JP7595609B2 - Base station, central station and phased array antenna system - Google Patents

Description

The present invention relates to a base station, a central station, and a phased array antenna system.

Phased array antenna technology is used in the field of wireless communications, and is particularly essential for 5G (5th Generation), the next-generation mobile communications system. Phased array antennas change their directional pattern by emitting the same radio signal with different amplitudes and phases between adjacent antennas. Therefore, accurate control requires calibration of the amplitude and phase errors between adjacent antennas.

Patent Documents 1 and 2 disclose technology that makes it possible to obtain a desired directional pattern by arranging multiple antenna elements in an array and calibrating the phase and amplitude errors of each transmission branch, which is a set of multiple parallel transmission systems that feed power to each antenna element.

JP 2014-179785 A JP 2016-122895 A

However, in both Patent Document 1 and Patent Document 2, the calibration function is provided on the base station side, such as in a phased array antenna transmission device. This requires a calibration function to be provided for each base station, which increases costs such as power consumption and installation. Furthermore, Patent Document 1 does not take into consideration cases where errors occur due to differences in transmission paths.

The present invention was made in consideration of these circumstances, and aims to provide a phased array antenna system that uses photomixing technology to provide a calibration function on the central station side, thereby simplifying the configuration on the base station side.

(1) In order to achieve the above object, the present invention provides the following means: That is, the base station of the present invention is a base station applied to a phased array antenna system composed of a central station and a base station having a plurality of antennas connected by an optical transmission line, and includes an optical/electrical signal conversion unit that converts an optical signal received from the central station into an electric signal, a signal division/distribution unit that separates the electric signal into a radio signal and a control signal, a control unit that adjusts the high frequency, amplitude or phase of the radio signal transmitted to a transmission branch based on the separated control signal, a signal combination unit that combines the radio signals output from the transmission branches, and an analog electric/optical signal conversion unit that converts the combined radio signal into an optical signal, and is characterized in that an error between adjacent antennas is calibrated based on the control signal acquired from the central station.

In this way, by using photomixing technology, the amplitude and phase errors measured at the base station can be transmitted as analog values to the central station, making it possible to calibrate the amplitude and phase errors at the central station. This eliminates the need to install equipment for measuring errors at the base station, making it possible to achieve low power consumption, compact size, and low costs.

(2) In addition, in the base station of the present invention, the transmission branch further includes a phase adjustment unit that adjusts the phase of the radio signal output from the signal division distribution unit, and the phase adjustment unit changes the phase of one of the adjacent transmission branches within a range not exceeding 360 degrees from the initial value to correct the phase error. This allows the central station to correct the amplitude error and phase error of the adjacent transmission branch based on the measured information.

(3) In the base station of the present invention, the transmitting branch further includes a phase adjustment unit that adjusts the phase of the radio signal output from the signal division/distribution unit, and the phase adjustment unit changes the phase of one of the adjacent transmitting branches within a range not exceeding 180 degrees from an initial value, and corrects the phase error based on at least one of the maximum and minimum values of the radio signal within the range . In this way, since the phase change need only be 180 degrees, the measurement time can be shortened.

(4) The central station of the present invention is an central station applied to a phased array antenna system composed of a central station and a base station having a plurality of antennas connected by an optical transmission path, and is characterized in that it includes a signal generating unit that generates a radio signal and a measurement signal, a signal multiplexing unit that multiplexes the generated radio signal and a control signal to generate an electrical signal, an electrical/optical signal converting unit that converts the generated electrical signal into an optical signal and outputs it to the base station, an analog optical/electrical signal converting unit that receives an optical signal from the base station and converts it into an electrical signal, a measuring unit that measures the amplitude and phase of each antenna of the base station based on the electrical signal converted from the optical signal, and a control calculation unit that calculates a phase error and an amplitude error from the measurement results and generates the control signal, and is characterized in that the control signal is transmitted to the base station to calibrate the error between adjacent antennas of the base station.

In this way, photomixing technology makes it possible to calibrate the amplitude and phase errors of multiple base stations at a single central station, eliminating the need to install equipment for measuring errors at the base stations, and enabling lower power consumption, smaller size, and lower costs.

(5) In addition, in the central station of the present invention, the control and calculation unit is characterized in that it estimates the transmission line length in the base station from the measurement results. This makes it possible to correct amplitude and phase errors caused by differences in transmission line length.

(6) In the central station of the present invention, the amplitude error and phase error between the transmitting branches in the base station are corrected from the estimated transmission line length. This makes it possible to correct the amplitude and phase errors caused by the difference in the transmission line length even between non-adjacent transmitting branches.

(7) A phased array antenna system according to the present invention is a phased array antenna system including a central station and a base station having a plurality of antennas, the central station including a signal generating unit that generates a radio signal and a measurement signal, a signal multiplexing unit that multiplexes the generated radio signal and a control signal to generate an electric signal, an electric/optical signal converting unit that converts the generated electric signal into an optical signal and outputs it to the base station, an analog optical/electrical signal converting unit that receives an optical signal from the base station and converts it into an electric signal, a measuring unit that measures an amplitude and a phase based on the electric signal converted from the optical signal, and a phase error and an amplitude error based on the measurement result. and a control calculation unit which calculates the signal and generates the control signal, the base station comprises an optical/electrical signal conversion unit which converts the optical signal received from the central station into an electrical signal, a signal dividing and distribution unit which separates the electrical signal into a radio signal and a control signal, a control unit which adjusts the high frequency, amplitude or phase of the radio signal transmitted to the transmitting branch based on the separated control signal, a signal combining unit which combines the radio signals output from the transmitting branches, and an analog electrical/optical signal conversion unit which converts the combined radio signal into an optical signal, and the base station is characterized in that it calibrates an error between adjacent antennas based on the control signal acquired from the central station.

In this way, by using photomixing technology, the amplitude and phase errors measured at the base station can be transmitted as analog values to the central station, making it possible to calibrate the amplitude and phase errors at the central station. This eliminates the need to install equipment for measuring errors at the base station, making it possible to achieve low power consumption, compact size, and low costs.

(8) In the phased array antenna system of the present invention, the control and calculation unit estimates a transmission line length in the base station from the measurement result, and corrects amplitude and phase errors between transmitting branches in the base station from the estimated transmission line length. Amplitude and phase errors caused by differences in transmission line length can also be corrected.

c(9) A phased array antenna system according to the present invention is a phased array antenna system including a central station and a base station having a plurality of antennas, the central station including a signal generating unit that generates a radio signal, a signal multiplexing unit that multiplexes the generated radio signal and a control signal to generate an electric signal, an electric/optical signal converting unit that converts the generated electric signal into an optical signal and outputs it to the base station, an analog optical/electrical signal converting unit that receives an optical signal from the base station and converts it into an electric signal, a measuring unit that outputs a measurement signal and measures the amplitude and phase from the converted electric signal, a control calculation unit that calculates a phase error and an amplitude error from the measurement result and generates the control signal, and and a switching unit that switches the output source between the signal generating unit and the measuring unit depending on the signal to be output to the base station, the base station comprising an optical/electrical signal conversion unit that converts the optical signal received from the central station into an electrical signal, a signal dividing and distributing unit that separates the electrical signal into a radio signal and a control signal, a control unit that adjusts the high frequency, amplitude or phase of the radio signal transmitted to the transmitting branch based on the separated control signal, a signal combining unit that combines the radio signals output from the transmitting branches, and an analog electrical/optical signal conversion unit that converts the combined radio signal into an optical signal, and the base station is characterized in that it calibrates the error between adjacent antennas based on the control signal obtained from the central station.

In this way, by using photomixing technology, the amplitude and phase errors measured at the base station can be transmitted as analog values to the central station, making it possible to calibrate the amplitude and phase errors at the central station. This eliminates the need to install equipment for measuring errors at the base station, enabling low power consumption, compact size, and low costs. In addition, since the measuring unit can be shared among multiple central stations, low power consumption, compact size, and low costs can also be achieved at the central stations.

According to the present invention, by using photomixing technology, it is possible to reduce the power consumption, size, and cost of a phased array antenna system.

1 is a block diagram showing a configuration of a phased array antenna system according to a first embodiment. FIG. 5 is a flowchart showing a procedure (calibration method) for correcting errors related to phase errors and amplitude errors between transmitting branches in the first embodiment. 13A and 13B are diagrams illustrating an output (sine wave) G1 of an optical/electrical conversion unit and an output (sine wave) of an optical/electrical conversion unit. FIG. 13 is a block diagram showing a modified example of a connection in a signal synthesis unit and analog optical/electrical signal conversion. 13 is a flowchart showing a procedure (calibration method) for correcting errors related to phase errors and amplitude errors between transmitting branches in the second embodiment. 13 is a diagram showing an output (sine wave) G3 of the optical/electrical conversion unit. FIG. 13 is a diagram showing the output (sine wave) G4 of the optical/electrical conversion unit. FIG. FIG. 13 is a diagram showing the number of maximum values and the number of minimum values. FIG. 2 is a diagram illustrating an example of an RF circuit. FIG. 13 is a diagram showing a change in impedance. FIG. 13 is a diagram showing a change in impedance. 13 is a flowchart showing a procedure for estimating a transmission line length difference by each transmission line and a signal selection unit in the third embodiment. FIG. 13 is a block diagram showing a configuration of a phased array antenna system according to a modified example of the third embodiment. FIG. 13 is a block diagram showing a configuration of a phased array antenna system according to a modified example of the fourth embodiment. FIG. 13 is a block diagram showing a configuration of a phased array antenna system according to a modification of the fifth embodiment.

That is, the present invention is a phased array antenna system consisting of a central station and a base station connected by an optical transmission path, the central station including a signal generating unit that generates a radio signal and a measurement signal, a signal multiplexing unit that multiplexes the generated radio signal and a control signal to generate an electrical signal, an electrical/optical signal converting unit that converts the generated electrical signal into an optical signal and outputs it to the base station, an analog optical/electrical signal converting unit that receives an optical signal from the base station and converts it into an electrical signal, a measuring unit that measures the amplitude and phase from the converted electrical signal, and a phase error and amplitude error measuring unit that measures the phase error and amplitude error from the measurement results. and a control calculation unit that calculates the control information and generates the control information, and the base station is characterized by having an optical/electrical signal conversion unit that converts the optical signal received from the central station into an electrical signal, a signal division and distribution unit that separates the electrical signal into a radio signal and a control signal, a radio frequency/phase/amplitude control unit that adjusts the radio frequency, amplitude, or phase of the radio signal transmitted to the transmission branch based on the separated control signal, a signal synthesis unit that synthesizes the radio signals output from the transmission branches, and an analog electrical/optical signal conversion unit that converts the synthesized radio signal into an optical signal.

The following describes an embodiment of the present invention in detail with reference to the drawings. To facilitate understanding of the description, the same reference numbers are used for the same components in each drawing, and duplicate descriptions are omitted. In this specification, multiple antenna elements are arranged in an array, and multiple parallel transmission systems that feed power to each antenna element are referred to as "transmission branches."

[First embodiment]
(Configuration of phased array antenna system)
1 is a block diagram showing a configuration of a phased array antenna system according to a first embodiment. In the first embodiment, a configuration example is shown in which a base station 2 has three transmission branches B1, B2, and B3 as a plurality of parallel transmission systems, but the present invention is not limited to this. A configuration having two transmission branches or a configuration having four or more transmission branches may also be used.

The phased array antenna system according to the first embodiment includes a central station 1, an optical transmission path 13, and a base station 2. The central station 1 is connected to the base station 2 via the optical transmission path 13. In the first embodiment, for ease of explanation, one base station is shown as an example, but the central station 1 may be connected to two or more base stations.

The central station 1 has the functions of generating radio signals to be transmitted from the base station, controlling the phased array antenna, storing control information, correcting the control information, and transmitting and receiving signals required for these (transmission and reception of control signals, transmission of radio signals, and photomixing output). That is, the central station 1 comprises a signal generating unit 100, a signal multiplexing unit 111, an electrical/optical signal converting unit 121, an analog optical/electrical signal converting unit 240, a measuring unit 250, a control calculation unit 260, and a control information storage unit 270. Next, the details of each element constituting the central station 1 will be described.

The signal generating unit 100 has a function to generate a radio signal to be radiated into space from the base station 2 described later, and a function to generate a signal required to calibrate the directivity pattern radiated from the phased array antenna (antenna units 211 to 213) described later. The signal generating unit 100, which serves as a signal source, can be realized by, for example, a device equipped with a DAC (Digital to Analog Converter) and a function to control it (FPGA (Field Programmable Gate Array), DSP (Demand Side Platform), embedded system such as a computer). The signal generating unit 100 may also have a receiving function. The signal generating unit 100 may also have a function to switch the radio signal ON/OFF for each of the transmission branches B1 to B3 described later, and a function to generate radio signals with different phases and amplitudes for each of the transmission branches B1 to B3.

The signal multiplexing unit 111 has a function of multiplexing the radio signal generated by the signal generating unit 100 and the control signal generated by the control and calculation unit 260 described below. The signal multiplexing unit 111 can be realized, for example, by a configuration that combines analog methods such as an RF (Radio Frequency) power combiner.

The electrical/optical signal conversion unit 121 has the function of converting the electrical signal generated by the signal multiplexing unit 111 into an optical signal that can be transmitted through the optical transmission path 13 described below.

The analog optical/electrical signal conversion unit 240 has a function of converting optical signals generated by the analog electrical/optical signal conversion units 231 and 232 described below into electrical signals. The analog optical/electrical signal conversion unit 240 can be realized, for example, by a photodiode.

The measurement unit 250 has a function of measuring the electrical signal converted by the analog optical/electrical signal conversion unit 240 and transmitting the measurement result to the control calculation unit 260. The measurement unit 250 can be realized by, for example, but is not limited to, a DAC, an oscilloscope, an FPGA, etc. Any other device that can convert analog values such as voltage into a format that can be read by a personal computer may be used. Note that if the signal generation unit 100 has a receiving function, the receiving function of the signal generation unit 100 may be used.

The control calculation unit 260 has functions such as controlling the signal generating unit 100, linking the signal generating unit 100 with the measurement unit 250 to calculate the phase error and amplitude error between each of the transmission branches B1 to B3 described later, outputting the calculation results to the control information storage unit 270 described later, and generating a signal for controlling the radio frequency/phase/amplitude control unit 160 described later based on information from the control information storage unit 270. The control calculation unit 260 can be realized, for example, by an electronic computer or an FPGA.

The control information storage unit 270 stores the control information of the radio frequency/phase/amplitude control unit 160 described later. In addition, when the control calculation unit 260 newly calculates the amplitude error and phase error, it updates the control information to one in which the errors have been corrected. The control information storage unit 270 may be connected to the radio frequency/phase/amplitude control unit 160 described later.

The optical transmission path 13 has the function of transmitting, amplifying, and branching an optical signal, and includes optical transmission paths 131 and 132. The optical transmission paths 131 and 132 have the function of transmitting, amplifying, and branching an optical signal converted by the electrical/optical signal conversion unit 121 or the analog electrical/optical signal conversion units 231 and 232 described later. The optical transmission paths 131 and 132 are composed of, for example, optical fibers and splitters. The optical transmission paths 131 and 132 may also be integrated by using multiplexing techniques such as wavelength division multiplexing and time division multiplexing. In FIG. 1, the optical transmission paths 131 and 132 are configured to be divided into two optical fibers, but are not limited to this. For example, a single optical fiber may be used using WDM (Wavelength Division Multiplexing) or the like.

The base station 2 has the functions of feeding radio signals to each of the transmitting branches B1 to B3 that make up the phased array antenna, controlling the directivity of the phased array antenna, and detecting errors in each of the transmitting branches B1 to B3. The base station 2 comprises an optical/electrical signal conversion unit 141, a signal division and distribution unit 151, the transmitting branches B1 to B3, a high frequency/phase/amplitude control unit 160, signal synthesis units 221 and 222, and analog electrical/optical signal conversion units 231 and 232. Next, the elements that make up the base station 2 will be described in detail.

The optical/electrical signal conversion unit 141 has a function of converting the optical signal generated by the electrical/optical signal conversion unit 121 of the aggregation station 1 into an electrical signal. The optical/electrical signal conversion unit 141 can be realized, for example, by a photodiode.

The signal division distribution unit 151 has a function of separating an electrical signal into a radio signal generated by the signal generation unit 100 and a control signal generated by the control calculation unit 260, and a function of distributing and feeding the separated radio signals to the transmission branches B1 to B3 described below. Furthermore, the signal division distribution unit 151 does not necessarily need to feed the same radio signal to each of the transmission branches B1 to B3, and may have a function of feeding different radio signals to each transmission branch, for example, feeding the same radio signal to the transmission branches B1 and B2 and feeding a different radio signal to the transmission branch B3.

Furthermore, rather than simply branching the same signal, it may have a function of allocating different signals that have been multiplexed by wavelength multiplexing or frequency multiplexing to appropriate transmission branches. The signal division/distribution unit 151 may also have a function of switching the power supply ON/OFF for each of the transmission branches B1 to B3. The signal division/distribution unit 151 can be realized, for example, by an analog method such as an RF power distributor, or a digital method such as a demultiplexer, or a configuration that combines analog and digital methods.

Based on the control signal generated by the control calculation unit 260, the high frequency/phase/amplitude control unit 160 generates signals to control the amplitude adjustment units 171-173, phase adjustment units 181-183, and high frequency adjustment units 191-193 of the transmission branches B1-B3 (described below). This controls the directivity patterns radiated from the antenna units 211-213. The high frequency/phase/amplitude control unit 160 can be realized by a device equipped with a DAC and a function to control it (an embedded system such as an FPGA, DSP, or electronic computer).

By providing the control information storage unit 270 to the radio frequency/phase/amplitude control unit 160, the distance over which control signals are exchanged is shortened, and this is expected to result in faster switching of directivity patterns. In this way, the control information storage unit 270 may be provided in the radio frequency/phase/amplitude control unit 160 instead of the control calculation unit 260. Alternatively, the control information storage unit 270 may be provided in both the control calculation unit 260 and the radio frequency/phase/amplitude control unit 160.

The transmitting branches B1 to B3 have the function of arranging multiple antenna elements in an array, feeding a radio signal to each antenna element, and controlling the phase and amplitude of the radio signal. Each of the transmitting branches B1 to B3 has the same configuration. The transmitting branch B1 comprises an amplitude adjustment unit 171, a phase adjustment unit 181, a high frequency adjustment unit 191, a signal distribution unit 201, and an antenna unit 211. The transmitting branch B2 comprises an amplitude adjustment unit 172, a phase adjustment unit 182, a high frequency adjustment unit 192, a signal distribution unit 202, and an antenna unit 212. The transmitting branch B3 comprises an amplitude adjustment unit 173, a phase adjustment unit 183, a high frequency adjustment unit 193, a signal distribution unit 203, and an antenna unit 213.

The antenna units 211 to 213 radiate radio signals into space, and an array antenna is formed by arranging multiple antennas. In the case of a phased array antenna, the directivity pattern changes depending on the directivity of each antenna, the spacing between each antenna, and the amplitude and phase of the radio signal.

The amplitude adjustment units 171 to 173 have the function of adjusting the amplitude of the radio signal in each of the transmission branches B1 to B3. The amplitude adjustment units 171 to 173 can be realized by circuits such as variable gain amplifiers or variable attenuators. The amplitude adjustment of the radio signal does not necessarily have to be performed in the same frequency band as the transmission frequency, and when frequency conversion is performed, it may be performed for either the baseband band or the intermediate frequency band. When a mixer or the like is used for frequency conversion, it may be performed for the output of a local oscillator. In other words, it is not limited to the arrangement shown in FIG. 1, and may be provided inside the high-frequency adjustment units 191 to 193 described later, or may be provided between the signal distribution units 201 to 203 and the high-frequency adjustment units 191 to 193, or may be provided between the high-frequency adjustment units 191 to 193 and the phase adjustment units 181 to 183.

In addition to these methods, since there is a proportional relationship between the optical power input to the optical/electrical signal conversion unit and the RF power output, the amplitude may be adjusted by inserting an erbium doped fiber amplifier (EDFA) or an optical attenuator into the optical transmission path 131. The amplitude may also be adjusted between the signal generating unit 100 and the signal multiplexing unit 111. A signal with an adjusted amplitude may also be output directly from the signal generating unit 100. When a signal with a changed amplitude is output from the signal generating unit 100, there is no particular problem even if the amplitude adjustment units 171 to 173 are not provided. Note that adjustment between the signal multiplexing unit 111 and the electrical/optical signal conversion unit 121 changes the amplitude adjustment of the control signal, which is not preferable.

The phase adjustment units 181 to 183 have the function of adjusting the phase of the radio signal in each of the transmission branches B1 to B3. The phase adjustment units 181 to 183 can be realized by circuits such as a phase shifter and a delay unit, for example. Note that the phase adjustment of the radio signal does not necessarily have to be performed in the same frequency band as the transmission frequency, and when frequency conversion is performed, it may be performed in either the baseband band or the intermediate frequency band.

Furthermore, when a mixer or the like is used for frequency conversion, it may be performed on the output of a local oscillator. In other words, like the amplitude adjustment units 171-173, the phase adjustment units 181-183 may be provided inside the high frequency adjustment units 191-193 described below, or may be provided between the signal distribution units 201-203 and the high frequency adjustment units 191-193, or may be provided between the high frequency adjustment units 191-193 and the phase adjustment units 181-183.

In addition to these methods, since there is a proportional relationship between the phase of the light input to the optical/electrical signal conversion unit and the phase of the RF power output, the phase may be adjusted by inserting an optical phase shifter or the like into the optical transmission line 131. Also, as proposed as a method of using analog RoF (Radio over Fiber), the phase may be adjusted by assigning light of different wavelengths to each of the transmission branches B1 to B3. Also, the adjustment may be made between the signal generating unit 100 and the signal multiplexing unit 111. Also, a signal with the phase adjusted may be output directly from the signal generating unit 100. When a signal with a changed phase is output from the signal generating unit 100, there is no particular problem even if the phase adjustment units 181 to 183 are not provided. Note that adjustment between the signal multiplexing unit 111 and the electrical/optical signal conversion unit 121 is not preferable because it also changes the phase of the control signal.

The arrangement order of the high frequency adjustment units 191 to 193, the phase adjustment units 181 to 183, and the amplitude adjustment units 171 to 173 is not limited to the order shown in the figure, and they may be arranged in any order.

The signal distribution units 201-203 are provided near the antenna ends in front of the antenna units 211-213, and have the function of extracting a portion of the radio signal fed to the signal distribution units 201-203. The signal distribution units 201-203 can be realized, for example, by distributed coupling lines that couple electric field or magnetic field to the transmission path of the radio signal, or by a passive circuit such as a capacitor with a relatively small capacity, or an unequal distributor. Furthermore, if it is not necessary to evaluate the radio signal in a state in which it is emitted into space from the antenna units 211-213, the radio signal may be extracted using, for example, an RF switch. Furthermore, if the environment allows direct access to the base station function, the radio signal may be extracted using, for example, a coaxial cable.

The signal synthesis unit 221 has the function of synthesizing the radio signals input from the signal distribution units 201 and 202, and is arranged in a position where the transmission line connecting the signal distribution unit 201 and the signal synthesis unit 221 and the transmission line connecting the signal distribution unit 202 and the signal synthesis unit 221 are the same length.

The signal synthesis unit 222 has the function of synthesizing the radio signals input from the signal distribution units 202 and 203, and is arranged in a position where the transmission line connecting the signal distribution unit 202 and the signal synthesis unit 222 and the transmission line connecting the signal distribution unit 203 and the signal synthesis unit 222 are the same length.

Signal combiners 221 and 222 can be realized by using an RF power combiner, such as a Wilkinson power combiner, that can ensure separation between signal distribution units 201 and 202, or between signal distribution units 202 and 203.

The analog electric/optical signal conversion units 231 and 232 have a function of converting the combined radio signals input from the signal combining units 221 and 222 from electric signals to optical signals without digital conversion. The analog electric/optical signal conversion units 231 and 232 can be realized by using a laser equipped with a modulator such as a Directly Modulated Laser (DML) or an Electro-absorption Modulator Laser (EML), for example.

If the analog electrical/optical signal converters 231 and 232 use the same wavelength at the same time, noise will occur when the optical signal is converted to an electrical signal by the analog optical/electrical signal converter 240 of the central station 1. For this reason, when measuring any two adjacent transmission branches, it is advisable to output only the analog electrical/optical signal converter connected to the signal synthesis unit provided between the transmission branches to be measured. To do this, the power supply of the analog electrical/optical signal converters 231 and 232 (not shown) may be turned on and off to prevent simultaneous output. Alternatively, the analog electrical/optical signal converters 231 and 232 may be switched between optical switches (not shown) provided in the optical transmission path 132 and the analog electrical/optical signal converters 231 and 232 to prevent simultaneous output. Alternatively, lasers of different wavelengths may be used in the analog electrical/optical signal converters 231 and 232.

By using the signal synthesis units 221, 222 and analog electrical/optical signal conversion units 231, 232 of the base station 2, and the analog optical/electrical signal conversion unit 240 of the central station 1, the central station 1 can detect the amplitude and phase difference of adjacent transmission branches B1, B2, or B2, B3. This detection method is explained using mathematical expressions. For simplicity, the case of only transmission branches B1 and B2 is considered. That is, the explanation focuses on the signal synthesis unit 221, analog electrical/optical signal conversion unit 231, and analog optical/electrical signal conversion unit 240. For simplicity, the case of transmitting radio signals as sine waves with different phases and amplitudes in transmission branches B1 and B2 is considered.

First, the radio signal of the transmission branch B1 is distributed by the signal distribution unit 201 and input to the analog electrical/optical signal conversion unit 231 via the signal synthesis unit 221, and the analog electrical/optical signal conversion unit 231 outputs the electric field E1 expressed by equation (1).

ω=2πf
Here, A1 is an amplitude value proportional to the amplitude of the radio signal of the transmitting branch B1, j is an imaginary number, f1 is the frequency of the radio signal of the transmitting branch B1, φ1 is a phase value proportional to the phase of the radio signal of the transmitting branch B1, and ω is an angular frequency.

Similarly, when the radio signal of the transmission branch B2 is distributed by the signal distribution unit 202 and input to the analog electrical/optical signal conversion unit 231 via the signal synthesis unit 221, the analog electrical/optical signal conversion unit 231 outputs an electric field E2 expressed by equation (2).

Here, A2 is an amplitude value proportional to the amplitude of the radio signal of the transmitting branch B2, j is an imaginary number, f2 is the frequency of the radio signal of the transmitting branch B2, and φ2 is a phase value proportional to the phase of the radio signal of the transmitting branch B2. Therefore, when the transmitting branches B1 and B2 are input simultaneously, a signal obtained by adding together the formulas (1) and (2) is output.

When an electric field is input to the analog optical/electrical signal conversion unit 240, a component proportional to the square of the absolute value of the electric field is output as a current. In other words, the analog optical/electrical signal conversion unit 240 outputs the current I of equation (3).

If the frequencies of the radio signals of the transmitting branch B1 and the transmitting branch B2 are equal, then f1 = f2. In this case, calculating equation (3) gives the DC component shown in equation (4).

Since the phase value φ1 and the phase value φ2 are proportional to the phase components of the transmitting branch B1 and the transmitting branch B2, the phase difference between the transmitting branch B1 and the transmitting branch B2 can be obtained from the formula (4). In addition, since the amplitudes A1 and A2 can be grasped by transmitting only one of the transmitting branch B1 or the transmitting branch B2, each amplitude of the transmitting branch B1 and the transmitting branch B2 can be obtained.

As described above, by using the signal synthesis unit 221, the analog electrical/optical signal conversion unit 231, and the analog optical/electrical signal conversion unit 240, the aggregate station 1 can detect the amplitude and phase difference of adjacent transmission branches B1 and B2. Note that this explanation also applies to adjacent transmission branches B2 and B3, and also applies when there are four or more transmission branches.

In addition, when a radio signal is expanded into a Fourier series, it becomes the sum of multiple sine waves with different frequencies, so the idea behind this explanation also applies to general radio signals. However, when multiple sine waves with different frequencies are multiplied, not only DC components but also AC components are generated, so when measuring the phase error, it is necessary to combine a circuit that selects only DC components, such as a low-pass filter, between the analog optical/electrical signal conversion unit 240 and the measurement unit 250. In addition, if a low-pass filter is directly inserted between the analog optical/electrical signal conversion unit 240 and the measurement unit 250, it will not be possible to measure the amplitude using the method described above, so it is necessary to provide a switch that switches between passing through the low-pass filter and not passing through it.

The frequencies calculated using f1 and f2 in equations (1) and (2) are significantly higher than the cutoff frequency of a low-pass filter designed to extract only the DC component, so if the signal is directly input without bypassing the low-pass filter, no output will be obtained. Therefore, by utilizing this, it is possible to provide the aggregation station with the ability to detect amplitude and phase errors.

(Error correction method)
2 is a flowchart showing a procedure (calibration method) for correcting errors related to phase errors and amplitude errors between each transmitting branch in the first embodiment. For ease of explanation, the case of adjacent transmitting branches B1 and B2 will be described. For ease of explanation, the case will be considered in which the wireless signals transmitted are sine waves having different phases and amplitudes in the transmitting branches B1 and B2. In other words, the same conditions as those in the above-mentioned formulas (1) to (4) will be considered.

[1] Step for correcting the amplitude error of the transmitting branch B1 (T11)
First, the procedure (T11) for correcting the amplitude error of the transmitting branch B1 will be described. First, the transmitting branch B2 does not output, and only the transmitting branch B1 outputs a radio signal (T111). The control of outputting and stopping the radio signal may be performed by the high frequency adjustment units 191 and 192 as described above, by the signal division and distribution unit 151, or by the signal generation unit 100.

Next, the amplitude of the transmission branch B1 is measured (T112). To measure the amplitude, a wireless signal (sine wave) is generated from the signal generating unit 100, the wireless signal distributed by the signal distributing unit 201 is sent to the analog electrical/optical signal converting unit 231 via the signal synthesizing unit 221, and the electrical signal converted by the analog optical/electrical signal converting unit 240 is measured by the measuring unit 250. At this time, the wireless signal output from the signal generating unit 100 for use in the measurement is recorded in the control and calculation unit 260.

Next, the error with respect to the estimated amplitude of the transmitting branch B1 is corrected (T113). To correct the error with respect to the estimated amplitude, first, the wireless signal distributed by the signal distribution unit 201 is sent to the analog electrical/optical signal conversion unit 231 via the signal synthesis unit 221, and converted into an electrical signal by the analog optical/electrical signal conversion unit 240, and an amplitude estimate is calculated when the electrical signal is measured by the measurement unit 250, based on the information in the control information storage unit 270 and the wireless signal previously recorded in the control calculation unit 260. Note that the amplitude estimation (T113) may be performed before step T111, or may be performed between steps T111 and T112.

Next, the amplitude previously measured by the measuring unit 250 is compared with the amplitude previously estimated. At this time, if there is an error between the estimated amplitude and the measured amplitude, it is necessary to adjust the amplitude using the amplitude adjustment unit 171 so that the error is eliminated. In other words, the control information of the amplitude adjustment unit 171 stored in the control information storage unit 270 is updated. With the above, the amplitude error correction of the transmitting branch B1 is completed.

[2] Step for correcting the amplitude error of the transmitting branch B2 (T12)
Next, a procedure (T12) for correcting the amplitude error of the transmitting branch B2 will be described. First, as shown in procedure T121, the transmitting branch B1 does not output, and only the transmitting branch B2 outputs a radio signal. The control of outputting and stopping the radio signal may be performed by the high frequency adjustment units 191 and 192 as described above, by the signal division/distribution unit 151, or by the signal generation unit 100. In addition, when the optical transmission line 131 is assigned to each transmitting branch, the control may be performed by the optical transmission line 131.

Next, the amplitude of the transmission branch B2 is measured (T122). To measure the amplitude, a wireless signal (sine wave) is generated from the signal generating unit 100, the wireless signal distributed by the signal distributing unit 202 is sent to the analog electrical/optical signal converting unit 231 via the signal synthesizing unit 221, and the electrical signal converted by the analog optical/electrical signal converting unit 240 is measured by the measuring unit 250. At this time, the wireless signal output from the signal generating unit 100 for use in the measurement is recorded in the control and calculation unit 260.

Next, the error with respect to the estimated amplitude of the transmitting branch B2 is corrected (T123). To correct the error with respect to the estimated amplitude, first, the wireless signal distributed by the signal distribution unit 202 is sent to the analog electrical/optical signal conversion unit 231 via the signal synthesis unit 221, and converted into an electrical signal by the analog optical/electrical signal conversion unit 240, and an amplitude estimate is calculated when the electrical signal is measured by the measurement unit 250, based on the information in the control information storage unit 270 and the wireless signal previously recorded in the control calculation unit 260. Note that the amplitude estimation (T123) may be performed before step T121, or may be performed between steps T121 and T122. It may also be performed before step T11.

Next, the amplitude previously measured by the measuring unit 250 is compared with the amplitude previously estimated. At this time, if there is an error between the estimated amplitude and the measured amplitude, it is necessary to adjust the amplitude using the amplitude adjustment unit 172 so that the error is eliminated. In other words, the control information of the amplitude adjustment unit 172 stored in the control information storage unit 270 is updated. With the above, the amplitude error correction of the transmission branch B2 is completed.

The order of steps T11 and T12 may be any. If step T12 is performed first, the amplitude estimation of step T11 may be performed before step T12, in addition to the timing described above.

[3] Procedure for determining the phase error between adjacent transmitting branches B1 and B2 (T2)
Finally, the procedure (T2) for calculating the phase error of the adjacent transmitting branches B1 and B2 will be described. First, the control calculation unit 260 adjusts the phase adjustment units 181 and 182 based on the information in the control information storage unit 270, and sets the phases φ1 and φ2 of the transmitting branches B1 and B2 to initial values (e.g., 0 degrees) (T21).

Next, the transmitting branches B1 and B2 are output simultaneously (T22). At this time, the analog optical/electrical signal conversion unit outputs a DC component as shown in equation (4), so the output is measured by the measurement unit 250 (T23), and the measured values of the phase φ1 and amplitude at that time are recorded by the control calculation unit 260 (T24).

Next, of the adjacent transmitting branches B1 and B2, the phase of which has already been corrected for phase error is fixed, and the phase of the other is changed. However, if the phase of neither transmitting branch has yet been corrected, any one of the phases is fixed. In this case, for example, phase φ2 is fixed. At this time, it can be seen from equation (4) that if phase φ1 is swept within a range not exceeding 360 degrees from the initial value, an output having two maximum values is obtained. To obtain this characteristic, it is determined whether phase φ1 exceeds 360 degrees from the initial value (T25).

If the determination result shows that the phase φ1 does not exceed 360 degrees from the initial value, the phase adjustment unit 181 of the transmission branch B1 is adjusted to advance the phase φ1 by an arbitrary angle Δφ (for example, 1 degree) (T26). Note that the phase may also be delayed.

Figure 3 shows the output (sine wave) of the optical/electrical conversion unit. By repeating the above-mentioned steps T23 to T26, a sine wave-shaped measurement result G1 as shown in Figure 3 is obtained, and the phase φ1max at which the amplitude is maximum can be determined from the measurement result G1 (T27).

On the other hand, by performing calculations in the control calculation unit 260 based on the information in the control information storage unit 270, it is possible to estimate the measurement value obtained by the measurement unit 250 when the phase φ1 is changed relative to the phase φ2, and thus an estimated value G2 is obtained. Since it is also possible to infer φ1max' at which the measurement result is expected to be maximum from the estimated value G2, it is possible to determine the error with the control information recorded in the control information storage unit 270 by comparing it with the phase φ1max described above.

Next, the control information recorded in the control information storage unit 270 is corrected based on the above-mentioned error judgment result (T28). Note that here, the correction is performed based on the phase when the amplitude is maximum, but the correction may be performed based on the phase φ1min when the amplitude is minimum. In addition, in order to reduce the error, the error may be estimated at both the phase φ1max when the amplitude is maximum and the phase φ1min when the amplitude is minimum, and the correction may be performed by averaging the two. Similarly, when a sine wave is changed in a range of less than 360 degrees, the amplitude exceeds the minimum value and is less than the maximum value twice (for example, in a sine wave with a maximum value of 1 volt and a minimum value of 0 volt, 0.5 volts appears twice in the range from 0 degrees to less than 360 degrees), and the error may be estimated based on the two phases and the correction may be performed by averaging the two. As a result, the correction of the phase error of the adjacent transmission branches B1 and B2 is completed.

In this way, it is possible to correct the amplitude error and phase error of adjacent transmitting branches B1 and B2 based on the information measured by central station 1. As explained in equations (1) to (4), this explanation also applies to adjacent transmitting branches B2 and B3, and also applies when there are four or more transmitting branches. In addition, because a radio signal is expanded into a Fourier series and becomes the addition of multiple sine waves with different frequencies, the concept of this explanation also applies to general radio signals.

[Modification of the first embodiment]
4 is a block diagram showing a modified example of the connection in the signal combining unit and the analog optical/electrical signal conversion. In the phased array antenna system according to the first embodiment, the path length after the signals between the transmission branches are combined in the signal combining units 221 and 222 can be ignored. This can be explained using equation (4).

A phase value φ1 proportional to the phase of the radio signal of the transmitting branch B1 and a phase value φ2 proportional to the phase of the radio signal of the transmitting branch B2 are expressed as follows:
If we define φ1 = phase of branch B1 + phase that changes on the transmission line after combination, and φ2 = phase of branch B2 + phase that changes on the transmission line after combination, then in "φ1 - φ2" in equation (4), the phases that change on the transmission line after combination cancel each other out.

For this reason, as shown in Figure 4, the RF transmission path may be extended from the signal synthesis units 221 and 222, and the input symmetrical signals may be switched using an RF switch or the like, so that the analog electrical/optical signal conversion unit may be shared. However, as the frequency increases, the loss due to the transmission path increases, and there is a possibility that sufficient output may not be obtained from the analog optical/electrical signal conversion unit 240. For this reason, if sharing is to be used, it is better to use a frequency below 6 GHz (up to 5G Sub6), or to make the transmission line as short as possible when using 6 GHz or higher (for example, millimeter waves).

Converting electrical signals into optical signals significantly reduces losses along the transmission path. For this reason, from the standpoint of miniaturization and cost reduction, it is acceptable to share the analog electrical/optical signal conversion section, but from the standpoint of power consumption (power loss), it is better to provide the analog electrical/optical signal conversion section immediately after the signal synthesis section, as shown in the first embodiment.

In addition, in the first embodiment and this embodiment, if a separate analog electrical/optical signal conversion unit is provided to transmit the radio signal received by the antenna from the base station 2 to the central station 1, it may be used instead of the analog electrical/optical signal conversion units 231 and 232.

Furthermore, in the first and present embodiments, in the case of an antenna that converts a radio signal into an optical signal, such as a photonic antenna, an analog electrical/optical signal conversion unit may be provided for transmitting an upstream signal (a radio signal sent from the base station to the central station). In that case, a switch or the like may be provided on the circuit, and the output of the signal synthesis unit may be input to the analog electrical/optical signal conversion unit for the upstream signal.

Second Embodiment
FIG. 5 is a flowchart showing the procedure (calibration method) of error correction regarding phase error and amplitude error between each transmission branch in the second embodiment. In the second embodiment, an example of a modified calibration procedure is shown. The same or similar reference numerals are used for configurations that perform the same or similar operations as in the first embodiment, and description thereof is omitted. In addition, for simplicity of description, the case of adjacent transmission branches B1 and B2 will be described as in the first embodiment. In addition, for simplicity of description, a case will be considered in which the wireless signal transmits a sine wave having different phases and amplitudes in the transmission branches B1 and B2. That is, a case will be considered in which the conditions are the same as those of the above-mentioned formulas (1) to (4). The procedure of error correction regarding phase error and amplitude error between each transmission branch in the second embodiment will be described with reference to the flowchart of FIG. 5.

As in the first embodiment (T11, T12, T21 to T24), the phase of the adjacent transmitting branches B1 and B2, which has already been corrected for phase error, is fixed, and the phase of the other is changed. However, if the phase of neither transmitting branch has yet been corrected, any one of the phases is fixed. In this case, for example, the phase φ2 is fixed. At this time, it can be seen from equation (4) that if the phase φ1 is swept within a range not exceeding 180 degrees from the initial value, an output having either the phase φ1max at which the amplitude is maximized, or the phase φ1min at which the amplitude is minimized, as described in the first embodiment, can be obtained. To obtain this characteristic, it is determined whether the phase φ1 is not exceeding 180 degrees from the initial value (T25b).

If the result of the determination is that the phase φ1 does not exceed 180 degrees from the initial value, the phase adjustment unit 181 of the transmission branch B1 is adjusted to advance the phase φ1 by an arbitrary angle Δφ (for example, 1 degree) (T26). Note that the phase may also be delayed.

Figure 6 shows the output (sine wave) G3 of the optical/electrical conversion unit. Figure 7 shows the output (sine wave) G4 of the optical/electrical conversion unit. By repeating the above-mentioned steps T23, 24, 25b, and 26, the sine wave-shaped measurement result G3 or G4 as shown in Figure 6 or Figure 7 is obtained, and it is determined whether the measurement result G3 contains a maximum value (T27b).

The method of determination is that, for the amplitudes B1 to B3 for any consecutive phases φ1a-Δφ, φ1a, and φ1a+Δφ in the measurement results, if any satisfy B1<B2 and B2>B3, then it contains a maximum value, and if any satisfy B1>B2 and B2<B3, then it contains a minimum value. Note that when the amplitude for φ1a+2·Δφ is B4, if the interval between Δφ is not small enough, or if two or more consecutive maximum amplitudes are obtained, such as B2=B3 and B1<B2 and B3>B4 due to the performance of the measurement unit 250, then the average of the two or more consecutive amplitudes is taken as the maximum value, and the result is deemed to include the maximum value. Similarly, if two or more consecutive minimum amplitudes are obtained, such as B2=B3 and B1>B2 and B3<B4, then the average of the two or more consecutive amplitudes is taken as the minimum value, and the result is deemed to include the minimum value. If only a maximum value or a minimum value is included, the result is set as the maximum value or minimum value, and the phase at that time is set as φ1max or φ1min.

Figure 8 is a diagram showing the number of maximum values and the number of minimum values. When both maximum values and minimum values exist as shown in Figure 8, if the number of maximum values > the number of minimum values, the maximum values are compared, and the larger value is taken as the maximum value, and the phase at this time is taken as φ1max. Alternatively, if the number of maximum values < the number of minimum values, the minimum values are compared, and the smaller value is taken as the minimum value, and the phase at this time is taken as φ1min. As a result, if φ1max is included, it is considered that the measurement result G3 contains the maximum value, and if φ1min is included, it is considered that the measurement result G3 does not contain the maximum value. Note that if the number of maximum values and minimum values are the same, it is advisable to perform phase correction according to the first embodiment.

On the other hand, by performing calculations in the control calculation unit 260 based on the information in the control information storage unit 270, it is possible to estimate the measurement value obtained by the measurement unit 250 when the phase φ1 is changed relative to the phase φ2, and thus an estimated value G2 is obtained. From the estimated value G2, it is possible to infer φ1max' at which the measurement result is expected to be maximum, and φ1min' at which the measurement result is expected to be maximum, and therefore by comparing with the aforementioned phase φ1max or phase φ1min, it is possible to determine the error with the control information recorded in the control information storage unit 270.

Next, the control information recorded in the control information storage unit 270 is corrected based on the error determination result described above (T28b1, T28b2). This completes the correction of the phase error of the adjacent transmission branches B1 and B2.

In this way, the same effect as in the first embodiment can be achieved with half the sweep steps compared to the first embodiment in which the phase φ1 is swept 360 degrees. Also, as in the first embodiment, this explanation also applies to adjacent transmission branches B2 and B3, and also applies when there are four or more transmission branches. Furthermore, because a wireless signal is expanded into a Fourier series and becomes the sum of multiple sine waves with different frequencies, the concept of this explanation also applies to general wireless signals.

[Third embodiment]
In the third embodiment, a correction method is shown for the case where the path length difference between the signal distribution unit and the signal synthesis unit, which was ignored in the first and second embodiments, cannot be ignored. The same or similar reference numerals are used for configurations that perform the same or similar operations as in the first and second embodiments, and the description is omitted.

In the first embodiment, the signal combiner units 221 and 222 are arranged so that the transmission line lengths connecting the two adjacent signal distributor units and the signal combiner unit are the same, making it possible to ignore the phase difference caused by the difference in transmission line length. However, if a difference in path length occurs due to manufacturing errors or external factors, an error occurs in the amplitude output from the analog optical/electrical signal converter unit 240.

This will be explained using mathematical expressions. To simplify the explanation, the case will be considered where only the transmitting branches B1 and B2 are used. That is, the explanation will focus on the signal distribution units 201 and 202, the signal synthesis unit 221, the analog electrical/optical signal conversion unit 231, and the analog optical/electrical signal conversion unit 240. To simplify the explanation, the case will be considered where the wireless signals transmitted by the transmitting branches B1 and B2 are sine waves with different phases and amplitudes. First, when the wireless signal of the transmitting branch B1 is distributed by the signal distribution unit 201 and input to the analog electrical/optical signal conversion unit 231 via the signal synthesis unit 221, the analog electrical/optical signal conversion unit 231 outputs an electric field E1 expressed by equation (5).

Here, D1 is a phase delay caused by the transmission line length between the signal distributor 201 and the signal combiner 221, and other parameters are as explained in formula (1). Similarly, when the radio signal of the transmission branch B2 is distributed by the signal distributor 202 and input to the analog electric/optical signal converter 231 via the signal combiner 221, the analog electric/optical signal converter 231 outputs an electric field E2 expressed by formula (6).

Here, D2 is a phase delay caused by the transmission line length between the signal distributor 202 and the signal combiner 221, and other parameters are as explained in formula (2). Therefore, when the transmission branches B1 and B2 are input simultaneously, a signal obtained by adding formulas (5) and (6) is output.

When an electric field is input to the analog optical/electrical signal conversion unit 240, a current I of formula (3) is output. If the frequencies of the radio signals of the transmitting branch B1 and the transmitting branch B2 are equal, then f1 = f2. In this case, calculating formula (3) gives the DC component shown in formula (7).

Compared to equation (4), cos contains phase delay components D1 and D2, so the phase difference between transmitting branch B1 and transmitting branch B2 shown in equation (4) cannot be measured accurately. In addition, when the loss of the substrate is large or when transmitting a high frequency, the amplitude difference caused by attenuation during propagation along the transmission line may not be negligible. In other words, if correction is performed according to the procedure shown in the first and second embodiments, the amplitude error of each transmitting branch may not be corrected accurately. For this reason, it is necessary to estimate the transmission line length between the signal distribution unit 201 and the signal synthesis unit 221 and the transmission line length between the signal distribution unit 202 and the signal synthesis unit 221. Therefore, a method for estimating each line length will be described below.

In general, a TDR (Time Domain Reflectometry) analysis can be performed by performing an FFT (Fast Fourier Transform) on the reflection coefficient of any RF circuit, and the transmission line length of the RF circuit, etc. can be estimated from the results.

On the other hand, in the configuration shown in the first embodiment, an electrical/optical signal converter 121 and an optical/electrical signal converter 141 are inserted between the central station 1 and the base station 2, and these are not bidirectional. For this reason, the reflection coefficient cannot be measured, and the length of each transmission line in the base station 2 cannot be obtained using the central station 1. Therefore, a wireless signal is transmitted from the signal generator 100, which is then returned by the signal distributor 201. The transmission coefficient measured by the measuring unit 250 is then subjected to FFT to estimate the length of each transmission line.

Figure 9 is a diagram showing an example of an RF circuit. The RF circuit in Figure 9 includes input ports P1 to P4, microstrip lines L1 and L2, and a directional coupler C1. A signal source, measuring instrument, or load with an impedance of 50 ohms is connected to the input ports P1 to P4, respectively. The line widths of the microstrip lines L1 and L2 and the directional coupler C1 are designed so that the impedance is 50 ohms. The spacing between the lines of the microstrip line C1 is 1/40 times the wavelength of the wireless signal to be transmitted. The line length of the microstrip lines L1 and L2 is twice the wavelength of the wireless signal to be transmitted. Note that these parameters are merely examples, and it is not necessary to use the same values when actually implementing. In this case, when the transmission coefficients for input ports 1 to 4 are subjected to FFT, the characteristics shown in Figure 10 are obtained.

Figures 10 and 11 are diagrams showing changes in impedance. As shown in Figure 10, when a device other than a transmission line is inserted in between the transmission line, a discontinuity, which is a characteristic variation, appears in the results after FFT. For example, when a directional coupler is inserted, a peak like that shown in Figure 10 appears.

Next, when the length L of the microstrip line L2 is changed to the same length as the wavelength of the wireless signal to be transmitted and the transmission coefficients for input ports 1 to 4 are subjected to FFT, the characteristics shown in Figure 11 are obtained. As shown in Figure 11, compared to Figure 10, when the transmission line length is changed, the position of the peak also changes.

By using this, the transmission line length can be estimated by interpreting the results of FFT of the transmission coefficient. However, in reality, various devices are included between the signal generating unit 100 and the measuring unit 250, so the FFT results become even more complicated. Therefore, when estimating the transmission line length from the transmission coefficient, the transmission coefficient of each device is subjected to FFT in advance to grasp the characteristics of each device, and the transmission line length is estimated by calculation by reading the characteristics from the graph, or the devices between the signal generating unit 100 and the measuring unit 250 are reproduced in advance on a circuit simulation software, and the transmission line length is estimated by comparing the measured FFT results with the FFT results obtained by circuit simulation, or machine learning is used to estimate the transmission line length from the features of the FFT results. Alternatively, the estimation accuracy of the transmission line length may be improved by combining multiple estimation methods described above.

(Method of estimating the transmission line length difference between each transmission line and the signal selection unit)
12 is a flowchart showing a procedure for estimating a transmission line length difference by each transmission line and a signal selection unit in the third embodiment. For simplicity of explanation, the case of the transmitting branch B1 will be explained.

First, the control and calculation unit 260 coordinates the operation of the signal generating unit 100 and the measurement unit 250. This makes it possible to simulate functions such as a vector network analyzer. That is, the signal generating unit 100 generates a measurement signal, and the measurement unit 250 measures the amplitude and phase, making it possible to measure the complex number of the transmission coefficient. At this time, for example, the signal generating unit 100 and the measurement unit 250 are calibrated with SOLT (Short-Open-Load-Thru) or TRL (Thru-Reflect-Line) to remove phase and amplitude errors caused by the measuring device.

Next, the signal generating unit 100 transmits a measurement signal only from the transmitting branch B1 using the method described above (T31). Next, the measurement signal propagated from the signal generating unit 100 via the signal distributing unit 201 is measured by the measuring unit 250 (T32). This measured value becomes the transmission coefficient, so the measured value is subjected to FFT (T33). Based on the FFT results, the transmission line length at each position is found using the method described above (T34).

In this way, by determining the transmission line length at each position using the above-mentioned method based on the FFT results, it is possible to estimate the transmission line length of the transmission line 291 and the signal selection unit 310 combined. The phase delay component D1 and attenuation α1 can be determined (D1=β・d, α1=α・d) by multiplying the transmission line length (d) of the transmission line 291 and the signal selection unit 310 combined by the phase constant (β) and attenuation constant (α) of the board on which the transmitting branch B1 is mounted.

Therefore, in the first and second embodiments, when performing amplitude error correction in step T11, the control calculation unit 260 performs correction taking into account the attenuation α1, and when performing phase error correction in step T2, the control calculation unit 260 performs correction taking into account the phase delay component D1.

As a result, the correction of the transmission line length of the transmission line 291 and the signal selection unit 310 combined is completed, and a calibration procedure that reflects the influence of the transmission line length can be performed. The procedure in FIG. 12 also applies to other transmission branches. Therefore, after making the correction in FIG. 12, the same configuration processing as in the first and second embodiments can be performed to achieve the same effects as in each of the embodiments.

[Modification of the third embodiment]
13 is a block diagram showing a configuration of a phased array antenna system according to a modification of the third embodiment. In the modification of the third embodiment, a part of the configuration of the base station 2 is different from that of the first embodiment. The same or similar reference numerals are used for the configuration that performs the same or similar operation as the first embodiment, and the description thereof will be omitted.

The base station 2 includes an optical/electrical signal conversion unit 141, a signal division/distribution unit 151, transmission branches B1 to B3, a high frequency/phase/amplitude control unit 160, transmission lines 291, 292, and 293, a signal selection unit 310, a signal synthesis unit 220, and an analog electrical/optical signal conversion unit 230.

The transmission lines 291 to 293 have the function of transmitting a portion of the radio signal extracted by the signal distribution units 201 to 203 to the signal selection unit 310. The transmission lines 291 to 293 can be realized by transmission lines such as coaxial cables, microstrip lines, or waveguides, for example.

The signal selection unit 310 has the function of selecting the radio signals of any two transmission branches for which the phase error and amplitude error are to be corrected from among the radio signals of the transmission lines 291 to 293, and inputting them to the signal synthesis unit 220. The signal selection unit 310 can be realized, for example, by using an RF switch such as a matrix switch.

In addition, if the RF power combiner can ensure the separation of the transmission lines 291 to 293 and the number of input ports can be prepared equal to the number of transmission lines, the method described in the first embodiment can be used to feed power to only any two transmission branches for which the phase error and amplitude error are to be corrected, so that the radio signals of the two transmission branches can be input to the signal combiner 220, and there is no particular problem even if the signal selector 310 is not provided.

By correcting the transmission line difference caused by the transmission lines 291 to 293 and the signal selection unit 310 using the method described in the third embodiment, it becomes possible to correct the amplitude and phase errors with non-adjacent transmission branches, as described above.

[Fourth embodiment]
(Configuration of phased array antenna system)
14 is a block diagram showing the configuration of a phased array antenna system according to a modification of the fourth embodiment. In the fourth embodiment, another form of the central station 1 is shown. The configurations that perform the same or similar operations as those in the first to third embodiments are denoted by the same or similar reference numerals and the description thereof is omitted.

The measurement unit 251 has a function to output the measurement signal that was output from the signal generating unit 100 in the first to third embodiments, and a function to measure the signal that was measured by the measurement unit 250 in the first to third embodiments. The measurement unit 251 can be realized, for example, by a device equipped with a DAC and ADC and a function to control them (DPGA, DSP, electronic computer, etc.), or a vector network analyzer, or a device in which a test signal source and an oscilloscope can be switched with an RF switch.

This allows the signal generating unit 100 to use a device that can only output wireless signals and does not have the function of outputting a measurement signal. The measurement signal output from the measuring unit 251 may be the same as the wireless signal output from the signal generating unit 100, or a dedicated signal such as a sine wave. However, when outputting a dedicated signal, it is necessary to align the center frequencies of the wireless signal output from the signal generating unit 100 and the wireless signal output from the measuring unit 251.

The switching unit 301 has a function of switching the signal input to the signal multiplexing unit 111 between the signal generating unit 100 and the measuring unit 251. The switching unit 301 can be realized, for example, by an RF switch.

(Error correction method)
The calibration procedure (calibration method) in the fourth embodiment will be described. First, the switching unit 301 is switched to the measuring unit 251 side. Next, a measurement signal is output from the measuring unit 251 instead of the signal generating unit 100, and the phase error and amplitude error are corrected according to the calibration procedure of the first or second embodiment. When performing the calibration procedure, the control and calculation unit 260 performs a linked operation with the measuring unit 251 instead of the signal generating unit 100 and the measuring unit 250. Finally, by switching the switching unit 301 to the signal generating unit 100 side, it is possible to radiate a wireless signal into space reflecting the results of correcting the phase error and amplitude error.

As is clear from equation (7), the measurement signal output to each transmission branch is output from the same measurement unit 251, so when measuring the phase difference, the same phase difference is obtained as when the measurement signal is output from the signal generation unit 100. In addition, the central station 1 described in this embodiment can also be applied to the third embodiment, and can also be combined with the first and second embodiments. Therefore, the same effects as those of the first to third embodiments can be achieved even if a device that can output only wireless signals to the signal generation unit 100 and does not have the function of outputting measurement signals is used.

Although not shown, when there are multiple base stations and multiple corresponding signal generating units, it is possible to use a multi-port switching unit 301 to share the measuring unit 251, and use a single measuring unit 251 to calibrate multiple base stations. This makes it possible to realize each of the first to third embodiments using a small number of measuring units 251. In other words, because the number of measuring units can be reduced compared to each of the first to third embodiments, the central station can also be realized at low cost, in a smaller size, and with lower power consumption.

[Fifth embodiment]
(Configuration of phased array antenna system)
15 is a block diagram showing the configuration of a phased array antenna system according to a modification of the fifth embodiment. In the fifth embodiment, another form of the aggregation station is shown. The configurations that perform the same or similar operations as those in the first to fourth embodiments are denoted by the same or similar reference numerals and the description thereof is omitted.

The central station 1 includes central station 1a, which is mainly composed of a measurement unit; central station 1b, which is mainly composed of a signal generation unit, a control calculation unit, a control information storage unit, etc.; and central station 1c, which is mainly composed of an optical switch. Note that the electrical/optical signal conversion units 121a and 121b have the same functions as the electrical/optical signal conversion unit 121. The central stations 1a to 1c may be provided in the same building, or may be provided separately in different buildings. Of course, some of the functions of the central stations 1a to 1c may be provided in the same building, and the remaining functions may be provided in different buildings. The central station 1c may also be incorporated into the optical transmission path 13.

The optical switch 320 has a function of switching the signal input to the optical transmission path 131 to the electrical/optical signal conversion unit 121a or the electrical/optical signal conversion unit 121b. The optical switch 320 can be realized, for example, using a mechanical type, a MEMS (Micro Electro Mechanical Systems) type, or an optical waveguide type optical switch.

(Error correction method)
The calibration procedure (calibration method) in the fifth embodiment will be described. First, the optical switch 320 is switched to the electrical/optical signal conversion unit 121a side. Next, a measurement signal is output from the measurement unit 251 instead of the signal generation unit 100, and the phase error and amplitude error are corrected according to the calibration procedure of the first or second embodiment. When the calibration procedure is performed, the control and calculation unit 260 performs a linking operation with the measurement unit 251 instead of the signal generation unit 100 and the measurement unit 250. When the central station 1a and the central station 1b are installed in separate locations, the linking between the measurement unit 251 and the control and calculation unit 260 is performed using, for example, Ethernet. Finally, by switching the optical switch 320 to the electrical/optical signal conversion unit 121b side, a wireless signal can be emitted into space reflecting the results of correcting the phase error and amplitude error.

As is clear from equation (7), the measurement signals output to each transmission branch are output from the same measurement unit 251, so when measuring the phase difference, the same phase difference is obtained as when the measurement signal is output from the signal generation unit 100. Furthermore, the aggregation station 1 described in this embodiment can also be applied to the third embodiment, and can also be combined with the first and second embodiments. Therefore, the same effects as those of the first to third embodiments can be achieved even if a device that can only output wireless signals to the signal generation unit 100 and does not have the function of outputting measurement signals is used.

Although not shown, when there are multiple base stations and multiple corresponding signal generating units, it is possible to use a single measuring unit 251 to calibrate multiple base stations by sharing the measuring unit 251 using a multi-port optical switch 320. Unlike the fourth embodiment, the measuring unit 251 switches in the optical domain instead of the RF domain, so there is less loss on the transmission path, and the measuring unit 251 can be installed at a position farther away from the signal generating unit 100 than in the fourth embodiment. This increases the number of base stations that can be serviced by a single measuring unit 251. This allows the central station to be even cheaper, more compact, and consume less power than in the fourth embodiment.

As described above, according to the above embodiment, by providing the central station with a calibration function, the configuration of the phased array antenna system can be simplified, and as a result, it is possible to achieve low power consumption, miniaturization, and cost reduction of the base station.

Reference Signs List 1, 1a, 1b, 1c Aggregation station 2 Base station 13, 131, 132 Optical transmission path 100 Signal generation unit 111 Signal multiplexing unit 121, 121a, 121b Electrical/optical signal conversion unit 141 Optical/electrical signal conversion unit 151 Signal division/distribution unit 160 High frequency/phase/amplitude control unit 171, 172, 173 Amplitude adjustment unit 181, 182, 183 Phase adjustment unit 191, 192, 193 High frequency adjustment unit 201, 202, 203 Signal distribution unit 211, 212, 213 Antenna unit 220, 221, 222 Signal synthesis unit 230, 231, 232 Analog electrical/optical signal conversion unit 240 Analog optical/electrical signal conversion unit 250, 251 Measurement unit 260 Control and calculation unit 270 Control information storage units 291, 292, 293 Transmission line 301 Switching unit 310 Signal selection unit 320 Optical switches B1, B2, B3 Transmission branch

Claims (9)

A base station applied to a phased array antenna system including a central station and a base station having a plurality of antennas, the base station being connected by an optical transmission line,
an optical/electrical signal conversion unit that converts an optical signal received from the central station into an electrical signal;
a signal division/distribution unit that divides the electrical signal into a radio signal and a control signal;
a control unit that adjusts a frequency, an amplitude, or a phase of a radio signal transmitted to a transmitting branch based on the separated control signal;
a signal combining unit that combines the radio signals output from the transmission branches;
an analog electrical/optical signal converter for converting the combined radio signal into an optical signal;
A base station which calibrates an error between adjacent antennas based on the control signal obtained from the central station. the transmission branch further includes a phase adjustment unit that adjusts a phase of the radio signal output from the signal division/distribution unit,
2. The base station according to claim 1, wherein the phase adjustment unit changes the phase of one of the adjacent transmission branches within a range not exceeding 360 degrees from an initial value to correct a phase error. the transmission branch further includes a phase adjustment unit that adjusts a phase of the radio signal output from the signal division/distribution unit,
2. The base station according to claim 1, wherein the phase adjustment unit changes the phase of one of the adjacent transmitting branches within a range not exceeding 180 degrees from an initial value, and corrects a phase error based on at least one of a maximum value and a minimum value of the radio signal within the range . A central station applied to a phased array antenna system including a central station and a base station having a plurality of antennas, the central station being connected by an optical transmission line,
a signal generating unit that generates a radio signal and a measurement signal;
a signal multiplexing unit that multiplexes the generated radio signal and a control signal to generate an electrical signal;
an electrical/optical signal converter that converts the generated electrical signal into an optical signal and outputs the optical signal to the base station;
an analog optical/electrical signal conversion unit that receives an optical signal from the base station and converts it into an electrical signal;
a measurement unit that measures the amplitude and phase of each antenna of the base station based on the electrical signal converted from the optical signal;
a control and calculation unit that calculates a phase error and an amplitude error from the measurement result and generates the control signal;
a central station for calibrating an error between adjacent antennas of the base station by transmitting the control signal to the base station. The central station according to claim 4, characterized in that the control and calculation unit estimates the transmission line length within the base station from the measurement results. 6. The central station according to claim 5, wherein an amplitude error and a phase error between transmitting branches in said base station are corrected from said estimated transmission line length. A phased array antenna system including a central station and a base station having a plurality of antennas, the phased array antenna system being connected by an optical transmission line,
The aggregation station includes:
a signal generating unit for generating a radio signal and a measurement signal;
a signal multiplexing unit that multiplexes the generated radio signal and a control signal to generate an electrical signal;
an electrical/optical signal converter that converts the generated electrical signal into an optical signal and outputs the optical signal to a base station;
an analog optical/electrical signal conversion unit that receives an optical signal from the base station and converts it into an electrical signal;
a measurement unit that measures an amplitude and a phase based on an electrical signal converted from the optical signal;
a control and calculation unit that calculates a phase error and an amplitude error from the measurement result and generates the control signal;
The said station is
an optical/electrical signal conversion unit that converts an optical signal received from the central station into an electrical signal;
a signal division/distribution unit that divides the electrical signal into a radio signal and a control signal;
a control unit that adjusts a frequency, an amplitude, or a phase of a radio signal transmitted to a transmitting branch based on the separated control signal;
a signal combining unit that combines the radio signals output from the transmission branches;
an analog electrical/optical signal converter for converting the combined radio signal into an optical signal;
The phased array antenna system according to claim 1, wherein the base station calibrates an error between adjacent antennas based on the control signal obtained from the central station. The control and calculation unit estimates a transmission line length in the base station from the measurement result,
8. The phased array antenna system according to claim 7, wherein an amplitude error and a phase error between transmitting branches in said base station are corrected from said estimated transmission line length. A phased array antenna system including a central station and a base station having a plurality of antennas, the phased array antenna system being connected by an optical transmission line,
The aggregation station includes:
A signal generating unit that generates a wireless signal;
a signal multiplexing unit that multiplexes the generated radio signal and a control signal to generate an electrical signal;
an electrical/optical signal converter that converts the generated electrical signal into an optical signal and outputs the optical signal to a base station;
an analog optical/electrical signal conversion unit that receives an optical signal from the base station and converts it into an electrical signal;
a measurement unit that outputs a measurement signal and measures the amplitude and phase from the converted electrical signal;
a control calculation unit that calculates a phase error and an amplitude error from the measurement result and generates the control signal;
a switching unit that switches an output source between the signal generating unit and the measurement unit in response to a signal to be output to the base station,
The said station is
an optical/electrical signal conversion unit that converts an optical signal received from the central station into an electrical signal;
a signal division/distribution unit that divides the electrical signal into a radio signal and a control signal;
a control unit that adjusts a frequency, an amplitude, or a phase of a radio signal transmitted to a transmitting branch based on the separated control signal;
a signal combining unit that combines the radio signals output from the transmission branches;
an analog electrical/optical signal converter for converting the combined radio signal into an optical signal;
The phased array antenna system according to claim 1, wherein the base station calibrates an error between adjacent antennas based on the control signal obtained from the central station.