This paper presents the multiplexing of unpowered wireless antenna sensors for crack monitoring at multiple locations. Four antenna sensors were multiplexed to form a sensor array based on two multiplexing principles, namely frequency division and spatial division. For frequency division, a dual-antenna sensor array with each sensor operating at different frequencies was designed and implemented. Simultaneous interrogation of these two sensor elements has been achieved. For spatial division, two single antenna sensors with the same resonant frequencies as the dual-antenna sensor array were installed at different locations. By steering the illumination light toward their wireless impedance-switch circuits, these two single antenna sensors can be interrogated individually. The capability of the antenna sensor array to monitor multiple crack growth in a fatigue specimen was evaluated. Compared to a single antenna sensor, the antenna sensor array enables us to track the status of cracks over a large area.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.