Frequency-Multiplication Transponder Radar for Geological Hazard Deformation Monitoring

Remote micro-deformation monitoring of large structures and geological hazards presents significant challenges for conventional phase-interferometric radar due to limitations in range, transmitter leakage, and multi-target identification. This study proposed a deformation monitoring radar utilizing a frequency-multiplication transponder. Frequency isolation effectively suppresses transmitter leakage, while active frequency-multiplication amplification enhances echo signals over long distances. Additionally, on–off keying (OOK) frequency division allows for the separation of multiple targets. A transponder interferometric model established a relationship between target displacement and echo phase. A prototype-measured link budget established the theoretical operational range limit. Each measurement point required a dedicated active transponder. Consequently, the system conducted sparse point-wise radial displacement monitoring rather than full-field imaging. Field experiments were performed to evaluate displacement measurement at 129 m, 345 m, and 570 m. A dual-target experiment was also conducted at 129 m. All test configurations successfully resolved 2.5 mm micro-displacements. The measurement error was approximately 0.1 mm under unobstructed conditions. The maximum absolute error remained below 0.8 mm in complex environments. Dual-target demodulation yielded a root-mean-square error of 0.14 mm. The maximum experimentally verified distance is 570 m. The 1 km design range represents a theoretical link-budget target. This target is constrained by the transponder saturation threshold and receiver sensitivity. Field validation at 1 km remains unachieved.