Multi resonance based chipless RFID tag with high data encoding capacity

A chipless RFID tag utilizing fundamental (f₀) and first harmonic (fs₁) frequencies of the Stepped Impedance Resonator (SIR) for data encoding is proposed in this paper. Impedance Ratio (K) and Length ratio (α) are the two parameters which determine the resonant frequencies of an SIR. The Fundamental or first harmonic frequencies of the SIR can be changed without affecting one another. First harmonic frequency can be selected between the frequency, ranging from 1.16f₀ to 3.7f₀ by changing K from 0.25 to 7.5. These features along with Frequency Shift Coding technique provide higher bit encoding capacity up to 4bits/cm². Numerical and experimental analyses are carried out to verify the theoretical results. Data from the tag is decoded using backscattered signal from the tag. Four SIR working in the UWB band is fabricated on an RT Duroid substrate of dielectric constant 2.2 and loss tangent of 0.0009, that can represent 32 bit of information. The tag response is measured inside and outside the anechoic chamber and the data can be measured outside the anechoic chamber up to 50cm distance away from the antenna.