Abstract-A zero-bias dual-mode mixing antenna for wireless transponders is proposed in this paper.Designed over an Enhancement-mode Pseudomorphic HEMT (E-PHEMT), the mixer takes advantage of the device nonlinear characteristics around cold operation. Simple closed form expressions, obtained from time-varying circuit analysis, predict good conversion efficiency in two different operating modes without requiring DC bias. For validation, a lab prototype has been implemented and tested, to be finally integrated in a compact active printed antenna suitable for wireless sensor networks or other radio frequency identification (RFID) applications.