Patent Publication Number: US-2022231713-A1

Title: Wireless communication apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2021-008081, filed on Jan. 21, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to wireless communication apparatuses. 
     BACKGROUND 
     Conventionally, there is a radio frequency (RF) transmitter which includes a mixer, a first amplifier connected to an output of the mixer, a plurality of phase shifters connected to an output of the first amplifier, and a plurality of second amplifiers connected to respective outputs of the plurality of phase shifters. This RF transmitter transmits signals amplified by the plurality of second amplifiers, via a phased antenna array (or array antenna). An example of such an RF transmitter is proposed in Japanese National Publication of International Patent Application No. 2020-507230, for example. 
     However, in the RF transmitter illustrated in FIG. 26 of Japanese National Publication of International Patent Application No. 2020-507230, for example, the first amplifier and the plurality of second amplifiers are not configured to variably control the gain. On the other hand, if a plurality of first variable gain amplifiers and a plurality of second variable gain amplifiers were connected in series, a circuit scale would become large. 
     SUMMARY 
     Accordingly, one aspect of the embodiments provides a wireless communication apparatus which can reduce the circuit scale thereof. 
     According to one aspect of the embodiments, a wireless communication apparatus includes a signal terminal configured to receive a transmitting signal; N antenna elements, where N is an integer greater than or equal to 2; a first variable amplifier including a first input terminal coupled to the signal terminal, and a first output terminal; and N second variable amplifiers including N second input terminals coupled to the first input terminal, and N second output terminals coupled to the N antenna elements, respectively, wherein the first variable amplifier is configured to amplify the transmitting signal received from the signal terminal via the first input terminal with a gain which is weighted and adjustable according to a first weight, and output the amplified transmitting signal via the first output terminal, and wherein the N second variable amplifiers are configured to amplify the amplified transmitting signal received from the first output terminal via the N second input terminals with gains which are weighted and adjustable according to N second weights, and output the amplified transmitting signal, which is amplified by the N second variable amplifiers, to the N antenna elements via the N second output terminals. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a base station, and a radio unit including a wireless communication apparatus according to one embodiment. 
         FIG. 2  is a diagram illustrating an array antenna of the wireless communication apparatus. 
         FIG. 3A ,  FIG. 3B , and  FIG. 3C  are diagrams for explaining a Chebyshev weighting. 
         FIG. 4  is a diagram illustrating the wireless communication apparatus. 
         FIG. 5A  and  FIG. 5B  are diagrams illustrating two beams. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Preferred embodiments of the present invention will be described with reference to the accompanying drawings. 
     A description will now be given of the wireless communication apparatus according to each embodiment of the present invention. 
       FIG. 1  is a block diagram illustrating a base station  10 , and a radio unit (RU)  20  including a wireless communication apparatus  100  according to one embodiment. The base station  10  is formed by a distributed unit (DU), and a central unit (CU). The base station  10  includes an ID output circuit  11 , and signal output circuits  12  and  13 . The base station  10  includes components other than the ID output circuit  11  and the signal output circuits  12  and  13 , however, illustration of such other components will be omitted. 
     The ID output circuit  11  outputs an ID number to a decoder  21  of the RU  20 . The ID number output from the ID output circuit  11  includes multiple kinds of ID numbers. Each kind of ID number is allocated to information related to a direction of a beam output from an array antenna of the wireless communication apparatus  100 . The signal output circuit  12  outputs a transmitting signal to the wireless communication apparatus  100  of the RU  20 . The signal output circuit  13  outputs a local signal to the wireless communication apparatus  100  of the RU  20 . 
     The RU  20  includes the decoder  21 , a memory  22 , a controller  23 , and the wireless communication apparatus  100 . The decoder  21  decodes the ID number input from the ID output circuit  11  to acquire an address, and supplies the address to the memory  22 . The memory  22  includes a memory controller, and reads control data therefrom based on the address input from the decoder  21 , and supplies the read control data to the controller  23 . The control data includes gain weighting data for weighting a gain when amplifying the transmitting signal in the wireless communication apparatus  100 , and phase weighting data for weighting a phase when shifting the phase of the transmitting signal. 
     The controller  23  controls an amplification and a phase shift of the transmitting signal input to the wireless communication apparatus  100 , using the gain weighting data and the phase weighting data input from the memory  22 . The controller  23  may be formed by an integrated circuit (IC), for example. 
     The base station  10  and the RU  20  are devices for data communication in conformance with the fifth generation mobile communication system (5G), for example. The wireless communication apparatus  100  of the RU  20  can simultaneously output a plurality of beams by beam forming. Details of the beam forming will be described later. 
       FIG. 2  is a diagram illustrating an array antenna  110  of the wireless communication apparatus  100 . The XYZ coordinate system will be defined as follows in the following description. In addition, a plan view refers to a view of an XY plane. For the sake of convenience, a −Z direction may also be referred to as a direction toward a bottom or a downward direction, and a +Z direction may also be referred to as a direction toward a top or an upward direction, however, such a directional relationship does not represent a universal up-and-down (or vertical) relationship. 
     The array antenna  110  includes a substrate  111 , antenna elements  112 , and a ground layer  113 . A communication frequency of the array antenna  110  may be in a 3.7 GHz band, a 4.5 GHz band, or a 28 GHz band, for example. 
     The substrate  111  may be a wiring board in conformance with the flame retardant type 4 (FR4) standard, for example. The antenna elements  112  are provided on a top surface of the substrate  111 , and the ground layer  113  is provided on a bottom surface. The antenna elements  112  are arranged in an array on the top surface of the substrate  111 , and for example, 64 antenna elements  112 , made up of an array of 8×8 antenna elements  112 , are arranged at a constant pitch in both the X direction and the Y direction. The array of the antenna elements  112  may also be treated as a matrix. The antenna element  112  has a square shape in the plan view, and a length of one side of the square is set to approximately ½ an electrical length in wavelengths at the communication frequency. Because the ground layer  113  is provided on the bottom surface of the substrate  111  which has the antenna elements  112  provided on the top surface thereof, and all of the antenna elements  112  overlap the ground layer  113  in the plan view, the antenna elements  112  and the ground layer  113  form a patch antenna (or microstrip antenna). 
     Power is supplied to each antenna element  112  via a through hole and a wiring (or interconnect) of the substrate  111 . Gains and phases of radio waves emitted from the plurality of antenna elements  112  are adjusted to form a single beam. 
     In this example, 64 antenna elements  112  are divided into 16 groups  112 G. Each group  112 G includes 4 antenna elements  112  made up of an array of 2×2 antenna elements  112 . In each group  112 G, the 4 antenna elements  112  are arranged adjacent to each other in the plan view. The antenna elements  112 , which are adjacent to each other in the plan view, are arranged in close proximity to each other in the plan view. The 4 antenna elements  112  included in one group  112 G are examples of N antenna elements  112 , where N is a positive integer, and N=4 in this example. 
     Straight lines A 1  and A 2  will be defined. In the plan view, the straight line A 1  passes through a center C of the 64 antenna elements  112 , and is parallel to the X-axis. In the plan view, the straight line A 2  passes through the center C of the 64 antenna elements  112 , and is parallel to the Y-axis. In the plan view, the 16 groups  112 G are arranged in line symmetry with respect to an axis of symmetry formed by the straight line A 1 . Further, in the plan view, the 16 groups  112 G are arranged in line symmetry with respect to an axis of symmetry formed by the straight line A 2 . Accordingly, the 16 groups  112 G are arranged symmetrically in the plan view. Moreover, the 64 antenna elements  112  are arranged in line symmetry with respect to the axis of symmetry formed by the straight line A 1 , and are arranged in line symmetry with respect to the axis of symmetry formed by the straight line A 2 . 
     Although one group  112 G includes the 4 antenna elements  112  made up of the array of 2×2 antenna elements  112  in this example, the arrangement of the plurality of antenna elements  112  included in one group  112 G is not limited to such an arrangement, as will be described later in more detail. Further, the array antenna  110  is not limited to the configuration illustrated in  FIG. 2 , and may have a configuration different from that illustrated in  FIG. 2 , as long as the plurality of antenna elements  112  are arranged in an array. 
     Next, a reduction of a side lobe by a Chebyshev weighting will be described, with reference to  FIG. 3A ,  FIG. 3B , and  FIG. 3C .  FIG. 3A  through  FIG. 3C  are diagrams for explaining the Chebyshev weighting. For the sake of convenience, it is assumed that 8 antenna elements are arranged linearly as illustrated in  FIG. 3A , and antenna elements numbers 1 to 8 are allocated to the antenna elements from the leftmost antenna element to the rightmost antenna element in the linear arrangement. 
     It is also assumed that 8 variable amplifiers are connected to the 8 antenna elements, respectively, and the gain is weighted when amplifying the power radiated from the 8 antenna elements. 
     In  FIG. 3B , an abscissa indicates the antenna element number, and the ordinate indicates the weighted gain. The gain of the power radiated from the 8 antenna elements is weighted in steps, so that the gain given to the power radiated from the eight antenna elements is such that the gain of the power radiated from the antenna elements arranged at the ends of the linear arrangement and having the antenna element numbers 1 and 8 is the smallest, and the gain of the power radiated from the antenna elements arranged at the center of the linear arrangement and having the antenna element numbers 4 and 5 is the largest. Such a weighting is the Chebyshev weighting, and a difference in the weighting is small between the adjacent antenna elements. 
       FIG. 3C  illustrates the output (radiated power) of a main lobe and a side lobe when the power is radiated from the 8 antenna elements of  FIG. 3A  without the weighting by a dashed line, and the output (radiated power) of the main lobe and the side lobe when the power is radiated from the 8 antenna elements of  FIG. 3A  with the weighting described above by a solid line. In both the cases without the weighting and with the weighting, one waveform having a largest output at the center represents the output of the main lobe, and three waveforms on both sides of the main lobe represent the output of the side lobe. 
     When the weighting is reduced from the center towards the ends of the linear arrangement of the 8 antenna elements, the output of the main lobe at the center indicated by the solid line is almost the same as the output of the main lobe at the center for the case without the weighting indicated by the dashed line, as illustrated by the solid line in  FIG. 3C . However, the output of the side lobes for the case with the weighting indicated by the solid line is reduced compared to the output of the side lobes for the case without the weighting indicated by the dashed line. Hence, the Chebyshev weighting enables selective reduction of the output of the side lobes, while maintaining the output of the main lobe approximately the same as the output of the main lobe for the case without the Chebyshev weighting. 
       FIG. 4  is a diagram illustrating the wireless communication apparatus  100 . The wireless communication apparatus  100  includes a signal terminal  101 , the array antenna  110 , an amplifier  120 , a phase shifter  130 , an amplifier  140 , a mixer  150 , and a power amplifier (PA)  160 . The amplifier  120  is an example of a first variable amplifier, and the amplifier  140  is an example of a second variable amplifier. The signal terminal  101  is connected to the signal output circuit  12  illustrated in  FIG. 1 , and is an example of an input terminal to which the transmitting signal is input. 
       FIG. 4  illustrates the antenna elements  112  of the array antenna  110 . Although there are 64 antenna elements  112  as illustrated in  FIG. 2 ,  FIG. 4  illustrates the configuration related to 4 of the 64 antenna elements  112 . The 4 antenna elements  112  illustrated in  FIG. 4  are included in one group  112 G illustrated in  FIG. 2 . 
     As an example, 1 amplifier  120 , 4 phase shifters  130 , 4 amplifiers  140 , 4 mixers  150 , and 4 PAs  160  are connected to the 4 antenna elements  112 . Because the wireless communication apparatus  100  includes 64 antenna elements  112 , the wireless communication apparatus  100  includes 16 amplifiers  120 , 64 phase shifters  130 , 64 amplifiers  140 , 64 mixers  150 , and 64 PAs  160 . 
     In this example, the 4 antenna elements  112 , the 1 amplifier  120 , the 4 phase shifters  130 , the 4 amplifiers  140 , the 4 mixers  150 , and the 4 Pas  160  included in one group  112 G, are referred to as a set  100 A. Although the wireless communication apparatus  100  includes 16 sets  100 A, the configuration of one set  100 A will be described because all of the 16 sets  100 A have the same configuration. In each set  100 A, the 4 phase shifters  130  are connected to an output of the 1 amplifier  120 , and 1 amplifier  140 , 1 mixer  150 , and 1 PA  160  are connected in series to an output of each phase shifter  130 . 
     The amplifier  120  has an input terminal  121  connected to the signal terminal  101 , an output terminal  122 , and a control terminal  123  connected to the controller  23  illustrated in  FIG. 1 . The input terminal  121  is an example of a first input terminal, and the output terminal  122  is an example of a first output terminal. The transmitting signal from the signal terminal  101  is input to the input terminal  121 , the 4 phase shifters  130  are connected to the output terminal  122 . A first weight for the gain, received from the controller  23 , is input to the control terminal  123 . 
     The gain of the amplifier  120  is variably controlled according to the first weight for the gain when amplifying the transmitting signal, and the amplifier  120  amplifies the transmitting signal input to the input terminal  121 . The amplifier  120  outputs the transmitting signal, input to the input terminal  121 , from the output terminal  122  after amplifying the transmitting signal. The first weight is controlled by the controller  23 . The first weight is included in the gain weighting data input to the controller  23  from the memory  22 . 
     The gain of amplifier  120 , weighted by the first weight, can be controlled in 6 stages in steps (variation width of the gain) of 3 dB in a range of −15 dB to 0 dB, for example. In other words, the gain of the amplifier  120  is controllable to −15 dB, −12 dB, −9 dB, −6 dB, −3 dB, and 0 dB. The range of −15 dB to 0 dB is an example of a range of the first gain. The steps of 3 dB is an example of a first variation width. 
     The phase shifter  130  includes an input terminal  131 , an output terminal  132 , and a control terminal  133 . Within one set  100 A, the output terminal  122  of the amplifier  120  is connected to the input terminals  131  of the 4 phase shifters  130 . The 4 output terminals  132  are connected to input terminals  141  of the 4 amplifiers  140 , respectively. The control terminals  133  are connected to the controller  23  illustrated in  FIG. 1 , and the phase weighting data are input to the control terminals  133  of the 4 phase shifters  130 . The phase shifter  130  shifts the phase of the transmitting signal (transmitting signal amplified by the amplifier  120 ) input to the input terminal  131 , according to the phase weighting data input to the control terminal  133 , and outputs the phase-shifted transmitting signal from the output terminal  132 . 
     The amplifier  140  includes the input terminal  141  connected to the output terminal  132 , an output terminal  142 , and a control terminal  143  connected to the controller  23  illustrated in  FIG. 1 . The input terminal  141  is an example of a second input terminal, and the output terminal  142  is an example of a second output terminal. The input terminal  141  receives the phase-shifted transmitting signal from the output terminal  132 . An input terminal  151  of the mixer  150  is connected to the output terminal  142 . A second weight for the gain, received from the controller  23 , is input to the control terminal  143 . 
     The gain of the amplifier  140  is variably controlled according to the second weight for the gain when amplifying the transmitting signal, and the amplifier  140  amplifies the transmitting signal input to the input terminal  141 . The amplifier  140  outputs the transmitting signal, input to the input terminal  141 , from the output terminal  142  after amplifying the transmitting signal. The second weight is controlled by the controller  23 . The second weight is included in the gain weighting data input to the controller  23  from the memory  22 . 
     The gain of amplifier  140 , weighted by the second weight, can be controlled in 6 stages in steps (variation width of the gain) of 1 dB in a range of −5 dB to 0 dB, for example. In other words, the gain of the amplifier  140  is controllable to −5 dB, −4 dB, −3 dB, −2 dB, −1 dB, and 0 dB. The range of −5 dB to 0 dB is an example of a range of the second gain, and is narrower than the range of the first gain of the amplifier  120 . The steps of 1 dB is an example of a second variation width. 
     In addition, the range (−5 dB to 0 dB) in which the gain of the amplifier  140  is adjustable is smaller than the range (−15 dB to 0 dB) in which the gain of the amplifier  120  is adjustable, for example. 1 amplifier  140  is provided with respect to each antenna element  112 , and this 1 amplifier  120  is provided with respect to 4 antenna elements  112 . Because the amplifier  120  has a larger spatial range in which the gain is adjusted in the plan view of the array antenna  110  compared to the amplifier  140 , the adjustable range of the gain of the amplifier  120  is set larger than the adjustable range of the gain of the amplifier  140 , for example. If the adjustable range of the gain of the amplifier  120  does not need to be larger than the adjustable range of the gain of the amplifier  140 , the adjustable range of the gain of the amplifier  120  may be set smaller than or equal to the adjustable range of the gain of the amplifier  140 . 
     The mixer  150  includes input terminals  151  and  152 , and an output terminal  153 . The input terminal  151  is connected to the output terminal  142  of the amplifier  140 , and the amplified transmitting signal from the amplifier  140  is input to the input terminal  151 . The input terminal  152  is connected to the signal output circuit  13  of the base station  10 , and the local signal is input to the input terminal  152 . The output terminal  153  is connected to an input terminal  161  of the PA  160 . The mixer  150  multiplies the transmitting signal input to the input terminal  151  by the local signal input to the input terminal  152 , and outputs a multiplied signal from the output terminal  153 . 
     The PA  160  is a power amplifier including an input terminal  161 , and an output terminal  162 . The input terminal  161  is connected to the output terminal  153  of the mixer  150 , and the output terminal  162  is connected to the antenna element  112 . The PA  160  amplifies the signal input from mixer  150 , and outputs the amplified signal to the antenna element  112 . An amplification factor of PA  160  is constant. 
     The wireless communication apparatus  100  having the configuration described above outputs the plurality of beams from the array antenna  110 , for example. Because each beam includes the main lobe and the side lobes, and has a unique beam ID, interference between the main lobe of each beam and the side lobes of other beams needs to be reduced. In order to reduce the interference between the beams, the gain of the signal emitted from each antenna element  112  needs to be adjusted. The gain of the signal emitted from each antenna element  112  needs to be adjusted for each antenna element  112  in the group  112 G by the amplifier  140 , in addition to being adjusted for each group  112 G by the amplifier  120 . 
       FIG. 5A  and  FIG. 5B  illustrate two beams  50 A and  50 B. In this example, a beam  50 A is indicated by a solid line, and a beam  50 B is indicated by a dashed line. For the sake of convenience,  FIG. 5A  and  FIG. 5B  indicate a magnitude of each signal to interference ratio (SIR: a ratio of a signal power and an interfering power) by a length of each double-headed arrow. Terminals  30 A and  30 B may be smartphones or the like, for example. 
     The beam  50 A includes 1 main lobe  51 A, and a plurality of side lobes  52 A. The beam  50 B includes 1 main lobe  51 B, and a plurality of side lobes  52 B. The main lobe  51 A is output from the array antenna  110  toward the terminal  30 A, and the main lobe  51 B is output from the array antenna  110  toward the terminal  30 B.  FIG. 5A  illustrates a state where the weighting data are not utilized and the output of the side lobes  52 A and  52 B is not reduced, for comparison purposes.  FIG. 5B  illustrates a state where the weighting data are utilized and the output of the side lobes  52 A and  52 B is reduced. 
     In  FIG. 5A , the main lobe  51 A of the beam  50 A and the side lobes  52 B of the beam  50 B overlap, and the output of the side lobes  52 B is large to a certain extent. Similarly, the main lobe  51 B of the beam  50 B and the side lobes  52 A of the beam  50 A overlap, and the output of the side lobes  52 A is large to a certain extent. In this state, the interference between the main lobe  51 A and the side lobes  52 B is large, and the SIR between the main lobe  51 A and the side lobes  52 B is small. Similarly, the interference between the main lobe  51 B and the side lobes  52 A is large, and the SIR between the main lobe  51 B of the beam  50 B and the side lobes  52 A of the beam  50 A is small. When the SIR is small, the communication state is not good because of a throughput of the communication deteriorates. 
     On the other hand, in  FIG. 5B , when compared to  FIG. 5A , the outputs of the side lobes  52 A and  52 B overlapping the main lobes  51 A and  51 B are reduced, as illustrated inside circles indicated by a one-dot chain line. For this reason, the interference between the main lobe  51 A and the side lobes  52 B is small, and the SIR between the main lobe  51 A and the side lobes  52 B is large. Similarly, the interference between the main lobe  51 B and the side lobes  52 A is small, and the SIR between the main lobe  51 B and the side lobes  52 A is large. When the SIR is large, a good communication state can be obtained because the throughput of the communication improves. 
     As illustrated in  FIG. 5B , the outputs of the side lobes  52 A and  52 B overlapping the main lobes  51 A and  51 B can be reduced by adjusting the first weight of the 16 amplifiers  120 , adjusting the second weight of the 64 amplifiers  140 , and individually adjusting the gains of the signals output from the antenna elements  112 . 
     Accordingly, it is possible to individually adjust the gains of the signals output from the antenna elements  112 , by connecting 1 amplifier (variable gain amplifier) having the weight of the gain variable in steps of 1 dB in a range of −20 dB to 0 dB, to each antenna element  112 , so as to adjust the weight of the gain of all of the amplifiers connected to the antenna elements  112 , for example. In other words, the gains of the signals output from the antenna elements  112  can be adjusted by connecting 64 amplifiers (variable gain amplifiers), having the weights of the gains variable in steps of 1 dB in a range of −20 dB to 0 dB, to 64 antenna elements  112 , respectively, and adjusting the 64 weights input to the 64 amplifiers. It is known that reducing the output of the side lobes by the weighting described above can also be achieved by the Chebyshev weighting. 
     However, an amplifier, having a weight of the gain thereof variable in steps of 1 dB in a range of −20 dB to 0 dB, needs to set the gain in multiple stages, and a size of the amplifier becomes large, thereby increasing the size of the wireless communication apparatus. In addition, the weighting data for adjusting the weight of the gain in steps of 1 dB in the range of −20 dB to 0 dB greatly increases the amount of data. Moreover, because the closer the amplifier is to the antenna element  112 , the larger the signal output becomes, it is difficult to provide, within a limited space, 64 high-performance amplifiers having the weights of the gains variable in steps of 1 dB in the range of −20 dB to 0 dB. 
     On the other hand, according to the wireless communication apparatus  100 , the amplifiers can be arranged with ease by employing a 2-stage configuration including the 16 amplifiers  120  and the 64 amplifiers  140 . Further, the amplifiers  120  close to the signal terminal  101  are arranged so that, within one group  112 G, 1 amplifier  120  is provided with respect to the 4 amplifiers  140  connected to the 4 antenna elements  112  of the same group  112 G, respectively. It is conceivable to employ an arrangement in which 64 amplifiers  120  are connected to the 64 amplifiers  140 , respectively, however, the circuit scale of the wireless communication apparatus cannot be reduced by such a conceivable arrangement. 
     When adjusting the gains of the signals output from the 64 antenna elements  112 , the gains of the signals output from the antenna elements  112  arranged close to each other have relatively close values. For example, among the 64 antenna elements  112 , the gains of the signals output from the antenna elements  112  positioned at the end along a +X direction and the end along a +Y direction may greatly differ from the gains of the signals output from antenna elements  112  positioned at the end along a −X direction and the end along a −Y direction. In contrast, among the 64 antenna elements  112 , the gains of the signals output from some of the antenna elements  112  adjacent to each other have relatively close values, as is evident from  FIG. 3C  illustrating the example of the Chebyshev weighting. As illustrated in  FIG. 3B , the weighting gradually varies from the antenna element having the antenna element number 1 to the antenna element having the antenna element number 8. In other words, the difference between the weights of the adjacent antenna elements is small. 
     For this reason, the wireless communication apparatus  100  employs a configuration in which the 4 antenna elements  112 , made up of the array of 2×2 antenna elements  112 , are regarded as one group  112 G, and 1 amplifier  120  is provided with respect to each group  112 G, to roughly adjust the gain, and further, 1 amplifier  140  is connected to each of the antenna elements  112  to individually adjust the gains of the antenna elements  112 . This configuration can reduce the number of amplifiers  120  positioned near the signal terminal  101 , and thus reduce the circuit scale of the wireless communication apparatus  100 . 
     Accordingly, it is possible to provide the wireless communication apparatus  100  having a reduced circuit scale. In addition, because the number of amplifiers  120  can be reduced, the amount of weighting data can be reduced, and the size (or storage capacity) of the memory  22  can be reduced. For example, in a wireless communication apparatus having 64 amplifiers having the weight of the gain variable in steps of 1 dB in a range of −20 dB to 0 dB, the amount of weighting data required becomes 20 dB×64=1280 dB. On the other hand, in the wireless communication apparatus  100 , the size (or storage capacity) of the memory  22  can be reduced, because the amount of weighting data required is only 15 dB/3 dB (steps)×16+5 dB/1 dB (steps)×64=400 dB. 
     Moreover, because the gain of the amplifier  120  is adjustable in a range of −15 dB to 0 dB, and the gain of the amplifier  140  is adjustable in a range of −5 dB to 0 dB, the gain can be adjusted in a range of −20 dB to 0 dB by a 2-stage adjustment enabled by the 2-stage configuration. Thus, the transmitting signal can be amplified with a gain in the same range as when using 64 amplifiers having the gain adjustable in the range of −20 dB to 0 dB. 
     The amplifier  140  positioned close to the antenna element  112  can adjust the gain in steps of 1 dB, and the amplifier  120  positioned close to the signal terminal  101  can adjust the gain in steps of 3 dB. Thus, by employing the configuration in which the amplifier  120  adjusts the gain in steps coarser than the gain adjusting steps of the amplifier  140 , the circuit scale of the amplifier  120  can be reduced, thereby enabling the circuit scale of the wireless communication apparatus  100  to be reduced. 
     Further, by making the gain of the amplifier  140  adjustable in a range smaller than the gain adjustable range of the amplifier  120 , the circuit scale of the amplifier  140  can be reduced, thereby enabling the circuit scale of the wireless communication apparatus  100  to be reduced. 
     The number of amplifiers  120  is preferably 3 or more. An example will be described under a precondition that the gains of the signals output from M antenna elements  112  are adjusted in a range of −20 dB to 0 dB, where M is an integer greater than or equal to 10. Further, it is assumed that the range of −20 dB to 0 dB of the gain of the signals output from the M antenna element  112  is divided into the range of −15 dB to 0 dB of amplifiers  120 , and the range of −5 dB to 0 dB of M amplifiers  140 , to form 2 beams by the signals output from the M antenna elements  112 . When outputting the two beams in mutually different directions, gain data indicating the gains with which the signals output from the M antenna elements  112  are amplified, respectively, are determined. It is assumed that a minimum value and a maximum value of the gains of the signals output from the M antenna elements  112  indicated by the gain data are −20 dB and 0 dB, respectively. 
     First, if 1 amplifier  120  is provided, the signals output from the 64 antenna elements  112  are uniformly amplified with one of the gains within the range of −15 dB to 0 dB, and it is not possible to cope with the gain data. For this reason, it may be seen that a plurality of amplifiers  120  are required. In addition, if 2 amplifiers  120  are provided, both the 2 amplifiers  120  will likely be connected to the antenna element  112  which outputs the signal amplified with the minimum gain or the maximum gain, and it is extremely difficult to cope with the gain data. But if 3 amplifiers  120  are provided, one of the 3 amplifiers  120  will likely be not connected to the antenna element  112  which outputs the signal amplified with the minimum gain or the maximum gain, and it is more likely possible to cope with the gain data. For this reason, the number of amplifiers  120  is preferably 3 or more. 
     Further, because 64 antenna elements  112  are divided into 16 groups  112 G, and the 16 groups  112 G are symmetrically arranged in the plan view, the gains can be coarsely adjusted by the 16 amplifiers  120  connected to the 16 groups  112 G, respectively, and the gains can be individually adjusted by the 4 amplifiers  140  connected to the 4 antenna elements  112  included in each of the 16 groups  112 G. Hence, similar to when the gains are adjusted by connecting 64 amplifiers to 64 antenna elements, respectively, it is possible to adjust the gains by using the 16 amplifiers  120  and the 64 amplifiers  140 . In other words, the circuit scale can be reduced without sacrificing the adjustability of the gain. 
     Because the 4 antenna elements  112  included in each group  112 G are arranged adjacent to each other in the plan view, it is possible to freely adjust the gains of the signals output from all the antenna elements  112  by the coarse gain adjustment by the amplifiers  120  and the individual gain adjustment by the amplifiers  140 . 
     In the example described above, one group  112 G includes the 4 antenna elements  112  (N=4) arranged adjacent to each other in the array of 2×2 antenna elements  112 . However, the plurality of antenna elements  112  included in one group  112 G need only be adjacent to each other, and the arrangement of the antenna elements  112  in one group  112 G is not limited to the array of 2×2 antenna elements  112 . Further, although N may be greater than or equal to 2, if N is greater than or equal to 3, the plurality of antenna elements  112  are preferably arranged two-dimensionally in the plan view, than being arranged linearly in the plan view. In other words, if N=3, the 3 antenna elements  112  are preferably arranged at positions corresponding to 3 vertices of a triangle, because the 3 antenna elements  112  arranged at the positions corresponding to the 3 vertices of the triangle will be closer to each other compared to 3 antenna elements  112  arranged linearly. The arrangement of the 4 antenna elements  112  is not limited to the array of 2×2 antenna elements  112  illustrated in  FIG. 2 , and the 4 antenna elements  112  may be arranged at positions corresponding to 4 vertices of a rhombus, for example. Further, N may be greater than or equal to 5. 
     Moreover, in the example described above, the wireless communication apparatus  100  includes the 64 antenna elements  112  arranged in the array of 8×8 antenna elements  112 , however, the number and arrangement of the antenna elements  112  in the wireless communication apparatus  100  are not limited to those described above. 
     Although the wireless communication apparatus  100  described above has a configuration including 16 amplifiers  120 , the number of amplifiers  120  is not limited to 16, and 8 amplifiers  120  may be provided with respect to 64 antenna elements  112 , or 32 amplifiers  120  may be provided with respect to 64 antenna elements  112 , for example. 
     In addition, although the number of antenna elements  112  and the number of amplifiers  140  are the same in the example described above, a plurality of antenna elements  112  may be connected to 1 amplifier  140 . For example, 2 antenna elements  112  may be connected to the PA  160  illustrated in  FIG. 4 . 
     The wireless communication apparatus  100  described above has the two-stage configuration formed by the amplifiers  120  and the amplifiers  140 . However, a number of variable gain amplifiers, smaller than the number of amplifiers  120 , may be provided between the signal terminal  101  and the amplifiers  120 . Moreover, a number of variable gain amplifiers, larger than the number of amplifiers  120  and smaller than the number of amplifiers  140 , may also be provided between the amplifiers  120  and the amplifiers  140 . 
     In the example described above, the amplifier  140 , provided closer to the antenna element  112  than the amplifier  120 , can adjust the gain in steps of 1 dB, and the amplifier  120 , provided closer to the signal terminal  101  than the amplifier  140 , can adjust the gain in steps of 3 dB. However, the steps with which the amplifier  120  adjusts the gain is not limited to 3 dB. The steps with which the amplifier  140  adjusts the gain may be the same as the steps with which the amplifier  120  adjusts the gain. 
     Further, in the example described above, the gain adjustable range of −5 dB to 0 dB of the amplifier  140  is smaller than the gain adjustable range of −15 dB to 0 dB of the amplifier  120 . However, the gain adjustable range of the amplifier  140  may be the same as the gain adjustable range of the amplifier  120 , and the gain adjustable range of the amplifier  140  may be larger than the gain adjustable range of the amplifier  120 . 
     Although the wireless communication apparatus  100  described above has a configuration which does not include the controller  23 , the memory  22 , and the decoder  21 , the wireless communication apparatus  100  may include the controller  23 , the memory  22 , and the decoder  21 . 
     According to each of the embodiments and modifications described above, it is possible to provide a wireless communication apparatus which can reduce the circuit scale thereof. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.