Radio frequency identification (RFID) tag antenna based passive wireless sensors are receiving increasing attentions for structural health monitoring (SHM) in large-scale infrastructure. For permanently-installed monitoring, robustness to measurement variation including environmental conditions is a practical issue. This paper retrospects the communication principle of magnetic resonant coupling (MRC) for low frequency (LF) passive wireless RFID antenna sensors. The influence of communication is uncovered and essentially separated from sensing through two steps: sweep (source) frequency to capture the system behavior, i. e., resonance frequency range; multiple feature extraction, fusion, and selection in conjunction with normalization for the selected time-domain feature of peak to peak (P2P). By this way, the robustness of the low-cost RFID sensing system is enhanced. The proposed method is validated by the case study in open crack detection and characterization under varied measurement conditions.