Abstract:
A built-in antenna module includes a main board including a feed pad, a ground pad, and a ground layer having a predetermined area; an antenna radiator installed on the main board to have a predetermined height, and including a feed pin and a ground pin, the feed pin and the ground pin being electrically connected to the feed pad and the ground pad of the main board, respectively; a conductor disposed on an inner surface of a case frame and having a predetermined area and thickness, the case frame providing an installation space for the main board and forming an exterior of the terminal; and at least one electrical connection unit interposed between the conductor and the main board and serving as a medium that electrically connects the conductor to the ground pad and the ground layer of the main board.

Description:
PRIORITY 
       [0001]    This application claims priority under 35 U.S.C. §119 to an application filed in the Korean Intellectual Property Office on Oct. 27, 2006 and assigned Serial No. 2006-105324, the contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to a built-in antenna module embedded in a portable wireless terminal, and in particular, to a built-in antenna module for a portable wireless terminal configured to improve a radiation characteristic of a Planar Inverted-F Antenna (PIFA), and antenna performance such as reducing the Specific Absorption Rate (SAR). 
         [0004]    2. Description of the Related Art 
         [0005]    Recently, terminals with various functions and designs are being introduced. Consumers&#39; demands for smaller, lighter and slimmer terminals with various functions are increasing. To meet such consumers&#39; demands, terminal providers are focusing on reducing the volume of a terminal while maintaining or improving functions thereof. 
         [0006]    In regard to an antenna, a rod antenna (or a whip antenna) and a helical antenna that protrude outwardly of a terminal are susceptible to drop damage, and reduce portability of the terminal. Therefore, a plate type built-in antenna (i.e., a so called ‘internal antenna’ or ‘intenna’) installed inside a terminal is widely used, and various efforts have been made to improve a characteristic of the built-in antenna and also improve productivity and assembly thereof. 
         [0007]    In general, the built-in antenna module includes a predetermined plate-type antenna radiator that is electrically connected onto a main board (i.e., Radio Frequency board) of a terminal. The built-in antenna radiator has two feed lines. One of the feed lines is electrically connected to an antenna feed unit of the main board, and the other one is operated, grounded to a ground layer formed as a conductor of the main board having a multi-layered structure. Here, the ground layer is formed or installed at the farthest location of the main board from the antenna radiator. The antenna radiator has a predetermined distance from the ground layer. The antenna radiator is grounded with only a ground point and a feed point extending downward, separated from the main body at the predetermined distance by a predetermined antenna carrier. Here, the antenna carrier is formed to facilitate fixation to the main board. 
         [0008]    The plate type built-in antenna radiator having such feed and ground structures is called a Planar Inverted F-Antenna (PIFA) radiator. The PIFA has been known to improve antenna performance as the size of a radiator, an area of a ground surface, and a distance between the radiator and the ground surface increase. 
         [0009]    To meet such conditions for improving the PIFA characteristics while minimizing the volume of a terminal, a separate ground plate with a predetermined distance is used on a surface of a main board opposite to a surface where the antenna radiator is installed, so that the distance between the antenna radiator and the ground surface can be increased as much as possible and thus the radiation characteristic can be improved. 
         [0010]    However, the structure requires a complicated assembly process and a high terminal manufacturing cost because of the installation of the separate ground plate, and has limitations in expanding the distance between the antenna radiator and the ground surface using the ground plate. 
       SUMMARY OF THE INVENTION 
       [0011]    An aspect of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an aspect of the present invention is to provide a built-in antenna module for a portable wireless terminal configured to improve antenna performance without increasing the volume of the terminal, by maximizing a distance between a radiator and a ground surface using a case frame of the terminal. 
         [0012]    Another aspect of the present invention is to provide a built-in antenna module of a portable wireless terminal configured to improve a radiation characteristic of the built-in antenna module by providing a maximum distance between an antenna radiator and a ground surface without using a separate ground plate. 
         [0013]    Still another aspect of the present invention is to provide a built-in antenna module for a portable wireless terminal configured to improve a radiation characteristic of the antenna module and reduce the Specific Absorption Rate (SAR) by grounding an antenna radiator with an inner surface of a case frame together with a ground surface of the main board. 
         [0014]    Further another aspect of the present invention is to provide a built-in antenna module for a portable wireless terminal configured to implement a high-quality terminal by achieving a slim profile of the terminal and also improving radiation performance of the antenna module. 
         [0015]    According to one aspect of the present invention, a built-in antenna module for a portable wireless terminal includes a main board having a feed pad, a ground pad, and a ground layer having a predetermined area; an antenna radiator installed on and at a predetermined distance from the main board, and including a predetermined feed pin and a predetermined ground pin, the feed pin and the ground pin being electrically connected to a feed pad and a ground pad of the main board, respectively; a conductor installed or formed on an inner surface of a case frame and having a predetermined area and thickness, the case frame providing an installation space for the main board and forming an exterior of the terminal; and at least one electrical connection unit interposed between the conductor and the main board and serving as a medium that electrically connects the conductor to the ground pad and the ground layer of the main board. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
           [0017]      FIG. 1  is a front perspective view of a slide type portable wireless terminal including a built-in antenna module according to an embodiment of the present invention; 
           [0018]      FIG. 2  is a rear perspective view of a slide type portable wireless terminal, showing an installation location of a built-in antenna module according to an embodiment of the present invention; 
           [0019]      FIG. 3  is an exploded perspective view of a built-in antenna module according to the present invention; 
           [0020]      FIG. 4  is a rear perspective view of a main board according to the present invention; 
           [0021]      FIG. 5  is a cross-sectional view of a main part, illustrating that a built-in antenna module is installed on a main board according to the present invention; and 
           [0022]      FIGS. 6A and 6B  are graphs showing Voltage Standing Wave Ratio (VSWR) according to opening and closing of a slide type terminal including a built-in antenna module according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. 
         [0024]    A slide type terminal is illustrated in describing the present invention, but the present invention is not limited thereto. For example, the present invention may be applied to various wireless devices such as Personal Digital Assistants (PDAs), general terminals, and wireless notebook computers including plate type built-in antenna modules. 
         [0025]    As illustrated in  FIGS. 1 and 2 , the slide type portable wireless terminal  100  includes a main body  110 , and a slide body  120  that can slide a predetermined length on the main body  100  in a length direction of the terminal  100 . The slide body  120  is installed on the main body  110 . As illustrated in  FIG. 2 , the slide body  120  is slid over the main body  110  to the predetermined length, and is used for overall functions of the terminal such as a call operation. 
         [0026]    A display unit  121  is installed on a front surface of the slide body  120 . The display unit  121  may be a color wide Liquid Crystal Display (LCD) module, and may be a touch screen panel. A speaker unit  122  is installed above the display unit  121 , and at least one keypad assembly  123  is installed under the display unit  121 . The keypad assembly  123  may include a functional key button or a navigating key button so that a user can use a portion of functions of the terminal without opening the slide body  120  on the main body  110 . 
         [0027]    Another keypad assembly  111  including a plurality of key buttons may be installed on a surface of the main body  110  viewed when the slide body  120  is opened on the main body  110 . The keypad assembly may be number key buttons (3×4 key buttons). A microphone unit  112  is installed under the keypad assembly  111 . 
         [0028]    The main body  110  includes upper and lower case frames  13  and  14 , respectively, and a built-in antenna module ( 10  of  FIG. 3 ) is provided within a predetermined space defined by the upper and lower case frames  13  and  14 . As the built-in antennal module, a Planar Inverted F-Antenna (PIFA) may be used. The built-in antenna module  10  may be installed in an inner side (indicated by a dotted line in  FIG. 2 ) of a rear upper portion of the main body  110  above a battery pack  113 . 
         [0029]      FIG. 3  is an exploded perspective view of a built-in antenna module  10  according to the present invention. The built-in antenna module  10  includes the upper case frame  13  of the terminal, a main board  20  installed in the case frame  13 , an antenna radiator  40  installed on the main board  20 , and an Electro-Magnetic Interference (EMI) pigment  132  applied on an inner surface  131  of the case frame  13  to face a bottom surface  24 ′ (see  FIG. 4 ) opposite a top surface  24  of the main board  20  on which the antenna radiator  40  is installed. 
         [0030]    The main board  20  includes a ground pad  21  and a feed pad  22  on the top surface  24 . The ground pad  21  and the feed pad  22  are electrically connected respectively to a ground pin  41  and a feed pin  42  extending from the antenna radiator  40 . The feed pad  22  is electrically connected to a Radio Frequency (RF) connector  25  by a pattern  23  formed on the main board  20 . 
         [0031]    The antenna radiator  40  may be fixed on an antenna carrier  30  having a predetermined height. The antenna carrier  30  may be formed of a synthetic resin. This is because if the antennal radiator  40 , a thin metallic plate, is fixed directly onto the main board  20  without the antenna carrier  30 , the shape of the antenna radiator  40  might be twisted afterward, deteriorating a radiation characteristic of the antenna module. Thus, the antenna radiator  40  may include a plurality of opening  43  and thus be fixed to the antenna carrier  30  by, for example, ultrasonic welding. The antenna carrier  30  may include through holes  31  and  32  at predetermined locations, so that the ground pin  41  and the feed pin  42  of the antenna radiator  40  pass through the through holes  31  and  32  and are connected to the ground pad  21  and the feed pad  22  of the main board  20 , respectively. Also, fixing protrusions  36  protrude downwardly from both sides of the antenna carrier  30 . The fixing protrusions  36  are inserted in fixing grooves  26  formed in the main board  20  so that the antenna carrier  30  can be firmly fixed to the main board  20 . 
         [0032]    The EMI pigment  132  is formed on the inner surface  131  of the case frame  13  of the terminal. The EMI pigment  132  may be deposited or applied on the inner surface  131  of the case frame  13 . The EMI pigment  132  may have a greater area than that of the antenna radiator  40 , and may be applied or deposited at a location overlapping a portion of the main board  20  where the antenna radiator  40  is installed. Thus, one end of the EMI pigment  132  is electrically connected to the ground pad  21 , and the other end thereof is electrically connected to a ground layer ( 29  of  FIG. 4 ) of the main board  20 , so that the EMI pigment  132  may serve as a ground surface for the antenna radiator  40 . 
         [0033]    However, the present invention is not limited to the above description. Besides the EMI pigment  132 , similar conductors may be used. Examples of the conductor may include a metal plate or a Flexible Printed Circuit (FPC) that has a predetermined area and thickness, and the conductor is attached to the inner surface  131  of the case frame  13 . For example, the metal plate excluding a portion for the electrical connection may be inserted into the case frame  13  by insertion molding when the case frame  13  is fabricated. 
         [0034]    Of course, an electrical connection unit is used for an electrical connection of the ground pad  21  and the ground layer (item  29  in  FIG. 4 ) with the EMI pigment  132  as the conductor. As the electrical connection unit, conductive tapes  11  and  12 , each formed by being wound a plurality of times and having a predetermined height, are used. However, the electrical connection unit is not limited to the conductive tapes, but other materials such as a conductive foam or a plate type metal spring may also be used. 
         [0035]      FIG. 4  is a rear perspective view of the main board  20  according to the present invention. The ground layer  29  is formed on the bottom surface  24 ′ of the main board  20  opposite the top surface  24  where the antenna radiator  40  is installed. The ground layer  29  serves to ground various electronic function groups used in the portable wireless terminal  100 , and also serves as a ground surface of the antenna radiator  40 . Thus, the ground layer  29  may be formed on a bottom surface of the main board  20 , which is located at the farthest vertical distance from the antenna radiator  40 . The ground layer  29  may not be formed in a clearance area on the bottom surface  24 ′; the clearance area is an area in which the antenna radiator  40  is orthogonally projected on the bottom surface  24 ′. 
         [0036]    Of course, a first contact point  27  electrically connected to the ground pad  21  is formed on the bottom surface  24 ′ opposite the top surface  24  where the ground pad  21  is formed, therefore the first contact point  27  may be electrically connected to the ground pad  21  through a via. Also, a second contact point  28  electrically connected to the ground layer  29  is exposed on the bottom surface  24 ′, and the ground layer  29  is not exposed from the main board  20  in general. Particularly, the first and second contact points  27  and  28  may be used as contact points with the conductive tapes  11  and  12 , the electrical connection unit ( FIG. 5 ). 
         [0037]      FIG. 5  is a cross-sectional view of a main part, illustrating that the built-in antenna module is installed at the main board according to the present invention, which will now be described with reference to  FIGS. 3 through 5 . 
         [0038]    First, the antenna radiator  40  is fixed on the top surface  24  of the main board  20  via the antenna carrier  30 . Here, the feed pin  42  of the antenna radiator  40  is connected to the feed pad  22  of the main board  20 , and the ground pin  41  is connected to the ground pad  21  of the main board  20 . In this case, the ground pad  21  of the main board  20  and the ground pin  41  of the antenna radiator  40  are electrically connected together, but are not yet connected to the ground layer  29  of the main board  20 . 
         [0039]    Thereafter, when the main board  20  having the antenna radiator  40  is mounted to the case frame  13 , the main board  20  and the EMI pigment  132  are electrically connected together by the conductive tapes  11  and  12 . Here, the first contact point  27  of the main board  20  contacts one end of the EMI pigment  132  by the conductive tape  11 , and the second contact point  28  contacts the other end of the EMI pigment  132  by another conductive tape  12 . Consequently, the antenna radiator  40  is grounded in the order of ground pin  41  of antenna radiator  40 →ground pad  21  of main board  20 →first contact portion  27  of main board  20 →conductive tape  11 →EMI pigment (conductor)  132 →conductive tape  12 →ground layer  29  of main board  20 . 
         [0040]    Thus, the EMI pigment  132  is used as a ground surface together with the ground layer  29  for the antenna radiator  40  of the main board  20 . Also, since the EMI pigment  132  is formed on the inner surface  131  of the case frame  13 , an effect of maximizing a distance from the antenna radiator  40  can be obtained. That is, as illustrated in  FIG. 5 , the distance between the antenna radiator  40  and the ground surface is t 1 +t 2 . The maximum distance between the antenna radiator  40  and the ground surface may contribute to improving radiation performance of the antenna radiator  40 . 
         [0041]      FIGS. 6A and 6B  are graphs showing Voltage Standing Wave Ratio (VSWR) according to opening and closing of a slide type terminal including a built-in antenna module according to the present invention. The antenna was designed to optimize its characteristic in a Slide-up mode, an actual call mode of the terminal. Since a Slide-down mode is a reception stand-by mode in most cases, somewhat high VSWR (marker  1  and marker  3  in the drawing) in transmission does not have significant influence on the terminal performance. In actuality, it is almost impossible to implement a design that satisfies performance in both the Slide-up and Slide-down modes. Based on a mutual trade-off relation, the transmission characteristic in the Slide-down mode which less affects the terminal performance is sacrificed. 
         [0042]    The SAR in the case of the Global System for Mobile communications (GSM) and the SAR in the case of the Digital Cellular System (DCS) are shown in Tables 1 and 2 below. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 Slide 
                   
                 10 g SAR 
               
               
                 Mode 
                 Power 
                 Head 
                 Position 
                 type 
                 CH. 
                 (W/kg) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 EGSM900 
                 33 dBm 
                 Left 
                 Cheek 
                 Up 
                 975 
                 0.240 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 975 
                 0.134 
               
               
                   
                   
                   
                 Cheek 
                 Up 
                 37 
                 0.399 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 37 
                 0.315 
               
               
                   
                   
                   
                 Cheek 
                 Up 
                 124 
                 0.451 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 124 
                 0.373 
               
               
                   
                   
                   
                 Tilt 
                 Up 
                 37 
                 0.169 
               
               
                   
                   
                   
                 Tilt 
                 Down 
                 37 
                 0.165 
               
               
                   
                   
                 Right 
                 Cheek 
                 Up 
                 975 
                 0.243 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 975 
                 0.138 
               
               
                   
                   
                   
                 Cheek 
                 Up 
                 37 
                 0.388 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 37 
                 0.261 
               
               
                   
                   
                   
                 Cheek 
                 Up 
                 124 
                 0.472 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 124 
                 0.401 
               
               
                   
                   
                   
                 Tilt 
                 Up 
                 37 
                 0.179 
               
               
                   
                   
                   
                 Tilt 
                 Down 
                 37 
                 0.175 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                 Slide 
                   
                 10 g SAR 
               
               
                 Mode 
                 Power 
                 Head 
                 Position 
                 type 
                 CH. 
                 (W/kg) 
               
               
                   
               
             
             
               
                 EGSM900 
                 33 dBm 
                 Left 
                 Cheek 
                 Up 
                 512 
                 0.109 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 512 
                 0.118 
               
               
                   
                   
                   
                 Cheek 
                 Up 
                 700 
                 0.105 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 700 
                 0.128 
               
               
                   
                   
                   
                 Cheek 
                 Up 
                 885 
                 0.098 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 885 
                 0.137 
               
               
                   
                   
                   
                 Tilt 
                 Up 
                 700 
                 0.071 
               
               
                   
                   
                   
                 Tilt 
                 Down 
                 700 
                 0.073 
               
               
                   
                   
                 Right 
                 Cheek 
                 Up 
                 512 
                 0.108 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 512 
                 0.119 
               
               
                   
                   
                   
                 Cheek 
                 Up 
                 700 
                 0.088 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 700 
                 0.111 
               
               
                   
                   
                   
                 Cheek 
                 Up 
                 885 
                 0.109 
               
               
                   
                   
                   
                 Cheek 
                 Down 
                 885 
                 0.125 
               
               
                   
                   
                   
                 Tilt 
                 Up 
                 700 
                 0.071 
               
               
                   
                   
                   
                 Tilt 
                 Down 
                 700 
                 0.055 
               
               
                   
               
             
          
         
       
     
         [0043]    As shown in Table 1 and Table 2, the SAR was maximum 0.472 W/kg in the case of the GSM, and was maximum 0.137 W/kg in the case of the DCS. It can be seen that excellent performance can be achieved compared to the average 2.0 W/kg per log of the European standard. Because the SAR characteristic has recently been emphasized to a great extent and strictly managed internationally, such results are very much satisfactory, and may be used as a reference in developing a like terminal. 
         [0044]    In the built-in antenna module according to the present invention, a ground surface interacting with the antenna radiator is applied to the case frame of the terminal. Thus, a distance between the antenna radiator and the ground surface is maximized without increasing the volume of the terminal, so that radiation performance can be improved, and thus the slimness and high quality of the terminal can be achieved. 
         [0045]    While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.