Abstract:
Disclosed is a method for tuning an antenna module in a portable wireless terminal and built-in antenna module using the same. According to the method and built-in antenna module, the built-in antenna module is provided with a plate type radiator defining a slot with a predetermined width to form a pattern. The plate type radiator is provided with downwardly protruded feed and ground pins that are spaced apart, and at least one passive element having a predetermined value is connected to the radiator to optimally tune the antenna module. Therefore, various frequency response properties of the built-in antenna module can be attained by altering such a passive element as a variable design parameter without changing the radiator. Also, this construction can take the place of a matching circuit in a signal line, such that radiation performance can be increased without insertion loss.

Description:
PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. §119 to an application entitled “Method for Tuning Antenna Property in Portable Wireless Terminal and Built-In Antenna Module Using Thereof” filed in the Korean Intellectual Property Office on Dec. 24, 2004 and assigned Serial No. 2004-112163 and the contents of which are herein incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a built-in antenna module of a portable wireless terminal and, more particularly, to a method for tuning an antenna module in a portable wireless terminal and built-in antenna module using the same, in which a matching unit is added to facilitate the design of a Planar Inverted-F Antenna (PIFA).  
         [0004]     2. Discussion of the Prior Art  
         [0005]     Mobile wireless terminals, such as Personal Communication Service (PCS) terminals, Digital Cellular System (DCS) terminals, Global Positioning System (GPS) terminals, Personal Digital Assistants (PDAs), cellular phones and wireless notebooks, are popular and have introduced various functions and designs. New terminals, being introduced, must be small, slim and lightweight. At the same time, the terminals are required to have improved functionality. Therefore, the design of the terminals is focused on size reduction while maintaining or improving the functions demanded by the public.  
         [0006]     Today, a rod antenna (also known as a whip antenna) and a helical antenna are widely used owing to their good omnidirectional radiation properties. The rod antenna and the helical antenna protrude outward from the terminal and are easy to break when dropped. This fragility decreases the portability of the terminal. Therefore, a plate type built-in antenna, installed within the terminal, has been widely used in recent times. This arrangement is also called a built-in antenna, internal antenna, or intenna. Various efforts are being made to improve the performance and capability of the built-in antenna.  
         [0007]     The built-in PIFA antenna includes a plate type radiator and is electrically connected to a multiple-layer mainboard of a main body of a portable wireless terminal. Also, the PIFA includes two feed lines. One feed line is electrically connected to a feed portion of the mainboard, and the other is electrically connected to a ground portion of the mainboard for grounding. The plate type radiator can function at a desired performance when it is spaced apart from a conductive layer (ground layer) of the mainboard. Therefore, the plate type radiator is mounted on a carrier with a predetermined height to provide separation and then the carrier is mounted on the mainboard.  
         [0008]     When designing the PIFA, fixed design parameters and variable design parameters are considered to optimize the performance of the PIFA. Different design parameters may be invoked depending on the requirements necessary to implement various features of the portable wireless terminal. The fixed design parameters, such as radiator length, radiator width, and the distance between the radiator and the ground layer, are firmly fixed depending on the type and size of the portable wireless terminal. Therefore, adjustment of the variable design parameters is important in antenna matching to obtain optimized antenna performance. The variable design parameters may include a feed pin location, feed pin and ground pin widths, the distance between the feed pin and the ground pin, and a pattern configuration formed on the radiator.  
         [0009]     However, the tuning of the antenna device using the variable design parameters requires many test samples. Also, since the antenna has to be tested with respect to each variable design parameter, tuning the antenna device is a lengthy process.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention provides a method for tuning an antenna module in a portable wireless terminal and built-in antenna module using the same, which does not require extensive testing because a desired antenna property can be easily attained without considering variable design parameters.  
         [0011]     Also, the present invention provides a method for tuning an antenna module in a portable wireless terminal and built-in antenna module using the same, in which a matching circuit is installed separate from a mainboard of the portable wireless terminal, to easily perform resonant frequency tuning and bandwidth tuning.  
         [0012]     Further, the present invention provides a method for tuning an antenna module in a portable wireless terminal and built-in antenna module using the same, in which a passive element with a specific characteristic value is used to easily perform an antenna tuning for a Planar Inverted-F antenna (PIFA). The passive element is used instead of, for example, adjusting the distance between a feed pin and a ground pin.  
         [0013]     According to an aspect of the present invention, a method is provided for tuning an antenna module in a portable wireless terminal, in which the antenna module is provided with a plate type radiator in which a slot with a predetermined width is defined to form a pattern and the plate type radiator is provided with downwardly protruding feed and ground pins that are spaced apart. The method includes the step of connecting at least one passive element having a predetermined value to the radiator to optimally tune the antenna module.  
         [0014]     According to another aspect of the present invention, a built-in antenna module in a portable wireless terminal is provided, including a mainboard having a feed portion and a ground portion for the built-in antenna module; a plate type radiator mounted on the mainboard, the plate type radiator having a feed pin and a ground pin that are electrically connected to the feed portion and the ground portion, respectively; and at least one passive element having a predetermined value, the passive element being electrically connected to a predetermined portion of the radiator.  
         [0015]     According to the present invention, a matching unit, which is conventionally located on a mainboard, is installed on an antenna radiator to attain various advantages. For example, though the matching unit on the mainboard is considered as a fixed design parameter because it is hard to replace, the matching unit on the radiator can be easily replaced with another one to tune the antenna module. Therefore, the antenna tuning can be carried out conveniently and quickly while considering less variable design parameters.  
         [0016]     The matching unit may also be a well-known passive element. Passive elements with various characteristic values may be used depending on the various fixed design parameters of the radiator. The passive element may be selected from the group consisting of a resistor (R), a capacitor (C), an inductor (I), and combinations thereof.  
         [0017]     Consequently, adjustment of the variable design parameters, such as the feed pin width and length, the ground pin width and length, and the distance between the feed pin and the ground pin, is minimized when tuning the antenna module. Thereby, productivity and yield are improved without frequent sample replacement and the accompanying loss of time.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0019]      FIG. 1  is a front perspective view of a typical slide type portable wireless terminal;  
         [0020]      FIG. 2  is a rear perspective view of a typical slide type portable wireless terminal, showing an installation location of a built-in antenna module;  
         [0021]      FIG. 3  is an exploded perspective view of a built-in antenna module according to an embodiment of the present invention;  
         [0022]      FIG. 4  is an assembled side sectional view of the built-in antenna module depicted in  FIG. 3 ;  
         [0023]      FIG. 5  is an exploded perspective view of a built-in antenna module according to another embodiment the present invention;  
         [0024]      FIGS. 6A  to  6 C are graphs showing Voltage Standing Wave Ratio (VSWR) of built-in antenna modules, each being obtained by applying a capacitor of a different capacitance;  
         [0025]      FIG. 7  is a graph showing VSWR of a built-in antenna module without a matching unit;  
         [0026]      FIG. 8  is a graph showing VSWR of a built-in antenna module with a 1.2-nH inductor as a matching unit; and  
         [0027]      FIG. 9  is a graph showing VSWR of a built-in antenna module with a 56-pF capacitor as a matching unit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. A detailed description of well-known features will be omitted for conciseness.  
         [0029]     A slide-type portable wireless terminal is illustrated to describe the present invention. However, the present invention is not limited to the illustrated terminal. The present invention can be applied to various kinds of wireless devices with a plate type built-in antenna module, such as PDAs, other types of portable wireless terminals, and wireless notebooks.  
         [0030]      FIG. 1  is a front perspective view of a typical slide type portable wireless terminal, and  FIG. 2  is a rear perspective view of a typical slide type portable wireless terminal, showing an installation location of a built-in antenna module.  
         [0031]     Referring to  FIGS. 1 and 2 , a portable wireless terminal  100  such as a slide-type terminal is illustrated. The portable wireless terminal  100  includes a main body  110  and a slide body  120 , slidably coupled to the main body  110 . The slide body  120  is capable of sliding on the main body  110  within a predetermined range in the length direction. The slide body  120  includes a display  121  at a front, an earpiece  122  above the display  121 , and a first keypad assembly  123  under the display  121 . The display  121  may be a wide color Liquid Crystal Display (LCD) module. Also, the display  121  may be a touch screen panel. The earpiece  122  is provided to output voice or sound. The first keypad assembly  123  may include navigation buttons.  
         [0032]     The main body  110  may include a second keypad assembly  111  on a front lower portion and a microphone  112  under the second keypad assembly  111 . The second keypad assembly  111  shows up when the slide terminal is opened. The second keypad assembly  111  may be a 3×4 keypad assembly. The microphone  112  is provided to receive the user&#39;s voice. Also, the main body  110  includes a battery pack  130  and a built-in antenna module. The battery pack  130  is installed on a back of the main body  110  to supply power to the portable wireless terminal  100 . The built-in antenna is installed in the main body  110  at a dashed-line portion depicted in  FIG. 2 .  
         [0033]      FIG. 3  is an exploded perspective view of a built-in antenna module according to an embodiment of the present invention, and  FIG. 4  is an assembled side sectional view of the built-in antenna module depicted in  FIG. 3 .  
         [0034]     Referring to  FIGS. 3 and 4 , a built-in antenna module  10  includes a mainboard  20  installed in the portable wireless terminal  100  and a radiator  50  installed on the mainboard  20 . To install the radiator  50  on the mainboard  20 , the radiator  50  may be fixed on a top of a carrier  30  having a predetermined height, and the carrier  30  may be mounted on the mainboard  20 . The radiator  50  has a plate shape and defines a slot  55  having a predetermined width to form a pattern. The configuration of the pattern may be changed depending on terminal features and operating frequency band.  
         [0035]     The mainboard  20  includes a ground portion  21  and a feed portion  22 . The radiator  50  includes a ground pin  52  and a feed pin  53 . The ground portion  21  and feed portion  22  are electrically connected with the ground pin  52  and feed pin  53 , respectively. The feed portion  22  is electrically connected to a Radio Frequency (RF) connector  25  by a pattern  23  formed on the mainboard  20 .  
         [0036]     The carrier  30 , on which the radiator  50  is fixed, may be made of synthetic resin. Since the radiator  50  is made of thin metal plate, the radiator  50  can be easily deformed when it is directly fixed to the mainboard. This deformation may cause degradation in radiation pattern of the radiator  50 . Therefore, the radiator is instead fixed to the carrier  30  to prevent deformation and degradation of the radiation pattern. A plurality of small holes  54  may be defined in the radiator  50  to fix the radiator  50  to the carrier  30  by ultrasonic welding. The carrier  30  may define through-holes  31  and  32  through which the ground pin  52  and feed pin  53  are respectively inserted to make contact with the ground portion  21  and feed portion  22 . The carrier  30  also includes downward protrusions  36  at both sides. The mainboard  20  defines corresponding protrusion holes  26  through which the protrusions  36  are tightly inserted, such that the carrier  30  can be securely fixed to the mainboard  20 .  
         [0037]     A passive element  40  is installed in the radiator  50 . To install the passive element  40 , the ground pin  52  of the radiator  50  may be bisected in the middle and the passive element  40  may be electrically connected between the bisected ends of the ground pin  52 . That is, the ground pin  52  is cut in two parts, and both ends of the passive element  40  are respectively connected to the cut ends of the ground pin  52  by soldering. The passive element  40  may be a resistance (R), a capacitor (C), or an inductor (L), each having a predetermined characteristic value such as resistance, capacitance or inductance.  
         [0038]     A capacitor with a predetermined capacitance is illustrated as a non-exclusive example of the passive element  40 . When fixed design parameters such as the width and height of the radiator are determined, a variable design parameter can be adjusted by changing the passive element  40  with new one having a different characteristic value to carry out an antenna matching in order to optimize the performance of the built-in antenna module. Though one passive element  40  is used in this embodiment illustrated in  FIGS. 3 and 4 , two or more passive elements may be used in the radiator  50 .  
         [0039]      FIG. 5  is an exploded perspective view of a built-in antenna module according to another embodiment the present invention. Since the radiator  50 , the carrier  30 , and the mainboard  20  are already described with reference to  FIGS. 3 and 4 , descriptions thereof will be omitted.  
         [0040]     Referring to  FIG. 5 , a passive element such as a resistor  40 ′ is installed across the slot  55  of the radiator  50 . Resistors having different resistance values can be applied to establish an optimized antenna matching condition.  
         [0041]     One or more passive elements of the same kind may be used for the antenna matching. Also, a plurality of passive elements of different kinds may be used together for the antenna matching.  
         [0042]      FIGS. 6A  to  6 C are graphs showing Voltage Standing Wave Ratio (VSWR) of built-in antenna modules, each being obtained by applying a capacitor of a different capacitance to the built-in antenna module shown in  FIG. 4 .  FIGS. 6A  to  6 C are obtained by applying a 12-pF, 27-pF, and 47-pF capacitor, respectively.  
         [0043]     Referring to  FIGS. 6A  to  6 C, the graphs show that the frequency response property and bandwidth are changed depending on the capacitance of the capacitor in 800-MHz band. Therefore, the built-in antenna can be tuned to have a desired property by selecting a proper capacitor.  
         [0044]      FIG. 7  is a graph showing VSWR of a built-in antenna module without a matching unit.  FIG. 8  is a graph showing VSWR of a built-in antenna module with a 1.2-nH inductor as a matching unit.  FIG. 9  is a graph showing VSWR of a built-in antenna module with a 56-pF capacitor as a matching unit.  
         [0045]     Referring to  FIG. 8 , a graph is obtained by applying a 1.2-nH inductor to the radiator  50  between the ground pin  52  and radiation surface. When the graph in  FIG. 7  obtained without a matching unit is compared with the graph in  FIG. 8 , the frequency response property of the built-in antenna module is changed. That is, VSWRs are changed in Code Division Multiple Access (CDMA) band (between marker  1  and marker  2 ): from 8.5:1 to 2.6:1 at marker  1 , and from 1.3:1 to 2.9:1 at marker  2 . As shown, bandwidth is widened though the VSWR at marker  2  is increased.  
         [0046]     Referring to  FIG. 9 , a graph is obtained by applying a 56-pF capacitor to the radiator  50  between the ground pin  52  and the radiation surface. When the graph in  FIG. 7  obtained without a matching unit is compared with the graph in  FIG. 9 , the frequency response property of the built-in antenna module is changed. That is, VSWRs are changed in Code Division Multiple Access (CDMA) band (between marker  1  and marker  2 ): from 8.5:1 to 2.9:1 at marker  1 , and from 1.3:1 to 2.8:1 at marker  2 . As shown, bandwidth is slightly narrowed when compared with the graph in  FIG. 8 .  
         [0047]     As described above, when the passive element, such as the inductor and the capacitor, is disposed between the ground pin and radiation surface, the characteristic value of the passive element changes the frequency response property and bandwidth of the built-in antenna module. Therefore, various frequency response properties can be attained via altering a variable design parameter, such a passive element, without physically changing the radiator. Also, the application of the passive element can take the place of a matching circuit in a signal line, such that radiation performance can be increased without insertion loss.  
         [0048]     The foregoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.