Patent Publication Number: US-2006019712-A1

Title: Calibration apparatus for smart antenna and method thereof

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application is a continuation-in-part of U.S. Ser. No. 10/491,724, filed Apr. 5, 2004, which is the National Phase of PCT Application No. PCT/KR01/01939, filed Nov. 14, 2001. These applications, in its entirety, is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION  
      This invention is related to calibration apparatus and its method for array antenna system, especially for adaptive array antenna system. More specifically, this invention is related to calibration apparatus and its method for compensating differences or irregularities of phase characteristics in said adaptive array antenna system for both receiving and transmitting mode.  
     DESCRIPTION OF RELATED ARTS  
      Said adaptive array antenna system denotes a communication system that optimizes its antenna beam pattern utilizing a predetermined adaptive beamforming algorithm based on the information acquired from the received signals at each of antenna elements. Although this invention is focued mainly on said adaptive array antenna system, this invention is also valid for said array antenna system of which the beam pattern is not adaptively optimized by said adaptive algorithm but is determned by selecting procedure from preserved values.  
      The applicants of this invention have submitted following documents, which are related to said adaptive array antenna system, to Korean patent office for patents: 1996-12171, 1996-12172, 1996-17931, 1996-25377, 1997-73901, 1999-58065, 2000-30655, 2000-30656, 2000-30657, 2000-30658, 2001-14671, 2001-20971, 2001-7008066, 2001-62792, 2001-63543, 2001-64498, 2001-67953, 2001-71055, 2001-71284, and 2001-77674.  
      Said adaptive array antenna system is to provide each subscriber an ideal beam pattern, which has its maximum gain along the direction of the target subscriber maintaining its gain at as low level as possible to the other directions, utilizing a beamforming parameter such as weight vector that is obtained from received signals at each snapshot. Said snapshot denotes a time interval for which said beamforming parameter is updated. Said ideal beam pattern should be provided for transmitting mode as well as for receiving mode of said adaptive array antenna system.  
      However, it is not easy to provide said ideal beam pattern to said adaptive array antenna system in even said receiving mode because of many techinical restrictions. In order to provide a beam pattern that is close to said ideal beam pattern in said trnasmitting mode as well as in said receiving mode, said phase characteristics of the signal path associated with each of antenna elements in said adaptive array antenna system should be equalized through a proper compensation procedure. The compensation procedure described above is referred to as “calibration”. In many cases, calibration may include said compensation procedure for magnitude characteristics as well as for said phase characteristics, though our main interest lies in said compensation of phase characteristics in this invention. It does not mean that techiniques disclosed in this invention is valid ony for said compensation of phase characteristics. It is valid for said compensation of both magnitude and phase characteristics of the signal path associated with each of antenna elements in said adaptive array antenna system.  
      The ultimate goal of said calibration in this invention is to equalize said beam pattern for said transmitting mode to that for said receiving mode. In general, said beam forming parameter for providing a transmitting beam pattern is based on said beam forming parameter that has been obtained during said receiving mode for the same time slot. Therefore, assuming said beam forming parameter for said receiving mode provides a nice beam pattern that is close to said ideal beam pattern, the same beam pattern can be provided during said transmitting mode if the differences and/or irregularities in said phase characteristics among signal paths associated with corresponding antenna elements in said adaptive array antenna system are properly resolved through said calibration procedure.  
      Prior art related to said calibration can be found from “Adaptive Array Antenna Transceiver Apparatus” (Pub. No.: US2001/0005685 A1, Pub. Date: Jun. 28, 2001.) by K. Nishimori, et al. This prior art is concerned with “an adaptive array antenna transceiver apparatus for automatically calibrating the amplitude and phase differences between branches of the antenna for the respective transmitter and receiver”.  
      Above prior art has a restriction on the location of additional antenna according to given array antenna structure as illustrated in  FIG. 1  and  2 .  
       FIG. 1  illustrates planar drawings showing the arrangement of the antenna elements and the additional antenna according to the prior art. As illustrated in  FIG. 1 , in the case that the antenna elements arranged on one line are equally spaced, the additional antenna  128  should be disposed at a position in the middle of two antenna elements  111  such that the distances d between each of the antenna elements  111  on the two branches that are the object of calibration and the additional antenna  128  are equal. Therefore, it is the restriction in the prior art that said additional antenna should be located at the very center of the antenna elements in said adaptive array antenna system. It also implies that N- 1  additional antennas would be needed in the case of linear array system consisting of N antenna elements.  
       FIG. 2  illustrates planar drawings showing the arrangement of the antenna elements and the additional antenna. As shown in  FIG. 2 , in the case of cylinderical array anstenna system in which antenna elements  111  are located along the circle with equal spacing, said additional antenna  128  should be positioned at the center of the circle such that distance d between said additonal antenna  128  and each of the to-be-calibrated antennas  111  is all the same. It is, however, very difficult to find said center of the circle in said cylinderical array system operating in RF (radio Frequency) band. Consequently, it is the most serious hindrance in prior art that said additional antenna should be installed at the exact position in such a way that the distance between said additional antenna and each of acting antenna elements is the same for the phase delay between said additional antenna and each of acting antenna elements to be the same as one another. Furthermore, accroding to said prior art shown in  FIG. 2 , said additional antenna should be omni-directional.  
      As a conclusion, it is an inherent problem in said prior art that the position where the additional antenna  128  is disposed and the number of the additional antenna  128  must be determined depending on the position and the number of the antenna elements  111  that form the array antenna  
     SUMMARY OF THE INVENTION  
      It is the objective of this invention, which has been proposed to resolve the problems in the prior art, to provide calibration apparatus of said array antenna system and its method for compensating the differences of said phase characteristics in the signal paths associated with each of antenna elements without any restriction on the architechure or topology of said array antenna.  
      It is another objective of this invention, which has been proposed to resolve the problems in the prior art, to provide calibration apparatus of said array antenna system and its method for compensating the differences of said phase characteristics in the signal paths associated with each of antenna elements without any restriction on the architechure or position of said additional antenna element.  
      It is another objective of this invention, which has been proposed to resolve the problems in the prior art, to provide calibration apparatus of said array antenna system and its method for compensating the differences of said phase characteristics in the signal paths associated with each of antenna elements without any restriction on whether or not said array antenna system is in active mode.  
      The goal in the calibration procedure discussed above can be achieved in this invention due to the fact that the phase delay between said additional antenna and each of antenna elements to be calibrated is measured in advance and the value of said phase delay that has been measured in advance is properly reflected in the calibration procedure of compensating the phase delay characteristics among signal paths associated with each of antenna elements. Also, the goal in the calibration procedure discussed above can be achieved in this invention due to another fact that the signal transmitted or received at said additional antenna element for the calibration function is distinguishable from the other signals used for the original purposes during the normal operation of said array antenna system.  
      In accordance with one aspect of the present invention, there is provided a calibration apparatus of an adaptive array antenna system, the calibration apparatus comprising: calibrator means that generates the “Rx calibration signal” and performs the calibration procedure based on the “Rx calibration signal” received at each of receiving antenna elements of the array antenna means; additional antenna means that transmits the “Rx calibration signal” to the receiving antenna elements of the array antenna means with an arbitrary arrangement and spacing in a freuqency band of receiving RF (radio frequency); and array antenna means with an arbitrary arrangement and spacing of antenna elements that transfers the “Rx calibration signal”, which have been received from the additional antenna means, to the calibrator means, wherein the calibration procedure is performed by a step of compensating the differences or irregularities in phase characteristics at each of signal paths associated with each of the receiving antenna elements of the array antenna means utilizing φ RX, n  (phase delay between each of receiving antenna elements of the array antenna means and each corresponding port of the calibrator means) that is related with the two sets of phase delay values φ″ RX, n  (phase delay between the additional antenna means and the calibrator means) and φ′ RX, n  (phase delay between the additional antenna means and each of the receiving antenna elements of the antenna array means) by a mathematical equation φ RX, n =φ″ RX, n −φ′ RX, n  where φ′ RX, n  is obtained in advance of the calibration procedure.  
      In accordance with another aspect of the present invention, there is provided a calibration method of an adaptive array antenna system including calibrator means, additional antenna means, and array antenna means with an arbitrary arrangement and spacing—the calibrator means generates the “Rx calibration signal” and performs the calibration procedure based on the “Rx calibration signal” received at each of receiving antenna elements of the array antenna means, the additional antenna means transmits the “Rx calibration signal” to the receiving antenna elements of the array antenna means with an arbitrary arrangement and spacing in a freuqency band of receiving RF (radio frequency), and the array antenna means transfers the “Rx calibration signal” which have been received from the additional antenna means, to the calibrator means—the calibration procedure comprises a step of compensating the differences or irregularities in phase characteristics at each of signal paths associated with each of the receiving antenna elements of the array antenna means utilizing φRX, n (phase delay between each of receiving antenna elements of the array antenna means and each corresponding port of the calibrator means) that is related with the two sets of phase delay values φ″ RX, n  (phase delay between the additional antenna means and the calibrator means) and φ′ RX, n  (phase delay between the additional antenna means and each of the receiving antenna elements of the antenna array means) by a mathematical equation φ RX, n =φ″ RX, n−φ′   RX, n  where φ′ RX, n  is obtained in advance of the calibration procedure.  
      In accordance with further another aspect of the present invention, there is provided a calibration apparatus of an adaptive array antenna system, the calibration apparatus comprising: calibrator means that generates the “Tx calibration signal” and performs the calibration procedure based on the “Tx calibration signal” received at additional antenna means; array antenna means with an arbitrary arrangement and spacing of antenna elements that transmits the “Tx calibration signal”, which has been generated at the calibrator means, to the additional antenna means; and additional antenna means that receives the “Tx calibration signal” from the transmitting antenna elements of the array antenna means with an arbitrary arrangement and spacing in a freuqency band of transmitting RF (radio frequency), wherein the calibration procedure is performed by a step of compensating the differences or irregularities in phase characteristics at each of signal paths associated with each of the transmitting antenna elements of the array antenna means utilizing φ TX, n  (phase delay between calibrator means and each of transmitting antenna elements of the array antenna means and) that is related with the two sets of phase delay values φ″ TX, n  (phase delay between the calibrator means and the additional antenna means) and φ′ TX, n  (phase delay between each of the transmitting antenna elements of the antenna array means and the additional antenna means) by a mathematical equation φ TX, n =φ″ TX, n −φ′ TX, n  where φ′ TX, n  is obtained in advance of the calibration procedure.  
      In accordance with still further another aspect of the present invention, there is provided a calibration method of an adaptive array antenna system including calibrator means, additional antenna means, and array antenna means with an arbitrary arrangement and spacing—the calibrator means generates the “Tx calibration signal” and performs the calibration procedure based on the “Tx calibration signal” received at the additional antenna means, each of the transmitting antenna elements of the array antenna means transmits the “Tx calibration signal” to the additional antenna means in a freuqency band of transmitting RF (radio frequency) of the array antenna system, and the “Tx calibration signal” received at the additional antenna means is transferred to the calibrator means after the frequency band is converted from the transmitting RF to the base band—the calibration procedure comprises a step of compensating the differences or irregularities in phase characteristics at each of signal paths associated with each of the receiving antenna elements of the array antenna means utilizing φ TX, n  (phase delay between each of receiving antenna elements of the array antenna means and each corresponding port of the calibrator means) that is related with the two sets of phase delay values φ″ TX, n  (phase delay between the additional antenna means and the calibrator means) and φ′ TX, n  (phase delay between the additional antenna means and each of the receiving antenna elements of the antenna array means) by a mathematical equation φ TX, n =φ″ TX, n −φ′ TX, n  where φ′ TX, n  is obtained in advance of the calibration procedure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  and  FIG. 2  illustrate planar drawings showing the arrangement of the antenna elements and the additional antenna according to the prior art.  
       FIG. 3A  illustrates a block diagram of a receiving array antenna system which adopts a single antenna element connected with the plural antenna channels through a divier. This figure shows how the phase characteristics of each of receiving antenna paths can be measured.  
       FIG. 3B  illustrates a block diagram of a transmitting array antenna system which adopts a single antenna element connected with the plural antenna channels through a combiner. This figure shows how the phase characteristics of each of transmitting antenna paths can be measured.  
       FIG. 4  illustrates the phase characteristics of an array antenna system consisting of 6 antenna elements. Letting the phase characteristic along one antenna element, which has been arbitrarily selected, be zero, the phase characteristics along the other 5 antenna elements, A, B, C, D, and E, are measured to be all different as shown in  FIG. 4 .  
       FIG. 5  illustrates a block diagram of said calibration apparatus for said array antenna system in receiving mode according to the first application example of this invention.  
       FIG. 6  shows how to measure the phase characteristic of the signal path associated with each of antenna elements of said array antenna system in receiving mode shown in  FIG. 5 .  
       FIGS. 7A, 7B ,  7 C, and  7 D show the calibration procedure performed in said calbration apparatus of receiving array antenna system according to the first application example of this invention.  
       FIG. 8  illustrates a block diagram of said calibration apparatus for said array antenna system in transmitting mode according to the first application example of this invention.  
       FIG. 9  shows how to measure the phase characteristic of the signal path associated with each of antenna elements of said array antenna system in transmitting mode shown in  FIG. 8 .  
       FIGS. 10A, 10B ,  10 C, and  10 D show the calibration procedure performed in said calbration apparatus of transmitting array antenna system according to the first application example of this invention.  
       FIG. 11  illustrates a block diagram of said calibration apparatus for said array antenna system in receiving mode according to the second application example of this invention.  
       FIG. 12  illustrates a block diagram of said calibration apparatus for said array antenna system in transmitting mode according to the second application example of this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION  
      The objectives, special features, and advantages described in this invention will be more clarified through detailed explanations and figures given below. We describe the first application example of this invention as a preferred embodiment using proper figures as follows.  
       FIG. 3A  illustrates a block diagram of a general array antenna system which describes the conceptual view of calibration. Using the system structure shown in  FIG. 3A , the different characteristics of each of antenna channels can be measured.  
      As shown in  FIG. 3A , the differences of phase characteristics in each of antenna channels (the phase differences will be refered to as “phase error” from now on) can be obtained at each of receiving paths,  121 ,  122 ,  123 ,  124 ,  125 , and  126 , while the signal has been transmitted from the terminal  110  and received at a single antenna and fed to each of the receiving paths through the divider. The phase error has been measured as shown in  FIG. 3A  using an array antenna system consisting of 6 antenna elements. As the signal path  121  is arbitrarily selected as a reference one, the relative phase delay along the other signal paths  122 - 126  can be established as shown in  FIG. 4  and Tables 1-4. Table 1 shows an average values of said phase errors in radian measured at the 5 antenna paths, {φ i  for i=2, 3, . . . , 5}, which represent the phase delay differences relatively to the phase delay associated with  121 , φ 1 . Table 2 shows the standard deviations of said phase errors measured at the 5 antenna channels. Table 3 shows variations of said phase errors which have been obtained by subtracting the average phase errors from the maximum phase errors. Similarly, Table 4 shows variations of said phase errors which have been obtained by subtracting the minimum phase errors from the average phase errors.  
                                   TABLE 1                       mean(φ 1 )   mean(φ 2 )   mean(φ 3 )   mean(φ 4 )   mean(φ 5 )   mean(φ 6 )                  0   1.7710   3.3234   0.4026   0.9678   4.5984                  
 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
               
               
                 std(φ 1 ) 
                 std(φ 2 ) 
                 std(φ 3 ) 
                 std(φ 4 ) 
                 std(φ 5 ) 
                 std(φ 6 ) 
               
               
                   
               
             
            
               
                 0 
                 0.0716 
                 0.1157 
                 0.1021 
                 0.1473 
                 0.0958 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
               
             
            
               
                 max(φ 1 ) 
                 max(φ 2 ) 
                 max(φ 3 ) 
                 max(φ 4 ) 
                 max(φ 5 ) 
                 max(φ 6 ) 
               
               
                   
               
               
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 mean(φ 1 ) 
                 mean(φ 2 ) 
                 mean(φ 3 ) 
                 mean(φ 4 ) 
                 mean(φ 5 ) 
                 mean(φ 6 ) 
               
               
                   
               
               
                 0 
                 0.1556 
                 0.2911 
                 0.2752 
                 0.4101 
                 0.3006 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
               
             
            
               
                 mean(φ 1 ) 
                 mean(φ 2 ) 
                 mean(φ 3 ) 
                 mean(φ 4 ) 
                 mean(φ 5 ) 
                 mean(φ 6 ) 
               
               
                   
               
               
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 min(φ 1 ) 
                 min(φ 2 ) 
                 min(φ 3 ) 
                 min(φ 4 ) 
                 min(φ 5 ) 
                 min(φ 6 ) 
               
               
                   
               
               
                 0 
                 0.1939 
                 0.3678 
                 0.3092 
                 0.4213 
                 0.2670 
               
               
                   
               
            
           
         
       
     
      From Tables 1-4, it can surely be observed that, when a signal is received from a terminal  110 , the phase values observed at each of antenna channels are not equal to one another because the phase characteristics along the signal path corresponding to each of antenna channels are all different. The differences or irregularities at each of antenna channels, which cause the phase characteristics at each of antenna channels become all different, should be compensated through calibration.  
       FIG. 4  illustrates the phase characteristics of an array antenna system consisting of 6 antenna elements. Letting the phase characteristic of one antenna channel,  121 , which has been arbitrarily selected, be zero, the phase characteristics of the other 5 antenna channels,  122 ,  123 ,  124 ,  125 , and  126 , are found to be all different as shown in  FIG. 4 . In  FIG. 4 , “A”-“E” denote the phase error at the signal paths  122 - 126 , respectively, when the phase delay associated with the signal path  121  is assumed to be zero. It can also be observed that the phase error at each of signal paths along the corresponding antenna elements remains near its average value as time passes by, although the phase delay at each of antena channels itself is different from one another. From the analysis discussed above, it can be observed that the phase differences or irregularities at each of signal paths associated with the corresponding antenna elements in array antenna system can be compensated through a proper calibration procedure in which the compensating phase value is obtained by reflecting the pre-computed value of phase delay between said additional antenna and each of antenna elements of the array system.  
      The key part of this invention is that the phase delay between said additional antenna element and each of antenna elements in a given array antenna system is computed in advance such that the pre-computed phase delay is reflected in the calibration procedure for the phase characteristic at each of antenna channels to be effectively compensated. Detailed application examples are shown in the following part of this invention.  
       FIG. 5  and  FIG. 10  illustrate block diagrams of array antenna system designed in accordance with the first application example of this invention.  
       FIG. 5  is a block disgram of calibration apparatus of receiving array antenna system design in accordance with the first application example of this invention. According to the first application example of this invention, as the phase delay between said additional antenna element  510  and each of receiving antenna elements  520  is computed in advance of the calibration procedure, there is no restriction at all on the location of said additional antenna  510  or topology of array antenna element  520 . In the meantime, the receiving antenna elements  520  do not have to be prepared separately from transmitting antenna elements (shown as transmitting antenna  820  in  FIG. 8 ) in array antenna system. It means a single antenna element can be used for both receiving and transmitting mode. Duplexer or switch can be used to distinguish the receiving and transmitting function from each other. Duplexer is used for FDD (frequency dividion duplexing) system and switch is used for TDD (time division duplexing) system.  
      As shown in  FIG. 5 , calibration apparatus according to the first application example of this invention consists of additional antenna element  510  and frequency up-converter (U/C)  511  and digital-to-analog converter (DAC) that are connected to the additional antenna  510 , plural receiving antenna elements  520  with arbitrary spacing and topology, low noise amplifiers (LNA)  521 , frequency down-converters (D/C)  523 , analog-to-digital converters (ADC)  525 , and claribrator  530 . Note that each of LNA&#39;s  521 , D/C&#39;s  523 , and ADC&#39;s  525  is connected to each of receiving antenna elements  520 , correspondingly.  
      Calibration procedure performed in the calibration apparatus shown in  FIG. 5  can be summarized as follows. Said additional antenna element  510  transmits a signal that is generated in said calibrator  530  and provided through said DAC  513  and U/C  511 . The signal transmitted from said additional antenna element  510  will be denoted in this invention as “Rx calibration signal” from now on. Said Rx calibration signal generated in base-band at said calibrator  530  is first modulated into its analog form in said DAC  513  and then the frequency range of said analog-converted Rx calibration signal is converted to the receiving carrier frequency band of said array antenna system in said U/C  511 . It is recommanded not to use high power amplifier (HPA) when said Rx calibration signal is transmitted from said additional antenna element  510  in order to reduce interference due to the Rx calibration signal itself. Each of said receiving antenna elements  520  receives said Rx calibration signal which is transmitted from said additional antenna element  510 , and the received Rx calibration signal is tranferred to said calbrator  530  by way of said LNA  521 , D/C  523 , and ADC  525 . Said LNA  521  amplifies the received Rx calibration signal with a minimum noise, D/C  523  converts the frequency range of the received Rx calibration signal into base-band, and ADC  525  converts the Rx calibration signal into digital data.  
      In the meantime, said Rx calibration signal should be distinguished from the other signals used for normal communication purposes because the calibration can be performed while the array antenna system is operating. In order for said Rx calibration signal to be distinguished from the other communication signals used by the subscribers communicating with the array antenna system, it is recommanded that said “Rx calibration signal” is orthogonal or quasi-orthogonal to the other signals such that said “Rx calibration signal” can be separated from the other signals at the calibrator  530 .  
      Based on the phase delay of the “Rx calibration signal” obtained from said ADC  525 , said calibrator  530  measures the differences of phase delays at each of signal paths associated with each of receiving antenna elements  520  such that the phase delays associated with each of antenna elements  520  can be resolved as a result of calibration procedure. Said calibrator  530  computes the differences of the phase delays associated with each of the antenna elements  520  using “Rx calibration signal” received from each of the receiving antenna elements  520 . It is important that the phase delay between additional antenna  510  and each of antenna elements  520  that are obtained in advance of the calibration procedure should appropriately be taken into consideration in computing the phase differences.  
       FIG. 6  shows a block diagram of calibration apparatus according to the first application example, which can be applied to calibration apparatus shown in  FIG. 5 .  FIG. 6  shows how the phase delay between the additional antenna element and each of receiving antenna elements is computed during the calibartion period. The phase delay at each of signal paths is defined as follows: 
          φ′ RX, n  Phase delay between the additional antenna element  510  and the n_th receivng antenna  520  for n=1, 2, . . . , N where N is the total number of receiving antenna elements in the array antenna system. Note that φ′ RX, n  for n=1, 2, . . . , N is measured in advance of the calibration procedure. It can even be measured in advance of the normal operation of the array antenna system.     φ″ RX, n  Phase delay between the additional antenna element  510  and calibrator  530 . Note that the phase delay φ″ RX, n  is associated with the following signal path: additional antenna  510 →n_th receiving antenna  520 →n_th LNA  521 →n_th D/C  523 →n_th ADC  525 → calibrator  530 .     φ RX, n  Phase delay between the n_th receiving antenna element  520  and calibrator  530 . Note that the phase delay φ RX, n  is associated with the following signal path: n_th receiving antenna  520 →n_th LNA  521 →n_th D/C  523 →n_th ADC  525 → calibrator  530 .        
      From the discussions given above, it can be found that the phase delay that has to be compensated for calibrating the signal path associated with each of receiving antenna elements  520  is 
 
φ RX, n =φ″ RX, n −φ′ RX, n  
 
 for n=1, 2, . . . , N where N is the number of said receiving antenna elements in the array antenna system. 
 
      According to the first application example of this invention, in advance of the calibration procedure for the array antenna system, the phase delay (φ′ RX, n ) between the additional antenna element  510  and each of plural receiving antenna elements  520  should be obtained. It particularly means that φ′ RX, n  should be obtained for all n. In order to obtain the phase delay (φ′ RX, n ) between the additional antenna element  510  and each of plural receiving antenna elements  520 , the phase delay (φ RX, n ) between each of receiving antenna elements  520  and the calibrator  530  and the phase delay (φ″ RX, n ) between the additional antenna element  510  and the calibrator  530  are computed in advance. After computing the phase delays φ RX, n  and φ″ RX, n , the phase delay φ′ RX, n  is obtained by φ′ RX, n =φ″ RX, n −φ RX, n . Note that the phase delay φ′ RX, n  between the additional antenna element  510  and each of receiving antenna elements  520  is computed in advance of normal operation of array antenna system only once at the initial stage, for example, when the array antenna system is first installed. This phase delay φ′ RX, n  is then used whenever the calibration is performed in the array antenna system.  
      The calibration disclosed in this invention is based upon the the phase delay φ′ RX, n  between the additional antenn element  510  and each of receiving antenna elements  520  More specifically, the calibrator  530  produces the phase delay φ″ RX, n  between the additional antenna element  510  and the calibrator  530  from the “Rx calibration signal” received at each of N receiving antenna elements  520 . The phase delay φ RX, n  to be compensated at each of signal paths associated with N receiving antenna elements  520  is obtained by subtracting the pre-computed phase delay φ′ RX, n  between the additional antenna element  510  and each of N receiving antenna elements  520  from the phase delay φ″ RX, n  between the additional antenna element  510  and the calibrator  530  The computation of the phase delay φ′ RX, n  is performed for all N receiving antenna elements  520 , i.e., for n=1, 2, . . . , N, thus {φ RX, 1 , . . . , φ RX, n , . . . , φ RX, N } are obtained as a result of the calibration procedure. The calibrator  530  produces the phase delay compensation {φ RX, 1 , . . . , φ RX, n , . . . , φ RX, N } to resolve the differences or irregularities of the phase delays at the signal paths associated with N receiving antenna elements  520 .  
      The calibration procedure of which the major part is to compute the differences or irregularities of phase characteristic at each of signal paths associated with each of N receiving antenna elements  520  can be performed without any restriction on the array structure or antenna topology or location of additional antenna by utiling the phase delay (φ′RX, n) between the additional antenna  510  and each of N receiving antenna elements  520 , which is obtained in advance of the calibration procedure.  
      Furthermore, as the “Rx calibration signal” is distinguishable from the other signals being used by the subscribers, the calibration procedure disclosed in this invention can be performed while the array antenna system is operating for its original purpose.  
       FIG. 7A-7D  represent receiving calibration procedure used in calibration apparatus of the array antenna system in accordance with the first application example of this invention. As an example, the calibration procedure shown in  FIGS. 7A-7D  are applied to the calibration apparatus shown in  FIG. 5 .  
      As shown in  FIG. 7A , the calibration according to the first application example consists mainly of two steps, i.e., a step S 710  of computing the phase delay (φ′ RX, n ) between the additional antenna  510  and each of receiving antenna elements  520  in advance of the calibration procedure and the other step S 750  of performing the calibration with the phase delay (φ RX, n ) between each the receiving antenna elements  520  and the calibrator  530 .  
      As mentioned earlier, it is normal that the step S 710  is performed just one time after the structure of the additional antenna  510  and that of plural receiving antenna elements  520  are determined. Note, however, that the phase delay (φ′ RX, n ) which is obtained in the step S 710  is needed whenever the calibration step S 750  is performed. Meanwhile, the calibration procedure of step S 750  can be executed repeatedly or periodically depending upon the signal environment where the array antenna system is operating.  
      As shown in  FIG. 7B , the phase delay (φ RX, n ) between each of N receiving antenna elements  520  and the corresponding port of the calibrator  530  and the phase delay ((φ″ RX, n ) between the additional antenna  510  and the calibrator  530  are obtained in S 711  and S 730  respectively, in the step S 710  of computing the phase delay(φ′ RX, n ). The order of performing steps S 711  and S 730  does not cause any difference in the calibration performance. The difference between the phase delay φ″ RX, n  and φ RX, n , i.e., (φ″ RX, n −φ RX, n ), each of which is obtained in S 711  and S 730  respectively, produces the phase delay (φ′ RX, n ) between the additional antenna element  510  and each of N receiving antenna elements  520 . The step of computing the phase delay (φ′ RX, n ) between the additional antenna element  510  and each of N receiving antenna elements  520  from the difference between φ″ RX, n  and φ RX, n  will be denoted as step S 713 .  
      The phase delay (φ RX, n ) is obtained in S 711  after the differences in all the φ′ RX, nS  as are removed such that it becomes φ′ RX, n =φ′ RX,m  for all 0≦n≦N and 0≦m≦N.  FIG. 3A  shows one way of removing the differences among the phase delays {φ′ RX, n  for n=1, 2, . . . , N} utilizing a divider. It particularly means that the phase delay between the additional antenna  510  and each of receiving antenna elements  520  becomes all the same, i.e., φ′ RX, n =φ′ RX,m  for all 0≦n≦N and 0≦m≦N, if the “Rx calibration signal” is received at a single common receiving antenna element and fed to each of receiving signal paths through the divider as shown in  FIG. 3A . Then, the relative differences among the phase delay φ″ RX, n , which is obtained in S 730  of which the details are described below, can be used as the phase delay compensation of the calibration.  
      As shown in  FIG. 7C , the step S 730  of computing the phase delay (φ″ RX, n ) starts from the step S 731  in which the calibrator  530  genrates “Rx calibration signal”. As mentioned earlier, said “Rx calibration signal” is distinguishable from the other signals used for normal communication purpose during the operation of array antenna system. The additional antenna  510  transmits the “Rx calibration signal” that is provided by the calibrator  530  in step S 731  through the DAC  513  and U/C  511 . The step of transmitting the “Rx calibration signal” from the additional antenna to the plural receiving antenna elements will be denoted as step S 733 . In the U/C  511  the frequency of “Rx calibration signal” that has been modulated into an analog signal is up-converted into the receiving RF (radio frequency) band of the receiving array antenna system. Each of the plural receiving antenna elements  520  receives the “Rx calibration signal” that has been transmitted during the step of S 733  and sends the received “Rx calibaration signal” to the calibrator  530  by way of the LNA  521 , D/C  523 , and ADC  525 . The step of passing the “Rx calibration signal” from each of receiving antenna elements  520  to the corresponding port of the calibrator  530  will be denoted as step S 735  The calibrator  530  produces the phase delay (φ″ RX, n ) between the additional antenna and the calibrator  530  from the “Rx calibration signal” received through the step S 735  The step of producing the phase delay (φ″ RX, n ) between the additional antenna and the calibrator  530  will be denoted as step S 737 .  
      Once the phase delay (φ′ RX, n ) between the additional antenna and each of receiving antenna elements  520  is obtained as shown in S 710  in advance of the calibration prcedure, the calibration procedure is performed as shown in  FIG. 7D  for computing the phase compensation value (φ RX, n ). Note that, as mentioned earlier, the computation of the phase delay (φ′ RX, n ) between the additional antenna and each of receiving antenna elements  520  is performed only once while the calibration procedure for computing the phase compensation value (φ RX, n ) is performed repeatedly or periodically according to the need of calibration. As shown in  FIG. 7D , the calibration procedure of step S 750  for computing the phase delay (φ RX, n ) between each of the receiving antenna elements  520  and the corresponding port of the calibrator  530  starts from the step S 730  in which the phase delay (φ″ RX, n ) is generated. The step S 750  also includes a substep S 730  for measuring the phase delay (φ″ RX, n ) between the additional antenna  510  and each of corresponding ports of the calibrator  530  as in step S 710 . The difference between S 730  in S 750  and that in S 710  can be summarized as follows.  
      In S 730  of S 710  the “Rx calibration signal” is received at a single antenna in order to equalize all the phase delays (φ′ RX, n ) associated with each of receiving antenna elements  520  and the received “Rx calibration signal” is provided to each of antenna channels by way of the divider as shown in  FIG. 3A  for measuring the phase delay (φ″ RX, n ) at each of corresponding ports of the calibrator  530 , whereas the “Rx calibration signal” is received at each of receiving antenna elements  520  in S 730  of S 750  and fed to each of antenna channels for measuring the phase delay (φ″ RX, n ) at each of corresponding ports of the calibrator  530 .  
      The phase delay (φ′ RX, n ) is obtained from the step S 710  whereas the phase delay (φ″ RX, n ) is obtained from the step S 730 . From these two sets of phase delays (φ′ RX, n ) and (φ″ RX, n ), the calibrator  530  produces the phase compensation (φ RX, n ) by (φ RX, n =φ″ RX, n −φ′ RX, n ). The step of producing the phase compensation (φ RX, n ) will be denoted as step S 751 . Note that the phase compensation in the early part of this invention was referred to as “phase error” . As the phase characteristics at each of antenna channels can vary from time to time, the phase compensation (φ RX, n ) need to be computed repeatedly or periodically according to the need of given signal environment. The calibrator  530  produces the phase compensation values {φ RX, 1 , . . . , φ RX, n , . . . , φ RX, N } for each of receiving antenna channels through the step S 751 . Based on the phase compensation values {φ RX, 1 , . . . , φ RX, n , . . . , φ RX, N }, the calibrator  530  compensates the differences or irregularities, which was referred to as “phase error” in the preceding parts of this invention, at each of signal paths associated with each of receiving antenna elements  520 . This compensating procedure is referred to as step S 753 . The calibration procedure for the receiving mode is completed as the step S 753  is performed.  
      Summarizing the discussions above, the first application example of the present invention makes it possible that the calibration be performed while the array antenna system is operating without any restriction on the structure of the array antenna element, the location of the additional antenna, topology of each antenna element, etc. The above merits are indeed provided by the present invention because of the following two main reasons: firstly, the “Rx calibration signal” is distinguishable from the other signals that are used by the subscribers, secondly, the phase delay (φ′ RX, n ) between the additional antenna element and each of receiving antenna elements is measured in advance of the calibration procedure as shown in step S 710  and reflected properly in computing the phase compensation value as shown in step S 750 .  
       FIG. 8  illustrates a block diagram of calibration apparatus of transmitting array antenna system designed in accordnace with the first application example of the present invention. According to the first application example of the present invention, as the phase delay between the additional antenna element  810  and each of transmitting antenna elements  820  is computed in advance of the trasnmitting calibration procedure and reflected properly duirng the transmitting calibration procedure, the transmitting calibration technology disclosed in the present invention does not have any restrictions on the location of the additional antenna element or structure of the transmitting array antenna element or topology of each antenna element, etc. In the meantime, the transmitting antenna elements  820  do not always have to be prepared separately from the receiving antenna elements (shown as the receiving antenna elements  520  in  FIG. 5 ) in the array antenna system. It particularly means that a single antenna element can be shared for both receiving and transmitting purposes. In this case, duplexer or switch can be used to distinguish the receiving and transmitting function from each other. Duplexer is used for FDD (frequency dividion duplexing) system and switch is used for TDD (time division duplexing) system.  
      As shown in  FIG. 8 , calibration apparatus according to the first application example of this invention consists of additional antenna element  810  and low noise amplifier (LNA)  811 , frequency down-converter (U/C)  813  and analog-to-digital converter (ADC)  815  that are connected to the additional antenna  810 , plural transmitting antenna elements  820  with arbitrary spacing and topology, high power amplifier (HPA)  821 , frequency up-converters (U/C)  823 , digital-to-analog converters (DAC)  825 , and calibrator  830 . Note that each of HPA&#39;s  821 , U/C&#39;s  823 , and DAC&#39;s  825  is connected to each of transmitting antenna elements  820 , correspondingly.  
      Calibration procedure performed in the calibration apparatus shown in  FIG. 8  can be summarized as follows. The plural transmitting antenna elements  820  transmit a signal that is generated in said calibrator  830  and provided through said DAC  825  and U/C  823 . The signal transmitted from said plural transmitting antenna elements  820  will be denoted in this invention as “Tx calibration signal” from now on. Said Tx calibration signal generated in base-band at said calibrator  830  is first modulated into its analog form in said DAC  825  and then the frequency range of said analog-converted Tx calibration signal is converted to the transmitting carrier frequency band of said array antenna system in said U/C  823 .  
      The aditional antenna element  810  receives said Tx calibration signal which is transmitted from said plural transmitting antenna elements  820 , and the received Tx calibration signal is tranferred to said calbrator  830  by way of said LNA  811 , D/C  813 , and ADC  815 . Said LNA  811  amplifies the received Tx calibration signal with a minimum noise, D/C  813  converts the frequency range of the received Tx calibration signal into base-band, and ADC  815  converts the Tx calibration signal into digital data.  
      As the calibration may be executed during the normal operation of the array antenna system, “Tx calibration signal” must be distinguishable from the other signals used by subscribers. In order for said Tx calibration signal to be distinguished from the other communication signals used by the subscribers communicating with the array antenna system, it is recommanded that said “Tx calibration signal” is orthogonal or quasi-orthogonal to the other signals such that said “Tx calibration signal” can be separated from the other signals at the calibrator  830 .  
      Furthermore, “Tx calibration signal” transmitted from each of the transmitting antenna elements  820  of the array antenna system should also be distinguishable from one another when all the transmitting antenna elements  820  transmits the “Tx calibration signal” at the same time. However, when the “Tx calibration signal” is transmitted at each of the transmitting antenna elements  820  sequencially, i.e., when only one transmitting antenna element transmits the Tx calibration signal at a time, then a single “Tx calibration signal” can be used in common at all the transmitting antenna elements  820 .  
      The calibrator  830  compensates for the phase differences in the signal paths associated with each of the transmitting antenna elements  820  utilizing the “Tx calibration signal” provided through the ADC  815 . The calibrator  830  explicitly computes the differences of the phase characteristics of each of signal paths associated with each of transmitting antenna elements  820  utilizing the “Tx calibration signal” that has been received through the signal path associated with each of transmitting antenna elements  820 . In computing the phase differences at each of transmitting antenna channels, the phase delay between the additional antenna  810  and each of transmitting antenn elements  820 , which has been obtained apriori to the calibration procedure, should appropriately be encountered.  
       FIG. 9  shows a block diagram of calibration apparatus according to the first application example, which can be applied to calibration apparatus shown in  FIG. 8 .  FIG. 9  shows how the phase delay between the additional antenna element and each of the transmitting antenna elements is computed during the calibartion period. The phase delay at each of signal paths is defined as follows: 
          φ′ TX, n  Phase delay between the additional antenna element  810  and the n_th transmitting antenna  820  for n=1, 2, . . . , N where N is the total number of transmitting antenna elements in the array antenna system. Note that φ′ TX, n  for n=1, 2, . . . , N is measured in advance of the calibration procedure. It can even be measured in advance of the normal operation of the array antenna system.     φ″ TX, n  Phase delay between the calibrator  830  and additional antenna element  810 . Note that the phase delay φ″ TX, n  is associated with the following signal path: calibrator  830 →DAC  825 →U/C  823 →HPA  821 →n_th transmitting antenna  820 → additional antenna  810 .     φ TX, n  Phase delay between the calibrator  830  and n_th transmitting antenna element  820 . Note that the phase delay φ TX, n  is associated with the following signal path: calibrator  830 →DAC  825 →U/C  823 →HPA  821 →n_th transmitting antenna  820 .        
      From the discussions given above, it can be found that the phase delay that has to be compensated for calibrating the signal path associated with each of transmitting antenna elements  820  is 
 
φ TX, n =φ″ TX, n −φ″ TX, n  
 
 for n=1, 2, . . . , N where N is the number of said transmitting antenna elements in the array antenna system. 
 
      According to the first application example of this invention, in advance of the calibration procedure for the transmitting array antenna system, the phase delay (φ′ TX, n ) between the additional antenna element  810  and each of plural transmitting antenna elements  820  should be obtained. It particularly means that φ′ TX, n  should be obtained for all n. In order to obtain the phase delay (φ′ TX, n ) between the additional antenna element  810  and each of plural transmitting antenna elements  820 , the phase delay (φ TX, n ) between the calibrator  830  and each of transmitting antenna elements  820  and the phase delay (φ″ TX, n ) between the calibrator  830  and the additional antenna element  810  are computed in advance. After computing the phase delays φ TX, n  and φ″ TX, n , the phase delay φ′ TX, n  between each of the transmitting antenna elements  820  and the additional antenna  810  is obtained by φ″ TX, n =φ″ TX, n −φ TX, n . Note that the phase delay φ′ TX, n  between each of the transmitting antenna elements  820  and the additional antenna  810  is computed in advance of normal operation of array antenna system only once at the initial stage, for example, when the array antenna system is first installed. This phase delay φ′ TX, n  is then used whenever the calibration is performed in the array antenna system.  
      The calibration disclosed in this invention is based upon the phase delay φ′ TX, n  between each of the transmitting antenna elements  820  and the additional antenna  810 . More specifically, the calibrator  830  produces the phase delay φ″ TX, n  between the calibrator  830  and the additional antenna element  810  from the “Tx calibration signal” that is transmitted from each of transmitting antenna elements  820  and received at the additional antenna element  810 . The phase delay φ TX, n  to be compensated at each of signal paths associated with N transmitting antenna elements  820  is obtained by subtracting the pre-computed phase delay φ′ TX, n  between each of N transmitting antenna elements  820  and the additional antenna element  810  from the phase delay φ″ TX, n  between the calibrator  830  and the additional antenna element  810 . The computation of the phase delay φ′ TX, n  is performed for all N transmitting antenna elements  820 , thus {φ TX, 1 , . . . , φ TX, n , . . . , φ TX, N } are obtained as a result of the calibration procedure. The calibrator  830  produces the phase delay compensation {φ TX, 1 , . . . , φ TX, n , . . . , φ TX, N } to resolve the differences or irregularities of the phase delays at the signal paths associated with N transmitting antenna elements  820 .  
      The calibration procedure of which the major part is to compute the differences or irregularities of phase characteristic at each of signal paths associated with each of N transmitting antenna elements  820  can be performed without any restriction on the array structure or antenna topology or location of additional antenna by utiling the phase delay (φ′ TX, n ) between each of N transmitting antenna elements  820  and the additional antenna  810 , which is obtained in advance of the calibration procedure.  
      Furthermore, as the “Tx calibration signal” is distinguishable from the other signals being used by the subscribers, the calibration procedure disclosed in this invention can be performed while the array antenna system is operating for its original purpose.  
       FIG. 10A-10D  represent transmitting calibration procedure used in calibration apparatus of the array antenna system in accordance with the first application example of this invention. As an example, the calibration procedure shown in  FIGS. 10A-10D  are applied to the calibration apparatus shown in  FIG. 8 .  
      As shown in  FIG. 10A , the calibration according to the first application example consists mainly of two steps, i.e., a step S 1010  of computing the phase delay (φ′ TX, n ) between each of transmitting antenna elements  820  and the additional antenna  810  in advance of the calibration procedure and the other step S 1050  of performing the calibration with the phase delay (φ TX, n ) between the calibrator  830  and each the transmitting antenna elements  820 .  
      As mentioned earlier, it is normal that the step S 1010  is performed just one time after the structure of the additional antenna  810  and that of plural transmitting antenna elements  820  are determined. Note, however, that the phase delay (φ′ TX, n ) which is obtained in the step S 1010  is needed whenever the calibration step S 1050  is performed. Meanwhile, the calibration procedure of step S 1050  can be executed repeatedly or periodically depending upon the signal environment where the array antenna system is operating.  
      As shown in  FIG. 10B , the phase delay (φ TX, n ) between the corresponding port of the calibrator  830  and each of N transmitting antenna elements  820  and the phase delay (φ″ TX, n ) between the calibrator  830  and the additional antenna  810  are obtained in S 1011  and S 1030 , respectively, in the step S 1010  of computing the phase delay(φ′ TX, n ). The order of performing steps S 1011  and S 1030  does not cause. any difference in the calibration performance. The difference between the phase delay φ″ TX, n  and φ TX, n , i.e., (φ″ TX, n −φ TX, n ), each of which is obtained in S 1011  and S 1030 , respectively, produces the phase delay (φ′ TX, n ) between each of N transmitting. antenna elements  820  and the additional antenna element  810  The step of computing the phase delay (φ′ TX, n ) between each of N transmitting antenna elements  820  and the additional antenna element  810  from the subtraction of φ TX, n  from φ″ TX, n  will be denoted as step S 1013 .  
      The phase delay (φ TX, n ) is obtained in S 1011  after the differences in all the φ′ TX, n s are removed such that it becomes φ′ TX, n =φ′ TX,m  for all 0≦n≦N and 0≦m≦N.  FIG. 3B  shows one way of removing the differences among the phase delays {φ′ TX, n  for n=1, 2, . . . , N} utilizing a divider. It particularly means that the phase delay between each of transmitting antenna elements  820  and the additional antenna  810  becomes all the same, i.e., φ′ TX, n =φ′ TX,m  for all 0≦n≦N and 0≦m≦N, if the “Tx calibration signal” is transmitted from a single common transmitting antenna element as shown in  FIG. 3B . Then, the relative differences among the phase delay φ″ TX, n , which is obtained in S 1030  of which the details are described below, can be used as the phase delay compensation of the calibration.  
      As shown in  FIG. 10C , the step S 1030  of computing the phase delay (φ″ TX, n ) starts from the step S 1031  in which the calibrator  830  genrates “Tx calibration signal”. As mentioned earlier, said “Tx calibration signal” is distinguishable from the other signals used for normal communication purpose during the operation of array antenna system. Furthermore, “Tx calibration signal” transmitted from each of the transmitting antenna elements  820  of the array antenna system should also be distinguishable from one another when all the transmitting antenna elements  820  transmits the “Tx calibration signal” at the same time. However, when the “Tx calibration signal” is transmitted at each of the transmitting antenna elements  820  sequencially, i.e., when only one transmitting antenna element transmits the Tx calibration signal at a time, then a single “Tx calibration signal” can be used in common at all the transmitting antenna elements  820 . Each of transmitting antenna elements  820  transmits the “Tx calibration signal” that is provided by the calibrator  830  in step S 1031  through the DAC  825  and U/C  823 . The “Tx calibration signal” transmitted from each of transmitting antenna elements  820  is to be received by the additional antenna element  810  The step of transmitting the “Tx calibration signal” from each of transmitting antenna elements  820  to the additional antenna element  810  will be denoted as step S 1033  In the U/C  823 , the frequency of “Tx calibration signal” that has been modulated into an analog signal at the DAC  825  is up-converted into the transmitting RF (radio frequency) band of the transmitting array antenna system. The additional antenna element  810  receives the “Tx calibration signal” that has been transmitted during the step of S 1033  and sends the received “Tx calibaration signal” to the calibrator  830  by way of the LNA  811 , D/C  813 , and ADC  815 . The step of passing the “Tx calibration signal” from the additrional antenna  810  to the corresponding port of the calibrator  830  will be denoted as step S 1035 . The calibrator  830  produces the phase delay (φ″ TX, n ) between the calibrator  830  and the additional antenna element  810  from the “Tx calibration signal” received through the step S 1035 . The step of producing the phase delay (φ″ TX, n ) between the calibrator  830  and the additional antenna element  810  will be denoted as step S 1037 .  
      Once the phase delay (φ′ TX, n ) between each of N transmitting antenna elements  820  and the additional antenna element  810  is obtained as shown in S 1010  of  FIG. 10A-10C  in advance of the calibration prcedure, the calibration procedure is performed as shown in  FIG. 10D  for computing the phase compensation value (φ TX, n ). Note that, as mentioned earlier, the computation of the phase delay (φ′ TX, n ) between each of N transmitting antenna elements  820  and the additional antenna element  810  is performed only once while the calibration procedure for computing the phase compensation value (φ TX, n ) is performed repeatedly or periodically according to the need of calibration. As shown in  FIG. 10D , the calibration procedure of step S 1050  for computing the phase delay (φ TX, n ) between the corresponding port of the calibrator  830  and each of the transmitting antenna elements  820  starts from the step S 1030  in which the phase delay (φ″ TX, n ) is generated. The step S 1050  also includes a substep S 1030  for measuring the phase delay (φ″ TX, n ) between each of corresponding ports of the calibrator  830  and the additional antenna  810  as in step S 1010  The difference between S 1030  in S 1050  and that in S 1010  can be summarized as follows.  
      In S 1030  of S 1010 , the “Tx calibration signal” which is provided from each of antenna channels consisting of DAC&#39;s  825 , U/C&#39;s  823 , and HPA&#39;s  821  is combined at the combiner as shown in  FIG. 3B , is fed to a single antenna in order to equalize all the phase delays (φ′ TX, n ) between each of transmitting antenna elements  810  and the additional antenna  810  in measuring the phase delay (φ″ TX, n ) between the corresponding ports of the calibrator  830  and the additional antenna element  810 , whereas, in S 1030  of S 1050 , the “Tx calibration signal” is transmitted from each of transmitting antenna elements  820  and received at the additional antenna  810  for measuring the phase delay (φ″ TX, n ) at the calibrator  830 .  
      The phase delay (φ′ TX, n ) is obtained from the step S 1010  whereas the phase delay (φ″ TX, n ) is obtained from the step S 1030  From these two sets of phase delays (φ′ TX, n ) and (φ″ TX, n ), the calibrator  830  produces the phase compensation (φ TX, n ) by (φ TX, n =φ″ TX, n −φ′ TX, n ). The step of producing the phase compensation (φ TX, n ) will be denoted as step S 1051 . Note that the phase compensation in the early part of this invention was referred to as “phase error”. As the phase characteristics at each of antenna channels can vary from time to time, the phase compensation (φ TX, n ) need to be computed repeatedly or periodically according to the need of given signal environment. The calibrator  830  produces the phase compensation values {φ TX, 1 , . . . , φ TX, n , . . . , φ TX, N } for each of transmitting antenna channels through the step S 1051 . Based on the phase compensation values {φ TX, 1 , . . . , φ TX, n , . . . , φ TX, N }, the calibrator  830  compensates the differences or irregularities, which was referred to as “phase error” in the preceding parts of this invention, at each of signal paths associated with each of transmitting antenna elements  820 . This compensating procedure is referred to as step S 1053 . The calibration procedure for the transmitting mode is completed as the step S 1053  is performed.  
      Summarizing the discussions above, the first application example of the present invention makes it possible that the calibration be performed while the array antenna system is operating without any restriction on the structure of the array antenna element, the location of the additional antenna, topology of each antenna element, etc. The above merits are indeed provided by the present invention because of the following two main reasons: firstly, the “Tx calibration signal” is distinguishable from the other signals that are used by the subscribers, secondly, the phase delay (φ′ TX, n ) between each of transmitting antenna elements  820  and the additional antenna element  810  is measured in advance of the calibration procedure as shown in step S 1010  and reflected properly in computing the phase compensation value as shown in step S 1050 .  
       FIG. 11  and  FIG. 12  are related to the array antenna system according to the second application example of this invention.  
       FIG. 11  shows a structure of the calibration apparatus of receiving array antenna system designed in accordance with the second application example of the present invention. The second application example shown in  FIG. 11  employs a structure in which the signal path between the DAC  825  and U/C  823  associated with one of the transmitting antenna elements  820  that have been shown in  FIG. 8  as the first application example is shared with the additional antenna element  1110  for sending the “Rx calibration signal” generated from the calibrator  530 . Consequently, the signal path consisting of DAC  513  and U/C  511 , which exist only for the additional antenna  510 , is not needed in the second application example. In short, the transmitting signal path associated with one of the transmitting antenna elements  820  is shared with the additional antenna element  1110  for sending the “Rx calibration signal” from the calibrator  530  to the additional antenna element  1110 .  
      In the meantime, the receiving antenna elements  520  does not have to be prepared separately from transmitting antenna elements (shown as transmitting antenna  820  in  FIG. 11 ) in array antenna system. It means a single antenna element can be used for both receiving and transmitting mode. Duplexer or switch can be used to distinguish the receiving and transmitting function from each other. In general, duplexer is used for FDD (frequency dividion duplexing) system while switch is used for TDD (time division duplexing) system.  
      In  FIG. 11 , the “Rx calibration signal” generated in the calibrator  530  is sent to frequency converter  1111  by way of the transmitting signal path consisting of DAC  825 , U/C  823 , and divider  1143 . The frequency band of the “Rx calibration signal”, which has arrived at the frequency converter  1111 , is the transmitting RF (radio frequency) band of the array antenna system due to the function of U/C  823  as described previously. The frequency converter  1111  converts the freuqency band of the “Rx calibration signal” to the receiving RF band of the array antenna system and transfers it to the additional antenna  810 . In the meantime, said “Rx calibration signal” should be distinguished from the other signals used by the subscribers because the calibration can be performed while the array antenna system is operating. In order for said Rx calibration signal to be distinguished from the other communication signals used by the subscribers communicating with the array antenna system, it is recommanded that said “Rx calibration signal” is orthogonal or quasi-orthogonal to the other signals such that said “Rx calibration signal” can be separated from the other signals at the calibrator  530  even when it is received together with the other signals used by the subscribers. The rest parts other than the sharing of the transmitting signal path can be implemented in exactly the same way as in the first application example of the array antenna system which are shown in  FIG. 5  or  FIG. 7 .  
       FIG. 12  shows a structure of the calibration apparatus of transmitting array antenna system designed in accordance with the second application example of the present invention. The second application example shown in  FIG. 12  employs a structure in which the signal path consisting of the LNA  521 , D/C  523 , and ADC  525  associated with one of the receiving antenna elements  520  that have been shown in  FIG. 5  as the first application example is shared with the additional antenna element  510  for receiving the “Tx calibration signal” that has been generated at the calibrator  830  and sent by way of the signal paths of each of transmitting antenna elements  820 . Consequently, the signal path consisting of LNA  521 , D/C  523 , and ADC  525 , which exist only for the additional antenna  1210 , is not needed in the second application example. In short, the signal path associated with one of the receiving antenna elements  520  is shared with the additional antenna element  510  for transferring the “Tx calibration signal” from the additional antenna element  510  to the calibrator  830 .  
      In the meantime, the transmitting antenna elements  820  does not have to be prepared separately from receiving antenna elements (shown as receivinh antenna  520  in  FIG. 12 ) in array antenna system. It means a single antenna element can be used for both receiving and transmitting mode. Duplexer or switch can be used to distinguish the receiving and transmitting function from each other. In general, duplexer is used for FDD (frequency dividion duplexing) system while switch is used for TDD (time division duplexing) system.  
      In  FIG. 12 , the “Tx calibration signal” which is generated at the calibrator  830 , is sent to the signal paths consisting of DAC  825 , U/C  823 , and HPA  821  to be transmitted from each of the transmitting antenna elements  820 . The “Tx calibration signal” is then received at the additional antenna element  510 .  
      In the meantime, said “Tx calibration signal” should be distinguished from the other signals used by the subscribers because the calibration can be performed while the array antenna system is operating. In order for the Tx calibration signal to be distinguished from the other communication signals used by the subscribers communicating with the array antenna system, it is recommanded that said “Tx calibration signal” is orthogonal or quasi-orthogonal to the other signals such that said “Tx calibration signal” can be separated from the other signals at the calibrator  830  even when it is received together with the other signals used by the subscribers.  
      Furthermore, “Tx calibration signal” transmitted from each of the transmitting antenna elements  820  of the array antenna system should also be distinguishable from one another when all the transmitting antenna elements  820  transmits the “Tx calibration signal” at the same time. However, when the “Tx calibration signal” is transmitted at each of the transmitting antenna elements  820  sequencially, i.e., when only one transmitting antenna element transmits the Tx calibration signal at a time, then a single “Tx calibration signal” can be used in common at all the transmitting antenna elements  820 .  
      In  FIG. 12 , the “Tx calibration signal” that is received at the additional antenna element  510  is sent to frequency converter  1211  The frequency band of the “Tx calibration signal” which has arrived at the frequency converter  1211 , is the transmitting RF (radio frequency) band of the array antenna system due to the function of U/C  823  as described previously. The frequency converter  1211  converts the freuqency band of the “Tx calibration signal” to the receiving RF band of the array antenna system and transfers it to the combiner shown in  FIG. 12 . The rest parts other than the sharing of the receiving signal path can be implemented in exactly the same way as in the first application example of the array antenna system which are shown in  FIG. 8  or  FIG. 10 .  
      Summarizing the discussions above, the second application example of the present invention makes it possible that the calibration can be performed while the array antenna system is operating without any restriction on the structure of the array antenna element, the location of the additional antenna, topology of each antenna element, etc. The above merits are indeed provided by the present invention because of the following two main reasons: firstly, both “Rx calibration signal” and “Tx calibration signal” are distinguishable from the other signals that are used by the subscribers, secondly, the phase delay (φ′ RX/TX, n ) between the additional antenna element and each of receiving and transmitting antenna elements is measured in advance of the calibration procedure as shown in step S 710  and S 1010  and reflected properly in computing the phase compensation value as shown in step S 750  and S 1050 , respectively.  
      It is clear and straightforward that the scope of the technologies dosclosed in the present invention is not limited by the above mentioned application examples or figures. It should also be noted that the calibration technologies shown in this invention can easily be transformed, modified, or changed in many different ways within the scope of the present invention by ordinary engineers with normal amount of knowledge in the related fields.  
      As summarized in this document, the phase error, i.e., differences or irregularities of the phase characteristics at each of antenna channels associated with each of receiving and transmitting antenna elements, can be compensated using the pre-computed phase delay values of the additional antenna element, of which the location can be arbitrary.  
      Due to the calibration procedure which equalizes the phase characteristics of all the signal paths associated with both receiving and transmitting antenna element, the beamforming parameters such as the weight vector of the array antenna system, especially the adaptive array antenna system, obtained for the receiving mode can be used for the transmitting mode. Ultimately, the system performance of array antenna system is greatly enhanced by the accurate calibration.