Dual Frequency Selective Multiple Access With Quasi-Chipless/Powerless RFID Mixer Tags

A novel concept of quasi-chipless RFID Mixer tags is introduced in this letter, that extends the harmonic radar principle by a multiple access scheme. In this scheme, two RF signals being transmitted by a reader are downconverted in the tag by an unbiased diode mixer after reception only when the interrogation frequencies of both signals do match the filter characteristics of the two narrow-band receiving antennas. Only in this case, the downconverted RF signal is backscattered toward the reader by a third narrow-band antenna. Thus, several tags can be addressed by individual frequency pairs, what allows for the implementation of a multiple access scheme. This scheme is discussed in detail and accompanied by a proof-of-concept implementation. The functionality has been verified by corresponding measurements of different tag combinations and a read range analysis has been performed.