Novel Multi-Resonator Circuits for Chipless RFID Tags Using Asymmetrical Triple-Mode Resonators

In this paper, a new asymmetrical triple-mode resonator (TMR) that can be used in chipless radio frequency identification (RFID) tags is introduced. The proposed resonator is constructed by locating two open-circuited stubs in different electrical length to an open loop resonator (OLR). Two resonant frequencies can be controlled by these asymmetrical stubs, while the main resonant frequency is resulted from the nature of the OLR. It is proven that the proposed resonator can allow obtaining 5 frequency codes from a single TMR. A multi-resonator circuit is also designed by coupling 6 TMRs to a bended transmission line which connects input to output port. For the experimental verifications, three circuits having different frequency code combinations have been fabricated and measured in an excellent agreement with the simulated results. Totally 18 resonant frequencies resulted from the 6 TMRs have been clearly observed in the measurements. The proposed multi-resonator circuit can be utilized for chipless RFID tags and 56 frequency codes can be generated.