Patent Publication Number: US-2006019730-A1

Title: Antenna for mobile communication terminal

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an antenna for a mobile communication terminal, and more particularly, to an antenna for a mobile communication terminal capable of implementing a dual band, enhancing a bandwidth in a low frequency band, and being minimized.  
      2. Description of the Conventional Art  
      A mobile communication terminal has been continuously developed in pursuit of a minimization, a multifunction, a light characteristic, and a low consumption power. An antenna, one of necessary factors to the mobile communication terminal manages a starting and an ending of a signal input/output and determines a calling quality. The antenna has to be differently designed according to a shape and a material of the mobile communication terminal.  
       FIG. 1  is a view showing a structure of a mobile communication terminal in accordance with the conventional art.  
      As shown, the conventional mobile communication terminal comprises a body  110  having a main PCB (not shown) for inputting information and controlling communication therein, and a folder  120  having an LCD panel  121  for outputting information as an image and coupled to the body  110 .  
      A camera  130  for photographing an object is installed at an upper end of a front surface of the body  110 , and an antenna  140  for transmitting and receiving a wireless communication signal is installed at one side of an upper end of the body  110 .  
      As the antenna  140  used for a wireless communication of the mobile communication terminal, a mono-pole antenna or a helical antenna, one of external antennas is mainly used.  
      However, a mobile communication terminal to which the external antenna is applied has an inferior appearance by the antenna  140  protruded outward in order to transmit and receive a wireless communication signal, and has a difficulty in being carried or stored. Also, the mobile communication terminal can be easily damaged by an external impact.  
      Also, as the antenna  140  is fixed to the mobile communication terminal as a protruded state, the size of the mobile communication terminal is increased and various installations are limited.  
      Accordingly, a mobile communication terminal having an internal antenna (not shown) has been proposed in order to solve the problems of the external antenna  140 .  
      That is, an internal antenna such as a chip antenna or a planar inverted-F antenna is applied to the mobile communication terminal thereby to solve the problems due to the external antenna.  
      However, in case of the planar inverted-F antenna, a bandwidth is narrow and thus an emitting efficiency of the antenna is lowered according to a reflection loss of an input terminal, thereby decreasing an antenna gain. Also, since the planar inverted-F antenna has a resonance in ¼ of wavelength, the size of the antenna is increased and the size of the terminal is increased due to a limitation of an inner space of the mobile communication terminal. Accordingly, it is difficult to minimize the mobile communication terminal and make the mobile communication terminal light.  
      Also, in case of the ceramic chip antenna, a high dielectric material is used thereby to lower an emitting efficiency and to decrease an antenna gain.  
     SUMMARY OF THE INVENTION  
      Therefore, an object of the present invention is to provide an antenna for a mobile communication terminal capable of implementing a dual band, enhancing a bandwidth of a low frequency band, and being minimized.  
      To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an antenna of a mobile communication terminal comprising: a first antenna portion having a plurality of strip portions curved with a certain interval, and having a feed point for an electric connection at one end thereof; a second antenna portion having a plurality of strip portions curved with a certain interval, having an earth point for contacting a ground surface at one end thereof, and spaced from the first antenna portion with a certain interval; and a connecting unit for connecting the first antenna portion and the second antenna portion.  
      The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
      In the drawings:  
       FIG. 1  is a view showing a structure of a mobile communication terminal in accordance with the conventional art;  
       FIG. 2  is a view showing a structure of an antenna according to the present invention;  
       FIGS. 3A and 3B  are sectional views taken along line III-III in  FIG. 2 ;  
       FIGS. 4A  to  4 C are views showing a modification example of each antenna portion according to the present invention;  
       FIGS. 5 and 6  are views showing another embodiment of the antenna according to the present invention;  
       FIG. 7  is a sectional view taken along line VII-VII in  FIG. 6 ;  
       FIG. 8  is a view schematically showing that the antenna of the present invention is applied to a mobile communication terminal;  
       FIG. 9  is a graph showing a reflection loss in a dual band of the antenna according to the present invention; and  
       FIG. 10  is a graph showing a reflection loss in a triple band of the antenna according to the present invention.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
      Hereinafter, an antenna for a mobile communication terminal according to the present invention will be explained with reference to attached drawings.  
       FIG. 2  is a view showing a structure of an antenna according to the present invention,  FIGS. 3A and 3B  are sectional views taken along line III-III in  FIG. 2 , and  FIGS. 4A  to  4 C are views showing a modification example of each antenna portion according to the present invention.  
      As shown in  FIG. 2 , an antenna of a mobile communication terminal according to the present invention comprises a first antenna portion  10  having a plurality of strip portions  11  curved with a certain interval and having a feed point  12  for an electric connection at one end thereof; a second antenna portion  20  having a plurality of strip portions  21  curved with a certain interval, having an earth point  22  for contacting a ground surface at one end thereof, and spaced from the first antenna portion with a certain interval; and a connecting unit  25  for connecting the first antenna portion  10  and the second antenna portion  20 .  
      As the antenna of the present invention, two folded mono-pole antennas (first antenna portion and second antenna portion) are used.  
      The first antenna portion  10  comprises a first strip portion  11   a  having a feed point  12  for an electric connection at one end thereof, a second strip portion  11   b  curved from the end of the first strip portion  11   a , a third strip portion  11   c  curved from the end of the second strip portion  11   b , and a fourth strip portion  11   d  curved from the end of the third strip portion  11   c . The respective strip portions  11  are consecutively connected to each other thereby to form a strip pattern.  
      The second antenna portion  20  comprises a first strip portion  21   a  having an earth point  22  for contacting a ground surface at one end thereof, a second strip portion  21   b  curved from the end of the first strip portion  21   a , a third strip portion  21   c  curved from the end of the second strip portion  21   b , and a fourth strip portion  21   d  curved from the end of the third strip portion  21   c . The respective strip portions  21  are consecutively connected to each other thereby to form a strip pattern.  
      A line for supplying electric energy to an antenna is called as a feed line, and a contact point for contacting the feed line is called as a feed point. Also, a contact point for contacting a ground surface is called as an earth point. The feed point may be formed at the second antenna portion  10  and the earth point may be formed at the first antenna portion  20 .  
      Each strip portion  11  and  21  constituting the first antenna portion  10  and the second antenna portion  20  is inwardly curved. Preferably, each strip portion  11  of the first antenna portion  10  and each strip portion  21  of the second antenna portion  20  are inwardly curved in an opposite direction to each other.  
      That is, the second strip portion  11   b  of the first antenna portion  10  is curved from the end of the first strip portion  11   a  so as to have a certain length and a certain width in a right direction, and the third strip portion  11   c  of the first antenna portion  10  is curved from the end of the second strip portion  11   b  so as to have a certain length and a certain width in a back direction. Also, the fourth strip portion  11   d  of the first antenna portion  10  is curved from the end of the third strip portion  11   c  so as to have a certain length and a certain width in a left direction.  
      The second strip portion  21   b  of the second antenna portion  20  is curved from the end of the first strip portion  21   a  so as to have a certain length and a certain width in a right direction, and the third strip portion  21   c  of the second antenna portion  20  is curved from the end of the second strip portion  21   b  so as to have a certain length and a certain width in a forward direction. Also, the fourth strip portion  21   d  of the second antenna portion  20  is curved from the end of the third strip portion  21   c  so as to have a certain length and a certain width in a left direction.  
      Each strip portion  11  and  21  constituting the first antenna portion  10  and the second antenna portion  20  is respectively composed of first to fourth strip portions ( 11   a  to  11   d ,  21   a  to  21   d ). However, as shown in  FIGS. 4A  to  4 C, a plurality of strip portions  11   e  and  11   f ,  21   e  and  21   f  may be additionally curved from the end of the fourth strip portions  11   d  and  21   d  of the first antenna portion  10  and the second antenna portion  20  thereby to form a consecutive strip pattern.  
      As each strip portion  11  and  21  is inwardly curved, different internal angles (Θ1, Θ2, Θ3 . . . Θn) are formed. Preferably, the internal angle of each strip portion  11  and  21  is formed to have a range of 45° to 135°.  
      When the internal angle of each strip portion  11  and  21  is less than 45°, an interval between each strip portion is narrow thereby to lower an antenna characteristic. On the contrary, when the internal angle of each strip portion  11  and  21  is more than 135°, an entire size of the antenna is increased. Accordingly, the internal angle of each strip portion  11  and  21  is formed to have a range of 45° to 135°. More preferably, the internal angle of each strip portion  11  and  21  is formed to be 90°.  
      Each strip portion  11  and  21  for forming the first antenna portion  10  and the second antenna portion  20  is formed on the same plane.  
      At least one of the strip portion  11  and  21  of the first antenna portion  10  and the second antenna portion  20  is curved along a thickness direction in order to prevent a width increment at the time of a plane projection of the first antenna portion  10  and the second antenna portion  20 .  
      That is, as shown in  FIG. 2 , the fourth strip portion  11   d  of the first antenna portion  10  is curved from the end of the third strip portion in the left direction, and is curved along the thickness direction (preferably, curved as 90°) thereby to decrease the size of the antenna.  
      The third strip portion  21   c  and the fourth strip portion  21   d  of the second antenna portion  20  can be selectively curved in the thickness direction or together with the fourth strip portion  11   d  of the first antenna portion  10 .  
      The thickness of the first antenna portion  10  and the second antenna portion  20  can be variously implemented along the width direction thereof. That is, as shown in  FIG. 3A , the first antenna portion  10  and the second antenna portion  20  may have a constant thickness t 1  that is not varied in the width direction. Also, as shown in  FIG. 3B , the first antenna portion  10  and the second antenna portion  20  may have thickness t 1  and t 2  varied according to steps. Also, although not shown, the first antenna portion  10  and the second antenna portion  20  may have a thickness consecutively varied in the width direction. Also, the first antenna portion  10  and the second antenna portion  20  may have thickness varied according to each strip portion thereof.  
      In the first antenna portion  10  and the second antenna portion  20 , each strip portion  11  and  21  is inwardly curved to form a strip pattern. Also, the first antenna portion  10  and the second antenna portion  20  are spaced from each other with a certain interval and are connected to each other by the connecting unit  25 . Accordingly, the antenna can be minimized, a resonance characteristic of the entire antenna can be enhanced, a wide bandwidth can be obtained, and a power loss generated from an input terminal is decreased thereby to minimize a lowering of a reception sensitivity.  
      Also, each width of the first antenna portion  10  and the second antenna portion  20  and an interval l therebetween are controlled thereby to control an impedance properly.  
      Hereinafter, another embodiment of the present invention will be explained with reference to the attached drawings.  FIGS. 5 and 6  are views showing another embodiment of the antenna according to the present invention, and  FIG. 7  is a sectional view taken along line VII-VII in  FIG. 6 .  
      The same reference numerals were given to the same parts as those of the aforementioned embodiment, and the minute explanation will be omitted.  
      As shown in  FIG. 5 , the antenna according to another embodiment of the present invention comprises a first antenna portion  10  having a plurality of strip portions  11  curved from each end with a certain angle thereby to be consecutively connected to form a strip pattern and having a feed point  12  for an electric connection at one end thereof; a second antenna portion  20  having a plurality of strip portions  21  curved from each end with a certain angle thereby to be consecutively connected to form a strip pattern and having an earth point  22  for contacting a ground surface at one end thereof, and spaced from the first antenna portion  10  with a certain interval; a connecting unit  25  for connecting the first antenna portion  10  and the second antenna portion  20 ; and an auxiliary antenna portion  30  integrally connected to at least one of the first antenna portion  10  and the second antenna portion  20  for implementing a dual band with the first antenna portion  10  and the second antenna portion  20 .  
      The auxiliary antenna portion  30  comprises a first strip portion  31   a  connected to one of the first antenna portion and the second antenna portion, and a second strip portion  31   b  curved from the end of the first strip portion  31   a . A plurality of strip portions curved from the end of the second strip portion  31   b  with a certain angle and consecutively connected to each other to form a strip pattern may be further formed.  
      Each strip portion  31  constituting the auxiliary antenna portion  30  is inwardly curved, and thereby different internal angles (Θ1, Θ2, Θ3 . . . Θn) are formed. Preferably, the internal angle of each strip portion  31  is formed to have a range of 45° to 135°.  
      Each strip portion  31  of the auxiliary antenna portion  30  is formed on the same plane as that of each strip portion of the first antenna portion  10  and the second antenna portion  20 .  
      In the present invention, not only the first antenna portion  10  and the second antenna portion  20  but also the auxiliary antenna portion  30  for implementing a dual band is provided, thereby implementing a dual band such as a CDMA band/a GPS band and a CDMA band/a PCS band selectable in a frequency band. The details will be explained with reference to  FIGS. 9 and 10 .  
      As another embodiment of the present invention, the aforementioned antenna portions may be selectively provided with an antenna supporting unit  40  for supporting each antenna portion  10 ,  20 , and  30  as shown in  FIG. 6 .  
      That is, the antenna supporting unit  40  has a shape corresponding to each antenna portion  10 ,  20 , and  30  at the time of a plane projection and is formed of a dielectric material such as ceramic, resin, etc. with a certain thickness, thereby supporting each antenna portion  10 ,  20 , and  30 . Each antenna portion  10 ,  20 , and  30  may be formed as an electrode having a certain thickness, and may use an air layer instead of the antenna supporting unit  40 .  
      Each antenna portion  10 ,  20 , and  30  constituting the antenna can be deposited on the antenna supporting unit  40  by a conductive material such as gold, silver, copper, etc.  
      A ground portion  50  to which the earth point  22  is electrically connected may be selectively provided at a lower portion of each antenna portion  10 ,  20 , and  30  with the antenna supporting portion  40 .  
      As shown in  FIG. 6 , the ground portion  50  is a limited ground having a plate shape corresponding to the first antenna portion  10  and the second antenna portion  20  at the time of a plane projection. As shown in  FIG. 7 , the ground portion  50  is formed as a polygonal shape that each edge (L 1 , L 2 , L 3  . . . . Ln) has a length less than ¼ of a wavelength, and internal angles (Θ1, Θ2, Θ3 . . . Θn) are differently formed. Preferably, the internal angles are respectively formed to have a range of −90° to 90°.  
      It is also possible to form an air layer at a lower portion of each antenna portion  10 ,  20 , and  30  instead of the ground portion  50 .  
       FIG. 8  is a view schematically showing that the antenna of the present invention is applied to a mobile communication terminal.  
      As shown, the mobile communication terminal having an antenna of the present invention comprises a body  210  having a main PCB  230  therein, a folder  220  having an LCD panel  221  for outputting information as an image and coupled to the body  210 , and an antenna installed in the body.  
      The antenna comprises a first antenna portion  10 , a second antenna portion  20 , an auxiliary antenna portion  30 , an antenna supporting unit  40  for supporting each antenna portion  10 ,  20 , and  30 , and a ground portion  50 . Each antenna portion  10 ,  20 , and  30  is formed of an electrode having a certain thickness by the antenna supporting unit  40 .  
      A feeding pad  231  formed as a ground layer (not shown) is partially removed for connecting the feed point  12  of the first antenna portion  10  is provided at one side of an upper portion of the main PCB  230 . The ground point  12  is connected to the main PCB  230  through the feeding pad  231 , and the earth point  22  of the second antenna portion  20  is connected to the ground layer of the main PCB  230 .  
      The ground potion  50  is arranged at a lower portion of each antenna portion  10 ,  20 , and  30  and is electrically connected to the ground layer of the main PCB  230 . The ground portion  50  and the antenna supporting unit  40  may be selectively removed.  
      The antenna according to the present invention can be mounted in the mobile communication terminal as an internal type or can be mounted outside the mobile communication terminal as an external type. Also, the antenna can be applied to any kind of mobile communication terminal such as a bar type, a flip type, a PDA type, etc.  
       FIG. 9  is a graph showing a reflection loss in a dual band of the antenna according to the present invention.  
      Referring to  FIG. 9 , the antenna according to the present invention can implement a dual band selectable between 800 MHz band and 1500 MHz band, and can increase a bandwidth more than approximately 10%.  
      The low frequency band (800 MHz) of the antenna according to the preset invention is implemented by the first antenna portion  10  and the second antenna portion  20 , and the high frequency band (1500 MHz) is implemented by the auxiliary antenna portion  30 .  
       FIG. 10  is a graph showing a reflection loss in a triple band of the antenna according to the present invention.  
      Referring to  FIG. 10 , the antenna according to the present invention can implement a triple band selectable among 800˜1000 MHz band, 1500 MHz, and 1800˜2200 MHz band.  
      As aforementioned, the antenna according to the present invention can implement a dual band to be selectable in a necessary frequency band, and can implement a high function for increasing a bandwidth of a low frequency band.  
      Also, the antenna according to the present invention can be minimized.  
      Additionally, as the antenna according to the present invention can be applied to the mobile communication terminal as an internal type, the mobile communication terminal can be minimized and light.  
      As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.