Circular Polarized RFID Tag Antenna Design using Characteristic Mode Analysis

摘要

This paper presents a circularly polarised RFID tag antenna using characteristic mode analysis. The proposed design consists of a leaf-shaped radiator with two cross slots and shorting stubs etched on a grounded FR4 substrate. By analyzing the characteristic modes, the diagonal slots are created at suitable locations to enable modes to resonate in the required frequency band. In addition to this, edge rounding is performed to create modes with orthogonal current distribution for circular polarisation. Moreover, the RFID chip is placed as a capacitive coupling element at current minima to excite these orthogonal modes. Furthermore, the tag parameters are optimized to give a conjugate match with Alien H4 RFID chip in US UHF RFID band (902 - 928 MHz). The proposed tag provides a read range of 3.5 m and 5 m after mounting on low permittivity substrate and 100 × 100 mm²metallic plate, respectively.