Polarization-Domain Encoding Based on Pauli Decomposition of Scattering Responses for Chipless Resonators

Polarization diversity provides an extra encoding axis for chipless radiofrequency identification (RFID), yet most reported tags rely on ultra-wideband excitation and imaging readers. This work shows that narrowband encoding is possible by expressing the four-element Sinclair scattering matrix in the Pauli basis and mapping data onto the reduced vector p2,p3T, where p2 quantifies differential co-polarized scattering and p3 characterizes symmetric cross-polarized conversion. Two fixed linearly polarized microstrip-patch antennas on FR-4 interrogate a 3 × 3 array of 20 mm split-ring resonators on RO4003, whose gap orientations of 0°, 90°, +45°, and − 45° create four distinct signatures within a 170 MHz window cantered at 5.8 GHz. Full-wave simulation and two-port vector-network-analyzer measurements confirm that the dominant Pauli component and its phase separate the four tag states. These results verify that polarization-based encoding can be achieved with compact hardware and without widening the spectral footprint.