Patent Publication Number: US-2022239002-A1

Title: Antenna apparatus and feed network thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0010209 filed in the Korean Intellectual Property Office on Jan. 25, 2021, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present disclosure relates to an antenna apparatus and a feed network thereof. 
     (b) Description of the Related Art 
     Antenna apparatuses generating dual-orthogonal circular polarization may be implemented in various forms. A phase difference of a dual-orthogonal component is generated in a single radiation element through an artificial transformation (e.g., a slot is placed at the center) to generate dual circular polarization. However, the antenna apparatus having such a structure has a low antenna gain, and a narrow band property in which an input matching and axial ratio property is within approximately 3%. In addition, there is an antenna apparatus structure constituted by the single radiation element and a 90° hybrid combiner. The structure performs dual-orthogonal feed by using a circuit operation property of the 90° hybrid combiner to generate the dual circular polarization. Such a structure also has the low antenna gain and operates in a band in which the input matching and axial ratio property is approximately 10%. 
     Meanwhile, there is an antenna apparatus generating single circular polarization by using four radiation elements. The antenna apparatus generating the circular polarization by using four radiation elements may increase the antenna gain through adjustment of an arrangement interval among four radiation elements, and improve the axial ratio property in a wide observation angle area. However, different feed networks are required for generating the dual-orthogonal circular polarization through the antenna apparatus generating the single circular polarization. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     At least one exemplary embodiment among exemplary embodiments may provide an antenna apparatus capable of generating dual-orthogonal polarization by a single feed network 
     An exemplary embodiment of the present invention may provide an antenna apparatus. The antenna apparatus may include: a feed network including a plurality of first internal transmission lines arranged in a cross form and a plurality of second internal transmission lines arranged in a ring form around the plurality of first internal transmission lines; and a plurality of radiation elements positioned around the feed network and radiating signals fed by the feed network. 
     The number of plurality of first internal transmission lines may be at least 4 and the number of plurality of second internal transmission lines may be at least 8, and the number of input ports of the feed network may be at least 2 and the number of output ports of the feed network may be at least 4. 
     Each internal transmission line included in the plurality of first internal transmission lines and the plurality of second internal transmission lines may have a first property impedance and a predetermined electrical length. 
     The feed network may further include an input transmission line connected to the input port and an output transmission line connected to the output port. 
     The input transmission line and the output transmission line may have a second property impedance, and the first property impedance may be twice larger than the second property impedance, and the predetermined electrical length may be 90°. 
     A first input signal corresponding to a right-handed circular polarization may be input into a first input port of the at least two input ports, and a second input signal corresponding to a left-handed circular polarization may be input into a second input port of the at least two input ports. 
     At least one output port of the at least four output ports may be positioned between the first input port and the second input port. 
     The number of plurality of radiation elements may be at least 4, and the antenna apparatus may further include at least four transmission lines connected to each of the at least four output ports and each of the at least four radiation elements. 
     Two transmission lines of the at least four transmission lines may be transmission lines having a phase delay of 0° and two remaining transmission lines may be transmission lines having a phase delay of 90°. 
     The feed network may be formed on a first printed circuit board, the plurality of radiation elements may be formed on a second printed circuit board, and the second printed circuit board may be formed to be erected perpendicular to the first printed circuit board. 
     Another exemplary embodiment of the present invention may provide a feed network providing feed signals to a plurality of radiation elements. The feed network may include: a first input port into which a first signal is input; a second input port into which a second signal is input; a plurality of first internal transmission lines arranged in a cross form; a plurality of second internal transmission lines arranged around the plurality of first internal transmission lines; and a plurality of output ports providing feed signals to the plurality of radiation elements, respectively. 
     In the plurality of first internal transmission lines, an internal transmission line corresponding to one line and an internal transmission line corresponding to the remaining line constituting the cross form may not be connected to each other, but may cross. 
     The number of plurality of first internal transmission line may be at least 4 and the number of plurality of second internal transmission lines may be at least 8, the number of plurality of output ports may be at least 4, and the number of plurality of radiation elements may be at least 4. 
     The feed network may further include: a first input transmission line connected to the first input port; a second input transmission line connected to the second input port; and a plurality of output transmission lines connected to the plurality of output ports, respectively. 
     Each internal transmission line included in the plurality of first internal transmission lines and the plurality of second internal transmission lines may have a first property impedance and a predetermined electrical length, and the first input transmission line, the second input transmission line, and each of the plurality of output transmission lines may have a second property impedance larger than the first property impedance. 
     The first property impedance may be twice larger than the second property impedance, and the predetermined electrical length may be 90°. 
     The first signal may be a signal corresponding to a right-handed circular polarization, and the second signal may be a signal corresponding to a left-handed circular polarization. 
     At least one output port of the plurality of output ports may be positioned between the first input port and the second input port. 
     According to at least an exemplary embodiment of the exemplary embodiments, a dual-orthogonal circular polarization can be generated through a single feed network. 
     According to at least an exemplary embodiment of the exemplary embodiments, a dual-orthogonal circular polarization having a high antenna gain and an axial ratio property can be generated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an antenna apparatus according to an exemplary embodiment. 
         FIG. 2  is a block diagram illustrating an internal configuration of a feed network according to an exemplary embodiment. 
         FIGS. 3A to 3C  are diagrams illustrating an implementation example of an antenna apparatus according to an exemplary embodiment. 
         FIG. 4  is a graph showing a simulation result for an input return loss and inter-port isolation property of an antenna system according to an exemplary embodiment. 
         FIGS. 5A and 5B  are graphs showing a simulation result for a 2D radiation pattern property of an antenna system according to an exemplary embodiment. 
         FIGS. 6A and 6B  are graphs showing a simulation result for an axial ratio property of an antenna system according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present invention will be described in detail so as to be easily implemented by those skilled in the art, with reference to the accompanying drawings. The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. Further, it is to be understood that the accompanying drawings are just used for easily understanding the exemplary embodiments disclosed in this specification and a technical spirit disclosed in this specification is not limited by the accompanying drawings and all changes, equivalents, or substitutes included in the spirit and the technical scope of the present invention are included. 
     Terms including an ordinary number, such as first and second, are used for describing various elements, but the elements are not limited by the terms. The terms are used only to discriminate one element from another element. 
     It should be understood that, when it is described that a component is “connected to” or “accesses” another component, the component may be directly connected to or access the other component or a third component may be present therebetween. In contrast, when it is described that a component is “directly connected to” or “directly accesses” another component, it is understood that no element is present between the element and another element. 
     Through the specification, it should be understood that the term “include” or “have” indicates that a feature, a number, a step, an operation, a component, a part or the combination thereof described in the specification is present, but does not exclude a possibility of presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof, in advance. Accordingly, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
       FIG. 1  is a block diagram illustrating an antenna apparatus according to an exemplary embodiment. 
     As illustrated in  FIG. 1 , an antenna apparatus  100  according to an exemplary embodiment may include first to fourth radiation elements  100   a  to  100   d , first to fourth transmission lines  110   a  to  100   d , and a feed network  200 . 
     The feed network  200  may include two input ports IN 1  and IN 2 , and four output ports OUT 1 , OUT 2 , OUT 3 , and OUT 4 . A first input signal corresponding to right-handed circular polarization may be input into a first input port IN 1 , and a second input signal corresponding to left-handed circular polarization may be input into a second input port IN 2 . Here, a first input signal S M1  input into the first input port IN 1  and a second input signal S M2  input into the second input port IN 2  are orthogonal and isolated from each other. As illustrated in  FIG. 1 , the first output port OUT 1  may be positioned between the first input port IN 1  and the second input port IN 2 . As one example the ports of the feed network  200  may be arranged clockwise in an order of the first input port IN 1 , the first output port OUT 1 , the second input port IN 2 , the second output port OUT 2 , the third output port OUT 3 , and the fourth output port OUT 4 . The feed network  200  having such a structure may be a plane type 6-port feed network. A detailed internal configuration of the feed network  200  will be described in detail in  FIG. 2  below. 
     The first to fourth radiation elements  100   a  to  100   d  may be radiation elements generating linear polarization. The first to fourth radiation elements  100   a  to  100   d  may be positioned around (outside) the feed network  200 . The first radiation element  100   a  may be positioned on a first lateral surface of the feed network  200  and the second radiation element  100   b  may be positioned on a second lateral surface of the feed network  200 . In addition, the third radiation element  100   c  may be positioned on a third lateral surface of the feed network  200  and the fourth radiation element  100   d  may be positioned on a fourth lateral surface of the feed network  200 . That is, the first to fourth radiation elements  100   a  to  100   d  may be positioned in order clockwise based on the first input port IN 1 . Each of the first to fourth radiation elements  100   a  to  100   d  may be implemented as a dipole radiation element. 
     The first transmission line  110   a  may be connected between the first output port OUT 1  and the first radiation element  100   a  of the feed network  200 , and the second transmission line  110   b  may be connected between the second output port OUT 2  and the second radiation element  100   b  of the feed network  200 . In addition, the third transmission line  110   c  may be connected between the third output port OUT 3  and the third radiation element  100   c  of the feed network  200 , and the fourth transmission line  110   d  may be connected between the fourth output port OUT 4  and the fourth radiation element  100   d  of the feed network  200 . Each of the first transmission line  110   a  and the third transmission line  110   c  may be a transmission line having a phase delay of 0°. In addition, each of the second transmission line  110   b  and the fourth transmission line  110   d  may be a transmission line having a phase delay of 90°. 
     Signals radiated from the first to fourth radiation elements  100   a  to  100   d  to a free space are spatially combined with each other, and therefore, right-handed circular polarization (RHCP) and left-handed circular polarization (LHCP) may be generated. That is, the first to fourth radiation elements  100   a  to  100   d  may generate the right-handed circular polarization (RHCP) in response to the first input signal S M1  input into the first input port IN 1  of the feed network  200 . In addition, the first to fourth radiation elements  100   a  to  100   d  may generate the left-handed circular polarization (LHCP) in response to the second input signal S M2  input into the second input port IN 2  of the feed network  200 . 
       FIG. 2  is a block diagram illustrating an internal configuration of a feed network  200  according to an exemplary embodiment. 
     As illustrated in  FIG. 2 , a feed network  200  according to an exemplary embodiment may include two input ports IN 1  and IN 2 , and four output ports OUT 1 , OUT 2 , OUT 3 , and OUT 4 . The first input port IN 1  and the second input port IN 2  may have a high isolation property from each other, and the first to fourth output ports OUT 1 , OUT 2 , OUT 3 , and OUT 4  may also have the high isolation property from each other. 
     The feed network  200  according to an exemplary embodiment may include first and second input transmission lines  210 _ 1  and  210 _ 2 , first to fourth output transmission lines  211   a  to  211   d , and a plurality of internal transmission lines  220 . 
     One end of the first input transmission line  210 _ 1  may correspond to the first input port IN 1  and one end of the second input transmission line  210 _ 2  may correspond to the second input port IN 2 . Ends of the respective first to fourth output transmission lines  211   a  to  211   d  may correspond to the first to fourth output ports OUT 1  to OUT 4 , respectively. Each of the first and second input transmission lines  210 _ 1  and  210 _ 2  may have a characteristic impedance Z 0  and an electrical length θ 0 . In addition, each of the first to fourth output transmission lines  211   a  to  211   d  may also have the characteristic impedance Z 0  and the electrical length θ 0 . 
     A plurality of internal transmission lines  220  may include first to twelfth internal transmission lines  220 _ 1  to  220 _ 12 . Each of the first to twelfth internal transmission lines  220 _ 1  to  220 _ 12  may also have a property impedance Z 1  and an electrical length 90°. Here, the characteristic impedances Z 1  and Z 0  may satisfy a relationship of Equation 1 below. 
         Z   1 =2* Z   0   (Equation 1)
 
     That is, characteristic impedances of the internal transmission lines  220 _ 1  to  220 _ 12  may have values which are twice larger than the characteristic impedances of the input and output transmission lines  210 _ 1  and  210 _ 2 , and  211   a  to  211   d . When the impedances of the input and output transmission lines are 50 ohms (Ω), the impedances of the internal transmission lines are 10 ohms (Ω). 
     The ninth to twelfth internal transmission lines  220 _ 9  to  220 _ 12  may be arranged in a cross form based on the center of the feed network  200 . In addition, the first to eighth internal transmission lines  220 _ 1  to  220 _ 8  may be arranged in a ring form around the ninth to twelfth internal transmission lines  220 _ 9  to  220 _ 12 . 
     In  FIG. 2 , a point where at least one transmission line of the input transmission lines  210 _ 1  and  210 _ 2  and the output transmission lines  211   a  to  211   d  and at least one transmission line of the internal transmission lines  220 _ 1  to  220 _ 12  are connected to each other is represented as contacts N 1  to N 8 . The first input transmission line  210 _ 1 , the first internal transmission line  220 _ 1 , the eighth internal transmission line  220 _ 8 , and the ninth internal transmission line  220 _ 9  may be connected to each other through the contact N 1 . The first output transmission line  211   a , the first internal transmission line  220 _ 1 , and the second internal transmission line  220 _ 2  may be connected to each other through the contact N 2 . The second input transmission line  210 _ 2 , the second internal transmission line  220 _ 2 , the third internal transmission line  220 _ 3 , and the eleventh internal transmission line  220 _ 11  may be connected to each other through the contact N 3 . The second output transmission line  211   b , the third internal transmission line  220 _ 3 , and the fourth internal transmission line  220 _ 4  may be connected to each other through the contact N 4 . The fourth internal transmission line  220 _ 4 , the fifth internal transmission line  220 _ 5 , and the tenth internal transmission line  220 _ 10  may be connected to each other through the contact N 5 . The third output transmission line  211   c , the fifth internal transmission line  220 _ 5 , and the sixth internal transmission line  220 _ 6  may be connected to each other through the contact N 6 . The sixth internal transmission line  220 _ 6 , the seventh internal transmission line  220 _ 7 , and the twelfth internal transmission line  220 _ 12  may be connected to each other through the contact N 7 . The fourth output transmission line  211   d , the seventh internal transmission line  220 _ 7 , and the eighth internal transmission line  220 _ 8  may be connected to each other through the contact N 8 . Further, the ninth internal transmission line  220 _ 9  and the tenth internal transmission line  220 _ 10  may be connected to each other, and the eleventh internal transmission line  220 _ 11  and the twelfth internal transmission line  220 _ 12  may be connected to each other. Contrary to this, the ninth and tenth internal transmission lines  220 _ 9  and  220 _ 10  and the eleventh and twelfth internal transmission lines  220 _ 11  and  220 _ 12  are cross while not being connected to each other (that is, connected to each other by RF crossover). Such a cross area is represented as A in  FIG. 2 . 
     In the feed network  200  having such a configuration and such a connection relationship, signals output from the first to fourth output ports OUT 1  to OUT 4  may have the same amplitude property and a phase difference of 180° from each other. A relationship of the signals in the case of the first input signal S M1  and the second input signal S M2  is as follows. 
     First, a case where the first input signal S M1  is input into the first input port IN 1  will be described. As illustrated in  FIG. 2 , the signal output from the first output port OUT 1  and the signal output from the fourth output port OUT 4  have the same magnitude as each other and also have the same phase difference. In addition, the signal output from the second output port OUT 2  and the signal output from the third output port OUT 3  have the same magnitude as each other and also have the same phase difference. Contrary to this, the signal output from the first output port OUT 1  and the signal output from the second output port OUT 2  have the same magnitude as each other, but have a phase difference of 180°. 
     Next, a case where the second input signal S M2  is input into the second input port IN 2  will be described. As illustrated in  FIG. 2 , the signal output from the first output port OUT 1  and the signal output from the second output port OUT 2  have the same magnitude as each other and also have the same phase difference. In addition, the signal output from the third output port OUT 2  and the signal output from the fourth output port OUT 4  have the same magnitude as each other and also have the same phase difference. Contrary to this, the signal output from the first output port OUT 1  and the signal output from the third output port OUT 3  have the same magnitude as each other, but have the phase difference of 180°. 
     Relationships of the signals output from the first to fourth output ports OUT 1  to OUT 4  are organized in response to the first input signal S M1  and the second input signal S M2  are shown in Table 1 below. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Input port 
                 OUT1 
                 OUT2 
                 OUT3 
                 OUT4 
               
               
                   
               
             
            
               
                 IN1(S M1 ) 
                 0.25S M1 ∠0° 
                 0.25S M1 ∠−180° 
                 0.25S M1 ∠−180° 
                 0.25S M1 ∠0°    
               
               
                 IN2(S M2 ) 
                 0.25S M2 ∠0° 
                 0.25S M2 ∠0°    
                 0.25S M2 ∠−180° 
                 0.25S M2 ∠−180° 
               
               
                   
               
            
           
         
       
     
     Meanwhile, as described in  FIG. 1  above, each of the first transmission line  110   a  and the third transmission line  110   c  may have a phase delay of 0° and each of the second transmission line  110   b  and the fourth transmission line  110   d  may have a phase delay of 90°. The signals input into the radiation elements  100   a  to  100   d  are represented as arrows in  FIG. 1  by considering the relationship in Table 1 above and the properties of the first to fourth transmission lines  110   a  to  110   d  of the feed network  200 . 
     Referring to  FIG. 1 , when the first input signal S M1  is input into the first input port IN 1 , signals having the same amplitude and the phase delay of 90° from each other are fed to the fourth, third, second, and first radiation elements  100   d ,  100   c ,  100   b , and  100   d , respectively. That is, the signals having the phase delay of 90° counterclockwise are fed to the fourth, third, second, and first radiation elements  100   d ,  100   c ,  100   b , and  100   d , respectively. As a result, the first to fourth radiation elements  100   a  to  100   d  generate the radiation signal of the right-handed circular polarization in the free space. 
     Referring to  FIG. 1 , when the second input signal S M2  is input into the second input port IN 2 , the signals having the same amplitude and the phase delay of 90° from each other are fed to the second, third, fourth, and first radiation elements  100   b ,  100   c ,  100   d , and  100   a , respectively. That is, the signals having the phase delay of 90° clockwise are fed to the second, third, fourth, and first radiation elements  100   b ,  100   c ,  100   d , and  100   a , respectively. As a result, the first to fourth radiation elements  100   a  to  100   d  generates the radiation signal of the left-handed circular polarization in the free space. 
     Since the arrangement interval of the first to fourth radiation elements  100   a  to  100   d  generating the linear polarization is related to a gain property of an entire antenna apparatus  1000 , mutual combination properties among elements, and a size (or volume) of the entire antenna apparatus  1000 , the arrangement interval may be optimally determined according to a required specification of the antenna apparatus  1000 . 
       FIGS. 3A to 3C  are diagrams illustrating an implementation example of an antenna apparatus according to an exemplary embodiment.  FIG. 3A  is a plan view of an antenna apparatus  1000  according to an exemplary embodiment and  FIG. 3B  is a perspective view of an antenna apparatus  1000  according to an exemplary embodiment. In addition,  FIG. 3C  illustrates that a substrate where the radiation elements  100   a  to  100   d  are formed is removed in  FIG. 3B . 
     Referring to  FIG. 3A , the feed network  200  and the first to fourth transmission lines  110   a  to  110   d  may be formed on a substrate  300 . The substrate  300  may be a printed circuit board (PCB) and the feed network  200  to the first to fourth transmission lines  110   a  to  110   d  may be printed on the printed circuit board  300 . Meanwhile, the feeding to the first to fourth radiation elements  100   a  to  100   d  may form a Balun circuit configured by a microstrip-to-strip line. 
     Referring to  FIG. 3B , the first to fourth radiation elements  100   a  to  100   d  may be formed on substrates  400   a  to  400   d , respectively. The substrates  400   a  to  400   d  may also be the printed circuit boards, and the first to fourth radiation elements  100   a  to  100   d  may be printed on the printed circuit boards, respectively. That is, the first to fourth radiation elements  100   a  to  100   d  may be printed dipole elements. Meanwhile, referring to  FIGS. 3B and 3C , the first to fourth radiation elements  100   a  to  100   d  may be printed on both surfaces of the printed circuit boards, respectively. Referring to  FIG. 3B , a substrate  400   a  may be formed by being erected perpendicular to the substrate  300  on a first lateral surface of the feed network  200 , and a substrate  400   b  may be formed by being erected perpendicularly to the substrate  300  on a second lateral surface of the feed network  200 . In addition, a substrate  400   c  may be formed by being erected perpendicular to the substrate  300  on a third lateral surface of the feed network  200 , and a substrate  400   d  may be formed by being erected perpendicularly to the substrate  300  on a fourth lateral surface of the feed network  200 . That is, the substrate  300  and the substrates  400   a  to  400   d  may form a rectangular parallelepiped structure. The first to fourth radiation elements  100   a  to  100   d  may provide maximum radiation properties in vertical directions of the substrates  400   a  to  400   d , respectively. As a result, the antenna apparatus  1000  having the structures of  FIGS. 3A to 3C  may provide a high antenna gain compared with a limited space (antenna size). Meanwhile, in order to provide additional antenna directivity or gain, parasitic elements of a multi-layer conduct arrangement structure may be attached to upper portions of the first to fourth radiation elements  100   a  to  100   d.    
     Referring to  FIGS. 3B and 3C , each of the first to fourth radiation elements  100   a  to  100   d  may be disposed while rotating at 90° around the feed network  200 . In addition, as described in  FIGS. 1 and 2  above, after the first input signal S M1  or the second input signal S M2  are distributed with the same amplitude through the feed network  200 , the phase delay occurs due to the first to fourth transmission lines  110   a  to  110   d . As a result, the signals radiated by the first to fourth radiation elements  100   a  to  100   d  generate orthogonal circular polarization. The antenna apparatus  1000  according to an exemplary embodiment may provide an excellent axial ratio property by referring to a simulation result described below. 
     The substrate  300  and the substrates  400   a  to  400   d  may be implemented by using a TRF-45 substrate (a dielectric constant Er=4.5, a dielectric thickness H=0.61 mm, an operating thickness T=0.018, and a loss tangent tan δ=0.003@1.9 GHz) of Taconic. Operating bands of the first to fourth radiation elements  100   a  to  100   d  may be set as a GPS band. The feed network  200  and the first to fourth transmission lines  110   a  to  110   d  may be implemented as a non-combination meander line in order to reduce a circuit size. In an area A where the ninth and tenth internal transmission lines  220 _ 9  and  220 _ 10  and the eleventh and twelfth internal transmission lines  220 _ 11  and  220 _ 12  are not connected to each other, but cross, an operating frequency is low and a wavelength becomes thus larger, and as a result, the area A may be implemented as a short wire line of 1 mm (0.005λ 0 ). Meanwhile, referring to  FIGS. 3B and 3C , the first to fourth radiation elements  100   a  to  100   d  and the first to fourth transmission lines  110   a  to  110   d  may be vertically connected to each other, and a 1:1 impedance Balun circuit (50Ω unbalance line⇒50Ω balance line) may be used for inputs of the first to fourth radiation elements  100   a  to  100   d . A vertical and horizontal interval of the radiation elements  100   a  to  100   d  may be 76.6 mm (0.4λ 0 ) and a total size of the antenna apparatus  100  may be 86 (W)×86 (L)×40 (H) mm or less. 
       FIG. 4  is a graph showing a simulation result for input return loss and inter-port separation characteristics of an antenna system according to an exemplary embodiment. 
     Referring to  FIG. 4 , input return loss (S1,1 parameter) shows an excellent property of 19.6 dB or more at an operating frequency band (1575.42±12 MHz). In addition, an inter-port isolation property (S2,1 or S1,2) shows an excellent property of 21.7 dB or more at the operating frequency band (1575.42±12 MHz). Since a reflection property by input port mismatch of each radiation element is delivered to an orthogonal port, a frequency band property of the inter-port isolation property largely depends on a frequency band property of a unit radiation element. 
       FIGS. 5A and 5B  are graphs showing a simulation result for 2D radiation pattern characteristics of an antenna system according to an exemplary embodiment. In addition,  FIGS. 6A and 6B  are graphs showing a simulation result for an axial ratio property of an antenna system according to an exemplary embodiment. 
       FIGS. 5A and 6A  illustrate a simulation result corresponding to the left-handed circular polarization and  FIGS. 5B and 6B  illustrate a simulation result for the right-handed circular polarization. Meanwhile, in the simulations of  FIGS. 5A, 5B, 6A, and 6B , a center frequency is set to 1.57542 GHz. 
     Referring to  FIGS. 5A and 5B , the antenna gain at the center frequency (1.57542 GHz) shows 8.2 dBi or more in a forward direction. Referring to  FIGS. 6A and 6B , the axial ratio property of the dual-orthogonal circular polarization is 0.43 dB or less in the forward direction and shows an excellent property as 1.8 dB within a beam width of 3 dB. The results are results shown by the feed network structure and the radiation elements according to an exemplary embodiment, and are results shown when main polarization and cross polarization properties are mutually reinforced and offset. 
     In Table 2 below, the main radiation property parameter of the antenna in the simulation is organized. Here, the radiation property parameter may include the antenna gain, a beam width of 3 dB, and the axial ratio property. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                 Axial ratio 
               
               
                   
                   
                   
                   
                 property 
               
               
                   
                   
                 Antenna 
                 3 dB beam 
                 @Forward 
               
               
                 Frequency/Item 
                 Polarization 
                 gain 
                 width [0°/90°] 
                 direction 
               
               
                   
               
             
            
               
                 1.56342 GHz 
                 RHCP 
                 8.20 dBi 
                 70.7°/70.6° 
                 0.22 dB 
               
               
                   
                 LHCP 
                 8.22 dBi 
                 66.8°/66.8° 
                 0.31 dB 
               
               
                 1.57542 GHz 
                 RHCP 
                 8.23 dBi 
                 70.7°/70.6° 
                 0.30 dB 
               
               
                   
                 LHCP 
                 8.28 dBi 
                 66.9°/66.9° 
                 0.30 dB 
               
               
                 1.58742 GHz 
                 RHCP 
                 8.22 dBi 
                 70.7°/70.5° 
                 0.43 dB 
               
               
                   
                 LHCP 
                 8.30 dBi 
                 67.1°/67.0° 
                 0.36 dB 
               
               
                   
               
            
           
         
       
     
     As such, the antenna apparatus according to an exemplary embodiment may generate independent dual-orthogonal circular polarization, and provide a high antenna gain and a high axial ratio property. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.