Abstract:
A multiport amplifier modulates a reference quadrature phase shift keying (QPSK) signal using an input RF signal to an input hybrid network, generates a plurality of binary phase shift keying (BPSK) signals by demodulating RF signals that are amplified by a plurality of power amplifiers, detects an amplitude error and a phase error of two corresponding amplified RF signals by comparing a QPSK signal that is generated by coupling two RF signals having a phase difference of 90° among the plurality of BPSK signals with a reference QPSK signal, and compensates the detected amplitude error and phase error.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0057560 and 10-2012-0059390 filed in the Korean Intellectual Property Office on Jun. 14, 2011 and Jun. 1, 2012, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to an apparatus for calibrating amplitude and phase errors, a multiport amplifier including the same, and a method of amplifying the multiport amplifier. More particularly, the present invention relates to a method and apparatus for simultaneously detecting and calibrating phase and magnitude errors in a multiport amplifier. 
         [0004]    (b) Description of the Related Art 
         [0005]    A multiple beam antenna system that can provide narrow beams having a high antenna gain within a service coverage area is widely used as a mounting body system of a communication and broadcasting satellite due to excellent equivalent isotropically radiated power (EIRP) and G/T performance, which is a ratio of a gain G of an antenna and a noise temperature T. 
         [0006]    In the multiple beam antenna system, a multiport amplifier that can perform output power control according to an operation condition is widely used. 
         [0007]    The multiple beam antenna system using a multiport amplifier installs several spot beams within a service area to provide communication and broadcasting services and flexibly provides high power allocation to an area requiring higher EIRP due to rainfall or a rapid increase of a communication service. Further, because the multiport amplifier combines and uses high power amplifiers having the highest failure rate in parallel among components for a satellite repeater, when using the multiport amplifier, a system can be formed using a high power amplifier redundancy of a fewer number, compared with when using an existing satellite repeater. 
         [0008]    The multiport amplifier has a plurality of input terminals and output terminals and the number of input terminals and output terminals may be 2 n , but in consideration of ease of embodiment or optimal performance, the most available structures are a 4×4 structure and an 8×8 structure. 
         [0009]    The multiport amplifier generally operates using hybrid matrix characteristics, and an operation principle of such a multiport amplifier is achieved when connection components such as input and output hybrid networks, a power amplifier, and other transmission lines perform an ideal operation. 
         [0010]    Actually, when embodying a multiport amplifier, a hybrid matrix has a difference in insertion loss of terminals and has an error in phases. In a power amplifier, by nonlinearity, a phase of an output signal has different values according to the magnitude of an input signal. When connection components such as a transmission line are not manufactured in the same size and form, the amplitude (magnitude) and phase of a signal may be changed. In this way, in components constituting a multiport amplifier, when an error occurs in an amplitude and a phase, as in an ideal operation, an in-phase or out-of-phase condition of signals that are distributed in input and output hybrid networks is not achieved and thus isolation performance between input terminals and output terminals of the multiport amplifier is deteriorated. 
         [0011]    In order to solve such a problem, the multiport amplifier includes a signal magnitude and phase calibration circuit. In order to prevent power loss of an output terminal, the magnitude and phase calibration circuit is disposed at a front stage of the power amplifier, and in an output hybrid network, the multiport amplifier maintains magnitude and phase differences of a signal, as in a ideal multiport amplifier, thereby performing a function of improving isolation performance of the multiport amplifier. In the phase and magnitude calibration circuit, values of a phase and a magnitude are determined as values that can embody optimum performance while including actual performance of each component when embodying a multiport amplifier system. However, when a change occurs in the performance of constituent elements of a multiport amplifier by an environment condition change such as degradation of a component performance or a temperature change, the performance of the multiport amplifier cannot be maintained in an optimal state. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention has been made in an effort to provide an apparatus for calibrating amplitude and phase errors, a multiplex amplifier including the same, and a method of amplifying the multiplex amplifier having advantages of maintaining performance of the multiport amplifier in an optimal state, even if an environment condition changes. 
         [0013]    An exemplary embodiment of the present invention provides a multiport amplifier. The multiport amplifier includes an input hybrid network, a plurality of power amplifiers, an output hybrid network, an error detector, and a plurality of amplitude and phase controllers. The input hybrid network generates a plurality of RF signals using an input RF signal. The plurality of power amplifiers amplify and output the plurality of RF signals, respectively. The output hybrid network generates at least one output RF signal from output signals of the plurality of power amplifiers. The error detector generates at least one quadrature phase shift keying (QPSK) signal using the input RF signal and the output signals of the plurality of power amplifiers, and detects an amplitude error and a phase error of the output signals of the plurality of power amplifiers by comparing the at least one QPSK signal and the reference QPSK signal. The plurality of amplitude and phase controllers control amplitudes and phases of the plurality of RF signals according to the amplitude error and the phase error. 
         [0014]    The error detector may include a modulator, a plurality of BPSK demodulators, and a QPSK signal generator. The modulator may modulate the reference QPSK signal to an RF signal by the input RF signal. The plurality of BPSK demodulators may demodulate a reference QPSK signal that is modulated to the RF signal to an I signal or a Q signal using each of the output signals of the plurality of power amplifiers. The QPSK signal generator may generate the at least one QPSK signal by coupling a pair of an I signal and a Q signal of an I signal or a Q signal of the plurality of BPSK demodulators. 
         [0015]    The error detector may further include a signal analyzer that detects an amplitude error and a phase error by comparing the reference QPSK signal and the one generated QPSK signal. An amplitude and phase controller that is related to the one generated QPSK signal among the plurality of amplitude and phase controllers may control amplitude and phase of a corresponding RF signal according to the detected amplitude error and phase error. 
         [0016]    The error detector may further include a phase converter that changes a phase of the reference QPSK signal that is modulated to the RF signal based on phase delay of the at least one QPSK signal. 
         [0017]    The error detector may further include a signal selector that selects an output signal of two BPSK demodulators that receive an input of an output signal of two power amplifiers having a phase difference of 90° among the plurality of BPSK demodulators and that outputs the output signal to the QPSK signal generator. 
         [0018]    The plurality of BPSK demodulators may each include: a phase converter that converts a phase of the output signal of the input power amplifier by 180°; a first RF coupler that adds and outputs a signal having a phase that is converted by 180° and a reference QPSK signal that is modulated to the RF signal; a second RF coupler that adds and outputs an output signal of the input power amplifier and a reference QPSK signal that is modulated to the RF signal; first and second low pass filters that detect only a signal of a baseband from output signals of the first and second RF couplers; and an analog decoder that generates an I signal or a Q signal of a baseband from a difference between signals of the baseband that are detected from each of the first and second low pass filters. 
         [0019]    Another embodiment of the present invention provides a method of amplifying a multiport amplifier. The method includes: distributing an input RF signal to a plurality of RF signals having the same amplitude and phase difference; amplifying each of the plurality of RF signals; generating at least one output RF signal by distributing each of the amplified plurality of RF signals to a plurality of RF signals having the same magnitude and phase difference; and controlling amplitudes and phases of the plurality of RF signals using at least one QPSK signal that is generated from a reference QPSK signal and the amplified plurality of RF signals. 
         [0020]    The controlling of amplitudes and phases may include: demodulating the plurality of RF signals to a plurality of binary phase shift keying (BPSK) signals, respectively; generating a QPSK signal using two BPSK signals having a phase difference of 90° among the plurality of BPSK signals; detecting an amplitude error and a phase error by comparing the reference QPSK signal and the generated QPSK signal; and calibrating amplitudes and phases of two RF signals that are related to the generated QPSK signal among the amplified plurality of RF signals with the amplitude error and the phase error. 
         [0021]    The calibrating of amplitudes and phases may include calibrating a phase and an amplitude of the other RF signal based on one RF signal of the two RF signals. 
         [0022]    The demodulating of the plurality of RF signals may include: modulating the reference QPSK signal to an RF signal using the input RF signal; and demodulating a reference QPSK signal that is modulated to the RF signal to the plurality of BPSK signals using each of the amplified plurality of RF signals. 
         [0023]    The demodulating of the plurality of RF signals may further include changing a phase of a reference QPSK signal that is modulated to the RF signal based on phase delay of the generated QPSK signal. 
         [0024]    Yet another embodiment of the present invention provides an apparatus that compensates an amplitude and a phase of a multiple signal in a multiport amplifier including an input hybrid network that distributes an input RF signal to a plurality of RF signals, a plurality of power amplifiers that amplify a plurality of RF signals, and an output hybrid network that generates at least one output signal from the plurality of amplified RF signals. The apparatus includes a modulator, a plurality of BPSK demodulators, a QPSK signal generator, a signal analyzer, and a plurality of amplitude and phase controllers. The modulator modulates a reference QPSK signal to an RF signal using the input RF signal. The plurality of BPSK demodulators generate a plurality of BPSK signals by demodulating the plurality of amplified RF signals. The QPSK signal generator generates at least one QPSK signal by coupling two BPSK signals having a phase difference of 90° among the plurality of BPSK signals. The signal analyzer detects an amplitude error and a phase error by comparing the reference QPSK signal and each of the at least one generated QPSK signal. The plurality of amplitude and phase controllers control amplitudes and phases of a plurality of RF signals according to the amplitude error and the phase error. 
         [0025]    The apparatus may further include a signal selector that selects two BPSK signals having a phase difference of 90° among the plurality of BPSK signals. 
         [0026]    The apparatus may further include a phase converter that compensates phase delay of the generated QPSK signal. 
         [0027]    The phase converter may change a phase of the reference QPSK signal according to a phase change amount of the generated QPSK signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a drawing illustrating a concept of a general multiport amplifier. 
           [0029]      FIG. 2  is a diagram illustrating an example of a hybrid that is shown in  FIG. 1 . 
           [0030]      FIG. 3  is a diagram illustrating operation of a multiport amplifier that is shown in  FIG. 1 . 
           [0031]      FIG. 4  is a diagram illustrating another example of a general multiport amplifier. 
           [0032]      FIG. 5  is a diagram illustrating a multiport amplifier according to a first exemplary embodiment of the present invention. 
           [0033]      FIG. 6  is a diagram illustrating an example of a signal constellation of a BPSK demodulator according to amplitude and phase errors of the multiport amplifier that is shown in  FIG. 5 . 
           [0034]      FIG. 7  is a diagram illustrating a detailed configuration of a BPSK demodulator that is shown in  FIG. 5 . 
           [0035]      FIG. 8  is a diagram illustrating an example of a signal waveform of a detailed configuration of a BPSK demodulator that is shown in  FIG. 7 . 
           [0036]      FIG. 9  is a diagram illustrating an example of a detailed circuit configuration of a phase converter, two RF couplers, and two power detectors that are shown in  FIG. 7 . 
           [0037]      FIG. 10  is a graph illustrating a reference QPSK signal and a QPSK signal that are generated by two BPSK demodulators through a simulation result when amplitude and phase errors do not occur in a multiport amplifier according to an exemplary embodiment of the present invention. 
           [0038]      FIG. 11  is a diagram illustrating a multiport amplifier according to a second exemplary embodiment of the present invention. 
           [0039]      FIG. 12  is a diagram illustrating a multiport amplifier according to a third exemplary embodiment of the present invention. 
           [0040]      FIG. 13  is a diagram illustrating a signal constellation by delay that may occur in modulation of a modulator and demodulation of a BPSK demodulator. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0041]    In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
         [0042]    In addition, in the entire specification and claims, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
         [0043]    Hereinafter, an apparatus for calibrating amplitude and phase errors, a multiport amplifier including the same, and a method of amplifying the multiport amplifier according to an exemplary embodiment of the present invention will be described in detail with reference to the drawings. 
         [0044]      FIG. 1  is a drawing illustrating a concept of a general multiport amplifier, and  FIG. 2  is a diagram illustrating an example of a hybrid that is shown in  FIG. 1 . 
         [0045]      FIG. 1  illustrates 4×4 multiport amplifiers as an example of a multiport amplifier. 
         [0046]    The 4×4 multiport amplifiers of  FIG. 1  include four input terminals I 1 -I 4 , four output terminals O 1 -O 4 , an input hybrid network  10 , an output hybrid network  20 , and four power amplifiers  31 - 34 . 
         [0047]    The input hybrid network  10  includes four hybrids  11 - 14 , and the output hybrid network  20  also includes four hybrids  21 - 24 . 
         [0048]    As shown in  FIG. 2 , each of the hybrids  11 - 14  includes two input terminals  1  and  2  and two output terminals  3  and  4 , divides a signal that is input to the input terminal  1  into signals of two paths having the same amplitude (magnitude) and phase difference, combines signals advancing to the same output terminals  3  and  4 , and outputs the combined signal to the output terminals  3  and  4 . 
         [0049]    The two input terminals  1  and  2  of the two hybrids  11  and  12  form four input terminals I 1 -I 4  of the 4×4 multiport amplifiers, and the two output terminals  3  and  4  of the two hybrids  13  and  14  are connected to the four power amplifiers  31 - 34 , respectively. One output terminal  3  of the hybrid  11  is connected to one input terminal  1  of the hybrid  13 , the other output terminal  4  of the hybrid  11  is connected to one input terminal  1  of the hybrid  14 , one output terminal  3  of the hybrid  12  is connected to the other input terminal  2  of the hybrid  13 , and the other output terminal  4  of the hybrid  12  is connected to the other input terminal  2  of the hybrid  14 . 
         [0050]    As the input hybrid network  10  operates using operation characteristics of the hybrids  11 - 14 , one input RF signal is divided into four RF signals and output. 
         [0051]    The four power amplifiers  31 - 34  amplify each of output signals of the input hybrid network  10  and output the output signals to the output hybrid network  20 . 
         [0052]    The output hybrid network  20  includes the four hybrids  21 - 24 , and each of the hybrids  21 - 24  is formed as shown in  FIG. 2 . 
         [0053]    The two input terminals  1  and  2  of the two hybrids  21  and  22  are connected to the four power amplifiers  31 - 34 , and the two output terminals  3  and  4  of the two hybrids  23  and  24  form four output terminals O 1 -O 4  of the 4×4 multiport amplifiers. One output terminal  3  of the hybrid  21  is connected to one input terminal  1  of the hybrid  23 , other output terminal  4  of the hybrid  21  is connected to one input terminal  1  of the hybrid  24 , one output terminal  3  of the hybrid  22  is connected to the other input terminal  2  of the hybrid  23 , and the other output terminal  4  of the hybrid  22  is connected to the other input terminal  2  of the hybrid  24 . 
         [0054]    As each of the hybrids  21 - 24  operates using operation characteristics of the hybrids  21 - 24 , one amplified RF signal is output from four RF signals that are amplified by four power amplifiers  31 - 34 . 
         [0055]      FIG. 3  is a diagram illustrating operation of a multiport amplifier that is shown in  FIG. 1 . 
         [0056]    As shown in  FIG. 3 , when an RF signal of a frequency f 1  is input to the input terminal  1  of the hybrid  11 , which is the input terminal  11 , the input RF signal is divided into signals of two paths having the same amplitude and a phase difference of 90° by the hybrid  11 , and is output to two output terminals  3  and  4  of the hybrid  11 . That is, signals that are output to the two output terminals  3  and  4  of the hybrid  11  have a phase difference of 90°. 
         [0057]    A signal of the output terminal  3  of the hybrid  11  is input to the input terminal  1  of the hybrid  13 , and a signal that is input to the input terminal  1  of the hybrid  13  is divided into signals of two paths having the same amplitude and a phase difference of 90° by the hybrid  13  and is output to the two output terminals  3  and  4  of the hybrid  13 . 
         [0058]    Further, a signal of the output terminal  4  of the hybrid  11  is input to the input terminal  1  of the hybrid  14 , and a signal that is input to the input terminal  1  of the hybrid  14  is divided to two signals having a phase difference of 90° by the hybrid  14  and is output to the two output terminals  3  and  4  of the hybrid  14 . 
         [0059]    Finally, signals of the two output terminals  3  and  4  of the hybrid  13  and signals of the two output terminals  3  and  4  of the hybrid  14  have the same amplitude, but have phases of 0°, 90°, 90°, and 180°, respectively. 
         [0060]    The signals of the two output terminals  3  and  4  of the hybrids  13  and  14  are input to and amplified in the power amplifiers  31 - 34 , respectively, and signals that are amplified by the power amplifiers  31 - 34  are input to the two input terminals  1  and  2 , respectively, of the hybrids  21  and  22 , which are four input terminals of the output hybrid network  20 . 
         [0061]    Because the signals that are input to the two input terminals  1  and  2  of the hybrid  21  have the same amplitude and phases of 0° and 90°, respectively, two signals that are input to the two input terminals  1  and  2  of the hybrid  21  have a phase difference of 90°. 
         [0062]    The signals that are input to the input terminals  1  and  2  are divided into two signals having a phase difference of 90° by the hybrid  21 . Therefore, because two signals being out of phase are output to the output terminal  3  of the hybrid  21 , the two signals are combined and cancelled. Because two signals being in phase are output to the output terminal  4  of the hybrid  21 , the signal of the output terminal  4  of the hybrid  21  becomes a signal in which two signals being in phase at 90° are combined, and the signal is again input to the input terminal  1  of the hybrid  24 . 
         [0063]    Similarly, because signals that are input to the two input terminals  1  and  2  of the hybrid  22  have the same amplitude and phases of 90° and 180°, respectively, the two signals that are input to the two input terminals  1  and  2  of the hybrid  22  also have a phase difference of 90°. 
         [0064]    The signals that are input to the input terminals  1  and  2  are divided into two signals having a phase difference of 90° by the hybrid  21 . Therefore, two signals being out of phase are output to the output terminal  3  of the hybrid  22  and thus the two signals are combined and cancelled. Because the two signals being in phase at 180° are output to the output terminal  4  of the hybrid  22 , the signal of the output terminal  4  of the hybrid  22  becomes a signal in which two signals being in phase are combined, and the signal is again input to the input terminal  2  of the hybrid  24 . 
         [0065]    A signal in which two signals being in phase at 90° are combined is input to the input terminal  1  of the hybrid  24 , and a signal in which two signals being in phase at 180° are combined is input to the input terminal  2  of the hybrid  24 . Therefore, two signals being out of phase are output to the output terminal  3  of the hybrid  24  and thus the two signals are combined and cancelled. Because two signals being in phase at 180° are output to the output terminal  4  of the hybrid  24 , a signal of the output terminal  4  of the hybrid  24  becomes a signal in which two signals being in phase at 180° are combined. 
         [0066]    As a result, in the 4×4 multiport amplifiers, a signal that is input to the input terminal  1  of the hybrid  1  is output only to the output terminal  4  of the hybrid  24 , and an input signal of the 4×4 multiport amplifiers and an output signal of the 4×4 multiport amplifiers have a phase difference of 180°. 
         [0067]    The hybrids  11 - 14  and  21 - 24  may have an amplitude difference between output signals and may have an error in a phase. Further, in the power amplifiers  31 - 34 , a phase of an output signal may have different values by non-linearity according to the amplitude of an input signal. In this way, when errors of amplitude and phase occur in the hybrids  11 - 14  and  21 - 24  and the power amplifiers  31 - 34  constituting the multiport amplifier, an in-phase or out-of-phase condition is not achieved in signals that are distributed in the input and output hybrid networks  10  and  20 , as in an ideal operation, and thus an isolation performance of the input terminals I 1 -I 4  and the output terminals O 1 -O 4  of the multiport amplifier is deteriorated. 
         [0068]    Therefore, as shown in  FIG. 4 , the multiport amplifier further includes amplitude and phase controllers  41 - 44  that control the amplitude and phase of a signal. 
         [0069]      FIG. 4  is a diagram illustrating another example of a general multiport amplifier. 
         [0070]    As shown in  FIG. 4 , the multiport amplifier further includes amplitude and phase controllers  41 - 44 . 
         [0071]    In order to prevent power loss of an output terminal of the multiport amplifier, the amplitude and phase controllers  41 - 44  are disposed at a front stage of the power amplifiers  31 - 34 . 
         [0072]    The amplitude and phase controllers  41 - 44  control the amplitude and phase of a signal that is output from the input hybrid network  10  so that amplitude and phase differences of a signal in the output hybrid network  20  of the multiport amplifier have the same values as those in an ideal multiport amplifier, thereby performing a function of improving isolation performance of the multiport amplifier. In this case, when embodying the multiport amplifier, values of the controlled phase and amplitude are determined as values that can embody optimum performance while including an actual performance of each constituent element. 
         [0073]    However, an environment condition change such as performance degradation or a temperature change of a constituent element of the multiport amplifier may occur, and by such an environment condition change, the performance of constituent elements of the multiport amplifier may be changed. Therefore, the performance of the multiport amplifier cannot be maintained in an optimal state with values of a phase and a magnitude that are controlled in the amplitude and phase controllers  41 - 44 . An exemplary embodiment that can maintain performance of the multiport amplifier in an optimal state even if an environment condition changes will be described hereinafter in detail with reference to  FIG. 5 . 
         [0074]      FIG. 5  is a diagram illustrating a multiport amplifier according to a first exemplary embodiment of the present invention, and  FIG. 6  is a diagram illustrating an example of a signal constellation of a BPSK demodulator according to amplitude and phase errors of the multiport amplifier that is shown in  FIG. 5 . 
         [0075]    For convenience of description,  FIG. 5  illustrates 2×2 multiport amplifiers, and unlike the 4×4 multiport amplifiers, in the 2×2 multiport amplifiers of  FIG. 5 , an input hybrid network includes one input hybrid  100 , and an output hybrid network includes one output hybrid  200 . Accordingly, the 2×2 multiport amplifiers include two power amplifiers  310  and  320  and two amplitude and phase controllers  410  and  420 . 
         [0076]    Further, even if an environment condition changes, in order to maintain performance of a multiport amplifier in an optimal state, the 2×2 multiport amplifiers according to an exemplary embodiment of the present invention further includes an error calibration unit  500 . 
         [0077]    The error calibration unit  500  detects amplitude and phase errors of multiple signals of the multiport amplifier. The amplitude and phase controllers  410  and  420  control amplitude and phase according to amplitude and phase errors of a corresponding signal. The error calibration unit  500  and the amplitude and phase controllers  410  and  420  are referred to as an amplitude and phase error calibration apparatus of the multiport amplifier. 
         [0078]    The input hybrid  100 , the output hybrid  200 , the two power amplifiers  310  and  320 , and the two magnitude and phase controllers  410  and  420  have the same functions as those of the hybrids  11 - 14  and  21 - 24 , the power amplifiers  31 - 34 , and the magnitude and phase controllers  41 - 44  that are described with reference to  FIGS. 1 to 4 , and therefore a detailed description thereof will be omitted. 
         [0079]    The error calibration unit  500  includes a modulator  510 , two BPSK demodulators  520   a  and  520   b  corresponding to the number of input terminals of the output hybrid  200 , a QPSK signal generator  530 , and a signal analyzer  540 . 
         [0080]    The modulator  510  modulates a reference QPSK signal of a baseband to an RF signal by an RF signal that is input to one input terminal  1  of the input hybrid  100 , and outputs a reference QPSK signal that is modulated to the RF signal to the BPSK demodulators  520   a  and  520   b . In this case, the reference QPSK signal may have a constellation of (a) of  FIG. 5 . 
         [0081]    Further, RF signals Sa and Sb that are input to two input terminals  1  and  2  of the output hybrid  200  are input to the BPSK demodulators  520   a  and  520   b . In this case, the RF signal Sa that is input to the input terminal  1  of the output hybrid  200  has a phase of 0°, and the RF signal Sb that is input to the input terminal  2  of the output hybrid  200  has a phase of 90°. 
         [0082]    The BPSK demodulator  520   a  demodulates (downward converts) a QPSK signal that is modulated to an RF signal by the modulator  510  to an I signal Io of a baseband by an RF signal Sa that is input to the input terminal  1  of the output hybrid  200 , and the BPSK demodulator  520   b  demodulates a QPSK signal that is modulated to an RF signal by the modulator  510  to a Q signal Qo of a baseband by an RF signal Sb that is input to an input terminal  2  of the output hybrid  200 . In this case, it is assumed that phase and amplitude changes generated in the two BPSK demodulators  520   a  and  520   b  are the same. Further, the RF signals Sa and Sb may be continuous wave (CW) signals. 
         [0083]    The QPSK signal generator  530  couples a pair of I and Q signals Io and Qo of a baseband that are demodulated by the BPSK demodulators  520   a  and  520   b , generates a QPSK signal of one baseband, and outputs the generated QPSK signal to the signal analyzer  540 . That is, because an I signal and a Q signal of a baseband that are demodulated by the BPSK demodulators  520   a  and  520   b  correspond to BPSK signals, when the I signal and the Q signal are combined, a QPSK signal of one baseband is generated, as shown in (b) of  FIG. 5 . 
         [0084]    The signal analyzer  540  compares a reference QPSK signal and a QPSK signal that is generated by the QPSK signal generator  530 , and detects amplitude and phase errors. 
         [0085]    It is assumed that a constellation of a reference QPSK signal is shown in (a) of  FIG. 5 . In an ideal multiport amplifier, a constellation of a QPSK signal that is demodulated by the BPSK demodulators  520   a  and  520   b  is the same as a constellation that is shown in (a) of  FIG. 5 , as shown in (a) of  FIG. 6 . However, when an amplitude error occurs in the multiport amplifier according to an environment change, a constellation of a QPSK signal that is generated by the QPSK signal generator  530  and the BPSK demodulators  520   a  and  520   b  is as shown in (b) of  FIG. 6 . Further, when a phase error occurs in the multiport amplifier, a constellation of a QPSK signal that is generated by the QPSK signal generator  530  and the BPSK demodulators  520   a  and  520   b  is as shown in (c) of  FIG. 6 . Therefore, the signal analyzer  540  compares a reference QPSK signal and a QPSK signal that is generated by the QPSK signal generator  530  and the BPSK demodulators  520   a  and  520   b , and detects amplitude and phase errors of the multiport amplifier. 
         [0086]    The signal analyzer  540  outputs the detected amplitude and phase errors to the magnitude and phase controllers  410  and  420 . 
         [0087]    The magnitude and phase controllers  410  and  420  each control an amplitude and a phase of an input RF signal according to amplitude and phase errors that are detected by the signal analyzer  540 . 
         [0088]      FIG. 7  is a diagram illustrating a detailed configuration of a BPSK demodulator that is shown in  FIG. 5 , and  FIG. 8  is a diagram illustrating an example of a signal waveform of a detailed configuration of a BPSK demodulator that is shown in  FIG. 7 . 
         [0089]      FIG. 7  illustrates only a BPSK demodulator  520   a  of the BPSK demodulators  520   a  and  520   b.    
         [0090]    Referring to  FIG. 7 , the BPSK demodulator  520   a  includes a phase converter  521 , RF couplers  522  and  523 , power detectors  524  and  525 , low pass filters  526  and  527 , and an analog decoder  528 . 
         [0091]    The phase converter  521  converts a phase of an RF signal (Sa) that is input to the input terminal  1  of the output hybrid  200  by 180° and outputs an RF signal S 1  having a phase that is converted by 180° to the RF coupler  522 . 
         [0092]    The RF coupler  522  adds (couples) an RF signal S 1  having a phase that is converted by 180° by the phase converter  521  and a reference QPSK signal that is modulated to an RF signal and outputs the added (coupled) signal to the power detector  524 . 
         [0093]    The RF coupler  523  adds the RF signal S 1  and a reference QPSK signal that is modulated to an RF signal and outputs the added signal to the power detector  525 . 
         [0094]    The power detectors  524  and  525  detect only signals S 4  and S 5  of a baseband from output signals S 2  and S 3  of the RF couplers  522  and  523 , and output the signals S 4  and S 5  to the low pass filters  526  and  527 , respectively. 
         [0095]    The low pass filters  526  and  527  select and pass through a predetermined frequency band of frequency from the signals S 4  and S 5  of a baseband that are detected from the power detectors  524  and  525 , respectively. 
         [0096]    The analog decoder  528  subtracts and outputs signals S 6  and S 7  of a baseband that pass through the low pass filters  526  and  527 . An output signal S 8  of the analog decoder  528  becomes an I signal of a baseband. 
         [0097]    When a reference QPSK signal that is modulated to an RF signal is defined as Vmod, Vmod may be represented by Equation 1. 
         [0000]        v   mod   =A   mod  cos(ω mod   t+φ   mod )  [Equation 1]
 
         [0098]    When the reference QPSK signal that is modulated to an RF signal and the RF signal Sa that is input to the input terminal  1  of the output hybrid  200  are input to the BPSK demodulator  520   a , the output signals S 6  and S 7  of the low pass filters  526  and  527  may be represented by Equation 2 and Equation 3, respectively. 
         [0000]    
       
         
           
             
               
                 
                   
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                   [ 
                   
                     Equation 
                      
                     
                         
                     
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                     2 
                   
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         [0099]    Here, P 1  is an output signal S 6  of the low pass filter  526 , and P 2  is an output signal S 7  of the low pass filter  527 . A CW  cos(ω CW t) corresponds to an RF signal S 1  that is input to the input terminal  1  of the output hybrid  200 . 
         [0100]    The output signals S 6  and S 7  of the low pass filters  526  and  527  are processed in the analog decoder  528  and become an I signal of a baseband of Equation 4. 
         [0000]        y ( t )=2 A   mod   A   CW  cos(φ mod )  [Equation 4]
 
         [0101]    Here, y(t) is an output signal of the analog decoder  528  and represents an I signal of a baseband. 
         [0102]    For example, it is assumed that a reference QPSK signal that is modulated to an RF signal is as shown in (a) of  FIG. 8  and an RF signal Sa that is input to the input terminal  1  of the output hybrid  200  is as shown in (b) of  FIG. 8 . In this case, an RF signal S 1  having a phase that is converted by 180° by the phase converter  521  is as shown in (c) of  FIG. 8 . Therefore, the output signal S 2  of the RF coupler  522  is shown as in (d) of  FIG. 8 , and the output signal S 6  of the low pass filter  526  is as shown in (e) of  FIG. 8 . Further, the output signal S 3  of the RF coupler  523  is as shown in (f) of  FIG. 8 , and the output signal S 7  of the low pass filter  527  is as shown in (g) of  FIG. 8 . Therefore, an output signal S 8  of the analog decoder  528  becomes a BPSK signal that is as shown in (h) of  FIG. 8 , i.e., an I signal of a baseband. 
         [0103]    That is, when a phase difference between a reference QPSK signal that is modulated to an RF signal and an RF signal S 1  is 0°, the BPSK demodulator  520   a  generates a BPSK signal of (h) of  FIG. 8  using the reference QPSK signal that is modulated to an RF signal and the RF signal Sa. 
         [0104]    The remaining BPSK demodulator  520   b  is also formed similarly to the BPSK demodulator  520   a . In this case, the reference QPSK signal that is modulated to an RF signal and the RF signal Sb that is input to the input terminal  2  of the output hybrid  200  are input to the BPSK demodulator  520   b , and the RF signal Sb has a phase of 90°. Therefore, a signal of a base band Q is output to the BPSK demodulator  520   b , as shown in Equation 5. 
         [0000]        y ( t )=2 A   mod   A   CW  sin(φ mod )  [Equation 5]
 
         [0105]    Here, y(t) represents a Q signal of a baseband. 
         [0106]    An I signal of a baseband of Equation 4 and a Q signal of a baseband of Equation 5 are coupled by the QPSK signal generator  530  to generate one QPSK signal. Therefore, the signal analyzer  540  detects an I or Q signal of the QPSK signal according to an input phase and compares a reference QPSK signal and a QPSK signal that is generated by the QPSK signal generator  530 , thereby distinguishing and detecting amplitude and phase errors. 
         [0107]    When amplitude and phase errors are detected by the signal analyzer  540 , the amplitude and phase controllers  410  and  420  control a phase and an amplitude of an input RF signal according to the amplitude and phase errors. 
         [0108]    The amplitude and phase controllers  410  and  420  calibrate phase and amplitude errors while not being influenced by a delay effect according to each signal path with a method of minimizing a relative phase error and a relative amplitude error of two signals S 1  and S 2 . 
         [0109]    That is, when an amplitude error and a phase error are detected, the amplitude and phase controller  420  calibrates an amplitude and a phase of the input RF signal according to an amplitude error and a phase error based on an amplitude and a phase of an RF signal that is input to the amplitude and phase controller  410 . In this way, because a relative amplitude and a relative phase of two signal paths are compared and calibrated, a phase calibration procedure according to a signal path can be reduced. 
         [0110]    Known technology of an error calibration unit of the multiport amplifier includes a method of using a superheterodyne transmitter based on a multiplicative mixing method. The known method is a method of calibrating a phase or an amplitude by detecting a signal magnitude of an output terminal in which a signal is not output, i.e., a null point, among output terminals of an output hybrid, and is a method of minimizing a signal magnitude of the detected null point. In the known method, it cannot be known whether a phase error or an amplitude error occurs in a multiple signal path. Therefore, in the known method, a calibration time of a phase or an amplitude is extended, and phase and amplitude error ranges may be decreased according to a signal magnitude of the detected null point. 
         [0111]    Further, because the known method uses a multiplicative mixing method, an intermediate frequency IF is necessary, and because hardware that embodies the intermediate frequency should be added, the size, weight, and power consumption of an apparatus increase, compared with an additive mixing method of the BPSK demodulators  520   a  and  520   b  according to an exemplary embodiment of the present invention. 
         [0112]    That is, because the error calibration unit  500  according to an exemplary embodiment of the present invention uses a direct conversion method based on an additive mixing method, the size, weight, and power consumption of a circuit can be reduced, compared with a superheterodyne method based on a known multiplicative mixing method, and a phase error and an amplitude error can be distinguished and detected. 
         [0113]      FIG. 9  is a diagram illustrating an example of a detailed circuit configuration of a phase converter, two RF couplers, and two power detectors that are shown in  FIG. 7 . 
         [0114]    As shown in  FIG. 9 , the phase converter  521  is formed using a balun circuit that converts an RF signal of a single phase that is input to a node N 1  to a differential phase. In this case, an RF signal Sa is input to the node N 1  of the phase converter  521 . In  FIG. 9 , a balun circuit is formed using a passive element such as an inductor and a capacitor. 
         [0115]    Further, the RF couplers  522  and  523  and the power detectors  524  and  525  may each be formed using an active element such as a transistor and a passive element such as a capacitor or a resistor, a QPSK signal that is modulated to an RF signal is input to a node N 4 , and signals of nodes N 2  and N 3  become an output signal of the RF couplers  522  and  523 , while signals of nodes N 5  and N 6  become an output signal of the power detectors  524  and  525 . 
         [0116]    In this way, because the BPSK demodulators  520   a  and  520   b  may be formed using an active element such as a transistor and a passive element such as an inductor, a resistor, and a capacitor, there is a merit that the BPSK demodulators  520   a  and  520   b  may have a light weight and a small size. 
         [0117]    Further, the BPSK demodulators  520   a  and  520   b  may be formed using a ring hybrid and a diode detector. 
         [0118]    It is known technology to embody the phase converter  521 , the RF couplers  522  and  523 , and the power detectors  524  and  525  using a passive element or an active element and therefore a detailed description thereof will be omitted. 
         [0119]      FIG. 10  is a graph illustrating a reference QPSK signal and a QPSK signal that is generated by two BPSK demodulators through a simulation result when amplitude and phase errors do not occur in a multiport amplifier according to an exemplary embodiment of the present invention. 
         [0120]    In  FIG. 10 , Io is an I signal (BPSK signal) that is demodulated by the BPSK demodulator  520   a , and Qo is a Q signal (BPSK signal) that is demodulated by the BPSK demodulator  520   b . Further, BIT_I and BIT_Q represent an I signal and a Q signal, respectively, when a reference QPSK signal is separated to a BPSK signal. 
         [0121]    As shown in  FIG. 10 , when phase and amplitude errors do not occur in the multiport amplifier, a reference QPSK signal and a QPSK signal that is generated by the QPSK signal generator  530  and two BPSK demodulators  520   a  and  520   b  are very similar. 
         [0122]    However, when phase and amplitude errors occur in the multiport amplifier, a constellation of a QPSK signal that is generated by the BPSK demodulators  520   a  and  520   b  is changed to another form instead of a square, as shown in  FIG. 6 . When an amplitude error occurs, the amplitude error is represented in a quadrangle form in which a width and a length are different, and when a phase error occurs, the amplitude error is represented in a quadrangle form in which lengths of a diagonal are different. 
         [0123]    The amplitude and phase controllers  410  and  420  calibrate amplitude and phase errors according to a degree in which a constellation of a QPSK signal that is generated by the BPSK demodulators  520   a  and  520   b  is changed to correspond to a reference QPSK signal. Thereby, even if a change occurs in performance of constituent elements of the multiport amplifier by an environment condition change, amplitude and phase errors of an input RF signal can be successfully calibrated and thus performance of the multiport amplifier can be maintained in an optimal state. 
         [0124]      FIG. 11  is a diagram illustrating a multiport amplifier according to a second exemplary embodiment of the present invention. 
         [0125]      FIG. 11  illustrates 4×4 multiport amplifiers, unlike  FIG. 5 . 
         [0126]    Referring to  FIG. 11 , the 4×4 multiport amplifiers have the same structure and function as those of  FIG. 4 , except for an error calibration unit  500 ′. 
         [0127]    That is, an input hybrid network  1100 , an output hybrid network  1200 , four power amplifiers  1310 ,  1320 ,  1330 , and  1340 , and four amplitude and phase controllers  1410 ,  1420 ,  1430 , and  1440  of the 4×4 multiport amplifiers have the same functions as those of the input hybrid network  10 , the output hybrid network  20 , the power amplifiers  31 - 34 , and the magnitude and phase controllers  41 - 44  that are described with reference to  FIGS. 1 to 4 , and therefore a detailed description thereof will be omitted. 
         [0128]    Unlike 2×2 multiport amplifiers including one input hybrid  100  and one output hybrid  200 , the error calibration unit  500 ′ of the 4×4 multiport amplifiers further includes a signal selector  550 . 
         [0129]    The signal selector  550  includes two switches SW 1  and SW 2 , and controls switching of the switches SW 1  and SW 2 . 
         [0130]    The switch SW 1  is switched by the control of the signal selector  550  to selectively output one of output signals of BPSK demodulators  520   a  and  520   d  to the QPSK signal generator  530 , and the switch SW 1  is switched by the control of the signal selector  550  to selectively output one of output signals of BPSK demodulator  520   b  and  520   c  to the QPSK signal generator  530 . In this case, the signal selector  550  controls switching of the switches SW 1  and SW 2  so that an I signal and a Q signal of a baseband may be coupled to generate one QPSK signal. 
         [0131]    For example, when an RF signal having a phase of 0° is input to the input hybrid network  1100 , each of RF signals of 0°, 90°, 90, and 180° is ideally input to the output hybrid network  1200 , and the RF signals of 0°, 90°, 90, and 180° are input to the BPSK demodulators  520   a - 520   d , respectively. 
         [0132]    First, in order to calibrate an amplitude and a phase of a signal Sb based on a signal Sa, the switch SW 1  is connected to the BPSK demodulator  520   a  by the control of the signal selector  550 , and the switch SW 2  is connected to the BPSK demodulator  520   b  by the control of the signal selector  550 . The QPSK signal generator  530  generates one QPSK signal by coupling an I signal of a baseband that is demodulated by the BPSK demodulator  520   a  and an Q signal of a baseband that is demodulated by the BPSK demodulator  520   b . Therefore, the signal analyzer  540  compares a reference QPSK signal and one QPSK signal that is generated by the BPSK demodulators  520   a  and  520   b  and detects amplitude and phase errors, and the amplitude and phase controller  1420  controls a magnitude and a phase of an input RF signal according to the detected amplitude and phase errors. 
         [0133]    Next, in order to calibrate an amplitude and a phase of a signal Sc based on a signal Sa, the switch SW 1  is connected to the BPSK demodulator  520   a  by the control of the signal selector  550 , and the switch SW 2  is connected to the BPSK demodulator  520   c  by the control of the signal selector  550 . The QPSK signal generator  530  generates one QPSK signal by coupling an I signal of a baseband that is demodulated by the BPSK demodulator  520   a  and a Q signal of a baseband that is demodulated by the BPSK demodulator  520   c . Therefore, the signal analyzer  540  compares a reference QPSK signal and one QPSK signal that is generated by the BPSK demodulators  520   a  and  520   c  and detects amplitude and phase errors, and the amplitude and phase controller  1430  controls a magnitude and a phase of an input RF signal according to the detected amplitude and phase errors. 
         [0134]    Finally, in order to calibrate an amplitude and a phase of a signal Sd based on the signal Sb or Sc, the switch SW 1  is connected to a BPSK demodulator  520   d  by the control of the signal selector  550 , and the switch SW 2  is connected to the BPSK demodulator  520   b  or  520   c  by the control of the signal selector  550 . When it is assumed that the switch SW 2  is connected to the BPSK demodulator  520   b , the QPSK signal generator  530  generates one QPSK signal by coupling an I signal of a baseband that is demodulated by the BPSK demodulator  520   d  and a Q signal of a baseband that is demodulated by the BPSK demodulator  520   b . Therefore, the signal analyzer  540  compares a reference QPSK signal and one QPSK signal that is generated by the BPSK demodulators  520   d  and  520   b  and detects amplitude and phase errors, and the amplitude and phase controller  1440  controls a magnitude and a phase of an input RF signal according to the detected amplitude and phase errors. 
         [0135]    In this way, the error calibration unit  500 ′ relatively detects amplitude and phase errors of each of multiple signals and thus amplitudes and phases of each signal are compensated. 
         [0136]      FIG. 12  is a diagram illustrating a multiport amplifier according to a third exemplary embodiment of the present invention, and  FIG. 13  is a diagram illustrating a signal constellation by delay that may occur in modulation of a modulator and demodulation of a BPSK demodulator. 
         [0137]    Referring to  FIG. 12 , an error calibration unit  500 ″ further includes a phase converter  560 . 
         [0138]    As shown in  FIG. 13 , a delay may occur in a modulation process of a modulator  510  and a demodulation process of BPSK demodulators  520   a - 520   d  by a transmission path between the modulator  510  and the BPSK demodulators  520   a - 520   d . By a delay occurring in a transmission process between the modulator  510  and the BPSK demodulators  520   a - 520   d , a phase of a QPSK signal that is generated by the QPSK signal generator  530  may be changed within 360°, as shown in (a) of  FIG. 13 . 
         [0139]    A signal analyzer  540  analyzes a phase of the QPSK signal that is generated by the QPSK signal generator  530 , detects a phase change amount by delay, and outputs the detected phase change amount to the phase converter  560 . 
         [0140]    The phase converter  560  changes a phase of a reference QPSK signal that is modulated to an RF signal according to a phase change amount by delay and outputs the phase to the BPSK demodulators  520   a - 520   d . Therefore, as shown in (a) of  FIG. 13 , a phase of the QPSK signal that is changed by delay is normally compensated, as shown in (b) of  FIG. 13 . 
         [0141]    According to an exemplary embodiment of the present invention, a multiport amplifier having an error calibration function that can auto-calibrate phase and amplitude errors of a multiport amplifier due to an environment condition change such as degradation of a component performance or a temperature change can be embodied. 
         [0142]    Further, a multiport amplifier including a small error calibration apparatus of low power can be embodied, and it can be distinguished whether an error occurring when manufacturing the multiport amplifier is a phase error or an amplitude error. 
         [0143]    An exemplary embodiment of the present invention may not only be embodied through the above-described apparatus and/or method, but may also be embodied through a program that executes a function corresponding to a configuration of the exemplary embodiment of the present invention or through a recording medium on which the program is recorded, and can be easily embodied by a person of ordinary skill in the art from a description of the foregoing exemplary embodiment. 
         [0144]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.