Extracting the ID Code of a Time/Frequency Chipless-RFID Tag with Only One Power Splitter Output

In this paper, a time/frequency domain chipless-RFID system, working in near-field is presented. The reader is based on a microstrip power splitter and the tag consists of two columns of split ring resonators (SRRs) etched in a dielectric substrate. The SRRs are designed in five different sizes (lengths), corresponding to five different resonance frequencies. As a result, the tag is able to encode more than 2 bits per resonator, and since there are two resonators per row, the tag can encode 4.9 bits of information per row. Reading the identification (ID) code of the tag is carried out by displacing it at short vertical distance (airgap) over the reader (power splitter), with the tag columns crossing the output power splitter branches. The proposed system encodes the information in frequency, provided that there are five resonator sizes, each one associated to a different resonance frequency. For tag reading, five different harmonic signals, tuned to the resonance frequencies of resonators, are sequentially injected to the input port of the power splitter. The bits are read sequentially, row by row, in a time division multiplexing scheme, where resonator size (and hence the ID) is identified from the envelope of the amplitude modulated (AM) signal for each harmonic at the output ports of the splitter. Thus, the proposed system is a hybrid time/frequency domain chipless-RFID system. The most important aspect of this contribution concerns the fact that only one of the output ports of the power splitter is needed to read the tag´s ID code, since the reflected signals contain the information of the two tag chains. Finally, in this paper, a proof-of concept demonstrator of this approach is presented.