Antenna generating an electromagnetic field for transponder

Abstract

The invention concerns an antenna generating an electromagnetic field for an electromagnetic transponder. and a terminal provided with such an antenna, comprising a first inductive element (Lp) designed to be connected to two terminals ( 3, 4 ) applying an energizing voltage (Vg), and a parallel resonant circuit ( 21 ) coupled with the first inductive element.

1 . An antenna for generating an electromagnetic field for an electromagnetic transponder, including: 
 a first inductive element (Lp) intended for being connected to two terminals ( 3 ,  4 ) of application of an excitation voltage (Vg); and    a parallel resonant circuit ( 21 ,  21 ′) coupled with the first inductive element.    
     
     
         2 . The antenna of  claim 1 , characterized in that the first inductive element (Lp) is formed of several inductances ( 31 ,  32 ,  33 ,  34 ,  35 ,  36 ,  37 ) organized in a network.  
     
     
         3 . The antenna of  claim 1  or  2 , characterized in that the inductive element(s) (Lp), Lb) are formed of planar windings.  
     
     
         4 . The antenna of  claim 3  characterized in that the two inductive elements (Lp, Lb) are in parallel planes.  
     
     
         5 . The antenna of  claim 4 , characterized in that the distance that separates the respective planes of the inductive elements (Lp, Lb) is chosen according to the power consumption of the transponders for which the antenna is intended and to the desired range.  
     
     
         6 . A terminal ( 20 ,  45 ) for generating a high-frequency electromagnetic field for at least one transponder ( 10 ) entering this field, characterized in that it includes a resonant circuit ( 21 ,  21 ′), magnetically coupled to an excitation circuit including a first inductive element (Lp) and having no capacitive element, said resonant circuit including a second inductive element (Lb), the value of which is chosen to be greater than the value of the first inductive element with a ratio depending on a desired field amplification.  
     
     
         7 . The terminal of  claim 1 , characterized in that the resonant circuit ( 21 ,  21 ′) is formed of a second inductive element (Lb) and of a capacitive element (Cb) in parallel, and is tuned to the frequency of an excitation signal (Vg) of the first inductive element (Lp).  
     
     
         8 . The terminal of  claim 6  or  7 , characterized in that said inductive elements (Lp, Lb) form the antenna of any of  claims 1  to  6 .  
     
     
         9 . The terminal of any of  claims 6  to  8 , characterized in that said resonant circuit ( 21 ′) includes a control switch ( 46 ).