A transponder 14.1 for an electronic radio frequency identification system
comprises an antenna 18 having an antenna impedance at a feedpoint thereof.
The transponder further comprises an electronic circuit 19 having an input
connected to the antenna. The antenna impedance having impedance characteristics
for developing first and second voltage maxima (36, 38) across the input
at first and second frequencies (fL and fH) respectively,
thereby to provide a continuous operative frequency band for the transponder including
the first and second frequencies.
