Abstract:
Disclosed herein are a method and divider for dividing power between and supplying the parts of the power to respective radiation elements of an array antenna, and an antenna device using the divider. The division method includes the steps of dividing power, applied to a feeding unit, into two parts at a first stage of division, and supplying a first of the two parts to at least one central radiation element, and dividing a second of the two parts and supplying sub-parts of the second part to respective peripheral radiation elements, thereby supplying relatively high power to the central radiation element and relatively low power to the peripheral radiation elements.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a Radio Frequency (RF) repeater array antenna and, more particularly, to a method and divider for efficiently dividing power between respective radiation elements of an array antenna. 
   2. Description of the Related Art 
   An RF repeater antenna generally includes a radiation element array for transmitting and receiving radio waves, a reflector disposed behind the radiation element array and configured to reflect radio waves, and a division circuit for equally dividing power and providing equally divided power to respective radiation elements. According to the typical characteristics of an antenna, the antenna has non-uniform radio wave intensity at the locations of respective radiation elements, and exhibits a radiation pattern that has developed back and side lobes due to the scattering of radio waves at the edge of a reflector and the like. 
   Due to the above-described phenomena, signal interference occurs between transmission and reception signals or between repeaters. Schemes for improving the Front to Back (F/B) and Front to Side (F/S) ratios of an antenna by suppressing undesired waves that generate back and side lobes have been proposed. 
   For example, the above-described schemes include a scheme using a multi-reflecting plate structure and a radio wave absorption body, and a scheme based on the arrangement of radiation elements and the adjustment of the intervals between elements. However, the first scheme has problems in that the scale, size, and weight of the entire antenna are increased and in that an auxiliary side lobe is generated in front of an antenna, so that it is difficult to realize an F/S ratio equal to or higher than 20 dB. Meanwhile, the second scheme has a problem in that the design of the arrangement of radiation elements, the design of the intervals between the radiation elements, and means for adjusting a radiation pattern are complicated, so that the design and implementation thereof are difficult. 
   As known from theory, an F/B ratio and an F/S ratio can be improved by relatively increasing power for the center patch of an array and relatively decreasing power for the side patch of the array. Meanwhile, in order to feed a large amount of power to the center of the array using a typical parallel feeding method, a low division rate is required, so that the width of a division pattern must be designed so that it is very small. For example, in the case where, in a typical 3×3 patch array shown in  FIG. 1 , 1:8 power division is performed for a dielectric substrate having a dielectric constant of 3.0 and a thickness of 0.8t, a pattern having a width equal to or less than 0.2 mm is required. For this reason, problems arise in that it is difficult to implement such a scheme and it is difficult to use the increased normal transfer capability of an antenna. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an improved method of dividing power, and a divider using the method so as to improve the F/B and F/S ratio characteristics of an array antenna. 
   Another object of the present invention is to provide an array antenna device to which the divider is applied. 
   In order to accomplish the above object, the present invention provides a method of dividing power between and supplying divided power to respective radiation elements of an array antenna, including the steps of dividing power, applied to a feeding unit, into two parts at a first stage of division, and supplying a first of the two parts to at least one central radiation element, and dividing a second of the two parts and supplying sub-parts of the second part to respective peripheral radiation elements, thereby supplying relatively high power to the central radiation element and relatively low power to the peripheral radiation elements. The division method is implemented on a dielectric feeding substrate, thereby forming a divider according to the present invention. The divider constitutes an antenna device according to the present invention, along with an array substrate and a reflector. 
   The present invention has as its foundation the idea that, in order to improve the F/B and F/S characteristics of an array antenna, the power of a central patch must be enhanced and the power of peripheral patches must be weakened. According to the present invention, advantages arise in that the characteristics of an antenna are improved and the design and implementation of the antenna are easily achieved. The features and effects of the present invention will be apparent from the detailed description of embodiments that will be given in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a perspective view of a typical radiation element array; 
       FIG. 2  is a schematic circuit diagram illustrating a method of dividing power according to the present invention; 
       FIG. 3  is a perspective view of a power divider according to the present invention; 
       FIG. 4  is a perspective view of an antenna device to which the power divider of  FIG. 3  is applied; 
       FIG. 5  is a sectional view taken along line A-A of  FIG. 4 ; 
       FIG. 6  is a plan view of  FIG. 4 ; 
       FIG. 7A  is a diagram showing the vertical pattern of the antenna device shown in  FIG. 4 ; 
       FIG. 7B  is a diagram showing the horizontal pattern of the antenna device shown in  FIG. 4 ; and 
       FIG. 7C  is a diagram showing the standing wave ratios of the antenna device shown in  FIG. 4 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components. 
     FIG. 2  is a schematic diagram of a division circuit  10  for dividing power between radiation elements  15   a - 15   i , arranged in a 3×3 array as shown in  FIG. 1 , according to the present invention. The division circuit  10  includes a single feeding unit  11  connected to a feeding connector, and a feeding line  12  connected from the feeding unit  11  to respective radiation element  15   a - 15   i  arranged on an array substrate. The feeding line  12  is branched into a first branch line  13  and a second branch line  14  at the first stage of the feeding unit  11 . Of the first and second branch lines  13  and  14 , the first branch line  13  is connected to a central radiation element  15   a , and the second branch line  14  is branched again and connected to peripheral radiation elements  15   b - 15   i.    
   As a result, according to the present invention, the division of power is performed in such a manner that the power applied to the feeding unit  11  is divided into two parts at the first stage of division, one of the parts is supplied to the central radiation element  15   a , and the other part is divided again and supplied to the peripheral radiation elements  15   b - 15   i . For the shown 3×3 array, power is supplied in series to the central radiation element  15   a , and is supplied in parallel to the peripheral radiation elements  15   b - 15   i . Meanwhile, in the case where two or more central radiation elements are used, as in a 4×4 array, power is supplied from the first branch line  13  in parallel. According to this power supply method, the power of the central radiation element  15   a  is enhanced and the power of the peripheral radiation elements  15   b - 15   i  is weakened. As a result, the F/B and F/S ratios of the antenna can be improved. 
     FIG. 3  is an example of a divider to which the above-described power division method is applied. A divider  20  includes a dielectric feeding substrate  21  on which a feeding unit  22  and a feeding line  24  are formed, and feed lines  23  which are secured onto the substrate  21  and supply power to respective radiation elements (reference numerals  15   a - 15   i  of  FIG. 1 ) constituting the array antenna. The feed lines  23  are inserted into and secured onto the ends of the feeding line  24 . The feed lines  23  can be inserted into and firmly secured onto the substrate  21 . 
   The feeding line  24  is branched from the feeding unit  22  into two branch lines at the first stage of division, and the first branch line  25  of the two branch lines extends in series to the central end of the substrate  21 , and the second branch line  26  is branched again and connected in parallel to the peripheral ends of the substrate  21 . According to the above-described structure of the divider  20 , the power of the central end of the substrate  21  is enhanced and the power of the peripheral ends of the substrate  21  is weakened. In order to make the phases of respective radiation elements (reference numerals  15   a - 15   i  of  FIG. 1 ) uniform, the first branch line  25  is configured in a meandering form. 
   In order to divide power between respective peripheral ends of the feeding substrate  21 , the second branch line  26  is designed to extend to respective peripheral ends via continuous secondary branch lines  27 ,  28  and  29  in the present embodiment. However, the present invention is not limited to a specific design for the second branch line  26 , and various variations of the design can be made. In the drawing, the reference numeral ‘S’ designates a Direct Current (DC) short circuit that functions to protect the antenna from lightening or some other excessive load. 
   Meanwhile, power applied to the feeding unit  22  is divided into two parts at the first stage of the feeding line  24 . One of the two parts is supplied to the central radiation element  15   a  via the central end of the substrate  21  and the feed line  23 , and the other is supplied to the peripheral radiation elements  15   b - 15   i  via respective peripheral ends of the substrate  21  and the feed line  23 . According to this structure, the power of the central radiation element  15   a  is enhanced and the power of the peripheral radiation elements  15   b - 15   i  is weakened. Accordingly, the F/B ratio and side lobe characteristic of the antenna can be improved. 
     FIGS. 4 to 6  show an antenna device  30  to which the divider  20  is applied. The antenna device  30  includes an array substrate  31 , a divider  20  provided behind the substrate  31 , and a reflector  32  disposed behind the divider  20  and uniformly spaced apart from the divider  20 . In the drawing, reference numeral  33  designates a feed connector. 
   The divider  20  includes a feeding substrate  21  on which a feeding line  24  is formed, and feed lines  23  which are secured on the feeding substrate  21 . In detail, the first ends of the feed lines  23  are vertically secured to respective ends of the feeding line  24 , and the feed lines  23  are ‘L’-shaped feed lines that are bent parallel to the array substrate  31 . The feed lines  23  do not come into direct contact with the array substrate  31 , and are coupled to respective radiation elements  15   a ˜ 15   i , disposed on the array substrate  11 , in an Electro-Magnetic (EM) manner. As a result, the feed lines  23  form first radiation units in the antenna device  30 , and the radiation elements  15   a ˜ 15   i  form second radiation units on the array substrate  31 . 
   From  FIGS. 5 and 6 , it can be seen that the array substrate  31  is not located above the center portion of the reflector  32 , but is offset from the reflector  32 . This results from the shape of the feed lines  23 . According to the actual measurement for the asymmetric shape of the ‘L’-shaped feed lines  23 , a phenomenon in which a side lobe beam pattern was generated in a specific 90° direction occurred. Accordingly, the array substrate  31  is disposed to be offset to one side, as shown in the drawing, so that a side lobe phenomenon attributable to the asymmetry of the feed lines  23  can be eliminated. In this case, the extent of the offset of the array substrate  31  may be adjusted based on the results of actual measurement. 
   The reflector  32  is one in number. The central portion of the reflector  32  is spaced apart backward from the feeding substrate  21  of the divider  20  by a distance ‘d’, and the skirt portion  32   a  of the reflector  32  is outwardly inclined. In this structure, the reflector  32  functions to minimize the leakage of radiation power of the feel line  23  as a first radiation unit and to efficiently combine a side lobe with a main beam. From a structural aspect, the divider  20  is placed and secured over the central portion of the reflector  32 , and the array substrate  31  is secured over the feeding substrate  21  at a uniform interval using spacers  34  that extend between the feeding substrate  21  and the array substrate  31 . 
     FIGS. 7A ,  7 B and  7 C are graphs showing the vertical pattern, horizontal pattern and standing wave ratio of an antenna device that is configured to have the following dimensions: an area of 410 mm×420 mm and a width of 100 mm. As seen from the graphs, the antenna device exhibited superior characteristics, including an F/B ratio and an F/S ratio greater than 35 dB, and could achieve a desirable standing wave ratio. 
   The present invention provides the method and divider for dividing power, applied to the feeding unit, into two equal parts, supplying one of the two parts in series to the central radiation element, and supplying the other in parallel to the peripheral radiation elements. The present invention is advantageous in that it can be easily implemented, and the characteristics of an antenna can be improved by applying the present invention to the antenna device. 
   Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.