Patent Publication Number: US-9843100-B2

Title: Antenna having broad bandwidth and high radiation efficiency

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2012-0007886, filed on Jan. 26, 2012, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
     BACKGROUND 
     1. Field 
     The following description relates to an antenna having a broad bandwidth and a high radiation efficiency. 
     2. Description of Related Art 
     A slot antenna includes a metal surface, such as a flat plate, with a hole or slot cut out. When the plate is driven as an antenna by a driving frequency, the slot radiates electromagnetic waves. 
     For a slot antenna to include a wide bandwidth, a width of a slot may be increased. However, when a conductor is disposed at a back surface of the slot antenna including a low height, the width of the slot may be larger than a height of a substrate of the slot antenna. In this example, the bandwidth may not be effectively increased. 
     SUMMARY 
     In one general aspect, there is provided an antenna including a conductor, and a dielectric substrate disposed on the conductor. The antenna further includes a slot portion formed on the dielectric substrate, and a cavity formed in the dielectric substrate that corresponds to the slot portion. 
     In another general aspect, there is provided an antenna including a conductor, and a dielectric substrate disposed on the conductor. The antenna further includes a slot portion formed on the dielectric substrate. A portion of the dielectric substrate that corresponds to the slot portion is filled with air to reduce a permittivity of the slot portion. 
     In still another general aspect, there is provided an antenna including a dielectric substrate, and a conductive substrate disposed on the dielectric substrate. The antenna further includes a slot formed through the conductive substrate, and a hole formed in the dielectric substrate that corresponds to the slot. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view illustrating an example of a high-efficiency wide-bandwidth antenna. 
         FIG. 2  is an enlarged perspective view illustrating an example of a portion A of the high-efficiency wide-bandwidth antenna of  FIG. 1 . 
         FIG. 3  is a sectional view illustrating an example of a section that is cut along a line B-B of the high-efficiency wide-bandwidth antenna of  FIG. 1 . 
         FIG. 4  is a diagram illustrating an example of an equivalent circuit of the high-efficiency wide-bandwidth antenna of  FIG. 1 . 
         FIG. 5  is a plan view illustrating an example of the high-efficiency wide-bandwidth antenna of  FIG. 1  that includes a meandering slot portion. 
         FIG. 6  is a partial perspective view illustrating another example of a high-efficiency wide-bandwidth antenna. 
     
    
    
     Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the systems, apparatuses, and/or methods described herein will be suggested to those of ordinary skill in the art. The progression of processing steps and/or operations described is an example; however, the sequence of steps and/or operations is not limited to that set forth herein and may be changed as is known in the art, with the exception of steps and/or operations necessarily occurring in a certain order. Also, description of well-known functions and constructions may be omitted for increased clarity and conciseness. 
     It is understood that the features of the disclosure may be embodied in different forms and should not be constructed as limited to the example(s) set forth herein. Rather, example(s) are provided so that this disclosure will be thorough and complete, and will convey the full scope of the disclosure to those skilled in the art. The drawings may not be necessarily to scale, and, in some examples, proportions may have been exaggerated in order to clearly illustrate features of the example(s). When a first layer is referred to as being “on” a second layer or “on” a substrate, it may not only refer to a case where the first layer is formed directly on the second layer or the substrate but may also refer to a case where a third layer exists between the first layer and the second layer or the substrate. 
       FIG. 1  is a plan view illustrating an example of a high-efficiency wide-bandwidth antenna  100 .  FIG. 2  is an enlarged perspective view illustrating an example of a portion A of the high-efficiency wide-bandwidth antenna  100  of  FIG. 1 . Referring to  FIGS. 1 and 2 , the high-efficiency wide-bandwidth antenna  100  includes a dielectric substrate  110 , a lower conductor portion  122 , an upper conductor portion  124 , a slot portion  130 , and a cavity portion  140 . 
     The high-efficiency wide-bandwidth antenna  100  may be used on, and attached to, a human body. Since the human body may cause a great loss of a power of a transmitter, and may limit the power for safety, the high-efficiency wide-bandwidth antenna  100  is configured to achieve a high radiation efficiency and a wide bandwidth. 
     Accordingly, the high-efficiency wide-bandwidth antenna  100  includes a cavity-backed slot antenna including a relatively small thickness. The cavity-backed slot antenna includes a cavity formed to a back surface of the slot antenna, and is not greatly affected by electrical characteristics of a material on which the slot antenna is placed. Therefore, the cavity-backed slot antenna may be used in a system including a lossy medium, such as a ground surface or a human body disposed at the back surface of the slot antenna. 
     In more detail, the dielectric substrate  110  may include a substantially rectangular plate form, but a shape of the dielectric substrate  110  is not limited thereto. For example, the dielectric substrate  110  may include a polygonal or circular plate form. 
     The lower conductor  122  is disposed below a lower surface of the dielectric substrate  110 , e.g., at the back surface of the cavity-backed slot antenna. The upper conductor  124  is disposed above an upper surface of the dielectric substrate  110 . 
     The slot portion  130  is formed in (e.g., through) the upper conductor  124  and on the upper surface of the dielectric substrate  110 . The slot portion  130  includes a slot (e.g., a trench) partially exposing the dielectric substrate  110 . The dielectric substrate  110  is exposed by removing the upper conductor  124  in a predetermined pattern. The slot portion  130  may include a linearly extended portion including a length corresponding to about one half of a wavelength of a transmission wave. 
     As will be described in detail with reference to  FIG. 3 , the cavity portion  140  is formed in the dielectric substrate  110 , under the slot portion  130 , and on the lower conductor  122 . The cavity portion  140  includes a cavity filled with air. 
       FIG. 3  is a sectional view illustrating an example of a section that is cut along a line B-B of the high-efficiency wide-bandwidth antenna  100  of  FIG. 1 . Referring to  FIG. 3 , the cavity portion  140  includes a cavity (e.g., a trench) formed by removing the dielectric substrate  110  disposed under the slot portion  130  through the upper surface of the dielectric substrate  110  and the lower surface of the dielectric substrate  110 . That is, the cavity portion  140  is formed by removing a portion of the dielectric substrate  110  that corresponds to (e.g., is under and aligned with) the slot portion  130 . The cavity portion  140  extends to a position (e.g., a depth) contacting the lower conductor  122  that includes the back surface of the cavity-backed slot antenna, to form the cavity of the high-efficiency wide-bandwidth antenna  100 . 
     Alternatively, the cavity portion  140  may be formed through the upper surface of the dielectric substrate  110  and partially into the dielectric substrate  110  to a position (e.g., a depth) that does not contact the lower conductor  122 . That is, the cavity portion  140  may be formed by removing a smaller portion of the dielectric substrate  110  that corresponds to (e.g., is under and aligned with) the slot portion  130  to reduce a size of the cavity. This may be achieved by using a high-permittivity substrate (e.g., FR-4) as the dielectric substrate  110 . 
     Hereinafter, an increase in the radiation efficiency and the bandwidth of the high-efficiency wide-bandwidth antenna  100  due to the cavity portion  140  will be described in detail. 
       FIG. 4  is a diagram illustrating an example of an equivalent circuit of the high-efficiency wide-bandwidth antenna  100  of  FIG. 1 . Referring to  FIG. 4 , the high-efficiency wide-bandwidth antenna  100  includes the cavity-backed slot antenna including a slot portion, e.g., the slot portion  130  of  FIG. 1 . The slot portion may include the length corresponding to about one half of the wavelength. The cavity-backed slot antenna may be implemented by a transmission circuit (e.g., a parallel RLC circuit as shown in  FIG. 4 ) of about one quarter of the wavelength with a short-circuited end. Therefore, the cavity-backed slot antenna may include impedance characteristics similar to those of a parallel resonator. 
     A Q factor is a sharpness degree of a resonance of a tuning circuit. That is, the Q factor may be a multiple of a sum of voltages at both ends of an inductor or a capacitor in a serial resonator, or a multiple of a current flowing through the ends in a parallel resonator. A Q factor of a parallel resonator (e.g., the high-efficiency wide-bandwidth antenna  100 ) may be determined based on the example of Equation 1:
 
 Q=ω   0   CR   (1)
 
     In Equation 1, Q denotes the Q factor, ω 0  denotes a frequency at a time of a resonance of the parallel resonator, C denotes a capacitance of a capacitor in the parallel resonator, and R denotes a resistance of a resistor in the parallel resonator. 
     A bandwidth BW of the parallel resonator may be determined based on the example of Equation 2:
 
 BW= 1/ Q= 1/ω 0   CR   (2)
 
     Thus, since the capacitance C and the bandwidth BW are reciprocal values of each other, the bandwidth BW is increased as the capacitance C is reduced. 
     Referring again to  FIG. 3 , when the portion of the dielectric substrate  110  that is under and aligned with the slot portion  130  is removed, a permittivity of the slot portion  130  is reduced. That is, when the cavity portion  140  is formed, the air fills in the cavity portion  140 . A permittivity ∈ 0  of the air is lower than a permittivity of the dielectric substrate  110 . Accordingly, the permittivity of the slot portion  130  is reduced when the air fills the cavity portion  140  compared to when the dielectric substrate  110  fills the cavity portion  140 . Therefore, the capacitance C of the high-efficiency wide-bandwidth antenna  100  is reduced. 
     Due to the reduction in the capacitance C, the Q factor Q of the high-efficiency wide-bandwidth antenna  100  is reduced. As a result, the bandwidth BW of the high-efficiency wide-bandwidth antenna  100  is increased. 
     In addition, a strong electric field E is generated in the slot portion  130 . When the high-efficiency wide-bandwidth antenna  100  is used, a dielectric loss occurring at the dielectric substrate  110  is reduced, thereby increasing a radiation efficiency of the high-efficiency wide-bandwidth antenna  100 . 
     By including the cavity portion  140 , the high-efficiency wide-bandwidth antenna  100  includes the low capacitance C so that the wide bandwidth is achieved. The resonance frequency ω 0  may be determined based on the example of Equation 3:
 
ω 0 =1/( LC )0.5  (3)
 
     In Equation 3, L denotes an inductance of an inductor in the parallel resonator. The capacitance C and the inductance L are inversely proportional to each other. That is, in order to constantly maintain the resonance frequency ω 0 , the inductance L is increased by as much as the capacitance C is reduced. The inductance L is increased by increasing the length of the slot portion  130 . 
     Referring again to  FIG. 1 , the slot portion  130  includes a first slot  132  extending from a center of the high-efficiency wide-bandwidth antenna  100  to opposite outer sides of the high-efficiency wide-bandwidth antenna  100  in a symmetrical shape, and second slots  134  extending from both respective ends of the first slot  132 . Therefore, the slot portion  130  includes an H shape. That is, the length of the slot portion  130  is increased by as much as the second slots  132  formed at the respective ends of the first slot  132 . Thus, the inductance L of the high-efficiency wide-bandwidth antenna  100  is increased, thereby compensating for the reduced capacitance C of the high-efficiency wide-bandwidth antenna  100 . 
       FIG. 5  is a plan view illustrating an example of the high-efficiency wide-bandwidth antenna  100  of  FIG. 1  that includes a meandering slot portion  136 . Referring to  FIG. 5 , the meandering slot portion  136  extends from the center of the high-efficiency wide-bandwidth antenna  100  to the opposite outer sides of the high-efficiency wide-bandwidth antenna  100  in a symmetrical shape. 
     The meandering slot portion  136  includes a length that is increased from the length of the slot portion  130  of  FIGS. 1 through 3 . Accordingly, the inductance L of the high-efficiency wide-bandwidth antenna  100  is increased, thereby compensating for the reduction in the capacitance C of the high-efficiency wide-bandwidth antenna  100 . 
     Alternatively, a slot portion of the high-efficiency wide-bandwidth antenna  100  may extend symmetrically from the center to the opposite outer sides in a zigzag shape, a wave shape, and/or a step shape. Although the slot portions  130  and  136  of  FIGS. 1 through 3 and 5  include the H shape and the meandering shape, respectively, the shape of the slot portion is not limited thereto. Therefore, any other shape is applicable as far as the shape increases a length of the slot portion, and increases the inductance L to compensate for the reduction in the capacitance C. 
       FIG. 6  is a perspective view illustrating another example of a high-efficiency wide-bandwidth antenna  200 . Referring to  FIG. 6 , the high-efficiency wide-bandwidth antenna  200  includes a dielectric substrate  210 , a conductive substrate  220 , a slot portion  230 , and a hole portion  240 . 
     The conductive substrate  220  is disposed on an upper surface of the dielectric substrate  210 . The slot portion  230  is formed in the conductive substrate  220  and on the upper surface of the dielectric substrate  210 . 
     A hole portion  240  is formed in the dielectric substrate  210  and under the slot portion  230 , and is filled with air. The hole portion  240  is formed by removing a portion of the dielectric substrate  210  that corresponds to (e.g., is under and aligned with) the slot portion  230 . In contrast to the high-efficiency wide-bandwidth antenna  100 , the high-efficiency wide-bandwidth antenna  200  does not include a dedicated conductive substrate disposed below the dielectric substrate  210  and that includes a back surface of the high-efficiency wide-bandwidth antenna  100 . 
     As the portion of the dielectric substrate  210  is removed and filled with air, a permittivity of the slot portion  230  is reduced, and therefore, a capacitance of the high-efficiency wide-bandwidth antenna  200  is reduced. A bandwidth of the high-efficiency wide-bandwidth antenna  200  is increased due to the reduction in the capacitance. 
     In addition, a strong electric field is generated in the slot portion  230 . When the high-efficiency wide-bandwidth antenna  200  is used, a dielectric loss occurring at the dielectric substrate  210  is reduced, thereby increasing a radiation efficiency of the high-efficiency wide-bandwidth antenna  200 . 
     Referring to  FIG. 6 , the hole portion  240  is a via formed through the upper surface of the dielectric substrate  210  and a lower surface of the dielectric substrate  210 . Alternatively, the hole portion  240  may be a cavity (e.g., a trench) formed through the upper surface of the dielectric substrate  210  and partially into the dielectric substrate  210 . 
     The slot portion  230  may include a meandering shape or an H shape to increase a length of the slot portion  230 , thereby increasing an inductance of the high-efficiency wide-bandwidth antenna  200  that corresponds to the reduced capacitance. 
     An experiment has been performed to compare a bandwidth and a radiation efficiency between a general cavity-backed slot antenna and the high-efficiency wide-bandwidth antenna  100  or  200  of  FIGS. 1 through 6 . Results of the experiment are shown below. 
     The experiment has been performed on a presumption that each antenna is placed on a human body, and that a model of the human body includes a permittivity ∈ r  of about 35.15, a conductivity σ of about 1.16 siemens per meter (S/m), and a size of about 100×100×30 millimeters (mm) A width of a slot portion of each antenna has been set to about 1 mm Three different types RT 6010, RT 5800, and FR-4 of a substrate of each antenna has been used. Three different heights of each antenna, that is, 1 mm, 2 mm, and 3 mm, have been applied. Under the aforementioned conditions, the bandwidth and the radiation efficiency have been measured. 
     Experimental Example 1 
     In experimental example 1, a substrate RT 5880 has been used, of which a permittivity is 2.2 and a loss tangent is 0.0009. Results of the experimental example 1 are shown below: 
     
       
         
           
               
               
               
               
               
            
               
                   
                   
               
               
                   
                 Bandwidth(MHz) 
                   
                 Rad. Eff. (%) 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Not applied 
                 applied 
                 Not applied 
                 applied 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 mm 
                 26.6 
                 29 
                 75.5 
                 76.3 
               
               
                 2 mm 
                 38.9 
                 48.8 
                 81.8 
                 82.6 
               
               
                 3 mm 
                 50.6 
                 62.9 
                 84 
                 84.3| 
               
               
                   
               
            
           
         
       
     
     According to the results of experimental example 1, comparing the general cavity-backed slot antenna (not applied) with the high-efficiency wide-bandwidth antenna (applied) at the various heights of the antennas, the bandwidth and the radiation efficiency are both increased in the high-efficiency wide-bandwidth antenna irrespective of the heights of the antennas. 
     Experimental Example 2 
     In experimental example 2, a substrate RT 6010 has been used, of which a permittivity is 10.2 and a loss tangent is 0.0023. Results of the experimental example 2 are shown below: 
     
       
         
           
               
               
               
               
               
            
               
                   
                   
               
               
                   
                 Bandwidth(MHz) 
                   
                 Rad. Eff. (%) 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Not applied 
                 applied 
                 Not applied 
                 applied 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 mm 
                 14.4 
                 16.5 
                 38 
                 38.4 
               
               
                 2 mm 
                 16.5 
                 24.2 
                 46.4 
                 49.5 
               
               
                 3 mm 
                 18.8 
                 28 
                 51.6 
                 54.5 
               
               
                   
               
            
           
         
       
     
     According to the results of experimental example 2 comparing the general cavity-backed slot antenna (not applied) with the high-efficiency wide-bandwidth antenna (applied) at the various heights of the antennas, the bandwidth and the radiation efficiency are both increased in the high-efficiency wide-bandwidth antenna irrespective of the heights of the antennas. 
     Experimental Example 3 
     In experimental example 3, a substrate FR-4 has been used, of which a permittivity is 10.2 and a loss tangent is 0.0023. Results of the experimental example 3 are shown below: 
     
       
         
           
               
               
               
               
               
            
               
                   
                   
               
               
                   
                 Bandwidth(MHz) 
                   
                 Rad. Eff. (%) 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Not applied 
                 applied 
                 Not applied 
                 applied 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 mm 
                 35.2 
                 37 
                 31.5 
                 34.3 
               
               
                 2 mm 
                 39.1 
                 48.5 
                 41.4 
                 48.2 
               
               
                 3 mm 
                 46.4 
                 56.7 
                 47.6 
                 55.4 
               
               
                   
               
            
           
         
       
     
     According to the results of experimental example 3, comparing the general cavity-backed slot antenna (not applied) with the high-efficiency wide-bandwidth antenna (applied) at the various heights of the antennas, the bandwidth and the radiation efficiency are both increased in the high-efficiency wide-bandwidth antenna irrespective of the heights of the antennas. 
     As can be appreciated from the experimental examples, both the bandwidth and the radiation efficiency are increased in the high-efficiency wide-bandwidth antenna. In addition, the height and a size (e.g., of a cavity) of the high-efficiency wide-bandwidth antenna may be reduced. 
     According to the teachings above, there is provided an antenna that achieves a high radiation efficiency and a wide bandwidth. To achieve such characteristics, a dielectric of the antenna is removed from below a slot to form a cavity, and accordingly, the antenna includes a low height. In addition, the dielectric may include a high-permittivity substrate to reduce a size of the cavity. 
     A number of examples have been described above. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.