A transponder for a radio frequency identification system, the transponder comprising a UHF antenna, an LF antenna, an HF antenna, a charge storing device and an electronic circuit comprising UHF, LF and HF antenna ports; a UHF RFID protocol engine; a DF RFID protocol engine; shared memory for the two protocol engines; a UHF receiver, rectifier and data extractor; an LF receiver, rectifier and data extractor; a UHF modulator; an HF modulator; a decision circuit for selecting either the UHF energy source or the LF energy source; and a digital controller capable of selecting either the UHF protocol engine or the DF protocol engine or both, depending on which energy source is present and the strength of that energy source.