Design of Dual-Loaded RFID Tag for Higher Order Modulations

A touchstone for selecting two scattering states for scalar differential backscattering in passive scatterers was introduced by Green in 1963. According to this model, a scatterer has one global minimum and one global maximum scattering states on its $\Gamma $ plane. The variation of radar cross section (RCS) of the scatterer between these two states is monotonic. Thus, to achieve to the highest differential backscattering the scatterer should switch between these two states. In this paper, we verify, by measurements and simulations, that a linear half-wave dipole antenna behaves as predicted by the Green model. However, we show that the RCS of a T-match bow tie antenna over its $\Gamma $ plane cannot be modeled by the Green model and instead the antenna has two maximum scattering states on its $\Gamma $ plane. In the next step, we use dual loading on the T-match bowtie antenna structure. By appropriate selection of the loads, the antenna can provide various scattering states with various magnitudes in 360° phase span in its in-phase and quadrature plane. This feature of the proposed antenna can be used to increase the modulation depth up to 170%, provide a quasi-32-quasi-quadrature amplitude shift keying, and increase the coverage range in backscattering links.