In this paper, a novel fully passive ID generation circuit for radio frequency identification (RFID) applications is presented. The circuit encodes data in frequency domain, however, it reuses the frequency band to yield more bits compared to existing spectral signature based tags. The circuit comprises of two multiresonating circuits and one broadband power divider. The circuit is interrogated with a short duration Ultra-Wideband (UWB) pulse. The specific ID generated by the circuit is retrieved by analyzing the retransmitted UWB pulses. When combined with compact planar UWB antennas, the ID generation circuit has potential for ultra-low cost item tagging.