Patent Publication Number: US-10326212-B2

Title: Phase lag cell and antenna including same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY 
     This patent application is a National Phase application under 35 U.S.C. § 371 of International Application No. PCT/KR2014/004574, filed May 22, 2014, which claims the priority based on KR 10-2013-0059621 filed May 27, 2013, entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a phase lag cell and an antenna including the same, and more particularly, to a phase lag cell capable of compensating for phase differences of reflected waves generated when a parabolic reflector antenna is implemented in a planar shape, and an antenna including the same. 
     BACKGROUND ART 
     Parabola antennas are antennas using reflectors having a parabolic shape, and utilize a principle that radio waves radiated toward a reflector having a cross section of a parabola are reflected by the reflector and focused on a focal point or converged in one direction to be intensively radiated. Since such a reflector in the parabolic shape is difficult to be processed and is heavy and large, the reflector has a demerit in that it is difficult to manufacture for portable use. Accordingly, planar antennas, in which a parabolic reflector is replaced with a planar reflecting plate, has been widely used for homes, satellite communications, etc. However, when the parabolic reflector is implemented with the planar reflecting plate, since a distance between a radiation source and each portion of the parabolic reflector and a distance between the radiation source and each portion of the planar reflecting plate are different, phase differences between the reflected waves are generated, and thus, there is a problem in that the directivity of the antenna declines. 
       FIG. 1  is a view illustrating a reflector of a general parabola antenna, and  FIG. 2  is a view illustrating a radiation pattern at a frequency of 8.5 GHz when the reflector of the parabola antenna illustrated in  FIG. 1  is used. 
     As illustrated in  FIG. 2 , when a parabolic reflector is used, it can be confirmed that an antenna peak gain (dBi) is 23.7 dBi at the frequency of 8.5 GHz, and thus directivity is a significantly high, and radiated power is radiated at 0°. 
       FIG. 3  is a view illustrating a reflecting plate of a planar antenna when the parabolic reflector illustrated in  FIG. 1  is replaced with a planar reflecting plate, and  FIG. 4  is a view illustrating a radiation pattern at the frequency of 8.5 GHz when the planar reflecting plate illustrated in  FIG. 3  is used. 
     As illustrated in  FIG. 4 , when the planar reflecting plate is used, it can be confirmed that an antenna peak gain (dBi) is 8.7 dBi at the frequency of 8.5 GHz, and thus directivity thereof is much worse than that of the parabolic reflector in  FIG. 1 , and radiated power is radiated as being inclined by 34.0° instead of 0°. As described above, when the parabolic reflector is implemented with the planar reflecting plate, since the distance between the radiation source and the each portion of parabolic reflector and the distance between the radiation source and each portion of the planar reflecting plate are different, the phase differences of the reflected waves are generated. 
       FIG. 5  is a graph showing phase differences of reflected waves generated when the parabolic reflector is implemented with the planar reflecting plate. 
     As illustrated in  FIG. 5 , when the parabolic reflector is implemented with the planar reflecting plate, a difference of a distance between a radiation source and each portion of the parabolic reflector and a distance between the radiation source and each portion of the planar reflecting plate increase in a direction opposite the center of the reflecting plate, and thus, the phase differences of reflected waves increase. Table 1 is a table which represents phase differences in specific values of the reflected waves generated when the parabolic reflector is implemented with the planar reflecting plate. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 DISTANCE FROM A CENTER OF 
                 PHASE DIFFERENCE OF 
               
               
                 REFLECTING PLATE (MM) 
                 REFLECTED WAVE (°) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 0 
                 6.428 
               
               
                 18 
                 −40.48 
               
               
                 36 
                 −121.732 
               
               
                 54 
                 −237.328 
               
               
                 72 
                 −387.268 
               
               
                 90 
                 −571.552 
               
               
                 108 
                 −790.18 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, the phase difference of the reflected wave is only about −40° when a distance is about 18 mm from the center of the reflecting plate, but the phase difference of the reflecting plate is about −571° when a distance is about 90 mm from the center of the reflecting plate. Accordingly, the directivity of the planar antenna is greatly lowered due to phase differences of the reflected waves generated when the parabolic reflector is implemented with the planar reflecting plate. 
     To overcome the above problems, a patch antenna, of which a size and a phase of a resonance element are adjustable and which can be manufactured and integrated easily, is being used, but since the patch antenna has a relatively narrow bandwidth, an adjustable range of the resonance element is limited. 
     SUMMARY 
     The present invention is directed to providing a phase lag cell capable of compensating for phase differences of reflected waves generated by adjusting a stub length when a parabolic reflector antenna is implemented with a planar reflecting plate, and an antenna including the same. 
     One aspect of the present invention provides a phase lag cell including a reflecting plate having a planar shape, a substrate positioned to be spaced apart from the reflecting plate by a predetermined distance, and a phase lag circuit in which L-shaped patterns are formed to be vertically and horizontally symmetrical around a cross-shaped slot, and stubs having a predetermined length are formed on one surface of the substrate to extend from ends of the L-shaped patterns. 
     Meanwhile, another aspect of the present invention provides an antenna including a reflecting plate having a planar shape, a substrate positioned to be spaced apart from the reflecting plate by a predetermined distance, and a plurality of phase lag circuits in which L-shaped patterns are formed to be vertically and horizontally symmetrical around cross-shaped slots, and stubs having a predetermined length are formed on one surface of the substrate to extend from ends of the L-shaped patterns. 
     According to an embodiment of the present invention, sequential phase shifts of reflected waves can be performed in a wide range by adjusting stub lengths of a phase lag cell, and thus, a synthesis of the reflected waves can be easily performed. 
     In addition, since a phase lag circuit according to an embodiment of the present invention has a symmetrical structure, the phase lag circuit can be applied to all of a vertically polarized wave, a horizontally polarized wave, a left-handed circularly polarized wave, and a right-handed circularly polarized wave. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating a reflector of a general parabola antenna. 
         FIG. 2  is a view illustrating a radiation pattern at a frequency of 8.5 GHz when the reflector of the parabola antenna illustrated in  FIG. 1  is used. 
         FIG. 3  is a view illustrating a reflecting plate of a planar antenna when the parabolic reflector illustrated in  FIG. 1  is replaced with a planar reflecting plate. 
         FIG. 4  is a view illustrating a radiation pattern at a frequency of 8.5 GHz when the planar reflecting plate illustrated in  FIG. 3  is used. 
         FIG. 5  is a graph showing phase differences of reflected waves generated when the parabolic reflector is implemented with the planar reflecting plate. 
         FIG. 6  is a view illustrating a phase lag cell according to an embodiment of the present invention. 
         FIG. 7  is a view illustrating a phase lag circuit according to an embodiment of the present invention. 
         FIG. 8  is a graph showing phases of reflected waves shifted by a change in the length of a stub and a frequency according to an embodiment of the present invention. 
         FIG. 9  is a view illustrating a case when the phase lag circuit according to an embodiment of the present invention forms a second stub. 
         FIG. 10  is a view illustrating an antenna according to an embodiment of the present invention. 
         FIG. 11  is a view illustrating a radiation pattern at a frequency of 15 GHz when the phase lag cell of the antenna is used according to an embodiment of the present invention. 
     
    
    
     Hereinafter, specific embodiments of the present invention will be described in accordance with the following drawings, however, they are only exemplary embodiments of the invention, and the present invention is not limited thereto. 
     In descriptions of the invention, when it is determined that detailed descriptions of related well-known functions unnecessarily obscure the essence of the invention, detailed descriptions thereof will be omitted. Some terms described below are defined by considering functions in the invention and meanings may vary depending on, for example, a user or operator&#39;s intentions or customs. Therefore, the meanings of terms should be interpreted based on the scope throughout this specification. 
     The spirit and scope of the invention are defined by the appended claims. The following embodiments are only made to efficiently describe the progressive technological scope of the invention to those skilled in the art. 
       FIG. 6  is a view illustrating a phase lag cell according to an embodiment of the present invention. A phase lag cell  600  according to the embodiment of the present invention is a cell for compensating for phase differences of reflected waves generated when a reflector in a parabolic shape is implemented with a reflecting plate in a planar shape, and delays phases of radio waves reflected by the reflecting plate. As illustrated in  FIG. 6 , the phase lag cell  600  includes a reflecting plate  602 , a separating object  604 , a substrate  606 , and a phase lag circuit  608 . 
     The reflecting plate  602  is formed of a conductive material, and serves as a reflecting object and a ground. The reflecting plate  602  may be formed in various shapes, which have a planar shape of which both ends are not bent, such as a square shape or a circular shape. 
     The separating object  604  is a material or a structure which separates the reflecting plate  602  from the substrate  606  by a predetermined distance. The substrate  606  may be disposed to have an interval of the predetermined distance from the reflecting plate  602  by the separating object  604 , and a distance between the reflecting plate  602  and the substrate  606  may be changed by the sizes of phases of reflected waves. The separating object  604  preferably uses the air or a material having a dielectric constant similar to that of the air to minimize a loss of a reflected wave, but is not limited thereto. The separating object  604  may be, for example, a honeycomb, a foam, a Jig, or the like. 
     The substrate  606  may be a plate on which the phase lag circuit  608  is formed on one or the other surface thereof, and may be formed in various planar shapes such as a square and a circular shape similar to the reflecting plate  602 . The substrate  606  preferably has a shape corresponding to the shape of the reflecting plate  602 , but is not limited thereto. 
     The phase lag circuit  608  may be a circuit configured to compensate for phase differences of reflected waves generated when a parabolic reflector is implemented with a planar reflecting plate, and may be formed on one surface of the substrate  606 . Meanwhile, as illustrated in  FIG. 6 , when the phase lag cell  600  is formed in a square shape, each of a length and a width of the phase lag cell  600  may be, for example, in a range of 0.4λ, to 0.5λ. 
       FIG. 7  is a view illustrating a phase lag circuit according to an embodiment of the present invention. As illustrated in  FIG. 7 , the phase lag circuit  608  according to the embodiment of the present invention has a basic structure in which L-shaped patterns  608 - 1  are formed to be vertically and horizontally symmetrical around a cross-shaped slot. A thickness of the slot may be in a range of about 0.1λ, to 0.2λ. Since the L-shaped patterns  608 - 1  are formed to be vertically and horizontally symmetrical around a cross-shaped slot, the phase lag circuit  608  may be applied to all of a vertically polarized wave, a horizontally polarized wave, a left-handed circularly polarized wave, and a right-handed circularly polarized wave. 
     In addition, the phase lag circuit  608  is formed by extending stubs  608 - 2  which have a predetermined length from ends of the L-shaped patterns  608 - 1 . According to the embodiment of the present invention, when phases of radio waves reflected by the reflecting plate  602  are delayed, lengths of the stubs  608 - 2  may be adjusted. At this time, each of the stubs  608 - 2  included in the phase lag circuit  608  may be adjusted to have a predetermined length, and in addition, the lengths of the stubs  608 - 2  may also be adjusted to have different lengths. That is, the basic structure in which the L-shaped patterns  608 - 1  are formed to be vertically and horizontally symmetrical around the cross-shaped slot is maintained, but the lengths of the stubs  608 - 2  formed at the ends of the L-shaped patterns  608 - 1  are adjusted, and thus the phases of the reflected waves may be shifted. Through the process of adjusting the lengths of the above-described stubs  608 - 2 , sequential phase shifts of the reflected waves may be performed in a wide range, and thus the reflected waves may be synthesized easily. In addition, the phases of the reflected waves may also be shifted by adjusting widths of the stubs  608 - 2 . As illustrated in  FIG. 7 , the stubs  608 - 2  may be formed to extend perpendicular to ends of the L-shaped patterns  608 - 1 , but are not limited thereto, and may be formed to extend to be inclined with respect to the ends of the L-shaped patterns  608 - 1  at a predetermined angle. 
       FIG. 8  is a graph showing phases of reflected waves shifted by a change in the length of a stub and a frequency according to an embodiment of the present invention. 
       FIG. 8  shows phase shifts of reflected waves by a change in the frequency when lengths of the stubs  608 - 2  according to the embodiment of the present invention are 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, and 3.5 mm. As illustrated in  FIG. 8 , the phase lag cell  600  according to the embodiment of the present invention shows significant phase shifts of the reflected waves around a specific frequency, for example, a frequency of about 8 GHz. That is, the phase lag cell  600  has a structure having a surface with a magnetic conductor characteristic at the specific frequency, that is, an artificial magnetic conductor (ACM) structure. In addition, since the lengths of the stubs  608 - 2  according to the embodiment of the present invention are changed, the phases of the reflected waves are shifted by the change in the frequency, and the phase shifts are sequentially performed in a wide range. Accordingly, the phase lag cell  600  according to the embodiment of the present invention has a wider bandwidth for phase shifts compared to a conventional patch antenna, and as the lengths of the stubs  608 - 2  are adjusted, the sequential phase shifts of the reflected waves in the wide range may be performed. 
       FIG. 9  is a view illustrating a case when the phase lag circuit according to an embodiment of the present invention forms a second stub. 
     As described above, the stubs  608 - 2  are formed in the phase lag circuit  608  according to the embodiment of the present invention, and by adjusting the lengths of the stubs  608 - 2 , the phases of the reflected waves may be shifted. In addition, as illustrated in  FIG. 9 , the phase lag circuit  608  may be formed on the other surface of the substrate  606  to have a predetermined length, and may further include second stubs  608 - 3  connected to ends of the stubs  608 - 2  through via holes of the substrate. As illustrated in  FIG. 9 , the second stubs  608 - 3  may be formed to extend parallel to the stubs  608 - 2 , but are not limited thereto. According to the embodiment of the present invention, as lengths of the second stubs  608 - 3  may be adjusted, the sequential phase shifts of the reflected waves may be performed in a narrow range. Here, the lengths of the second stubs  608 - 3  included in the phase lag circuit  608  may be adjusted to have a predetermined length, and in addition, the lengths of the second stubs  608 - 3  may also be adjusted to have different lengths. The second stubs  608 - 3  are for a fine tuning of the phases of the reflected waves, and may more precisely adjust the phases of the reflected waves than the stubs  608 - 2 . For example, when it is assumed that the phase of the reflected wave shifts −20° when the length of the stub  608 - 2  extends 0.5 mm at the same frequency, when the length of the second stub  608 - 3  extends 0.5 mm, the phase of the reflected wave may shift −2°. In addition, similar to the stubs  608 - 2 , as the widths of the second stubs  608 - 3  are adjusted, the phases of the reflected waves may also be shifted. A shape of the second stubs  608 - 3  is only one embodiment, and the second stubs  608 - 3  may be formed in various shapes which may precisely shift the phases of the reflected waves. 
       FIG. 10  is a view illustrating an antenna according to an embodiment of the present invention. As illustrated in  FIG. 10 , an antenna  1000  according to the embodiment of the present invention includes a reflecting plate  602 , a separating object  604 , a substrate  606 , and a plurality of phase lag circuits. For the sake of convenience in the description, the plurality of phase lag circuits are described based on an assumption of a first phase lag circuit  801 , a second phase lag circuit  802 , and a third phase lag circuit  803 , and the number of the phase lag circuits is not limited thereto. Since specific descriptions of the reflecting plate  602 , the separating object  604 , and the substrate  606  according to the embodiment of the present invention are the same as those described above, the specific description herein will be omitted. 
     As described above, the phase lag circuit according to the embodiment of the present invention is formed so that the L-shaped patterns  608 - 1  are vertically and horizontally symmetrical around the cross-shaped slots, and the stubs  608 - 2  having predetermined lengths extend from ends of the L-shaped patterns  608 - 1 , on one surface of the substrate  606 . Here, the first phase lag circuit  801 , the second phase lag circuit  802 , and the third phase lag circuit  803  may be arranged to be spaced apart from each other by a predetermined distance on one surface of the substrate  606 , and the arrangement distance of the phase lag circuit may be, for example, in a range of 0.5λ, to 0.8λ. As illustrated in  FIG. 10 , when the substrate  606  has a circular plane shape, each of the first phase lag circuit  801 , the second phase lag circuit  802 , and the third phase lag circuit  803  may be arranged around the reflecting plate  602  in a circular shape. The first phase lag circuit  801  may be arranged in a circular shape at a position of 5 mm from the center of the reflecting plate  602 , the second phase lag circuit  802  may be arranged in a circular shape at a position of 7 mm from the center of the reflecting plate  602 , and the third phase lag circuit  803  may be arranged in a circular shape at a position of 9 mm from the center of the reflecting plate  602 . 
     The stubs having different lengths may be formed in the first phase lag circuit  801 , the second phase lag circuit  802 , and the third phase lag circuit  803 , and the lengths of the stubs are determined according to a degree of delayed phase of a radio wave reflected by the reflecting plate  602 . As described above, when the parabolic reflector is implemented with the planar reflecting plate, phase differences of radio waves reflected by the reflecting plate  602  increases in a direction opposite the center of the reflecting plate  602 . Accordingly, the first phase lag circuit  801 , the second phase lag circuit  802 , and the third phase lag circuit  803  respectively having different distances from the center of the reflecting plate  602  may respectively have stubs having different lengths. For example, the first phase lag circuit  801  may be formed by extending the stubs  608 - 2  to have a length of 0.5 mm from ends of the L-shaped patterns  608 - 1 , the second phase lag circuit  802  may be formed by extending the stubs  608 - 2  to have a length of 0.6 mm from ends of the L-shaped patterns  608 - 1 , and the third phase lag circuit  803  may be formed by extending the stubs  608 - 2  to have a length of 0.7 mm from ends of the L-shaped pattern  608 - 1 . Meanwhile, a part of the plurality of phase lag circuits may further include the above-described second stubs  608 - 3 . 
     That is, according to the embodiment of the present invention, the plurality of phase lag circuits may be arranged to be spaced apart from each other by a predetermined distance on one surface of the substrate  606 , and as the lengths of the stubs  608 - 2  in the phase lag circuit are adjusted according to the positions of the arrangement, phase lags of the reflected waves can be effectively compensated for. However, the above-described method of the arrangement of the phase lag circuits  608  and the lengths of the stubs  608 - 2  are only one embodiment, but are not limited thereto. 
     In addition, the antenna  1000  according to the embodiment of the present invention may include at least two phase lag cells, and here, each of the phase lag cells may include a phase lag circuit including lengthwise stubs. Here, as illustrated in  FIG. 10 , each of the phase lag cells may be arranged in the circular shape, and since the effects according thereto are the same as described above, the description will be omitted. 
       FIG. 11  is a view illustrating a radiation pattern at a frequency of 15 GHz when the phase lag cell of the antenna according to an embodiment of the present invention is used. 
     As illustrated in  FIG. 11 , when the phase lag cell of the antenna according to the embodiment of the present invention is used, it can be confirmed that an antenna peak gain (dBi) is 28.0 dBi at a frequency of 15 GHz, and thus directivity is significantly high, and a radio power is radiated at 0° similar to the case in which the parabolic reflector of a parabola antenna is used. That is, when the phase lag cell  600  according to the embodiment of the present invention and the antenna  1000  including the same are used, since sequential phase shifts of a wide range may be performed in a wide frequency band, phase differences of reflected waves generated when a parabolic reflector antenna is implemented with a planar reflecting plate may be compensated for, and thus high directivity may be maintained. 
     While representative embodiments of the preset invention have been described above in detail, it may be understood by those skilled in the art that the embodiments may be variously modified without departing from the scope of the present invention. Therefore, the scope of the present invention is defined not by the described embodiment but by the appended claims, and encompasses equivalents that fall within the scope of the appended claims.