Abstract:
Disclosed is an antenna bandwidth expander capable of improving transmission/reception performance of a wireless communication device by expanding a bandwidth of an antenna in which broadband frequency characteristics including various communication bands are necessary like an LTE smartphone. The antenna bandwidth expander may improve the transmission and reception performance of a terminal by easily and conveniently expanding a bandwidth of an antenna in first and second resonant frequency bands.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority benefit of Korean Patent Application No. 10-2015-0023812 filed on Feb. 17, 2015, and Korean Patent Application No. 10-2015-0146862 filed on Oct. 21, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to an antenna bandwidth expander installed between an antenna and an internal RF circuit, and more particularly, to a technology for applying the antenna bandwidth expander to a broadband communication system of which a frequency band is broadening to improve transmission/reception performance of a communication terminal. 
       BACKGROUND OF THE INVENTION 
       [0003]    Recently, according to commercialization of long term evolution (LTE) mobile communication terminals and various communication services such as the Internet of things, frequency bands required to be supported by one terminal are gradually increased and the antenna size becomes small due to a slim design of a product and employment of a high-capacity battery. 
         [0004]    Under such a situation, researches for developing antennas capable of realizing multi-bands and a broadband with a small size are being performed in various aspects of a design technique and manufacturing process methods, but these can&#39;t overcome the size limitation of the antenna. In particular, for an LTE communication terminal, in order to overcome the difficulty in realizing broadband antenna characteristics, frequency band switching using a tunable antenna module or an RF switch such as SPDT is applied thereto, but there are disadvantages in cost and complexity of circuit design. 
         [0005]    For example,  FIG. 1A  illustrates a method for controlling an LC value inside a TAM to tune antenna matching in real time by determining a traveling wave toward an antenna and a reflection wave from the antenna respectively through power detection and by digitally adjusting a DAC value in order to maintain a relative reflection amount smaller than a certain reference value (i.e. to manage on the basis of a voltage standing wave ratio (VSWR)). 
         [0006]      FIG. 1B  illustrates a structure for controlling grounding and feeding terminal positions of an antenna to switch it to a desired frequency. In the drawing, SW 1  and SW 2  denote switches, and M 1  and M 2  denote matching circuits. 
         [0007]    This structure uses a resonant frequency shift according to a difference between resonant lengths of an antenna when the SW 1  is connected and when the SW 2  is connected. 
         [0008]    According to a typical technique illustrated in  FIG. 1A , there is a limitation in that a software algorithm for optimizing performance is complicated, a manufacturing cost increases due to the application of the TAM, a complex control circuit is necessary for controlling the TAM, and it causes a lack of PCB mounting area. In addition, since highly lossy L and C are applied to broaden the tuning range, loss by the lumped elements grows. Furthermore, application of external DC power may cause a noise issue on the antenna. 
         [0009]    According to a typical technique illustrated in  FIG. 1B , a degree of frequency shift varies according to an adequate separation distance d between the grounding and feeding lines, and when a distance from the feeding terminal is out of a certain distance, an antenna matching characteristic becomes worse in a specific frequency band. Accordingly, when a large amount of frequency shift is necessary, a characteristic of an unselected frequency band according to on/off of the switch becomes degraded. In addition, since an antenna element and a DC power line are electrically connected, sensitivity of a received signal may be degraded by an influence of antenna noise due to the power line. 
       SUMMARY OF THE INVENTION 
       [0010]    An object of the present invention is to provide an antenna bandwidth expander capable of improving transmission/reception performance of a communication terminal by improving a troublesome limit of a narrow band characteristic of a small antenna and by applying it to a broadband communication system of which frequency band is getting broader. 
         [0011]    Another object of the present invention is to provide an antenna bandwidth expander of which a structure is simple and a manufacturing cost is cheap, and which does not occupy a large mounting area. 
         [0012]    Still another object of the present invention is to provide a method for replacing a switch-based circuit design, which requires a high cost and a complex design, by using an antenna bandwidth expander, and to secure technology for application of low-low LTE carrier aggregation (CA). 
         [0013]    According to an aspect of the present invention, there is provided an antenna bandwidth expander mounted between an RF system and an antenna to be electrically connected thereto in a circuit board. The antenna bandwidth expander includes: a first conduction terminal electrically connected to the antenna; a second conduction terminal electrically connected via the first conduction terminal and a first capacitor; a first coil electrically connected between the first and second conduction terminals; a third conduction terminal electrically connected to an output port of the RF system; a fourth conduction terminal electrically connected via the third conduction terminal and a second capacitor; a second coil electrically connected between the third and fourth conduction terminals; and third and fourth capacitors respectively disposed between the second and third conduction terminals and between the first and fourth conduction terminals, wherein the second and fourth capacitors respectively connected to the second coil in parallel and in serial to form a resonant circuit in a first frequency band that is a low frequency band, and the first and third capacitors respectively connected to the first coil in parallel and in serial to form a resonant circuit in a second frequency band that is a high frequency band, and wherein the first and second coils are wound in opposite directions to be magnetically coupled. 
         [0014]    According to another aspect of the present invention, there is provided an antenna bandwidth expander mounted between an RF system and an antenna to be electrically connected thereto in a circuit board. The antenna bandwidth expander includes: a ceramic body having first to fourth conduction terminals separately formed on a bottom surface and including therein a first coil electrically connected between the first and second conduction terminals and a second coil electrically connected between the third and fourth terminals; and first to fourth capacitors disposed between first to fourth conduction pads formed in correspondence to the first to fourth conduction terminals in the circuit board, wherein the first conduction terminal is electrically connected to the antenna, the third conduction terminal is electrically connected to an output port of the RF system, the second and fourth capacitors are respectively connected to the second coil in parallel and in serial to form a first resonant circuit in a first frequency band that is a low frequency band, and the first and third capacitors are respectively connected to the first coil in parallel and in serial to form a resonant circuit in a second frequency band that is a high frequency band, and wherein the first and second coils are wound in opposite directions to be magnetically coupled. 
         [0015]    The first coil may be positioned inside the second coil. 
         [0016]    Horizontal cross-sectional shapes of the first and second coils may be a circle or a polygon. 
         [0017]    The second and fourth conduction terminals may be electrically connected to a ground via an external inductor. 
         [0018]    According to still another aspect of the present invention, there is provided an antenna bandwidth expander including a first ceramic sheet having conduction terminals at four bottom corners and a ground terminal at a center; a second ceramic sheet having a first capacitor pattern formed thereon; a plurality of third ceramic sheets having the first capacitor pattern or a second capacitor pattern, and first and second coil patterns formed thereon; and a fourth ceramic sheet having the first capacitor pattern formed thereon, wherein the ceramic sheets are sequentially stacked, the first and second coil patterns are connected through via holes to form a coil and to be magnetically coupled, and the first and second capacitor patterns overlap to form a capacitor in the stacked state, and wherein the coil and the capacitor are electrically connected to the conduction terminal through a via hole. 
         [0019]    According to still another aspect of the present invention, there is provided an antenna bandwidth expander including: a first ceramic sheet having conduction terminals at four bottom corners and a ground terminal at a center; a second ceramic sheet having one connection pattern formed thereon; a plurality of ceramic sheets having first and second coil patterns formed thereon; and a fourth ceramic sheet having another connection pattern formed thereon, wherein the ceramic sheets are sequentially stacked and the first and second coil patterns are connected through respective via holes to form a coil and to be mutually magnetically coupled, and wherein the coil is electrically connected to the conduction terminal through the connection pattern and a via hole. 
         [0020]    The first and second coil patterns may be formed on different ceramic sheets. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The above objects and other advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0022]      FIGS. 1A and 1B  illustrate related arts; 
           [0023]      FIGS. 2A and 2B  illustrate an antenna bandwidth expander and respective layer structures thereof according to an embodiment of the present invention; 
           [0024]      FIGS. 3A, 3B and 3C  illustrate an internal connection structure of an antenna bandwidth expander according to an embodiment of the present invention.  FIG. 3A  illustrates a structure in which coil patterns influencing low and high frequency bands are joined and  FIG. 3B  illustrates a structure in which coil patterns influencing low and high frequency bands are separated, and  FIG. 3C  illustrates an alternative embodiment of coil pattern; 
           [0025]      FIG. 4  is an internal plan view of an antenna bandwidth expander according to an embodiment of the present invention; 
           [0026]      FIG. 5  is an equivalent circuit diagram of an antenna bandwidth expander according to an embodiment of the present invention; 
           [0027]      FIGS. 6A and 6B  illustrate magnetic field distributions at a first resonant frequency (925 MHz) and a second resonant frequency (1990 MHz); 
           [0028]      FIGS. 7A and 7B  are graphs of influences of return loss with respect to the sizes of coil  1  and coil  2 ; 
           [0029]      FIGS. 8A and 8B  are graphs of influences of return loss with respect to external inductors L 3  and L 4 ; 
           [0030]      FIG. 9  is a graph representing a return loss measured through inductance values of the external inductors L 3  and L 4 ; 
           [0031]      FIG. 10A  is a graph representing a return loss value measured by optimizing the coil size, and  FIG. 10B  is a graph representing a frequency characteristic for an insertion loss in first and second resonant frequency bands; 
           [0032]      FIG. 11  is a graph obtained by comparing to measure a return loss of an antenna on which LC matching is performed in a specific product and S 11  [dB] of an antenna to which an antenna bandwidth expander according to an embodiment of the present invention is applied; 
           [0033]      FIG. 12A  is a graph illustrating a radiation efficiency in the first resonant frequency band and  FIG. 12B  is a graph illustrating a radiation efficiency in the second resonant frequency band; 
           [0034]      FIG. 13  illustrates an antenna bandwidth expander according to another embodiment of the present invention; 
           [0035]      FIG. 14  is a connection diagram of an antenna bandwidth expander according to another embodiment of the present invention; and 
           [0036]      FIG. 15  is an internal plan view of an antenna bandwidth expander according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    Hereinafter, an antenna bandwidth expander according to the embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0038]      FIG. 2A  illustrates an antenna bandwidth expander according to an embodiment of the present invention, and  FIG. 2B  illustrates structures of respective layers according to an embodiment of the present invention.  FIGS. 3A and 3B  illustrate an internal connection structure of an antenna bandwidth expander according to an embodiment of the present invention.  FIG. 3A  illustrates a structure in which coil patterns influencing low and high frequency hands are coupled and  FIG. 3B  illustrates a structure in which coil patterns influencing low and high frequency hands are separated and  FIG. 3C  illustrates an alternative embodiment of coil pattern.  FIG. 4  is an internal plan view of an antenna bandwidth expander according to an embodiment of the present invention. In  FIG. 3B , reference numerals will be omitted for similar conductive patterns. 
         [0039]    An antenna bandwidth expander is provided with a ceramic body  10  having a pentagonal shape, and the ceramic body  10  is configured with stacked ceramic sheets  11 ,  12 ,  13 ,  14 ,  15 , and  16 , each of which has a conductive pattern thereon. On the bottom surface of the ceramic body  10 , conductive terminals  21 ,  22 ,  23 , and  24  and a ground terminal  25  are exposed. Here, the ground terminal  25  may be a dummy terminal for increasing the strength of soldering and has little influence on characteristics even if being omitted. When the ground terminal  25  is omitted, the conductive terminals  21 ,  22 ,  23 , and  24  exposed on the bottom surface may have structure extending to side surfaces of the ceramic body  10 . 
         [0040]    The antenna bandwidth expander is surface-mountable by a vacuum pickup. For example, the antenna bandwidth expander is mounted in a circuit board installed in a mobile phone and electrically connected between an output port of an RF system and a feeding port connected to an antenna. 
         [0041]    Conductive patterns printed on respective ceramic sheets (or green sheets)  11 ,  12 ,  13 ,  14 ,  15 , and  16  of the ceramic body  10  electrically and magnetically connected in a three-dimensional form through via holes to form a circuit. 
         [0042]    In other words, as illustrated in  FIG. 2B , in the ceramic sheets  11  to  16  of respective layers, for example, 6 layers in the embodiment, the conductive patterns (i.e. coil patterns, capacitor patterns, or connection patterns) are formed by printing, for example, Ag paste, and the ceramic body  10  may be formed by stacking the ceramic sheets  11  to  16  and by plastic working in a low temperature co-fired ceramic (LTCC) technique. 
         [0043]    As described above, the conductive terminals  21 ,  22 ,  23 , and  24  are formed at bottom four corners of the ceramic sheet  11 , the ground or dummy terminal  25  is formed at the center thereof, and via holes  101 ,  104 ,  201 , and  204  are formed in the ceramic sheet  11  at certain positions of respective conductive terminals  21 ,  22 ,  23 , and  24 . 
         [0044]    Here, same reference numerals are given to via holes formed at the same position of the ceramic sheets. 
         [0045]    Capacitor patterns  112 ,  121 ,  212 , and  221  and connection patterns  241 ,  242 ,  243 , and  244  are formed on the top surface of the ceramic sheet  12  and in order to electrically connect these to the conductive terminals  21 ,  22 ,  23 , and  24  of the ceramic sheet  11 , via holes are formed at the same positions as those of the via hole  101 ,  104 ,  201 , and  204  formed on the ceramic sheet  11 . 
         [0046]    Capacitor patterns  111 ,  122 ,  211 , and  222 , and coil patterns  131  and  231  are formed on the ceramic sheet  13 , capacitor patterns  112 ,  121 ,  212 , and  221 , and coil patterns  132 , and  232  are formed on the ceramic sheet  14 , capacitor patterns  111 ,  122 ,  211 , and  212 , and coil patterns  133  and  233  are formed on the ceramic sheet  15 , and capacitor patterns  112 ,  121 ,  212 , and  221 , and connection patterns  245  and  246  are formed on the ceramic sheet  16 . 
         [0047]    Via holes for electrical and vertical connection are formed in each of the ceramic sheets  13 ,  14 ,  15 , and  16 , as illustrated in  FIG. 2B . Via holes  101 ,  104 ,  201 , and  204  for direct electrical connection to the conductive terminals  21 ,  22 ,  23 , and  24 , via holes (not numerically referenced) for mutual electrical connection of the coil patterns  131 ,  132 , and  133 , and  231 ,  232 , and  233 , and via holes  102  and  103 ,  105  and  106 ,  202  and  203 , and  205  and  206  for respective electrical connections of capacitor patterns  111  and  112 ,  121  and  122 ,  211  and  212 , and  221  and  222  to conductive terminals  21 ,  22 ,  23 , and  24 , are formed at proper positions in each ceramic sheet  13 ,  14 ,  15 , and  16 . Via holes including via holes not described above are represented black quadrangular points in  FIG. 2B . 
         [0048]    Stereoscopically representing these as illustrated in  FIG. 3B , the conductive terminals  21 ,  22 ,  23 , and  24  are respectively connected to the capacitor patterns  111  and  112 ,  121  and  122 ,  211  and  212 , and  221  and  222  through conductive plugs  101 ′,  104 ′,  201 ′, and  204 ′ filled in the via holes  101 ,  104 ,  201 , and  204 , and conductive plugs  102 ′ and  103 ′,  105 ′ and  106 ′,  202 ′ and  203 ′, and  205 ′ and  206 ′ filled in the via holes  102 ′ and  103 ′,  105 ′ and  106 ′,  202 ′ and  203 ′, and  205 ′ and  206 ′, and respectively connected to the coil  1   130  and the coil  2   230  through conductive plugs  103 ′,  106 ′,  203 ′, and  206 ′ filled in the via holes  103 ,  106 ,  203 , and  206 . 
         [0049]    Overall, respective capacitor patterns  111  and  112 ,  121  and  122 ,  211  and  212 , and  221  and  222  form capacitors, and the coil patterns  131 ,  132 , and  133 , and  231 ,  232 , and  233  form coil  1   130  and coil  2   230  that are magnetically coupled, and description about a circuit related thereto will be described later. 
         [0050]    The embodiment exemplifies that, the coil patterns  131 ,  132 , and  133  forming the coil  1   130  are encompassed with the coil patterns  231 ,  232 , and  233  forming the coil  2   230 , respectively, and they are all formed on the same ceramic sheets  13 ,  14 , and  15 , but they may be also formed on ceramic sheets forming different layers, if necessary. 
         [0051]    For example,  FIG. 3C  illustrates only a coupling relation of coils, while other elements are excluded therefrom for convenience of drawing. A coil  1   130  and a coil  2   230  are formed on ceramic sheets, which have the same size but configure different layers, and have different numbers of turns 
         [0052]    Hereinafter, configurations and operations of an antenna bandwidth expander according to an embodiment of the present invention will be described in detail. 
         [0053]      FIG. 5  is an equivalent circuit diagram of an antenna bandwidth expander according to an embodiment of the present invention. 
         [0054]    The antenna bandwidth expander is disposed between an antenna and an internal RF system, and in  FIG. 3 , the conductive terminal  21  is electrically connected to a feeding port connected to the antenna and the conductive terminal  23  is electrically connected to an output port of the RF system. 
         [0055]    Accordingly, signal energy delivered from the RF system through the conductive terminal  23  is delivered to the coil  2   230 , and induction current is coupled to the coil  1   130  by a magnetic flux component of a magnetic field generated by the coil  2   230  and is delivered to the conductive terminal  21  and then to the feeding port of the antenna. 
         [0056]    As illustrated in  FIG. 5 , the coil  1   130  is wound in an opposite direction to that of the coil  2   230  to mutually induce magnetic coupling. As the result, in a low frequency band (i.e. a first resonant frequency band), a strong magnetic field coupling may be induced in a region between the coil  1   130  and coil  2   230  by the wound directions of the coil  1   130  and coil  2   230 , and in a high frequency band (i.e. a second resonant frequency band), the signal energy may be delivered through the strong magnetic field in a central part region of the coil  1   130  and the coil  2   230 . 
         [0057]    In the present embodiment in which the coil  1   130  is formed inside the coil  2   230 , coils are formed such that the wound directions of the coil  1   130  and the coil  2   230  are opposite to each other. However, a structure may also be possible in which magnetic coupling is formed at a central part of the coils by realizing the wound directions of the coil  1   130  and the coil  2   230  as the same. 
         [0058]    Capacitor patterns  111  and  221 ,  112  and  122 ,  121  and  211 ,  212  and  222  respectively include stack structures to form capacitors C 14 , C 12 , C 32 , and C 34 , and the coil patterns  131 ,  132 , and  133 , and  231 ,  232 , and  233  formed on each ceramic sheet  13 ,  14  and  15  are stacked to form the coil  1   130  and the coil  2   230 . 
         [0059]    Accordingly, capacitors C 12  and C 14 , and C 32  and C 34  are respectively connected to the coil  1   130  and the coil  2   230  in parallel to load capacitance values between the conductive terminals  21 ,  22 ,  23 , and  24 . 
         [0060]    Here, although each of the coil  1   130  and the coil  2   230  is not electrically connected, the induction current is coupled to the coil  1   130  by a magnetic flux component of the magnetic field generated by the coil  2   230  and the signal energy at the output port of the RF system is delivered to the feeding port of the antenna. 
         [0061]    As described above, in the embodiment, the coil patterns  131 ,  132 , and  133 , and  231 ,  232 , and  233 , which are parts of the coil  1   130  and the coil  2   230 , are formed on each ceramic sheet  13 ,  14 ,  15  at the same time, but are not limited thereto. In addition, the coil  1   130  and the coil  2   230  are formed in different sizes to have a structure in which one coil is positioned inside the other one, and the present embodiment has a structure such that the coil  1   130  is completely included in the coil  2   230 , in other words, a structure for maximizing coupling between coils to minimize a loss of signal energy. 
         [0062]    The capacitor C 14  connected to the coil  2   230  in serial and the capacitor C 12  connected to the coil  2   230  in parallel are coupled to the coil  2   230  to form an LC resonant circuit, and the capacitor C 12  connected to the coil  1   130  in serial and the capacitor C 32  connected to the coil  1   130  in parallel are coupled to the coil  1   130  to form another LC resonant circuit. 
         [0063]    Referring to  FIG. 5 , an antenna bandwidth expander is divided into a first resonant frequency block  100  influencing a low frequency band and a second resonant frequency block  200  influencing a high frequency band. 
         [0064]    Accordingly, elements mainly influencing the first resonant frequency are the coil  2   230 , the capacitors C 14  and C 34 , and the external inductor L 4 , and elements influencing the second resonant frequency are the coil  1   130 , the capacitors C 12  and C 32 , and the external inductor L 3 . Mutual inductance L M  formed by the coil  1  and coil  2   130  and  230  influences the first and second resonant frequencies at the same time. 
         [0065]    In brief, the coil  2   230 , the capacitors C 14  and C 34 , and the external inductor L 4  form the first resonant frequency block  100  influencing the low frequency band, and the coil  1   130 , the capacitors C 12  and C 32 , and the external inductor L 3  form the second resonant frequency block  200  influencing the high frequency band. 
         [0066]    Here, the conductive terminals  22  and  24  are disposed between the external inductors L 3  and L 4  and are electrically connected to the ground. 
         [0067]    The magnetic coupling of the coil  1   130  and the coil  2   230  is required to be strong in order to efficiently deliver the signal energy from the conductive terminal  23  connected to the output port of the RF system to the conductive terminal  21  connected to the feeding port of the antenna. 
         [0068]    Typically, a coupling coefficient k is used for explaining coupling between coils, and k has a value between 0 to 1, wherein 0 means the coils are decoupled and 1 means the coils are ideally coupled. Typically, the k value is dependent on the shape, separation distance, and direction between the coils. 
         [0069]    An antenna bandwidth expander of the present invention has a structure in which the coil  2   230  completely includes the coil  1   130  and the two coils are wound in opposite directions to be magnetically coupled. In such a structure, the signal insertion loss at the first frequency band can be minimized by reducing a separation distance between the coils and at the second frequency band, it is able to transmit the signal energy across a wideband while minimizing the insertion loss by strengthening the magnetic coupling at the central parts of the coils. 
         [0070]      FIGS. 6A and 6B  illustrate magnetic field distributions at a first resonant frequency (925 MHz) and a second resonant frequency (1990 MHz). A magnetic field is strongly formed in a region between the coil  1   130  and the coil  2   230  in the first resonant frequency and a magnetic field is strongly formed in the inner side of the coil  1   130  in the second resonant frequency. 
         [0071]      FIG. 7A  is a graph of influence of a return loss with respect to the size of coil  1   130 . As the size of the coil  1  becomes greater, the first resonant frequency does not have a large variation but the second resonant frequency moves to the lower frequency side. 
         [0072]      FIG. 7B  is a graph of influence of a return loss with respect to the size of coil  2   230 . As the size of the coil  2  becomes greater, the first resonant frequency moves to the lower frequency side and the second resonant frequency does not have a large variation. 
         [0073]      FIG. 8A  illustrates an influence of a return loss with respect to the external inductor L 3 . As the inductance value of L 3  becomes lower, the second resonant frequency moves to a higher frequency side and may optimize impedance matching at the second resonant frequency through a proper value. 
         [0074]      FIG. 8B  illustrates an influence of a return loss with respect to the external inductor L 4 . As the inductance value of L 4  becomes lower, the first resonant frequency moves to a higher frequency side and may optimize impedance matching at the second resonant frequency through a proper value. 
         [0075]      FIG. 9  represents return loss characteristics measured through proper inductance values of the external inductors L 3  and L 4 , when horizontal cross-sectional shapes of the coil  1  and coil  2  respectively have rectangular shapes and the sizes of 0.5 mm×0.5 mm and 1.0 mm×1.0 mm, and influences on capacitance values of the C 14 , C 12 , C 32  and C 34  connected to each coil in serial and in parallel are actually measured. 
         [0076]    The following Table 1 and Table 2 are coil sizes of a sample S and inductance values of the external inductors L 3  and L 4  applied to the measurement result of  FIG. 9 , and Table 3 is capacitance values applied to the measurements result of  FIG. 9 . 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Size (mm) 
                 Inductance 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Coil 1 
                 0.5 × 0.5 
                  5.5 nH 
               
               
                 Coil 2 
                 1.0 × 1.0 
                 16.0 nH 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Matching values of L 3  and L 4   
               
             
          
           
               
                 Sample type 
                 L 3   
                 L 4   
               
               
                   
               
               
                 S1 
                 12 nH 
                 47 nH 
               
               
                 S2 
                 15 nH 
                 68 nH 
               
               
                 S3 
                 18 nH 
                 82 nH 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Size (mm) 
                 Capacitance 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 S1 
                 C 34   
                 0.4 × 0.2 
                 0.8 pF 
               
               
                   
                   
                 C 14   
                 0.4 × 0.2 
                 0.8 pF 
               
               
                   
                   
                 C 12   
                 0.2 × 0.2 
                 0.4 pF 
               
               
                   
                   
                 C 32   
                 0.2 × 0.2 
                 0.4 pF 
               
               
                   
                 S2 
                 C 34   
                 0.6 × 0.2 
                 1.0 pF 
               
               
                   
                   
                 C 14   
                 0.6 × 0.2 
                 1.0 pF 
               
               
                   
                   
                 C 12   
                 0.3 × 0.2 
                 0.4 pF 
               
               
                   
                   
                 C 32   
                 0.3 × 0.2 
                 0.4 pF 
               
               
                   
                 S3 
                 C 34   
                 0.8 × 0.2 
                 1.2 pF 
               
               
                   
                   
                 C 14   
                 0.8 × 0.2 
                 1.2 pF 
               
               
                   
                   
                 C 12   
                 0.4 × 0.2 
                 0.6 pF 
               
               
                   
                   
                 C 32   
                 0.4 × 0.2 
                 0.6 pF 
               
               
                   
                   
               
             
          
         
       
     
         [0077]      FIG. 10A  illustrates return loss values measured by optimizing the coil size, that is, first and second resonant frequencies are optimized to a specific product, and  FIG. 10B  illustrates frequency characteristics with respect to an insertion loss in the first and second resonant frequency bands. 
         [0078]      FIG. 11  is a graph obtained by comparing to measure a return loss of an antenna on which LC matching is performed in a specific product and a return loss of an antenna to which an antenna bandwidth expander according to an embodiment of the present invention is applied. Table 4 represents an effect of improving a bandwidth of an antenna to which a bandwidth expander is added in comparison to an antenna provided only with an LC matching circuit. 
         [0000]    
       
         
               
               
             
               
               
               
             
               
               
               
             
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                 Antenna bandwidth 
               
               
                   
                 comparison (VSWR = 4.0) 
               
             
          
           
               
                   
                 Low frequency band 
                 High frequency band 
               
               
                   
                   
               
             
          
           
               
                 Antenna only 
                 765-864 
                 1711-2017 
               
               
                 (22 nH shunt) 
                 (BW = 99 MHz) 
                 (BW = 306 MHz) 
               
               
                 Antenna + expander 
                 722-920 
                 1608-2115 
               
               
                 (L 3  = 10 nH, L 4  = 22 nH) 
                 (BW = 198 MHz) 
                 (BW = 507 MHz) 
               
               
                 Expanding effect of 
                 100% 
                 65% 
               
               
                 bandwidth (BW) 
               
             
          
           
               
                 Size of sample circuit board 
                 130 mm × 65 mm × 0.8 mm 
               
               
                   
               
             
          
         
       
     
         [0079]    Referring to Table 4, compared to the bandwidth of an antenna designed only with an LC matching circuit, the bandwidth of an antenna including the bandwidth expander is improved by 100% at the first resonant frequency and by 65% at the second resonant frequency on the basis of a VSWR of 4.0. 
         [0080]      FIG. 12A  is a graph representing radiation efficiencies in the first resonant frequency band for a case where the bandwidth expander proposed in the present invention is provided and a case where only an LC matching circuit is provided. 
         [0081]    As seen from the graphs, compared to the case where only the matching circuit is applied, the case (represented with a solid line) where the bandwidth expander is included has a lower peak radiation efficiency at a resonant frequency but the total radiation efficiency is improved by reducing a mismatching loss due to a bandwidth expansion effect at frequencies around both end boundaries and an entirely flat radiation efficiencies may be obtained. 
         [0082]      FIG. 12B  is a graph representing radiation efficiencies in the second resonant frequency band for a case where the bandwidth expander proposed in the present invention is provided and a case where only an LC matching circuit is provided. Like  FIG. 12A , compared to the case where only the matching circuit is applied, in the case (represented with a solid line) where the bandwidth expander is included, the total radiation efficiency is improved by reducing a mismatching loss due to a bandwidth expansion effect at frequencies around both end boundaries and an entirely similar or better radiation efficiency may be obtained. 
         [0083]    As described above, a bandwidth expander according to the present invention, which is disposed between an internal RF system and an antenna having an arbitrary characteristic, may be applied to a front stage or a rear stage of a matching circuit and expands the bandwidth of the antenna, or may be directly applied to a rear stage of the antenna without the matching circuit and expands the bandwidth at the same time with impedance matching of the antenna. 
         [0084]    In the embodiment, it is exemplified that the horizontal cross-sectional shapes of the coil  1  and coil  2  are rectangular, but they are not limited thereto and may have circular or other polygonal shapes. 
         [0085]      FIG. 13  illustrates a bandwidth expander according to another embodiment of the present invention,  FIG. 14  is a connection diagram of the bandwidth expander according to the other embodiment of the present invention, and  FIG. 15  is an internal plan view of the bandwidth expander according to the other embodiment of the present invention. 
         [0086]    The antenna bandwidth expander of the present embodiment does not include a capacitor pattern therein in comparison to the antenna bandwidth expander of the above-described embodiment, but includes the coil  1   130  and the coil  2   230  and the connection patterns  241 ,  243 ,  245 , and  246 . 
         [0087]    In detail, referring to  FIG. 13 , conduction terminals  21 ,  22 ,  23 , and  24  are formed at the four bottom corners of the ceramic body  10  and the conduction terminals  21 ,  22 ,  23 , and  24  may extend along the side walls of the ceramic body  10  in order to improve soldering strength. 
         [0088]    As illustrated in  FIG. 15 , at the bottom center, the ground terminal  25  may be formed or a dummy terminal for improving the soldering strength may be formed, or none may be formed. 
         [0089]    As illustrated in  FIG. 15 , the ceramic body  10  may be formed by stacking the ceramic sheets  11  to  16  and by plastic-working them in an LTCC technique. 
         [0090]    The conductive terminals  21 ,  22 ,  23 , and  24  are formed at the bottom four corners of the ceramic sheet  11 , the ground terminal  25  is formed at the center thereof, and the via holes  101 ,  104 ,  201 , and  204  are formed in the ceramic sheet  11  at certain positions of the respective conductive terminals  21 ,  22 ,  23 , and  24 . 
         [0091]    The connection patterns  241  and  243  are formed on, and the via holes  104  and  204  electrically connecting them to the conduction terminals  21 ,  22 ,  23 , and  24  of the ceramic sheet  11  are formed in the top surface of the ceramic sheet  12 . 
         [0092]    In addition, the coil patterns  131 ,  132 , and  133 , and  231 ,  232 , and  233  are formed on, and the via holes  104  and  204  are formed in the ceramic sheets  13 ,  14 , and  15 . The connection patterns  245  and  246  are formed on and the via holes  104  and  204  are formed in the ceramic sheet  16 . 
         [0093]    Overall, the coil patterns  131 ,  132 , and  133 , and  231 ,  232 , and  233  form the magnetically coupled coil  1   130  and coil  2   230 . 
         [0094]    Like the above-described embodiments, the antenna bandwidth expander of the present embodiment is disposed between the antenna and the internal RF system, and the conductive terminal  21  is electrically connected to the feeding port connected to the antenna and the conductive terminal  23  is electrically connected to the output port of the RF system. 
         [0095]    Accordingly, the signal energy delivered from the RF system through the conductive terminal  23  is delivered to the coil  2   230 , and the induction current is coupled to the coil  1   130  by a magnetic flux component of a magnetic field generated by the coil  2   230  and is delivered to the conductive terminal  21  and then to the feeding port of the antenna. 
         [0096]    Referring to  FIG. 14 , the ceramic body  10  is mounted on a circuit board, and conduction pads corresponding to the conduction terminals  21 ,  22 ,  23 , and  24  are formed on the circuit board and capacitors C 14 , C 12 , C 32 , and C 34  are mounted between the conduction pads. 
         [0097]    Accordingly, as the ceramic body  10  of the antenna bandwidth expander is mounted in the circuit board, the capacitors C 14  and C 12 , and C 32  and C 34  are connected in parallel with the coil  1  and coil  2 , and load capacitance values between the conduction terminals  21 ,  22 ,  23 , and  24 . 
         [0098]    As the above-described embodiment, the capacitor C 14  connected to the coil  2   230  in serial and the capacitor C 12  connected to the coil  2   230  in parallel are coupled to the coil  2   230  to form an LC resonant circuit, and the capacitor C 12  connected to the coil  1   130  in serial and the capacitor C 32  connected to the coil  1   130  in parallel are coupled to the coil  1   130  to form another LC resonant circuit. 
         [0099]    Similarly, although each of the coil  1   130  and the coil  2   230  is not electrically connected, the induction current is coupled to the coil  1   130  by the magnetic flux component of the magnetic field generated by the coil  2   230  and the signal energy at the output port of the RF system is delivered to the feeding port of the antenna. 
         [0100]    According to the embodiment, since it is not necessary to implement a capacitor inside the ceramic body of the antenna bandwidth expander, the structure is simple and it is easy to change capacities of the capacitors C 14 , C 12 , C 32 , and C 34 , and therefore, the characteristic may be easily adjusted. 
         [0101]    In addition, according to the impedance characteristic of an antenna and a terminal structure, the structure may be changed such that the conduction terminal  21  is connected to the output port of the RF system and the conduction terminal  23  is connected to the antenna. 
         [0102]    According to the foregoing configuration, the antenna bandwidth expander may expand a bandwidth of an antenna in which a broad frequency characteristic is necessary. 
         [0103]    In addition, due to the simple structure of the antenna bandwidth expander, the manufacturing cost thereof is low and a mounting area thereof in an electronic device, such as a smartphone, is not largely occupied. 
         [0104]    Furthermore, the antenna bandwidth expander may be used independently or together with a matching circuit at a rear end of an antenna, and may increase the degree of freedom for system design since it is applicable to a front or rear stage of the matching circuit. 
         [0105]    While the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.