A resonant antenna circuit for a radio frequency identification (RFID) reader generates an electrical signal for activating a passive identification tag. The identification tag in turn generates a coded electrical signal that is detected by the reader. The electrical characteristics of the resonant circuit are dynamically altered so that the antenna performs more optimally as a transmitter and receiver for different types of transponders. The resonant circuit uses only passive components and the instantaneous resonant frequency tuning point is determined by the state of the activation signal transmitter.