Patent Publication Number: US-2010109957-A1

Title: Apparatus for measuring antenna radiation performance and method of designing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention claims priority of Korean Patent Application No. 10-2008-0109013, filed on Nov. 4, 2008, which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for measuring antenna radiation performance and a method of designing the same and, more particularly, to an apparatus for measuring radiation performance including a radiation pattern and a gain of an antenna and a method of designing the same. 
     2. Description of Related Art 
     In general, a wireless communication system transmits or receives a signal and data using a predetermined frequency. The wireless communication system includes an antenna as an essential element for transmitting and receiving a signal. The antenna needs to be designed to effectively transmit and receive an electromagnetic wave. Many researchers have been proposed various designs for an antenna to effectively transmit and receive an electromagnetic wave. 
     An antenna has properties changing according to a material and a shape thereof. Therefore, it is very important to accurately analyze the antenna properties. After designing an antenna with a predetermined material and shape, it is required to actually measure antenna properties thereof as well as theoretical verification. 
     Hereinafter, a method for measuring antenna radiation performance according to the prior art will be described. 
     Generally, a method of measuring antenna radiation performance may be classified into two methods. As a first method, a fully-anechoic chamber with an electromagnetic wave absorber attached is used to measure the antenna radiation performance. The specifications of an electromagnetic wave absorber attached on interior walls of the fully-anechoic chamber are decided according to a radiation frequency of an antenna. The lower the radiation frequency of an antenna is, the longer the wavelength of the radiation frequency of an antenna becomes. That is, a size or a volume of the electromagnetic wave absorber must be enlarged in proportion to a wavelength. 
     For example, a fully-anechoic chamber for measuring 200 MHz is required to have a sufficient space to dispose a transmit antenna and a receive antenna with a distance longer than 15 m. Also, an electromagnetic wave absorber is required to have a thickness of 1.5 m. The performance of the fully-anechoic member is decided by error of electric field uniformity in the quiet zone. Allowable error of the electric field uniformity in the quiet zone is about 0.25 dB and 22.5 degrees. Therefore, a fully-anechoic chamber for measuring a property of an antenna for a low radiation frequency requires a large space and a high cost to build. 
     As a second method, a semi-anechoic chamber is used to measure the radiation performance of an antenna. The semi-anechoic chamber is designed to easily absorb a low frequency band electric wave except a metal floor thereof. The method of measuring antenna radiation performance using a semi-anechoic chamber will be described with reference to  FIG. 1 . 
       FIG. 1  is a vertical cross-sectional view of a semi-anechoic chamber according to the prior art. 
     As shown in  FIG. 1 , the semi-anechoic chamber  10  according to the prior art includes a hexahedron interior space. The semi-anechoic chamber  10  includes a metal floor  12 . Electromagnetic wave absorbers  14  are attached on side walls and a ceiling except the metal floor  12 . A transmit antenna  20  and a receive antenna  30  are disposed with a height D from the metal floor  12  as shown in  FIG. 1 . The transmit antenna  20  and the receive antenna  30  are separated at a distance R. The distance R is decided according to a frequency or an antenna property. The receive antenna  30  is disposed on a rotator  42 . The rotator  42  rotates the receive antenna  30  on an x-z plane with a predetermined angular speed step. A vector network analyzer  50  supplies an electric signal to the transmit antenna  20  and receives an electric signal corresponding to an electromagnetic wave received at the receive antenna  30 . A data processor  52  calculates a radiation pattern and a gain of the receive antenna  30  based on the supplied electric signal from the vector network analyzer  50  and the received electric signal. A controller  54  controls the rotation of the rotator  42 . The data processor  52  also applies a control signal for rotating the rotator  42 . 
     In case of measuring the radiation characteristics of the receive antenna  30 , the transmit antenna  20  outputs a signal having a predetermined frequency. Here, the transmit antenna  20  radiates electromagnetic waves in various directions. For example,  FIG. 1  shows the transmit antenna  20  radiating first to fourth electromagnetic waves  22 ,  23 ,  24 , and  26  in various directions. 
     The first electromagnetic wave  22  propagates toward the receive antenna  30  in parallel to the metal floor  12 . The second, third, and fourth electromagnetic waves  23 ,  24 , and  26  propagate toward the metal floor  12  or the ceiling. Such second, third, and fourth electromagnetic waves  23 ,  24 , and  26  may cause error when the radiation performance of the receive antenna  30  is measured. Therefore, the electromagnetic wave absorbers  14  are attached on the sidewalls and the ceiling of the semi-anechoic chamber  10  except the metal floor. That is, the second electromagnetic wave  23  propagating toward the ceiling does not inference the measurement of the radiation performance because it is absorbed by the electromagnetic wave absorber  14  attached on the ceiling of the semi-anechoic chamber  10 . 
     On the contrary, the third electromagnetic wave  24  and the fourth electromagnetic wave  26  propagating toward the metal floor  12  are reflected to the metal floor  12 . Such the reflected electromagnetic waves  25  and  27  of the third and fourth electromagnetic waves  24  and  26  act as interference to the first electromagnetic wave  22 . As described above, it is difficult to form a uniform electric field at the receive antenna  30  in the semi-anechoic chamber  10 . That is, non-uniform electric field makes it difficult to accurately measure the radiation performance of the receive antenna  30 . 
     Therefore, the semi-anechoic chamber  10  has been used only for measuring an effective radiated power (ERP) or for measuring interference of an electromagnetic wave radiated from the transmit antenna  20 . 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention is directed to providing an antenna radiation performance measuring apparatus for making an electromagnetic wave radiated from an antenna to form a uniform electric field, and a method for designing the same. 
     Another embodiment of the present invention is directed to providing an antenna radiation performance measuring apparatus for accurately measuring radiation performance of an antenna using a low frequency band including a VHF band (174 to 216 MHz). 
     In accordance with an aspect of the present invention, there is provided an apparatus for measuring an antenna radiation performance including a chamber configured to include a transmit antenna radiating electromagnetic wave, a receive antenna receiving the electromagnetic wave, and an electromagnetic wave absorber absorbing the electromagnetic wave, and a reflector disposed on one side of the chamber between the transmit antenna and the receive antenna, inclined at a predetermined angle, and configured to reflect an electromagnetic wave radiated in a direction to the one side from the transmit antenna. 
     In accordance with another aspect of the present invention, there is provided a method for designing an antenna radiation performance measuring apparatus including a chamber configured to have a transmit antenna radiating electromagnetic wave, a receive antenna receiving the electromagnetic wave, and an electromagnetic wave absorber absorbing the electromagnetic wave, and a reflector disposed on one side of the chamber between the transmit antenna and the receive antenna, inclined at a predetermined angle, and configured to reflect an electromagnetic wave radiated from the transmit antenna, the method including deciding parameters according to locations of the transmit antenna and the receive antenna in the chamber, measuring an angle and a location of the reflector based on the decided parameters, confirming performance of uniformity of electric field of an electromagnetic wave received at the receive antenna within the quiet zone, and measuring a radiation pattern and a gain of the receive antenna. 
     Other objects and advantages of the present invention can be understood by the following description, and become apparent with reference to the embodiments of the present invention. Also, it is obvious to those skilled in the art to which the present invention pertains that the objects and advantages of the present invention can be realized by the means as claimed and combinations thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical cross-sectional view of a semi-anechoic chamber according to the prior art. 
         FIG. 2  is a vertical cross-sectional view of an antenna radiation performance measuring apparatus in accordance with an embodiment of the present invention. 
         FIG. 3  is a flowchart describing a method for designing an antenna radiation performance measuring apparatus in accordance with an embodiment of the present invention. 
         FIGS. 4A and 4B  are graphs showing normalized amplitude and a phase of a measured electric field formed in a typical fully-anechoic chamber. 
         FIGS. 5A and 5B  are graphs showing normalized amplitude and a phase of a measured electric field formed in a typical semi-anechoic chamber. 
         FIGS. 6A and 6B  are graphs showing normalized amplitude and a phase of a measured electric field formed in an antenna radiation performance measurement apparatus according to the present embodiment. 
         FIGS. 7A and 7B  are graphs showing normalized amplitudes and phases of electric field formed in a fully-anechoic chamber. 
         FIGS. 8A and 8B  are graphs showing normalized amplitudes and phases of electric field formed in a semi-anechoic chamber. 
         FIGS. 9A and 9B  are graphs showing normalized amplitudes and phases of electric field formed in an antenna radiation performance measuring apparatus. 
     
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENTS 
     The advantages, features 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. 
       FIG. 2  is a vertical cross-sectional view of an antenna radiation performance measuring apparatus in accordance with an embodiment of the present invention. 
     Referring to  FIG. 2 , the antenna radiation performance measuring apparatus according to the present embodiment includes a chamber  200 , a transmit antenna  210 , a receive antenna  220 , reflectors  230  and  240 , and electromagnetic wave absorber  250 . In  FIG. 2 , an x-axis, a y-axis, and a z-axis are shown with the receive antenna  220  as origin for convenience. The x-axis, the y-axis, and the z-axis form 90 degrees to each other, and the z-axis is parallel with the floor  201 . 
     The chamber  200  provides a space designed to measuring the radiation performance of the receive antenna  220 . As shown in  FIG. 2 , the chamber  200  is formed in a rectangular shape in a 2-D plane or in a hexahedron shape in a 3-D plane. However, the present invention is not limited thereto. The chamber may be formed in various shapes such as polyhedral structure including an ellipsoid shape and a sphere shape. The chamber  200  includes a metal floor  201 . Except the metal floor  201 , the electromagnetic wave absorber  250  is attached on sidewalls and ceiling of the chamber  200 . 
     The transmit antenna  210  radiates electromagnetic waves having a predetermined frequency. The transmit antenna  210  is disposed in the chamber  200  at a predetermined height D from the metal floor  201 . 
     The receive antenna  220  receives an electromagnetic wave radiated from the transmit antenna  210 . It is preferable to dispose the receive antenna  220  in the chamber  200  at the same height D from the metal floor. 
     The reflectors  230  and  240  are disposed between the transmit antenna  210  and the receive antenna  220  on the metal floor  201 . The reflectors  230  and  240  are inclined at a predetermined angle from the metal floor  201 . Although the antenna radiation performance measuring apparatus according to the present embodiment is described to include two reflectors  230  and  240 , the present invention is not limited thereto. The antenna radiation performance measuring apparatus according to another embodiment of the present invention may include only one of two reflectors  230  and  240 . The locations of the first and second reflectors will be described in later. 
     In Eq. 1, R denotes a distance between the transmission antenna  210  and the receive antenna  220 , and D denotes a height of the transmission antenna  210  and the receive antenna  220  from the metal floor  201 . θ 1  indicates an angle between the metal floor  201  and an electromagnetic wave entering at a location R/2 on the metal floor  201 . The unit of the angle θ 1  is a degree “°”. 
     The first reflector  230  forms an angle θ 2  from the metal floor  230 . The angle θ 2  is approximated by Eq. 1. 
     
       
         
           
             
               
                 
                   
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     The first reflector  230  reflects the electromagnetic wave  213  propagating toward the metal floor  201  from the transmit antenna  210  in a positive z direction. The reflected wave  214  is absorbed by the electromagnetic wave absorber  250  attached at the interior wall of the chamber  200 . 
     The second reflector  240  forms an angle θ 3  from the metal floor  230  and forms an angle (180°−θ 3 ) in a direction to the transmit antenna  210 . The angle θ 3  is approximated by Eq. 2. 
     
       
         
           
             
               
                 
                   
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     In Eq. 3, the angle θ 1  is identical to the angle θ 1  in Eq. 1. The unit of the angle θ 3  is a degree)(°). 
     The second reflector  240  reflects the electromagnetic wave  215  propagating from the transmit antenna  210  toward the metal floor  201  in a negative z direction. The reflected wave  216  of the electromagnetic wave  215  passes through a rotator  260  formed of low reflective material and is absorbed by the electromagnetic wave absorber  250  attached at the interior walls of the chamber  200 . 
     The antenna radiation performance measuring apparatus according to the present embodiment can form a uniform electric field in a measurement area of the receive antenna  220  because the reflected waves  214  and  216  transferred to the receive antenna  220  propagate in parallel with the metal floor  201 . Also, it is possible to measure the radiation pattern and the gain of the receive antenna  220  operating in a frequency band lower than a VHF band identically to the fully-anechoic chamber. Further, the antenna radiation performance measuring apparatus according to the present embodiment may be applied to measure the radiation performance of the receive antenna  220  for a frequency lower than a low limit frequency of a fully-anechoic chamber. Particularly, the antenna radiation performance measuring apparatus according to the present embodiment provide the effect of obtaining a direct wave in a semi-anechoic chamber where many reflected waves are generated. Furthermore, the utilization of the semi-anechoic chamber can be improved in views of time and cost. 
     Meanwhile, the antenna radiation performance measuring apparatus according to the present embodiment further includes a reflective plate  270 . 
     The reflective plate  270  is disposed around the transmit antenna  210  for concentrating the electromagnetic waves to the location of the receive antenna  220 . The reflective plate  270  further improves the directivity of the transmit antenna  210 . 
     The receive antenna  220  is disposed on the rotator  260 . The rotator  260  rotates the receive antenna  220  in parallel with an x-z plane and is formed of a less reflective material. 
     An antenna radiation performance measuring system  290  includes a vector network analyzer  291 , a data processor  293 , and a controller  295 . 
     The vector network analyzer  291  applies an electric signal to the transmit antenna  210  and receives an electric signal corresponding to an electromagnetic waves received at the receive antenna  220 . 
     The data processor  293  calculates the radiation pattern and the gain of the receive antenna  220  based on the electric signal from the vector network analyzer  291  and the received electric signal. The data processor  293  transmits the calculated radiation performance of the receive antenna  220  to a user interface (not shown) to show the radiation performance of the receive antenna  220  to a user. The data processor  293  receives a signal from a user for rotating the rotator  260  at a predetermined angle and generates a corresponding control signal thereof. 
     The controller  295  controls the rotation of the rotator  260 . The controller  295  receives a control signal from the data processor  293  to rotate the rotator  260 . 
       FIG. 3  is a flowchart describing a method for designing an antenna radiation performance measuring apparatus in accordance with an embodiment of the present invention. 
     Referring to  FIG. 3 , measurement environment parameters and an angle θ 1  are decided at step S 310 . The measurement environment parameters includes a distance R between the transmit antenna  310  and the receive antenna  220  and target frequency bands such as a lower limit frequency f 1  and an upper limit frequency f 2 . Eq. 1 is used to decide the angle θ 1 . 
     At step S 320 , the measurement environment of the antenna radiation performance measurement apparatus is modified. That is, the reflective plate  270  in the behind of the transmit antenna  210  and the reflectors  230  and  240  on the metal floor  201  are designed. The reflective plate  270  is designed by describing a parabola at the center of the transmit antenna  210  in consideration of the size of the chamber  200 . The center of the reflective plate  270  is controlled by shifting the center in parallel with a z-axis based on the directivity of each frequency band. The angles of the reflectors  230  and  240  are designed using Eq. 2 and Eq. 3. The reflectors  230  and  240  may be disposed at about a location of R/2. 
     At step S 330 , the uniformity of electric field is measured at a measurement area of an electromagnetic wave radiated from the transmit antenna  210  to determine whether the receive antenna has target specifications that a user wants. If it is not satisfied, the step S 320  is performed again. At step S 320 , the uniformity of the electric field is re-measured after tilting the reflective plate  270  to up and down directions based on the center of the transmit antenna  210 . Or, the electric field uniformity is re-measured after moving the reflectors  230  and  240  in parallel with a z-axis. 
     When the electric field uniformity is satisfied in the target specifications of a user, the receive antenna  220  is installed and the radiation performance of the receive antenna  220  is measured by each angle at step S 340 . 
     As described above, the method of designing an antenna radiation performance measurement apparatus according to the present enables designing an antenna radiation performance measurement apparatus to make an electromagnetic wave radiated from the transmit antenna  210  to form uniform electric field. 
     Also, the method of designing an antenna radiation performance measuring apparatus according to the present embodiment enables designing an antenna radiation performance measurement apparatus to accurately measure the radiation performance of a receive antenna using a low frequency band including a VHF band 174 to 216 MHz. 
     Hereinafter, the uniformity of electric fields measured by an antenna radiation performance measurement apparatus according to the present embodiment will be compared with those measured in a fully-anechoic chamber and in a semi-anechoic chamber according to the prior art. 
     Referring to  FIGS. 4 and 6 , when the electromagnetic wave radiated from the transmit antenna is a lower limit frequency f 1 , the uniformity of electric field will be described. The measurement area of the electric field is shown on an x-y plane with a receive antenna as an origin. 
       FIGS. 4A and 4B  are graphs showing normalized amplitude and a phase of a measured electric field formed in a typical fully-anechoic chamber.  FIGS. 5A and 5B  are graphs showing normalized amplitude and a phase of a measured electric field formed in a typical semi-anechoic chamber.  FIGS. 6A and 6B  are graphs showing normalized amplitude and a phase of a measured electric field formed in an antenna radiation performance measurement apparatus according to the present embodiment. Since a permissible error of the electric field uniformity is about 0.25 dB and 22.5 deg from the center, the measurable size of an antenna is about 70 cm in  FIGS. 4 to 6 . 
     The graphs of  FIGS. 4A and 4B  show that a normalized amplitudes and phases of an isotropic electric field are distributed based on an origin (x=0, y=0). The graphs of  FIGS. 5A and 5B  show that the maximum values of the normalized amplitudes and phase |[a1]s of the electric field are shifted from the center due to the reflected lights. The graphs of  FIGS. 5A and 5B  also show that the graph does not have isotropic distribution. The graphs of  FIGS. 6A and 6B  show that the graphs have the isotropic distribution of normalized amplitudes and a phase |[a2]s of the electric field based on the origin (x=0, y=0) like the graphs of  FIGS. 4A and 4B . As shown, the antenna radiation performance measurement apparatus according to the present embodiment can provide an excellent measurement area because the maximum value is located at the origin and the amplitude and the phase of the electric field are isotropic-distributed although the measuring result of the antenna radiation performance measuring apparatus according to the present embodiment is not identically to the ideal measuring result of the fully-anechoic chamber of  FIG. 4 . 
     Referring to  FIGS. 7 to 9 , the uniformity of electric field formed when the transmit antenna radiates an electromagnetic wave having an upper limit frequency f 2  will be described. Here, the measurement area of electric field is an x-y plane with a receive antenna as an origin. 
       FIGS. 7A and 7B  are graphs showing amplitudes and phases of electric field formed in a fully-anechoic chamber.  FIGS. 8A and 8B  are graphs showing amplitudes and phases of electric field formed in a semi-anechoic chamber.  FIGS. 9A and 9B  are graphs showing amplitudes and phases of electric field formed in an antenna radiation performance measuring apparatus. Since an allowable error of an antenna is about 0.25 dB and 22.5 deg from the center of the antenna, the measurement size is about 80 cm in  FIGS. 7 to 9 . 
     As shown in  FIGS. 7 to 9 , the antenna radiation performance measurement apparatus according to the present embodiment can provide an excellent measurement area because the maximum value is located at the origin and the amplitude and the phase of the electric field are isotropic-distributed although the measuring result of the antenna radiation performance measuring apparatus according to the present embodiment is not identically to the ideal measuring result of the fully-anechoic chamber of  FIG. 5 . 
     As described above, the antenna radiation measurement apparatus according to the present invention makes the electromagnetic wave radiated from the transmit antenna to form a uniform electric field. Accordingly, it is possible to accurately measure the radiation performance of an antenna using a low frequency band including VHF band (174 to 216 MHz). 
     The method for designing an antenna radiation performance measurement apparatus according to the present embodiment can design an antenna radiation performance measurement apparatus to make the electromagnetic wave radiated from the transmit antenna to form uniform electric field. It is possible to design an antenna radiation performance measuring apparatus to accurately measure the radiation performance of an antenna using a low frequency band such as VHF band (174 to 216 MHz). 
     While the present invention has been described with respect to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.