Synthesis and Realization of Multiband Bandpass Filters Based on Frequency Transformation for the Encoding of Chipless RFID Tags

This paper presents new design methodology of multiband bandpass filter based on coupled resonators and frequency transformation for the implementation of frequency coded retransmission based chipless RFID tags. By utilizing the frequency transformation, transmission zeros are introduced in the single band response, and thus multiple passbands are generated. Furthermore, the position and bandwidth of each band can be solely and arbitrarily controlled by controlling the location and number of transmission zeroes. The synthesizing algorithm is implemented in MATLAB to calculate the coupling matrix, external Q-factors and relating parameters. Afterwards, the methodology is verified with CST full wave simulations and measurements for the quad-band bandpass filter that is implemented with microstrip open-loop resonators. The simulation and measurement results of different codes are in good agreement, and thus prove the feasibility of the introduced approach for designing the encoding elements of frequency coded chipless RFID tags.