Active antenna system and method

Abstract

To enable calibration suitable for product architectures where sub-units, each with multiple antenna elements and multiple RF chains, are manufactured and these multiple sub-units are combined into one active antenna system (AAS).SOLUTION: A controller (150) performs intra-subunit transmit calibration to compensate for relative differences in amplitude and phase between multiple transmitter RF chains in each subunit (110, 120) of an AAS (100). The controller (150) performs inter-subunit transmit calibration for compensating for relative differences in amplitude and phase between a plurality of representative transmitter RF chains respectively selected from the plurality of subunits (110, 120).SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] This disclosure relates to active antenna systems, and more particularly to their calibration. [Background technology]

[0002] Massive Multi-Input Multi-Output (MIMO) and Multi-User MIMO (MU-MIMO) using an active antenna system (AAS) are key technologies for improving network capacity in wireless communication systems such as fifth-generation (5G) cellular systems. AAS supports full digital beamforming. For example, AAS can be applied to the base station of a 5G cellular system, specifically to the Radio Unit (RU). For example, but not limited to, when the AAS is used as an RU, it performs low physical layer signal processing and beamforming in the digital domain.

[0003] The AAS includes an antenna array, multiple radio frequency (RF) chains, and a digital front end. Each RF chain includes a transmitter (or transmit) RF chain and a receiver (or receive) RF chain. A transmitter RF chain includes a transmitter, one or more power amplifiers (e.g., high power amplifiers (HPA)), and one or more RF filters (e.g., bandpass filters). The transmitter includes, for example, a digital-to-analog converter (DAC), a baseband filter (e.g., lowpass filters), and an IQ modulator. Meanwhile, a receiver RF chain includes a receiver, one or more low-noise amplifiers (LNA), and one or more RF filters (e.g., bandpass filters). The receiver includes, for example, an analog-to-digital converter (ADC), a baseband filter (e.g., lowpass filters), and an IQ demodulator.

[0004] To achieve accurate directivity in beamforming, the multiple elements (multiple RF chains) that make up the antenna array must have the same phase and amplitude response. Any mismatch in the amplitude and phase relationships between elements in the antenna array will result in relative changes in the amplitude and phase between the radiated or received signals, affecting the radiation pattern characteristics. Relative differences in amplitude (or gain) and phase between RF chains can arise from, for example, thermal effects, component aging, and manufacturing tolerances. To solve this problem, calibration of the multiple antenna elements (or multiple RF chains) is required.

[0005] Discussions and proposals regarding calibration of AASs are described, for example, in two international applications by the present inventor (see Patent Documents 1 and 2). Patent Document 1 discloses a method for calibrating multiple RF chains across multiple AASs when multiple AASs are connected and used as a single active antenna system. Patent Document 2 provides a configuration and method for simultaneously calibrating multiple transmitters (multiple transmitter RF chains) of an AAS. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2019 / 176388 [Patent Document 2] International Publication No. 2021 / 019885 Summary of the Invention [Problem to be solved by the invention]

[0007] The inventors have devised a product architecture in which subunits, each having multiple antenna elements and multiple RF chains, are manufactured and then combined into a single AAS. In one example, these subunits are mounted in a single antenna system housing. The subunits can also be called modules or cards. Calibration appropriate for the configuration of such an AAS product is required.

[0008] One of the objectives that the embodiments disclosed in this specification aim to achieve is to provide an apparatus, a method, and a program that enable calibration suitable for the above-mentioned AAS product architecture. It should be noted that this objective is only one of the objectives that the embodiments disclosed in this specification aim to achieve. Other objectives or problems and novel features will become apparent from the description of this specification or the accompanying drawings. [Means for solving the problem]

[0009] In a first aspect, an active antenna system includes first and second subunits and a controller. The first subunit includes a first set of antenna elements, a first set of transmitter radio frequency (RF) chains coupled to the first set of antenna elements, a first set of receiver RF chains coupled to the first set of antenna elements, and a first digital front end coupled to the first set of transmitter RF chains and the first set of receiver RF chains. Similarly, the second subunit includes a second set of antenna elements, a second set of transmitter RF chains coupled to the second set of antenna elements, a second set of receiver RF chains coupled to the second set of antenna elements, and a second digital front end coupled to the second set of transmitter RF chains and the second set of receiver RF chains. The controller is configured to perform a first transmit calibration, a second transmit calibration, and a third transmit calibration. The first transmit calibration corrects for relative differences in amplitude and phase between the transmitter RF chains in the first set of transmitter RF chains. The second transmit calibration corrects for relative differences in amplitude and phase between transmitter RF chains in the second set of transmitter RF chains, and the third transmit calibration corrects for relative differences in amplitude and phase between a first representative transmitter RF chain included in the first set of transmitter RF chains and a second representative transmitter RF chain included in the second set of transmitter RF chains.

[0010] In a second aspect, a method performed by a controller of an active antenna system includes the following steps: (a) performing a first transmit calibration to correct for relative differences in amplitude and phase among a plurality of transmitter RF chains in a first subunit of the active antenna system; (b) performing a second transmit calibration to correct for relative differences in amplitude and phase among a plurality of transmitter RF chains in a second subunit of the active antenna system; and (c) performing a third transmit calibration to correct relative differences in amplitude and phase between a first representative transmitter RF chain included in the plurality of transmitter RF chains in the first subunit and a second representative transmitter RF chain included in the plurality of transmitter RF chains in the second subunit;

[0011] A third aspect is directed to a program, comprising instructions (software code) that, when loaded into a computer (e.g., a controller for an active antenna system), cause the computer to perform the method according to the second aspect. [Effects of the Invention]

[0012] According to the above-described aspects, it is possible to provide an apparatus, a method, and a program that enable calibration suitable for a product architecture in which subunits each having multiple antenna elements and multiple RF chains are manufactured and these multiple subunits are combined to form a single AAS. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating a configuration example of an active antenna system according to an embodiment. [Figure 2A] 1 is a flowchart illustrating an example of a transmission calibration procedure of an active antenna system according to an embodiment. [Figure 2B] 10 is a flowchart illustrating an example of a reception calibration procedure of the active antenna system according to the embodiment. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a subunit in an active antenna system according to an embodiment. [Figure 4]FIG. 2 is a diagram illustrating an example of the configuration of a subunit in an active antenna system according to an embodiment. [Figure 5A] 1 illustrates an example of a configuration of a transmitter RF chain and a receiver RF chain in an active antenna system according to an embodiment. [Figure 5B] 1 illustrates an example of a configuration of a transmitter RF chain and a receiver RF chain in an active antenna system according to an embodiment. [Figure 6] FIG. 10 is a diagram illustrating an example of a signal path in intra-subunit transmission calibration of an active antenna system according to an embodiment. [Figure 7] FIG. 10 is a diagram illustrating an example of a signal path in intra-subunit receive calibration of an active antenna system according to an embodiment. [Figure 8] 10 is a flowchart illustrating an example of a procedure for inter-subunit transmission calibration of the active antenna system according to the embodiment. [Figure 9] 10 is a flowchart illustrating an example of a procedure for inter-subunit transmission calibration of the active antenna system according to the embodiment. [Figure 10] 10 is a flowchart illustrating an example of a procedure for inter-subunit reception calibration in the active antenna system according to the embodiment. [Figure 11] 10 is a flowchart illustrating an example of a procedure for inter-subunit reception calibration in the active antenna system according to the embodiment. [Figure 12] FIG. 2 is a diagram illustrating an example of the configuration of a subunit in an active antenna system according to an embodiment. [Figure 13] 10 is a flowchart illustrating an example of a procedure for inter-subunit transmission calibration of the active antenna system according to the embodiment. [Figure 14] 10 is a flowchart illustrating an example of a procedure for inter-subunit reception calibration in the active antenna system according to the embodiment. [Figure 15]FIG. 2 is a diagram illustrating an example of the configuration of a subunit in an active antenna system according to an embodiment. [Figure 16] FIG. 2 is a diagram illustrating an example of the configuration of a subunit in an active antenna system according to an embodiment. [Figure 17] FIG. 10 is a diagram illustrating an example of a signal path in intra-subunit transmission calibration of an active antenna system according to an embodiment. [Figure 18] FIG. 10 is a diagram illustrating an example of a signal path in intra-subunit receive calibration of an active antenna system according to an embodiment. [Figure 19] FIG. 10 is a diagram illustrating an example of a signal path in inter-subunit transmission calibration of an active antenna system according to an embodiment. [Figure 20] FIG. 10 is a diagram illustrating an example of a signal path in inter-subunit transmission calibration of an active antenna system according to an embodiment. [Figure 21] FIG. 10 is a diagram illustrating an example of a signal path in inter-subunit reception calibration of an active antenna system according to an embodiment. [Figure 22] FIG. 10 is a diagram illustrating an example of a signal path in inter-subunit reception calibration of an active antenna system according to an embodiment. [Figure 23] 10 is a flowchart illustrating an example of a sub-unit transmission calibration procedure of the active antenna system according to the embodiment. [Figure 24] 10 is a flowchart illustrating an example of a procedure for receiving calibration within a sub-unit of the active antenna system according to the embodiment. [Figure 25] 10 is a flowchart illustrating an example of a procedure for inter-subunit transmission calibration of the active antenna system according to the embodiment. [Figure 26] 10 is a flowchart illustrating an example of a procedure for inter-subunit reception calibration in the active antenna system according to the embodiment. [Figure 27]FIG. 2 is a diagram illustrating an example of the configuration of a subunit in an active antenna system according to an embodiment. [Figure 28] FIG. 2 is a diagram illustrating an example of the configuration of a subunit in an active antenna system according to an embodiment. [Figure 29] FIG. 10 is a diagram illustrating an example of a signal path in intra-subunit transmission calibration of an active antenna system according to an embodiment. [Figure 30] FIG. 10 is a diagram illustrating an example of a signal path in intra-subunit receive calibration of an active antenna system according to an embodiment. [Figure 31] FIG. 10 is a diagram illustrating an example of a signal path in inter-subunit transmission calibration of an active antenna system according to an embodiment. [Figure 32] FIG. 10 is a diagram illustrating an example of a signal path in inter-subunit transmission calibration of an active antenna system according to an embodiment. [Figure 33] FIG. 10 is a diagram illustrating an example of a signal path in inter-subunit reception calibration of an active antenna system according to an embodiment. [Figure 34] FIG. 10 is a diagram illustrating an example of a signal path in inter-subunit reception calibration of an active antenna system according to an embodiment. [Figure 35] FIG. 2 is a diagram illustrating an example of the configuration of a controller according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, specific embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and for clarity of explanation, duplicate explanations will be omitted as necessary.

[0015] The multiple embodiments described below can be implemented independently or in appropriate combination. These multiple embodiments have different novel features. Therefore, these multiple embodiments contribute to solving different purposes or problems and to achieving different effects.

[0016] As used herein, depending on the context, "if" may be construed to mean "when," "at or around the time," "after," "upon," "in response to determining," "in accordance with a determination," or "in response to detecting." These expressions may be construed to have the same meaning, depending on the context.

[0017] First Embodiment 1 shows an example configuration of an AAS 100 according to this embodiment. The AAS 100 may be used for a base station of a 5G cellular system, and more specifically, may be used as a Radio Unit (RU). The AAS 100 includes multiple subunits and a controller 150. The subunits may also be referred to as modules or cards. Each subunit includes multiple antennas (or antenna elements), multiple transmitter RF chains, multiple receiver RF chains, and a digital front end (DFE).

[0018] A transmitter RF chain includes a transmitter, one or more power amplifiers (e.g., HPA), and one or more RF filters (e.g., bandpass filters). The transmitter includes, for example, multiple DACs, multiple baseband filters (e.g., lowpass filters), and an IQ modulator. Meanwhile, a receiver RF chain includes a receiver, one or more power amplifiers (e.g., LNA), and one or more RF filters (e.g., bandpass filters). The receiver includes, for example, multiple ADCs, multiple baseband filters (e.g., lowpass filters), and an IQ demodulator. The DFE may perform, for example, but not limited to, low physical layer signal processing and digital radio signal processing. Low physical layer signal processing includes, for example, fast Fourier transform (FFT) and inverse FFT (IFFT). Digital radio signal processing includes, for example, digital pre-distortion (DPD), crest factor reduction (CFR), digital up-conversion (DUC), digital down-conversion (DDC), and transmit / receive baseband channel filters.

[0019] 1, the AAS 100 may have four subunits 110, 120, 130, and 140. Each subunit may have 16 transmitter RF chains, 16 receiver RF chains, and 16 or more antenna elements, in which case the AAS 100 may operate as an active phased array antenna with 64 or more antenna elements.

[0020] A particular subunit (e.g., subunit 110) is connected to other subunits (e.g., subunits 120, 130, and 140) via RF lines (e.g., RF lines 162, 163, and 164). Each RF line may include a coaxial cable, a coaxial connector, or a distributed constant line, or a combination thereof. These RF lines are used for inter-subunit calibration, which will be described later.

[0021] The controller 150 performs first-stage transmit calibration and second-stage transmit calibration to correct for relative differences in amplitude and phase among all transmitter RF chains of multiple subunits (e.g., subunits 110, 120, 130, and 140). The first-stage transmit calibration is also called intra-subunit transmit calibration, while the second-stage transmit calibration is also called inter-subunit transmit calibration. Similarly, the controller 150 performs first-stage receive calibration and second-stage receive calibration to correct for relative differences in amplitude and phase among all receiver RF chains of multiple subunits (e.g., subunits 110, 120, 130, and 140). The first-stage receive calibration is also called intra-subunit receive calibration, while the second-stage receive calibration is also called inter-subunit receive calibration.

[0022] In some implementations, the multiple subunits 110, 120, 130, and 140 may be mounted on respective circuit boards. The AAS 100 may include a single housing that houses the multiple subunits 110, 120, 130, and 140 and the controller 150. The first subunit 110 may be connected to the other subunits 120, 130, and 140 by RF lines 162, 163, and 164 that connect within the housing.

[0023] 2A shows an example of a transmit calibration method or procedure, where step 201 is intra-subunit transmit calibration and step 202 is inter-subunit transmit calibration.

[0024] In step 201, the controller 150 performs transmit calibration between the transmitter RF chains in each subunit. Specifically, the controller 150 corrects relative differences in amplitude and phase between the multiple transmitter RF chains in the first subunit (e.g., subunit 110). Similarly, the controller 150 corrects relative differences in amplitude and phase between the multiple transmitter RF chains in the second subunit (e.g., subunit 120). If there are three or more subunits, the controller 150 similarly performs transmit calibration for each of the third subunit and subsequent subunits (e.g., subunits 130 and 140). The controller 150 can independently perform multiple first-stage transmit calibrations for multiple subunits. In other words, the multiple first-stage transmit calibrations for multiple subunits may be performed simultaneously or at different times.

[0025] In intra-subunit transmit calibration (step 201), controller 150 may control a subunit so that transmitters of multiple transmitter RF chains in the subunit transmit calibration signals and a receiver of any one receiver RF chain in the subunit receives these calibration signals. The calibration signal may be, for example, a multi-tone signal in which multiple known OFDM subcarriers are superimposed. Controller 150 may cause all transmitter RF chains in the subunit (except for a faulty one) to transmit the calibration signal. Based on the results of receiving the calibration signal, controller 150 may calculate correction coefficients (or offsets or weights) to be applied to each transmitter RF chain to correct relative differences in amplitude and phase between the multiple transmitter RF chains in the subunit.

[0026] One transmitter RF chain in a sub-unit may be used (or selected) as a reference transmitter RF chain. The reference transmitter RF chain is used as a reference for determining correction coefficients for each transmitter RF chain except for the reference transmitter RF chain to correct for relative differences in amplitude and phase. The correction coefficient for each transmitter RF chain may be the ratio of the transmission path characteristics (or frequency response) of that transmitter RF chain to the transmission path characteristics (or frequency response) of the reference transmitter RF chain. The correction coefficient may also be called a calibration coefficient, calibration weight, or offset.

[0027] As an example, consider a case where the AAS 100 has four subunits 110, 120, 130, and 140, each of which has 16 transmitter RF chains. In the transmission calibration in subunit #i (i is an integer from 1 to 4), the calibration weight W1 of transmitter RF chain #n (n is an integer from 1 to 16) is calculated. i,n TX may be calculated using the following formula (1):

number

[0028] The characteristics (frequency response) of passive components (e.g., circulators and RF filters) and lines present between the signal branching point (e.g., splitter) provided in each transmit RF chain for calibration and the connection point of the corresponding antenna element, as well as the characteristics of the antenna element itself, are measured at the factory before shipping the AAS 100. If there are substantially no factors that cause fluctuations in these characteristics, representative fixed values ​​based on these measurements are set and stored in the AAS 100. These measured and stored characteristics may be recorded or stored in the memory of the controller 150 or the corresponding subunit. These measured and stored characteristics may also be used for the above-mentioned intra-subunit calibration. Specifically, in equation (1), TX i,n Instead of TX i,n To TX i,n, const Similarly, in equation (1), TX i,Ref Instead of TX i,Ref To TX i,Ref, const The value multiplied by TX may be used. i,n, const is the sum of the characteristics of the passive components and lines existing between the signal branch point of the transmitter RF chain #n of the subunit #i and the connection point of the corresponding antenna element, and the characteristics of the antenna itself, and TX i,Ref, constis the sum of the characteristics of the passive components and lines present between the signal branch point of the reference transmitter RF chain of subunit #i and the connection point of the corresponding antenna element, and the characteristics of the antenna itself. As mentioned above, if there is little variation in the amplitude, phase, and frequency characteristics of the passive components up to the antenna between the transmitter RF chains and there is also little uniform temperature fluctuation, the amplitude, phase, and frequency up to the antenna of each chain can be added in advance as a fixed value.

[0029] After the first-stage transmit calibration for each subunit is completed, the controller 150 performs inter-subunit transmit calibration (step 202). Specifically, the controller 150 corrects relative differences in amplitude and phase among a plurality of representative transmitter RF chains selected from each of a plurality of subunits. In the configuration example of FIG. 1, the controller 150 corrects relative differences in amplitude and phase among four representative transmitter RF chains selected from each of the four subunits 110, 120, 130, and 140. Note that the representative transmitter RF chain of each subunit may be the same as the reference transmitter RF chain used in the first-stage transmit calibration.

[0030] In the inter-subunit transmission calibration (step 202), the controller 150 may control multiple subunits so that multiple representative transmitter RF chains of the multiple subunits transmit calibration signals and a receiver of any one receiver RF chain of any one of the subunits receives these calibration signals. In the configuration example of FIG. 1 , calibration signals from three representative transmitter RF chains of the second to fourth subunits 120, 130, and 140 are supplied to the first subunit 110 via RF lines 162, 163, and 164. Therefore, a receiver of one receiver RF chain in the first subunit 110 is used to receive the calibration signal. The receiver of any subunit that receives a calibration signal in the inter-subunit transmission calibration may be the same as or different from the receiver used to receive the calibration signal during the intra-subunit transmission calibration of that subunit.

[0031] Based on the received calibration signal, the controller 150 may calculate a correction coefficient (or offset or weight) to be applied to each representative transmitter RF chain to correct relative differences in amplitude and phase among the multiple representative transmitter RF chains. In other words, the controller 150 may calculate a correction coefficient (or offset) to be applied to each representative transmitter RF chain to correct relative differences in amplitude and phase among the sub-units. One of the multiple representative transmitter RF chains may be used (or selected) as a reference representative transmitter RF chain. The correction coefficient of each representative transmitter RF chain may be a ratio of the transmission path characteristics (or frequency response) of the representative transmitter RF chain to the transmission path characteristics (or frequency response) of the reference representative transmitter RF chain.

[0032] As an example, consider a case where the AAS 100 has four subunits 110, 120, 130, and 140. In the inter-subunit transmission calibration, the calibration weight W2 of the representative transmitter RF chain of the subunit #i (i is an integer from 1 to 4) is i TX may be calculated using the following formula (2):

number

[0033] Furthermore, equation (2) may be modified as follows: For convenience of explanation, consider the case where the representative transmitter RF chain of subunit #1 is the reference representative transmitter RF chain. In this case, the calibration weight W3 defined by the following equation (3) is used. i TXis the calibration weight W2 in Eq. (2). i TX may be used instead of:

number

[0034] Here, W3 in equation (3) i TX is W2 in equation (2) i TX In other words, we will explain how the relational expression shown in equation (4) can be derived.

number

[0035] First, the calibration weight W2 of each subunit is calculated. i TX is calculated by the following equation (5).

number

[0036] Similarly, the calibration weight W2 of the reference representative transmitter RF chain Ref TX is calculated by the following equation (6).

number

[0037] Therefore, W2 in equation (5) i TX W2 in equation (6) Ref TX By dividing by this, the relationship in equation (7) below is obtained, and it can be seen that the relationship in equation (4) is obtained.

number

[0038] Controller 150 can remove (or compensate for or correct) mismatches in amplitude and phase relationships between all transmitter RF chains of multiple subunits by using the correction coefficients obtained in the intra-subunit transmit calibration (step 201) and the inter-subunit transmit calibration (step 202). In some implementations, controller 150 may calculate a correction coefficient to be applied to each transmitter RF chain by multiplying the correction coefficient obtained in the intra-subunit transmit calibration by the correction coefficient obtained in the inter-subunit transmit calibration. This calculation is appropriate when the representative transmitter RF chain of each subunit is the same as the reference transmitter RF chain in the first-stage transmit calibration. Controller 150 may control the DFE of each subunit to add the corresponding phase and amplitude differences as offsets in the digital domain based on the obtained correction coefficients.

[0039] As an example, consider a case where the AAS 100 has four subunits 110, 120, 130, and 140, each with 16 transmitter RF chains. The controller 150 calculates the total calibration weight Wtotal to be applied to the signal of transmitter RF chain #n in subunit #i. i,n TX may be calculated by the following equation (8):

number

[0040] Alternatively, the controller 150 may calculate a total calibration weight Wtotal to be applied to the signal of the transmitter RF chain #n in the subunit #i. i,n TX may be calculated by the following equation (9):

number

[0041] 2B shows an example of a receive calibration method or procedure. Step 241 is intra-subunit receive calibration, and step 242 is inter-subunit receive calibration. The intra-subunit and inter-subunit receive calibrations may be performed in a similar manner to the intra-subunit and inter-subunit transmit calibrations described above.

[0042] In step 241, controller 150 performs receive calibration between the receiver RF chains in each subunit. Specifically, controller 150 corrects relative differences in amplitude and phase between the multiple receiver RF chains in the first subunit (e.g., subunit 110). Similarly, controller 150 corrects relative differences in amplitude and phase between the multiple receiver RF chains in the second subunit (e.g., subunit 120). If there are three or more subunits, controller 150 similarly performs receive calibration for each of the third subunit and subsequent subunits (e.g., subunits 130 and 140). Controller 150 can independently perform multiple first-stage receive calibrations for multiple subunits. In other words, multiple first-stage receive calibrations for multiple subunits may be performed simultaneously or at different times.

[0043] In intra-subunit receiver calibration (step 241), controller 150 may control a subunit so that a transmitter of one transmitter RF chain in the subunit transmits a calibration signal and receivers of multiple receiver RF chains in the subunit receive the calibration signal. Controller 150 may cause all receiver RF chains in the subunit (except for a failed one) to receive the calibration signal. Based on the results of receiving the calibration signal, controller 150 may calculate correction coefficients (or offsets or weights) to be applied to each receiver RF chain to correct for relative differences in amplitude and phase between the multiple receiver RF chains in the subunit.

[0044] One receiver RF chain in the subunit may be used (or selected) as a reference receiver RF chain. The reference receiver RF chain is used as a reference for determining correction coefficients for each receiver RF chain other than the reference receiver RF chain to correct for relative differences in amplitude and phase. The correction coefficient for each receiver RF chain may be the ratio of the transmission path characteristics (or frequency response) of that receiver RF chain to the transmission path characteristics (or frequency response) of the reference receiver RF chain. The correction coefficients may also be called calibration coefficients, calibration weights, or offsets.

[0045] After the first-stage receive calibration for each subunit is completed, the controller 150 performs inter-subunit receive calibration (step 242). Specifically, the controller 150 corrects relative differences in amplitude and phase among multiple representative receiver RF chains selected from each of the multiple subunits. In the configuration example of FIG. 1, the controller 150 corrects relative differences in amplitude and phase among four representative receiver RF chains selected from each of the four subunits 110, 120, 130, and 140. Note that the representative receiver RF chain of each subunit may be the same as the reference receiver RF chain used in the first-stage receive calibration.

[0046] In the inter-subunit receive calibration (step 242), the controller 150 may control multiple subunits so that a transmitter of any one transmitter RF chain of any one subunit transmits a calibration signal and multiple representative receiver RF chains of the multiple subunits receive this calibration signal. In the configuration example of FIG. 1, a calibration signal output from any transmitter of the first subunit 110 is supplied to three representative transmitter RF chains of the second to fourth subunits 120, 130, and 140 via RF lines 162, 163, and 164. The transmitter of any subunit that transmits a calibration signal in the inter-subunit receive calibration may be the same as or different from the transmitter used to transmit a calibration signal during the intra-subunit receive calibration of that subunit.

[0047] Based on the results of receiving the calibration signal, the controller 150 may calculate a correction coefficient (or offset or weight) to be applied to each representative receiver RF chain to correct relative differences in amplitude and phase among the multiple representative receiver RF chains. In other words, the controller 150 may calculate a correction coefficient (or offset) to be applied to each representative receiver RF chain to correct relative differences in amplitude and phase among the sub-units. One of the multiple representative receiver RF chains may be used (or selected) as a reference representative receiver RF chain. The correction coefficient for each representative receiver RF chain may be a ratio of the transmission path characteristics (or frequency response) of the representative receiver RF chain to the transmission path characteristics (or frequency response) of the reference representative receiver RF chain.

[0048] Controller 150 can remove (or compensate for or correct) mismatches in amplitude and phase relationships between all receiver RF chains of multiple subunits by using the correction coefficients obtained in the intra-subunit receive calibration (step 241) and the inter-subunit receive calibration (step 242). In some implementations, controller 150 may calculate a correction coefficient to be applied to each receiver RF chain by multiplying the correction coefficient obtained in the intra-subunit receive calibration by the correction coefficient obtained in the inter-subunit receive calibration. This calculation is appropriate when the representative receiver RF chain of each subunit is the same as the reference receiver RF chain in the first-stage receive calibration. Controller 150 may control the DFE of each subunit to add the corresponding phase and amplitude differences as offsets in the digital domain based on the obtained correction coefficients.

[0049] The calculation of the correction coefficients or calibration weights in the receive calibration may be performed in the same manner as the calculation of the correction coefficients or calibration weights in the transmit calibration described with reference to equations (1) to (9).

[0050] 2A and 2B may be performed during manufacturing (before product shipment) of the AAS 100. In addition, the calibration described with reference to Fig. 2A and 2B may be performed as needed while the AAS 100 is in operation.

[0051] By way of example and not limitation, the intra-subunit transmit and receive calibration in step 201 of FIG. 2A and step 241 of FIG. 2B may be performed according to the method described in International Application WO 2021 / 019885 (Patent Document 2).

[0052] The adoption of the AAS architecture having multiple subunits described with reference to FIG. 1 and the two-stage calibration described with reference to FIG. 2 can provide the following advantages, for example. For example, the first-stage calibration and the second-stage calibration can be performed independently and separately. This contributes to improving the first-pass yield of the AAS100 during pre-shipment inspection. Specifically, the first-pass yield during inspection of each subunit can be improved. Furthermore, by manufacturing subunits that have completed the first-stage transmit and receive calibrations and assembling them into the AAS100, the first-pass yield during equipment inspection of the AAS100 can also be improved. In addition, by separating the first-stage calibration and the second-stage calibration, the time constraints on calibration performed while the AAS100 is in operation can be alleviated.

[0053] <Second embodiment> This embodiment provides a specific example of the configuration and calibration method of the AAS 100 described in the first embodiment. Fig. 3 shows an example of the configuration of the first subunit 110, and Fig. 4 shows an example of the configuration of the second subunit 120. If the AAS 100 has three or more subunits, the configurations of the third subunit and subsequent subunits (e.g., subunits 130 and 140) may be the same as that of the second subunit 120. Note that, as shown in Figs. 3 and 4, all subunits may have the same configuration, with only differences in their connection relationships with the RF lines 162 to 164.

[0054] 3, the subunit 110 includes multiple transceiver RF chains. In the example of FIG. 3, the number of transceiver RF chains in the subunit 110 is 16. The transceiver RF chain 10 is configured to provide a calibration signal to the receiver RF chain 16 within the transceiver RF chain 10 and the receiver RF chains 26 in the other 15 transceiver RF chains 20 during intra-subunit receive calibration. In addition, the transceiver RF chain 10 is configured to receive a calibration signal from the transmitter RF chain 15 within the transceiver RF chain 10 and the transmitter RF chains 25 in the other 15 transceiver RF chains 20 during intra-subunit transmit calibration. Furthermore, the transceiver RF chain 10 is configured to provide a calibration signal to representative receiver RF chains of other subunits (e.g., subunits 120, 130, and 140) during inter-subunit receive calibration. Similarly, transceiver RF chain 10 is configured to receive calibration signals from representative transmitter RF chains of other subunits (eg, subunits 120, 130, and 140) during inter-subunit transmit calibration.

[0055] The transceiver RF chain 10 includes a transmitter RF chain 15 and a receiver RF chain 16. The transmitter RF chain 15 is connected to the DFE 30 and to one or more antenna elements 11 via RF passive components such as a circulator 14 and an RF filter 13 (e.g., a bandpass filter). Reference numeral 12 denotes a connection point (e.g., a transceiver array boundary (TAB) connector) with the antenna element 11. A splitter 17 is disposed at the output end of the transmitter RF chain 15 and splits the output signal of the transmitter RF chain 15 and supplies it to a calibration signal path via a divider 19 for transmit calibration. A splitter (or combiner) 18 is disposed at the input end of the receiver RF chain 16 and inputs a calibration signal from the calibration signal path to the receiver RF chain 16 for receive calibration.

[0056] Each of the 15 transceiver RF chains 20 has similar components to the transceiver RF chain 10. Specifically, each transceiver RF chain 20 includes a transmitter RF chain 25 and a receiver RF chain 26. The transmitter RF chain 25 is connected to the DFE 30 and to one or more antenna elements 21 via RF passive components such as a circulator 24 and an RF filter 23 (e.g., a bandpass filter). Reference numeral 22 denotes a connection point (e.g., a TAB connector) with the antenna element 21. A splitter 27 is disposed at the output end of the transmitter RF chain 25 and splits the output signal of the transmitter RF chain 25 for transmit calibration and supplies it to a calibration signal path via a divider 29. A splitter (or combiner) 28 is disposed at the input end of the receiver RF chain 26 and inputs a calibration signal from the calibration signal path to the receiver RF chain 26 for receive calibration.

[0057] However, transmitter RF chain 15 of transceiver RF chain 10 requires a switch to select its transmitter output between a path directed to antenna element 11 and a path for calibration (switch 42). Similarly, receiver RF chain 16 of transceiver RF chain 10 requires a switch to select its receiver input between a path connected to antenna element 11 and a path for calibration (switch 42). In contrast, each of the other transceiver RF chains 20 does not require such a switch.

[0058] The 16-way divider network 41 and switches 42 and 43 are used as signal paths for intra-subunit transmit and receive calibration. During intra-subunit transmit calibration, the 16-way divider network 41 operates to provide calibration signals from the 16 transmitter RF chains (15, 25) to the receivers of the receiver RF chain 16 via switches 42 and 43. Additionally, during intra-subunit receive calibration, the 16-way divider network 41 operates to receive calibration signals from the transmitters of the transmitter RF chain 15 via switches 42 and 43 and provide them to the 16 receiver RF chains (16, 26).

[0059] The 4-way divider network 51 and switches 42 and 43 are used as signal paths for inter-subunit transmit and receive calibration. During inter-subunit transmit calibration, the 4-way divider network 51 receives calibration signals from the representative transmitter RF chains of the other three subunits 120, 130, and 140 via RF lines 162, 163, and 164 and provides them to the receivers of the receiver RF chain 16 via switches 42 and 43. Additionally, during inter-subunit receive calibration, the 4-way divider network 51 receives calibration signals from the transmitters of the transmitter RF chain 15 via switches 42 and 43 and provides them to the representative receiver RF chains of the other three subunits 120, 130, and 140. The 4-way divider network 51 may be connected to the RF lines 162, 163, and 164 via multiple RF connectors 54 (e.g., coaxial connectors).

[0060] In the subunit 110, the switch 52 and the RF connector 53 are not necessarily required, and therefore may be omitted. If the switch 52 is provided, it may always select the line to the 16-way divider network 41.

[0061] The DFE 30 may perform, for example, but is not limited to, low physical layer signal processing and digital radio signal processing. Low physical layer signal processing includes, for example, FFT and IFFT. Digital radio signal processing includes, for example, DPD, CFR, DUC, and DDC. Although not shown, the DFE 30 is communicatively coupled to a controller 150. The controller 150 controls the DFE 30 for intra-subunit and inter-subunit calibration. The controller 150 also controls the DFE 30 of each subunit to multiply the transmit signal of each transmitter RF chain by the calibration weight of that transmitter RF chain determined by transmit calibration. In this way, the controller 150 matches the amplitude and phase characteristics among all transmitters of all subunits. Similarly, the controller 150 controls the DFE 30 of each subunit to multiply the receive signal of that receiver RF chain by the calibration weight of that receiver RF chain determined by receive calibration. In this way, the controller 150 matches the amplitude and phase characteristics among all receivers of all subunits. The DFE 30 may have an interface for communicating with a digital baseband unit (eg, a Distributed Unit (DU) in 5G gNB).

[0062] 4, subunit 120 has the same configuration as subunit 110 shown in FIG. 3. However, for inter-subunit transmit and receive calibration, transceiver RF chain 10 can be connected to RF line 162 via switch 52. In inter-subunit transmit calibration, transmitter RF chain 15 of transceiver RF chain 10 operates as a representative transmitter RF chain and supplies a calibration signal to first subunit 110 via RF line 162. In inter-subunit receive calibration, receiver RF chain 16 of transceiver RF chain 10 operates as a representative receiver RF chain and receives a calibration signal from first subunit 110 via RF line 162.

[0063] In subunit 120, switch 43, 4-way divider network 51, and multiple RF connectors 54 are not necessarily required and may therefore be omitted. If switch 43 is provided, it may always select the line to 16-way divider network 41.

[0064] 5A shows a non-limiting example of the configuration of the transmitter RF chain 15 and the receiver RF chain 16 of the transceiver RF chain 10. In this example, the transmitter RF chain 15 includes two DACs 501, two low-pass filters 502, an IQ modulator 503, a variable attenuator 504, a driver amplifier 505, and a high-power amplifier (HPA) 506. Meanwhile, the receiver RF chain 16 includes two ADCs 521, two low-pass filters 522, an IQ demodulator 523, a variable gain amplifier 524, and an LNA 525. By way of example and not limitation, the elements of the transmitter RF chain 15 from the DAC 501 to the variable attenuator 504 and the elements of the receiver RF chain 16 from the ADC 521 to the variable gain amplifier 524 may be implemented as a single transceiver integrated circuit (IC) 540.

[0065] 5A, a switch 531 is arranged in the transmitter RF chain 15, and a switch 532 is arranged in the receiver RF chain 16. The switch 531 enables the calibration signal output from the transmitter (DAC 501, low-pass filter 502, IQ modulator 503) to be sent to a calibration path during receive calibration within a subunit and between subunits. The switch 532 enables the calibration signal to be sent from the calibration path to the receiver (ADC 521, low-pass filter 522, IQ demodulator 523) during transmit calibration within a subunit and between subunits.

[0066] 5B shows another non-limiting example of the configuration of the transmitter RF chain 15 and the receiver RF chain 16 of the transceiver RF chain 10. FIG. 5B differs from FIG. 5A in that a switch 531 is disposed at the output of the driver amplifier 505. According to the configuration of FIG. 5B, the calibration signal for intra-subunit and inter-subunit receive calibration is amplified by the gain of the driver amplifier 505 before being sent to the calibration path (switch 42). This can contribute to improving the signal-to-noise ratio (SNR) of the calibration signal for intra-subunit and inter-subunit receive calibration.

[0067] The following describes calibration in the configurations of the subunits 110, 120, 130, and 140 described with reference to Figures 3, 4, 5A, and 5B. The bold lines in Figure 6 indicate signal paths used during intra-subunit transmit calibration of the first subunit 110. In this case, under the control of the controller 150, calibration signals generated by the DFE 30 are sent to the 16 transmitter RF chains (15, 25) and received by the receiver of the receiver RF chain 16 via the 16-way divider network 41. The DFE 30 detects the received calibration signals. Based on the results of receiving the calibration signals, the controller 150 calculates correction coefficients (or offsets or weights) to be applied to each transmitter RF chain. The correction coefficients may also be referred to as calibration coefficients, calibration weights, or offsets. The signal paths used during intra-subunit transmit calibration of the other subunits 120, 130, and 140 are similar to those in Figure 6.

[0068] For example, in intra-subunit transmit calibration, the controller 150 may calculate the calibration weights according to the specific example described with reference to Equation (1) in the first embodiment. As described in the first embodiment, the characteristics (frequency response) of the passive components (e.g., the circulator 14 and the RF filter 13) and lines present between the splitters 17 and 18 of the transceiver RF chain 10 and the connection point 12 of the antenna element 11 may be measured at the factory before shipping the AAS 100. Similarly, the characteristics of the passive components and lines present between the splitters 27 and 28 of each of the other transceiver RF chains 20 and the connection point 22 of the antenna element 21 may be measured at the factory before shipping the AAS 100. These measured characteristics may be recorded in the memory of the controller 150 or the corresponding subunit and used for calibration.

[0069] The bold lines in FIG. 7 indicate signal paths used during intra-subunit receive calibration of the first subunit 110. In this case, under the control of the controller 150, a calibration signal is generated by the DFE 30, sent to the calibration path by the transmitter of the transmitter RF chain 15, and received by the 16 receiver RF chains (16, 26) via the 16-way divider network 41. The DFE 30 detects the received calibration signal. Based on the calibration signal reception results, the controller 150 calculates correction coefficients (or offsets or weights) to be applied to each receiver RF chain. The signal paths used during intra-subunit receive calibration of the other subunits 120, 130, and 140 are similar to those in FIG. 7. The correction coefficients may also be referred to as calibration coefficients, calibration weights, or offsets. For example, the controller 150 may calculate the calibration weights for intra-subunit receive calibration in a manner similar to that of the transmit calibration described with reference to Equation (1) in the first embodiment.

[0070] The paths indicated by bold lines in FIG. 8 indicate the signal paths of the first subunit 110 used during inter-subunit transmit calibration. In this case, under the control of the controller 150, the calibration signal generated by the DFE 30 is sent to the transmitter RF chain 15 (i.e., the representative transmitter RF chain of the subunit 110) and received by the receiver of the receiver RF chain 16 via the 16-way divider network 41. In addition, the switch 43 is switched to select the 4-way divider network 51, and the calibration signals transmitted from the representative transmitter RF chains of the second to fourth subunits 120, 130, and 140 are received by the receiver of the receiver RF chain 16 via the 4-way divider network 51. The DFE 30 detects the received calibration signals. Based on the results of receiving the calibration signals, the controller 150 calculates correction coefficients (or offsets or weights) to remove (or compensate for or correct) mismatches in the amplitude and phase relationships between the four representative transmitter RF chains.

[0071] 9 indicates the signal path of the second subunit 120 used during inter-subunit transmission calibration. In this case, under the control of the controller 150, the calibration signal generated by the DFE 30 of the subunit 120 is sent to the transmitter RF chain 15 (i.e., the representative transmitter RF chain of the subunit 120) and output to the RF line 162. The signal paths of the third and fourth subunits 130 and 140 used during inter-subunit transmission calibration are the same as those in FIG. 9.

[0072] The correction coefficients may be referred to as calibration coefficients, calibration weights, or offsets. For example, in inter-subunit transmission calibration, the controller 150 may calculate the calibration weights according to any of the specific examples described with reference to equations (2) to (7) in the first embodiment. Furthermore, the controller 150 may calculate the overall calibration weight according to any of the specific examples described with reference to equations (8) to (9) in the first embodiment.

[0073] 10 indicates the signal path of the first subunit 110 used during inter-subunit receive calibration. In this case, under the control of the controller 150, a calibration signal is generated by the DFE 30, sent to the calibration path by the transmitter of the transmitter RF chain 15, and received by the receiver RF chain 16 (i.e., the representative receiver RF chain of the subunit 110) via the 16-way divider network 41. In addition, the switch 43 is switched to select the 4-way divider network 51, and the calibration signal is sent to the representative receiver RF chains of the second to fourth subunits 120, 130, and 140.

[0074] The paths shown by bold lines in Fig. 11 indicate the signal paths of the second subunit 120 used during inter-subunit receive calibration. In this case, under the control of the controller 150, the receiver RF chain 16 (i.e., the representative receiver RF chain of the subunit 120) receives a calibration signal from the first subunit 110. The signal paths of the third and fourth subunits 130 and 140 used during inter-subunit receive calibration are similar to those in Fig. 11.

[0075] 10 and 11, the DFE 30 of each sub-unit detects the received calibration signal. Based on the reception of the calibration signal, the controller 150 calculates correction coefficients (or offsets or weights) to remove (or compensate or correct) mismatches in amplitude and phase relationships between the four representative receiver RF chains.

[0076] For example, the controller 150 may calculate the calibration weights in inter-subunit receive calibration in a manner similar to the case of transmit calibration described with reference to equations (2) to (7) in the first embodiment. The controller 150 may also calculate the overall calibration weights for receive calibration in a manner similar to the case of transmit calibration described with reference to equations (8) to (9) in the first embodiment.

[0077] As shown in Fig. 8, in the inter-subunit transmission calibration of this embodiment, the calibration signal transmitted from the representative transmitter RF chain 15 of the first subunit 110 is input to the receiver of the receiver RF chain 16 within the circuit board of the first subunit 110, without passing through any lines outside the circuit board of the first subunit 110. Similarly, as shown in Fig. 10, in the inter-subunit reception calibration of this embodiment, the calibration signal transmitted from the transmitter of the transmitter RF chain 15 of the first subunit 110 is supplied to the representative receiver RF chain 16 of the first subunit 110 within the circuit board of the first subunit 110, without passing through any lines outside the circuit board of the first subunit 110.

[0078] <Third embodiment> This embodiment provides another specific example of the configuration and calibration method of the AAS 100 described in the first embodiment. FIG. 12 shows an example of the configuration of the first subunit 110. The configuration shown in FIG. 12 is the same as the configuration shown in FIG. 3. However, in the example of FIG. 12, an RF line 901 is provided. As a result, as shown in FIG. 13, during inter-subunit transmission calibration, a calibration signal transmitted from the representative transmitter RF chain 15 of the first subunit 110 is output to the line 901 outside the circuit board of the first subunit 110, then folded back within the circuit board, and input to the receiver of the receiver RF chain 16. Similarly, as shown in FIG. 14, during inter-subunit reception calibration, a calibration signal transmitted from the transmitter of the transmitter RF chain 15 of the first subunit 110 is output to the line 901 outside the circuit board of the first subunit 110, then folded back within the circuit board, and supplied to the representative receiver RF chain 16 of the first subunit 110.

[0079] <Fourth embodiment> This embodiment provides yet another specific example of the configuration of the AAS 100 and the calibration method described in the first embodiment. Fig. 15 shows an example of the configuration of the first subunit 110, and Fig. 16 shows an example of the configuration of the second subunit 120. If the AAS 100 has three or more subunits, the configurations of the third subunit and subsequent subunits (e.g., subunits 130 and 140) may be the same as that of the second subunit 120. Note that, as shown in Figs. 15 and 16, all subunits may have the same configuration, with only differences in their connection relationships with the RF lines 162 to 164.

[0080] Comparing Figure 15 with Figure 12, Figure 15 differs from Figure 12 in that the 4-way divider network 51 for inter-subunit calibration is connected to a transceiver RF chain 70, which is different from the transceiver RF chain 10, via a switch 81. The configuration of the transceiver RF chain 70 may be the same as the configuration of the transceiver RF chain 10. The configurations of the transceiver RF chains 10 and 70 shown in Figure 15 may be the same as the configuration of the transceiver RF chain 10 described with reference to Figures 3, 5A, and 5B.

[0081] 16, subunit 120 has the same configuration as subunit 110 shown in FIG. 15. However, for inter-subunit transmit and receive calibration, transceiver RF chain 10 can be connected to RF line 162 via switch 52. In subunit 120, switch 81, 4-way divider network 51, and multiple RF connectors 54 are not necessarily required. Therefore, they may be omitted.

[0082] The following describes calibration in the configurations of the subunits 110, 120, 130, and 140 described with reference to FIGS. 15 and 16. The paths indicated by bold lines in FIG. 17 indicate signal paths used during intra-subunit transmit calibration of the first subunit 110. The signal paths shown in FIG. 17 are identical to those shown in FIG. 6. Specifically, under the control of the controller 150, calibration signals generated by the DFE 30 are sent to the 16 transmitter RF chains (15, 25, and 75) and received by the receiver of the receiver RF chain 16 via the 16-way divider network 41. The DFE 30 detects the received calibration signals. Based on the results of receiving the calibration signals, the controller 150 calculates correction coefficients (or offsets or weights) to be applied to each transmitter RF chain. The signal paths used during intra-subunit transmit calibration of the other subunits 120, 130, and 140 are similar to those shown in FIG. 17.

[0083] The correction coefficient may be referred to as a calibration coefficient, a calibration weight, or an offset. For example, in intra-subunit transmission calibration, the controller 150 may calculate the calibration weight according to the specific example described with reference to Equation (1) in the first embodiment.

[0084] The signal paths shown in bold in FIG. 18 are used during intra-subunit receive calibration of the first subunit 110. The signal paths shown in FIG. 18 are identical to those shown in FIG. 7. Specifically, under the control of controller 150, a calibration signal is generated by DFE 30, sent to the calibration path by the transmitter of transmitter RF chain 15, and received by 16 receiver RF chains (16, 26, 76) via 16-way divider network 41. DFE 30 detects the received calibration signal. Based on the calibration signal reception results, controller 150 calculates correction coefficients (or offsets or weights) to be applied to each receiver RF chain. The signal paths used during intra-subunit receive calibration of the other subunits 120, 130, and 140 are similar to those shown in FIG. 18.

[0085] The correction coefficient may be referred to as a calibration coefficient, a calibration weight, or an offset. For example, the controller 150 may calculate the calibration weight in the intra-subunit receive calibration in a manner similar to the case of the transmit calibration described with reference to Equation (1) in the first embodiment.

[0086] The path indicated by the bold line in FIG. 19 indicates the signal path of the first subunit 110 used during inter-subunit transmission calibration. The signal path shown in FIG. 19 is essentially the same as that shown in FIG. 13. The calibration signal transmitted from the representative transmitter RF chain 15 of the first subunit 110 is output to a line 901 outside the circuit board of the first subunit 110 and then folded back within the circuit board. However, FIG. 19 differs from FIG. 13 in that the folded back calibration signal is input to the receiver of the receiver RF chain 76 rather than the receiver of the receiver RF chain 16. Similarly, the calibration signals from the representative transmitter RF chains of the second to fourth subunits 120, 130, and 140 are also input to the receiver of the receiver RF chain 76 via the 4-way divider network 51. The DFE 30 detects the received calibration signal. Based on the results of receiving the calibration signals, the controller 150 calculates correction factors (or offsets or weights) to remove (or compensate or correct) mismatches in amplitude and phase relationships between the four representative transmitter RF chains.

[0087] The paths indicated by bold lines in Fig. 20 indicate the signal paths of the second subunit 120 used during inter-subunit transmission calibration. The signal paths shown in Fig. 20 are the same as those shown in Fig. 9. Specifically, under the control of the controller 150, a calibration signal generated by the DFE 30 of the subunit 120 is sent to the transmitter RF chain 15 (i.e., the representative transmitter RF chain of the subunit 120) and output to the RF line 162. The signal paths of the third and fourth subunits 130 and 140 used during inter-subunit transmission calibration are the same as those in Fig. 20.

[0088] The correction coefficients may be referred to as calibration coefficients, calibration weights, or offsets. For example, in inter-subunit transmission calibration, the controller 150 may calculate the calibration weights according to any of the specific examples described with reference to equations (2) to (7) in the first embodiment. Furthermore, the controller 150 may calculate the overall calibration weight according to any of the specific examples described with reference to equations (8) to (9) in the first embodiment.

[0089] The paths shown by bold lines in Figure 21 indicate signal paths in the first subunit 110 used during inter-subunit receive calibration. The signal paths shown in Figure 21 are basically the same as those shown in Figure 14. However, Figure 21 differs from Figure 14 in that the transmitter of the transmitter RF chain 75, rather than the transmitter RF chain 15, transmits the calibration signal. The calibration signal transmitted by the transmitter of the transmitter RF chain 75 is output to a line 901 outside the circuit board of the first subunit 110, then folded back within the circuit board, and supplied to the representative receiver RF chain 16 of the first subunit 110. The calibration signal is then supplied to the representative receiver RF chains of the second to fourth subunits 120, 130, and 140 via RF lines 162 to 164.

[0090] The paths shown by bold lines in Figure 22 indicate the signal paths of the second subunit 120 used during inter-subunit receive calibration. The signal paths shown in Figure 22 are the same as those shown in Figure 11. Specifically, under the control of the controller 150, the receiver RF chain 16 (i.e., the representative receiver RF chain of the subunit 120) receives a calibration signal from the first subunit 110. The signal paths of the third and fourth subunits 130 and 140 used during inter-subunit receive calibration are the same as those shown in Figure 11.

[0091] 21 and 22, the DFE 30 of each sub-unit detects the received calibration signal. Based on the reception of the calibration signal, the controller 150 calculates correction coefficients (or offsets or weights) to remove (or compensate or correct) mismatches in amplitude and phase relationships between the four representative receiver RF chains.

[0092] For example, the controller 150 may calculate the calibration weights in inter-subunit receive calibration in a manner similar to the case of transmit calibration described with reference to equations (2) to (7) in the first embodiment. The controller 150 may also calculate the overall calibration weights for receive calibration in a manner similar to the case of transmit calibration described with reference to equations (8) to (9) in the first embodiment.

[0093] In this embodiment, the receiver used to receive the calibration signal during intra-subunit transmit calibration of subunit 110 (e.g., the receiver of receiver RF chain 16) is different from the receiver used to receive the calibration signal during inter-subunit transmit calibration (e.g., the receiver of receiver RF chain 76). Similarly, the transmitter used to transmit the calibration signal during intra-subunit receive calibration of subunit 110 (e.g., the transmitter of transmitter RF chain 15) is different from the transmitter used to transmit the calibration signal during inter-subunit receive calibration (e.g., the transmitter of transmitter RF chain 75).

[0094] <Fifth embodiment> This embodiment provides a fallback operation in case an amplifier in the transceiver RF chain fails or is unavailable. An example configuration of the AAS 100 of this embodiment is similar to that described in any of the first to fourth embodiments.

[0095] If an amplifier (e.g., driver amplifier 505 or HPA 506 in FIG. 5A ) of a reference transmitter RF chain 15 for intra-subunit transmit calibration fails, controller 150 uses one of the other transmitter RF chains 25 in that subunit as an alternative reference transmitter RF chain. Controller 150 continues to use the receiver of the receiver RF chain 16 associated with the transmitter RF chain 15 whose amplifier has failed to receive calibration signals from all other transmitter RF chains 25 in intra-subunit transmit calibration.

[0096] FIG. 23 shows adjustments made by the controller 150 when an amplifier in the reference transmitter RF chain 15 for intra-subunit calibration fails. In step 2301, the controller 150 detects that an amplifier in the reference transmitter RF chain 15 for intra-subunit transmit calibration has failed. For example, the controller 15 may detect a transmit amplifier failure, i.e., a failure or abnormality in the transmit system, by detecting that the receive level at a receiver (e.g., a receiver in the receiver RF chain 16) that receives a calibration signal in intra-subunit transmit calibration has fallen below a specified level. In step 2302, the controller 150 uses one of the other transmitter RF chains 25 in the subunit as an alternative reference transmitter RF chain. In step 2303, the controller 150 uses the receiver in the receiver RF chain 16 associated with the transmitter RF chain 15 whose amplifier has failed to receive a calibration signal from the other transmitter RF chain 25 in the subunit.

[0097] If an amplifier (e.g., LNA 525 in FIG. 5A ) of a reference receiver RF chain 16 for intra-subunit receive calibration fails, the controller 150 uses one of the other receiver RF chains 26 in the subunit as an alternative reference receiver RF chain. The controller 150 continues to use the transmitter of the transmitter RF chain 15 associated with the receiver RF chain 16 whose amplifier has failed to transmit calibration signals to all other receiver RF chains 26 in intra-subunit receive calibration.

[0098] FIG. 24 shows adjustments made by the controller 150 when an amplifier in the reference receiver RF chain 16 for intra-subunit receive calibration fails. In step 2401, the controller 150 detects that an amplifier in the reference receiver RF chain 16 for intra-subunit receive calibration has failed. For example, the controller 150 may detect a failure of the receiver low-noise amplifier, i.e., a failure or abnormality in the receive system, by detecting that the received level of the calibration signal at the receiver of the reference receiver RF chain 16 during intra-subunit receive calibration has fallen below a certain specified level. In step 2402, the controller 150 uses one of the other receiver RF chains 26 in the subunit as an alternative reference receiver RF chain. In step 2403, the controller 150 uses the transmitter of the transmitter RF chain 15 associated with the receiver RF chain 16 whose amplifier has failed to transmit a calibration signal to the other receiver RF chains 26 in the subunit.

[0099] If an amplifier fails in the representative transmitter RF chain 15 of the first subunit 110 for inter-subunit transmission calibration, the controller 150 uses one of the other transmitter RF chains 25 in that subunit 110 as an alternative representative transmitter RF chain. The controller 150 continues to use the receiver of the receiver RF chain 16 associated with the transmitter RF chain 15 whose amplifier has failed to receive calibration signals from the alternative representative transmitter RF chain and the representative transmitter RF chains of the other subunits in inter-subunit transmission calibration.

[0100] Similarly, if the amplifier of the representative transmitter RF chain 15 of the second subunit 120 for inter-subunit transmission calibration fails, the controller 150 uses one of the other transmitter RF chains 25 in that subunit 120 as an alternative representative transmitter RF chain.

[0101] 25 shows adjustments made by the controller 150 when an amplifier in the representative transmitter RF chain 15 for inter-subunit transmission calibration fails. In step 2501, the controller 150 detects that an amplifier in the representative transmitter RF chain 15 of the first subunit 110 for inter-subunit transmission calibration has failed. In step 2502, the controller 150 uses any other transmitter RF chain 25 in that subunit 110 as an alternative representative transmitter RF chain. In step 2503, the controller 150 uses the receiver of the receiver RF chain 16 associated with the transmitter RF chain 15 whose amplifier has failed to receive calibration signals from the alternative representative transmitter RF chain and the representative transmitter RF chains of the other subunits.

[0102] If an amplifier fails in the representative receiver RF chain 16 of the first subunit 110 for inter-subunit receive calibration, the controller 150 uses one of the other receiver RF chains 26 in that subunit 110 as an alternative representative receiver RF chain. The controller 150 continues to use the transmitter of the transmitter RF chain 15 associated with the receiver RF chain 16 whose amplifier has failed to transmit a calibration signal to the alternative representative receiver RF chain and the representative receiver RF chains of the other subunits in the inter-subunit receive calibration.

[0103] Similarly, if the amplifier of the representative receiver RF chain 16 of the second subunit 120 for inter-subunit receive calibration fails, the controller 150 uses one of the other receiver RF chains 26 in that subunit 120 as an alternative representative receiver RF chain.

[0104] 26 shows adjustments made by controller 150 when an amplifier in a representative receiver RF chain 16 for inter-subunit receive calibration fails. In step 2601, controller 150 detects that an amplifier in a representative receiver RF chain 16 of a first subunit 110 for inter-subunit receive calibration has failed. In step 2602, controller 150 uses any other receiver RF chain 26 in that subunit 110 as an alternative representative receiver RF chain. In step 2603, controller 150 uses the transmitter of the transmitter RF chain 15 associated with the receiver RF chain 16 whose amplifier has failed to transmit calibration signals to the alternative representative receiver RF chain and the representative receiver RF chains of the other subunits.

[0105] The following paragraphs describe improvements to the subunit configuration to enable fallback operation in the event of an amplifier failure, as described with reference to Figures 23 to 26. Figure 27 shows an example configuration of the first subunit 110, and Figure 28 shows an example configuration of the second subunit 120. If the AAS 100 has three or more subunits, the configurations of the third and subsequent subunits (e.g., subunits 130 and 140) may be the same as that of the second subunit 120. Note that, as shown in Figures 27 and 28, all subunits may have the same configuration, with only differences in their connection relationships with the RF lines 162 to 164.

[0106] Comparing Figure 27 with Figure 12, Figure 27 differs from Figure 12 in that the location of switch 52 has been moved from one of the 16 output ports of 16-way divider network 41 to the input port of that network 41. This allows the output of any of the 16 transmitter RF chains to be used for inter-subunit transmit calibration. In addition, a calibration signal for inter-subunit receive calibration can be supplied to any of the 16 receiver RF chains.

[0107] 28, the outputs of any of the 16 transmitter RF chains can be sent to the first subunit 110 for inter-subunit transmit calibration. In addition, a calibration signal for inter-subunit receive calibration can be supplied from the first subunit 110 to any of the 16 receiver RF chains.

[0108] 27 and 28 show modifications of the subunit configuration example (FIG. 12) of the third embodiment. Similarly, in the subunit configuration example (FIGS. 3 and 4) of the second embodiment, the location of switch 52 may be moved from one of the 16 output ports of 16-way divider network 41 to an input port of said network 41. Similarly, in the subunit configuration example (FIGS. 15 and 16) of the fourth embodiment, the location of switch 52 may be moved from one of the 16 output ports of 16-way divider network 41 to an input port of said network 41.

[0109] The paths shown in bold in Figure 29 indicate the signal paths used during intra-subunit transmit calibration of the first subunit 110. If the amplifier in the reference transmitter RF chain 15 fails, another transmitter RF chain 25 is selected as the alternative reference transmitter RF chain. The calibration signals transmitted from the alternative reference transmitter RF chain 25 and the other 14 transmitter RF chains are received by the receiver in the receiver RF chain 16 via the 16-way divider network 41.

[0110] The paths shown in bold in Figure 30 indicate the signal paths used during intra-subunit receiver calibration of the first subunit 110. If the amplifier in the reference receiver RF chain 16 fails, another receiver RF chain 26 is selected as the alternate reference receiver RF chain. The calibration signal transmitted from the transmitter RF chain 15 is received by the alternate reference receiver RF chain 26 and the other 14 receiver RF chains via a 16-way divider network 41.

[0111] The path indicated by the bold line in Figure 31 indicates the signal path of the first subunit 110 used during inter-subunit transmit calibration. If the amplifier of the representative transmitter RF chain 15 fails, another transmitter RF chain 25 is selected as an alternative representative transmitter RF chain. The calibration signal transmitted from the alternative representative transmitter RF chain 25 is input to the receiver of the receiver RF chain 16 via the 4-way divider network 51. Similarly, the calibration signals from the representative transmitter RF chains of the second to fourth subunits 120, 130, and 140 are also input to the receiver of the receiver RF chain 16 via the 4-way divider network 51.

[0112] 32 indicates the signal path of the second subunit 120 used during inter-subunit transmission calibration. If the amplifier of the representative transmitter RF chain 15 of the second subunit 120 fails, another transmitter RF chain 25 is selected as an alternative representative transmitter RF chain. The calibration signal transmitted from the alternative representative transmitter RF chain 25 is sent to the first subunit 110.

[0113] The paths shown in bold in Figure 33 indicate the signal paths of the first subunit 110 used during inter-subunit receive calibration. If the amplifier in the representative receiver RF chain 16 of the first subunit 110 fails, another receiver RF chain 26 is selected as an alternative representative receiver RF chain. The alternative representative receiver RF chain 26 receives the calibration signal transmitted from the transmitter in the transmitter RF chain 15.

[0114] 34 indicates the signal path of the second subunit 120 used during inter-subunit receive calibration. If the amplifier of the representative receiver RF chain 16 of the second subunit 120 fails, another receiver RF chain 26 is selected as an alternative representative receiver RF chain. The alternative representative receiver RF chain 26 receives the calibration signal transmitted from the transmitter of the transmitter RF chain 15 of the first subunit 110.

[0115] 35 shows an example configuration of the controller 150 in the above-described embodiments. The controller 150 includes a processor 3501 and a memory 3502. The processor 3501 may include multiple processors. The memory 3502 may store one or more software modules (computer programs) including instructions and data for performing the processing by the controller 150 described in the above-described embodiments. In some implementations, the processor 3501 may be configured to read and execute the software modules from the memory 3502, thereby performing the processing of the controller 150 described in the above-described embodiments with reference to the drawings.

[0116] As described with reference to FIG. 35 , the processor included in the controller 150 according to the above-described embodiment can execute one or more programs including instructions for causing a computer to perform the algorithms described with reference to the drawings. The programs include instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The programs may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disk (DVD), Blu-ray® disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage, or other magnetic storage device. The programs may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0117] The above-described embodiments are merely examples of application of the technical ideas obtained by the inventors. In other words, the technical ideas are not limited to the above-described embodiments, and various modifications are possible.

[0118] For example, some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes.

[0119] (Appendix 1) first and second subunits; A controller; Equipped with The first subunit comprises: a first set of antenna elements; a first set of transmitter Radio Frequency (RF) chains coupled to the first set of antenna elements; a first set of receiver RF chains coupled to the first set of antenna elements; a first digital front end coupled to the first set of transmitter RF chains and the first set of receiver RF chains; Equipped with The second subunit comprises: a second set of antenna elements; and a second set of transmitter RF chains coupled to the second set of antenna elements; a second set of receiver RF chains coupled to the second set of antenna elements; a second digital front end coupled to the second set of transmitter RF chains and the second set of receiver RF chains; Equipped with The controller a first transmit calibration to correct for relative differences in amplitude and phase between transmitter RF chains in the first set of transmitter RF chains; a second transmit calibration to correct for relative differences in amplitude and phase between transmitter RF chains in the second set of transmitter RF chains; a third transmit calibration to correct for relative differences in amplitude and phase between a first representative transmitter RF chain included in the first set of transmitter RF chains and a second representative transmitter RF chain included in the second set of transmitter RF chains; configured to: Active antenna system. (Appendix 2) The controller a first receive calibration to correct for relative differences in amplitude and phase between receiver RF chains in the first set of receiver RF chains; a second receive calibration to correct for relative differences in amplitude and phase between receiver RF chains in the second set of receiver RF chains; a third receive calibration to correct for relative differences in amplitude and phase between a first representative receiver RF chain included in the first set of receiver RF chains and a second representative receiver RF chain included in the second set of receiver RF chains; configured to: 10. An active antenna system as defined in claim 1. (Appendix 3) The controller the first transmit calibration using a first receiver in one of the first set of receiver RF chains to receive a calibration signal from the first set of transmitter RF chains; the second transmit calibration using a second receiver in one of the second set of receiver RF chains to receive a calibration signal from the second set of transmitter RF chains; the third transmit calibration uses a third receiver included in one of the first set of receiver RF chains to receive calibration signals from the first representative transmitter RF chain and the second representative transmitter RF chain; It is configured as follows: 3. An active antenna system according to claim 1 or 2. (Appendix 4) the third receiver is the same as the first receiver; 10. An active antenna system as described in Appendix 3. (Appendix 5) the third receiver is different from the first receiver; 10. An active antenna system as described in Appendix 3. (Appendix 6) the first subunit is configured such that, in the third transmission calibration, a calibration signal transmitted from the first representative transmitter RF chain is input to the third receiver within the circuit board of the first subunit without passing through a line outside the circuit board of the first subunit; 5. An active antenna system according to claim 3 or 4. (Appendix 7) the first subunit is configured such that, in the third transmission calibration, a calibration signal transmitted from the first representative transmitter RF chain is output to a line outside a circuit board of the first subunit, then folded back into the circuit board, and input to the third receiver; 6. An active antenna system according to claim 3 or 5. (Appendix 8) The controller the first receive calibration using a transmitter in one of the first set of transmitter RF chains to transmit a calibration signal to the first set of receiver RF chains; the second transmit calibration using a transmitter in one of the second set of transmitter RF chains to transmit a calibration signal to the second set of receiver RF chains; the third transmit calibration uses a transmitter included in one of the first set of transmitter RF chains to transmit a calibration signal to the first representative receiver RF chain and the second representative receiver RF chain; It is configured as follows: 2. An active antenna system as described in claim 2. (Appendix 9) a transmitter RF chain used to transmit the calibration signal in the first receive calibration includes a first transmitter, a first amplifier connected to an output of the first transmitter, and a first RF switch disposed at an output of the first amplifier; the first RF switch is configured to switch between a signal line connected to one or more of the first set of antenna elements and a calibration signal line; 9. An active antenna system as described in claim 8. (Appendix 10) a transmitter RF chain used to transmit the calibration signal in the second receive calibration includes a second transmitter, a second amplifier connected to an output of the second transmitter, and a second RF switch disposed at an output of the second amplifier; the second RF switch is configured to switch between a signal line connected to one or more of the second set of antenna elements and a calibration signal line. 10. An active antenna system according to claim 8 or 9. (Appendix 11) the first representative transmitter RF chain in the third transmit calibration is the same as a reference transmitter RF chain in the first transmit calibration; the reference transmitter RF chain is used as a reference for determining correction factors or offsets for each transmitter RF chain except for the reference transmitter RF chain to correct for relative differences in amplitude and phase; 11. An active antenna system according to any one of claims 1 to 10. (Appendix 12) the controller is configured to use another transmitter RF chain in the first set of transmitter RF chains as an alternative reference transmitter RF chain if an amplifier of the reference transmitter RF chain in the first transmit calibration fails. 12. An active antenna system according to any one of claims 1 to 11. (Appendix 13) the controller is configured to use a receiver of a receiver RF chain associated with the transmitter RF chain whose amplifier has failed to receive calibration signals from other transmitter RF chains of the first set of transmitter RF chains in the first transmit calibration. 13. The active antenna system of claim 12. (Appendix 14) the controller is configured to use another receiver RF chain in the first set of receiver RF chains as an alternative reference receiver RF chain if an amplifier of the reference receiver RF chain in the first receiver calibration fails. 2. An active antenna system as described in claim 2. (Appendix 15) the controller is configured to use a transmitter of a transmitter RF chain associated with the receiver RF chain whose amplifier has failed to transmit a calibration signal to other receiver RF chains of the first set of receiver RF chains in the first receive calibration. 15. The active antenna system of claim 14. (Appendix 16) the controller is configured to use another transmitter RF chain in the first set of transmitter RF chains as an alternative first representative transmitter RF chain if an amplifier of the first representative transmitter RF chain for the third transmit calibration fails. 16. An active antenna system according to any one of claims 1 to 15. (Appendix 17) the controller is configured to use a receiver of a receiver RF chain associated with the transmitter RF chain whose amplifier has failed to receive calibration signals from the alternative first representative transmitter RF chain and the second representative transmitter RF chain in the third transmit calibration. 17. The active antenna system of claim 16. (Appendix 18) the controller is configured to use another transmitter RF chain in the second set of transmitter RF chains as an alternative second representative transmitter RF chain if an amplifier of the second representative transmitter RF chain for the third transmit calibration fails. 18. An active antenna system according to any one of claims 1 to 17. (Appendix 19) the controller is configured to use another receiver RF chain in the first set of receiver RF chains as an alternative first representative receiver RF chain if an amplifier of the first representative receiver RF chain for the third receive calibration fails. 2. An active antenna system as described in claim 2. (Appendix 20) the controller is configured to use a transmitter of a transmitter RF chain associated with the receiver RF chain whose amplifier has failed to transmit a calibration signal to the alternative first representative receiver RF chain and the second representative receiver RF chain in the third receive calibration. 19. The active antenna system of claim 19. (Appendix 21) the controller is configured to use another receiver RF chain in the second set of receiver RF chains as an alternative second representative receiver RF chain if an amplifier of the second representative receiver RF chain for the third receive calibration fails. 21. The active antenna system of claim 2, 19, or 20. (Appendix 22) the first subunit and the second subunit are mounted on respective circuit boards; 22. An active antenna system according to any one of claims 1 to 21. (Appendix 23) a housing that houses the first and second subunits and the controller; 23. An active antenna system according to any one of claims 1 to 22. (Appendix 24) an RF line connecting the first subunit and the second subunit within the housing; 24. The active antenna system of claim 23. (Appendix 25) 1. A method performed by a controller of an active antenna system, comprising: performing a first transmit calibration to correct for relative differences in amplitude and phase among a plurality of transmitter radio frequency (RF) chains in a first subunit of the active antenna system; performing a second transmit calibration to correct for relative differences in amplitude and phase among a plurality of transmitter RF chains in a second subunit of the active antenna system; and performing a third transmit calibration to correct a relative difference in amplitude and phase between a first representative transmitter RF chain included in the plurality of transmitter RF chains in the first subunit and a second representative transmitter RF chain included in the plurality of transmitter RF chains in the second subunit; A method for providing (Appendix 26) 1. A computer program product for causing a controller of an active antenna system to perform a method, comprising: The method comprises: performing a first transmit calibration to correct for relative differences in amplitude and phase among a plurality of transmitter radio frequency (RF) chains in a first subunit of the active antenna system; performing a second transmit calibration to correct for relative differences in amplitude and phase among a plurality of transmitter RF chains in a second subunit of the active antenna system; and performing a third transmit calibration to correct a relative difference in amplitude and phase between a first representative transmitter RF chain included in the plurality of transmitter RF chains in the first subunit and a second representative transmitter RF chain included in the plurality of transmitter RF chains in the second subunit; Prepare, program. [Explanation of symbols]

[0120] 100 Active Antenna System (AAS) 110, 120, 130, 140 subunits 150 Controller 162, 163, 164 RF lines 10, 20, 70 Transceiver RF Chain 15, 25, 75 Transmitter RF Chain 16, 26, 76 Receiver RF Chain 30 Digital Front End (DFE) 3501 processor 3502 memory

Claims

1. first and second subunits; A controller; Equipped with The first subunit comprises: a first set of antenna elements; a first set of transmitter radio frequency (RF) chains coupled to the first set of antenna elements; a first set of receiver RF chains coupled to the first set of antenna elements; a first digital front end coupled to the first set of transmitter RF chains and the first set of receiver RF chains; Equipped with The second subunit comprises: a second set of antenna elements; and a second set of transmitter RF chains coupled to the second set of antenna elements; a second set of receiver RF chains coupled to the second set of antenna elements; a second digital front end coupled to the second set of transmitter RF chains and the second set of receiver RF chains; Equipped with The controller a first transmit calibration to correct for relative differences in amplitude and phase between transmitter RF chains in the first set of transmitter RF chains; a second transmit calibration to correct for relative differences in amplitude and phase between transmitter RF chains in the second set of transmitter RF chains; a third transmit calibration to correct for relative differences in amplitude and phase between a first representative transmitter RF chain included in the first set of transmitter RF chains and a second representative transmitter RF chain included in the second set of transmitter RF chains; configured to: The controller the first transmit calibration using a first receiver in one of the first set of receiver RF chains to receive a calibration signal from the first set of transmitter RF chains; the second transmit calibration using a second receiver in one of the second set of receiver RF chains to receive a calibration signal from the second set of transmitter RF chains; the third transmit calibration uses a third receiver included in one of the first set of receiver RF chains to receive calibration signals from the first representative transmitter RF chain and the second representative transmitter RF chain; It is configured as the first subunit is configured such that, in the third transmission calibration, a calibration signal transmitted from the first representative transmitter RF chain is input to the third receiver within the circuit board of the first subunit without passing through a line outside the circuit board of the first subunit. Active antenna systems.

2. The controller a first receive calibration to correct for relative differences in amplitude and phase between receiver RF chains in the first set of receiver RF chains; a second receive calibration to correct for relative differences in amplitude and phase between receiver RF chains in the second set of receiver RF chains; a third receive calibration to correct for relative differences in amplitude and phase between a first representative receiver RF chain included in the first set of receiver RF chains and a second representative receiver RF chain included in the second set of receiver RF chains; configured to:

10. The active antenna system of claim 1.

3. the third receiver is the same as the first receiver; 3. An active antenna system according to claim 1 or 2.

4. the first representative transmitter RF chain in the third transmit calibration is the same as the reference transmitter RF chain in the first transmit calibration; the reference transmitter RF chain is used as a reference for determining correction factors or offsets for each transmitter RF chain except for the reference transmitter RF chain to correct for relative differences in amplitude and phase; An active antenna system according to any one of claims 1 to 3.

5. the controller is configured to use another transmitter RF chain in the first set of transmitter RF chains as an alternative reference transmitter RF chain if an amplifier of the reference transmitter RF chain in the first transmit calibration fails. An active antenna system according to any one of claims 1 to 4.

6. 1. A method performed by a controller of an active antenna system, comprising: performing a first transmit calibration to correct for relative differences in amplitude and phase among a plurality of transmitter radio frequency (RF) chains in a first subunit of the active antenna system; performing a second transmit calibration to correct for relative differences in amplitude and phase among a plurality of transmitter RF chains in a second sub-unit of the active antenna system; and performing a third transmit calibration to correct a relative difference in amplitude and phase between a first representative transmitter RF chain included in the plurality of transmitter RF chains in the first subunit and a second representative transmitter RF chain included in the plurality of transmitter RF chains in the second subunit; Equipped with the first transmit calibration using a first receiver included in one of a first set of receiver RF chains in the first subunit to receive a calibration signal from the first set of transmitter RF chains; the second transmit calibration using a second receiver included in one of a second set of receiver RF chains in the second subunit to receive a calibration signal from the second set of transmitter RF chains; the third transmit calibration using a third receiver included in one of the first set of receiver RF chains to receive calibration signals from the first representative transmitter RF chain and the second representative transmitter RF chain; In the third transmission calibration, a calibration signal transmitted from the first representative transmitter RF chain is input to the third receiver within the circuit board of the first sub-unit without passing through a line outside the circuit board. method.

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