A multi-modulation retrodirective feed network for backscatter communications

Short ranges and limited field-of-views in semi-passive radio frequency identification (RFID) tags are the most prominent obstacles that limit the number of RFID applications relying on backscatter modulation to exchange data between a reader and a tag. We propose a retrodirective array structure that, if equipped on a tag, can increase the field-of-view and the coverage area of RFID systems by making the tag insensitive to its orientation with respect to one or more RFID readers. In this article, we derive and experimentally validate the conditions under which a rat-race coupler is retrodirective. The performance of the fabricated passive retrodirective structure is evaluated through the retrodirective ideality factor (RIF) amounting to a value of 1.003, which is close to the ideal RIF of one. The article ends with a discussion on how the proposed design can improve current RFID systems from a communication perspective.

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