Patent Publication Number: US-2023163866-A1

Title: Device and method of estimating output power of array antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0162792, filed on Nov. 23, 2021, and Korean Patent Application No. 10-2022-0069577, filed on Jun. 8, 2022, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties. 
     TECHNICAL FIELD 
     This disclosure relates generally to wireless communications, and more particularly, to a device and a method of estimating output power of an array antenna. 
     Discussion of Related Art 
     To increase data throughput in wireless communication, extended frequency bands may be used, such that wireless communication devices may require a capability of processing signals with high frequencies. For example, allocation of 5-th generation (5G) millimeter wave (mmWave) frequencies, which are defined by the 3rd Generation Partnership Project (3GPP), includes high frequency bands of 20 GHz or higher. Signals with such high frequencies, however, have high transmission loss in free space, reducing receive power at the receiving device. 
     To alleviate this problem, array antennas at the transmitting device may be used to increase antenna gain and thereby compensate for the high transmission loss. A tradeoff exists, however, between the amount of output power and power consumption/heat emission at the transmitting device. Therefore, it is desirable to reduce output power when a lower output power will suffice for a particular communication environment. To this end, it is desirable to accurately measure the output power dynamically. 
     SUMMARY 
     Embodiments of the inventive concept provide a device and method of accurately estimating output power of an array antenna. 
     According to an aspect of the inventive concept, there is provided a wireless communications device including an array antenna, which includes a plurality of antennas, a plurality of power amplifiers including a first power amplifier configured to drive a first antenna of the plurality of antennas, a plurality of power detectors including a first power detector configured to detect output power of the first power amplifier, and a controller configured to, in a calibration mode, obtain a first output value of the first power detector after setting the first power amplifier to a first gain and obtain a second output value of the first power detector after setting the first power amplifier to a second gain, while the plurality of antennas are respectively driven by the plurality of power amplifiers, wherein the controller may estimate, in a normal mode, output power of the first antenna from an output value of the first power detector, based on a correction coefficient calculated using the first output value and the second output value. 
     According to another aspect of the inventive concept, there is provided a wireless communication method through an array antenna, the wireless communication method including controlling, in a calibration mode, a plurality of power amplifiers such that a plurality of antennas included in the array antenna are driven, in the calibration mode, setting a first power amplifier, which drives a first antenna from among the plurality of antennas, to a first gain and generating a first output value by detecting output power of the first power amplifier, in the calibration mode, setting the first power amplifier to a second gain and generating a second output value by detecting the output power of the first power amplifier, in a normal mode, generating a third output value by detecting the output power of the first power amplifier, and estimating, in the normal mode, output power of the first antenna from the third output value, based on a correction coefficient calculated using the first output value and the second output value. 
     According to yet another aspect of the inventive concept, there is provided a method of generating a correction coefficient used for estimating output power of an array antenna, the method including, in a calibration mode: driving a plurality of antennas included in the array antenna respectively by a plurality of power amplifiers included in a device including the array antenna; setting a first power amplifier from among the plurality of power amplifiers to respectively a first gain and a second gain; obtaining a first output value and a second output value respectively corresponding to the first gain and the second gain by detecting output power of the first power amplifier; obtaining a first measurement value and a second measurement value respectively corresponding to the first gain and the second gain by measuring the output power of the array antenna; calculating a correction coefficient, based on the first output value, the second output value, the first measurement value, and the second measurement value; and storing the correction coefficient in the device. 
     According to another aspect, a wireless communications device includes an array antenna comprising a plurality of antennas; a plurality of power amplifiers, including a first power amplifier configured to drive a first antenna of the plurality of antennas; a plurality of power detectors, including a first power detector configured to detect output power of the first power amplifier; a memory; and a controller configured to execute operations of the wireless device in a normal mode during communications with a second wireless communications device. The operations include estimating output power of the first antenna from an output value of the first power detector, based on a correction coefficient stored in the memory, wherein the correction coefficient is a coefficient previously calculated using a first output value and a second output value of the first power detector, the first and second output values obtained in a calibration mode with the first power amplifier set to first and second gains, respectively, while the plurality of antennas are respectively driven by the plurality of power amplifiers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the inventive concept will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG.  1    is a diagram illustrating a wireless communication system according to an example embodiment; 
         FIG.  2    is a block diagram illustrating a user equipment according to an example embodiment; 
         FIGS.  3 A and  3 B  are diagrams each illustrating a method of obtaining a correction value for estimating output power of an array antenna, according to an example embodiment; 
         FIG.  4    is a graph depicting an example reflection coefficient of an antenna element in a single antenna element environment vs. an active array antenna environment 
         FIGS.  5 A and  5 B  are diagrams each illustrating radiation patterns of an array antenna, according to example embodiments; 
         FIG.  6    is a flowchart illustrating a method of estimating output power of an array antenna, according to an example embodiment; 
         FIGS.  7 A and  7 B  are message diagrams respectively illustrating examples of a method of estimating output power of an array antenna, according to example embodiments; 
         FIG.  8    is a flowchart illustrating a method of estimating output power of an array antenna, according to an example embodiment; 
         FIG.  9    is a diagram illustrating an example of a correction coefficient according to an example embodiment; 
         FIG.  10    is a graph depicting active modulation phenomena according to an example embodiment; 
         FIG.  11    is a diagram illustrating an example of a correction coefficient according to an example embodiment; and 
         FIG.  12    is a flowchart illustrating a method of estimating output power of an array antenna, according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG.  1    is a diagram illustrating a wireless communication system  5  according to an example embodiment. Some examples of the wireless communication system  5  include a cellular network, such as a 5th generation wireless (5G) system, a Long Term Evolution (LTE) system, an LTE-Advanced system, a Code Division Multiple Access (CDMA) system, or a Global System for Mobile Communications (GSM) system, a Wireless Personal Area Network (WPAN) system. Hereinafter, although descriptions will be made with main reference to a wireless communication system using a cellular network, it will be understood that embodiments of the inventive concept are not limited thereto and may be applied to any suitable wireless communication system. 
     A base station  1  may generally refer to a fixed station communicating with a user equipment and/or another base station and may exchange data and control information by communicating with the user equipment and/or the other base station. For example, the base station  1  may be referred to as a Node B, an evolved-Node B (eNB), a next generation Node B (gNB), a sector, a site, a base transceiver system (BTS), an access point (AP), a relay node, a remote radio head (RRH), a radio unit (RU), a small cell, or the like. As used herein, the term “base station” or “cell” may have a comprehensive meaning representing some areas or functions covered by a base station controller (BSC) in CDMA, a Node-B in WCDMA, an eNB in LTE, a gNB of 5G, a sector (site), or the like, and may include all various coverage areas, such as megacell, macrocell, microcell, picocell, femtocell, relay node, RRH, RU, and small cell communication ranges. 
     A user equipment  10  may refer to any wireless communications equipment, which may be stationary or mobile and may transmit and/or receive data and/or control information by wireles sly communicating with a base station, for example, the base station  1 . For example, the user equipment  10  may be referred to as a terminal, a terminal equipment, a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, a handheld device, or the like. Hereinafter, although embodiments of the inventive concept will be described by mainly taking the user equipment  10  as a wireless communication device for reference, it will be understood that embodiments of the inventive concept are not limited thereto. 
     A wireless communication network between the user equipment  10  and the base station  1  may support a large number of users to communicate with each other by sharing available network resources. For example, in the wireless communication network, information may be transferred by various multiple access schemes, such as CDMA, Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA), OFDM-FDMA, OFDM-TDMA, OFDM-CDMA, and the like. As shown in  FIG.  1   , the user equipment  10  may communicate with the base station  1  through an uplink (UL) and a downlink (DL). In some embodiments, as in Device-to-Device (D2D) communication, user equipments may communicate with each other through a sidelink. As shown in  FIG.  1   , the user equipment  10  may include an array antenna  12 , front-end circuitry (“module”)  14 , back-end circuitry (“module”)  16 , and signal processing circuit  18 . In some embodiments, the array antenna  12 , the front-end module  14 , and the back-end module  16  may be embedded in one antenna module. 
     The array antenna  12  may include a plurality of antennas (interchangeably, “antenna elements”) and may be connected to the front-end module  14 . The array antenna  12  may be used for various purposes such as spatial diversity, polarization diversity, spatial multiplexing, beamforming, or the like. Each of the plurality of antennas in the array antenna  12  may include any suitable type of antenna, for example, a patch antenna, a dipole antenna, or the like. 
     To increase throughput, high microwave and millimeter wave (mmWave) frequencies such as the Frequency Range 2 (FR2) band (24.25 GHz to 52.6 GHz) may be selected for communication. MmWave frequencies, as well as a higher range of microwave frequencies, have high transmission loss in free space. Note that microwave frequencies are often defined as frequencies in the range of 300 MHz to 300 GHz whereas mmWave frequencies are often defined as frequencies in the range of 30 GHz to 300 GHz. Embodiments herein are applicable to any frequency at which it is desirable to accurately measure array antenna output power. For high transmission loss cases, to compensate for the high transmission loss, the user equipment  10  may include the array antenna  12  that increases antenna gain, and may achieve a target or requisite effective isotropically radiated power (EIRP) through the array antenna  12 . Meanwhile, the amount of transmission power needed may depend on the UL channel state: when the UL channel state is poor, high transmission power may be required, but low transmission power may suffice when the UL channel state is good. However, since high transmission power may increase the power consumption of the user equipment  10 , it is desirable to optimize transmission power to achieve high efficiency of the user equipment  10 . In other words, it may be desirable to limit the transmission power to that which is satisfactory (but not excessive) for the current UL channel condition. Herein, the transmission power, which is the power radiated by the array antenna  12  (e.g., defined by EIRP), may be referred to as the output power of the array antenna  12 . 
     The front-end module  14  may be connected to the array antenna  12 . The front-end module  14  may generate a signal, which is output through the array antenna  12 , in a transmission mode and may process a signal, which is received through the array antenna  12 , in a reception mode. As described below with reference to  FIG.  2   , the front-end module  14  may include a power detector and may detect the power of a signal that is output through the front-end module  14 . As described below, e.g., with reference to  FIGS.  3 A,  3 B and  4   , output power of the front-end module  14  may be different from the output power of the array antenna  12 , and thus, it may be desirable to estimate the output power of the array antenna  12  relative to the output power of the front-end module  14 . For instance, there may be significant mismatch losses between the front-end module  14  and the array antenna  12 . As described below, a correction coefficient for estimating the output power of the array antenna  12  may be accurately calculated. Therefore, the output power of the array antenna  12  may be accurately estimated, allowing the transmission power to be accurately controlled. By accurately controlling transmission power, the power consumption and heat emission of the user equipment  10  may be reduced. 
     The back-end module  16  may process a signal provided by the signal processing circuit  18  and provide the signal to the front-end module  14 , in the transmission mode. For example, the back-end module  16  may generate a radio frequency (RF) band signal up-converted from a baseband signal according to a local oscillating signal, in the transmission mode. In addition, the back-end module  16  may process a signal provided by the front-end module  14  and provide the signal to the signal processing circuit  18 , in the reception mode. For example, the back-end module  16  may generate a baseband signal down-converted from an RF band signal according to a local oscillating signal, in the reception mode. In some embodiments, the back-end module  16  may include a phased locked loop (PLL) generating the local oscillating signal. 
     The signal processing circuit  18  may generate a baseband signal, which includes information intended to be transferred to the base station  1 , and provide the baseband signal to the back-end module  16 , in the transmission mode. In addition, the signal processing circuit  18  may extract information from a baseband signal received from the back-end module  16 , in the reception mode. In some embodiments, the signal processing circuit  18  may include a programmable component, such as a central processing unit (CPU) or a digital signal processor (DSP), a reconfigurable component, such as a field programmable gate array (FPGA), and/or a component providing a fixed function, such as an intellectual property (IP) core. 
       FIG.  2    is a block diagram illustrating a user equipment  20  according to an example embodiment. As shown in  FIG.  2   , the user equipment  20  may include an array antenna  21 , a front-end module  22 , a controller  23 , and a memory  24 . In some embodiments, the controller  23  and the memory  24  in  FIG.  2    may be included in the signal processing circuit  18  of  FIG.  1   . The memory  24  may store correction coefficients used for an accurate output power measurement as described below. In addition, the memory  24  (a non-transitory recording medium) may store program instructions that may be read and executed by a processor within the controller  23  to carry out the controller operations as described hereafter. 
     The array antenna  21  may include first to fourth antennas A 1  to A 4 . The front-end module  22  may include first to fourth front-end circuits FE 1  to FE 4  respectively corresponding to the first to fourth antennas A 1  to A 4 , where the first to fourth front-end circuits FE 1  to FE 4  may each have the same structure. As shown in  FIG.  2   , the first front-end circuit FE 1  may include a transmission phase shifter  22 _ 1 , a power amplifier (PA)  22 _ 2 , a transmit/receive (T/R) switch  22 _ 3 , a low noise amplifier (LNA)  22 _ 4 , a reception phase shifter  22 _ 5 , a coupler  22 _ 8 , and a power detector  22 _ 6 . Hereinafter, although an array antenna including four antennas as shown in  FIG.  2    will be mainly described, it should be noted that embodiments of the inventive concept are not limited thereto. 
     In the transmission mode, the transmission phase shifter  22 _ 1  may adjust the phase of a signal TXIN 1  received from the back-end module  16  of  FIG.  1   . The power amplifier  22 _ 2  may amplify an output signal TX 1  of the transmission phase shifter  22 _ 1 . An output signal TXOUT 1  of the power amplifier  22 _ 2  may be provided to the T/R switch  22 _ 3  and may be provided to the first antenna A 1  by the T/R switch  22 _ 3 , set to the transmission mode. In the reception mode, the T/R switch  22 _ 3  may provide a signal RXIN 1 , which is received through the first antenna A 1 , to the LNA  22 _ 4 . The LNA  22 _ 4  may amplify the signal RXIN 1  provided by the T/R switch  22 _ 3 . The reception phase shifter  22 _ 5  may adjust the phase of an output signal RX 1  of the LNA  22 _ 4 , and an output signal RXOUT 1  of the reception phase shifter  22 _ 5  may be provided to the back-end module  16  of  FIG.  1   . It is noted here that in other embodiments, the antennas A 1 -A 4  are used exclusively on transmit and are not shared for receiving operations. In this case, the T/R switch  22 _ 3  may be omitted and the receive path components may be connected directly to other (receive only) antenna elements. 
     The power detector  22 _ 6  may detect output power of the first power amplifier  22 _ 2  by detecting a small portion of the output power coupled through the coupler  22 _ 8 . For example, the power detector  22 _ 6  may sample the output signal TXOUT 1  of the power amplifier  22 _ 2 , and may generate a first detection signal PDET 1  by detecting the output power of the power amplifier  22 _ 2 . The value of the first detection signal PDET 1  may represent the magnitude of the output power of the power amplifier  22 _ 2  and may be referred to herein as an output value of the power detector  22 _ 6 . 
     The controller  23  may receive the first detection signal PDET 1  from the power detector  22 _ 6  and may provide a first gain control signal GCTR 1  to the power amplifier  22 _ 2 . In addition, the controller  23  may receive a first correction coefficient CORR 1  from the memory  24 . The controller  23  may estimate output power of the first antenna A 1 , based on the value of the first detection signal PDET 1  and the first correction coefficient CORR 1 . The controller  23  may adjust the gain of the power amplifier  22 _ 2  through the first gain control signal GCTR 1 , based on the estimated output power of the first antenna A 1 . As a result, the output power of the first antenna A 1  may be adjusted. Although not shown for clarity of illustration, the controller  23  may respectively receive second to fourth detection signals PDET 2 , PDET 3  and PDET 4  from the second to fourth front-end circuits FE 2  to FE 4  and may respectively provide second to fourth gain control signals to the second to fourth front-end circuits FE 2  to FE 4  in a similar manner. Each gain control signal may be based on a respective one of PDET 2 , PDET 3  or PDET 4  and a respective correction coefficient CORR 2 , CORR 3  or CORR 4  (not shown). 
     The memory  24  may store the first correction coefficient CORR 1  and may provide the first correction coefficient CORR 1  to the controller  23 . As described above, the output power of the first antenna A 1  may be calculated based on the first correction coefficient CORR 1 , and thus, the accuracy of the output power of the first antenna A 1  may depend on the first correction coefficient CORR 1 . The memory  24  may store second to fourth correction coefficients CORR 2 , CORR 3  and CORR 4  respectively corresponding to the second to fourth antennas A 2  to A 4 . Examples of correction coefficients stored in the memory  24  will be described below with reference to  FIGS.  9  and  11   . The memory  24  may have any suitable structure for storing correction coefficients. For example, the memory  24  may include volatile memory, such as dynamic random access memory (DRAM) or static random access memory (SRAM), or non-volatile memory, such as flash memory. 
       FIGS.  3 A and  3 B  are diagrams each illustrating a method of obtaining a correction value for estimating output power of an array antenna, according to an example embodiment. The method of  FIG.  3 A  and the method of  FIG.  3 B  may be sequentially performed in the process of manufacturing a user equipment  31  in a calibration mode. 
     Referring to  FIG.  3 A , the user equipment  31  may include the first to fourth antennas A 1  to A 4 . A signal analyzer  32  may receive a signal, which is transmitted by the user equipment  31 , through an antenna A 0  and may measure transmission power of the user equipment  31 . Herein, the magnitude of the transmission power measured by the signal analyzer  32  may be referred to as a measurement value. As shown in  FIG.  3 A , the user equipment  31  may drive only the first antenna A 1  from among the first to fourth antennas A 1  to A 4 . For example, in the user equipment  31 , only one power amplifier (e.g.,  22 _ 2  of front end circuit FE 1  in  FIG.  2   ) from among first to fourth power amplifiers, which respectively correspond to the first to fourth antennas A 1  to A 4 , may be enabled, and the remaining power amplifiers may be disabled (e.g., their bias voltages are turned off). 
     The signal analyzer  32  may measure the output power of the first antenna A 1  by measuring the power of the receive signal and then multiplying it by a multiplier to obtain a measurement value. The measurement value may be in terms of EIRP, in which case the multiplier may be based on both the RF input power to the transmitting antenna, and the free space loss, where the free space loss is positively correlated to the distance between the user equipment  31  and the signal analyzer  32 . In the user equipment  31 , the power detector (e.g.,  22 _ 6  in  FIG.  2   ) associated with the first antenna A 1  may generate the output value PDET 1  by detecting the power of a signal provided to the first antenna A 1 , that is, output power of the first power amplifier. A correction value may be calculated as a difference between the measurement value of the signal analyzer  32  and an output value of the power detector. The correction value may be calculated by the user equipment  31 , as described below with reference to  FIG.  7 A , or may be calculated by the signal analyzer  32 , as described below with reference to  FIG.  7 B . In a similar manner to that described above, correction values respectively for the second to fourth antennas A 2  to A 4  may be calculated. Accordingly, the correction values respectively corresponding to the first to fourth antennas A 1  to A 4 , that is, antenna correction values, may be obtained. 
     Referring to  FIG.  3 B , the user equipment  31  may drive all the first to fourth antennas A 1  to A 4 . For example, in the user equipment  31 , all the first to fourth power amplifiers respectively corresponding to the first to fourth antennas A 1  to A 4  may be enabled, and the first to fourth power amplifiers may respectively drive the first to fourth antennas A 1  to A 4 . 
     The signal analyzer  32  may measure the collective output power of the first to fourth antennas A 1  to A 4  by measuring the power of the receive signal and optionally performing the same adjustment based on estimated free space loss as above. In the user equipment  31 , the first to fourth power detectors respectively corresponding to the first to fourth antennas A 1  to A 4  may generate four output values by detecting powers of signals provided to the first to fourth antennas A 1  to A 4 , that is, output powers of the first to fourth power amplifiers, respectively. The user equipment  31  may then respectively estimate the output power of each of the first to fourth antennas A 1  to A 4  from the four output values generated in  FIG.  3 B , based on the correction values calculated in  FIG.  3 A , that is, the four antenna correction values respectively corresponding to the first to fourth antennas A 1  to A 4 . To this end, a correction value of the array antenna including the first to fourth antennas A 1  to A 4  may be calculated as a difference between the measurement value of the signal analyzer  32  and a sum of the estimated output powers. The correction value of the array antenna may be calculated by the user equipment  31 , as described below with reference to  FIG.  7 A , or may be calculated by the signal analyzer  32 , as described below with reference to  FIG.  7 B . 
     The correction values (i.e., the antenna correction values) obtained in  FIG.  3 A  and the correction value (i.e., the correction value of the array antenna) obtained in  FIG.  3 B  may be used for the user equipment  31  to estimate the output power of the array antenna including the first to fourth antennas A 1  to A 4  from the output values of the first to fourth power detectors, in a normal mode, for example, a mode of communicating with a base station (e.g.,  1  in  FIG.  1   ). As described below with reference to  FIG.  4   , the correction values obtained by the methods of  FIGS.  3 A and  3 B  and the output power of the array antenna, which is estimated by using the correction values, may each include an error. 
       FIG.  4    is a graph depicting an example reflection coefficient of an antenna element, and illustrates how the reflection coefficient may differ in an active array antenna environment vs. a single antenna element environment. In the graph of  FIG.  4   , the horizontal axis represents frequencies, and the vertical axis represents reflection coefficients. Hereinafter, descriptions regarding  FIG.  4    will be made with reference to  FIGS.  3 A and  3 B . 
     In the normal mode, for example, a mode of communicating with a base station (e.g.,  1  of  FIG.  1   ), all the first to fourth antennas A 1  to A 4  included in the array antenna may be driven. Accordingly, the power measured by the signal analyzer  32  while only one antenna is driven, as described above with reference to  FIG.  3 A , may be different from a normalized power (normalized to a single antenna, e.g., one quarter of the array antenna power) measured in the actual normal mode. For example, in  FIG.  3 A , the first antenna A 1  may not be influenced by the second to fourth antennas A 2  to A 4 , for example, mismatch (due to the transmissions of the other antennas), coupling to/from the other antennas (“mutual coupling”), and the like. Therefore, the state of driving only the first antenna A 1  in  FIG.  3 A  may correspond to the S-parameter “S 11 ” (reflection coefficient “looking into” the first antenna A 1 ) in the graph of  FIG.  4    (where the lowest loss due to S 11  occurs at the lowest point in the graph). On the other hand, as described above with reference to  FIG.  3 B , a reflection coefficient measured on the first antenna A 1  while all the first to fourth antennas A 1  to A 4  are driven may correspond to the Active S-parameter in  FIG.  4   . In the example of  FIG.  4   , higher loss due to S 11  occurs at most frequencies for the Active S-parameter case. 
     As shown in  FIG.  4   , the S-parameter and the Active S-parameter may be significantly different from each other over a wide range of frequencies. The load impedance of a power amplifier may depend on a reflection coefficient of an antenna, and thus, when a correction value obtained by driving only one antenna is applied to a state in which an array antenna is driven in the normal mode, an error may be generated. 
       FIGS.  5 A and  5 B  are diagrams each illustrating radiation patterns of an array antenna, according to example embodiments. Specifically, the array antenna radiation diagram of  FIG.  5 A  represents a beam formed in a boresight direction, and the array antenna radiation diagram of  FIG.  5 B  represents a beam formed in a 30-degree direction off boresight. Hereinafter, descriptions regarding  FIGS.  5 A and  5 B  will be made with reference to  FIG.  2   . 
     While a beam is formed by the array antenna  21 , when the gain of a power amplifier driving one antenna is slightly changed, the beam may approximately maintain a pointing angle thereof but may exhibit a change in EIRP. Accordingly, in the calibration mode, a correction coefficient may be calculated based on a change in the EIRP corresponding to a change in the gain of the power amplifier, and in the normal mode, the correction coefficient may be used to accurately estimate the EIRP. 
     Referring to  FIG.  5 A , a reference curve  50   a  represents main lobes formed in the boresight direction, and sidelobes. A first curve  51   a  represents a beam formed when the gain of the first power amplifier  22 _ 2  driving the first antenna A 1  is increased by one step size from the gain corresponding to the reference curve  50   a . As shown in  FIG.  5 A , the first curve  51   a  may have a boresight direction like the reference curve  50   a  and have higher EIRP than the reference curve  50   a . A second curve  52   a  represents a beam formed when the gain of the first power amplifier  22 _ 2  driving the first antenna A 1  is increased by three step sizes from the gain corresponding to the reference curve  50   a . As shown in  FIG.  5 A , the second curve  52   a  may have a boresight direction like the reference curve  50   a  and the first curve  51   a  and have higher EIRP than the reference curve  50   a  and the first curve  51   a.    
     Referring to  FIG.  5 B , a reference curve  50   b  represents main lobes formed in a 30-degree direction off boresight, and sidelobes. A first curve  51   b  represents a beam formed when the gain of the first power amplifier  22 _ 2  driving the first antenna A 1  is increased by one step size from the gain corresponding to the reference curve  50   b . As shown in  FIG.  5 B , the first curve  51   b  may have a 30-degree direction like the reference curve  50   b  and have higher EIRP than the reference curve  50   b . A second curve  52   b  represents a beam formed when the gain of the first power amplifier  22 _ 2  driving the first antenna A 1  is increased by three step sizes from the gain corresponding to the reference curve  50   b . As shown in  FIG.  5 B , the second curve  52   b  may have a 30-degree direction like the reference curve  50   b  and the first curve  51   b  and have higher EIRP than the reference curve  50   b  and the first curve  51   b.    
       FIG.  6    is a flowchart illustrating a method of estimating output power of an array antenna, according to an example embodiment. As shown in  FIG.  6   , the method of estimating output power of an array antenna may include a plurality of operations S 61  to S 69 . Herein, the method of estimating output power of an array antenna may be referred to as a wireless communication method through an array antenna. In some embodiments, the method of  FIG.  6    may be performed by the user equipment  20  of  FIG.  2   . Hereinafter, descriptions regarding  FIG.  6    are given with reference to  FIG.  2   . 
     As described with reference to  FIGS.  5 A and  5 B , when the gain of a power amplifier driving one of the antennas included in an array antenna is slightly changed, a direction of a beam formed by the array antenna may be maintained, but the EIRP thereof may change. Accordingly, as described below with reference to  FIG.  6   , a correction coefficient may be calculated based on output values and measurement values, both corresponding to two or more different gains. With this technique, the correction coefficient may be highly accurate. 
     Referring to  FIG.  6   , in operation S 61 , a calibration mode may be set. For example, as described above with reference to  FIGS.  3 A and  3 B , during the process of manufacturing the user equipment  20 , a signal analyzer may be used to measure the output power of the array antenna  21 . The user equipment  20  may be set to the calibration mode and may transmit an appropriate signal through the array antenna  21  according to conditions described below. 
     In operation S 62 , a plurality of antennas may be driven. For example, the controller  23  may control the front-end module  22  such that all the first to fourth antennas A 1  to A 4  of the array antenna  21  are driven. Accordingly, power amplifiers respectively included in the first to fourth front-end circuits FE 1  to FE 4  may respectively drive the first to fourth antennas A 1  to A 4 . 
     In operation S 63 , a first power amplifier may be set to a first gain. For example, the controller  23  may generate the first gain control signal GCTR 1  to set, to the first gain, the gain of the first power amplifier  22 _ 2 , which drives the first antenna A 1  from among the first to fourth antennas A 1  to A 4  of the array antenna  21 . The first gain may be different from a second gain described below. The second to fourth antennas A 2  to A 4  may also be driven by their respective power amplifiers which may be biased to have the same respective gains as they have in the normal mode (“normal mode gains”). These gains may be different from the first gain. In other words, the first gain of the first power amplifier may be a gain that is changed from its normal mode gain. It is noted that in some embodiments, all the antennas A 1  to A 4  are driven with the same power in the normal mode (which may be realized by setting the same gain for each of the power amplifiers). In other embodiments, different powers are applied to different ones of the antennas A 1  to A 4  in the normal mode. 
     In operation S 64 , output power of the first power amplifier may be detected. For example, the first power detector  22 _ 6  may sample the output signal TXOUT 1  of the first power amplifier  22 _ 2  and may generate the first detection signal PDET 1  by detecting the output power of the first power amplifier  22 _ 2 . The controller  23  may identify the magnitude of the output power of the first power amplifier  22 _ 2 , based on a value of the first detection signal PDET 1  corresponding to the first gain (a “first output value” of the first power amplifier  22 _ 2 ). In addition, a signal analyzer (e.g.,  32  of  FIGS.  3 A and  3 B ) a certain distance away from the user equipment  20  may measure the output power of the array antenna  21 , which includes the first antenna A 1  driven by the first power amplifier  22 _ 2  that is set to the first gain, and may generate a first measurement value. The first measurement value, e.g., defined in terms of EIRP, may be obtained by the signal analyzer measuring received signal power and multiplying the same by a multiplier. The multiplier may be based on free space loss and RF input power at the transmitting antenna, where the RF input power is associated with the first gain. 
     In operation S 65 , the first power amplifier may be set to the second gain. For example, the controller  23  may generate the first gain control signal GCTR 1  to set, to the second gain, the gain of the first power amplifier  22 _ 2 , which drives the first antenna A 1  from among the first to fourth antennas A 1  to A 4  of the array antenna  21 . The second gain may be different from the first gain described above and may be different from the normal mode gain of the first power amplifier. The remaining power amplifiers driving the second to fourth antennas A 2  to A 4  may be biased to have the same gain as in operation S 63 . In some embodiments, a difference between the first gain and the second gain may correspond to a minimum step size of the gain of the first power amplifier  22 _ 2 . In some embodiments, the difference between the first gain and the second gain may have a magnitude resulting in no change, or only a slight change, in the radiation pattern of the array antenna (e.g., the main lobe still points in the same direction within a tolerance range). In operation S 66 , the output power of the first power amplifier may again be detected, in the same manner as described above for operation S 64 , to obtain a second output value of the first power amplifier  22 _ 2 . Correspondingly, the signal analyzer may generate a second measurement value in the same manner as described above. 
     A correction coefficient of the first antenna A 1  may be calculated based on the first output value and the first measurement value, which correspond to the first gain, and the second output value and the second measurement value, which correspond to the second gain. The correction coefficient of the first antenna A 1  may be calculated based on a difference between the first output value and the second output value and a difference between the first measurement value and the second measurement value. For example, a correction coefficient Ci of the first antenna A 1  may be calculated based on Equation 1: 
     
       
         
           
             
               
                 
                   
                     C 
                     1 
                   
                   = 
                   
                     
                       
                         EIRP 
                         1 
                       
                       - 
                       
                         EIRP 
                         2 
                       
                     
                     
                       
                         OUT 
                         1 
                       
                       - 
                       
                         OUT 
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     In Equation 1, EIRP 1  and EIRP 2  are respectively the first measurement value and the second measurement value, and OUT 1  and OUT 2  are respectively the first output value and the second output value. The correction coefficient may be calculated by the user equipment  20 , as described below with reference to  FIG.  7 A , or may be calculated by the signal analyzer receiving a signal from the user equipment  20 , as described below with reference to  FIG.  7 B . The calculated correction coefficient may be stored in the memory  24 . It is noted here that EIRP 1  may be referenced to an isotropic radiator driven by a first RF input power associated with the first gain, and EIRP 2  may be referenced to an isotropic radiator driven by a second RF input power associated with the second gain. Thus, the first and second measurement values may be obtained by multiplying the actual respective receive powers at the signal analyzer by different respective multipliers, which reflect the same free space loss but different RF input power, with reference to a hypothetical lossless, effective isotropic radiator in the two cases. 
     In operation S 67 , a normal mode may be set. For example, the process of manufacturing the user equipment  20  may be completed, and the user equipment  20  may be set to the normal mode. The user equipment  20  may communicate with another wireless communication device, for example, the base station  1  of  FIG.  1   , through the array antenna  21 , in the normal mode. 
     In operation S 68 , the output power of the first power amplifier  22 _ 2  may be detected, based on the value of the first detection signal PDET 1  obtained in the same manner as in the calibration mode. 
     In operation S 69 , the output power of the first antenna A 1  may be estimated. For example, the controller  23  may estimate the output power of the first antenna A 1 , based on the correction coefficient calculated in the calibration mode and the output value obtained in operation S 68 . For example, the output power, when defined in terms of EIRP, of the first antenna A 1  may be calculated based on Equation 2. 
       EIRP= C   1 *OUT   [Equation 2]
 
     In Equation 2, C 1  may be the correction coefficient of Equation 1, and OUT may be the output value obtained in operation S 68 . As described below with reference to  FIG.  12   , the controller  23  may estimate the respective output powers of the first to fourth antennas A 1  to A 4  and may control the respective gains of the first to fourth power amplifiers, based on the estimated output powers. 
       FIGS.  7 A and  7 B  are message diagrams respectively illustrating examples of a method of estimating output power of an array antenna, according to example embodiments. Specifically, the message diagrams of  FIGS.  7 A and  7 B  respectively illustrate operations of signal analyzers  72   a  and  72   b  and user equipments  71   a  and  71   b  set to the calibration mode, over time. 
     Referring to  FIG.  7 A , in operation S 71   a , the user equipment  71   a  may transmit a first signal to the signal analyzer  72   a . For example, the user equipment  71   a  may transmit the first signal to the signal analyzer  72   a  through an array antenna, and the signal analyzer  72   a  may receive the first signal through an antenna. During the transmission of the first signal, the user equipment  71   a  may set, to a first gain, a first power amplifier, which drives a first antenna from among antennas included in the array antenna. 
     In operation S 72   a , the user equipment  71   a  may detect output power of the first power amplifier. For example, a first power detector included in the user equipment  71   a  may detect the output power of the first power amplifier and may generate a first output value. In operation S 73   a , the signal analyzer  72   a  may measure the power of the first signal. For example, the signal analyzer  72   a  may measure the power of the first signal, which is received from the user equipment  71   a  in operation S 71   a , and may generate a first measurement value in the manner described above. 
     In operation S 74   a , the user equipment  71   a  may transmit a second signal to the signal analyzer  72   a . For example, the user equipment  71   a  may transmit the second signal to the signal analyzer  72   a  through the array antenna, and the signal analyzer  72   a  may receive the second signal through the antenna. During the transmission of the second signal, the user equipment  71   a  may set, to a second gain, the first power amplifier, which drives the first antenna from among the antennas included in the array antenna. 
     In operation S 75   a , the user equipment  71   a  may detect the output power of the first power amplifier. For example, the first power detector included in the user equipment  71   a  may detect the output power of the first power amplifier and may generate a second output value. In operation S 76   a , the signal analyzer  72   a  may measure the power of the second signal. For example, the signal analyzer  72   a  may measure the power of the second signal, which is received from the user equipment  71   a  in operation S 74   a , and may generate a second measurement value as described earlier. 
     In operation S 77   a , the signal analyzer  72   a  may provide the first measurement value and the second measurement value to the user equipment  71   a . In some embodiments, the signal analyzer  72   a  may transmit a signal including the first measurement value and the second measurement value to the user equipment  71   a  through the antenna, and the user equipment  71   a  may receive the signal including the first measurement value and the second measurement value through the array antenna. In some embodiments, the signal analyzer  72   a  and the user equipment  71   a  may have a communication channel (e.g., a wired or wireless communication channel) that is different from a wireless communication channel through the array antenna of the user equipment  71   a , and the signal analyzer  72   a  may provide the first measurement value and the second measurement value to the user equipment  71   a  through the corresponding communication channel. 
     In operation S 78   a , the user equipment  71   a  may calculate a correction coefficient. For example, the user equipment  71   a  or a controller in the user equipment  71   a  may calculate the correction coefficient, based on the first output value and the second output value, which are respectively obtained in operations S 72   a  and S 75   a , and the first measurement value and the second measurement value, which are provided by the signal analyzer  72   a  in operation S 77   a . In some embodiments, the user equipment  71   a  may calculate the correction coefficient, based on Equation 1. 
     In operation S 79   a , the user equipment  71   a  may store the correction coefficient. For example, the controller of the user equipment  71   a  may store, in a memory, the correction coefficient calculated in operation S 78   a . The correction coefficient stored in the memory may be used for the user equipment  71   a  to estimate the output power of the array antenna, in the normal mode. 
     The operations of  FIG.  7 A  may be repeated for each of the remaining antennas A 2 -A 4  of the antenna array, resulting in a respective correction coefficient being calculated and stored in association with each of the antennas A 1 -A 4 . 
     Referring to  FIG.  7 B , operations S 71   b , S 72   b , S 73   b , S 74   b , S 75   b  and S 76   b  may be the same as operations S 71   a -S 76   a  of  FIG.  7 A  described above, but using user equipment  71   b  and signal analyzer  72   b.    
     In operation S 77   b , the user equipment  71   b  may provide the first output value and the second output value to the signal analyzer  72   b . The user equipment  71   b  may transmit a signal including the first output value and the second output value to the signal analyzer  72   b  through the array antenna, and the signal analyzer  72   b  may receive the signal including the first output value and the second output value through the antenna. Note that the signal analyzer  72   b  and the user equipment  71   b  may have a communication channel (e.g., a wired or wireless communication channel) that is different from a wireless communication channel through the array antenna of the user equipment  71   b , and the signal analyzer  72   b  may receive the first output value and the second output value from the user equipment  71   b  through the corresponding communication channel. 
     In operation S 78   b , the signal analyzer  72   b  may calculate a correction coefficient. For example, the signal analyzer  72   b  may calculate the correction coefficient, based on the first measurement value and the second measurement value, which are respectively obtained in operations S 73   b  and S 75   b , and the first output value and the second output value, which are provided by the user equipment  71   b  in operation  77   b . The signal analyzer  72   b  may calculate the correction coefficient, based on Equation 1. 
     In operation S 79   b , the signal analyzer  72   b  may provide the correction coefficient to the user equipment  71   b.  For example, the signal analyzer  72   b  may provide the correction coefficient calculated in operation S 78   b  to the user equipment  71   b , through the communication channel through which the first output value and the second output value are received from the user equipment  71   b  in operation S 77   b.    
     In operation S 80   b , the user equipment  71   b  may store the correction coefficient. For example, the controller of the user equipment  71   b  may store, in a memory, the correction coefficient provided by the signal analyzer  72   b  in operation S 79   b . The correction coefficient stored in the memory may be used for the user equipment  71   b  to estimate the output power of the array antenna, in the normal mode. 
     The operations of  FIG.  7 B  may be repeated for each of the remaining antennas A 2 -A 4  of the antenna array, resulting in a respective correction coefficient being calculated and stored in association with each of the antennas A 1 -A 4 . 
       FIG.  8    is a flowchart illustrating a method of estimating output power of an array antenna, according to an example embodiment. As shown in  FIG.  8   , the method of estimating output power of an array antenna may include a plurality of operations S 81  to S 86 . As described above with reference to  FIGS.  7 A and  7 B , the method of  FIG.  8    may be performed by a user equipment or a signal analyzer. Hereinafter, although it is assumed that the method of  FIG.  8    is performed by the user equipment  20 , it should be noted that embodiments of the inventive concept are not limited thereto. Hereinafter, descriptions regarding  FIG.  8    will be made with reference to  FIG.  2   . 
     Referring to  FIG.  8   , in operation S 81 , a first output value and a first measurement value may be obtained. For example, the first output value may be generated by detecting, by the first power detector  22 _ 6 , the output power of the first power amplifier  22 _ 2 , while the first power amplifier  22 _ 2  is set to a first gain. In addition, the first measurement value may be generated by measuring, by a signal analyzer, the output power of the array antenna  21 , while the first power amplifier  22 _ 2  is set to the first gain. 
     In operation S 82 , a second output value and a second measurement value may be obtained. For example, the second output value may be generated by detecting, by the first power detector  22 _ 6 , the output power of the first power amplifier  22 _ 2 , while the first power amplifier  22 _ 2  is set to a second gain that is different from the first gain. In addition, the second measurement value may be generated by measuring, by the signal analyzer, the output power of the array antenna  21 , while the first power amplifier  22 _ 2  is set to the second gain. 
     In operation S 83 , a first correction coefficient may be calculated. For example, the controller  23  may calculate the first correction coefficient, based on the first output value and the first measurement value, which are obtained in operation S 81 , and the second output value and the second measurement value, which are obtained in operation S 82 . In some embodiments, the controller  23  may calculate the first correction coefficient, based on Equation 1. 
     In operation S 84 , a third output value and a third measurement value may be obtained. For example, the third output value may be generated by detecting, by the first power detector  22 _ 6 , the output power of the first power amplifier  22 _ 2 , while the first power amplifier  22 _ 2  is set to a third gain that is different from the first gain and the second gain. In addition, the third measurement value may be generated by measuring, by the signal analyzer, the output power of the array antenna  21 , while the first power amplifier  22 _ 2  is set to the third gain. In some embodiments, the second gain may correspond to a gain obtained by increasing the first gain by as much as a step size, and the third gain may correspond to a gain obtained by decreasing the first gain by as much as the step size. 
     In operation S 85 , a second correction coefficient may be calculated. In some embodiments, the controller  23  may calculate the second correction coefficient, based on the first output value and the first measurement value, which are obtained in operation S 81 , and the third output value and the third measurement value, which are obtained in operation S 84 . In some embodiments, the controller  23  may calculate the second correction coefficient, based on the second output value and the second measurement value, which are obtained in operation S 82 , and the third output value and the third measurement value, which are obtained in operation S 84 . For example, the controller  23  may calculate the second correction coefficient, based on Equation 1. 
     In operation S 86 , a final correction coefficient may be calculated. For example, the controller  23  may calculate a correction coefficient of a first antenna, based on the first correction coefficient calculated in operation S 83  and the second correction coefficient calculated in operation S 85 . In some embodiments, the controller  23  may calculate an average of the first correction coefficient and the second correction coefficient as the final correction coefficient. Although  FIG.  8    illustrates an example of calculating the final correction coefficient from two correction coefficients, the final correction coefficient may also be calculated based on three or more correction coefficients, in some embodiments. 
       FIG.  9    is a diagram illustrating an example of a correction coefficient according to an example embodiment. In some embodiments, the memory  24  of  FIG.  2    may store the correction coefficients of  FIG.  9   . Hereinafter, descriptions regarding  FIG.  9    will be made with reference to  FIG.  2   . 
     The memory  24  may store four correction coefficients C 1  to C 4  respectively corresponding to the first to fourth antennas A 1  to A 4  included in the array antenna  21 . As described above with reference to  FIGS.  6 ,  7 A,  7 B, and  8   , in the calibration mode, each of the four correction coefficients C 1  to C 4  may be calculated, and the controller  23  may store the four correction coefficients C 1  to C 4  in the memory  24 . In the normal mode, the controller  23  may read the four correction coefficients C 1  to C 4  from the memory  24  and may accurately estimate the output power of the array antenna  21 , based on the four correction coefficients C 1  to C 4  and the output values of the first to fourth power detectors. For example, the output power, that is, EIRP est , of the array antenna  21  may be calculated based on Equation 3: 
     
       
         
           
             
               
                 
                   
                     EIRP 
                     
                       e 
                       ⁢ 
                       s 
                       ⁢ 
                       t 
                     
                   
                   = 
                   
                     
                       ∑ 
                       
                         k 
                         = 
                         1 
                       
                       4 
                     
                     
                       
                         C 
                         k 
                       
                       * 
                       
                         OUT 
                         k 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     In Equation 3, C k  is a correction coefficient corresponding to a k-th antenna, and OUT k  is output power of a k-th power amplifier driving the k-th antenna. 
       FIG.  10    is a graph depicting an example “active reflection coefficient” vs. frequency in an array antenna. In the graph of  FIG.  10   , the horizontal axis represents frequencies, and the vertical axis represents an Active S-parameter (“Active S 11 ”), representing a reflection coefficient looking into one of the antenna elements while all antenna elements of the array are actively driven. Hereinafter, descriptions regarding  FIG.  10    will be made with reference to  FIG.  1   . 
     In the normal mode, for example, a mode of communicating with the base station  1 , phases of signals respectively provided to the antennas included in the array antenna  12  may be changed according to beam steering. Accordingly, reflection coefficients of the respective antenna elements of the array antenna  12  may be changed according to an angle of a beam, and the change in the reflection coefficients of the may cause changes in load impedances of power amplifiers. For example, the graph of  FIG.  10    illustrates Active S 11  of an antenna element during respective beamforming environments of six beams (for example, Beam # 0  to Beam # 5 ) respectively having different angles. As shown in  FIG.  10   , when beams respectively having different angles are formed, the Active S 11  for an antenna element may differ from beam to beam over a wide range of frequencies. Therefore, for the accurate estimation of EIRP, the angle of the beam may be considered. 
       FIG.  11    is a diagram illustrating examples of correction coefficients according to an example embodiment. In some embodiments, the memory  24  of  FIG.  2    may store the correction coefficients of  FIG.  11   . Hereinafter, descriptions regarding  FIG.  11    will be made with reference to  FIG.  2   . 
     The memory  24  may store correction coefficients corresponding to each of the first to fourth antennas A 1  to A 4  included in the array antenna  21 . For example, as shown in  FIG.  11   , the memory  24  may store correction coefficients C 11  to C 1n  corresponding to the first antenna A 1  and may store correction coefficients C 41  to C 4n  corresponding to the fourth antenna A 4  (where n is an integer greater than 1). In addition, the memory  24  may store correction coefficients according to beam steering. For example, as shown in  FIG.  11   , the memory  24  may store correction coefficients (e.g., C 11 , C 41 , and the like) corresponding to a first angle θ 1  of the beam and may store correction coefficients (e.g., C 1n , C 4n , and the like) corresponding to an n-th angle θ n  of the beam. 
     Each of the correction coefficients of  FIG.  11    may be calculated based on power detected and measured while the array antenna  21  forms the beam having an angle corresponding to each of the correction coefficients. For example, the correction coefficient C 11 , which corresponds to the first antenna A 1  and the first angle θ 1 , may be calculated based on output values and measurement values, which are obtained by changing the gain of the first power amplifier  22 _ 2  driving the first antenna A 1 , while the phase shifters of the front-end module  22  are set such that the beam formed by the array antenna  21  has the first angle θ 1 . Similarly, the correction coefficient C 1n , which corresponds to the first antenna A 1  and the n-th angle θ n , may be calculated based on output values and measurement values, which are obtained by changing the gain of the first power amplifier  22 _ 2  driving the first antenna A 1 , while the phase shifters of the front-end module  22  are set such that the beam formed by the array antenna  21  has the n-th angle θ n . In the normal mode, the controller  23  may read correction coefficients corresponding to an angle of the beam from the memory  24  and may estimate the output power of the array antenna  21 , based on the correction coefficients and output values, and thus, the output power corresponding to the angle of the beam may be accurately estimated. 
       FIG.  12    is a flowchart illustrating a method of estimating output power of an array antenna, according to an example embodiment. Specifically, the flowchart of  FIG.  12    represents the method performed by a user equipment in the normal mode. As shown in  FIG.  12   , the method of estimating output power of an array antenna may include a plurality of operations S 121  to S 124 . In some embodiments, the method of  FIG.  12    may be performed by the user equipment  20  of  FIG.  2   , and hereinafter, descriptions regarding  FIG.  12    will be made with reference to  FIG.  2   . 
     Referring to  FIG.  12   , in operation S 121 , a plurality of output values may be obtained. For example, in the normal mode, the user equipment  20  may communicate with another wireless communication device (e.g., the base station  1  of  FIG.  1   ) and may transmit a signal to the other wireless communication device through the array antenna  21 . During the transmission of the signal through the array antenna  21 , first to fourth power detectors may respectively detect output powers of first to fourth power amplifiers and may respectively generate detection signals. The controller  23  may identify the output powers of the first to fourth power amplifiers, based on values of the detection signals (“output values”). 
     In operation S 122 , a plurality of correction coefficients may be obtained. For example, the controller  23  may read, from the memory  24 , four correction coefficients respectively corresponding to the first to fourth antennas A 1  to A 4 . In some embodiments, as described above with reference to  FIG.  11   , when the memory  24  stores correction coefficients corresponding to various angles of a beam, the controller  23  may identify an angle of the beam formed by the array antenna  21  and may read, from the memory  24 , correction coefficients corresponding to the identified angle. 
     In operation S 123 , output power of an array antenna may be estimated. For example, the controller  23  may estimate the output power of the array antenna  21 , based on the plurality of output values obtained in operation S 121  and the plurality of correction coefficients obtained in S 122 . In some embodiments, the controller  23  may estimate an output power of the first antenna A 1 , based on the output value and the correction coefficient, which correspond to the first antenna A 1 . Similarly, the controller  23  may estimate respective output powers of the second to fourth antennas A 2  to A 4  and may estimate the output power of the array antenna  21  by summing the estimated output powers. 
     In operation S 124 , a plurality of gains of a plurality of power amplifiers may be controlled. For example, the controller  23  may compare the output power of the array antenna  21 , which is estimated in operation S 123 , with target transmission power. The target transmission power may refer to a desired transmission power or a transmission power required for the communication with another wireless communication device and may be defined based on an error rate, such as a bit error rate (BER), block error rate (BLER), or the like. For example, the target transmission power may be defined by the base station  1  of  FIG.  1    and provided to the user equipment  20 , or may be defined by the user equipment  20 . The controller  23  may compare the output power of the array antenna  21 , which is estimated in operation S 123 , with the target transmission power. When the estimated output power is lower than the target transmission power, the controller  23  may increase the gains of the first to fourth power amplifiers. On the other hand, when the estimated output power is higher than the target transmission power, the controller  23  may decrease the gains of the first to fourth power amplifiers. Due to the accurately estimated output power of the array antenna  21 , the gains of the first to fourth power amplifiers may be accurately set according to the target transmission power. As a result, power consumption by the first to fourth power amplifiers may be optimally controlled, and the transmission of signals with incorrect power levels may be prevented. 
     Exemplary embodiments of the inventive concept have been described herein with reference to signal arrows, block diagrams, flowcharts and/or algorithmic expressions. Each block of the block diagrams and combinations of blocks in the block diagrams, and operations according to the algorithmic expressions can be implemented by hardware (e.g., processing circuitry of controller  23  in cooperation with memory  24  accompanied by computer program instructions). Such computer program instructions may be stored in a non-transitory computer readable medium (e.g., memory  24 ) that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the block diagram. 
     While the inventive concept has been particularly shown and described with reference to embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the following claims.