Spectral Scalability Analysis of Multi-Tag Chipless RFID Using Frequency Encoding

Abstract

This paper presents a spectral scalability study of planar multi-tag chipless RFID configurations using a frequency encoding technique. Multiple patch-based chipless RFID tags operating at distinct resonant frequencies are designed and analyzed under simultaneous interrogation. The study focuses on the ID bit allocation strategy, minimum spectral spacing, and the influence of increased tag density along with spectral distinguishability. A planar multi-tag arrangement is investigated through full-wave simulation and experimental validation using a bistatic measurement setup. To further examine scalability limitations, an extended six-tag configuration is analyzed within the same operating bandwidth. The results show that although resonance depth gradually decreases with increasing tag density due to spectral crowding and electromagnetic interaction, the individual resonant frequencies remain distinguishable when sufficient spectral spacing is maintained. Finally, a resonance spacing investigation is performed by considering fixed resonance spaces such as 700 MHz, 500 MHz, 300 MHz, and 100 MHz. The proposed investigation provides practical insight into ID bit allocation and scalability constraints in dense multi-tag chipless RFID systems.