Abstract:
Provided is an antenna aligning apparatus for near-field measurement, which can perform alignment between a measurement target antenna and a probe antenna precisely by using an antenna pattern and detecting coordinates of the least error. The antenna aligning apparatus includes: a receiving antenna, a signal dividing means, a vertical polarization port, a horizontal polarization port, a first amplitude/phase detector, a second amplitude/phase detector, a coordinate determining means for, and a position adjuster.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to an antenna aligning apparatus for near-field measurement; and, more particularly, to an antenna aligning apparatus for near-field measurement which can perform alignment between a measurement target antenna and a probe antenna quickly and precisely for near-field measurement.  
       DESCRIPTION OF THE RELATED ART  
       [0002]     Generally, alignment should be performed between a measurement target antenna, which will be referred to as a target antenna hereinafter, and a probe antenna to measure an antenna pattern in a near field. Any alignment error between the two antennas eventually causes an error in the near-field measurement of the antenna pattern.  
         [0003]     The two antennas should be aligned to make their aperture planes be parallel to each other and the probe antenna is aligned to be located in the very center of the aperture plane of the target antenna. The probe antenna can be moved in the x-y plane and z axial directions and an elevation angle, an azimuth angle, and the z-axis of the target antenna can be moved by operating a driving motor.  
         [0004]     The alignment of the two antennas is performed in the mechanical manner by using an optical tracer on the target antenna. However, this method takes a lot of cost and time.  
         [0005]     To solve the problem, F. H. Larson suggests a technological solution in an article entitled “A Dual-Polarized System for Near-Field Measurement,” IEEE AP-S, Volume 2, pp. 557-560, June, 1979.  
         [0006]     Generally, a linear or circular polarization antenna is measured by aligning the target antenna and the probe antenna and then carrying out the measurement twice when the probe antenna is at 0° and 90°. However, the technology suggested by Larson utilizes a dual probe in order to resolve the trouble of measuring the pattern of the target antenna twice so that the measurement time can be reduced by half since the probe antenna does not need to be rotated at 90°.  
         [0007]     Since the above technology, too, should perform mechanical alignment, it requires a lot of time and cost. Moreover, if there is an error or a change in the position of the antenna, the measurement should be performed again from the very first. It also has a problem that it requires much manpower to operate mechanical equipment.  
       SUMMARY OF THE INVENTION  
       [0008]     It is, therefore, an object of the present invention to provide an antenna aligning apparatus for near-field measurement which can carry out alignment between a measurement target antenna, which will be referred to as a target antenna, and a probe antenna precisely by using the pattern of the target antenna and detecting coordinates of the least error.  
         [0009]     In accordance with an aspect of the present invention, there is provided an apparatus for aligning antennas for near-field measurement, which includes: a probe antenna for receiving a signal transmitted from a measurement target antenna, which will be referred to as a target antenna herein; an orthomode transducer for dividing the signal received in the receiving antenna into a vertical polarization signal and a horizontal polarization signal; a vertical polarization port for receiving the vertical polarization signal from the orthomode transducer; a horizontal polarization port for receiving the horizontal polarization signal from the orthomode transducer; a first amplitude/phase detector for detecting an amplitude and phase of the signal transmitted from the vertical polarization port; a second amplitude/phase detector for detecting an amplitude and phase of the signal transmitted from the horizontal polarization port; a coordinate comparator for determining coordinates by comparing the amplitude and phase detected by the first amplitude/phase detector with the amplitude and phase detected by the second amplitude/phase detector based on the polarization of the target antenna; and a position adjuster for adjusting the position of the receiving antenna based on the coordinates determined in the coordinate comparator.  
         [0010]     The present invention provides an antenna aligning apparatus which can perform precise alignment between the target antenna and the probe antenna by using the characteristics of the target antenna pattern and detecting coordinates of the least error.  
         [0011]     The present invention takes an advantage of a characteristic that, if the target antenna and the probe antenna are aligned and the target antenna is a linear polarization antenna, the near-field measurement result shows that the maximum amplitude appears in the antenna aperture plane with respect to co-polarization and it shows null with respect to cross-polarization. The present invention, also, takes an advantage of a characteristic that, if the target antenna and the probe antenna are aligned and the target antenna is a circular polarization antenna, the same amplitude appears with respect to both co-polarization and cross-polarization and the phases has a 90° difference from each other. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0013]      FIG. 1  is a block diagram illustrating an antenna aligning apparatus for near-field measurement in accordance with an embodiment of the present invention;  
         [0014]      FIG. 2  is an exemplary diagram describing an amplitude characteristic based on a distance in a case where a measurement target antenna of  FIG. 1  is a linear polarization antenna and the alignment of a probe antenna is ideal;  
         [0015]      FIG. 3  is an exemplary diagram describing an amplitude characteristic based on a distance in a case where the measurement target antenna of  FIG. 1  is a circular polarization antenna and the alignment of the probe antenna is ideal; and  
         [0016]      FIG. 4  is an exemplary diagram showing a phase characteristic based on a distance in a case where the measuring antenna of  FIG. 1  is a circular polarization antenna and the alignment of the probe antenna is ideal. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter.  
         [0018]      FIG. 1  is a block diagram illustrating an antenna aligning apparatus for near-field measurement in accordance with an embodiment of the present invention.  
         [0019]     As shown, the antenna aligning apparatus  120  includes a probe antenna  121 , an orthomode transducer  122 , a vertical polarization port  123 , a horizontal polarization port  124 , a first amplitude/phase detector  125 , a second amplitude/phase detector  126 , an amplitude/phase comparator  127 , and a position adjuster  128 .  
         [0020]     The probe antenna  121  receives a signal transmitted from a measurement target antenna  111 , which will be simply referred to as a target antenna hereafter. The orthomode transducer (OMT)  122  divides the signal received in the probe antenna  121  into a vertical polarization signal and a horizontal polarization signal. The vertical polarization port  123  receives the vertical polarization signal obtained in the orthomode transducer  122 , and the horizontal polarization port  124  receives the horizontal polarization signal obtained in the orthomode transducer  122 . The first amplitude/phase detector  125  detects the amplitude and phase of the vertical polarization signal received from the vertical polarization port  123 , and the second amplitude/phase detector  126  detects the amplitude and phase of the horizontal polarization signal received from the horizontal polarization port  124 . The amplitude/phase comparator  127  determines coordinates by comparing the amplitude and phase detected in the first amplitude/phase detector  125  with the amplitude and phase detected in the second amplitude/phase detector  126  in order to align the probe antenna  121  according to the polarization of the target antenna. The position adjuster  128  adjusts the position of the probe antenna  121  based on the coordinates determined in the amplitude/phase comparator  127 . Herein, the coordinates are placed as illustrated in  FIG. 1 .  
         [0021]     A measurement transmitter  110  includes a target antenna  111  and an antenna driving unit  112 .  
         [0022]     The target antenna  111  can transmit plane wave or spherical wave to the antenna aligning apparatus of the present invention according to the shape of the target antenna. It can also transmit linear or circular polarization.  
         [0023]     FIGS.  2  to  4  show the amplitude characteristic based on the distance, when the antennas are aligned ideally.  
         [0024]      FIG. 2  is an exemplary diagram describing an amplitude characteristic based on a distance in a case where a target antenna of  FIG. 1  is a linear polarization antenna and the alignment of a probe antenna is ideal.  
         [0025]     As shown, if the target antenna  111  is a linear polarization antenna and it is aligned with the probe antenna  121  ideally, ‘A’ is co-polarization of the polarization of the target antenna  111  and ‘B’ is cross-polarization of the polarization of the target antenna  111 . A straight line connecting the maximum amplitude point of the co-polarization and a null point of the cross-polarization is parallel to the y-axis. Therefore, the points can be the alignment coordinates between the target antenna  111  and the probe antenna  121 .  
         [0026]      FIG. 3  is an exemplary diagram describing an amplitude characteristic based on a distance in a case where the target antenna of  FIG. 1  is a circular polarization antenna and the alignment of the probe antenna is ideal.  FIG. 4  is an exemplary diagram showing a phase characteristic based on a distance in a case where the target antenna of  FIG. 1  is a circular polarization antenna and the alignment of the probe antenna is ideal.  
         [0027]     As shown, if the target antenna  111  is a circular polarization antenna, the amplitudes in the vertical polarization port  123  and the horizontal polarization port  124  of  FIG. 1  are ‘C’ and ‘D,’ respectively. The phase differences between the two polarization signals are ‘E’ and ‘F,’ respectively. In short, if the target antenna  111  is a circular polarization antenna, the amplitudes of the vertical polarization signal and the horizontal polarization signal are the same approximately and their phases have a phase difference of 90°.  
         [0028]     The antenna aligning apparatus of the present invention detects the coordinates where the phase and amplitude characteristics are determined, which is shown in FIGS.  2  to  4 . Hereafter, elements of  FIG. 1  will be described in detail.  
         [0029]     Referring to  FIG. 1 , the probe antenna  121  receives a signal transmitted from the target antenna  111 , and the orthomode transducer  122  divides the signal received in the probe antenna  121  into vertical and horizontal polarization signals.  
         [0030]     The vertical polarization port  123  and the horizontal polarization port  124  receive the vertical polarization signal and horizontal polarization signal divided by the orthomode transducer  122 , individually.  
         [0031]     The first and second amplitude and phase detectors  125  and  126  detect the amplitude and phase of the vertical polarization signal and the horizontal polarization signal transmitted from the vertical polarization port  123  and the horizontal polarization port  124 .  
         [0032]     If the target antenna  111  is a linear polarization antenna, the amplitude/phase comparator  127  determines points at which a straight line connecting the maximum amplitude point of the vertical polarization signal and a null point of the horizontal polarization signals is parallel to the y-axis.  
         [0033]     Also, if the target antenna  111  is a circular polarization antenna, it determines coordinates at which the amplitudes of the vertical polarization signal and the horizontal polarization signal are the same and the signals have a phase difference of 90°. The position adjuster  128  adjusts the probe antenna  121  into the points determined by the amplitude/phase comparator  127 .  
         [0034]     The technology of the present invention measures two linear polarizations that are perpendicular to each other, i.e., co-polarization and cross-polarization, simultaneously by using a dual-polarized probe antenna. Thus, it can reduce rotation error and measuring time.  
         [0035]     In addition, the technology of the present invention can perform antenna alignment efficiently by measuring the two linear polarizations simultaneously and performing electronic alignment.  
         [0036]     The present application contains subject matter related to Korean patent application No. 2003-0090288, filed in the Korean Intellectual Property Office on Dec. 11, 2003, the entire contents of which is incorporated herein by reference.  
         [0037]     While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.