Abstract:
A top-loaded whip antenna particularly suitable for use in a compact mobile communication device having dual band resonance and including an elongate conductive whip antenna portion and a choke defined over a portion of the elongate conductive whip antenna portion, thereby providing top loading.

Description:
REFERENCE TO COPENDING APPLICATION  
       [0001]     Reference is made to U.S. Provisional Patent Application Ser. No. 60/470,929 entitled SHORTENED WHIP STRUCTURE HAVING EXTENDED ELECTRICAL LENGTH AND DUAL BAND RESONANCE, filed May 14, 2003, the disclosure of which is hereby incorporated by reference and priority of which is hereby claimed. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to antennas and more particularly to whip type antennas.  
       BACKGROUND OF THE INVENTION  
       [0003]     The following U.S. patent documents are believed to represent the current state of the art: U.S. Pat. Nos.: 6,693,600; 6,476,766; 6,140,975; 6,091,369; 5,936,583; 5,548,827; 5,204,687; 4,876,709; 4,821,040; 4,443,803; 4,366,486; 4,328,501; 4,161,737 and 4,101,898. U.S. Published Patent Application 20030048227.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention seeks to provide an improved whip type antenna.  
         [0005]     There is thus provided in accordance with a preferred embodiment of the present invention a top-loaded whip antenna particularly suitable for use in a compact mobile communication device and including an elongate conductive whip antenna portion and a choke defined over a portion of said elongate conductive whip antenna portion, thereby providing top loading, the top-loaded whip antenna having dual band capability.  
         [0006]     Preferably, a helical antenna portion is mounted onto the whip antenna portion and is electrically insulated therefrom.  
         [0007]     In accordance with a preferred embodiment of the present invention there is also provided a base element suitable for mounting onto the mobile communication device and the whip antenna portion is slidably retractable and extendible with respect to the base element.  
         [0008]     Preferably, the choke is defined by a conductive tube which is arranged to coaxially overlie part of said elongate conductive whip antenna portion, one end of the conductive tube being mechanically and galvanically coupled to the whip antenna portion and the remainder of the conductive tube being spaced from the whip antenna portion. A dielectric insulator preferably is interposed between the conductive tube and the elongate conductive whip antenna portion.  
         [0009]     Preferably, the conductive tube is galvanically connected to the conductive whip antenna portion at a location adjacent an outward facing end of the conductive whip antenna portion.  
         [0010]     The dual-band capability of the antenna preferably includes capability for simultaneously handling transmission of a first band including at least one of GSM and CDMA and a second band including at least one of GPS and Bluetooth.  
         [0011]     Additionally or alternatively, the dual-band capability of the antenna includes capability for simultaneously handling transmission of a first band including a cellular communication band and a second band including a GPS band.  
         [0012]     In accordance with a preferred embodiment of the present invention, the conductive whip antenna portion functions as a ¼ wave element.  
         [0013]     Preferably, 50-ohm impedance matching is realized for dual bands without requiring a matching circuit. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:  
         [0015]      FIG. 1  is a partially exploded, partially sectional illustration of an antenna constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0016]      FIGS. 2 and 3  are pictorial illustrations of the antenna of  FIG. 1  in respective extended and retracted operative positions;  
         [0017]      FIGS. 4 and 5  are respective sectional illustrations corresponding to  FIGS. 2 and 3 ;  
         [0018]      FIGS. 6 and 7  are sectional illustrations taken along lines VI-VI and VII-VII respectively in  FIG. 4 ;  
         [0019]      FIG. 8  is a partially exploded, partially sectional illustration of an antenna constructed and operative in accordance with another preferred embodiment of the present invention;  
         [0020]      FIGS. 9 and 10  are pictorial illustrations of the antenna of  FIG. 8  in respective extended and retracted operative positions;  
         [0021]      FIGS. 11 and 12  are respective sectional illustrations corresponding to  FIGS. 9 and 10 ;  
         [0022]      FIGS. 13 and 14  are sectional illustrations taken along lines XIII-XIII and XIV-XIV respectively in  FIG. 11 ;  
         [0023]      FIG. 15  is a simplified electrical equivalent circuit corresponding to the antenna of  FIGS. 1-14  for operation in a high frequency band; and  
         [0024]      FIG. 16  is a simplified electrical equivalent circuit corresponding to the antenna of  FIGS. 1-14  for operation in a low frequency band. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]     Reference is now made to  FIGS. 1-7 , which illustrate an antenna constructed and operative in accordance with a preferred embodiment of the present invention.  FIGS. 1-7  illustrate the present invention embodied in a top helical antenna of the general type described in U.S. Pat. No. 5,204,687, the disclosure of which is hereby incorporated by reference.  
         [0026]     As seen in  FIGS. 1-7 , the antenna is particularly characterized in that it includes an electrically conductive elongate whip portion  100  preferably formed of NiTi wire which is coated along a portion of its length with a conventional plastic electrically insulative coating  102 . At an inward facing end  104  of whip portion  100 , at which the plastic insulative coating  102  is removed, there is mounted a conductive, forwardly tapered connector element  106 .  
         [0027]     At its outward facing end  108 , at which the plastic insulative coating  102  is also removed, whip portion  100  is mechanically attached to a dielectric antenna shaft portion  110 , typically formed of plastic, and electrically and mechanically attached, preferably by crimping, to an electrically conductive tube  112 , which overlies a portion  114  of whip portion  100 . Tube  112  is electrically insulated from whip portion  100 , other than at end  108  where it is electrically connected thereto. Preferably a dielectric material  116  of preselected electrical characteristics is interposed between whip portion  100  and tube  112  in place of plastic insulative coating  102 . Alternatively plastic insulative coating  102  is disposed between tube  112  and the underlying length of whip portion  100 . Tube  112  defines, together with whip portion  100 , a choke having characteristics which substantially enhance antenna performance.  
         [0028]     Mounted onto a portion of dielectric shaft portion  110  is a conductive sleeve  118 , onto which is fixedly mechanically and electrically connected a top helical antenna assembly  120 . Assembly  120  includes an electrically insulative base element  122 , which defines a bore  124  of dimensions selected so as to fixedly engage an outer surface  126  of conductive sleeve  118 .  
         [0029]     Disposed in electrically conductive engagement with base element  122  and supported on a conductive base  128 , preferably integrally formed with sleeve  118 , and partially wound around an end portion  130  of dielectric shaft portion  110  is a helical antenna element  132 . Helical antenna element  132  is preferably surrounded by a dielectric top helical antenna assembly housing  134 .  
         [0030]     An outwardly threaded, electrically conductive base element  142  engages a suitably threaded socket (not shown) in a communications device such as a cellular telephone. Preferably base element  142  defines a bore  144  of dimensions and surface friction characteristics selected so as to slidably but frictionally retainably engage the outer surface  146  of connector element  106  and the outer surface  126  of sleeve  112 , which preferably has generally the same outer dimensions as surface  146 . In such a way, depending on whether a user has placed the whip portion  100  in an extended or retracted position, illustrated in  FIGS. 2 &amp; 4  and  3  &amp;  5  respectively, frictional engagement with bore  144  retains the whip portion  100  in the user-selected position.  
         [0031]     Either but not both of connector element  106  and sleeve  118  electrically engages electrically conductive base element  142 . In such a way, depending on whether a user has placed the whip portion  100  in an extended or retracted position, illustrated in  FIGS. 2 &amp; 4  and  3  &amp;  5  respectively, frictional engagement with bore  144  retains the whip portion  100  in the user-selected position.  
         [0032]     It may be appreciated from a consideration of  FIGS. 1-7  and more particularly  FIGS. 4 and 5 , that when the whip portion  100  is in an extended position, as shown in  FIG. 4 , the whip portion  100  is directly electrically coupled to base element  142  and radiates in at least two different frequency bands. When the whip portion  100  is in a retracted position, as shown in  FIG. 5 , helical antenna portion  132  is directly electrically coupled to base element  142  via sleeve  118  and also preferably radiates in the two different frequency bands.  
         [0033]     It is a particular feature of the present invention that the above-described structure provides a top-loaded whip antenna having a relatively short whip length, but having dual band functionality as well as performance characteristics of a whip antenna whose whip length is significantly greater.  
         [0034]     The antenna of  FIGS. 1-7 , due to its robust design and operation in two bands, effectively provides two antennas in a single structure. Such two antennas can be, for example, a CDMA or GSM antenna and a GPS or Bluetooth antenna.  
         [0035]     Reference is now made to  FIGS. 8-14 , which illustrate an antenna constructed and operative in accordance with a preferred embodiment of the present invention.  FIGS. 8-14  illustrate the present invention embodied in a whip antenna.  
         [0036]     As seen in  FIGS. 8-14 , the antenna is particularly characterized in that it includes an electrically conductive elongate whip portion  200  preferably formed of NiTi wire which is coated along a portion of its length with a conventional plastic electrically insulative coating  202 . At an inward facing end  204  of whip portion  200 , at which the plastic insulative coating  202  is removed, there is mounted a conductive, forwardly tapered connector element  206 , which extends outwardly over part of the insulative coating  202 .  
         [0037]     At its outward facing end  208 , at which the plastic insulative coating  202  is also removed, whip portion  200  is mechanically attached to an antenna top member  210 , typically formed of a dielectric material, and electrically and mechanically attached, preferably by crimping, to an electrically conductive tube  212 , which overlies a portion  214  of whip portion  200 . Tube  212  is electrically insulated from whip portion  200 , other than at end  208  where it is galvanically connected thereto. Preferably a dielectric material  216  of preselected electrical characteristics is interposed between whip portion  200  and tube  212  in place of plastic insulative coating  202 . Alternatively plastic insulative coating  202  is disposed between tube  212  and the underlying length of whip portion  200 . Tube  212  defines together with whip portion  200  a choke having characteristics which substantially enhance antenna performance.  
         [0038]     At a given time, either but not both of connector element  206  and antenna top member  210  mechanically engage an antenna assembly retaining collar assembly  220 . Assembly  220  includes an electrically conductive base element  222 , which engages a suitably configured electrical connector (not shown) in a communications device such as a cellular telephone. Assembly  220  also preferably includes a bayonet-type mechanical connector portion  224 , which engages a suitably configured bayonet-type socket (not shown) in the communications device such as a cellular telephone. Preferably base element  222  defines a bore  225  of dimensions and surface friction characteristics selected so as to slidably but frictionally retainably engage the outer surface  226  of connector element  206  and the outer surface  228  of antenna top member  210 , which preferably has generally the same outer dimensions as surface  226 . In such a way, depending on whether a user has placed the whip portion  200  in an extended or retracted position, illustrated in  FIGS. 9 &amp; 11  and  10  &amp;  12  respectively, frictional engagement with bore  225  retains the whip portion  200  in the user-selected position.  
         [0039]     It may be appreciated from a consideration of  FIGS. 8-14  and more particularly  FIGS. 11 and 12 , that when the whip portion  200  is in an extended position, as shown in  FIG. 11 , the whip portion  200  is directly electrically coupled to base element  222 . When the whip portion  200  is in a retracted position, as shown in  FIG. 12 , the whip portion  200  is no longer electrically coupled to base element  222 .  
         [0040]     It is a particular feature of the present invention that the above-described structure provides a top-loaded whip antenna having a relatively short whip length, but having dual-band capability as well as performance characteristics of a whip antenna whose whip length is significantly greater.  
         [0041]     Reference is now made to  FIGS. 15 and 16 , which illustrate electrical equivalent circuits for operation of the antennas of  FIGS. 1-14 , respectively in a relatively high frequency band, such as 1500-2100 MHZ and in a relatively low frequency band, such as 750-1000 MHZ. In the electrical equivalent circuit of  FIG. 15 , the circuitry within block  250  is not operative, due to the resonance of inductor L 1  and capacitor C 1 . In the electrical equivalent circuit of  FIG. 16 , inductor L 1  ( FIG. 15 ) is not effective due to top loading, producing a capacitance C 2  appearing in block  252  and thus, the entire circuit appearing in  FIG. 16  is operative.  
         [0042]     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereof which would occur to persons reading the foregoing description and which are not in the prior art.