A review of microwave radar technology for monitoring bridges and other civil structures: Applications, challenges, and prospects

Microwave radar technology, owing to its non-contact, high-precision, and all-weather monitoring capabilities, has gradually emerged as an important tool for the structural health monitoring (SHM) of bridges and other civil structures. This review systematically summarizes recent research advances and engineering applications of microwave radar in structural safety assessment, dynamic response identification, and long-term deformation monitoring. First, from the perspectives of measurement principles and system classification, the performance characteristics and applicability of frequency-modulated continuous-wave (FMCW), stepped-frequency continuous-wave (SFCW), synthetic aperture radar (SAR), and multiple-input multiple-output (MIMO) radar in different monitoring scenarios are discussed. Particular attention is then given to key applications in bridge engineering, including environmental interference suppression, synchronous multi-target measurement, cable-force and deflection identification, as well as modal parameter extraction and damage diagnosis. Existing studies indicate that microwave radar can achieve high accuracy and stability in the non-contact monitoring of bridges. Nevertheless, several technical bottlenecks remain, particularly in interference resistance under extreme environmental conditions, signal aliasing mitigation, and the identification of subtle damage. On this basis, the review further examines the expanded application of microwave radar in complex structures such as high-rise buildings, dams, slopes, and heritage buildings, highlighting its engineering value in deformation monitoring and disaster early warning. Finally, future research directions are outlined, including the development of multi-frequency fusion and adaptive compensation techniques; intelligent identification algorithms informed by structural dynamics; deeper integration of radar monitoring with existing SHM systems, BIM/digital twin frameworks, and operation and maintenance platforms; and new radar architectures that are low-cost, easy to deploy, and suitable for urban complexes and lifeline infrastructure.