Taking Advantage of PHEMT Nonlinear Behavior for RFID Applications

This paper presents two frequency converting PHEMT-based active antennas to be used in RFID applications. A proper characterization of the transistor nonlinear behavior revealed the existence of two biasing regions where the response signal, the second harmonic or the IF component, can be generated with maximum conversion gain and phase opposition. This attractive issue has been taken advantage of, to BPSK modulate the response in two approaches: in a frequency doubling active antenna and in a phase conjugating circuit for retrodirective arrays. Aperture coupled patch radiators were designed, to integrate these modulators in low cost, compact and high performance transponders