Patent Publication Number: US-8115682-B2

Title: Multi-band HAC compatible antenna module

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to antenna module designs and more particularly, to a multi-band HAC compatible antenna module, which has a metal shield mounted therein around the built-in antenna for resonant coupling with the antenna to lower electromagnetic interference and to provide HAC characteristic. 
     The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
     2. Description of the Related Art 
     FCC (Federal Communications Commission) introduced new regulations regarding digital cellular telephones. In order not to interfere with concomitant use of a cellular telephone and hearing aids, cellular telephone providers are responsible to keep EMI (electromagnetic interference) below a certain level. Cellular telephone provides are also requested to prepare some types of cellular telephones for enabling audio signal to be transmitted to hearing aids by means of telcoil coupling. 
     FCC established the aforesaid regulations just because analog cellular telephones are being disappeared from the market FCC indicates no significant problems are found during the concomitant use of an analog cellular telephone and hearing aids. 
     With respect to the problem of concomitant use between cellular telephones and hearing aids, ANSI (American National Standards Institute) established compatibility between hearing aids and cellular telephone under “ANSI C63.19”. 
     Regular cell phone antennas cannot meet HAC (Hearing Aids Compatibility) standards. Therefore, HAC compatible cellular telephones are continuously created. US20060140428 discloses a mobile wireless communications device including an upper housing and a lower housing being slidably connected together for sliding between a retracted position and an extended use position. 
     US20070003088 discloses an electronic device including a ground plane with two opposed edges, an electrical component, and an electrical conductor coupling the electrical component to a point on the ground plane that is substantially spaced from each of the opposed edges. These methods are not applicable to antenna designs for straight cellular telephone for improving HAC characteristic. 
     The built-in antennas of regular straight cellular telephones show low performance in HAC. The HAC design of a single-pole antenna for straight cellular telephone does not have a reference ground plane, resulting in a high field strength at the reference location that is disposed near the antenna. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a multi-band HAC compatible antenna module, which is mounted with a metal shield to provide excellent HAC characteristic, showing 3 dB˜4 dB HAC improvement in GSM850 and GSM900, and 1 dB HAC improvement in DCS and PCS bands when compared with a reference antenna without metal shield. 
     To achieve this and other objects of the present invention, a multi-band HAC compatible antenna module includes a dielectric substrate, which has a metal ground covered on a part thereof, an antenna holder protruded from the dielectric substrate beyond the cover range of the metal ground, a single-pole antenna mounted in the antenna holder and adapted to produce a radiation in GSM850, GMS900, DCS and PCS bands, a microband feed line connected to the single-pole antenna for feeding in signals, and a metal shield mounted in the dielectric substrate opposite to the antenna holder for resonant coupling with the single-pole antenna to lower electromagnetic interference and to improve hearing aids compatibility characteristic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
         FIG. 1  is an oblique front elevation of a multi-band HAC compatible antenna module in accordance with the present invention. 
         FIG. 2  is a top plain view of a part of the multi-band HAC compatible antenna module according to the present invention. 
         FIG. 3  is a rear elevation of a part of the multi-band HAC compatible antenna module according to the present invention. 
         FIG. 4  illustrates the arrangement of the component parts of the metal shield of the multi-band HAC compatible antenna module according to the present invention. 
         FIG. 5(   a ) is a perspective view of the present invention, showing the relationship between the single-pole antenna and the metal shield. 
         FIG. 5(   b ) is a side view of  FIG. 5(   a ). 
         FIG. 6(   a ) illustrates the HAC test result of the multi-band HAC compatible antenna module in 925 MHz according to the present invention. 
         FIG. 6(   b ) illustrates the HAC test result of the reference antenna module without metal shield in 925 MHz according to the present invention. 
         FIG. 7(   a ) illustrates the HAC test result of the multi-band HAC compatible antenna module in 1850.2 MHz according to the present invention. 
         FIG. 7(   b ) illustrates the HAC test result of the reference antenna module without metal shield in 1850.2 MHz according to the present invention. 
         FIG. 8  is a stationary wave ratio comparison chart between the multi-band HAC compatible antenna module and the reference antenna module without metal shield according to the present invention 
         FIG. 9(   a ) illustrates a near-field field-strength at 925 MHz of the multi-band HAC compatible antenna module according to the present invention. 
         FIG. 9(   b ) illustrates a near-field field-strength at 925 MHz of the reference antenna module without metal shield according to the present invention. 
         FIG. 10(   a ) illustrates the near-field field-strength RMS value at 1850.2 MHz of the multi-band HAC compatible antenna module according to the present invention. 
         FIG. 10(   b ) illustrates the near-field field-strength RMS value at 1850.2 MHz of the reference antenna module without metal shield according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1˜3 , an antenna module  1  includes a dielectric substrate  11 , an antenna holder  12 , a single-pole antenna  13 , a microband feed line  14 , and a metal shield  15 . 
     The dielectric substrate  11  has a metal ground  111  covered on a part thereof. According to this embodiment, as shown in  FIG. 3 , the metal ground  111  is covered on a part of the back side of the dielectric substrate  11 . The part of the dielectric substrate  11  beyond the metal ground  111  is the non-metal ground part  112 . Further, the dielectric substrate  11  is made of FR4 (Flame Retardant 4). 
     The antenna holder  12  is made of an electrically insulative material and protruded from one side, for example, the front side of the non-metal ground part  112 . 
     The single-pole antenna  13  is installed in the antenna holder  12 . As shown in  FIGS. 5(   a ) and  5 ( b ), the single-pole antenna  13  wound on the antenna holder  12  and adapted to generate radiation for applications in GSM, DCS and PCS bands. 
     The microband feed line  14  is connected to the single-pole antenna  13  for feeding in signals. 
     The metal shield  15  is mounted on the non-metal ground part  112  of the dielectric substrate  11  at the opposite side relative to the single-pole antenna  13  for resonant coupling with the single-pole antenna  13  to lower electromagnetic interference, improving HAC (Hearing Aids Compatibility) characteristic. 
     Referring to  FIGS. 4(   a ) and  4 ( b ), the metal shield  15  extends around the single-pole antenna  13 . As illustrated, the metal shield  15  includes: 
     a metal sheet  151  covered on the back side of the non-metal ground part  112  of the dielectric substrate  11  opposite to the single-pole antenna  13 ; 
     a top metal strip  152  connected to the metal sheet  151  at right angles; and 
     two side metal strips  153  perpendicularly extended from the metal sheet  151  and respectively perpendicularly connected to the two distal ends of the top metal strip  152 . 
     The top metal strip  152  and the side metal strips  153  perpendicularly extend along the border of the metal sheet  151  around the single-pole antenna  13 , providing an excellent EMI-protective shielding effect to the single-pole antenna  13 . 
     Further, the distance between the single-pole antenna  13  and the metal sheet  151  of the metal shield  15  is approximately equal to the thickness of the dielectric substrate  11 , for example, 1 mm. 
     The antenna holder  12  is filled up with a dielectric material. The dielectric parameters may be adjusted subject to requirements, for enabling the single-pole antenna  13  to work in GSM850, GSM900, DCS and PCS bands. 
     Further, when designing the antenna module, adjust the dielectric material in the antenna holder  12  subject to the radiation length of the reference single-pole antenna to have the single-pole antenna  13  produce a resonant frequency slightly above the desired working band, and then adjust the coupling between the metal shield  15  and the single-pole antenna  13  to shift the resonance toward the desired working frequency, thereby improving HAC characteristic. 
     When testing an antenna module with the metal shield and an antenna module without the metal shield, a near-field field-strength comparison chart is obtained as follows: 
     
       
         
           
               
               
               
               
            
               
                   
                   
               
               
                   
                 With/Without 
                 Total 
                 HAC 
               
            
           
           
               
               
               
               
               
            
               
                 Frequency 
                 metal shield 
                 efficiency 
                 E-field(V/m) 
                 H-field(A/m) 
               
               
                   
               
               
                   925 MHz 
                 Yes 
                 88.06% 
                 336 
                 0.729 
               
               
                   925 MHz 
                 No 
                 88.46% 
                 498 
                 0.818 
               
               
                 1850.2 MHz 
                 Yes 
                 86.20% 
                 110 
                 0.318 
               
               
                 1850.2 MHz 
                 No 
                 82.01% 
                 123 
                 0.347 
               
               
                   
               
            
           
         
       
     
     Based on the reference antenna (antenna module without metal shield) without changing the other structure, the installation of the metal shield  15  effectively improves the performance of the antenna module in HAC.  FIG. 9  illustrates the near-field field-strength at 925 MHz of the reference antenna without metal shield and the antenna with the metal shield.  FIG. 9(   a ) illustrates the performance of the antenna with the metal shield.  FIG. 9(   b ) illustrates the performance of the reference antenna without metal shield. 
       FIG. 10  illustrates the near-field field-strength RMS value of the reference antenna without metal shield and the antenna with the metal shield at 1850.2 MHz.  FIG. 10(   a ) illustrates the performance of the antenna with the metal shield.  FIG. 10(   b ) illustrates the performance of the reference antenna without metal shield. As illustrated, the invention shows an improvement of 4 dB at low frequency, and 1 dB at high frequency. 
     Further, the non-metal ground part  112  of the dielectric substrate  11  has sufficient space for the installation of other components such as speaker and CCD (charge-coupled device). According to tests, HAC variation is within 1% after installation of a speaker and a CCD in the antenna module. 
       FIG. 5  shows the relative positioning between the metal shield  15  and the single-pole antenna  13 . As shown in  FIG. 5(   a ), the distance between the single-pole antenna  13  and microband feed line  14  and the metal shield  15  is about 1 mm. As shown in  FIG. 5(   b ), the distance between the single-pole antenna  13  and the metal shield  15  is just equal to the thickness of the dielectric substrate  11 , i.e., 1 mm. 
     As stated above, the invention is based on the reference antenna module and with added metal shield  15  to improve HAC characteristic. At first, adjust the radiation length of the reference single-pole antenna  13 . The dielectric material field in the antenna holder  12  is then adjusted to have the single-pole antenna  13  produce a resonant frequency slightly above the desired working band. Thereafter, the metal shield  15  is added to the module. By means of coupling between the metal shield  15  and the single-pole antenna  13 , the actual working frequency of the antenna module is shifted downwards to the desired range. Because the metal shield  15  is disposed near the single-pole antenna  13 , SII parameters may become worse. Matching adjustment is necessary to have the antenna module function normally in the desired frequency band. 
     Further,  FIG. 8  illustrates the SII parameters of the reference antenna without shield and the antenna with the metal shield  15 . The antenna with the metal shield  15  shows stationary wave ratio below 4 when working in GSM850, GSM900, DCS and PCS bands. 
       FIGS. 6 and 7  show HAC test results of the antenna module on radiation efficiency, matching efficiency, total efficiency and E-field and H-field in 925 MHz and 1850.2 MHz. The rest results show an improvement of 3 dB˜4 dB at low frequency band and 1 dB at high frequency band. 
     Further, a matching circuit or slot (not shown) may be formed in the dielectric substrate  11 , increasing the bandwidth of the antenna module. 
     A prototype of multi-band HAC compatible antenna module has been constructed with the features of  FIGS. 1˜10 . The multi-band HAC compatible antenna module functions smoothly to provide all of the features disclosed earlier. 
     Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.