A Fully ISM-Band Chipless RFID Tag With Hybrid Encoding for Micro-Scale Asset Identification

Micro-scale asset identification requires cost-effective, spectrum-compliant radio-frequency identification (RFID) solutions capable of distinguishing a small, fixed number of items. Chip-based RFID raises manufacturing costs by requiring integrated circuits, while chipless RFID removes that expense by eliminating the chip. Nevertheless, many existing chipless designs focus on high-bit capacity over practical deployment, relying on broadband spans (3–7 GHz or more) that conflict with regulatory restrictions and reduce the cost advantage. To address this limitation, this work proposes a chipless RFID tag that operates entirely within the unlicensed 2.40–2.48 GHz industrial, scientific, and medical (ISM) band. Even though this allocation offers only 80 MHz, the encoding mechanism still defines 24 resolvable states by using the frequency separation between two co-polarized resonances and the cross-polarized magnitude difference, both extracted from a dual-resonator structure composed of a fixed L-shaped preamble and a tunable fan-based data resonator. This architecture enables independent and systematic control over spectral and polarimetric features. Experimental validation across all tag variants confirms correct decoding, with frequency deviations confined within ±2 MHz and magnitude classification errors under ±1.5 dB. Demonstrating a low-cost, regulation-compliant tag, this study shifts chipless RFID from conceptual encoding to practical solutions for compact, low-density tracking.