming and the like by digital signal processing. As a specific example, the DBF signal processing unit multiplies the signal of each antenna element by an excitation coefficient necessary for forming a desired beam, and then synthesizes all the signals and outputs them as an output signal. Here, in order to realize desired beamforming in the DBF signal processing unit, it is necessary that the amplitude difference and phase difference between antenna elements in the high-frequency band of the signals received by each antenna element are also preserved in the digital signal, that is, in the baseband band. Generally, there are individual differences in each antenna element, the low-noise amplifier, frequency converter, and AD converter connected to each antenna element, and the input / output lines connecting them (hereinafter, these are collectively referred to as the antenna element system). Therefore, each antenna element system has different electrical characteristics (pass characteristics). Due to the difference in the electrical characteristics of each component connected to each antenna element, an error occurs between each antenna element system. Due to this error, the amplitude difference and phase difference between antenna elements in the baseband band become different from those in the high-frequency band, and as a result, it becomes impossible to realize the desired beamforming.

[0004] On the other hand, in order to reduce the influence of errors (amplitude difference and phase difference) between antenna element systems, there is a method of calibration by multiplying a predetermined calibration value to the received digital signal of each antenna element. As a specific example, in the DBF antenna mounted on an artificial satellite described in Patent Document 1, from the received signals of each antenna element with respect to the calibration high-frequency signal transmitted from a ground communication device (hereinafter, the ground communication device used for calibration is referred to as a calibration station), in the digital signal region, the autocorrelation value and cross-correlation value (hereinafter, the autocorrelation value and cross-correlation value are collectively referred to as the correlation value) are calculated, and the information regarding the calculated correlation value is transmitted as a telemetry signal toward another ground communication device (hereinafter, referred to as a ground station). In the calibration system connected to the ground station, the calibration value is determined based on the information regarding the received correlation value, the amplitude and phase values of the radiation pattern design value (hereinafter, referred to as the radiation pattern design value) of each antenna element of the DBF antenna, and the direction of the calibration station as seen from the DBF antenna. As the direction of the calibration station as seen from the DBF antenna, usually, the design direction when there is no attitude error in the artificial satellite is used. However, when there is an attitude error in the artificial satellite, since the design direction and the actual direction of the calibration station are different from each other, an error occurs in the calibration value.

[0005] Therefore, in Patent Document 1, an appropriate sampling grid is defined centered on the direction of the calibration station when there is no attitude error, one intersection of the defined sampling grid is selected, and the calibration value is calculated assuming that the calibration station is at the selected intersection. Further, the calculated calibration value is reflected in the DBF antenna, and again, a calibration high-frequency signal is transmitted from the calibration station, and the reception intensity in the DBF antenna with respect to the transmitted signal is measured. At this time, the measured reception intensity can be calculated and predicted using the radiation pattern design value, the direction of the calibration station as seen from the DBF antenna, and the excitation coefficient. When the direction of the actual calibration station coincides with the selected intersection, the measured value and the calculated value of the reception intensity are equal. By utilizing this property, in Patent Document 1, the difference between the measured value and the calculated value of the reception intensity is evaluated, and the selection of the intersection, the calculation of the calibration value, the reflection of the calculated calibration value in the DBF antenna, the measurement of the reception intensity of the high-frequency signal from the calibration station, and the evaluation of the difference between the measured value and the calculated value of the reception intensity are repeated, and the calibration value is determined based on the direction of the calibration station corresponding to the intersection where the above difference is minimized.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the antenna calibration method disclosed in Patent Document 1, even when there is an attitude error in the platform on which the DBF antenna is mounted, antenna calibration can be performed with relatively high accuracy. However, when determining the calibration value, it is necessary to repeatedly perform a procedure consisting of calculating the calibration value, reflecting it on the DBF antenna, and measuring the reception intensity of the high-frequency signal from the calibration station. Depending on the definition of the above sample grid, signal transmission and reception between the DBF antenna and the calibration station will be repeated many times. Therefore, this antenna calibration method has the problem that it takes a long time to determine the calibration value. In particular, when a DBF antenna is mounted on a platform such as a satellite or an aircraft where the attitude error varies over time, if the attitude error varies during the above procedure, the difference between the measured value and the calculated value of the reception intensity becomes minimum at a plurality of intersection points. Therefore, it is not possible to accurately calculate the calibration value, and there is a possibility that a calibration error may occur.

[0008] An object of the present disclosure is to perform antenna calibration without repeating signal transmission and reception between an array antenna and a calibration station in a system for calibrating an amplitude difference and a phase difference generated between antenna elements constituting the array antenna.

Means for Solving the Problems

[0009] The antenna calibration system according to the present disclosure is an antenna calibration system that calibrates the difference in passing characteristics between antenna element systems of an array antenna having a digital beamforming function based on calibration signals transmitted from each of one or more antennas, An estimation value calculation unit calculates a passing characteristic difference estimation value and a signal arrival direction estimation value by solving an optimization problem based on an evaluation function related to a radiation pattern design value, which is a design value of an amplitude and a phase value of a radiation pattern of each antenna element included in the array antenna, a calibration signal received as a reception signal by each antenna element included in the array antenna, a passing characteristic difference estimation value, which is an estimation value corresponding to each antenna element system of the array antenna and is an estimation value of a difference in relative passing characteristics between the antenna element systems of the array antenna, and a signal arrival direction estimation value, which is an estimation value of a direction of arrival of the reception signal as viewed from the array antenna. A calibration value calculation unit calculates a calibration value used to correct a difference in relative passing characteristics between the antenna element systems of the array antenna based on any one of the calculated passing characteristic difference estimation value, the calculated signal arrival direction estimation value, and the radiation pattern design value.

Advantages of the Invention

[0010] According to the present disclosure, the estimation value calculation unit calculates a passing characteristic difference estimation value and a signal arrival direction estimation value by solving an optimization problem based on an evaluation function related to a radiation pattern design value of each antenna element included in an array antenna having a digital beamforming function, a reception signal of each antenna element included in the array antenna, a passing characteristic difference estimation value corresponding to each antenna element system of the array antenna, and a signal arrival direction estimation value of a calibration signal. Further, the calibration value calculation unit calculates a calibration value based on any one of the calculated passing characteristic difference estimation value, the calculated signal arrival direction estimation value, and the radiation pattern design value. Therefore, according to the present disclosure, in a system for calibrating an amplitude difference and a phase difference generated between antenna elements constituting an array antenna, antenna calibration can be performed without repeatedly transmitting and receiving signals between the array antenna and a calibration station.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

MODE FOR CARRYING OUT THE INVENTION

[0012] In the description of the embodiments and the drawings, the same elements and corresponding elements are denoted by the same reference numerals. The description of the elements denoted by the same reference numerals may be omitted or simplified as appropriate. The arrows in the figures mainly indicate the flow of data or the flow of processing. Also, "section" may be appropriately read as "circuit", "step", "procedure", "process" or "circuitry".

[0013] Embodiment 1. Hereinafter, this embodiment will be described in detail with reference to the drawings.

[0014] ***Description of the configuration*** FIG. 1 is a block diagram showing a configuration example of the antenna calibration system 1 in Embodiment 1. In FIG. 1, the antenna calibration system 1 includes an array antenna 2 and calibration antennas 3-1 to 3-M (M indicates the number of calibration antennas 3). The antenna calibration system 1 calibrates the difference in the passing characteristics between the antenna element systems of the array antenna 2 based on calibration signals transmitted from each of one or more antennas.

[0015] The array antenna 2 is a DBF (Digital Beam Forming) antenna that receives high-frequency signals and is an antenna device to be calibrated. The DBF antenna has a digital beam forming function. The array antenna 2 may be a primary radiator of a reflector antenna. The array antenna 2 includes antenna elements 4-1 to 4-N (N indicates the number of antenna elements 4), receivers 5-1 to 5-N, a DBF signal processing unit 6, and an output terminal 7. The array antenna 2 also includes an element pattern storage unit 8, an estimated value calculation unit 9, and a calibration value calculation unit 10. The array antenna 2, the element pattern storage unit 8, the estimated value calculation unit 9, and the calibration value calculation unit 10 may be mounted on either one platform or one device. The array antenna 2 may be mounted on an artificial satellite that is a platform.

[0016] Each calibration antenna device 3 is an antenna device that transmits a high-frequency signal for calibration to the array antenna 2. Each of the calibration antenna devices 3-1 to 3-M includes a transmitting antenna 11-1 to 11-M and a transmitter 12-1 to 12-M. Any signal may be adopted as the high-frequency signal as long as it is a signal suitable as a calibration signal.

[0017] Each antenna element 4 is an antenna that receives a high-frequency signal. Each antenna element 4 receives the calibration signal received as a received signal.

[0018] Each receiver 5 is a circuit that amplifies the high-frequency signal received by each antenna element 4, converts the frequency of the amplified signal to an intermediate frequency band, and converts the frequency-converted analog signal to a digital signal. As a specific example, each receiver 5 is composed of a low-noise amplifier, a frequency mixer, an analog-to-digital conversion circuit, and the like. Note that the signal converted by the receiver 5 may also be referred to as a received signal.

[0019] The DBF signal processing unit 6 is a signal processing unit that performs so-called DBF by multiplying each received signal of each antenna element 4 output by each receiver 5 by the calibration value corresponding to each antenna element 4 calculated by the calibration value calculation unit 10 and performing predetermined signal processing on the signal. As a specific example, the DBF signal processing unit 6 is composed of a digital circuit that multiplies each signal by a predetermined excitation coefficient and then adds all the received signals.

[0020] The output terminal 7 is a terminal that outputs the output signal of the DBF signal processing unit 6.

[0021] The element pattern storage unit 8 is a storage unit that stores information indicating a radiation pattern design value, which is a design value of the amplitude and phase value of the radiation pattern of each antenna element 4. As a specific example, the design value consists of at least one of the theoretical value, the calculated value, and the measured value of the radiation pattern. As a specific example, the element pattern storage unit 8 may store the design value in the form of a function representing the amplitude and phase values of the radiation pattern of each antenna element 4 with respect to the azimuth defined by a predetermined coordinate system, or may store the design value as a data set of the amplitude and phase values of the radiation pattern of each antenna element 4 in the sample directions set in a grid pattern on the same coordinate system.

[0022] The estimated value calculation unit 9 executes an evaluation based on a predetermined evaluation function using the reception signals of each antenna element 4 output by each receiver 5 and the radiation pattern design values of each antenna element 4 read from the element pattern storage unit 8, thereby estimating the difference in relative passing characteristics between each antenna element system (hereinafter referred to as the passing characteristic difference estimated value), and the estimated value of the direction of each calibration antenna device 3 as seen from the array antenna 2 (hereinafter referred to as the signal arrival direction estimated value). The passing characteristic difference estimated value is an estimated value corresponding to each antenna element system. The signal arrival direction estimated value is also an estimated value of the arrival direction of the reception signal as seen from the array antenna 2. The estimated value calculation unit 9 calculates the passing characteristic difference estimated value and the signal arrival direction estimated value by solving an optimization problem based on the evaluation function. The evaluation function is a function related to the radiation pattern design value, the reception signal of each antenna element 4, the passing characteristic difference estimated value, and the signal arrival direction estimated value. In the evaluation function, the reception signal of each antenna element 4 may be expressed by the relative value of the reception signals of the other antenna elements 4 when the reception signal of one antenna element 4 is used as a reference.

[0023] The calibration value calculation unit 10 is a calculation unit that calculates a calibration value used to calibrate the difference in relative passing characteristics between the antenna element systems of the array antenna 2. The calibration value is also a value used to calibrate the amplitude difference and the phase difference between the antenna element systems. As a specific example, the calibration value calculation unit 10 may calculate the calibration value based on the passing characteristic difference estimated value calculated by the estimated value calculation unit 9. As another specific example, the calibration value calculation unit 10 may calculate the calibration value based on the reception signal of each antenna element 4 output by each receiver 5, the signal arrival direction estimated value calculated by the estimated value calculation unit 9, and the radiation pattern design value of each antenna element 4 read from the element pattern storage unit 8. When calculating the calibration value according to the former specific example, each of the input / output lines connecting each receiver 5 and the calibration value calculation unit 10, and the input / output lines connecting the element pattern storage unit 8 and the calibration value calculation unit 10 may be omitted from the antenna calibration system 1 shown in FIG. 1.

[0024] Each transmission antenna 11 is an antenna that transmits a calibration signal and radiates the high-frequency calibration signal generated by each transmitter 12 into space. Each transmission antenna 11 may be installed at a position where the radio wave radiated from each transmission antenna 11 can be received by the array antenna 2 and at a position where the radio wave transmitted and received between each transmission antenna 11 and each antenna element 4 can be regarded as a so-called far-field.

[0025] Each transmitter 12 is a signal source that generates, as a calibration high-frequency signal, for example, a continuous wave or various modulated waves as specific examples. Each transmitter 12 is, for example, composed of a circuit combining an oscillator, a synthesizer circuit, a modulation circuit, a frequency mixer, and an amplifier.

[0026] FIG. 2 shows a hardware configuration example of the computer 70 according to the present embodiment. The computer 70 realizes the functions of the element pattern storage unit 8, the estimated value calculation unit 9, and the calibration value calculation unit 10. The antenna calibration system 1 may include a plurality of computers. The computer 70 may be referred to as a calibration value calculation device.

[0027] As shown in this figure, the computer 70 is a computer including hardware such as a processor 71, a memory 72, an auxiliary storage device 73, an input / output IF (Interface) 74, and a communication device 75. These hardware components are appropriately connected via a signal line 79.

[0028] The processor 71 is an IC (Integrated Circuit) that performs arithmetic processing and controls the hardware included in the computer. The processor 71 is, for example, a CPU (Central Processing Unit), a DSP (Digital Signal Processor), or a GPU (Graphics Processing Unit). The computer 70 may include a plurality of processors that replace the processor 71. The plurality of processors share the role of the processor 71.

[0029] The memory 72 is typically a volatile storage device, and as a specific example, it is a RAM (Random Access Memory). The memory 72 is also called the main storage device or the main memory. The data stored in the memory 72 is saved in the auxiliary storage device 73 as needed.

[0030] The auxiliary storage device 73 is typically a non-volatile storage device, and as specific examples, it is a ROM (Read Only Memory), an HDD (Hard Disk Drive), or a flash memory. The data stored in the auxiliary storage device 73 is loaded into the memory 72 as needed. The memory 72 and the auxiliary storage device 73 may be integrally configured.

[0031] The input / output IF 74 is a port to which an input device and an output device are connected. As a specific example, the input / output IF 74 is a USB (Universal Serial Bus) terminal. As specific examples, the input device is a keyboard and a mouse. As a specific example, the output device is a display.

[0032] The communication device 75 is a receiver and a transmitter. As a specific example, the communication device 75 is a communication chip or a NIC (Network Interface Card).

[0033] When the estimated value calculation unit 9 and the calibration value calculation unit 10 communicate with other devices or the like, the input / output IF 74 and the communication device 75 may be appropriately used.

[0034] The auxiliary storage device 73 stores an antenna calibration program. The antenna calibration program is a program that causes a computer to realize the functions of the estimated value calculation unit 9 and the calibration value calculation unit 10. The antenna calibration program is loaded into the memory 72 and executed by the processor 71. The functions of the estimated value calculation unit 9 and the calibration value calculation unit 10 are realized by software.

[0035] Data used when executing the antenna calibration program, data obtained by executing the antenna calibration program, etc. are appropriately stored in the storage device. The estimated value calculation unit 9 and the calibration value calculation unit 10 appropriately use the storage device. The element pattern storage unit 8 is realized by the storage device. The storage device is composed of at least one of, as specific examples, a memory 72, an auxiliary storage device 73, a register in the processor 71, and a cache memory in the processor 71. Note that the term "data" may have the same meaning as the term "information". The storage device may be independent of the computer 70. The functions of the memory 72 and the auxiliary storage device 73 may be realized by other storage devices.

[0036] The antenna calibration program may be recorded on a computer-readable non-volatile recording medium. As specific examples, the non-volatile recording medium is an optical disk or a flash memory. The antenna calibration program may be provided as a program product.

[0037] ***Explanation of Operations*** The operation procedures of each component of the antenna calibration system 1 are collectively referred to as an antenna calibration method. Also, a program that realizes the operations of each component of the antenna calibration system 1 is collectively referred to as an antenna calibration program.

[0038] The operation of the antenna calibration system 1 will be described with reference to FIG. 3. FIG. 3 is a flowchart showing an operation example of the antenna calibration system 1.

[0039] (Step ST1-1) Based on an instruction by an operator of the array antenna 2 or a periodic trigger signal, the calibration process is started.

[0040] (Step ST1-2) A calibration high-frequency signal is sent from each calibration antenna device 3 toward the array antenna 2. Specifically, each transmitter 12 generates a calibration high-frequency signal, and the generated signal is radiated into space from each transmitting antenna 11, whereby the calibration high-frequency signal is transmitted toward the array antenna 2.

[0041] (Step ST1-3) Each antenna element 4 receives the transmitted high-frequency signal. Each receiver 5 amplifies the high-frequency signal received by each antenna element 4, then frequency-converts the amplified signal to an intermediate frequency band, further converts the frequency-converted signal to a digital signal, and acquires the digital signal as a received signal. In order to receive the signals of each calibration antenna device 3 individually, each of the calibration antenna devices 3-1 to 3-M transmits a calibration high-frequency signal sequentially in a time-division manner, and each antenna element 4 receives the transmitted high-frequency signal. That is, steps ST1-2 and ST1-3 are repeatedly performed M times, where M is the number of calibration antenna devices 3.

[0042] Here, it is assumed that each calibration antenna device 3-m (m = 1, 2,..., M) is arranged in the direction of (θ m , φ m ) as viewed from the array antenna 2. The high-frequency signal x nm transmitted by the calibration antenna device 3-m and received by the antenna element 4-n is as shown in [Equation 1]. Here, the calibration high-frequency signal transmitted by each calibration antenna device 3-m is expressed as s m , the propagation characteristic between the transmitting antenna 11-m and the array antenna 2 is expressed as H m , and the electric field value in the direction of (θ, φ) of the antenna element 4-n (n = 1, 2,..., N) is expressed as E n (θ, φ).

[0043]

Equation

[0044] Note that E nLet (θ,φ) be stored in the element pattern storage unit 8 as a radiation pattern design value in the form of a function of (θ,φ). In step ST1-3, the high-frequency signal x nm is amplified by the receiver 5-n, then the amplified signal is frequency-converted to an intermediate frequency band, and further the frequency-converted signal is converted to a digital signal. Here, the received signal of the complex digital signal corresponding to the high-frequency signal x nm is expressed as shown in [Equation 2].

[0045]

Equation

[0046] However, y nm,I represents the in-phase component of y nm , j represents the imaginary unit, and y nm,Q represents the quadrature component of y nm . Also, A n represents the passing characteristics of the receiver 5-n. Usually, the value of A n is different for each receiver 5. In the calibration process, in order to perform correction so that the difference in A n between the receivers 5 is removed, it is necessary to estimate the value of A n from the received signal. Here, H m is an unknown value. Therefore, in order to cancel its influence, the relative value between the antenna elements 4 is considered. Here, the reference antenna element 4 is taken as the antenna element 4-1, and the relative value z n1 (m) of the received signal as shown in [Equation 3] is considered.

[0047]

Equation

[0048] Note that the above is an example, and the reference antenna element 4 does not have to be the antenna element 4-1. When (θ m , φ m ) is a known direction, the radiation pattern design value E n stored in the element pattern storage unit 8From (θ, φ) to E n (θ m , φ m ) / E1(θ m , φ m ) can be calculated. E n (θ m , φ m ) / E1(θ m , φ m ) and the relative value z n1 (m) of the received signal are used to calculate the value of A n / A1 by [Equation 3]. However, here we consider the case where (θ m , φ m ) is an unknown direction. In this case, not only the value of A n / A1 but also (θ m , φ m ) needs to be calculated. Here, the relative value A n / A1 of the passing characteristics of the receiver 5 - n is expressed as shown in [Equation 4].

[0049]

Equation

[0050] Next, consider the relative value z nm of the received signals from the antenna element 4 - 2 to the antenna element 4 - N with respect to the calibration high - frequency signals for each of the calibration antenna devices 3 - 1 to 3 - M in matrix form as shown in [Equation 5].

[0051]

Equation

[0052] However, G n1 (m) = E n (θ m , φ m ) / E1(θ m , φ m ) is. In [Equation 5], the matrix Z is a matrix obtained from the received signals. The matrix K is from k2 to k Nis a diagonal matrix with diagonal components and is an unknown matrix. Matrix G is a matrix obtained from the directions of the respective calibration antenna devices 3-m and the radiation pattern design values. Matrix G is an unknown matrix because the direction (θ m , φ m ) of each calibration antenna device 3-m is unknown. If Equation [5] is solved, k and (θ N , φ m , φ m ) can be calculated from the unknown k2. However, both K and G on the right side of Equation [5] are unknown matrices. Therefore, Equation [5] is an indeterminate equation and cannot be uniquely calculated. Normally, although there are individual differences in the passing characteristics of the receivers 5-n, the receivers 5 are manufactured to have approximately the same magnitude of passing characteristics. Therefore, here it is assumed that the difference in passing characteristics between the receivers 5 is small, and k n is expressed as shown in Equation [6].

[0053]

Equation

[0054] Here, δ n is a complex quantity indicating the relative difference in passing characteristics between the receiver 5-n and the receiver 5-1. Here, it is considered that the difference in passing characteristics is small as described above, that is, δ n is considered to be small. Therefore, in the antenna calibration system 1, as a specific example, instead of solving Equation [5], the problem of minimizing the evaluation function shown in Equation [7] is considered.

[0055]

Equation

[0056] Here, the norm symbol with subscript F indicates the Frobenius norm of a matrix, and c1 is an appropriate positive coefficient. In [Equation 7], the first term on the right side indicates the sum of the magnitudes of the differences in the passing characteristics. The second term on the right side indicates the magnitude of the difference between the matrix Z determined from the received signal and the product KG of the matrices K and G. The matrix K is a matrix obtained from the estimated value of the relative difference in passing characteristics δ n , that is, the passing characteristic difference estimated value. The matrix G is a matrix calculated from the estimated value of the direction (θ m , φ m ) of the calibration antenna device 3-m, that is, the estimated value of the signal arrival direction.

[0057] (Step ST1-4) To numerically solve the problem of minimizing the evaluation function defined by [Equation 7], the estimated value calculation unit 9 first tentatively sets each of the passing characteristic difference estimated value and the signal arrival direction estimated value to appropriate initial values. As a specific example, the estimated value calculation unit 9 sets all the passing characteristic difference estimated values to 0 and sets all the signal arrival direction estimated values to the direction corresponding to the front direction of the array antenna 2.

[0058] (Step ST1-5) The estimated value calculation unit 9 reads out the electric field value of the antenna element 4-n corresponding to the signal arrival direction estimated value set in Step ST1-4 from the radiation pattern design value stored in the element pattern storage unit 8. Specifically, the estimated value calculation unit 9 reads out the radiation pattern design value stored in the element pattern storage unit 8 in the form of a function of (θ, φ), substitutes the signal arrival direction estimated value into the read design value, and calculates the electric field value.

[0059] (Step ST1-6) The estimated value calculation unit 9 uses the passing characteristic difference estimated value set in Step ST1-4, the electric field value of the antenna element 4-n calculated in Step ST1-5, and the received signal to calculate the value of the evaluation function defined by [Equation 7] based on [Equations 3] to [Equation 6].

[0060] (Step ST1-7) The estimated value calculation unit 9 determines, based on a predetermined determination condition, the evaluation function value calculated in step ST1-6 and the number of times the propagation characteristic difference estimated value and the signal arrival direction estimated value are updated in step ST1-8. As a specific example, the estimated value calculation unit 9 determines whether the evaluation function value calculated in step ST1-6 is less than or equal to a predetermined threshold value, or whether the number of updates of each estimated value is equal to or greater than a predetermined number of times. When the antenna calibration system 1 satisfies a predetermined determination condition, it proceeds to step ST1-9, and when it does not satisfy the predetermined determination condition, it proceeds to step ST1-8.

[0061] (Step ST1-8) When the predetermined determination condition is not satisfied, since the temporarily determined propagation characteristic difference estimated value and the signal arrival direction estimated value are inappropriate, the estimated value calculation unit 9 updates these estimated values. As a specific example, the estimated value calculation unit 9 adds a value corresponding to a predetermined step width to the propagation characteristic difference estimated value and the signal arrival direction estimated value, or adds a value corresponding to the step width calculated based on the derivative of the value of the evaluation function defined by [Equation 7] to the propagation characteristic difference estimated value and the signal arrival direction estimated value. Thereafter, the estimated value calculation unit 9 returns to step ST1-5 and repeats steps ST1-5 to ST1-8 until the predetermined determination condition is satisfied in step ST1-7.

[0062] (Step ST1-9) The calibration value calculation unit 10 calculates a calibration value for correcting the difference in relative propagation characteristics between antenna element systems using the final propagation characteristic difference estimated value or the signal arrival direction estimated value calculated by the estimated value calculation unit 9, and outputs the calculated calibration value to the DBF signal processing unit 6. These are the calibration values for each antenna element 4 calculated. As a specific example, the calibration value calculation unit 10 calculates the relative propagation characteristic value A of the receiver 5-n based on [Equation 4] and [Equation 6] from the final propagation characteristic difference estimated value nCalculate / A1, and calculate the reciprocal of the calculated relative pass characteristic value as a calibration value. As another specific example, the calibration value calculation unit 10 uses the electric field value read from the radiation pattern design value stored in the element pattern storage unit 8, which is the electric field value of the antenna element 4-n corresponding to the signal arrival direction estimation value, and the reception signals of the respective antenna elements 4 output by the respective receivers 5, and based on [Equation 3], calculates the relative pass characteristic value A of the receiver 5-n n Calculate / A1.

[0063] (Step ST1-10) The DBF signal processing unit 6 calibrates the received signal by multiplying the received signal for applications such as communication, which separately receives the calibration value output by the calibration value calculation unit 10, by the calibration value.

[0064] ***Explanation of the effects of Embodiment 1*** As described above, in the antenna calibration system 1 according to Embodiment 1, the calibration value is calculated by numerically calculating and minimizing a predetermined evaluation function calculated based on the received signal of the DBF antenna, the radiation pattern design value of the antenna elements of the DBF antenna, the estimated pass characteristic difference of each antenna element system, and the estimated signal arrival direction. By using the calibration value, antenna calibration can be performed without repeating calibration signal transmission and reception between the DBF antenna and each calibration antenna device when the directions of the respective calibration antenna devices are unknown.

[0065] In the description of the operation of the antenna calibration system 1, an example in which the estimation value calculation unit 9 minimizes the evaluation function defined by [Equation 7] has been shown, but the evaluation function is not limited thereto. As a specific example, the first term on the right side of [Equation 7] may be a function that monotonically increases with respect to the magnitude of the difference in pass characteristics, such as the sum of squares of the magnitudes of the differences in pass characteristics. Similarly, the second term on the right side of [Equation 7] may be a function that monotonically increases with respect to the magnitude of each element of the matrix Z-KG, such as the square value of the Frobenius norm of Z-KG.

[0066] ***Other configurations*** <Modification Example 1> FIG. 4 shows a hardware configuration example of the computer 70 according to this modified example. Instead of the processor 71, the processor 71 and the memory 72, the processor 71 and the auxiliary storage device 73, or the processor 71, the memory 72, and the auxiliary storage device 73, the computer 70 includes a processing circuit 78. The processing circuit 78 is hardware that realizes at least a part of each unit included in the computer 70. The processing circuit 78 may be dedicated hardware or may be a processor that executes a program stored in the memory 72.

[0067] When the processing circuit 78 is dedicated hardware, as a specific example, the processing circuit 78 is a single circuit, a composite circuit, a programmed processor, a parallel-programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. The computer 70 may include a plurality of processing circuits that replace the processing circuit 78. The plurality of processing circuits share the role of the processing circuit 78.

[0068] In the computer 70, some functions may be realized by dedicated hardware and the remaining functions may be realized by software or firmware.

[0069] As a specific example, the processing circuit 78 is realized by hardware, software, firmware, or a combination thereof. The processor 71, the memory 72, the auxiliary storage device 73, and the processing circuit 78 are collectively referred to as a "processing circuitry". That is, the functions of the functional components of the antenna calibration system 1 are realized by the processing circuitry. The functions of the functional components according to other embodiments may also be realized by a hardware configuration similar to that of this modified example.

[0070] Embodiment 2. Hereinafter, mainly differences from the above-described embodiments will be described with reference to the drawings.

[0071] ***Description of Configuration*** FIG. 5 is a block diagram showing a configuration example of the antenna calibration system 20 according to Embodiment 2. The antenna calibration system 20 is obtained by replacing the estimated value calculation unit 9 with the estimated value calculation unit 21 and the calibration value calculation unit 10 with the calibration value calculation unit 22 as compared with the antenna calibration system 1 according to Embodiment 1. For each component that is the same as the component of the antenna calibration system 1, the same reference numeral is given and the description thereof is omitted.

[0072] The estimated value calculation unit 21 uses the reception signal of each antenna element 4 output by each receiver 5 and the radiation pattern design value of each antenna element 4 read from the element pattern storage unit 8, and performs an evaluation based on a predetermined evaluation function set in advance, thereby calculating an estimated value of the amplitude difference of the relative passing characteristics of each antenna element system (hereinafter referred to as the amplitude difference estimated value), an estimated value of the relative phase difference of each antenna element system (hereinafter referred to as the phase difference estimated value), and an estimated value of the signal arrival direction. The estimated value of the signal arrival direction is an estimated value of the direction of each calibration antenna device 3 as seen from the array antenna 2. The evaluation function may be a function composed of the sum of a term corresponding to the magnitude of the difference between the reception signal of each antenna element 4 and the estimated value of the reception signal of each antenna element 4, and a term corresponding to the sum of the magnitudes of the estimated values of the relative amplitude differences in each antenna element system of the array antenna 2. The estimated value of the reception signal of each antenna element 4 is an estimated value obtained from the radiation pattern design value of each antenna element 4, the estimated value of the signal arrival direction, and the estimated value of the passing characteristic difference, and is the estimated value of the reception signal of each antenna element 4.

[0073] The calibration value calculation unit 22 is a calculation unit that calculates a calibration value for correcting differences in relative passing characteristics between antenna element systems. As a specific example, the calibration value calculation unit 22 may calculate a calibration value based on the amplitude difference estimation value and the phase difference estimation value calculated by the estimation value calculation unit 21. As another specific example, the calibration value calculation unit 22 may calculate a calibration value based on the reception signals of each antenna element 4 output by each receiver 5, the signal arrival direction estimation value calculated by the estimation value calculation unit 21, and the radiation pattern design value of each antenna element 4 read from the element pattern storage unit 8. In the case of calculating the calibration value according to the former specific example, from the antenna calibration system 20 shown in FIG. 5, each of the input / output line connecting each receiver 5 and the calibration value calculation unit 22 and the input / output line connecting the element pattern storage unit 8 and the calibration value calculation unit 22 may be omitted.

[0074] ***Description of Operations*** The operation of the antenna calibration system 20 will be described with reference to FIG. 6. FIG. 6 is a flowchart showing an example of the operation of the antenna calibration system 20. Steps corresponding to the same operations as those of the antenna calibration system 1 are denoted by the same reference numerals and the description thereof is omitted.

[0075] Regarding the reception signals received by the array antenna 2, the relationships from [Equation 1] to [Equation 5] hold as in the first embodiment. In the first embodiment, as shown in [Equation 6], k n was expressed, but in the second embodiment, as shown in [Equation 8], k n is expressed.

[0076]

Equation

[0077] Here, Δ n indicates the amplitude difference in relative passing characteristics between the transmitter 5-n and the receiver 5-1. φ n indicates the phase difference between the receiver 5-n and the receiver 5-1. j indicates the imaginary unit. In Embodiment 1, the case where the magnitude of the passing characteristic difference itself is small was considered. However, particularly when the frequency of the calibration high-frequency signal is extremely high, such as in the millimeter-wave band, a large phase difference occurs due to a slight difference in the passing characteristics of the receiver 5-n. Therefore, the magnitude of the relative passing characteristic difference δ n tends to increase. Thus, in Embodiment 2, among the differences in passing characteristics, it is considered that the amplitude difference Δ n is small, but the phase difference φ n can take any value. That is, in the antenna calibration system 20, instead of the evaluation function shown in [Equation 7], the problem of minimizing the evaluation function shown in [Equation 9] is considered.

[0078] [Equation]

[0079] Here, c2 is an appropriate positive coefficient. The first term on the right side of [Equation 9] represents the sum of the magnitudes of the amplitude differences in passing characteristics. The first term on the right side corresponds to the term for the sum of the magnitudes of the estimated values of the relative amplitude differences in each antenna element system of the array antenna 2. Also, the second term on the right side of [Equation 9] represents the magnitude of the difference between the matrix Z determined from the received signal and the product KG of the matrix K and the matrix G. The matrix K is a matrix calculated from the estimated value of the relative passing characteristic amplitude difference Δ n and the estimated value of the phase difference φ n , that is, a matrix calculated from the amplitude difference estimated value and the phase difference estimated value. The matrix G is a matrix calculated from the signal arrival direction estimated value. The second term on the right side corresponds to the term for the magnitude of the difference between the received signal of each antenna element 4 and the estimated value of the received signal of each antenna element 4.

[0080] (Step ST2-4) In order to numerically solve the problem of minimizing the evaluation function defined by [[Equation 9]], the estimation value calculation unit 21 first sets each of the amplitude difference estimation value, the phase difference estimation value, and the signal arrival direction estimation value to appropriate initial values. As a specific example, the estimation value calculation unit 21 sets each of the amplitude difference estimation value and the phase difference estimation value to 0, and sets all of the signal arrival direction estimation values to a direction corresponding to the front direction of the array antenna 2.

[0081] (Step ST2-6) Using the amplitude difference estimation value and the phase difference estimation value set in step ST2-4, the electric field value of the antenna element 4-n calculated in step ST1-5, and the received signal, the estimation value calculation unit 21 calculates the value of the evaluation function defined by [[Equation 9]] based on [[Equations 3]] to [[Equation 5]] and [[Equation 8]].

[0082] (Step ST2-7) The estimation value calculation unit 21 determines, based on a predetermined determination condition, the evaluation function value calculated in step ST2-6 and the number of times the amplitude difference estimation value, the phase difference estimation value, and the signal arrival direction estimation value are updated in step ST2-8. As a specific example, the estimation value calculation unit 21 determines whether the value of the evaluation function calculated in step ST2-6 is less than or equal to a predetermined threshold, or whether the number of updates of each estimation value is equal to or greater than a predetermined number of times. When the antenna calibration system 20 satisfies the predetermined determination condition, it proceeds to step ST2-9, and when it does not satisfy the predetermined determination condition, it proceeds to step ST2-8.

[0083] (Step ST2-8) When the predetermined condition is not satisfied, since the tentatively determined amplitude difference estimation value, phase difference estimation value, and signal arrival direction estimation value are inappropriate, the estimation value calculation unit 21 updates these estimation values. As a specific example, the estimation value calculation unit 21 adds a value corresponding to a predetermined step width to each estimation value, or adds a value corresponding to a step width calculated based on the differential coefficient of the value of the evaluation function defined by [[Equation 9]] to each estimation value. Thereafter, the estimated value calculation unit 21 returns to step ST1-5 and repeats steps ST1-5 to ST2-8 until a predetermined determination condition is satisfied in step ST2-7.

[0084] (Step ST2-9) The calibration value calculation unit 22 calculates a calibration value for correcting the difference in relative passing characteristics between the antenna element systems using the final amplitude difference estimated value and phase difference estimated value calculated by the estimated value calculation unit 21, or the final signal arrival direction estimated value calculated by the estimated value calculation unit 21, and outputs the calculated calibration value to the DBF signal processing unit 6. As a specific example, the calibration value calculation unit 22 calculates the relative passing characteristic value A n / A1 of the receiver 5-n based on [Equation 4] and [Equation 8] from the final amplitude difference estimated value and phase difference estimated value, and calculates the reciprocal of the calculated relative passing characteristic value as the calibration value. As another specific example, the calibration value calculation unit 22 uses the electric field value read from the radiation pattern design value stored in the element pattern storage unit 8, which is the electric field value of the antenna element 4-n corresponding to the signal arrival direction estimated value, and the received signals of each antenna element 4 output by each receiver 5, and calculates the relative passing characteristic value A n / A1 of the receiver 5-n based on [Equation 3].

[0085] (Step ST2-10) The DBF signal processing unit 6 corrects the received signal by multiplying the received signal for applications such as communication received separately with the calibration value output by the calibration value calculation unit 22.

[0086] ***Explanation of the effects of Embodiment 2*** As described above, in the antenna calibration system 20 according to the second embodiment, a calibration value is calculated by numerically calculating and minimizing a predetermined evaluation function calculated based on the received signal of the DBF antenna, the designed radiation pattern value of the antenna elements of the DBF antenna, the estimated amplitude difference and the estimated phase difference of each antenna element system, and the estimated signal arrival direction. By using the calibration value, antenna calibration can be performed without repeating calibration signal transmission and reception between the DBF antenna and the calibration antenna device when the directions of the respective calibration antenna devices are unknown.

[0087] In the description of the operation of the antenna calibration system 20, an example in which the estimated value calculation unit 21 minimizes the evaluation function defined by [Equation 9] has been shown, but the evaluation function is not limited thereto. As a specific example, the first term on the right side of [Equation 9] may be a function that monotonically increases with respect to the sum of the squares of the magnitudes of the amplitude differences of the pass characteristics, for example. Similarly, the second term on the right side of [Equation 9] may be a function that monotonically increases with respect to the magnitudes of the elements of the matrix Z-KG, such as the square value of the Frobenius norm of Z-KG.

[0088] Embodiment 3. Hereinafter, mainly the points different from the above-described embodiments will be described with reference to the drawings.

[0089] ***Description of Configuration*** FIG. 7 is a block diagram showing a configuration example of an antenna calibration system 30 according to the third embodiment. In FIG. 7, the antenna calibration system 30 includes an array antenna 31, calibration antenna devices 32-1 to 32-M (M indicates the number of calibration antenna devices 32), a calibration information transmission / reception device 33, and a calibration value calculation device 34. The array antenna 31 and the calibration information transmission / reception device 33 may be mounted on either one platform or one device. As a specific example, the array antenna 31 and the calibration information transmission / reception device 33 are mounted on an artificial satellite which is a platform. The calibration value calculation device 34 may be provided on a platform or device different from the one on which the array antenna 31 and the calibration information transmission / reception device 33 are mounted.

[0090] The array antenna 31 is a DBF antenna that receives high-frequency signals. As a specific example, it is an antenna device to be calibrated mounted on a platform such as a satellite or an aircraft. The array antenna 31 includes antenna elements 35-1 to antenna elements 35-N (where N indicates the number of antenna elements 35), receivers 36-1 to receivers 36-N, a DBF signal processing unit 37, and an output terminal 38.

[0091] Each calibration antenna device 32 is an antenna device that transmits a high-frequency signal for calibration to the array antenna 31 and is installed on the ground. Each of the calibration antenna devices 32-1 to 32-M includes transmission antennas 39-1 to 39-M and transmitters 40-1 to 40-M.

[0092] The calibration information transmission / reception device 33 transmits information regarding the received signal for the calibration high-frequency signal received by the array antenna 31 to the calibration value calculation device 34 installed on the ground. Further, it receives information indicating the calculation result of the calibration value sent from the calibration value calculation device 34 and outputs the calibration value indicated by the received information to the array antenna 31. It is installed on the platform on which the array antenna 31 is mounted. The calibration information transmission / reception device 33 includes a correlation processing unit 41, a first transmission / reception device 42, a first transmission / reception antenna 43, and a calibration value setting processing unit 44. The calibration information transmission / reception device 33 transmits information corresponding to the generated received signal to the calibration value calculation device 34 using the first transmission / reception antenna 43 and the first transmission / reception device 42. The calibration information transmission / reception device 33 receives the calibration value information transmitted from the calibration value calculation device 34 using the first transmission / reception antenna 43 and the first transmission / reception device 42 and executes calibration processing using the calibration value indicated by the received calibration value information.

[0093] The calibration value calculation device 34 is a device that receives information regarding the received signal of the array antenna 31 transmitted by the calibration information transmission / reception device 33, calculates a calibration value based on the information, and transmits the calculated calibration value to the calibration information transmission / reception device 33. It is installed on the ground. The calibration value calculation device 34 includes a second transmission / reception antenna 45, a second transceiver 46, a received signal information acquisition processing unit 47, an element pattern storage unit 48, a calibration antenna position information storage unit 49, an estimated value calculation unit 50, a calibration value calculation unit 51, and a calibration value information generation processing unit 52. The calibration value calculation device 34 receives information corresponding to the received signal transmitted from the calibration information transmission / reception device 33 using the second transmission / reception antenna 45 and the second transceiver 46. The calibration value calculation device 34 transmits calibration value information indicating the calculated calibration value toward the calibration information transmission / reception device 33 using the second transmission / reception antenna 45 and the second transceiver 46.

[0094] Each antenna element 35 is an antenna that receives a high-frequency signal. Hereinafter, consider the case where the radiation patterns of the respective antenna elements 35 on the ground are in a beam pattern arranged such that the irradiation regions thereof partially overlap as shown in FIG. 8 as a specific example.

[0095] Each receiver 36 is a circuit that amplifies the high-frequency signal received by each antenna element 35, converts the frequency of the amplified signal into an intermediate frequency band, and converts the frequency-converted analog signal into a digital signal. Each receiver 36 is, as a specific example, composed of a low-noise amplifier, a frequency mixer, an analog-to-digital conversion circuit, and the like.

[0096] The DBF signal processing unit 37 multiplies each received signal of each antenna element 35 output by each receiver 36 by a calibration value output by the calibration value setting processing unit 44, which is a calibration value corresponding to each antenna element 35, performs predetermined signal processing on the signal, and is a signal processing unit that performs so-called DBF. The DBF signal processing unit 37 is, as a specific example, composed of a digital circuit that multiplies each signal by a predetermined excitation coefficient and then adds all the received signals.

[0097] The output terminal 38 is a terminal that outputs the output signal of the DBF signal processing unit 37.

[0098] Each transmission antenna 39 is an antenna that transmits a calibration signal, and is an antenna that radiates the high-frequency calibration signal generated by each transmitter 40 into space. Each transmission antenna 39 is installed at a position where each antenna element 35 can receive the radio waves radiated from each of them. Here, as shown in FIG. 8, consider a case where the radiation pattern is arranged such that the irradiation regions of the respective antenna elements 35 partially overlap. When each transmission antenna 39 is arranged outside the region irradiated by each antenna element 35, the received power of the high-frequency signal becomes low at each antenna element 35, and thus the high-frequency signal cannot be received with sufficient measurement accuracy. Therefore, each transmission antenna 39 is arranged inside the region irradiated by each antenna element 35. Also, from the viewpoint of reducing the overall system scale of the antenna calibration system 30, it is desirable to minimize the number of installation platforms of the calibration antenna device 32. Therefore, when the radiation pattern is as shown in FIG. 8, it is preferable to arrange each calibration antenna device 32 within the region where the irradiation regions of the radiation patterns of the respective antenna elements 35 overlap (irradiation overlap region). That is, in the beam pattern shown in FIG. 8, as a specific example, the transmission antenna 39-1 is arranged at a point P1 within the irradiation overlap region R1 corresponding to the antenna element 35-1, the antenna element 35-2, and the antenna element 35-3. Also, the transmission antenna 39-2 is arranged at a point P2 within the irradiation overlap region R2 corresponding to the antenna element 35-3, the antenna element 35-4, and the antenna element 35-5. That is, the main beams of the respective antenna elements 35 may irradiate different directions. At this time, regarding the irradiation regions of two adjacent main beams, a part of the irradiation region of one main beam may overlap with a part of the irradiation region of the other main beam. Also, at this time, each antenna that transmits a calibration signal may be arranged within the region where the irradiation regions of two or more main beams overlap.

[0099] Each transmitter 40 is a signal source that generates, as a calibration high-frequency signal, for example, a continuous wave or various modulated waves. Each transmitter 40 is, for example, composed of a circuit that combines an oscillator, a synthesizer circuit, a modulation circuit, a frequency mixer, and an amplifier.

[0100] The correlation processing unit 41 performs predetermined processing on the reception signals of each antenna element 35 output by each receiver 36, calculates the correlation value between the reception signals, and executes processing to convert the calculated value into a format for transmission to the calibration value calculation device 34 as reception signal information. The correlation processing unit 41 corresponds to a reception signal information generation processing unit. The reception signal information generation processing unit generates information corresponding to the reception signals of each antenna element 35. This information is, for example, reception signal information.

[0101] The first transceiver 42 modulates the reception signal information output by the correlation processing unit 41 to generate a modulation signal, converts the generated modulation signal into a high-frequency signal, and generates the converted high-frequency signal (hereinafter referred to as a signal for transmitting reception signal information). Further, the first transceiver 42 is a circuit that amplifies the calibration value information transmission signal, which is the signal received by the first transceiver antenna 43 and transmitted from the calibration value calculation device 34, converts the frequency of the amplified signal into an intermediate frequency band, and converts the frequency-converted analog signal into a digital signal. The first transceiver 42 is, for example, composed of an oscillator, a synthesizer circuit, a modulation circuit, a frequency mixer, an amplifier, a low-noise amplifier, a frequency mixer, an analog-to-digital conversion circuit, and the like.

[0102] The first transceiver antenna 43 is an antenna that radiates the signal for transmitting reception signal information output by the first transceiver 42 into space and is also an antenna that receives the calibration value information transmission signal transmitted from the calibration value calculation device 34.

[0103] The calibration value setting processing unit 44 acquires a calibration value for correcting the difference in relative passing characteristics between the antenna element systems from the received signal with respect to the calibration value information transmission signal output by the first transceiver 42, and outputs the acquired calibration value to the DBF signal processing unit 37.

[0104] The second transceiver antenna 45 is an antenna that receives the received signal information transmission signal transmitted from the calibration information transceiver device 33, and is also an antenna that radiates the calibration value information transmission signal output from the second transceiver 46 into space.

[0105] The second transceiver 46 amplifies the received signal information transmission signal received by the second transceiver antenna 45, converts the frequency of the amplified signal into an intermediate frequency band, and converts the frequency-converted analog signal into a digital signal. Further, the second transceiver 46 is a circuit that modulates the calibration value information output by the calibration value information generation processing unit 52 to generate a modulation signal, converts the generated modulation signal into a high-frequency signal, and generates a calibration value information transmission signal that is the converted high-frequency signal. As a specific example, the second transceiver 46 is composed of an oscillator, a synthesizer circuit, a modulation circuit, a frequency mixer, an amplifier, a low-noise amplifier, a frequency mixer, an analog-to-digital conversion circuit, and the like.

[0106] The received signal information acquisition processing unit 47 acquires the correlation value between the received signals of the respective antenna elements 35 of the array antenna 31 from the received signal with respect to the received signal information transmission signal output by the second transceiver 46, and outputs the acquired correlation value to the estimated value calculation unit 50.

[0107] The element pattern memory unit 48 is a memory unit that stores information indicating the design values of the amplitude and phase values of the radiation pattern of each antenna element 35. As a specific example, the design values consist of at least any one of the theoretical value, the calculated value, and the measured value of the radiation pattern. As a specific example, the element pattern memory unit 48 may store the design values in the form of a function representing the amplitude and phase values of the radiation pattern of each antenna element 35 with respect to the azimuth defined by a predetermined coordinate system, or may store the design values as a data set of the amplitude and phase values of the radiation pattern of each antenna element 35 in the sample directions set in a grid pattern on the same coordinate system.

[0108] The calibration antenna position information storage unit 49 is a storage unit that stores, as calibration antenna position information, information indicating the direction of each calibration antenna device 32 as seen from the array antenna 31. That is, the calibration antenna position information storage unit 49 stores information indicating the positions of the antennas that transmit the calibration signals. Note that the above direction is the direction at a pre-designed nominal value when there is no attitude error in the platform on which the array antenna 31 is mounted.

[0109] The estimated value calculation unit 50 uses the correlation values between the received signals of each antenna element 35 output by the received signal information acquisition processing unit 47, the radiation pattern design values of each antenna element 35 read from the element pattern memory unit 48, and the position information of each calibration antenna device 32 read from the calibration antenna position information storage unit 49, and performs an evaluation based on a predetermined evaluation function set in advance, thereby obtaining an estimated value of the difference in the relative pass characteristics of each antenna element system (hereinafter referred to as the pass characteristic difference estimated value) and an estimated value of the pointing error of the array antenna 31 caused by the attitude error of the platform on which the array antenna 31 is mounted (hereinafter referred to as the pointing error estimated value). The estimated value calculation unit 50 calculates the pass characteristic difference estimated value and the signal arrival direction estimated value based on the information received from the calibration information transceiver 33. The evaluation function may be a function composed of the sum of a term corresponding to the sum of the magnitudes of the differences between the received signals of each antenna element 35 and the estimated values of the received signals of each antenna element 35, and a term corresponding to the sum of the magnitudes of error components obtained by subtracting a reference complex quantity from a complex quantity obtained from the transfer characteristics in each antenna element system of the array antenna 31. The estimated value of the received signal of each antenna element 35 is an estimated value obtained from the radiation pattern design value, the estimated value of the signal arrival direction, and the estimated value of the transfer characteristic difference, and is the estimated value of the received signal of each antenna element 35. In the evaluation function, it may be expressed by a correlation value defined by the time average value of the product of the complex conjugate value of the received signal of one antenna element 35 and the received signals of the other antenna elements 35. When the positions of the antennas that transmit the calibration signals are known, the estimated value calculation unit 50 may calculate the estimated value of the signal arrival direction based on the positions of the antennas that transmit the known calibration signals and the estimated value of the pointing error of the array antenna 31.

[0110] The calibration value calculation unit 51 is a calculation unit that calculates a calibration value for correcting the difference in relative transfer characteristics between antenna element systems. The calibration value calculation unit 51 calculates a calibration value based on the information received from the calibration information transmission / reception device 33. As a specific example, the calibration value calculation unit 51 may calculate a calibration value based on the transfer characteristic difference estimated value calculated by the estimated value calculation unit 50. As another specific example, the calibration value calculation unit 51 may calculate a calibration value based on the correlation value between the received signals of each antenna element 35 output by the received signal information acquisition processing unit 47, the pointing error estimated value calculated by the estimated value calculation unit 50, the radiation pattern design value of each antenna element 35 read from the element pattern storage unit 48, and the position information of each transmitting antenna 39 read from the calibration antenna position information storage unit 49. When calculating the calibration value according to the former specific example, the input / output lines connecting the received signal information acquisition processing unit 47, the element pattern storage unit 48, and the calibration antenna position information storage unit 49 and the calibration value calculation unit 51 from the antenna calibration system 30 shown in FIG. 7 may be omitted.

[0111] The calibration value information generation processing unit 52 executes a process of converting a calibration value for correcting the difference in relative passing characteristics between antenna element systems calculated by the calibration value calculation unit 51 into a format for transmission to the calibration information transmission / reception device 33 as calibration value information.

[0112] The hardware configurations of each of the calibration information transmission / reception device 33 and the calibration value calculation device 34 may be the same as that of the computer 70.

[0113] ***Explanation of Operations*** The operation of the antenna calibration system 30 will be described with reference to FIG. 9. FIG. 9 is a flowchart showing an example of the operation of the antenna calibration system 30.

[0114] (Step ST3-1) Based on an instruction by an operator of the array antenna 31 or a periodic trigger signal, the calibration process is started.

[0115] (Step ST3-2) A calibration high-frequency signal is sent from each calibration antenna device 32 toward the array antenna 31. Specifically, in each transmitter 40, a calibration high-frequency signal is generated, and the generated signal is radiated into space from each transmission antenna 39, whereby the calibration high-frequency signal is transmitted toward the array antenna 31.

[0116] (Step ST3-3) Each antenna element 35 receives the transmitted high-frequency signal. Each receiver 36 amplifies the high-frequency signal received by each antenna element 35, then frequency-converts the amplified signal to an intermediate frequency band, further converts the frequency-converted signal to a digital signal, and acquires the digital signal as a received signal. In addition, in order to receive the signals of each calibration antenna device 32 individually, each of the calibration antenna devices 32-1 to 32-M sequentially transmits calibration high-frequency signals in a time-division manner, and each antenna element 35 receives the transmitted high-frequency signals. That is, steps ST3-2 and ST3-3 are repeatedly executed M times, where M is the number of calibration antenna devices 32.

[0117] In addition, when the radiation pattern of each antenna element 35 is a beam pattern as shown in FIG. 8, each antenna element 35 cannot receive signals from all the calibration antenna devices 32 at a sufficient signal level. Therefore, each antenna element 35 receives only the high-frequency signals transmitted from each calibration antenna device 32 within the region irradiated by the radiation pattern of each antenna element 35. In the example shown in FIG. 8, the antenna elements 35-1 and 35-2 receive only the high-frequency signals transmitted from the transmitting antenna 39-1 arranged at point P1, that is, the calibration antenna device 32-1. Also, the antenna element 35-3 receives only the high-frequency signals transmitted from the transmitting antenna 39-1 arranged at point P1, that is, the calibration antenna device 32-1, and the high-frequency signals transmitted from the transmitting antenna 39-2 arranged at point P2, that is, the calibration antenna device 32-2. Here, consider the case where the calibration antenna device 32-m (m = 1, 2,..., M) transmits a high-frequency signal and the antenna element 35-n (n = 1, 2,..., N. However, n is the identification number of each antenna element 35 within the region irradiated according to the radiation pattern of the transmitting antenna 39-m) receives the high-frequency signal. First, consider the case where the transmitting antenna 39-m of each calibration antenna device 32-m is arranged in the direction of (θ m , φ m ) as viewed from the array antenna 31, and there is no attitude error in the platform on which the array antenna 31 is mounted. Note that (θ m , φ m) corresponds to the calibration antenna position information stored in the calibration antenna position information storage unit 49 and is the direction at the nominal value designed in advance. The high-frequency signal x transmitted by the calibration antenna device 32-m and received by the antenna element 35-n nm becomes as shown in [several tens]. Here, the calibration high-frequency signal transmitted by each calibration antenna device 32-m is represented as s m and the propagation characteristics between the transmitting antenna 39-m and the array antenna 31 are represented as H m and the electric field value in the (θ, φ) direction of the antenna element 35-n is represented as E n (θ, φ).

[0118]

Equation

[0119] Note that E n (θ, φ) is in the form of a function of (θ, φ) and is assumed to be stored in the element pattern storage unit 48 as the radiation pattern design value. In step ST3-3, the high-frequency signal x nm is amplified by the receiver 36-n, then the amplified signal is frequency-converted to an intermediate frequency band, and further the frequency-converted signal is converted to a digital signal. Here, the received signal of the complex digital signal with respect to the high-frequency signal x nm is represented as shown in [Equation 11].

[0120]

Equation

[0121] However, y nm,I indicates the in-phase component of y nm , j indicates the imaginary unit, and y nm,Q indicates the quadrature component of y nm . Also, A n indicates the pass characteristic of the receiver 36-n. Usually, the value of A n is different depending on the receiver 36. In the calibration process, A nIn order to perform correction so as to remove the difference, it is necessary to estimate the value of A n from the received signal.

[0122] (Step ST3-4) The correlation processing unit 41 calculates the correlation value C m (i,j) defined by [Equation 12] for the received signals of the complex digital signals output by each receiver 36, and executes a process of converting the calculated value into a format for transmission as received signal information to the calibration value calculation device 34.

[0123]

Equation

[0124] Here, z * represents the complex conjugate value of the complex number z. y im (k) is the signal transmitted from the calibration antenna device 32-m and represents the k-th signal among the signals received by the antenna element 35-i. y jm (k) is the signal transmitted from the calibration antenna device 32-m and represents the k-th signal among the signals received by the antenna element 35-j. K is a predetermined positive integer and represents the average time or number of times. Also, i and j represent the identification numbers of the antenna elements 35 that receive the high-frequency signals transmitted from the transmission antenna 39-m. In [Equation 12], the correlation value is defined by the time-average value of the product of the complex conjugate value of the received signal of one antenna element 35 and the received signals of the other antenna elements 35.

[0125] (Step ST3-5) The first transceiver antenna 43 transmits a high-frequency signal (signal for transmitting received signal information) including the received signal information output by the correlation processing unit 41.

[0126] (Step ST3-6) The calibration value calculation device 34 receives the signal for transmitting received signal information transmitted from the calibration information transceiver device 33 as a received signal using the second transceiver antenna 45 and the second receiver 46. The received signal information acquisition processing unit 47 obtains received signal information, that is, the correlation value C m (i,j) between the received signals of each antenna element 35.

[0127] Here, when substituting [Equation 11] into [Equation 12], the correlation value becomes as shown in [Equation 13].

[0128]

Equation

[0129] However, except for the high-frequency signal s m , it is assumed that all values do not change with time. E[|s m | 2 represents the average value of |s m (k)| 2 (k = 1,..., K), and s m (k) represents the k-th signal transmitted from the calibration antenna device 32-m. Here, although it is necessary to estimate A n , H m is an unknown value in [Equation 13]. Therefore, in order to cancel its influence, the relative value between the antenna elements 35 is considered as shown in [Equation 14].

[0130]

Equation

[0131] [Equation 14] shows the relative value of the correlation value of the antenna element 35-j with respect to the reference element of the antenna element 35-i. In [Equation 14], (θ m , φ m ) is the calibration antenna position information stored in the calibration antenna position information storage unit 49 and is known. Therefore, from the radiation pattern design value E n (θ, φ) stored in the element pattern storage unit 48, E j (θ m , φ m ) / E i (θ m , φ m) can calculate the value of E j (θ m , φ m ) / E i (θ m , φ m ) and the relative value X of the correlation value calculated from the received signal m (i, j) are used to calculate A by [Equation 14] j / A i 's value can be calculated. However, here, a posture error occurs in the platform equipped with the array antenna 31, that is, a pointing error occurs in the array antenna 31, and as a result, (θ m , φ m ) becomes (θ m + Δθ, φ m + Δφ). In this case, not only the value of A j / A i but also the pointing error (Δθ, Δφ) needs to be calculated. Here, the relative value of the passing characteristic A of the receiver 36 - n j / A i is expressed as shown in [Equation 15].[[]END]]

[0132]

Equation

[0133] Here, consider the case where the calibration high - frequency signal transmitted from the calibration antenna device 32 - m is received by the antenna element 35 - n m (l) (l = 1, 2,..., N m ). Here, n m represents a row vector having the identification number of the antenna element 35 that receives the calibration high - frequency signal transmitted from the calibration antenna device 32 - m as an element. N m represents the number of antenna elements 35 that receive the calibration high - frequency signal transmitted from the calibration antenna device 32 - m. At this time, as shown in [Equation 16], the relative value of the correlation value of the antenna element 35 that receives the calibration high - frequency signal transmitted from the calibration antenna device 32 - m, and the antenna element 35 - n mConsider a matrix form arranging relative values when (1) is used as a reference element.

[0134]

Number

[0135] However, G m (i,j) = E j (θ m +Δθ, φ m +Δφ) / E i (θ m +Δθ, φ m +Δφ). In [Equation 16], Z m is a matrix obtained from the relative values of the correlation values calculated from the received signals. K m is a diagonal matrix with k(i,j) as diagonal elements and is an unknown matrix. G m is a matrix obtained from the calibration antenna position information stored in the calibration antenna position information storage unit 49, the pointing error (Δθ, Δφ), and the radiation pattern design value. Since the pointing error (Δθ, Δφ) is unknown, G m is an unknown matrix. Furthermore, Z m and G m are summarized as shown in [Equation 17] for all m.

[0136]

Number

[0137] If [Equation 17] is solved, the unknowns k(i,j) and (Δθ, Δφ) can be calculated. However, since both K and G on the right side of [Equation 17] are unknown matrices, [Equation 17] becomes an indeterminate equation. Therefore, they cannot be uniquely calculated. Here, usually, although there are individual differences, the receiver 36-n is manufactured to have approximately the same magnitude of pass characteristics. Therefore, here, it is assumed that the difference in pass characteristics among the receivers 36 is small, and k(i,j) is expressed as shown in [Equation 18].

[0138] [Math]

[0139] Here, δ(i,j) is a complex quantity indicating the difference in relative passing characteristics between receiver 36-i and receiver 36-j. As described above, the magnitude of the difference in passing characteristics is small, that is, δ(i,j) is considered to be small. Therefore, in the antenna calibration system 30, as a specific example, instead of solving [Equation 17], the problem of minimizing the evaluation function shown in [Equation 19] is considered.

[0140] [Math]

[0141] Here, the norm symbol with subscript F indicates the Frobenius norm of the matrix, and c3 is an appropriate positive coefficient. The first term on the right side of [Equation 19] indicates the sum of the magnitudes of the passing characteristic differences δ(i,j). The first term on the right side corresponds to the term that is the sum of the magnitudes of the error components obtained by subtracting the reference complex quantity from the complex quantity obtained from the passing characteristics in each antenna element system of the array antenna 31. The second term on the right side of [Equation 19] indicates the magnitude of the difference between the matrix Z determined from the received signal and the product KG of the matrices K and G. The matrix K is a matrix obtained from the estimated value of the passing characteristic difference δ(i,j), that is, the passing characteristic difference estimate. The matrix G is a matrix obtained from the estimated value of the pointing error (Δθ,Δφ), that is, the pointing error estimate. The second term on the right side corresponds to the term that is the sum of the magnitudes of the differences between the received signals of each antenna element 35 and the estimated values of the received signals of each antenna element 35.

[0142] (Step ST3-7) The estimated value calculation unit 50 first sets the passing characteristic difference estimate and the pointing error estimate to appropriate initial values in order to numerically solve the problem of minimizing the evaluation function defined by [Equation 19]. As a specific example, the estimated value calculation unit 50 sets all of the passing characteristic difference estimate and the pointing error estimate to 0.

[0143] (Step ST3-8) The estimated value calculation unit 50 reads out the electric field value of the antenna element 35-n corresponding to the direction determined from the direction error estimated value set in step ST3-7 and the calibration antenna position information stored in the calibration antenna position information storage unit 49 from the radiation pattern design value stored in the element pattern storage unit 48. Specifically, the estimated value calculation unit 50 reads out the radiation pattern design value stored in the element pattern storage unit 48 in the form of a function of (θ, φ), substitutes the direction determined from the direction error estimated value and the calibration antenna position information into the read design value, and calculates the electric field value.

[0144] (Step ST3-9) The estimated value calculation unit 50 uses the pass characteristic difference estimated value set in step ST3-7, the electric field value of the antenna element 35-n calculated in step ST3-8, and the correlation value C m (i,j) to calculate the value of the evaluation function defined by [Equation 19] based on [Equation 14] to [Equation 18].

[0145] (Step ST3-10) The estimated value calculation unit 50 determines, based on a predetermined determination condition, the value of the evaluation function calculated in step ST3-9 and the number of times the pass characteristic difference estimated value and the direction error estimated value are updated in step ST3-11. As a specific example, the estimated value calculation unit 50 determines whether the evaluation function value calculated in step ST3-9 is less than or equal to a predetermined threshold value, or whether the number of updates of the estimated value is equal to or more than a predetermined number of times. When the antenna calibration system 30 satisfies a predetermined determination condition, it proceeds to step ST3-12, and when it does not satisfy the predetermined determination condition, it proceeds to step ST3-11.

[0146] (Step ST3-11) When the predetermined determination conditions are not satisfied, the provisionally determined passing characteristic difference estimation value and the direction error estimation value are inappropriate, so the estimation value calculation unit 50 updates these estimation values. As a specific example, the estimation value calculation unit 50 adds a value corresponding to a predetermined step width to the passing characteristic difference estimation value and the direction error estimation value, or adds a value corresponding to the step width calculated based on the derivative of the value of the evaluation function defined by [Equation 19] to the passing characteristic difference estimation value and the direction error estimation value. Thereafter, the estimation value calculation unit 50 returns to step ST3-8 and repeatedly executes steps ST3-8 to ST3-11 until the predetermined determination conditions are satisfied in step ST3-10.

[0147] (Step ST3-12) The correction value calculation unit 51 calculates a correction value for correcting the difference in relative passing characteristics between the antenna element systems using the final passing characteristic difference estimation value or the direction error estimation value calculated by the estimation value calculation unit 50. As a specific example, the correction value calculation unit 51 calculates the relative passing characteristic value A n / A1 of the receiver 36-n from the final passing characteristic difference estimation value based on [Equation 15] and [Equation 18], and calculates the reciprocal of the calculated value as the correction value. As another specific example, the correction value calculation unit 51 uses the electric field value read from the radiation pattern design value stored in the element pattern storage unit 48, which is the electric field value of the antenna element 35-n corresponding to the direction determined from the direction error estimation value and the antenna position information for correction, and the reception signal information output by the reception signal information acquisition processing unit 47, that is, the correlation value C m (i,j) to calculate the relative passing characteristic value A n / A1 of the receiver 36-n based on [Equation 14].

[0148] (Step ST3-13) The calibration value information generation processing unit 52 executes a process of converting a calibration value for correcting the difference in relative passing characteristics between antenna element systems calculated in step ST3-12 into a format for transmission as calibration value information to the calibration information transceiver 33. Further, the calibration value information generation processing unit 52 transmits a signal indicating the calibration value information as a calibration value information transmission signal toward the calibration information transceiver 33 via the second transceiver 46 and the second transmission / reception antenna 45.

[0149] (Step ST3-14) The calibration information transceiver 33 receives the calibration value information transmission signal transmitted from the calibration value calculation device 34 as a reception signal using the first transmission / reception antenna 43 and the first transceiver 42. The calibration value setting processing unit 44 acquires a calibration value for correcting the difference in relative passing characteristics between antenna element systems from the reception signal.

[0150] (Step ST3-15) The DBF signal processing unit 37 corrects the reception signal by multiplying the reception signal for uses such as communication received separately with the calibration value output by the calibration value setting processing unit 44.

[0151] ***Explanation of the effects of Embodiment 3*** As described above, in the antenna calibration system 30 according to Embodiment 3, a predetermined evaluation function calculated based on the reception signal of the DBF antenna mounted on a platform such as a satellite, the radiation pattern design value of the antenna element, the passing characteristic difference estimation value in each antenna element system, and the pointing error estimation value is minimized by numerical calculation processing to calculate the calibration value. Further, by using the calculated calibration value, even when the pointing error caused by the attitude error of the platform or the like is unknown, antenna calibration can be performed without repeating the calibration signal transmission and reception between the DBF antenna and each calibration antenna device 32.

[0152] In the description of the operation of the antenna calibration system 30, an example was shown in which the estimated value calculation unit 50 minimizes the evaluation function defined by [Equation 19], but the evaluation function is not limited thereto. As a specific example, the first term on the right side of [Equation 19] may be any function that monotonically increases with respect to the magnitude of the passing characteristic difference, such as the sum of the squares of the magnitudes of the passing characteristic differences. Similarly, the second term on the right side of [Equation 19] may be any function that monotonically increases with respect to the magnitude of each element of the matrix Z-KG, such as the square value of the Frobenius norm of Z-KG.

[0153] Also, similar to the antenna calibration system 20 according to Embodiment 2, the amplitude difference Δ(i,j) of the relative passing characteristics between the receiver 36-i and the receiver 36-j and the phase difference φ(i,j) between the receiver 36-i and the receiver 36-j are used to express the passing characteristic difference k(i,j) between the receivers 36 as shown in [Equation 20], and the first term on the right side of [Equation 19] may be replaced with a function that monotonically increases with respect to the magnitude of the amplitude difference of the passing characteristics, such as the sum or the sum of squares of the magnitudes of the amplitude differences of the passing characteristics. At this time, the matrix K in the second term on the right side of [Equation 19] is a matrix obtained from the estimated values of the amplitude difference Δ(i,j) of the relative passing characteristics and the phase difference φ(i,j), that is, the estimated values of the amplitude difference and the phase difference. Note that the coefficient j in [Equation 20] is the imaginary unit.

[0154]

Equation

[0155] Also, according to the antenna calibration system according to the present disclosure, a calibration value is calculated by numerically calculating and minimizing a predetermined evaluation function calculated based on the received signal of the DBF antenna, or the correlation value of the received signal, the radiation pattern design value, the estimated values of the amplitude difference and the phase difference of each antenna element system, and the signal arrival direction estimated value or the attitude error estimated value, and calibration is performed using the calculated calibration value. Therefore, according to the present disclosure, even when there is an attitude error in the platform on which the DBF antenna is mounted, antenna calibration can be performed with relatively high accuracy without repeating signal transmission and reception between the DBF antenna and the calibration station.

[0156] ***Other configurations*** <Modification Example 2> The correction value calculation device 34 may calculate a correction value in the same manner as in Embodiment 1 or 2 without including the correction antenna position information storage unit 49.

[0157] ***Other embodiments*** Free combinations of the above-described embodiments, modifications of any components of each embodiment, or omissions of any components in each embodiment are possible. Also, the embodiments are not limited to those shown in Embodiments 1 to 3, and various changes can be made as necessary. The procedures described using flowcharts and the like may be changed as appropriate.

[0158] Hereinafter, aspects of the present disclosure will be summarized and described as appendices.

[0159] (Appendix 1) An antenna calibration system that calibrates differences in passing characteristics between antenna element systems of an array antenna having a digital beamforming function based on calibration signals transmitted from each of one or more antennas, By solving an optimization problem based on an evaluation function related to a radiation pattern design value that is a design value of the amplitude and phase value of the radiation pattern of each antenna element included in the array antenna, the calibration signal received by each antenna element included in the array antenna as a received signal, a passing characteristic difference estimation value that is an estimation value corresponding to each antenna element system of the array antenna and is an estimation value of the relative passing characteristic difference between the antenna element systems of the array antenna, and a signal arrival direction estimation value that is an estimation value of the arrival direction of the received signal as seen from the array antenna, the passing characteristic difference estimation value and the signal arrival direction estimation value are calculated. An estimation value calculation unit, A calibration value calculation unit that calculates a calibration value used to calibrate the difference in relative passing characteristics between antenna element systems of the array antenna based on any one of the calculated passing characteristic difference estimation value, the calculated signal arrival direction estimation value, and the radiation pattern design value. An antenna calibration system comprising:

[0160] (Appendix 2) The evaluation function is The received signal of each antenna element included in the array antenna, An estimated value obtained from the radiation pattern design value, the signal arrival direction estimation value, and the passing characteristic difference estimation value, and being an estimated value of the received signal of each antenna element included in the array antenna, and the received signal estimated value A term corresponding to the sum of the magnitudes of the differences, A term corresponding to the sum of the magnitudes of error components obtained by subtracting a reference complex quantity from a complex quantity obtained from the passing characteristics of each antenna element system of the array antenna. The antenna calibration system according to Appendix 1, which is a function composed of the sum of

[0161] (Appendix 3) The evaluation function is The received signal of each antenna element included in the array antenna, The radiation pattern design value of each antenna element included in the array antenna, an estimated value obtained from the signal arrival direction estimation value and the passing characteristic difference estimation value, and being an estimated value of the received signal of each antenna element included in the array antenna, and the received signal estimated value A term corresponding to the magnitude of the difference, A term corresponding to the sum of the magnitudes of the estimated relative amplitude differences in each antenna element system of the array antenna. The antenna calibration system according to Appendix 1, which is a function composed of the sum of

[0162] (Appendix 4) In the evaluation function, the received signal of each antenna element included in the array antenna is ​​The relative value of the received signal of each other antenna element included in the array antenna with respect to the received signal of one antenna element included in the array antenna, and The correlation value defined by the time average value of the product of the complex conjugate value of the received signal of one antenna element included in the array antenna and the received signals of each other antenna element included in the array antenna The antenna calibration system according to any one of Appendices 1 to 3, represented by any one of the above.

[0163] (Appendix 5) When the positions of the antennas that transmit the calibration signals are known, The antenna calibration system according to Appendix 4, wherein the estimated value calculation unit calculates the estimated value of the signal arrival direction based on the positions of the antennas that transmit the known calibration signals and the estimated value of the directivity error of the array antenna.

[0164] (Appendix 6) The antenna calibration system further includes An element pattern storage unit that stores information indicating the radiation pattern design value And is provided with The array antenna, the element pattern storage unit, the estimated value calculation unit, and the calibration value calculation unit are mounted on either one platform or one device. The antenna calibration system according to Appendix 4.

[0165] (Appendix 7) The antenna calibration system further includes An element pattern storage unit that stores information indicating the radiation pattern design value, and A calibration antenna position information storage unit that stores information indicating the positions of the antennas that transmit the calibration signals And is provided with The array antenna, the element pattern storage unit, the calibration antenna position information storage unit, the estimated value calculation unit, and the calibration value calculation unit are mounted on either one platform or one device. The antenna calibration system according to Appendix 5.

[0166] (Appendix 8) The antenna calibration system includes a first transceiver antenna, a first transceiver, a received signal information generation processing unit that generates information corresponding to the received signals of the respective antenna elements included in the array antenna, a calibration information transceiver device including an element pattern storage unit that stores information indicating the radiation pattern design value, the estimated value calculation unit, the calibration value calculation unit, a second transceiver antenna, a second transceiver and a calibration value calculation device including and includes The calibration information transceiver device transmits information corresponding to the generated received signal to the calibration value calculation device using the first transceiver antenna and the first transceiver. The calibration value calculation device receives information corresponding to the received signal transmitted from the calibration information transceiver device using the second transceiver antenna and the second transceiver. The estimated value calculation unit calculates the transmission characteristic difference estimated value and the signal arrival direction estimated value based on the received information. The calibration value calculation unit calculates a calibration value based on the received information. The calibration value calculation device transmits calibration value information indicating the calculated calibration value to the calibration information transceiver device using the second transceiver antenna and the second transceiver. The calibration information transceiver device receives the calibration value information transmitted from the calibration value calculation device using the first transceiver antenna and the first transceiver, and executes a calibration process using the calibration value indicated by the received calibration value information. The array antenna and the calibration information transceiver device are mounted on either one platform or one device. The calibration value calculation device is the antenna calibration system described in Supplementary Note 4 provided in a platform or device different from those on which the array antenna and the calibration information transceiver are mounted.

[0167] (Supplementary Note 9) The antenna calibration system includes a first transceiver antenna, a first transceiver, a received signal information generation processing unit that generates information corresponding to the received signals of the respective antenna elements included in the array antenna, a calibration information transceiver device including an element pattern storage unit that stores information indicating the radiation pattern design value, a calibration antenna position information storage unit that stores information indicating the positions of the respective antennas that transmit the calibration signals, the estimated value calculation unit, the calibration value calculation unit, a second transceiver antenna, a second transceiver, a calibration value calculation device including and includes The calibration information transceiver device transmits information corresponding to the generated received signals to the calibration value calculation device using the first transceiver antenna and the first transceiver. The calibration value calculation device receives information corresponding to the received signals transmitted from the calibration information transceiver device using the second transceiver antenna and the second transceiver. The estimated value calculation unit calculates the transmission characteristic difference estimated value and the signal arrival direction estimated value based on the received information. The calibration value calculation unit calculates a calibration value based on the received information. The calibration value calculation device transmits calibration value information indicating the calculated calibration value to the calibration information transceiver device using the second transceiver antenna and the second transceiver. The calibration information transmission / reception device receives the calibration value information transmitted from the calibration value calculation device using the first transmission / reception antenna and the first transceiver, and executes a calibration process using the calibration value indicated by the received calibration value information. The array antenna and the calibration information transmission / reception device are mounted on either one platform or one device. The calibration value calculation device is provided on a platform or device different from the one on which the array antenna and the calibration information transmission / reception device are mounted. The antenna calibration system according to Supplementary Note 5.

[0168] (Supplementary Note 10) The array antenna is mounted on an artificial satellite which is a platform. Each antenna that transmits the calibration signal is installed on the ground. The antenna calibration system according to Supplementary Note 6 or 7.

[0169] (Supplementary Note 11) The array antenna and the calibration information transmission / reception device are mounted on an artificial satellite which is a platform. Each antenna that transmits the calibration signal and the calibration value calculation device are installed on the ground. The antenna calibration system according to Supplementary Note 8 or 9.

[0170] (Supplementary Note 12) The array antenna is the primary radiator of a reflector antenna. The main beams of the antenna elements of the array antenna irradiate in different directions from each other. Regarding the irradiation regions of two adjacent main beams, a part of the irradiation region of one main beam overlaps with a part of the irradiation region of the other main beam. Each antenna that transmits the calibration signal is arranged within a region where the irradiation regions of two or more main beams overlap. The antenna calibration system according to Supplementary Note 10 or 11.

Explanation of Signs

[0171] 1, 20, 30 Antenna calibration system, 2, 31 Array antenna, 3, 32 Antenna device for calibration, 4, 35 Antenna element, 5, 36 Receiver, 6, 37 DBF signal processing unit, 7, 38 Output terminal, 8 Element pattern memory unit, 9, 21 Estimated value calculation unit, 10, 22 Calibration value calculation unit, 11, 39 Transmitting antenna, 12, 40 Transmitter, 33 Calibration information transceiver device, 34 Calibration value calculation device, 41 Correlation processing unit, 42 First transceiver, 43 First transceiver antenna, 44 Calibration value setting processing unit, 45 Second transceiver antenna, 46 Second transceiver, 47 Received signal information acquisition processing unit, 48 Element pattern memory unit, 49 Antenna position information memory unit for calibration, 50 Estimated value calculation unit, 51 Calibration value calculation unit, 52 Calibration value information generation processing unit, 70 Computer, 71 Processor, 72 Memory, 73 Auxiliary storage device, 74 Input / output IF, 75 Communication device, 78 Processing circuit, 79 Signal line.

Claims

1. An antenna calibration system for calibrating differences in passing characteristics between antenna element systems of an array antenna having a digital beamforming function based on calibration signals transmitted from each of one or more antennas, by solving an optimization problem based on an evaluation function related to a radiation pattern design value which is a design value of an amplitude and a phase value of a radiation pattern of each antenna element included in the array antenna, the calibration signal received as a received signal by each antenna element included in the array antenna, an estimated value corresponding to each antenna element system of the array antenna which is an estimated value of a relative passing characteristic difference between antenna element systems of the array antenna, and a signal arrival direction estimated value which is an estimated value of a direction of arrival of the received signal as seen from the array antenna, an estimated value calculation unit that calculates the passing characteristic difference estimated value and the signal arrival direction estimated value; a calibration value calculation unit that calculates a calibration value used to calibrate a relative passing characteristic difference between antenna element systems of the array antenna based on any one of the calculated passing characteristic difference estimated value, the calculated signal arrival direction estimated value, and the radiation pattern design value; An antenna calibration system comprising.

2. The evaluation function is a term corresponding to the sum of the magnitudes of differences between the received signals of each antenna element included in the array antenna, an estimated value obtained from the radiation pattern design value, the signal arrival direction estimated value, and the passing characteristic difference estimated value, which is an estimated value of the received signal of each antenna element included in the array antenna, and the received signal estimated value and a term corresponding to the sum of the magnitudes of error components obtained by subtracting a reference complex quantity from a complex quantity obtained from the passing characteristics of each antenna element system of the array antenna; The antenna calibration system according to claim 1, which is a function composed of the sum.

3. The evaluation function is a term corresponding to the magnitude of the difference between the received signals of each antenna element included in the array antenna, an estimated value obtained from the radiation pattern design value, the signal arrival direction estimated value, and the passing characteristic difference estimated value, which is an estimated value of the received signal of each antenna element included in the array antenna, and the received signal estimated value and a term corresponding to the sum of the magnitudes of estimated relative amplitude differences in each antenna element system of the array antenna; and a term corresponding to the magnitude of the difference between the received signals of each antenna element included in the array antenna, The antenna calibration system according to claim 1, which is a function composed of the sum. The antenna calibration system according to claim 1, which is a function composed of the sum of

4. In the evaluation function, the received signal of each antenna element included in the array antenna is The relative value of the received signal of each other antenna element included in the array antenna when the received signal of one antenna element included in the array antenna is used as a reference, The complex conjugate value of the received signal of one antenna element included in the array antenna, and the correlation value defined by the time average value of the product of the received signal of each other antenna element included in the array antenna The antenna calibration system according to claim 1, which is expressed by any one of

5. When the positions of the antennas for transmitting the calibration signals are known, The estimated value calculation unit calculates the estimated value of the signal arrival direction based on the positions of the antennas for transmitting the calibration signals, which are known, and the estimated value of the pointing error of the array antenna. The antenna calibration system according to claim 4.

6. The antenna calibration system further includes An element pattern storage unit that stores information indicating the radiation pattern design value And is provided with The array antenna, the element pattern storage unit, the estimated value calculation unit, and the calibration value calculation unit are mounted on either one platform or one device. The antenna calibration system according to claim 4.

7. The antenna calibration system further includes An element pattern storage unit that stores information indicating the radiation pattern design value, and A calibration antenna position information storage unit that stores information indicating the positions of the antennas for transmitting the calibration signals And is provided with The array antenna, the element pattern storage unit, the calibration antenna position information storage unit, the estimated value calculation unit, and the calibration value calculation unit are mounted on either one platform or one device. The antenna calibration system according to claim 5.

8. The antenna calibration system A first transceiver antenna, A first transceiver, A received signal information generation processing unit that generates information corresponding to the received signals of the antenna elements included in the array antenna A calibration information transceiver device including An element pattern storage unit that stores information indicating the radiation pattern design value, The estimated value calculation unit, The calibration value calculation unit, A second transceiver antenna, A second transceiver A calibration value calculation device including And is provided with The calibration information transceiver transmits information corresponding to the generated received signal to the calibration value calculation device using the first transceiver antenna and the first transceiver. The calibration value calculation device receives information corresponding to the received signal transmitted from the calibration information transceiver using the second transceiver antenna and the second transceiver. The estimated value calculation unit calculates the transmission characteristic difference estimated value and the signal arrival direction estimated value based on the received information. The calibration value calculation unit calculates a calibration value based on the received information. The calibration value calculation device transmits calibration value information indicating the calculated calibration value to the calibration information transceiver using the second transceiver antenna and the second transceiver. The calibration information transceiver receives the calibration value information transmitted from the calibration value calculation device using the first transceiver antenna and the first transceiver, and executes a calibration process using the calibration value indicated by the received calibration value information. The array antenna and the calibration information transceiver are mounted on either one platform or one device. The calibration value calculation device is provided on a platform or device different from that on which the array antenna and the calibration information transceiver are mounted. The antenna calibration system according to claim 4.

9. The antenna calibration system includes a first transceiver antenna, a first transceiver, a received signal information generation processing unit that generates information corresponding to the received signals of the respective antenna elements included in the array antenna, a calibration information transceiver including the same, an element pattern storage unit that stores information indicating the radiation pattern design value, a calibration antenna position information storage unit that stores information indicating the positions of the respective antennas that transmit the calibration signals, the estimated value calculation unit, the calibration value calculation unit, a second transceiver antenna, a second transceiver and a calibration value calculation device including the same and includes The calibration information transceiver transmits information corresponding to the generated received signal to the calibration value calculation device using the first transceiver antenna and the first transceiver. The calibration value calculation device receives information corresponding to the received signal transmitted from the calibration information transceiver using the second transceiver antenna and the second transceiver. The estimated value calculation unit calculates the transmission characteristic difference estimated value and the signal arrival direction estimated value based on the received information. The correction value calculation unit calculates a correction value based on the received information. The correction value calculation device transmits correction value information indicating the calculated correction value to the correction information transmission / reception device using the second transmission / reception antenna and the second transceiver. The correction information transmission / reception device receives the correction value information transmitted from the correction value calculation device using the first transmission / reception antenna and the first transceiver, and executes a correction process using the correction value indicated by the received correction value information. The array antenna and the correction information transmission / reception device are mounted on either one platform or one device. The antenna calibration system according to claim 5, wherein the correction value calculation device is provided on a platform or a device different from the one on which the array antenna and the correction information transmission / reception device are mounted.

10. The array antenna is mounted on an artificial satellite which is a platform. The antenna calibration system according to claim 6 or 7, wherein each antenna for transmitting the calibration signal is installed on the ground.

11. The array antenna and the correction information transmission / reception device are mounted on an artificial satellite which is a platform. The antenna calibration system according to claim 8 or 9, wherein each antenna for transmitting the calibration signal and the correction value calculation device are installed on the ground.

12. The array antenna is a primary radiator of a reflector antenna. The main beams of the antenna elements of the array antenna irradiate different directions. Regarding the irradiation regions of two adjacent main beams, a part of the irradiation region of one main beam overlaps with a part of the irradiation region of the other main beam. The antenna calibration system according to claim 10, wherein each antenna for transmitting the calibration signal is arranged in a region where the irradiation regions of two or more main beams overlap.

13. The array antenna is a primary radiator of a reflector antenna. The main beams of the antenna elements of the array antenna irradiate different directions. Regarding the irradiation regions of two adjacent main beams, a part of the irradiation region of one main beam overlaps with a part of the irradiation region of the other main beam. The antenna calibration system according to claim 11, wherein each antenna that transmits the calibration signal is arranged within a region where the irradiation regions of two or more main beams overlap.

14. An antenna calibration method executed in an antenna calibration system that calibrates differences in passing characteristics between antenna element systems of an array antenna having a digital beamforming function based on calibration signals transmitted from each of one or more antennas, The computer solves an optimization problem based on an evaluation function related to the radiation pattern design value, which is the design value of the amplitude and phase value of the radiation pattern of each antenna element included in the array antenna, the calibration signal received as a received signal by each antenna element included in the array antenna, the estimated value corresponding to each antenna element system of the array antenna, which is an estimated value of the relative passing characteristic difference between the antenna element systems of the array antenna, and the estimated value of the arrival direction of the received signal as seen from the array antenna, thereby calculating the passing characteristic difference estimated value and the signal arrival direction estimated value, An antenna calibration method in which the computer calculates a calibration value used to calibrate the relative passing characteristic difference between the antenna element systems of the array antenna based on any one of the calculated passing characteristic difference estimated value, the calculated signal arrival direction estimated value, and the radiation pattern design value.

15. An antenna calibration program executed in an antenna calibration system that calibrates differences in passing characteristics between antenna element systems of an array antenna having a digital beamforming function based on calibration signals transmitted from each of one or more antennas, An optimization problem based on an evaluation function related to a radiation pattern design value which is a design value of the amplitude and phase value of the radiation pattern of each antenna element included in the array antenna, the calibration signal received as a received signal by each antenna element included in the array antenna, an estimated value corresponding to each antenna element system of the array antenna, which is an estimated value of the difference in relative passing characteristics between the antenna element systems of the array antenna, i.e., a passing characteristic difference estimated value, and an estimated value of the arrival direction of the received signal as seen from the array antenna, i.e., a signal arrival direction estimated value, is solved to perform an estimated value calculation process for calculating the passing characteristic difference estimated value and the signal arrival direction estimated value. A correction value calculation process for calculating a correction value used to correct the difference in relative passing characteristics between the antenna element systems of the array antenna based on any one of the calculated passing characteristic difference estimated value, the calculated signal arrival direction estimated value, and the radiation pattern design value. An antenna calibration program for causing a computer to execute the above.

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