A novel, frequency selective surface (FSS) inspired, fully passive, chipless data encoding circuit capable of being operated as a radio frequency identification (RFID) tag is presented. The tag is composed of finite repetitions of the unit cell realized on a grounded FR4 substrate having an overall size of 27.5 × 30 mm 2 . The unit cell is made up of several triangleshaped resonators patterned in a looped fashion. Variation in the geometric structure of the tag, achieved by addition or removal

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... f nested loops, corresponds to a specific bit sequence. Each sequence is represented in the spectral domain as a unique frequency signature of the resonators. The proposed 10-bit tag covers the spectral range from 4 to 11 GHz. The tag is compact, robust, and exhibits a stable response to impinging signals at different angles of incidence. Fig. 5. Comparison between measured and computed RCS response of data encoding circuits. (a) 5-bit. (b) 10 bit.