This review paper summarizes a new flexible sensor concept based on the microstrip patch antenna technology. The principle of the patch antenna as a sensing element and the wireless interrogation of the antenna sensors are presented first, followed by the description of the antenna design and fabrication using flexible film components. The applications of the flexible antenna sensor for wireless strain sensing and crack detection are presented. The design and testing of inserting a flexible layer to improve the reliability of the flexible antenna sensor is also discussed. Because the flexible antenna sensors can be wirelessly interrogated with ultra-low power consumption and can be frequency division multiplexed, the complexity of implementing a large sensor array is greatly reduced.